Demulsification of waste emulsion wastewater
With the rapid development of machinery manufacturing industry, the amount of emulsion increases rapidly. The discharged waste emulsion will cause pollution and damage to the environment. According to the formation mechanism and structural characteristics of emulsion, the main way to deal with waste emulsion is to make it lose emulsion stability, that is to destroy the amphiphilic group of surfactant, so as to achieve the purpose of oil-water separation. This method is called demulsification, which is the key process to deal with waste emulsion.
The necessity of machining cutting fluid treatment
At present, the world's machinery manufacturing industry is based on three major processing technologies: cutting, grinding and casting forging. Among them, the application proportion of cutting is high, accounting for about 30% - 40% of the total labor of machining, and the metal cutting fluid accounts for about 52% of the total metal processing fluid [1-3]. In the machining industry, cutting fluid is widely used to cool, lubricate, clean and rust proof in the process of turning, grinding, cutting and rolling, so as to improve the quality of products and extend the service life of machine tools. With the rapid development of modern machinery manufacturing industry, cutting fluid is widely used in machining, and the amount of cutting fluid is increasing rapidly. However, cutting fluid will cause pollution and damage to the environment and human body, so the use of cutting fluid and waste liquid treatment has been increasingly restricted by environmental laws and regulations.
Properties and composition of emulsion
In the mechanical manufacturing industry, a large number of emulsions are used for lubrication and cooling in metal cutting. After a period of use, the emulsions will become waste water and be discharged.
The emulsion mainly contains engine oil and surfactant, which is prepared by diluting emulsified oil with water and adding emulsifier as required. In order to improve the antirust property of emulsion used in machine tool cutting, sodium nitrite is added.
Because emulsifiers are surfactants, when they are added into water, the free energy of the oil water interface is greatly reduced to a low value, and then the oil is dispersed in water. At the same time, the surfactant also produces ionization, which makes the oil droplet charged, and also adsorbs a layer of water molecules fixed, forming a hydration ion membrane, while the anti ion in water is adsorbed around its surface, which is divided into a fixed adsorption layer and a movable diffusion layer, forming a double electric layer. In this way, the oil droplet is surrounded by a layer of elastic, solid and same-sex charged hydration ion membrane, which prevents the possible combination of oil droplets when they collide with each other, and enables the oil droplet to be stable in the water for a long time and become a white emulsion.
The pH value of the prepared emulsion is generally between 8 and 9, and some of them are even as high as 10-11.
Design water quality and discharge standard
The average concentration of emulsion is about 5000-50000mg / L.
The treated water quality shall be in accordance with the class II standard in table 2-III of the integrated wastewater discharge standard (GB8978-1996) and the relevant standards of the wastewater connecting pipe discharge in Taihu Basin.
Treatment process flow
According to the above characteristics of wastewater, advanced treatment process is adopted: oil separation tank - demulsification reaction - air flotation - intermediate tank - UASB anaerobic - high efficiency fluidized bed - sedimentation tank - connecting pipe discharge. Because the content of oil and organic matter in wastewater is relatively high, the main body is sequencing batch intermittent activated sludge process to strengthen aerobic process and degrade organic matter in wastewater.
Treatment process description
The waste emulsion wastewater enters into the oil separator to reduce the difficulty of subsequent treatment and facilitate the recovery and reuse of tears; the effluent enters into the demulsification reaction tank, which is equipped with a stirring device, which is called stirring, adding the demulsifier, adding the sodium hydroxide solution to adjust the pH to 7.5 left and right, and the effluent to the air flotation tank to stabilize the demulsification of emulsified oil by adding chemicals and releasing the dissolved gas water In order to remove the suspended matter in the water, mainly for the suspended organic matter, it can effectively reduce the COD and BOD value of the wastewater; after treatment, it enters the intermediate pool for temporary storage, and then improves the UASB anaerobic pool, forming the granular sludge with good settling performance and high methane production in the anaerobic pool, and the excellent physical and biochemical performance of the granular sludge greatly improves the operation status of the reactor and improves the operation efficiency of the reactor 。 The effluent flows to an efficient fluidized bed. Under the action of aeration, the microorganisms in the mixed suspended microbial micelles and the microorganisms in the biofilm of the packing get enough dissolved oxygen and are in full contact with the waste water. The soluble organic pollutants in the waste water are absorbed by the biofilm and the microbial micelles, absorbed and decomposed by the microorganisms living on the packing, and the waste water is purified. After sedimentation , the activated sludge is returned to the aerobic tank, and the excess sediment is discharged into the sludge tank, and the supernatant is discharged after reaching the standard. The sludge in the air flotation tank and the surplus sludge in the sedimentation tank are collected in the sludge tank, and then transported out after the plate and frame pressure filtration.
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