But Kroll and his colleagues have confirmed in their study that the stability of the monochloramine may have its drawbacks as well. Treatment with free chlorine, because it is more reactive, can lead to rapid degradation of chemical threats as well as early detection of contamination. As it reacts with a contaminant, chlorine levels in the water drop. Many municipalities use chlorine levels as indicators of possible contamination.
Monochloramine also requires more time to kill microbial contaminants in water. This should not be an issue in treatment plants, as water in monochloramine facilities can be held longer. "In the event of contamination of the water supply after it leaves the treatment plant, though, monochloramine has the potential as being not as effective as chlorine, since there is little control over the contact time," says Kroll.
Kroll is not recommending that system that have already switched to monochloramine switch back. Instead, he wants water quality professionals to recognize that if they have a monochloramine system, they can no longer rely solely on a sudden drop in disinfectant levels to alert them to a potential contaminant. He also recommends that, where possible, some level of free chlorine should be kept in the system.
And if a municipality has a free chlorine-based system, provides water to a high-profile target such as a military base, and are considering the switch to monochloramine, they may want to consider other methods of controlling disinfection byproducts to help comply with EPA regulations.
"The findings in these studies have significant repercussions as to the safety and security of our nations water supplies," says Kroll.
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Contact: Jim Sliwa
jsliwa@asmusa.org
202-942-9297
American Society for Microbiology
1-Mar-2007