Cost-effective sequential biogas and bioethanol production from the cotton stem waste

The objective of this study was to characterize and evaluate a wild inedible cotton waste as feedstock for bioenergy production. The conversion of organics of cotton stem into bioenergy could serve the dual role of renewable energy production and waste reduction. Composition analysis demonstrated that cotton stem is a suitable feedstock for both bioethanol and biogas production. Anaerobic digestion of cotton stem achieved 40.35% total biogas with 12.76% increased net CH4 volume compared to co-digestion of cotton stem with buffalo dung. Undigested cotton stem residues from anaerobic digestion were directly subjected to sequential alkali-acid pretreatment for conversion into ethanol with a yield of 325 L t(-1) or 50% of theoretical yield. Mechanical and thermal energy consumption for pretreatment were determined the efficiency of sugar recoveries and net energy production values. Overall 2.88 +/- 0.25 GJ more energy production in sequential anaerobic digestion-simultaneously saccharification fermentation (SSF) over direct SSF of cotton stem waste was observed. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.