Energy Self‐Sufficient Direct Membrane Filtration of Municipal Wastewater: Impact of Biological Pre‐Treatment

Abstract Municipal wastewater treatment philosophy shall shift from the conventional energy‐ and chemical‐intensive approach to a more circular, energy self‐sufficient system aligned with Sustainable Development Goals (SDGs) 7, 9, 11, and 13. Direct membrane filtration (DMF) using ultrafiltration provides a low‐energy alternative for recovering organics, which are utilized for energy recovery through anaerobic digestion (AD). However, DMF faces challenges from membrane fouling and elevated dissolved organics in the permeate. To address these issues, this study implements biological contact tank pre‐treatment before DMF, with a short hydraulic retention time (HRT) of 60 min. This pre‐treatment selectively removes 62% of dissolved organics without compromising the recovery of suspended or colloidal organic matter and enhances permeate quality by 40% in terms of chemical oxygen demand (COD). The DMF system without pre‐treatment exhibits 1.84 times higher irreversible pore‐blocking membrane resistance, with higher foulant concentrations per membrane unit area (up to 2.54 times) and enzymatic activity (up to 3.04 times). The recovered organics undergo AD, yielding methane up to 336 ± 23 mL‐CH 4 /g‐VS, making the DMF system net energy positive. Life cycle assessment (LCA) reveals that the DMF system has lesser environmental impacts than the conventional system in 10 out of 18 impact categories.