Fouling of nanofiltration and ultrafiltration membranes applied for wastewater regeneration in the textile industry

Textile effluents usually contain high concentrations of inorganics as well as organics, and are therefore difficult to treat. Membrane processes can be used for many of these wastewaters in the textile industry. Two typical examples are discussed: (1) the use of nanofiltration for the treatment of exhausted dye baths, in view of water recycling, and (2) the use of ultrafiltration for the removal of spin finish from waste water resulting from rinsing of textile fibres. Both applications are in principle feasible, but in practice the process is negatively influenced by membrane fouling. In the first application, fouling is assumed to be caused by (ad)sorption of organic compounds, which has a large influence because of the high concentrations used in textile dyeing. Furthermore, the high salt concentrations result in a decrease of the effective driving force because of the high osmotic pressures obtained for typical dye baths. Experimental results are discussed, and the applicability of nanofiltration is related to the characteristics of the dye baths for different dyeing methods. In the second application, the concentration of organic compounds is relatively low, but because of the hydrophobic nature of the spin finish compounds, a significant effect of membrane fouling is expected. An improvement is suggested by using nanofiltration membranes instead of ultrafiltration membranes.

Membrane fouling during the filtration of textile effluents is caused by the adsorption of organic compounds present in the wastewater. Depending on their ability to penetrate into the membrane, a significant effect can be observed. This is similar for UF and NF. A possible solution is to use tighter membranes, which might even lead to a flux increase in the specific case of surfactants. In NF, high salt concentrations cause a large osmotic pressure difference, which also leads to lower fluxes. Although this is not a fouling effect (it is reversible), the result in terms of water fluxes is the same as for membrane fouling.