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; <EOS>