Effects of ultrasonic treatment on the pyrolysis characteristics and kinetics of waste activated sludge

In this study, physicochemical analysis, thermogravimetric analysis, and kinetic analysis were used to investigate the effects of ultrasonic treatment on waste activated sludge (WAS), with emphasis on its kinetic parameters and pyrolysis behaviors. Thermogravimetric analysis results indicated that the pyrolysis of ultrasonic WAS might be divided into three stages. The main pyrolysis behavior occurred in the second stage (180-540 °C), and its pyrolysis behavior and activation energy were similar to the thermal decomposition of lignocellulosic biomass. Moreover, the physicochemical analysis indicated that ultrasonic treatment reduced the content of lignocellulose and ash, thus changing the pyrolysis characteristics of WAS. Ultrasonic WAS exhibited a higher residual weight (54.93 wt%), a larger average activation energy (140.09 kJ/mol), a lower maximum weight loss rate (-5.71%/min), and a change in the weight loss peak to a higher temperature (304.7 °C), reflecting the decrease of the pyrolysis reaction rate. In addition, the kinetic parameters were calculated using the Starink method and Coats-Redfern method.