Review on Treatment Technologies of Emulsified Liquid Wastewater
Release time：
2026-05-08
Emulsified liquid is widely used in mechanical processing, automobile engine machining, as well as the cooling and lubrication of rollers and steel plates. During recycling, emulsified liquid deteriorates and ages under the influence of metal dust and ambient environmental media, requiring regular replacement. The spent emulsified wastewater features extremely stable chemical properties, posing great difficulties for treatment. Based on years of industry experience, our company summarizes the treatment technologies for emulsified liquid wastewater for the reference of all users.
I. Characteristics of Emulsified Liquid Wastewater
1. Formation of Emulsified Liquid: A large amount of surfactant is added to emulsified liquid, which reduces the surface free energy of the system. Surfactant molecules directionally adsorb at the oil-water interface and form an interfacial film, preventing oil droplets from colliding and coalescing into larger ones, thus enabling oil droplets to exist stably in water for a long time. Therefore, it is necessary to destroy the stability of emulsified liquid wastewater during treatment, eliminate or weaken the stabilizing effect of surfactants, so as to realize oil-water separation.
2. Features of Emulsified Liquid Wastewater: As a kind of refractory industrial wastewater, emulsified liquid wastewater has high chemical stability and high pollution load. Relevant data shows that the oil mass concentration in emulsified liquid wastewater is as high as 15,000~20,000 mg/L, COD ranges from 18,000 to 35,000 mg/L, and BOD is 5,000~10,000 mg/L. To improve the performance of emulsified liquid, a variety of additives are added in large quantities, such as oil-based additives, extreme pressure additives, rust inhibitors, mildew inhibitors and defoaming additives. This makes the composition of emulsified liquid extremely complex and further increases the difficulty of treatment.
II. Treatment Technologies for Emulsified Liquid Wastewater
1. Chemical Coagulation Method: It is a traditional technology for emulsified liquid wastewater treatment. Chemical coagulants are dosed into the wastewater. On the one hand, hydrolysis reaction occurs to generate colloids that adsorb oil droplets; on the other hand, polymerization forms macromolecular polymers of different molecular weights. Oil droplets are removed through adsorption, flocculation and bridging effects to achieve demulsification and oil-water separation.
2. Co-coagulation Air Flotation Method: Developed by combining chemical coagulation with air flotation process. Large-sized oil droplets and flocs generated after chemical coagulation can collide and adhere to microbubbles produced by the air flotation machine, forming larger bubble-bearing flocs. It delivers a more remarkable removal effect than coagulation sedimentation, with stronger adaptability to pH, water temperature and pollutant load, lower chemical dosage and shorter reaction time.
3. Electrocoagulation Method: This method adopts soluble metals as electrodes. Under the action of an electric field, metals lose electrons and are oxidized to form hydroxide colloids. Oil contaminants are removed via adsorption, coagulation and redox reactions during electrolysis. This method can greatly reduce the dosage of coagulants with excellent treatment effect, holding broad application prospects.
4. Ultrafiltration Method: Ultrafiltration treats emulsified liquid wastewater by utilizing the significant molecular size difference between oil and water. Cross-flow filtration is adopted: water molecules are smaller than membrane pores and permeate the ultrafiltration membrane, while oil molecules are larger and intercepted, thereby realizing oil-water separation.
5. Combined Biochemical Process: Demulsification can destroy the stabilizing effect of surfactants and achieve oil-water separation, yet the COD of treated wastewater remains at a high level and requires further treatment to meet discharge or reuse standards. With oil substances removed, demulsified emulsified wastewater possesses biodegradability, making biochemical treatment feasible.
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