New insights into thermal-chemical pretreatment of organic fraction of municipal solid waste: Solubilization effects, recalcitrant formation, biogas yield and energy efficiency

Abstract

This study investigates the effects of thermal and thermal-chemical pretreatments on organics solubilization, biogas yield, recalcitrant formation, and energy efficiency at variable temperatures and alkali dosage. The organic fraction of municipal solid waste (OFMSW) was subjected to thermal pretreatment (100-200℃, 1.6–15.8 bar pressure, and 30–120 min reaction time) alone and in conjugation with alkali dosage (1–7 g/L NaOH). The thermal reaction time of 30 min and alkali dosage of 3 g/L NaOH were optimised for variable temperatures, based on solubilisation of chemical oxygen demand (COD). The highest biogas yield increment of 43% (474 mL/gVSadded) and 87% (618 mL/gVSadded) was observed at 125℃ and 125℃+3g/L NaOH dose, respectively, over control (331 mL/gVSadded). Above 150℃, a significant decrease of biogas yield was observed due to recalcitrant formation, i.e., 5-HydroxyMethyl furfurals (5-HMF) and furfurals. In terms of biogas yield, energy recovery was 44% higher in thermal-chemically pretreated substrate than in the thermally pretreated feedstock. The kinetic analysis of different experimental and operational parameters was carried out using principal component analysis (PCA). The experimental values of biogas yield and hydrolysis coefficient have been predicted by the First order model (FO). The FO model justified the biogas production with an R2 value of ≥ 0.91.