Biogas Production

Biogas is generated when bacteria degrade biological material in the absence of oxygen, in a process known as anaerobic digestion. Biogas consists of about 50-75% methane and about 25-50% carbon dioxide. According to the United Nations' Food and Agricultural Organization (FAO), there are about 1.3 billion cattle worldwide (one for every five people), slightly more than 1 billion sheep, around 1 billion pigs, 800 million goats and 17 billion chickens. The total fecal matter produced by these animals is around 13 billion tons per year according to various estimates. It has been estimated that one cubic foot of biogas can be produced from one pound of cow manure (heated at around 28o C, or 82.4o F), which is enough to cook one day's worth of meals for four to six people in India (Ecofriend 2005). One cow in one year can produce enough manure, which when converted into methane can meet the fuel needs equivalent to 200 liters-plus (about 53 US gallons) of gasoline. According to a report from the University of Alberta, Canada, around 7,500 cattle can produce 1 megawatt (MW) of electricity (1 MW can power the average home in the developed world). The manure of 6 million cows can fulfill the needs of 1 million homes or about six cows per home. Table 5 shows the annual biogas energy potential in Alberta, Canada, with all feed material contributing to > 50% of methane production.

Table 5. Inventory of livestock materials and biogas energy potential in Alberta, Canada (Source: Alberta Agriculture and Rural Development)

Feed

Total

Volatile

Biogas

Annual

Annual

Methane

material

Solids

solids (%)

yield

biomass

energy

content

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