Inactivation of Pseudomonas aeruginosa and Aeromonas hydrophila by silver in tap water

Abstract

This study was conducted to assess the efficacy of silver as a secondary disinfectant to replace or reduce the level of chlorine utilized in water distribution systems. Pseudomonas aeruginosa and Aeromonas hydrophila are opportunistic pathogens present in drinking water and have been associated with waterborne disease. After 8 hours of exposure to 100 μ g/L of silver, there was a > 6-log₁₀ reduction in P. aeruginosa in tap water at room temperature at pH7 and a 5.55-log₁₀ reduction in the presence of 3 mg/L humic acid. Similar reductions were observed at pH9. At 4°C, reductions greater than 4-log₁₀ were observed after 24 hours. For A. hydrophila, a > 6-log₁₀ reduction occurred at both pH7 and pH9 within nine hours. The World Health Organization has determined that this amount of silver could be used for water disinfection without health risks. Furthermore, silver shows promise as a secondary disinfectant, even in the presence of organic matter in concentrations that would reduce the effectiveness of free chlorine.

Keywords:

• Silver
• drinking water
• Aeromonas
• Pseudomonas
• distribution systems
• residual disinfectant

Acknowledgments

This study was supported in part by a grant from the National Science Foundation Water Quality Center at the University of Arizona.