A waste disposal plant includes a combustion chamber (2) inside which waste laid on a combustion grate (3) is burnt. The grate permits the entrance of an adequate quantity of combustion air in the chamber through it. The combustion grate includes at least a handling group formed by fire bars or plates (7), which move alternatively one with respect to the other by advancing the waste on the grate. A handling group allows the alternate movement of the fire bars (7) which are divided in movable fire bars (7a) and fixed fire bars (7b), alternately disposed one with respect to the other, on transversal rows resting one upon the other according to a longitudinal placement with alternate steps.