Assess of physical antiscale-treatments on conventional electrodialysis pilot unit during brackish water desalination

Abstract

In electrodialysis (ED) desalination plants, calcium carbonate is the main component of meted scales. To prevent its formation several treatments were proposed. For more efficiency, treatments must be assessed at experimental conditions close to real ones. Thus, this work is a contribution to understand and evaluate three anti-calcareous physical treatments for ED desalination systems simulating real conditions. Magnetic field (MF) and ultrasonic field (UF) were applied to concentrate solution, compartment where scaling is imminent in the used ED pilot unit. The third treatment was a pulsed electric field (PEF) application. Tested solution was a synthetic brackish water. Results show that magnetic and ultrasonic treatments accelerate the precipitation of CaCO3 by reducing the nucleation time and the metastable domain. It is also shown that pulsed electric treatment accelerates CaCO3 precipitation resulting from desalination improvement comparing to stationary mode. However, all these treatments favor the homogeneous precipitation which prevents scale formation on membrane surfaces. It seems that MF improves the desalination only by preventing membrane scaling. However, UF and PEF application improve desalination by preventing membrane scaling and by improving the ions transfer during desalination; UF application acts on ions mobility or diffusion, while PEF application reduces the concentration polarization layer.