This paper describes the production of biodiesel fuel (BDF) from oil in oily wastewater exhausted from cafeteria that is used by 120~150 people per day. Here, solvent extraction was applied to extract and purify oil from oily wastewater, and this paper also focuses degradation of recovered oil, then acid value of oil exhausted on the day was enough low so that alkyl catalysts methods can be applied, however, that of oil older than 180 days after exhausted was over 200 mgKOH/g then single-step acid catalyst method leads to acquire BDF. It also clarifies energy profit ratio of two above method can achieve almost equivalent to that of BDF production using waster-cooking oil, and acid value of recovered oil keeps almost constant after solvent extraction different from oil in oily wastewater left untreated, therefore, storing oil after solvent extraction is effective way in terms of increasing an amount of acquired BDF from the exhausted oil, refraining from producing BDF production in small lots and recovering a certain amount of oil from many cafeterias etc.
