Tank (Float) System

The polyculture tank design was driven by the need to hold at least eight inches of water for aquatic species. A twelve inch tank depth was chosen to allow for additional flexibility. The tank width of 48-inches was a compromise between the three proposed uses. The tank length of 96-inches was flexible. We found a boat builder in Rhode Island that had a mold for a worm growing tank that met our need. He was willing to supply ten 3/16" gel-coated fiberglass tanks at his construction cost ($225.00) because of his interest in aquaculture applications.

The ten tanks have been piped together in two systems. Each system has two under-bench holding tanks. One holding tank contains the Bio-Cord filter and is connected to the second tank that contains a 1200 gph submersible pump. A U/V sterilizer has been connected so that it can be placed in-line with either system. The tanks are blocked up slightly on the inlet side to allow for easy draining during cleaning.

The tanks are supported on a table type structure. The design load specified was one cubic foot of water per square foot of bench area (65 lbs/sq ft). The structure is assembled with Speed-rail fittings and 1.25-inch inch galvanized steel pipe. In fact, it would be much less expensive to build standard greenhouse benches using this approach compared to marketed greenhouse bench systems for the same design loads. The bench assembly took two men about eight hours. The tank builder recommended that the bench have a continuous solid top so the bench was covered with three-quarter inch plywood supported by 1 x 4 cross-pieces on 24-inch centers laid flat. The top was secured to the steel bench by the use of galvanized pipe clamps. This is not an optimal design but it works. In the long-term builders may want to consider a closely spaced galvanized steel cross section (i.e, square tubing) to support the tank tops.

In each tank system the water flows from a 1200 gph submersible pump, in continuous operation located in the holding tank, either through a recirculating line or an electrically controlled valve to the tank inlets. The recirculating line can pass through the U/V sterilizer and back to the filter tank. This line also contains a venturi that aerates the water and/or injects ozone from the ozone generator on the sterilizer. The tank inlets contain manually controlled valves to adjust the flow rates. The outlets of the hydroponic tanks in System One contain stand pipes to keep the water level at two inches; the hydroponic tanks in System Two have stand pipes that maintain eight inches of water because the system contained golden shiners and crayfish. The hydroponic tanks contain sheets of foam with holes for plastic net baskets. Lettuce and other crops are started in oasis cubes and are placed in the net baskets. Additional aeration is provided by a separate blower supplying air stones in each tank.

Gully (NFT) System

Three gully systems were constructed in order to utilize the nutrient film technique (NFT). Each system is forty feet long by four feet wide and consists of five gullies. Each gully is constructed of four ten foot sections of plastic rain gutter, four inches wide and two inches deep, purchased at a local hardware store. The gullies are held up off the ground on a four foot wide table or frame constructed of four foot lengths of 2" x 4" lumber spaced four feet apart. In the outside systems, these crossbars are supported on legs made of one inch EMT tubing, cut into five foot lengths, held to the lumber by pipe clamps. The EMT tubing is driven into the ground to provide a slope to the table of 1/4" per four feet of table length; a total of ten inches for the forty foot table. The height from the ground to top of the gullies ranged from 3'6" to 4'4". The gullies are held in place by blocking attached to the crossbars. The legs of the inside system are made out of lumber and sit on cement blocks. The table slope is obtained by utilizing additional blocks at the high end and setting the blocks into the ground as required. The table has wooden bracing for stability.

The top of each gully is covered by sections of vinyl siding cut to the width of the gully. Two inch holes were cut into this cover at ten inch intervals providing 48 planting sites per gully. Two inch diameter plastic mesh hydroponic growing pots snap fit into the holes in the cover and reach down to within 1/8" of the gully bottom. In the wind-exposed outside gully systems the vinyl siding covers are held in place with tie-downs. Some of the vinyl covers were cut to fit inside of the gullies and were held up by small blocks. This allowed the net baskets to sit on the gully bottom eliminating the need for developed roots extending from the oasis cube.

The supply end of the gully system is closed off by a rain gutter end piece. A 3/4" poly pipe from the nutrient tank supplies a header with a valve above each gully. The discharge side of each gully is terminated with a rain gutter down spout that delivers the nutrient solution to a return pipe to the nutrient tank by gravity. In the inside gully system the nutrient tank is the same one for Tank System One. Each outside gully system contains an independent supply tank. The tanks are simply Rubbermaid 50 gallon plastic storage boxes with covers purchased at a local Bradley=s store. The supply pump located in each tank is a Surpreme 350 gph mag-drive submersible utility pump powered by 110 volts (see Appendix).

Initially the outside gully system supply tanks were placed outside under the gully systems. As cold weather approached we moved the supply tanks inside the greenhouse to keep the nutrient solution as warm as possible. This worked very well.
 
 

Monitoring System

We continued the use of existing greenhouse and aquaculture monitoring systems. Continuous automatic data logging of the tank systems was accomplished with an Aquadyne Octopus 3000 environmental controller. Parameters measured were water temperature, ph, and conductivity. The system also has the potential to measure oxidation reduction potential (ORP). The unit can hold up to seven days of data, can activate electric controls, and send alarms. The unit can also be attached, via remote access, to a computer for downloading of data or continuous monitoring.

Two water test kits were acquired to monitor additional water quality parameters. The hydroponics test kit is used to measure pH, nitrate nitrogen, ammonia nitrogen, phosphorus, sulphate, calcium, magnesium, and potassium. The freshwater test kit is used for detecting lower levels of nitrogen and ammonia, alkalinity, carbon dioxide and hardness. An electronic test pen was used for routine checking of pH and conductivity (EC).

Bio-Cord Filters

The Bio-Cord, a man-made Bio-Reactor, was utilized within the polyculture system.

Racks containing the Bio-cord were constructed of PVC and placed into the filter tanks under the bench. In spite of our efforts, we still were not able to conduct a controlled experiment of the Bio-cord filters because too many variables are uncontrolled. We firmly believe that the Bio-cord adds a great deal of stability to the system. Ph was highly stable and we never had a build up of nitrites or ammonia. The nutrient solution was biologically active; never sterile.

Nutrient Solutions

The control nutrient solution is a standard solution recommended by Peters. The mix for 100 gallons of solution consists of 5-11-26 Hydro-Sol (13 oz), 15-0-0 Cal-Lite (9 oz), and 10-0-0 Magnitrate (6.5 oz). The EC level of the components is 0.98, 0.74, and 0.34 respectively for a total EC value of 2.02. The EC level and pH are continuously monitored using an electronic data logging system and also checked using a Hanna Instruments Agritest pocket pH/EC pen. Calibration is routinely checked with test solutions provided by Hanna.

The experimental organic solutions are based on liquid fish and seaweed blends provided by Neptune=s Harvest; a Division of Ocean Crest Seafoods. The fish blend had an NPK of 2-4-0.5. The blend contains a host of vitamins, amino acids, enzymes, growth hormones, and other micro nutrients. The supplier asserts that university studies have shown the product to outperform 20-20-20 chemical fertilizers. Our initial trials with this material had problems with foaming at levels needed for adequate plant nutrition. 

We also experimented with a compost Atea@ in one of the tanks in Float System One. Several pounds of compost were placed in a loosely woven cloth bag and placed directly into the tank. The water in this tank was not recirculated.

CROP PRODUCTION

Five tanks (tanks 1-5), referred to as Float System One, were placed into the hydroponic operational mode. Each tank was outfitted with an outflow standpipe that maintains a nutrient solution level of two inches. The nutrient is constantly recirculated so that the exchange rate is about four times per day. Each tank has two sheets, 2' x 4', of one inch thick Styrofoam floating on the nutrient solution. Each piece of foam has 36 holes for plastic mesh pots on eight inch centers allowing for 72 planting sites per tank. During part of the project we isolated tank four from the recirculating system and informally experimented with a compost Atea@. The other five tanks (tanks 6-10) were in Float System Two. This system operated in the same manner as system One except the nutrient solution depth was kept at eight inches and the tanks contained various amounts of golden shiners and crayfish throughout the project.

Three gully systems, set-up for Nutrient Film Technique (NFT), were constructed and placed into test status. One system (NFT One) was placed in the 30 x 90 greenhouse and two systems (NFT Two and NFT Three) were placed outside in the space between two greenhouses. Each of the outside systems consists of five 40-foot long gullies; a sump tank, and a pump. NFT One is provided nutrient solution from the Float System One recirculating system.

Up until July, 1998, we tested a number of crops in the hydroponic systems including lettuce, greens, herbs, squash, and edible flowers. At the end of July the hydroponic systems were cleared of most of the spring crops, cleaned, and set-up for a production experiment. There are five systems; four were placed into production throughout the summer and fall while the fifth, NFT Three, was modified. To summarize, System One contains tanks 1-5; System Two contains tanks 6-10; System Three contains gullies 1-5; and System Four contains gullies 6-10. System Four was located outside of the greenhouse. System Five also outside of the greenhouse, containing gullies 11-15, was left empty to allow for re-design. Systems One and Three run off the same recirculating supply.

The hydroponic solution during this production experiment was the same formulation in all systems as specified earlier in this report. Float System Two also contained crayfish and bait fish which were fed a minimal diet of fish flakes. The crayfish and bait fish thrived and reproduced in the hydroponic solution! This has significant ramifications for polyculture, or aquaponic, activities.

During the July period we had significant problems with lettuce and basil suffering major leaf burn in the outside gully system. To remedy this situation we installed row cover over the gullies for the production
experiment which solved the problem. The row cover also protected the crop through several frosts late in this production period. System Five was modified to be closer to the ground to allow the row cover to
completely enclose the gullies and ground underneath the system. In addition, the supply tank and supply piping were moved into the greenhouse to provide extra warmth during the fall/winter test period.