Extrusion as a pretreatment to increase biogas production.

Application of an extruder to increase the methane yield in a biogas production was examined, and large potential was proved. An extruder was tested on five agricultural biomass types, represented by 13 samples. The samples were analyzed for temperature, maximum particle size, biogas potential, and energy consumption. The extruder treatment increased biomass temperature by 5-35 °C. Large particles (>1mm) were most affected by the extruder. Extrusion accelerated the degradation of slowly degradable organic compounds, and some otherwise nondegradable organic compounds were also degraded. The methane yield increased significantly: by 18-70% after 28 days, and by 9-28% after 90 days. The electrical energy equivalent of the extra methane, after subtracting the energy used by the extruder, resulted in energy surpluses of 6-68%. By day 90, the energy-efficiency of the extrusion process was ranked as follows: grass = straw = solids of flocculated manure < solids of screw-pressed manure<deep litter.