Removal of azo-dye Acid Red 18 in two hybrid membrane systems employing a photodegradation process

An investigation of the application of the hybrid processes photocatalysis-ultrafiltration (UF) and photocatalysis-membrane distillation (MD) for degradation of an azo-dye in an aqueous solution is presented. Acid Red 18 was applied as a model dye and titanium dioxide Aeroxide (R) P25 (Degussa, Germany) was used as a photocatalyst. It was found that the photocatalyst was completely separated in the membrane processes applied. However, during UF a significant flux decline due to membrane fouling caused by TiO2 particles was observed. During 5 h of the process performance, the permeate flux was constant, but lower for ca. 25% in comparison with the maximum permeate flux (i.e., when distilled water was applied as a feed). Moreover, the products and by-products of photodegradation of model azo-dye passed completely through the UF membrane. The results obtained during the combined processes of photocatalysis-MD were much more promising. After 5 h of the processes performance, the model dye was removed completely, whereas TOC concentration was lowered by ca. 80%.