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. on 1 Mar. The blocks were set on top of a capillary mat and were Feed samples (1 g) were added to 99 mL of sterile distilled water covered by a sheet of polystyrene to block sunlight. A solution of and mixed until the feed dissolved. Samples were then enumerated nitrifying bacteria was poured into the center of the mat along its for coliforms/E. coli using the Quanti-tray system described above. entire length. There were two rows per channel with six varieties replicated four times in a completely randomized design. Variet- Results and Discussion ies were ‘Tenato’ and ‘Derby’ (yellow), ‘Orangela’ and ‘Paramo’ (orange), and ‘Fantasy’ and ‘Fascinato’ (red peppers). Seeds Two vegetable crops were grown using fish tank water. The were obtained from Hydro-Gardens, Inc., Colorado Springs, CO. pepper variety trial utilized recirculating water through NFT Rock wool blocks were fertilized once per week with a drench of channels placed above the tank, while the cucumber variety/ “MiracleGro” water soluble tomato plant food (N–P–K analysis growth media trial utilized tank effluent discharged to sub-irrigate of 18–7.9–17.4) at 1.3 g fertilizer per L of water with each row nursery pots placed inside a waterproof trough. Both vegetable receiving 1.5 gal of fertilizer solution. Peppers were harvested crops were supplemented with liquid fertilizer placed at the root on 30 May, 6 June, and 12 June when color was visible on the surface once (for pepper) or twice per week (for cucumber). sidewalls of the pepper fruits. Preliminary data from the first three pepper harvests suggested For the cucumber (Cucumis sativus) variety/root media trial, a trend toward higher early yields for the yellow ‘Tenato’ and a 5.1-cm-deep trough (4.27 × 0.30 m2) was constructed 0.91 ‘Derby’ varieties (Table 1). Rating average plant vigor (5=excel- m east of the aquaponics system on 28 Feb. with 5.1 × 5.1 cm2 lent, 1=poor) revealed pepper plants at the inlet side of the NFT pressure-treated wood and lined with pond liner. A media trial trough were much more vigorous (4.4) than those at the outlet was established by putting plastic pots (9.46 L) in the troughs side (1.8). This result was most likely due to low overall plant and filling them with either coarse horticulture grade perlite, nutrient concentration in the tank water, with plants at the inlet vermiculate or Fafard 4 (from BMI, Inc. Apopka, FL) potting side using up the available nutrition before the water reached mix in a completely randomized design with four replications. the outlet. For start-up aquaponic systems where nutrients have Seeds of two cucumber varieties (‘Discover’ and ‘Manar’ from not reached sufficient concentrations in the tank water, it will be Hydro-Gardens, Inc.) were planted in the media and replicated necessary to supplement plant fertilizer to the plant root zone to two times in a completely randomized design. The trough was obtain optimum yields. Nutrient concentrations will need to be kept full of aquaponic water discharged from the bottom of the monitored to avoid plant nutrient deficiencies. solids filter. Each pot was drenched from the top twice per week Since sub-irrigation of nursery pots with aquaponic effluent is with 0.95 L of “MiracleGro” fertilizer using 1.3 g fertilizer per not a common means of producing vegetables, a trial was initi- L of water. Cucumber harvest began on 9 Apr. and continued ated to determine if there were differences in cucumber yields until 30 May. due to the rooting media. Data indicated a trend toward higher Microbial water quality of the aquaponic system was tested on fruit yields when cucumbers were grown in vermiculite for both 17, 21, and 23 May. Two 100-mL water samples were collected the European cucumber variety Discover and the beit alpha-type from the aquaponic system before 0930 hr. Samples (≈120 mL) Manar cucumber (Table 2). Fruit yield results comparing Perlite were collected using sterile gloved hands into sterile specimen containers from the filter return, close to the point where the Table 1. Bell pepper fruit yields for first three harvests. pump pulls water to irrigate the plants. After collection, samples were placed on ice and immediately returned to the laboratory Type and Avg/plant Total for microbial screening. Processing of all samples began 3 h or variety No. Wt (g)z No. Wt (g) less following collection. Yellow The Most Probable Number (MPN) of coliform and generic Tenato 5.0 110 20 2,195 Escherichia coli (E. coli) present in the water samples were de- Derby 5.0 131 20 2,619 termined using Colilert reagent in the Quani-Tray/2000 (IDEXX Orange Laboratories, Westbrook, ME). Briefly, one package of Colilert Orangela 4.5 95 18 1,948 reagent was added to 100 mL of water sample and mixed. The Paramo 3.8 65 15 981 sample containing the reagent was then poured into the Quanti- Red Tray/2000, and sealed in the Quanti-Tray Sealer. Following in- Fantasy 4.8 105 19 1,997 cubation for 24 h at 37 °C, Quanti-Tray/2000 results are read by Fascinato 3.0 91 12 1,093 noting the number of yellow wells (fluorescent) and the number zBell pepper fruit weight in grams.
Proc. Fla. State Hort. Soc. 125: 2012. 383 Table 2. Cucumber fruit yield as affected by root media. tested, where E. coli was below our detection limit in all samples Variety Avg/plant Total tested, was of acceptable microbial quality as defined by both the and media No. Wt (g)z No. Wt (g) LGMA and TGAPs non-foliar water requirements. Discovery Production of multiple concurrent vegetable crops is possible Perlite 6.0 369 12 4,428 utilizing fish tank re-circulating water and waste effluent as -ir Vermiculite 8.0 392 16 6,272 rigation and nutrient source. However, fish tank water seldom Fafard 4 6.5 456 13 5,928 contains all the nutrients required for optimum plant production, Manarx thus the water will need to be monitored to ensure that nutrient Perlite 21.0 153 42 6,426 deficiencies do not occur. Supplementation of plant nutrients Vermiculite 27.0 145 54 7,830 should be expected in start-up aquaponic systems. Fafard 4 17.0 168 34 5,712 Literature Cited zCucumber fruit weight in grams. yEuropean type cucumber. Adler, P.R., F. Takeda, D.M. Glenn, and S.T. Summerfelt. 1996. Utilizing xBeit alpha type cucumber. byproducts to enhance aquaculture sustainability. World Aquaculture 27:24–26. with Fafard 4 media were variable. Adler, P.R., J.K. Harper, F. Takeda, E.D. Wade, and S.T. Summerfelt. 2000. Maintaining food safety is an important production practice. Economic evaluation of hydroponics and other treatment options for phosphorus removal in aquaculture effluent. HortScience 35:993–999. No federally-mandated microbial water quality requirements Campbell, N.A. and J.B. Reese. 2002. Biology, 6th ed. Pearson Educa- currently exist for water used in production of fresh fruits and tion (Benjamin Cummings), San Francisco, CA. vegetables beyond the guidance that they should be of quality Chapman, F.A. 2009. Culture of hybrid tilapia: A reference profile. Circ. “adequate for their intended use” (US FDA, 1998). However, 1051. Dept. of Fisheries and Aquatic Sci., Florida Coop. Ext. Serv., two commonly-referenced industry standards exist that describe Inst. of Food and Agr. Sci., Univ. of Florida, Gainesville.
384 Proc. Fla. State Hort. Soc. 125: 2012. Vol. 1. World Aquaculture Soc., Baton Rouge, LA. and challenges to sustainability in aquaponic systems. HortTechnol- Rakocy, J.E., D.S. Bailey, K.A. Shultz, and W.M. Cole. 1997. Evaluation ogy 21:6–13. of a commercial-scale aquaponic unit for the production of tilapia and Tyson, R.V., E.H. Simonne, D.D. Treadwell, J.M. White, and A. Simonne. lettuce. 4th Intl. Symp. on Tilapia in Aquaculture 1:357–372. 2008. Reconciling pH for ammonia biofiltration and cucumber yield in Rakocy, J.E., T.M. Losordo, and M.P. Masser. 2006. Recirculating a recirculating aquaponic system with perlite biofilters. HortScience aquaculture tank production systems: Aquaponics—integrating fish 43:719–724. and plant culture. Southern Reg. Aquaculture Ctr. Publ. No. 454. Tyson, R.V., J.M. White, and K.W. King. 1999. Outdoor floating hy- Sweat, M., R. Tyson, and R. Hochmuth. 2009. Building a floating droponic systems for leafy salad crop and herb production. Proc. Fla hydroponic garden. Univ. of Florida Hort. Sci. Publ. HS943. Florida State Hort. Soc. 112:313–315. Coop. Ext. Serv.
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