Single-stage and two-stage anaerobic digestion of extruded lignocellulosic biomass

This study investigated in single-stage and two-stage batches, the anaerobic digestibility of hydrolysates obtained from poplar wood biomass pretreated using the twin screw extrusion (TSE) process. The TSE process produced two distinct sugar-rich streams i.e. the liquid and solid streams. The liquid streams showed significantly higher hydrogen production potential and rates, comparable methane production potential and yields, but higher methane production rates than the solid streams in the single-stage BMP tests. This study revealed that the two-stage process for separate acidogenic and methanogenic processes, maximized both COD removal efficiencies and energy recovery as well as enhanced the overall process efficiency. Energy yields of 11.6 kJ/gCODfeedstock and 9.8 kJ/gCODfeedstock were obtained from the liquid and solid streams respectively in the two-stage anaerobic digestion process compared with 8.7 kJ/gCODfeedstock and 8.3 kJ/gCODfeedstock obtained in the single stage BMP process which are a 33% and 18% increase respectively. Feedstock COD removal efficiency was enhanced in the second-stage BMP process after acidification by 16% and 14% for the liquid and solid streams respectively compared to the single-stage BMP process. This work demonstrated the overall potential of poplar wood hydrolysates for sequential hydrogen and methane production.