A Hydroponic System for Purification of Anaerobically Treated Dairy Manure and Production of Wheat as a Nutritional Forage Crop

A hydroponic system was developed and used for purification of an anaerobically treated dairy manure and production of forage crops. The effect of light duration, seeding rate and wastewater application rate on the crop yield and pollution potential reduction were studied. The results indicated that a wheat forage crop can be produced in 21 days from germination to harvest in this system and removal efficiencies of up to 89.9, 94.6, and 86.7 % can be achieved for the total solids, chemical oxygen demand (COD) and ammonium nitrogen, respectively. Increasing the wastewater application rate increased the crop yield and decreased the pollutants removal efficiencies. A treatment combination of wastewater application rate of 900 mL/day, a seeding rate of 400 g and a light duration of 12 hours gave the best results for crop yield (3.65 kg of wheat/tray). A total possible yield of 3160 tonnes per hectare per year can be achieved with the system (with thirteen harvests per year). This is more than 98 times greater than the yield obtainable from a field grown conventional forage of 245 tonnes per hectare per year. At the optimum forage production, removal efficiencies of 75.7, 85.9 and 75.6% were achieved for the solids, COD, ammonium nitrogen, respectively. A nitrate nitrogen concentration of 6.7 mg/L was found in the effluent from the hydroponic system. This is below the Canadian Environmental and Health Guidelines of 10 mg/L.