Degradation and transformation of bisphenol A in UV/Sodium percarbonate: Dual role of carbonate radical anion.

The bicarbonate and carbonate ions (HCO &CO) will consume hydroxyl radical (HO) to generate carbonate radical anion (CO) in hydroxyl radical based advanced oxidation processes (HO-AOPs) resulting in reduced oxidation efficiencies of the systems. However, despite the HO quenching effect of carbonate species, the contribution of CO to the degradation of bisphenol A (BPA) was observed in UV/sodium percarbonate (UV/SPC). In order to study the performance of UV/SPC for BPA degradation and the role of CO in this process, the degradation kinetics and mechanisms of BPA in UV/SPC and in UV/hydrogen peroxide (UV/HO) were compared at equivalent concentration of HO. In this study, the observed degradation rates of BPA by UV/SPC and by UV/HO in Milli-Q water were similar. Variation of the BPA degradation rates in the presence of radical quenchers, tert-butanol and phenol, suggested that both CO and HO contributed to the degradation of BPA in UV/SPC. Second order rate constant of CO towards BPA ( [Formula: see text]  = 2.23 × 10 M s) and steady state concentrations of CO ( [Formula: see text]  = 2.3 × 10 M) and HO ( [Formula: see text]  = 1.82 × 10 M) in UV/SPC were determined with competition kinetics at 1 mM SPC and pH 8.5. The high [Formula: see text] observed in UV/SPC compensated for the smaller [Formula: see text] compared to [Formula: see text] and the consumption of HO making the degradation rate of BPA in UV/SPC comparable to that in UV/HO. Detailed studies on identification of transformation products (TPs) of BPA in UV/SPC revealed that phenol ring and isopropylidene bridge were the main reactive sites of BPA. Degradation pathways were proposed accordingly. The results of kinetic and mechanistic studies provide better fundamental understanding of the degradation of BPA in UV/SPC and HCO&CO impact on BPA degradation by HO-AOPs. This also demonstrates potential for CO based water purification technologies.