Side-stream anaerobic membrane bioreactor system for energy-positive sewage treatment

Anaerobic membrane bioreactors (AnMBRs) present a promising solution for developing energy-neutral wastewater treatment systems. However, their application in mainstream settings, where they treat sewage directly, faces challenges such as dissolved methane loss and performance deterioration at low temperatures. To address these issues, this study developed a side-stream mode AnMBR system by integrating chemically enhanced primary treatment (CEPT) with AnMBR. In this system, sewage is first concentrated in a CEPT unit, and the concentrates are then digested in an AnMBR. A laboratory-scale mesophilic AnMBR, fed with CEPT sludge from a full-scale plant, was operated to demonstrate the design and verify its performance. The results showed that the CEPT-AnMBR system removed approximately 65.7 % of the COD from sewage, converted roughly 51.4 % into methane, with a methane yield of 0.26 L-CH₄/g-COD. By altering the waste flow from low-strength, high-volume sewage to high-strength, low-volume sludge, the side-stream AnMBR system reduced dissolved methane to <1 % of the generated methane, minimized membrane requirement to approximately 0.56 m²/m³-sewage/day, and achieved energy positivity at 0.61 kWh/m³-sewage. These findings demonstrate a successful "capture + digestion" strategy for energy-saving sewage treatment, advancing the application of AnMBR technology in regions with low-temperatures.