Performance Evaluation of Lab Scale Anaerobic Membrane Bioreactor for Domestic Wastewater Treatment

Abstract

The aim of this study was to evaluate the applicability of lab scale anaerobic membrane bioreactor (AnMBR) for domestic wastewater treatment. In initial stage, the hydraulic retention time (HRT) of lab scale continuously stirred tank reactor (CSTR) was optimized for maximum COD removal and biogas production. The CSTR was operated for 16 days and the COD removal observed at HRT of 24 hours and OLR of 0.5 kgCOD/m3-day was 64.43% with the average biogas production of 2.51 L/day. In the attempt to reduce the HRT of the system, the CSTR was also operated at HRTs of 18, 12 and 6 hours in ‘test study’ for consecutive 3 days. Based on the results obtained, the HRT of the system was reduced to 12 hours resulting in OLR of 1.0 kgCOD/m3-day for next phase of operation and the system was run for consecutive 42 days until steady state results were achieved. The COD removal obtained was 64.8% with the biogas yield of 5.15 L/day. In the next stage, the AnMBR was designed and established coupling CSTR with membrane tank while the membrane being in side stream submerged configuration. The performance of AnMBR was evaluated employing different sludge recirculation ratios at different fluxes. The system was fed with synthetic domestic wastewater of 500 mg/L COD at three different fluxes; 10.28 (R=1, phase I), 8.8 (R=2, phase II and R=3, phase III) and 6 LMH (R=2, phase IV and R=3, phase V) respectively. The operational cycle adopted was 8 min permeation and 2 min relaxation to reduce membrane fouling. The performance of the system was evaluated in terms of COD removal, VFAs and alkalinity accumulation and biogas yield. Sludge characteristics were measured in terms of mixed liquor suspended solids (MLSS), and mixed liquor volatile suspended solids (MLVSS). In comparison with the all operating protocols tested, optimum efficacy of the system was found at the net flux of 6 LMH and recirculation ratio (R) of 3 with the average COD removal of 96.7% and biogas yield of 0.44 L/gCODremoved while allowing the longest membrane run.