Electrodialysis: From an idea to realization

The historical validity demands some clarifications in the early history of electrodialysis. Early investigations with non-selective membranes are not to be recognized as electrodialysis-related although some of them have used the term "electrodialysis." Only in 1950 the first synthetic ion-exchange membranes were produced (W. Juda and W.A. McRay). Preceding them membranes manufactured by T.R.E. kressman were in fact a modified natural product-impregnated parchment membranes. Major electrodialysis' shortcomings such as membrane fouling and scaling were mostly overcome with electrodialysis reversal (EDR) commercial introduction by Ionics in 1967. Synthesis of novel sodium-selective membrane did not spark a burst in ED manufacturing. However higher demand for sodium-selective membranes can be expected in conjunction with nitrate-selective membranes for potable water denitrification - the essential step in water treatment in Europe. New break-through in ED progress was associated with development of apparatuses with ion-exchange resin beads filling desalting compartment. The analysis of energy consumption in ED process shows that the possibility of its reduction by traditional ways of membranes and spacers improvements is practically exhausted. However there is practically undeveloped option to lower the polarization resistance with help of electrodynamic instability (volumetric-charge development). Another possible improvement is creating membranes with special profile. As EDI targets higher levels of water purity the removal of weakly ionized ions becomes important issue.