Improving biodegradability and biogas production of corn stover through sodium hydroxide solid state pretreatment

Sodium hydroxide (NaOH) was used to pretreat corn stover in solid state at ambient temperature to improve biodegradability and anaerobic biogas production. Four NaOH doses of 4%, 6%, 8%, and 10% on dry matter basis of corn stover were applied. The untreated and NaOH-treated corn stovers were then anaerobically digested at four loading rates of 35, 50, 65, and 80 g L-1, respectively. The biodegradability and the changes of the main compositions of the corn stovers were analyzed. The results showed that 6% NaOH-treated corn stover digested at the loading rate of 65 g L-1 achieved 48.5% more biogas production and 71.0% more bioenergy gain, as compared to the untreated corn stover. Therefore, the NaOH dose and the loading rate were determined as the optimal parameters for Pretreatment and anaerobic digestion, respectively. Under the optimal conditions, the total solids (TS) and volatile solids (VS) reductions and the biogas production based on TS digested (B/ TSd) were increased by 23.6%, 56.3%, and 20.1%, respectively. The digestion time DT90, defined as the time reaching 90% total biogas production, was shortened by 24.1%. The results indicated remarkably improved biodegradability of the NaOH-treated corn stover. The improved biodegradability made more substrate available to be digested and resulted in the increase of biogas production. The main compositions of the NaOH-treated corn stovers were changed obviously. The contents of lignin, cellulose, and hemicellulose decreased by 4.3%-39.2%, but the hot-water extractives increased by 64.8%. Both changes had positive effects on the biodegradability improvement. The results from this study proved that NaOH pretreatment was one of efficient methods to improve biodegradability and enhance biogas production of corn stover.