Insight into a novel post-anoxic integrated biofilm process for wastewater treatment and reclamation

Abstract

A novel pilot scale post-anoxic integrated biofilm activated sludge system of capacity 50 m3/d, was used to treat municipal wastewater. Treatment process comprised of three biological reactors which includes aerobic tank with PVA-gel beads followed by anoxic tank and aerobic tank. The plant was operated at HRT of 6 h, with an average SRT of 10 days. Long term performance evaluation of the combined system showed that BOD, COD, TSS and TN removal efficiencies were 91, 90, 93 and 84 % respectively. In PVA-gel tank, significant removal of NH4-N and NO3-N occurred due to nitrification and denitrification process (85 %) in the system. It was observed that the efficiency of SND process varied with temperature and COD/N ratio variation. Maximum TN removal of 80–90 % was noted at temperature range (10–25 °C) and COD/N ratio was 10–22 kg COD/kg of TN. Removal of organic matter and NH4-N in first media tank was dependent on temperature and the loading rates. Significant removal was observed at loading rate 16 kg SCOD/m3 gel/d and 2.4 kg NH4+/m3 gel/d, respectively. The pathogens removal efficacy of the system was higher (>90 %). Bacterial community analysis of immobilized biomass (PVA-gel beads) revealed the presence of Alpha proteobacteria genera, Actinobacterium, Nitrosococcus, Pseudomonas, Fusobacterium and Nitrosomanas species responsible for high carbon and nitrogen removal efficiency of the system. The study concluded that BOD, TSS and TN (<10 mg/L) values were below Indian effluent discharge standards. Average cost to treat 1 m3 of wastewater was calculated as INR 36.05 (electricity input cost: INR 9.6). Overall, post-anoxic integrated biofilm process achieved significant removal of nitrogen and carbon.