Ultrafiltration for colour removal of tannery dyeing wastewaters

Investigation of ultrafiltration (UF) performance for the purpose of removing the colour of three different effluents coming from the dyeing cycle of a tannery industry was carried out using four polyethersulphone (PES) membranes with molecular weight cutoffs (MWCO) of 40, 10, 5 and 3 kDa. A closed-loop recycle (CLR) and batch (B) modes of operation were used. For the first mode of operation, the evolution of permeate flux and colour rejection vs. time of operation was evaluated. For the batch concentration experiments, attention was focused upon the evolution of the rejection and/or concentration of colour with the volume reduction factor (VRF) and on the decrease of the permeate flux as a function of VRF for all the membranes under study. All experiments showed the occurrence of concentration polarization and adsorptive fouling with a pronounced effect for the membranes with higher MWCO. Due to that, the 40 and 10 kDa membranes did not offer a significant regaining of permeate productivity. High-colour and low-solids rejections were observed for all the experiments, showing a marked dependence on the type of effluent used.