Nanofiltration as a final step towards textile wastewater reclamation

Water scarcity makes industrial wastewater reuse necessary, especially in those industries characterized by both high water consumptions and extremely polluted effluents as textile industries. Membrane technologies are very efficient to treat industrial effluents for water reuse successfully, since their application entails important reductions in pollutant concentration. In the present work, a direct treatment of a textile industry effluent by means of a combination of ultrafiltration (UF) followed by a final nanofiltration (NF) stage is presented. Two different NF membranes were tested in order to compare their behaviors. For that, the influence of the feed water pH and transmembrane pressure (TMP) of the NF process were investigated. The UF results showed that the highest permeate fluxes were achieved at pH 11. Related to NF experiments, NF270 reached for the same operational conditions higher fluxes and salts rejection values than the Duraslick NF. No influence of pH was found for the permeate flux. However, the pH effect was manifest for the salts rejection. Although COD, color, and turbidity removals were high in all tests, Duraslick NF showed an average slightly better removal of COD and color. The results obtained confirm the viability of this treatment for water reuse in most of the different processes carried out in these kinds of industries.

UF serves as a good alternative to treat raw effluents of textile industries for a later NF stage, producing a permeate stream with enough quality to be reused in lesser quality demanding processes. Since it is proposed as a direct treatment for the raw water, exhaustive prefiltering prior to this UF process is needed in order to avoid damaging and rapid fouling of the UF membrane surface. The results of UF experiments indicate similar permeate characteristics at the tested pH. However, the maximum permeate flux was obtained at pH 11.