Effects of ensiling, silage additives and storage period on methane formation of biogas crops

Effects of the ensiling process, storage periods of up to 1 year and several chemical and biological silage additives on biomethanation were assessed for maize, sorghum, forage rye and triticale with the aim to identify optimised conditions for silage production of crops used as feedstock in biogas plants. Ensiling, prolonged storage and biological silage additives showed positive effects on methane yield of up to 11%. These could be attributed to increases in organic acids and alcohols during ensiling. A regression model including acetic acid, butyric acid and ethanol accounts for 75–96% of the variation in methane yield. Storage periods of up to 1 year for properly ensiled crops could be possible without losses in methane production, considering the increase in methane yield and the losses of dry matter during this period. However, taking storage losses into account silage additives showed little effect on methane production.