Almost all the refineries are faced with the problem of the high oil content of EDW. In are finery, oily EDW is generally sent to a wastewater treatment plant to separate the oil from wastewater through gravity settling. However, the separated waste oil(SWO) has high water content(approximately40%) and emulsifies intensely. Only a small proportion of waste oil can be fed into the delayed coking unit, whereas large proportion must be stored in tanks, thus resulting in increased storage costs.