Degradation of chloroquine phosphate during UV/H2O2 process: Performance, kinetics, and degradation pathways

Residues of chloroquine phosphate (CQP) in the aquatic environment pose a potential hazard to aquatic organisms and human health. Herein, the degradation kinetics and pathways of CQP during ultraviolet/hydrogen peroxide (UV/H2O2) process were investigated. Results demonstrated that UV/H2O2 process exhibited the highest performance for CQP degradation compared to the single UV or H2O2 process. The second-order rate constants of CQP with hydroxyl radicals were determined as 8.9x109-1.2x1010 M-1 s-1 at pH 4.8-10.8. With the increase of H2O2 dosage from 0.2 to 3.0 mM, the degradation rate constant of CQP firstly improved from 0.0164 to 0.1267 min-1 and then slightly reduced to 0.1104 min-1 at 6.0 mM. The degradation efficiency of CQP by UV/ H2O2 was significantly promoted at pH 4.8. Cl- and HCO3- showed the unobvious effects on the CQP degradation. Meanwhile, a kinetic model was established to simulate the evolution of CQP and various reactive species during UV/H2O2 process. The trend of predicted values of CQP degradation obtained from model simulation were well compared with experimental values. According to the identified intermediates of CQP degradation, the possible degradation pathways of CQP were proposed, which mainly involved N-deethylation, C-N bond cleavage, hydrogen abstraction, and N-oxidation. The aquatic toxicity of CQP degradation products was reduced relative to CQP, while the developmental and mutagenic toxicities of some intermediates were higher than CQP. Moreover, the economic consumption of UV/H2O2 treatment of CQP was determined under varied H2O2 concentrations. In general, UV/H2O2 process may constitute an effective option for treating CQP-contaminated water.