Abstract: A plant for the biological treatment of solid organic waste, where the organic mass is fed into a treatment tank with a horizontal bottom, while screw propellers, suspended from a sliding bridge parallel to tank base, operate immersed in the matter and whose axis is inclined according to a convenient angle, preferably between 5° and 50°, compared to its vertical, moving the organic matter from the bottom upwards and from the inflowing side of the treatment tank to the outflowing one, continuously immersed in a direction which is at right angles compared to the direction of movement of the organic mass and remaining continuously active, that is without any idle return of the screw propellers across the treatment tank after each process cycle.