Method for synchronously enhancing removal of dissolved oil and weakening pollution of ultrafiltration membrane
By using hydrogen peroxide ultrasonic treatment, hardness ion shearing and mixing, ozone regulation, and ferrous chloride demulsification in oily wastewater, the problems of dissolved oil removal and ultrafiltration membrane fouling were solved, achieving efficient dissolved oil removal and membrane fouling mitigation without secondary pollution.
Patent Information
- Application Number
- CN202511303683.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-12
- Publication Date
- 2025-12-12
AI Technical Summary
Existing technologies struggle to simultaneously enhance the removal of dissolved oil and mitigate ultrafiltration membrane fouling, and traditional pretreatment methods often result in a decrease in contaminant removal rates.
The process involves ultrasonic treatment with hydrogen peroxide added to oily wastewater, followed by the addition of hardness ions and shear mixing, then the introduction of ozone for interfacial performance regulation, and finally the addition of a saturated ferrous chloride solution for demulsification. The resulting dissolved oil then enters the ultrafiltration system.
It achieves efficient removal of dissolved oil and mitigation of ultrafiltration membrane fouling. The reaction products are water and oxygen, with no risk of secondary pollution. It is easy to operate and has wide applicability.
Smart Images
Figure SMS_1 
Figure SMS_2 
Figure SMS_3
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the field of membrane separation technology, and relates to membrane pollution control, in particular to a method for simultaneously strengthening dissolved oil removal and weakening ultrafiltration membrane pollution. BACKGROUND
[0002] With the rapid development of industrialization and urbanization, a large amount of oil-containing wastewater is generated in various life and industrial production processes, and the main sources include petroleum chemical industry, mechanical processing, steel industry and food processing, etc. The oil-containing wastewater is complex in composition and difficult to biodegrade, and has a great pollution risk to the environment. Therefore, the discharge of oil-containing wastewater is strictly limited in the world, and the oil-containing wastewater must be treated to meet the standards before being discharged into nature or downstream receiving water.
[0003] The oil-containing wastewater can be divided into four types according to the phase form of oil, namely, floating oil, dispersed oil, emulsified oil and dissolved oil. Among them, the floating oil and dispersed oil can be efficiently removed by traditional processes such as oil separation tank, air flotation or coagulation sedimentation because the particles are large; while the emulsified oil and dissolved oil, especially the dissolved oil, usually have a size less than 0.1 μm, resulting in high stability of the dissolved oil in the water body, and the traditional methods are difficult to effectively separate. The ultrafiltration membrane technology has become a key means for removing dissolved oil due to its nanoscale pore size screening effect, but the pore size of the ultrafiltration membrane is similar to the size of the dissolved oil, resulting in two major problems of serious membrane pollution and insufficient removal rate during operation.
[0004] A large number of studies have focused on the pollution control of ultrafiltration membranes, and the pretreatment processes such as oxidation, coagulation, filtration and adsorption have become an important strategy for controlling membrane pollution due to their simple and efficient characteristics. However, these traditional pretreatment technologies mainly aim at the membrane pollution problem caused by dissolved organic matter such as polysaccharide, protein and humic substance. Unlike dissolved organic matter, dissolved oil has a hydrocarbon chain structure as the core, has strong hydrophobicity, low reactivity and non-degradability, and is mainly dispersed in the form of molecules or micelles in the water body, resulting in the difficulty of traditional pretreatment technologies to solve the membrane pollution problem caused by dissolved oil. In addition, the traditional pretreatment methods often accompany with significant decrease of pollutant removal rate while controlling membrane pollution, that is, the efficiency of organic matter removal is sacrificed to achieve membrane pollution control. Therefore, in view of the limitations of the existing technology, it is particularly urgent to develop a new method that can both strengthen the removal of dissolved oil and effectively alleviate the pollution of ultrafiltration membrane, which has important significance for expanding the application of ultrafiltration technology in the field of oil-containing wastewater treatment. SUMMARY
[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for simultaneously strengthening dissolved oil removal and weakening ultrafiltration membrane pollution, which solves the technical problem that it is difficult to simultaneously strengthen dissolved oil removal and weaken ultrafiltration membrane pollution in the treatment of oil-containing wastewater containing dissolved oil.
[0006] To solve the above technical problems, the application adopts the following technical solutions to achieve the purpose: A method for synchronously strengthening dissolved oil removal and weakening ultrafiltration membrane pollution, comprising the following steps: Step one, dissolved oil solubilization: Hydrogen peroxide is added to the oil-containing wastewater to be treated and ultrasonic treatment is carried out at a constant temperature, so that the interfacial tension of the dissolved oil in the oil-containing wastewater to be treated is reduced, smaller-sized dissolved oil is formed, and the dissolved oil is fully combined with hydrogen peroxide, to obtain solubilized dissolved oil.
[0007] Step two, adding hardness ions: Hardness ions are added to the solubilized dissolved oil obtained in step one, and shearing mixing is carried out at 10000-25000 r / min for 2-5 min, to obtain dissolved oil after adding hardness ions.
[0008] Step three, interfacial property regulation of dissolved oil: Ozone is introduced into the dissolved oil after adding hardness ions obtained in step two for continuous reaction for 20-40 min, and the interfacial properties of the dissolved oil after adding hardness ions obtained in step two are changed by ozone and hydroxyl radicals, the dispersion stability of the dissolved oil after adding hardness ions obtained in step two is further destroyed on the basis of the hardness ions in step two, to obtain interfacial property-regulated dissolved oil.
[0009] Step four, strengthening dissolved oil demulsification: Saturated ferrous chloride solution is added to the interfacial property-regulated dissolved oil obtained in step three, and reaction is carried out at 50-100 r / min for 20-30 min, and after standing for 10-15 min, the dissolved oil after demulsification is obtained, and then enters an ultrafiltration system for treatment.
[0010] The application also has the following technical features: Preferably, in step one, the relationship between the addition concentration of hydrogen peroxide and the content of dissolved oil in the oil-containing wastewater to be treated in step one is: When the content of dissolved oil in the oil-containing wastewater to be treated is less than 100 mg / L, the addition concentration of hydrogen peroxide is 0.4-0.8 mmol / L.
[0011] When the content of dissolved oil in the oil-containing wastewater to be treated is 100-500 mg / L, the addition concentration of hydrogen peroxide is 0.8-1.5 mmol / L.
[0012] When the content of dissolved oil in the oil-containing wastewater to be treated is greater than 500 mg / L, the addition concentration of hydrogen peroxide is 1.5-2.2 mmol / L.
[0013] Specifically, in step one, the constant temperature is 40-60℃.
[0014] The ultrasonic treatment is 20-100 kHz ultrasonic treatment for 5-10 min.
[0015] Specifically, in the step two, the hardness ions include calcium chloride and magnesium chloride.
[0016] The molar ratio of the calcium chloride and the magnesium chloride is calcium chloride:magnesium chloride=1:2.4.
[0017] Specifically, in the step two, the relationship between the adding concentration of the hardness ions and the content of the dissolved oil in the oil-containing wastewater to be treated in the step one is as follows: When the content of the dissolved oil in the oil-containing wastewater to be treated is less than 100 mg / L, the adding concentration of the hardness ions is 2-5 mmol / L.
[0018] When the content of the dissolved oil in the oil-containing wastewater to be treated is 100-500 mg / L, the adding concentration of the hardness ions is 5-10 mmol / L.
[0019] When the content of the dissolved oil in the oil-containing wastewater to be treated is more than 500 mg / L, the adding concentration of the hardness ions is 10-25 mmol / L.
[0020] Specifically, in the step three, the relationship between the adding concentration of the ozone and the content of the dissolved oil in the oil-containing wastewater to be treated in the step one is as follows: When the content of the dissolved oil in the oil-containing wastewater to be treated is less than 100 mg / L, the adding concentration of the ozone is 5-25 mg / L.
[0021] When the content of the dissolved oil in the oil-containing wastewater to be treated is 100-500 mg / L, the adding concentration of the ozone is 25-55 mg / L.
[0022] When the content of the dissolved oil in the oil-containing wastewater to be treated is more than 500 mg / L, the adding concentration of the ozone is 55-90 mg / L.
[0023] Specifically, in the step three, the volume flow rate of the ozone is 10-40 L / min.
[0024] Specifically, in the step four, the relationship between the adding concentration of the ferrous chloride in the saturated ferrous chloride solution and the adding concentration of the hydrogen peroxide in the step one is as follows: the adding concentration of the ferrous chloride in the saturated ferrous chloride solution=the adding concentration of the hydrogen peroxide x (10%-15%).
[0025] Compared with the prior art, the present application has the following technical effects: (I) The method in the application realizes the synergistic regulation of the interfacial performance and size of dissolved oil, strengthens the removal of dissolved oil by the ultrafiltration membrane and slows down the pollution of the ultrafiltration membrane, the reaction product is only water and oxygen, there is no secondary pollution risk, and the method has the advantages of simple operation and wide applicability.
[0026] (II) The method in the application first utilizes the ultrasonic cavitation effect to reduce the interfacial tension and viscosity of dissolved oil in the oil-containing wastewater to be treated, reduces the particle size of dissolved oil, and promotes the full combination of dissolved oil and hydrogen peroxide; then, the hardness ions are uniformly distributed on the interface of dissolved oil molecules through shearing mixing, and the hardness ion hydration is utilized to enhance the stability of dissolved oil; on this basis, the hydroxyl radicals are generated around the molecular chain of dissolved oil through the cooperation of ozone and hydrogen peroxide, so that the local oxidation modification of the molecular chain is realized; at the same time, the charge shielding and bridging complexation of hardness ions are utilized to reduce the interfacial charge of dissolved oil, so that the instability of dissolved oil is promoted; finally, ferrous ions are introduced, which not only consume residual oxidants to avoid affecting the ultrafiltration system, but also assist in demulsification through the coagulation effect of multivalent iron ions.
[0027] The specific content of the application will be further described in combination with the following examples. DETAILED DESCRIPTION
[0028] It should be noted that all the systems and raw materials in the application, such as without special instructions, all use the commonly used systems and raw materials known in the art in the prior art, for example, the ultrafiltration system uses a known ultrafiltration system, the hydrogen peroxide uses a known hydrogen peroxide with a mass concentration of 30%, the calcium chloride uses a known calcium chloride, the magnesium chloride uses a known magnesium chloride, the ozone uses a known ozone, and the saturated ferrous chloride solution uses a known saturated ferrous chloride solution.
[0029] According to the above technical solution, the specific embodiments of the application are given below, and it should be noted that the application is not limited to the following specific embodiments, and any equivalent transformation based on the technical solution of the application falls within the protection scope of the application.
[0030] Example 1 Taking the filtration of 60 mg / L sulfonated kerosene wastewater (i.e. the oil-containing wastewater of the present embodiment, also referred to as sulfonated kerosene wastewater) by using a 30 kDa polyvinylidene fluoride ultrafiltration membrane (referred to as polyvinylidene fluoride ultrafiltration membrane) as an example, the present embodiment gives a method for simultaneously strengthening the removal of dissolved oil and weakening the pollution of the ultrafiltration membrane, which comprises the following steps: Step one, solubilization of dissolved oil: The hydrogen peroxide (the concentration of the hydrogen peroxide is 0.6 mmol / L) is added to the oil-containing wastewater to be treated, and the oil-containing wastewater to be treated is treated at 55°C for 8 min under the ultrasonic treatment of 80 kHz, so that the interfacial tension of the dissolved oil in the oil-containing wastewater to be treated is reduced, the size of the dissolved oil is reduced, and the dissolved oil is combined with the hydrogen peroxide.
[0031] In step one, the concentration of the hydrogen peroxide refers to the proportion of the effective amount of the hydrogen peroxide (the amount of the solute) in the oil-containing wastewater to be treated in step one.
[0032] In this embodiment, the concentration of the hydrogen peroxide is 0.6 mmol / L, that is, the proportion of the effective amount of the hydrogen peroxide (the amount of the solute) in the oil-containing wastewater to be treated in step one is 0.6 mmol / L.
[0033] In step two, the hardness ions are added. The hardness ions (the concentration of the hardness ions is 4 mmol / L) composed of calcium chloride and magnesium chloride are added to the dissolved oil after the solubilization in step one, and the mixture is sheared at 22000 r / min for 3 min to obtain the dissolved oil after the hardness ions are added.
[0034] In the hardness ions in step two, the molar ratio of calcium chloride to magnesium chloride is calcium chloride:magnesium chloride = 1:2.4.
[0035] The concentration of the hardness ions refers to the proportion of the hardness ions in the oil-containing wastewater to be treated in step one.
[0036] In this embodiment, the concentration of the hardness ions is 4 mmol / L, that is, the proportion of the hardness ions in the oil-containing wastewater to be treated in step one is 4 mmol / L.
[0037] In step three, the interfacial properties of the dissolved oil are regulated. The ozone with a volume flow rate of 10 L / min is introduced into the dissolved oil after the hardness ions are added in step two for continuous reaction for 25 min (the concentration of the ozone is 25 mg / L), so that the interfacial properties of the dissolved oil after the hardness ions are added in step two are changed by the ozone and hydroxyl radicals, the dispersion stability of the dissolved oil after the hardness ions are added in step two is further destroyed on the basis of the hardness ions in step two, and the dissolved oil after the interfacial properties are regulated is obtained.
[0038] In step three, the concentration of the ozone refers to the proportion of the ozone in the oil-containing wastewater to be treated in step one.
[0039] In this embodiment, the concentration of the ozone is 25 mg / L, that is, the proportion of the ozone in the oil-containing wastewater to be treated in step one is 25 mg / L.
[0040] Step four, strengthening the dissolved oil demulsification: The saturated ferrous chloride solution was added to the interface performance regulated dissolved oil obtained in step three, and reacted for 25 min under the condition of 50 r / min. After standing for 12 min, the demulsified dissolved oil was obtained, and then entered the ultrafiltration system for treatment. After filtering for 120 min, physical backwashing was carried out. The flux decay rate, flux recovery rate and dissolved oil removal rate of the ultrafiltration membrane were monitored.
[0041] In step four, the addition concentration of ferrous chloride in the saturated ferrous chloride solution was 0.06 mmol / L.
[0042] The addition concentration of ferrous chloride in the saturated ferrous chloride solution refers to the proportion of ferrous chloride in the oil-containing wastewater to be treated in step one.
[0043] In this embodiment, the concepts and calculation methods of the flux decay rate, flux recovery rate and dissolved oil removal rate of the ultrafiltration membrane were respectively the commonly used concepts and calculation methods known in the art.
[0044] In this embodiment, the 30 kDa polyvinylidene fluoride ultrafiltration membrane was the commonly used 30 kDa polyvinylidene fluoride ultrafiltration membrane known in the art; the 60 mg / L sulfonated kerosene wastewater was the commonly used 60 mg / L sulfonated kerosene wastewater known in the art.
[0045] In this embodiment, the method of physical backwashing of the polyvinylidene fluoride ultrafiltration membrane was the commonly used method of physical backwashing known in the art.
[0046] Table 1: Pollution behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of sulfonated kerosene wastewater
[0047] The results of the pollution behavior of the polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of the sulfonated kerosene wastewater using the method of simultaneous strengthening of dissolved oil removal and weakening of ultrafiltration membrane pollution in this embodiment as the pretreatment method are shown in Table 1.
[0048] The results in Table 1 show that within the same running time, the flux decay rate of the polyvinylidene fluoride ultrafiltration membrane caused by the pretreated sulfonated kerosene wastewater decreased from 72% to 51%, while the flux recovery rate increased from 45% to 68%, and the membrane pollution rate and irreversible pollution amplitude were significantly slowed down; at the same time, the dissolved oil removal rate after pretreatment increased by 18%. Obviously, this pretreatment method realizes the simultaneous strengthening of dissolved oil removal rate and membrane pollution mitigation.
[0049] Example 2: With the 50kDa polyether sulfone ultrafiltration membrane (referred to as polyether sulfone ultrafiltration membrane) for filtering 200mg / L sulfonated kerosene wastewater (i.e. the oil-containing wastewater of the present embodiment, also referred to as sulfonated kerosene wastewater) as an example, the present embodiment gives a method of synchronously strengthening oil removal and weakening membrane fouling, which is basically the same as the method in step one, and the only difference is that in step one, the oil-containing wastewater to be treated is changed from 60mg / L sulfonated kerosene wastewater to 200mg / L sulfonated kerosene wastewater, the hydrogen peroxide concentration is changed from 0.6mmol / L to 1mmol / L, and the 80kHz ultrasonic treatment time is changed from 8min to 100kHz ultrasonic treatment for 10min; in step two, the hardness ion concentration is changed from 4mmol / L to 7mmol / L, the shear mixing speed is changed from 22000r / min to 24000r / min, and the shear mixing time is changed from 3min to 5min; in step three, the ozone volume flow rate is changed from 10L / min to 25L / min, the ozone continuous reaction time is changed from 25min to 30min, and the ozone concentration is changed from 25mg / L to 45mg / L; in step four, the ferrous chloride concentration in the saturated ferrous chloride solution is changed from 0.06mmol / L to 0.15mmol / L, the reaction time under the condition of 50r / min is changed from 25min to 60r / min for 25min, and the ultrafiltration membrane is changed from 30kDa polyvinylidene fluoride ultrafiltration membrane to 50kDa polyether sulfone ultrafiltration membrane.
[0050] In the present embodiment, the 50kDa polyether sulfone ultrafiltration membrane adopts the commonly known 50kDa polyether sulfone ultrafiltration membrane in the art; the 200mg / L sulfonated kerosene wastewater adopts the commonly known 200mg / L sulfonated kerosene wastewater in the art.
[0051] In the present embodiment, the method of physical backwashing of the polyether sulfone ultrafiltration membrane adopts the commonly known method of physical backwashing in the art.
[0052] Table 2 Membrane fouling behavior of polyether sulfone ultrafiltration membrane before and after pretreatment of sulfonated kerosene wastewater
[0053] With the method of synchronously strengthening oil removal and weakening membrane fouling in the present embodiment as the pretreatment method, the results of the membrane fouling behavior of the polyether sulfone ultrafiltration membrane before and after pretreatment of the sulfonated kerosene wastewater are shown in Table 2.
[0054] The results in Table 2 show that, in the same running time, the flux decay rate of the polyether sulfone ultrafiltration membrane caused by the sulfonated kerosene wastewater after pretreatment is reduced from 88% to 71%, while the flux recovery rate is increased from 30% to 51%, and the membrane fouling rate and the irreversible fouling amplitude are significantly slowed down; at the same time, the removal rate of dissolved oil after pretreatment is increased by 12%. Obviously, the pretreatment method realizes the simultaneous enhancement of the removal rate of dissolved oil and the mitigation of membrane fouling.
[0055] Example 3 In this example, the method for simultaneously enhancing the removal of dissolved oil and mitigating the fouling of ultrafiltration membrane is given by taking the filtration of 600 mg / L sulfonated kerosene wastewater (i.e. the oil-containing wastewater in this example, also referred to as sulfonated kerosene wastewater) using a 50 kDa polyvinylidene fluoride ultrafiltration membrane (referred to as polyvinylidene fluoride ultrafiltration membrane) as an example. The method is basically the same as that in Step 1, and the only difference is that in Step 1, the oil-containing wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 600 mg / L sulfonated kerosene wastewater, the concentration of hydrogen peroxide is changed from 0.6 mmol / L to 1.8 mmol / L, the 80 kHz ultrasonic treatment at 55°C for 8 min is changed to 100 kHz ultrasonic treatment at 60°C for 10 min; in Step 2, the concentration of hardness ions is changed from 4 mmol / L to 15 mmol / L, the rotation speed of shear mixing is changed from 22,000 r / min to 25,000 r / min, and the shear mixing time is changed from 3 min to 5 min; in Step 3, the volume flow rate of ozone is changed from 10 L / min to 40 L / min, the continuous reaction time of ozone is changed from 25 min to 40 min, and the concentration of ozone is changed from 25 mg / L to 80 mg / L; in Step 4, the concentration of ferrous chloride in the saturated ferrous chloride solution is changed from 0.06 mmol / L to 0.2 mmol / L, the reaction at 50 r / min for 25 min is changed to the reaction at 80 r / min for 30 min, and the ultrafiltration membrane is changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 50 kDa polyvinylidene fluoride ultrafiltration membrane.
[0056] In this example, the 50 kDa polyvinylidene fluoride ultrafiltration membrane is a commonly used 50 kDa polyvinylidene fluoride ultrafiltration membrane known in the art, and the 600 mg / L sulfonated kerosene wastewater is a commonly used 600 mg / L sulfonated kerosene wastewater known in the art.
[0057] In this example, the method for physical backwashing of the polyvinylidene fluoride ultrafiltration membrane is a commonly used method for physical backwashing known in the art.
[0058] Table 3 Fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of sulfonated kerosene wastewater
[0059] The method of simultaneously enhancing the removal of dissolved oil and weakening the pollution of ultrafiltration membrane in this embodiment is used as a pretreatment method. The results of the pollution behavior of polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of sulfonated kerosene wastewater are shown in Table 3.
[0060] The results in Table 3 show that, in the same running time, the flux decay rate of the polyvinylidene fluoride ultrafiltration membrane caused by the sulfonated kerosene wastewater after the pretreatment is reduced from 95% to 83%, while the flux recovery rate is increased from 15% to 30%, and the membrane pollution rate and the irreversible pollution amplitude are significantly slowed down; at the same time, the removal rate of dissolved oil after the pretreatment is increased by 7%. Obviously, the pretreatment method realizes the simultaneous enhancement of the removal rate of dissolved oil and the weakening of the membrane pollution.
[0061] Embodiment 4 In this embodiment, a method of simultaneously enhancing the removal of dissolved oil and weakening the pollution of ultrafiltration membrane is given by taking the filtration of 100 mg / L soluble diesel wastewater (i.e. the oil-containing wastewater in this embodiment) by using a 20 kDa polyether sulfone ultrafiltration membrane (hereinafter referred to as a polyether sulfone ultrafiltration membrane) as an example. The method is basically the same as that in Step 1, and the only difference is that in Step 1, the oil-containing wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 100 mg / L soluble diesel wastewater, the concentration of hydrogen peroxide to be added is changed from 0.6 mmol / L to 0.8 mmol / L, and the ultrasonic treatment time is changed from 8 min to 10 min; in Step 2, the concentration of hardness ions to be added is changed from 4 mmol / L to 5 mmol / L, and the time of shear mixing is changed from 3 min to 5 min; in Step 3, the volume flow rate of ozone is changed from 10 L / min to 20 L / min, and the continuous reaction time of ozone is changed from 25 min to 30 min; in Step 4, the concentration of ferrous chloride in the saturated ferrous chloride solution is changed from 0.06 mmol / L to 0.1 mmol / L, the reaction under the condition of 50 r / min for 25 min is changed to the reaction under the condition of 60 r / min for 25 min, the standing time is changed from 12 min to 15 min, and the ultrafiltration membrane is changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 20 kDa polyether sulfone ultrafiltration membrane.
[0062] In this embodiment, the 20 kDa polyether sulfone ultrafiltration membrane is a commonly used 20 kDa polyether sulfone ultrafiltration membrane known in the art, and the 100 mg / L soluble diesel wastewater is a commonly used 100 mg / L soluble diesel wastewater known in the art.
[0063] In this embodiment, the method of physical backwashing of the polyether sulfone ultrafiltration membrane is a commonly used method of physical backwashing known in the art.
[0064] Table 4 Pollution behavior of polyether sulfone ultrafiltration membrane before and after the pretreatment of soluble diesel wastewater
[0065] The method of simultaneously enhancing the removal of dissolved oil and weakening the pollution of ultrafiltration membrane in this embodiment is used as a pretreatment method. The results of the pollution behavior of polyether sulfone ultrafiltration membranes before and after the pretreatment of soluble diesel wastewater are shown in Table 4.
[0066] The results in Table 4 show that, in the same running time, the flux decay rate of the polyether sulfone ultrafiltration membrane caused by the soluble diesel wastewater after the pretreatment is reduced from 80% to 73%, while the flux recovery rate is increased from 40% to 56%, and the membrane pollution rate and the irreversible pollution amplitude are significantly slowed down; at the same time, the removal rate of dissolved oil after the pretreatment is increased by 9%. Obviously, the pretreatment method realizes the simultaneous enhancement of the removal of dissolved oil and the weakening of the pollution of ultrafiltration membrane.
[0067] Embodiment 5 In this embodiment, a method of simultaneously enhancing the removal of dissolved oil and weakening the pollution of ultrafiltration membrane is given by taking the filtration of 150 mg / L soluble diesel wastewater (i.e., the oil-containing wastewater in this embodiment) by using a 100 kDa polyvinylidene fluoride ultrafiltration membrane (referred to as a polyvinylidene fluoride ultrafiltration membrane) as an example. The method is basically the same as the method in Step 1, and the only difference is that in Step 1, the oil-containing wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 150 mg / L soluble diesel wastewater, the hydrogen peroxide concentration is changed from 0.6 mmol / L to 1 mmol / L, and the ultrasonic treatment time is changed from 8 min to 10 min; in Step 2, the hardness ion concentration is changed from 4 mmol / L to 6 mmol / L, and the shear mixing time is changed from 3 min to 5 min; in Step 3, the ozone volume flow rate is changed from 10 L / min to 20 L / min, the continuous ozone reaction time is changed from 25 min to 30 min, and the ozone concentration is changed from 25 mg / L to 30 mg / L; in Step 4, the ferrous chloride concentration in the saturated ferrous chloride solution is changed from 0.06 mmol / L to 0.15 mmol / L, the reaction under the condition of 50 r / min for 25 min is changed to the reaction under the condition of 60 r / min for 25 min, the standing time is changed from 12 min to 15 min, and the ultrafiltration membrane is changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 100 kDa polyvinylidene fluoride ultrafiltration membrane.
[0068] In this embodiment, 150 mg / L soluble diesel wastewater refers to that the content of dissolved oil in the oil-containing wastewater to be treated is 150 mg / L.
[0069] In this embodiment, the 100 kDa polyvinylidene fluoride ultrafiltration membrane refers to a commonly used 100 kDa polyvinylidene fluoride ultrafiltration membrane in the art, and the 150 mg / L soluble diesel wastewater refers to a commonly used 150 mg / L soluble diesel wastewater in the art.
[0070] In this embodiment, the method of physical backwashing of polyvinylidene fluoride ultrafiltration membrane adopts the commonly used method of physical backwashing known in the art.
[0071] Table 5: The pollution behavior of polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of soluble diesel oil wastewater
[0072] The results of the pollution behavior of polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of soluble diesel oil wastewater are shown in Table 5, using the method of simultaneous enhancement of removal of soluble oil and mitigation of membrane fouling in this embodiment as the pretreatment method.
[0073] The results in Table 5 show that, within the same running time, the flux decay rate of polyvinylidene fluoride ultrafiltration membrane caused by soluble diesel oil wastewater after pretreatment is reduced from 85% to 75%, while the flux recovery rate is increased from 32% to 53%, and the membrane pollution rate and the irreversible pollution amplitude are significantly slowed down; at the same time, the removal rate of soluble oil after pretreatment is increased by 8%. Obviously, this pretreatment method realizes the simultaneous enhancement of removal of soluble oil and mitigation of membrane fouling.
[0074] Example 6: Taking the filtration of 420 mg / L soluble vegetable oil wastewater (i.e. the oil-containing wastewater in this embodiment) using 50 kDa polyvinylidene fluoride ultrafiltration membrane (hereinafter referred to as polyvinylidene fluoride ultrafiltration membrane) as an example, this embodiment gives a method of simultaneous enhancement of removal of soluble oil and mitigation of membrane fouling, which is basically the same as the method in Step 1, with the only difference being that in Step 1, the oil-containing wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 420 mg / L soluble vegetable oil wastewater, the concentration of hydrogen peroxide is changed from 0.6 mmol / L to 1.5 mmol / L, and the ultrasonic treatment is changed from 80 kHz for 8 min to 100 kHz for 10 min; in Step 2, the concentration of hardness ions is changed from 4 mmol / L to 9 mmol / L, the rotation speed of shear mixing is changed from 22000 r / min to 24000 r / min, and the shear mixing time is changed from 3 min to 5 min; in Step 3, the volume flow rate of ozone is changed from 10 L / min to 35 L / min, the continuous reaction time of ozone is changed from 25 min to 35 min, and the concentration of ozone is changed from 25 mg / L to 55 mg / L; in Step 4, the concentration of ferrous chloride in the saturated ferrous chloride solution is changed from 0.06 mmol / L to 0.2 mmol / L, the reaction under 50 r / min for 25 min is changed to the reaction under 80 r / min for 30 min, the standing time is changed from 12 min to 15 min, and the ultrafiltration membrane is changed from 30 kDa polyvinylidene fluoride ultrafiltration membrane to 50 kDa polyvinylidene fluoride ultrafiltration membrane.
[0075] In this embodiment, the 50 kDa polyvinylidene fluoride ultrafiltration membrane is a 50 kDa polyvinylidene fluoride ultrafiltration membrane commonly known in the art; the 420 mg / L soluble plant oil wastewater is a 420 mg / L soluble plant oil wastewater commonly known in the art.
[0076] In this embodiment, the method of physical backwashing of the polyvinylidene fluoride ultrafiltration membrane is a method of physical backwashing commonly known in the art.
[0077] Table 6: The pollution behavior of the polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of the soluble plant oil wastewater
[0078] The results of the pollution behavior of the polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of the soluble plant oil wastewater are shown in Table 6, using the method of simultaneous enhancement of soluble oil removal and mitigation of ultrafiltration membrane pollution in this embodiment as the pretreatment method.
[0079] The results in Table 6 show that, within the same running time, the flux decay rate of the polyvinylidene fluoride ultrafiltration membrane caused by the soluble plant oil wastewater after the pretreatment is reduced from 87% to 80%, while the flux recovery rate is increased from 26% to 43%, the membrane pollution rate and the irreversible pollution amplitude are significantly slowed down; at the same time, the removal rate of soluble oil after the pretreatment is increased by 9%. Obviously, the pretreatment method realizes the simultaneous enhancement of soluble oil removal rate and membrane pollution mitigation.
[0080] Example 7: With the 100 kDa polyvinylidene fluoride ultrafiltration membrane (hereinafter referred to as polyvinylidene fluoride ultrafiltration membrane) filtration of 420 mg / L soluble vegetable oil wastewater (i.e. the oil-containing wastewater of the present embodiment) as an example, the present embodiment gives a method of simultaneously strengthening the removal of dissolved oil and weakening the membrane pollution, which is basically the same as the method in step one, the only difference is that in step one, the oil-containing wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 420 mg / L soluble vegetable oil wastewater, the hydrogen peroxide concentration is changed from 0.6 mmol / L to 1.5 mmol / L, and the 80 kHz ultrasonic treatment for 8 min is changed to 100 kHz ultrasonic treatment for 10 min; in step two, the hardness ion concentration is changed from 4 mmol / L to 9 mmol / L, the shear mixing speed is changed from 22000 r / min to 24000 r / min, and the shear mixing time is changed from 3 min to 5 min; in step three, the ozone volume flow rate is changed from 10 L / min to 35 L / min, the ozone continuous reaction time is changed from 25 min to 35 min, and the ozone concentration is changed from 25 mg / L to 55 mg / L; in step four, the ferrous chloride concentration in the saturated ferrous chloride solution is changed from 0.06 mmol / L to 0.2 mmol / L, the reaction time under the condition of 50 r / min is changed from 25 min to 30 min under the condition of 80 r / min, the standing time is changed from 12 min to 15 min, and the ultrafiltration membrane is changed from 30 kDa polyvinylidene fluoride ultrafiltration membrane to 100 kDa polyvinylidene fluoride ultrafiltration membrane.
[0081] In the present embodiment, the 100 kDa polyvinylidene fluoride ultrafiltration membrane uses the commonly known 100 kDa polyvinylidene fluoride ultrafiltration membrane in the art; the 420 mg / L soluble vegetable oil wastewater uses the commonly known 420 mg / L soluble vegetable oil wastewater in the art.
[0082] In the present embodiment, the method of physical backwashing of the polyvinylidene fluoride ultrafiltration membrane uses the commonly known method of physical backwashing in the art.
[0083] Table 7 Membrane pollution behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of soluble vegetable oil wastewater
[0084] Using the method of simultaneously strengthening the removal of dissolved oil and weakening the membrane pollution in the present embodiment as the pretreatment method, the results of the membrane pollution behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of soluble vegetable oil wastewater are shown in Table 7.
[0085] The results in Table 1 show that the flux decline rate of polyvinylidene fluoride ultrafiltration membrane caused by the dissolved vegetable oil wastewater after pretreatment is reduced from 90% to 78% in the same running time, while the flux recovery rate is increased from 26% to 45%, the membrane fouling rate and the irreversible fouling amplitude are significantly slowed down; at the same time, the removal rate of dissolved oil after pretreatment is increased by 7%. Obviously, this pretreatment method realizes the simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.
[0086] Example 8 In this example, the method for simultaneously enhancing the removal of dissolved oil and mitigating the fouling of ultrafiltration membrane is given by taking the filtration of 650 mg / L dissolved vegetable oil wastewater (i.e. the oil-containing wastewater in this example) using 30 kDa polyether sulfone ultrafiltration membrane (hereinafter referred to as polyether sulfone ultrafiltration membrane) as an example. The method is basically the same as that in step one, and the only difference is that in step one, the oil-containing wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 650 mg / L dissolved vegetable oil wastewater, the concentration of hydrogen peroxide is changed from 0.6 mmol / L to 2 mmol / L, and the ultrasonic treatment at 80 kHz for 8 min at a constant temperature of 55 ℃ is changed to ultrasonic treatment at 100 kHz for 10 min at a constant temperature of 60 ℃; in step two, the concentration of hardness ions is changed from 4 mmol / L to 20 mmol / L, the rotation speed of shear mixing is changed from 22,000 r / min to 25,000 r / min, and the shear mixing time is changed from 3 min to 5 min; in step three, the volume flow rate of ozone is changed from 10 L / min to 40 L / min, the continuous reaction time of ozone is changed from 25 min to 40 min, and the concentration of ozone is changed from 25 mg / L to 80 mg / L; in step four, the concentration of ferrous chloride in the saturated ferrous chloride solution is changed from 0.06 mmol / L to 0.2 mmol / L, the reaction under the condition of 100 r / min for 30 min is changed to the reaction under the condition of 50 r / min for 25 min, the standing time is changed from 12 min to 15 min, and the ultrafiltration membrane is changed from 30 kDa polyvinylidene fluoride ultrafiltration membrane to 30 kDa polyether sulfone ultrafiltration membrane.
[0087] In this example, the 30 kDa polyether sulfone ultrafiltration membrane is the commonly used 30 kDa polyether sulfone ultrafiltration membrane known in the art, and the 650 mg / L dissolved vegetable oil wastewater is the commonly used 650 mg / L dissolved vegetable oil wastewater known in the art.
[0088] In this example, the method for physical backwashing of polyether sulfone ultrafiltration membrane is the commonly used method for physical backwashing known in the art.
[0089] Table 8 Fouling behavior of polyether sulfone ultrafiltration membrane caused by dissolved vegetable oil wastewater before and after pretreatment
[0090] The results of the pollution behavior of the polyether sulfone ultrafiltration membrane before and after the pretreatment of the soluble plant oil wastewater by the method of simultaneously enhancing the removal of the soluble oil and weakening the pollution of the ultrafiltration membrane are shown in Table 8.
[0091] The results in Table 8 show that, in the same running time, the flux decay rate of the polyether sulfone ultrafiltration membrane caused by the soluble plant oil wastewater after the pretreatment is reduced from 95% to 86%, the flux recovery rate is increased from 25% to 42%, the membrane pollution rate and the irreversible pollution amplitude are significantly slowed down, and the removal rate of the soluble oil after the pretreatment is increased by 8%. Apparently, the method of the pretreatment simultaneously enhances the removal of the soluble oil and the weakening of the membrane pollution.
Claims
1. A method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling, characterized in that, The method includes the following steps: Step 1, dissolving and solubilizing the oil: Hydrogen peroxide is added to the oily wastewater to be treated and ultrasonic treatment is carried out at a constant temperature to reduce the interfacial tension of the dissolved oil in the wastewater, forming smaller dissolved oil and promoting the full combination of dissolved oil and hydrogen peroxide to obtain solubilized dissolved oil. Step 2, add hardness ions: Add hardness ions to the solubilized dissolved oil obtained in step one, and shear and mix at 10000-25000 r / min for 2-5 min to obtain the dissolved oil after adding hardness ions; Step 3, Adjustment of the interfacial properties of the dissolved oil: Ozone is introduced into the dissolved oil after adding hardness ions in step two and reacted continuously for 20-40 minutes. Ozone, in conjunction with hydroxyl radicals, changes the interfacial properties of the dissolved oil after adding hardness ions in step two. Based on the hardness ions in step two, the dispersion stability of the dissolved oil after adding hardness ions in step two is further destroyed, resulting in a dissolved oil with regulated interfacial properties. Step 4, Enhance the dissolving oil demulsification: Add a saturated ferrous chloride solution to the dissolved oil with regulated interfacial properties obtained in step three, and react at 50–100 r / min for 20–30 min. After standing for 10–15 min, the dissolved oil after demulsification is obtained and then processed by an ultrafiltration system.
2. The method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling as described in claim 1, characterized in that, In step one, the relationship between the concentration of hydrogen peroxide added and the content of dissolved oil in the oily wastewater to be treated in step one is as follows: When the dissolved oil content in the oily wastewater to be treated is less than 100 mg / L, the concentration of hydrogen peroxide added is 0.4–0.8 mmol / L; When the dissolved oil content in the oily wastewater to be treated is 100–500 mg / L, the concentration of hydrogen peroxide added is 0.8–1.5 mmol / L; When the dissolved oil content in the oily wastewater to be treated is greater than 500 mg / L, the concentration of hydrogen peroxide added should be 1.5–2.2 mmol / L.
3. The method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling as described in claim 1, characterized in that, In step one, the constant temperature is 40–60°C; The ultrasonic treatment is performed using 20-100 kHz ultrasound for 5-10 minutes.
4. The method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling as described in claim 1, characterized in that, In step two, the hardness ions include calcium chloride and magnesium chloride; The molar ratio of calcium chloride to magnesium chloride is 1:2.
4.
5. The method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling as described in claim 1, characterized in that, In step two, the relationship between the concentration of hardness ions added and the dissolved oil content in the oily wastewater to be treated in step one is as follows: When the dissolved oil content in the oily wastewater to be treated is less than 100 mg / L, the concentration of hardness ions added is 2–5 mmol / L; When the dissolved oil content in the oily wastewater to be treated is 100–500 mg / L, the concentration of hardness ions added is 5–10 mmol / L; When the dissolved oil content in the oily wastewater to be treated is greater than 500 mg / L, the concentration of hardness ions added should be 10–25 mmol / L.
6. The method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling as described in claim 1, characterized in that, In step three, the relationship between the ozone concentration and the dissolved oil content in the oily wastewater to be treated in step one is as follows: When the dissolved oil content in the oily wastewater to be treated is less than 100 mg / L, the ozone dosage concentration is 5–25 mg / L. When the dissolved oil content in the oily wastewater to be treated is 100–500 mg / L, the ozone dosage concentration is 25–55 mg / L. When the dissolved oil content in the oily wastewater to be treated is greater than 500 mg / L, the ozone dosage concentration is 55–90 mg / L.
7. The method for simultaneously enhancing dissolved oil removal and reducing ultrafiltration membrane fouling as described in claim 1, characterized in that, In step three, the volumetric flow rate of ozone is 10–40 L / min.
8. The method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling as described in claim 1, characterized in that, In step four, the relationship between the concentration of ferrous chloride in the saturated ferrous chloride solution and the concentration of hydrogen peroxide in step one is: the concentration of ferrous chloride in the saturated ferrous chloride solution = the concentration of hydrogen peroxide × (10%~15%).