Abstract: The invention concerns an apparatus including an air diffuser device and process useful in the domestic scale aerobic composting of organic wastes. The air diffuser has within its air admitting opening means to exclude insects, small animal pests and to also exclude waste from entering the air diffuser. Containers may be employed which have only a single opening admitting access to the contents of the container and the side walls of the container need not have apertures. The air diffuser device may be used with a variety of types of containers and particularly with plastic bags. By using containers which do not have openings to the exterior, except for the opening in which the air diffuser is located and possible small liquid drainage openings, composting may be undertaken with control of pests and flies in regions near residences and without excessive drying of the edges of the compost mass, in a way not previously known.