A process to recover energy, reduce pollution potential, and add value to organic waste such as animal manure is described. The process involves the anaerobic digestion of feedstocks, such as animal manure, at low to high temperatures in batch, semi-continuous or continuous reactors. The process makes use of existing handling and storage equipment at the farm and requires minimal supervision and skill by the operator. The system is not affected by high concentrations of volatile acids and ammonia or nitrogen. The productivity of the anaerobic digester system, in terms of methane a gas production and quality, is exceptionally high. The anaerobic digester requires only a singe reaction vessel. Consequently, the process is low cost and does not interfere with regular farm operations.