NOVELTY - Reactor (4) for anaerobic production of biogas from pre-treated wet waste comprises a reaction chamber (6) with stirring system (22) having at least one shaft (20) interacting with mixture of wet waste to maintain it in a state of continuous motion in chamber. The stirring system comprises supplying unit of at least one biogas jet into chamber. The supplying unit is feedable with biogas produced by biochemical reaction, passing through a side wall (8) of chamber facing away from shaft; and comprises at least one supplying mouth (23), at least one nozzle (22), and pipe (26).    USE - For anaerobic production of biogas from pre-treated wet waste (claimed).    ADVANTAGE - The nozzles supply the biogas into the chamber one by one, the displacement of the reacting wet waste and water mixture towards the device is promoted, and the formation of a circular crown of solidified mixture on the internal surface of the reactor is avoided. The gas jets supplied by the nozzles allow to maintain corresponding regions of the chamber adjacent to the wall and spaced from the shaft in constant state of stirring without interfering with the rotation of the shaft itself. The nozzles are sufficiently stiff to not be dragged away by the viscous action of the wet waste and water mixture rotating inside the chamber. Thus avoided the danger of dragging away by the viscosity of the waste and water mixture against the shaft. The reactor is simple and cost-effective.    DETAILED DESCRIPTION - A reactor (4) for the anaerobic production of biogas from pre-treated wet waste, comprises a reaction chamber (6) feedable with a mixture comprising wet waste, and adapted to house a biochemical reaction in anaerobic environment, in which the mixture is transformed into biogas and a reject; and stirring system having at least one shaft (20) rotational inside the chamber about an axis (A) and interacting with the mixture to maintain it in a state of continuous motion in the chamber. The stirring system comprises supplying unit of at least one biogas jet into the chamber. The supplying unit is feedable with the biogas produced by the biochemical reaction, passing through a side wall (8) of the chamber facing away from the shaft. The supplying unit comprises at least one supplying mouth (23) of the biogas jet inside the chamber in a position adjacent to the side wall to maintain at least one region of the mixture spaced from the shaft and adjacent to the side wall in a continuous state of stirring; at least one nozzle (22) having a first reception segment (24) of the biogas and a second segment (25) transversally extending with respect to the first segment and forming the supplying mouth of the jet; and conveying pipe (26) of the biogas produced in the chamber and fluidically connected to the nozzle. The reactor comprises a compressor member (29) receiving the biogas produced in the chamber, adapted to compress the biogas and fluidically connected to the conveying pipe so as to pressurize the biogas meant to be supplied into the chamber; and at least two conveying pipes, two adjustment valves (28) each interposed along a corresponding pipe, and control unit acting on the valves so as to maintain at least one of the valve opened and to allow only one corresponding nozzle to supply the biogas into the chamber. INDEPENDENT CLAIMS are included for the following:    (1) a plant for the production of biogas from wet waste, comprising a pre-treatment unit receiving the wet waste and adapted to crush and sieve the wet waste; the reactor fluidically connected to the pre-treatment unit and to a treatment unit of the reject; and a tank (12) fluidically connected to the reactor and adapted to store the biogas produced in the chamber; and    (2) a stirring method of a mixture comprising pre-treated wet waste in the reactor having the chamber involving rotating the shaft about an axis so that the shaft itself interacts with the mixture in the chamber and maintains it in a state of continuous motion in the chamber itself; conveying the biogas produced in the chamber through a side wall of the chamber; facing and spaced from the shaft; and supplying at least one jet of the biogas conveyed through the side wall into the chamber in a position adjacent to the side wall itself to maintain at least the corresponding region of the mixture adjacent to the side wall in continuous state of stirring.    DESCRIPTION OF DRAWING(S) - The figure shows an axial section of the reactor of anaerobic digestion plant of pre-treated wet waste.    Reactor (4)    Reaction chamber (6)    side wall (8)    Tank (12)    Shaft (20)    Nozzle (22)    Supplying mouth (23)    First reception segment (24)    Second segment (25)    Conveying pipe (26)    Valves (28)    Compressor member (29)    Axis (A)