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Effects of Dairy Manure Management Systems and Wastewater Disinfection Processes on E. coli Phylotype Distribution
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Sections of streams located downstream from dairy farms and wastewater treatment plants (WWTPs) in central Texas are listed on the 303 (d) List of Impaired Waters due to bacterial contamination (possibly due to fecal contamination), specifically Escherichia coli (E. coli). E. coli can be subtyped into phylogroups that indicate potential pathogenicity; including A, B1, B2, C, D, E, F, and clades I-V; phylogroups B2 and D are considered potentially pathogenic. E. coli phylotype distributions were studied throughout dairy manure management systems, and before and after disinfection at WWTPs to better understand pathogenicity and reactivation of E. coli in downstream environments. Four dairy farms in the Leon River Watershed of central Texas, each utilizing a different dairy manure management practice, were sampled for E. coli using EPA Method 1603, with a percentage of E. coli isolates phylotyped using the Clermont quadruplex PCR method. E. coli phylotypes showed no seasonal or management practice trend. B1 was the most common phylotype isolated from all dairies and time periods. Effluent from two WWTPs (one utilizing chlorination disinfection, the other Ultra Violet (UV) light) in central Texas were sampled before and after disinfection using EPA Method 1603 for E. coli enumeration, and a portion of isolates were phylotyped using Clermont quadruplex PCR. E. coli from effluent post-disinfection was composed of higher proportions of potentially pathogenic phylotypes. A Quantitative Microbial Risk Assessment (QMRA) revealed swimming downstream from the WWTP employing UV-irradiation may result in a slightly elevated risk of infection due to a higher portion of potentially pathogenic E. coli, compared to the WWTP employing chlorination. Photoreactivation and dark repair of E. coli were studied in effluent from the WWTP employing UV irradiation. E. coli photoreactivation rates were higher than dark repair rates at 12 & 48 hours. Potentially pathogenic phylotypes represented two-thirds of all E. coli detected immediately after UV irradiation. However, treated effluent kept in dark conditions showed a steady decrease in potentially pathogenic phylotypes. Results from this research could help wastewater stewards lower E. coli concentrations and potentially pathogenic phylotype proportions in WWTP effluent.
Howard, Keya J. (2016). Effects of Dairy Manure Management Systems and Wastewater Disinfection Processes on E. coli Phylotype Distribution. Doctoral dissertation, Texas A & M University. Available electronically from