Bromate-reducing capability of nitrate/nitrite-dependent methane driven membrane biofilm reactors

Bromate (BrO₃⁻) contamination poses a significant environmental and health risk, often coexisting with nitrate pollution in water sources. As a sustainable wastewater treatment strategy, methane-driven removal of oxidized contaminants removal has emerged as a promising low-carbon solution. However, interactions between bromate and nitrate reduction remain poorly understood. This study investigates two methane-based membrane biofilm reactors (MBfRs) enriched with either nitrate (MBfR-W1) or nitrite (MBfR-W2) as electron acceptors. Both MBfRs achieved near-complete bromate removal at a maximum reduction rate of 5.6 ± 0.1 mg BrO₃⁻-Br L⁻¹·d⁻¹ while simultaneously eliminating nitrate or nitrite when present. Notably, nitrate and nitrite consistently outcompeted bromate as preferred electron acceptors, yet MBfR-W2 demonstrated greater resilience to dynamic operational changes and higher bromate loads, suggesting benefits from nitrite pre-enrichment. Unexpectedly, under high influent concentrations, nitrate and nitrite appeared to enhance bromate reduction, suggesting regulatory stimulation. Microbial community analysis revealed a dominance of heterotrophic denitrifiers (Pseudomonas, Ochrobactrum, Stenotrophomonas) rather than classical methanotrophs, indicating alternative methane oxidation pathways. Short-chain fatty acids (SCFAs), particularly acetate, were continuously produced from methane and consumed, serving as key intermediates linking methane oxidation to electron acceptor reduction. It was hypothesized that methane was initially converted into complex carbon intermediates, such as extracellular polymeric substances (EPS), which were then fermented into SCFAs. These findings highlight the central role of methane-derived SCFAs in facilitating multi-contaminant removal and offer new insights into methane-based denitrification processes relevant for sustainable water treatment design.