NOVELTY - Biological wastewater treatment apparatus comprises an unit for separating fat and oil from fat and oil containing wastewater into low concentration fat and oil wastewater and high concentration fat and oil wastewater, an unit for performing methane fermentation of the low concentration fat and oil wastewater using microorganisms sludge, an unit for performing lipolysis of the high concentration fat and oil wastewater, an unit for stirring the high concentration fat and oil wastewater, acquisition unit, and a control unit.    USE - The biological wastewater treatment apparatus is useful for decomposing organic substance in fat and oil containing wastewater (claimed).    ADVANTAGE - The method and apparatus are reliable.    DETAILED DESCRIPTION - Biological wastewater treatment apparatus (100) comprises an unit for separating and concentrating (1) fat and oil from fat and oil containing wastewater into low concentration fat and oil wastewater and high concentration fat and oil wastewater, an unit (2) for performing methane fermentation of the low concentration fat and oil wastewater using microorganisms sludge (5), an unit (3) for performing lipolysis of the high concentration fat and oil wastewater, an unit (11) for stirring the high concentration fat and oil wastewater, acquisition unit (10), and a control unit (4) in which stirring state of the stirring unit is changed. An INDEPENDENT CLAIM is included for method for treating biological wastewater, which involves decomposing organic substance in fat and oil containing wastewater, introducing the fat and oil containing wastewater into a fat and oil concentration-separation apparatus, separating the fat and oil into low concentration and high concentration fat and oil wastewater, subjecting the low concentration fat and oil wastewater to methane fermentation using microorganisms sludge and high concentration fat and oil wastewater into lipolysis unit, stirring the high concentration fat and oil wastewater and microorganisms sludge, acquiring the state of fats and oils, changing the stirring state of high concentration fat and oil wastewater, and decomposing fats and oils.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic block diagram of biological wastewater treatment apparatus.    Fat and oil concentration unit (1)    Methane fermentation unit (2)    Lipolysis unit (3)    Control unit (4)    Microorganisms sludge (5)    Fat and oil acquisition unit (10)    Stirring unit (11)    Biological wastewater treatment apparatus (100)