NOVELTY - The method comprises operating an upflow anaerobic reactor to create an upflow in a vessel by introducing an influent including biodegradable material into a lower portion of the vessel (12) via an inlet, withdrawing an effluent from an upper portion of the vessel via an effluent outlet of the reactor, and operating an auger assembly of the reactor to disrupt solid material contained in the effluent that collects at a fluid-air interface of a fluid filled gas-trap (42) of the effluent outlet. The upflow anaerobic reactor is arranged for anaerobically digesting biodegradable matter.    USE - The method is useful for operating an upflow anaerobic reactor for digesting biodegradable matter such as sewage, animal waste or wastewater and collecting biogas produced from the biodegradable matter, where the biogas is a mixture of methane, carbon dioxide, hydrogen sulfide and other volatile organic compounds.    ADVANTAGE - The method is capable of continuously operating the upflow anaerobic reactor thus maintaining the high rate of digestion of biodegradable matter for an extended period of time with low energy consumption and without loss of biogas, and prevents clogging of the effluent line of an upflow anaerobic reactor.    DETAILED DESCRIPTION - The method comprises operating an upflow anaerobic reactor to create an upflow in a vessel by introducing an influent including biodegradable material into a lower portion of the vessel (12) via an inlet, withdrawing an effluent from an upper portion of the vessel via an effluent outlet of the reactor, and operating an auger assembly of the reactor to disrupt solid material contained in the effluent that collects at a fluid-air interface of a fluid filled gas-trap (42) of the effluent outlet. The upflow anaerobic reactor is arranged for anaerobically digesting biodegradable matter using a bacterial culture. The bacterial culture comprises a sludge layer in the lower portion of the vessel of the reactor for biodegradation of biodegradable material and production of biogas. The upflow anaerobic reactor comprises a vessel having an upper portion of the vessel and a lower portion that define a volume of the vessel, an effluent outlet (24) coupled to the upper portion of the vessel, an auger assembly (34a) operatively coupled to the effluent outlet and positioned at or through the fluid-air interface, an inlet (22) coupled to the vessel for introducing biodegradable matter into the lower portion of the vessel, and a gas port coupled to the upper portion of the vessel for collecting biogas produced in the vessel. The effluent outlet includes a fluid filled gas-trap having a fluid-air interface for preventing escape of biogas through the effluent outlet. The auger assembly includes auger or a screw pump, and a helical screw conveyor that pierces the fluid-air interface and rotates to remove solid material from the fluid-air interface. The effluent outlet defines a fluid level in the vessel, and includes a column of liquid configured to prevent escape of biogas from the vessel through the effluent outlet. The upflow anaerobic reactor further includes a septum (14) positioned below the effluent outlet in the upper portion of the vessel to maintain the bacterial culture in the lower portion of the vessel below the septum, and an internal auger device operatively coupled to the vessel and positioned within the aperture to prevent clogging of the aperture. The septum has a central aperture for allowing digested biodegradable matter and liquid to flow from the lower portion of the vessel to the upper portion of the vessel. An INDEPENDENT CLAIM is included for an upflow anaerobic reactor.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of an upflow anaerobic reactor for digesting organic material.    Vessel (12)    Septum (14)    Inlet (22)    Effluent outlet (24)    Auger assembly (34a)    Fluid filled gas-trap. (42)