NOVELTY - The method comprises: (i) separating and removing the fat and/or oil-containing phase from waste water in a fat separator; (ii) biochemically converting the emulsion-containing effluent into a biomass (107); and (iii) feeding the biomass into a biogas plant. The method further comprises: introducing the waste water into a first settling tank before the step (i); venting the emulsion-containing effluent from the first settling tank; and deriving the emulsion-containing effluent to an aeration tank (102).    USE - The method is useful for recovering biomass from fat and/or oil containing effluent, insertable in biological gas facilities (claimed).    ADVANTAGE - The method is capable of recovering the biomass from the fat and/or oil containing effluent in an energy-efficient manner.    DETAILED DESCRIPTION - The method comprises: (i) separating and removing the fat and/or oil-containing phase from waste water in a fat separator; (ii) biochemically converting the emulsion-containing effluent into a biomass (107); and (iii) feeding the biomass into a biogas plant. The method further comprises: introducing the waste water into a first settling tank before the step (i); venting the emulsion-containing effluent from the first settling tank; and deriving the emulsion-containing effluent to an aeration tank (102). The biochemical reaction of the emulsion-containing effluent is performed in a fluidized bed reactor (104) in the presence of atmospheric oxygen, and the biomass obtained from the biochemical reaction is provided to a biogas plant. The step (i) separates grease and/or fat containing phase form the effluent. The effluent comprises 8-10% or 5-15% of the fats and oils. A grease trap (101) is integrated into downstream or upstream of the first sedimentation tank. An INDEPENDENT CLAIM is included for a plant for producing biomass from fat and/or oil-containing waste water.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a plant for producing biomass from fat and/or oil-containing waste water.    Grease trap (101)    Aeration tank (102)    Fluidized bed reactor (104)    Biomass (107)    Pipeline. (204)