Membrane deposition electrodialysis for cooling water treatment: Ion step removal and stable membrane regeneration

Abstract

Membrane-based electrochemical precipitation (MEP) has been pioneered and demonstrated effective for hardness ion removal in cooling water, however, the removal of other ions was quite poor. To overcome such a problem, in this study, we presented a novel process, denoted membrane deposition electrodialysis (MDED), which incorporated MEP with electrodialysis (ED), for cooling water treatment. Desalination results demonstrated that MDED exhibited good ion step removal performance with a resultant high concentration selectivity of 4.2, which was attributed to the synergistic effect between membrane deposition and electro-migration, realizing zero-emission. The gradual scale formation caused by membrane deposition induced membrane property variation and then treatment performance deterioration, but delightedly, by using a distinct bi-pair electrode switching, the scale adhered to the membrane could be detached efficiently with a scale recovery reaching 96 %, bringing about subsequent membrane regeneration. More importantly, the bi-pair electrode switching displayed a super stable nature in the 1800 h accelerated life experiment, substantially eliminating the electrode stability decay problem that occurred in conventional polarity reversal. All these features allowed MDED to achieve satisfactory removal rate being about 5.8–15.9 M/h/m2, which was 1.5–26.5 folds those of conventional processes, and it could work stably for at least 3 years under normal conditions, with almost no performance decay.