Pyrolysis of post-methanated distillery effluent (PMDE) solid waste: Thermogravimetric degradation, kinetic and thermodynamic study with a circular bioeconomy approach

Abstract

Post-methanated distillery effluent (PMDE) is a harmful dark brown to black color distillery effluent and is often released in open pond systems after anaerobic digestion by molasses-based distilleries. Due to the high standards imposed by Environmental Protection Acts, various methods of treating effluent were explored. However, pyrolysis showed excellent potential to treat it and recover energy. Hence, the present study explores the viability of producing energy from PMDE solid waste through pyrolysis. The reaction was performed at 900 °C with 20 °C min −1 heating rate in a fixed bed reactor, resulting in 36.12 wt% condensable volatiles, 22.6 wt% non-condensable gases, and 41.28 wt% solid biochar. The gas chromatographic (GC) analysis of the non-condensable gas revealed the presence of CO (17.83 vol%), H2 (8.10 vol%), and CH4 (4.30 vol%) in significant amounts, and C2H4, C2H6, C3H8, and C4H10 in minor quantities. Biochar obtained from the process has a microscopic surface area of 62.13 m2 g−1. A kinetic and thermodynamic study was performed using isoconversional methods to understand the reaction mechanism. Kinetic analysis showed the activation energy of PMDE solid waste pyrolysis to vary from 120 kJ mol −1 to 180 kJ mol −1 as conversion increases, and thermodynamic parameters (ΔH, ΔS, and ΔG) show the explanation for variation in activation energy. Additionally, the bio-circular economic approach of PMDE solid waste was presented.