| abstract |
In the disclosed method, organic waste material of a water content of at least about 50% and a solid content of at least about 15% is biologically digested into compost. The organic waste material contains a flora of different species of microorganisms having different oxygen consumption requirements and different metabolism. The organic waste material is introduced into an aerating reactor with top inlet and bottom discharge so as to form an air permeable material column in the reactor. Air, which may be enriched with oxygen, is blown through the column in an upward direction without mechanical agitation of the column. Since the flora of microorganism species present in the material has different oxygen consumption requirements and different metabolism, the air flow is controlled in such a way that the microorganisms can settle at distinct levels within the reactor space where the environmental conditions are most favorable. In this manner a plurality of distinct zones of different temperature and different oxygen content are formed at different levels of the reactor. These zones remain substantially stationary while the method is carried out, although the material column descends through the reactor. The organic waste material is permitted to digest until compost has been formed in the lowermost portion of the reactor space. This compost is withdrawn and fresh material is added through the top of the reactor to make up for the withdrawn compost. |