NOVELTY - The process comprises: feeding organic substrates in reactors, which are arranged in series; heating the substrates at a controlled temperature of 20-55 degrees C for a time sufficient to cause the process of hydrolysis and acidogenesis of the substrate, to mineralize part of the organic nitrogen into ammonia nitrogen until getting, at the exit from the hydrolysis step, 25% of total nitrogen in the form of ammonia nitrogen (NH4) and to facilitate the contextual release and accumulation in the substrate of carbon dioxide (CO2) and volatile fatty acids; and overheating the hydrolyzed substrate.    USE - The process is useful for the pretreatment of organic substrates having elevated concentrations of total nitrogen suitable for removing nitrogen to reduce toxicity due to ammonia and then allow their use, as biomass, at 100% in the anaerobic digestion and producing biogas, where the substrates comprise sewage livestock, preferably poultry manure or a mixture of livestock waste or other substrate (all claimed).    ADVANTAGE - The process allows efficient pretreatment of organic substrates having elevated concentrations of total nitrogen thus eliminating the toxicity for anaerobic digestion.    DETAILED DESCRIPTION - The process comprises: feeding organic substrates in reactors, which are arranged in series; heating the substrates at a controlled temperature of 20-55 degrees C for a time sufficient to cause the process of hydrolysis and acidogenesis of the substrate, to mineralize part of the organic nitrogen into ammonia nitrogen until getting, at the exit from the hydrolysis step, 25% of total nitrogen in the form of ammonia nitrogen (NH4) and to facilitate the contextual release and accumulation in the substrate of carbon dioxide (CO2) and volatile fatty acids; overheating the hydrolyzed substrate up to a controlled temperature of 65-95 degrees C and aiming at the reduction of the solubility of CO2, the leakage of CO2 from the substrate, the subsequent alkalization of the substrate to reach pH values of greater than or equal to 9 and the shift of the chemical equilibrium of the ammonia from the aqueous phase to the gaseous phase free (NH3 (aq) NH3 (g)), which involves a greater volatility of ammonia; and stripping and removing the nitrogen-free from the substrate. The step of hydrolysis/acidogenesis is temporally separated from the heat treatment and from the nitrogen stripping process. In the step of feeding the substrate, the substrate is a sewage livestock, preferably poultry manure or a mixture of livestock waste or other substrate with a high nitrogen content in organic form that is greater than 40 kg Norg per tonne of dry matter. The substrate is mixed with water and/or slurry, and/or digestate to obtain a pumpable mixture and/or to promote the processes of hydrolysis and acidogenesis. The coarse solids, solids and/or floating materials are removed from the substrate. The process and/or the individual phases are performed in a continuous manner or in a batch manner. Between one phase and the other phase, an accumulation of substrate is placed. An INDEPENDENT CLAIM is included for a plant for carrying out the pretreatment of organic substrates.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a process for the pretreatment of organic substrates.    Manure (1)    Water and/or digestate (3)    Hydrolisis/acidogenesis process (6)    Thermal treatment (7)    Stripping ammonia. (9)