The role of carbonate radicals on the kinetics, radical chemistry, and energy requirement of UV/chlorine and UV/H2O2 processes

Abstract

Quantitative insight into the HCO3−-dependent degradation kinetics is critical to improve understanding of the UV processes for the most-cost effective application. In this study, we developed a kinetic model to precisely predict the kinetics in UV/H2O2 and UV/chlorine processes. The second-order rate constants of HO, Cl, ClO, Cl2−, and CO3− with carbamazepine (CBZ) were fitted as 1.3 × 109, 1.9 × 109, 1.8 × 106, 1.1 × 105, and 4.5 × 106 M−1 s−1, respectively. Based on the model, we investigated the significant impact of bicarbonate (HCO3−) and subsequently generated carbonate radical (CO3−) on CBZ degradation, radical chemistry, and energy requirement of UV/H2O2 and UV/chlorine processes. The presence of HCO3− inhibited CBZ degradation in UV/H2O2 and UV/chlorine processes to different degree. Contributions of HO, Cl, ClO, Cl2−, and CO3− to CBZ degradation in UV/H2O2 and UV/chlorine processes in the absence/presence of HCO3− were investigated. HO and CO3− make comparable contributions to CBZ degradation in UV/H2O2 process in the presence of HCO3− (2 mM), while ClO is always the main contributor at various HCO3− concentration of 0–2 mM. Furthermore, the presence of HCO3− in both processes increased the corresponding EE/O, when CBZ was degraded by an order of magnitude. Overall, HCO3− and CO3− influence the reactions and mechanism of UV/H2O2 and UV/chlorine processes, and have higher impact on UV/H2O2 process.