Aquaponics—Sustainable Vegetable and Fish Co-Production
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Natural Resources Section Proc. Fla. State Hort. Soc. 125:381–385. 2012. Aquaponics—Sustainable Vegetable and Fish Co-Production RichaRd V. Tyson*1, Michelle d. danyluk2, eRic h. siMonne3, and danielle d. TReadwell4 1University of Florida, IFAS Extension at Orange County, 6021 S. Conway Road, Orlando, FL 32812 2University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850 3University of Florida, IFAS, Office of the District Extension Directors, 1052 McCarty Hall, Gainesville, FL 32611 4University of Florida, IFAS, Horticultural Sciences Department, PO Box 110690, Gainesville, FL 32611 AdditionAl index words. hydroponics, aquaculture, biofiltration, ammonia, Escherichia coli, nitrifying bacteria Aquaponics combines hydroponic plant and aquaculture fish production into a sustainable agriculture system that uses natural biological cycles (nitrification) to supply nitrogen and reduces the use of non-renewable fertilizer and water inputs. This paper provides a review of existing aquaponic systems with emphasis on opportunities and challenges to systems sustainability. Preliminary data from a startup aquaponic greenhouse research/demonstration project at UF/ IFAS Extension-Orange County’s Exploration Gardens show the potential for growing two vegetable crops concur- rently to facilitate the recirculation and re-use of aquaponic waste water. In addition, microbial water quality testing of the aquaponic system water was conducted across three sampling dates. No Escherichia coli was detected in either re-circulating irrigation or filter-return water samples or from a single sampling of flake and pellet fish feed. The loss of prime agricultural lands and the competition for systems currently in use employ either a media-filled raised bed water to accommodate growing human populations requires the (Lennard and Leonard, 2006; McMurtry et al., 1997; Tyson et al., development of new crops and agricultural systems to meet the 2008), NFT or nutrient-film technique (Adler et al., 2000; Len- demands for food while reducing the environmental impacts of nard and Leonard, 2006; Nelson, 2007), or a floating raft system their production (Fedoroff et al., 2010). The potential for plants (Lennard and Leonard, 2006; Nelson, 2007; Rakocy, 1997) for to use the nutrient by-products of aquaculture, helping to keep the plant growing area integrated with a recirculating aquaculture recirculating water clean, has been well documented (Adler et tank system (Timmons et al., 2002) for the fish production area. al., 1996, 2000; Lin et al., 2002). A review of existing aquaponic systems and research has been Producing plants hydroponically and farming fish using aqua- conducted (Tyson et al., 2011). The most researched system and culture have their own special requirements in order to properly one which is being widely adopted is the “Rakocy” system. Dr. manage each system. When the two systems are connected, it adds Rakocy, Emeritus Professor from the University of the Virgin a layer of complexity for the commercial grower when systems Islands, developed a year-round recirculating tank/floating raft are maintained at plant and fish population levels that produce system for the tropics (Rakocy et al., 1997, 2006). This system maximum yields. Aquaponic systems maintained for education was carefully sized and managed for optimum yields of both fish and demonstration purposes with low species populations are and vegetables. The hydroponic floating raft system has been much easier to manage since changes in water quality occur less adapted for low-tech use in Florida to produce leafy salad crops rapidly compared with those in commercial production systems. and herbs (Sweat et al., 2009; Tyson et al., 1999). Currently there are no UF/IFAS Extension production recom- Aquaculture production recommendations include replacing mendations for farming aquaponically due to a lack of research 5% to10% of the recirculating tank water daily (Timmons et al., on the many, varied crops and production systems possible (type 2002). This practice, along with system biofilters, helps keep tank of fish × type of plant × densities × filtration system × hydroponic water clean. Sizing aquaponic systems so the plant production system × aquaculture system). The most common aquaponic area is large enough to re-use this excess water through plant uptake and evapotranspiration increases system sustainability by reducing waste effluent discharges to the environment while supplying nitrogen and other nutrients to the plants. Danger areas that require special attention by aquaponic The authors would like to thank Angela Valadez and Lorrie Friedrich for their production managers are: technical support in sampling and testing for E. coli. 1) Fish seldom produce all the nutrients required for optimum *Corresponding author; phone: (407) 254-9201; email: [email protected] plant production compared with hydroponics alone. Thus, some Proc. Fla. State Hort. Soc. 125: 2012. 381 nutrient supplementation for optimum plant growth should be where F = feed weight, PC = percent protein content of the feed, expected. and T (time) = 1 d. Thus, 1 kg of fish feed with 30% protein will 2) The most critical aquaculture water quality parameters that produce 27.6 kg of N in 1 d (Timmons et al., 2002). As plants + + need to be managed are oxygen and ammonia concentrations. take up NH4 , some of the NH3 is converted to NH4 to maintain Oxygen is essential for respiration and its concentration must equilibrium. The net result is that the amount of NH3 decreases. – be maintained continuously. Ammonia kills fish and must be Most of the plant uptake of N will be in the NO3 form due to converted to non-lethal nitrogen forms that plants can use or be the nitrification occurring in system biofilters. Nitrification is the – discharged as effluent. biochemical conversion by nitrifying bacteria of NH3 to NO3 Aquaculture tank water oxygen concentrations should be main- (Hagopian and Riley, 1998; Madigan et al., 2003; Prosser, 1986) tained between 4 to 6 and 6 to 8 mg/L for tilapia (Oreochromis and is a critical component of aquaculture biofilters (Prinsloo et – niloticus) and trout (Oncorhynchus sp.), respectively (Timmons al., 1999). It is a two-step process with NO3 as the end result: et al., 2002). This maintenance requires a dependable supply of electricity for aerators and pumps to keep the water circulating. Primarily Nitrosomonas spp. – + –1 In water, ammonia exists in two forms, which together are NH3 + 1½ O2 ↔ NO2 + H2O + H + 84 kcal·mol Eq. [3] called the total ammonia nitrogen (Francis-Floyd et al., 2009), or TAN. The equilibrium reaction is (Campbell and Reese, 2002): Primarily Nitrobacter spp. – – –1 NO2 + ½ O2 ↔ NO3 +17.8 kcal·mol Eq. [4] + + NH4 ↔ NH3 + H Eq. [1] – + Plants can absorb NO3 and NH4 . Since N is the nutrient – Water temperature and pH affect the percentage of each required in largest amounts by plants, and NO3 is often the pre- compound in the TAN equilibrium. For example, at 28 °C, the ferred source (Marschner, 2003), management of these systems to percentage of NH3 increases by nearly a factor of 10 for each encourage beneficial nitrifying bacteria has potential to improve 1.0 increase in pH and is 0.2%, 2%, and 18% of the TAN for system sustainability. pH values of 6.5, 7.5, and 8.5, respectively (Francis-Floyd et al., The purpose of this paper is to advance the knowledge base 2009). Non-ionized ammonia (NH3) is dangerous and can kill fish available for aquaponic growers, researchers, and extension at concentrations as low as 0.05 mg/L. Several recommendations agents so that adoption of these sustainable agriculture systems put TAN concentrations at between 0.5 and 1 mg/L for tilapia will be successful. production (Chapman, 2009), or 1 mg/L for cool water and 2 to 3 mg/L for warm-water fish species (Timmons et al., 2002). Materials and Methods In aquaculture, the introduction of nitrogen into the system as NH3-N is based on the fish feeding rate (Fig. 1): An aquaponic system was constructed inside the Exploration Gardens greenhouse at the UF/IFAS Extension–Orange County PTAN = F × PC × 0.092 Eq. [2] Office, Orlando, FL in Feb. 2012. An aquaculture tank (3.66 × 1.83 T × 0.61 m3) was lined with pond liner from Aquatic Eco Systems, Fig. 1. Nitrogen cycle in aquaponics. 382 Proc. Fla. State Hort. Soc. 125: 2012. Apopka, FL and filled with City of Orlando municipal water on of yellow and fluorescing wells E.( coli). Populations of cells, in 24 Feb. Two 3.66 × 0.30 m2 aluminum roofing panels [henceforth MPN/100 mL, were calculated using the Free MPN Generator called Nutrient Film Technique (NFT) channels] were placed over Software for Quanti-tray/2000 available online (http://www.idexx. the tank from north to south with a 2.8% slope. A 40-W Kyocera com/view/xhtml/en_us/water/mpn-generator.jsf). solar panel was direct-connected to a DC marine bilge pump that When large coliform/E. coli populations were suspected, a was connected by hose to the high end of the NFT channel—one 1:100 dilution of the original water sample was prepared in sterile setup for each channel. A solids filter was constructed using a distilled water. The dilution (0.1) was surface-plated onto Chrom- 114-L barrel supplied with tank water from a sump pump. A filter ECC agar (Chrom Agar, Paris, France) and incubated at 37 °C was placed in the barrel just below the 7.6-cm discharge pipe for 24 hr. Total coliform (pink colonies) and presumptive E. coli 15.2 cm from the top. The filter was soaked with a solution of (blue colonies) populations were enumerated by hand counting nitrifying bacteria obtained from Aquatic Eco Systems. and reported as Colony Forming Units (CFU)/mL. Bell pepper (Capsicum annuum) seeds were planted in 2.5-cm On the first day of sampling, two additional samples ≈( 5 g of rock wool cubes and grown for 3 weeks, then were transplanted each Flake and Pellet food) of fish feed were also collected to into 10.1-cm rock wool blocks and placed into the NFT channels determine their influence on bacteria population concentrations.