Unlocking biosolid pyrolysis: Towards tailored biochar with different surface properties

Abstract

To develop a thorough understanding of the thermal decomposition process of biosolids and the qualities of biosolid-derived biochar, this study performs a thermogravimetric analysis (TGA) of biosolids and examines the properties of biosolid-derived biochar produced from varying temperatures of pyrolysis. The pyrolysis of biosolid is conducted under varying heating rates (10, 15, 20 and 25 °C/min) until reaching the maximum temperature of 900 °C. The kinetic triplet (kinetic model, activation energy, and frequency factor) at the corresponding conversion point is determined by analysing the TGA results of the biosolids. The thermal degradation of hydrated compounds shows activation energies ranging from 80 to 100 kJ/mol, whereas the thermal decomposition of organic matter in biosolids exhibits activation energies ranging from 120 to 497 kJ/mol. As the temperature increases, the thermal reactions transition from simple surface reactions with frequency factors below 109 s−1 to more complex reactions with frequency factors above 109 s−1. The distributed activation energy model (DAEM) is established using the approximated temperature function and the activation energy distribution functions. The DAEM shows the mean activation energies of 93–128 kJ/mol, 279–287 kJ/mol and 359–377 kJ/mol for activation energy distribution peaks. The standard deviations of the mean activation energies are 30–64 kJ/mol, 23–30 kJ/mol and 23–41 kJ/mol, respectively. As the pyrolysis temperature is raised from 700 °C to 900 °C, both the specific surface area and micropore volume of biosolid-derived biochar increase, from 48.25 m2/g to 65.74 m2/g and 0.0313 cm3/g to 0.0369 cm3/g, respectively. The findings of this study demonstrate biosolid pyrolysis kinetics, which is essential for establishing a pyrolysis facility for biosolid management and producing biosolid-derived biochar with varying qualities.