Treatment and reuse of textile effluents based on new ultrafiltration and other membrane technologies

Different membrane processes were experimented on at pilot scale to verify the possibility of reusing textile wastewater. The pilot plant used sand filtration and ultrafiltration (UF) as pre-treatments for a membrane process of nanofiltration (NF) or reverse osmosis (RO). UF was obtained by the installation of an innovative module designed on flat membranes operating under vacuum; the configuration of the NF and RO membranes was spiral wound. The efficiency of the various treatments in removing pollutants from textile wastewater from an activated sludge plant was tested on the reduced scale to optimize the industrial plant design. The UF module tested works at low operating pressure (that involves low energy costs) and guarantees a constant permeate (feed of the next membrane process of NF or RO). The RO permeate can be reused in the dyeing processes as demonstrated by many yam dyeing tests on the industrial scale. NF does not reach the retention behaviour of RO (total hardness removal of 75% and > 90% for NF and RO respectively). Nevertheless, a change in the freshwater treatment (at present an ion-exchange resin softening) downstream from the use of process water in the factory would decrease the secondary effluent salinity, so the design of the advanced purification industrial plant could reasonably foresee a NF treatment instead of RO, allowing a reduction of the costs.