Production of reactive species during UV photolysis of chlorite for the transformation of micropollutants in simulated drinking water

Chlorite (ClO2-) is a dominant product during chlorine dioxide (ClO2) disinfection. This study investigated the mechanism for UV photolysis of ClO2- and the production of reactive species. The apparent quantum yield of ClO2- is 1.21 similar to 1.29 mol einstein- 1 by UV photolysis at 254 nm at pH 7. UV photolysis primarily transforms ClO2- to ClO2, and then to HOCl/OCl-, ClO3- and Cl-. Both ClO2 and HOCl/OCl- are major reactive chlorine species, which maximum concentrations are 8.4 and 11.0 & mu;M, respectively, at 50 mu M ClO2- and pH 7. Meanwhile, hydroxyl radical (HO circle) and chlorine atom (Cl & BULL;) are also formed with the concentrations of 3.1 x 10(-14) and 7.8 x 10-15 M, respectively. The abatement of structurally diverse pharmaceuticals and personal care products (PPCPs) by UV/ClO2- is compound specific, depending on their reactivity toward ClO2, HOCl/OCl- and HO circle. The first order rate constants of PPCPs primarily relying on ClO2 and HOCl/OCl- range from 0.043 to 1.533 min(- 1) and from 0.240 to 2.071 min (-1), respectively, while those relying on HO circle range from 0.012 to 0.020 min 1. As for phenolics, phenol and bisphenol A (BPA) are completely removed within 15 min and ClO2 plays a dominant role. Natural organic matter (NOM) inhibits the degradation of phenol and BPA in UV/ClO2-, while chloride and bicarbonate shows slight impacts. The transformation pathways of BPA in the UV/ClO2- system initiate with electron transfer, and then hydroxylation, carbonylation, chlorination, and coupling reactions. The formation of disinfection byproducts (DBPs) and total organic chlorine (TOCl) is not significant during UV/ClO2- treatment, and over 90% TOCl are unknown DBPs. This study improves the understanding of the water chemistry of UV photolysis of ClO2-.

Automated summary

This study investigated the mechanism of UV photolysis of ClO2- and the production of reactive species. It was found that UV photolysis primarily transforms ClO2- to ClO2 and then to HOCl/OCl-, ClO3-, and Cl-. Both ClO2 and HOCl/OCl- are major reactive chlorine species. Additionally, hydroxyl radical (HO·) and chlorine atom (Cl·) are also formed.