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Inactivation of Microbial Indicators by the Sequential Chlorination Process

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Wastewater treatment plants commonly disinfect with chloramines, but recent research has shown that chloramines can form the disinfection byproduct N-nitrosodimethylamine (NDMA). Previous plant-scale tests with fully nitrified effluents demonstrated that adding free chlorine before chloramines (sequential chlorination) reduced NDMA concentrations and consistently complied with total coliform standards. However, California regulations for recycled water require that alternatives to chloramination at 450 mg Cl2-min/L demonstrate 5-log inactivation of poliovirus or F-specific bacteriophage MS2 (MS2). To make this demonstration, bench-scale experiments testing sequential chlorination of these microbial indicators in fully nitrified secondary effluent samples were conducted. Sequential chlorination successfully achieved >5-log inactivation of both poliovirus and MS2 at lower contact times and/or chlorine residuals than currently required for chloramination. Investigation of the individual disinfection steps showed that free chlorine provided more disinfection than chloramines, and that MS2 was highly resistant to chloramine disinfection.

Document Type: Research Article


Publication date: 2008-01-01

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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