Integrating Multiple Disinfectants UV, Ozone, and Chlorine Dioxide
The trend in drinking water regulations is to increase the requirements for pathogen inactivation while decreasing the concentration of disinfection byproducts (DBPs). The new 80 mgd Lake Pleasant Water Treatment Plant (WTP) takes an innovative approach to meeting future regulations and protecting public health by using six barriers for removal/inactivation of pathogens as well as six barriers for reducing DBP formation. This approach is similar to the European approach of using processes that produce a low-organics, biologically-stable finished water. The treatment process consists of preoxidation with chlorine dioxide, coagulation, ballasted flocculation and high-rate sedimentation, ozonation, biological filtration, adsorption on granular activated carbon (GAC), and disinfection with ultraviolet light (UV) and chlorine. While chlorine dioxide is used primarily for preoxidation of iron and manganese, and ozone is used primarily for taste-and-odor control, both will provide a disinfection barrier. The high rate sedimentation process and the granular media filtration both will provide a disinfection barrier by physically removing pathogens. The UV system will be used for inactivation of Cryptosporidium and chlorine will be used for primary disinfection of Giardia and viruses and for secondary disinfection. Also, the integrated disinfection and other treatment processes create a multiple barrier to reduce DBP formation. Coagulation, biological filtration, and GAC adsorption will each remove DBP precursors, which will reduce the chlorinated DBPs. And delaying chlorination until the very end of the treatment process will further reduce chlorinated DBPs. Although chlorine dioxide and ozone have their own DBPs, the chlorite from the chlorine dioxide will be removed with ferrous chloride and bromate formation during ozonation will be controlled with low ozone doses and with hydrogen peroxide.
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Document Type: Research Article
Publication date: 2005-01-01
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