Methane has an energy content of about 39 MJ per cubic metre. This means approximately 0.5 kg of VS must be added to the digester per day to produce 120 litres of methane. For example a 60 kg pig will provide the 0.5 kg VS needed per day in 5 kg of manure. Digester Size Waste must be held in the digester for a period of time for digestion to occur, just how long depends on temperature. BUT you do need a larger digester to hold the effluent long enough.
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ASAE Standards, American Society of Agricultural Engineers. An, B. X., L. Rodriguez, et al. World Animal Review. Simplified Monod Kinetics of Methane Fermentation of Animal Wastes. Ram, M. S., L. Singh, et al.