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Browsing by Subject "Disinfection byproducts"

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    Biodegradation of haloacetic acids in biofilters and water distribution systems: microbiology and modeling.
    (2011-07) Grigorescu, Alina Sabina
    There is concern over the potential deleterious health effects of haloacetic acids (HAAs) in drinking water and their removal is of great interest for water utilities. The overall goal of this research was to obtain more detailed information about the diversity of HAA-degrading bacteria and their corresponding dehalogenase (deh) genes in drinking water systems and other environments. This research further aimed to model the biodegradation of HAAs in drinking water systems, thus demonstrating that biodegradation could be exploited as a means to effectively remove HAAs during water treatment. A direct plating technique was used to isolate HAA degraders from different environments (river water, tap water and agricultural soil). The obtained isolates included several species that were not isolated in previous studies: Mycobacterium sp., Streptomyces sp., Stenotrophomonas sp. and Pantoea sp. Furthermore, a deh gene was detected for the first time in a Gram positive bacterium. This gene had 89.4% nucleotide sequence similarity with the dehII sequence from an α-Proteobacterium, suggesting that lateral gene transfer of deh genes across unrelated bacterial species occurred. A culture-independent technique, the terminal restriction fragment length polymorphism (tRFLP) of two classes of deh genes (dehI and dehII), was then used to fingerprint the HAA degraders in drinking water systems. The tRFLP profiles of both deh genes showed similar patterns for all analyzed drinking water samples (from Minneapolis, MN; St. Paul, MN and Bucharest, Romania) and for one biologically-active granular activated carbon filter (Hershey, PA). The tRFLP profiles of dehI genes from the drinking water samples matched the pattern from Afipia spp. that were previously isolated from drinking water. The tRFLP profiles of dehII genes did not match any previously characterized dehII genes. Finally, a biodegradation kinetic model was developed to predict the fate of HAAs in biologically-active filters and water distribution systems. The model calculations indicated that biodegradation is likely to lead to significant HAA removals in biologically-active filters but not in most distribution systems. A sensitivity analysis showed that while the controlling parameter was the HAA-degrader biomass Bucharest, Romania) and for one biologically-active granular activated carbon filter (Hershey, PA). The tRFLP profiles of dehI genes from the drinking water samples matched the pattern from Afipia spp. that were previously isolated from drinking water. The tRFLP profiles of dehII genes did not match any previously characterized dehII genes. Finally, a biodegradation kinetic model was developed to predict the fate of HAAs in biologically-active filters and water distribution systems. The model calculations indicated that biodegradation is likely to lead to significant HAA removals in biologically-active filters but not in most distribution systems. A sensitivity analysis showed that while the controlling parameter was the HAA-degrader biomass physical parameters, such as water flow velocity and pipe length, also had an influence on the HAA removal.