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Recirculating Aquaculture Tank Production Systems: Aquaponics—Integrating Fish and Plant Culture

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Recirculating Aquaculture Tank Production Systems: Aquaponics—Integrating Fish and Plant Culture SRAC Publication No. 454 November 2006 VI Revision PR Recirculating Aquaculture Tank Production Systems: Aquaponics—Integrating Fish and Plant Culture James E. Rakocy1, Michael P. Masser2 and Thomas M. Losordo3 Aquaponics, the combined culture of many times, non-toxic nutrients and Aquaponic systems offer several ben- fish and plants in recirculating sys- organic matter accumulate. These efits. Dissolved waste nutrients are tems, has become increasingly popu- metabolic by-products need not be recovered by the plants, reducing dis- lar. Now a news group (aquaponics- wasted if they are channeled into charge to the environment and [email protected] — type sub- secondary crops that have economic extending water use (i.e., by remov- scribe) on the Internet discusses value or in some way benefit the pri- ing dissolved nutrients through plant many aspects of aquaponics on a mary fish production system. uptake, the water exchange rate can daily basis. Since 1997, a quarterly Systems that grow additional crops be reduced). Minimizing water periodical (Aquaponics Journal) has by utilizing by-products from the pro- exchange reduces the costs of operat- published informative articles, con- duction of the primary species are ing aquaponic systems in arid cli- ference announcements and product referred to as integrated systems. If mates and heated greenhouses where advertisements. At least two large the secondary crops are aquatic or water or heated water is a significant suppliers of aquaculture and/or terrestrial plants grown in conjunc- expense. Having a secondary plant hydroponic equipment have intro- tion with fish, this integrated system crop that receives most of its required duced aquaponic systems to their is referred to as an aquaponic system catalogs. Hundreds of school districts (Fig. 1). are including aquaponics as a learn- Plants grow rapidly with dissolved ing tool in their science curricula. At nutrients that are excreted directly least two short courses on aquapon- by fish or generated from the micro- ics have been introduced, and the bial breakdown of fish wastes. In number of commercial aquaponic closed recirculating systems with operations, though small, is increas- very little daily water exchange (less ing. than 2 percent), dissolved nutrients Aquaponic systems are recirculating accumulate in concentrations similar aquaculture systems that incorporate to those in hydroponic nutrient solu- the production of plants without soil. tions. Dissolved nitrogen, in particu- Recirculating systems are designed lar, can occur at very high levels in to raise large quantities of fish in rel- recirculating systems. Fish excrete atively small volumes of water by waste nitrogen, in the form of ammo- treating the water to remove toxic nia, directly into the water through waste products and then reusing it. their gills. Bacteria convert ammonia In the process of reusing the water to nitrite and then to nitrate (see SRAC Publication No. 451, “Recirculating Aquaculture Tank 1 Agricultural Experiment Station, University of the Production Systems: An Overview of Virgin Islands Critical Considerations”). Ammonia 2 Department of Wildlife and Fisheries Sciences, and nitrite are toxic to fish, but Texas A&M University 3 nitrate is relatively harmless and is Biological and Agricultural Engineering Figure 1. Nutrients from red tilapia Department, North Carolina State University the preferred form of nitrogen for growing higher plants such as fruit- produce a valuable crop of leaf let- ing vegetables. tuce in the UVI aquaponic system. nutrients at no cost improves a sys- tem’s profit potential. The daily application of fish feed provides a steady supply of nutrients to plants and thereby eliminates the need to Rearing Solids Hydroponic Biofilter Sump discharge and replace depleted nutri- tank removal subsystem ent solutions or adjust nutrient solu- tions as in hydroponics. The plants remove nutrients from the culture water and eliminate the need for Combined separate and expensive biofilters. Combined Aquaponic systems require substan- tially less water quality monitoring Figure 2. Optimum arrangement of aquaponic system components (not to than separate hydroponic or recircu- scale). lating aquaculture systems. Savings are also realized by sharing opera- goldfish, Asian sea bass (barramun- tional and infrastructural costs such can be located after the biofilter and as pumps, reservoirs, heaters and water would be pumped up to the di) and Murray cod, most commer- alarm systems. In addition, the troughs and returned by gravity to cial systems are used to raise tilapia. intensive, integrated production of the fish-rearing tank. Most freshwater species, which can fish and plants requires less land The system can be configured so tolerate crowding, will do well in than ponds and gardens. Aquaponic that a portion of the flow is diverted aquaponic systems (including orna- systems do require a large capital to a particular treatment unit. For mental fish). One species reported to investment, moderate energy inputs perform poorly is hybrid striped and skilled management. Niche mar- example, a small side-stream flow may go to a hydroponic component bass. They cannot tolerate high lev- kets may be required for profitabili- els of potassium, which is often sup- ty. after solids are removed, while most of the water passes through a biofil- plemented to promote plant growth. System design ter and returns to the rearing tank. To recover the high capital cost and The biofilter and hydroponic compo- operating expenses of aquaponic sys- The design of aquaponic systems tems and earn a profit, both the fish- closely mirrors that of recirculating nents can be combined by using plant support media such as gravel rearing and the hydroponic veg- systems in general, with the addition etable components must be operated of a hydroponic component and the or sand that also functions as biofil- ter media. Raft hydroponics, which continuously near maximum pro- possible elimination of a separate duction capacity. The maximum bio- biofilter and devices (foam fractiona- consists of floating sheets of poly- styrene and net pots for plant sup- mass of fish a system can support tors) for removing fine and dissolved without restricting fish growth is solids. Fine solids and dissolved port, can also provide sufficient biofiltration if the plant production called the critical standing crop. organic matter generally do not Operating a system near its critical reach levels that require foam frac- area is large enough. Combining biofiltration with hydroponics is a standing crop uses space efficiently, tionation if aquaponic systems have maximizes production and reduces the recommended design ratio. The desirable goal because eliminating the expense of a separate biofilter is variation in the daily feed input to essential elements of an aquaponic the system, an important factor in system are the fish-rearing tank, a one of the main advantages of aquaponics. An alternative design sizing the hydroponic component. settleable and suspended solids There are three stocking methods removal component, a biofilter, a combines solids removal, biofiltra- tion and hydroponics in one unit. that can maintain fish biomass near hydroponic component, and a sump the critical standing crop: sequential (Fig. 2). The hydroponic support media (pea gravel or coarse sand) captures solids rearing, stock splitting and multiple Effluent from the fish-rearing tank is and provides surface area for fixed- rearing units. treated first to reduce organic matter film nitrification, although with this Sequential rearing in the form of settleable and sus- design it is important not to overload pended solids. Next, the culture the unit with suspended solids. Sequential rearing involves the cul- water is treated to remove ammonia As an example, Figures 3 and 4 show ture of several age groups (multiple and nitrate in a biofilter. Then, water cohorts) of fish in the same rearing flows through the hydroponic unit the commercial-scale aquaponic sys- tem that has been developed at the tank. When one age group reaches where some dissolved nutrients are marketable size, it is selectively har- taken up by plants and additional University of the Virgin Islands (UVI). It employs raft hydroponics. vested with nets and a grading sys- ammonia and nitrite are removed by tem, and an equal number of finger- bacteria growing on the sides of the Fish production lings are immediately restocked in tank and the underside of the poly- the same tank. There are three prob- styrene sheets (i.e., fixed-film nitrifi- Tilapia is the fish species most com- lems with this system: 1) the period- cation). Finally, water collects in a monly cultured in aquaponic sys- ic harvests stress the remaining fish reservoir (sump) and is returned to tems. Although some aquaponic sys- and could trigger disease outbreaks; the rearing tank. The location of the tems have used channel catfish, 2) stunted fish avoid capture and sump may vary. If elevated hydro- largemouth bass, crappies, rainbow accumulate in the system, wasting ponic troughs are used, the sump trout, pacu, common carp, koi carp, space and feed; and 3) it is difficult The UVI Aquaponic System ing crop of the initial rearing tank is reached. The fish are either herded Effluent line through a hatch between adjoining Fish rearing tanks Degassing Hydroponic tanks tanks or into “swimways” connect- Base addition ing distant tanks. Multiple rearing units usually come in modules of two to four tanks and are
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