Coupling of porous filtration and ion-exchange membranes in an electrodialysis stack and impact on cation selectivity: A novel approach for sea water demineralization and the production of physiological water

Conventional electrodialysis (ED) and electrodialysis with ultrafiltration (EDUF) or nanofiltration (EDNF) membrane treatments were carried-out for partial desalination of sea water and to evaluate their potential for the production of physiological water. A demineralization rate of 10.6% was obtained with the EDNF and of 40.25% with EDUF and conventional ED processes. The nanofiltration membrane, due to its high electrical resistance, slowed down the migrations of ions. Moreover, the use of an ultrafiltration membrane had no significant effect on the demineralization rate of sea water and the electrodialytic parameters in comparison with the use of conventional ED membranes. A demineralization rate between 20.5 and 30.1% was obtained for each cation analyzed following EDNF treatments and between 43.3 and 64.4% when conventional ED or EDUF was used. Moreover, the decrease in the concentration of monovalent ions was slightly larger than for divalent ions in the case of ED and EDUF while for EDNF, the higher decrease was observed for calcium ion. This means that the replacement of a cation-exchange membrane by an ultrafiltration membrane would not change the selectivity of the process for ion separation but with a nanofiltration membrane a cation-selectivity appears.

Research highlights
► Use of ultrafiltration membrane had no significant effect on the demineralization rate of sea water.
► Use of ultrafiltration membrane had no significant effect on the electrodialytic parameters.
► Replacement of a cation-exchange membrane by an ultrafiltration membrane would not change the selectivity of the process.
► With a nanofiltration membrane a cation-selectivity appears.