Effects of ferroferric oxide on azo dye degradation in a sulfate-containing anaerobic reactor: From electron transfer capacity and microbial community

Abstract

Anaerobic decolorization of azo dye in sulfate-containing wastewater has been regarded as an economical and effective method, but it is generally limited by the high concentration of azo dye and accumulation of toxic intermediates. To address this problem, Fe3O4 was added to one of the anaerobic reactors to investigate the effects on system performances. Results showed that AO7 removal rate, COD removal rate, and sulfate reduction were enhanced with the addition of Fe3O4 under various influent AO7 concentrations (153 mgCOD/L – 1787 mgCOD/L). According to the proposed pathway for the degradation of AO7, more intermediates (2-hydroxy-1,4-naphthoquinone, phthalide, 4-methylphenol) were produced in the presence of Fe3O4. The electron transfer capacity of sludge was also increased since Fe3O4 could stimulate to secrete humic acid-like organics in EPS. Microbial analysis showed that iron-reducing bacteria like Clostridium and Geobacter were also enriched, which were capable of azo dye and aromatic compounds degradation.