Autothermal thermophilic aerobic digestion is a faecal sludge treatment design concept that uses the nutrients in the sludge and the metabolic heat of the bacteria to create high temperatures in the aerobic digester. This gradually shifts the microbial community towards thermophilic at temperatures typically at 55-degree Celsius or above. While the higher aeration requirements of autothermal thermophilic aerobic digestion further increases energy use and potential smell nuisance, the increased temperature makes the resulting biosolids much safer for re-use.