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.