Method and device for removing COD in high-salt and high-organic wastewater

Abstract

This invention belongs to the field of wastewater treatment technology, specifically relating to a method and apparatus for removing COD from high-salt, high-organic-content wastewater. The removal method employs two organic matter retention membranes connected in series to treat the high-salt, high-organic-content wastewater. By controlling appropriate process conditions, these organic matter retention membranes primarily retain organic matter while retaining as little salt as possible, ensuring stable operation of subsequent processes or achieving compliant wastewater discharge. Furthermore, the concentrate obtained after treatment by each organic matter retention membrane is returned in a specific proportion to the inlet of the membrane that produced the concentrate, thereby ensuring efficient and stable membrane operation, improving system recovery rate, and extending membrane lifespan. This invention achieves COD removal from high-salt, high-organic-content wastewater using only a single process, exhibiting high removal rate, good decolorization effect, and high recovery rate. It significantly shortens the process flow and is characterized by being green, efficient, energy-saving, environmentally friendly, and highly reliable.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method and apparatus for removing COD from high-salt, high-organic-content wastewater. Background Technology

[0002] Reverse osmosis membrane separation technology has been widely used in many industries due to its advantages such as low energy consumption, high desalination rate, mature and reliable process, high degree of automation, and ease of operation and management. Currently, the recovery rate of reverse osmosis processes is typically 70-80%. The volume of reverse osmosis concentrate plus the wastewater from the cleaning process is approximately 25-35% of the actual treated water volume. This wastewater contains not only high concentrations of inorganic salts but also organic matter at 3-4 times the concentration of the reverse osmosis feed water, and has poor biodegradability (B / C ratio is generally less than 0.2). The high salt and high organic matter content of reverse osmosis wastewater, and its recalcitrant nature, has always been a difficult technical challenge for the environmental protection sector.

[0003] Chemical Oxygen Demand (COD) is a chemically measured amount of reducing substances in a water sample that require oxidation. It reflects the degree of pollution by reducing substances in the water and is one of the comprehensive indicators of the relative content of organic matter. Currently, advanced oxidation methods are mainly used to remove COD from high-salt, high-organic-matter reverse osmosis concentrate. However, commonly used advanced oxidation methods generally have low degradation efficiency for large, recalcitrant organic molecules, and high concentrations of inorganic salts have a significant impact on COD removal. · The generation and migration of OH radicals are strongly inhibited, making it difficult to guarantee treatment effectiveness. Furthermore, subsequent treatment units in advanced oxidation processes require additional steps such as flocculation precipitation, multi-media filtration, and ultrafiltration to reduce turbidity, resulting in a lengthy and cumbersome process flow. Therefore, achieving efficient COD removal from reverse osmosis concentrate while simultaneously streamlining the process and reducing costs is a pressing technical challenge in this field. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is that the existing technology has poor degradation effect on organic matter in high-salt and high-organic-matter wastewater, and high concentration of inorganic salt has an inhibitory effect on the degradation of organic matter. Therefore, the present invention provides a method for preparing an organic matter-retaining membrane, and a method and apparatus for efficiently removing COD from high-salt and high-organic-matter wastewater using the organic matter-retaining membrane prepared by the method. The COD removal effect of the method and apparatus is not affected by the concentration of inorganic salt.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] According to an embodiment of the present invention, in a first aspect, the present invention provides a method for preparing an organic matter-retaining membrane, comprising the following steps:

[0007] S1. Polysulfone, polyethersulfone and a pore-forming agent are dissolved in an organic solvent to prepare a casting solution, and the casting solution is coated onto a polyester nonwoven fabric; wherein, based on the mass of the casting solution, the mass percentage concentration of polysulfone is 10%-20% and the mass percentage concentration of polyethersulfone is 5%-10%.

[0008] Carboxylated carbon nanotubes, silane coupling agents, and dispersants are mixed to form a dispersion, and the dispersion is heated and refluxed for a first time to obtain modified carbon nanotubes.

[0009] S2. The polyester nonwoven fabric coated in step S1 is placed in an aqueous alcohol solution for phase inversion to obtain a base film, which is then soaked in deionized water for a second time.

[0010] The modified carbon nanotubes obtained in step S1 were poured onto the surface of the soaked base film, deposited for a third time, and then removed and soaked in pure water for a fourth time.

[0011] In an embodiment of the present invention, the mass percentage concentration of the pore-forming agent is 3%-5% based on the mass of the casting solution.

[0012] In an embodiment of the present invention, the mass percentage concentration of the carboxylated carbon nanotubes in the dispersion is 1%-5%, and the mass percentage concentration of the silane coupling agent is 0.5%-1.5%.

[0013] In an embodiment of the present invention, the first time is 6h-15h.

[0014] In an embodiment of the present invention, the second time is 24h-48h.

[0015] In an embodiment of the present invention, the third time is 10h-14h.

[0016] In an embodiment of the present invention, the fourth time is 12h-24h.

[0017] In an embodiment of the present invention, the mass percentage concentration of the alcohol in the aqueous solution of the alcohol is 5%-10%.

[0018] In embodiments of the present invention, the alcohol is at least one of ethylene glycol, ethanol, and acetone.

[0019] In an embodiment of the present invention, the silane coupling agent is KH550.

[0020] In embodiments of the present invention, the organic solvent is at least one of N-methylpyrrolidone and dimethylacetamide.

[0021] In embodiments of the present invention, the dispersant is at least one of anhydrous ethanol and anhydrous acetonitrile.

[0022] In an embodiment of the present invention, the maximum pressure resistance of the organic matter retrieval membrane is 1.5 MPa, the operating pH value is 2-11, the operating free chlorine tolerance is <10 ppm, and the operating flux is 15-30 LMH.

[0023] In an embodiment of the present invention, the preparation method further includes step S3, which uses a roll-up membrane technology to prepare a roll-up membrane element from the membrane material that has been soaked in pure water in step S2, and then wets it with a 1% sodium bisulfite protective solution before packaging and storing it.

[0024] According to an embodiment of the present invention, in a second aspect, the present invention also provides an organic matter-retaining membrane prepared by the above-described preparation method.

[0025] According to an embodiment of the present invention, in a third aspect, the present invention provides a method for removing COD from high-salt, high-organic-content wastewater, comprising the following steps:

[0026] High-salt, high-organic-content wastewater undergoes a first-stage organic matter interception membrane treatment to obtain a first-stage concentrate and a first-stage permeate.

[0027] Part of the first-stage concentrate is refluxed and then treated by the first-stage organic matter interception membrane. The remaining part of the first-stage concentrate is treated by the second-stage organic matter interception membrane to obtain second-stage concentrate and second-stage permeate.

[0028] A portion of the second-stage concentrate is refluxed and then treated by the second-stage organic matter retention membrane. The remaining portion of the second-stage concentrate enters the concentrate tank, while the first-stage permeate and the second-stage permeate enter the permeate tank.

[0029] Wherein, both the first organic matter retention membrane and the second organic matter retention membrane are the aforementioned organic matter retention membranes;

[0030] The operating pressure of the organic matter retrieval membrane is 0.7-1.2 MPa, and the flow rate of the concentrated water used for reflux is 3 to 8 times the influent flow rate of the organic matter retrieval membrane.

[0031] The operating pressure of the two-stage organic matter retrieval membrane is 0.8-1.5 MPa, and the flow rate of the two-stage concentrate used for reflux is 6 to 12 times the influent flow rate of the two-stage organic matter retrieval membrane.

[0032] In an embodiment of the present invention, the first membrane assembly for accommodating the first organic matter retention membrane is composed of M membrane shells connected in parallel, and the second membrane assembly for accommodating the second organic matter retention membrane is composed of N membrane shells connected in parallel, where M and N are both positive integers and M:N = 2-3:1, and each membrane shell is filled with 3-5 membrane elements connected in series.

[0033] In an embodiment of the present invention, the high-salt, high-organic-content wastewater is concentrated water produced after coal chemical industry wastewater has undergone biochemical treatment, advanced treatment and membrane concentration in sequence. Depending on the concentration factor, the TDS content is 10,000-70,000 mg / L and the COD content is 400-1,000 mg / L.

[0034] The organic matter in the high-salt, high-organic-matter wastewater is mainly composed of chlorinated hydrocarbons, aromatic hydrocarbons, and alkanes, which are difficult to biodegrade. Among them, organic matter with a molecular weight of less than 500 Da accounts for 30% to 40%, organic matter with a molecular weight between 500 and 1000 Da accounts for 30% to 60%, and organic matter with a molecular weight greater than 1000 Da accounts for 5% to 20%.

[0035] TDS (Total Dissolved Solids) indicates how many milligrams of dissolved solids are dissolved in 1 liter of water. The higher the TDS value, the more dissolved substances are present in the water.

[0036] In embodiments of the present invention, the removal method further includes a step of chemically cleaning or rinsing the organic matter-retaining membrane with water;

[0037] The water rinsing cycle is 12-24 hours, with each rinsing lasting 2-3 minutes, and the rinsing water comes from the product water tank; or

[0038] The chemical cleaning cycle is 6-12 months, and the cleaning agent is at least one of sodium hydroxide aqueous solution, hydrochloric acid aqueous solution, sodium hypochlorite aqueous solution, and citric acid aqueous solution; during chemical cleaning, the organic matter retention membrane is tolerant to pH=1-12 and free chlorine ≤100ppm.

[0039] According to an embodiment of the present invention, in a fourth aspect, the present invention also provides a device for removing COD from high-salt, high-organic-content wastewater, comprising:

[0040] The system includes a first-stage organic matter retention membrane unit and a second-stage organic matter retention membrane unit. The concentrate outlet of the first-stage organic matter retention membrane unit is connected to the inlet of the second-stage organic matter retention membrane unit and the inlet of the first-stage organic matter retention membrane unit, respectively. The concentrate outlet of the second-stage organic matter retention membrane unit is connected to the inlet of the second-stage organic matter retention membrane unit and the concentrate tank, respectively.

[0041] Wherein, the organic matter retention membranes in the first organic matter retention membrane unit and the second organic matter retention membrane unit are both the aforementioned organic matter retention membranes.

[0042] In an embodiment of the present invention, the organic matter retention membrane unit includes a first circulation pump and a first membrane module, the first membrane module being composed of M membrane shells connected in parallel; the inlet of the first circulation pump is connected to the concentrate outlet of the first membrane module, and the outlet of the first circulation pump is connected to the inlet of the first membrane module.

[0043] The two-stage organic matter retention membrane includes a second circulation pump and a second membrane module. The second membrane module is composed of N membrane shells connected in parallel, where M and N are positive integers and M:N = 2-3:1. Each membrane shell is filled with 3-5 membrane elements connected in series. The inlet of the second circulation pump is connected to the concentrate outlet of the second membrane module, and the outlet of the second circulation pump is connected to the inlet of the second membrane module.

[0044] In an embodiment of the present invention, the removal device further includes:

[0045] The water inlet unit includes a water inlet tank, a water inlet pump, a first security filter and a high-pressure pump connected in sequence, and the outlet of the high-pressure pump is connected to the water inlet of the organic matter interception membrane unit.

[0046] The cleaning unit includes a chemical cleaning water tank, a chemical cleaning pump, and a second security filter connected in sequence, as well as a flushing water tank, a flushing water pump, and the second security filter connected in sequence. The outlet of the second security filter is connected to the inlet of the organic matter interception membrane unit.

[0047] The control unit is used to control the start and stop of the inlet pump, the high-pressure pump, the first circulation pump, the second circulation pump, the chemical cleaning pump, the flushing water pump, and the valves;

[0048] The product water tank is connected to the product water outlet of the first organic matter retention membrane unit and the product water outlet of the second organic matter retention membrane unit.

[0049] In an embodiment of the present invention, the head of the high-pressure pump is 50-100m, and the head of the first circulation pump and the second circulation pump is 30-50m.

[0050] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0051] 1. The method for preparing organic matter-retaining membranes provided by the present invention uses polysulfone and polyethersulfone in a specific ratio as raw materials, which can adjust the structure of the support layer to change the flux. At the same time, the deposition of modified carbon nanotubes on the surface of the membrane material can improve the hydrophilicity of the membrane element and increase the surface charge of the membrane, thereby obtaining a membrane element with high COD rejection rate and low desalination rate.

[0052] 2. The COD removal method for high-salt, high-organic-content wastewater provided by this invention employs a two-stage organic matter interception membrane connected in series to treat the wastewater. Based on information such as the content and molecular weight of substances contributing to COD in different wastewaters, an organic matter interception membrane with a suitable molecular weight cutoff is determined. Under appropriate pressure, this specific organic matter interception membrane mainly intercepts organic matter and retains as little salt as possible to ensure the stable operation of subsequent processes or to ensure that the produced water meets discharge standards. Furthermore, the concentrate obtained after treatment by each stage of the organic matter interception membrane is returned to the inlet of the organic matter interception membrane that produced the concentrate in a specific proportion. The higher the COD content in the wastewater, the greater the return proportion. This creates a large-flow cross-flow within the membrane shell containing the organic matter interception membrane. On the one hand, this reduces the influence of concentration polarization, ensuring the efficient and stable operation of the organic matter interception membrane and improving the COD removal rate. On the other hand, the large-flow cross-flow flushing greatly slows down the rate of fouling of the organic matter interception membrane, extending the cleaning cycle and service life.

[0053] Compared with existing advanced oxidation methods, the method of this invention achieves high COD removal rates, clear effluent, and high recovery rates in high-salt, high-organic-content wastewater using only a single process. This significantly shortens the process flow and is characterized by its green efficiency, energy conservation, environmental friendliness, and high reliability. The membrane elements used possess strong chemical resistance and antifouling properties, ensuring that the COD removal efficiency is unaffected by inorganic salt concentrations. Furthermore, the high-proportion reflux circulation operation guarantees the high efficiency and stability of this method in practical applications.

[0054] 3. The COD removal method for high-salt, high-organic-content wastewater provided by this invention comprises a first membrane module for accommodating a first organic matter retention membrane, consisting of M membrane shells connected in parallel; and a second membrane module for accommodating a second organic matter retention membrane, consisting of N membrane shells connected in parallel. M and N are positive integers, and the ratio of M to N is 2-3:1. Each membrane shell contains 3-5 membrane elements connected in series. This arrangement of membrane modules increases the wastewater treatment capacity, thereby improving wastewater treatment efficiency.

[0055] 4. In addition to the advantages mentioned above, the COD removal device for high-salt and high-organic-content wastewater provided by this invention can achieve fully automated operation, one-button start-up, and online monitoring. In particular, the high-pressure pump and the two-stage circulation pump can automatically adjust the flow rate according to the flow meter feedback, so as to achieve precise control of the proportion of concentrated water return at each stage. Attached Figure Description

[0056] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0057] Figure 1 This is a schematic diagram of the COD removal device for high-salt, high-organic-content wastewater provided in Example 1; the reference numerals are explained as follows:

[0058] 1-Inlet water tank; 2-Inlet water pump; 3-First security filter; 4-High pressure pump; 5-First circulation pump; 6-First membrane module; 7-Second circulation pump; 8-Second membrane module; 9-Concentrate tank; 10-Product water tank; 11-Chemical cleaning water tank; 12-Chemical cleaning pump; 13-Second security filter; 14-Flush water tank; 15-Flush water pump. Detailed Implementation

[0059] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0060] For any experimental steps or conditions not specified in the examples and comparative examples, the procedures or conditions described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0061] Preparation Example 1

[0062] A method for preparing an organic matter-retaining membrane includes the following steps:

[0063] S1: Dissolve polysulfone and polyethersulfone in N-methylpyrrolidone solvent in a certain proportion, then add polyvinylpyrrolidone as a pore-forming agent to prepare a casting solution, and uniformly coat the casting solution onto polyester nonwoven fabric.

[0064] The casting solution contains 10% polysulfone, 8% polyethersulfone, and 3% porogen.

[0065] Carboxylated carbon nanotube powder was added to anhydrous ethanol and then sonicated to obtain a dispersion with a carboxylated carbon nanotube concentration of 4%. Then, 1.2% of silane coupling agent KH550 was added and mixed. The mixture was then refluxed and stirred at 80°C for 12 hours to obtain modified carbon nanotubes.

[0066] S2. The polyester nonwoven fabric coated in step S1 is placed in an ethylene glycol aqueous solution (ethylene glycol mass percentage concentration is 8%). After phase inversion, a base film is obtained. Then, it is soaked in deionized water for 24 hours to completely remove pore-forming agents and other substances from the surface of the base film.

[0067] The modified carbon nanotubes obtained in step S1 were poured onto the surface of the soaked base film. After deposition for 14 hours, they were taken out and soaked in pure water for 12 hours to remove residual dispersants and other substances.

[0068] S3. Using conventional film-winding technology, the membrane material that has been soaked in pure water in step S2 is prepared into a spiral-wound membrane element 1, which is then moistened with a 1% sodium bisulfite protective solution and packaged for storage.

[0069] The membrane element 1 was tested and found to have a molecular weight cutoff of 200 Da, a maximum pressure of 1.5 MPa, an operating pH of 2-11, a free chlorine tolerance of <10 ppm, and an operating flux of 15-30 LMH.

[0070] Preparation Example 2

[0071] A method for preparing an organic matter-retaining membrane includes the following steps:

[0072] S1: Dissolve polysulfone and polyethersulfone in N-methylpyrrolidone solvent in a certain proportion, then add polyvinylpyrrolidone as a pore-forming agent to prepare a casting solution, and uniformly coat the casting solution onto polyester nonwoven fabric.

[0073] The casting solution contains 20% polysulfone, 6% polyethersulfone, and 3% porogen.

[0074] Carboxylated carbon nanotube powder was added to anhydrous ethanol and then sonicated to obtain a dispersion with a carboxylated carbon nanotube concentration of 3%. Then, 0.5% of silane coupling agent KH550 was added and mixed. The mixture was then refluxed and stirred at 80°C for 10 hours to obtain modified carbon nanotubes.

[0075] S2. The polyester nonwoven fabric coated in step S1 is placed in an ethylene glycol aqueous solution (ethylene glycol mass percentage concentration is 8%). After phase inversion, a base film is obtained. Then, it is soaked in deionized water for 24 hours to completely remove pore-forming agents and other substances from the surface of the base film.

[0076] The modified carbon nanotubes obtained in step S1 were poured onto the surface of the soaked base film. After deposition for 10 hours, they were taken out and soaked in pure water for 12 hours to remove residual dispersants and other substances.

[0077] S3. Using conventional film-winding technology, the membrane material that has been soaked in pure water in step S2 is prepared into a spiral-wound membrane element 2, which is then moistened with a 1% sodium bisulfite protective solution and packaged for storage.

[0078] The membrane element 2 was tested and found to have a molecular weight cutoff of 500 Da, a maximum pressure of 1.5 MPa, an operating pH of 2-11, a free chlorine tolerance of <10 ppm, and an operating flux of 15-30 LMH.

[0079] Preparation Example 3

[0080] A method for preparing an organic matter-retaining membrane includes the following steps:

[0081] S1: Dissolve polysulfone and polyethersulfone in N-methylpyrrolidone solvent in a certain proportion, then add polyvinylpyrrolidone as a pore-forming agent to prepare a casting solution, and uniformly coat the casting solution onto polyester nonwoven fabric.

[0082] The casting solution contains 15% polysulfone by mass, 3% polyethersulfone by mass, and 5% porogen by mass.

[0083] Carboxylated carbon nanotube powder was added to anhydrous ethanol and then sonicated to obtain a dispersion with a carboxylated carbon nanotube concentration of 2%. Then, 0.8% of silane coupling agent KH550 was added and mixed. The mixture was then refluxed and stirred at 80°C for 8 hours to obtain modified carbon nanotubes.

[0084] S2. The polyester nonwoven fabric coated in step S1 is placed in an ethylene glycol aqueous solution (ethylene glycol mass percentage concentration is 8%). After phase inversion, a base film is obtained. Then, it is soaked in deionized water for 24 hours to completely remove pore-forming agents and other substances from the surface of the base film.

[0085] The modified carbon nanotubes obtained in step S1 were poured onto the surface of the soaked base film. After deposition for 8 hours, they were taken out and soaked in pure water for 12 hours to remove residual dispersants and other substances.

[0086] S3. Using conventional film-winding technology, the membrane material that has been soaked in pure water in step S2 is prepared into a spiral-wound membrane element 3, which is then moistened with a 1% sodium bisulfite protective solution and packaged for storage.

[0087] The membrane element 3 was tested and found to have a molecular weight cutoff of 1000 Da, a maximum pressure of 1.5 MPa, an operating pH of 2-11, a free chlorine tolerance of <10 ppm, and an operating flux of 15-30 LMH.

[0088] Example 1

[0089] This embodiment provides a device for removing COD from high-salt, high-organic-content wastewater, such as... Figure 1 As shown, it includes an inlet water unit, a first-stage organic matter retention membrane unit, a second-stage organic matter retention membrane unit, a cleaning unit, a control unit, a product water tank 10, and a concentrate tank 9, wherein:

[0090] The water inlet unit includes a water inlet tank 1, a water inlet pump 2, a first security filter 3 and a high-pressure pump 4 connected in sequence. The outlet of the high-pressure pump 4 is connected to the inlet of an organic matter interception membrane unit.

[0091] The concentrate outlet of the first organic matter retention membrane unit is connected to the inlet of the second organic matter retention membrane unit and the inlet of the first organic matter retention membrane unit. The first organic matter retention membrane unit includes a first circulation pump 5 and a first membrane module 6. The first membrane module 6 is composed of M membrane shells connected in parallel, where M is a positive integer. Each membrane shell is filled with 5 membrane elements connected in series. The inlet of the first circulation pump 5 is connected to the concentrate outlet of the first membrane module 6 (i.e., the concentrate outlet of the first organic matter retention membrane unit), and the outlet of the first circulation pump 5 is connected to the inlet of the first membrane module 6 (i.e., the inlet of the first organic matter retention membrane unit). The first circulation pump 5 is used to return a portion of the first-stage concentrate to the inlet of the first membrane module 6, so that the returned portion of the first-stage concentrate is treated again by the first organic matter retention membrane.

[0092] The concentrate outlet of the two-stage organic matter retention membrane unit is connected to the inlet of the two-stage organic matter retention membrane unit and the concentrate tank 9, respectively. The two-stage organic matter retention membrane unit includes a second circulation pump 7 and a second membrane module 8. The second membrane module 8 is composed of N membrane shells connected in parallel, where N is a positive integer. Each membrane shell contains 5 membrane elements connected in series. The inlet of the second circulation pump 7 is connected to the concentrate outlet of the second membrane module 8 (i.e., the concentrate outlet of the two-stage organic matter retention membrane unit), and the outlet of the second circulation pump 7 is connected to the inlet of the second membrane module 8 (i.e., the inlet of the two-stage organic matter retention membrane unit). The second circulation pump 7 is used to return a portion of the second-stage concentrate to the inlet of the second membrane module 8, so that this returned portion of the second-stage concentrate is treated again by the two-stage organic matter retention membrane.

[0093] This allows for a high-flow cross-flow within the membrane housings of the first membrane module 6 and the second membrane module 8. On the one hand, it reduces the impact of concentration polarization, ensuring the efficient and stable operation of the organic matter retention membrane and improving the COD removal rate. On the other hand, the high-flow cross-flow scouring greatly slows down the rate at which the organic matter retention membrane becomes fouled, extending the cleaning cycle and service life.

[0094] Based on information such as the content and molecular weight of substances contributing to COD in different wastewaters, an organic matter-retaining membrane with a suitable molecular weight cutoff is determined. Under appropriate pressure, this specific organic matter-retaining membrane primarily retains organic matter and retains as little salt as possible to ensure the stable operation of subsequent processes or to ensure that the produced water meets discharge standards. Since the amount of organic matter in the wastewater is constant, and its molecular weight distribution is within a certain range, after a period of concentration, only the concentration of organic matter increases, but the molecular weight distribution of organic matter in the wastewater remains unchanged. Therefore, in this embodiment, the first membrane module 6 and the second membrane module 8 use the same membrane element, which is membrane element 1 or 2 prepared in Preparation Example 1 or 2 of this invention, with M:N = 2:1. In other embodiments, M, N, and the number of membrane elements packed in each membrane shell can be adaptively adjusted according to the wastewater treatment volume.

[0095] The cleaning unit includes a chemical cleaning water tank 11, a chemical cleaning pump 12, and a second security filter 13 connected in sequence, as well as a flushing water tank 14, a flushing water pump 15, and a second security filter 13 connected in sequence. The outlet of the second security filter 13 is connected to the inlet of an organic matter interception membrane unit. By regularly flushing and chemically cleaning the membrane module, the degree of fouling of the membrane element can be reduced, and its service life can be extended.

[0096] The control unit is used to control the start and stop of the inlet pump 2, high-pressure pump 4, first circulation pump 5, second circulation pump 7, chemical cleaning pump 12 and flushing water pump 15, as well as the working status of the flow regulating valves and flow meters on each pipeline. This enables the entire system to achieve fully automated operation, one-button start, and online monitoring. In particular, the automatic flow regulating valves installed on each pipeline allow the high-pressure pump and the two-stage circulation pump to automatically adjust the flow based on the flow meter feedback, achieving precise control of the return flow ratio at each stage.

[0097] The product water tank 10 is connected to the product water outlet of the first organic matter retention membrane unit and the product water outlet of the second organic matter retention membrane unit.

[0098] In this embodiment, the head of the high-pressure pump 4 is 50-100m, and it adopts frequency conversion control to adjust according to the water quality. The head of the first circulation pump 5 and the second circulation pump 7 is 30-50m. Through the operation mode of high-proportion circulation of concentrate, membrane fouling is reduced and the system recovery rate is improved.

[0099] The working principle of the COD removal device for high-salt, high-organic-content wastewater provided in this embodiment is as follows:

[0100] The high-salt, high-organic-content wastewater stored in the inlet tank 1 is filtered by the first security filter 3 under the action of the inlet pump 2, and then enters the first membrane module 6 under the appropriate pressure of the high-pressure pump 4 for organic matter rejection membrane treatment, resulting in first-stage permeate and first-stage concentrate. Part of the first-stage concentrate is returned to the inlet of the first membrane module 6 under the action of the first circulation pump 5 and treated again by the first membrane module 6. The remaining part of the first-stage concentrate enters the second membrane module 8 for organic matter rejection membrane treatment, resulting in second-stage permeate and second-stage concentrate. Part of the second-stage concentrate is returned to the inlet of the second membrane module 8 under the action of the second circulation pump 7 and treated again by the second membrane module 8. The remaining part of the second-stage concentrate enters the concentrate tank 9. Both the first-stage and second-stage permeate enter the permeate tank 10 for later use.

[0101] To minimize membrane fouling, the organic matter-retaining membrane can be chemically cleaned or rinsed with water periodically. The water rinsing cycle is 12-24 hours, and each rinse lasts 2-3 minutes. The rinsing water can be the product water from the product water tank. The chemical cleaning cycle is 6-12 months, and the cleaning agent can be at least one of sodium hydroxide aqueous solution, hydrochloric acid aqueous solution, sodium hypochlorite aqueous solution, and citric acid aqueous solution.

[0102] Compared with advanced oxidation methods in existing technologies, the removal method of this invention achieves high COD removal rate, clear effluent, and high recovery rate in high-salt and high-organic-content wastewater using only a single process. This significantly shortens the process flow and is characterized by its green efficiency, energy saving, environmental friendliness, and high reliability. The membrane elements used have the advantages of strong chemical resistance and antifouling properties, ensuring that the COD removal effect of this invention is not affected by the concentration of inorganic salts. Furthermore, the high-proportion reflux circulation operation mode guarantees the high efficiency and stability of this removal method in practical applications.

[0103] The invention will be further explained below with reference to specific application examples.

[0104] Application examples

[0105] The organic matter in coal chemical wastewater is mainly composed of chlorinated hydrocarbons, aromatic hydrocarbons, and alkanes, which are difficult to biodegrade. Among them, organic matter with a molecular weight of less than 500 Da accounts for 30% to 40%, organic matter with a molecular weight between 500 and 1000 Da accounts for 30% to 60%, and organic matter with a molecular weight greater than 1000 Da accounts for 5% to 20%.

[0106] Wastewater 1: High-salt wastewater from coal chemical wastewater after one concentration (recovery rate 75%), with COD of 420 mg / L and TDS of 12000 mg / L, is a brownish-yellow transparent liquid.

[0107] For wastewater 1, the COD removal device for high-salt, high-organic-content wastewater provided in Example 1 of this invention was used for testing. The test method includes the following steps:

[0108] Wastewater is pumped by the inlet pump and passed through the first security filter, then pressurized by the high-pressure pump. It first passes through an organic matter interception membrane to obtain a concentrated water and a product water.

[0109] Part of the first-stage concentrate is returned to the inlet of the first-stage organic matter interception membrane by the first circulation pump, and then treated by the first-stage organic matter interception membrane. The remaining part of the first-stage concentrate is treated by the second-stage organic matter interception membrane to obtain second-stage concentrate and second-stage permeate.

[0110] Part of the second-stage concentrate is returned to the inlet of the second-stage organic matter interception membrane via the second circulation pump, and then treated by the second-stage organic matter interception membrane. The remaining part of the second-stage concentrate enters the concentrate tank, and the first-stage permeate and the second-stage permeate enter the permeate tank.

[0111] The relevant experimental parameters and results are as follows:

[0112]

[0113] Explanation: "First-stage circulation ratio" refers to the ratio of the flow rate of the first-stage concentrate used for recirculation to the influent flow rate of the first-stage organic matter retention membrane; "Second-stage circulation ratio" refers to the ratio of the flow rate of the second-stage concentrate used for recirculation to the influent flow rate of the second-stage organic matter retention membrane.

[0114] Application Example 1: A COD removal device for high-salt, high-organic-content wastewater filled with membrane element 1 was tested.

[0115] During the operation of the device, the flow rate of the first-stage concentrate used for recirculation is set to 5 times the inlet flow rate of the first-stage organic matter retrieval membrane, and the flow rate of the second-stage concentrate used for recirculation is set to 9 times the inlet flow rate of the second-stage organic matter retrieval membrane, so as to maintain the system recovery rate at about 90%. At this time, the operating pressure of the first-stage organic matter retrieval membrane unit is 1.20 MPa, and the operating pressure of the second-stage organic matter retrieval membrane unit is 1.38 MPa.

[0116] After the device was running stably, the system recovery rate was 90.06%, the operating throughput was 15.3 LHM, the measured COD removal rate was 80.6%, the desalination rate was 38.3%, and the effluent was basically colorless.

[0117] Application Example 2: A COD removal device for high-salt, high-organic-content wastewater equipped with membrane element 2 was tested.

[0118] During the operation of the device, the flow rate of the first-stage concentrate used for recirculation is set to 5 times the inlet flow rate of the first-stage organic matter retrieval membrane, and the flow rate of the second-stage concentrate used for recirculation is set to 9 times the inlet flow rate of the second-stage organic matter retrieval membrane, so as to maintain the system recovery rate at about 90%. At this time, the operating pressure of the first-stage organic matter retrieval membrane unit is 0.82 MPa, and the operating pressure of the second-stage organic matter retrieval membrane unit is 0.96 MPa.

[0119] After the device was running stably, the system recovery rate was 90.11%, the operating throughput was 23.6 LHM, the measured COD removal rate was 72.2%, the desalination rate was 10.9%, and the effluent was basically colorless.

[0120] Application Example 3: A COD removal device for high-salt, high-organic-content wastewater filled with membrane element 3 was tested.

[0121] During the operation of the device, the flow rate of the first-stage concentrate used for recirculation is set to 5 times the inlet flow rate of the first-stage organic matter retrieval membrane, and the flow rate of the second-stage concentrate used for recirculation is set to 9 times the inlet flow rate of the second-stage organic matter retrieval membrane, so as to maintain the system recovery rate at about 90%. At this time, the operating pressure of the first-stage organic matter retrieval membrane unit is 0.70 MPa, and the operating pressure of the second-stage organic matter retrieval membrane unit is 0.82 MPa.

[0122] After the device stabilized, the COD removal rate was measured to be 18.7%, the operating flux was 29.2 LHM, the desalination rate was 6.6%, and the effluent was slightly yellow.

[0123] A comprehensive comparison of COD removal rate, desalination rate, operating flux, and operating pressure shows that membrane element 2 is more suitable for coal chemical wastewater treatment.

[0124] Based on Example 2, the loop ratios of the two segments were adjusted to verify the system's performance. The results are as follows:

[0125]

[0126] Application Example 4: A COD removal device for high-salt, high-organic-content wastewater equipped with membrane element 2 was tested.

[0127] During the operation of the device, the flow rate of the first stage concentrate used for reflux is adjusted to 3 times the inlet flow rate of the first stage organic matter retention membrane, and the flow rate of the second stage concentrate used for reflux is 6 times the inlet flow rate of the second stage organic matter retention membrane. At this time, the operating pressure of the first stage organic matter retention membrane unit is 0.76 MPa, and the operating pressure of the second stage organic matter retention membrane unit is 0.90 MPa.

[0128] After the device stabilized, the system recovery rate decreased to 86.56%, the operating throughput decreased to 22.7 LHM, the measured COD removal rate was 73.2%, which was slightly improved, and the desalination rate was 10.2%, which was slightly lower. At the same time, the cleaning cycle was significantly shortened. The water washing cycle of Application Example 2 could be maintained at 15-18 hours, and the chemical cleaning cycle could be maintained at about 8 months, while the water washing cycle of Application Example 4 was only 5-8 hours, and the cleaning cycle was only 1 month.

[0129] Application Example 5: A COD removal device for high-salt, high-organic-content wastewater equipped with membrane element 2 was tested.

[0130] During the operation of the device, the flow rate of the first stage concentrate used for reflux is adjusted to 8 times the inlet flow rate of the first stage organic matter retention membrane, and the flow rate of the second stage concentrate used for reflux is 12 times the inlet flow rate of the second stage organic matter retention membrane. At this time, the operating pressure of the first stage organic matter retention membrane unit is 0.90 MPa, and the operating pressure of the second stage organic matter retention membrane unit is 1.10 MPa.

[0131] After the device stabilized, the system recovery rate increased to 91.60%, the operating throughput increased to 24 LHM, the measured COD removal rate decreased to 64.8%, and the desalination rate was 12.3%. The desalination rate increased slightly, and the cleaning cycle was slightly extended. In Application Example 2, the water washing cycle could be maintained at 15-18 hours, and the chemical cleaning cycle could be maintained at about 8 months. In Application Example 5, the water washing cycle was 15-19 hours, and the cleaning cycle was 8-9 months, with little improvement.

[0132] Therefore, considering stability, economy, and applicability, the operating mode of Application Example 2 is the most effective for treating wastewater 1.

[0133] Wastewater 2: The reverse osmosis concentrate of Wastewater 1 after pre-membrane treatment and secondary concentration (total recovery rate of 95%), with COD of 900 mg / L and TDS of 60000 mg / L, is a dark brown transparent liquid.

[0134] Application Example 5

[0135] Due to a significant deterioration in the quality of the incoming water, while ensuring a system recovery rate of 90%, and considering factors such as system operational stability, cleaning cycle, and treatment requirements, compared to Application Example 2, the circulation ratio and operating pressure of the two organic matter retention membranes were increased, and the operating flux was appropriately reduced. Through continuous debugging, the final operating conditions were determined as follows:

[0136] During the operation of the device, the flow rate of the first stage concentrate used for recirculation is adjusted to 7 times the inlet flow rate of the first stage organic matter retention membrane, and the flow rate of the second stage concentrate used for recirculation is 10 times the inlet flow rate of the second stage organic matter retention membrane. At this time, the operating pressure of the first stage organic matter retention membrane unit is 1.20 MPa, and the operating pressure of the second stage organic matter retention membrane unit is 1.43 MPa.

[0137] After the device stabilized, the system recovery rate remained stable at around 90%, with an operating throughput of 21.4 LHM. The measured COD removal rate was 62.6%, and the desalination rate was 14.2%. The water washing cycle can be maintained at 10-15 hours, and the chemical cleaning cycle can be maintained at around 6 months.

[0138] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for removing COD in high-salt high-organic wastewater, characterized in that, Includes the following steps: High-salt, high-organic-content wastewater undergoes a first-stage organic matter interception membrane treatment to obtain a first-stage concentrate and a first-stage permeate. Part of the first-stage concentrate is refluxed and then treated by the first-stage organic matter interception membrane. The remaining part of the first-stage concentrate is treated by the second-stage organic matter interception membrane to obtain second-stage concentrate and second-stage permeate. A portion of the second-stage concentrate is refluxed and then treated by the second-stage organic matter retention membrane. The remaining portion of the second-stage concentrate enters the concentrate tank, while the first-stage permeate and the second-stage permeate enter the permeate tank. The operating pressure of the organic matter retrieval membrane is 0.7-1.2 MPa, and the flow rate of the concentrated water used for reflux is 3 to 8 times the influent flow rate of the organic matter retrieval membrane. The operating pressure of the two-stage organic matter retrieval membrane is 0.8-1.5 MPa, and the flow rate of the two-stage concentrate used for reflux is 6 to 12 times the influent flow rate of the two-stage organic matter retrieval membrane. The preparation methods of the first-stage organic matter-retaining membrane and the second-stage organic matter-retaining membrane include the following steps: S1. Polysulfone, polyethersulfone, and a pore-forming agent are dissolved in an organic solvent to prepare a casting solution, and the casting solution is coated onto a polyester nonwoven fabric; wherein, based on the mass of the casting solution, the mass percentage concentration of polysulfone is 10%-20%, and the mass percentage concentration of polyethersulfone is 5%-10%; Carboxylated carbon nanotubes, silane coupling agents, and dispersants are mixed to form a dispersion. The dispersion is then heated and refluxed for a first time to obtain modified carbon nanotubes. In the dispersion, the mass percentage concentration of the carboxylated carbon nanotubes is 1%-5%, and the silane coupling agent is KH550. S2. The polyester nonwoven fabric coated in step S1 is placed in an aqueous alcohol solution for phase inversion to obtain a base film, which is then soaked in deionized water for a second time. The modified carbon nanotubes obtained in step S1 were poured onto the surface of the soaked base film, deposited for a third time, and then removed and soaked in pure water for a fourth time.

2. The method for removing COD from high-salt, high-organic-content wastewater according to claim 1, characterized in that, The pore-forming agent has a mass percentage concentration of 3%-5% based on the mass of the casting solution; and / or, In the dispersion, the mass percentage concentration of the silane coupling agent is 0.5%-1.5%; and / or, The first time period is 6h-15h; and / or, The second time period is 24h-48h; and / or, The third time period is 10h-14h; and / or, The fourth time period is 12h-24h; and / or, The aqueous solution of the alcohol has a mass percentage concentration of 5%-10%; and / or, The alcohol is at least one of ethylene glycol and ethanol; and / or, The organic solvent is at least one of N-methylpyrrolidone and dimethylacetamide; and / or The dispersant is at least one of anhydrous ethanol and anhydrous acetonitrile; and / or, The maximum pressure resistance of the organic matter-retaining membrane is 1.5 MPa, the operating pH is 2-11, the operating free chlorine tolerance is <10 ppm, and the operating flux is 15-30 LMH; and / or, The preparation method further includes step S3, in which the membrane material soaked in pure water in step S2 is prepared into a spiral membrane element using the film winding technology, and then packaged and stored after being moistened with a 1% sodium bisulfite protective solution.

3. The method for removing COD from high-salt, high-organic-content wastewater according to claim 1, characterized in that, The first membrane assembly for accommodating the first organic matter retention membrane consists of M membrane shells connected in parallel, and the second membrane assembly for accommodating the second organic matter retention membrane consists of N membrane shells connected in parallel. M and N are both positive integers, and M:N = 2-3:

1. Each membrane shell is filled with 3-5 membrane elements connected in series.

4. The method for removing COD from high-salt, high-organic-content wastewater according to claim 3, characterized in that, The high-salt, high-organic-content wastewater is concentrated water produced after the coal chemical industry wastewater has undergone biochemical treatment, advanced treatment, and membrane concentration. Depending on the concentration ratio, the TDS content is 10,000-70,000 mg / L and the COD content is 400-1,000 mg / L. The organic matter in the high-salt, high-organic-matter wastewater is mainly composed of chlorinated hydrocarbons, aromatic hydrocarbons, and alkanes, which are difficult to biodegrade. Among them, organic matter with a molecular weight of less than 500 Da accounts for 30% to 40%, organic matter with a molecular weight between 500 and 1000 Da accounts for 30% to 60%, and organic matter with a molecular weight greater than 1000 Da accounts for 5% to 20%.

5. The method for removing COD from high-salt, high-organic-content wastewater according to any one of claims 1-4, characterized in that, The removal method further includes the steps of rinsing the organic matter-retaining membrane with water or chemical cleaning; The water rinsing cycle is 12-24 hours, with each rinsing lasting 2-3 minutes, and the rinsing water comes from the product water tank; or The chemical cleaning cycle is 6-12 months, and the cleaning agent used is one or more of the following: sodium hydroxide aqueous solution, hydrochloric acid aqueous solution, sodium hypochlorite aqueous solution, and citric acid aqueous solution. During chemical cleaning, the organic matter-retaining membrane is resistant to pH 1-12 and free chlorine ≤100ppm.

6. A device for removing COD from high-salt, high-organic-content wastewater, characterized in that, include: A first-stage organic matter retention membrane unit and a second-stage organic matter retention membrane unit, wherein the concentrate outlet of the first-stage organic matter retention membrane unit is connected to the inlet of the second-stage organic matter retention membrane unit and the inlet of the first-stage organic matter retention membrane unit, respectively, and the concentrate outlet of the second-stage organic matter retention membrane unit is connected to the inlet of the second-stage organic matter retention membrane unit and the concentrate tank (9), respectively. The method for preparing the organic matter-retaining membrane in the first-stage organic matter-retaining membrane unit and the second-stage organic matter-retaining membrane unit includes the following steps: S1. Polysulfone, polyethersulfone, and a pore-forming agent are dissolved in an organic solvent to prepare a casting solution, and the casting solution is coated onto a polyester nonwoven fabric; wherein, based on the mass of the casting solution, the mass percentage concentration of polysulfone is 10%-20%, and the mass percentage concentration of polyethersulfone is 5%-10%; Carboxylated carbon nanotubes, silane coupling agents, and dispersants are mixed to form a dispersion. The dispersion is then heated and refluxed for a first time to obtain modified carbon nanotubes. In the dispersion, the mass percentage concentration of the carboxylated carbon nanotubes is 1%-5%, and the silane coupling agent is KH550. S2. The polyester nonwoven fabric coated in step S1 is placed in an aqueous alcohol solution for phase inversion to obtain a base film, which is then soaked in deionized water for a second time. The modified carbon nanotubes obtained in step S1 were poured onto the surface of the soaked base film, deposited for a third time, and then removed and soaked in pure water for a fourth time.

7. The COD removal device for high-salt, high-organic-content wastewater according to claim 6, characterized in that, The organic matter retention membrane unit includes a first circulation pump (5) and a first membrane module (6). The first membrane module (6) is composed of M membrane shells connected in parallel. The inlet of the first circulation pump (5) is connected to the concentrate outlet of the first membrane module (6), and the outlet of the first circulation pump (5) is connected to the inlet of the first membrane module (6). The two-stage organic matter retention membrane includes a second circulation pump (7) and a second membrane module (8). The second membrane module (8) is composed of N membrane shells connected in parallel, where M and N are both positive integers and M:N=2-3:

1. Each membrane shell is filled with 3-5 membrane elements connected in series. The inlet of the second circulation pump (7) is connected to the concentrate outlet of the second membrane module (8), and the outlet of the second circulation pump (7) is connected to the inlet of the second membrane module (8).

8. The COD removal device for high-salt, high-organic-content wastewater according to claim 7, characterized in that, The removal device further includes: The water inlet unit includes a water inlet tank (1), a water inlet pump (2), a first security filter (3) and a high-pressure pump (4) connected in sequence, and the outlet of the high-pressure pump (4) is connected to the inlet of the section of organic matter interception membrane unit; The cleaning unit includes a chemical cleaning water tank (11), a chemical cleaning pump (12), and a second security filter (13) connected in sequence, as well as a flushing water tank (14), a flushing water pump (15), and the second security filter (13) connected in sequence. The outlet of the second security filter (13) is connected to the inlet of the organic matter interception membrane unit. The control unit is used to control the start and stop of the water inlet pump (2), the high pressure pump (4), the first circulation pump (5), the second circulation pump (7), the chemical cleaning pump (12), the flushing water pump (15), and the valves; The product water tank (10) is connected to the product water outlet of the first organic matter retention membrane unit and the product water outlet of the second organic matter retention membrane unit; The head of the high-pressure pump (4) is 50-100m, and the head of the first circulating pump (5) and the second circulating pump (7) is 30-50m.

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