Electrochemical Catalytic Oxidation Technique For Treatment Of Coking Wastewater

Nowadays, coke plants and coal gasification plants are available in developing countries, so a large volume of wastewater generated from the coking industry contains phenolic compounds, cyanide, thiocyanide and polynuclear aromatic hydrocarbons (PAHs). The presence of these pollutants in water sources produces long-term environmental and ecological impacts, and which makes it difficult to treat the wastewater by conventional technologies. Advanced Oxidation Processes (AOPs) is the technical key points in treatment of wastewater. It is widely accepted that the mechanism of AOPs is the free radical oxidation mechanism. AOPs employ composite oxidant, irradiation, electricity or catalyst to produce kinds of strong oxydants (·OH, HO₂·, O₂^- ). Expecially OH, it can degrade any organic pollutements to CO₂, H₂O or mineral salt. Coking wastewater was treated by AOPs in this article.The first part of this thesis is treatment of coking wastewater with AOPs which employ potassium permanganate as catalyst and use kaolin as carrier, in the presence of ozone. The article discussed the effect of parameters like initial pH, current density and catalyst dose on chemical oxygen demand (COD) removal rate with time. The study results showed that at 298 K and 1 atm in the presence of ozone, COD removal efficiency with coking wastewater of 92.5% was obtained in 80 min at pH 3 and 30 mAcm^-2 current density. Catalyst lifetime was also tested, and the results showed that catalyst activity still remained even if the catalyst was used three times. Further discussion about the sustainable use of the treated wastewater was made when using it to irrigate the ornament clover. The chlorophyll concentration of clover was selected as parameter to evaluate the using feasibility of the treated water. The steady amount of chlorophyll indicated that the treated wastewater could be applied to irrigation completely.The second part of this thesis is to use kaolin as carrier, synthesize Fe and Mo modified catalyst which was used in wastewater treatment. Catalyst was charactered by X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FT-IR), Scanning electron microscope (SEM) and Thermo-gravimetric Analyzer (TGA). Study indicated there's a total difference in its micro-sized morphology and structure before and after the modification. The results showed that the previous structure of kaolin had almost disappeared, the stable Al-O ocatahedron structure in neat kaolin had broken, and the losses in crystallinity and the structure deformation. It existed large amount of micro-sized and loose particles. The study results showed that employing modified kaoln catalyst, COD removal efficiency with coking wastewater of 90.3% was obtained in 90 min at pH 6 and 30 mAcm^-2 current density.The third part of this thesis is treatment of coking wastewater with AOPs which employ Fe, Mo and V modified kaolin as catalyst, based on the second part study. Micro-sized morphology and structure of the catalyst were investigated before and after the modification. The effect of current density, initial pH, the presence of Fe³⁺ and Cl^- on COD removal rate with time were tested to find the optimal parameter combination. Experimental results showed that Fe, Mo and V modified kaolin was effectual catalyst in treatment of coking wastewater. In the presence of it at 298 K and 1 atm, COD removal efficiency with coking wastewater of 95.5% was obtained in 90 min at optimal parameter combination. The treatment results were compared using three different systems (multi-phase electrochemical system, traditional two-electrode electrochemical system and only catalyst existed system) to eliminate the pollutants with coking wastewater in this part. The study indicated that the COD degradation rate with coking wastewater under multi-phase electrochemical system was higher than that of two others by 26.1% and 62.2%.