Persulfate activation by Fe(III) with bioelectricity at acidic and near-neutral pH regimes: Homogeneous versus heterogeneous mechanism

Highlights: • Efficient degradation of BPA in MFC/Fe(III)/PDS system achieved at pH 2.5 and 6.0. • Homogeneous activation at pH 2.5 with main reactive species of SO₄^{• −} in the solution. • Heterogeneous activation at pH 6.0 with dominant reactive species of adsorbed SO₄^{• −}. • The precipitate formed at pH 6.0 determined as amorphous iron oxyhydroxides. -- Abstract: The combination of persulfate (PS) activation by iron ions with electrochemical process (electro/Fe³⁺/PS) is a promising advanced oxidation process. However, almost all these systems were performed in an unbuffered solution and actually under acidic pH condition, with the electricity being frequently supplied by external power. Considering the high buffering capacity of wastewater and energy saving, peroxydisulfate (PDS) activation by Fe(III) species with bioelectricity provided by microbial fuel cell (MFC) for bisphenol A (BPA) oxidation was investigated at fixed near-neutral pH as well as acidic pH. The results indicate that 90.8% of BPA could be removed at pH 2.5. Though the iron existed in the form of precipitate, BPA could still be efficiently removed at pH 6.0. The precipitate formed in the system at pH 6.0 was identified as the amorphous iron oxyhydroxides. Sulfate radicals in the bulk solution and that adsorbed on the precipitate were the dominant reactive species responsible for the oxidation of BPA in the homogeneous and heterogeneous MFC/Fe(III)/PDS processes, respectively. The mechanisms of BPA degradation at both pH values were proposed via EPR and quenching tests as well as XPS analysis. The effects of operating parameters, the mineralization, the mineralization current efficiency and energy consumption were also explored.