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What is Behind Chlorine Residuals? - Two Plants with Two Strategies in the Same City

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Chlorination is the oldest and the most common disinfection method used by wastewater treatment facilities. It has been proven to be an effective disinfection process providing a reliable, high germicidal efficiency. One of the advantages of chlorination is that chlorine residual can be used as a process control indicator. However, chlorine residual is impacted by many factors, such as ammonia nitrogen and organic nitrogen. Different levels of ammonia nitrogen and organic nitrogen existing in the untreated water will significantly influence chlorine residual species. In this paper, the chlorination process at two large municipal nitrification plants was studied through a series of field and bench tests. It was found that a high organic nitrogen content above 2 mg/l could strongly compete with limited available ammonia nitrogen, < 0.5 mg/l, to form organic chloramines which accounted for the major fraction of the total chlorine residual. This made the total residual measurement a poor indicator for the process germicidal efficiency. In this case, oxidation-reduction potential is a good alternative process control parameter. Conversely, a low organic nitrogen level, around 1 mg/l, showed little effect on the chlorine residual species. A great portion of the chlorine residual was monochloramines, dichloramines and free chlorine. Thus, the chlorine residual measurement still can be used as an effective indicator for chlorination process.

Keywords: chlorination; disinfection; organic chloramines; organic nitrogen

Document Type: Research Article


Publication date: January 1, 2009

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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 These proceedings are not peer reviewed.

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