The Effect Of Increased Hydrophobicity On Water Flux And Salt Rejection In A Solar Membrane Distillation Module

Water scarcity is a problem experienced by millions of people around the world. To help solve this problem, a thermally driven membrane separation technique was proposed. The aims of the research were to construct a solar distillation module capable of converting saline water into fresh water through membrane distillation and to gauge the impacts and drawbacks of increased hydrophobicity in a polypropylene membrane. It was hypothesized that increasing hydrophobicity through the use of water repellent treatment would hinder mass transfer and enhance salt rejection. To test this, treated and untreated polypropylene membranes were used to distill 125 ml of 3.5g/L NaCl salt water in the membrane distillation module. After the allotted test period, weight and conductivity measurements were taken for the distilled water. The salt rejection factors (%) and water flux rates (g/hr/dm2) were calculated, and a two-sample t-test was conducted for both indices at the alpha=0.05 level. The t-statistic revealed a significant difference in salt rejection, t(4) = -6.99, p \u3c .01, with the treated membrane (M = 97.53%) producing better quality fresh water than the untreated membrane (M = 55.6%). There was also a significant difference between the water flux rates of the two membrane types; t(4) = 2.81, p = 0.03. As expected, the untreated membrane allowed for more efficient mass transfer, resulting in faster distillation. These data supported the hypothesis that increased hydrophobicity does slow down the transfer of water vapor across a polypropylene membrane while enhancing the quality of distillation