Desalination and reuse of industrial waste water by electrodialysis

Abstract

An economical desalination system for industrial waste water reuse has been developed using electrodialysis. The system consists of pretreatment and electrodialysis sections. With a conventional pretreatment of feed water through a sand filter, an increase of pressure drop in an electrodialyzer and also a decrease of performance of ion-exchange membranes occured. They resulted from a deposition of suspended solids in a feed water on membranes. A new pretreatment method has been developed by a dual media sand filtration with addition of small quantity of ferric chloride and sodium hypochlolite into a feed water. In a pilot test with a capacity of 0.7 m 3/day, the new pretreatment process was verified to be effective for removing suspended solids below 0.1 ppm, which was corresponded to plugging index (P.I.) below 50 %, and it was also proved that the increase of pressure drop in the electradialyzer was suppressed with the feed of the filtrate. Based on these results, a commercial plant with a capacity of 400 m 3/day was constructed for desalting cooling waste water from glassware manufacturing plant in our company containing TDS of 500–1000 ppm and 1–2 ppm colloidal suspended solids. Since August 1980, the system has been operated successfully with little increase of pressure drop of the electrodialyzers. The power consumption of desalination was 0.15 KWH-DC/m 3-water and the running cost was estimated to be about 33 ¥/m 3 in case of power cost of 15 ¥/KWH.