Treatment of dye aqueous solutions using nanofiltration polyamide composite membranes for the dye wastewater reuse

Five different kinds of dye aqueous solutions (Direct Red 75, 80 and 81, and Direct Yellow 8 and 27) were treated with nanofiltration (NF) polyamide (PA) composite membranes to obtain basic information on the dyeing wastewater reuse. The separation of dyes by the NF PA membrane appeared to be a good process for the effective removal of dyes from dyeing wastewater. The extent of the separation of dyes by the membrane was almost 100% for all of the dyes used, producing colorless water. When artificial dyeing wastewater containing Direct Red 75, PVA, NaCl and Na2SO4 as components of the wastewater was used as a feed solution for the membrane separation process, the separation efficiency turned out to be good, especially when one of the chemical coagulants, alum, was used for the pretreatment of the artificial dyeing wastewater. About 20% of improvement of flux was obtained by the pretreatment of the wastewater.