An organic waste material treatment process for organic waste material received in a vessel characterized by comprising the sequential steps of: a. subjecting contents of the vessel to conditions under which preliminary aerobic pre-conditioning of the contents of the vessel proceeds for a period comprised between 1 day and 28 days in order to raise the temperature of the contents of the vessel to at least 50°C, the preliminary aerobic pre-conditioning comprising the step of adjusting the moisture content of the contents of the vessel to between 40% and 60% wet weight; b. sealing the vessel after step a) to prevent ingress of air thereto so that aerobic bacteria in the vessel cause the oxygen content thereof to be depleted, wherein metabolic processes of the aerobic bacteria convert oxygen to carbon dioxide; c. adjusting water content of the contents of the vessel after step b) to 50 to 95% wet weight; d. simultaneously with or subsequently to step c) adding an anaerobic bacterial inoculum to the contents of the vessel; e. anaerobically digesting the contents of the vessel after steps c) and d) at a temperature comprised between 50°C and 75°C, for a period comprised between 4 days and 20 days; f. separating gaseous byproducts resulting from step e); g. reducing the water content of residues in the vessel to between 40% and 60% wet weight; h. evenly distributing air to the residues in the vessel to create conditions suitable for aerobic composting of the residues to proceed without agitating the contents of the vessel at a pressure of between 1-1000 kPa above atmospheric pressure to ensure even penetration of the residues by the air; i. aerobically composting the residues in the vessel by action of aerobic bacteria; and j. recovering compost resulting from step i) from the vessel upon completion of the aerobic composting stage. a. subjecting contents of the vessel to conditions under which preliminary aerobic pre-conditioning of the contents of the vessel proceeds for a period comprised between 1 day and 28 days in order to raise the temperature of the contents of the vessel to at least 50°C, the preliminary aerobic pre-conditioning comprising the step of adjusting the moisture content of the contents of the vessel to between 40% and 60% wet weight; b. sealing the vessel after step a) to prevent ingress of air thereto so that aerobic bacteria in the vessel cause the oxygen content thereof to be depleted, wherein metabolic processes of the aerobic bacteria convert oxygen to carbon dioxide; c. adjusting water content of the contents of the vessel after step b) to 50 to 95% wet weight; d. simultaneously with or subsequently to step c) adding an anaerobic bacterial inoculum to the contents of the vessel; e. anaerobically digesting the contents of the vessel after steps c) and d) at a temperature comprised between 50°C and 75°C, for a period comprised between 4 days and 20 days; f. separating gaseous byproducts resulting from step e); g. reducing the water content of residues in the vessel to between 40% and 60% wet weight; h. evenly distributing air to the residues in the vessel to create conditions suitable for aerobic composting of the residues to proceed without agitating the contents of the vessel at a pressure of between 1-1000 kPa above atmospheric pressure to ensure even penetration of the residues by the air; i. aerobically composting the residues in the vessel by action of aerobic bacteria; and j. recovering compost resulting from step i) from the vessel upon completion of the aerobic composting stage.