Oily wastewater is a multiphase system with suspended solids, oil, dissolved gas and salt. It mainly comes from petrochemical industry, iron and steel casting, mechanical processing and other industrial sectors. The main oil substances in oily wastewater include petroleum products, tar products and their fractions, as well as animal and vegetable oils and fats. The main reason is that oil and tar pollute the water. There are many ways to treat oily wastewater, including air flotation, adsorption, microorganism, magnetic flocculation, Fenton reagent oxidation and so on. Using air flotation to treat oily wastewater can promote oil-water separation, but the content of COD in the wastewater treated by this method is still high, which can not meet the national discharge standard. The oil-bearing wastewater is deeply treated by ozone biochar process, and the oil removal effect is very good. Moreover, the COD content in the treated wastewater can be reduced to the national discharge standard, and the cost is relatively low, but the process is more complex. The oily wastewater was treated by talc powder as adsorbent, and the oily wastewater was purified by using the lipophilic and adsorption properties of talc powder. Although talc is rich in sources and low in cost, this method can not effectively treat a variety of oily wastewater. Therefore, it is necessary to find a method with relatively simple process and high efficiency.

Microbial treatment of oily wastewater is a new method in recent years. By putting different bacteria into the wastewater, under the condition of aeration, microorganisms are used to degrade the organic matter in the environment and decompose it into inorganic matter such as CO2. At the same time, microbial cell material is synthesized to degrade the COD content in the wastewater and make the wastewater meet the discharge standard. The pretreatment of wastewater by microorganism can reduce the treatment cost.

Magnetic flocculation technology is a new water treatment technology, which has many advantages in the process of sewage treatment. Magnetic flocculation technology refers to the combination of pollutants and magnetic powder by adding magnetic powder, flocculant, polyferric sulfate and coagulant aid polyacrylamide to form magnetic flocculant, which is separated from water body by self sedimentation. The experimental results show that the treatment effect of PFS combined with magnetic powder is better than that of PFS or magnetic powder alone, and the removal rate of COD in wastewater is 30% - 40% higher than that of flocculant alone. Therefore, a large amount of oil in wastewater can be removed by magnetic flocculation technology, and the effect is better.