Kinetic study into the wet air oxidation of printing and dyeing wastewater

This paper presents the results of a study on the treatment of printing and dyeing wastewater from the textile industry by wet air oxidation (WAO). Experiments were conducted in a 2 l autoclave batch reactor. The range of operating temperatures examined was between 423 and 573 K at an oxygen partial pressure of 1.69 MPa standardized at 298 K. Chemical oxygen demand (COD) were measured at regular intervals during each experiment. Experimental data indicate that a certain amount of COD in the printing and dyeing wastewater can be removed by simple WAO. The extent of COD removal by the oxidation process increases with temperature until 523 K. Thermal decomposition during preheating was found to play a significant role in the COD removal with up to 18% COD removed at an operating temperature of 573 K. A first order kinetic model is proposed and tested for the removal of COD by WAO. The fit between the experimental data and the kinetic equation is good. The activation energy obtained is 37.5 kJ/mol K. The model prediction of overall COD removal agrees well with the experimental measurements. The results obtained here are useful for the design of WAO reactor and for the prediction of WAO performance in treating printing and dyeing wastewater.