Oily wastewater mainly comes from industrial sectors such as petroleum, petrochemicals, steel, coking, gas generation stations, and mechanical processing. The relative density of oil pollutants in wastewater, excluding heavy tar, is1．1Except for the above, the relative densities of the rest are less than1.

Oil substances usually exist in the following states in wastewater.

(1)Floating oil, oil droplet size greater than15MmEasy to separate from wastewater. The dispersed particles of oil in wastewater are relatively large, with a particle size greater than100micron,Easy to separate from wastewater. In petroleum wastewater, this oil accounts for the total oil content in the water60～80%.

(2)Dispersed oil. Oil droplet size greater than1MmSuspended in water.

(3)Emulsified oil, oil droplet size less than1MmThe dispersed particle size of oil in wastewater is very small, in an emulsified state, and it is not easy to separate from the wastewater.

(4)Dissolved oil, the state in which oil dissolves in water.

The oily substances contained in oily wastewater include natural petroleum, petroleum products, tar and its fractions, as well as edible animal and vegetable oils and fats. In terms of water pollution, the main ones are oil and tar. Due to the significant differences in oil concentration in wastewater discharged from different industrial sectors, such as wastewater generated during oil refining processes, the oil content is approximately150one1000mg/LThe tar content in coking wastewater is about500one800mg/LThe tar content in the wastewater discharged from the gas generation station can reach up to2000one3000mg/LTherefore, the treatment of oily wastewater should first use oil separators to recover floating oil or heavy oil, with a treatment efficiency of60%one80%The oil content in the effluent is approximately100one200mg/LEmulsified oil and dispersed oil in wastewater are difficult to treat, so emulsification should be prevented or reduced. One method is to pay attention to reducing the emulsification of oil in wastewater during the production process; Secondly, during the treatment process, try to minimize the number of times a pump is used to lift the wastewater, in order to avoid increasing the degree of emulsification. The processing methods usually include air flotation and emulsion breaking.

If oily wastewater is not recycled and treated, it will result in waste; Discharge into rivers, lakes, or bays,Will pollute water bodies,Affects the survival of aquatic organisms; If used for agricultural irrigation, it will block soil voids and hinder crop growth.

The treatment of oily wastewater should first consider the recovery of oily substances and fully utilize the treated water resources. Therefore, the treatment of oily wastewater can first utilize oil separators to recover floating oil or heavy oil. The oil separator is suitable for separating larger oil particles in wastewater, with a treatment efficiency of60～80%The oil content in the effluent is approximately100～200milligram/Raise. Small oil droplets and emulsified oil in wastewater are difficult to remove.