Coping with Resistance to Copper / Silver Disinfection

www.waterinfocenter.com The biocidal effects of copper and silver have been used for centuries. The early Greeks and Romans made water storage and drinking vessels out of these metals, and enough dissolved in the water stored in them to produce substantial disinfection. More recently, copper and silver ions have been used in hospital, recreational, drinking and industrial water systems. Unlike chlorine, they do not result in dangerous halogenated organic byproducts such as trihalomethanes (THM), chloramines and chloroform, and these ions are stable, making it easier to maintain an effective residual. However, using soluble metal salts as a source of these ions and monitoring their concentrations to maintain consistent effects is cumbersome at best . Consequently, most modern copper/silver systems use electrolytic ion generators to control the concentrations of the dissolved metals. Electrolytic generators usually are composed of a negatively charged cathode and a positively charged anode made of the metal or an alloy of the metals to be ionized.The electrodes are contained in a chamber through which passes the water to be disinfected. A DC power source provides current at a potential of a few volts, causing the copper and silver in the anode to ionize and dissolve in the passing water. The concentration of metal ions in water leaving the electrolytic cell depends on the current and water flow past the electrodes. Therefore, production of metal ions can be controlled by the current applied to