Sulfide-mediated azo dye degradation and microbial community analysis in a single-chamber air cathode microbial fuel...

Several textile industry processes produce complex organics, azo dyes and sulfide streams that pose a severe challenge to environmental protection. In this work, single-chamber air cathode microbial fuel cells were used to investigate the interaction mechanisms among Congo red decolorization, sulfide oxidation and bioelectricity generation. The results showed that effective removal of sulfide (>98%) and azo dyes (>88%) was achieved at an initial sulfide/dye ratio of 0.9 under neutral conditions, accompanied by a maximum power output of approximately 23.50 mW m^-2. In this study, biogenic sulfide played a major role in azo dye decolorization and power generation compared with the chemical sulfide. The results indicated that bulk reduction of sulfide and cell lysis products during biogenic sulfide production by sulfate-reduction bacteria could accelerate the chemical reduction of azo dyes. Moreover, S⁰, SO₄^2- and S₂O₃^2- were identified as degradation products, and the intermediates primarily included 3,4-diaminonaphthalene-1-sulfonic acid, sodium 4-aminonaphthalene-1-sulfonate and 4, 4'-diamine biphenyl. Microbial community analysis showed that Proteobacteria (80.7%), Gammaproteobacteria (48.1%), and Dokdonella (29.5%) dominated at the phylum, class, and genus levels, respectively, of the anodic biofilm. This study offers a feasible option for the treatment of recalcitrant organics, azo dyes and sulfide pollutants using single-chamber air cathode MFCs.