Co-PIs: Tim LaPara (U. Minnesota), Anne Camper (Montana State U.), Simon Parsons (Cranfield U.), and Yuefeng Xie (Penn State U.-Harrisburg)
Funding agency: AWWA Research Foundation
Haloacetic acids (HAAs) are halogenated disinfection byproducts formed when chlorine is added to water. HAAs are potentially hazardous to human health and their levels in drinking water are currently regulated by the USEPA. Initial work in this area by the Hozalski research group began in 2001. Results from batch HAA biodegradation experiments demonstrated that HAAs can be biodegraded and serve as sole carbon and energy source at the low concentrations found in drinking water. Furthermore, bromoacetic acid was rapidly degraded under aerobic conditions by a chloroacetic acid-degrading enrichment culture, suggesting that the dehalogenase enzyme is relatively non-specific. We also determined the kinetics of HAA biodegradation over a range of concentrations including typical values for surface waters and treated drinking water. In addition, the bacteria in the HAA-degrading enrichment cultures were identified using molecular techniques (PCR-DGGE-DNA sequencing). These results were summarized in a journal article (McRae et al., Chemosphere , 2004).
The aforementioned results, obtained using enrichment cultures derived from wastewater activated sludge, lead to financial support from the AWWA Research Foundation to continue our research on HAA biodegradation using drinking water bacteria. The main goal of this research is to improve our understanding of HAA biodegradation and HAA-degrading bacteria in order to facilitate the development of models for predicting HAA fate in distribution systems, to better assess temporal and spatial variability in HAA exposure and to facilitate the development of HAA control strategies. This research involves a detailed investigation of the kinetics of HAA biodegradation, the organisms responsible for HAA biodegradation, and the diversity of dehalogenase genes involved. Enrichment cultures were established by inoculating with biomass from tap water, water distribution system biofilms, and pre-chlorinated granular activated carbon and supplying HAAs as sole carbon and energy source. Isolates were obtained by spread and streak plating on HAA-amended agar (Figure 1). We are developing a novel and highly sensitive method for detecting HAA-degrading bacteria in environmental samples using molecular techniques (quantitative PCR). In addition, we are collecting water and biofilm samples from a wide range of distribution systems to evaluate the prevalence of HAA-degrading bacteria. Kinetic models will be developed from the data generated in the HAA biodegradation experiments. The results of this work will improve our understanding of HAA fate in distribution systems and aid in the development of new treatment approaches for removing HAAs from water supplies.
Significant findings to date from this ongoing research are: (1) mixed cultures and isolates enriched from an oligotrophic drinking water environment demonstrated slower HAA degradation kinetics than mixed cultures and isolates enriched from wastewater activated sludge, (2) mixed cultures or isolates that can degrade chloroacetic acid are able to degrade bromoacetic acid and iodoacetic acid, and (3) a HAA-degrading methylobacterium was isolated from a water distribution system. The methylobacterium is especially intriguing for several reasons. First, it can grown on HAAs, while methylobacteria are known to grow on C1 compounds such as methanol. Furthermore, the organism does not contain either of the two known classes of haloacid dehalogenase genes (dehI and dehII), suggesting that it may contain a novel dehalogenase. Transposon mutagenesis will be used to attempt to identify and sequence the dehalogenase gene(s) in this bacterium. As a result of this project, we have assembled a rich and diverse collection of HAA-degrading isolates from a variety of environments including pipe wall biofilms, tap water, wastewater, and GAC filters. The results of this work should significantly improve understanding of HAA biodegradation, including kinetics, the organisms involved, and haloacid dehalogenase genes.
Questions? Contact Ray Hozalski at hozal001@umn.edu or (612)626-9650 or any of the co-PIs listed above.