Innovative Ion Exchange for Multi-Contaminant Treatment and Regeneration

Ion exchange is a robust process that can selectively remove a wide range of chemical contaminants, can perform effectively under changing water chemistry, can operate for several hours per day or continuously, and can be used in different reactor configurations and at different locations in a treatment train, therefore contributing to more sustainable water treatment. This research investigated combining anion exchange resin with cation exchange resin (hereafter combined ion exchange) for multi-contaminant removal. The combined ion exchange process used a single reactor for simultaneous removal of dissolved organic carbon (DOC) and hardness followed by a single reactor for simultaneous resin regeneration using sodium chloride (NaCl). The combined ion exchange process generates one liquid waste stream that contains predominantly NaCl, DOC, and hardness cations. DOC and hardness were selected as the focus of combined ion exchange because of their different chemistry and numerous problems related to water treatment. In addition, combined ion exchange can be applied to other combinations of contaminants including nitrate, perchlorate, sulfate, strontium, and barium. Two applications of combined ion exchange that are supported by the results of this research are: (1) as an alternative to coagulation and precipitative softening, and (2) as an intermediate treatment step between primary and secondary nanofiltration or reverse osmosis. This presentation will highlight results from the combined ion exchange research and also discuss alternative approaches to ion exchange regeneration that are more environmentally friendly.