Method for simultaneously enhancing oil removal and weakening membrane fouling by using ultrafiltration

Abstract

The application provides a method for synchronously strengthening removal of dissolved oil and weakening pollution of an ultrafiltration membrane, and the method comprises the following steps: step one, hydrogen peroxide is added to the oil-containing wastewater to be treated, and ultrasonic treatment is performed at a constant temperature to obtain dissolved oil after solubilization; step two, hardness ions are added to the dissolved oil after solubilization obtained in step one and shearing mixing is performed to obtain dissolved oil after addition of hardness ions; step three, ozone is continuously introduced into the dissolved oil after addition of hardness ions obtained in step two to perform reaction, and the dissolved oil after interfacial performance regulation is obtained; step four, saturated ferrous chloride solution is added to the dissolved oil after interfacial performance regulation obtained in step three to perform reaction and standing, and the dissolved oil after demulsification is obtained, and then the dissolved oil after demulsification is subjected to ultrafiltration system treatment. The method in the application realizes synergistic regulation of the interfacial performance and size of the dissolved oil, strengthens removal of the dissolved oil by the ultrafiltration membrane and slows down pollution of the ultrafiltration membrane, the reaction product is only water and oxygen, there is no secondary pollution, and the method has the advantages of simple operation and wide applicability.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology and relates to membrane fouling control, specifically to a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. Background Technology

[0002] With the rapid development of industrialization and urbanization, a large amount of oily wastewater is generated in various domestic and industrial production processes. Its main sources include petrochemicals, machinery processing, the steel industry, and food processing. Oily wastewater has a complex composition and is difficult to biodegrade, posing a significant pollution risk to the environment. Therefore, countries around the world have imposed strict restrictions on the discharge of oily wastewater, requiring it to undergo appropriate treatment to meet standards before being discharged into natural or downstream receiving water bodies.

[0003] Oily wastewater can be classified into four categories based on the oil phase morphology: floating oil, dispersed oil, emulsified oil, and dissolved oil. Floating oil and dispersed oil, due to their larger particle size, can be efficiently removed using traditional processes such as oil separators, flotation, or coagulation sedimentation. However, emulsified oil and dissolved oil, especially dissolved oil, typically have a size smaller than 0.1 μm, resulting in extremely high stability in water bodies, making effective separation difficult using traditional methods. Ultrafiltration membrane technology, with its nanoscale pore size, has become a key means of removing dissolved oil. However, the pore size of ultrafiltration membranes is similar to that of dissolved oil, leading to two major challenges during operation: severe membrane fouling and insufficient removal rate.

[0004] Numerous studies have focused on ultrafiltration membrane fouling control, with pretreatment processes such as oxidation, coagulation, filtration, and adsorption becoming important strategies for controlling membrane fouling due to their simplicity and efficiency. However, these traditional pretreatment technologies primarily target membrane fouling caused by dissolved organic matter such as polysaccharides, proteins, and humic substances. Unlike dissolved organic matter, dissolved oils, with hydrocarbons forming their core structure, exhibit strong hydrophobicity, low reactivity, and recalcitrant degradation. They are mainly dispersed in water as molecules or micelles, making traditional pretreatment technologies ineffective in addressing membrane fouling caused by dissolved oils. Furthermore, traditional pretreatment methods often result in a significant decrease in pollutant removal rates while controlling membrane fouling, meaning that membrane fouling control is achieved by sacrificing organic matter removal efficiency. Therefore, developing a new method that can both enhance dissolved oil removal and effectively mitigate ultrafiltration membrane fouling is particularly urgent, and is of great significance for expanding the application of ultrafiltration technology in the treatment of oily wastewater. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling, thereby solving the technical problem in existing technologies where it is difficult to simultaneously enhance the removal of dissolved oil and reduce ultrafiltration membrane fouling when treating oily wastewater containing dissolved oil.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling, the method comprising the following steps: Step 1, dissolving and solubilizing the oil: Hydrogen peroxide is added to the oily wastewater to be treated and ultrasonically treated 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, thus obtaining the solubilized dissolved oil.

[0007] Step 2, add hardness ions: Hardness ions are added to the solubilized dissolved oil obtained in step one, and the mixture is sheared and mixed at 10,000–25,000 r / min for 2–5 min to obtain the dissolved oil after adding hardness ions.

[0008] 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, alters the interfacial properties of the dissolved oil after adding hardness ions in step two. Based on the hardness ions in step two, it further disrupts the dispersion stability of the dissolved oil after adding hardness ions in step two, resulting in a dissolved oil with regulated interfacial properties.

[0009] 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.

[0010] The present invention also has the following technical features: Preferably, 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.

[0011] 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.

[0012] 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.

[0013] Specifically, in step one, the constant temperature is 40–60°C.

[0014] The ultrasonic treatment is performed using 20-100 kHz ultrasound for 5-10 minutes.

[0015] Specifically, in step two, the hardness ions include calcium chloride and magnesium chloride.

[0016] The molar ratio of calcium chloride to magnesium chloride is 1:2.4.

[0017] Specifically, in step two, the relationship between the concentration of hardness ions 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.

[0018] 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.

[0019] 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.

[0020] Specifically, 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.

[0021] 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.

[0022] 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.

[0023] Specifically, in step three, the volumetric flow rate of ozone is 10–40 L / min.

[0024] Specifically, in step four, the relationship between the concentration of ferrous chloride added to the saturated ferrous chloride solution and the concentration of hydrogen peroxide added in step one is as follows: the concentration of ferrous chloride added to the saturated ferrous chloride solution = the concentration of hydrogen peroxide added × (10%~15%).

[0025] Compared with the prior art, the present invention has the following technical effects: (I) The method in this invention achieves synergistic control of the properties and size of the dissolved oil interface, enhances the removal of dissolved oil by the ultrafiltration membrane and reduces the fouling of the ultrafiltration membrane, and the reaction products are only water and oxygen, with no risk of secondary pollution. It has the advantages of simple operation and wide applicability.

[0026] (II) The method of this invention first utilizes the ultrasonic cavitation effect to reduce the interfacial tension and viscosity of dissolved oil in the oily wastewater to be treated, thereby reducing the particle size of the dissolved oil and promoting the full combination of dissolved oil and hydrogen peroxide. Then, through shear mixing, hardness ions are uniformly distributed at the interface of dissolved oil molecules, and the hydration effect of hardness ions is used to enhance the stability of dissolved oil. On this basis, ozone and hydrogen peroxide are used to generate hydroxyl radicals around the molecular chains of dissolved oil, thereby achieving local oxidation modification of the molecular chains. At the same time, the charge shielding and bridging complexation effect of hardness ions is used to reduce the interfacial charge of dissolved oil, thereby promoting its destabilization. Finally, ferrous ions are introduced, which not only consume the residual oxidant to avoid affecting the ultrafiltration system, but also assist in demulsification through the coagulation effect of polyvalent iron ions.

[0027] The specific content of the present invention will be further described in detail below with reference to the embodiments. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, all systems and raw materials in this invention are commonly used in the art in the prior art. For example, the ultrafiltration system is a known ultrafiltration system, the hydrogen peroxide is a known hydrogen peroxide with a mass concentration of 30%, the calcium chloride is a known calcium chloride, the magnesium chloride is a known magnesium chloride, the ozone is a known ozone, and the saturated ferrous chloride solution is a known saturated ferrous chloride solution.

[0029] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0030] Example 1: Taking the filtration of wastewater containing 60 mg / L sulfonated kerosene (i.e., the oily wastewater in this embodiment, also referred to as sulfonated kerosene wastewater) using a 30 kDa polyvinylidene fluoride ultrafiltration membrane (hereinafter referred to as polyvinylidene fluoride ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. The method includes the following steps: Step 1, dissolving and solubilizing the oil: Hydrogen peroxide (0.6 mmol / L) was added to the oily wastewater to be treated, and the wastewater was treated with ultrasound at 80 kHz for 8 min at a constant temperature of 55℃. This reduced the interfacial tension of the dissolved oil in the wastewater, resulting in smaller dissolved oil particles and promoting the full combination of the dissolved oil and hydrogen peroxide, thus obtaining the solubilized dissolved oil.

[0031] In step one, the concentration of hydrogen peroxide refers to the proportion of the effective amount of hydrogen peroxide (the amount of solute) to the amount of oily wastewater to be treated in step one.

[0032] In this embodiment, the concentration of hydrogen peroxide added is 0.6 mmol / L, which means that the effective amount of hydrogen peroxide (the amount of solute) accounts for 0.6 mmol / L of the oily wastewater to be treated in step one.

[0033] Step 2, add hardness ions: Add hardness ions composed of calcium chloride and magnesium chloride (at a concentration of 4 mmol / L) to the solubilized dissolved oil obtained in step one, and shear and mix at 22000 r / min for 3 min to obtain the dissolved oil after adding hardness ions.

[0034] In step two, the molar ratio of calcium chloride to magnesium chloride in the hardness ions is 1:2.4.

[0035] The concentration of hardness ions refers to the proportion of hardness ions in the oily wastewater to be treated in step one.

[0036] In this embodiment, the concentration of hardness ions is 4 mmol / L, which means that the proportion of hardness ions in the oily wastewater to be treated in step one is 4 mmol / L.

[0037] Step 3, Adjustment of the interfacial properties of the dissolved oil: Ozone at a volumetric flow rate of 10 L / min (ozone concentration of 25 mg / L) was continuously introduced into the dissolved oil after adding hardness ions in step two and reacted for 25 min. Ozone, in conjunction with hydroxyl radicals, altered 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 was further disrupted, resulting in a dissolved oil with regulated interfacial properties.

[0038] In step three, the ozone concentration refers to the proportion of ozone in the oily wastewater to be treated in step one.

[0039] In this embodiment, the ozone concentration is 25 mg / L, which means that the ozone accounts for 25 mg / L of the oily wastewater to be treated in step one.

[0040] Step 4, Enhance the dissolving oil demulsification: Saturated ferrous chloride solution was added to the dissolved oil with regulated interfacial properties obtained in step three, and the mixture was reacted at 50 r / min for 25 min. After standing for 12 min, the dissolved oil after demulsification was obtained. The oil was then processed by an ultrafiltration system and filtered for 120 min. Physical backwashing was then performed, and the flux decay rate, flux recovery rate, and dissolved oil removal rate of the ultrafiltration membrane were monitored.

[0041] In step four, the concentration of ferrous chloride in the saturated ferrous chloride solution is 0.06 mmol / L.

[0042] The concentration of ferrous chloride in a saturated ferrous chloride solution refers to the proportion of ferrous chloride to the oily wastewater to be treated in step one.

[0043] In this embodiment, the concepts and calculation methods for the flux decay rate, flux recovery rate, and dissolved oil removal rate of the ultrafiltration membrane are adopted using commonly known concepts and calculation methods in the art.

[0044] In this embodiment, the 30kDa polyvinylidene fluoride ultrafiltration membrane is a commonly used 30kDa polyvinylidene fluoride ultrafiltration membrane known in the art; the 60mg / L sulfonated kerosene wastewater is a commonly used 60mg / L sulfonated kerosene wastewater known in the art.

[0045] In this embodiment, the physical backwashing method for the polyvinylidene fluoride ultrafiltration membrane adopts a commonly used physical backwashing method known in the art.

[0046] Table 1. Fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of sulfonated kerosene wastewater

[0047] The method of simultaneously enhancing dissolved oil removal and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of sulfonated kerosene wastewater are shown in Table 1.

[0048] The results in Table 1 show that, within the same operating time, the flux decline rate of the polyvinylidene fluoride ultrafiltration membrane caused by pretreated sulfonated kerosene wastewater decreased from 72% to 51%, while the flux recovery rate increased from 45% to 68%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 18% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

[0049] Example 2: Taking the filtration of 200 mg / L sulfonated kerosene wastewater (i.e., the oily wastewater in this embodiment, also referred to as sulfonated kerosene wastewater) using a 50 kDa polyethersulfone ultrafiltration membrane (hereinafter referred to as polyethersulfone ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. This method is basically the same as the method in step one, except that: in step one, the oily wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 200 mg / L sulfonated kerosene wastewater, the concentration of hydrogen peroxide is changed from 0.6 mmol / L to 1 mmol / L, and the ultrasonic treatment at 80 kHz for 8 min is changed to ultrasonic treatment at 100 kHz for 10 min; in step two, the concentration of hardness ions is changed from 4 mmol / L to 7 mmol / L. In step three, the ozone volumetric flow rate was changed from 10 L / min to 25 L / min, the ozone continuous reaction time was changed from 25 min to 30 min, and the ozone concentration was changed from 25 mg / L to 45 mg / L. In step four, the ferrous chloride concentration in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.15 mmol / L, the reaction time was changed from 50 r / min for 25 min to 60 r / min for 25 min, and the ultrafiltration membrane was changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 50 kDa polyethersulfone ultrafiltration membrane.

[0050] In this embodiment, the 50kDa polyethersulfone ultrafiltration membrane is a commonly used 50kDa polyethersulfone ultrafiltration membrane known in the art; the 200mg / L sulfonated kerosene wastewater is a commonly used 200mg / L sulfonated kerosene wastewater known in the art.

[0051] In this embodiment, the physical backwashing method for the polyethersulfone ultrafiltration membrane adopts a commonly used physical backwashing method known in the art.

[0052] Table 2. Fouling behavior of polyethersulfone ultrafiltration membrane before and after pretreatment of sulfonated kerosene wastewater

[0053] The method of simultaneously enhancing dissolved oil removal and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling behavior of polyethersulfone ultrafiltration membrane before and after the pretreatment of sulfonated kerosene wastewater are shown in Table 2.

[0054] The results in Table 2 show that, within the same operating time, the flux decline rate of the polyethersulfone ultrafiltration membrane caused by the pretreated sulfonated kerosene wastewater decreased from 88% to 71%, while the flux recovery rate increased from 30% to 51%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 12% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

[0055] Example 3: Taking the filtration of 600 mg / L sulfonated kerosene wastewater (i.e., the oily wastewater in this embodiment, also referred to as sulfonated kerosene wastewater) using a 50 kDa polyvinylidene fluoride ultrafiltration membrane (hereinafter referred to as polyvinylidene fluoride ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. This method is basically the same as the method in step one, except that: in step one, the oily 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 added is changed from 0.6 mmol / L to 1.8 mmol / L, and the ultrasonic treatment at 80 kHz at 55℃ for 8 min is changed to ultrasonic treatment at 100 kHz at 60℃ for 10 min; in step two, the concentration of hardness ions added is changed from 4 mg / L to 100 mg / L. The concentration of ferrous chloride in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.2 mmol / L, the reaction time was changed from 25 min to 30 min, and the ozone volumetric flow rate was changed from 10 L / min to 40 L / min. The reaction time was changed from 25 min to 40 min, and the ozone concentration was changed from 25 mg / L to 80 mg / L. In step four, the concentration of ferrous chloride in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.2 mmol / L, the reaction time was changed from 25 min at 50 r / min to 30 min at 80 r / min, and the ultrafiltration membrane was changed from 30 kDa polyvinylidene fluoride ultrafiltration membrane to 50 kDa polyvinylidene fluoride ultrafiltration membrane.

[0056] In this embodiment, the 50kDa polyvinylidene fluoride ultrafiltration membrane is a commonly used 50kDa polyvinylidene fluoride ultrafiltration membrane known in the art; the 600mg / L sulfonated kerosene wastewater is a commonly used 600mg / L sulfonated kerosene wastewater known in the art.

[0057] In this embodiment, the physical backwashing method for the polyvinylidene fluoride ultrafiltration membrane adopts a commonly used physical backwashing method 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 dissolved oil removal and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling 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, within the same operating time, the flux decline rate of the polyvinylidene fluoride ultrafiltration membrane caused by pretreated sulfonated kerosene wastewater decreased from 95% to 83%, while the flux recovery rate increased from 15% to 30%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 7% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

[0061] Example 4: Taking the filtration of wastewater containing 100 mg / L dissolved diesel fuel (i.e., the oily wastewater in this embodiment) using a 20 kDa polyethersulfone ultrafiltration membrane (hereinafter referred to as polyethersulfone ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. This method is basically the same as the method in step one, except that: in step one, the oily wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 100 mg / L dissolved diesel fuel wastewater, the concentration of hydrogen peroxide added is changed from 0.6 mmol / L to 0.8 mmol / L, and the ultrasonic treatment is changed from 8 min to 10 min; in step two, the concentration of hardness ions added is changed from 4... The concentration of ferrous chloride in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.1 mmol / L, the reaction time was changed from 50 r / min to 60 r / min, the standing time was changed from 12 min to 15 min, and the ultrafiltration membrane was changed from 30 kDa polyvinylidene fluoride ultrafiltration membrane to 20 kDa polyethersulfone ultrafiltration membrane. In step three, the ozone volume flow rate was changed from 10 L / min to 20 L / min, and the ozone continuous reaction time was changed from 25 min to 30 min. In step four, the concentration of ferrous chloride in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.1 mmol / L, the reaction time was changed from 50 r / min for 25 min to 60 r / min for 25 min, the standing time was changed from 12 min to 15 min, and the ultrafiltration membrane was changed from 30 kDa polyvinylidene fluoride ultrafiltration membrane to 20 kDa polyethersulfone ultrafiltration membrane.

[0062] In this embodiment, the 20kDa polyethersulfone ultrafiltration membrane is a commonly used 20kDa polyethersulfone ultrafiltration membrane known in the art; the 100mg / L dissolved diesel wastewater is a commonly used 100mg / L dissolved diesel wastewater known in the art.

[0063] In this embodiment, the physical backwashing method for the polyethersulfone ultrafiltration membrane adopts a commonly used physical backwashing method known in the art.

[0064] Table 4. Fouling behavior of polyethersulfone ultrafiltration membrane before and after pretreatment of dissolved diesel wastewater

[0065] The method of simultaneously enhancing dissolved oil removal and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling behavior of polyethersulfone ultrafiltration membrane before and after the pretreatment of dissolved diesel wastewater are shown in Table 4.

[0066] The results in Table 4 show that, within the same operating time, the flux decline rate of the polyethersulfone ultrafiltration membrane caused by dissolved diesel wastewater after pretreatment decreased from 80% to 73%, while the flux recovery rate increased from 40% to 56%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 9% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

[0067] Example 5: Taking the filtration of wastewater containing 150 mg / L dissolved diesel fuel (i.e., the oily wastewater in this embodiment) using a 100 kDa polyvinylidene fluoride ultrafiltration membrane (hereinafter referred to as polyvinylidene fluoride ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. This method is basically the same as the method in step one, except that: in step one, the oily wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 150 mg / L dissolved diesel fuel wastewater, the concentration of hydrogen peroxide added is changed from 0.6 mmol / L to 1 mmol / L, and the ultrasonic treatment is changed from 8 min to 10 min; in step two, the concentration of hardness ions added is changed from 4 mmol / L to 6 mmol / L. In step three, the ozone volumetric flow rate was changed from 10 L / min to 20 L / min, the ozone continuous reaction time was changed from 25 min to 30 min, and the ozone concentration was changed from 25 mg / L to 30 mg / L. In step four, the ferrous chloride concentration in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.15 mmol / L, the reaction time was changed from 50 r / min for 25 min to 60 r / min for 25 min, the standing time was changed from 12 min to 15 min, and the ultrafiltration membrane was changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 100 kDa polyvinylidene fluoride ultrafiltration membrane.

[0068] In this embodiment, "150 mg / L dissolved diesel wastewater" refers to wastewater containing 150 mg / L of dissolved oil.

[0069] In this embodiment, the 100kDa polyvinylidene fluoride ultrafiltration membrane is a commonly used 100kDa polyvinylidene fluoride ultrafiltration membrane in the art; the 150mg / L dissolved diesel wastewater is a commonly used 150mg / L dissolved diesel wastewater in the art.

[0070] In this embodiment, the physical backwashing method for the polyvinylidene fluoride ultrafiltration membrane adopts a commonly used physical backwashing method known in the art.

[0071] Table 5. Fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of dissolved diesel wastewater.

[0072] The method of simultaneously enhancing dissolved oil removal and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of dissolved diesel wastewater are shown in Table 5.

[0073] The results in Table 5 show that, within the same operating time, the flux decline rate of the polyvinylidene fluoride ultrafiltration membrane caused by dissolved diesel wastewater after pretreatment decreased from 85% to 75%, while the flux recovery rate increased from 32% to 53%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 8% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

[0074] Example 6: Taking the filtration of wastewater containing 420 mg / L dissolved vegetable oil (i.e., the oily wastewater in this embodiment) using a 50 kDa polyvinylidene fluoride ultrafiltration membrane (hereinafter referred to as polyvinylidene fluoride ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. This method is basically the same as the method in step one, except that: in step one, the oily wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 420 mg / L dissolved vegetable oil wastewater, the concentration of hydrogen peroxide added is changed from 0.6 mmol / L to 1.5 mmol / L, and the ultrasonic treatment at 80 kHz for 8 min is changed to ultrasonic treatment at 100 kHz for 10 min; in step two, the concentration of hardness ions added is changed from 4 mmol / L to 9 mmol / L, and shear mixing... The rotation speed was changed from 22000 r / min to 24000 r / min, and the shearing and mixing time was changed from 3 min to 5 min. In step three, the ozone volumetric flow rate was changed from 10 L / min to 35 L / min, the ozone continuous reaction time was changed from 25 min to 35 min, and the ozone concentration was changed from 25 mg / L to 55 mg / L. In step four, the ferrous chloride concentration in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.2 mmol / L, the reaction time was changed from 25 min at 50 r / min to 30 min at 80 r / min, the settling time was changed from 12 min to 15 min, and the ultrafiltration membrane was changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 50 kDa polyvinylidene fluoride ultrafiltration membrane.

[0075] In this embodiment, the 50kDa polyvinylidene fluoride ultrafiltration membrane is a commonly used 50kDa polyvinylidene fluoride ultrafiltration membrane known in the art; the 420mg / L soluble vegetable oil wastewater is a commonly used 420mg / L soluble vegetable oil wastewater known in the art.

[0076] In this embodiment, the physical backwashing method for the polyvinylidene fluoride ultrafiltration membrane adopts a commonly used physical backwashing method known in the art.

[0077] Table 6. Fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of soluble vegetable oil wastewater

[0078] The method of simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of dissolved vegetable oil wastewater are shown in Table 6.

[0079] The results in Table 6 show that, within the same operating time, the flux decline rate of the polyvinylidene fluoride ultrafiltration membrane caused by the pretreated soluble vegetable oil wastewater decreased from 87% to 80%, while the flux recovery rate increased from 26% to 43%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 9% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

[0080] Example 7: Taking the filtration of wastewater containing 420 mg / L dissolved vegetable oil (i.e., the oily wastewater in this embodiment) using a 100 kDa polyvinylidene fluoride ultrafiltration membrane (hereinafter referred to as polyvinylidene fluoride ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. This method is basically the same as the method in step one, except that: in step one, the oily wastewater to be treated is changed from 60 mg / L sulfonated kerosene wastewater to 420 mg / L dissolved vegetable oil wastewater, the concentration of hydrogen peroxide added is changed from 0.6 mmol / L to 1.5 mmol / L, and the ultrasonic treatment at 80 kHz for 8 min is changed to ultrasonic treatment at 100 kHz for 10 min; in step two, the concentration of hardness ions added is changed from 4 mmol / L to 9 mmol / L, and shear mixing... The rotation speed was changed from 22000 r / min to 24000 r / min, and the shearing and mixing time was changed from 3 min to 5 min. In step three, the ozone volumetric flow rate was changed from 10 L / min to 35 L / min, the ozone continuous reaction time was changed from 25 min to 35 min, and the ozone concentration was changed from 25 mg / L to 55 mg / L. In step four, the ferrous chloride concentration in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.2 mmol / L, the reaction time was changed from 25 min at 50 r / min to 30 min at 80 r / min, the settling time was changed from 12 min to 15 min, and the ultrafiltration membrane was changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 100 kDa polyvinylidene fluoride ultrafiltration membrane.

[0081] In this embodiment, the 100kDa polyvinylidene fluoride ultrafiltration membrane is a commonly used 100kDa polyvinylidene fluoride ultrafiltration membrane in the art; the 420mg / L soluble vegetable oil wastewater is a commonly used 420mg / L soluble vegetable oil wastewater in the art.

[0082] In this embodiment, the physical backwashing method for the polyvinylidene fluoride ultrafiltration membrane adopts a commonly used physical backwashing method known in the art.

[0083] Table 7. Fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after pretreatment of soluble vegetable oil wastewater.

[0084] The method of simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling behavior of polyvinylidene fluoride ultrafiltration membrane before and after the pretreatment of dissolved vegetable oil wastewater are shown in Table 7.

[0085] The results in Table 1 show that, within the same operating time, the flux decline rate of the polyvinylidene fluoride ultrafiltration membrane caused by the pretreated soluble vegetable oil wastewater decreased from 90% to 78%, while the flux recovery rate increased from 26% to 45%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 7% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

[0086] Example 8: Taking the filtration of wastewater containing 650 mg / L of dissolved vegetable oil (i.e., the oily wastewater in this embodiment) using a 30 kDa polyethersulfone ultrafiltration membrane (hereinafter referred to as polyethersulfone ultrafiltration membrane) as an example, this embodiment provides a method for simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling. This method is basically the same as the method in step one, except that: in step one, the oily 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 at 55°C for 8 min is changed to ultrasonic treatment at 100 kHz at 60°C for 10 min; in step two, the concentration of hardness ions is changed from 4 mmol / L to 20 mmol / L. In step L, the rotation speed of shear mixing was changed from 22000 r / min to 25000 r / min, and the shear mixing time was changed from 3 min to 5 min; in step three, the volumetric flow rate of ozone was changed from 10 L / min to 40 L / min, the continuous reaction time of ozone was changed from 25 min to 40 min, and the ozone concentration was changed from 25 mg / L to 80 mg / L; in step four, the concentration of ferrous chloride in the saturated ferrous chloride solution was changed from 0.06 mmol / L to 0.2 mmol / L, the reaction time was changed from 25 min at 50 r / min to 30 min at 100 r / min, the settling time was changed from 12 min to 15 min, and the ultrafiltration membrane was changed from a 30 kDa polyvinylidene fluoride ultrafiltration membrane to a 30 kDa polyethersulfone ultrafiltration membrane.

[0087] In this embodiment, the 30kDa polyethersulfone ultrafiltration membrane is a commonly used 30kDa polyethersulfone ultrafiltration membrane known in the art; the 650mg / L soluble vegetable oil wastewater is a commonly used 650mg / L soluble vegetable oil wastewater known in the art.

[0088] In this embodiment, the physical backwashing method for the polyethersulfone ultrafiltration membrane adopts a commonly used physical backwashing method known in the art.

[0089] Table 8. Fouling behavior of polyethersulfone ultrafiltration membrane before and after pretreatment of soluble vegetable oil wastewater

[0090] The method of simultaneously enhancing the removal of dissolved oil and reducing ultrafiltration membrane fouling in this embodiment was used as a pretreatment method. The results of the fouling behavior of polyethersulfone ultrafiltration membrane before and after the pretreatment of dissolved vegetable oil wastewater are shown in Table 8.

[0091] The results in Table 8 show that, within the same operating time, the flux decline rate of the polyethersulfone ultrafiltration membrane caused by the pretreated soluble vegetable oil wastewater decreased from 95% to 86%, while the flux recovery rate increased from 25% to 42%, significantly slowing down the membrane fouling rate and the extent of irreversible fouling. Simultaneously, the removal rate of dissolved oil increased by 8% after pretreatment. Clearly, this pretreatment method achieves simultaneous enhancement of dissolved oil removal rate and membrane fouling mitigation.

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 dissolved oil removal 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 dissolved oil removal 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 added to the saturated ferrous chloride solution and the concentration of hydrogen peroxide added in step one is as follows: the concentration of ferrous chloride added to the saturated ferrous chloride solution = the concentration of hydrogen peroxide added × (10%~15%).

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