A composting apparatus and method is described. The apparatus comprises a cylindrical drum which is horizontally rotatably supported. A hopper is disposed at a feed end of the drum for receiving organic waste material in soft or hard form. A material shredding mechanism and a grinding mechanism are rotatably secured in the hopper and driven in counter-rotation for shredding and grinding the organic waste material and feeding it into an inlet opening of the drum. A series of material mixing and conveying vane assemblies are secured spaced-apart inside the drum and define sub-composting compartments therebetween. The material mixing and conveying vane assemblies have a plurality of vanes secured in spaced-apart relationship and project interiorly towards a central longitudinal axis of the drum and are oriented at a common angle to mix, further shred and displace shredded and ground material from the inlet opening towards the rear discharge end of the drum. The gases escaping from the drum are vented from an enclosure of the composting apparatus and the material inside the drum is discharged by suction.