Closed-circuit ethanol-methane fermentation via biomass shifting of switchgrass, wheat, and corn straw

Biomass material shifting (BMS) is critical to improve the closed-cycle process of ethanol-methane fermentation. The adaptability of dual-fermentation process to the conversion of three typical biomass materials (SW: switchgrass to wheat-straw, SC: switchgrass to corn-straw) was studied. This study employed subcritical water pretreatment coupled with simultaneous saccharification and fermentation (SSF) technology, establishing a cyclic production model based on high-performance liquid chromatography and metagenomic sequencing, followed by 30-cycle stability testing. Subcritical water pretreatment demonstrated stable repeatability, with switchgrass showing the highest treatment efficiency. During SSF, enzymatic hydrolysis rates followed the order: switchgrass > wheat-straw > corn-straw. BMS extended stable ethanol production from 12 to 30 cycles, ethanol yield increase from 2.32 g/L to 6.14 g/L. Concurrently, methane production rose from 490.20 mL/cycle to 599.24 mL/cycle in SW, which may be related to the lower furan compounds content and higher methanogens abundance in SW. The BMS exhibiting high potential for bio ethanol-methane production. • Design biomass material shifting closed cycle process to product methane and ethanol. • Biomass material shifting extend the stable closed-circuit cycles to 30-cycles. • Biomass material shifting can increase methane production. • Converting switchgrass to wheat straw process has the higher ethanol-methane yield. • The recycling of ethanol fermentation waste slurry promotes methane production.