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Characterization of microbial water quality using molecular technology and its applicability for assessing treatment performance in a building model home plumbing system
Citation:
Boczek, L., M. Tang, M. McNeely, V. Gomez-Alvarez, C. Muhlen, D. Williams, D. Lytle, H. Ryu, AND J. Wright. Characterization of microbial water quality using molecular technology and its applicability for assessing treatment performance in a building model home plumbing system. WQTC 2022 Conference, Cincinnati, OH, November 13 - 17, 2022.
Impact/Purpose:
Potable water is delivered to buildings via water treatment and distribution systems. USEPA regulates the delivery of this water; however, the regulations stop at the distribution system, and they don’t continue into the buildings. Water management plans often employ low-cost easy treatments such as heat treatment, flushing protocols, and water drainage. In this study, we aimed at monitoring the occurrence of three major OPPPs and phagocytic amoebae using molecular assays and investigated the efficacy of different treatment options on the microbial population of a simulated home plumbing system (HPS) located in EPA’s lab, Cincinnati, OH. The results suggest that additional research is needed in distribution system treatment options.
Description:
Opportunistic premise plumbing pathogens (OPPPs) are frequently detected in the plumbing systems of large buildings. There are three major OPPPs such as Legionella pneumophila, three nontuberculous mycobacterial species (NTM) (e.g., Mycobacterium avium, M. intracellulare, and M. abscessus), and Pseudomonas aeruginosa closely associated with drinking-water-related disease outbreaks in the United States. The ability of these organisms to form biofilms and to grow in phagocytic amoeba are thought to provide some insulation from conventional water disinfectants including chlorine. In this study, we investigated the efficacy of different treatment options on the microbial population and occurrence of these OPPPs along with phagocytic amoebae in a simulated home plumbing system (HPS). Water samples were collected from eight locations in the HPS on a weekly basis for 8 months. Three groups of sampling events were designed for demonstrating baseline of microbial levels, stagnation impact, and post water drainage (i.e., draining of the hot water system and then filling with fresh cold water). Samples were analyzed for three major OPPPs and two amoebae using 13 qPCR assays. A metagenome and next generation sequencing technology targeting bacterial 16S rRNA gene approach was used to characterize the microbial communities and metabolic functional profile of selected bulk water and biofilm samples. Results show that the microbial community is highly diverse with evidence of spatial and temporal structuring influenced by environmental conditions. L. pneumophila were the most prevalent pathogen (86%, 187 out of 217 samples), followed by M. intracellulare (67%) and P. aeruginosa (22%). The M. avium and M. abscessus were not detected in any of the samples. While relatively low prevalence of Acanthamoeba spp. (4%) was observed, Vermamoeba vermiformis were detected in all the sampling locations. The concentration of L. pneumophila ranged from 4 to 105 gene copy/mL with the greatest average concentration of 104 at Faucet 1 which is 2-3 orders of magnitude higher than the other sampling locations and coincided with the highest detection of V. vermiformis. This result suggested potential growth of L. pneumophila in phagocytic amoeba which could provide additional protection in chlorinated water. Mycobacteria spp. were detected in all hot water locations as well as one cold water location with consistently high levels over the entire sampling period, indicating that mycobacteria are very persistent in chlorinated water. Overall, bacterial levels right after stagnation (at least 2-weeks) increased and then decreased gradually back to the baseline. The result of microbial monitoring after hot water drainage demonstrated no significant mitigation of the testing OPPPs. This observation should encourage further studies on the reduction in microbial risks from waterborne pathogens afforded by new disinfection practices and low-cost easy treatments including heat treatment.