Electrochemical degradation of bisphenol A in chloride electrolyte—Factor analysis and mechanisms study

Abstract

Electrochemical oxidation technology is a powerful method in the degradation of recalcitrant organics, due to the high oxidizing ability of active chlorine and reactive oxygen species generated in the cell. However, influencing factor analysis and intermediates detection during the electrochemical removal of organics has not been extensively studied in the chloride electrolyte. In this study, an orthogonal test array design of L16(4)3 was carried on with Pt anode in NaCl electrolyte, using the typical endocrine disruptor bisphenol A (BPA) as the model pollutant. The influencing order of the three main factors for BPA degradation rate was current density>initial organic concentration>chloride concentration, based on the analysis of variance in this experiment. This emphasized the very significance of the active chlorine and hydroxyl radicals which were closely related with the potential of the system and the applied current density. Then both organic and inorganic Cl-byproducts were determined. The concentration of chloride decreased to 9.88mM with an initial of 10mM in the 480-min electrolysis and extremely low concentration of active chlorine was produced in this system (maximized at 0.037mM) for the first set. Neither chlorate nor perchlorate was detected with the Pt anode. The factor of current density influenced greatest on the formation of chloroform due to the amount of active chlorine affected by the current density. Finally, intermediates generated in the electrolysis cell were concretely investigated. Compared with traditional chlorination, the amount of chlorinated-BPA (2, 2′-D2CBPA and T4CBPA) generated was relatively less (2.46 and 10.00μM equiv BPA), which might be due to their fast simultaneously transformation in the electrochemical system. With the isopropylidene bridge cleavage of chlorinated-BPA, one-ring aromatic compounds (2,6-dichlorophenol, 2,6-dichloro-2,5-cyclohexadiene, 2,4,6-trichlorophenol) occurred at the same time. Finally, chlorinated-BPA was totally transformed and low molecular chlorinated compounds were detected to the end of the experiment. This is one of the very few studies dealing with chlorinated organic intermediates formed in chloride electrolyte, and thus these findings may have significant technical implications for electrochemical treatment of wastewater containing BPA.