Methane Yields and Digestion Dynamics of Press Fluids from Mechanically Dehydrated Maize Silages Using Different Types of Digesters

The mechanical dehydration of ensiled agricultural crops results in two major products: a fibrous press cake and a press fluid containing mainly easily digestible constituents. This study is aimed at the investigation on methane yields and digestion dynamics of the press fluids from maize silages using different types of digesters. Methane yields investigated in batch experiments account for 390–506 lN CH4/kg volatile solids (VS) with a degree of degradation of the organic matter in the fluid of more than 90%. The investigation of digestion dynamics in a continuously working stirrer tank digester at different levels of retention time and volume load suggests that a stable fermentation of press fluids can only be achieved with retention times of more than 20 days and with volume loads below 2 g VS/l/day. In a continuously working fixed bed digester a steady fermentation could be achieved at a retention time of 8 days and a volume load of 3 g VS/l/day.