A novel combination of bioelectrochemical system with peroxymonosulfate oxidation for enhanced azo dye degradation and MnFe2O4 catalyst regeneration

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Advanced oxidation process (AOP) based on peroxymonosulfate (PMS) activation was established in microbial fuel cell (MFC) system with MnFe2O4 cathode (MFC-MnFe2O4/PMS) aimed to enhance azo dye degradation and catalyst regeneration. The effects of loading amount of MnFe2O4 catalyst, applied voltage, catholyte pH and PMS dosage on the degradation of Orange II were investigated. The stability of the MnFe2O4 cathode for successive PMS activation was also evaluated. The degradation of Orange was accelerated in the MFC-MnFe2O4/PMS with apparent degradation rate constant increased to 1.8 times of that in the MnFe2O4/PMS control. A nearly complete removal of Orange II (100 mg L−1) was attained in the MFC-MnFe2O4/PMS under the optimum conditions of 2 mM PMS, 10 mg cm−2 MnFe2O4 loading, pH 7–8 and 480 min reaction time. MFC driven also extended the longevity of the MnFe2O4 catalyst for PMS activation due to the in-situ regeneration of ≡Mn2+ and ≡Fe2+ through accepting electrons from the cathode, and over 80% of Orange II was still removed in the 7th run. Additionally, the MFC-MnFe2O4/PMS system could recover electricity during Orange II degradation with a maximum power density of 206.2 ± 3.1 mW m−2. PMS activation by MnFe2O4 was the primary pathway for SO4- generation, and SO4- based oxidation was the primary mechanism for Orange II degradation. MFCs driven coupled with PMS activated AOP systems provides a novel strategy for efficient and persistent azo dye degradation.