Insight into the feed/permeate flow velocity on the trade-off of water flux and scaling resistance of superhydrophobic and welding-pore fibrous membrane in membrane distillation

Abstract The primary problem with membrane distillation (MD) for concentrating hypersaline wastewaters is its severe membrane scaling induced by increasing salt concentration of wastewater. Herein, we developed a superhydrophobic and welded-pore polyimide fibrous membranes (SH-welded PI FM) combined with optimizing feed/permeate flow velocity to alleviate membrane scaling and improve membrane water flux simultaneously. The experiments reveal that the SH-welded PI FM functionalized with welding pores avoids membrane pore deformation induced by increasing flow velocity and superhydrophobicity reduces the overall adhesive interaction between crystal and membrane surface to against membrane scaling. Comparative experiments and simulation results reveal that increasing flow velocity is also beneficial for vapor transmission by partially overcoming membrane temperature and concentration polarization and alleviating membrane scaling by producing asymmetrical disturbation on membrane two surfaces. However, the progressive increase will aggravate membrane scaling because of the excessive disturbance of flow velocity to fibers enlarging membrane pores. Therefore, designing welded-pore and superhydrophobic fibrous membrane combined with optimizing flow velocity is extraordinarily effective in simultaneously improving membrane water flux and mitigating membrane scaling for concentrating hypersaline wastewaters. These findings are significant to break the trade-off of membrane water flux and scaling for MD to concentrate hypersaline wastewaters for practical application in industries.