Optimization of lime impregnation coupled with twin-screw extrusion pretreatment to improve biomethane production from corn stover

Abstract

This study investigated the impact of lime addition coupled with twin-screw extrusion pretreatment to enhance biomethane production from corn stover at laboratory-scale (i.e., inlet flows of 5 kg FM/h for extrusion). A dry matter optimization phase was firstly conducted to identify the ideal solid loading for lime impregnation within the extruder technical limits. It resulted in an optimal dry matter content of 30gDM/100gFM for a biochemical methane potential (BMP) increase of +18 % compared to raw CS. Then, a comparison between lime impregnation upstream or downstream extrusion was investigated. No statistical differences between lime impregnation upstream or downstream extrusion was evidenced for biochemical methane potential with +22 % and +27 % BMP increases, respectively. However, higher lignocellulosic depolymerization in the case of lime impregnation downstream extrusion (up to 17 %) was obtained and resulted in a higher increase of the specific biomethane production rate (up to +93 %). Consequently, both methods are equivalent for incrementing BMP, but downstream impregnation is superior for improving the production rate. Ultimately, scale-up semi-continuous AD trials should be investigated to provide a more realistic assessment of industrial biomethane production.