Ion-nucleating competition cooperated with antiscalant for effectively mitigating gypsum scaling in membrane distillation

Abstract

Membrane distillation (MD) that can sustainably recover freshwater until salt crystallization is a potential candidate for hypersaline wastewater treatment. However, a huge challenge for MD is membrane scaling, which sharply decreases membrane flux and salts rejection efficiency. This study reported an ion-nucleating competition cooperated with commercial antiscalants to mitigate membrane scaling. Results showed that the superhydrophobic PVDF (SH-PVDF) membrane could effectively delay the gypsum nucleation on the slippery membrane surface owing to the increased membrane surface roughness, but scaling inevitably occurs on the membrane surface in the supersaturated condition. Introducing the foreign ions such as one-component Na+ or Mg2+ and two-component Na+/Mg2+ mixture can improve the gypsum solubility and delay gypsum nucleation for mitigating membrane scaling. Besides, the synergistic combination of commercial antiscalant and ion-nucleating competition is extraordinarily effective in retarding membrane scaling and preventing membrane pore wetting, achieving a high-water recovery of ~85 % and robust salt rejection of ~100 %. The mechanisms of ion-nucleating competition cooperated with antiscalants were also discussed with the help of characterizations. This work provided a novel ion-nucleating competition in collaboration with antiscalants for hypersaline wastewater management, which is important for MD to be applied in near-zero liquid discharge (ZLD).