SEAWATER DESALINATION BY FREEZE DESALINATION AND MEMBRANE DISTILLATION

Abstract

Effective and sustainable seawater desalination can be achieved by two consecutive processes of freeze desalination and membrane distillation. Because the latent heat of ice fusion is only 1/7 of the latent heat of water vaporization, it is much more energy-effective to harvest ice crystals from seawater than to produce potable water by means of evaporation. It was found that potable water could be produced from seawater by freeze desalination with a 25% recovery rate within 1 h. Subsequently, the concentrated brine was treated by membrane distillation that is insensitive to high feed concentrations. When fabricating PVDF hollow fiber membranes, the green solvent triethyl phosphate (TEP) was used for the first time. The membranes had exceptionally high porosity (83 ~ 93%) and remained robust. It was demonstrated the much safer solvent TEP was able to replace toxic solvents commonly used in membrane manufacture and to produce membranes with highly competitive performance.