Efficient perchlorate reduction in microaerobic environment facilitated by partner methane oxidizers

The conventional perchlorate (ClO₄^-) reduction typically necessitates anaerobic conditions. However, in this study, we observed efficient ClO₄^- reduction using CH₄ as the electron donor in a microaerobic environment. The maximum ClO₄^- removal flux of 2.18 g/m²·d was achieved in CH₄-based biofilm. The kinetics of ClO₄^- reduction showed significant differences, with trace oxygen increasing the reduction rate of ClO₄^-, whereas oxygen levels exceeding 2 mg/L decelerated the ClO₄^- reduction. In the absence of exogenous oxygen, anaerobic methanotrophic (ANME) archaea contribute more than 80% electrons through the reverse methanogenesis pathway for ClO₄^- reduction. Simultaneously, microorganisms activate CH₄ by utilizing oxygen generated from chlorite (ClO₂^-) disproportionation. In the presence of exogenous oxygen, methane oxidizers predominantly consume oxygen to drive the aerobic oxidation of methane. It is indicated that methane oxidizers and perchlorate reducing bacteria can form aggregates to resist external oxygen shocks and achieve efficient ClO₄^- reduction under microaerobic condition. These findings provide new insights into biological CH₄ mitigation and ClO₄^- removal in hypoxic environment.