You are here:
A Long-Term Study of the Microbial Community Structure in a Simulated Chloraminated Drinking Water Distribution System - abstract
Citation:
Revetta, R., S. Pfaller, J. Pressman, D. Wahman, AND V. Gomez-Alvarez. A Long-Term Study of the Microbial Community Structure in a Simulated Chloraminated Drinking Water Distribution System - abstract. Presented at AWWA-WQTC, Salt Lake City, UT, November 15 - 19, 2015.
Impact/Purpose:
These results provide an ecological insight into the succession of microbial communities in chloraminated DWDS subjected to nitrification and chlorine burn treatments with potential relevance to the development of guidance for optimization of nitrification control strategies.
Description:
Many US water treatment facilities use chloramination to limit regulated disinfectant by-product formation. However, chloramination has been shown to promote nitrifying bacteria, and 30 to 63% of water utilities using secondary chloramine disinfection experience nitrification episodes. In this study, we examined the Bacterial population in a simulated chloraminated drinking water distribution system (DWDS). After six months of continuous operation, coupons were incubated in CDC reactors receiving water from the simulated DWDS to study biofilm development. The DWDS was then subjected to episodes of nitrification, followed by a ‘chlorine burn’ by switching disinfectant from chloramine to chlorine, a common nitrification control strategy. The study was organized into five distinct operational schemes: (1) PRE-MODIFIED; system stabilization, (2) STANDARD I; stable chloramine residual, (3) FAILURE; complete nitrification and minimal chloramine residual, (4) RESTORE; chlorine burn, and (5) STANDARD II; stable chloramine residual. Bulk water and biofilm samples were collected and analyzed for water quality parameters and microbial composition. No change in microbial biomass (ATP) in bulk water and biofilm samples was detected during the STANDARD I scheme, while an increase in biofilms was detected after 80 days (FAILURE, i.e. nitrification) followed by a decrease after a chlorine burn with a final increase to previous values (STANDARD I) during the STANDARD II scheme. The estimated populations of heterotrophs (HPC) were constant for all samples. Approximately 68% of the total diversity in the viable microbial community was associated with the class Alphaproteobacteria, Actinobacteria, and Gammaproteobacteria. Community comparison showed significant differences in functional and taxonomic structures based on source (e.g. disinfection treatment), surface material and operational schemes. For example, members of the family Methylobacteriaceae (22%) dominated chlorine-treated water (i.e. municipal water), while early stages of operation (PRE-MODIFIED) were dominated by Novosphingobium (38%). Environmental Mycobacterium-like OTUs peaked during the STANDARD I scheme (40%) but decreased to <10% in later periods, and an increase in the abundance of nitrifying bacteria Nitrospira (<0.3% to 4%) was observed during the FAILURE scheme. Ammonia-oxidizing bacteria related to Nitrosomonas were detected during nitrification. In addition, genes associated with multiple disinfectant resistance mechanisms and virulence factors, such as antibiotic resistance mechanisms, were found to be a component of the core genome of bacterial isolates. Overall, these results provide an ecological insight into the succession of microbial communities in chloraminated DWDS subjected to nitrification and chlorine burn treatments with potential relevance to the development of guidance for optimization of nitrification control strategies.
URLs/Downloads:
http://www.awwa.org/portals/0/files/education/conferences/wqtc/wqtc15/pdfs/2015wqtctechnicalprogramweb.pdf