Oil substances usually exist in three states in wastewater:
(1) Floating the oil, the particle size of the oil droplets is greater than 100 μm, and it is easy to separate from the wastewater. Oil products have larger particles dispersed in wastewater, and the particle size is greater than 100 microns, which is easy to separate from wastewater. In petroleum sewage, this oil accounts for 60 to 80% of the total oil content in water.
(2) Disperse the oil, the diameter of the oil droplets is between 10 and 100 μm, and it is suspended in water.
(3) Emulsified oil, the particle size of the oil droplets is less than 10 μm, the particle size of the oil dispersed in the waste water is small, it is in an emulsified state, and it is not easy to be separated from the waste water.
(4) A state in which oil is dissolved, and oils are dissolved in water.
Oily substances contained in oily wastewater include natural petroleum, petroleum products, tars and their fractions, as well as edible animal and vegetable oils and fats. In terms of pollution to water bodies, mainly oil and tar. Due to the large differences in oil concentration in wastewater discharged from different industrial sectors, such as wastewater generated during the refining process, the oil content is about 150 to 1000 mg / L, the tar content in coking wastewater is about 500 to 800 mg / L, and the gas generation station discharges wastewater into the wastewater. The tar content can reach 2000-3000mg / L. Therefore, the treatment of oily wastewater should first use an oil trap to recover oil slicks or heavy oil. The treatment efficiency is 60% to 80%, and the oil content in the effluent is about 100 to 200mg / L. It is difficult to emulsify and disperse oil in wastewater. Treatment, it should prevent or reduce the emulsification phenomenon. One method is to pay attention to reducing the emulsification of oil in the wastewater during the production process; the other is to reduce the number of times that the pump is used to raise the wastewater during the treatment pr