providing an upflow anaerobic digester for anaerobically digesting biodegradable matter using a bacterial culture, the upflow anaerobic digester comprising:

a vessel having a volume with a top that defines an upper portion of the vessel and a bottom that defines a lower portion of the vessel,

a septum positioned within the vessel for maintaining the bacterial culture in the lower portion of the vessel,

an aperture formed in the septum for allowing digested biodegradable matter and liquid to flow from the lower portion of the vessel to the upper portion of the vessel,

an inlet coupled to the vessel for introducing biodegradable matter into the lower portion of the vessel,

a gas port coupled to the upper portion of the vessel for collecting gasses produced in the vessel,

a first outlet coupled to the upper portion of the vessel for directing digested biodegradable matter to the outside of the vessel, and

a second outlet coupled to the bottom of the vessel for removing accumulated solid, non-digestible matter from the vessel;

providing a bacterial culture comprising a sludge layer in the lower portion of the vessel;

introducing an influent into the lower portion of the vessel, wherein the influent comprises a biodegradable component, a liquid component, and an amount of solid non-digestible matter;

operating the upflow anaerobic digester in a steady-state, wherein the biodegradable component is continuously available to the bacterial culture as a food source;

accumulating the solid, non-digestible matter below the sludge layer in the bottom of the vessel; and

flushing at least a portion of the accumulated solid, non-digestible matter from the upflow anaerobic digester through the second outlet as a slurry that includes a liquid component, wherein the portion of the accumulated solid, non-digestible matter removed as a slurry does not exceed 30% of the volume of the vessel, so as to maintain the upflow anaerobic digester in the steady-state.