Scaling mitigation and salt reduction of vacuum membrane distillation using sacrificial zeolites

Seawater which is characterized by high concentrations of sodium chloride (NaCl) salts and hardness i.e. calcium (Ca) and magnesium (Mg) is vulnerable to membrane scaling. The performance of an integrated zeolite-submerged vacuum membrane distillation (SVMD) system was evaluated for seawater desalination. The results showed that the zeolites achieved 15-29 % and 10-22 % removal of sodium (Na) and hardness, respectively. The metal removal by the zeolites followed the order of Na > hardness and agreed well with pseudo second order kinetics model. The integration of SVMD system with powdered zeolites achieved stable water flux throughout the long-term operation. Salt and metal (particularly Ca and Mg) removal from seawater via zeolites induced crystallization, mitigated scaling on the hollow fibre membrane surface while producing high quality clean water. Compared to the hydrophobic membranes, the nuclei of Ca and Mg salts tend to nucleate and crystallize on the surrounding of zeolites due to the higher surface energy of zeolites.