Ultrafiltration as a pre-treatment of other membrane technologies in the reuse of textile wastewaters

Water consumption in textile processes is very high and moreover a large amount of polluted effluents is generated. Many textile industries perform only a biological treatment of these effluents. In countries with water scarcity, the reuse of the secondary effluents represents an interesting solution. In this work, ultrafiltration (UF) has been studied as a pre-treatment of nanofiltration (NF) and reverse osmosis (RO) in the reuse of the secondary effluent of textile wastewaters from different processes of textile industry. In the first experimental stage, experiments in a flat module were carried out with four UF membranes in order to select the most suitable one. The secondary effluent after a 50 micron cartridge was treated and the COD was analyzed. According to the highest COD removal, the membrane selected was the IRIS 3028 from Rhodia–Orelis with a cut-off of 10 kDa. In the second stage, experiments were performed with the membrane selected in a spiralwound module. The aim of these experiments was to characterize the membrane performance and to optimize the cleaning procedure. The results showed that the COD removal obtained with this membrane was not enough to directly reuse the permeate in the industry. However, the permeate quality obtained guaranteed optimal conditions for its use as a NF feed. The combined UF/NF process was more efficient than a process exclusively based on NF as the NF fouling was reduced considerably and the total water recovery was higher.

A membrane with MWCO of 20 kDa or less is necessary in order to reduce COD and to protect a posterior treatment using NF or RO. Flux Table 6 COD rejection for one-step concentration experiments Feed COD (mgO2 L−1) COD rejection (%) Final volume of concentrate (L) 29.4 39.8 38.9 39.4 37.6 38.5 Flux (L m–2 h–1) Test Normalized flux 134 138 142 146 150 154 158 162 166 170 174 178 182 186 190 t (h) Fig. 5. Flux for multi-step concentration experiments.