Dye wastewater treatment by direct contact membrane distillation using polyvinylidene fluoride hollow fiber membranes

The potential of 18 wt.% polyvinylidene fluoride (PVDF) hollow fiber membrane blended with ethylene glycol (EG) for the treatment of dye solution using direct contact membrane distillation (DCMD) system was investigated. The PVDF membrane was prepared using the dry-jet wet spinning method and was characterized in terms of membrane morphology, porosity, wetting pressure, gas permeability and degree of hydrophobicity. The membrane was tested using dye solution containing 0.5 g l(-1) reactive black 5 (RB5). The experimental period was prolonged to 6 h in order to analyze the fouling tendency and membrane durability during the DCMD process. The results showed that the modified PVDF membrane was able to produce consistent flux (i.e., 9.82 +/- 0.52 kg m(-2) h(-1)) throughout the DCMD experiment while maintaining excellent dye rejection (i.e., 99.86 +/- 0.04%). With respect to membrane fouling, it was found that the lumen side of the membrane was significantly stained with color (compared to outer membrane surface) due to the physical-chemical interaction between reactive dye and membrane structure. Although membrane fouling was experienced in this study, its impact on MD performance in terms of flux and rejection was negligible, mainly because MD is not a pressure-driven process.