One cow produces an average of 10 kg of wet dung a day, equivalent to approximately 2 kg of dry matter. If cow dung is to be the main feedstock, the dung of approximately six cows (diluted with water) will be sufficient for a small biodigester of 9 m3. This biodigester would produce 2 m3 of biogas a day at 25°C, sufficient for the cooking needs of a family of around six people. At 30°C, the same digester would yield 3 m3 of biogas a day, sufficient for the cooking and lighting needs of the same family. In this case, the biogas would replace an average of 10 kg of fuelwood and 0.5 litres of kerosene per day, or roughly 4 000 kg of fuelwood and 200 litres of kerosene a year. It has been demonstrated that gas produced from the manure of at least three cows is sufficient to replace about 75 percent of the fuelwood normally used by a family of six people (Dalibard, 1995).
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