Application of two anaerobic membrane bioreactors with different pore size membranes for municipal wastewater treatment

Abstract

Pore size is one of the most important properties in the successful operation of membrane-based bioprocesses for the treatment of municipal wastewater. The characteristics of two anaerobic membrane bioreactors (AnMBRs), one with a hollow fiber membrane of 0.4 μm pore size (AnMBR1), and the other with a membrane of 0.05 μm pore size (AnMBR2) were investigated for the treatment of real municipal wastewater at room temperature (25 °C) under varied hydraulic retention times (HRTs). Process performance was evaluated in terms of organic removal efficiency, biogas production and membrane filtration behaviours during a long-term continuous operation. Both AnMBRs showed good organic removal performance with COD and BOD removal efficiencies of around 89% and 93%, respectively. High energy recovery potential was achieved, with the biogas yield ranging between 0.20 and 0.26 L-gas/g-CODrem and a methane content of approximately 75%. The differences in the membrane filtration behaviours in the two AnMBRs included different permeate flux and total filtration resistance (Rt). In the AnMBR with a 0.4 μm pore size membrane, an average Rt of 1.08 × 10^12 m−1 was obtained even when the permeate flux was a high 0.274 m/day, while a higher average Rt of 1.51 × 10^12 m−1 was observed in the AnMBR with 0.05 μm pore size membrane even when the flux was a low 0.148 m/day. The off-line membrane cleaning strategy used for AnMBR1 indicated that the membrane restoration efficiency was 90.2%.