Integration of seeding- and heating-induced crystallization with membrane distillation for membrane gypsum scaling and wetting control

Although membrane distillation (MD) has great potential in treating high-salinity wastewater, continuous accumulation of inorganic salt due to increasing concentration inevitably causes supersaturation and subsequent membrane scaling. Crystallizer is an effective tool used for removal of salts; however, it has been hardly applied for sparingly soluble salts. In this study, a simultaneous membrane distillation-crystallization (SMDC) system was developed for gypsum scaling control. Induced crystallization was adopted to retard the membrane scaling. The transmittance and ion concentration of the concentrate were measured to investigate the performance of the induced crystallization. The membrane scaling was characterized by both vapor flux measurements and scanning electron microscopy. Besides, the permeate conductivity was monitored to assess the membrane wetting during MD, and the energy evaluation was performed for the SMDC system during the reverse osmosis brine treatment. Results showed that the seeding of gypsum at dosage of 1 g L-1 effectively restricted the membrane scaling and wetting. Although the combination of seeding and heating showed better membrane scaling control