Development of a conductive gas-permeable membrane for electro-stimulated biofilm engineering and rapid startup in membrane aerated biofilm reactors

Conductive membranes deliver oxygen and electrical stimulation at one interface. • CNT/rGO coating preserved gas permeability and membrane hydrophobicity. • Electro-stimulation collapses the long startup bottleneck of MABRs. • Rapid biofilm establishment achieved within the first 7–10 days. • Biofilm growth rate increased by ∼ 2.5 × under low electrical input. Membrane aerated biofilm reactors offer high oxygen transfer efficiency and compact nitrogen removal; however, their practical application is strongly limited by slow and unstable startup associated with delayed biofilm establishment. In this study, a conductive gas-permeable membrane was developed by immobilizing a carbon nanotubes / reduced graphene oxide-silane nanolayer onto a Polyvinylidene fluoride substrate to enable localized electro-stimulation directly at the membrane-biofilm interface. The modified membrane preserved hydrophobicity, pore structure, and oxygen permeability while exhibiting stable electroactive behaviour. When applied in a laboratory-scale membrane aerated biofilm reactor (MABR) under low-intensity electrical stimulation, biofilm formation was significantly accelerated, achieving near-complete surface coverage and functional maturity-defined by the establishment of a stable and well-developed biofilm together with sustained ammonium removal exceeding 90%-within 7–10 days, representing a reduction of more than two weeks compared to conventional MABR startup. The biofilm growth rate increased from 7.9 ± 0.9 to 19.8 ± 1.3 µm day -1 (approximately 2.5-fold) compared to the non-stimulated control, resulting in markedly earlier chemical oxygen demand removal and complete nitrification. Response surface analysis revealed that electro-stimulation guided biofilm development toward an optimal structural configuration, characterized by near-complete surface coverage and a balanced intermediate biofilm thickness (∼120–200 µm) associated with peak treatment performance. These findings demonstrate that conductive gas-permeable membranes provide a scalable and mechanistically robust approach to overcome startup limitations in MABR systems. Download: Download high-res image (235KB) Download: Download full-size image