Photocatalysis And Membrane Separation Hybrid System Used In Dyeing Wastewater Treatment And Reutilization

As a novel water treatment technology emerged in recent years, photocatalysis/membrane hybrid process has unique advantages and great application potential especially for a varity of high concentration organic wastewater treatment and reutilization. In this study, TiO₂ particle was first prepared by a mild acid-sol route under low temperature （<100℃）, whose X-ray diffriaction patterns showed that the average crystal size was 3.6 nm with all anatase phase. Then, the catalytic degradation process of reactive brilliant red X-3B azo dye was taken in a slurry photocatalytic membrane reactor with a 250 W ultraviolet lame. Two kinds of commercial polymeric flat sheet microfiltration （MF） membranes N6 and CN-CA with pore sizes ranged 0.1-3μm were selected aiming at purifying the reaction raffinate and recycling the TiO₂. Operating parameters which impacted the efficiency of photocatalytic degradation and membrane separation were investigated in detail.Results showed that self-made TiO₂ photocatalyst had a great degradation capability against X-3B dye wastewater. The optimal bleaching rate was 99% after 60 min reaction time when the concentration of dye and TiO2 was 50 mg/L and 25 mg/L respectively. The reaction obeyed L-H first order reaction kinetic model. Based on the principle of colloid isoelectric point, the average particle size of TiO₂ increased to 16μm because of its reunion in solution, which was doubled comparing to that in acidic and alkaline conditions. This became the main reason for the significant influence of pH to the X-3B bleaching rate. Although ultrasonic treatment dispersed the reunion of TiO₂, it could not work long.The aggregation of TiO₂ in solution made it possible that MF had good retention effect to TiO₂. In neutral pH, the structure of TiO₂ interception layer on membrane surface was found to be the loosest through the scanning electron microscope （SEM）, and the membrane flux reached a high value of 18 m3/（m2·h） with a rejection of 98%. The self-rejection by TiO2 cake layer was confirmed to dominate the separation process.Based on the experiments, the optimal operating condition for hybrid process was pH at 4.0 and dosage ratio of dye to TiO₂ was 2:1. All six MF membranes N6 and CN-CA with different pore sizes tested showed high TiO2 rejection and recovery rate above 94%.