Fouling mechanism and effective cleaning strategies for vacuum membrane distillation in brackish water treatment

Abstract

Membrane scaling is an enormous challenge in the desalination of hypersaline water using membrane distillation (MD). In this study, vacuum membrane distillation (VMD) was employed for brackish water treatment, with an emphasis on scaling mechanisms and mitigation strategies. Four methods, including deionized water, hydrochloric acid, and acetic acid, ultrasonication, were utilized for membrane cleaning. The cleaning efficiency was assessed through a comprehensive analysis of residual foulant layers. It was determined that mineral scaling constituted the primary fouling mechanism, and a minor amount of organic fouling was present at the interface between scaling-scaling and scale-membrane. Calcium and magnesium carbonate were the primary scaling components observed in brackish water desalination, appearing as needle-like and block crystals. Notably, CaCO3 predominantly existed as the aragonite crystal structure. Ultrasonication and deionized water demonstrated limited effectiveness due to the alkaline nature of the scaling. Conversely, the application of dynamic hydrochloric acid and acetic acid treatments resulted in a significant reduction in scaling, with acetic acid demonstrating superior efficacy in removing carbonate scaling. The results presented in this study can provide valuable theoretical guidance for the treatment of brackish water using membrane desalination techniques.