Combined magnetic ion exchange and cation exchange for removal of DOC and hardness

The overall goal of this research was to evaluate an innovative combined ion-exchange process for multi-contaminant treatment. Magnetically enhanced anion exchange resin and conventional cation exchange resin were used in a single completely mixed vessel for simultaneous removal of dissolved organic carbon (DOC) and hardness. Following treatment, exhausted anion exchange resin and cation exchange resin were regenerated together in a single completely mixed vessel using sodium chloride (NaCl). The performance of the combined ion-exchange process was evaluated using three groundwaters and two nanofiltration (NF) membrane concentrates. The test waters provided a wide range of water quality in terms of DOC (2.9-56mg/L), total hardness (300-1000mg/L as CaCO₃), and sulfate (10-830mg/L). Combined ion-exchange treatment of groundwater achieved 76% DOC removal and 97% total hardness removal using a 20% (m/v) NaCl regeneration solution. Combined ion-exchange also achieved high removals of DOC (e.g., 83%) and total hardness (e.g., 86%) from NF concentrate using a 30% (m/v) NaCl regeneration solution. These results provide water treatment engineers with a new application of ion-exchange that can be used in place coagulation and precipitative softening or as an intermediate treatment step between primary and secondary NF or reverse osmosis membranes.