Cu- and Ag-mediated inactivation of L. pneumophila in bench- and pilot-scale drinking water systems
Citation:
Hintz, C., B. Morris, S. Witt, N. Sojda, AND H. Buse. Cu- and Ag-mediated inactivation of L. pneumophila in bench- and pilot-scale drinking water systems. 2023 EPA International Decontamination Research and Development Conference, Charleston, SC, December 05 - 07, 2023.
Impact/Purpose:
Dissociation was used to produce Cu and Ag ions at thebench- and pilot-scale. At the bench-scale, Cu (0.3 ppm) and Ag (0.03 ppm) were tested independently and Cu and Ag ions were successfully used to inactivate Lp in an experimental test solution. However, when dechlorinated tap water was used, inactivation was much slower for Ag and ineffectivefor Cu. There were differences in pH and carbon content (DIC) between test solutions. At the pilot-scale, it took time to reach target ion levels, no impact was observed on microbial parameters, and there was a potential impact on chlorine residual (Zhang &Andrews, 2012). In conclusion, prior knowledge of a system’s water chemistry is important in determining if the addition of Cu and Ag ions are an appropriate tool for managing Lp. Cu and Ag are suggested as a solution for controlling Lp in spite of known limitations for certain water quality parameters (which are often common fordrinking water). Ag alone was observed to be effective at Lp inactivation (at the bench-scale) and might be less impacted by pH and carbon levels and needsfurther examination. Variation across studies in the effectiveness of Cu and Ag within buildings could be a result of variation in building(s) water chemistry. Using dissociation as a method at a building-scale would likely prove difficultvgiven the wide variation in building water use. However, CSI units also require maintenance, etc.
Description:
Legionella pneumophila (Lp) is an opportunistic drinking water pathogen that can cause infections through the inhalation of Lp-containing aerosols. Lp can occur in premise plumbing systems as these systems often have low disinfection residual, high surface area-to-volume ratios, water stagnation, and various water temperatures and velocities. These are all features that can lead to the colonization of Lp within plumbing systems. In this work the use of copper and silver ions was evaluated at the bench- and pilot-scale to determine 1) effective independent concentrations of copper and silver for inactivating Lp, 2) the impact of various water quality parameters on the effectiveness of copper and silver ions and 3) the effectiveness and practicality of using dissociation to produce ions at the pilot scale. At the bench-scale, it was determined that 0.3 ppm and 0.03 ppm of Cu and Ag, respectively, were effective at inactivating Lp in 5 hours in experimental buffer. But, in dechlorinated filter-sterilized tap water, the same concentrations of Cu were not effective, and the effectiveness of Ag was slower. pH and dissolved inorganic carbon content were found to be important parameters in determining if the use of Cu and Ag ions is appropriate. At the pilot-scale, dissociation was successfully used to produce Cu and Ag ions, but target levels of ions were difficult to achieve, and no impact was observed on Lp concentrations. Results from this study suggest that water chemistry in a plumbing system can impact the effectiveness of Lp disinfection using Cu and Ag.