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
MCD-68
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EPA 430/9-80-007
AQUACULTURE SYSTEMS
FOR WASTEWATER TREATMENT:
AN ENGINEERING ASSESSMENT
Sherwood C. Reed, USA/CRREL
Robert K. Bastian, EPA/OWPO
Project Officers
June 1980
U.S. Environmental Protection Agency
Office of Water Program Operations
Municipal Construction Division
Washington, D.C. 20460
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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)
% 7
\/
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CONTENTS
Engineering Assessment of Aquaculture Systems for Wastewater
Treatment: An Overview
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 Gulp
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 Wasteuater 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.
111
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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
iv
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ENGINEERING ASSESSMENT OF AQUACULTURE SYSTEMS FOR
WASTEWATER TREATMENT: AN OVERVIEW
Sherwood Reed USACRREL, 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 full 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
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innovative technologies. The team included:
Mr. Gordon Gulp
Gulp Wesner and Gulp.
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 & Gulp
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
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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 have 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.
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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 poten-
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
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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 PLANT 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
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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.
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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
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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.
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Solar Aquacell System
Hercules, CA
This 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
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of the year and the water temperature in the system was 2°C 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
10
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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 "combined
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.
Re commenda t i ons
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
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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).
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WETLAND SYSTEMS FOR WASTEWATER TREATMENT:
AN ENGINEERING ASSESSMENT
George Tchobanoglous Department of Civil Engineering,
University of California, Davis, CA
Gordon L. Gulp Gulp, Wesner, and Gulp,
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, ^) 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.
13
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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.
14
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Table 1
HYDROLOGICAL CLASSIFICATION OF NATURAL WETLANDS*
Type
Description
Freshwater
Riverine
Lacustrine
Palustrine
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.
Wetlands adjacent to or near lakes.
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.
Derived in part from References 11 and 30.
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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.
Derived in part from References 11 and 30.
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THE USE OF WETLANDS FOR WA5TEWATER 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
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 effluent. 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 ^.
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
17
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Table 3
TYPICAL NATURAL WETLANDS USED FOR
WASTEWATER TREATMENT AND DISPOSAL
Type
(location)
Type of
Wastewater
Applied
Remarks
References
Cypress
domes
(Florida)
Northern
peatlands
(Michigan,
Wisconsin)
Cattail
marshes
(Wisconsin)
Freshwater
tidal marsh
(New Jersey)
Lacustrine
marsh
(Hamilton Ontario,
Canada)
Swamplands
(Hay River,
Canada)
Wetlands, general
(Massachusetts,
Florida)
Secondary
Secondary
Secondary
Secondary
Secondary
Geographically limited
9,10
Secondary
Secondary
Marshland percolation/ 7,15,16,17,34
disposal system
Significant nutrient
reductions
Possible tertiary
treatment
Sediment ion most
important
21,23,24,29
33
19
12,13
8,35,36
18
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Table f
TYPICAL ARTIFICIAL WETLAND SYSTEMS USED FOR THE
TREATMENT AND DISPOSAL OF WASTEWATER
Type
(location)
Type of
Wastewater
Applied
Remarks
References
Meadow-marsh-pond
system/
(New York)
Ponds with
reeds or rushes/
(Germany, Holland)
Peat filled trench
systems/
(Finland)
Peat filter/
(Minnesota)
Marsh-pond
system/
(California)
Screened-
comminuted-
aerated-unsettled
raw wastewater
Settled
primary,
secondary
Settled
primary,
secondary
Secondary
Secondary
22
Process defined
in U.S. Patent
No. 3,770,623
Variable trench
depths
Need 20 percent
air space volume
in soil
Enhancement
project
5,27
7,25
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Table 5
REMOVAL MECHANISMS IN WETLANDS FOR THE CONTAMINANTS IN WASTEWATER
Mechanism
Contaminant Affected
Description
Physical
Sedimentation
Filtration
Adsorption
Chemical
Precipitation
Adsorption
Decomposition
Biological
Bacterial Metabolism0
Plant Metabolism0
Plant Absorption
Natural Die-Off
P
S
S
S
S
P
I
P
I
P
S
I
P
P
S
I
P
P
S
I
S
P
P
S
S
1
P
S
P
Gravitational settling of solids (and constituent contaminants)
in pond/marsh settings.
Participates filtered mechanically as water passes through
substrate, root masses, or fish.
Interparticle attractive force (van der Waals force).
Formation of or co-precipitation with insoluble compounds.
Adsorption on substrate and plant surfaces.
Decomposition or alteration of less stable compounds by
phenomena such as UV irradiation, oxidation, and reduction.
Removal of colloidal solids and soluble organics by suspended,
benthic, and plant-supported bacteria. Bacterial nitrification/
denitrification.
Uptake and metabolism of organics by plants. Root excretions
may be toxic to organisms of enteric origin.
Under proper .conditions significant quantities of these
contaminants will be taken up by plants.
Natural decay of organisms in an unfavorable environment.
ro
O
aAdopted from Reference 26.
P=primary effect, S=secondary
°The term metabolism includes
effect, [^incidental effect (effect occurring incidental to removal of another contaminant).
both biosynthesis and catabolic reactions.
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understanding of these mechanisms and their corresponding rates of reaction is
important in 1) 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
21
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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 BOD^,
TOG, and COD can be described with a first order function of the form:
Ct . C0e-kt (1)
where C = concentration remaining at the time t, mg/1
C = concentration at time t=0, mg/1
k° = specific removal rate constant for given constituent,
at 20°C, 1/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 wastewater 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.
k - k e(T-20) (2)
KT - i<20y (2)
where k_ = removal rate constant at temperature T, 1/d
k_ = removal rate constant at 20°C, 1/d
0 = temperature coefficient, 1.05-1.08
T = temperature, °C
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.
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Table 6
REPORTED REMOVAL EFFICIENCY RANGES
FOR THE CONSTITUENTS IN WASTEWATER
IN NATURAL AND ARTIFICIAL WETLANDS
Removal efficiency, 96
Constituent
Total solids
Dissolved solids
Suspended solids
BOD5
TOC
COD
Nitrogen (total as N)
Phosphorus vtotal as P)
Natural wetlands
Primary Secondary
40-75
5-20
60-90
70-96
50-90
50-80
40-90
10-50
Artificial wetlands
Primary Secondary
50-90
50-90
30-98
20-90
Refractory organics
Heavy metals
Pathogens
20-100
Removal efficiency varies with each metal.
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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.
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WASTEWATER
. . .COARSE SCREENING
(6)| \AND COMMINUTION ONLY
REUSE
DISCHARGE
AOUACULTURE
Figure 1
APPLICATION OF ARTIFICIAL WETLANDS (AW)
FOR THE TREATMENT OF WASTEWATER
(Adapted from Reference 26)
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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 BOD5 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
26
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ro
Table 7
PRELIMINARY DESIGN PARAMETERS FOR PLANNING
ARTIFICIAL WETLAND WASTEWATER TREATMENT SYSTEMS3
Characteristic/design
Type of
system
Trench (with
reeds or rushes)
Marsh (reeds
rushes, others)
Marsh-pond
i. Marsh
2. Pond
Lined trench
Detention
Flow , time, d
Range
PF 6-15
AF 8-20
AF 4-12
AF 6-12
PF 4-20
(hr.)
Typ.
10
10
6
8
6
(hr.)
Depth of
flow, ft (m)
Range
1.0-1.5
(0.3-0.5)
0.3-2.0
(0. 15-0.6)
0.3-2.0
(0.15-0.6)
1.5-3.0
(0.5-1.0)
—
parameter
Typ.
1.3
(0.4)
0.75
0.25
0.73
(0.25)
2.0
(0.6)
—
Loading rate
g/fr-d (cm/d)
Range
0.8-2.0
(3.25-8.0)
0.2-2.0
(0.8-8.0)
0.3-3.8
(0.8-15.5)
0.9-2.0
(4.2-18.0)
5-15
(20-60)
Typ.
1.0
(4.0)
0.6
(2.5)
1.0
(4.0)
1.8
(7.5)
12
(50)
Based on the application of primary or secondary effluent.
'PF = plug flow, AF = arbitrary flow.
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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 BOD- 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 ^1 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 1 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.^9/1000 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.
28
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Table 8
ENERGY AND RESOURCE CONSUMING FUNCTIONS IN
SELECTED WASTEWATER TREATMENT SYSTEMS
AS+c
P+AW+c
FP+AWC
Influent pumping
(TDH=i2it)
Screening
Primary settling
Aeration, mechanical
Secondary settling
Chlorination (lOrng/U
Thickening
Truck hauling of
sludge
Landspreading
Bidg heating, cooling
Vehicle operation
(2000 gal/y)
Misc, lighting, etc.
Primary
Influent pumping
(TDH = 12ft)
Screening
Primary settling
Truck hauling of
sludge
Landspreading
Bldg heating, cooling
Vehicle operation
(500 gal/y)
Misc, lighting, etc.
Artificial wetland
Pumping (TDH = 12ft)
Vehicle operation
(1500 gal/y)
Chlorination
(5 mg/L)
Facultative pond
Influent pumping
(TDH = 12ft)
Screening
Bldg heating, cooling
Vehicle operation
(1500 gal/y)
Misc, lighting, etc.
Artificial wetland
Pumping (TDH = 12ft)
Vehicle operation
(1500 gal/y)
AS+c = activated sludge + Chlorination.
P+AW+c = primary + artificial wetlands + Chlorination.
CFP+AW = facultative pond + artificial wetlands.
Not included in plants with a capacity less than 1.0 mgci.
29
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to
O
Table 9
LAND REQUIREMENTS
OPERATIONAL AND COST DATA FOR TREATMENT SYSTEMS IDENTIFIED IN TABLE 8a
ITEM
Land required, acre
Labor, p»h/y
Parts and supplies, $/y
Capital cost, $ x 10"6
AS+c
Plant size, mgd
0.1 0.5 1.0
1.0 2.5 4.0
1,600 3,600 5,500
8,000 12,000 16,000
0.71 1.23 1.60
P+AW+c
Plant size, mgd
0.1
0.5b+
4.0d
1,250
3,000
0.37
0.5 1.0
0.8b+ 1.5b+
20d 40d
3,000 4,500
5,000 7,000
0.55 0.90
FP+AW
Plant size, mgd
0.1 0.5 1.0
5C+ 15C. 30C.
4.0d 20d 40d
1,250 3,000 4,500
3,500 4,500 6,500
0.49 1.12 1.80
From Reference 28
Area for primary treatment
Area for facultative ponds
Area for artificial wetlands
-------
Table 10
BASIC DATA AND INFORMATION USED TO ADJUST COST DATA
AND FOR ENERGY CONSUMPTION COMPUTATIONS3
Item
Value
Cost indexes
ENRCC Index
EPA STP Index
EPA O & M Index
Bases for energy computations
Mechanical equivalent of heat
Heat rate
c,d
Heat rate used in report
Heating value for gasoline
Energy required for
manufacture of chlorine
Factor used to estimate
secondary energy for construction
Factor used to estimate second-
ary energy for supplies and parts
3,000
334.1*
2.54f
3413 Btu/kW'h
heat supplied in fuel, Btu
energy generated, kW»h
3413 Btu/kW'h
conversion efficiency
10,800 Btu/kW-hg
124,000 Btu/galh
42 x 106 Btu/ton
70,000 Btu/$ in 19631
75,000 Btu/$ in 19631
From Reference 28
""Reported values are for 3une 1979
"Basis for adjusting cost data given in this paper
d!913 = 100
S1957 - 1959 = 100
f
1967 = 1.0
"Assumed 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
To 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.
31
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ro
Table 11
ENERGY AND RESOURCE CONSUMPTION ESTIMATES FOR TREATMENT SYSTEMS
IDENTIFIED IN TABLE 8
ITEM
Primary energy, Btu/yxlO~
Electricity
Fuel
Secondary energy, Btu/yxlCf
Construction
Chemicals
Parts and supplies
Total, Btu/yxlCf6
O.I
367
515
746
64
180
1,872
AS+c
Plant size,
0.5
1,447
1,700
1,292
320
270
5,029
P+AW+c
mgd
1.0
2,560
2,240
1,680
640
360
7,480
Plant
0.1
130
384
389
32
68
1,003
size,
0.5
432
765
578
160
113
2,048
mgd
1.0
799
1,280
945
320
158
3,502
FP+AW
Plant size,
0.1 0.5
65 292
400 500
515 1,176
__
79 101
1,059 2,069
mgd
1.0
562
750
1,890
—
146
3,348
From Reference 28
-------
CO
CO
Table 12
ANNUAL AND UNIT COSTS, EXCLUDING LAND, FOR TREATMENT SYSTEMS
IDENTIFIED IN TABLE 8
ITEM
Capital cost, $ x 10"6
O
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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.
34
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Specifically, techniques must be developed to control 1) 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 through 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 BOD5. Thus the impact of overloading or poor management
will be specific for eacn 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 factors 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.
35
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Treatment Efficiency 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*, 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 for 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 for 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
36
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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
37
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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
38
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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. 3. Tourbier and R.W. Pierson,
Jr. (eds), University of Pennsylvania Press, Philadelphia, 1976.
6. Duffer, W.R. and 3.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 Wetlands 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 3.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.
39
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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 3. 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.
40
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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, 3. Tourbier and R.W.
Pierson, 3r., (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.3. Richardson (eds). The University of Michigan, Ann Arbor,
Michigan 1976.
26. Stowell, R., G. Tchobanoglous, 3. 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., 3.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.3. Richardson (eds), "Freshwater Wetlands
and Sewage Effluent Disposal," Symposium proceedings, The University of
Michigan, Ann Arbor, Michigan 1976.
30. Tourbier, 3. 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 3. 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, 3. Tourbier and R.W. Pierson, 3r.
(eds), University of Pennsylvania Press, Philadelphia 1976.
34. Williams, T.C. and 3.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.
41
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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, J., et al, "Removal of Nutrient From Treated Municipal Wastewater
By Freshwater Marshes," Center for Wetlands, University of Florida,
Gainsville, Florida, September 1978.
42
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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 Recommendations
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.
43
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A. A shallow hyacinth pond (< 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/1.
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.
8. 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.
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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 10°C or lower. The optimum temperature for
water hyacinth growth ranges between 21 and 30°C. 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
47
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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
48
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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
cons traint.
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
49
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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 tnVha-day when treating secondary
effluent will produce an effluent quality that would satisfy advanced
secondary standards (BOD5=<10 mg/i; SS=<10 mg/1; TKN=<5 mg/1; 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
BODej 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 6005 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/1). Approximately 50 percent reduction in the total phosphorus
concentration could be expected.
50
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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
51
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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 kg/ha-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/1 of
BODj 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 1 mg/1 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 1 experiment, all of the other studies with water
hyacinth systems reporting hydraulic retention times are based upon
52
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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
53
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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 hyacinth 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
54
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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
55
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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 parts
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.
56
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Table 2. Design criteria for water hyacinth wastewater treatment sys-
tems based upon best available data and to be operated in warm
climates.
Parameter
A. RAW WASTEWATER SYSTEM
(Algae Control)
Hydraulic Residence Time
Hydraulic Loading Rate
Depth, Maximum
Area of Individual Basins
Organic Loading Rate
Length to Width Ratio of
Hyacinth Basin
Water Temperature
Mosquito Control
Diffuser at Inlet
Dual Systems, Each Designed
to Treat Total Flow
B. SECONDARY EFFLUENT
SYSTEM
(Nitrogen Removal and
Algae Control)
Hydraulic Residence Time
Hydraulic Loading Rate
Depth, Maximum
Area of Individual Basins
Organic Loading Rate
Length to Width Ratio of
Hyacinth Basin
Water Temperature
Mosquito Control
Diffuser at Inlet
Dual Systems, Each Designed
to Treat Total Flow
Nitrogen Loading Rate
Design Value
Metric
> 50 days
200 m3/ha-day
= 1.5 meters
0. 4 hectare
^ 30 kg BOD5/
ha- day
> 3:1
> 10°C
Essential
Essential
Essential
> 6 days
800 m3 /ha- day
0.91 meter
0. 4 hectare
S 50 kg BOD5/
ha- day
> 3:1
> 20°C
Essential
Essential
Essential
* 15 kg TKN/
ha' day
English
> 50 days
0.0214 mgad
^ 5 feet
1 acre
^26.7 Ibs
BOD 5 /ac- day
> 3:1
> 50°F
Essential
Essential
Essential
> 6 days
0.0855 mgad
3 feet
1 acre
< 44.5 Ibs
BOD5/aC'day
> 3:1
> 68°F
Essential
Essential
Essential
£ 13.4 Ibs
TKN/ac-day
Expected
Effluent
Quality
BOD5^ 30 mg/1
SS < 30 mg/1
BOD5 < 10 mg/1
SS < 10 mg/1
TP < 5 mg/1
TN S 5 mg/1
57
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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 lack 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 data were collected at the
Williamson Creek, Texas, Phase 1 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
58
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Table 3. Summary of nutrient loading rates applied to water hyacinths wastewater treatment systems.
Location
Williamson Creek, Texas
Phase I (109 m3/d)
Phase II (109 m3/d)
Coral Springs, Florida
National Space
Technology Labs
Organic
Loading
Rate
kg BOD5/ha-day
43
89
31
26
Nutrient Loading Rates
to First Unit
kg TN/ha-day
15.3
18.5
19.5
2.9
kg TP/ha-day
_
-
4.8
0.9
Nutrient
Removal ,
%
TN
70
64
96
72
TP
—
-
67
57
Comments
Single Basin, surface
area = 0.0585 ha
Single Basin, surface
area = 0.0585 ha
Five Basins in Series
Total surface area
= 0.52 ha
Single Basin Receiving
Raw Wastewater, Surface
area = 2 ha
en
vo
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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/m3 of wastewater treated.
This compares to 1.8 x 10" 3 m3 of sludge/m3 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),
60
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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 1 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.
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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.
62
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ENGINEERING ASSESSMENT
USE OF AQUATIC PLANT SYSTEMS
FOR WASTEWATER 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.,
63
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Spirodela sp., and Wolffia sp. The basis for this restriction is simply that
most of the information now available on 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.
64
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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)
Parameter
BOD
TSS
Total Nitrogen mg/1 as N
Total Phosphorous mg/1 as P
The magnitude for each of the parameters given in Table 1 for advanced waste-
water treatment will vary for specific treatment facilities. However, the values
given in Table 1 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
Secondary
Treatment
30
30
—
Advanced Secondary
Treatment
10
10
5
5
Advanced Waste
Treatment
5
5
3
1
65
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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 28° to 30°C. Growth ceases at water temperature above 40°C or
below 10°C. (2) Air temperatures of -3°C for 12 hours will destroy the leaves
and exposure at -5°C 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
66
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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 BODc 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
67
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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.
68
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Duckweed (Lemma sp., SpJLrodela sp., and Wolf jia sp.) has been investigated less
extensively than hyacinth for use in wastewater treatment. However, it has a
much wider geographic range because it vegetates at temperatures above 1 to 3 C
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 27°C, under laboratory conditions, were reported to double
in frond number, and thus area, every A 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,
Pcecilia, Astyanax).
69
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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 BOD^ of about 7 mg/1 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 1.2m and the hydraulic retention time
was approximately 54 days.
70
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A second hyacinth covered lagoon, also located in southern Mississippi, produced
an effluent 8005 of about 23 mg/1 and TSS of about 6 mg/1 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 BODc of approximately 28 mg/1 and TSS of
about 23 mg/1 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)
71
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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 consist 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.
72
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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
o
cost estimates for 3785 m /d (1 mgd) plants designed to achieve advanced second-
ary and advanced waste treatment are summarized in Tables 4 and 5. (35)
73
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TABLE 4
COMPARISON OF TOTAL COSTS,
ALTERNATIVE METHODS FOR ACHIEVING
ADVANCED SECONDARY TREATMENT
(Plant Capacity 3785 m3/day)
Source Ref (28)
TOTAL COST C/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 C/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
74
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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.
75
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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
76
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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.
77
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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., Ill, "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.
78
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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, (±, 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 N78-164S1.
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).
79
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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 Ac[uaculture Systems for Wastewater
Treatment, University of California, Davis (1979).
30. Swett, D., "A Water Hyacinth Advanced Wastewater Treatment System", Seminar
on Aquacu]ture 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 Stabij-ization 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).
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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
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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 (Binges, 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.
Binges (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
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TABLE 1
PERFORMANCE OF A 5-STEP POLYCULTURE SYSTEM
(Dinges, 1976)
Wastewater
Constituent
BOD3
BOD2Q
COD
Suspended solids
Total organic nitrogen
Ammonia
Fecal coliform/100 ml
Influent
mg/1
15
90
70
35
4.8
2.1
1400
Effluent
mg/1
3.5
18
40
7
1.2
0.1
10
Percent reduction
of influent
concentration
77
76
43
80
75
95
99
Loading*
Ib/day/acre
20.3
122.0
94.9
47.4
--
--
—
* Calculated based on 31,336 gpd flow.
83
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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 net
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,, and suspended solids concentrations
of 30 mg/1 could be met with only one fish pond in the Henderson's case
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TABLE 2. PERFORMANCE OF POLYCULTURE SYSTEMS UTILIZING FISH
Source
Location
Period
Major Culture
Minor Culture
Flow (MGD)
Unit Area (acres/MGD)
Average Depth (ft)
Detention time (days)
Loading (lb BOD5/acre/day)
(Ib TSS/acre/day)
Coleman. et al. (1974)
Oklahoma
June - Oct., 1973
Channel catfish
Tilapia
Minnows
1.0
26
3.9 - 4.3
35
7.8
23
Henderson (1979)
Arkansas
Dec., 1978 - July, 1979
Silver and bighead carp
Channel catfish
Buffalofish
Grass carp
0.45
36
4.0
47
6.5
8.7
Initial fish stocked (Ib/acre) 27
Net fish production (Ib/acre/mo) 34
(Ib/lb BOD5 removed) 0.2
(Ib/lb TSS removed) 0.06
378
340
2.9
2.4
Performance: Influent - Effluent (% Removal)
BOD5
TSS (mg/1)
Total N (mg/1)
N02-N
N03-N
Total P (mg/1)
Fecal coliform (No/ 100 ml)
24-6 (75)
71 - 12 (83)
7.04 - 2.74 (61)
0.4 - 0.12 (70)
0.96 - 0.16
2.31 - 0.29
7.97 - 2.11 (74)
1380 - 20
28.1 - 9.4 (67)
38.0 - 17.1 (55)
5.1 - 2.0 (60)
0.02 - 0.11
0.01 - 0.5
3.0 - 2.5 (17)
PH
DO (mg/1)
8.2 - 8.3
7.88 - 8.19
3.0 - 7.4
85
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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 BOD,, and suspended solids
Influent Effluent
Range
BOD5 (mg/1) 125.0 - 400.0
SS (mg/1) 69.0 - 285.7
DO (mg/1)
Average Ranj
232.3 2.8 -
183.0 2.8 -
8.0 -
je
16.2
15.2
12.0
Average
5.9
6.5
--
averaged about 6 mg/1 and, on a monthly average basis, did not exceed
86
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about 16 mg/1 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.
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Results for the phytoplankton production cell show that the
mean nitrogen removal rate was 2.7 Ibs/acre/day during the winter and
7.1 Ibs/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/1. 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
2 2
yield was 3 g dry organic matter/m /day in the winter and 10 g/m /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 93.67,, 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/1 and 3-6 mg/1 in the facultative and aerobic
cells, respectively. The results show that reduction of BOD- and
suspended solids to less than 30 mg/1 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
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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/1 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, e_t al. , 1979). Another
important advantage that plants have over animals is that they afford
more avenues for potential utilization.
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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
2
with 2-3 ft 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
2
4.0 days and 6-9 ft /gpd, respectively. These values for fixed film
2 3
requirements are equivalent to 10.6-15.9 ft /ft 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).
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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 1 mg/1 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
92
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winter months. Binges (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.
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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
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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.
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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/1
BOD, and 12 mg/1 suspended solids, while the effluent from the same
system, but without fish contained 13 mg/1 BOD,, and 39 mg/1 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
96
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removal are dependent upon growth and harvesting rate. Stewart (1979)
found that water hyacinths grow exponentially with time, and he used the
Michaelis-Menten 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 amount 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
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TABLE 3. SUMMARY OF PRODUCTION DATA FOR FISH CULTURED IN
WASTEWATER LAGOONS (Colt, et al. , 1979)
OO
Biomass (dry) Production (dry) %
Species
kg/ha
kg/ha. d
kg/ha. yr HO Location Season
Notes and Comments
Channel Catfish
Channel Catfish
Raibow Trout
Coho Salmon
Chinook Salmon
Carp
Carp
Nile Tilapia
Java Tilapia
Chinese Carp
Chub
Perch
Roach
256
0
0-2
16.3
126
218
0
0-58
175
50 - 150
16
4,400
682
67 Arizona
67 Oklahoma May - Oct
Arizona
71 N. Calif.
75 Germany
75 England
78 Oklahoma May - Oct
78 Tenn.
74 Arkansas Aug - Dec
118 - 238 75 England all year
Tertiary treatment ponds,
not fed
Wastewater lagoons
Tertiary treatment ponds,
not fed. Total mortality
due to ammonia toxicity and
low dissolved oxygen.
In ponds receiving waste-
water (67 percent wastewater,
33 percent seawater). Based
on the growth of juveniles
only.
Sewage ponds, no feeding
Sewage ponds, no feeding
Wastewater lagoons, mortality
due to low temperature
Sewage oxidation ponds, pro-
jection based on maintenance
of optimum temperature, may
require aeration and nitrogen
removal
Sewage oxidation ponds, mor-
tality due to low temperature
Sewage oxidation ponds
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TABLE 4. METAL AND CHLORINATED HYDROCARBON
CONTENTS OF FATHEAT MINNOWS GROWN IN
STABILIZED WASTEWATER l
(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
DDT 0.238
PCB2 0.84
Analysis made on Gas Chromatograph.
2
Measured as Aroclor 1254.
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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 RECOMMENDATIONS
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
TOO
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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.
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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 a_l. (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. Binges, 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.
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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., Ill (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., e_t 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.
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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.
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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 application 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.
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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 BOD, 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 ari acceptable level for design purposes without
making them unduly large and land consumptive.
Aquatic processing units (APU) 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
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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 pclyculture 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
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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 aguatic 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
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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 sOiiie 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 ever a minimum period of
two years.
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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.
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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
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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.
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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.
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Selection of specific species of aquatic plants 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, additional 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 aquaculture
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.
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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 forms 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.
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DETAILS AND PERFORMANCE OF COMBINED AQUACULTURE SYSTEMS
The common type aguaculture 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 guality 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 guality.
Water hyacinths in the first pond grew to large size
amidst a thriving fish population. Unusually high removals
of phosphorus were attained which were attributed to uptake
by mosguito 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,
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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 Suspended
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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.
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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
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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 Henderson 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.
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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 units 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 nodules. In
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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.
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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
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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
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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 Considerations
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-
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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.
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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: 1981-677-094/1130 Region No. 8
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