NOVELTY - Crushed surplus sludge is added into water, stirred and flocking settling is carried out to form an upper layer, an intermediate layer and a lower layer triple layer. The liquid fats-and-oils type substance, extracted liquid starch type substance, liquid protein substance and extracted liquid cellulose substance are added into a mixing vessel and mixed. A hydrotropic substance is introduced into a liquid mixture and solid content of the starch and cellulose in the liquid mixture is dissolved, and the liquid mixture is filtered to obtain liquid fuel.    USE - Manufacture of liquid fuel such as fuel oil and kerosene oil using surplus sludge produced in biological waste treatment.    ADVANTAGE - The liquid fuel which burns uniformly is produced, and is free of heavy metal.    DETAILED DESCRIPTION - Surplus sludge is dehydrated and crushed after polymeric flocculation process. The crushed surplus sludge is added into water and stirred in a settling tank, and flocking settling is carried out by adding a flocculant and separates into an upper layer, an intermediate layer and a lower layer triple layer. The intermediate layer containing fats-and-oils type substance, starch type substance, protein type substance and cellulose substance is introduced to a processing tank. The liquid fats-and-oils type substance is obtained by stirring, introducing fats-and-oils type solvent, extracting and distilling water content and an oil component, and cooling oil component, during heating and pressurizing the substance in the processing tank. The substance in the processing tank is pressure-reduced, cooled and stirred, and starch type solvent is introduced, liquefied and the starch is extracted to form extracted liquid starch type substance. The substance in the processing tank is heated, pressurized and stirred, a protein type solvent is introduced and the solid protein is liquefied and extracted by distillation. The protein type solvent is introduced into the extracted liquid and phosphoric acid compound in the protein type compound is decomposed to form liquid protein substance. The substance in the processing tank is heated, pressurized and stirred, and extracted by liquefying by introducing cellulose solvent to form extracted liquid cellulose substance. The liquid fats-and-oils type substance, extracted liquid starch type substance, liquid protein substance and extracted liquid cellulose substance are added into a mixing vessel and mixed. A hydrotropic substance is introduced into a liquid mixture and solid content of the starch and cellulose in the liquid mixture is dissolved, and the liquid mixture is filtered to obtain liquid fuel.