Pilot-scale assessment of twin-screw extrusion combined with lime pretreatment to improve semi-continuous biomethane production from corn stover, and potential of produced digestate as fertilizer

This study investigated the effect of lime pretreatment coupled with twin-screw extrusion on corn stover to improve anaerobic digestion at pilot-scale. The extrusion pretreatment was successfully optimized at pilot-scale with limited energy consumption of 537 W h/kg DM and water losses at 6%. Extrusion followed by lime impregnation resulted in 14% total cellulose, hemicelluloses and lignin depolymerization, increase of specific surface area by a factor of 5, and particle size reduction up to 16%. Consequently, biomethane production was increased up to +33% during batch tests, and up to +35% during the semi-continuous biomethane production trials. Additional calcium (up to +80 g/kg DM) contained in lime-pretreated digestates improved their fertilizing potential and induced a reduction of their viscosity up to a 17.5 factor. Consequently, lime combined with extrusion pretreatment could be an efficient solution to improve biomethane production, allowing improved corn stover valorization.