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Ultraviolet Irradiation + Ozone


A number of organic micropollutants cannot be removed by conventional drinking water treatment alone. Chemical oxidants such as ozone (O3) are able to oxidize a wide range of these substances; however even these technologies are ineffective in removing number of emerging contaminants. Advanced oxidation processes such as O3/H2O2, UV/H2O2 and UV/ O3 can be used to remove persistent organic contaminants in drinking water treatment. Some of these contaminants include pesticides, gasoline additives, taste and odor compounds, and pharmaceutical compounds.

See the Ozone and the Ultraviolet Irradiation overviews for descriptions of those treatment processes. In the UV/ O3 process, ozone is applied ahead of UV so that the UV irradiates water with dissolved ozone.

In the UV/O3 process, dissolved ozone absorbs UV light. The photolysis reaction of ozone reacting with UV light forms hydroxyl radicals (·OH), which are very strong oxidants. This photolytic reaction is effective in lowering dissolved organic matter (measured as TOC). TOC removal by UV light or ozone alone is negligible while substantial removal can be expected for UV/O3 processes. In the presence of UV radiation, the initial ozonation rate of organic substances is increased 10 to 10,000 times. This process has been shown to be capable of mineralizing up to 50% of the total organic matter and thus is capable of oxidizing disinfection by-products precursors. This process can be used to oxidize many persistent compounds that are hard to remove such as pesticides and other organic refractory compounds. This technology can be considered viable complement to conventional treatment in drinking water; however, the process is still not fully understood from a chemical viewpoint and cannot yet be optimized for engineering applications.

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