20th Annual EPA Drinking Water Workshop: Session 6A
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Disinfection and Pathogen Control
Track A: Distribution Systems and Water Quality
Presentation summaries and speaker and moderator biographies for Session 6A of the 20th Annual EPA Drinking Water Workshop.
September 13, 2023 from 10:45 a.m. to 12:30 p.m. ET
See the full workshop agenda for all sessions.
Moderator:
Laura Boczek, M.S. | EPA Office of Research and Development
Laura is a research microbiologist with EPA's Office of Research and Development, Center for Environmental Solutions and Emergency Response. Her research areas have focused on disinfection efficacy of various microorganisms in drinking water, including the study of premise plumbing pathogens with an emphasis on Legionella; specifically, the ecology of these organisms, understanding how they persist, and what steps can be taken to mitigate the risk of infection to insure public health protection. She has also been involved with antibiotic resistance studies in various environmental matrixes and with pathogens and method development in biosolids. Laura holds an M.S. in biological science from the University of Cincinnati and a B.S. in biological science from Northern Kentucky University.
Home Plumbing Systems: Legionella and Other Pathogens
Opportunistic premise plumbing pathogens (OPPPs) have been detected in the buildings’ plumbing systems causing waterborne disease outbreaks in the United States. This presentation will discuss a study aimed to evaluate microbial water quality in a simulated home plumbing system (HPS) by monitoring the occurrence of three major OPPPs along with free-living amoeba (FLA) using quantitative PCR. The OPPPs monitored included Legionella pneumophila; nontuberculous mycobacterial species, such as Mycobacterium avium, M. intracellulare, and M. abscessus; and Pseudomonas aeruginosa. The FLA monitored were Acanthamoeba spp. and Vermamoeba vermiformis. Water samples were also analyzed for heterotrophic bacteria and culturable L. pneumophila, and a metagenomic approach was employed to further characterize microbial communities.
Results showed that the microbial community is highly diverse and exhibited spatial and temporal structuring influenced by environmental conditions. L. pneumophila was the most prevalent pathogen (detected in 86% of samples), followed by M. intracellulare (66%) and P. aeruginosa (21%). A relatively low prevalence of Acanthamoeba spp. (4%) was observed, while V. vermiformis was widely detected (81%) across all sampling locations within the HPS. Locations with high concentrations of L. pneumophila and M. intracellulare coincided with the highest detection of V. vermiformis, suggesting potential growth of both populations within FLA and additional protection in treated water. After a period of stagnation lasting at least two weeks, concentrations of OPPPs and amoeba immediately increased and then decreased gradually back to baseline levels. This study demonstrates that these organisms can adapt to their environment during such events, potentially surviving in biofilms or growing within FLA to protect themselves from stressors in supplied water.
Hodon Ryu, Ph.D. | EPA Office of Research and Development
Hodon is an environmental engineer and microbiologist with EPA’s Office of Research and Development, Center for Environmental Solutions and Emergency Response. He earned his doctoral degree from Arizona State University and has been with the EPA since 2009. Hodon’s research focuses on health-related environmental microbiology and biotechnology, with an emphasis on interdisciplinary studies that combine engineering and microbiology. He is a member of the EPA’s Pathogen Equivalency Committee and CCL5 Microbial Workgroup. In 2018, he received the Trudy A. Speciner award for his contributions to advancing environmental protection. Hodon has also served on the international editorial board of “Journal of Water and Health” and “Journal Water” and has published over 100 papers in peer-reviewed journals.
Evaluation of Distribution System Chemical Water Quality During a Free Chlorine Conversion
Chloraminated drinking water systems commonly implement a temporary free chlorine conversion (FCC) to control or minimize nitrification in the distribution system (DS), but unintended water quality changes may occur with the FCC, including increased disinfection byproduct (DBP) and metals concentrations. This presentation will discuss a study that evaluated temporal water quality changes at multiple DS and residential sample locations in a United States chloraminated drinking water DS before, during, and after an FCC. Water quality through the DS alternated between relatively consistent (steady state) and variable (non-steady state) periods when converting from monochloramine to free chlorine and subsequently converting back to monochloramine. At the DS maximum residence time sample location, 4-8 days were required to stabilize disinfectant concentrations after switching disinfectants, but less time was required for sample locations closer to the DS entry point. Conversion to free chlorine increased the regulated four trihalomethane (THM4) and five haloacetic acid (HAA5) concentrations 4 and 7 times, respectively, compared to monochloramine and exceeded THM4 and HAA5 maximum contaminant levels (MCLs) during the FCC. Furthermore, implications of requiring DBP regulatory compliance sampling during an FCC was quantified, resulting in a modified locational running annual average (mLRAA) calculation that accounted for the duration of increased DBP concentrations from an FCC. Systems implementing a single, annual FCC with LRAAs relatively close to either the THM4 or HAA5 MCL may exceed MCLs using an mLRAA calculation. For metals, the FCC had minor impacts to DS concentrations and did not appear to impact residential concentrations. Overall, variable water quality observed in this study appeared primarily associated with changing disinfectants where the duration depended on DS hydraulics to move water through the system.
David Wahman, Ph.D. | EPA Office of Research and Development
Dave is a research environmental engineer with EPA’s Office of Research and Development, Center for Environmental Solutions and Emergency Response in Cincinnati, Ohio. His research interests include disinfectant chemistry, disinfectant biofilm penetration, and distribution system water quality issues, including nitrification. He is a registered professional engineer with over 27 years of experience. Dave holds a Ph.D. in civil engineering and an M.S.E. in environmental and water resources engineering and from The University of Texas at Austin and a B.S. in civil engineering from Rose-Hulman Institute of Technology. Following graduation with his Ph.D., he conducted a post-doctoral fellowship at the EPA before accepting his permanent position.
Evaluation of Distribution System Microbial Water Quality During a Free Chlorine Conversion
Opportunistic pathogens (OPs) are the dominant infectious agents in engineered water systems (EWS), but the responses of OPs to a chlorine burn are unknown. This presentation will discuss a study aimed to assess the impact of a 1.5-month chlorine burn on OPs in a representative full-scale chloraminated EWS in the United States. Four OPs (Legionella, Mycobacterium, Pseudomonas, and Vermamoeba vermiformis) were qualified in the water main and at residential sites before, during, and after the chlorine burn. Legionella and Mycobacterium were more abundant, and Legionella was the most dominant OP. In the water main, the concentration of the four OPs showed a temporary decrease effect of the chlorine burn, but it is ineffective in suppressing OP (re)growth in chloraminated EWSs and should be reconsidered, enhanced, or extended the chlorine burn.
Jingrang Lu, Ph.D. | EPA Office of Research and Development
Jingrang is a research biologist with EPA’s Office of Research and Development, Center for Environmental Measurement and Modeling in Cincinnati, Ohio. His main interests are to apply molecular approaches to applied environmental microbiology and public health research. His research work focuses on the molecular method development, detection, and microbial exposure assessment. His research in drinking water opportunistic pathogens includes exploring relationship between opportunistic pathogens and disinfection byproducts, insights into pathogenicity of disinfection-stressed bacteria and biomarker exploration, and dose-response assessment from inhalation of aerosols containing Legionella pneumophila and other opportunistic pathogens. Jingrang holds a Ph.D. in microbial ecology, an M.S. in zoology, and an M.S. in statistics.
Disclaimer: The views expressed in these presentations are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency. Any mention of trade names or commercial products does not constitute EPA endorsement or recommendation for use.