Experimental Reserch On Photocatalytic Oxidation Technology Treating Toxic Pollutants In Coking Wastewater

The problem of coking wastewater treatment has always been the difficult problem in the wastewater treatment domain at home and abroad. It is one of the focus problems to research and exploit the economic and effective treatment technology and process of the coking wastewater.The topic selected the alumina ceramic membrane as support, and made supported nanometer TiO₂ photocatalyst by sol-gel method, and then studied the morphology, phase composition and structure of the catalyst, which were characterized by scanning electron microscope and x-ray diffraction. The research showed that the nanometer TiO₂ catalyst supported ceramic membrane by sol-gel method was compact and uniform in structure and adhered well to the substrate, its particle was smaller and the size was less than 100nm, the film was porous morphology and the the crystal type of the films was anatase. The porous structure of the film surface was helpful to improve the photocatalyst to the degraded matter adsorption property and to improve the degradation efficiency.The experiment studied the degradation of photocatalytic oxidation technology treating the toxic pollutants in the coking wastewater by the nanometer TiO₂ catalyst supported ceramic membrane. Under the constant conditions of the UV light intensity and wastewater concentration, it used the method of orthogonal experiment to study the influence factors of the solution PH value, the UV irradiation time, the quantity of the catalysts, the additon of H₂O₂ and so on to the degradation rate of CODcr, ammonia nitrogen, cyanides and volatile phenol in coking wastewater. According to the result of the orthogonal experiment, it was different among different level of influence factors to the degradation trend of each monitored index. After the orthogonal experiment, single factor anaysis was done to the monitored indexes, and determined the optimal conditions of each monitored index:1.The optimum condition of the degradation of CODcr was that the UV irradiaton time was 27h, the seven layers number of the ceramic membrane, the addition of H₂O₂ was 0.1ml per 100ml coking wasterwater and the PH value was 3. Under the optimal condition, the degradation of CODcr was 95.5%.2. The optimum condition of the degradation of ammonia nitrogen was that the UV irradiaton time was 24h, the three layers number of the ceramic membrane, the addition of H₂O₂ was 2.2ml per 100ml coking wasterwater and the PH value was 10. Under the optimal condition, the degradation of ammonia nitrogen was 74.9%.3. The optimum condition of the degradation of cyanides was that the UV irradiaton time was 8h, the three layers number of the ceramic membrane, the addition of H₂O₂ was 0.1ml per 100ml coking wasterwater and the PH value was 7. Under the optimal condition, the degradation of cyanides was 99.9%.4. The optimum condition of the degradation of volatile phenol was that the UV irradiaton time was 26h, the seven layers number of the ceramic membrane, the addition of H₂O₂ was 0.1ml per 100ml the coking wasterwater and the PH value was 3. Under the optimal condition, the degradation of volatile phenol was 99.2%.On the basis of the above research, the composite indexes were studied ulteriorly. Comprehensively considered the degration condition, the economic benefit and the outlet water quality and so on of each index, determined the optimal condition of degradation of the toxic pollutants in the coking wastewater was that the UV irradiaton time was between 15-24h, the layers number of the ceramic membrane was between 2-4 layer, the addition of H₂O₂ was between 0.4- 1.0ml per 100ml coking wasterwater and the PH value was between 8-9. Under the optimal condition, the degradation of CODcr was between 84.6-85.5%, ammonia nitrogen was between 36.6 - 63.0%, cyanides was between 92.6 - 94.4%, volatile phenol was between 97.3-97.5%.In addition, using the nanometer photocatalyst of ZnO, SiO₂ and the composite catalysts of ZnO, SiO₂ and TiO₂ supported the same substrate, respectively contrasted them with the optimal condition of TiO₂ degradation of the toxic pollutants in the coking wastewater. Using ZnO coated by TiO₂, the research showed that degradation of the four contaminations was all optimal, and the degradation of CODcr, ammonia nitrogen, cyanides and volatile phenol was respectively 87.6%, 75.7%, 96.9% and 98.7%, therefore, the optimal photocatalyst was ZnO coated by TiO₂.The research showed that the toxic pollutants CODcr, ammonia nitrogen, cyanides and volatile phenol in the coking wastewater treated by photocatalytic oxidation had higher degradation under different condition, on the same condition, TiO₂ was the best one among the single photocatalyst, ZnO coated by TiO₂ was the best one among the composite catalysts.Figure 35 table 13 reference 62...