Photolysis of aqueous free chlorine species (NOCI and OCI-) with 254 nm ultraviolet light

University of Alberta, Edmonton, Alberta, Canada
Journal of Environmental Engineering and Science (Impact Factor: 0.67). 05/2007; 6(3):277-284. DOI: 10.1139/S06-052


The quantum yields of the UV photolysis of free chlorine (OCl− and HOCl) at 254 nm were measured in a series of batch reactor experiments from pH 5 to 10 and at various concentrations. When the concentration of free chlorine is low (3.5 mg Cl/L) to moderate (70 mg Cl/L), the quantum yields of HOCl and OCl− are 1.0 ± 0.1 and 0.9 ± 0.1, respectively. When the concentration increases to higher levels (>70 mg Cl/L), the quantum yield of HOCl photolysis increases significantly, whereas the quantum yield of OCl − photolysis is essentially independent of concentration. In addition, based on the experimental results obtained in this research, a mathematic model was developed that can be used for the prediction of the quantum yield for the UV photolysis of free chlorine at 254 nm. The quantum yields predicted by this model agree very well with the measured data. Also, the dependence of free chlorine decomposition on the fluence (UV dose) and the effect of water quality on the quantum yield of free chlorine species were investigated in this research.

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    • ". Time profiles of MPT byproducts in (a) deionized water, (b) surface water, (c) tap water, and (d) filtered water during the UV/chlorination reaction (experimental conditions; [MTP]0 = 100 ng/L, [Cl2] = 5 mg/L, UV–C intensity = 4.4 mW/cm 2 , pH 7, 20 • C). (Fig. 4(d)). Feng et al. [28] proposed two chain reactions related to DOM in water by OH and Cl radicals during the UV/chlorination reaction (Eqs. (14)–(17)). "
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