Inactivation of Legionella pneumophila by copper-silver ions and free chlorine

Abstract

Water disinfection systems utilizing electrolytically generated copper:silver ions (200:20 to 400:40 ug/L) and low levels of free chlorine (0.1 to 0.4 mg/L) were evaluated at room (21-23°C) and elevated (39-40°C) temperatures in filtered well water (pH 7.3) for their efficacy in inactivating Legionella pneumophila (ATCC 33155). A contact time of 24 hr was necessary for copper:silver (400:40 ug/L) to achieve a 3 log₁₀ reduction in bacterial numbers at room temperature. As the copper:silver concentration increased to 800:80 ug/L (K = 7.50 x 10⁻³ log₁₀ reduction/min), the inactivation rate significantly (p ≤ 0.05) increased. In water systems at room temperature with and without copper:silver (400:40 ug/L), the inactivation rates significantly increased as the free chlorine concentration increased from 0.1 mg/L (K = 0.397 log₁₀ reduction/min) to 0.4 mg/L (K = 1.047 log₁₀ reduction/min). All disinfection systems, regardless of temperature or free chlorine concentration, showed increased inactivation rates when 400:40 ug/L copper:silver was added; however, this trend was significant only at 0.4 mg/L free chlorine.