Performance of ozonation on bisphenol a degradation: Efficiency, mechanism and toxicity control

In this study, the degradation of bisphenol A (BPA) by ozonation was studied systematically by investigating the effects of different factors, including ozone dosages (0.25–1.50 mg/L), temperatures (10–50°C), initial solution pH (3.0–11.0) and interfering ions. The reaction kinetics were analyzed at the same time. In addition, the generation of intermediates was analyzed and the possible mechanism was proposed by combining with the density functional theory (DFT) calculation. At last, the variation and controlling effect of toxicity was also evaluated. The results showed that ozonation had a stronger degrading ability of BPA (1.0 mg/L). A complete removal efficiency was obtained within 10 min when dosing only 1.0 mg/L ozone. The BPA degradation reactions were well fitted with pseudo-second-order kinetics and could well adapt with the wide range of pH (3.0–9.0), during which over 91% removal of BPA was achieved. The indirect pathway by •OH oxidation was proved mainly responsible for BPA degradation by the scavenging and electron paramagnetic resonance experiments. HCO₃⁻, NH₄⁺ and humic acid showed a certain inhibiting effect. Fe³⁺ and Cu²⁺ played a catalytic role on BPA degradation. The DFT calculation has identified that the active regions of BPA was focused at C6, C4, C5 and C1 in terms of radical and electrophilic attack. Thus, combining the results of DFT with GC/MS-MS detection, two degradation pathways of BPA were proposed. Toxicity evaluation showed that, due to the generation and accumulation of more toxic intermediates, values of T% had a sharp increase at initial stage. However, with ozone dosage increasing to 1.50 mg/L, the toxicity could be effectively controlled much lower (5%) than BPA itself (49%).