The removal of reactive dye printing compounds using nanofiltration

A synthetically prepared reactive dye print wastewater, mimicking real wastewater obtained from a local textile mill, was treated by nanofiltration using an NFT-50 membrane in a plate and frame module configuration at different cross-flow velocities (0.4, 0.6 and 0.8 m/s) and pressures (2–15 bar). The nanofiltration membrane was evaluated for membrane fouling, permeate flux and its suitability for removing colour, conductivity, Na+ ions and COD as a function of operating pressure and feed concentration. The permeate separation efficiency was monitored by measuring the removal efficiency of colour, conductivity, Na+ ions and COD retention. The membrane achieved high dye retention for each of the four dyes (from 99.4 to 99.9%) and electrolytes used (63–73%). The retention of organic substances varied between 20 and 50%, depending on the pressure used; higher retentions were achieved at higher pressure and by using higher cross-flow velocities.