Aquaculture systems for wastewater treatment an engineering assessment

[From the U.S. Government Printing Office, www.gpo.gov]

United States Office of Water June 1980 /
Environmental Protection Program Operations (WH-547) 430/9-80-007
Agency Washington DC 20460
Water
',EPA Aquaculture Systems
for Wastewater
Treatment

An Engineering
Assessment

TD
!523
R.44
1981

MCD-68

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and approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Environmental Protection
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or commercial products constitute endorsement or recommendation for use.

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Treatment: An Engineering Assessment," write to:

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EPA 430/9-80-007

A QUA CULTURE SYSTEMS
FOR WASTEWA TER TREA TMENT:
AN ENGINEERING ASSESSMENT

Sherwood C. Reed, USA/CRREL
Robert K. Bastian, EPAIOWPO
Project Officers

r
Property of CSC Library

June 1980
U.S. Environmental Protection Agency
Office of Water Program Operations
Municipal Construction Division
Washington, D.C. 20460

t t ~ ~u. Ci DEPARTMENT OF COMMERCE NOAA
6 ~~~~N ~COASI AL SERVICES CENTER
2234 SOUTH HOBSON AVENUE
/_ CI-IARLESTON, SC 29405-2413

EPA Comment

This report is one of a series planned for publication by the U.S.
EPA Office of Water Program Operations to supply detailed information
for use in evaluating, selecting, developing, designing, and operating
innovative and alternative (I/A) technologies for municipal wastewater
treatment. This series will provide indepth presentations of available
information on topics of major interest and concern related to I/A
technologies. An effort will be made to provide the most current state-
of-the-art information available concerning I/A technologies for
municipal wastewater treatment.

These reports are being prepared to assist EPA Regional Administrators
in evaluating grant applications for construction of publicly owned
treatment works under Section 203(a) of the Clean Water Act of 1977. They
also will provide state agencies, regulatory officials, designers, consulting
engineers, municipal officials, environmentalists and others with detailed
information on I/A technologies.

Harold P. Cahill, Jr.
Director
Municipal Construction Division (WH-547)

CONTENTS

Engineering Assessment of Aquaculture Systems for Wastewater
Treatment: An Overview ........................... I
Sherwood C. Reed; U.S. Army Corps of Engineers
Robert K. Bastian; U.S. Environmental Protection Agency
William J. Jewell; Cornell University

Wetland Systems for Wastewater Treatment: An Engineering Assessment . . . .13
George Tchobanoglous; University of California-Davis
Gordon L. Culp; Culp, Wesner, and Culp

Aquatic Plant Processes Assessment .....................43
E. Joe Middlebrooks; Utah State University

Engineering Assessment: Use of Aquatic Plant Systems for Wastewater
Treatment .................................63
Walter J. O'Brien; Black & Veatch Consulting Engineers

Combined Aquaculture Systems for Municipal Wastewater Treatment - An
Engineering Assessment . . . .........................81
H. G. Schwartz, Jr. and B. S. Shin; Sverdrup & Parcel and Assoc., Inc.

Combined Aquaculture Systems for Wastewater Treatment in Cold Climates -
An Engineering Assessment ..........................105
Edward R. Persche; Whitman & Howard, Inc.

iii

This publication contains the results of an effort to assess
the current status of aquaculture technologies for wastewater
treatment. The assessment includes an overview and individual
engineering assessments covering various wastewater aquaculture
systems involving wetlands processes, aquatic plant processes,
and combined aquatic processes. The project was sponsored by the
EPA Office of Water Program Operations and the U.S. Army Corps of
Engineers Cold Regions Research and Engineering Laboratory and
involved contractor assistance by the following individuals:

Mr. Gordon Culp
Culp, Wesner, and Culp

Dr. E. J. Middlebrooks
Utah State University

Dr. Walter J. O'Brien
Black & Veatch

Dr. Edward Pershe
Whitman & Howard, Inc.

Dr. H. G. Schwartz, Jr.
Sverdrup & Parcel and Assoc., Inc.

Dr. George Tchobanoglous
University of California-Davis

ENGINEERING ASSESSMENT OF AQuAcULTURE SYSTEMS FOR
WASTEWATER TREATMENT: AN OVERVIEW

Sherwood Reed USACRREI, Hanover, N.H.
Robert Bastian US EPA/OWPO, Washington, DC
William Jewell Cornell University, Ithaca, NY

BACKGROUND

The use of aquaculture concepts for wastewater treatment has
received increasing attention in recent years. Systems studied to
date have included both natural and constructed wetlands, ponds,
raceways and other structures based on various combinations of
aquatic plants and animals.
In some cases these systems were not optimized for wastewater
treatment since the principal goal was biomass production or the re-
covery of some other beneficial product. In other cases wastewater
treatment has been the primary objective with byproduct recovery of
secondary importance. Both types have been studied at the research
level, tested at the pilot scale, and in some cases demonstrated as
a 'Lull scale operational system.
Some of these systems have shown a potential for reducing energy
requirements and operation and maintenance costs. The incentives
of the Clean Water Act of 1977 provide a strong encouragement for
increased use of such "innovative and alternative" technologies
for wastewater treatment. However, much of the engineering profession,
which is responsible for the design of municipal treatment facilities,
is not familiar with these aquaculture concepts or their capabilities
and limitations.
The purpose of this assessment was to define the current status
of aquaculture technologies and to determine if they are ready for
routine use in municipal wastewater treatment. If they are not ready
for such use the assessment was to recommend procedures for reaching
that goal. This could take the form of further research, demonstra-
tion, or construction of full scale "innovative" systems at selected
locations.
A team of six internationally recognized engineers was retained
to help conduct the engineering assessment. They represented a broad
range of expertise and included both practicing consultants and uni-
versity professors. All were experienced in both research and
design and were knowledgeable regarding biological systems and

innovative technologies. The team included:

Mr. Gordon Culp
Culp Wesner and Culp.

Dr. E.J. Middlebrooks
Utah State University

Dr. Walter J. O'Brien
Black & Veatch

Dr. Edward Pershe
Whitman & Howard, Inc.

Dr. H.G. Schwartz, Jr.
Sverdrup & Parcel & Assoc. Inc.

Dr. George Tchobanoglous
University of California-Davis

This team was organized and directed by Mr. Sherwood Reed, USACRREL
and Mr. Robert Bastian, EPA/OWPO. The basis for the assessment was a
multi agency sponsored seminar entitled "Aquaculture Systems for Waste-
water Treatment" held at the University of California - Davis, on
September 11-13, 1979 (EPA 430/9-80-006). At this meeting research
scientists, operating system personnel and others presented papers on
various projects and concepts relative to aquaculture systems for waste-
water treatment. The final day of the seminar was reserved for direct
discussion and interchange between the team of engineers and the seminar
speakers. Each member of the engineer team then prepared his assessment
based on the seminar presentations, supplemented by other information
available with general literature. The areas addressed were organized
into three major categories and two team members assigned to each one:

1. Wetland processes - Tchobanoglous & Culp

2. Processes primarily dependent on aquatic plants - Middle-
brooks & O'Brien

3. Combined processes where more than one element has a sig-
nificant role - Schwartz & Pershe

This overview is based on those individual reports plus a
review and analysis of the available information by the authors of the
overview. This overview is organized in three topical areas with
discussion, conclusions and recommendations presented for each.

WETLAND PROCESSES

For purposes of this assessment wetlands are defined as land

where the water table is at or above the surface for long enough
each year to maintain saturated soil conditions and the growth of
related vegetation. These can be either preexisting natural wetlands
(eg. marshes, swamps, bogs, cypress domes and strands, etc.) or con-
structed wetland systems. Constructed systems can range from creation
of a marsh in a natural setting where one did not permanently exist
before to intensive construction involving earth moving, grading,
impermeable barriers or erection of containers such as tanks or
trenches. The vegetation that is introduced or emerges from these
constructed systems will generally be similar to that found in the
natural wetlands.
Studies in the United States 'nave focused on peatlands, bogs,
cypress domes and strands, as well as cattails, reeds, rushes, and
related plants in wetland settings. A constructed wetland involving
bullrushes in gravel filled trenches was developed at the Max Planck
Institute in Germany. This patented process has seen limited appli-
cation to date in the U.S. A number of projects have been developed
in the U.S. in recent years for restoration or enhancement of wetlands.
These use wastewater but are not necessarily optimized for wastewater
treatment.
Current experience with wetland systems is generally limited
to the further treatment of secondary effluents. In a few cases
primary effluent has been applied in constructed systems. The
removal efficiency of typical pollutants are reported as:

% Removal
Natural Wetland Constructed Wetland
(Sec. Effluent) (Pri. Effluent)

BOD5 70-96 50-90
Ss 60-90
N 40-90 30-98
P 10-50 20-90

It is assumed that bacteria attached to plant stems and the humic
deposits are the major factor for BOD and for nitrogen removal when
plant harvest is not practiced. Plant production can play a more
significant role in nutrient removal when harvesting is included.
With respect to phosphorus removal the contact opportunities with the
soil are limited in most natural wetland systems (an exception might
be peat bogs) and a release of phosphorus has been observed during
the winter in some cases. Based on current experience the land area
being used for natural wetland systems ranges from 30 to over 60
acres per million gallons of wastewater applied. The surface area
for constructed marshes range from 23 to 37 acres per million gallons
of wastewater applied.
The major costs and energy requirements for natural wetlands are
the preapplication treatment, pumping and transmission to the site,
distribution at the site, minor earthwork, and land costs. In
addition to these factors a constructed system may require the instal-
lation of a barrier layer and additional containment structures.

Other factors to be considered are potential disruption of the existing
wildlife habitat and ecosystems in a natural wetland, loss of water
via evapotranspiration for all wetlands in arid climates, the pote-n-
tial for increased breeding of mosquitoes or flies, and the development
of odor. The major benefits that can be realized from use of wet-
lands include preservation of open space, wildlife habitat enhancement,
increased recreation potential, streamflow stabilization and augmenta-
tion in addition to wastewater treatment.

Conclusions

1. Wetland systems can achieve high removal efficiencies for BOD,
SS, trace organics and heavy metals. Their potential may exceed that
achieved in mechanical treatment systems. The specific factors
responsible for these high treatment levels are not clearly under-
stood at this time.
2. Optimum, cost effective criteria are not yet available for
routine design of wetland type municipal wastewater treatment systems
throughout the U.S. The concept has been shown to be viable and
should certainly qualify under current EPA definitions as an innova-
tive technology.
3. The use of constructed wetlands has a greater promise of
more general application. These have potential for better reliability
and process control with a lesser risk of adverse environmental
impact.
4. The use of natural wetlands offers a lesser opportunity for
process control due to natural variability within the system. They
do however have considerable potential as a low cost, low energy
technique for upgrading wastewater effluents, especially for smaller
communities located in areas of abundant wetlands. The prevention
of adverse impacts on the existing, sensitive wetland ecosystem will
require adequate monitoring and appropriate management practices.
5. Optimization of criteria for constructed wetlands should
result in much lower land and preapplication treatment requirements
as compared to the use of natural systems.
6. Health risks for wetland systems are probably not higher
than for conventional treatments assuming that insect vectors are
controlled and that harvested materials are not used for direct human
consumption.
7. The potential for general, routine use of wetland systems,
particularly the constructed type, seems high as soon as reliable,
cost effective engineering criteria are available.

Recommendations

1. Development of reliable engineering criteria will require
additional research and study. These efforts should focus on con-
structed wetlands or on large scale carefully controlled plots in
natural wetlands.
2. Several large scale natural systems should be installed in
different geographical locations, representing the major types of
wetland systems, with a range of design loadings. These should be

extensively monitored to obtain "real world" operating information
and to serve as the data base for development of design criteria.
This development should be an interdisciplinary effort involving
engineers, scientists and regulatory agencies.
3. A number of constructed wetland systems should be established
concurrently in a variety of geographical settings with other vari-
ables held to the minimum. This should allow development of region-
ally applicable criteria and eventually of generalized relationships
for universal application.
4. Studies of constructed systems should be directed towards
minimizing cost and energy inputs. Therefore, tests with very
dilute or highly treated effluents should be avoided. The focus
should be on untreated wastewaters, primary effluents, and on nutrient
removal mechanisms.

AQUATIC PLAN~T SYSTEMS

This assessment is based primarily on those systems that use
free floating aquatic plants (macrophytes) for the treatment or
polishing of wastewater. Most of the information that is available
is limited to the use of either water hyacinths or duckweeds and most
of these data are from water hyacinth systems in warm climates. These
systems are all constructed and are generally similar in concept to
wastewater treatment pond technology.
Water hyacinths have been studied in systems treating primary
effluents, as the final treatment cells in multiple cell ponds, and
as an advanced waste treatment step after conventional secondary
treatment. A field scale system for treating industrial wastewaters
is in operation at the NASA facilities in Bay St. Louis, MS and
pilot scale systems are under study at a refinery in Baytown, TX.
A field scale system incorporating duckweed is located in N. Biloxi,
MS. Effluent from this two cell pond system is much better than
secondary quality.
Water hyacinth systems are capable of removing high levels of
BOD, SS, metals, and nitrogen, and significant removal of refractory
trace organics. Removal of phosphorus is limited to the plant needs
and probably will not exceed 50 to 70% of the phosphorus present in
the wastewater. Phosphorus removal will not even approach that
range unless there is a very careful management program with regular
harvests. In addition to plant uptake the root system of the
water hyacinth supports a very active mass of organisms which assist
in the treatment. The plant leaves also shade the water surface
and limit algae growth by restricting light penetration.
Multiple cell pond systems where water hyacinths are used on one
or more of the ponds are the most common system design. Based on
current experience a pond surface area of approximately 15 acres per
million gallons seems reasonable for treating primary effluent to
secondary or better quality. For systems designed to polish secondary
effluent to achieve higher levels of BOD and SS removal an area of
about 5 acres per million gallons should be suitable. For enhanced
nutrient removal from secondary effluent an area of approximately 12

acres per million gallons seems reasonable. Effluent quality from
such a system might achieve: less than 10 mg/L for BOD and SS,
less than 5 mg/L for N, and approximately 60% P ~removal. This level
of nutrient removal can only be obtained with careful management and
harvest to yield 50 dry tons or more, per acre per year.
The organic loading rates and detention times used for water
hyacinth systems are similar to those used for conventional stabili-
zation ponds that treat raw sewage. However, the effluent from the
water hyacinth system can be much better in quality than from a con-
ventional stabilization pond, particularly with respect to: SS
(algae), metals, trace organics, and nutrients.
Harvest of the water hyacinth or duckweed plants may be essential
to maintain high levels of system performance. It is essential for
high levels of nutrient removal. Equipment and procedures have been
demonstrated for accomplishing these tasks. Disposal and/or reuse
of the harvested materials is an important consideration. The
water hyacinth plants have a moisture content similar to that of
primary sludges. The amount of plant biomass produced (dry basis)
in a water hyacinth pond system is about 4 times the quantity of
waste sludge produced in conventional activated sludge secondary
wastewater treatment. Composting, anaerobic digestion with methane
production, and processing for animal feed are all technically feas-
ible. However, the economics of these reuse and recovery operations
do not seem favorable at this time. Therefore only a portion-of the
solids disposal costs will be recovered unless the economics can be
improved.
The major cost and energy factors for water hyacinth systems
are construction of the pond system, water hyacinth harvesting and
disposal operations, aeration if provided, and greenhouse covers
where utilized. Evapotranspiration in arid climates can be a critical
factor. The water loss from a water hyacinth system will exceed
the evaporation from a comparable sized pond with open water. Green-
house structures may be necessary where such water loss and related
increase in effluent TDS are a concern. Mosquito control is essential
for water hyacinth systems and can usually be effectively handled
with Gambusia or other mosquito fish. Legal aspects are also a con-
cern. The transport or sale of water hyacinth plants is prohibited
by federal and state law in many situations. The inadvertant release of
the plants from a system to local waterways is a potential concern to a
-number of different agencies. Water hyacinth plants cannot survive or
reproduce ,in cool waters so the concept will be limited to "warm" areas
unless climate control is provided. Other floating plants such as
duckweed, alligator weed, and water primrose have a more extensive
natural range but limited data as their performance in wastewater
treatment is available.

Conclusions

1. Aquatic plant systems using water hyacinths can achieve high
removal efficiencies for BOD, SS, trace organics, heavy metals and
nitrogen. The potential can equal, and may exceed that achieved in
mechanical treatment systems.

2. Water hyacinth systems are ready for routine use in municipal
wastewater treatment, at least within the geographical range where
such plants grow naturally. Reliable engineering criteria are avail-
able for the design of systems for-treating primary effluent, for up-
grading existing systems, for advanced secondary treatment and for
full AWT.
3. It is unlikely at this time that the costs of plant harvest
and processing will be completely offset by the value of useful
products (eg: animal feeds, compost, biogas, etc.).
4. Water hyacinth systems may be technially feasible even in
northern climates if operated in a protected environment or run as
a seasonal activity. However, this has yet to be shown to be cost
effective for climatic zones where the plants cannot exist naturally.
5. Nutrient removal in water hyacinth systems is more complex
than uptake by the plant alone, but the responsible mechanisms are not
yet clearly defined.
6. Duckweeds are a more cold tolerant plant than the water hya-
cinth. Wastewater treatment experience with these plants is limited and
engineering criteria for routine design are not yet available.
7. Many other cold tolerant aquatic plants exist but their
potential for wastewater treatment has not been evaluated.

Recommendations

1. Further optimization of water hyacinth system design is
possible. This should include: tracer studies of existing systems
to determine actual detention time, the full range of organic and
hydraulic loadings that may be possible, and on mass balances of water
and pollutant materials.
2. Additional study is needed to establish optimum plant har-
vesting and utilization techniques and to evaluate alternative methods
for removing additional phosphorus with water hyacinth systems.
3. A study should be undertaken to evaluate the potential for
water hyacinth systems in cooler climates. This should include energy
requirements and overall cost effectiveness. If results of the paper
study are favorable a pilot testing/demonstration program might be
considered.
4. Research and demonstration projects should focus on the use
of duckweed and other plants (especially the more cold tolerant types)
for wastewater treatment. These efforts should include: removal
kinetics for pollutants as a function of detention time, temperature,
plant type, etc.; and the effect of system configuration, season,
benthic materials, and plant harvest on degree of treatment,

COMBINED SYSTEMS
For purposes of this assessment, combined systems are defined
as treatment systems derived from aquaculture concepts that either
contain more than one active aquaculture component in a single unit
or that are combined with other aquaculture or conventional units
to form a process. An example of the former are the experiments at
Woods Hole Oceanographic Institute involving a number of different

marine organisms. Examples of the latter are the Solar Aquacell
System at Hercules CA, the marsh/pond systems studied at Brookhaven
National Laboratories, LI, and the use of fish in the final cells of
wastewater stabilization ponds in Arkansas.
Based upon the results of experimental and pilot testing work to
date, it is clear that both agricultural and municipal wastewater in
treated or partially treated forms can be used in fish culture and
other aquatic protein or biomass production systems. Fin fish such
as Tilapia, carp, gamefish and bait minnows have been very successfully
raised in and harvested from wastewater stabilization pond systems.
Daphnia, shellfish, vascular plants, algae, and other aquatic organisms
have also been successfully produced and harvested. However, it is
-not clear that such systems can be optimized for both waste treatment
and protein production purposes at the same time.
Since each concept is unique it is not possible to present a
general summary of performance for "combined systems". The potential
for routine use must also be discussed on an individual basis. For
that reason, the examples cited above are discussed individually
below. Discussion of this limited number of projects is not intended
to imply that there are not other viable systems or combinations, but
space limitations have precluded an exhaustive presentation. It is
hoped that the assessment of these few projects will provide some
general indications or trends regarding combined systems.

Marine Polyculture
Woods Hole Oceanographic Institute, MA

This pilot scale, continuous flow system was designed to remove
nitrogen from secondary effluents and at the same time culture marine
organisms that have commercial value. The secondary effluent was di-
luted with seawater and introduced to a system that consisted of
shallow algae ponds, followed by aerated raceways containing stacked
trays of shellfish and then into a final unit for seaweed production.
The algae ponds were designed as the initial nitrogen removal
step. The projected area requirement for this step was comparable
to that required for conventional facultative stabilization ponds.
Problems encountered at this step included inhibition of algae produc-
tion by particulate matter in the secondary effluent, seasonal varia-
tion of algae species and protozoan predation. Some algae species
proved detrimental to shellfish culture and the problem of algae
species control was not resolved. The shellfish experiments with the
American oyster and hard clams indicated slow growth rates and high
mortality. The last unit contained seaweeds for final nutrient removal
with vigorous circulation to keep the seaweed in suspension. Overall
nitrogen removal was 89% with all components functioning but the
overall cost effectiveness was questionable since the shellfish pro-
duction unit was not successful. It appears that nitrogen removal
could be achieved by just a seaweed unit without the preliminary
algae and shellfish steps.

Solar Aquacell System
Hercules, CA

Thi-s system was developed through bench and pilot scale testing
of combined aquaculture and conventional technologies. A full scale
system has been recently constructed at Hercules, CA. The system
consists of a two cell anerobic unit, followed by an aerated cell
followed by a final aerated cell covered with water hyacinths and
some duckweeds. An internal feature of all cells are buoyant plastic
strips to serve as a substrate for the growth of attached organisms.
The entire system is covered by a (double layer polyethylene, air in-
flated roof) greenhouse structure. Aeration is provided by submerged
tubing and is low to moderate in intensity.
Performance results are not yet available from the Hercules
system. Based upon pilot units, tested elsewhere, it was predicted
that final effluent quality would be 5 mg/L or less for BOD and SS
if 5 days detention time is provided in the final water hyacinth cell.
The buoyant plastic webbing, with its attached growth is credited with
80% or more of the removal achieved in this cell. Removal of total
nitrogen was about 50% in the same 5 day detention pilot tests and the
water hyacinth plants accounted for only 10% of that removal. Phos-
phorus removal was relatively low (1-2 mg/L removed in 5 days) since
the aquatic plants and organisms are the only pathways available.
The Solar Aquacell concept requires a regular schedule of water
hyacinth harvest, processing and disposal. The Hercules, CA system
also includes ozone disinfection and a sand filter for final polishing
to maximize reuse potential for the effluent. A functional analysis
of the various elements and components in the system seems to indicate
that the major portion of BOD, SS, and nitrogen removal is provided
by the anaerobic cells and by the attached biomass on the plastic
webs in the aerated cells. The major function of the water hyacinths
and duckweeds may be in shading the water surface to prevent algae
growth. The use of the buoyant plastic web in an aerated pond is a
novel and innovative application. The system can then benefit from
both suspended and attached organisms and the presence of the webs
should reduce or eliminate short circuiting of flow in the system.

Marsh-Pond System
Brookhaven National Laboratory, NY

This 20,000 gpd, pilot unit included an aerated holding cell with
2 1/2 days detention time followed by a 0.2 acre constructed marsh
followed by a 0.2 acre unaerated pond with a partial cover of floating
duckweeds. Effluent from the pond was then applied to the land at a
forested site in a groundwater recharge experiment. This assessment
is not concerned with the land application step or a parallel experi-
ment involving overland flow ahead of another marsh/pond combination.
The system was studied for several years (1975-1978) and received
a wide variation of flow and pollutant loadings. Effluent recycle from
the pond to the head end of the marsh was conducted frequently to
maintain flow in the system. However, neither this recirculation or
the preaeration were controlled in a regular manner. The system was
operated on a year-round basis in the relatively temperate winter
climate on-Long Island (average air temperature below freezing 5 months

of the year and the water temperature in the system was 20C or less
4 months of the year). Reported effluent characteristics averaged
for the period 1975-1977 were:

mg/L % Removal

BOD 21 89
Ss 42 91
TKN 11 63
Total P 2 66

The parallel overland flow marsh/pond produced slightly better
results in all categories. Neither system during the period under
discussion could consistantly meet secondary treatment standards for
suspended solids. Both however, provided an excellent, and probably
cost effective preapplication treatment for the groundwater recharge
operation. It is not possible from the published data on the Brook-
haven studies to develop optimum engineering criteria for rational
design since detention times, mass balances, effect of configuration,
season, plant type, etc. were not quantified.

Fin Fish in Stabilization Ponds
Benton, Ark.

There are numerous examples of successful fish culture operations,
with a variety of species, in cooling ponds and wastewater stabiliza-
tion ponds. This assessment will focus on studies in Arkansas where
the effect of fin fish on water quality improvement was evaluated
in controlled experiments.
The preliminary experiments compared parallel 3 cell stabiliza-
tion ponds receiving equal volumes of the same wastewater (BOD 260
mg/L, SS 140 mg/L). The cells in one set were stocked with silver,
grass, and bighead carp while the other set received no fish
and was operated as a conventional stabilization pond. The compari-
tive study continued for a full annual cycle. Results indicated
generally similar performance of the two systems but the fish culture
units consistantly performed somewhat better than the conventional
pond. For example, the effluent BOD from the fish system ranged
from about 7 to 45 mg/L with values less than 15 mg/L obtained more
than 50% of the time. The conventional pond system had effluent BOD
ranging from 12 to 52 mg/L with values less than 23 mg/L about 50%
of the time. Suspended solids were very similar in the effluents
for both systems except in July when the concentration was about
110 mg/L for the conventional pond and 60 mg/L for the fish system.
The second phase of the study was conducted at the same location
with the same wastewater. The six pond cells were all connected in
series and a baffle constructed in each to reduce short circuiting.
Silver carp and bighead carp were stocked in the last four cells and
additional grass carp, buffalofish and channel catfish in the final
cell. No supplemental feed or nutrients were added to the fish culture
cells. Estimated fish production after 8 months was over 3000 pounds
per acre.
Effluent quality steadily improved during passage through the six

cell system. The BOD removal for the entire system averaged 96% for
the 12 month study period. About 89% of that removal was achieved in
the first two conventional stabilization cells. Removal of suspended
solids averaged 88% in the entire system with 73% of the removal
occurring in the first two conventional stabilization cells. It is
not clear wether the fish or the additional detention time or some
combination is responsible for the additional 7% BOD removal in the
final 4 fish culture cells. The final average effluent concentration
of about 9 mg/L is typical for six cell conventional stabilization
ponds of comparable detention time. It seems very likely that the fish
contributed significantly to the low suspended solids value in the
final effluent (17 mg/L) via algal predation. A value two or
three times that high might be expected for conventional stabilization
ponds.

Conclusions

1. Finfish were effective in providing further treatment in
wastewater treatment ponds. Their major role seems to be suspended
solids control for final polishing.
2. It does not appear that aquaculture components in "icombined
systems" can be optimized for both protein or biomass production
and waste treatment in the same unit.
3. Systems involving higher forms of animals seem to be less
efficient (at waste treatment), require more land area, or are more
difficult to control than systems primarily based on plants.
4. There is sufficient information available to install fish
culture units in the final cells of stabilization ponds. There is
not enough information available to permit routine design of such
units for wastewater treatment. Specific removal rates and growth
rates and O&M requirements under different environmental and waste-
water conditions need further definition.
5. Most of the other combined systems discussed here are
either in the exploratory or developmental stage and rational criteria
for their routine design are not available at this time.

Recommendations

1. Development of new concepts in the use of polyculture or
combined systems for wastewater treatment should be strongly encouraged.
The focus should be on high rate, low energy combinations involving
plants and possibly animals or mechanical elements.
2. Further study and evaluation of combined systems is necessary.
This should focus on identifying critical components and on the de-
velopment of engineering design criteria.
3. The most promising concepts should be tested in a variety of
geographical settings to define removal kinetics and develop criteria
for a range of wastewaters and environmental conditions. This would
include the degree of thermal protection and energy required for opera-
tion in cooler climates.
4. Studies should focus on the health effects of the direct use
of animal protein harvested from these systems in human foods. Studies

should also consider development of alternative products from the
animal protein.

REFERENCES

References are not included in this Overview since it was drawn
from the six engineering assessments listed previously and from pre-
sentations at the Davis, CA aquaculture seminar (EPA 430/9-80-006;
Sept. 1979).

WETLAND SYSTEMS FOR WASTEWATER TREATMENT:
AN ENGINEERING ASSESSMENT

George Tchobanoglous Department of Civil Engineering,
University of California, Davis, CA

Gordon L. Culp Culp, Wesner, and Culp,
Cameron Park, CA

ABSTRACT

The use of natural and artificial wetlands for the treatment of wastewater
is examined in this engineering assessment. The primary objective of the
assessment is to answer the question of whether the technology of using natural
and artificial wetlands for the treatment of wastewater is ready for routine use
and, if not, what must be done to make it a reality. Assessed on the basis of
1) treatment efficiency and reliability, 2) availability of design criteria and
procedures, 3) availability of proven management techniques, 4) energy and
resource consumption, 5) costs, and 6) health risks, it is concluded that the
current status of wetlands technology is not yet developed to the point where
the use of wetland systems can be considered routine. Data and information
that must be developed before the design of wetland systems can become a
rational undertaking are identified and discussed.

INTRODUCTION

It has been estimated that wetlands occupy about four percent of the
surface of the continental United States. Within the past 20 years, the use of
natural wetlands as a low cost alternative to conventional and advanced waste-
water treatment has received considerable attention. The use of artificial
wetlands for the same purpose is also an outgrowth of this interest. It is,
therefore, the purpose of this paper to present an engineering assessment of the
use of both natural and artificial wetlands for the treatment of wastewater.
To accomplish this purpose, the material to be presented has been organized
into sections dealing with 1) the characteristics of natural and artificial wetlands,
2) the use of wetlands for wastewater treatment, 3) the implementation of
wetland treatment systems, 4) the management of wetland systems, 5) an
assessment of what is known and 6) research needs. What is known from an
engineering point of view is discussed in the first four sections. What needs
to be known is considered in the last two sections.

The findings contained in this report were derived, in part, from
information gained from participation in a three-day workshop/seminar entitled,
"Aquaculture Systems For Wastewater Treatment," held on the University of
California, Davis, Campus on September 11, 12, and 13, 1979. Additional
information and data were gathered from the literature. Because this report
is an engineering assessment, the primary objective is to answer the question
of whether the technology of using natural and artificial wetlands for the
treatment of wastewater is ready for routine use and, if not, what must be
done to make it a reality.

CHARACTERISTICS OF WETLANDS

Wetlands have been defined as "... land where the water table is at or
above the land surface for long enough each year to promote the formation of
hydric soils and to support the growth of hydrophytes as long as other
environmental conditions are favorable." (2). Because water is such a fundamental
component of all wetlands, most wetland classification schemes are based on a
consideration of hydrogeological factors. From the standpoint of wastewater
treatment and water quality management, such a classification is useful because
the hydrogeology of wetlands is the factor that can be controlled most easily.
Both natural and artificial wetlands are considered in the following discussion.

Natural Wetlands

The principal types of natural wetlands may be classified as 1) riverine,
2) lacustrine, 3) palustrine, and 4) tidal. The important characteristics of these
wetlands are reported in Table 1. Reviewing the descriptions of the natural
wetlands given in Table 1, it is clear that performance of these wetlands when
used for the treatment or disposal of wastewater will depend to a large extent,
on the local surface and groundwater hydrology. With respect to each of the
major water inputs (surface, ground, atmosphere, and tidal), natural wetlands
can be classified as 1) inflow/outflow, 2) no inflow/outflow, and 3) inflow/no
outflow. For example, a number of palustrine wetlands in the central states
have no surface water inflow or outflow. When these wetlands are used for
the disposal of wastewater, the survival of the existing natural ecosystems will
be highly dependent of the organic and inorganic nutrient loadings. Where
riverine wetlands are used, the treatment capacity will depend on the surface
water inflow and outflow. Thus, detailed hydrologic studies must be conducted
before natural wetlands are used for the treatment or disposal of wastewater
if this resource is to be protected.

Artificial Wetlands

Wetlands constructed in locations where none existed previously are usually
termed "artificial." Such wetlands have been implemented for a variety of
purposes including habitat enhancement, recreation and wastewater treatment.
Because the purpose of this report is to assess the use of wetlands for wastewater
treatment, only those constructed for such use will be considered in this
discussion. The principal types of artificial wetlands used for wastewater
treatment are reported in Table 2.

Table I
HYDROLOGICAL CLASSIFICATION OF NATURAL WETLANDS a

Type Description

Freshwater

Riverine Wetlands adjacent to or near rivers or streams where the water in the river
or stream is the principal inflow to the wetlands. Inflow may be direct or by
subsurface seepage.

Lacustrine Wetlands adjacent to or near lakes.

Palustrine Wetlands not confined by channels and not adjacent to lakes. Because palustrine
wetlands are isolated from open bodies of water, such as streams, rivers, or
lakes, there is little exchange of water. Ombrogenous bogs, blanket bogs, and
sunkan minerotrophic marshes are examples of palustrine wetlands.

Saline

Tidal Wetlands whose waters are subject to tidal fluctuations. Four distinct wetlands
can be defined: 1) wetlands adjacent to streams, 2) areas continually covered
with water in which the direction of flow changes with the tide, 3) areas that
are normally covered with water, but are drained at low tide, and 4) high
marsh areas covered with water only of high tides.

aDerived in part from References II and 30.

Table 2
ARTIFICIAL WETLANDS USED FOR THE TREATMENT OF WASTEWATER

Type Description

Freshwater

Marshes Areas with semi-pervious bottoms planted with various wetlands plants such
as reeds or rushes.

Marsh-pond Marsh wetlands followed by pond.

Ponds Ponds with semi-pervious bottoms with embankments to contain or channel
the applied water. Often, emergent wetland plants will be planted in clumps
or mounds to form small sub-ecosystems.

Trench Trenches or ditches planted with reeds or rushes. In some cases, the trenches
have been filled with peat.

Trench (lined) Trenches lined with an impervious membrane usually filled with gravel or sand
and planted with reeds.

aDerived in part from References 11 and 30.

THE USE OF WETLANDS FOR WASTEWATER TREATMENT

It is the purpose of this section to review what use has been made of
wetlands for wastewater treatment. To do this, the material to be presented
F ~~~is organized into three sections: 1) an overview of the principal types of natural
and artificial wetlands that have been used for the treatment of wastewater,
2) the physical, chemical, and biological transformations that occur in wetlands
that effect water quality, and 3) documentation of the removal efficiencies
observed in wetlands for the various constituents found in wastewater.

Wastewater Treatment in Wetlands

The purposeful use of wetlands for wastewater treatment is a relatively
recent development dating back to the early 1960's. It should be noted, however,
that there are a number of instances where wastewater discharges to wetlands
date back to the 1920's and earlier. For example, the Brillion Marsh in Wisconsin
has been receiving domestic sewage since 1923 (21). In many cases,. discharge
to wetlands represented the only means of disposing of a community's wastes.

Treatment in Natural Wetlands To date, where natural wetlands have
been used for the treatment of wastewater, the usual practice has been to apply
treated eff luent. In most cases, the objective has been the improvement of
water quality. In a few instances, enhancement of the wetlands habitat has
been the major objective.
Summary information on representative natural wetlands that have been
used for wastewater treatment are reported in Table 3. As reported, secondary
effluent has been applied most commonly. It is also interesting to note that
most applications were started within the past ten years.

Treatment in Artificial Wetlands One of the pioneers in the use of
artificial wetlands for the treatment of wastewater is Kathe Seidel (21). She
and her co-workers at the Max Planck Institute in Germany have been studying
the use of plants for this purpose since the early 1950's. A patented system
in which gravel and sand are placed in a lined trench with central drainage and
planted with reeds or rushes is an outgrowth of her work at the Institute (21).
Representative examples of artificial wetland systems used for the treatment
of wastewater are presented in Table 4.

Transformations Occurring in Wetlands

The physical, chemical, and biological transformations occurring in wet-
lands must be understood if the removal of the constituents in wastewater is
to become a scientific undertaking. From an engineering standpoint, the transfor-
mations that are of most importance are those occurring to reduce or alter the
concentrations of the various constituents contained in wastewater and those
associated with the decomposition of the dead organic matter that is produced
in wetlands.

Removal Mechanisms For Wastewater Contaminants The principal removal
mechanisms for the contaminants in wastewater in wetlands are summarized in
Table 5. The mechanisms have been identified on the basis of observations of
natural systems and laboratory and pilot scale aquatic treatment systems. An

Table 3
TYPICAL NATURAL WETLANDS USED FOR
WASTEWATER TREATMENT AND DISPOSAL

Type of
Type Wastewater
(location) Applied Remarks References

Cypress Secondary Geographically limited 9,10
domes
(Florida)

Northern Secondary Marshland percolation/ 7,15,16,17,34
peatlands disposal system
(Michigan,
Wisconsin)

Cattail Secondary Significant nutrient 21,23,24,29
marshes reductions
(Wisconsin)

Freshwater Secondary Possible tertiary 33
tidal marsh treatment
(New Jersey)

Lacustrine Secondary Sediment ion most 19
marsh important
(Hamilton Ontario,
Canada)

Swamplands Secondary 12,13
(Hay River,
Canada)

Wetlands, general Secondary 8,35,36
(Massachusetts,
Florida)

Table 4
TYPICAL ARTIFICIAL WETLAND SYSTEMS USED FOR THE
TREATMENT AND DISPOSAL OF WASTEWATER

Type of
Type Wastewater
(location) Applied Remarks References

Meadow-marsh-pond Screened- 22
system/ comminuted-
(New York) aerated-unsettled
raw wastewater

Ponds with Settled Process defined 5,27
reeds or rushes/ primary, in U.S. Patent
(Germany, Holland) secondary No. 3,770,623

Peat filled trench Settled Variable trench 7
systems/ primary, depths
(Finland) secondary

Peat filter/ Secondary Need 20 percent 7,25
(Minnesota) air space volume
in soil

Marsh-pond Secondary Enhancement 4
system/ project
(California)

Table 5

REMOVAL MECHANISMS IN WETLANDS FOR THE CONTAMINANTS IN WASTEWATERa

Contaminant Affectedb/

Mechanism ~ o4 $~6'Description

Physical
Sedimentation P 5 I I I I I I Gravitational settling of solids (and constituent contaminants)
in pond/marsh settings.
Filtration S S Particulates filtered mechanically as water passes through
substrate, root masses, or fish.
Adsorption S Interparticle attractive force (van der Waals force).
r") Chemical
CD
Precipitation P P Formation of or co-precipitation with insoluble compounds.
Adsorption P P 5 Adsorption on substrate and plant surfaces.
Decomposition P P Decomposition or alteration of less stable compounds by
phenomena such as UV irradiation, oxidation, and reduction.
Biological
Bacterial Metabolismc P P P P Removal of colloidal solids and soluble organics by suspended,
benthic, and plant-supported bacteria. Bacterial nitrification/
denitrification.
Plant Metabolismc S S Uptake and metabolism of organics by plants. Root excretions
may be toxic to organisms of enteric origin.
Plant Absorption S S S S Under proper conditions significant quantities of these
contaminants will be taken up by plants.
Natural Die-Off P Natural decay of organisms in an unfavorable environment.

aAdopted from Reference 26.
bp=primary effect, S=secondary effect, I=incidental effect (effect occurring incidental to removal of another contaminant).
cThe term metabolism includes both biosynthesis and catabolic reactions.

understanding of these mechanisms and their corresponding rates of reaction is
important in I) assessing the performance of existing natural wetlands in the
treatment of wastewater and 2) the design of artificial wetlands treatment
systems.
Referring to Table 5, the removal mechanisms have been classified as
physical, chemical, and biological. This classification has been used so that the
factors governing each mechanism can be defined and ultimately modelled. In
wetlands, these removal mechanisms are operative in the water column; in the
soil column beneath the wetland; and at the interface between the water and
soil columns. Most of the biological transformations that occur in wetlands
take place on or near a surface to which the bacteria are attached. Thus, the
presence of emergent vegetation and humus (discussed below) is very important
with respect to the biological transformations that occur in wetlands.

Decomposition of Dead Organic Matter In addition to the removal of
the constituents in wastewater, processes leading to the eventual decomposition
of the dead organic matter found in wetlands, derived primarily from plant
tissue, are of fundamental importance in the operation and management of
wetland treatment systems. Two basic processes must be considered. They are
mineralization and humification (14,31).
Mineralization occurs as a result of the metabolism of microoganisms.
As noted in Table 5, the term metabolism refers to both biosynthesis, in which
organic matter is assimilated into cell tissue, and to catabolism, in which organic
matter is converted to simple compounds to obtain energy for cell systhesis and
maintenance. Dead organic matter not used for cell production is released in
the form of minerals or simple organic compounds. This release of minerals
and organic compounds may effect the quality of effluent from wetlands.
Humification is the process by which organic compounds are transformed
into a material called humus. The process of humification involves a long series
of biochemical transformations in which a variety of organic compounds are
slowly converted into complex organic heteropoly-condensates with bonds of
different strengths (31). Bonding with mineral constituents in the environment,
such as metal ions in solution and clays in the substrate affects both the
formation and stability of humic substances (31).
The development of humus in wetlands is especially important in the
treatment of wastewater because this material forms an attachment medium
for bacteria. Denitrification is thought to occur as wastewater flows through
humus layers in wetlands.

Treatment Efficiency in Wetlands

If wetlands are to be used for the treatment of wastewater, it is important
to know which constituents will be removed, the extent to which they will be
removed, and the factors controlling their removal. The constituents that are
removed and the extent to which they are removed are considered in the following
discussion. Some of the factors affecting their removal have been considered
in the previous discussion dealing with the transformations occurring in wetlands.
These and other factors are also considered in the section dealing with the
design of wetland systems.

Constituent Removal Efficiencies In reviewing the literature dealing with
wetlands, a great deal of confusion exists in the reporting of performance data

for natural and artificial systems used for the treatment of wastewater. In
most cases, the data are so confounded in a statistical sense that little or no
usable information can be derived. Also, there is no standardization regarding
the basis on which performance data are reported. For example, in some articles,
performance data are reported as a function of time, while in others as a
function of distance. Usually, no basis or information is given on how time or
distance are interrelated. Further, the data for most of the natural systems
are extremely site specific and should not be generalized.
Recognizing the above limitations, the reported removal ranges for the
constituents of concern in wastewater are presented in Table 6. From a review
of the limited data presented in Table 6 it can be concluded that the performance
of wetlands with respect to most constituents of concern is not well defined.
Further, the range of the values reported in Table 6 is also of concern, especially
the lower removal efficiencies.

Constituent Removal Kinetics Based on a review of the data in the
literature on both natural and artificial wetlands and on overland flow systems,
which can be considered to be wetlands, it appears that the removal of BODs,
TOC, and COD can be described with a first order function of the form:

C = Coe-kt (1)
t- 0
where Ct = concentration remaining at the time t, mg/I
Ct = concentration at time t=0, mg/l
k� = specific removal rate constant for given constituent,
at 200C, l/d
t = detention time in wetland, d.

Based on preliminary evidence, it appears that such a relationship may also
apply to the removal of pathogenic microorganisms, certain trace organics, and
heavy metals.
If it is assumed that 95 percent of the BOD5 in primary 1~vastewater is
removed in 10 days, the value of k is on the order of 0.3 day- . Because of
the areal extent of most wetlands the value of k will depend,to a large extent,
on the temperature. From experience with other biological systems, the effect
of temperature can probably be modelled with sufficient accuracy using the
following expression.

kT = k20 (T-20) (2)

where kT = removal rate constant at temperature T, 1/d
kT = removal rate constant at 200C, l/d
0 = temperature coefficient, 1.05-1.08
T = temperature, 0C

The temperature is assumed to be that of the water in the wetland. The
significance of the above equation for cold regions is that the area of most
wetlands must be increased by a factor of two or more during the winter to
achieve the same level of treatment. Because it is assumed that the bacteria
attached to the plant stems and humus are responsible for treatment, the fact
that the wetland plants may be dormant or die in the winter is of little concern
with respect to BOD removal unless the physical plant support structure is lost.

Table 6
REPORTED REMOVAL EFFICIENCY RANGES
FOR THE CONSTITUENTS IN WASTEWATER
IN NATURAL AND ARTIFICIAL WETLANDS

Removal efficiency, %

Natural wetlands Artificial wetlands

Constituent Primary Secondary Primary Secondary

Total solids 40-75

Dissolved solids 5-20

Suspended solids 60-90

BOD5 70-96 50-90

TOC 50-90

COD 50-80 50-90

Nitrogen (total as N) 40-90 30-98

Phosphorus ttotal as P) 10-50 20-90

Refractory organics

Heavy metalsa 20-i00

Pathogens

bRemoval efficiency varies with each metal.

The removal kinetics for nitrogen and phosphorus are not as well defined.
In most natural systems, receiving wastewater, little or no plant management
or harvesting is practiced. The net annual nitrogen requirements of the plants,
in most cases, is insignificant in terms of the applied nitrogen. Thus, nitrogen
removal is primarily dependent upon nitrification-denitrification reactions which
are accomplished by bacteria attached to plant stems or present at the soil
water interface. The reactions are dependent upon the temperature, the concen-
tration of dissolved oxygen, the nature of the support structure, and the detention
time (which is related to depth of water and flow rate). In natural wetlands it
appears that a moving concentration front of phosphorus often develops in a
manner similar to that observed in ion exchange columns. It has also been
observed, in some cases, that phosphorus is released during the winter, usually
in association with scoured particulate matter. Thus, operational control may
be a key factor in optimizing the removal efficiency of natural wetlands with
respect to nitrogen and phosphorus. The control of phosphorus may be more
manageable in artificial systems.

IMPLEMENTATION OF WETLAND TREATMENT SYSTEMS

To design wetland systems for the treatment of wastewater, information
must be available on 1) treatment objectives, 2) usable system configurations,
3) the applicable design criteria, 4) the plant and animals, available locally, 5)
the operational requirements, 6) resource and energy consumption, 7) the cost
of facilities for each type of wetland system, and 8) related legal and
environmental impacts. To the extent possible, each of these topics is considered
briefly in the following discussion.

Treatment Objectives

The first step in implementing the use of wetlands for wastewater
treatment is to establish the treatment objectives to be achieved. To date, the
most common use of natural wetlands is for the advanced treatment of wastewater
following conventional secondary treatment. Their use for the treatment of raw
or primary wastewater is not well defined. As a consequence, this latter
application should be approached with great caution.
At this time, based on a limited amount of operational data, the use of
artificial wetlands for the treatment of primary effluent appears to be justified.
The application of secondary effluent appears to be justified where nitrogen
limits must be met. In the future, it is anticipated that artificial wetlands can
be designed to be used with screened effluent.

System Configuration

System configuration refers to the location of the wetlands in the overall
treatment flowsheet. The location of the wetlands will affect the design criteria
and management techniques to be used. The application of artificial wetlands
for the treatment of wastewater is shown in Figure 1. The applications shown
in Figure 1 are arranged from the least to most complex. For example, in
Figure 1 a wetland system would be used for the removal of nutrients, refractory
organics, and heavy metals.

WATE'AER CONVENTIONAL AWDISCHARGE
ITREATMENT I AQCUTR

~~~~~IC

3 IREENINV >

(e) I ADCMMINUTION ONLY

(f)~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PRIMARY SECONDARY ADVANCED
TREATMENT TREATMENT TREATMENT

Figure I

APPLICATION OF ARTIFICIAL WETLANDS (AW)
FOR THE TREATMENT OF WASTEWATER
(Adapted from Reference 26)

Design Criteria

At present, few if any design criteria are available that can be used to
predict reliably the performance of natural wetlands or to determine the size
of artificial wetlands.

Natural Wetlands Based on a review of the literature dealing with the
use of natural systems for the treatment of secondary effluent all that can be
said is that the area of land required is large, somewhere in the range of 30
to 60 acres per million gallons of wastewater applied per day. Even with these
quantities of land, removal of nitrogen and phosphores are uncertain and may
require even larger areas for significant removal. Because the climatology,
hydrology, hydrogeology, geology, and biology of each natural wetland is so
specific it may be necessary to conduct pilot studies at each location to establish
the proper loading rates.

Artificial Wetlands Design criteria for artificial wetlands developed using
data found in the literature, are presented in Table 7. The criteria presented
are for the application of primary or secondary effluent. For a given wastewater
the corresponding organic loading rates can be derived from the hydraulic loading
rates. Where primary effluent is applied it is assumed that the removal of SS
and BOD are of principal concern. Where secondary effluent is applied it is
assumed that nitrogen control is of prime concern, although some phosphorus
will be removed.

Selection of Plants and Animals

In natural wetlands, plants and animals already present will affect the
degree of treatment that can be achieved. In artificial wetlands, selection of
plants and animals to be used will depend on their ability to remove, or to
contribute to the removal of, the contaminants of concern under the conditions
in which they are to operate. In general, plants that are available locally should
be used. From what little factual information is available, it appears that an
adequate stand of plants can be expected to develop within six to 12 months
after planting. Compared to reeds and rushes, sedges require the shortest time
to develop.

Operational Requirements

The operational requirements of wetland systems are related to the
techniques that will be used to manage these systems. Some of the management
techniques that have been used include seasonal application, inflow and outflow
regulation, flushing, upland application, underground application, harvesting of
vegetation, and chemical treatment (21). These and other management techniques
are considered in more detail in the following section. Suffice it to say that
the management technique(s) that will be used will impact the design and
operation of wetland systems.

Energy and Resource Consumption

To assess the consumption of energy in natural and artificial wetlands,
the activated sludge process, a conventional treatment system, will be compared
to two artificial wetland systems. The difference between the two wetland

Table 7
PRELIMINARY DESIGN PARAMETERS FOR PLANNING
ARTIFICIAL WETLAND WASTEWATER TREATMENT SYSTEMSa

Characteristic/design parameter

Detention Depth of Loading rate
Type of Flow b time, d flow, ft (m) g/ft *d (cm/d)
system regime
Range Typ. Range Typ. Range Typ.

Trench (with PF 6-15 10 1.0-1.5 1.3 0.8-2.0 1.0
reeds or rushes) (0.3-0.5) (0.4) (3.25-8.0) (4.0)

Marsh (reeds AF 8-20 10 0.5-2.0 0.75 0.2-2.0 0.6
rushes, others) (n. 15-0.6) 0.25 (0.8-8.0) (2.5)

Marsh-pond

1. Marsh AF 4-12 6 0.5-2.0 0.7) 0.3-3.8 1.0
(0.15-0.6) (0.25) (0.8-15.5) (4.0)

2. Pond AF 6-12 8 1.5-3.0 2.0 0.9-2.0 1.8
(0.5-1.0) (0.6) (4.2-18.0) (7.5)

Lined trench PF 4-20 6 -- -- 5-15 12
(hr.) (hr.) (20-60) (50)

aBased on the application of primary or secondary effluent.
bPF = plug flow, AF = arbitrary flow.

systems will be the type of pretreatment used: 1) conventional primary and 2)
facultative ponds. It is assumed that the influent in each case is domestic
wastewater with BOD5 and SS equal to 220 mg/L. The effluent from each of
the three treatment systems will meet the secondary requirements specified by
EPA (BOD and SS = 30 mg/L).
Energy and resource consuming functions for these three systems are
summarized in Table 8. Where appropriate, important factors affecting the
estimation of energy and resource consumption such as the total dynamic head
and the chlorine dosage are also identified. Corresponding land requirements,
labor requirements, parts and supplies costs, and capital costs are presented in
Table 9.
The basic data and information used for adjusting costs and preparing
energy consumption estimates are given in Table 10. In evaluating the energy
consumption for the systems identified in Table 8, both primary and secondary
energy were considered. The factors required to convert the cost of construction
and parts and supplies to energy are also given in Table 10.
Estimates of energy and resource consumption for the three systems to
be compared are given in Table 11. These estimates are based on the data and
information presented previously in Tables 8, 9, and 10. Based on the data
presented in Table 11, it appears that the consumption of energy in artificial
wetlands treatment systems may be as low as 41 percent of that used for
conventional activated sludge treatment. The corresponding value of natural
wetlands systems would be lower. Ultimately, it may be possible to reduce the
energy consumption to 10 or 15 percent of that for conventional treatment if
screened domestic effluent can be applied directly to wetlands. Chlorine is the
only resource consumed in the first two systems considered in this analysis.
Note also that the secondary energy for the facultative pond + wetlands systems
amounts to about 60 percent of the total energy consumed on an annual basis.

Cost of Wetland Treatment Systems

To assess the costs of wetland treatment systems, it will be instructive
to compare the annual and unit costs for the systems identified previously (see
Table 8). Such an analysis has been made and the results are presented in Table
12. Note that the cost of land is not included in the reported annual or unit
costs. As shown, the primary + artificial wetland system is the least costly
option. Even if the cost of land (without any salvage value) is considered, this
option is still the least costly. For example, for a plant size of I mgd, if the
cost of land is $4000/acre, the increase in the annual cost is $16,907; the total
annual cost is $178,361 (16,907 + 161,457). The corresponding unit cost is
$0.49/1000 gal, which is well below the unit cost of the activated sludge treatment
process without land. At a cost of $10,000/acre, the unit cost becomes $0.56/1000
gal, which is still well below the cost of the activated sludge process.

Related Legal Environmental Impacts

In arid or semi-arid climates, there is the potential for significant
consumptive use of water by wetlands vegetation. This will decrease ultimate
downstream water discharges which maly adversely affect the water rights of
others. Also, the salinity of the water may increase significantly.

Table 8
ENERGY AND RESOURCE CONSUMING FUNCTIONS IN
SELECTED WASTEWATER TREATMENT SYSTEMS

AS+ca P+AW+cb FP+AWC

Influent pumping Primary Facultative pond
(TDH=12ft)

Screening Influent pumping Influent pumping
(TDH=12ft) (TDH=12ft)

Primary settling Screening Screening

Aeration, mechanical Primary settling Bldg heating, cooling

Secondary settling Truck hauling of Vehicle operation
sludge (1500 gal/y)

Chlorination (10mg/L) Landspreading Misc, lighting, etc.

Thickeningd Bldg heating, cooling Artificial wetland

Truck hauling of Vehicle operation Pumping (TDH=12ft)
sludge (500 gal/y)

Landspreading Mlisc, lighting, etc. Vehicle operation
(1500 gal/y)

Bldg heating, cooling Artificial wetland

Vehiicle operation Pumping (TDH=12ft)
(2000 gal/y)

Misc, lighting, etc. Vehicle operation
(1500 gal/y)

Chlorination
(5 mg/L)

aAS+c = activated sludge + chlorination.
P+AW+c = primary + artificial wetlands + chlorination.
cFP+AW = facultative pond + artificial wetlands.
dNot included in plants with a capacity less than 1.0 mgd.

Table 9
LAND REQUIREMENTS
OPERATIONAL AND COST DATA FOR TREATMENT SYSTEMS IDENTIFIED IN TABLE 8a

AS+c P+AW+c FP+AW

ITEM Plant size, mgd Plant size, mgd Plant size, mgd

0.1 0.5 1.0 0.1 0.5 1.0 0.1 0.5 1.0

Land required, acre 1.0 2.5 4.0 0.5b+ 0.8b+ 1.5 + 5C+ 15+ 30c+
4.0d 20d 40d 4.0d 20d 40d

Labor, poh/y 1,600 3,600 5,500 1,250 3,000 4,500 1,250 3,000 4,500

Parts and supplies, $/y 8,000 12,000 16,000 3,000 5,000 7,000 3,500 4,500 6,500

Capital cost, $ x 10-6 0.71 1.23 1.60 0.37 0.55 0.90 0.49 1.12 1.80

aFrom Reference 28
bArea for primary treatment
CArea for facultative ponds
dArea for artificial wetlands

Table 10
BASIC DATA AND INFORMATION USED TO ADJUST COST DATA
AND FOR ENERGY CONSUMPTION COMPUTATIONSa

Item Value

Cost indexesb

ENRCC Index 3,000c'd

EPA STP Index 334.1

EPA O & M Index 2.54f

Bases for energy computations

Mechanical equivalent of heat 3413 Btu/kW'h

Heat rate heat supplied in fuel, Btu
energy generated, kW*h

3413 Btu/kW-h
conversion efficiency

Heat rate used in report 10,800 Btu/kW-hg

Heating value for gasoline 124,000 Btu/galh

Energy required for 6
manufacture of chlorine 42 x 10 Btu/ton

Factor used to estimate
secondary energy for construction 70,000 Btu/$ in 1963

Factor used to estimate second-
ary energy for supplies and parts 75,000 Btu/$ in 1963

aFrom Reference 28
bReported values are for June 1979
CBasis for adjusting cost data given in this paper
d1913 = 100
e1957- 1959 = 100
f1967 = 1.0
gAssumed conversion efficiency = 31.6 percent
"To convert the Btu value of gasoline to primary energy in terms of
fuel oil, the given value must be multiplied by 1.208
ITo use the reported conversion factors, current cost data must be
converted to the equivalent cost in 1963. This conversion can be
accomplished using the 1963 ENRCC index which was equal to 900.

Table 11
ENERGY AND RESOURCE CONSUMPTION ESTIMATES FOR TREATMENT SYSTEMS
IDENTIFIED IN TABLE 8

AS+c P+AW+c FP+AW

ITEM Plant size, mgd Plant size, mgd Plant size, mgd

0.1 0.5 1.0 0.1 0.5 1.0 0.1 0.5 1.0

Primary energy, Btu/yxl106a
Electricity 367 1,447 2,560 130 432 799 65 292 562

Fuel 515 1,700 2,240 384 765 1,280 400 500 750

Secondary energy, Btu/yxlO 6
Construction 746 1,292 1,680 389 578 945 515 1,176 1,890

Chemicals 64 320 640 32 160 320 -- -- --

Parts and supplies 180 270 360 68 113 158 79 101 146

Total, Btu/yxlO-6 1,872 5,029 7,480 1,003 2,048 3,502 1,059 2,069 3,348

aFrom Reference 28

Table 12
ANNUAL AND UNIT COSTS, EXCLUDING LAND, FOR TREATMENT SYSTEMS
IDENTIFIED IN TABLE 8

AS+c P+AW+c FP+AW

ITEM Plant size, mgd Plant size, mgd Plant size, mgd

0.1 0.5 1.0 0.1 0.5 1.0 0.1 0.5 1.0

Capital cost, $ x 10-6 0.71 1.23 1.60 0.37 0.55 0.90 0.49 1.12 1.80

O & M cost, $/y
Labor, $10/p-h 16,000 36,000 55,000 12,500 30,000 45,000 12,500 30,000 45,000

Power, $ 0.06/kW-h 10,400 27,940 41,556 5,572 11,378 19,456 5,883 11,494 18,600

Chlorine, $300/ton 457 2,283 4,566 228 1,142 2,283 -- -- --

Parts and supplies 8,000 12,000 16,000 3,000 5,000 7,000 3,500 4,500 6,500
Subtotal 34,857 78,223 117,122 21,300 47,520 73,739 21,883 45,990 70,100
Amortized capital
(8% at'20 y) 72,313 125,275 162,960 37,684 52,962 91,655 49,905 114,072 183,330

Total annual cost, $ 107,170 203,498 280,082 58,984 100,482 165,404 71,788 160,062 253,430

Unit cost, $/1000 gal 2.94 1.12 0.76 1.62 0.55 0.45 1.97 0.88 0.69

aExcluding the cost of the land.

MANAGEMENT OF WETLAND SYSTEMS

Proper management will be an important factor in the application of
wetland treatment systems. While most management techniques are designed
to improve performance, some are designed to maintain local environmental
conditions; others are related to the use of the by-products from these systems.
The effects of improper management must also be considered.

Management Techniques For Improved Performance

Techniques available for use in the management of wetland systems include
pretreatment, seasonal application, outflow regulation, flushing, surface and
subsurface application, and harvesting vegetation (21). For the most part, these
management techniques are directed towards the improvement or control of the
quality of effluent from wetlands.

Pretreatment The type and degree of pretreatment required will depend
on the constituents to be removed. For example, if the effluent from the
wetlands is to contain little or no phosphorus, it may be necessary to remove
a portion of the phosphorus in the influent wastewater by chemical precipitation.

Seasonal Application Based on the results of full scale studies, it has
been shown that it is possible to use wetlands as a temporary nutrient trap.
Nutrients applied during the critical summer period could be stored and released
in the winter during periods of high flow.

Outflow Regulation The hydraulic detention time can be controlled by
regulating the depth of water in the wetland. This operational technique is
especially important in the control of nitrogen through
nitrification-denitrification, of seasonally released nutrients or for the treatment
of toxic compounds.

Flushing Periodic flushing of a wetlands can be used to control the build
up and/or release of specific constituents. For example, phosphorus could be
flushed from the system during periods of high stream flow. In some cases, it
may be desirable to pass silt laden water through the wetland to restore the
adsorptive characteristics of the wetland.

Varying Points of Application By varying the surface or subsurface point(s)
of wastewater application it may be possible to achieve improved removals for
certain constituents.

Harvesting of Vegetation Harvesting of the biomass produced in wetlands
can be an important factor in maintaining the removal capacity of the wetland.
The time and extent of the harvesting will depend on the type of plants and
the constituents of concern. In some cases, harvesting may not be compatible
with other uses of the wetland(s), such as wildlife habitat.

Maintenance of Environmental Quality

In addition to techniques designed to improve performance, techniques
must be developed to maintain the environmental quality of the wetlands.

Specif ically, techniques must be developed to control I) the breeding and growth
of disease vectors, mosquitos, and flies; 2) the development of plants and animals
considered to be pests; and 3) the development of odors.
Perhaps one of the most serious problems is the development of mosquitos.
Recognizing this potential problem, some type of mosquito control program
should be included in the development of any wetland treatment system. Natural
control measures such as the use of mosquito fish appear to be most favored.

By-Product Recovery and Utilization

Depending on the quality of the wastewater that is applied, it may be
possible to recover a useful by-product from a wetland treatment system. For
example, rice which is grown in a marsh environment could be grown with
wastewater. In many locations, harvesting of valuable crops could be an important
added benefit of such systems.
Harvested biomass could be used in the production of livestock feed,
compost, soil amendments, or energy. The economics of resource recovery will
depend on the availability of local markets and uses for the products. Local
consumption of these would reduce the need for expensive processing and transport
equipment. When the economics of a resource recovery operation are favorable,
criteria related to resource recovery should be considered in the design. Resource
recovery should be considered carefully if its inclusion might diminish the
performance or reliability of the aquatic treatment system.

Impact of Improper Management

In general, the improper management of natural or artificial wetlands will
lead to a deterioration in effluent quality and in local environmental conditions.
Water quality constituents affected most readily are nitrogen and phosphorus.
For example, if a wetlands is overloaded with nitrogen and phosphorus; passage
of the wastewater throoigh the wetlands will have little or no effect on the
concentration of these constituents in the effluent. However, even though
nitrogen and phosphorus overloading can occur, it may have no effect on the
removal of SS and BOD .Thus the impact of overloading or poor management
will be specific for eacA constituent. The development of a habitat that may
encourage breeding of undesirable disease vectors, mosquitos, and flies is the
major environmental impact of improper management. The development of
plants and animals considered to be pests is another impact.

WETLAND TREATMENT SYSTEMS: AN ASSESSMENT

The success and acceptance of wetland treatment systems will depend
largely on how well they compare with conventional systems. Key factors that
must be considered in an assessment of these systems include: 1) treatment
efficiency and reliability, 2) availability of usable process design criteria and
procedures, 3) availability of proven management techniques, 4) energy and
resource consumption, 5) costs, and 6) health risks. Each of these f actors is
assessed in light of the material presented in the four preceeding sections.
Finally, the question of the technology needed to make the use of wetlands a
routine undertaking is addressed.

Treatment Eff iciency and Reliability

Treatment efficiency and reliability are important factors in assessing the
applicability of natural and artificial wetland systems for wastewater treatment.

Efficiency At the present time there are insufficient long-term
performance data that can be used as a basis for making a thorough comparison
between natural and artificial wetlands, and conventional secondary and advanced
wastewater treatment facilities. Although spectacular removal efficiencies have
been reported, they are either for a specific wetland system, or the results of
short-term testing programs, or from systems that are so lightly loaded
hydraulically and organically that they are not cost-effective. Nevertheless,
there is ample evidence in the literature to support the thesis that the removal
efficiencies that are possible for SS, BOD 59 trace organics, and heavy metals
in both natural and artificial wetland systems will equal or exceed those achieved
in conventional treatment systems. The conditions under which these efficiencies
can be achieved in a cost-effective manner are at present undefined.

Reliability An important design consideration is system reliability (freedom
from failures in treatment). Reliability problems in wetland treatment systems
are related to changing climatic conditions, variable wastewater characteristics,
local environmental factors, and disease that disturb, injure, or kill the
microorganisms, plants, and animals used for treating the wastewater. In some
regards, the potential for and consequences of poor system reliability is greater
in wetland systems than in conventional systems because of greater environmental
exposure. On the other hand, they may be less prone to upsets caused by errors
in operator judgment. In summary, the statistical reliability of natural or
artificial wetland treatment systems is undefined.

Availability of Process Design Criteria and Procedures

At the present time there are no reliable process design criteria or
procedures for either natural or artificial wetland treatment systems. For this
reason, the use of natural wetlands f or the treatment of wastewater should be
approached with great caution if this important habitat is not to be damaged.
Even the use of general "rules of thumb" is unacceptable. Clearly, the opportunity
to develop usable design and process application criteria is greatest with the
artificial wetland systems.

Availability of Proven Management Techniques

Few, if any, proven operational techniques are available for the
management of either natural or artificial wetlands. "Rules of thumb" are the
order of the day f or most systems. Nevertheless, as noted previously, there
are potentially a great number of management techniques that are deserving of
more study. Development of operable management techniques for artificial
wetlands is a necessary objective.

Energy and Resource Consumption

Based on the data reported in Table 11, it is clear that significant savings
can be achieved in the amount of energy and resources consumed for the

treatment of wastewater by using wetland systems. To achieve the ultimate
savings that may be possible, it will be necessary to develop operating techniques
that will allow for the direct application of screened wastewater to wetlands.

Costs

Proper assessment of the costs of wetland treatment must ultimately be
based on properly designed full scale units. In this regard, it will be important
to consider the total cost. This will include the capital and operating costs
and the salvage value. Most of the capital costs of wetland systems will be in
land which should have a high salvage worth.
With lesser mechanization, lower energy and resource consumption, (see
Table 11), and the possibility of some resource recovery, operating costs should
be lower for wetland systems as compared to conventional systems. Further,
the useful life of wetland systems should be longer than for conventional systems.
For these reasons, it may be feasible to build wetland systems with capital costs
similar to, or even higher than, the costs of conventional systems. The societal
benefits of using wetland systems that may not be cost-effective when evaluated
by current methods should also be considered.
Depending on the site, wetland systems may have additional costs and/or
benefits. Additional costs may include the control of vectors, such as mosquitoes,
or other problems relating to the presence of marshlike environments, e.g. odor
and fog generation. Beneficially, wetland systems may serve as recreation areas,
wildlife habitat, or greenbelts.

Health Risks

Health risks for wetland systems are probably not higher than for
conventional treatment. This is assuming that harvested plant tissue or animals
are not used for human consumption and that potential vector problems are
controlled. The public health hazards of direct consumption of organisms grown
in domestic wastewater are very serious and complicated. Their use for animal
feeds may be possible if the residues of heavy metals, trace organics, and
pesticides meet state and federal regulations.

The Status of Wetlands Technology

While both natural and artificial wetland treatment systems represent an
extremely attractive alternative to conventional secondary and advanced
treatment, the technology involved in their application is not yet developed to
the point where the use of these systems can be considered routine. These
systems are currently considered by the USEPA to be included within the scope
of the innovative and alternative technology provisions of Public Law 95-217.
Based on information reviewed for this assessment, this classification is
appropriate. Some of the needed research is identified in the following section.

RESEARCH NEEDS IN WETLAND TREATMENT

It is the purpose of this section to identify some of the data and information
that must be developed so that the design of wetland treatment systems can
become a rational undertaking. Because natural wetlands are site specific, they

are considered separately in the following discussion. It should be noted, however,
that much of the information developed for artificial wetland systems should be
useful in the development of methods that can be used to assess the performance
of natural wetlands.

Natural Wetlands

Because the hydrology, hydrogeology, geology, and biology of most natural
wetlands is unique, it will probably be necessary to conduct limited pilot scale
testing before wastewater is applied. In time, as more experience is gained, it
may be possible to develop some generalized design parameters that can be used
to predict the removal efficiency for a given type of plant as a function of the
biomass per unit area; the hydraulic, organic, and inorganic nutrient loadings;
and temperature. Site specific variables could then be superimposed to develop
a more complete analysis of the expected performance of the wetland.
Experiments such as those described in the following section for artificial wetlands
could be undertaken in controlled plots in natural wetlands.

Artificial Wetlands

The following are some of the important factors that must be quantified
before the use of artificial wetlands can become a routine undertaking. Because
all of the factors that must be defined for artificial wetlands are to interrelated
it is suggested that the initial studies be conducted using no more than two or
three plant species (reeds, rushes, and sedges).

1. Effect of plant type and biomass on degree of treatment achieved
(e.g. reeds, rushes, sedges)
2. Effect of plant harvesting on nutrient uptake and degree of treatment
3. Effect of bottom substrate on plant uptake and degree of treatment
4. Effect of detention time on degree of treatment
5. Effect of seasonal conditions on the degree of treatment
6. Effect of humus and litter component on degree of treatment
7. Definition of removal kinetics as a function of plant type, biomass
detention time, and temperature
8. Effect of wetland configuration on degree of treatment
9. Definition of steady-state constituent removal capacity and constituent
holding capacity as a function of detritus accumulation

REFERENCES

1. Benemann, J.R., "Energy From Wastewater Aquaculture Systems," Paper
presented at A Seminar On Aquaculture Systems For Wastewater
Treatment, University of California, Davis, California, September 1979.

2. Cowadin, L. et al, "Interin Classification of Wetlands and Aquatic Habitats
of the United States," U.S. Dept. of Interior, Fish and Wildlife Service,
Washington, D.C. 1976

3. Crites, R.W., "Economics of Aquatic Treatment Systems," Paper presented
at A Seminar On Aquaculture Systems For Wastewater Treatment,
University of California, Davis, California, September 1979.

4. Demgen, F.C., "Wetlands Creation For Habitat and Treatment -At Mt.
View Sanitary District, California," Paper presented at A Seminar On
Aquaculture Systems For Wastewater Treatment, University of California,
Davis, California, September 1979.

5. deJong, J., "The Purification of Wastewater With the Aid of Rush or Reed
Ponds," Biological Control of Water Pollution. J. Tourbier and R.W. Pierson,
Jr. (eds), University of Pennsylvania Press, Philadelphia, 1976.

6. Duffer, W.R. and J.E. Moyer, Municipal Wastewater Aquaculture, U.S.
Environmental Protection Agency, EPA-600//2-78-110, Ada, Oklahoma
1978.

7. Farnham, R.S. and D.H. Boelter, "Minnesota's Peat Resources: Their
Characteristics and Use in Sewage Treatment, Agriculture, and Energy,"
In Freshwater Wetiands and Sewage Effluent Disposal, D.L. Tilton, R.H.
Kadlec, and C.J. Richardson (eds), The University of Michigan, Ann Arbor,
Michigan 1976.

8. Feasibility Study of Wetland Disposal of Wastewater Treatment Plant
Effluent, Draft Report to Commonwealth of Massachusetts, Water
Resources Commission, Research Project 78-01, January 1979.

9. Fritz, W.R. and S.C. Helle, Cypress Wetlands For Tertiary Treatment,
Boyle Engineering Corporation, Orlando, Florida, March 1979.

10. Fritz, W.R. and J.C. Helle, "Cypress Wetland: A Natural Tertiary
Treatment Alternative," Water and Sewage Works, April 1979.

11. Good, R.E., D.F. Whigham, and R.L. Simpson (eds), Freshwater Wetlands
Ecological Processes and Management Potential, Academic Press, New
York 1978.

12. Grainge, J.W., "Use of Wetlands for Effluent Disposal from Small
Communities and Settlements in Northern Canada," Personal
Communication, November 1979.

13. Hartland-Rowe, R.C.B. and P.B. Wright, Swamplands For Sewage Effluents:
Final Report, Environmental-Social Committee Northern Pipelines, Report
No 74-4, Information Canada Cat. No R72-13174, #QS-1553-000-E-A1,
Canada, May 1974.

14. Jankovska, V., "Development of Wetland and Aquatic Vegetation in the
Trebon Basin Since the Late Glacial Period," Pond Littoral Ecosystems:
Structure and Functioning, D. Dykyjova and J. Kvet (eds), Springer-Verlag,
Berlin 1978.

15. Kadlec, R.H., "Wetland Tertiary Treatment at Hougton Lake, Michigan,"
Paper presented at A Seminar On Aquaculture Systems For Wastewater
Treatment, University of California, Davis, California, September 1979.

16. Kadlec, R.H. (ed), Wetland Utilization for Management of Community
Wastewater: 1978 Operations Summary, Wetland Ecosystem Research
Group, University of Michigan, March 1979.

17. Kappel, B., "The Drummond Project: Applying Lagoon Sewage Effluent
to a Bog - An Operational Trial," Paper presented at A Seminar On
Aquaculture Systems For Wastewater Treatment, University of California,
Davis, California, September 1979.

18. Lohman, L.C., "An Overview of the Legal, Political, and Social Implications
of Wastewater Treatment Through Aquaculture," Paper presented at A
Seminar On Aquaculture Systems For Wastewater Treatment, University
of California, Davis, California, September 1979.

19. Mudroch, A. and J.A. Capobianco, "Effects of Treated Effluent on a
Natural Marsh," Journal WPCF, Vol 51, No 9, September 1979.

20. Richardson, C.J. et al., "Nutrient Dynamics of Northern Wetland
Ecosystems, " Freshwater Wetlands Ecological Processes and Management
Potential, R.E. Good et al (eds) Academic Press, New York 1978.

21. Sloey, W.E., F.L. Spangler, and C.W. Fetter, Jr., "Management of
Freshwater Wetlands For Nutrient Assimilation," Freshwater Wetlands
Ecological Processes and Management Potential, R.E. Good et al (eds),
Academic Press, New York 1978.

22. Small, M.M., "Wetland Wastewater Treatment Systems," in State of
Knowledge In Land Treatment of Wastewater, H.L. McKim (coordinator),
Proceedings of the International Symposium on Land Treatment, Vol 2,
Hanover, N.H., August 1978.

23. Spangler, F., W. Sloey, and C.W. Fetter, "Experimental Use of Emergent
Vegetation for the Biological Treatment of Municipal Wastewater in
Wisconsin," Biological Control of Water Pollution, J. Tourbier and R.W.
Pierson, Jr., (eds), University of Pennsylvania Press, Philadelphia 1976.

24. Spangler, F.L., W.E. Sloey and C.W. Fetter, "Wastewater Treatment by
Natural and Artificial Marshes," EPA-600/2-76-207, 1976.

25. Stonlick, H.T., "Treatment of Secondary Effluent Using A Peat Bed," In
Freshwater Wetlands and Sewage Effluent Disposal, D.L. Tilton, R.H.
Kadlec, and C.J. Richardson (eds), The University of Michigan, Ann Arbor,
Michigan 1976.

26. Stowell, R., G. Tchobanoglous, J. Colt, and A. Knight, The Use of Aquatic
Plants and Animals For the Treatment of Wastewater, Departments of
Civil Engineering and Land, Air, and Water Resources, University of
California, Davis, September 1979.

27. System For Purification of Polluted Water, U.S. Patent No 3,770, 623,
U.S. Patent Office, November 6, 1973.

28. Tchobanoglous, G., J.E. Colt, and R.W. Crites, "Energy and Resource
Consumption in Land and Aquatic Treatment Systems," Paper presented
at the Energy Optimization of Water and Wastewater Management for
Municipal and Industrial Applications Conference, Sponsored by Department
of Energy Urban Waste and Municipal Systems Branch, New Orleans,
Louisiana, December 10-13, 1979.

29. Tilton, D.L., R.H. Kadlec, and C.J. Richardson (eds), "Freshwater Wetlands
and Sewage Effluent Disposal," Symposium proceedings, The University of
Michigan, Ann Arbor, Michigan 1976.

30. Tourbier, J. and R.W. Pierson (eds) Biological Control of Water Pollution,
University of Pennsylvania Press, Philadelphia 1976.

31. Ulehlova, B., "Decomposition Processes in the Fishpond Littoral," Pond
Littoral Ecosystems: Structure and Functioning, D. Dykyjova and J. Kvet
(eds), Springer-Verlag, Berlin 1978.

32. Wesner, G.M. et al, Energy Conservation in Municipal Wastewater
Treatment, MCD-32, EPA 430-9-77-011, Washington, D.C., March 1978.

33. Whigham, D.F. and R.L. Simpson, "The Potential Use of Freshwater Tidal
Marshes in the Management of Water Quality in the Delaware River,"
Biological Control of Water Pollution, J. Tourbier and R.W. Pierson, Jr.
(eds), University of Pennsylvania Press, Philadelphia 1976.

34. Williams, T.C. and J.C. Sutherland, "Engineering, Energy, and Effectiveness
Features of Michigan Wetland Tertiary Wastewater Treatment Systems,"
Paper presented at A Seminar On Aquaculture Systems For Wastewater
Treatment, University of California, Davis, California, September 1979.

35. Yonika, D.A., "Effectiveness of a Wetland in Eastern Massachusetts in
Improvement of Municipal Wastewater," Paper presented at A Seminar On
Aquaculture Systems For Wastewater Treatment, University of California,
Davis, California, September 1979.

36. Zoltec, 3., et al, "Removal of Nutrient From Treated Municipal Wastewater
By Freshwater Marshes," Center for Wetlands, University of Florida,
Gainsville, Florida, September 1978.

AQUATIC PLANT PROCESSES' ASSESSMENT

E. Joe Middlebrooks

Introduction

A summary of the known water hyacinth systems that were constructed

or modified to treat wastewater are summarized in Table 1. There are few

consistencies in the design criteria used or developed during the evalua-

tion of these systems. Water hyacinth wastewater treatment systems are

used to treat raw wastewater as well as effluents from various stages of

treatment. The most common system incorporates a stabilization pond

followed by series-type water hyacinth culturing tanks. The design

characteristics of hyacinth systems are discussed in this report.

Conclusions and Kecommendations

1. The water hyacinth wastewater treatment process appears to be appli-

cable in warm temperate and tropical climates, and adequate data

appear to be available to assist in the design of a system capable

of producing an advanced secondary effluent.

2. Water hyacinths thrive in municipal wastewaters and appear to do well

in mixtures of municipal and industrial wastewaters.

3. A hydraulic loading rate of 2,000 m3/ha-day to a hyacinth system

appears reasonable when treating secondary wastewater treatment plant

effluent if nutrient control is not an objective. When treating raw

wastewater in a hyacinth system, a hydraulic loading rate of 200

m3/ha-day appears reasonable if nutrient control is not an objective.

4. A shallow hyacinth pond (Z 0.4 m) and a hydraulic loading rate of

approximately 500 m3 of stabilization pond effluent per hectare

per day should produce an-effluent containing a total nitrogen con-

centration of less than 2 mg/I.

5. Total phosphorus removals of approximately 50 percent are normal

with a hyacinth system.

6. Considerable experimentation remains to be performed before phos-

phorus control with hyacinth systems can be accomplished.

7. Dye studies should be conducted to determine the actual hydraulic

residence times in hyacinth systems.

S. Algae growth appears to be controlled in hyacinth systems by simple

shading by the plant.

9. Nutrient removal in hyacinth systems is more complex than plant up-

take alone. Excellent nitrogen and phosphorus reductions occur in

wastewater stabilization ponds without water hyacinths.

10. Sludge accumulation in hyacinth systems does not appear to be a

significant problem.

11. Harvesting and utilizing the water hyacinth after harvesting requires

considerable investigation to develop satisfactory methods and

procedures.

12. The use of more cold tolerant plants such as duckweed should be

investigated more extensively.

13. More extensive investigations should be conducted on the range of

organic and hydraulic loading rates that the hyacinth system is

capable of treating particularly with systems processing raw

wastewater.

Table 1. Summary of design and performance characteristics of aquatic weed wastewater treatment systems.

Surface Area Depth Hydraulic Hydraulic Organic Percent Nutrient Conte
Type of of of Loading Rate Residence Loading Hyacinth of Plants,
Location Pretreatment Hyacinth Pond Hyacinth Pond Time Rate Cover % Dry Weight
ha m m3/ha Days kg/ha-day % TKN 1

Nat. Space Tech. Lab None 2 1.22 240 54 26 2.73 0.4
Before Hyacinths
After Hyacinths 100
Lucedale, Miss. None 3.6 1.73 260a ,67a 44 3.56 0.8
Before Hyacinths
After Hyacinths 100
Orange Grove, Miss. 2-Aerated 0.28 1.83 3,570 6.8 179 3.74 0.8
Without Hyacinths 3-Facul.
With Hyacinths in parallel 100
Exp conducted
in parallel
systems
Cedar Lake, Miss. 1-Aerated 0.07 1.5 700 22 31 Duckweed
(Duckweed) and 100
Facultative
Williamson Creek, Tx
Phase I Plant A 0.0585 1.0 1,860 5.3 43 100
Aeration
Basin,
Clarifier,
3 Lagoons
in series
Phase II Plant B 0.85 1,860 4.5 89 100
T2-Wration
Basins in
Parallel,
3-lagoons
Full-Scale Plant A' 1.2 0.7 - 1,100- 6-9 56-72 100
Aeration 1.3 1,400
Basin,
Clarifier,
two lagoons
(1.2 ha each)
in series
Austin-Hornsby Bend, Excess Act. 1.4 1.23 430 '3 100
Texas Sludge Lagoons
Overflow to
Hyacinth Pond
San Juan, Texas Aerated 1.0 0.61 870 N7 100
Lagoon, (2 hyacinth of 0.91 850
Stabilization 1.0 ha, only 1 0.91 1,550 6
Pond in operation) 1.37 1,860 u7
Alamo, Texas Imhoff Tank, Two Basins
Before Hyacinths Trickl. Filter 1.35
After Hyacinths Aeration Basin 1.05 <25
Two 4.04 ha
Stab. Ponds
in Parallel
San Benito, Texas Stab. Pond, 3 in series, 3,100;3,100, & 1st - 0
Before Hyacinths 4 Ponds in 0.8, 0.8, & 1,200 (overall 2nd - 50
After Hyacinths Series 2.0 system 0.068) 3rd - 100
680

Rio Hondo, Texas None 3 in series 1,110; 1,110 Basin 1,
0.41, 0.41, & 1.110 197
0.41
Lakeland, Florida Secondary 3 in series,
Treatment 0.40, 0.40, &
0.40
Walt Disney World, 3 exp. basins Var. 0.38, 550 to 7,850
Florida 8.84 x 109.8 m 0.61 & 0.91 m
Coral Springs, Activated 5 in series, 0.38 870 6 Basin 1, 100
Florida Sludge 0.18, 0.08, 2,1 1, 31
Effluent 0.08, 0.08, & 1, 1
0.08
aBased on effluent flow rate.

Biochemical Oxygen Suspended Solids Total Nitrogen Total Phosphorus Effluent Effluent
Demand, mg/i mg/i mg/k mg/i Dissolved pH Values Sampling Period
Oxygen and Reference
Influent Effluent Influent Effluent Influent Effluent Influent Effluent mg/.t Units Comments

91 17 70 49 9.8 5.2 2.9 2.1 6.9 9.3 5-74 to 5-76 Wolverton and McDonald [1979]
110 7 97 10 12.0 3.4 3.7 1.6 2.3 7.1 6-76 to 9-77 and Wolverton [1979]
Wolverton [1979]
127 57 140 77 0 Odors at night
161 23 125 6
Wolverton [1979]
50 37 49 53
50 14 49 15 2.0

44 18 188 11 0.5 Wolverton [1979]

23 5 43 7 8.2 2.5 Dinges [1978] and Dinges [1979]

46 6 117 8 9.9 3.6 Dinges [1978] and Dinges [1979]

42 12 40 9 10-77 to 8-79 Dinges [1978] and Dinges [1979]

No change at Dinges [1979]
loading rates
used

20 30 4-78 to 3-79 Dinges [1979]
9 11
35 30
31 32

33 86 4-78 to 3-79 Dinges [1979]
38-50 68-82 5-79, 6-79

17 35 4-78 to 3-79 Dinges [1979]
17 20 6-79

16 24 7-78 to 5-79 Dinges [1979]

Only partial cover and limited preliminary data Stewart [1979]

Experimental units not fully operational Kruzic [1979]

13 3 3 22.4 1.0 11.0 3.6 3-79 to 5-79 Swett [1979]

14. Mosquito control is essential in hyacinth wastewater treatment

systems.

15. Water hyacinths must not be introduced into areas where it does not

currently grow.

16. Consideration should be given to conducting a greenhouse experiment

with water hyacinths in a cold climate. Partial temperature control

and carbon dioxide enrichment utilizing gases produced with the

harvested plants in anaerobic fermentation systems may make a green-

house system viable and economical.

Physical Characteristics

Location. All of the water hyacinth systems that are currently

treating wastewater are located in tropical or warm temperate climates.

The water hyacinth is very sensitive to temperature and does not grow in

water with a temperature of 100 Cor lower. The optimum temperature for

water hyacinth growth ranges between 21 and 300C. If a water hyacinth

system were to be used in a colder climate, it would be necessary to house

the system in a greenhouse and maintain the temperature in the range of

the optimum. There are possibilities of utilizing methane produced from

harvesting the plant to produce heat to partially control the temperature

and carbon dioxide to enrich the environment above the plants. The

benefits of such a system must be investigated on a large scale to

establish the economics as well as the operational problems.

Based upon the limited data available, it appears that it would be

uneconomical to attempt to develop a water hyacinth wastewater treatment

system in cold regions. Even if the system were selected to operate

only during the warmer months of the year in the cold region, it would

be necessary to provide a culturing unit to maintain a hyacinth crop for

introduction into the system in the spring. It is likely that hauling a

culture of hyacinths to a relatively large system would be prohibitive,

and the cost of maintaining a culture remains to be determined. Intro-

duction of the hyacinth plant to areas where it does not currently grow

must be avoided. The damages from an infestation of hyacinth plants

would far exceed the benefits derived in wastewater treatment.

Wastewater Characteristics. Many domestic wastewaters have been

applied to water hyacinth systems, and hyacinths thrive in wastewaters

because of the high nutrient content normally available. The hyacinth

has also been grown in mixtures of industrial waste and municipal waste-

waters. The growth of hyacinths has been very good in these mixtures.

There is limited experience with projects using hyacinths to treat just

industrial wastes. Hyacinth systems have the capability of removing heavy

metals and other difficult-to-remove organics. This ability to remove

the materials might be a significant disadvantage. The presence of

toxic substances would make the disposal of the solid material difficult

and expensive and would prohibit the use of the plant material as a feed

supplement. High accumulations of heavy metals might also interfere with

the anaerobic digestion of the solid materials to produce methane as a

source of energy.

Water hyacinths thrive in municipal wastewater and can survive in

relatively high concentrations of heavy metal contaminants. The impact

of heavy metals and toxic organics has not been investigated to any

significant degree.

Size. All of the water hyacinth wastewater treatment systems

presently operating are less than four hectares in surface area, and

the majority of the systems are less than one hectare in surface area.

The majority of the systems currently in operation are experimental

systems and even the ones that are serving a community are still classi-

fied as being in the experimental stage.

The recommendation by Dinges (1979) that individual water hyacinth

wastewater treatment systems be kept to a surface area of 0.4 hectare

appears reasonable, and this size selection is based on the convenience

of harvesting the water hyacinths and cleaning the basins periodically.

However, long rectangular basins would not necessarily be limited by this

constraint.

The depth of the hyacinth pond varies from location to location.

Depths vary from 0.38 to 1.83 meters with the majority of the investi-

gators recommending a depth of 0.91 meters or less. The critical concern

is to provide adequate depth for the root system to penetrate through the

majority of the liquid flowing through the hyacinth pond. Systems that

have been designed for nutrient removal have been designed at a depth of

approximately 0.4 meter to ensure complete contact of the wastewater with

the root system.

Hydraulic Loading Rates. The hydraulic loading rates applied to

water hyacinth facilities have varied from 240 m3/ha-day up to 3,570

m3/ha-day when treating domestic wastewaters. Higher hydraulic loading

rates have been applied to the Austin-Hornsby Bend, Texas, hyacinth system

treating overflow from a lagoon receiving excess activated sludge, but

this treatment process was ineffectual because of high organic and hydrau-

lic loading rates. The Disney World, Florida, system was designed to

process hydraulic loading rates between 650 and 780 m3/ha-day, and once

these experiments are completed a better set of design criteria can be

presented for design of hyacinth systems to be used principally as polish-

ing device for secondary treatment processes.

Based upon the results currently available, it appears that an

hydraulic loading rate of 2,000 m3/ha.day when treating secondary

effluent will produce an effluent quality that would satisfy advanced

secondary standards (BOD5=<10 mg/I; SS=<10 mg/I; TKN=<5 mg/I; and TP=<5

mg/1). Hydraulic loading rates applied to three water hyacinth systems

treating raw wastewater have ranged from 240 to 680 m3/ha.day. All

three of the systems operated effectively, but the lower hydraulic loading

rates appear to produce a higher quality effluent measured in terms of

BOD5 and suspended solids concentrations.

A reasonable design hydraulic loading rate for a hyacinth system

receiving raw wastewater appears to be approximately 200 m3/ha.day.

There are few data supporting this decision, but an analysis of the

available data would support this lower hydraulic loading rate for

systems treating raw wastewater. Hyacinth systems processing a second-

ary effluent could be designed to process approximately 2,000 m3/ha.day

if the principal objective was the control of BOD5 and suspended solids

in the effluent. With nutrient removal as the principal objective,

little data exists as to what might be the best hydraulic loading rate.

A nutrient removal hyacinth system probably would be used in conjunction

with a wastewater stabilization pond or another secondary effluent would

be applied. A shallow pond (0.4 meters) and a hydraulic loading rate of

approximately 500 m3/ha.day should produce good nitrogen removals

(<2 mg/I). Approximately 50 percent reduction in the total phosphorus

concentration could be expected.

Number of Units in System. The majority of *the water hyacinth

systems have been designed to operate with 3 cells in series. Single

cell stabilization ponds with water hyacinths have been employed success-

fully, but the majority of the systems currently being evaluated are

considering the nutrient removal aspects of the hyacinth systems, and

the 3-cells in series system appears to be preferred. If the objective

is the control of algae in the effluent from a wasteater stabilization

pond, it is likely that the single unit would work just as effectively

as the series configuration. it appears that the control of the algae

in wastewater stabilization pond effluents is principally a physical

process of shading sunlight.

Active Components. In a water hyacinth system, during the active

growth phase, hyacinths are capable of sorbing organics, heavy metals,

pesticides and other organic contaminants. The root system of the

water hyacinth also supports a very active mass of organisms which

assist in breaking down and removing the pollutants in wastewaters.

As mentioned above, the control of algae in wastewater stabilization

pond effluent by the introduction of water hyacinths appears to be a

physical process by limiting the light available to the algae. Nutrient

removal apparently is a result of hyacinth growth, physiochemical

reactions, and accumulation by other organisms growing in the ecosystem.

Organic Loading Rates. Water hyacinth wastewater treatment systems

processing raw wastewater in a stabilization pond appear to be able to

process wastewater organics at approximately the same loading rates used

in lightly loaded wastewater stabilization ponds. The system operating

at the National Space Technology Laboratories (NSTL) was loaded at 26 kg

of BOD5/ha-day and operated without significant odors, whereas the

system also processing raw wastewater at the Lucedale, Mississippi, loca-

tion was loaded at 44 kg/ha-day and odors developed at night. These

results indicate that organic loading rates of less than 30 kglha-day

would provide satisfactory results when processing a raw wastewater.

Only three systems are known to be processing raw wastewater, and opera-

tional data from one of these (Rio Hondo, Texas) were extremely limited.

Water hyacinth wastewater treatment systems receiving secondary ef-

fluents or wastewater stabilization pond effluents are more numerous, and

a much wider range of organic loading rates have been employed with these

systems. Organic loading rates applied to the first basin in hyacinth

systems have ranged from 197 kg/ha-day to 31 kg/ha-day. All of the

systems receiving organic loading rates within this range have produced

an effluent which would satisfy the secondary standards of 30 mg/I of

BOD5 and suspended solids. In addition significant reductions in the

total nitrogen concentrations entering the hyacinth system have also been

reported. However, the data are limited except for the Williamson Creek,

Texas, National Space Technology Laboratories and the Coral Springs,

Florida, experiments. These studies show significant reductions in total

nitrogen as well as total phosphorus. Unfortunately, the phosphorus con-

centrations were not reduced to the desired level of less than I mg/I at

the Coral Springs, Florida, operation, and total phosphorus concentrations

were not measured at the Williamson Creek, Texas, experiments. Consider-

able experimentation remains to be done before phosphorus control with

hyacinth systems can be fully evaluated.

Hydraulic Detention Time. With the exception of the Williamson

Creek, Texas, phase I experiment, all of the other studies with water

hyacinth systems reporting hydraulic retention times are based upon

theoretical calculations. The degree to which the actual hydraulic resi-

dence time approaches the theoretical depends upon the care with which

the original design was carried out. Systems consisting of long, narrow

rectangular channels probably approach a ratio of actual to theoretical

hydraulic detention time of 0.75 as a rough approximation. The circular

or free-form ponds and systems adapted to water hyacinths probably have

a ratio of actual to theoretical hydraulic detention time of 0.5 or less.

All experiments that are presently being conducted should definitely

incorporate a dye study to evaluate the actual hydraulic residence time

in the hyacinth system.

Engineering Criteria

The application of water hyacinth systems to treat wastewater is

limited to tropical and warm temperate climates. It is unlikely that

such a system can be economically adapted to cold regions successfully.

Greenhouses and plant digestion to produce methane for partial heating

and carbon dioxide enrichment are theoretical possibilities, but with

the absence of experience in this area, it is impossible to recommend

such a system for cold regions. A large scale research project in a

cold climate would be necessary to answer the majority of the questions

involving the use of plant systems in cold regions. Many suggestions

have been made that a more cold tolerant plant such as duckweed be con-

sidered for cold climates. However, duckweed would not survive the low

temperatures and ice cover in the northern U.S. Winter protection or

only warm weather use of the plants would be necessary. Duckweeds, in

theory, offer a greater geographical range and longer operational season

when compared to hyacinths. It is possible that such a system would

work, but again there are no data available to prove that the system will

operate in cold climates or on which to base engineering design criteria.

In areas with warm temperate climates, the application of water

hyacinth wastewater treatment technology appears to be feasible. The

system is based upon essentially the same criteria utilized in design of

wsatewater stabilization ponds. Frequently a water hyacinth system is

installed in an existing wastewater stabilization pond.

The role of hyacinths in algae control appears to be that of a light

screening function that controls algae growth. Wolverton (1979) has

presented results supporting the sorption of nutrients and pollutants by

hyacinths, but significant nitrogen and phosphorus reductions occur in

lagoons without hyacinths. Numerous reports summarize nitrogen and phos-

phorus removals by lagoon systems with total nitrogen removals frequently

exceeding 70 percent and total phosphorus removals exceeding 50 percent

without hyacinths. Nutrient reductions in hyacinth systems is far more

complicated than plant uptake alone.

If the water hyacinth system is used to remove nutrients, it is

necessary to maintain the hyacinth culture in an active growth phase

which means that harvesting must be conducted frequently. There is still

need for definition as to what the proper harvesting schedule should be.

With intensive harvesting, it is necessary to construct the hyacinth

ponds so that harvesting can be easily accomplished. This has a tendency

to increase the cost of the hyac'inth system, and also develops the problem

of disposing of the excess material. Most of the cost data associated

with the harvesting and processing of hyacinth plants is based on small

scale experiments (Bagnall, 1979). These small scale experiments indi-

cate that the cost for harvesting and processing will be expensive, but

perhaps not prohibitive. in systems such as those recommended by Dinges

for use in Texas, where harvesting is recommended only once each year,

the cost would be far more attractive.

Sludge accumulation information is very limited for hyacinth sys-

tems, but the experimental systems and the full scale system utilized at

Williamson, Texas, indicate that a sizable mass of sludge accumulates in

the course of a year. With multiple cell hyacinth systems it is likely

that one pond could be drained and cleaned while the other ponds assume

the total loading. It is unlikely that much of an upset would occur with

this type operation. Therefore, it would be possible to drain the hyacinth

ponds completely and allow the materials to dry in place before removing

the materials. Whether this would be the most satisfactory method of

cleaning and ponds or not depends upon the degree of sophistication an

engineer may choose to design into the system. There are numerous harvest-

ing opportunities described in the literature, and as mentioned above,

there is too little data at this time to select an optimum harvesting and

utilization technique. Basing calculations upon one cleaning and harvest-

ing per year, it is very unlikely that the cost associated with this would

be prohibitive, and when nutrient control is not a consideration, this is

probably the best approach to disposing of the accumulated sludge and

plants.

When a hyacinth system is combined with wastewater stabilization

pond technology in warm climates, it is an attractive system for the

production of an advanced secondary effluent. The system can be ef-

ficient and economical and it requires very little energy for operation.

When properly designed and operated, the system apparently does not have

an odor problem and can be aesthetically attractive. During the active

growing system, the evapotranspiration losses from hyacinth systems can

approach half of the flow entering the system. The rate of evapotrans-

piration varies widely and is directly related to the rate of growth

of the water hyacinth. In a water-short area such as Arizona and part's

of California, this evapotranspiration could be significant and may make

the process unattractive because of the loss of water.

In summary, the water hyacinth wastewater treatment process appears

to be applicable in warm temperate and tropical climates, and adequate

data appear to be available to assist in the design of a system capable

of producing an advanced secondary effluent. The recommended design

criteria for such a system are summarized in Table 2. These design data

are based upon the work of the individuals referred to in Table 1. Similar

design criteria developed by Dinges (1979) for the State of Texas also

appear reasonable.

By-Product Recovery

The literature on water hyacinths as a wastewater treatment process

contains considerable speculation on the use of the water hyacinth upon

harvesting. Composting, anaerobic digestion for the production of methane,

and the fermentation of the sugars into alcohol are techniques proposed

as a means to cover the costs of wastewater treatment (Benemann, 1979).

All of these techniques may have application in limited areas; however,

it is very unlikely that a production system will be developed in the

near future which would even approach paying for the treatment of the

wastewater (Crites, 1979). One cannot deny the possibility of reclaiming

a product, but at this stage of development, it is very unlikely that the

recovery of useful products from water hyacinth wastewater treatment will

be economically viable.

Table 2. Design criteria for water hyacinth wastewater treatment sys-
tems based upon best available data and to be operated in warm
climates.

Design Value Expected
Parameter Effluent
Metric English Quality

A. RAW WASTEWATER SYSTEM
(Algae Control) BOD5a 30 mg/l
Hydraulic Residence Time > 50 days > 50 days SS < 30 mg/l
Hydraulic Loading Rate 200 m3/ha.-day 0.0214 mgad
Depth, Maximum _ 1.5 meters - 5 feet
Area of Individual Basins 0.4 hectare 1 acre
Organic Loading Rate _ 30 kg BOD5/ - 26.7 lbs
ha.-day BOD5/ac.day
Length to Width Ratio of > 3:1 > 3:1
Hyacinth Basin
Water Temperature > 10�C > 50�F
Mosquito Control Essential Essential
Diffuser at Inlet Essential Essential
Dual Systems, Each Designed Essential Essential
to Treat Total Flow

B. SECONDARY EFFLUENT
SYSTEM
(Nitrogen Removal and
Algae Control) BOD5 < 10 mg/l
Hydraulic Residence Time > 6 days > 6 days SS < 10 mg/l
Hydraulic Loading Rate 800 m3/ha.day 0.0855 mgad TP < 5 mg/l
Depth, Maximum 0.91 meter 3 feet TN _ 5 mg/l
Area of Individual Basins 0.4 hectare 1 acre
Organic Loading Rate _ 50 kg BOD5/ < 44.5 lbs
ha-day BOD5/ac.day
Length to Width Ratio of > 3:1 > 3:1
Hyacinth Basin
Water Temperature > 200C > 68�F
Mosquito Control Essential Essential
Diffuser at Inlet Essential Essential
Dual Systems, Each Designed Essential Essential
to Treat Total Flow
Nitrogen Loading Rate _ 15 kg TKN/ s 13.4 lbs
ha-day TKN/ac-day

Removal of Pollution

The greatest difficulty in interpreting the data presented by the

various papers describing the Work with water hyacinth systems is the

infrequency of sampling and the tack of 24-hour composite samples. Al-

though many of the studies include relatively large numbers of samples,

most are grab samples collected twice each week. Even with large numbers

of samples, it is still possible to make sizable errors in predicting

the performance of a wastewater treatment system. Only the data for

the Coral Springs, Florida, system are based upon 24-hour or 48-hour

composite samples. All others are grab samples collected at various

frequencies. The performance of typical water hyacinth systems is sum-

marized in Table 1.

The most complete nutrient removal dat'a were collected at the

Williamson Creek, Texas, Phase I and Phase 2 experiments and at the

Coral Springs, Florida, water hyacinth treatment facility. The organic

loading rates, nutrient loading rates and removals obtained during these

three studies are summarized in Table 3. The lowest total nitrogen load-

ing rate occurred at the National Space Technology Laboratories (NSTL)

experimental water hyacinth facility, but the effluent quality at the,

NSTL facility was no better than that experienced at the Williamson

Creek facility. A higher percentage of phosphorus removal was experi-

enced at the Coral Springs, Florida, facility than at the NSTL facility.

The total phosphorus effluent concentration at the NSTL was lower than

that at the Coral Springs, Florida, effluent. However, the influent

total phosphorus concentration at Coral Springs, Florida, was approxi-

mately three times greater than that at the NSTL facility. These dif-

ferences are possibly due to the influence of the low concentrations

Table 3. Summary of nutrient loading rates applied to water hyacinths wastewater treatment systems.

Nutrient
Organic Nutrient Loading Rates Removal,
~Location Loading to First Unit Comments
Location Rae% Comments
Rate
kg BOD5/ha.-day kg TN/ha.-day kg TP/ha-day TN TP

Williamson Creek, Texas
Phase I (109 m3/d) 43 15.3 -70 - Single Basin, surface
area = 0.0585 ha
Phase II (109 m3/d) 89 18.5 - 64 - Single Basin, surface
area = 0.0585 ha
Five Basins in Series
Coral Springs, Florida 31 19.5 4.8 96 67surface area
Total surface area
= 0.52 ha
National Space 26 2.9 0.9 72 57 Single Basin Receiving
Technology Labs Raw Wastewater, Surface
area = 2 ha

being applied at the NSTL facility. In general, higher percentage re-

movals are experienced with higher concentrations. In addition harvesting

at the NSTL facility was not conducted at a frequency to optimize nutrient

removal.

Sludge Accumulation

Very little data are presented in the water hyacinth studies showing

the quantities of sludge that accumulate during the rapid growth of plants.

The only measurements of sludge accumulation reported were for the pilot

plant and full scale studies at Williamson Creek, Texas. In the pilot

studies the sludge accumulation was measured after the material dried,

and in the full scale operation, the sludge was measured while wet. The

area covered by the sludge was not reported in either case and only the

depth of the sludge was apparently measured. However, the dimensions of

both the pilot and the full scale facility were given, and making reason-

able assumptions, the quantities of sludge that accumulated were estimated

to be between 1.5 and 8 x 10-4 m3 of sludge/in3 of wastewater treated.

This compares to 1.8 x 10-3 m3 of sludge/in3 of wastewater treated for

conventional primary stabilization ponds (Middlebrooks et al., 1965).

The quantities of sludge accumulated per cubic meter of wastewater

treated in the pilot plant were approximately five times less than that

estimated in the full scale unit. However, because of the lack of ac-

curate measurement for the quantity of sludge accumulated, these esti-

mates are the best available. Regardless of which figure is used to

estimate sludge production, it is apparent that the rate of sludge

accumulation in a hyacinth growth basin is relatively slow and by

cleaning the systems once each season, as recommended by Dinges (1979),

would probably be adequate to prevent the passing of solids out of the

system. Compared with the accumulation of plants in the system, the mass

of sludge would be relatively insignificant and could easily be disposed

of along with the harvested hyacinths.

Hydraulics of Triangular Basins

Dinges (1979) has recommended that rectangular basins with a length-

to-width ratio of 3 to I be constructed and then divided into two triangles

to improve the hydraulic characteristics of the hyacinth basin. Such a

design would result in an increase in cross-sectional velocity as the

wastewater flowed toward the apex of the triangle. A preliminary hydraulic

analyses of the triangular basin concept indicates that the use of such a

hydraulic design should be approached with caution since small organic

particles near the overflow weir may be washed out of the basin. Before

installing such a system, a more detailed hydraulic analysis should be

conducted.

Mosquito Control

Various experiences with mosquito problems at water hyacinth waste-

water treatment systems are reported by the investigators listed in Table

1. Although some investigators did not encounter a mosquito problem, all

recommended that some means of mosquito control be incorporated into the

design of such a facility. Most investigators recommended that natural

control measures be employed such as the mosquito fish (Gambusia). In

quiescent bodies of water, the growth of mosquito larvae is encouraged;

therefore, it appears imperative that control measures be incorporated

into hyacinth wastewater treatment systems.

REFERENCES

Bagnall, L. 0. 1979. Resource Recovery from Wasteawater Aquaculture.
Presented at the Seminar on Aquaculture Systems for Wastewater
Treatment, 11-12 September 1979, University of California, Davis.

Benemann, J. R. 1979. Energy from Wastewater Aquaculture Systems.
Presented at the Seminar on Aquaculture Systems for Wastewater
Treatment, 11-12 September 1979, University of California, Davis.

Camp, T. R. 1946. Sedimentation and the Design of Settling Tanks.
Transaction, ASCE, 111.

Crites, R. W. 1979. Economics of Aquatic Treatment Systems. Presented
at the Seminar on Aquaculture Systems for Wastewater Treatment, 11-
12 September 1979, University of California, Davis.

Dinges, Ray. 1978. Upgrading Stabilization Pond Effluent by Water
Hyacinth Culture. Journal Water Pollution Control Federation,
50, 5, 833-845.

Dinges, Ray. 1979. Development of Hyacinth Wastewater-Treatment Systems
in Texas. Presented at the Seminar on Aquaculture Systems for
Wastewater Treatment, 11-12 September 1979, University of California,
Davis.

Kruzic, A. P. 1979. Water Hyacinth Wastewater Treatment System at Walt
Disney World. Presented at the Seminar on Aquaculture Systems for
Wastewater Treatment, 11-12 September 1979, University of California,
Davis.

Middlebrooks, E. J., A. J. Panagiotou, and H. K. Williford. 1965. Sludge
Accumulation In Municipal Sewage Lagoons. Water and Sewage Works,
112, 2, 62.

Stewart, E. A., III. 1979. Utilization of Water Hyacinths for Control
of Nutrients in Domestic Wastewater - Lakeland, Florida. Presented
at the Seminar on Aquaculture Systems for Wastewater Treatment,
11-12 September 1979, University of California, Davis.

Swett, Dan. 1979. A Water Hyacinth Advanced Wastewater Treatment System.
Presented at the Seminar on Aquaculture Systems for Wastewater
Treatment, 11-12 September 1979, University of California, Davis.

Wolverton, B. C. 1979. Engineering Design Data for Small Vascular Aquatic
Plant Wastewater Treatment Systems. Presented at the Seminar on
Aquaculture Systems for Wastewater Treatment, 11-12 September 1979,
University of California, Davis.

Wolverton, B. C., and R. C. McDonald. 1979. Upgrading Facultative Waste-
water Lagoons with Vascular Aquatic Plants. Journal Water Pollution
Control Federation, 51, 2, 305-313.

ENGINEERING AS SESSMENT

USE OF AQUATIC PLANT SYSTEMS

FOR WAS TEWATER TREATMENT

Walter J. O'Brien
Black & Veatch Consulting Engineers
Dallas, Texas

INTRODUCTION

Aquaculture, the production of aquatic organisms under controlled conditions,

has been practiced for many centuries to produce food, fiber, and fertilizer.

This legacy is both a boon and a liability when the feasibility for using

aquatic plants in municipal wastewater treatment is evaluated. In the first

place, the terms "aquaculture" and "aquatic plants" are much too broad to per-

mit meaningful analysis of wastewater treatment systems unless boundary condi-

tions are established. The boundaries used in this assessment are:

(1) The aquatic plants used in the treatment processes are free floating

macrophytes;

(2) The primary objective of the treatment systems is wastewater renova-

tion. Byproduct recovery is a useful adjunct to this objective but

it is of secondary importance, and;

(3) Aquatic plant treatment processes can be used to replace, or upgrade

existing conventional treatment processes but they must successfully

compete with these processes in terms of performance, reliability,

and total costs.

Another restriction imposed upon this assessment is limitation of the plant

species to water hyacinth, Eichhornia Crassipes, and duckweed, Lemma sp.,

Spirodela sp., and Woiffia sp. The basis for this restriction is simply that

most of the information now available an the performance of aquatic plants in

wastewater treatment processes is based upon these species.

Many individuals working with aquaculture systems will consider the constraints

listed above unduly restrictive, but currently existing federal and state

water pollution control legislation preclude adoption of a wider view. However,

in many respects these restraints are beneficial in that they force a more

critical evaluation on the use of aquaculture technology in wastewater treatment

than has usually occurred in the past.

TREATMENT CONCEPTS

The evaluation of any biological treatment process requires: (1) definition

of physical and chemical characteristics of the raw waste; (2) specification of

treatment objectives, and; (3) an understanding of biological and physical

responses of the plants or animals used in the treatment process. In actual

practice, knowledge in one or more of these areas is often incomplete. However,

use of this approach provides a powerful tool for defining and solving waste-

water treatment problems.

The raw wastewater characteristics of primary importance are (1) range of

flow rates; (2) range of water temperatures; (3) BOD5, TS, TSS, TVSS, and

nutrient concentrations; (4) concentrations of pathogens, and; (5) concentrations

of toxic, organic, and inorganic constituents. Standard analytical techniques

are available for measuring these constituents in existing wastewater discharges.

Characterization of effluents from projected sources of wastewater is more dif-

ficult but can usually be done with information obtained from literature sources.

Establishment of treatment objectives is done by regulatory officials acting

under federal or state authority. In many cases, secondary or advanced secondary

treatment will be sufficient. In other situations, advanced waste treatment

processes which will achieve nutrient removal are required. In all cases, the

concentrations of toxic substances must be reduced to acceptable levels by

either pretreatment at the source or by the treatment process. Typical effluent

characteristics achieved by different treatment levels are summarized in Table 1.

TABLE 1

ASSUMED EFFLUENT CONCENTRATIONS FOR SELECTED PARAMETERS
AFTER SPECIFIED LEVELS OF WASTEWATER TREATMENT

(Values in mg/1)

Secondary Advanced Secondary Advanced Waste
Parameter Treatment Treatment Treatment

BOD 30 10 5

TSS 30 10 5

Total Nitrogen mg/l as N --5 3

Total Phosphorous mg/l as P --5 1

The magnitude for each of the parameters given in Table I for advanced waste-

water treatment will vary for specific treatment facilities. However, the values

given in Table I will be used as a basis for defining advanced wastewater treat-

ment in this assessment.

PLANT CHARACTERISTICS

Understanding the biological response of water 'hyacinths or duckweed in relatively

straight forward when compared to the population dynamics of activated sludge or

anaerobic digestion. Unfortunately, however, the literature now available con-

tains wide variations for growth responses which are of interest in wastewater

treatment systems. This situation is partly due to differences in the environ-

ments encountered in natural systems and in the enriched media provided by

wastewater.

The water hyacinth is commonly found in waterways in tropical and semitropical

areas around the world. It grows throughout Florida, in southern Georgia,

Alabama, Mississippi, Louisiana, and in parts of Texas and California. It is

usually free-floating, obtaining nutrients from the water. The individual

plants measure from 50 to 120 cm from root tip to the top of the flower cluster

when grown in wastewater. (1) This corresponds to a standing crop ranging

from 100 to 410 metric tons/hectacre (wet weight). (1) Approximately 95 per

cent of the weight of the plant tissue is water.

Productivity is also controlled by water temperature with plants growing most

rapidly from 280 to 300C. Growth ceases at water temperature above 400C or

below 100C. (2) Air temperatures of -30C for 12 hours will destroy the leaves

and exposure at -50 for 48 hours will kill the plants. (3) This restricts the

area of uniform year around plant growth to southern Florida and southern Texas.

Throughout the remainder of the present range of the plant, active growth occurs

from 7 to 10 months per year. (4) The geographic distribution and length of the

active growing season could be extended by the use of transparent covers placed

over the plants. However, use of this technique to expand the geographic range

may be influenced by the legal implications of Public Law 874, the Grass and Plants

Interstate Shipment Act, Amendment to Chapter 3, Title 18, USC, which prohibits

the interstate transport or sale of water hyacinths, alligator grass, water

chestnuts, and the seeds of these plants. (4) Similar state regulations also

apply in some areas.

Plants which are not in the active growth phase will shield the underlaying

water from sunlight but will not produce significant nutrient removal. Plants

killed by low air temperatures will also act as a barrier to sunlight but should

be harvested prior to significant breakdown of the plant tissue. Failure to

remove these plants will produce a significant BOD5 load in the treatment system.

The composition of water hyacints removed from a treatment system will provide an

initial estimate of the nutrient removal potential of these plants. These

characteristics are summarized in Table 2.

TABLE 2

DRY WEIGHT COMPOSITION OF
WHOLE WATER HYACINTH PLANTS GROWN IN WASTEWATER

Source Ref.(5)

% DRY WEIGHT
PARAMETER AVERAGE RANGE

Crude Protein 18.1 9.7 - 23.4

Fat 1.88 1.59 - 2.20

Fiber 18.6 17.1 - 19.5

Ash 16.6 11.1 - 20.4

Carbohydrate* 44.8 36.9 - 51.6

Kjeldahl Nitrogen (as N) 2.90 1.56 - 3.74

Phosphorous (as P) 0.63 0.31 - 0.89

*Computed by mass balance

Use of the values given in Table 2 will give a conservative estimate for

nutrient removal by hyacinth systems. More complete material balances should

also include denitrification and nitrogen and phosphorous uptake and removal by

other biota in the treatment system-. Preliminary estimates for material balances

across secondary pond systems in central Florida are available. (6) The composi-

tion of hyacinth leaves and stems has also been measured. (5)(7)(8) This informa-

tion can be used to provide order of magnitude estimates applicable to treatment

systems which harvest only the plant tops by mowing the standing crop. (9) How-

ever, if byproduct recovery is an integral component of the treatment facility,

additional research will be required to more fully characterize parts of the

plants obtained by mowing.

Hyacinths will also remove dissolved inorganic constituents and heavy metals from

wastewater by sorption onto the root system and by' incorporation into plant

tissue. (4)(7)(8)(10)(11)(12) Phenols can also be removed. (13)

Growth rates for hyacinth systems are a function of water temperature, waste-

water composition, and the procedures used for plant harvesting. (6)(14) Instal-

lations used for the removal of nutrients or toxic materials should be operated

at the maximum practical growth rate.

Evapotranspiration from hyacinth covered ponds has been reported to be from 3.2

to 5.7 times greater than evaporation from open water under the same climatologi-

cal conditions. (3)(15)(16) These values have been chanllenged by Idso who

claims the evapotranspiration measurements conducted by previous investigators

were distorted by the small sizes of the experimental facilities. (17) Resolution

of this controversy is needed before water hyacinth systems are used in water

short areas or in water recycle systems.

Duckweed (Lemma sp., Spirodela sp., and Woiffia sp.) has been investigated less

extensively than hyacinth f or use in wastewater treatment. However, it has a

much wider geographic range because it vegetates at temperatures above I10 to 3 0C

and winters well. The plants are relatively small flat disks which float and

form mats on the water surface.

Harvesting is relatively simple because these plants can be removed from the

water by continuous belt skimmers similar to those used for oil removal. How-

ever, the small size of duckweed also means the plants are readily displaced by

wind and wave action. Wind screens and/or floating barriers are usually required

to maintain a continuous mat of plants on the surface of a pond.

Duckweeds grown at 270C, under laboratory conditions, were reported to double

in frond number, and thus area, every 4 days. (18)

The dry weight of duckweed grown under these conditions was 252 kg/ha. Duckweed,

like hyacinth, contains approximately 95 per cent water in the plant tissue when

harvested. The composition of this tissue is summarized in Table 3.

Duckweeds also show a capability for removing metals from wastewater. However,

essentially no quantitative data is available on the use of these plants for

treatment of industrial wastewater.

The surface mat of plants produced by duckweeds will prevent exchange of oxygen

between the atmosphere and the water in a pond. This produces anaerobic conditions

in the treatment system but also prevents mosquito production. Mosquito control

must be provided in water hyacinth systems by the use of fish (Gambusia,

Poecilia, Astyanax)

TABLE 3

DRY WEIGHT COMPOSITION OF
DUCKWEED PLANTS GROWN IN WASTEWATER

Sources Ref (18)(19)(20)

PARAMETER AVERAGE % DRY WEIGHT

Crude Protein 29.2

Fat 5.5

Fiber 11.8

Ash 17.7

Carbohydrate* 35.8

Kjeldahl Nitrogen (as N) 4.59

Phosphorous (as P) 0.80

*Computed by mass balance

TREATMENT PROCESSES

Aquatic macrophytes can be used in single cell ponds, in series pond systems,

in ponds providing tertiary treatment following conventional secondary treat-

ment, and in completely integrated facilities. The quality of the final

effluent from these systems improves with complexity of the facility.

A single cell hyacinth covered lagoon located in southern Mississippi produced

an effluent BOD5 of about 7 mg/l and TSS of about 10 mg/1 when loaded between

22 to 30 kg BOD5/ha/day. (21) The surface area of this lagoon was approximately

2 ha. The average water depth was about 1.2 m and the hydraulic retention time

was approximately 54 days.

A second hyacinth covered lagoon, also located in southern Mississippi, produced

an effluent BOD5 of about 23 mg/l and TSS of about 6 mg/l when loaded at 44 kg

BOD5/ha/day. This lagoon had a surface area of 3.6 ha and an average depth of

1.73 m. However, this system was almost entirely anaerobic and produced odors

at night when photosynthesis was not occurring. (22) These installations

indicate single cell hyacinth covered lagoons can meet advanced secondary treat-

ment standards when the lagoon is very lightly loaded.

Pilot scale hyacinth ponds treating effluent from conventional primary sedi-

mentation basins produced an effluent BOD5 of approximately 28 mg/l and TSS of

about 23 mg/l during the first month of operation. (23) The loading was 104 kg

BOD5/ha/day and the water depth was 0.38 m, A portion of the plants were har-

vested twice per week. Long term data will be needed to evaluate the feasibility

of this process.

Multicell lagoons followed by hyacinth covered cells have been evaluated in

Mississippi and Texas. (9)(24)(25)(25)(27) The complexity of these treatment

systems has varied through a relatively wide magnitude, Lightly loaded facilities

have produced efflents which meet advanced secondary treatment standards. More

heavily loaded facilities and/or plants designed for use with minimum supervision

and maintenance have met secondary treatment standards. Hyacinth cells appear

to be a very cost effective method for upgrading oxidation pond effluents when

these facilities are located in warm climates. (28) Design criteria for this

type of system have been proposed. (9)(29)

The use of hyacinth cells to provide advanced waste treatment to the effluent

from conventional secondary treatment plants has been pursued in Florida. (6)(30)

Preliminary operating results from two facilities indicate the final effluent

will meet advanced waste treatment standards for BOD., TSS, and TN but will not

meet phosphorous standards. This is to be expected because the N:P ratio of

secondary effluent is slightly greater than the N:P ratio found in the harvested

plants. Supplemental nitrogen addition to the hyacinth pond may be a 'Viable

method for correcting this problem. (6)(30) However, even if this approach is

successful, the capability of consistantly achieving advanced waste treatment

standards will require relatively intensive management practices. These will

include frequent harvesting of the plants and will probably include supplemental

feeding of iron salts to prevent chlorosis. Despite these potential problems,

hyacinth systems alone or in combination with other processes offer considerable

promise for economically achieving advanced waste treatment standards.

Integrated systems combining anaerobic, facultative, and aerobic processes into

a treatment sequence have been developed by the firm Solar AquaSystems. (31)

Their treatment facilities cqonsist of a series of reactors covered with greenhouse

type roofs to more fully utilize solar energy and to prevent the loss of water

by evapotranspiration. Water hyacinth or duckweed is used to shade the water

surface in the final cell. A demonstration plant is now under construction in

the City of Hercules, California. (32)

The only field scale industrial wastewater treatment facility using hyacinths

is located at the National Space Technology Laboratories, Bay St. Louis,

Mississippi. (12) This system receives discharges from photographic and

chemical laboratories and produces an effluent which meets discharge standards.

Plants removed from this facility must be disposed of in a sealed pit designed

to prevent ground water pollution.

Pilot scale tests are also being conducted with water hyacinth systems to treat

effluent from existing lagoons at the Exxon Refinery and Petrochemical Complex

in Baytown, Texas. (33) Substantial reductions in TSS have been achieved.

Biological concentration of zinc, chromium, cadimum, and lead has also been ob-

served to occur primarily in the bottom section of these plants.

Ultimate disposal of plants harvested from facilities treating domestic sewage

can be done by composting, by producing animal feed, or by generating biogas

during anaerobic digestion. All of these processes are technically feasible.

(6)(9)(29)(30)(34) In most field installations they will not be sufficiently

profitable at this time to offset the cost of solids disposal.

The only field scale installation now using duckweed is a two cell lagoon system

located in North Biloxi, Mississippi. (20) The first cell is aerated. The

second cell is covered with a layer of duckweed. This cell is anaerobic but

the cover produced by the duckweed has produced an odor free system. Effluent

from this facility is much better than secondary standards.

No large scale solids disposal facilities exist from duckweed at the present

time.

COSTS

The economic incentive for including hyacinth ponds in a wastewater treatment

facility is very attractive under favorable climatic conditions. Comparative

cost estimates for 3785 m3/d (I mngd) plants designed to achieve advanced second-

ary and advanced waste treatment are summarized in Tables 4 and 5. (35)

TABLE 4

COMPARISON OF TOTAL COSTS,
ALTERNATIVE METHODS FOR ACHIEVING
ADVANCED SECONDARY TREATMENT
(Plant Capacity 3785 m3/day)

Source Ref (28)

TOTAL COST �/3.785 m3'
FAVORABLE LESS FAVORABLE
TREATMENT SYSTEM CONDITIONS CONDITIONS

Oxidation pond plus hyacinths 45 74

Overland flow land treatment 96 115

Conventional advanced secondary treatment 130 130

*Cost includes amortized capital, operation, maintenance, and land

The hyacinth system considered in Table 4 consists of preliminary screening and

grit removal followed by conventional oxidation ponds and hyacinth ponds operated

in series. The harvested hyacinths are composted and sold or given away. The

conventional advanced secondary treatment system consists of activated sludge

followed by dual media filtration.

TABLE 5

COMPARISON OF TOTAL COSTS
ALTERNATIVE METHODS FOR ACHIEVING
ADVANCED WASTEWATER TREATMENT
(Plant Capacity 3785 m3/day)

Source Ref (28)

TREATMENT SYSTEM TOTAL COST �/3.785 m3*

Overland flow plus hyacinths 79

Slow rate land treatment 110

Conventional advanced waste treatment 240

*Cost includes amortized capital, operation, maintenance, and land

The hyacinth system considered in Table 5 consists of preliminary screening and

grit removal, chemical addition of alum or ferric chloride, an overland flow

facility, and water hyacinth ponds. Harvested hyacinths are composted. The

conventional advanced waste treatment system consists of activated sludge,

chemical precipitation of phosphorous, biological nitrification followed by

denitrification, and mixed media filtration.

The costs given in Tables 4 and 5 are based upon standardized estimation

techniques keyed to March 1978 national indices and are not site specific. (35)

However, the relatively broad range shown in these estimates clearly indicates

aquaculture systems are worthy of serious consideration in relatively small

treatment facilities. Less extensive analyses indicate the cost advantages of

aquaculture systems continues to be favorable for treatment facilities with

hydraulic capacities up to at least 37,850 m3/d (10 mgd). (28)

SUMMARY

Wastewater treatment by aquatic macrophytes is currently considered by the USEPA

to be included within the scope of the innovative and alternative technology

provisions of Public Law 95-217. (35) Information reviewed for this assessment

indicates this classification is correct. Hyacinth systems are now ready for

routine use to upgrade conventional lagoons to meet secondary treatment standards

in subtropical climates. Additional development is necessary to further define

conditions under which they can be effective as advanced secondary and advanced

waste treatment processes. The mechanism provided by the innovative and alterna-

tive technology program can be used to accelerate these investigations. These

comments are expanded below.

Hyacinth ponds offer a viable method for upgrading the effluent from waste

stabilization lagoons (both facultative and anaerobic) in warm climates.

Hyacinth facilities are much less attractive in colder regions because of the

increased complexity required in the treatment system. Legal ramifications, if

plants escape from the treatment facility, are also unresolved at the present

time.

Hyacinth ponds will provide some nutrient removal under all conditions. In

central and southern Florida they have very good potential for achieving advanced

waste treatment standards on a year around basis. Additional information is

needed to establish an optimum harvesting strategy for the plants and to develop

alternative methods for achieving the phosphorous effluent standards.

Present use of hyacinths for treatment of industrial wastes is very limited.

Hyacinths appear to have good potential for this application if satisfactory

solids disposal facilities are included as part of the process design.

Integrated lagoon systems will have application in areas where there is a market

for reclaimed water and the solid residues produced by the aquatic macrophytes.

The comparatively low level of interest in the use of duckweed treatment system

is surprising. This plant has a relatively wide geographic distribution and is

comparatively easy to harvest.

RECOMMENDATIONS

1. The concept of using water hyacinth ponds to upgrade the effluent from waste

stabilization lagoons to secondary standards has been sufficiently developed

to make it a viable wastewater treatment technique in warm climates. Federal

and state regulatory agencies should encourage use of this process in ap-

propriate localities.

2. The use of water hyacinth ponds to upgrade secondary effluent to advanced

waste treatment standards is a viable concept in central and southern

Florida. Additional research is needed to establish optimum plant harvesting

techniques and to evaluate alternative methods for removing additional

phosphorous from the wastewater. This research should be encouraged by

regulatory agencies because hyacinth systems have the potential for pro-

viding advanced waste treatment at a relatively economical cost.

3. Industry should be made aware of the potential treatment possibilities

offered by plant macrophytes. The low costs associated with these systems

should lead to rapid adoption.

4. Additional research emphasis should be directed toward the use of duckweed,

and other cold weather plants, in wastewater treatment systems.

5. Future aquaculture research projects should be designed to provide mass

balances of water and the pollutants of interest across each pond in the

system. Twenty-four hour composite sampling should be used so these mass

balances will reflect the actual flux of materials through each pond.

REFERENCES

1. Wolverton, B. C. and McDonald, R. C., "Water Hyacinth Productivity and
Harvesting Studies", NASA/ERL Report No. 171, NSTL Station, MS39529 (1978).

2. Bagnall, L. 0., et.al., "Feed and Fiber from Effluent Grown Water Hyacinth",
Wastewater Use in the Production of Food and Fiber, Proceedings, EPA 660/
2-74-041 (1974).

3. Penfound, W. T. and Earle, T. T., "'The Biology of the Water Hyacinth",
Ecological Monographs, 18, 447 (1948).

4. Robinson, A. C., et.al., "An Analysis of the Market Potential of Water Hyacinth
Based Systems for Municipal Wastewater Treatment", Report BCL-OA-TFR-76-5
Battelle, Columbus Laboratories (1976).

5. Wolverton, B. C. and McDonald, R. C., "Nutritional Composition of Water
Hyacinths Grown on Domestic Sewage", NASA/ERL Report No. 173, NSTL Station,
MS39529 (1978).

6. Stewart, E. A., III, "Utilization of Water Hyacinths for Control of Nutrients
in Domestic Wastewater - Lakeland, Florida". Seminar on Aquaculture Systems
for Wastewater Treatment, University of California, Davis (1979).

7. Dinges, R., Water Hyacinth Culture for Wastewater Treatment, Texas Department
of Health, Division of Wastewater Technology and Surveillance, Austin, Texas
(1976).

8. Dinges, R., "Upgrading Stabilization Pond Effluent by Water Hyacinth Culture",
Journal of Water Pollution Control Federation, 50, 833 (1978).

9. Dinges, R., "Development of Hyacinth Wastewater Treatment Systems in Texas",
Seminar on Aquaculture Systems for Wastewater Treatment, University of
California, Davis (1979).

10. Wolverton, B. C. and McDonald, R. C., "Bioaccumulation and Detection of
Trace Levels of Cadmium in Aquatic Systems by Eichhornia Crassipes",
Environmental Health Perspectives, 27, 161 (1978).

11. Wolverton, B. C. and McDonald, R. C., "Water Hyacinth Sorption Rates of
Lead, Mercury, and Cadmium", NASA/ERL Report No. 170, NSTL Station,
MS39529 (1978).

12. Wolverton, B. C. and McDonald, R. C., "Wastewater Treatment Utilizing
Water Hyacinths (Eichhornia Crassipes) (Mart.) Solms", National Conference
on Treatment and Disposal of Industrial Wastewater and Residues, Houston,
Texas (1977): also in "Compiled Data on the Vascular Aquatic Plant Program:
1975-1977", NASA, NSTL Station, MS, NTIS N78-26715.

13. Wolverton, B. C. and McKnown, M. M., "Water Hyacinths for Removal of Phenols
from Polluted Waters", Aquatic Botany, 2, 191 (1976); also in "Compiled Data
on the Vascular Aquatic Plant Program: 1975-1977", NASA, NSTL Station, MS,
NTIS N78-26715.

14. Wolverton, B. C. and McDonald, R. C., "Water Hyacinth (Eichhornia crassipes)
Productivity and Harvesting Studies", NASA/ERL.Report No. 171, NSTL Station,
MS39529 (1978).

15. Timmer, C. E. and Weldon, L. W., "Evapotranspiration and Pollution of Water
by Water Hyacinth", Hyacinth Control Journal, 6, 34 (1967).

16. Rogers, H. H. and Davis, D. E., "Nutrient Removal by Water Hyacinth", Weed
Science, 20, 423 (1972).

17. Idso, S. B., "Discussion: Evapotranspiration From Water Hyacinth (Eichhornia
crassipes (Mart.) Solms) in Texas Reservoirs", Water Resources Bulletin, 15,
1466, (1979).

18. Harvey, R. M. and Fox, J. L., "Nutrient Removal Using Lemma minor", Journal
of Water Pollution Control Federation, 45, 1928 (1973).

19. Culley, Jr., D. D. and Epps, E. A., "Use of Duckweed for Waste Treatment
and Animal Feed", Journal of Water Pollution Control Federation, 45, 337
(1973).

20. Sutton, D. L. and Ornes, W. H., "Phosphorous Removal From Static Sewage
Effluent Using Duckweed", Journal of Environmental Quality, 4, 367 (1975).

21. Wolverton, B. C., and McDonald, R. C., "Upgrading Facultative Wastewater
Lagoons with Vascular Aquatic Plants", Journal of Water Pollution Control
Federation, 51, 305 (1979).

22. McDonald, R. C., "A Comparative Study of a Domestic Wastewater Lagoon With
and Without Water Hyacinths", NASA Tech Memorandum TM-X-72535 (1979).

23. Kruzic, A. P., "Water Hyacinth Wastewater Treatment System at Walt Disney
World", Seminar on Aquaculture Systems for Wastewater Treatment, University
of California, Davis (1979).

24. Wolverton, B. C. and McDonald, R. C., "Water Hyacinths for Upgrading Sewage
Lagoons to Meet Advanced Wastewater Treatment Standards: Part II", NASA
Tech Memorandum TM-X-72730 (1976); also available from NTIS N78-16481.

25. Dinges, R., "Upgrading Stabilization Pond Effluent by Water Hyacinth Culture",
Journal of Water Pollution Control Federation, 50, 833 (1978).

26. Neuse, D. W., "Removal of Algae From an Oxidation Pond Effluent Through the
Use of a Tertiary Water Hyacinth Pond System", M.S. Thesis, University of
Texas at Austin (1976).

27. Dinges, R., "Texas Experimental Hyacinth Wastewater Treatment Systems: A
Synopsis", Annual Meeting, Aquatic Plant Management Society, Chattanooga,
Tennessee (1979).

28. Crites, R. W., "Economics of Aquatic Treatment Systems", Seminar on Aqua-
culture Systems for Wastewater Treatment, University of California, Davis
(1979).

29. Wolverton, B. C., "Engineering Design Data for Small Vascular Aquatic Plant
Wastewater Treatment Systems", Seminar on Aquaculture Systems for Wastewater
Treatment, University of California, Davis (1979).

30. Swett, D., "A Water Hyacinth Advanced Wastewater Treatment System", Seminar
on Aquaculture Systems for Wastewater Treatment, University of California,
Davis (1979).

31. Serfling, S. A. and Alsten, C., "An Integrated Controlled Environmental
Aquaculture Lagoon Process for Secondary or Advanced Wastewater Treatment",
Performance and Upgrading of Waste Stabilization Ponds, (Middlebrooks, et.al.
ed.) USEPA, Cincinnati, Ohio (1978).

32. Serfling, S. A. and Mendola, D. M., "The Solar Aquacell AWT Lagoon System
for the City of Hercules, California", Conference on Wastewater Reuse,
American Water Works Association, Washington, D.C. (1979).

33. Chambers, G. V., "Performance of Biological Alternatives for Reducing Algae
(TSS) in Oxidation Ponds Treatment Refinery/Chemical Plant Wastewater",
presented at the Fifty-First Annual Conference, Water Pollution Control
Federation (1978).

34. Wolverton, B. C. and McDonald, R. C. and Gordon, J., "Bio-Conversion of
Water Hyacinths into Methane Gas", NASA Tech Memorandum X-72725 (1975);
also available from NTIS N78-26715.

35. Crites, R. W., Dean, M. J., and Selznick, H. L., "Land Treatment versus
AWT - How Do Costs Compare?", Water and Wastes Engineering, 16, No. 8,
16 (1979).

36. U. S. Environmental Protection Agency, Innovative and Alternative Technology
Assessment Manual (Draft), EPA 430/9-78-009 (1978).

COMBINED AQUACULTURE SYSTEMS FOR MUNICIPAL

WASTEWATER TREATMENT - AN ENGINEERING ASSESSMENT

H. G. Schwartz, Jr. and B. S. Shin

INTRODUCTION

Concern over the cost of meeting increasingly stringent effluent

quality requirements has prompted an intensified search for alternative

technology for wastewater treatment. Wastewater aquaculture is one of

the technologies that has received considerable attention in recent

years. Traditionally, aquaculture means the science or art of producing

useful biomass from controlled aquatic media. Useful biomass may also

be produced in wastewater aquaculture systems, but the basic purpose is

the treatment of the wastewater. A combined aquaculture system, or

polyculture system, is defined for this paper as one in which major

wastewater treatment work is carried out by several different levels of

aquatic organisms. It includes wastewater treatment ponds with a com-

bination of components such as mechanical elements, aquatic plants,

invertebrates, and fish. The purpose of this paper is to assess the

current status of combined aquaculture systems developed for municipal

wastewater treatment and determine if these concepts are ready for

routine use and, if not, what must be done to make them a reality.

PERFORMANCE OF COMBINED AQUACULTURE SYSTEMS

Although most wastewater aquaculture systems contain a diver-

sified community of organisms and hence could be considered to be combined

aquaculture systems, this term has normally been applied only to those

in which the use of different trophic levels is originally planned.

Systems utilizing floating plants such as water hyacinths (Dinges, 1979;

Stewart, 1979; Wolverton and McDonald, 1979 A,B), are not covered in

this paper. In typical polyculture systems, nutrients in wastewater are

first converted to single-cell organisms that serve as food for organisms

of higher tropic levels in subsequent units.

Dinges (1976) studied, on a pilot scale basis, a five-step

biological treatment system that consisted of a filter and a four-cell

culture unit. The system was designed to treat the effluent from a

stabilization lagoon. The filter was intended to reduce the biological

solids content of the wastewater, caused by the growth of algae in the

stabilization pond. The culture unit, 280 ft long x 30 ft wide x 2 ft

deep, was divided into four segments. The first cell, approximately

one-half of the culture unit, contained water hyacinths, duckweeds,

snails, scuds, and insects. The second cell was devoted to culture

zooplankton and was covered with duckweed to restrict algae growth.

About 30% of this pond was 8 ft in depth to provide effective aeration

using an airlift pump. Shrimp and fish were grown in the third and

final cells, respectively. The theoretical detention time for the

system was 5.3 days. Results obtained during a five-month period (from

June to November), as presented in Table 1, show a substantial reduction

in BOD, suspended solids, total and ammonia nitrogen, and fecal coliform.

Calculated loading rates per unit surface area are also shown in Table 1

for BOD, COD, and suspended solids.

Full-scale polyculture systems utilizing various species of

fish have been studied by Coleman, et al. (1974) at the Quail Creek

TABLE 1
PERFORMANCE OF A 5-STEP POLYCULTURE SYSTEM
(Dinges, 1976)

Percent reduction
Wastewater Influent Effluent of influent Loading*
Constituent mg/1 mg/l concentration lb/day/acre

BOD3 15 3.5 77 20.3
BOD20 90 18 76 122.0
COD 70 40 43 94.9
Suspended solids 35 7 80 47.4
Total organic nitrogen 4.8 1.2 75 --
Ammonia 2.1 0.1 95
Fecal coliform/100 ml 1400 10 99

* Calculated based on 31,336 gpd flow.

Plant in Oklahoma City and by Henderson (1979) at the Benton Service

Center in Arkansas. Both studies utilized six-cell, serially operated

lagoon systems to treat raw wastewater, the first two cells for wastewater

stabilization and plankton culture and the remaining four for the cul-

ture of fish. Coleman, et al. used mechanical aeration for the initial

stabilization step and channel catfish as the major culture. Henderson

accomplished initial waste stabilization without mechanical aeration and

used silver and bighead carp as the major culture.

Table 2 summarizes the results for the last four cells of the

two culture systems. All parameters such as unit area, detention time,

loading, fish stocking, and fish yield are based on the fish culture

unit only. The influents to the two culture units had similar character-

istics with respect to BOD and suspended solids. With the exception of

initial fish stocked and net fish production, all operating conditions

and performance of the two fish culture units were very similar. Although
the difference in testing period (see Table 2) might have affected netI
fish production and effluent quality, the results indicate that the

quantity of fish initially stocked might have little effect on the

system performance. In addition, the results further indicate that net

fish production was not directly related to the amount of BOD or suspended

solids removed from the system, but to the quantity of fish initially

stocked. Both systems performed satisfactorily in removing organics and

suspended solids.

As compared to conventional lagoon systems, both of the afore-

mentioned culture units appear to have larger unit areas and lower

organic loadings, although effluent BOD 5and suspended solids concentrations

of 30 mg/l could be met with only one fish pond in the Henderson's case

TABLE 2. PERFORMANCE OF POLYCULTURE SYSTEMS UTILIZING FISH

Source Coleman, et al. (1974) Henderson (1979)
Location Oklahoma Arkansas
Period June - Oct., 1973 Dec., 1978 - July, 1979
Major Culture Channel catfish Silver and bighead carp
Minor Culture Tilapia Channel catfish
Minnows Buffalofish
Grass carp
Flow (MGD) 1.0 0.45
Unit Area (acres/MGD) 26 36
Average Depth (ft) 3.9 - 4.3 4.0
Detention time (days) 35 47

Loading (lb BOD5/acre/day) 7.8 6.5
(lb TSS/acre/day) 23 8.7

Initial fish stocked (lb/acre) 27 378
Net fish production (lb/acre/mo) 34 340
(lb/lb BOD5 removed) 0.2 2.9
(lb/lb TSS removed) 0.06 2.4

Performance: Influent - Effluent (% Removal)
BOD5 (mg/l) 24 - 6 (75) 28.1 - 9.4 (67)
TSS (mg/l) 71 - 12 (83) 38.0 - 17.1 (55)
Total N (mg/l) 7.04 - 2.74 (61) --
NH3-N (mg/l) 0.4 - 0.12 (70) 5.1 - 2.0 (60)
NO2-N (mg/l) 0.96 - 0.16 0.02 - 0.11
NO3-N (mg/l) 2.31 - 0.29 0.01 - 0.5
Total P (mg/l) 7.97 - 2.11 (74) 3.0 - 2.5 (17)
Fecal coliform (No/100 ml) 1380 - 20 --

pH 8.2 - 8.3 7.88 - 8.19
DO (mg/l) -- 3.0 - 7.4

and three fish ponds in the case of Coleman, et al. The behavior of

nitrogen species in the fish culture units of the two systems was quite

different, apparently reflecting the characteristics of the influent.

One received wastewater which was well nitrified while the other received

wastewater containing predominantly ammonia and possibly organic nitrogen.

No similarity is shown in the phosphorus removal efficiency. There were

no reported incidents of fish kills, indicating that the ammonia, nitrite,

dissolved oxygen, and pH levels shown in Table 2 were within tolerable

ranges.

A lagoon wastewater treatment system used to culture muskel-

lunge has been described by Hinde Engineering Company (undated). The

system, located in Dorchester, Wisconsin, consisted of two aerated

lagoons each at 1.36 acres x 10 ft deep followed by another aerated fish

culture lagoon with 0.5 acres x 10 ft deep. At a flow rate of 63,600 gpd,

the hydraulic detention times were 51.2 days for each of the first two

cells and 25.9 days for the fish culture unit. The culture unit was

stocked with 5,000 muskellunge infants of about 2.5 in. long. Two-year

data, shown below, indicated that both effluent BOD5 and suspended solids

Influent Effluent

Range Average Range Average

BOD (mg/1) 125.0 - 400.0 232.3 2.8 - 16.2 5.9
5
SS (mg/1) 69.0 - 285.7 183.0 2.8 - 15.2 6.5

DO (mg/1) .. 8.0 - 12.0 --

averaged about 6 mg/l and, on a monthly average basis, did not exceed

about 16 mg/i during the entire test period. Data for the fish culture

unit alone are not available and the extent to which fish contributed to

effluent quality improvement is not known. Experience with other aerated

lagoon systems of this type, however, suggests that the fish culture

pond may well have served as a polishing unit reducing suspended solids

and BOD values in the final effluent.

A two-stage culture unit designed to upgrade secondary effluent

was explored by the Las Virgenes Municipal Water District (1973). The

system consisted of a shallow algae culture pond followed by a zooplankton

(Daphnia pulex) culture pond, and was operated with a detention time of

about 10 days for each stage. System COD reduction was above 40%.

Nitrogen and phosphorus removal efficiency was hampered by occasional

invasion of Daphnia or rotifers in the first stage pond, which decimated

the algal population. Lack of success in controlling such events was

the principal obstacle to further development of the system. Dinges

(1976) also investigated a similar system and reported that production

of Daphnia was severely hampered by high pH caused by algal growth.

Ryther (1979) and Goldman and Ryther (1976) investigated a

pilot scale, continuous flow marine polyculture system at the Environ-

mental Systems Laboratory of the Woods Hole Oceanographic Institution.

The system was designed to remove nitrogen from secondary effluents and

at the same time to culture marine organisms that have commercial values.

The system consisted of shallow ponds (3 ft deep) to culture single-cell

marine algae, aerated raceways containing stacked trays of shellfish,

and, finally, a culture unit for seaweed production. The raceways were

stacked with different species of oysters and clams, and contained small

numbers of other shellfish together with lobsters and blackback flounders.

The secondary effluent was diluted with seawater at various proportions.

Results for the phytoplankton production cell show that the

mean nitrogen removal rate was 2.7 lbs/acre/day during the winter and

7.1 lbs/acre/day during the summer. Based on these results, Ryther

projected the area requirement for the algae pond at 77 acres/MGD in the

winter and 26 acres/MGD in the summer for secondary effluent with a

nitrogen content of 24 mg/l. Problems encountered in this process step

were inhibition of algal production by particulate organic matter in the

secondary effluent, seasonal variations of algal species, and their

protozoan predation. Since some algal species were detrimental to

shellfish culture, Ryther (1979) felt that algal species control was a

critical, unresolved problem.

Shellfish culture experiments with the American oyster and

hard clam indicated that these organisms have slow growth rates and high

mortality. Lack of success with these organisms was attributed to the

predominant growth of the marine algae, P. tricarnutem, in the algal

culture pond that were inferior and unsuitable as food for the shellfish.

Recent experiments (Ryther, 1979) have shown, however, that several

exotic shellfish species are capable of utilizing the kinds of algae

that could be mass produced. They include the Manila clams (T. japonica),

European oysters (0. edulis), and Japanese oysters (G. gigas).

Seaweeds were used in the last stage of the polyculture system

to remove nutrients not initially assimilated by the phytoplankton and

those originating from the excretions of the shellfish and other animals

used. The content of the culture unit was vigorously circulated to keep

the seaweed in suspension. With the seaweed, Gracilaria tikvahiae, the

yield was 3 g dry organic matter/m2/day in the winter and 10 g/m2/day in

the summer.

The mass balance for inorganic nitrogen for the entire system

was determined during a steady-state operation period. The nitrogen

removal efficiency was 89.3% when the nitrogen input from the seawater

was considered and 93.6% otherwise.

Stewart and Serfling (1979) reported on a proprietary lagoon

technology called Solar AquaCell system which consisted of a series of

two anaerobic cells, a facultative cell, and finally two aerobic cells.

The system is enclosed in greenhouse-type pond cover and utilizes fixed-film

"BioWebs" in cells 2 through 5 and floating aquatic macrophytes in the

aerobic cells. The anaerobic stage was basically similar in design to

large-scale septic tanks and had the function of removing suspended

solids and sludge storage/digestion. Oxygen in the facultative and

aerobic cells was supplied by coarse bubble diffused aeration.

The Solar AquaCell system was initially tested on a pilot

scale basis at the Solan Beach treatment plant in the San Diego area

using wastewater fed intermittently at an overall system detention time

of about four days (Serfling and Alsten, 1978). Another pilot scale

test was conducted recently at the San Elijo treatment plant in Cardiff,

California (Stewart, et al., 1979). The system was operated at a 4.5-day

detention time: 0.5 days for the anaerobic stage and about 1.3 days for

each of the three facultative and aerobic cells. Dissolved oxygen was

maintained at 1-3 mg/l and 3-6 mg/l in the facultative and aerobic

cells, respectively. The results show that reduction of BOD5 and

suspended solids to less than 30 mg/l could be achieved by the anaerobic

and facultative stages and that further improvement in the effluent

quality was possible with the addition of the aerobic stage. The

authors also reported a substantial reduction of total Kjeldahl

nitrogen, and attributed such reduction to nitrification occurring in

the facultative and aerobic cells. Phosphate removal was reported to be

low. Additional data for the aerobic and facultative stages were reported

by Stewart and Serfling (1979).

With the use of water hyacinths in the aerobic stage, the

Solar AquaCell was reported to achieve effluent BOD and suspended

solids levels of less than 5 mg/l at a system detention time of 5 days.

However, the removal of nitrogen attributable to the aquatic plants was

relatively minor, accounting for about 10 percent of the total nitrogen

removed from the aerobic stage. The remaining 90 percent was removed by

the "BioWeb" and bottom deposits (Stewart and Serfling, 1979).

ENGINEERING ASSESSMENT OF POLYCULTURE SYSTEMS

In the preceding section, a brief review was made on the

performance of polyculture systems that have been explored in recent

years for the treatment of municipal wastewater. Results indicate that

systems involving higher forms of animals are generally less efficient,

require more land area, or are more difficult to control than their

aquatic plant counterparts. It has been projected that plants will play

a more dominant role in future aquaculture systems because they grow

quicker, accumulate more contaminants, are generally more tolerant to

temperature variations, and are more adaptive to a harsh environment

that might prevail in wastewater (Stowell, et al., 1979). Another

important advantage that plants have over animals is that they afford

more avenues for potential utilization.

In order to design and operate an aquaculture system on a

rational basis, understanding and knowledge of its physical character-

istics, engineering criteria, treatment capability as a function of

system constraints, by-product disposal/utilization, and costs are

required. This section will address these topics with particular

emphasis on the availability of design and operational data.

Physical Characteristics

The combined aquaculture system as defined herein includes

lagoons with a combination of such active components as fixed film media

for bacterial growth, aquatic plants, invertebrates, and fish. The use

of fixed films has shown under controlled conditions of pilot scale

testing to be an effective means of reducing the required size of con-

ventional aerated lagoons. The optimum surface area required per unit

volume of lagoon should depend on the characteristic of wastewater to be

treated, hydraulic detention time, and the system's capability for

delivering the increased oxygen demand. Data presented by Stewart and

Serfling (1979) indicate that, for primary effluent, aerated lagoons

with 2-3 ft2 fixed films/gpd of wastewater could achieve secondary level

treatment at a detention time of about 1.3 days. Recommended detention

time and fixed film density for advanced secondary treatment are about

4.0 days and 6-9 ft2/gpd, respectively. These values for fixed film

requirements are equivalent to 10.6-15.9 ft 2/ft3 of lagoon volume. The

use of fixed films in aerated lagoons appears to be an attractive concept

and full-scale data on the merits of fixed films should be available

from the Solar AquaCell system for the City of Hercules, California,

which was scheduled for startup in January, 1980 (Stewart and Serfling,

1979).

The types of fish that have been commonly used in wastewater

aquaculture experiments are catfish, carp, tilapia, and minnows. Of

these, carp are recognized to have great potential for wastewater appli-

cations because of their hardiness and adaptability to a wide variety of

food. On the other hand, the use of tilapia may be restricted in cold

climatic areas due to their limited tolerance to low temperatures.

Dissolved oxygen is the most critical environmental factor which affects

the functioning of fish culture units. Dissolved oxygen concentrations

of less than about I mg/i are acutely toxic to the fish noted above, and

many of their physiological activities can be adversely affected at

higher concentrations. To date, fish-based wastewater aquaculture systems

have been applied to secondary effluent or its equivalent. Under such

conditions and with the use of shallow ponds, mechanical aeration was

not required. Most of the fish culture systems using wastewater as the

feed, as described in the preceding section and elsewhere, have been

largely oriented toward examining the suitability of conventional lagoon

effluent for biomass production. The practice of fish stocking varied

widely. Information on fish stocking requirements relative to wastewater

characteristics and treatment objective is not available at the present

time.

Aquatic macrophytes that have been used in the combined aqua-

culture system include water hyacinth and duckweed. The climatic condition

is the major constraint for the use of water hyacinth. The water hyacinth

is a tropical plant and its active growth is restricted to water temp-

eratures of 10 to 35'C with an optimum range from 25 to 27.5'C (Dinges,

1979). Duckweed can survive throughout the winter in milder temperate

climates and may be useful as a supplement for water hyacinth during the

winter months. Dinges (1979) noted that the most critical design factors

for water hyacinth culture basins are the rate of flow of wastewater

through the basin and uniform distribution of wastewater at inlet and

outlet zones. He observed solids breakthrough in a pilot scale unit

when the horizontal velocity was 2.5 - 2.9 ft/hr. No solids break-

through occurred at 1.6 - 1.9 ft/hr. Based on these observations, he

concluded that a broad rectangular shape would be the preferred con-

figuration for water hyacinth culture basins. Disadvantages of this

shape, however, would be high costs associated with maintaining uniform

flow across the basin.

By their very nature, combined aquaculture systems require

multiple cells, and the optimum number of cells to be used should depend

on individual circumstances. Specific reasons for the need for multiple

cells would be, among others, to regulate food chain relationships,

maintain proper culture population, and control the level of dissolved

oxygen. In addition, combined aquaculture systems should be designed to

allow maximum operational flexibility and uninterrupted services when

any cell must be taken out of operation for cleaning and other maintenance

purposes.

Most aquaculture systems have been explored using existing

lagoons and, hence, specifics on optimum number, size, and configuration

of culture cells have not been established. Hydraulic characteristics

of fish culture basins may be of less consequence than those of hyacinth

culture basins.

Engineering Criteria

Wastewaters from small municipalities have been commonly

treated in stabilization lagoons of various types. Although inexpensive

to construct and operate, lagoon systems frequently suffer poor effluent

quality during warm summer months due to excess growth of algae. Most

conventional lagoon systems can be converted with little or no modifica-

tion to aquaculture systems of the types described here, to upgrade the

effluent quality to the level of secondary or advanced secondary treat-

ment.

Major problem areas associated with animal-based aquaculture

systems have been the system instability, predation of low level organisms,

and fish mortality caused by low temperatures, while major problem areas

associated with hyacinth-based aquaculture systems include freezing of

the culture during winter months, breeding of mosquitoes and other

vectors, low efficiency during cold seasons, and occasional odor development.

Mosquitoes have been successfully controlled by the establishment of

large fish population in the culture unit (Stewart, 1979).

Aquaculture systems function under numerous variables, many of

which are beyond the control of the operator. It has been a general

consensus that the lack of system reliability caused by these uncontrol-

lable variables is the major shortcoming of aquaculture systems. Auxiliary

processes that could be used during system upset or for seasonal operation

have not been explored.

The maximum flow for which an aquaculture system can be economi-

cally built and operated is largely speculative at this time. To arrive

at such a flow, considerations should be given to the availability of

land, harvesting capabilities of existing equipment, practicability of

resource recovery and, if insulation is required, the feasibility of

building large greenhouse-type cover that can withstand snow and other

loads. For hyacinth-based systems, harvesting may be the limiting

factor for unit size based on the capacity of present equipment. Bagnall

(1979) suggested a maximum harvesting capacity of 10 tons/hr (wet weight)

with present equipment. Assuming a 6 hour per day operating time and a

2.5 ton/day/acre (wet weight) hyacinth production rate, the maximum area

that could be served by the equipment would be 24 acres/day. Further,

assuming an area requirement of 8 acres per 1 MGD of flow, the design

capacity of the system would be 3 MGD. Multiple trains of 3 MGD capacity,

each with its own harvester, would be technically possible, but the

labor costs for operators might be high.

A number of investigations have been made in recent years to

determine the cost-effectiveness of aquaculture systems. The major

difficulty encountered in such analyses was the lack of information on

system sizing, operation and maintenance requirements, and product

harvesting, processing, and utilization/disposal. Most analyses have

been based on data obtained from pilot scale experiments. Comprehensive

and reliable economic evaluations will not be possible until full-scale

data are available. Duffer and Moyer (1978) provided a review of economic

data for aquaculture systems. Additional cost data are presented by

Crites (1979). He concluded that for advanced secondary treatment at a

1-MGD level, conventional stabilization pond followed by water hyacinths

is significantly more cost-effective than conventional treatment consisting

of activated sludge plus dual media filtration. The analysis indicated

that the cost of water hyacinth harvesting and composting had a negligible

effect on overall costs.

Pollutant Removals

The operating conditions and performance of combined aqua-

culture systems based on fish, fixed films, and others were described in

the preceding section. Relevant information such as unit loadings, fish

stocking, and density of active components based on lagoon surface area

or volume has also been covered. Although comprehensive studies involving

side-by-side comparison between fish-based aquaculture systems and

equivalent conventional lagoon systems are not available, the former has

been shown to perform better in removing simple organics and suspended

solids. Carpenter, et al. (1976) showed that a six-cell lagoon system

with fish stocked in the last four cells produced effluent with 6 mg/l

BOD and 12 mg/l suspended solids, while the effluent from the same

system, but without fish contained 13 mg/l BOD5 and 39 mg/l suspended

solids. Henderson (1979) also indicated similar improvement in effluent

quality with the use of fish, and attributed such improvement to the

absence of algal growth. Information on the removal of heavy metals,

pathogens, and trace organics from combined aquaculture systems based on

fish or fixed films is not available.

Excellent removal of nitrogen by water hyacinths and duckweeds

has been well documented. In addition, these plants are known to accumu-

late phosphorus and a number of heavy metals. It has been well established

that the primary function of water hyacinths is suppression of algal

growth by blocking sunlight, taking up nutrients for growth, physically

filtering solids with their extensive root system, and supporting active

biota in the root system. Wolverton (1979) noted that the rate of BOD

or suspended solids removal in hyacinth basins is not strictly a function

of growth and harvesting rates, whereas the rates of nitrogen and phosphorus

removal are dependent upon growth and harvesting rate. Stewart (1979)

found that water hyacinths grow exponentially with time, and he used the

Michaelis-lMenten kinetic equation to correlate the growth rate with

limiting nutrient concentration.

Due to the lack of long-term experience with the combined

aquaculture systems described herein, data on sludge accumulation and

its effects on system performance are not available at the present time.

System Products

Any wastewater management system is complete only with proper

disposal or utilization of residue by-products. This aspect may be of

great importance for aquaculture systems because many of them have

potential for generating large quantities of such by-products. Table 3

shows production data for various species of fish grown in wastewater

lagoons, as obtained by Stowell, et al. (1979). Here, the term biomass

refers to the total amouiit of fish present in a system at some time and

the term production (or yield) means the change in biomass over a given

time. Wide variations in fish production are indicated, which might be

caused by differences in the amount of fish initially stocked and prevailing

environmental conditions in the culture unit.

Analytical results of metal and chlorinated hydrocarbon contents

of fathead minnows cultured in wastewater lagoons, obtained by Trimberger

(1972), are shown in Table 4. Some of them were in high concentrations,

but he indicated that results were similar to those obtained in fish

from nearby natural waters. Henderson (1979) also analyzed the flesh of

fish grown in stabilized wastewater for pesticides, heavy metals, and

pathogens commonly existing in wastewaters and found that the contaminant

TABLE 3. SUMMARY OF PRODUCTION DATA FOR FISH CULTURED IN
WASTEWATER LAGOONS (Colt, et al., 1979)

Biomass (dry) Production (dry) %
Species kg/ha kg/ha.d kg/ha.yr H20 Location Season Notes and Comments

Channel Catfish 126 67 Arizona Tertiary treatment ponds,
not fed

Channel Catfish 256 218 67 Oklahoma May - Oct Wastewater lagoons

Raibow Trout 0 0 0 Arizona Tertiary treatment ponds,
not fed. Total mortality
due to ammonia toxicity and
low dissolved oxygen.

Coho Salmon 0 - 2 0 - 58 71 N. Calif. In ponds receiving waste-
Chinook Salmon water (67 percent wastewater,
33 percent seawater). Based
on the growth of juveniles
only.

Carp 175 75 Germany Sewage ponds, no feeding

Carp 50 - 150 75 England Sewage ponds, no feeding

Nile Tilapia 16.3 16 78 Oklahoma May - Oct Wastewater lagoons, mortality
due to low temperature

Java Tilapia 4,400 78 Tenn. Sewage oxidation ponds, pro-
jection based on maintenance
of optimum temperature, may
require aeration and nitrogen
removal

Chinese Carp 682 74 Arkansas Aug - Dec Sewage oxidation ponds, mor-
tality due to low temperature

Chub 118 - 238 75 England all year Sewage oxidation ponds
Perch
Roach

TABLE 4. METAL AND CHLORINATED HYDROCARBON
CONTENTS OF FATHEAT MINNOWS GROWN IN
STABILIZED WASTEWATER
(Trimberger, 1972)

Amount
Metals mg/kg Wet Weight
Arsenic 0.5
Cadmium 0.1
Mercury 0.15
Lead 1.0
Zinc 48.0
Copper 0.5
Chrome (Hexavalent) 0.1
Nickel 0.2

Chlorinated Hydrocarbons
PCB2 0.84

DDT 0.238

1 Analysis made on Gas Chromatograph.
Measured as Aroclor 1254.

levels of those examined were all below the action guidelines established

by FDA or the Arkansas Department of Health.

Suggested utilization of fish products from wastewater aqua-

culture systems include direct human consumption, animal feed, and

extraction of protein. However, due to potential public health hazards

and problems associated with consumer acceptance, the use of these

products for human consumption may not be realized in the foreseeable

future. The technical and economic feasibility of protein extraction

has yet to be demonstrated, and marketability of the products as animal

feed or raw material for pet food production needs to be carefully

examined. Unless an economic means of by-product utilization is found,

they should be considered as a liability, requiring proper disposal.

CONCLUSIONS AND RECOMlENDATIONS

The combined aquaculture systems reviewed here are all still

in the exploratory or developmental stage and, as such, are not ready

for routine use. Combined aquaculture systems such as those involving

higher forms of animals are generally less attractive than their aquatic

counterpart. Nonetheless, they may find some wastewater treatment

applications particularly where use of a aquatic plant such as water

hyacinth is limited due to climatic or other constraints.

Aquaculture systems consisting of conventional stabilization

ponds followed by fish culture ponds have shown to be capable of consistently

producing secondary or advanced secondary quality effluent. However,

data on species-specific removal rates and inital fish stocking

100

requirements under different environmental and wastewater conditions

are still lacking, and rational design criteria need to be developed by

which the overall cost effectiveness of such systems can be determined.

These systems warrant additional developmental efforts oriented toward

developing such information.

The fixed film system discussed herein combines some unique

approaches to biological wastewater treatment with possible use of

aquatic plants or fish. Pilot studies indicate high levels of treatment

efficiencies on municipal wastewater. The first full scale system is

going in service early in 1980 and results from this plant should yield

more definitive information on performance and cost effectiveness.

One major concern with virtually all combined aquaculture

systems is the utilization/disposal of system products, i.e., the plants

or fish. Harvesting techniques, particularly for fish, are not well

developed and good cost data are very limited. The ultimate utili-

zation/disposal of harvested biomass has not given much attention, but

may prove to be a critical factor in the successful application of these

systems. Simplistic answers such as by-product recovery and composting

may prove technically or economically unattractive in many locations.

The presence of heavy metals, for example, may prevent utilization as a

soil conditioner. Even without such technical impediments, there may be

little market for compost or other by-products. Clearly, major research

and development emphasis needs to be placed on the utilization/disposal

of biomass from combined aquaculture systems.

101

REFERENCES

1. Bagnall, L. 0. (1979). Resource Recovery from Wastewater Aquaculture,
paper presented at the Seminar on Aquaculture Systems for Wastewater
Treatment, University of California at Davis, September, 1979.

2. Benemann, J. R. (1979). Energy from Wastewater Aquaculture Systems,
paper presented at the Seminar on Aquaculture Systems for Wastewater
Treatment, University of California at Davis, September, 1979.

3. Carpenter, et al. (1976). Aquaculture as an Alternative Wastewater
Treatment System, in Biological Control of Water Pollution, Tourvier,
J. and Pierson, R. W., Jr. editors, University of Pennsylvania,
Philadephia, PA, pp. 215-224.

4. Coleman, M. S., et al. (1974). Aquaculture as a Means to Achieve
Effluent Standards, in Wastewater Use in the Production of Food and
Fiber, EPA-660/2-74-041, U.S. Environmental Protection Agency, pp.
199-214.

5. Colt, J., et al. (1979). The Use and Potential of Aquatic Species
for Wastewater Treatment, Appendix B - The Environmental Requirements
of Fish, University of California at Davis, California.

6. Crites, R. W. (1979). Economics of Aquatic Treatment Systems,
paper presented at the Seminar on Aquaculture Systems for Wastewater
Treatment, University of California at Davis, September, 1979.

7. Dinges, R. (1976). A Proposed Integrated Biological Wastewater
Treatment System, in Biological Control of Water Pollution, Tourbier,
J. and Pierson, R. W., Jr. editors, University of Pennsylvania,
Philadelphia, PA, pp. 225-230.

8. Dinges, R. (1979). Development of Hyacinth Wastewater Treatment
Systems in Texas, paper presented at the Seminar on Aquaculture
Systems for Wastewater Treatment, University of California at
Davis, September, 1979.

9. Duffer, W. R., and Moyer, J. E. (1978). Municipal Wastewater
Aquaculture, EPA-600/2-78-110, U.S. Environmental Protection Agency,
Ada, Oklahoma.

10. Goldman, J. C., and Ryther, J. H. (1976). Waste Reclamation in an
Integrated Food Chain System, in Biological Control of Water Pollution,
Tourbier, J. and Pierson, R.W., Jr. editors, University of Pennsyl-
vania, Philadelphia, PA, pp. 197-214.

11. Henderson, S. (1979). Utilization of Silver and Bighead Carp for
Water Quality Improvement, paper presented on the Seminar on Aqua-
culture Systems for Wastewater Treatment, University of California
at Davis, September, 1979.

102

12. Hinde Engineering Company (undated). Little Fish Big Help in
Sewage Treatment, Reprint for Hinde Engineering Company, Highland
Park, IL.

13. Las Virgenes Municipal Water District (1973). Tertiary Treatment
With a Controlled Ecological System, EPA-660/2-73-022, U.S. Environ-
mental Protection Agency.

14. Ryther, J. H. (1979). Treated Sewage Effluent as a Nutrient Source
for Marine polyculture, paper presented at the Seminar on Aquaculture
Systems for Wastewater Treatment, University of California at
Davis, September, 1979.

15. Serfling, S. A., and Alsten, C. (1978). An integrated Controlled
Environmental Aquaculture Lagoon Process for Secondary or Advanced
Wastewater Treatment, paper presented at the Conference on Perfor-
mance and Upgrading of Waste Stabilization Ponds, Utah State
University, Logan, Utah, August 23-25, 1978.

16. Serfling, S. A., and Mendola, D. M. (1979). The Solar AquaCell AWT
Lagoon System for the City of Hercules, California, paper presented
at the American Water Works Association Conference on Wastewater
Reuse, March 1979, Washington, DC.

17. Stewart, E. A., III (1979). Utilization of Water Hyacinths for
Control of Nutrients in Domestic Wastewater - Lakeland, Florida,
paper presented at the Seminar on Aquaculture Systems for Waste-
water Treatment, University of California at Davis, September,
1979.

18. Stewart, W. C., and Serfling, S. A. (1979). The Solar AquaCell System
for Primary, Secondary or Advanced Treatment of Wastewaters, paper
presented at the Seminary on Aquaculture System for Wastewater
Treatment, University of California at Davis, September, 1979.

19. Stewart, W. C., et al. (1979). Pilot Studies of the Solar AquaCell
Controlled Aquaculture Process for Wastewater Reclamation, paper
presented at the American Water Works Associates Conference on
Wastewater Reuse, March, 1979, Washington, DC.

20. Stowell, R., et al. (1979). The Use of Aquatic Plants and Animals
for the Treatment of Wastewater, University of California at Davis,
California.

21. Trimberger, J. (1972). Production of Fathead Minnows (Pimephales
promelas) in a Municipal Wastewater Stabilization System. Michigan
Department of Natural Resources, Fisheries Division, Grand Rapids,
Michigan.

22. Wolverton, B. C. (1979). Engineering Design Data for Small Vascular
Aquatic Plant Wastewater Treatment Systems, paper presented at the
Seminar on Aquaculture Systems for Wastewater Treatment, University
of California at Davis, September, 1979.

103

23. Wolverton, B. C., and McDonald, R. C. (1979A). The Water Hyacinth:
from Prolific Pest to Potential Provider, AMBIO, Vol. 8(1), pp.
2-10.

24. Wolverton, B. C., and McDonald, R. C. (1979B). Upgrading Faculta-
tive Wastewater Lagoons with Vascular Aquatic Plants, Journal Water
Pollution Control Federation, Vol. 51(2), pp. 305-313.

~~~~~~~~~~104~~~~~
104~~~~~~~~~~~~~~~~~~~~~~~~~~

COMBINED AQUACULTURE SYSTEMS FOR

WASTEWATER TREATMENT IN COLD CLIMATES

AN ENGINEERING ASSESSMENT

Edward R. Pershe

INTRODUCTION

The Clean Water Act as amended in 1977 (PL 95-217)

encourages the use of innovative and alternative technologies

for the reclamation of wastewater. Furthermore, it speci-

fies that grants for conventional treatment works construc-

tion shall not be made unless the grant applicant has satis-

factorily demonstrated that innovative and alternative

treatment processes have been fully studied and evaluated.

During the past decade alternative processes utilizing

land app-liation methodology have been proposed for the

treatment and utilization of wastewater. These processes

have, in general, proved to be successful, however, they

were adopted for wastewater treatment purposes only after

they were adequately field tested and suitable design

criteria were developed.

The purpose of this assessment is to highlight some of

the more important aspects of combined aquaculture systems

and to evaluate their merit for use in cold climates. Much

of the assessment is based on presentations that were made

at a seminar held on the campus of the University of Cali-

fornia at Davis in September 1979.

105

ASSESSMENT OF AQUACULTURE SYSTEMS

In general, aquaculture appears useful as a wastewater

treatment tool, however, this treatment technology has many

gaps that need to be filled in before it can be used reliably

for engineered design. The use of water hyacinths, duckweeds

and other aquatic vascular plants is really limited to only

tropical and warm-temperate climates if unprotected, year-

round treatment by these means is proposed. In recent

years, surges of freezing cold weather have penetrated deep

into the South making even much of Florida inhospitable to

year-round usage of aquaculture.

Removal of BCD, suspended solids and nutrients is

highly variable in aquaculture systems. While they may

produce excellent effluents for long periods at a time, they

may fail unexpectedly and be difficult to restore to their

former efficiency in an acceptable time period. It appears

doubtful whether the reliability of such systems can be

increased to are acceptable level for design purposes without

making them unduly large and land consumptive.

Aquatic processing units (APIJ) seem to be used to

better advantage in treatment trains which are headed by

primary/secondary treatment units. The effluents from these

units have a more consistent quality and are much more

treatable in an aquaculture environment because gross pollu-

tants have been removed. In addition to making the aquatic

lagoon setting esthetically unattractive, gross pollutants,

such as grit, oil and grease, scum, and floatable and settleable

106

solids, interfere with natural treatment mechanisms and

become the focal point of foul odors and undesirable pre-

datory species.

Although fish are useful for mosquito vector control in

aquaculture systems, their usage to enhance wastewater

treatment or to improvE: effluent quality is dubious. in

spite of the fact that some filter-feeding fish are capable

of removing organisms or particulate matter that are micro-

scopically sized, it is the soluble organic and nutrient

components in the wastewater that must be removed to attain

effective treatment or effluent quality. Because the practical

aspect of developing fish culture for food supplies is

stymied by public health considerations, it is doubtful

whether polyculture systems can ever be cost effective in

the United States. Fish farming has been successfully

demonstrated, but aside from the need to have adequate

oxygen levels and a balance of upper and bottom filter-

feeding fish present in the systems, no hard and fast guide-

lines are available as yet.

In the area of operation and maintenance of aquaculture

systems, much still remains to be known. odor, insect and

other nuisance conditions may develop or occur for inexplic-

able reasons. Harvesting and disposal of biomass and sludge

still presents a problem, however, it may prove to be less

intractable to engineering solution than other problems.

Unplanned after-development of numerous species of plants

107

and animals in aquaculture systems raises concern about such

systems evolving into wild or mongrel-like facilities which

could readily lose their treatment effectiveness.

In addition, the use of recirculation to enhance treat-

ment and alleviate septic conditions has not been fully

exploited nor has much attention been given to ;Safeguarding

the systems and rejuvenating or restoring them in case there

is a wipeout of aquatic plants and animals by toxic wastes,

disease, or unforseen climatic conditions. It may be possible

to reduce the effects of a wipeout by always keeping a stock

supply of aquatic plants and animals on hand, however, this

would be expensive to maintain and unless the problem was

one of non-recurring nature, a second wipeout could follow

with disastrous consequences.

The so-called "solar aquacell" type system offers a

protective environment to aquatic plants and a means for

transferring solar heat energy from the contained atmosphere

of the system to the liquid mass. However, in spite of the

3-phase treatment given to the wastewater, very little

increased benefit is derived from the process and many

questions still unresolved must await solution until the

prototype installation is constructed.

In short, it is much too early at this time to attempt

to prescribe any guidelines or criteria that would be useful

for designing a reliable aquaculture system. The main

unresolved question is the susceptibility of these systems

108

to function under a wide number of variables, and the element

of risk that would be incurred. At the present time, enough

is known about the performance of such systems so that an

enterprising designer can probably develop a reasonably

efficient pilot facility, which given diligent and fastidious

care, might work for soitle time, perhaps even flawlessly.

But this is not the realistic situation and is highly

unlikely to occur. In the full-scale plant operation,

fastidious care is more likely to become simply routine

maintenance having concomitant shortcomings. It would be

prudent, therefore, to develop and verify any design criteria

or guidelines by first conducting a pilot study at the

intended location-for the facility. Such a study, at least

at this time, should be conducted over a minimum period of

two years.

109

SUMMARY AND RECOMMENDATIONS

It is evident from what has been learned so far that

the use of aquaculture to obtain secondary treatment of

wastewater has not developed or been studied sufficiently to

enable even generally applicable design criteria to be

formulated. Because some of the variables that affect

system design are greatly influenced by site-specific condi-

tions, it may be that firm design criteria are not attain-

able practically, or for that matter, really desirable given

the great difficulty that present conventional wastewater

treatment plants experience in trying to achieve effluent

standards. Perhaps the use of general guidelines coupled

with long-term pilot studies at the proposed site is the

best approach to attaining optimum system design.

on the other hand, the use of an aquatic processing

unit as a polishing or tertiary process following some type

of conventional secondary treatment plant, including stabili-.

zation or oxidation ponds, seems to offer much promise.

Such units should be capable of consistently reducing BOD

and suspended solids values to less than 10 mg/L. These

systems could be used in northern parts of the U.S. during

mild or growing seasons to produce high quality effluents

for recharging groundwater aquifers or other reuse purposes.

Their most beneficial usage would probably occur in resort

areas which have high summer populations since they could

provide low cost supplementary treatment to a secondary

treatment plant being operated at high loading rates.

In regard to the quality of the influent that enters an

aquaculture system, it should not be lower than primary

effluent quality. The cheapest removals of BOD and suspended

solids are obtained from the simple 'Sedimentation process.

Allowing grit, grease, scum and other floatable and settle-

able solids into an aquaculture system causes severe esthetic

impacts and interferes with treatment mechanisms.

Fish-type polyculture should not be considered as an

important component in the design of an aquaculture system

for wastewater treatment. The development and management of

such a system is dependent upon skills and expertise that

are basically removed from and only incidental to wastewater

treatment objectives.

At this time it does not appear to be feasible to

provide protection for aquaculture systems so that they can

be operated on a year-round basis in northern climates.

There are no strong arguments to support this hypothesis.

There is, of course, less sunshine during the winter months

and the low ambient air temperature within an enclosure,

together with the reduced amount of sunlight, would probably

render aquatic plants less active toward pollutant removals.

In summary we can state that under proper conditions,

the treatment efficiency of aquaculture systems should be

comparable to secondary treatment. The reliability of these

systems, on the other hand, is quite another thing; they are

greatly affected by cold weather, their ability to handle

hydraulic/organic shock loads is unknown, and their recovery

in the event of a plant/animal dieoff is probably too slow

to make the installation risk acceptable.

In view of the above, it is recommended that large

full-scale demonstration projects be used to obtain more

reliable information about aquaculture systems rather than

small pilot studies. The problem with the latter is that

lavish attention is often focused on such studies and because

of this inordinate surveillance, small flaws are readily

detected and quickly corrected. Because aberrations never

really get a chance to develop into significant problems

which could affect the results of the study, a false sense

of reliability and performance is generated. Thus, an

unrealistic picture is portrayed about a system which is not

true to life, and if followed as an example, might cause

disastrous consequences.

The sites for the demonstration projects should be

carefully chosen so that the results can be made applicable

to any region of the coutnry.

112

TREATMENT ASPECTS OF AQUACULTURE SYSTEMS

An aquaculture system treating wastewater functions in

a manner that is similar to a conventional wastewater treat-

ment facility. Each is made up of individual unit opera-

tions which are selected to perform at optimum capability in

a particular treatment train.

In a given aquaculture system, there may be one or more

APU's following a pretreatment phase that may include pri-

mary or even secondary treatment. The degree of treatment

given by the aquaculture portion of the overall system may

be secondary or advanced. In the simplest system, the

aquaculture units assume the full impact of the pollutional

load and the APU's function first as primary treatment

units, then as biological, and finally as clarification

units. Organic and inorganic solids and newly created

biomass are intended to remain within the system, decaying

into mineralized constituents and simpler molecules which

can be broken down. Such systems must be cleaned of sludge

and biomass at intervals but the undertaking is not simple.

In many cases; these simpler systems become overburdened and

emit nuisance odors or other problem vectors.

Those aquaculture systems which have adequate pretreat-

ment preceding them, receive a wastewater having more uniform

quality and also free of gross pollutants. This wastewater

is more easily treated in the system with fewer operational

problems.

113

Selection of specific species of aquatic pla nts and

animals to stock a given APU is dependent upon: (1) the

characteristics of the wastewater, (2) the amount or type of

pretreatment preceding the APU's, (3) the desired effluent

quality, and (4) local climatic conditions. In combined

aquaculture systems, ad~ditional components such as mechanical

aerators, fish or benthic plants, may be utilized to further

improve the quality of waste treatment or attain some other

goal.

Management practices for APU's, in turn, are also related

to the species selected. A major management problem has to

do with biomass harvesting and disposal. Other operational

considerations include using supplementary aeration and

recirculation, selection of the best means of pretreatment

to meet conditions, and maintenance of species support faci-

ties for restocking purposes.

As in the case of conventional wastewater treatment

facilities, it is possible to have similar aquacul ture

systems treating the same type of wastewater in the same

geographic area, and yet not achieve the same end result.

In essence, the variations in aquaculture system designs may

be as complex and intermixed with unit operations as in the

case of conventional wastewater treatment systems, and the

treatment results may be equally varied.

The principal mechanisms of wastewater pollutant removals

in APU's are physical, chemical, and biological in nature -

the same as those encountered in conventional treatment.

114

Where conventional pretreatment including settling is not

provided, settleable solids are removed in the first APU

unit. However, removal of very small particulates can also

occur as the result of mechanical filtration as the waste-

water passes through plant and root masses. in polyculture

systems, removal of settled solids and plant fo:-ms is accom-

plished by means of grazing fish or other animal forms.

Biodegradable matter is removed by adsorption on sub-

strate and plant surfaces, by decomposition or degradation

through oxidative and reductive processes, and by bacterial

and animal consumption or absorption. Heavy metals are

removed by adsorption on plant surfaces, precipitation, and

absorption by plants and animals.

In a certain sense, the mechanisms of removal may be

more efficient in aquaculture systems than in conventional

treatment systems because the living plant and animal net-

work presents a mesh-like straining environment which seems

to enhance removals. The principal difficulty in engineer-

ing or designing such systems lies in trying to determine

how to ascribe the removals of pollutants to a particular

mechanism or to different species of plants and animals.

Symbiosis would also seem to play an important but difficult

to define role in such systems.

DETAILS AND PERFORMANCE OF COMBINED AQUACULTURE SYSTEMS

The common type aquaculture system employs water hya-

cinth plants in a shallow lagoon to achieve wastewater

treatment. Lately, considerable interest has been shown in

modified aguaculture systems which employ some particular

feature to enhance the quality of the effluent or obtain

some other benefit. These modified systems, often times

referred to as combined systems, employ such devices as

supplementary aeration, polyculture or fish, etc.

Polyculture Systems

Stewart (1) studied a polyculture system consisting of

three one-acre lagoons in series seeded with water hyacinth

plants. Oxygen levels were always found to be high enough

so that septic conditions did not develop. However, algae

blooms developed in the last lagoon and contributed to

lowered effluent quality.

Water hyacinths in the first pond grew to large size

amidst a thriving fish populatior�. Unusually high removals

of phosphorus were attained which were attributed to uptake

by mosquito larvae that later left the pond as adult mosqui-

toes. When mosquito vector control was instituted, the

phosphorus level in the effluent increased from 0.6 mg/L to

6 mg/L.

Fish grew rapidly and appeared to favor residence in

the second pond. Unlike the first pond, hyacinth roots were

relatively clean and free of heavy bacterial slimes. Tadpoles

and mollusks also developed in the second pond, however,

116

there was very little mosquito life. In the third pond,

hyacinth plants became very chlorotic and required supple-

mentary iron treatments.

During the summer months, the system consistently

produced effluent values of 1.0 mg/L Total Nitrogen, 4 mg/L

BOD, 2 mg/L Suspended Solids, and 0.2 to 3 mg/L Phosphorus.

As in other studies, nutrient ratios in the wastewater were

found to be unbalanced so that good phosphorus removals

could not be attained. Other methods were advised if phos-

phorus removal was an important objective.

Henderson (2) studied silver carp (Hypopthalmichthyes

molitrix) and bighead carp (Aristichthyes nobilis) as low

trophic level filter feeders in fish production ponds.

Silver and bighead carp feed on free-floating or free-

swimming planktonic organisms as small as 4 microns in size,

and can reach a size of 40 to 50 pounds in 4 to 5 years.

Many finfish species ranging from the low esteemed carp to

the muskellunge have thrived successfully in wastewater

ponds converting various food forms and nutrients into fish

flesh.

Settled wastewater at a state institution, consisting

mainly of wastes from a laundry and food service facilities

in addition to sanitary wastes, was fed to a 3-pond poly-

culture system with fish and also to a similar 3-pond stabil-

ization system without fish. Each system was operated in

series and had a total surface area of 12 acres. The waste-

water fed to each system had a BOD of 260 mg/L and Suspendedi

117

Solids of 140 mg/L. The overall surface loading was 44

Kg/ha/day which is comparable to the loading of a stabiliza-

tion pond designed to achieve secondary treatment.

The results of the study show that both systems pro-

duced effluents having very similar quality although the

polyculture system appeared to consistently perform slightly

better than the simple stabilization system. Over a 12-

month period the effluent BOD of the polyculture system

ranged from about 7 to 45 mg/L with values less than 15 mg/L

obtained more than 50 percent of the time. Over the same

period, the effluent BOD of the stabilization system ranged

from 12 to 52 mg/L with values less than 23 mg/L obtained

about 50 percent of the time.

On an annual basis, Henderson reported that the BOD of

the effluent from the system without fish was 37.6 percent

higher than the series which employed fish. This would

appear to be an impressive improvement, however, it must be

remembered that this calculation is based on comparing

rather low figures to begin with, hence, the improvement is

more illusionary than real. For example, if the effluent

BOD of the the stabilization system is 12 mg/L and that of

the polyculture system is 8 mg/L, the effluent of the stabil-

ization system would calculate to be 50 percent higher than

the polyculture system. While that is true, the actual

difference between the two systems in this particular example

is statistically meaningless.

118

Over a 12-month period, effluent suspended solids from

the stabilization system ranged from about 9 to 110 mg/L

with values less than 20 mg/L obtained 50 percent of the

time. Effluent suspended solids for the polyculture system

during that same period ranged from about 7 to 78 mg/L with

values less than 20 mg/L obtained 50 percent of the time.

Henderson then studied a polyculture system using six

ponds in series. The pond depths averaged 1.2 to 1.3 m and

the flow through each pond was baffled to prevent short-

circuiting. The influent flow rate of 0.45 MGD allowed a

hydraulic residence time of 72 days. Ponds 1 and 2 served

as stabilization and plankton culture ponds and were not

stocked with fish. The remaining four ponds were stocked

with silver and bighead carp. The overall loading rates on

the system were 43.5 Kg/ha/day BOD and 20.4 Kg/ha/day Suspended

Solids. These loadings are quite comparable to those used

to design stabilization pond systems. During the first

eight months of operation, the 6-pond system reduced BOD by

about 96 percent and suspended solids by 86 percent. The

effluent BOD ranged from about 4 to 17 mg/L with values less

than 7 mg/L occurring 50 percent of the time. Values for

the effluent suspended solids ranged from 3 to 31 mg/L with

values exceeding 20 mg/L occurring more than 60 percent of

the time.

Ryther (3) evaluated tertiary treatment of secondary

treatment plant effluent in a marine aquaculture system at

Woods Hole, Massachusetts, over a 2-year period. The effluent

119

was diluted in seawater and fed first to shellfish, includ-

ing different species of oysters, clams and other shellfish,

and then passed through a seaweed culture. It was found

that the quality of the tertiary effluent fluctuated accord-

ing to the quality of the secondary effluent. When the

sewage treatment plant effluent had a bad quality, the

tertiary system effluent was also poor. The seaweed culture,

intended as a polishing step, frequently became infested

with fouling organisms and had to be discarded.

It is apparent from the above studies of polyculture

systems that much still remains to be done if these systems

are to be made useful and reliable components for a waste-

water treatment system. They do appear at times to yield

good quality effluents as Henderscn was able to demonstrate.

However, the amount of improvement that is obtained over the

treatment of a simple stabilization pond system is very

small and hardly seems worth the extra effort, especially

since the fish that are produced cannot be utilized for

human food consumption. A comparison of the effluent qual-

ity values for polyculture and stabilization pond treatment

of wastewater shows that there is very little difference in

the pollutant parameter trends throughout the year. In the

6-pond polyculture system studied by Henderson, the amount

of improvement that was obtained over the 3-pond polyculture

system was not very appreciable and it is doubtful whether

it would have been any better than a 6-pond stabilization

system.

120

The use of marine polyculture systems to treat waste-

water does not seem to offer much promise. The organisms

used in such cultures appear to be too sensitive to the

quality of the wastewater and as such are unable to survive

even short-term periods of exposure to waste flows carrying

high concentrations of pollutants.

Solar AquaCell

Stewart and Serfling (4) have devised a 3-phase aqua-

culture system which is protected from adverse climate

conditions by means of coverings. In the first phase,

wastes are treated anaerobically after which they pass

through facultative and aerobic aquatic processing units

before being filtered through sand and disinfected. Each of

the aquatic processing unit-s contains vertical. strips of a

plastic film which act as a substrate for bacterial films to

grow on. One end of each bio-web strip is anchored at the

bottom of the aquatic lagoon. This enables the film strip

to act as a waste treating substrate throughout the total

depth. Diffused air is used in the facultative and aerobic

phases to aid the treatment process by providing oxygen and

mixing.

The anaerobic phase is covered by a plastic sheet which

floats on the surface while the aerobic phases are covered

by a double polyethylene air inflated roof. Solar energy

penetrates the covering, heating the air above these units

and this ambient heat is captured and conducted to the

lagoon liquor by means of mists generated by nozzles. In

121

addition, floating aquatic macrophytes, particularly water

hyacinths and duckweeds, are used to provide treatment in

the aerobic phases.

The authors of this process, which is marketed as the

Solar AquaCell System, claim that this system can achieve

advanced tertiary treatment very economically. Among the

advantages that are claimed for the system are the follow-

ing:

(1) The average operating temperature can be 12 to

17�C and still not adversely affect the system.

(2) The heat exchange system transfers solar heat in

the air to the water phase and thereby increases

the metabolic rates of plants and. organisms.

(3) Macrophytes, such as duckweeds and water hya-

cinths, can be easily harvested and, presumably,

easily disposed of.

(4) Low energy and maintenance costs.

In small-scale pilot testing, the anaerobic aquacell

with a total hydraulic retention time of 14 hours was reported

to have achieved an average BOD removal of 50 percent and

suspended solids removal of 89 percent. The raw influent

had median values of 218 mg/L and 248 mg/L, for BOD and

Suspended Solids, respectively. With water hyacinths as the

major plant component in the aerobic phases, it is claimed

that BOD and Suspended Solids levels below 5 mg/L can be

achieved within a 5-day retention time.

122

While the innovators of the Solar AquaCell system have

made many claims and have conducted a small scale study to

show how their system will perform, it is unclear from their

presentation as to whether the results can be sustained in a

full scale system and whether many subordinate operations,

such as harvesting and disposing of macrophytes, can be

handled as easily as they foresee. Many statements are made

regarding the advantages and merits of the system, however,

it is difficult to accept such blandishments without having

supporting data from larger and more comprehensive studies.

Among the questions that need to be answered are: (1) Is

anaerobic treatment of weak wastewater, without adequate

mixing and temperature control, preferable to simple stabil-

ization pond treatment?, (2) Is methane production possible

in such a system?, (3) If sand filtration is required

after the aerobic phase, wouldn't a simple stabilization

system followed by sand filtration be cheaper and just as

effective?, and (4) Will enclosure of the aerobic phases

limit the use of mechanical equipment for the removal of

macrophytes and sludge?

Nutrient Removals

King (5) reported on studies that were made to assess

the effect of wastewater storage on phosphorus and nitrogen

removal. During the impoundment of wastewater in ponds and

lagoons, significant permanent phosphorus reduction takes

place by direct sorbtion onto bottom sediments, by precipi-

tation with metals, and by incorporation into biological

123

tissue. All bottom sediments have a finite capacity to sorb

phosphorus, however, the initial significant reduction in

phosphorus content through benthic sorption will decline

after the first two or three years as the bottom sediments

become saturated with phosphorus. Thus, phosphorus sorption

on bottom sediments in ponds cannot be relied upon as~a

long-term means of phosphorus removal.

In addition, the absence of significant precipitation

of phosphorus and the limited ability of aquatic plants to

remove phosphorus from wastewater signify that wastewater

ponds offer little hope in being able to meet phosphorus

discharge standards. It was estimated that if all- the

aquatic plants in a series of four stabilization ponds were

harvested, the maximum removal of phophorus during the

active summer period would be equal to a concentration of

only one mg/L.

Nitrogen loss from wastewater storage or stabilization

systems takes place primarily in the form of ammonia gas.

During periods of elevated pH, ammonium ion is converted to

free ammonia and the gas exits from the liquid phase at a

rate that is determined by the degree of wind mixing and

other factors. While nitrogen is also removed through

uptake by plant and animal species, studies showed that less

than 10 percent of the total nitrogen removed in a 4-pond

serially operated system could be accounted for by plant

harvest.

Long detention times in pond systems also allows oxida-

tion of nitrogenous forms to the nitrate stage to take

124

place. Under occasional severe respiratory demands, nitrates

may be reduced to nitrogen gas, however, supersaturated

oxygen levels and maintanance of high pH throughout much of

the warm season would tend to discourage denitrification.

In general, although stabilization ponds or aquaculture

systems cannot remove phosphorus to any great extent, parti-

cularly after benthic sediments become saturated after a

period of 2-3 years, they have been shown to be extremely

efficient at stripping nitrogen from wastewater. Studies

show that about 95 percent of the nitrogen can be removed if

sufficient detention time is provided. If good phosphorus

removals are desired, other methods such as chemical addi-

tion should be employed.

Energy ConsiLderatiLons

Benemann (6) believes that fuel produced from aqua-

culture biomass is. a promising solar energy option. At the

present time, use of aquatic biomass for animal feeds is

restricted because of the potential hazard to public health

if such animals are used for human consumption. It is

believed that a long period of testing will be required

before this option meets with acceptance.

Although the primary method of producing fuel from

biomass would be through anaerobic digestion, there is

practically little or no experience in disposing of aquatic

biomass by this means. A number of uncertainties exist

about the amount of biomass that can be produced by aquacul-

125

ture systems. While most of the assumptions about biomass

digestion are drawn from wastewater sludge digestion expe-

rience, studies of anaerobic digestion of marsh and aquatic

plants are still necessary because the higher ligno-cellu-

losic content of such plants may present significant problems.

It may be possible to use a high rate digestion process to

keep digester capacities low, however, current on-going

studies suggest that this may not be feasible.

Benemann prefers that unconventional digestion facil-

ities, such as landfills, covered anaerobic ponds, plug flow

reactors, etc., be used instead of conventional sewage

digesters. However, these methods also will require study

and testing to determine their merits and feasibility.

In summary, the derivation of fuel from the anaerobic

digestion of aquatic biomass is still in its embryonic

stage. Because much is unknown about the quantity, nature,

digestability and dewatering characteristics of biomass, as

well as the quality and quantity of fuel that would be

produced from it, it would be unwise to place any reliance

upon biomass as a fuel source at this time.

126

REFERENCES

1. Stewart III, E.A. "Utilization of Water Hyacinths for
Control of Nutrients in Domestic Wastewater at Lake-
land, Florida." Presented at Seminar on Aquaculture
Systems, University of California, Davis. Sept. 1979.

2. Henderson, S. "Utilization of Silver and Bighead Carp
for Water Quality improvement." Presented at Seminar
on Aquaculture Systems, University of California,
Davis. Sept. 1979.

3. Ryther, J.H. "Treated Sewage Effluent as a Nutrient
Source for Marine Polyculture." Presented at Seminar
on Aquaculture Systems, University of California,
Davis. Sept. 1979.

4. Stewart, W.C. and Serfling, S.A. "The Solar AquaCell
System for Primary, Secondary or Advanced Treatment of
Wastewaters." Presented at Seminar on Aquaculture
Systems, University of California, Davis. Sept. 1979.

5. King, D.L. "The Role of Ponds in Land Treatment of
Wastewater." Reference source unknown.

6. Benemann, J.R. "Energy from Wastewater Aquaculture
Systems." Presented at Seminar on Aquaculture Systems,
University of California, Davis, Sept. 1979.

U.S. GOVERNMENT PRINTING OFFICE: 1981-67709411130 Region No. 8

127