Investigation of clofibric acid removal by UV/persulfate and UV/chlorine processes: Kinetics and formation of disinfection byproducts during subsequent chlor(am)ination

Abstract

This study investigated the UV/persulfate (UV/PS) and UV/chlorine processes as alternative method for the removal of clofibric acid (CA). The formation of disinfection byproducts (DBPs) during subsequent chlor(am)ination was also evaluated. The degradation of CA followed the pseudo-first order kinetics. The second-order rate constants of CA with SO4−, OH and Cl were respectively determined as kSO4-,CA=(1.73±0.01)×109M−1s−1, kOH,CA=(2.72±0.08)×109M−1s−1 and kCl,CA=(9.76±0.15)×1010M−1s−1. The degradation rate constant increased with increasing oxidant dosage in UV/PS and UV/chlorine processes. The degradation rate constant was found to be the highest at pH 9 and decreased dramatically at pH 11 in UV/PS process. For UV/chlorine, the rate constant continuously decreased with increasing pH from 3 to 11. Presence of HCO3− and Cl− had different effects (promotion and/or inhibition) on CA degradation in both processes. An inhibition effect was observed in the presence of NOM for the two UV-based processes. The higher CA removal in real water suggested the two processes were suitable for treating water containing CA, and the UV/chlorine was more cost-effective than UV/PS based on the total cost of electrical energy. Compared with the chlor(am)ination of CA, the UV/PS and UV/chlorine pre-oxidation significantly impacted the DBP formation during subsequent chlor(am)ination, which indicated the application of the two UV-based processes needs to be carefully balanced against the downstream effect on DBP formation.