Comprehensive utilization of brackish water in ED — thermal system

Electrodialytic desalination/concentration of brackish water (TDS ca. 10 g/L) in an integrated ED — thermal desalination system was examined. The ED unit stacks geometry, and the ED system arrangement and operating conditions were optimized to identify minimum desalination/concentration costs. The ED stack with relatively low 0.19 mm membrane to membrane distance, and three stage ED system arrangement was investigated to identify optimum process parameters. The minimum total desalination/concentration cost found at 255 g/L NaCl concentrate content was equal to $0.22/m3 assuming $0.03/kWh electric power cost and $1/m3 fixed evaporation cost independently on the thermal plant capacity. Under optimal conditions the salt utilization cost was found to be $25.6/t of salt produced.It was also concluded that since optimum concentrate TDS found is high, the amount of water to be evaporated is relatively low. Thus the thermal unit costs increases the utilization costs to large extent and a mere system for electrodialytic desalination — concentration up to TDS of 300 g/L (close to NaCl saturation level) seems to be economically privileged. Despite high electric current density, relatively low value of energy consumption, equal to 275 kWh/t of salt was observed at optimum conditions.