Monitoring Chlorine Residuals For RO Membranes - ORP Versus Chlorine Analyzers

By Swan Analytical USA

By Randy Turner, Technical Director, Swan Analytical USA

In processes where disinfection is required chlorine is the most common and economic disinfectant followed by sodium hypochlorite (liquid bleach).  It is important to disinfect the RO feedwater to avoid fouling of the membranes which results in poor performance and frequent cleaning.  If dechlorination is required it is common to continuously monitor the process to ensure proper dechlorination is achieved to avoid oxidative damage to the membranes.  It is common to continuously monitor the process to ensure proper feed of the disinfectant.  It has been an industry standard to use ORP to monitor chlorination/dechlorination of RO feedwater. Any species that affects the redox potential of the solution will affect the ORP mV value.  Many end users, consultants, service providers, and OEM’s are employing chlorine analyzers rather than ORP.   This paper discusses these methods.