Biochar-augmented microaerophilic fixed-film bioreactor integrated with an aerobic membrane bioreactor effectively reduces persistent, mobile chemicals in the CETP effluent treatment.

Different classes of chemical compounds including persistent, mobile chemicals (PMCs) often bypass the conventional treatment processes of common effluent treatment plants (CETPs), resulting in their unmonitored release into aquatic environments. In this study, an integrated treatment system comprising a microaerophilic fixed-film bioreactor (MFB) and an aerobic membrane bioreactor (Ae-MBR) was engineered to treat secondary CETP effluent. Two types of packing materials in the engineered MFBs were evaluated: one with wood charcoal (C-MFB) and another with 30% (w/w) biochar-augmented charcoal (BAC-MFB). The BAC-MFB showed better treatment efficiency, achieving 69.17% colour (Pt-Co units) removal and 93.01% COD removal at an optimal 3d hydraulic retention time (HRT). Integration with Ae-MBR further enhanced the treatment, achieving > 95% COD and > 94% colour removal, with an overall > 85% reduction in total number of parent chemical compounds and a specific > 83% reduction in PMCs from CETP effluent. At 3d HRT, bacterial community analysis revealed dominance of Campylobacterota and Bacillota in BAC-MFB under microaerophilic conditions, whereas Bacillota dominated in the Ae-MBR under aerobic conditions. The predicted metagenome analysis revealed significant enrichment of benzoate and aminobenzoate degradation pathways in the integrated system. While the BAC-MFB treatment alone achieved sufficient COD removal, its integration with Ae-MBR markedly enhanced the reduction in overall chemical complexity including PMCs from the CETP effluent. This study demonstrates that the engineered hybrid BAC-MFB-Ae-MBR system is a sustainable solution for the treatment of industrial CETP effluents.