Purification method of oily sewage

Abstract

The invention relates to a method for purifying oily sewage. The oily sewage is purified through three main process units. According to the first-stage micro-channel extraction unit, high-oil-content wastewater and an extraction agent are in a micro-channel, grease components in the wastewater are rapidly and efficiently adsorbed, and primary oil-water separation is achieved. The second-stage wastewater enters a buffer separation unit, and in the buffer separation unit, oil-water emulsion in the wastewater is further separated through gravity settling and centrifugal separation. According to the third-stage photocatalytic filtering unit, active sites on the surface of graphene can adsorb and decompose organic matters in the wastewater and convert the organic matters into harmless substances. According to the method, more than 99.95% of grease components, oil-water emulsion and organic pollutants in the wastewater can be efficiently removed.

Description

Technical Field

[0001] A method for purifying oily wastewater belongs to the field of environmental protection technology, and specifically relates to a method for treating wastewater. The high-oil wastewater is purified through three main process routes: microchannel extraction, water-oil buffer separation, and graphene photocatalytic filtration, to achieve water quality requirements that can be directly discharged. Background Art

[0002] Oily wastewater mainly comes from the production process of petrochemical, chemical, printing and dyeing, textile and other industries, as well as wastewater generated in mechanical processing, automobile maintenance, food processing and other activities. These wastewaters contain different types of lipids such as fatty acids, soaps, fats, waxes, and various oils such as mineral oils, animal and vegetable oils. The discharge of oily wastewater poses a threat to the environment and human health. When oily wastewater enters the water body, it will cause the water body to be polluted and cause damage to aquatic resources and ecosystems. In addition, the discharge of oily wastewater may also pollute the atmosphere and soil, affecting air quality and crop growth. The composition of oily wastewater is complex and diverse, including oily substances, organic solvents and other pollutants. Oily substances include fatty acids, waxes, fats, animal and vegetable oils, etc. Organic solvents such as mineral oil, petroleum ether and organic solvents may also exist in oily wastewater.

[0003] In order to protect the environment and water resources, countries have established standards and limits for the discharge of oily wastewater. These standards usually specify parameters such as the maximum allowable oil concentration, COD (chemical oxygen demand) and BOD (biochemical oxygen demand).

[0004] Common methods for treating oily wastewater include gravity separation, flotation, electrocoagulation, adsorption and biochemical methods, etc. The selection of these methods depends on factors such as the nature of the wastewater, treatment requirements and economic feasibility.

[0005] Treatment methods for oily wastewater include gravity separation, flotation, electrocoagulation, adsorption and biochemical methods.

[0006] Gravity separation is one of the main methods for removing oil from wastewater in my country. Its principle is to use the difference in specific gravity between oil and water to separate oil and grease by setting up a sedimentation tank or oil-water separator. This method has the advantages of large processing capacity and low cost, but it occupies a large area, has a low degree of automation, and has a relatively complex processing flow. Flotation is a treatment method with simple equipment and low engineering cost. It uses the contact of oil and grease in wastewater with air to produce fine bubbles, thereby separating oil and grease. However, the scope of application of flotation is relatively narrow, and it is mostly used to treat solids with a particle size of 10-60nm such as specific dispersed oil and emulsified oil. Electrocoagulation is one of the commonly used methods for treating oily wastewater. It forms high-molecular floccules in electrochemical reactions by adding suitable flocculants to sewage, thereby separating oil and grease. This method has good treatment effect and occupies a small area, but has high energy consumption and cost. Adsorption uses adsorbents (such as activated carbon) to adsorb solids and organic matter in oil to achieve the purpose of purification. However, the adsorption method has limited adsorption capacity, high cost and difficulty in regeneration, and is mainly used for deep treatment of oily wastewater. The biochemical method is a more advanced treatment method that uses microorganisms to degrade organic matter in oily wastewater and convert it into harmless substances such as water and carbon dioxide. This method has a good treatment effect, high water purification degree, and more significant reduction in environmental pollution. However, the biochemical method has a long treatment process, high treatment cost, and requires strict operation control and equipment maintenance. It is mainly used for deep treatment of oily wastewater and post-treatment stage after the water quality meets the standards.

[0007] There are many factors that make oily wastewater treatment difficult, including complex composition: The composition of oily wastewater is complex and diverse, including different types of oils, organic solvents and other pollutants. The properties of these substances vary, so the treatment process needs to consider specific treatment methods for different components. High concentration and recalcitrance: Oily wastewater usually has a high oil concentration and COD (chemical oxygen demand), which means that the treatment process requires more energy and resources. In addition, some oils and organic pollutants are recalcitrant and require advanced treatment technologies to be effectively removed. Complexity of treatment process: The treatment process of oily wastewater involves multiple steps and operations, such as pretreatment, separation, flocculation, filtration, etc. These steps require reasonable process design and operation control to ensure that the treatment effect meets the standard requirements. Oil-water separation efficiency: The separation of oil and water in oily wastewater is a key step in the treatment process. Due to the fine particles and emulsification of oil, the oil-water separation efficiency is low, and appropriate technical means need to be adopted to improve the separation efficiency. Treatment cost and energy consumption: Oily wastewater treatment usually requires high cost and energy consumption. Some advanced treatment technologies such as membrane separation and biodegradation have high equipment and operating costs, and also have great demands on energy and resources. Summary of the invention

[0008] In order to overcome these challenges, continuous technological innovation and process improvement are necessary. Develop more efficient and economically feasible treatment technologies, improve oil-water separation efficiency and treatment effects, reduce treatment costs and energy consumption, and increase treatment capacity. The present invention provides a method for purifying oily wastewater.

[0009] The main technical solution of the present invention is a method for purifying oily wastewater, characterized in that the high-oil-containing raw wastewater after pretreatment is purified by a three-stage unit process of microchannel extraction, buffer separation and graphene photocatalytic filtration, and finally the oil removal rate is above 99.95%.

[0010] Furthermore, in the microchannel extraction unit, a single or compound extractant is used.

[0011] Furthermore, the extractant is selected from one to three of sodium dodecyl sulfate (SAS) or sodium hexadecyl sulfate (SLES), sodium dodecyl polyoxyethylene ether sulfate (AES) or sodium hexadecyl polyoxyethylene ether sulfate (LES), hexadecylamine (HDA) or octadecylamine (ODA), hexadecyltrimethylammonium bromide (CTAB) or hexadecyltrimethylammonium chloride (CTAC), octylphenol polyoxyethylene ether (OP-10) or nonylphenol polyoxyethylene ether (NP-10), and dodecanol polyoxyethylene ether.

[0012] Furthermore, high-oil-content raw wastewater and extractants are introduced into the microchannel extraction unit, and by adjusting the proportions and ratios of different extractants, its oil-water separation ability is enhanced and the oil removal rate is improved.

[0013] Further preferably, the volume ratio of the extractant introduced into the microchannel extraction unit to the high-oil-content raw sewage per unit time is 5-32%.

[0014] Furthermore, in the buffer separation unit, dichloromethane or n-hexane is added as a regulator to promote oil-water separation.

[0015] Further preferably, the amount of the regulator added does not exceed 5.5% of the volume of the high-oil-content raw sewage introduced per unit time.

[0016] Furthermore, in the buffer separation unit, a buffer is added to adjust the pH value of the wastewater to meet the environmental conditions for oil-water separation; the buffer includes sodium bicarbonate / sodium carbonate, dihydrogen phosphate / phosphate buffer system or acetic acid / acetic acid buffer system.

[0017] Further preferably, the amount of the buffer added does not exceed 5% of the volume of the raw sewage with high oil content introduced per unit time. Further, in the graphene photocatalytic filtration unit, the residence time of the treated water is 1 hour to 36 hours.

[0018] The beneficial effects of the present invention are as follows.

[0019] (1) Microchannel extraction technology is used. When high-oil-containing raw wastewater is introduced into the microchannel system, the high specific surface area, excellent mass transfer effect, adjustable flow pattern, low energy consumption and automated operation of the microchannel can be used to achieve efficient oil-water separation in the microchannel extraction unit. This helps to improve the oil removal rate and reduce the processing time, thereby achieving effective purification of oily wastewater.

[0020] (2) In the microchannel extraction unit, high-oil-content raw sewage is introduced into the microchannel system. Through the fluid mechanics effect and the action of the extractant, the oil-water interface changes, causing the oil to be adsorbed and captured. The extractant interacts with the oil to form a micelle structure, separating the oil from the raw sewage.

[0021] (3) A buffer separation unit is introduced to separate the oil extracted from the microchannel extraction from the water. This unit can effectively reduce the interference of the oil on the subsequent treatment units and improve the treatment efficiency.

[0022] (4) The buffer separation unit is a subsequent treatment step of the microchannel extraction unit. It separates the extracted grease and residual wastewater by physical isolation and separation. In this step, gravity sedimentation, centrifugal separation and other technologies can be used to precipitate or separate the grease to obtain relatively clean wastewater.

[0023] (5) Graphene photocatalytic materials can be used for filtration and treatment to efficiently degrade organic matter and other pollutants in wastewater. Graphene has a high specific surface area, photocatalytic activity and chemical stability, and can use light energy to decompose organic matter into harmless substances. It can generate highly active electrons and holes under the excitation of ultraviolet light or visible light, thereby degrading organic pollutants. By filtering residual wastewater through graphene photocatalysis, pollutants can be effectively removed and water quality can be improved.

[0024] (6) Small space footprint: The use of microchannels and modular design can significantly reduce the space footprint of the wastewater treatment system. This is very beneficial for limited sites or scenarios where integrated treatment is required, and can save valuable land resources.

[0025] (7) Increased processing capacity: Since the process uses a multi-level unit module, each unit module can treat and optimize specific wastewater components. By optimizing and increasing the number of unit modules, the processing capacity can be increased to meet larger-scale wastewater treatment needs.

[0026] In summary, the present invention has developed a process that combines three-stage units of microchannel extraction, buffer separation and graphene photocatalytic filtration through innovation, achieving efficient treatment of oily wastewater. At the same time, the process has the advantages of saving time and economic costs, reducing floor space and increasing processing capacity. After being treated by the method of the present invention, wastewater with high oil content can treat more than 99.95% of the oil content in the wastewater, and ultimately can achieve water quality that is better than the national emission standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic diagram of a method for purifying oily wastewater according to an embodiment of the present invention.

[0028] In the figure, the numbers represent the process units: 1-extraction agent recovery unit; 2-microchannel extraction unit; 3-water-oil buffer separation unit; 4-graphene photocatalytic filtration unit.

[0029] The letters represent the composition of the materials: a-high oil content raw sewage; b-primary sewage after microchannel extraction; c-secondary sewage after buffer separation; d-tertiary water after graphene photocatalytic filtration. e-extractant reflux.

[0030] In the figure, the numbers represent the process units: 1-filtration unit; 2-extraction agent recovery unit; 3-microchannel extraction unit; 4-water-oil buffer separation unit; 5-graphene photocatalytic filtration unit.

[0031] The letters represent the material composition: a-high-oil-content raw sewage; b-high-oil-content raw sewage after filtration pretreatment; c-primary sewage after microchannel extraction; d-secondary sewage after buffer separation; e-tertiary water after graphene photocatalytic filtration; f-extraction agent reflux. Implementation

[0032] The present invention can be better understood by referring to the following examples and drawings. However, it is easy for those skilled in the art to understand that the contents described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims. Example

[0033] A method for purifying oily wastewater Figure 1 , mainly combining microchannel extraction, buffer separation and graphene photocatalytic filtration three-stage processing units, including the following steps: Step 1: Preprocessing (not shown in the figure) The oily wastewater is initially filtered through a coarse filter to remove larger suspended particles and solid impurities, reducing the impact on subsequent treatment units.

[0034] Step 2: Microchannel Extraction The pre-treated oily wastewater is introduced into the microchannel extraction unit 2. The microchannel has the characteristics of high specific surface area and microscopic size. After adding the extractant, the difference in affinity between it and the oil is used to achieve selective adsorption and separation of the oil. By adjusting the proportion and ratio of different extractants, its oil-water separation ability can be enhanced and the oil removal rate can be improved. The microchannel uses a serrated or bow-shaped multi-layer extraction plate to enhance the oil-water separation effect and improve the oil recovery rate.

[0035] Step 3: Buffer separation The oily wastewater extracted through the microchannel is introduced into the water-oil buffer separation unit 3. In this unit, appropriate buffers and regulators are added to reduce the interfacial tension between oil and water and promote oil-water separation. Through flow rate control and separation structure, efficient oil-water separation effect is achieved, and the oil recovery rate is further improved. The extractant returns to the extractant recovery unit 1.

[0036] Step 4: Graphene photocatalytic filtration The oily wastewater after buffer separation is introduced into the graphene photocatalytic filtration unit 4. The unit can effectively remove residual grease and organic pollutants by utilizing the high adsorption and photocatalytic activity of graphene. Through photocatalytic reaction, organic matter is degraded into harmless substances, achieving deep purification of wastewater. At the same time, a multi-layer metal plate with uniformly distributed small holes coated with modified graphene is used to achieve efficient solid-liquid separation and separate the purified water from the sediment. Example 1

[0037] The extractants octylphenol polyoxyethylene ether (OP-10) and nonylphenol polyoxyethylene ether (50% each) and wastewater with an oil content of about 1100 mg / L after pretreatment were introduced into a microchannel extraction unit, wherein the volume ratio of the extractant to the raw sewage per unit time was 12%. In the microchannel extraction unit, preliminary oil-water separation was performed; then the treated primary sewage was introduced into a buffer separation unit, and at the same time, 2.5% of the volume of the raw sewage by volume of the regulator dichloromethane and 3.5% of the volume of the raw sewage by volume of the buffer sodium bicarbonate were added per unit time to reduce the interfacial tension between oil and water, and the mixture was allowed to stay for 2 hours and allowed to stand for stratification; then the treated secondary sewage was introduced into a graphene photocatalytic filtration unit and allowed to stay for 4 hours. The oil content of the treated tertiary water was 0.50 mg / L. Example 2

[0038] The extractants hexadecylamine (HDA) and octadecylamine (ODA) (50% each) and wastewater with an oil content of about 1200 mg / L after pretreatment were introduced into a microchannel extraction unit, wherein the volume ratio of the extractant to the raw sewage per unit time was 8%. In the microchannel extraction unit, preliminary oil-water separation was performed; then the treated primary sewage was introduced into a buffer separation unit, and at the same time, 2.5% of the volume of the raw sewage by volume of dichloromethane and 2.5% of the volume of the raw sewage by volume of sodium carbonate were added as a regulator to reduce the interfacial tension between oil and water. The wastewater was allowed to stay for 1.5 hours and allowed to stand for stratification; thereafter, the treated secondary sewage was introduced into a graphene photocatalytic filtration unit and allowed to stay for 6 hours. The oil content of the treated tertiary water was 0.48 mg / L. Example 3

[0039] The extractant hexadecylamine (HDA) and the wastewater with an oil content of about 1150 mg / L after pretreatment were introduced into a microchannel extraction unit, wherein the volume ratio of the extractant to the raw sewage per unit time was 8%. In the microchannel extraction unit, preliminary oil-water separation was performed; then the treated primary sewage was introduced into a buffer separation unit, and at the same time, 2.5% of the volume of the raw sewage by volume of the regulating agent n-hexane and 2.5% of the volume of the raw sewage by volume of the buffer sodium dihydrogen phosphate were added per unit time to reduce the interfacial tension between oil and water. The wastewater was kept for 2.5 hours and allowed to stand for stratification; thereafter, the treated secondary sewage was pumped into a graphene photocatalytic filtration unit and kept for 8 hours. The oil content of the treated tertiary water was 0.42 mg / L. Example 4

[0040] The extractant nonylphenol polyoxyethylene ether (NP-10) and wastewater with an oil content of about 1250 mg / L after pretreatment were introduced into a microchannel extraction unit, wherein the volume ratio of the extractant to the raw sewage per unit time was 5%. In the microchannel extraction unit, preliminary oil-water separation was performed; then the treated primary sewage was introduced into a buffer separation unit, and at the same time, 2.5% of the volume of the raw sewage by volume of the regulator n-hexane and 2.5% of the volume of the raw sewage by volume of the buffer sodium dihydrogen phosphate were added per unit time to reduce the interfacial tension between oil and water. The wastewater was allowed to stay for 2.5 hours and allowed to stand for stratification; thereafter, the treated secondary sewage was introduced into a graphene photocatalytic filtration unit and allowed to stay for 20 hours. The oil content of the treated tertiary water was 0.38 mg / L. Example 5

[0041] The extractant sodium dodecyl sulfate (SAS) and wastewater with an oil content of about 1250 mg / L after pretreatment were introduced into a microchannel extraction unit, wherein the volume ratio of the extractant to the raw sewage per unit time was 10%. In the microchannel extraction unit, preliminary oil-water separation was performed; then the treated primary sewage was introduced into a buffer separation unit, and at the same time, 2.5% of the volume of the raw sewage by volume of the regulating agent n-hexane and 1.5% of the volume of the raw sewage by volume of the buffer sodium dihydrogen phosphate were added per unit time to reduce the interfacial tension between oil and water. The wastewater was allowed to stay for 3 hours and allowed to stand for stratification; thereafter, the treated secondary sewage was introduced into a graphene photocatalytic filtration unit and allowed to stay for 10 hours. The oil content of the treated tertiary water was 0.43 mg / L.

Claims

1. A method for purifying oily wastewater, characterized in that The pretreated high-oil raw wastewater is purified through a three-stage process combining microchannel extraction, buffer separation and graphene photocatalytic filtration.

2. The purification method according to claim 1, characterized in that In the microchannel extraction unit, a single or compound extractant is used.

3. The purification method according to claim 2, characterized in that The extractant is selected from one to three of sodium dodecyl sulfate (SAS) or sodium hexadecyl sulfate (SLES), sodium lauryl polyoxyethylene ether sulfate (AES) or sodium hexadecyl polyoxyethylene ether sulfate (LES), hexadecylamine (HDA) or octadecylamine (ODA), hexadecyltrimethylammonium bromide (CTAB) or hexadecyltrimethylammonium chloride (CTAC), octylphenol polyoxyethylene ether (OP-10) or nonylphenol polyoxyethylene ether (NP-10), and dodecanol polyoxyethylene ether.

4. The purification method according to claim 1, 2 or 3, characterized in that High-oil-content raw wastewater and extractants are introduced into the microchannel extraction unit. By adjusting the proportions and ratios of different extractants, its oil-water separation ability is enhanced and the oil removal rate is improved.

5. The purification method according to claim 4, characterized in that The volume ratio of the extractant introduced into the microchannel extraction unit to the high-oil-content raw sewage per unit time is 5-32%.

6. The purification method according to claim 1, characterized in that In the buffer separation unit, dichloromethane or n-hexane is added as a regulator to promote oil-water separation.

7. The purification method according to claim 6, characterized in that The amount of regulator added shall not exceed 5.5% of the volume of high-oil-content raw sewage introduced per unit time.

8. The purification method according to claim 1, characterized in that In the buffer separation unit, a buffer is added to adjust the pH value of the wastewater to meet the environmental conditions for oil-water separation; the buffer includes sodium bicarbonate / sodium carbonate, dihydrogen phosphate / phosphate buffer system or acetic acid / acetic acid buffer system.

9. The purification method according to claim 8, characterized in that The amount of buffer added shall not exceed 5% of the volume of high-oil-content raw sewage introduced per unit time.

10. The purification method according to claim 1, characterized in that In the graphene photocatalytic filtration unit, the residence time of the treated water is 1 hour to 36 hours.

Images