The Cultivation, Characterization, and Detection of Bacteria that Biodegrade Haloacetic Acids in Drinking Water Distribution Systems
Principal Investigators: Raymond Hozalski, Associate Professor, and Tim LaPara, Associate Professor, Department of Civil Engineering, University of Minnesota
USGS-WRRI 104B/ CAIWQ Competitive Grants Program
March 2008 - February 2009
The disinfection of drinking water and wastewater is needed for the protection of public health. Typically, chlorine is used to disinfect drinking water and wastewater because of its effectiveness and low cost, but chlorination also leads to the formation of disinfection by-products (DBPs), the most common of which are trihalomethanes (THMs) and haloacetic acids (HAAs). Many of these compounds are known or suspected carcinogens and some have suggested other deleterious effects such as increased risk of spontaneous abortion. Numerous full-scale monitoring campaigns have demonstrated that THM levels generally increase with residence time in water distribution systems. Conversely, HAAs have been observed to decrease along the distribution systems in some cases. Based on these reports in the technical literature, the principal investigators hypothesized that HAAs (unlike THMs) would be biodegradable within drinking water distribution systems when the concentration of residual disinfectant declined to a level that permitted bacteria to become established (typically < 0.5 mg/L as Cl2). This HAA biodegradation is potentially beneficial because it would reduce the exposure of some water consumers to these compounds of concern. Thus, research is needed to understand the fate of HAAs in distribution systems and the role of bacteria in determining their fate. Relatively little information on the aerobic biodegradation of HAAs and even less information on the biodegradation of HAAs at the very low concentrations that occur in drinking water distribution systems (i.e., -10-100 parts per billion). In fact, most of what we know about HAA-degrading bacteria is based on studies of soil and wastewater systems at relatively high concentrations of HAAs, such as those found at spill sites. The long term goal of our research, therefore, has been to better understand the biodegradation of HAAs in drinking water distribution systems so that these processes can be optimized. During our preliminary research, we have determined that the HAA-degrading bacteria in drinking water distribution systems are substantially different than those previously isolated, thus complicating the cultivation-independent analysis of these important bacteria. The goals of the proposed project, therefore, are to isolate and to characterize HAA-degrading bacteria within drinking water distribution systems.