Comparison of premixing methods for solid-state anaerobic digestion of corn stover

• Three premixing methods were compared for SS-AD of corn stover.
• Two-layer partial premixing method showed the highest methane yield.
• Partial premixing methods increased regional inoculation ratio.
• VFA concentrations were affected by premixing methods.
• Adding extra inoculum to failed digesters partially recovered methane production.

The development of solid-state anaerobic digestion (SS-AD) has prompted studies to resolve practical challenges such as mixing of feedstock and inoculum. This study compared the performance of SS-AD using three premixing methods. Results showed that at feedstock to inoculum (F/I) ratios of 4 and 6, the two-layer partial premixing method obtained the highest methane yield, followed by one-layer partial premixing and complete premixing methods. Partial premixing methods also showed wider daily methane yield peaks than the complete premixing method. The volatile fatty acid (VFA) concentration was affected by the premixing method, and was highly correlated to methane yield; while the concentration of remaining holocellulose was correlated to pH and alkalinity. SS-AD digesters failed at an F/I ratio of 8, regardless of the premixing method. Adding extra inoculum to the top of failed digesters resulted in recovery of methane production.