Integration of photocatalysis with membrane processes for purification of water contaminated with organic dyes

The aim of the presented work was the investigation on the possibility of application of the hybrid photocatalysis/membrane processes system for removal of azo dyes (Acid Red 18, Direct Green 99 and Acid Yellow 36) from water. The photocatalytic reactions were conducted in the flow reactor with immobilized photocatalyst bed and in the suspended system integrated with ultrafiltration (UF). A commercially available titanium dioxide (Aeroxide (R) P25, Degussa, Germany) was used as a photocatalyst. The solution after the photocatalytic reaction was applied as feed in nanofiltration (NF) or membrane distillation (MD). The changes of various parameters, including concentration of dyes, pH and conductivity of the solution, and TOC and TDS contents were analyzed during the process. It was found that the solutions containing the model azo dyes could be successfully decolorized during the photocatalytic processes applied in the studies. The application of OF process results in separation of photocatalyst from the treated solutions whereas during the NF and MD high retention of degradation products was obtained.