11 Fecal material produced by ruminants, particularly buffalo, cattle, sheep and goats, is an ideal substrate for anaerobic fermentation because it is already buffered and contains large populations of methanogenic bacteria. Methane from manure has a value of 5 kcal per cubic meter which is 71 percent of the energy value of natural gas. It works well for household use but is difficult to handle in mobile power. Processing manure through bio-gas plants has the added advantages of better preservation of fertilizer in some areas where dung is burned. A major handicap for methane production is capital cost for small units.
Several countries have extensive research programs underway to reduce construction costs.
Even so, the use of bio-gas plants is not likely to approach anywhere near the level projected, unless prices of fossil fuels rise to extremely high levels. For the US, it is estimated that manure from 40 cows will be needed to supply fuel, including electricity, for an average farm family, but will not replace fossil fuel to operate tractors, trucks or automobiles. The average Indian village could potentially accrue high benefits from the use of digesters, but acceptance will be low because it will deprive individuals of one, if not their major, source of income. In spite of limitations, anaerobic fermentation technology will undoubtedly play a significant role in waste management. For developed countries, units will be employed on large farms or in conjunction with feedlots where the cost of production will be in line with other fuels.