Anion-exchange membrane coupled with methane-fed biofilm enables efficient co-removal of perchlorate and nitrate

Perchlorate and nitrate frequently co-occur in contaminated water posing significant risks to human health and the environment. However, their simultaneous and highly efficient removal remains a critical technical challenge. We report a high-performance hybrid system integrating Donnan exchange through an anion-exchange membrane (AEM) with reduction in methane-fed bio-reactor (AEM-MBfR), achieving high ClO₄⁻ and NO₃⁻ removal efficiencies. The AEM-MBfR attained volumetric removal fluxes up to 902.17 μg ClO₄⁻·L⁻¹·d⁻¹ and 22.74 mg N·L⁻¹·d⁻¹, representing 9.6- and 1.6-fold increases, respectively, over a standalone MBfR. Mechanistic analysis revealed that enzyme-independent Donnan dialysis in the AEM module enriched ClO₄⁻ into the MBfR zone, alleviating the competitive advantage of NO₃⁻ reduction over ClO₄⁻. This enrichment significantly enhanced bioreduction kinetics, enabling sustained high-throughput treatment. Multi-omics profiling identified a syntrophic microbial network dominated by Methylocystis, Methylosinus and Hyphomicrobium, with elevated transcription of key functional genes that drive ClO₄⁻ and NO₃⁻ reduction. Notably, VFAs-mediated electron transfer facilitated tight metabolic coupling between methanotrophs and denitrifiers. Compared to other MBfRs, the AEM-MBfR achieved one of the highest reported ClO₄⁻ removal fluxes. Coupled with the low cost of methane and NaCl, this study demonstrates a scalable and economically viable strategy for remediating anion-contaminated water through membrane-enhanced microbial processes.