AbstractThe influence of particle size and an alkaline pretreatment on the anaerobic digestion of corn stover was studied. Four particle sizes, 0.075 to 0.25, 0.25 to 1.0, 1.0 to 5.0, and 5.0 to 20.0 mm, were used. The highest and lowest methane yields were obtained from untreated corn stover at particle sizes of 0.25 to 1.0 and 5.0 to 20.0 mm, respectively. 4% NaOH and 2% Ca(OH)2 (combined alkaline pretreatment, CAP) were then used together to pretreat corn stover at these two particle sizes, compared with 6% NaOH pretreatment (single alkaline pretreatment, SAP). The cumulative methane yields from particle sizes 0.25 to 1.0 mm after CAP, 0.25 to 1.0 mm after SAP, 5.0 to 20.0 mm after CAP, and 5.0 to 20.0 mm after SAP were 286.9, 287.0, 268.7, and 272.6 mLg-1 VS, respectively. The particle size barely influenced the final cumulative methane yield of alkali-treated corn stover. Moreover, the cumulative methane yield of the corn stover after CAP was comparable with that of the corn stover after the SAP under the same conditions. These results provide us with a promising substitute of NaOH pretreatment for corn stover bioconversion in the future.