Computer simulation of ion-exchange membrane electrodialysis for salt concentration and reduction of RO discharged brine for salt production and marine environment conservation

Abstract The salt discharged from reverse osmosis is concentrated by ion-exchange membrane electrodialysis to produce salt for industrial use and the salt concentration is reduced to seawater level for preventing environmental impact on marine ecosystems. The technology was evaluated experimentally and discussed with a computer simulation program of the electrodialysis system incorporated with U shape cells. The algorithm computes mass transport, energy consumption, electric current leakage, concentrate NaCl purity, pressure drop and limiting current density. The seawater reverse osmosis discharged brine was supplied to the electrodialysis pilot plant and it was operated changing current density and temperature taking benefit of seasoning variations. The computed energy consumption ENaCl and NaCl concentration in concentrated solutions C″NaCl using developing algorithms provided a good description of the experimentally measured values with correlation coefficients of R(r) = 0.9 for ENaCl and R(r) = 0.6 for C″NaCl. Then the reasonability of the developed algorithms is supported by the experimental set of data. The current leakage is nearly 3% for any electric current. The pump driving force is very low. The limiting current density is very high. In order to decrease salt concentration at the outlets of desalting cells to seawater level, it is necessary to increase desalting ratio to 0.5. This technique however increases ENaCl and decrease C″NaCl. In spite of this operating circumstance, ENaCl and C″NaCl are comparable to the data in the salt manufacturing plant operation to produce edible salt. NaCl produced from in the reverse osmosis discharged brine electrodialysis is competitive in the edible salt market.