Evaluate UV-LEDs for UV/Chlorine Advanced Oxidation

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Ultraviolet light-emitting diodes (UV LEDs) are fast becoming an attractive water treatment tool to disinfect the microorganisms and to remove the micropollutants. Different from the conventional mercury lamps which are currently adopted by the water treatment plants, they are compact, mercury-free, and can be turned on and off instantly. As such, they have the potential to replace conventional UV lamps. One of the more novel applications for LEDs in water treatment is in advanced oxidation processes (AOPs). In UV-based AOPs, UV light is used to split chemicals into reactive 'radical' species that can quickly destroy pollutants in water. To-date, most UV-based AOPs employ mercury lamps to generate the UV light. However, among the different known AOPs, UV/Cl2, which uses UV photons to split chlorine into radicals, may be particularly well-suited to using LEDs as the light source. This is because chlorine shows a high UV absorptivity at the wavelengths where UV LEDs can produce light more efficiently than conventional mercury lamps. Unfortunately, there is no information on the performance of UV LEDs relative to mercury lamps in the context of micropollutant removal by UV/Cl2, nor is there information on the byproducts that may be generated and whether or not they may be toxic. For example, chlorate, is known to form from radicals produced during UV/Cl2 processes that employ conventional UV lamps, and the government of Ontario currently regulates chlorate at 1 mg/L in drinking water due to its toxicity. It is hypothesized that the specific radicals leading to chlorate may be less predominant when using LEDs due to their low intensity and low energy UV output. This will be the first study evaluating the UV/Cl2 AOP by quantifying the competitiveness of LEDs relative to low and medium pressure mercury lamps on the basis of (1) the control of micropollutants and (2) the production of chlorate and other relevant byproducts.