Microwave Assisted Catalytic Wet Air Oxidation For The Treatment Of Organic Wastewater With High Concentration Under Low Temperature And Low Pressure

Catalytic wet air oxidation (CWAO) is a promising method for the treatment of heavily contaminated wastewater. However, severe operation conditions (high pressure and high temperature) in CWAO leads to the restriction against its wide application. In this paper, a novel process, named microwave (MW) assisted catalytic wet air oxidation (MW-CWAO) is adopted for the treatment of phenol solution, petrol wastewater and pharmaceutical wastewater through a granular activated carbon (GAC) and fixed bed MW reactor under low temperature (<200℃) and low pressure (<2.0 MPa) comparing with traditional CWAO operation condition. The process is operated in intermittent mode, and oxygen or hydrogen peroxide is applied for oxidant. In order to investigate the possibility of its practical application, the process is applied to treat different industrial organic effluents with high concentration of pollutants. The main conclusions obtained in this dissertation are as follows:In the treatment for phenol solution, the initial concentration of 20000 mg/L phenol solution was investigated through reaction temperature, oxygen partial pressure, GAC dosage and MW power. The results showed that the phenol degradation could reach 91.5% under the optimal conditions of 150℃, partial oxygen pressure of 0.8 MPa, GAC dosage of 5% (wt) and MW power of 660 W in 30 min. Meanwhile TOC removal in the solution reached 73.3% and BOD5/COD increased from 0.04 to 0.36. Hydroquinone, catechol, benzoquinone and maleic acid are main course products for phenol degradation, pyrolysis and oxidation reaction coexist in the degradation pathways of phenol by microwave assisted catalytic wet air oxidation.A new process of oxygen aeration was applied in the treatment for petrol wastewater by MW-CWAO. The COD removal could further enhanced due to the velocity of oxygen from gas phase to liquid phase by means of oxygen aeration. The results showed that the COD removal was reached 91.8% under the oxygen aeration of 0.02 m³/h, temperature of 150℃, oxygen partial pressure of 0.8 MPa, GAC dosage of 5% (wt) and MW power of 660 W. The COD removal was influenced by temperature, pressure, GAC dosage and MW power.Temperature determination showed that rapid temperature rising of GAC resulted in temperature gradient from GAC to water, which possibly made the localization of GAC reaching high temperature, providing the condition of·OH generation. In the experiments of evaporation, the effects of temperature, pressure and MW power on evaporation value in the solution were investigated respectively. The results showed that less than 5% evaporation in the solution was observed under the optimal parameter due to the operation was carried out in a closed system and these evaporation was still maintained in MW kettle.Aiming at the treatment for more refractory wastewater of pharmaceutical with higher COD loading (80254mg/L), a MW assisted peroxide oxidation method was applied. The results showed that the COD removal reached 85.2% under the conditions of 0.3 mol H₂O₂, 160℃, 0.8 MPa pressure, 5% (wt) GAC catalyst and 660 W MW power. Biodegradability (BOD5/COD) increased from 0.06 to 0.42.Based on energy balance calculation, microwave assisted catalytic wet air oxidation process adapts to treat high concentration organic wastewater. If microwave energy utilization combined with heat exchanger system can reduce the economical cost evidently, and increase the possibility of its practical application.The results indicated that under the relatively moderate conditions, MW-CWAO could treat organic waste waters with high concentration effectively. The process made MW-CWAO operated under safer and more convenient conditions. It provided a new approach to treat biorefractory pollutants in wastewater.