Photocatalytic Degradation Of Quinoline Aqueous Solutions By P25 Films And Its By-products On The Effect Of Microbial Inhabition

Persistent pollution of multiple artificially synthesized organic compounds could be effectively solved by photocatalytic technology, while its combined with biological treatment technique shows a optimum advantage in the wastewater treatment. However, there exist some problems limit its application in practice, such as the difficult of recycled powder catalyst, the long time oxidation and high energy consumption, and so on. A great deal of lab-scale research proved that the wastewater contained many refractory organic matter still has inhibitory effect on microorganism after photocatalytic oxidation. Therefore, this research present an introduction of two photocatalysts, a newly three-dimensional photocatalytic reactor and a combined treatment of photocatalysis and biological technology. As a typical chemical raw material, quinoline, which contains a fused-ring result in hardly biodegradation, was selected for the research target. The research mainly aimed at the preparation of photocatalyst, photocatalytic degradation behavior and the biological effect of photocatalytic effluent. The main results are summarized as follow:In order to synthesize a segragative powder photocatalyst, nanomater Au was coated on the surface of superparamagnetic iron oxide （SPIN） to prepare a FeO_x@Au photocatalyst by a facile deposition-precipitation method. Although part of SPIN was oxidized intoα-Fe₂O₃ after calcination, the FeO_x@Au also remains a favorable effect of magnetic separation. What’s more, it displays a high photocatalytic activity for the degradation of quinoline aqueous solutions. Nano-Au loaded on the surface of SPIN could enhance the photocatalytic activity, while the degradation efficiency of quinoline was also lower than Deguessa P25 TiO₂.A kind of P25 TiO₂ films was synthesized by dip-coating/calcination route in situ without any binder. The porous nickel coated with 10 percent of P25 sol （named Ti-10） had an optimal photocatalytic activity for the degradation of quinoline aqueous solutions, which was attributed to porous surface structure fabricated by nano-sized titanium dioxide consisted of two crystal phase and incorporated with a NiO interlayer formed during calcination.Accordingly, Ti-10 film was used to fabricated a newly continuous-flow three-phase photocatalytic reactor. The effect of initial concentration, reaction time, light flux and aeration on the efficiency of photodegradation were also investigated. The result indicated that the photocatalytic efficiency could be significantly enhanced by increacing the light intensity, aeration and reaction time. The optimum pH value for quinoline degradation was at 4 and neither the initial concentration nor temperature was the primarily factors for the photocatalytic reaction.The second-order decomposition rate of quinoline may be approximately expressed in the terms of Langmuir-Hinshelwood kinetics, which indicated that the photooxidation of quinoline mainly occured on the surface of P25 film. So, the direct reduction and oxidation of photo-induced electron and hole were the predominant process of the innitial degradation of quinoline. Increasing the initial concentration of quinoline in water may led to the enhancement of decomposition efficiency of organic matter and the decrease of photooxidation rate of quinoline in water, which was mainly attributed to the influence of competitive sorption between the product and quinoline or free radicals on the film surface. The photocatalytic kinetics was obtain with the follow equation: r_a=0.35×10^-3exp（-16906/RT）I_a^0.53×1.29C₍o2_/(1+1.29C_o2)×0.024C_q/(1+0.024C_q0)Here, the overall apparent activation energy was 16.9 kJ/mol, while the rate constant of apparent adsorption was 0.024 L/mg.A number of intermediates were identified by the combined method of HPLC and GC/MS techniques during the photooxidation process of quinoline, include 2- and 3-Pyridinecarboxaldehyde, 2- and 3-Acetylpyridine and 2-（1H）-Quinolinone. A possible photooxidation pathways can be observed in aerobic conditions. At first, photo-induced electron quickly reduced the oxygen molecules absorbed on the TiO₂ surface with the formation of O₂-. The activated oxygen species generated on the TiO₂ surface can participate the photo-reduction process of quinoline just because it remains active for some time in water, and then released the photo-induced electron to the active sites on the TiO₂ surface. Considering the reaction between quinoline and O₂- an addition to the position -2 of quinoline may take place the same way as for an ordinary deprotonation. Thus, the product derived from deprotonation at position 2 is 2-hydroxyquinoline, which cause the increasement the electrostatic charge density of quinoline and led to easily oxidation by active radicals at position 3. Finaly, it led to ring opening process via quinoline（2,3）dion with the formation of organic compounds with aromatic ring.The effluent from photocatalytic reactor, which photooxidated at 30min and 60 min reaction time seperately, was directly biodegradated by activated sludge with the flask culture method for the determination of the influence on the culturable microbial and enzyme activity. The result showed that the effluent photooxidated for 30 min inhaibited the growth of culturable bacteria in activated sludge and the activity of dehydrogenase and protease was significantly inhabited by the decrease of the total biomass. However, the effluent was not affected the growth of bacteria after photocatalytic oxidation for 60 min, indicated that quinoline and intermediates could be biogradated by native bacteria in activated sludge.An integrated photocatalystic oxidation and biodegradation reactor was successful designed to study the biodegradation of photooxidated effluent from photocatalytic reactor. When the photooxidation reaction lasted for 60 minutes, the chemical oxygen demand of effluent from the intergrated reator remained at about 50mg/L, indicated the stable remove efficency. However, the water becomes pink when the photooxidation reaction time reduced to 30 minutes, and then the chemical oxygen demand of effluent rised to about 90 mg/L.The effect of microbial community structure caused by quinoline aqueous solutions photooxidated for 30 min was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis technology （PCR-DGGE）. The result showed that the effluent inhibited the microbial activity in activated sludge and led to the decrease of species diversity. Thereafter, in activated sludge, due to the adaptability of low nutrition medium, the community number of uncultured Clostridium sp. increased significantly and becomes one of dominant microflora. Accordingly, Sphingopyxis granuli sp. was believed to preferentially biodegradate or co-metabolish quinoline or it’s by-products and then multiply advantage bacterium group to be a dominant microflora, which is a culturable bacteria with high biodegradation ability could be isolated from sewage activated sludge.