Improving single- and two-stage anaerobic digestion of source separated organics by hydrothermal pretreatment

Abstract

This study aimed to investigate the effect of hydrothermal pretreatment (HTP) on single- and two-stage anaerobic digestion (AD) of source separated organics (SSO). The single stage AD was conducted in a batch mode. For the two-stage AD, the first stage (acidogenic fermentation) was perfromed under the semi-continuous flow regime, while, the second stage (methanogenesis) was conducted in a batch condition. The HTP was applied either before or after the acidogenic fermentation stage of the two-stage AD process at a temperature and pressure of 170 °C and 115 psi for 30 min. Thermal hydrolysis of SSO resulted in 32% suspended solids reduction, which was more than that of the acidogenic fermentation process (16–22%). Of all the investigated scenarios, the implementation of the two-stage AD fed with thermally pretreated SSO revealed the highest degree of COD solubilization (36%) and VFAs production (19,700 mg/L). This scenario also resulted in an ultimate biomethane recovery of 314 mL/g TCODadded, which was 35% higher than that of the single-stage AD of raw SSO (232 mL/g TCODadded). Considering the outcomes of this research, the combined HTP/two-stage AD can be suggested as an effective technique for enhanced bioconversion of SSO.