Organic contaminants, such as pharmaceuticals and personal care products, are ubiquitous in drinking water sources, but are not removed by conventional drinking water treatment processes. One approach to remove organic contaminants in drinking water is the use of advanced oxidation processes (AOPs). AOPs produce hydroxyl radical, an extremely powerful oxidant that is capable of degrading most organic compounds. Implementing AOPs often requires costly retrofits, and is often not feasible within the physical confines of existing drinking water plants. Our research focuses on chlorine (i.e., hypochlorous acid) photolysis, which generates hydroxyl radical, chlorine radical, and ozone. Chlorine photolysis is less expensive to implement than many commonly used AOPs because it utilizes existing treatment plant infrastructure. This study seeks to identify the optimal conditions for chlorine photolysis as an AOP by combining laboratory experiments with kinetic modeling. Radical production was evaluated from pH 6-9 with irradiation at 254, 311, and 356 nm. The production of hydroxyl and chlorine radicals was determined using nitrobenzene and benzoate as probe compounds. The production of reactive species is dependent on both the solution pH and on the wavelength of the irradiation source. For example, the rate of hydroxyl radical production is higher under acidic conditions using short photolysis wavelengths due to differences in the quantum yield and molar absorptivity of hypochlorous acid versus hypochlorite (pK<sub>a</sub> = 7.5). The laboratory results were used to validate a kinetic model that can be used to predict reactive species production as a function of pH and irradiance conditions (i.e., wavelength and light intensity).

Effect of solution conditions on reactive oxidant production during chlorine photolysis

253rd National Meeting (2017)

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