Study Raises Questions About Monochloramine's Effectiveness in Protecting Drinking Water

From a security standpoint, traditional chlorination may be more effective than treatment with monochloramine. This is the finding of what may be the most extensive comparison of two common disinfectants used by municipal water systems, researchers said.

"We have found something that is not necessarily a surprise but has important implications. These are considerations that water quality professionals should take into account if they have switched or are considering switching to a monochloramine disinfection system," says Dan Kroll, chief scientist at Hach Homeland Security ( in Loveland, Colo., and lead researcher on the study, presented on March 1 at the American Society for Microbiology (ASM) Biodefense and Emerging Disease Research Meeting.

As part of a recent endeavor to develop a system for online, continuous monitoring of drinking water distribution networks, Kroll and his colleagues, in coordination with the U.S. Army Corps of Engineers, studied the interactions of various potential waterborne threat agents (both biological and chemical) with different levels of either free chlorine or monochloramine present. They tested dozens of potential hazards, such as pesticides, disease-causing bacteria and chemical warfare agents.

The researchers discovered that not only is monochloramine less reactive against a number of chemical threats, it also is slightly less efficient than free chlorine, requiring more time to kill bacterial contaminants.

Scientists have long known that monochloramine is a more stable compound, and that is part of the reason it is becoming more popular as an alternative to chlorine in municipal water systems, the researchers said. Free chlorine has traditionally been the disinfectant of choice for municipal water systems throughout the 20th century, but it has some drawbacks. It can react with organic materials in drinking water to produce chlorine byproducts. Some of these byproducts are considered carcinogenic and their levels in drinking water are regulated by EPA.

Treatment with free chlorine, because it is more reactive, can lead to rapid degradation of chemical threats and 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.

Kroll and his colleagues said their study confirms that monochloramine may have its drawbacks as well. "In the event of contamination of the water supply after it leaves the treatment plant, monochloramine has the potential as being not as effective as chlorine, since there is little control over the contact time," Kroll said.

Kroll is not recommending that systems using 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.

Additionally, if a municipality has a free chlorine-based system, provides water to a high-profile target such as a military base and is considering the switch to monochloramine, operators 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," Kroll said.

This article originally appeared in the 03/01/2007 issue of Environmental Protection.

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