Integrated bioprocessing of urban organic wastes by anaerobic digestion coupled with hydrothermal carbonization for value added bio-carbon and bio-product recovery: A concept of circular economy

Abstract

The major challenges associated with the anaerobic digestion of urban lignocellulosic biomass are its recalcitrance nature and the disposal of resulted digestate. In this study yard waste was thermally pretreated to overcome inherent recalcitrant nature during anaerobic digestion. The resulted digestate after anaerobic digestion, which poses a serious land disposal problem was hydrothermally treated to produce energy-rich solid biofuel knows as hydrochar. After pretreatment the biogas production was improved from 328 to 364 mL/g VS. Then hydrochar prepared from the digestate at a temperature of 180 and 200 °C for a treatment duration of 6 h. The produced hydrochar had a calorific value in the range of 20–23.5 MJ/kg as compared to 15 MJ/kg for raw digestate. The present research on integration of anaerobic digestion and hydrothermal carbonization not only improved the bioenergy production but also minimized the waste production.