Oxidation efficiency and inorganic oxyhalide by-product formation during UV photolysis of chlorine and bromine species

Abstract

Since the treatment of emerging contaminants by chlorine or UV alone become challenging, advanced oxidation processes (AOPs) are being studied and used. Chlorination is one of conventional oxidation processes and widely used in water treatment and UV treatment can be easily established. Since the bromine species is also relevant for chlorination of bromide-containing water, a combination of chlorine and bromine oxidants with UV photolysis (i.e., UV/chlorine and UV/bromine) has been increasingly used as a new AOP for various water treatment applications such as drinking water treatment, swimming pool, and aquaculture. Photolysis of chlorine or bromine produce radical species (i.e., ·OH, Cl·, or Br·) which can produce inorganic by-products such as chlorite, chlorate and bromate through the reaction with chlorine or bromine species. The specific investigation topics included: (i) apparent and intrinsic quantum yields in absence and presence of tert-butanol and methanol as the radical scavenger, (ii) degradation rates and efficiency of organic solutes, (iii) rate constants for the reaction of ·OH and Cl· with HOCl and OCl−, (iv) quantum yields and pathways of XO3 − formation, and (v) kinetic model development and application.