The degradation of 8 PPCPs in UV/chlorine: Effect of chloride and sulfate ions and the role of radicals

Abstract

The degradation of 8 structurally diverse pharmaceuticals and personal care products (PPCPs) by UV/chlorine and the effects of Cl- and SO42- were systematically investigated. The 8 PPCPs are divided into 2 groups based on their stability under UV light. This is the first time the kinetic degradation of the 8 PPCPs in the presence of Cl- and SO42- have been intensively evaluated. The results showed that the high degradation rate of the PPCPs is attributed to their second-order rate constants towards radicals (i.e., •OH, and reactive chlorine species (RCS)). 0–500 mM Cl- enhanced kPPCPs, while this range of SO42- inhibited most of them (except in the case of ciprofloxacin (CIP)). An overview of the effect of 0–200 mM Cl-/SO42- on the degradation of micropollutants by different UV-based advanced oxidation processes (UV-AOPs) in previous studies indicates that Cl-/SO42- can cause varying effects on the degradation rate of pollutants (i.e., “increase”, “decrease”, or “no effect”), depending on the type of pollutant and the process. Cl-/SO42- did not change the trend of pH influence on the PPCPs degradation rates by UV/chlorine. Acidic and neutral conditions were favorable to the degradation of the PPCPs in all cases. Under three operating conditions (i.e., the control process, 500 mM Cl- and SO42-), [•OH]ss decreased considerably, but [Cl•]ss or ([Cl•]ss + [SO4•-]ss) slightly fluctuated when the pH was increased from 2.5 to 10.5. The synergistic effect of seawater and Cl-/SO42- significantly improved some kPPCPs, thereby, decreasing energy consumption.