Anaerobic digestion (AD) is a biochemical process that
converts a variety of organic matter using naturally occurring
microorganisms under oxygen depleted conditions to
produce a gaseous mixture mainly composed of methane and
carbon dioxide, known as biogas. The biogas results from
the microbial degradation of organic matter generally
generated by photosynthesis using solar energy. The process
can naturally occur in anaerobic environments like river
sediments, deep soil or waste landfills. The AD process can
also be engineered to take place in a dedicated facility
known as an anaerobic digester; primarily a closed vessel
kept with a culture of microorganisms, fed regularly with
digestible (organic) matter.