Effluent treatment in an aquaponics based closed aquaculture system with single stage nitrification denitrification using a down flow hanging sponge reactor
Abstract A laboratory scale demonstration of the aquaculture effluent treatment was conducted in a system that combined a down flow hanging sponge (DHS) reactor and a hydroponic cultivation bed (HCB) Cyprinus carpio was used as a model aquaculture fish and Cupsicum frutescens was used as a model hydroponic plant. The aquarium water was circulated through the HCB and DHS using a submerged pump. The experiment was divided into six phases in which the sodium acetate solution was supplied using different feeding patterns. The sodium acetate solution acted as a carbon source and not only eliminated nitrogen through denitrification but also increased the alkalinity through biological degradation of the acetate. Denitrification was observed to eliminate 7.7% of the total nitrogen at the inlet out of which 53.5% was converted by C. frutescens to form a fruit. The microbial community in the sludge that was retained in the DHS contained both nitrifying and denitrifying bacteria. Nitrososhaera was the dominant ammonia oxidizing bacterium, whereas Nitrospira was the dominant nitrite oxidizing bacterium. Further, Opitutus acted as the dominant denitrifying bacterium. No major bacterial pathogen was detected in the DHS HCB system. The study confirmed that the DHS system provided single stage nitrification denitrification and that the overall DHS HCB system provided a low cost and high performance aquaculture effluent treatment system that is capable of being used for safe food production.