A reactor for the hydrothermal oxidation treatment of an organic material in a reaction medium, comprising: - a main body extending along a longitudinal axis, being provided at a first one of its ends with a cold interface flange, sealing means being disposed between the main body and the flange; - an inner tube placed inside the main body so as to form an annular zone along the main body, the inner tube comprising a cold first end sealingly contacting with the cold flange, and a warm second end, the inner tube delimiting a reaction internal zone which is in fluid communication with the annular zone through at least one aperture disposed in the warm end of the inner tube; - a stirring means for agitating the reaction mixture located in the reaction internal zone of the inner tube, the stirring means being rotatably mounted about the longitudinal axis; - a refrigerating means for cooling an effluent located in the reaction internal zone of the inner tube before being discharged from the reactor through an outlet of the main body; - an inlet for a water-oxidant mixture located on the side of the cold first end of the main body, the water-oxidant mixture running through the annular zone from the cold first end to the warm second end of the inner tube, before penetrating the reaction internal zone of the inner tube; - an effluent outlet located at the cold first end of the main body; - an injection means for injecting the organic material to be treated in the inner tube; the reactor being characterised in that the inner tube is rotatably mounted to the cold flange, so as to be rotatably driven about the longitudinal axis; in that the injection means includes a sleeve, placed inside the inner tube, the sleeve having a first end which is sealingly attached to the cold flange and a second end which is located in the proximity of the warm end of the inner tube, the sleeve further having a bore which defines a passageway of the organic material to be treated from the first end to the second end of the sleeve; and in that the stirring means comprises a plurality of blades attached to the inner wall of the inner tube and spaced apart from each other along a longitudinal direction of the inner tube, the blades being rotatably driven by the rotation of the inner tube, and a plurality of counter-blades attached to the outer wall of the sleeve and spaced apart from each other along a longitudinal direction of the sleeve. - a main body extending along a longitudinal axis, being provided at a first one of its ends with a cold interface flange, sealing means being disposed between the main body and the flange; - an inner tube placed inside the main body so as to form an annular zone along the main body, the inner tube comprising a cold first end sealingly contacting with the cold flange, and a warm second end, the inner tube delimiting a reaction internal zone which is in fluid communication with the annular zone through at least one aperture disposed in the warm end of the inner tube; - a stirring means for agitating the reaction mixture located in the reaction internal zone of the inner tube, the stirring means being rotatably mounted about the longitudinal axis; - a refrigerating means for cooling an effluent located in the reaction internal zone of the inner tube before being discharged from the reactor through an outlet of the main body; - an inlet for a water-oxidant mixture located on the side of the cold first end of the main body, the water-oxidant mixture running through the annular zone from the cold first end to the warm second end of the inner tube, before penetrating the reaction internal zone of the inner tube; - an effluent outlet located at the cold first end of the main body; - an injection means for injecting the organic material to be treated in the inner tube;