NOVELTY - Organic wastes are biologically treated by providing anaerobic digestion phase and aerobic digestion phase in succession, a respective phase for filtration of solid substance between two digestion phases, a separation phase of biogas released in anaerobic digestion phase, and a phase of nitrogen recovery separated from aerobic digestion phase. The solid substance coming from each filtration phase is separately returned to respective digestion phase, while the liquid phase coming from filtration phase downstream of anaerobic digestion phase is sent to the aerobic phase.    USE - Process for biological treatment of organic wastes (claimed).    ADVANTAGE - The process can drastically reduce the chemical oxygen demand (COD) while mineralizing and recovering the pollutants, in particular carbon dioxide, nitrogen and phosphorus. Thus, disposal procedures are less complex. Further, the filtration units reduce the complexity and the cost of manufacture and running the plant since it is no longer necessary to provide within the plant the use of a sedimentation tank and to actuate all those technical devices necessary to obtain a high sedimentation capacity within reasonable times. The simplicity of the plant shows that this process is also suitable on small scale at waste-producing farm, such as an animal farm.    DETAILED DESCRIPTION - Biological treatment of organic wastes comprises providing a first anaerobic digestion phase and a second aerobic digestion phase in succession, a respective phase for filtration of solid substance provided between the two digestion phases, and further providing a separation phase of biogas released in anaerobic digestion phase, and a phase of nitrogen recovery from exhaust gases rich in ammoniac substances separated from aerobic digestion phase. The solid substance coming from each of the filtration phases is separately returned to the respective digestion phase, while the liquid phase coming from the filtration phase downstream of the anaerobic digestion phase is sent to the aerobic phase. An INDEPENDENT CLAIM is included for a plant for the biological treatment of organic wastes, comprising anaerobic digestion reactor (3) and aerobic digestion reactor (10) in succession, filtration units (7, 16) of the solid substance arranged downstream of each reactor, unit for separation of biogas which is released in first reactor and unit for separation of exhaust gases rich in ammoniac substances from second reactor and unit for mineralization into nitrogen salts. The solid substance retained by filtration units is recycled to the respective reactor while the liquid phase separated by filtration unit downstream of the anaerobic digestion reactor is sent to the aerobic digestion reactor.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a first fraction of the biodegradation plant in an anaerobic digester associated with an aerobic digester.    Anaerobic digestion reactor (3)    Filtration units (7, 16)    Pump (9)    Aerobic digestion reactor (10)    Biogas flow (19)