Bioenergy production from the organic fraction of municipal solid waste and sewage sludge using mesophilic anaerobic co-digestion: An experimental and kinetic modeling study

Abstract

Following the rapid surge in global demand for energy as well as the rising generation of municipal solid waste (MSW) worldwide, much more attention has been drawn to sustainable waste management solutions to tackle both problems. The present study investigated the potential for biogas production from the anaerobic co-digestion (ACD) of the organic fraction of MSW (OFMSW) and sewage sludge after physical and chemical pretreatments at three inoculum-to-substrate (I/S) ratios (ISR: 2, 4, & 6) and three levels of total solids (TS: 3, 5, & 7%). A series of experiments were further carried out in laboratory-scale (1-L) single-stage digesters in batch mode at the temperature of 35 °C (viz. Under mesophilic conditions) for 50 days. The results demonstrated that the digestion produced the best outputs at TS = 5% and ISR = 2, whereby it offered the biogas yield of 0.697, the methane (CH4) production of 0.448 m3/Kg-volatile solid (VS)added, and the total VS (TVS) removal by 65%. Moreover, it was observed that most reactors with TS = 7% encountered the phase separation problem while augmenting the TS content from 3 to 5% increased the biogas yield and CH4 production. The kinetic study of the mesophilic ACD additionally showed that both models of modified Gompertz (GM) equation and logistic function (LF) provided a reasonably accurate description of biogas production, but the first-order (FO) model failed in this task. Furthermore, the amount of sludge (namely, ISR) in the digester enlarged and the models showed a better fit to the experimental data.