Pilot-scale assessment reveals effects of anode type and orthophosphate in governing antimicrobial capacity of copper for Legionella pneumophila control

Shotgun Metagenomics Reveals Impacts of Copper and Water Heater Anodes on Pathogens and Microbiomes in Hot Water Plumbing Systems

“…Although copper dosing was found previously to increase hydrogen evolution in the magnesium anode water heaters, no enrichment effects were seen for Nitrospirae , which was likely due to their low tolerance of copper. Aluminum anodes produced a layer of thick biofilm/corrosion products . This could potentially contribute to the increased levels of Proteobacteria and decreased α diversity observed in the anode biofilm compared to hot water.…”

“…Annotated reads/L of L. pneumophila estimated by metagenomics positively correlated with their enumeration via culture (CFU/L) measured in a prior study (Spearman R = 0.51; p < 0.05) and qPCR (gc/L) (Spearman R = 0.37; p < 0.05) (Figure and Table SI-4). M.…”

“…57 The findings that L. pneumophila in these water heaters was less affected by copper relative to the rest of the microbial community is consistent with our prior hypothesis that this particular strain is copper resistant. 12 This finding has important implications given that the highest concentration of copper dosed in this study (2 mg/L) far exceeds established targeted concentrations used to control L. pneumophila and M. avium 58−61 and even exceeds the recommended amounts of copper in drinking water. 62,63 Consistent with prior studies, Proteobacteria, Actinobacteria, Deinococcus-Thermus, and Nitrospirae contain mesophilic/ thermophilic species and were found to be dominant in hot water plumbing systems.…”

“…pneumophila. We recently conducted a pilot-scale study on the effects of copper on Legionella and found that phosphate, which is commonly added by water utilities for corrosion control, can not only fully eliminate the antimicrobial properties of copper but also appeared to synergistically increase Legionella in the presence of copper . Further, stepwise increases in total copper doses up to 2 mg/L resulted in only ∼1 log reduction of L.…”

“…Water heaters are equipped with anodes, which sacrificially corrode to protect the steel tank. We previously documented that these anodic reactions can alter the chemistry throughout the water heater and release aqueous hydrogen. , Aluminum anodes are widely used because of their relatively low cost but tend to form a gelatinous layer of aluminum hydroxide corrosion products, which could affect the bioavailability of copper, phosphates, and other chemicals . Magnesium anodes, which are also common, were found to elevate pH and release more hydrogen than aluminum anodes, especially when copper is dosed .…”