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Oily Wastewater Conventional Treatment Methods and Inadequacies

At present, there are many methods for treating emulsified oil wastewater. Common methods include salting out, flocculation, flotation, coarse granulation, membrane separation, adsorption, and biological methods. However, the effect of mechanical separation methods is not ideal. If coagulant is added, oily sludge will be produced. In addition, this method has a long processing cycle and covers a large area. Gravity separation methods, coarse granulation methods, filtration methods, air floatation, etc., are also not satisfactory.

(1) The basic principle of the salting out method is to compress the thickness of the electric double layer at the interface of the oil surface, so that the oil particles are destabilized. Experiments show that the simple salting method has a large dosage (1% to 5%), the speed of polymerization is slow, sedimentation separation generally takes more than 24 hours, the equipment covers an area, and the treatment of oily emulsions stabilized by surfactants is also performed. Ineffective. However, due to its simple operation and low cost, this method is used more often and is more widely used as a primary treatment.

(2) At present, there are many methods used industrially to remove oil with flocculants. Commonly used inorganic flocculants are aluminum salts and iron salts, especially inorganic polymer agglomerating agents that have emerged in recent years, such as polyferric sulfate and polyaluminum chloride, and have characteristics of low consumption and high efficiency, and optimal pH when used. A wide range of values. Although the treatment speed of the inorganic flocculant is fast and the device is smaller than the salting-out method, the chemical is expensive and the amount of generated sludge is large. This inevitably brings annoying, troublesome and expensive sludge dewatering and sludge disposal problems. Recently, the research of organic polymer agglutinators has been rapidly developed, but according to Zame et al.'s theory of bridging, it is still difficult to treat dispersed oils and emulsified oils. At present, organic polymer flocculants can also be used as auxiliary agents for other methods in the treatment of oily wastewater.

(3) The method of electrolytic treatment of oily wastewater with metal aluminum or iron as anode is mainly applicable to the secondary treatment of chemical cooling after the cooling lubricant is used in the mechanical processing industry. Electro-flocculation has the advantages of good treatment effect, small floor area, simple operation and relatively small amount of scum, but it has a large amount of anode metal consumption, requires a lot of salts as an auxiliary agent, high power consumption, high operating costs, etc. Disadvantages.

(4) The effect of oil removal by the coarse granulation method is related to the presence and amount of surfactant. The presence of a trace amount of surfactant can inhibit the effect of the coarse granulation bed, so that the degreasing of emulsified oily wastewater containing the surfactant will be ineffective. Coarse granulation method does not require external chemicals, no secondary pollution, small equipment footprint, and lower infrastructure costs, the prospects are good, but the effluent oil content is high, such as processing wastewater containing more than 100mg/L, the effluent oil Generally higher than 10mg/L, so it is often necessary to perform further treatment.

(5) The activator is an excellent adsorbent, which not only has good adsorption performance for oil, but also can effectively absorb other organic substances in the wastewater at the same time, but the adsorption capacity is limited (typically for oils (30-80) Mg/L), which is expensive and difficult to regenerate, so it is generally used only for the deep treatment of oily wastewater.

(6) Pressurized dissolved gas flotation is generally used in flotation processes. Because the air microbubbles are composed of non-polar molecules, they can be combined with hydrophobic oils and float with the oil particles. Therefore, the oil and water separation efficiency of this method is high, but it is mainly used for dispersing oils without surfactants. The separation.