Boron removal from geothermal water by nanofiber-based membrane distillation membranes with significantly improved surface hydrophobicity

In this study, the hydrophobic nanofiber membranes were fabricated via electrospinning method for the removal of boron and salt from geothermal water by air gap membrane distillation (AGMD). Scanning electron microscopy (SEM), contact angle, liquid entry pressure (LEP) and membrane thickness were analyzed for the characterization of electrospun nanofiber membranes (ENMs). Firstly, ENMs were fabricated by using four different concentrations of polyvinylidene fluoride (PVDF) dope solution and PVDF concentration was optimized by considering both membrane characterization and filtration performance results. Then, the effect of heat treatment on membrane characterization and filtration performance was studied in which it was observed that the permeate flux was improved due to the decrease in membrane thickness while the mechanical strength of the ENMs was enhanced. Thereafter, different concentrations of polytetrafluoroethylene (PTFE) micro powder were added to the optimized PVDF membrane and the permeate flux was improved to 27.7 kg/m2 h. Finally, the real geothermal water experiments were examined using the optimized ENMs and it was concluded that the quality of permeate water was consistent with standard values for irrigation water which was less than 0.5 mg B/L and 250 μS/cm for both optimized membranes.