Kinetic, thermodynamic and TG-FTIR Analysis of industrial wastewater treatment sludge pyrolysis

Abstract

Industrial Wastewater Treatment Sludge (IWTS) is a potential feedstock for waste to energy conversion by pyrolysis, allowing simultaneous waste reduction and energy recovery. In this study, IWTS obtained from the chemical treatment unit of a wastewater treatment plant located in the Samsun-Central Organized Industrial Zone, Türkiye, was characterized and their pyrolytic behavior was studied using TGA, DSC and TG-FTIR. The feedstock had 63.82% volatile matter, 24.76% ash, 11.42% fixed carbon and higher heating value of 15.42 MJkg-1. The thermal decomposition process occurred in three stages, removal of moisture below 150 °C, a major devolatilization stage between 200 and 450 °C and slow decomposition of char/mineral above 500 °C, resulting approximately 46% residual mass at 800 °C. Kinetic evaluation was conducted by the Coats-Redfern method and the second order chemical reaction model provided the best fit with an activation energy of 53.15 kJmol-1 (R2 = 0.99883), an interpretation further supported by the master plot analysis. The thermodynamic parameters indicated that the activation process required a substantial energy input and involved the formation of a more ordered activated complex. TG-FTIR showed the evolution of H2O, CO2, phenolic compounds and minor aliphatic species during the devolatilization. These findings provided useful preliminary design parameters (decomposition stages, kinetic and thermodynamic parameters, and volatile product profile) for the development of sludge pyrolysis systems.