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UBC Theses and Dissertations

The use of 185 nm radiation for drinking water treatment Furatian, Laith

Abstract

The treatment of water via 185 nm radiation allows for the oxidative degradation of trace organic contaminants without the need for chemical addition. Critical information required for the practical application of such a process has been lacking. Carbamazepine was determined to be an ideal probe compound for study of the 185 nm regime due to negligible direct photolysis at 254 nm. An increase in probe degradation rate due to 185 nm is observed with increasing temperature when water is the only significant absorber of photons. A comparison with the temperature dependence of the 254 nm - H₂O₂ process is made and a fundamental explanation proposed. Experimental evidence reveals that probe degradation rate is strongly influenced by anionic composition at environmentally relevant concentrations, particularly chloride. Evidence for the role of the chlorine radical is obtained by kinetic studies involving select probes, radical scavengers, and ionic strength. Interactions between the major organic and inorganic solutes indicate that resulting degradation kinetics are highly sensitive to the composition of the water matrix, a fact that has been neglected from the literature. A method to quantify molar absorption coefficients is developed that is not prone to errors due to stray radiant energy or wavelength inaccuracies. A method to quantify the 185:254 nm output of a low pressure mercury lamp is presented with results in agreement with values reported in the literature. In addition to the hydroxyl radical (*OH), other radical species such as chlorine (C1*) and sulphate (SO₄*¯) are proposed to be involved in oxidative degradation of trace organics in the 185 nm regime. This suggests that the degradation rate of a given target contaminant depends on the composition of the water matrix, the second-order rate constants with the relevant radicals, and the relative reaction rate constants of the target and the matrix.

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