Application of Nitrate-Nitrite and Atrazine Actinometry for Determination of UV Fluence in Drinking Water and Reuse Applications

摘要

The use of nitrate-nitrite as a chemical actinometer for the determination of UV fluence during drinking water treatment has recently been reported. In wastewater treatment, UV radiation is used for disinfection as well as for destruction of trace organic compounds susceptible to direct photolysis, such as N-Nitrosodimethylamine. A common measure of UV radiation is expressed as fluence in units of mJ/cm~2, which may be difficult to measure in pilot-scale or full-scale UV reactors, where spiking a chemical at sufficient concentration prior to UV treatment is impractical. Actinometry provides a direct measure of UV fluence without knowledge of precise geometrical configuration of the UV reactor. Nitrate ion is also commonly present in reclaimed waters, allowing the determination of UV fluence. Atrazine, a well characterized actinometer may also be present in reclaimed waters and provide an alternative to the nitrate system. This study compared the measurements of UV fluence by nitrate-nitrite, atrazine, and radiometry in natural and reclaimed waters. The formation pathway of nitrite during UV exposure of nitrate ion is complex and can depend on various water quality parameters, such as dissolved organic matter (DOM) concentration and other constituents that react with intermediate radicals produced during photolysis of nitrate. In this study we examined the effects of DOM on the nitrite yield and discuss its practical uses for determination of UV fluence at disinfection and advanced oxidation doses. Our preliminary experiments show an enhanced nitrite yield in reclaimed waters where DOM is typically at higher concentration, which indicates that nitrate should be used with caution for determination of UV fluence. The effects of DOM on atrazine photolysis were negligible as compared to the nitrate system and atrazine provides a more robust alternative for determination of various UV fluence in reclaimed water treatment.