Utilization of Liquid Anaerobic Digestate using Recirculating Hydroponic Planting System
Abstract
A hydroponic planting technique employing organically treated anaerobic digestion digestate liquid fertiliser is becoming popular. This study examines the biological treatment of digestate from food processing waste anaerobic digestion using Cosmoball® uncoated and activated carbon-coated plastic media. In a pilot-scale recirculating hydroponic system (RHS), ammonia-to-nitrate conversion and plant development were assessed at varying digestate ammonia concentrations. Bench tests suggest that AC-coated Cosmoball® successfully treats digestate. After 21 days, the nitrate level reached 80 ppm, and 100% ammonia elimination and over 90% of the carbon oxygen demand (COD) were observed. The RHS maintained 116-ppm nitrate but reduced COD treatment to only 62–66%. High pH at the start of the RHS trial required pH control until day 40, after which it stabilised at 6.8. 15-ppm ammonia additions caused a substantial pH drop. Maintaining the pH at 5.8 on the RHS boosted plant growth. Finally, AC-coated media improves nitrification and produces plant-growth nitrate.
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