A Novesl rotary drum filtering reactor for photocatalytic decomposition of phenol in slurry containing titanium dioxide nanoparticles

Abstract

Two titania with different crystallite sizes (Tl (anatase, average crystallite size of 30 mn, BET surface area of 56-59 m2 g-1) and Nl (anatase, apatite coated particles of 400-500 nm, BET surface area of 64 m2 g-1) were investigated using a shaker-type photoreactor to find out the better photocatalyst for degrading the phenol solution and applying it in a novel rotary drum filtering photoreactor system. Tl proved to be the better photocalyst, whose highest decomposition and TOC depletion efficiency of phenol after 60 min were 19.72 and 14.86% respectively. A rotary drum filtering photoreactor used Tl as photocatalyst and it could eliminate the problem of catalyst loss by elutriator with the effluent stream. In this study, the thickness of TiO2 cake on the HEPA filter was 200 µm, the initial concentration of phenol was 25 ppm, and the volume of treated water was 25 dm3. The rotating speed of the drum was 5, 10, 20, or 30 rpm and the filtration velocity was 0.52, 0.73, or 0.84 cm min-1. Preliminary results on the effect of the rotating speed on the water film thickness as the rotating speed increased. The experimental results revealed that the decomposition rate of phenol and TOC depletion rate decreased against the increased rotating speed. The suitable speed of the drum was 5 rpm. As for the filtration velocity, the phenol decomposition rate and TOC depletion rate achieved the optimum when the filtration velocity was 0.73 cm min-1. To obtain the intrinsic capacity of TiO2 cake in degrading phenol, the photolysis of phenol was also studied. The results indicated that the photolysis efficiency of phenol after 360 min was 4.96% while the decomposition efficiency of phenol was 21.47%. They indicated that the presence of TiO2 cake was a key factor for degrading phenol. In addition, the dark adsorption of phenol on Tio2 cake was verified. We found that the adsorption efficiency of phenol on TiO2 cake for 30 min was insignificant, which was about 0.95%.