Aerobic digestion involves the metabolizing of the organic substances by micro­organisms, whose development is controlled by the presence of oxygen. These bacteria convert the complex substances into other simpler substances, freeing CO2 and H2O and result in high substrate heating (the layer under the biomass that is not yet digested by bacteria), which is proportional to their metabolic activity.

The heat produced can be transferred outside through a fluid exchanger. It is a process that is particularly suitable for liquid manures and industrial wastewater purification plants. In Europe, it is used (especially in Germany where strict rules were imposed for the destruction of pathogenic substances) in the thermophilic aerobic self-heated digestion process (auto-heated thermophilic aerobic digestion) for the treatment of the wastewater; more recently, this technology has also been used in Canada and the United States [3, 4, 35].