Flotation and Flocculation method in Oily Wastewater Treatment

The removal of emulsified oil is a key and difficult point in the treatment of oily wastewater.

Due to the extremely fine oil droplets in the emulsion, a layer of boundary film with electric charges is formed on its surface, and a double electric layer is formed around the oil droplets, making it extremely difficult for them to approach each other. Therefore, in order to separate oil and water, the first step is to break the boundary membrane of the oil droplets, so that they come close to each other and aggregate into large droplets, thus floating on the water surface, which is called demulsification.

The commonly used methods for treating emulsified oily wastewater include Air Flotation, Flocculation, Electrochemical, Coarse-grained, and Membrane methods.

Air Flotation Method

Air flotation method is a widely used technology in the treatment of oily wastewater.

Its principle is to introduce air or other gases into the water to generate micro bubbles, causing some small suspended oil droplets and solid particles in the water to adhere to the bubbles, and float together with the bubbles to form scum, thus completing solid liquid separation.

The air flotation method can be divided into bubbling air flotation, pressurized air flotation, and electrolytic air flotation according to the different ways in which bubbles are generated. The main method currently used is the pressurized flotation method. This method has low power consumption, simple equipment, and good results, and has been widely used in the treatment of oilfield wastewater, petrochemical wastewater, food and oil production wastewater, etc.

QDEVU Air Flotation System is a device for removing solid suspended solids, grease, and various colloidal substances from various industrial and municipal wastewater.

It is widely used for the treatment of industrial wastewater and municipal wastewater in oil refining, chemical engineering, brewing, vegetable oil production and refining, slaughtering, electroplating, printing and dyeing, etc.

Flocculation Method

Flocculation is an important process in the treatment of emulsified oily wastewater, used to remove oil and suspended impurities. The added flocculant has destabilization, coagulation, and adsorption effects on emulsified oil, aggregating dispersed oil particles into larger flocs to separate them from the water.

The flocculants used for the treatment of oily wastewater are divided into inorganic flocculants and organic flocculants.

• Traditional flocculants such as aluminum and iron salts, with high dosage and high sludge production, have gradually been replaced by polymer flocculants that have emerged in recent years.
• Inorganic polymer coagulants such as polyferric sulfate and polyaluminum chloride, while organic polymer coagulants such as polyacrylamide and acrylamide have the characteristics of low dosage and high efficiency, gradually becoming the mainstream.

The flocculation method is used to treat oily wastewater. Under suitable conditions, the removal rate of COD can reach 50% to 87%, and the removal rate of oil can reach 80% to 93%. However, there are problems with excessive waste residue and sludge, which are difficult to treat.

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