Study On Preparation And Application Of Catalytic Ozonation Membrane

Humic Acids?HA?are commonly found in surface water and notorious forcoloring the water brown,forming complexes with metals and organic pollutants,and reacting withactive chlorine and formingdisinfection by-products?DBPs?.Therefore,the removal of HA effectively is of significant importance.Membrane process has been gained considerable attention in HA treatment.However,the problems of single function and membrane fouling have been the major limitation to further development of this process.Catalytic ozonation can degrade organic pollutants effectively,but there are still some problems that catalyst running-off and recycling in its application.The catalytic ozonation membranes are prepared by loading the catalyst with the high catalytic activity to the membranes.The catalytic ozonation membranes coupling the catalytic ozonation probably result in increasing the efficiency of membrane separation,avoiding the catalyst running-off,and reducing the membrane fouling.In this work,a new kind of catalytic membrane with high catalytic activity was developed,which was coupled with catalytic ozonation to treat HA.The main results were obtained as below:?1?The nano-TiO₂ catalysts were synthesized by the sol-gelmethod.Then the optimal experimental conditions for the degradation of HA by nano-TiO₂ were optimized by response surface methodology.The optimal conditions were obtained: calcination temperature of nano-TiO₂,catalyst dose,ozone concentration,pH were 565?,0.31 g/L,16.91 mg/L,6.91,respectively.Under these conditions,the removal rate of HA was 87.15%.?2?Ti-Ce composite was fabricated by the sol-gelmethodat molar ratios of Ce³⁺ to Ti⁴⁺between 0.2 and 1.0.Under the same conditions as?1?,theresults of HA ozonation suggested that the Ti-Ce?1/0.8?composite had thehighest catalytic efficiency.In the comparison of ozone utilization efficiency,molecular weight distribution in the process of single ozonation,catalytic ozone by nano-TiO₂,and catalytic ozone by Ti-Ce?1/0.8?composite,the Ti-Ce?1/0.8?composite increased the ozoneutilization efficiency by 62.0% and had strong performance for the degradation of HA and intermediates,which indicated that Ti-Ce?1/0.8?composite had higher activity.Thekinetics of homogeneous and heterogeneous reactions were also investigated during the process of catalytic ozonation of HA.The apparent first-order rate constants of the homogeneous andheterogeneous reactions were 0.054 min-1and 0.066 g·L-1·min-1,respectively.Moreover,the kinetic contribution of the heterogeneousreactions to HA degradation??het?was less than 50% at all pH conditions,implying that the catalytic degradation of HA occurred in the solution.?3?Catalytic ozonation membranes were prepared by blending with different contents of Ti-Ce?1/0.8?composites into PVDF matrix.SEM images showed that Ti-Ce?1/0.8?compositewas loaded on the surface of PVDF membrane successfully,and the porosity and mean pore radius of membranes were enhanced after adding Ti-Ce?1/0.8?composites?2%?.The effects of Ti-Ce?1/0.8?composites content on the membrane performances,such as hydrophilicity,pure water flux,rejection rate,mean pore size and porosity were investigated in detail.The contact angle tests indicated that the contact angle of catalytic ozonation membranes decreased to the lowest by embedding 2% of addition,and a further increase of addition?more than 2%?did not result in decreasing in the contact angle.The pure water flux of 2% Ti-Ce?1/0.8?/PVDF membrane was the most obviously increased by 32.61 L·m-2·h-1,compared with PVDF membrane,1%Ti-Ce?1/0.8?/PVDF membrane and 3% Ti-Ce?1/0.8?/PVDF membrane,although the rejection of bovineserum albumin?BSA?was slightly decreased.The porosity and mean pore radius of 2%Ti-Ce?1/0.8?/PVDFmembrane were bigger than that of the other three.?4?On the basis of catalytic ozonation membranes,the experiments were designed and performed with HA as a target.As a result,the removal of HA and TOC were the order 2%Ti-Ce?1/0.8?/PVDF membrane +O3 > 3%Ti-Ce?1/0.8?/PVDF membrane +O3 > 1%Ti-Ce?1/0.8?/PVDF membrane +O₃ > PVDF membrane +O3 > O₃.The flux decline of PVDF membrane was the most serious with a reduction of approximately 31% of the initial fluxat the end of filtration,and the membrane flux of 2%Ti-Ce?1/0.8?/PVDF membrane was apparently improvedby 23%.Furthermore,compared with other membranes,the 2% Ti-Ce?1/0.8?/PVDF membrane exhibited the best performance with a reduction ofapproximately 37% and 58% for reversible and irreversible fouling,respectively.It was indicated that the 2% Ti-Ce?1/0.8?composite enhanced the catalytic ozonation in the membrane pores,and the catalytic ozonation membrane had the characteristic of self-cleaning.