Evaluating the secondary effects of magnetic ion exchange: Focus on corrosion potential in the distribution system

Abstract

In order to avoid the adverse effects of corrosion in water distribution systems, it is necessary to evaluate the secondary effects of magnetic ion exchange (MIEX) for the removal of dissolved organic matter (DOM). As DOM concentrations in surface waters increase and surface waters become more prevalent sources of drinking water, MIEX treatment will be increasingly used. This study evaluated the effects of MIEX treatment on iron and lead corrosion potential as measured by the Larson–Skold Index (LI) and chloride-to-sulfate mass ratio (CSMR), respectively. This was accomplished by analyzing data sets from bench- and pilot-scale MIEX experiments, as well as by monitoring a full-scale MIEX treatment plant. It was found that MIEX treatment consistently increased the CSMR, however, the extent of the increase was dependent on influent anion concentrations, MIEX resin regeneration, and other variables. MIEX treatment had only a minor effect on the LI. Both corrosion parameters were variable due to the periodic transfer of excess brine into the process train during regeneration cycles and fluctuations in raw water quality. It was also found that MIEX resin can re-release previously removed anions, such as sulfate and bicarbonate, which reinforces the need to evaluate secondary changes in water chemistry.