Impact of sludge recirculation ratios on the performance of anaerobic membrane bioreactor for wastewater treatment

[Display omitted] •PVDF hollow fiber membrane was applied in AnMBR for synthetic wastewater treatment.•Membrane flux 6 L/m2 h and recirculation ratio 3 were optimum operating conditions.•Lowest permeate COD 17.7 mg/L while highest biogas production 0.44 L/gCODremoved.•Side stream submerged membrane configuration enabled better hydrodynamic control. The performance of a lab scale anaerobic membrane bioreactor (AnMBR) was evaluated for wastewater treatment. The efficacy of the system was determined at different operating conditions in terms of fluxes and recirculation ratios (R); 10.28 L/m2 h (R = 1, Phase I), 8.8 L/m2 h (R = 2, Phase II and R = 3, Phase III) and 6 L/m2 h (R = 2, Phase IV and R = 3, Phase V), respectively. In comparison with all the operating conditions tested, optimum efficacy of the system was found at flux of 6 L/m2 h and R of 3 in terms of highest COD removal (96.7%), and maximum biogas yield (0.44 L/g CODremoved). The MLSS and MLVSS concentrations under optimum phase were 6.23 and 4.83 g/L, respectively at OLR of 0.46 kg COD/m3 day. The system also exhibited significant reduction of foulants i.e. extracellular polymeric substances (EPS) and soluble microbial products (SMP) resulting in longer membrane runs in optimized phase.