High-solids ethanol fermentation with single-stage methane anaerobic digestion for maximizing bioenergy conversion from a C4 grass (Pennisetum purpereum)

High-solids simultaneous saccharification and fermentation integrating single-stage anaerobic digestion was designed for bioenergy conversion from steam-exploded Pennisetum purpereum, a perennial C4 grass. Three scenarios for ethanol production, methane production and ethanol-methane co-production were investigated and compared in terms of production yield. A terminal ethanol titer of 62.6 ± 1.9 g/L with the highest ethanol yield of 90.9% was achieved when the fed-batch mode was carried out at a final substrate loading of 35% (w/v) dry matter content. The ethanol stillage was used for methane production in a semi-continuous CSTR system operated with different organic loading rates (OLRs) at a hydraulic retention time (HRT) of 30 days. The high performance was achieved at OLR of 6.0 g VS·L−1 d−1, average yielding 358.7L CH4 per kilogram volatile solid (VS) with a total VS removal rate of 73.8%. On the basis of mass balance, the overall production yield achieved in this study was: 121.6 g ethanol + 110.6 g methane per kilogram grass with a finally 89.6% of cellulose recovery + 62.5% hemicellulose recovery. These results indicated that the high-solids ethanol fermentation with single-stage methane anaerobic digestion of lignocellulosic biomass is a valid approach to maximize the holocellulose bioconversion and improve the bioenergy production.