Membrane-based electrochemical precipitation for water softening

Electrochemical precipitation has been widely employed for recirculating cooling water softening because of its environmental friendliness, convenient operation, and high treatment efficiency. However, this technique uses many expensive electrodes, and thus requires a very large investment. In this study, a novel process called membrane-based electrochemical precipitation (MEP) was proposed and tested for water softening. This new process utilises membrane polarisation, an undesirable phenomenon that occurs in conventional electrodialysis , to precipitate hardness ions on the surface of membranes. Compared with conventional electrodialysis , MEP involves only one kind of exchange membrane . Moreover, unlike traditional electrochemical precipitation, MEP only needs one pair of electrodes, and thus can reduce equipment cost significantly. Different types of membranes were examined, and heterogeneous anion exchange membranes were found to be the best. It was demonstrated that MEP could soften water effectively. The precipitation rate and energy consumption were 64.0–84.6 g/h/m 2 and 8.8–12.0 kW h/kg CaCO 3 , respectively. The scale deposited on the membranes could be detached easily through polarity reversal of electrodes. Repeated experiments showed that MEP could run stably without any performance deterioration .