Electrodialysis of brine solutions discharged from an RO plant

Electrodialysis (ED) experiments were carried out on RO brine solutions, saturated with CaSO4 and or silica with the aim to increase their concentrations from 1.5 to 10%, thus reducing both effluent volume and disposal costs. A pilot plant ED unit was built in which the brine circulating through the ED brine cells passed through a separate CaSO4 precipitator containing gypsum seeds. The feed to the ED unit was the brine discharged from the RO unit, which was operating on brackish water from Mashabei-Sadeh. The salt concentration of the ED feed was reduced to 18–20 mN and was then mixed with the RO permeate.