The Influence of Nitrifying Bacteria on Monochloramine Decay and Opportunistic Premise Plumbing Pathogen Growth

Drinking water infrastructure in homes and buildings provides a niche for water microbiomes. Higher surface area to volume ratios, stagnation, and disinfectant decay at point-of-use locations lead to microbial regrowth and a higher risk of exposure to opportunistic premise plumbing pathogens (OPPPs). Nitrifying bacteria are common inhabitants of drinking water systems and are known to contribute to the decay of disinfectant residuals, potentially leading to additional OPPPs growth. To examine the influence of nitrifying bacteria on monochloramine decay and opportunistic pathogen growth, simulated glass water heaters with and without the presence of nitrifying bacteria will be assembled. The microbial and chemical composition within the simulated glass water heaters set to different temperatures will be analyzed along the nitrifying bacteria’s optimal growth curve. High throughput Illumina sequencing of 16S rRNA amplicons, quantitative polymerase chain reaction, LegioLert Assays, and total cell count will be utilized to identify and quantify nitrifying bacteria and OPPPs, as modeled by Legionella pneumophila. Total chlorine, free chlorine, free ammonia, and monochloramine concentrations will all be determined using a HACH spectrophotometer.  With these methods, the microbial and chemical composition of the simulated glass water heaters will be elucidated at different temperatures along the nitrifying bacteria’s optimal growth curve to gain insight into the relative influence of the bacteria on the rate of monochloramine decay and opportunistic pathogen growth. Future studies focusing on the relative growth and inactivation of nitrite-oxidizing and ammonia-oxidizing bacteria in water infrastructure would help utilities control opportunistic pathogen regrowth in the distribution system and limit pathogen exposure at point-of-use locations.