Patent ID: 8202721

Claim:
A closed anaerobic digester for digesting high-solids waste material, the anaerobic digester comprising: a first section configured to receive the waste material from a source outside of the closed anaerobic digester and to preheat the waste material; a second section configured to receive the preheated waste material from the first section and to anaerobically digest the preheated waste material, the second section having a first passage and a second passage separated from the first passage by a center wall , wherein the waste material flows in a first direction in the first passage and flows in an opposite direction in the second passage; and a heating device positioned along and near the center wall configured to induce convection of the waste material flowing through the first passage and the second passage and to heat the waste material with a gas, wherein the heating device includes a conduit having at least one gas outlet positioned to promote upward movement of the heated waste material.