Abstract :
Wet air oxidation (WAO) is an efficient way to treat industrial wastewaters. In present study, wet air oxidation process was used for treatment of spent caustic effluents from ethylene unit in the petrochemical industry. After analysis and determination of wastewater properties, the process was performed using an experimental set-up having 1-L reactor in the temperature range of 170-200 ̊C and 6-9 bar partial pressure of oxygen. The effects of parameters including liquid volume, temperature, and pH were investigated. Performing experiments in two liquid volumes of 200 and 400 mL confirmed that required oxygen is provided at 190 ̊C and changing the partial pressure of oxygen has no significant effect on process efficiency due to abundant oxygen in the reactor. The values of reduction in chemical oxygen demands (COD) after 3 h at temperatures of 170, 190, and 200 C were 61, 63, and 67%, respectively. The process at 200 ̊C and pH of 12 and 10 for 3 h could decrease 69 and 82% of COD, respectively. Applying homogenous Fe3+ and Cu2+ catalysts could not enhance the performance of the process significantly. Furthermore, the kinetics of two-stage reactions of wet air oxidation process was also studied and the kinetic constants and activation energies were determined. Since the real sample from a petrochemical unit was used, determination of optimum operation conditions, investigation on the effect of catalyst, and also determination of kinetic degree of wet air oxidation reaction for spent caustic wastes of petrochemical units might be considered as the novelties of the current study.
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