TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: In the elimination of nitrogen from biomass DIG0 and reuse for energy purposes, the step (B) of stripping of the NH3 involves: injection of air into the first biomass DIG1, with generation of the fluid GAS1, in the gaseous state, containing air, NH3, and water vapor, and the second biomass DIG2, free from ammonia, with low nitrogen content and high pH. The alkaline conditioning of the starting biomass DIG0 is performed by adding CaO at a temperature of 50-70 degrees C and preferably greater than or equal to 65 degrees C with formation of the first biomass DIG1 with pH greater than 10 and free ammonia in gaseous form. The combustion of the ammonia contained in GAS1 takes place together with the main fuel in the cogenerator, while the air contained in GAS1 is used as part of the necessary combustive agent and the remaining part is composed of air taken from the atmosphere. The starting biomass DIG0 is composed of biological materials such as: digestates from methanogenic fermentation, livestock manure, biological sewage sludge, residual biomass. The starting biomass is composed of poultry manure from free-range farms, with a quantity of dry matter on average of 45-55% and a density of 0.4-0.6. The starting biomass is fed as such or following treatment with procedures for hydrolyzing the proteins so as to change the nitrogen from organic form into mineral form. The formation of calcium nitrate (Ca(NO3)2) is obtained by the reaction between nitrogen dioxide (NO2) and calcium hydroxide (Ca(OH)2). The formation of calcium nitrite (Ca(NO2)2) is obtained by the reaction between nitrogen oxide NO and calcium hydroxide (Ca(OH)2). The process involves a further step (F) of washing with water the gaseous fluid GAS3, purified from the NOx, for elimination of the residual NH3, with formation of a gaseous fluid GAS4 containing only CO2 and diatomic nitrogen (N2) and discharging into the atmosphere of the gaseous fluid GAS4; and/or a further step (E) of pH neutralization of the biomass DIG3 with transformation of the latter into an agricultural corrective for agricultural soils. The neutralization step (E) is performed by addition of sulfuric acid (H2SO4) with generation of a mixture of organic substance called defecation gypsum or by addition of CO2 from the cogenerator exhaust, with generation of a mixture of organic substance called defecation calcium carbonate. Step (B) involves condensation of the water vapor present in the GAS1. Preferred Plant: The plant comprises unit for condensation of the water vapor contained in the GAS1. The first reactor is closed and comprises a mixer for keeping the mass of biological material DIG0 thoroughly stirred, and a pH meter which controls the CaO input unit. The unit for NH3 stripping of the first reactor comprise: a jet pump for drawing off the air present in the free space of the first reactor and for injecting the air at the bottom of the first reactor; and venting unit for the ammonia extracted; and a blower for drawing off and conveying the ammonia extracted to the cogenerator. The cogenerator is equipped with a valve for introducing air into the intake manifolds, which regulates the flow of atmospheric air and GAS1 depending on the combustive agent required by the engine. The valve for introuding the air into the intake manifolds communicates with the jet pump placed in the reactor increasing or decreasing the stripping flow and therefore the GAS1 depending on the combustive agent required by the engine. The plant comprises unit for purification, from nitrogen oxides, of the gaseous fluid GAS3 containing CO2, N2 and NH3, the unit comprising: at least one water scrubber (300) for washing the gaseous fluid GAS3 and generating a gaseous fluid GAS4 which is ammonia-free and contains N2 and CO2.