Brackish water desalination in RO–single pass EDR system

Abstract

Electrodialysis reversal (EDR) treatment of inland brackish water reverse osmosis concentrate was examined. The resistance to CaSO4 and CaCO3 scaling in our single-pass and low residence time EDR is better than in the one that was originally developed by Ionics. Our approach is as follows. The RO concentrate of CaSO4 and CaCO3 content being close to the saturation level (or slightly supersaturated) is concentrated by EDR 4–5 times. This enables the concentrate volume to decrease and, probably, its disposal cost to the same extent. Assuming brackish water composition as follows (mg/L): Mg2+ — 95.4; Ca2+ — 208.4; Cl- — 1166; SO2- 4 — 868.8; HCO- 3 — 170.8; NO- 3 — 179.8 and 60% RO recovery, concentrate composition was calculated using Dow Chemical Co. RO system analysis (ROSA) software. Simulated RO concentrate containing (mg/L): Mg2+ — 237.7; Ca2+ — 519.2; Cl- — 2886; SO2- 4 — 2164; HCO- 3 — 414.4; NO- 3 — 424.3 was then treated in a laboratory EDR stand at 79.1% diluate recovery. The analysis of EDR stack...