The dosing accuracy of copper and silver ionisation systems: separate high purity copper and silver electrodes versus copper/silver alloys

Copper and silver ionisation is a widely accepted technique to abate and control Legionella bacteria in contaminated water. Currently two types of copper and silver ionisation systems are commercially available: (1) systems using separate high purity copper and silver electrodes and (2) systems using copper/silver alloys in various compositions. The aim of this study was to determine the dosing accuracy of these two distinguishable copper and silver ionisation systems. This study showed that both copper and silver can be dosed accurately, according to Faraday’s law, with systems using separate high purity copper and silver electrodes as anodes. Systems with new copper/silver alloys (Alloys 70/30 and 90/10) as anodes can only dose copper in predictable quantities. With new copper/silver alloys, silver concentrations were under dosed (<20 μg/l Ag; minimum silver target level at outlets specified to control Legionella in water distribution systems). This is most likely caused by a difference in the efficiency of the electrolysis process of copper and silver in alloys. Silver is more oxidation and corrosion resistant than copper (more noble). The dosed silver concentrations with copper/silver alloys remained below the minimum recommended concentration for effective Legionella abatement, making alloys unsuitable especially when dosing directly into the water supply.