NOVELTY - An aeration apparatus (7) comprises a trolley (8) comprising drive motor for bidirectionally translating the first trolley over the length of the pond; a second trolley (15) comprising second drive motor for bidirectionally translating the second trolley from one end to the other of the first trolley; at least one rotor (21) mounted on the second trolley, and a pump (51) for rotating the rotor along both senses of rotation.    USE - For the biomass waste aeration of the kind mechanically crushing and mixing a biomass waste basically made of human and/or animal excrements, semi-liquid organic waste, organic waste of industrial origin under composting and the like, to be treated by organic fermentation processes or other similar biological processes.    ADVANTAGE - The aeration apparatus allows for aerating the entire quantity of biomass waste along the entire front of the pond and over the entire length of the pond, regardless of the dimensions of the latter, and of transferring and treating the biomass waste with the utmost flexibility, on both senses of the pond length. Thus, there may be effected a re-accumulation of the material and a recovery of the volumes naturally lost owing to mass shrinkage by evaporation of water from the biomass waste. By virtue of the structure of the apparatus all motion drive members are positioned so as to avoid contacting the treated material, reducing the cleaning and maintenance interventions and hence the downtimes of the machine. By virtue of the presence of a single pair of rotors of a limited number, there can be reduced the installed power and the tool efforts, loads being equal, via an overturning management minimizing the drag opposed by the biomass waste to the motion of the machine itself. Such a management, basically enables the handling of small heaps of material at elevated rates, rather than of substantial heaps at reduced rates.    DETAILED DESCRIPTION - The first trolley (8) is movable over the length of pond and arranged transversally to the width of the pond and comprises drive motor. The rotor has a plane of rotation basically parallel to the longitudinal axis of the pond (5) having a diameter such that the periphery of the rotor may act onto the entire depth of the pond. The plane of rotation of the rotor is parallel to the longitudinal axis of the bond and has a diameter such that the periphery of the rotor may act on the entire depth of the pond.    An INDEPENDENT CLAIM is included for a plant for biomass waste treatment comprising at least one elongated pond with biomass waste and an aeration apparatus.    DESCRIPTION OF DRAWING(S) - The figure is a perspective view of a pond of biomass waste treatment plant with an aeration apparatus.    pond (5)    aeration apparatus (7)    first trolley (8)    second trolley (15)    rotor (21)    pump. (51)