6.2.3. Anaerobic digestion (biomethanation)
If the organic waste is buried in pits under partially
anaerobic conditions, it will be acted upon by anaerobic
microorganisms with the release of methane and carbon
dioxide; the organic residue left is good manure. This process
is slower than aerobic composting and occurs in fact
naturally in landfills. However, thermophilic digestion for
biomethanation is much faster and has been commercialized.
Anaerobic digestion leads to energy recovery through
biogas generation. The biogas, which has 55–60% methane,
can be used directly as a fuel or for power generation. It is
estimated that by controlled anaerobic digestion, 1 t of
MSW produces 2–4 times as much methane in 3 weeks in
comparison to what 1 t of waste in landfill will produce
in 6–7 years (Ahsan, 1999; Khan, 1994).