Submerged anaerobic membrane bioreactor applied for mainstream municipal wastewater treatment at a low temperature: Sludge yield, energy balance and membrane filtration behaviors

The anaerobic membrane bioreactor (AnMBR) has potential as a low-cost wastewater treatment process with the benefit of energy production. However, to ensure satisfactory treatment performance, an AnMBR is operated at a relatively high temperature currently. Research focused on the operation of the AnMBR at low temperature is significant since the energy required for heating is an impediment to the application of AnMBRs for municipal wastewater treatment. Hence, in this study, a constant low-temperature (15 °C) AnMBR was evaluated for the treatment of real municipal wastewater with hydraulic retention times (HRTs) in the range of 6–24 h. During the long-term experiment, a chemical oxygen demand (COD) removal efficiency of approximately 90.5% was obtained with a sludge yield below 0.13 g-VSS/g-CODrem at HRTs of 16 and 24 h. The amount of energy generated was theoretically calculated based on biogas production, with a high of 0.62 kWh/t. The energy balance analysis showed that the AnMBR process can be energy positive under the optimal operational conditions investigated. Membrane filtration performed well during operation at 15 °C with HRTs ranging between 12 and 24 h, while it was compromised at the extremely short HRT of 6 h. In this study, the effectiveness of optimizing the conditions on the performance of the AnMBR operating at low temperature was confirmed, along with the potential for energy recoverability under those conditions.