The role of carbonate radicals on the kinetics, radical chemistry, and energy requirement of UV/chlorine and UV/H_2O_2 processes

摘要

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 center dot, Cl center dot, ClO center dot, Cl-2(-center dot), and CO3-center dot with carbamazepine (CBZ) were fitted as 1.3 x 10(9), 1.9 x 10(9), 1.8 x 10(6), 1.1 X 10(5), and 4.5 x 106 M-1 s(-1), respectively. Based on the model, we investigated the significant impact of bicarbonate (HCO3-) and subsequently generated carbonate radical ( CO3-center dot) 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 center dot, Cl center dot, ClO center dot, Cl-2(-center dot), and CO3-center dot to CBZ degradation in UV/H2O2 and UV/chlorine processes in the absence/ presence of HCO3- were investigated. HO center dot and CO3-center dot make comparable contributions to CBZ degradation in UV/H2O2 process in the presence of HCO3- (2 mM), while ClO center dot 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-center dot influence the reactions and mechanism of UV/H2O2 and UV/chlorine processes, and have higher impact on UV/H2O2 process. (C) 2021 Elsevier Ltd. All rights reserved.