Draft Draft Draft

June 10, 1999

Links to other Aquaculture BMP's


Sub-Advisory Committee Report
George Brooks _ Gila River Indian Community, Natural Resources & University of Arizona
Marc Dahlberg _ Arizona Department of Game and Fish
Kevin Fitzsimmons _ University of Arizona
Jimmy Joy _ Blue River Fish Hatchery
Karl Meyer _ Arizona Department of Environmental Quality
Richard Rosenblatt _ Gila River Fishery
Tom Rothweiler _ Crescent Research Chemicals
Richard Willer _ Arizona Department of Agriculture

Table of Contents


BMP 9.100 ...3
BMP 9.200 ...9
BMP 9.300 ...16
References ...18

List of Figures

1. Use of effluent to water irrigate field crops ...4
2. Hand feeding fish in an irrigation ditch ...5
3. Demand feeders ...5
4. Feeding Tables ...6
5. Rotating drum filter ...7
6. Belt filter ...7
7. Rotating biological filter ...11
8. Sand filter ...12
9. Vertical screen filter ...13
10. Floating bead filters ...14
11. Settling basins ...14
12. Waterfowl in constructed wetlands ...14

Draft Draft Draft

By K. Fitzsimmons

for Department of Environmental Quality

June 2, 1999

Section I:

Nitrogen Management in Arizona Aquaculture

NITROGEN and Its Environmental Concerns

There are concerns about potentials for nitrogen in the form of nitrate (NO3) to impact groundwater. Monitoring results of groundwater quality reported by several government agencies indicates an increasing problem with nitrate levels in Arizona groundwater. Interpretation of recent compilation of water quality data suggested that 10.2% of the 6,864 wells tested in Arizona exceeded the drinking water standard of 10 milligrams per liter (mg/1) of N. This level is equivalent to 45 mg/1 nitrate (NO3).

The spatial distribution of the wells which tested above the 10 mg/1 standard does not appear to indicate any clear association with human activities. Intensive agricultural areas, as well as locations with no agriculture, have shown elevated nitrate concentrations in ground water. Nitrates can come from multiple sources, including leguminous desert plants, atmospheric transfer in rain, mineralized soil organic matter, geologic deposits, septic tanks, sewage treatment plants, concentrated animal operations and agricultural applications of nitrogen fertilizer. Elevated levels of nitrate in some Arizona wells prior to 1960 in predominately non-urban areas suggest that geological sources of nitrate can be locally important. It is probable that current nitrate contamination of groundwater is related to several sources. The identification of specific contributions from individual sources is presently not possible.

The presence of excessive nitrate in drinking water is most serious for bottle fed infants less than six months old. Their immature digestive systems are not able to properly metabolize nitrate. Bacteria in their stomachs convert nitrate to nitrite which then reacts with hemoglobin to form methemoglobin. This methemoglobin molecule, unlike hemoglobin, is unable to carry oxygen. As methemoglobin levels in the blood increase, symptoms of oxygen starvation causes a bluish discoloration of the body, methemoglobinemia is commonly referred to as blue baby disease. This condition if potentially fatal but is also very easily treated if properly diagnosed.

The incidence of methemoglobinemia in Arizona is very difficult to determine. It is not one of the diseases which are routinely reported to public health agencies. To date, no confirmed cases of methemoglobinemia resulting from agricultural contamination have been reported in Arizona, (Norm Peterson, Epidemiologist, Arizona State Department of Health and Dr. Lynn Tausig, Department of Pediatrics, University Medical Center, University of Arizona).

There is additional concern that elevated concentrations of nitrates in drinking water may increase the incidence of stomach cancer in adults. Nitrate can be converted to N-nitrosamines in the digestive system and these compounds have been identified as carcinogens.

Nitrogen in the waste water of an aquaculture facility will be generated primarily from the metabolic wastes of the aquaculture animals. In Arizona, aquaculture facilities principally raise fish, however a few do raise crustaceans which behave in a similar manner metabolically.

Commercial fish food contains protein, carbohydrates, fats, vitamins and minerals. The organic compounds in the food contain carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and a number of minor elements. Fish excrete some wastes in liquid form and some in solid form. Both fractions contain significant levels of nitrogen. These compounds react with dissolved oxygen in the water and reduce the amount of oxygen for fish. It is therefore preferable to remove the wastes as soon as possible. There are several filtration techniques available for owner/operators to remove solid wastes from the water and convert the waste into non-toxic forms.

Diagramitically, the impact to water quality can be represented as follows:

|-->Solids wastes = organic compounds with nitrogen = decompose to carbon dioxide,

| water and nitrate

Feed --> Fish ---|

|-->Liquid wastes = ammonia = bacteria convert to nitrites and then nitrates (requires



|-->CHON + O2 --> CO2 + H2O + NO3

Feed --> Fish ---|

|-->NH3 + O2 --> NO2 + O2 --> NO3

Nitrogen from aquaculture facilities will generally be found in two forms. First are the nitrogen compounds in solids. These would include settleable solids; fecal matter, uneaten food, algae, bacteria and other organic matter. The second form of nitrogen compounds are the dissolved nitrogen; ammonia, nitrites and nitrates. These are the primary metabolic wastes of fish can be a significant pollutant if high levels are present and discharged waters reach surface or groundwaters. The various forms of nitrogen can be determined by simple colorimetric test kits. These kits use a color reaction in a sample treated with a reagent to measure the amount of nitrogen in a sample. These kits are similar to the common pool test kits and are just as easy to use.





The 1986 Arizona Environmental Quality Act (EQA) was enacted to protect both surface and groundwater quality from point and non-point source discharges. In this legislation Aquaculture is recognized as a component of agricultural production as well as a potential source of nitrate contamination to groundwater which requires regulation. The Arizona Department of Environmental Quality has rules which regulate Aquaculture through three general, goal-oriented Best Management Practices (BMP). These BMPs address the importance of selecting the proper harvesting, stockpiling, disposing of animal manure and the proper control and disposing of nitrogen contaminated water and cessation of operations. It is assumed that compliance with these BMPs would minimize the discharge of agriculturally derived nitrates into groundwater supplies without being unduly restrictive for farm operations.

BMP's must be implemented if the producer is to be in compliance with the General Permit which regulates discharge of nitrogen from aquaculture facilities. The Guidance Practices (GP's) listed below are intended to provide owner/operators with guidelines on how to best implement the required Best Management Practices. These GP's are the actual methods which an owner/operator uses to achieve the BMP goals. The GP's represent the state-of-the-art technologies available to the owner/operator. The actual GP's chosen by different owner/operators may vary since they depend on such factors as soil type, available farm equipment, water quality impacts, land ownership, facility siting, and related economic criteria.

Aquaculture operations are considered to be Concentrated Animal Feeding Operations (CAFO's) by the U.S. and Arizona State governments (Clean Water Act, Section 318, 122.24, and 122.25 and A.R.S. Title 49 Chapter 2, respectively). As such, the discharges of CAFO's are regulated to minimize environmental effects. The contaminants of most concern to the environment are the nitrogen compounds discharged by CAFO's. The State of Arizona has developed a method of providing industry-wide regulation through the use of Agricultural General Permits. The General Permit allows each farm to operate and discharge, without obtaining an individual permit, so long as the operation implements Best Management Practices (BMP's). BMP's are defined as "those methods, measures or practices to prevent or reduce discharges and include structural and non-structural controls and operations and maintenance procedures. BMP's may be applied before, during and after discharges to reduce or eliminate the introduction of pollutants into receiving waters. Economic, institutional and technical factors shall be considered in developing Best Management Practices" (ARS 49-201).

The BMP's for CAFO's are listed below. Along with each BMP is a selection of Guidance Practices (GPs). These GPs have been developed just for aquaculture. GPs are specific techniques which can be implemented to reduce the nitrogen content of wastewaters discharged by an aquaculture facility. GPs are not meant to be exclusive of other techniques which may be effective, but are presented as options which a producer may utilize to demonstrate that BMP's are in fact being implemented.

Nitrogen from aquaculture facilities will generally be found in two forms. First are the nitrogen compounds in solids. These would include settleable solids; fecal matter, uneaten food, algae, bacteria and other organic matter. These forms of nitrogen are usually measured in a Kjeldahl test. This test is somewhat complicated and is typically conducted in a certified chemistry lab. The second form of nitrogen compounds are the dissolved nitrogen; ammonia, nitrites and nitrates. These are the primary metabolic wastes of fish which can be a significant pollutant if high levels are present and discharged waters reach surface or groundwaters. Various forms of dissolved nitrogen can be determined by simple colorimetric test kits. Colorimetric kits use a color reaction in a sample treated with a reagent to measure the amount of nitrogen in a sample. These kits are similar to the common pool test kits and are just as easy to use.

The owner/operator is encouraged to contact the Aquaculture Extension Specialist at the University of Arizona College of Agriculture, USDA-Natural Resource Conservation Service field office, an agricultural consultant, an irrigation engineer or the Arizona Department of Environmental Quality for assistance in implementing these BMPs and GPs.


BMP 9.100 Harvest, stockpile and dispose of animal manure from concentrated animal feeding operations to minimize discharge of nitrogen pollutants by leaching and runoff.

The fecal wastes of aquatic animals are similar to other animal manures. The wastes are primarily composed of digested and partially digested feed, bacteria from the gut of the animal and other materials that the animal has ingested. The feces have a high biological oxygen demand and also contain many nitrogen containing organic compounds. It is these nitrogen containing compounds that contribute to nitrogen pollution. A fish farm will generate significant amounts of solid wastes and if the feces are allowed to break up and become dissolved in the water, it is increasingly difficult to remove them. From a farm management aspect rapid removal of solid wastes benefit the farmer for several reasons; 1) the solid wastes have a high oxygen demand, 2) the solids will quickly break apart and contribute suspended solids which degrade water quality, 3) some parasites and pathogens can be transmitted to other fish from feces, 4) by rapidly removing the solids before the water is degraded it can be reused to grow more fish. Because nitrogen compounds, especially ammonia, nitrites and nitrates, are so easily dissolved in water, nitrogen pollution from fish farms is a special problem. If the nitrogen containing water can be used to irrigate field crops the problem can be avoided Otherwise the water enriched with nitrogen becomes a potential health hazard if it joins a surface water supply or percolates into the groundwater and causing nitrogen pollution there.

GP 9.101 Collect, stockpile and dispose of solid wastes.

Dispose, collect, or utilize aquaculture wastes for fertilizer, feed or composting. Waste water, settleable solids, dead fish and leftover feed can be utilized in compost systems or as soil conditioners. Proper care should be used to apply these materials in reasonable amounts to soil or compost. Leftover feed can be fed to a variety of other animals. Spoiled feed should not be fed to animals but can be used as soil conditioner or compost.

GP. 9.102 Apply animal waste to croplands.

Nitrogen containing solids which are collected in settling systems and filters in an aquaculture facility can be applied as fertilizers to croplands. This will provide nitrogen for crops and add organic content to the soil. However, the nitrogen containing wastes must be factored into the total nutrient plan that meets the requirements of the agronomic crop. Solids should be removed from the aquaculture system as soon as possible to maintain water quality.

GP 9.103 Convey aquaculture facility wastewater to settling basins or lagoons.


One of the most effective methods for reducing nitrogen level in aquaculture effluents is to remove solid wastes as soon as possible from the waste stream. Solids that are left in the water will dissolve and release nitrogen as dissolved compounds rather than remaining in a solid phase. Solids are much easier to remove and treat. There are a number of physical filtration methods available to remove settled and suspended solids. Simple settling in a basin or off-line settling pond is effective and is commonly used in the trout industry in North America. More sophisticated methods include rotating drum filters, belt filters, hydrocyclones, vertical screen filters, fluidized or static beds of sand, plastic media or gravel. All of these methods are effective and the feasibility for any given application will be dependent on wastes loads, water flow, availability of electricity, and capital costs.

Conveyance of waste waters and solids to an enclosed pond or similar basin, will allow solids to settle and natural processes to convert nitrogen to biomass (algae or aquatic plants). Solids that accumulate in the evaporation ponds or settling lagoons can be dried and removed on a periodic basis. Much of the nitrogen will have been removed by aerobic and anaerobic biological processes. The remaining sediments can be land applied to crops or landscaping, or can be sent to a sanitary landfill.

Settling ponds or basins can be effective methods to remove solids and nitrogen compounds from a water stream. However, the nitrogen and solids may need to be removed occasionally by removing the bottom mud (by dredging, vacuuming, or by drying and carting away the mud). These solids make excellent fertilizers and are used extensively in the trout and catfish rearing areas. Proper size, shape and retention time in the settling basin are critical to achieve the necessary reduction.

Settling ponds need to be sized according to the size and weight of particles being settled and the movement of water through the pond or basin. Shape, size and weight determine the settling velocity of a particle. This is the speed at which a particle will drop in water. Settling velocity is calculated as feet per second (ft/sec) or cm per second (cm/s) and particles will include fish feces, uneaten food, algae and bacterial colonies decomposing organic matter. Feces for trout and uneaten feed are relatively heavy and have a settling velocity of 0.066 to 0.164 ft/sec. Feces of catfish are lighter with a settling velocity of 0.01 to 0.09 ft/sec. Tilapia feces, bacterial mass and dead algae cells are lighter still with settling velocities of 0.001 to 0.01 ft/sec. To achieve proper settling at most farms, the 0.001 ft/sec figure is recommended.

The size or surface area of a settling pond that would be required to properly capture solid particles can be determined by comparing the overflow rate of the pond to the settling velocity. The overflow rate is calculated as the cubic feet per second of flow per square foot of settling area (ft3/s/ ft2). Note that in doing this math, when you divide the volume going into the pond by the area of the pond, you end up with the velocity of the water in feet per second. If the overflow rate (velocity of water in the pond) is less than the settling velocity of the particles, most of the particles will settle out.

The next important step is to determine the depth of the basin needed. The time the particle will take to sink to the bottom must be determined. Obviously the time required for the particle to fall must be greater that the time the water will be retained in the basin or the retention time. Retention time is not directly related to the settling velocity, but is important for determining the volume of solids that can be retained in the pond or basin. The retention time is determined as cubic feet of volume divided by the flow rate in cubic feet. This is also the time required to fill the basin with water or make a complete exchange. As solids accumulate in the bottom, the retention time will decrease because the effective volume is being reduced. When the depth of water is equal to the time required for particles to settle, the pond must be drained as no more settling occur.



    1. Settling rate for fish wastes 0.001 ft/sec
    2. Discharge rate from production 4 cubic feet per second
    3. 4 cfs / 0.001 ft/sec = 4,000 ft2 recommended pond area.
    4. 0.001 ft/sec = 1,000 seconds to settle one foot
    5. 1,000 seconds or 16.6 minutes per foot of pond depth.
    6. At 4 cfs, any depth in a 4,000 ft2 pond beyond one foot should accumulate solids
    7. If the effective depth is reduced to less than one foot, or if the retention time is less than 16.6 minutes, the waste should be removed.


FIGURE 8. Graphic of settling basin


If a settling pond fills with aquatic plants fixing the nitrogen, it may be necessary to remove some of the plants on a regular basis. However, care must be taken to avoid removal of too many plants. Aquatic plants will reduce available nutrients and support bacteria and other organisms that are very important for nitrogen transformation and removal. It is typical in the industry to have two settling basins so that one basin can be taken out of operation for maintenance or solids removal while the other basin remains on-line and functional.

GP 9.104 Convey aquaculture waters to filter strips.

Grass strips and plantings of aquatic plants can treat quantities of water containing high levels of nitrogen. The plants can significantly lower levels of nitrogen and solids. The goal should be to apply water just to the consumptive rate of the plants in the filter strip. Suggested application rates have been published for various crop plants around the state (Blaney - Criddle Models). The water and nitrogen will be used by the plants, leaving no water as runoff.

GP 9.104b. Convey aquaculture waters to constructed wetlands.


Reuse of aquaculture waters for recreational purposes, watering of livestock, for filtering strips of vegetation, waterfowl habitat, constructed wetlands, landscape irrigation, for evaporative cooling systems or washing of equipment are practices that recycle water and provide a beneficial use and will reduce the volume of discharge and the release of nitrogen. Constructed wetlands are an especially useful method of reducing nitrogen in effluent waters. The AZDEQ publishes a complete guide to the construction and operation of constructed wetlands for the disposal of wastes from CAFO’s. This publication, "Constructed Wetlands in Arizonafor Agricultural Wastewater Treatment " is available from AZDEQ. Constructed wetlands provide several benefits. The volume of effluent water is greatly reduced, the nitrogen in the water is converted to plant biomass and the habitat created is available to wildlife.

GP 9.105 Convey aquaculture waters to agricultural crop lands.

Disposal of wastes on crops lands is advantageous because both the water and the nitrogen are put to a beneficial use. Several states recognize utilization of aquaculture wastewaters for land application and irrigation as the preferred method of disposal. Good irrigation practices should be used when irrigating with aquaculture wastewaters. Doerge’s (1991) guide "Nitrogen fertilizer management in Arizona" is an excellent resource for determining the nitrogen demands for various crops in Arizona. More importantly, it helps with determining how best to apply fertilizers, especially nitrogen.

The amount of nitrogen from the aquaculture facility must be balanced with the other nitrogen inputs to ensure that the plants ability to use the total nitrogen supplied is not exceeded. It is when nitrogen, in all its forms, is applied in excess that the unused nitrogen will migrate with the water into the ground or into surface waters. The amount of water that can be disposed is a function of the consumptive use of the particular crop that is being grown. Several sources can be used to estimate the crop area that would be needed to use up a given amount of aquaculture water or conversely the amount of water needed to grow a given area of a particular crop. Blaney-Criddle models can be found in a textbook "Consumptive use of Water and Irrigation Water Requirements". An easier method is to use the AZMET system developed by the University of Arizona. The AZMET system uses many weather stations located around the state and calculates the amount of water that should be used for irrigating individual crops. The system is available on a Website free of charge.

FIGURE 1. Use of waste water to irrigate field crops.


GP 9.106 Convey aquaculture waters to ground water recharge system.

Arizona allows discharge of water to support a permitted recharge operation. This activity must be coordinated with the Department of Water Resources and the Department of Environmental Quality. Recharge conveys water back into the aquifer and takes advantage of natural processes to clean the water. However, an Aquifer Protection Permit must be secured from the AZDEQ before recharging is allowed. The water must be able to meet drinking water standards before recharging and records verifying that the water meets the requirements must be maintained.

GP. 9.107 Monitor and adjust feed and feeding activities for nitrogen.

A. Feeding fish in excess of what they can consume in a short period of time is inefficient and contributes to excess nitrogen in the wastewaters. Monitoring the delivery and consumption of feed are important factors in reducing nitrogenous wastes in the discharge waters. Adjustment of feeding to provide the proper amount of feed that the fish will consume in a short time is important.

Most successful aquaculture operations follow a procedure of initially feeding their fish by hand and having workers closely monitor their consumption. As the experience of the workers increases and a record of feed consumption is documented, mechanical or demand feeders may be added to reduce labor costs. A problem with these devices is that they require regular management to prevent over or under feeding the fish.


FIGURE 2. Hand feeding fish in an irrigation ditch with water going to irrigate cotton or agronomic crops.


FIGURE 3. Demand feeders used to control feeding rate.


One tool which producers can use to properly calculate daily feeding amount is a feeding table. Feeding tables have been developed for several aquatic species at various sizes and water temperatures. These tables provide an estimate for an owner/operator to weigh-out an appropriate amount of feed each day. The table takes into account the growth rate of the fish and adjusts the rate appropriately. The owner/operator uses the table as a guideline and then adjusts the predicted amount up or down slightly to reflect recent feeding behavior. Rapid and vigorous consumption could lead the owner/operator to increase feed above the predicted amount. Slow incomplete consumption could lead a owner/operator to decrease feed below the predicted amount. Examples of feeding charts for estimating feeding frequency and amounts are found in Tables 1 and 2.


Table 1. Recommended stocking and feeding rates for different size

groups of tilapia in tanks and estimated growth rates.

Stocking Rate


Weight (grams)


Weight (grams)


Growth Rate


Growth Period


Feeding Rate (%)
8,000 0.02 0.5-1 - 30 20-15
3,200 0.5-1 5 - 30 15-10
1,600 5 20 0.5 30 10-7
1,000 20 50 1.0 30 7-4
500 50 100 1.5 30 4-3.5
200 100 250 2.5 50 3.5-1.5
100 250 450 3.0 70 1.5-1.0

Table 2. Suggested maximum feeding rates and frequencies for channel catfish.


Water Temperature


Feeding Frequency

(times per day)

Feeding Rates

(% of total fish weight)

>90 1 1
80-86 2 3
68-80 1 2.5
58-68 1 1.5
50-58 0.5a 0.75-1
<50 0.3b 0.5-1

aFeed once on alternate days.

bFeed once every 3 to 4 days.


B. Fish will go off feed for a number of reasons including weather changes, algae blooms, recent handling, or change in feed manufacture or formulation. In these cases the owner/operators should reduce feeding for a short period until the fish are feeding vigorously again. Fish can exhibit compensatory growth; that is the ability to "catch up" in growth after a short period of reduced feed. If fish are lightly fed for a few days, their growth may slow. However, after a few days of heavy feeding they will catch up and attain weights equal to those fish fed at constant rates. Therefore, an owner/operator need not worry that fish are not fed to a target level as suggested by a table.

C. Excess nitrogen in facility water can also result from protein levels in feed which exceed the amount required for normal growth. Using a lower protein level feed can lower level of nitrogen in wastewater and save on feed costs. Low nitrogen waste feeds have been developed by the industry and may be cost effective. The protein level in any type of feed can be determined by examining the guaranteed analysis label on a bag. A feed designed specifically for a particular species is most likely to have a level and mix of proteins and will provide the most cost effective conversion of feed to body weight.

There are many aquaculture feeds on the market and owner/operators should compare the costs and benefits of specific feeds before purchase. Low quality feeds may not provide sufficient nutrition due to poor formulation, inferior ingredients or poor manufacturing practices. Poor manufacturing of feed, or poor handling after manufacturing, can lead to a high amount of fines and small particles of feed which will not be consumed by the fish. This is a waste of food, a cause of water fouling, and a factor in nitrogen loading of facility water.

Conversely, a diet that is high in protein does not necessarily mean that it will result in faster growth. Different species of fish require different protein levels and individual fish need different protein levels at various life stages.

D. Physical quality of the feed is also important. Pellets that are broken or contain lots of fines, feed particles not in the pellets, contribute to solid wastes in the water. These particles are not consumed by the fish and contribute to increased nitrogen in the water, reduced water quality in the culture units and represent money spent on food that is not eaten. Many owner/operators may screen their feed for fines and use the material collected to feed juvenile fish.

E. Floating feeds are available that enable the owner/operator to more closely monitor the amount of feed consumed by the fish. With sinking feed there may be a tendency to overfeed which would result in increased costs and nitrogen loading.

BMP 9.200 Control and dispose of nitrogen contaminated water resulting from activities associated with a concentrated animal feeding operation, up to a twenty-five year, twenty-four hour storm event equivalent, to minimize the discharge of nitrogen pollutants.

Many aquaculture facilities are located near watercourses because the groundwater is closer to the surface and because the fields that can be irrigated with the aquaculture water are in these locations. Storm events are critical because large amounts of water can quickly fill normally dry streambeds. The large volumes of water that accumulate in these storm events can overwhelm poorly designed facilities and release stored wastes into the environment. The poultry and hog industries in the Southeastern United States have contributed to nitrogen enrichment in several rivers along the Atlantic coast with serious results. The most damaging of these pollution events took place when rainstorms caused inadequately designed waste storage facilities to flood and release wastes directly into the rivers killing thousands of fish and contributing to other ecological problems. The sudden influx of aquaculture wastes can have the same effect since fish wastes are similar in content to other livestock wastes.

Obviously urinary wastes cannot be collected from fish as they can be from livestock which are maintained in facilities with concrete floors. Most of the urinary wastes from fish are released as ammonia. This ammonia is dissolved in the water and directly contributes to nitrogen pollution. Nitrification can convert this ammonia to nitrate, which is less toxic to fish but is still considered to be a form of nitrogen pollution which must be controlled.

GP 9.201 Collect and convey liquid wastes to a storage facility or treatment basin.

A storage facility or treatment basin should be designed to reduce infiltration and to hold a volume of water sufficient to handle normal discharges and storm events. Conveyance to a holding or treatment facility provides time for settling of solids and reduction of nitrogen content. Liquid wastes containing high levels of ammonia and nitrates that are stored will tend to lose the nitrogen over time. Bacteria will convert ammonia to nitrate and algae will fix the nitrate into biomass. Some will also be adsorbed onto clay and other sediments and settle to the bottom.

GP 9.202 Design and construct appropriate storage or treatment basins.

A wide variety of materials and compounds are available to reduce leakage from ponds. Concrete, plastic and rubber liners, clay, mineral compounds and other materials can be used if excessive amounts of water are lost due to seepage. Seepage should be minimized to conserve water and to reduce the amount of nitrogen carried away from the farm as leachate. Conveyance to a holding or treatment facility provides time for settling of solids and reduction of nitrogen content of the water before later reuse or discharge. The Natural Resource Conservation Service provides local expertise on the placement and construction of ponds on farms. This service is provided to insure safety and protection of resources which may be adversely impacted off the farm. If an NRSC representative is not available, private sector consultants can assist with facility design.

GP 9.203 Divert, collect and convey storm runoff to storage facility.

To minimize the discharge of nitrogen pollutants, the aquaculture operation may collect on-site storm waters for later aquacultural use or divert stormwater to irrigation of crop lands. The goal is to keep waters with low nutrient loads clean and to manage waters which may have a high load of nutrients, sediments or other undesirable characteristics from impacting the higher quality water that still may have several constructive uses. Gutters can be installed on buildings to collect and convey water to a spot where it could be used for aquaculture production. Settling basins can be used to store runoff water. The settling basin can serve a dual purpose of storage and also quality improvement. As the water is stored, the suspended solids will settle to the bottom and the quality may improve enough to be used for the aquatic animal production and/or for field crop irrigation.


GP 9.204 Design and construct appropriate diversion structures.

Earthen dikes or synthetic structural material retaining walls may be utilized by existing or newly designed aquaculture operations to divert or prevent storm waters from entering an aquaculture facility. Should stormwaters enter or become mixed with aquaculture operational waters, the mixed waters will require the owner/operator to manage nitrogen impacts to ground or surface water.

GP 9.205 Establish sufficient gradients in open lots and roofed confinement facilities to promote drainage (to keep clean water from becoming contaminated with operational water).

Utilize natural or engineered topographical or hydrological control measures. Existing terrain or engineered terrain alterations may be utilized when selecting a new, or renovating an existing, operation to prevent storm water run-off from mixing with operational waters. The primary goal is to protect the relatively clean water in the aquaculture operation from the runoff which may be poor quality water. Retention basins are a valuable storage unit for runoff. This provides safety, avoiding flooding, but also allows time for the water to settle, dropping sediments and improving in quality.

GP 9.206 Divert clean runoff from open lots or roofed confinement facilities.

The aquaculture operation may collect on-site storm waters for later aquacultural use. These waters should be monitored to insure that they are clean and have not accumulated nitrogen compounds. If high quality runoff is available, there is no reason that the producer cannot use it for aquaculture operations. Sufficient storage should be available as runoff is likely to accumulate quickly. Excess should be allowed to drain in a safe manner.

GP 9.207 Divert, collect and convey storm runoff to croplands.

The aquaculture operation may collect on-site storm waters for direct diversion to irrigation of crop lands. Runoff from the aquaculture facility is likely to be useful for direct field crop irrigation. This would be an efficient use of the water and any nitrogen entrained in the runoff (dropped feed, dried algae pulled from growing systems, etc.) would be sent to the cropland.

GP 9.208 Test water from wells and surface water adjacent to and on aquaculture operations for nitrogen.

Wells on or near an aquaculture operation should be monitored for nitrogen to check for migration of nitrogen enriched water from the facility to the water supply. Any well supplying the aquaculture facility will have a background level of nitrogen. The owner/operator should be aware of that background level. This may allow the owner/operator to adjust the source supply to use lower nitrogen water if needed. Also, if the background level should suddenly start to rise, this could be a sign of excessive leaching or runoff.

GP 9.209 Monitor input and discharge waters for nitrogen

The owner/operator should have a record of the nitrogen level (ammonia and nitrate) of the supply water and the discharge water. This information will be needed to quantify the efficacy of other nitrogen control practices.

Nitrogen from aquaculture facilities will generally be found in two forms. First are the nitrogen compounds in solids. These would include settleable solids; fecal matter, uneaten food, algae, bacteria and other organic matter. The second form of nitrogen compounds are the dissolved nitrogen; ammonia, nitrites and nitrates. These are the primary metabolic wastes of fish can be a significant pollutant if high levels are present and discharged waters reach surface or groundwaters. The various forms of nitrogen can be determined by simple colorimetric test kits. These kits use a color reaction in a sample treated with a reagent to measure the amount of nitrogen in a sample. These kits are similar to the common pool test kits and are just as easy to use.

GP 9.210 Use low nitrogen make-up water.

If excessive levels of nitrogen need to be reduced from discharge, it may be possible to start with lower nitrogen levels in the source water. Obviously, one way to have less nitrogen in water when you finish, is to start with less nitrogen. Well water, canal water and surface water will all tend to have different levels of nitrogen. Mixing percentages of source water may reduce final level of N in effluent. For example, if well water has 1 mg/l of total nitrogen and canal water has 0.5 mg/l, increasing the amount of canal water and reducing the amount of well water coming into the production unit will cause the overall level of nitrogen in the farm effluent to decrease. Of course the economics and operational considerations would need to be considered, but if all things are equal this may be an effective strategy for controlling nitrogen levels at certain times.

GP 9.211 Seal ponds and lagoons for water loss.

A wide variety of materials and compounds are available to prevent the leakage from ponds. Concrete, plastic and rubber liners, clay, mineral compounds and other materials can be used to minimize nitrogen discharge to groundwater.

GP 9.212 Mechanically treat water sources and discharged water.

Physically removing nitrogen releasing compounds is an effective measure to lessen nitrogen levels in discharged water. Facilities using groundwater should always screen water before it enters the production unit. This will remove unwanted trash, plant parts, and other fish, which are likely to introduce parasites and disease. As a side benefit, many of these items would decompose in the production system and release unwanted nitrogen.

Likewise, one of the most effective methods of reducing nitrogen in discharged water is to remove the solids from the wastes stream as soon as possible. Fecal matter and uneaten food will contribute considerable amounts of nitrogen and if these materials can be removed quickly the leaching and dissolved nitrogen can be avoided.

A variety of commercial filtration and treatment units are available to reduce nitrogen levels in water. Many effective systems can be constructed on the farm from available materials to mechanically and biologically treat water. Various media filters are used to remove solids from the water. Removing solids from the water can be an effective method of removing a significant fraction of nitrogen from the wastewater. The most basic of these filters are sand and gravel filters which trap solids as the water passes through the media. The standard swimming pool filter is an example. Media filters can be operated with the water passing through from the top or the bottom. The filter will usually have some mechanism for backwashing the media. Backwashing flows water or air bubbles through the media in the opposite direction to the normal flow. This dislodges solid waste particles and bacteria growing on the wastes and removes them from the system. The normal flow is then returned and the media again begins to accumulate solids.

Media filters combining mechanical and biological properties are often appropriate for reducing nitrogen. Settling basins and holding ponds are also effective and require minimal maintenance. Material and water that is backwashed or otherwise removed from filters or settling basins should be maintained separately from the waste stream and properly disposed

Rotating drum and belt filters are mechanical devices used to remove solids. The units operate by passing water through a moving screen which traps solids in the water. The screen is then rotated or conveyed out of the water where a small stream of water washes the material into another container where the concentrated material can be disposed. Most often the solids are dried, used in compost, land applied or taken to an appropriate landfill.

FIGURE 5. Graphic of rotating drum filter.

FIGURE 6. Graphic of belt filter.


Sand and gravel beds are also very effective filters. They work in two ways, first by physically trapping solids and second by providing substrate for bacterial action to convert ammonia to nitrate. The sand, which can also be replaced with diatomaceous earth, and gravel can be backflushed to remove the solids which have been concentrated on the surfaces of the beds.


FIGURE 7. Graphic of sand or gravel filter.

Settling basins are also used to concentrate and remove solids which can then be disposed more easily. The effectiveness of a settling basin is dependent upon the water flow through the basis; speed, volume and depth. The shape and flow through the basin can be determined and then the optimal size for various kinds of fish wastes can be predicted. There is a wealth of information regarding settling basins and improving efficiency of operation. Stechey (1988) and his colleagues in Canada have developed excellent guidelines for designing and operating off-line settling basins for the removal of fish wastes from an effluent stream.


FIGURE 8. Graphic of settling basin


GP 9.213 Biologically treat water sources and discharged water.


Biological Filters are primarily used to convert ammonia to nitrates and decomposing solids into smaller compounds. The filters sometimes encourage algae growth in a system, thereby fixing nitrogen compounds into algae which can be eaten by fish or filtered out of the water. A rotating biological filter is an adaptation of a system developed by the wastewater industry. Plastic or fiberglass plates are arranged into plates that are then fixed onto a water wheel apparatus or an external drive mechanism. The filter rotates so that the plates are constantly moving in and out of the water body. The plates provide substrate for the attachment of nitrifying bacteria which convert ammonia to nitrate and heterotrophic bacteria which decompose larger organic materials. By moving out of the water and into the air, the bacteria have adequate access to oxygen required for biological activity.

FIGURE 9. Rotating Biological Filter


A vertical screen filter operates by allowing the water to flow through upright screens which capture solids. The screens can then be lifted out of the frame and rinsed off outside the system. The screen are then replaced and begin to catch solids. While the screen are in place they are also effective by providing substrate for nitrifying bacteria that convert ammonia to nitrate and heterotrophic bacteria that decompose solids.


FIGURE 10. Graphic of vertical screen filter

A new type of filter incorporates the benefits of a biological filter and a media filter. Floating bead bed filters maintain a colony of bacteria to convert ammonia to nitrate, but also capture solids passing through the bed of plastic beads floating in the water column. Since the beads float, a design can be used which can be self cleaning and operate at lower water pressures. Many manufactures now supply bead filters built to accommodate waste streams for almost any size of operation.


FIGURE 11. Graphic of floating bead filter.

Many biological filters work more efficiently if a majority of solids are first removed by mechanical filters. Solids will physically cover substrates and use large amounts of oxygen during decomposition. Settling basins, sand filters or vertical screens are most often paired with a biological filter to prepare water for reuse or discharge.


GP 9.214 Chemically treat water sources and discharged water.

There are also strictly chemical methods of reducing nitrogen compounds in water. These methods are usually prohibitively expensive for normal use but may be appropriate for short term application to handle a single event or reduce a nitrogen spike.

GP 9.215 Whenever practicable, locate aquaculture operations in an area that will have minimum impact from a twenty-five year, twenty-four hour storm event.

Assistance in identifying the potential impact from a twenty-five year, twenty-four hour storm event is available from the offices of the Arizona Flood Plain Administration, the Natural Resources Conservation Service (formerly the Soil Conservation Service), the US Army Corps of Engineers, or County Extension.

GP. 9.216 Recycle aquaculture waters to reduced nitrogen impacts.

Utilization of aquaculture waters for recreational purposes, watering of livestock, for filtering strips of vegetation, waterfowl habitat, constructed wetlands, landscape irrigation, for evaporative cooling systems or washing of equipment are practices that recycle water and provide a beneficial use.



FIGURE 12. Use of waste water for constructed wetlands or wildlife habitat.


GP. 9.217 Use aeration of waters to volatilize ammonia.

A fraction of the nitrogen waste that is in water is ammonia. Some of this ammonia can be evaporated into the air. Aeration or splashing can increase the amount of ammonia which evaporates. Although this may not be economical on its own as a method for nitrogen removal, it may occur as a by-product of regular aeration.


BMP 9.300 Close facilities in a manner to minimize the discharge of nitrogen pollutants

{To close a facility refers to cessation of operations.}


When an aquaculture facility ceases operation, the farm should not leave materials that will become nitrogen pollutants after the operators leave the premise. The sediments, compost, dead animals and unused feed that usually accompany an operation in the process of being closed should be disposed in a proper fashion. Materials that are left stockpiled are likely to release large amounts of nitrogen when the first significant rains fall on the facility and wash materials into the surface or groundwaters. Dead animals and spoiled feed cause noxious odors as well as releasing nitrogen compounds and should be buried or taken to an appropriate landfill. Stockpiled sediments and compost should be land applied to field crops.

GP 9.301 Close facilities in a manner to minimize the discharge of nitrogen pollutants.

Steps should be taken to minimize future discharge of nitrogen pollutants by leaching or runoff. Any dead fish should be buried or taken to an appropriate landfill. Sludge and other solid wastes should be removed from ponds, settling basins, raceways or other facilities and applied to croplands. The Doerge handbook can be used to determine appropriate application rates. Surplus feed and other potential nitrogen producing materials should be taken to a landfill or applied to a field again taking into account the nitrogen application guidelines.

GP 9.302 Dispose of aquatic animals, animal wastes, and water.

At closure, animals and animal wastes may be sold to a processor or renderer, can be buried or land applied. Best Management Practices for nitrogen application of field crops should be observed. Animal wastes and water from the facility can be disposed by land application.


Anon. 1994. Idaho Waste Management Guidelines.

AZDEQ. 1995. Constructed Wetlands in Arizona for Agricultural Wastewater Treatment. TM 95-2.

Cowey, C.B., A.M. Mackie and J.G. Bell 1985. Nutrition and Feeding in Fish. Academic Press. London.

Doerge, T. A., Roth, R.L. and B.R. Gardner 1991. Nitrogen fertilizer management in Arizona. College of Agriculture, University of Arizona, 191025.

Fitzsimmons, K.M., 1992. Extending the value of aquaculture effluents through sustainable agriculture practices, p.344-346. In: National Livestock, Poultry, and Aquaculture Waste Management. Am. Soc. Ag. Eng. Pub. 03-92.

France, R. 1995. Stable nitrogen isotopes in fish: Literature synthesis on the influence of ecotonal coupling. Estuarine, Coastal and Shelf Science 41:737-742.

Hopkins, T.A. and W.E. Manci, 1989. Feed conversion, waste and sustainable aquaculture: the fate of the feed. Aquaculture Magazine 15(2):30-36.

Idaho Department of Environmental Quality 1996. Aquaculture total phosphorus waste load allocations.

Jensen, M.E. 1973. Consumptive use of water and irrigation water requirements. American Society of Civil Engineers. N.Y. , N.Y.

Liao, P.B. 1970. Salmonid hatchery wastewater treatment. Water and Sewage Works 117(12):439-443.

McMurtry, M.R. et al. 1993. Mineral nutrient concentration and uptake by tomato irrigated with recirculating aquaculture water as influenced by quantity of fish waste products supplied. Journal of Plant Nutrition 16(3): 407-419.

Mudrak, V. A. 1981. Guidelines for economical commercial fish hatchery wastewater treatment systems. In: Bio-Engineering Symposium for Fish Culture (L.J. Allen and E.C. Kinney, eds.) Fish Culture Section of the American Fisheries Society, Bethesda, MD

Olsen, M.W., K.M. Fitzsimmons, and D.W. Moore. 1993. Surface irrigation of cotton using aquaculture effluent, pp.159-165. In: Techniques for Modern Aquaculture (J.K. Wang, Ed.) St. Joseph, MI:ASAE Pub. 02-93.

Piedrahita R.H., Zachritz, W.H., Fitzsimmons, K, and Brockway, C. 1996. Evaluation and improvements of solids removal systems for aquaculture. pp. 141-150. In G. S. Libey and M. B. Timmons, editors. Successes and Failures in Commercial Recirculating Aquaculture. Aquacultural Engineering Proceedings II. Northeast Regional Agricultural Engineering Service Publication No. NRAES - 8.

Schaumann, P. 1988. Aquaculture engineering in developing countries. Thesis submitted to University of Arizona.

Skeen, B. , Brown, J.J., Fitzsimmons, K. and Dickenson, G. 1997. Performance characteristics of open and closed bead filters in a closed recirculating tilapia production system. In: Advances in Aquacultural Engineering: Proceedings of the Fourth International Symposium on Tilapia in Aquaculture (Timmons and Losordo, Eds.). NRAES-105, Ithaca, NY.

Stechey, D. 1988. Factors influencing the design of effluent quality control facilities for commercial aquaculture. Aquaculture Association of Canada Bulletin 88(4):208-210.

Stechey, D. and Y. Trudell 1990. Aquaculture wastewater treatment: Wastewater characterization and development of appropriate treatment technologies for the Ontario trout production industry. Ministry of the Environment, Ontario, Canada.

Uotila, J. 1991. Metal contents and spread of fish farming sludge in southwestern Finland. In: Marine Aquaculture and Environment.

Wheaton, F. 1985. Aquacultural Engineering. John Wiley and Sons. NY, NY.

Willet, I.R. and P. Jokobsen 1986. Fertilizing properties of trout farm waste. Agricultural Wastes 17:7-13.

World Wide Web Sites.

A Web Site for Arizona aquaculture

Links to aquaculture information, research, vendors

The proposed EPA/Idaho DEQ aquaculture discharge rules

A site with information regarding aquaculture bead filters

A site with information regarding aquaculture filters

The site for daily weather and water use data for crops in Arizona