This invention provides a waste-processing system capable of processing high-solids wastes such as manure. This invention provides a compact U-shaped digester that allows for recycling of activated sludge to improve the efficiency of the process. Efficiency is also improved through a sludge heating design that creates a current in the digester and efficiently heats the sludge. A composter is provided to further process the sludge through aerobic digestion to create usable fertilizer. Finally, one embodiment provides a turbine that is fueled by biological gases from the digester to generate heat and electricity to be used by the system.