Photo-Catalytic Degradation Of Humic Acid By Titanium Dioxide

The HA (Humic Acid) accounts for more than 50% of the total organics in the natural water body, which can produce undesirable color and smell. During the disinfection process in the drinking water treatment, it can produce disinfection byproducts as a precursor agent which is harmful to the water itself, now HA has become the object under strict control in the drinking water supply industry. Photo-catalytic oxidation process has grown to be a widely-used water treatment technology in the past 20 years and many researchers worldwide has performed deep studies on it since Carey succeeded in degrading the PCBs under UV/TiO2 system. On this basis, this paper studied the photocatalytic degradation of HA and the whole study can be divided into the four parts as follows:effect factors on the degradation and mineralization of HA, degradation process analysis, mechanism analysis, removal efficiency of THMFPs.The catalysts selection was operated firstly in order to select out the catalysts both economical and easy to get, by comparing the degradation efficiency of different catalysts with different crystals in the form of pure catalyst and Ag-doped counterparts, the result showed that the pure P25 has good efficiency though it is a bit lower than the Ag-doped P25, but it surely can be available more easily. Under the formal condition with the initial HA mass concentration being 20mg/L and TOC being 7mg/L, the factors effect was studied which told us that with the increase of catalyst dosage and UV strength, the efficiency was also increasing to some extent, while pumping air was not helpful, this could be explained as the Nitrogen might disturb the adsorption process of HA onto TiO2 surface though the added oxygen could prevent the recombination of electron and cavity. Similarly, the addition of H2O2 into the system did not make evident improvement on degradation and mineralization either, for one something, the H2O2 improves the production of·OH meanwhile it also assimilates the generated·OH as a clearance agent. In the acid ambient, the HA was degraded faster than in the alkaline environment which should be attributed to the enhanced adsorption ability. As for the Ag-P25, it got a significant increase in the beginning of the reaction due to the enhancement of the adsorption as the adsorption experiment proved, which gives a good idea to the industry field because the industry can't bear that long time for the total mineralization of the wastewater. All the reaction kinetics fitted the Langmuir and Freundich equation first-order well and the lower the concentration was the higher the rate parameter was. Besides, the same batch P25 was regenerated for 10 times and the result said the mineralization rate still got up to 80% which demonstrated that the P25 could be recycled quite well for a long time.Secondly, the degradation process of HA was explained by Size Exclusion Chromatography(SEC) and Liquid Chromatography Organic Caborn Dector(LC-OCD) analysis, the combining results told us that during the reaction, the large HA molecular which is consisted of hydrophobic organic carbon, humics, acids, neutrals and building blocks was decomposed into smaller moleculars, in details, the hydrophobic substrates was broke down and the other parts was degraded gradually into small molecular and finally converted into the environmental friendly CO2, H2O and other organic acids. Concerned with the Ag-doped P25, it shortened the degradation time for one thing and for another thing, the intermediates during the process were different.Third, fluorescence analysis was adopted to explain the mechanism of the·OH oxidation and the photo-catalytic reaction happening on the solid-liquid surface, the result showed that photo-catalytic reaction is a combination of adsorption, conglomeration, degradation, mineralization and desorption with the adsorption being the precondition.Finally, the disinfection process was simutated and the THMFPs analysis was executed before and after the HA solution was treated by UV/P25 system. The result indicated that the CHCl3 decreased from 326μg/L to 15μg/L, which supported that the UV/P25 system has great potential and good prospect in the disinfection field of drinking water.