Investigations in pyrolysis kinetics of sludges of different origins: chemical sludge, biological sludge and oily sludge

Thermochemical conversion is a possible solution for effective disposal of sludge. In this paper, we report physico-chemical characterization and pyrolysis kinetics of three sludges, viz. biological (BS), chemical (CS), and oily sludge (OS). An attempt was made to deduce the chemical composition of sludges using XPS and FTIR analysis. Pyrolysis of sludges was studied using a Thermo-Gravimetric Analyzer (TGA). The TGA data was analysed using four isoconversional models (viz. OFW, KAS, Starink and Vyazovkin_AIC) for deduction of kinetic triplet, viz. activation energy, pre-exponential factors and reaction mechanism. For all sludges, the activation energy increased with conversion. The ranges of activation energies were: BS = 87.82–303.89, CS = 72.12–200.62, OS = 67.26–130.99 kJ/mol. The ranges of pre-exponential factors were BS = 2.09E + 09 to 1.79 E + 27, CS = 2.31E + 04 to 9.72E + 13, OS = 1.20E + 06 to 5.99E + 11. s^–1. High pre-exponential factors indicated high reactivity of sludges during thermal conversion. The predominant mechanism of thermal conversion of all sludges was an order-based reaction (F1/F2/F3). This indicated homology among the components present in the organic matter in sludge. In essence, pyrolysis shows high promise as a useful pretreatment for the safe disposal of sludges of different origins.

Graphical abstract