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  Characterizing the Effect of Chlorine and Chloramines on the Formation of Biofilm in a Simulated Drinking Water Distribution System (46 pp, 504 KB) (EPA/600/R-01/024) September 1999

Drinking water treatment in the United States has played a major role in protecting public health through the reduction of waterborne disease. However, carcinogenic and toxic contaminants continue to threaten the quality of surface and ground water in the United States. The passage of the Safe Drinking Water Act of 1974 and the subsequent amendments reflect this concern.

To meet the requirements of the Safe Drinking Water Act and its amendments, some maximum contaminant levels (MCLs) promulgated under the Act shall be met at the consumer’s tap. Therefore, the entire distribution system should be included when considering compliance with the Act. The Surface Water Treatment Rule, which was promulgated under the Act, requires that a detectable disinfectant be maintained at representative locations in the distribution system to provide protection from microbial contamination and to maintain water quality in the distribution system.

One aspect of maintaining water quality in drinking water distribution systems is controlling biofilm on distribution system pipe walls. Investigators have demonstrated the occurrence of high concentrations of bacteria in tubercles that exist in water mains, especially unlined cast iron mains, and on various types of pipe surfaces. A study was conducted jointly by EPA and the University of Nancy in France to examine the control of microorganisms in treated water and on the pipe walls. A special pilot facility was constructed in which finished water from parallel water treatment pilot plants was discharged into pipe loops that contained sample tap locations to facilitate biofilm sampling.

The facility was used to compare the effects of post-chlorination and post-chloramination on the concentration of microorganisms in the bulk phase and on the pipe wall. The analysis used in this study characterizes these effects as measured by direct count epifluorescence and culture techniques. It found that chlorine is as effective or more effective as chloramine in reducing the concentration of microorganisms in the bulk phase and in controlling biofilm on the pipe wall.


Robert M. Clark

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