Resourcization Investigation And Applications Of Tar Deep Processing Wastewater Electrochemical Oxidation Treatment

Coal is the basic energy resource of our country. A large amount of fly ash is produced in coal to electricity process. In addition, lots of poisonous and harmful wastewaters were generated in coal chemical production processes. As an effective means to dispose the wastes, resourceful treatment could not only reduce the pollution mentioned above, but also recycle the resources contained in these wastes. Focused on the organic wastewater produced in tar deep processing at coal chemical industry, a novel electrochemical oxidation system was investigated to degrade the wastewater and produce hydrogen gas. On the other hand, fly ash and biomass were continuously used to prepare composite catalyst following with the adsorption of transition metal ions. The composite catalyst was applied to enhance the degradation of organics in tar deep processing wastewater electrochemical oxidation treatment. This new approach could be an effective exploration of fly ash and biomass utilization and achieve the purpose of "disposal of wastes by wastes". The achieved results show below:1. Results obtained from hydrogen gas production coupled with phenol degradation in the new system show that the concentration of collected hydrogen is greater than98%, the presence of phenol type organics could strengthen hydrogen production, and the first order kinetics equation could well describe the COD removal. Three stages were observed of phenol degradation, COD removal, hydrogen production, kinetic, Instantaneous Current Efficiency (ICECOD), Hydrogen Yield to COD (YH2). and energy efficiency during concentrated phenol electrochemical oxidation at3V applied voltage, and first order model could well describe each stage rather than the whole process, and the kinetics constant were1.86,4.11and7.77×10-3h-1, respectively. ICECOD of the anode reactions slowly rose from0.326to0.357and then rapidly increases to0.471in the first two stages, while sharply decreased to0.018in the third stage. YH2of the cathode reactions increased from2.629LH2/g COD to3.168L H2/g COD in the first stage, and then reduced to2.416L H2/g COD in the second stage. In addition, the removal rates of phenol degradation, COD removal and hydrogen gas production were improved by increasing the applied voltage, while the ICECOD, and hydrogen energy efficiency reduced compared with3V applied voltage.2. The characterization results of high aluminum fly ash (FA-A) show that FA-A is mainly composed of SiO2and Al2O3(>50%), which has higher chemical and thermal stability, and the C, N, O contained in straw dust (SD-C) are beneficial for transition metal ions adsorption. Results obtained from nickel ions adsorption by FA-A and SD-C show that the adsorption capacity increased with the rise of initial concentration, and decreased with adsorbent dosage, while the pH of the solution had little influence on nickel adsorption by FA-A and SD-C. The maximum adsorption capacity obtained from the Langmuir isotherm model is10.49mg/g and9.109mg/g, respectively. The adsorption process is a physical adsorption, which is controlled by external mass transfer and intra particle diffusion process.3. The research results obtained from the preparation of catalyst by FA-A and SD-C after transition metal ions adsorption and the application in electrochemical oxidation process show that FA-A could be the host due to its chemical stability and high aluminum content, and SD-C formed good pore structure of the composite catalyst surface. On the other hand, the COD removal increased from30%to nearly60%when composite catalyst added, which is higher than that of approximately50%with FA-A based catalyst. Compared with nickel and copper doped composite catalyst, iron doped composite catalyst had better removal efficiency of organics. Furthermore, the degradation time cut504h to144h, COD removal is approximately100%, and hydrogen production rate increased nearly10times in concentrated phenol electrochemical oxidation process with the application of the composite catalyst. The organics removal and hydrogen production could be strengthened by increasing the applied voltage and using the composite catalyst, but it could be more suitable with the composite catalyst considering the current efficiency and energy consumption. Besides, the mechanism of phenol electrochemical oxidation degradation is mainly oxidation/catalytic oxidation, while adsorption/electric-adsorption and electric flocculation occurred to the degree. Therefore, it is feasible that the direct preparation of composite catalyst by the FA-A and SD-C after the adsorption of transition metal ions and its application in organics electrochemical oxidation process.4. From the perspective of energy consumption, efficiency and economy and the degradation route of phenol, it is determined that organics were degraded to ring-open stage by catalytic electrochemical oxidation, and combined with biochemical and advanced processing in tar deep processing wastewater treatment. The catalytic electrochemical pretreatment could effectively reduce the organics and COD in the wastewater, and improve biodegradability of the wastewater. The final effluent could be reused. The cost and technical economy accounting were analized finally.