TECHNOLOGY FOCUS - BIOLOGY - Preferred Method: The fermentation step in the first bioreactor (b1) is obtained by maintaining a temperature of 30-40 degrees C, preferably 35-38 degrees C. The step of fermentation of the mixture in the first bioreactor (b1) is obtained by maintaining a pressure of 0.10-0.99 ata, preferably 0.68-0.82 ata. The fermentation of the mixture in the first bioreactor (b1) is obtained by maintaining a pH of 5-6. The step of methanogenic digestion in the second bioreactor (b2) is obtained at a temperature of 30-40 degrees C, preferably 35-38 degrees C; is obtained under conditions of anaerobiosis and darkness; and is obtained at atmospheric pressure. The step of methanogenic digestion in the second bioreactor (b2) is obtained by maintaining a pH of 6.5-7.5. An initialization stage is provided, by: charging the second bioreactor (b2) with the feeding mixture prepared in the first tank (s1); introducing nitrogen into the second bioreactor (b2), for allowing the realization of conditions of anaerobiosis inside the second bioreactor (b2); optionally bringing the biomass contained in the second bioreactor (b2) to the process temperature; introducing starter microorganisms into the second bioreactor (b2); awaiting the formation of stable digestate in the second bioreactor (b2); introducing nitrogen into the first bioreactor (b1); charging the first bioreactor (b1) with the feeding mixture coming from the tank (s1); optionally bringing the first bioreactor (b1) to the process temperature and pressure; and introducing starter microorganisms into the first bioreactor (b1). Preferred Components: The feeding mixture includes sludge, scotta and glycerol in quantities of volatile solids (VS) comprised between 8-54%, 46-92% and 0-28%, respectively. The feeding mixture includes 33.3% of VS from sludge and 66.6% of VS from scotta.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The units provided for controlling and adjusting the parameter pH of the biomass contained in the first bioreactor (b1) for the production of hydrogen and in the second bioreactor (b2) for the production of methane. The units for controlling and adjusting the parameter temperature of the biomass contained in the first bioreactor (b1) for the production of hydrogen and in the second bioreactor (b2) for the production of methane, the units acting on the heater/cooler for maintaining the process temperatures in the first and second bioreactors. The first and second bioreactors are continuous stirred tank bioreactors (CSTR). EXAMPLE - No suitable example given.