Using UV/HO pre-oxidation combined with an optimised disinfection scenario to control CXR-type disinfection by-product formation.

The effects of UV/HO pre-oxidation or disinfection methods on the formation of partial disinfection by-products (DBPs) have been studied previously. This study assessed the effect of UV/HO pre-oxidation combined with optimisation of the disinfection method on the formation of six classes of CXR-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs), halonitromethanes (HNMs), and haloacetamides (HAMs). Experimental results showed that a simulated distribution system (SDS) in-situ chloramination or pre-chlorination followed by chloramination effectively decreased total CXR-type DBP formation by 51.1-63.5% compared to SDS chlorination, but little reduction in DBP-associated toxicity was observed. The dominant contributors to the calculated toxicity were HANs and HALs. UV/HO pre-oxidation was able to destroy the aromatic and dissolved organic nitrogen components of natural organic matter. As a consequence, THM, HAA, and HAL formations increased by 49.5-55.0%, 47.8-61.9%, and 42.0-67.1%, respectively, whereas HAN, HNM, and HAM formations significantly decreased by 52.1-83.6%, 42.9-87.3%, and 74.1-100.0%. UV/HO pre-oxidation increased total CXR-type DBP formation, during SDS chlorination, whereas SDS in-situ chloramination or pre-chlorination followed by chloramination of UV/HO-treated water produced lower total CXR-type DBPs than water without UV/HO pre-oxidation. Nevertheless, the DBP-associated toxicity of water with UV/HO pre-oxidation was substantially lower than the toxicity for water without UV/HO pre-oxidation, decreased by 24.1-82.7%. HALs followed by HANs contribute to major toxic potencies in UV/HO treated water. The best DBP concentration and DBP-associated toxicity abatement results were achieved for water treated by UV/HO coupled with in-situ chloramination treatment.