A feasibility study on water softening by electrodeionization with the periodic polarity change

Interests on the polarity reversal have increased to prevent or minimize membrane fouling and scaling during the operation of electromembrane processes. In this study, the influence of the operation conditions on the process efficiency was investigated in the electrodeionization reversal (EDIR) system with an electrodeionization with the polarity reversal. The removal efficiencies of divalent cations (Mg2+ and Ca2+) kept high value without scale formation on the membrane surface. Through the EDIR operation, the process performance was affected by polarity reversal periods, and the operating polarity reversal period was determined to 40 min or shorter in this study.In the long term EDIR experiments with different cation exchange membranes, the homogeneous membranes showed marginally higher removal efficiency compared to the heterogeneous membrane. The scale powders and the surface of scaled membrane were analyzed using electron microscopes and it was observed that the scales formed as carbonate of divalent cations. The EDIR results showed the feasibility of the EDIR system for use in water softening process without significant scale formation even in a relatively high concentration.

The scale formed on the surface of cation exchange membrane (CMX) rather than anion exchange membrane (AMX) at long polarity reversal period and high hardness concentration.Figure optionsDownload as PowerPoint slideHighlights
► Influence of operation conditions on the EDIR performance was investigated.
► Acceptable range of the polarity reversal period was determined in the system.
► Scale formed on the membrane surface as carbonate form of Ca and Mg.
► EDIR system was successfully demonstrated in a wide hardness concentration range.