Oil substances contained in oily wastewater, including natural petroleum, petroleum products, tar and its fractionates, and edible animal and vegetable oils and fats. From the pollution of water, mainly oil and tar. Because the concentration of oil in the wastewater discharged from different industrial sectors varies greatly, such as the wastewater produced in the refining process, the oil content is about 150 to 1000mg/L, the tar content in the coking wastewater is about 500 to 800mg/L, and the tar content in the wastewater discharged from the gas generating station can reach 2000 to 3000mg/L. Therefore, the treatment of oily wastewater should first use the grease trap, recover the oil slick or heavy oil, the treatment efficiency is 60%-80%, the oil content in the output water is about 100-200mg /L; Emulsified oil and dispersed oil in wastewater are difficult to treat, so emulsification should be prevented or reduced