Dyestuff effluent treatment by integrated sequential photocatalytic oxidation and membrane filtration

In the present work, the combined photocatalytic oxidation/membrane filtration system is evaluated by decolorization, organic content and salinity reduction of a synthetic dyestuff effluent (SDE) containing the dye Reactive Black 5, with the scope to produce water that is able to be reused in the dyeing processes. The heterogeneous photocatalytic oxidation, as well as the photo-Fenton reagent, in the presence of UV-A or visible light, have been employed under various experimental conditions, in order to achieve complete decolorization and a substantial organic content reduction of the SDE. The addition of a membrane filtration unit, that is able to significantly reduce the high salinity of the photocatalytically treated SDE, can promote water reuse. The comparison of the performance of a nanofiltration and a reverse osmosis membrane by using operating variables, like applied pressure and recovery ratio, concerning the further polishing of the treated effluent shows that reverse osmosis produces water with low organic content and electrical conductivity. The integration of either photocatalytic methods with a reverse osmosis unit, leads to complete decolorization of the SDE, as well as to a more than 95% reduction of the initial organic content and salinity, thus, yielding a permeate with the potential to be reused in the dyeing process.