This disclosure provides a composting system and method. The system comprises: (a) a container configured to contain a composition and comprising (i) insulated walls, (ii) an air intake and (iii) a vent; and (b) a composition contained in the container. The composition comprises aerobic microorganisms, a carbon source and a nutrient source sufficient to support growth of the aerobic microorganisms. The container is sufficiently insulated so that heat generated by aerobic respiration is sufficiently retained in the container to maintain a heat gradient in the container. The container is dimensioned to generate a stack effect that moves air into the air intake, through the composition and out the vent. The moving air provides oxygen to support growth of aerobic microorganisms, making the stack effect self-sustaining as long as a carbon source and nutrients last. The insulation can maintain temperatures in the composting cell sufficient to kill pathogenic microorganisms.