Biogasification, a technology for recovering methane gas from organic matter in an anaerobic reactor, is also referred to as “anaerobic digestion.” This process was developed in the 1980s to treat organic wastewater. In 1997, 90 facilities operated worldwide (total throughput is 3.5 million tons/year). Japan has 12 facilities to treat human waste and food waste, and 3 of these treat only food waste. Fig. 2.15.1 illustrates the main processes of biogasification. Low solid concentrations (6 to 10%) are treated using a “wet system,” while high solid concentrations (25 to 40%) are treated using a “dry system.” Treatment systems are also classified by their dominant microorganisms: methophilic (used at 30 to 40°C) or thermophilic (used at 50 to

60°C).