ABSTRACT
In the literature, methane produced often is given the descriptive name "biogas", and the process through which biogas is produced is variously known as "anaerobic digestion", "anaerobic fermentation", or "biogasification". Anaerobic digestion may be defined in the sanitary engineering sense as a waste treatment in which liquid or slurried organic wastes are decomposed biologically under strictly anaerobic conditions with a concomitant production of a gas that is mostly methane and of a relatively stable residue. Anaerobic digestion characteristically is a two-stage process in which the first stage blends into the second without tangible interruption. Despite the long history of the utilization of anaerobic digestion in sludge stabilization, advances made in the technology of the process have been rather modest, especially with respect to lowering capital and operating costs. The end products of anaerobic digestion are a collection of gases and a residue in the form of slurry.
