1、 Introduction:
Waste oil in oily water mainly exists in three forms: suspended oil, dispersed oil, and emulsified oil, which are classified according to the distribution diameter of oil droplets in the water.
2、 Processing technology:
The sources of oily wastewater include industrial sectors such as petroleum and chemical industries. Methods such as flocculation, flotation, and filtration are often used. According to the characteristics of oily wastewater and the requirements for effluent quality, biological treatment should be used in the wastewater treatment process to achieve the expected goals. The available treatment processes are:
Salt precipitation method for oily wastewater treatment
The basic principle of the salt precipitation method for oily wastewater treatment is to compress the thickness of the double electric layer at the interface between the oil particles and the water surface, so as to destabilize the oil particles. The simple salting out method requires a large dosage (1%~5%), has a slow aggregation rate, and sedimentation separation generally takes more than 24 hours. The equipment occupies a large area, and the treatment effect on oil containing emulsions stabilized by surfactants is not good. However, due to its simple operation and low cost, this method is widely used and applied as a primary treatment.
2. Coagulation method for oily wastewater treatment
The commonly used inorganic coagulants are aluminum salts and iron salts, especially the inorganic polymer coagulants that have emerged in recent years, such as polyferric sulfate and polyaluminum chloride, which have attracted increasing attention due to their advantages of low dosage, high efficiency, and wide optimal pH range. Although inorganic flocculants have a faster processing speed and smaller equipment compared to salt precipitation methods, they are more expensive and generate more sludge. At present, organic polymer flocculants can also be used as auxiliary agents for other methods in the treatment of oily wastewater.
3. Oil containing wastewater treatment using electrocoagulation for oil removal method
The method of using aluminum or iron as anodes for electrolytic treatment of oily wastewater is mainly suitable for the secondary treatment of cooling lubricants after chemical flocculation in the mechanical processing industry. Electrocoagulation has the advantages of good treatment effect, small footprint, simple operation, and relatively less floating slag. However, it has disadvantages such as high anode metal consumption, requiring a large amount of salt as auxiliary agents, high power consumption, and high operating costs.
4. Coarse granulation method for oily wastewater treatment
The effectiveness of oil removal by coarsening method is related to the presence and amount of surfactants. The presence of trace amounts of surfactants can inhibit the effect of coarsening beds, therefore this method will fail to remove oil from emulsified oily wastewater containing surfactants. The coarsening method does not require external chemical agents, has no secondary pollution, occupies a small equipment area, has low infrastructure costs, and has a good prospect. However, the effluent content is high, so it often requires further deep treatment.