United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-145 Oct. 1984
&ER& Project Summary
Technology Assessment of
Aquaculture Systems for
Municipal Wastewater
Treatment
Henry C. Hyde, Roanne S. Ross, and Leslie Sturmer
An assessment was made of the
technical and economic feasibility of
using aquaculture systems for munici-
pal wastewater. Aquaculture involves
the production of aquatic flora and
fauna under controlled conditions,
primarily for the generation of feed,
fiber, and fertilizer. A variety of organ-
isms are used. Aquatic macrophytes
(water-tolerant vascular plants), f inf ish,
invertebrates, and integrated systems
are the major components considered
in this assessment.
Current research and development
efforts are concentrated on aquatic
plant systems, particularly water
hyacinths, which are routinely used in
municipal wastewater treatment.
Current constraints to the use of water
hyacinths are large land requirements
and the need for warm temperatures to
maintain the growth of these tropical
plants. Average annual cost and energy
requirements for aquaculture systems
are competitive with conventional
treatment systems at the capacities
assessed (up to 10 mgd). Fish,
invertebrates, and integrated systems
are in the exploratory or development
stage and as such are not ready for
routine use.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project that is fully document-
ed in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
Aquatic biological systems are used in
a variety of wastewater treatment pro-
cesses such as activated sludge, trickling
filters, and lagoons. Wastewater aqua-
culture is broad in scope involving a
variety of organisms, both freshwater and
marine environments, and wastewater
recycling through natural aquatic
habitats. Aquatic macrophytes (water-
tolerant vascular plants), finfish,
invertebrates, and integrated systems are
the components considered in the
assessment.
Wastewater aquaculture systems are
not a new concept. In many parts of the
world, fertilization of ponds with human
and animal wastes to increase growth
and production offish has been practiced
for centuries. Recently, increased atten-
tion has been given to improving water
quality and waste treatment system
capacity through the use of designed
aquaculture systems. For example, the
City of San Diego, California, recently
developed a large-scale water hyacinth
aquaculture system
Aquaculture systems are being used
for secondary, advanced secondary, and
advanced wastewater treatment. Many
current systems use aquaculture
components for removing specific
pollutants such as biochemical oxygen
demand (BOD), suspended solids (SS),
nutrients, or metals. Some are designed
only as a polishing step after
conventional forms of treatment The
fundamental purpose of aquatic plants
and animals is to improve the rate and/or
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reliability of one or more of the
contaminant removal mechanisms in the
wastewater treatment system.
Aquaculture wastewater treatment
systems consist of one or more shallow
basins, ponds, or raceways in which one
or several species of aquatic organisms
are cultured. The basins and the systems
are generally similar in concept to those
employed in wastewater treatment pond
technology. Frequently, aquatic plants or
fish are stocked in the final cells of
existing wastewater stabilization ponds.
The major physical difference between
aquaculture systems and stabilization
ponds is that the former contain, higher
aquatic plants or animals or both in
addition to suspended planktonic species
such as algae.
Aquatic plants, particularly water hya-
cinths, are used to treat raw wastewater
(screened and degritted) and effluents
from various stages of conventional
treatment units. The most common
system incorporates a stabilization pond
followed by aquatic plant culturing basins
in series. Animal-based aquaculture
wastewater treatment systems have
been applied to secondary effluent or to
its equivalent to produce the effluent
quality of advanced treatment levels. A
schematic process-flow diagram of aqua-
culture wastewater treatment of systems
is illustrated in Figure 1.
All aquatic macrophytes have
wastewater treatment potential. The
greatest emphasis has been placed on
the use of water hyacinths and, to a lesser
extent, duckweeds. Most of the
information now available on the
performance of aquatic plants in
wastewater treatment is based on these
two species.
Water hyacinths have been extensively
studied at the laboratory level and tested
on a pilot scale. These efforts have
produced several full-scale demonstra-
tion systems. The research completed on
invertebrate, fish, and integrated systems
is limited and only includes bench- and
pilot-scale studies. Fish, invertebrate,
and integrated systems are all still in the
exploratory or developmental stages and
are not ready for routine use. Systems
involving higher forms of animals are
generally efficient, but they are more
difficult to control than their aquatic plant
counterparts. Nevertheless, animal-
based systems may be applicable where
the use of an aquatic plant is limited
because of climatic or other constraints.
Under most conditions, the cost of an
aquaculture system is less than or equal
to the cost of a conventional system. The
Improving Water Quality
Primary
Treatment
Secondary
Treatment
Advanced Treatment
Wastewater Influent
Effluent Variations:
Post-Treatment
Discharge
Reuse
Figure 1. Process flow diagrams—aquaculture systems for wastewater treatment.
requirement for an aquaculture system
may be as little as 10 to 20 percent of that
for the conventional system.
Aquaculture systems are usually
limited to suburban and rural
communities because of the large land
requirements. Theoretically, an
aquaculture system can be designed for
any capacity; but because the system is
land-intensive, the cost and availability of
land are limiting factors in congested
urban settings.
Because water hyacinths are sensitive
to low temperatures, cold weather is the
major limitation to the universal use of
this tropical plant for wastewater treat-
ment. Year-round hyacinth production in
open basins is possible only in the semi-
tropical and warm climates of the United
States. Water hyacinth systems may be
technically feasible in northern climates
if they are operated in a protected
environment such as a greenhouse, or if
they are run on a seasonal basis (see
Figure 2). Such operations have yet to be
shown cost-effective for climatic zones
where the plant cannot exist naturally.
Duckweeds are more cold-tolerant and
theoretically offer a greater geographical
range and longer operational season than
water hyacinths. Wastewater treatment
experience with these plants is limited,
however. Many other cold-tolerant
aquatic plants exist, buttheirpotentialfor
wastewater treatment has not yet been,
evaluated.
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Areas with favorable
climatic conditions
for water hyacinth
growth 6 months a
Figure 2. Approximate climatic boundary for water hyacinths.
Technology Assessment
Procedure
An extensive literature review was
conducted and summarized for principal
types of aquaculture systems (aquatic
macrophytes, invertebrates, fish, and
integrated systems). The purpose was to
determine design objectives, design
criteria, performance characteristics, and
cost of aquaculture systems. A compari-
son of performance, cost, and energy
requirements with conventional systems
was completed to determine the viability
of aquaculture systems for municipal
wastewater treatment application.
Treatment Mechanisms
Wastewater treatment in an
aquaculture system is a function of the
physical conditions, the biological habitat
provided by the plants, and the removal of
soluble substances from the water by
plant growth. When aquatic plants (par-
ticularly water hyacinths) assume a
primary role in a wastewater pond, the
operation of the system is significantly
altered. The algae community is replaced
by rapidly growing macrophytes that
convert dissolved organics and nutrients
into a standing biomass that is not rapidly
recycled. The hyacinth plant biomass,
which remains with the system, is not
present in the effluent.
The culture of aquatic plants in a
shallow basin filled with wastewater
results in a unique ecosystem. The
canopy formed by the growth of the plant
leaves shades the water surface and
minimizes mixing of basin waters by wind
action. The shading also moderates water
temperature fluctuations. The pH level in
waters beneath a hyacinth mat remains
neutral. Surface basin waters contain
low levels of dissolved oxygen, and
bottom waters and sediment are
anaerobic.
The extensive, fibrous root system of
floating macrophytes extending down
into the wastewater provides surface
area and a suitable substrate for a very
active mass of organisms that assist in
the treatment. Bacteria, fungi, predators,
filter feeders, and detritovores have been
reported to be living in large numbers on
and among the plant roots. The biological
reduction, oxidation, and consumption
processes performed by this complex
community in a plant culture basin
stabilize the water by releasing stored
potential energy.
Removal of suspended solids in plant-
covered ponds is accomplished by the
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natural processes of filtration and
sedimentation, which is enhanced in the
still waters. Filtration is accomplished by
the root systems of the plants, which
physically entraps suspended solids and
which are mechanically removed from
the wastewater during harvesting.
Horizontal movement of suspended
solids in a basin is inhibited by the plant
roots.
The formation of the sludge-like
biomass on plant root systems also aids in
BOD removal. Soluble BOD is removed by
the process of adsorption and incorpora-
tion into bacterial cell mass, and
nitrogenous BOD is specifically removed
by the plant's use of nutrients. The" re-
moval rate depends on root absorption
and plant metabolic functions in
combination with natural biochemical
and physical treatment mechanisms.
During the active growth phase, plants
can absorb soluble organics, heavy
metals, pesticides, and other contami-
nants. Nitrogen, phosphorus, potassium,
sulfur, calcium, and other minerals are
incorporated into the plant tissues and
can be removed from the wastewaters to
some desirable degree by harvesting the
plant biomass. Removal of nutrients such
as nitrogen and phosphorous depends on
plant growth and harvesting rates
The primary treatment mechanism
operating in animal-based aquaculture
systems is the control of suspended
solids. By stocking and culturing fish
and/or invertebrates in wastewater
treatment ponds, simple organics, algae,
and suspended particulates are
converted into animal flesh. The control
of suspended solids may be accomplished
by several methods. Aquatic animals
such as phytophagous fish or bivalves
cultured in wastewater can directly filter
phytoplankton out of the water. The
addition of zooplanktivorous fish to
wastewater systems can reduce the
zooplankton. Polyculture systems use
fish that feed on different segments of the
plant and animal community in a
wastewater pond. A controlled
ecosystem can be developed to culture
organisms that progressively feed on
higher trophic levels.
Performance
Water hyacinth systems can remove
significant amounts of BOD, SS, heavy
metals, nitrogen, and trace organics.
Hyacinth culture may be used as a
complete treatment process. Aquatic
plant systems using duckweed show the
potential for achieving the same high
pollutant removal efficiencies.
The addition of aquatic plants to a
wastewater pond can promote treatment
stability, since these systems are more
tolerant of peak organic loadings, diurnal
organic variations, and hydraulic fluctua-
tion.
The review of pilot- and full-scale
projects indicates that well designed and
operated systems can achieve 50- to 90-
percent removals of BOD, SS, and
nitrogen. Data regarding the removal of
soluble organics, heavy metals,
pesticides, and other contaminants are
not as extensive.
Several existing hyacinth systems
consistently meet secondary, advanced
secondary, and tertiary effluent require-
ments.
Design Considerations
Design considerations for aquaculture
treatment systems are more complex
than those for conventional systems, as
more variables are involved and many are
beyond direct control. To design an
aquaculture system requires an
understanding of its physical character-
istics, engineering criteria, and treatment
capabilities as a function of system
constraints. Aquatic organisms selected
for culturing in the treatment systems
must be able to remove contaminants and
survive variable climatic and wastewater
conditions. The design of the aquaculture
treatment system should be formulated
to provide the environment necessary for
the selected aquatic species to function
as intended. A successful design requires
the teamwork of engineers and aquatic
biologists and a clear understanding of
the design objectives (e.g., removal of
solids rather than nutrients).
Adequate data exist to design water
hyacinth treatment systems, especially
for small-capacity systems in moderate
climates. Reliable design criteria appear
to be available to justify the design of
such systems for treating primary
effluent, for upgrading existing
systems, for advanced secondary
treatment, and for full advanced waste-
water treatment. Full-scale systems that
are currently in operation and new
systems being constructed will generate
additional data.
Sufficient information is available to
install fish culture units but not enough
data are available to permit routine
design of such units for wastewater
treatment. Such designs would require
further definition of species-specific
removal rates and growth rates under
different environmental and wastewater
conditions. Most of the other aquaculture
systems reviewed have not been m
developed or studied sufficiently and are ^
in the development stage. Thus it is too
early to formulate general applicable
criteria for designing a reliable system.
Firm design criteria may not be practical,
since some of the variables that affect
system design are greatly influenced by
site-specific conditions. The use of
general guidelines coupled with pilot
studies at specific sites is the best
approach to system design.
The criteria generally considered in the
design of wastewater stabilization ponds,
particularly physical factors, can be
applied to the design of aquaculture
treatment systems. These criteria are
discussed in several commonly used
design manuals. Most conventional pond
systems can be converted with little or no
modification to aquaculture systems that
can upgrade effluent quality to the level of
secondary or advanced secondary
treatment. Water hyacinth wastewater
treatment technology is based on the
same design procedure as those tor sta-
bilization ponds.
Operational Considerations
Aquaculture treatment systems
function under a number of variables,
many of which are beyond the control of
the operator. Thus operation and main-
tenance requirements are minimal for
these systems. Only a few control
variables are required to adjust treatment
efficiency. The process variables that can
be controlled allow a properly designed
system to be operated at maximum
efficiency. Managerial practices are the
key to successful aquaculture treatment
systems. Such practices include pretreat-
ment of the wastewater, aeration, con-
trolled recirculation, control of residence
times, and biomass harvesting.
Control of water hyacinth treatment
systems is primarily accomplished by
plant harvesting, basin cleaning, and, to a
lesser extent, control of environmental
conditions and influent characteristics.
Hyacinth disposal is also an important
factor in operation and maintenance.
Odors, insects, and other nuisance condi-
tions may develop and need to be
controlled.
The frequency of plant harvesting
depends on the required effluent quality,
plant condition, and climatic factors.
Generally, more frequent harvests will be
required during the warmer months of
the year. In colder regions where only
seasonal operation is possible without
adequate protection, all hyacinths should
be removed from the culture basins'
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. during the freezing period to prevent
them from dying and settling to the
pond bottom. During periods of
accelerated plant growth, harvesting
should be performed at least once every 2
weeks. Hyacinths that exhibit a slower
growth rate, leaf yellowing, or other
unhealthy characteristics should be
removed from the culture basins during
harvesting. Systems designed for
secondary treatment can be harvested
less frequently, but they may need to be
harvested at least once a month during
the hot, rapid-growth periods of the
summer season.
A wastewater management system is
complete only with proper disposal or use
of residual byproducts Harvested water
hyacinths may need to be processed to
reduce the moisture content and bulk of
the plants and thereby simplify disposal
or reuse Several alternative disposal
methods exist for properly processed
hyacinths.
Energy is required for pumping,
harvesting equipment, and disposal of
harvested material. The energy
requirements of the system are minimal,
however, if pumping is not required.
Major operational constraints involve
climate, control of nuisance conditions
and the vectors (e.g , mosquitos), and
legal constraints. The introduction of
water hyacinths or other exotic plants to
area where none currently grow may be
influenced by federal and state laws in
many situations. Public Law 874, the
Grass and Plants Interstate Shipment
Act, Amendment to Chapter 3, Title 18, of
the United States Code prohibits the
interstate transport or sale of water
hyacinths. The inadvertent release of
these plants from a system to local
waterways is a potential concern to many
state and federal agencies Containment
of the hyacinth plants within the system
is a major operational consideration.
Conclusions
Aquaculture systems are generally
limited to suburban and rural communi-
ties because of the land requirements.
Theoretically, an aquaculture system can
be designed for any capacity, but because
the system is land-intensive, the cost and
availability of land are limiting factors for
application in a congested urban setting.
An aquaculture system may also be
installed for seasonal use such as
nutrient removal during the spring and
summer months. Another option is to
cover aquaculture systems to provide a
controlled, year-round environment The
additional cost of a greenhouse or other
protective structure is generally not cost-
effective, however.
Aquaculture systems have been
designed to treat raw sewage, but to
reduce significant operating problems,
primary effluent is the lowest quality of
influent that should be used.
The average annual cost and energy
requirements of aquaculture systems are
competitive with conventional treatment
systems at the capacities evaluated (up to
10 mgd). Site specific comparisons are
nonetheless recommended because of
the many variables involved in the design
of such systems.
The use and reliability of aquaculture
processes in wastewater treatment
systems should increase as successful
experience is gained in the future. Costs
are expected to become more competitive
with conventional treatment systems as
aquaculture systems become optimum
Recommendations
The following recommendations re-
garding the use of aquaculture systems
for municipal wastewater treatment are
based on the foregoing assessment:
1. Construction and design of aquacul-
ture basins. The design of the basins
needs to be improved to increase
treatment efficiency, to minimize
energy requirements, and to
facilitate maintenance.
2 Engineering design criteria. Research
projects need to be developed for
improved design criteria (surface
and organic loadings).
3. Labor requirements. Limited infor-
mation available on labor require-
ments for operation and mainte-
nance of aquaculture systems.
Operating facilities need to
document actual labor require-
ments to enable other agencies to
estimate labor demands accurately.
4. Costs. Existing documentation of
costs is poor. Accurate documenta-
tion of the construction and opera-
tion and maintenance expenses
needs to be maintained by currently
operating facilities so that future
cost estimates can be developed.
5. Suitability of specific systems to
geographical regions. A guide
should be developed to identify geo-
graphic regions best suited for
various types of aquaculture
systems, plants, and animals.
6. Performance data. Performance
data for BOD, SS, nitrogen, phos-
phorus, and coliforms have been
collected and published for some
full-scale facilities. Additional data
for all full-scale facilities need to be
compiled to provide a better data
base for design. Additional
parameters that should be
monitored are total solids, dissolved
solids, SS, COD, heavy metals,
refractory organics, and pathogens
7. Information transfer. Successful
project information should be
printed in widely read professional
publications to inform wastewater
agencies of aquaculture opportuni-
ties. Guidance documents should be
published by the U.S Environmental
Protection Agency (EPA) for distri-
bution by state and regional regula
tory and funding agencies to waste-
water management agencies Such
documents would be useful for
developing aquaculture technology
State and local water quality en-
forcement agencies are not well
informed regarding the application
of aquaculture technology
8. Research and development needs
Water hyacinths have emerged as
the primary aquaculture mode
because of the historical interest
and development of this technology
by aquatic biologists. Alternative
systems have not received similar
attention and are not therefore at
the same level of development
Research and development are
needed for alternative plant systems
that overcome the constraints of
water hyacinths. Such projects are
needed to spur more widespread
use of aquaculture systems for
wastewater treatment.
The full report was submitted in
fulfillment of Contract No. 68-03-3016 by
WWI Consulting Engineers under the
sponsorship of the U.S Environmental
Protection Agency.
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Henry C. Hyde is currently with Henry Hyde & Associates, Sausalito. CA 94965.;
Roanne S. Ross is with Waste and Water International Consulting Engineers,
Emeryville, CA 94608; and Leslie Sturmer is with Humboldt State University,
Arcata, CA 95521.
Jon H. Bender is the EPA Project Officer (see below/.
The complete report, entitled "Technology Assessment of Aquaculture Systems
for Municipal Wastewater Treatment," (Order No. PB 84-246 347; Cost:
$14.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
U S GOVERNMENT PRINTING OFFICE; 1984 — 559-016/7837
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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