Comparison of the UV/chlorine and UV/H2O2 processes in the degradation of PPCPs in simulated drinking water and wastewater: Kinetics, radical mechanism and energy requirements

The degradation of pharmaceuticals and personal care products (PPCPs) by the UV/H2O2 and UV/chlorine processes was compared at practical concentrations in simulated drinking water and wastewater. In pure water, the UV/chlorine process performed better than the UV/H2O2 process for the degradation of 16 PPCPs among the investigated 28 PPCPs under neutral conditions. Interestingly, the UV/chlorine approach was superior to the UV/H2O2 approach for the removal of all PPCPs in simulated drinking water and wastewater at the same molar oxidant dosage. The radical sink by oxidants and/or H2O was 2–3 orders of magnitude higher in UV/chlorine than UV/H2O2 in pure water. Thus, the UV/chlorine process was less affected by the water and wastewater matrices than UV/H2O2. In UV/chlorine, the concentration of ClO• was calculated to be ∼3 orders of magnitude greater than that of HO• in pure water, and the reactivities of ClO• with some PPCPs were as high as > 108 M−1 s−1. ClO• was mainly scavenged by the effluent organic matter (EfOM) with a rate constant of 1.8 × 104 (mg L−1)−1 s−1 in wastewater. Meanwhile, secondary radicals such as Br•, Br2•-, ClBr•- and CO3•- further contributed to PPCP degradation by the UV/chlorine process in wastewater, whose concentrations were at least 2 orders of magnitude higher than that in UV/H2O2. Compared with the UV/H2O2 process, the UV/chlorine process saved 3.5–93.5% and 19.1%–98.1% electrical energy per order (EE/O) for PPCP degradation in simulated drinking water and wastewater, respectively.