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Nutrient fluxes in aquaponics systems

Nutrient fluxes in aquaponics systems. Harry Ako and Adam Baker Molecular Biosciences and Bioengineering College of Tropical Agriculture and Human Resources University of Hawaii at Manoa. I Definition. Aquaponics, our way of looking at it. Feed. Feed. Feed fish.

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Nutrient fluxes in aquaponics systems

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  1. Nutrient fluxes in aquaponics systems Harry Ako and Adam Baker Molecular Biosciences and Bioengineering College of Tropical Agriculture and Human Resources University of Hawaii at Manoa

  2. I Definition. Aquaponics, our way of looking at it. Feed Feed • Feed fish. • Fish metabolites remediated by bacteria. • Fish water nourishes plants. • And is recycled. Fish grow and excrete metabolites cleaner water bioremediated water Bacteria remediate toxic N species Plants take up metabolites to grow

  3. I Definition. Benefits. • 2 crops from 1 input • no effluent (negligible environmental impact) • productivity 6 times higher than soil agriculturevery suitable for islands Our experiment just before harvest

  4. Research began in the 1970’s • Plants (in raceways) added to a fish tank system (under black tent) II History. Prevailing system developed by James Rakocy http://rps.uvi.edu/AES/Aquaculture/basil2002.jpg

  5. II History. The system is very complex. • Complex equipment necessitate high capital expense and constant electricity • Operation and maintenance requires a trained staff • Attempted and failed in Saipan Fish tank clarifier sump screen filter tank degassing tank Air pumps, water pump, and 237 air stones (not shown)

  6. After we finished our work we discovered a nice quote: “Estimates of nutrient uptake and a deeper understanding of culture water nutrient dynamics are required for design criteria” Rakocy and Hargreaves, 1993 • Hypothesis: Plants have nutritional needs that can be discovered. Fish can supply these needs if their husbandry can be matched to the nutritional needs of the plants. • What model is the starting point? • The Virgin Island model of the ‘70s? Has problems. Failed once before. • UHM hydroponics systems not only academically successful but also commercially successful? • In some subject matter areas UHM and CTAHR are the places to be in the world as homes for intellectual property.

  7. III Determination of lettuce nutrients • Used hydroponics nutrients (Kratky, a UHM colleague) • Used ICP-AES to measure nutrients used up in intermediate (4 weeks) and full cycle (6 weeks) grow out • In the early weeks not much used up. • First benchmark, 48 heads lettuce. • Nutrients used up at full cycle were hypothesized to be required nutrients (remember these words in future slides)

  8. III Testing the required nutrients hypothesis. Try lower Ca and Mg from original formula. a a • 1st column, required nutrients. • 2nd column, lowered Ca and Mg in hydroponics mix should theoretically meet plant needs • No reduction in yield found

  9. III Testing the required nutrients hypothesis. Try higher nitrogen • 1st column, required nutrients. • High N trial theoretically exceeded plant needs • N uptake was greater (not shown) • But no benefit in yield, even when grown in better sunlight

  10. III Testing the required nutrients hypothesis. Try lowering the K a b Control Low K • 1st column, required nutrients. • Lowered K level trial theoretically inadequate for lettuce plants • Lettuce yields significantly reduced

  11. III Testing the required nutrients hypothesis. Temporal experiment. 1/4th nutrients, Week 4 • If use ¼ nutrients, the required nutrient curves predict that they will run out by week 4 • Growth stunted at Week 4 • Biochemical approach not only valid in terms of nutrient amounts but also valid in terms of time Control, Week 4

  12. III Testing the required nutrients hypothesis. Temporal experiment. Lettuce head weight (g) • If use 1/2 nutrients, the required nutrient curves predict that they will run out by week 6. • Growth stunted at Week 6 • Nutrient amounts defined as “required nutrients” seem accurate a b ½ nutrients Control

  13. Footnote: Supplemental Fe is required Aquaponics (no iron) Week 3 Control, Week 3 Aquaponics, Week 4 Fe chelate Lettuce head weight (g) • However, Mn supplementation was found to be unnecessary With Mn

  14. IV Determination of conditions to produce nutritious fish water. The math • Required nutrients from previous work • Assumed that these will be satisfied by a 20 L daily exchange • Second benchmark, 6% daily water exchange a day. • We need to do more work with flowing systems. Marissa’s is a start. For a tray of 48 lettuce heads

  15. IV Determination of conditions to produce nutritious fish water • Stocked tilapia in 200 L of water. Fed and removed 20 L daily. • Daily requirement in first data column • When fish biomass was such that they ate 14 or 20 g of feed daily, several nutrients would be deficient • When fish biomass was such that they are 40 g of feed daily, all requirements would be met (except iron and Mn). • Another consequence is that nitrogen may be used as a proxy for all nutrients

  16. IV Determination of conditions to produce nutritious fish water. The previous data suggested that 40 grams of feed per day provided to 2.3 kg of tilapia maintained target nutrient concentrations of 47 mg/L nitrate-N in a 200 L tank with a 20 L of water removed daily. Shown below. The above was replicated in 5 week experiments. As before 20 L of water were removed daily from a 200 L tank. The following resulted. Alternate third benchmarks, 44-49 mg nitrate N/L, 40-59 g feed/day, and 2.3-2.5 kg fish. Additional benchmark, have to bring the biofilter up slowly and carefully. Fish rearing the hard part.

  17. V Aquaponics = aquaculture + hydroponics, integration.Verification of predicted lettuce needs • If benchmarks can be hit, aquaponics lettuce heads were not significantly different in size to hydroponics lettuce heads.

  18. V Aquaponics = aquaculture + hydroponics, integration.Fish growth parameters During the 10 week aquaponics trial, fish growth was measured (tanks proportionate to 1.5 lettuce trays) Can be used to predict fish yields in aquaponics

  19. V Aquaponics = aquaculture + hydroponics, integration. Aquaponics is environmentally friendly • Of total nitrogen input into the system as feed, about 27% is captured as fish flesh, about 43% is captured as lettuce biomass, and a small fraction is lost as nitrogen gas or as solids used to fertilize garden plants • None released into the environment Denitrification a problem.

  20. Midterm conclusions • Our nutrient fluxes are for trays with 48 heads of lettuce. • Fish are held in 200 L (50 gallon) tanks at about 12.5 kg/m3 and are fed 40-60 g of feed a day. This is 5 times less than Rakocy’s. • Hence, our system proven with only one moving part, an air pump (which we are trying to get rid of) and is very simple and very inexpensive. Some people are using it with great success.

  21. VI Scenarios. Single family size Components Specifications • Water transfer, manual • Fish biomass, about 2.5 kg • Daily feed, 40-59 g • Iron chelate, 0.25 g/week • 1.4 heads lettuce/day; 1.8 kg tilapia/10 weeks • Cost, 250 USD • One lettuce tray (1.2 X 2.4 m) • One fish tank (200 L) • One small air pump • Shade cloth Other designs are permissible as long as the basic specifications are followed. In this instance fish are under the plants, water flows constantly, etc.

  22. VI Scenarios. Micro-farm size Components • 8 linked lettuce trays • one 1600 L fish tank • one air blower • water pump • Shade cloth (50%) Specifications • stock about 19.2 kg of fish • feed 0.32-0.47 kg/day • iron chelate 2 g/week • annual production, 3300 heads of lettuce and 75 kg tilapia • annual income about 8600 USD at Hawaii farmgate prices…ratio of lettuce to fish income • cost of construction, 2500 USD

  23. VI Scenarios. Small farm, 0.1 hectare Components • equivalent of 270 lettuce trays • 54,000 L in tanks • air blower • recirculate water with a water pump Specifications • stock about 648 kg of fish • daily feed, 11-16 kg • annual production, 112,000 heads of lettuce, 2,500 kg tilapia • Income 234,000 USD/year • Cost, <80,000 USD

  24. Summary • Fine tuned lettuce nutrient requirements • Set fish parameters that provide optimal nutrition to plants • Verified results in several aquaponics trials • These fluxes eliminated all electrical components but aeration in fish tanks • Rational parameters will allow for flexible aquaponics design to accommodate different needs and physical environmentsweidenbach, koch, May’s, Ho Farms, Dave Campbell • The methodology described can easily be applied to grow other crops

  25. Thank you This work was funded by the United States Department of Agriculture (USDA) Center for Tropical and Subtropical Aquaculture (CTSA) through Grant No. 2004-38500-14602

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