A Water Research Foundation Tailored Collaboration project was conducted to evaluate zero liquid discharge (ZLD) desalination of brackish water. The approach involved desalinating RO concentrate with a new electrodialysis process referred to as electrodialysis metathesis (EDM). EDM is a variation of electrodialysis that uses a unique configuration of ion exchange membranes to produce desalinated water and two concentrate streams containing highly soluble salts. This characteristic gives EDM a unique advantage in ZLD treatment because concentrate can be treated at a much higher recovery rate than is possible with RO or conventional electrodialysis. EDM recoveries of over 99 percent without membrane fouling were observed in pilot tests treating concentrate from RO, NF, and EDR membrane plants. Pilot data were used to develop full-scale treatment costs for ZLD with EDM. These costs were compared with treatment costs for ZLD with thermal technologies. It was concluded the EDM method has the potential to significantly reduce ZLD costs for brackish sources with TDS less than 5000 mg/L.
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