Influence of Feed Composition on Distillate Flux and Membrane Fouling in Direct Contact Membrane Distillation

Two polymeric membranes, PTFE and PVDF, were employed in a direct contact membrane distillation system to investigate the effects of NaCl concentration, feed temperature, and flow rate on distillate flux and NaCl rejection. The distillate flux increases with increasing the feed flow rate or temperature, PTFE membrane has a higher distillate flux than that of PVDF, and PTFE membrane also has a larger solute rejection than that of PVDF membrane. The decrease of solute rejection by PVDF membrane is owing to the membrane pore wetting, especially at high feed temperature and flow rate. The membrane fouling tests under various feed compositions show that increasing NaCl concentration from 4.5 wt% to 10 wt% or the addition of CaSO4 or BSA into NaCl solution does not cause severe fouling on the PTFE membrane. The distilled water flux recovery (FR) is about 0.96–0.97. The addition of MgCl2 or MgSO4 has a little significant fouling tendency, the distilled water FR is about 0.87–0.88.