An operational strategy for improved biomethanation of cattle-manure slurry in an unmixed, single-stage, digester

In the quiescent state, cattle-manure slurry stratifies into three discerni ble layers; a floating "scum" layer, a bottom "sludge" layer and a watery m iddle layer, with most of the biologically degradable component of the slur ry being contributed by the particulate matter in these layers. The top lay er has the highest biochemical methane potential and the middle layer the l east. In a single-stage digester, an improved operational strategy to enhan ce methane production was determined. This strategy took advantage of the d ifferent rates of biomethanation and biochemical methane potentials of the different layers of the slurry. This was achieved by allowing the slurry to digest without mixing and discharging the digested material from the middl e liquid layer rather than from the bottom or top layers. (C) 2000 Elsevier Science Ltd. All rights reserved.