Identification of produced powerful radicals involved in the mineralization of bisphenol A using a novel UV-Na2S2O8/H2O2-Fe(II,III) two-stage oxidation process

A two-stage oxidation (UV-Na2S2O8/H2O2-Fe(II,III)) process was applied to mineralize bisphenol A (BPA) at pHi (initial pH) 7. We take advantage of the high oxidation potential of sulfate radicals and use persulfate as the 1st-stage oxidant to oxidize BPA to less complex compounds (stoichiometric ratio: [S2O82−]0/[BPA]0 = 1). Afterwards, the traditional photo-Fenton process was used to mineralize those compounds to CO2. To the best of our knowledge, this is the first attempt to utilize the two processes in conjunction for the complete degradation of BPA. During the 2nd-stage reaction, other oxidants (H2O2 and Iron alone) were also employed to observe the extent of enhancement of photo-Fenton. Further, qualitative identification of both hydroxyl and sulfate radicals was performed to evaluate their dominance under different conditions. The BPA degradation in this UV/persulfate process formulated a pseudo-first-order kinetic model well, with a rate constant of approximately 0.038 min−1 (25 °C), 0.057 min−1 (35 °C), and 0.087 min−1 (50 °C), respectively. The much lower activation energy (ΔE = 26 kJ mol−1) was further calculated to clarify that the thermal-effect of an illuminated system differs from single heat-assisted systems described in other research. Final total organic carbon (TOC) removal levels of BPA by the use of such two-stage oxidation processes were 25-34%, 25%, and 87-91% for additional Fe(II,III) activation, H2O2 promotion, and Fe(II,III)/H2O2 promotions, respectively.