Abstract

Since reverse osmosis (RO) is often limited to a water recovery of 70–85 %, implementing a secondary process like electrodialysis metathesis (EDM) to treat concentrate can increase system water recovery. This study explores salt-free electrodialysis metathesis (SF-EDM) as an alternative to conventional EDM to investigate its performance in the zero discharge desalination (ZDD) process. SF-EDM utilizes monovalent-selective ion exchange membranes, eliminating the need for sodium chloride (NaCl) as a substitution solution. This approach generates one diluate stream and two highly soluble concentrate streams enriched in calcium and sulfate, respectively. In this article, a series of lab-scale tests based on synthetic and real RO concentrate were performed to investigate how SF-EDM performs operating at high water recovery with a feedwater with high scaling potential. We critically analyze the performance in terms of salinity reduction, selectivity, and energy consumption. Results of the study show that without the addition of NaCl, the process was able to selectively separate sulfate and calcium into two concentrate streams achieve a salinity reduction of 93 % and a total system water recovery (RO and SF-EDM) of 90 %. A technoeconomic analysis found SF-EDM to be 80 % of the cost of conventional EDM making it a competitive technology for brackish water RO concentrate management.

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