A method for purifying oily wastewater

Abstract

A method for purifying oily wastewater involves three main process units. The first stage is a microchannel extraction unit: high-oil-content wastewater and an extractant are rapidly and efficiently adsorbed in microchannels, achieving initial oil-water separation. The second stage involves a buffer separation unit: in this unit, gravity sedimentation and centrifugation are used to further separate the oil-water emulsion from the wastewater. The third stage is a photocatalytic filtration unit: the active sites on the graphene surface adsorb and decompose organic matter in the wastewater, converting it into harmless substances. This invention can efficiently remove over 99.95% of oil components, oil-water emulsions, and organic pollutants from wastewater.

Description

Technical Field

[0001] This invention relates to a method for purifying oily wastewater, falling under the field of environmental protection technology. Specifically, it involves wastewater treatment methods. High-oil-content wastewater is purified through three main process routes: microchannel extraction, water-oil buffer separation, and graphene photocatalytic filtration, achieving water quality requirements suitable for direct discharge. Background Technology

[0002] Oily wastewater mainly originates from the production processes of industries such as petrochemicals, chemicals, printing and dyeing, and textiles, as well as wastewater generated from activities such as machining, automobile repair, and food processing. This wastewater contains different types of lipids, including fatty acids, soaps, fats, and waxes, as well as various oils such as mineral oils and animal and vegetable oils. The discharge of oily wastewater poses a threat to the environment and human health. When oily wastewater enters water bodies, it pollutes them, damaging aquatic resources and ecosystems. Furthermore, the discharge of oily wastewater can 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, and animal and vegetable oils. Organic solvents such as mineral oils, petroleum ethers, and other organic solvents may also be present in oily wastewater.

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

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

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

[0006] Gravity separation is one of the main methods for oil removal from wastewater in my country. Its principle is to utilize the difference in specific gravity between oil and water, separating grease through sedimentation tanks or oil-water separators. This method has the advantages of large processing capacity and low cost, but it requires a large area, has low automation, and a relatively complex process. Air flotation is a simple and low-cost method. It utilizes the contact between grease in wastewater and air to generate microbubbles, thereby separating the grease. However, air flotation has a narrow application range, mostly used for treating specific dispersed oils, emulsified oils, and other solids with particle sizes of 10-60 nm. Electrocoagulation is a commonly used method for treating oily wastewater. It separates grease by adding a suitable flocculant to the wastewater, forming high-molecular-weight flocs in an electrochemical reaction. This method has good treatment effect and requires less space, but has higher energy consumption and cost. Adsorption uses adsorbents (such as activated carbon) to adsorb solids and organic matter from the oil to achieve purification. However, adsorption methods have limited adsorption capacity, high costs, and are difficult to regenerate, primarily used for the advanced treatment of oily wastewater. Biochemical methods are a more advanced approach, utilizing microorganisms to degrade organic matter in oily wastewater, converting it into harmless substances such as water and carbon dioxide. This method offers better treatment results, higher water purification levels, and more significant reductions in environmental pollution. However, biochemical treatment processes are lengthy and costly, requiring strict operational control and equipment maintenance. It is mainly used for the advanced treatment of oily wastewater and post-treatment stages after water quality standards have been met.

[0007] Several factors contribute to the difficulty of treating oily wastewater, including: Complex composition: Oily wastewater contains a diverse range of components, including different types of oils, organic solvents, and other pollutants. The varying properties of these substances necessitate specific treatment methods tailored to different components. High concentration and recalcitrant degradation: Oily wastewater typically exhibits high oil concentrations and COD (Chemical Oxygen Demand), requiring greater energy and resource investment in the treatment process. Furthermore, some oils and organic pollutants are recalcitrant, necessitating advanced treatment technologies for effective removal. Complex treatment process: The treatment of oily wastewater involves multiple steps and operations, such as pretreatment, separation, flocculation, and filtration. These steps require rational process design and operational control to ensure that the treatment effect meets the required standards. Oil-water separation efficiency: Separating oil and water from oily wastewater is a critical step in the treatment process. Due to the fine particles and emulsification of oils, oil-water separation efficiency is relatively low, requiring appropriate technologies to improve it. Treatment cost and energy consumption: Oily wastewater treatment generally requires significant investment in both cost and energy. Some advanced processing technologies, such as membrane separation and biodegradation, have high equipment and operating costs and require significant energy and resources. Summary of the Invention

[0008] To overcome these challenges, continuous technological innovation and process improvement are necessary. This invention provides a method for purifying oily wastewater by developing more efficient and cost-effective treatment technologies to improve oil-water separation efficiency and treatment results, reduce treatment costs and energy consumption, and increase processing capacity.

[0009] The main technical solution of this invention is a method for purifying oily wastewater, characterized by purifying pretreated high-oil-content raw wastewater through a three-stage process combining microchannel extraction, buffer separation, and graphene photocatalytic filtration. This ultimately achieves an oil removal rate of over 99.95%.

[0010] Furthermore, within the microchannel extraction unit, single or combined extractants are used.

[0011] Further, the extractant is selected from one or three of the following: sodium dodecyl sulfonate (SAS) or sodium hexadecyl sulfonate (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 dodecyl alcohol polyoxyethylene ether.

[0012] Furthermore, the high-oil-content wastewater and extractant are introduced into the microchannel extraction unit. By adjusting the proportion and ratio of different extractants, its oil-water separation capability is enhanced, and the oil removal rate is improved.

[0013] More preferably, the volume ratio of the extractant introduced into the microchannel extraction unit to the high-oil-content wastewater 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] More preferably, the amount of regulator added does not exceed 5.5% of the volume of the high-oil-content raw wastewater 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] More preferably, the amount of buffer added does not exceed 5% of the volume of the high-oil-content raw wastewater introduced per unit time. Furthermore, within the graphene photocatalytic filtration unit, the residence time of the treated water is 1 hour to 36 hours.

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

[0019] (1) Microchannel extraction technology is used. High-oil-content wastewater is introduced into a microchannel system. Utilizing the high specific surface area, excellent mass transfer effect, controllable flow mode, low energy consumption, and automated operation of microchannels, efficient oil-water separation can be achieved in the microchannel extraction unit. This helps to improve the oil removal rate and reduce the treatment time, thereby achieving effective purification of oily wastewater.

[0020] (2) In the microchannel extraction unit, the high-oil-content wastewater is introduced into the microchannel system. Through the effects of hydrodynamics 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 wastewater.

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

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

[0023] (5) Using graphene photocatalytic materials for filtration can 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 ultraviolet or visible light excitation, thereby degrading organic pollutants. By filtering residual wastewater through graphene photocatalysis, pollutants can be effectively removed and water quality improved.

[0024] (6) Small footprint: The microchannel and modular design can significantly reduce the footprint of the wastewater treatment system. This is very beneficial for limited sites or scenarios that require integrated treatment, saving valuable land resources.

[0025] (7) Increased processing capacity: Because the process uses multi-level unit modules, 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 the needs of larger-scale wastewater treatment.

[0026] In summary, this invention innovatively develops a three-stage process combining microchannel extraction, buffer separation, and graphene photocatalytic filtration, achieving highly efficient treatment of oily wastewater. Furthermore, this process offers advantages such as reduced time and economic costs, decreased land area requirements, and increased treatment capacity. After treatment using this method, high-oil-content wastewater can have over 99.95% of its oil content removed, ultimately achieving water quality exceeding national discharge standards. Attached Figure Description

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

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

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

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

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

[0032] The present invention can be better understood below with reference to the embodiments and accompanying drawings. However, those skilled in the art will readily understand that the descriptions of the embodiments are for illustrative purposes only and should not, and will not, limit the invention as described in detail in the claims. Example

[0033] A method for purifying oily wastewater (reference appendix) Figure 1 It mainly combines three processing units: microchannel extraction, buffer separation, and graphene photocatalytic filtration, including the following steps:

[0034] Step 1: Preprocessing (not shown in the figure)

[0035] Oily wastewater is initially filtered through a coarse filter to remove larger suspended particles and solid impurities, reducing the impact on subsequent treatment units.

[0036] Step 2: Microchannel extraction

[0037] Pretreated oily wastewater is introduced into microchannel extraction unit 2. Microchannels, characterized by their high specific surface area and microscopic size, utilize the difference in affinity between the extractant and oil to achieve selective adsorption and separation of oil. By adjusting the proportions and ratios of different extractants, the oil-water separation capability can be enhanced, increasing the oil removal rate. The microchannels employ serrated or arc-shaped multilayer extraction plates to further enhance the oil-water separation effect and improve the oil recovery rate.

[0038] Step 3: Buffer Separation

[0039] The oily wastewater, after microchannel extraction, is introduced into the oil-water buffer separation unit 3. In this unit, appropriate buffers and regulators are added to reduce the interfacial tension between the oil and water, promoting oil-water separation. Through flow rate control and separation structure, efficient oil-water separation is achieved, further improving the oil recovery rate. The extractant is returned to the extractant recovery unit 1.

[0040] Step 4: Graphene photocatalytic filtration

[0041] The oily wastewater, after buffer separation, is introduced into graphene photocatalytic filtration unit 4. This unit utilizes the high adsorption and photocatalytic activity of graphene to effectively remove residual grease and organic pollutants. Through photocatalytic reaction, organic matter is degraded into harmless substances, achieving deep purification of wastewater. Simultaneously, a multilayer metal plate coated with modified graphene and evenly distributed pores is used to achieve efficient solid-liquid separation, separating the purified water from the sediment. Example 1

[0042] Octylphenol polyoxyethylene ether (OP-10) and nonylphenol polyoxyethylene ether (each in a 50% ratio) were used as extractants, and wastewater with a pretreated oil content of approximately 1100 mg / L was introduced into a microchannel extraction unit. The volume ratio of extractant to wastewater injected per unit time was 12%. Preliminary oil-water separation was performed in the microchannel extraction unit. Then, the treated primary wastewater was introduced into a buffer separation unit, and 2.5% of the volume of dichloromethane and 3.5% of the volume of sodium bicarbonate were added per unit time to reduce the interfacial tension between oil and water. The mixture was allowed to stand for 2 hours and then allowed to separate into layers. After that, the treated secondary wastewater was introduced into a graphene photocatalytic filtration unit and allowed to stand for 4 hours. The oil content of the treated tertiary water was 0.50 mg / L. Example 2

[0043] Extractants hexadecylamine (HDA) and octadecylamine (ODA) (50% each) and pretreated wastewater with an oil content of approximately 1200 mg / L were introduced into a microchannel extraction unit. The volume ratio of extractant to wastewater injected per unit time was 8%. Preliminary oil-water separation was performed in the microchannel extraction unit. Then, the treated primary wastewater was introduced into a buffer separation unit. Simultaneously, 2.5% of the volume of the original wastewater was added as a regulator (dichloromethane) and 2.5% of the volume of the original wastewater as a buffer (sodium carbonate) to reduce the interfacial tension between oil and water. After 1.5 hours of settling, the wastewater was allowed to separate into layers. Subsequently, the treated secondary wastewater was fed into a graphene photocatalytic filtration unit and held for 6 hours. The oil content of the treated tertiary water was 0.48 mg / L. Example 3

[0044] Hexadecylamine (HDA) extractant and pretreated wastewater with an oil content of approximately 1150 mg / L were introduced into a microchannel extraction unit, where the volume ratio of extractant to wastewater per unit time was 8%. Preliminary oil-water separation was performed in the microchannel extraction unit. The treated primary wastewater was then introduced into a buffer separation unit, where 2.5% of the original wastewater volume of hexane and sodium dihydrogen phosphate were added per unit time to reduce the interfacial tension between oil and water. After 2.5 hours of settling, the wastewater was allowed to separate into layers. The treated secondary wastewater was then fed into a graphene photocatalytic filtration unit and held for 8 hours. The resulting tertiary water had an oil content of 0.42 mg / L. Example 4

[0045] Nonylphenol polyoxyethylene ether (NP-10) extractant and pretreated wastewater with an oil content of approximately 1250 mg / L were introduced into a microchannel extraction unit, where the volume ratio of extractant to wastewater injected per unit time was 5%. Preliminary oil-water separation was performed in the microchannel extraction unit. Then, the treated primary wastewater was introduced into a buffer separation unit, where 2.5% of the volume of the original wastewater was added as a regulator (n-hexane) and 2.5% of the volume of the original wastewater as a buffer (sodium dihydrogen phosphate) per unit time to reduce the interfacial tension between oil and water. After 2.5 hours of settling, the wastewater was allowed to separate into layers. Subsequently, the treated secondary wastewater was fed into a graphene photocatalytic filtration unit and held for 20 hours. The resulting tertiary water had an oil content of 0.38 mg / L. Example 5

[0046] Sodium dodecyl sulfate (SAS) extractant and pretreated wastewater with an oil content of approximately 1250 mg / L were introduced into a microchannel extraction unit, where the volume ratio of extractant to wastewater per unit time was 10%. Preliminary oil-water separation was performed in the microchannel extraction unit. Next, the treated primary wastewater was introduced into a buffer separation unit, where 2.5% of the original wastewater volume of hexane and 1.5% of the original wastewater volume of sodium dihydrogen phosphate were added per unit time to reduce the interfacial tension between oil and water. After 3 hours of settling, the wastewater was allowed to separate into layers. Finally, the treated secondary wastewater was fed into a graphene photocatalytic filtration unit and held for 10 hours. The resulting tertiary water had an oil content of 0.43 mg / L.

Claims

1. A method for purifying oily wastewater, characterized in that... The pretreated high-oil-content wastewater is purified using a three-stage process combining microchannel extraction, buffer separation, and graphene photocatalytic filtration. In the buffer separation unit, dichloromethane or n-hexane is added as a regulator to promote oil-water separation, with the amount of regulator added not exceeding 5.5% of the volume of high-oil-content wastewater introduced per unit time. 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 systems, or acetic acid / acetic acid buffer systems, with the amount of buffer added not exceeding 5% of the volume of high-oil-content wastewater introduced per unit time.

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

3. The purification method according to claim 2, characterized in that... The extractant is selected from one or three of the following: sodium dodecyl sulfonate (SAS) or sodium hexadecyl sulfonate (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 dodecyl alcohol polyoxyethylene ether.

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

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

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

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