The influence of the UV/chlorine advanced oxidation of natural organic matter for micropollutant degradation on the formation of DBPs and toxicity during post-chlorination

Abstract

This study compares the influences of UV/chlorine and UV/H2O2 advanced oxidation of natural organic matter at the equivalent degradation of two model micropollutants on the formation of disinfection by-products (DBPs) and toxicity during post-chlorination. At 90% degradation of carbamazepine, the UV/chlorine advanced oxidation process (AOP) at pH 6.0 (3.0 mg/L chlorine and 280 mJ/cm2) resulted in comparable yields of dichloroacetic acid, trichloroacetic acid, chloroform, chloral hydrate, dichloroacetonitrile, trichloropropanone and total organic chlorine (TOCl) during the post-chlorination, compared to the UV/H2O2 AOP (8.0 mg/L H2O2 and 280 mJ/cm2). The UV/chlorine AOP increased the chloroacetic acid yields by 28–43% at pH 7.0 and 8.0. The cytotoxicity with the UV/chlorine AOP was 32% lower than with the UV/H2O2 AOP, however, the genotoxicity was similar. At the 90% degradation of atrazine, the UV/chlorine AOP (6.0–13.9 mg/L chlorine and 750–1000 mJ/cm2) increased the chloroacetic acid yields by 35–81% but did not increase the yields of other four known DBPs and TOCl, compared to the UV/H2O2 AOP (8.0–12.9 mg/L chlorine and 750–1000 mJ/cm2). The cytotoxicity and genotoxicity with the UV/chlorine AOP at pH 6.0 were 22–27% lower than those with the UV/H2O2 AOP, likely due to the selective destruction of the precursors of cytotoxic and genotoxic DBPs by RCS. The TOCl yields were positively correlated to the decreases in the specific UV absorbance at 254 nm and humic-like fluorescence. The TOCl yields exhibited a linear relationship with the genotoxicity (R2 = 0.81) but were weakly correlated with the cytotoxicity (R2 = 0.40). Although the UV/chlorine AOP increases the formation of some DBPs under certain circumstances, compared to the UV/H2O2 AOP, it does not enhance the genotoxicity and even decreases the cytotoxicity.