NOVELTY - A fermenter which carries out methane fermentation of natural gas containing organic waste to generate biogas, comprises a vertical main heater with connectors which connect top and bottom ends of a main heater, alternately, where the main heater is installed in a cylindrical stirring unit.    USE - Bioreactor for processing organic waste such as human waste, purification tank sludge, and organic refuse.    ADVANTAGE - By using a cylindrical type stirring unit with the main heater, energy is saved and a bioreactor excellent in fermentation capability is obtained. Occurrence of dioxin during processing of organic waste is suppressed.    DETAILED DESCRIPTION - A fermenter which carries out methane fermentation of natural gas containing organic waste to generate biogas, comprises a vertical main heater with connectors which connect top and bottom ends of a main heater, alternately, where the main heater is installed in a cylindrical stirring unit. The main heater is a warm water pipe using warm water prepared by a sunlight heater, or by a hot water boiler using biogas as a heat source, or with surplus heat of an electric power generator which utilizes biogas. The internal diameter of the stirring unit is 350-800 % of the internal diameter of the warm water pipe.    An INDEPENDENT CLAIM is also included for an energy recovery system which comprises the bioreactor and carries out methane fermentation of organic waste slurry and the power generator. The residual organic matter in the digestive liquid of the bioreactor is purified. A secondary treatment plant processes a surplus sludge as compost material. The bioreactor is heated to an appropriate temperature with the power generator. An organic waste slurry making unit and secondary treatment plant are driven with a portion of electric power from the power generator. Thus electric power and compost material are produced.    DESCRIPTION OF DRAWING(S) - The figure shows the flowchart of the organic waste collection system. (Drawing includes non-English language text).