Pilot-scale verification of AEM-MBfR: Efficient perchlorate and nitrate co-removal with comprehensive process assessment

Perchlorate and nitrate frequently co-occur in contaminated water, posing substantial risks to ecosystem and human health. However, their simultaneous removal at practical treatment scales remains challenging because perchlorate reduction is often inhibited by excess nitrate and influent fluctuations. Here, we report a pilot-scale anion exchange membrane-membrane biofilm reactor (AEM-MBfR) that integrates Donnan dialysis-driven oxyanion enrichment with methane-fed microbial reduction. At a treatment capacity of 2 m³/d, the AEM-MBfR achieved stable removal efficiencies of 87.25% for perchlorate and 52.90% for nitrate, corresponding to total-volume-normalized removal fluxes of 6.39 g ClO₄⁻·m⁻³·d⁻¹ and 145.30 g N·m⁻³·d⁻¹. The system maintained robust performance under fluctuating flow and contaminant loads, with effluent concentrations consistently meeting relevant water-quality standards. Mechanistic analysis showed that the anion exchange membrane enriched perchlorate and nitrate by 6.2–8.0-fold in the bioreduction zone while protecting the methane-fed biofilm from influent disturbance. Response surface methodology identified a practical operating window governed by the balance between hydraulic retention time and Donnan dialysis-driven ion transport. Under optimized conditions, the pilot AEM-MBfR successfully treated ClO₄^--spiked real water matrix, achieving removal efficiencies of 87.96% for perchlorate and 55.64% for nitrate. Microbial analysis revealed a methane-driven, denitrifier-centered biofilm consortium that supported stable co-reduction under nitrate-rich conditions. Life cycle assessment further indicates lower carbon emissions, energy demand, toxicity-related impacts, and operating costs than conventional reverse osmosis and biofilter processes. These findings suggest that the AEM-MBfR is a scalable, resilient, and low-carbon strategy for treating perchlorate- and nitrate-contaminated water.