The process starts with the generation of sludge from the purification of wastewater. The sludge is dived in an anaerobic digester (HETAMIX). The digester system makes a heating of the sludge without oxygen, with a controlled injection of the generated biogas, and the pressure.
In the digester process takes part the digester, 3 exchanges-agitators, where the heating of the sludge is made by one hand through hot water with 60-80ºC and by the other hand through the injection of biogas. The hot water is produced from two 525 kWt boilers adapted to work with mixed-burner biogas or fuel-oil. Because of the burner is not modulating, the only regulation is the switch-on and switch-off of the boiler-burner.