Oily wastewater mainly comes from petroleum, petrochemical, steel, coking, coal gas station, mechanical processing and other industrial departments. Oil pollutants in the waste water, in addition to the heavy tar the relative density of 1.1 above, the rest of the relative density is less than 1. Oil substances in the waste water usually exist in three states

(1) floating oil, oil droplets size is larger than 100 microns and is easy to be separated from the wastewater.

(2) scattered oil. Oil droplets size between 10 a 100 microns, heartfelt floating in the water.

(3) the emulsified oil, the oil drop diameter less than 10 microns, not easily separated from the wastewater.

    Due to different industrial sectors the wastewater in oil concentration difference is very big, such as during the process of refining waste water, the oil content is about 150 an 150 mg/L, the tar content in the coking wastewater is about 500 an 500 mg/L, the gas occurrence station are the tar content in effluent can reach 2000 a 3000 mg/L. Oily waste water management, therefore, should first USES the separation tank, recovery of oil or heavy fuel oil, processing efficiency is 60% 80%, oil content in produced water about 100 an 100 mg/L; Of emulsified oil wastewater and dispersed oil is more difficult, therefore, should prevent or mitigate emulsifying phenomenon. One way, it is in the process of production attention to reduce the medium oil emulsion wastewater; Second, is in the process, as far as possible to lower the number of pump ascending wastewater, so as not to increase emulsification degree. Treatment usually adopt air flotation and demulsification method.