The potential of membrane distillation in recovering water from hot dyeing solution

The possibility of recovering water from hot dyeing solution has been investigated in this work by using membrane distillation (MD) made of polyvinylidene fluoride (PVDF). A series of PVDF hollow fibre membranes with various polymer concentrations (12–18 wt%) were prepared by dry-jet wet inversion method and were designed for direct contact membrane distillation (DCMD) application. Prior to the treatment of hot dyeing solution of 80 °C, the PVDF membranes were characterized in terms of scanning electron microscopy, atomic force microscopy, gas permeation, liquid entry pressure, contact angle and membrane porosity. It is reported that the surface roughness, contact angle and liquid entry pressure of PVDF membrane were increased while mean pore size and porosity decreased with increasing PVDF concentration in the dope from 12 to 18 wt%. Based on the DCMD results, it is found that 12 wt% PVDF membrane showed the highest permeate flux due to its smooth surface, high membrane porosity, large mean pore size as well as big macrovoids formed at the middle cross-section of the hollow fibre membrane. Although MD flux tended to decrease with increasing polymer concentration, all the resulting membranes were still able to achieve excellent dye rejection (at least 99.78%), indicating that MD is very potential to be employed in treating dyeing solution which normally discharged in hot condition from textile industry.