1, the necessity of sewage deoiling With the development of economy and the improvement of people's living standards, the water quality of urban sewage is also changing, and oil substances such as animal and vegetable oil and mineral oil in sewage are gradually increasing. According to relevant data, by 2000, there were about 180 urban sewage treatment plants built and put into operation in China, with the designed treatment capacity of 1.050× 1.04 m3/d, of which the secondary biochemical treatment capacity was about 750×1.04m3/. It has the advantages of simple equipment, convenient operation, no phase change, no chemical change, high treatment efficiency, energy saving and so on, and it has been paid more and more attention as a unit operation in the process of sewage deoiling. In the research and application of membrane technology, Tianjin Mo Tian Science and Technology Engineering Company used hollow fiber ultrafiltration membrane to treat oily wastewater [23], which showed that hollow fiber ultrafiltration membrane was ideal for treating pretreated low-oil wastewater, but it had good oil removal and turbidity removal effect for untreated high-oil wastewater; China Institute of Metrology used demulsification functional membrane to treat oily wastewater, and achieved good results [24]. However, in the application of membrane technology, there are membrane cleaning problems to varying degrees. 2.3 biochemical treatment biochemical treatment is the process of using microorganisms in water to treat organic pollutants in sewage. The existing biological treatment unit of sewage treatment plant has partial removal efficiency for oily substances in sewage, but the removal rate is low. At present, the application of biotechnology in sewage deoiling mainly focuses on the screening, optimization, culture and domestication of oil-loving microbial strains. Xinjiang Environmental Monitoring Center screened 28 strains with strong oil-removing ability by cultivating oily sewage from catering services. After reusing them in sewage, the average oil-removing rate reached 68%, and the oil-removing rate of the preferred strain reached 90% after 24 hours of reuse in sewage, while the oil-removing rate of the same batch of sewage was only 29% after natural storage 10. Selecting excellent strains for centralized and rapid treatment can significantly improve the treatment efficiency of this kind of sewage [25]. 3 Discussion on oil removal scheme In view of the oily substances in the sewage plant of Xike University, in the winter of 2003 ~ 2005, we carried out experiments by flushing the surface of oxidation ditch with water and adding lime in front of the grit chamber. Although hydraulic flushing can temporarily make the oil on the surface of oxidation ditch adsorb and precipitate on the surface of sludge, the oil will cover the pool surface again in the next operation stage; Adding lime in front of the grit chamber can reduce the oil pollution in the oxidation ditch, but at the same time, lime can inhibit some microorganisms. The precipitated substances produced by lime are difficult to settle in the grit chamber, and it is easy to block the microporous aerator in the oxidation ditch after being brought into the grit chamber, so the dosage is limited, while other flocculants have the problem of high price. In order to avoid the temporary lack of oxygen in the oxidation ditch, we remove the baffle of the outlet weir of the oxidation ditch, so that the oil slick will enter the contact pool with the effluent and be cleaned at the beginning of the contact pool. It can be said that the above measures have not achieved the ideal purpose of oil removal. When choosing the oil removal scheme, we also considered physical methods such as hydrocyclone, but because of the space limitation between the fine grid and the grit chamber, expensive energy consumption and the whereabouts of the separated oil, we did not adopt it. Because the source of oil in the sewage plant of West University of Science and Technology is relatively single, we consider setting oil separation tanks outside the two student canteens, and the separated oil will be treated together with the slops in the canteens. At the same time, oil-loving microorganisms are cultivated and domesticated in the oxidation ditch of sewage treatment plant, and residual oil is treated by microbial technology, which saves cost and improves oil removal efficiency. Conclusion 4. 1 There are many oil removal methods in sewage treatment plants, and chemical, physical and biochemical treatment methods are currently studied and applied. 4.2 Due to financial difficulties and other factors, oil removal facilities are often not considered in the design process of small and medium-sized town sewage treatment plants, and the oil pollution in operation directly affects its treatment effect, so the implementation of oil removal measures must be combined with the specific conditions of each plant. 4.3 For urban sewage treatment plants with single oil source, it will be simple, economical and practical to treat them from the source. 4.4 As a new technology, the research and application of microbial technology in the field of sewage deoiling are deepening. Screening, optimization, culture and domestication of oil-loving microbial strains have the advantages of energy saving and high efficiency for oil removal in small and medium-sized sewage treatment plants.