Micro-bubble stripping device and application thereof in ammonia-nitrogen wastewater treatment

Abstract

The application discloses a micro-bubble stripping device and application thereof in ammonia-nitrogen wastewater treatment. The device comprises a micro-bubble dispersion device, an absorption device and a gas-liquid separation device which are connected by pipelines in sequence. The micro-bubble dispersion device is filled with Janus hollow fiber membranes. The inner diameter of the Janus hollow fiber membranes is 0.1-2.0 mm, the wall thickness is 0.05-0.6 mm, the pore size is 0.05-2.0 um, the water contact angle of the hydrophilic layer is less than 65 DEG, and the water contact angle of the hydrophobic layer is greater than 110 DEG. Air is dispersed into micro-bubbles and contacted with ammonia-nitrogen wastewater. The micro-bubbles have the advantages of large specific surface area, high mass transfer efficiency and long gas-liquid contact time, so that the mass transfer of ammonia-nitrogen in water to gas phase is strengthened, the gas-liquid ratio is reduced, the energy consumption in the stripping process is reduced, and the equipment investment and operation cost in the stripping process are reduced.

Description

A microbubble stripping device and its application in ammonia nitrogen wastewater treatment Technical Field

[0001] This application relates to a microbubble stripping device and its application in ammonia nitrogen wastewater treatment, belonging to the field of chemical separation technology. Background Technology

[0002] Ammonia nitrogen has always been a challenge in wastewater treatment. Since ammonia nitrogen was designated as a binding pollutant control indicator, industries generating high-ammonia nitrogen wastewater urgently need technologies that can treat wastewater at a cost acceptable to businesses while meeting treatment efficiency requirements. According to the latest Environmental Statistics Yearbook, the total wastewater discharge in China was 73.53 billion tons, with ammonia nitrogen emissions reaching 2.299 million tons. Of this, industrial sources accounted for 217,000 tons, agricultural sources for 726,000 tons, and urban domestic sources for 1.341 million tons.

[0003] Ammonia nitrogen wastewater discharge mainly originates from the chemical raw material and chemical product manufacturing industry, agricultural and sideline food processing industry, petroleum processing, coking and nuclear fuel processing industry, and textile industry. Due to the complex chemical composition and poor biodegradability of this ammonia nitrogen wastewater, traditional biological denitrification processes are ineffective. Achieving ammonia nitrogen removal standards often becomes a bottleneck in the treatment of this type of wastewater. Furthermore, with the increasing severity of eutrophication and a deeper understanding of the harm ammonia nitrogen poses to aquatic environmental quality, the standards for ammonia nitrogen treatment in wastewater treatment are becoming increasingly stringent. Therefore, the economical and effective removal of ammonia nitrogen from wastewater has become one of the urgent problems to be solved in ammonia nitrogen wastewater treatment.

[0004] Stripping is a widely used method in current research and engineering applications. The principle of stripping is that under alkaline conditions, ammonia nitrogen in wastewater mainly exists in the form of free ammonia. Based on the concentration difference of volatile substances such as ammonia nitrogen in the gas and liquid phases, stripping technology is used to continuously transfer volatile substances such as ammonia nitrogen from the liquid phase to the gas phase and blow them out of the tower, thereby reducing the ammonia nitrogen content in the wastewater.

[0005] Ammonia nitrogen stripping is essentially a mass transfer process, related to the difference in equilibrium partial pressures of ammonia concentration in the gas and liquid phases of the wastewater, temperature, and mass transfer coefficient. The equilibrium partial pressure of ammonia in the gas phase and the equilibrium concentration of ammonia in the liquid phase conform to Henry's Law. Most of the ammonia nitrogen in the wastewater is in the form of ammonium ions (NH4+). 4+ Ammonia (NH3) and free ammonia exist in an equilibrium state.

[0006] Compared to stripping tanks, which have a large footprint and low treatment efficiency, stripping towers offer advantages such as high stripping efficiency, simple operation, and small footprint, making them widely used in industrial applications. Currently, the most significant drawbacks of stripping processes in industrial applications are poor treatment efficiency, high gas-liquid ratios, poor NH3 mass transfer efficiency during stripping, easy scaling and clogging of equipment, and high alkali consumption. These issues lead to high equipment investment and operating costs, hindering the application of stripping in ammonia nitrogen treatment in wastewater. Therefore, there is an urgent need to develop new stripping processes and integrated technologies to further improve ammonia nitrogen removal efficiency and reduce investment and operating costs.

[0007] In traditional stripping towers, the gas consists of millimeter- to centimeter-sized bubbles or gas streams, which have a small gas-liquid contact area, resulting in low mass transfer efficiency. Compared to millimeter- to centimeter-sized bubbles, micrometer-sized bubbles have better mass transfer performance. The advantages of micrometer-sized bubbles in the ammonia nitrogen stripping process are as follows:

[0008] (1) High gas partial pressure

[0009] For micrometer-sized bubbles, due to their small radius of curvature and the liquid surface tension, the pressure inside the bubble is higher than the pressure of the liquid at its location. This excess pressure P follows the Young-Laplace equation:

[0010] The gas pressure in the microbubble is P = 2σ / r (1)

[0011] In equation (1), σ is the surface tension of the liquid phase; r is the radius of the microbubble. The smaller the size of the microbubble particles, the higher the gas pressure inside them, which leads to an increase in the partial pressure of the gas inside the bubble, an increase in the driving force of gas film mass transfer, and enhanced mass transfer of NH3;

[0012] (2) The thickness of the gas film and liquid film decreased.

[0013] According to the two-film theory describing gas-liquid mass transfer, a stable gas film and a stable liquid film exist at the gas-liquid interface. Compared to traditional large bubbles, micron-sized bubbles have a shape closer to a rigid sphere, resulting in a thinner liquid film. That is, the smaller the diameter of the microbubble, the thinner its liquid film, thus enhancing gas-liquid mass transfer in microbubbles.

[0014] (3) Increase in mass transfer coefficient

[0015] According to literature research, the diameter of the bubble is inversely proportional to the gas film mass transfer coefficient, while the liquid film mass transfer coefficient is directly proportional to the gas partial pressure. As mentioned earlier, as the diameter of the microbubble decreases, both its gas film mass transfer coefficient and liquid film mass transfer coefficient increase significantly, thus enhancing gas mass transfer.

[0016] (4) Increased gas-liquid contact area

[0017] As the diameter of microbubbles decreases, their gas-liquid contact area increases significantly, and their effective gas-liquid contact area is 50-100 times that of traditional stripping towers, greatly enhancing the gas-liquid reaction.

[0018] The introduction of microbubbles significantly increases the gas-liquid contact area. Therefore, a gas-liquid contact area enhancement factor, A, can be added to the gas-film and liquid-film mass transfer equations. We initially estimate that A is in the range of 50-100.

[0019] Gas film mass transfer in microbubble absorption process N NH3 =Akg(PP) i (2)

[0020] Liquid film mass transfer in microbubble absorption process N NH3 =AEk L (C i -C) (3)

[0021] (5) Microbubbles have a carrying effect, which improves operational stability.

[0022] As the bubble diameter decreases, the probability of bubble coalescing decreases, the buoyancy of the bubbles in the absorbent decreases, and the bubble and absorbent are in a stable foam fluid state, preventing bubbling, flooding and other phenomena in the absorption tower, thus greatly increasing operational stability.

[0023] Microbubble preparation is crucial for increasing the gas-liquid contact area and enhancing gas-liquid reactions. Existing microbubble preparation methods mainly include: pressurized dissolved gas release, air dispersion, electrolysis, and microporous dispersion. The pressurized dissolved gas release method involves pressurizing gas in a liquid to form a supersaturated solution, then depressurizing to release it and form microbubbles. This method can be used to prepare uniform microbubbles with sizes ranging from 20 to 100 μm, but currently, this technology has low efficiency and gas-liquid ratio, high energy consumption, and high technical requirements. Water electrolysis produces microbubbles with sizes between 20 and 60 μm, but the electrolysis process consumes a lot of energy and has low efficiency. The entrained gas release method has a large gas production rate and low energy consumption, but the resulting bubbles have uneven particle sizes. Ammonia nitrogen stripping has a high gas-liquid ratio and requires a large number of microbubbles, placing high demands on the energy consumption of microbubble preparation. Compared to the microbubble preparation methods mentioned above, the micropore dispersion method involves the formation of tiny bubbles from gas under the shear force of a liquid. This method can achieve low-energy preparation of micron-sized bubbles with different sizes and gas-liquid ratios by optimizing operating conditions. Various microbubble preparation methods are shown in the table below.

[0024] Comparison of microbubble preparation methods and performance

[0025]

[0026] In microporous dispersion aeration processes, microporous membranes are commonly used aeration devices. Compared to existing microbubble preparation devices, microporous membranes have advantages such as simple preparation, high porosity, and low preparation cost. However, the hydrophilic / hydrophobic properties of the microporous membrane have a significant impact on microbubble preparation. Hydrophobic membranes have strong hydrophobic pores, making them difficult for water to wet, and can stably prepare bubbles. However, the interaction force between the bubbles and the membrane material is strong, making it difficult for small bubbles to desorb, and the particle size of the prepared bubbles is still in the millimeter range. On the other hand, the interaction force between the bubbles and hydrophilic membranes is weak, making it easy for small bubbles to desorb, and the particle size of the prepared bubbles can reach the micrometer range. However, during use, the pores of hydrophilic membranes are easily wetted by liquids, leading to pore blockage and difficulty in continuous gas production. Therefore, neither hydrophobic nor hydrophilic membranes can stably prepare microbubbles in a long-term manner.

[0027] In recent years, Janus membranes, possessing both hydrophilic and hydrophobic properties, have attracted widespread attention from researchers. The synergistic effect of the differences in microstructure and surface chemistry on both sides of the Janus membrane provides an "intrinsic" driving force for the transport of gas and liquid within the membrane. This characteristic gives Janus membranes unique advantages over traditional separation membranes in unidirectional liquid transport, mist collection, directional oil-water separation, membrane distillation, and nanofiltration. Researchers have used Janus membranes for aeration to supply oxygen to water. The hydrophilic layer of the Janus membrane generates microbubbles, while the hydrophobic layer inhibits water wetting of the membrane pores, achieving a sustained and stable production of microbubbles. Compared to hydrophilic membranes, the gas production pressure decreased from 0.2 MPa to 0.02 MPa after using Janus membranes. Compared to hydrophobic membranes, the oxygen supply rate of Janus membranes is significantly accelerated. During aeration, the hydrophilic layer of the Janus membrane generates microbubbles, while the hydrophobic layer inhibits water wetting of the membrane pores, maintaining continuous gas production. Therefore, Janus membranes can be used for low-cost, continuous, and stable microbubble production. Summary of the Invention

[0028] The principle of the stripping process is that under alkaline conditions, ammonia nitrogen in wastewater mainly exists in the form of free ammonia. Based on the concentration difference of volatile substances such as ammonia nitrogen in the gas and liquid phases, stripping technology is used to continuously transfer volatile substances such as ammonia nitrogen from the liquid phase to the gas phase and blow them out of the tower, thereby reducing the ammonia nitrogen content in the wastewater. However, existing stripping towers have relatively large bubble sizes, mostly millimeter and centimeter-sized bubbles, resulting in poor gas-liquid mass transfer performance. This leads to the need for a large amount of gas to complete the stripping of ammonia nitrogen from the wastewater.

[0029] To address this issue, this application utilizes the hydrophilic / hydrophobic properties of the Janus separation membrane to achieve continuous and low-cost microbubble preparation. The enhanced effect of the microbubbles enables highly efficient removal of ammonia nitrogen during wastewater treatment.

[0030] According to one aspect of this application, a microbubble stripping device is provided, comprising a microbubble dispersion device, an absorption device, and a gas-liquid separation device connected in sequence by pipelines.

[0031] The microbubble dispersion device is filled with a Janus hollow fiber membrane.

[0032] The inner diameter of the Janus hollow fiber membrane is 0.1–2.0 mm;

[0033] The Janus hollow fiber membrane has a wall thickness of 0.05–0.6 mm;

[0034] The Janus hollow fiber membrane has a pore size of 0.05–2.0 μm;

[0035] The water contact angle of the hydrophilic layer of the Janus hollow fiber membrane is less than 65°, and the water contact angle of the hydrophobic layer is greater than 110°.

[0036] Optionally, the water contact angle of the hydrophilic layer of the Janus hollow fiber membrane is less than 50°, and the water contact angle of the hydrophobic layer is greater than 125°.

[0037] The inner diameter of the Janus hollow fiber membrane is 0.6–0.8 mm;

[0038] The Janus hollow fiber membrane has a wall thickness of 0.2–0.3 mm;

[0039] The Janus hollow fiber membrane has a pore size of 0.3–1.0 μm;

[0040] The separation membrane material for the inner and outer layers of the Janus hollow fiber membrane is a commonly used organic membrane material, including but not limited to polysulfone, polyethersulfone, polyvinylidene fluoride, etc.

[0041] Stripping gas is introduced into the hydrophobic inner cavity of the Janus hollow fiber membrane. After passing through the membrane fibers, the stripping gas comes into contact with the ammonia nitrogen wastewater in the hydrophilic outer cavity of the Janus hollow fiber membrane, forming micron-sized bubbles. These micron-sized bubbles are used to strip ammonia nitrogen wastewater. The Janus hollow fiber membrane has a hydrophobic inner layer and a hydrophilic outer layer. Gas enters the membrane module from the hydrophobic layer inside the membrane fibers and comes into contact with the ammonia nitrogen-containing wastewater in the outer hydrophilic layer, forming micron-sized bubbles. It can be an organic membrane material and / or an inorganic membrane material.

[0042] The microbubble dispersion device is equipped with inlet I-1, inlet I-2, and outlet I;

[0043] The inlet I-1 is the stripping gas inlet;

[0044] The inlet I-2 is a liquid inlet;

[0045] The absorption device is equipped with an inlet II and an outlet II;

[0046] The gas-liquid separation device is equipped with inlet III, outlet III-1, and outlet III-2;

[0047] Outlet III-1 is a gas outlet;

[0048] The outlet III-2 is a liquid outlet.

[0049] The outlet I is connected to the inlet II pipeline;

[0050] The outlet II is connected to the inlet III pipeline.

[0051] The outlet III-2 is connected to the inlet I-2 pipeline.

[0052] The microbubble stripping device includes an acid absorption device;

[0053] The outlet III-1 is connected to the pipeline of the acid absorption device.

[0054] The stripping gas entering from the inlet I-1 is selected from at least one of nitrogen, carbon dioxide, helium, and argon.

[0055] In the microbubble dispersion device, the Janus hollow fiber membrane has a packing density of 5-60%.

[0056] Optionally, the Janus hollow fiber membrane has a packing density of 40-50%.

[0057] The epoxy resin or polyurethane sealant at both ends of the Janus hollow fiber membrane is flush with or slightly higher than the inlet I-2 to ensure that the liquid fully washes the outer surface of the Janus hollow fiber membrane and avoids flow dead zones.

[0058] The Janus hollow fiber membrane is prepared by the following steps:

[0059] The inner and outer film-forming solutions are co-extruded using a dual-channel nozzle with a spinning core solution to obtain a double-layer hollow fiber membrane. Modified monomers are then grafted onto the membrane to obtain the Janus hollow fiber membrane.

[0060] The inner layer film-forming solution contains film-forming polymer A, inner layer additive, organic solvent A, and amphiphilic polymer A;

[0061] The outer film-forming solution contains film-forming polymer B, outer layer additive, organic solvent B, and amphiphilic polymer B;

[0062] The amphiphilic polymer A and the amphiphilic polymer B are independently selected from amphiphilic polymer I and amphiphilic polymer II;

[0063] The amphiphilic polymers described herein contain both hydrophilic and hydrophobic structures. One type of amphiphilic polymer contains hydroxyl groups and hydrophobic groups, and is named amphiphilic polymer I. The other type of amphiphilic polymer is named amphiphilic polymer II. The amphiphilic polymers are synthesized via free radical polymerization, selecting hydrophilic and hydrophobic monomers, with the monomers containing olefin structures.

[0064] The amphiphilic polymer I is obtained by polymerizing hydrophilic monomer I and hydrophobic monomer I;

[0065] The amphiphilic polymer II is obtained by polymerizing hydrophilic monomer II and hydrophobic monomer II;

[0066] The hydrophilic monomer I is selected from olefin monomers containing hydroxyl groups, specifically from at least one of allyl alcohol and butenol;

[0067] The hydrophilic monomer II is selected from at least one of polyethylene glycol acrylate and vinylpyrrolidone;

[0068] The hydrophobic monomer I and the hydrophobic monomer II are independently selected from at least one of styrene, methyl acrylate, acrylonitrile, and hexafluorobutyl acrylate;

[0069] The amphiphilic polymer A in the inner layer film-forming solution and the amphiphilic polymer B in the outer layer film-forming solution are different from each other.

[0070] The modified monomer is selected from at least one of hexafluorohexyltriethoxysilane and tridecafluorooctyltriethoxysilane.

[0071] The film-forming polymer A and film-forming polymer B are independently selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, polymethyl methacrylate, polyvinyl chloride, and polyacrylonitrile;

[0072] The inner layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone.

[0073] The outer layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone.

[0074] The organic solvent A and organic solvent B are independently selected from at least one of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran;

[0075] The film-forming polymer A in the inner layer film-forming solution has a mass concentration of 10-25 wt%, the inner layer additive has a mass concentration of 5-20 wt%, and the amphiphilic polymer A has a mass concentration of 1-20 wt%.

[0076] Optionally, the mass concentration of film-forming polymer A in the inner layer film-forming solution is any value of 10wt%, 15wt%, 20wt%, 25wt%, or any range between two of these values; the mass concentration of the inner layer additive is any value of 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values; and the mass concentration of amphiphilic polymer A is any value of 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values.

[0077] The outer film-forming polymer B in the outer film-forming solution has a mass concentration of 10–25 wt%, the outer layer additive has a mass concentration of 5–20 wt%, and the amphiphilic polymer B has a mass concentration of 1–20 wt%.

[0078] Optionally, the mass concentration of film-forming polymer B in the outer film-forming solution is any value of 10wt%, 15wt%, 20wt%, 25wt%, or any range between two of these values; the mass concentration of the outer additive is any value of 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values; and the mass concentration of amphiphilic polymer B is any value of 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, or any range between two of these values.

[0079] The polymerization temperature is 50–80°C;

[0080] Optionally, the polymerization temperature is any value of 50°C, 60°C, 70°C, 80°C, or a range between any two.

[0081] The polymerization time is 40–600 min;

[0082] Optionally, the aggregation time is any value of 40 min, 60 min, or a range between both.

[0083] The polymerization involves a catalyst;

[0084] The catalyst is selected from at least one of azobisisobutyronitrile and benzoyl peroxide.

[0085] The grafted modified monomer includes the following steps:

[0086] The double-layer hollow fiber membrane is immersed in a solvent solution containing modified monomers;

[0087] The solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, toluene, ethylbenzene, and ethyl acetate;

[0088] In the solvent solution containing the modified monomer, the mass ratio of the modified monomer to the solvent is 0.01 to 0.15:1.

[0089] Optionally, in the solvent solution containing the modified monomer, the mass ratio of the modified monomer to the solvent is any value among 0.01:1, 0.05:1, and 0.15:1, or any range between two of them.

[0090] The inner layer film-forming solution is stirred I;

[0091] The temperature of stirring I is 10–120°C;

[0092] Optionally, the temperature of the stirring I is any value or a range between 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, and 120℃.

[0093] The stirring time for the first stirring step is 1 to 20 hours.

[0094] Optionally, the stirring time I is any value among 1h, 5h, 10h, 15h, and 20h, or a range between any two.

[0095] The outer film-forming solution is stirred (II);

[0096] The temperature of stirring II is 10–120°C;

[0097] Optionally, the temperature of the stirring II is any value or a range between 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, and 120°C.

[0098] The stirring time for the second stage is 1 to 20 hours.

[0099] Optionally, the stirring time II is any value among 1h, 5h, 10h, 15h, and 20h, or a range between any two.

[0100] The spinning core solution is selected from water or an aqueous solution containing ethanol, methanol, or an organic solvent;

[0101] The aqueous solution containing ethanol, methanol, or an organic solvent has a mass concentration of 10–80 wt%.

[0102] The total extrusion volume of the inner layer film-forming solution and the outer layer film-forming solution is 3-20 mL / min;

[0103] Optionally, the total extrusion volume of the inner layer film-forming solution and the outer layer film-forming solution is any value among 3 mL / min, 5 mL / min, 10 mL / min, 15 mL / min, and 20 mL / min, or any range between the two.

[0104] The ratio of the extrusion amount of the inner layer film-forming solution to the outer layer film-forming solution is 0.1 to 10:1.

[0105] Optionally, the ratio of the extrusion amount of the inner layer film-forming liquid to the outer layer film-forming liquid is any value among 0.1:1, 0.5:1, 1:1, 5:1, and 10:1, or any range between the two.

[0106] The double-layer hollow fiber membrane is gel-formed.

[0107] The solution used for gel molding is selected from water or an aqueous solution containing ethanol, methanol, or organic solvents.

[0108] The aqueous solution containing ethanol, methanol, or an organic solvent has a mass concentration of 10–80 wt%.

[0109] The Janus hollow fiber membrane undergoes washing, solvent exchange, and drying.

[0110] The washing is water washing;

[0111] The solvent exchange is a solvent exchange using ethanol and n-hexane as solvents;

[0112] The drying method is natural air drying or ethanol-n-hexane replacement air drying.

[0113] Janus hollow fiber membranes with different hydrophilic / hydrophobic layer thicknesses, hydrophilic / hydrophobic properties, and pore structures can be prepared by changing the composition, flow rate, core solution, and gel bath composition of the inner and outer membrane-forming solutions.

[0114] According to another aspect of this application, a method for treating ammonia nitrogen wastewater is provided, which employs the aforementioned microbubble stripping device.

[0115] The temperature of the ammonia nitrogen wastewater is 5–90℃.

[0116] Optionally, the temperature of the ammonia nitrogen wastewater is 30–90°C;

[0117] The gas-liquid ratio during the treatment process is 100–2000:1.

[0118] Optionally, the gas-liquid ratio during the treatment process is 100–500:1.

[0119] The beneficial effects that this application can produce include:

[0120] This application uses Janus separation membrane as a microbubble dispersion device to disperse air into microbubbles that come into contact with ammonia nitrogen wastewater. By taking advantage of the large specific surface area, high mass transfer efficiency, and long gas-liquid contact time of microbubbles, the mass transfer of ammonia nitrogen in water to the gas phase is enhanced, the gas-liquid ratio is reduced, the energy consumption of the stripping process is reduced, and the equipment investment and operating costs of the stripping process are reduced.

[0121] (1) The ammonia nitrogen wastewater treatment method provided in this application achieves low-cost, continuous preparation of micron-sized bubbles through a Janus separation membrane. Micron-sized bubbles can significantly enhance gas-liquid mass transfer, improve the stripping efficiency of ammonia nitrogen wastewater, and increase the treatment effect of ammonia nitrogen wastewater;

[0122] (2) The ammonia nitrogen wastewater treatment method provided in this application can significantly increase the residence time of microbubbles in liquid, resulting in high gas content in the liquid and sufficient gas-liquid contact.

[0123] (3) The ammonia nitrogen wastewater treatment method provided in this application can significantly reduce the volume of the stripping equipment and save floor space. Microbubbles are highly stable in liquids and are not easy to aggregate. The absorption equipment can be laid flat, which is especially suitable for applications where the tower height is limited.

[0124] (4) The ammonia nitrogen wastewater treatment method provided in this application can significantly reduce gas consumption during the stripping process, reduce the energy consumption of the blower, and reduce operating costs. At the same time, the reduced size of the stripping equipment can significantly reduce the investment cost of the equipment. Attached Figure Description

[0125] Figure 1 is a schematic diagram of the microbubble stripping device described in the present application, wherein: 1, ammonia nitrogen wastewater tank; 2, stripping gas; 3, water pump; 4, Janus hollow fiber membrane module (microbubble dispersion device); 4a, inlet I-1; 4b, inlet I-2; 4c, outlet I; 5, absorption pipeline (absorption device); 5a, inlet II; 5b, outlet II; 6, gas-liquid separator (gas-liquid separation device); 6a, inlet III; 6b, outlet III-1; 6c, outlet III-2; 7, gas flow meter; 8, acid absorption device. Detailed Implementation

[0126] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0127] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0128] Device example 1

[0129] The microbubble stripping device described in this application includes: 1. an ammonia nitrogen wastewater tank; 2. stripping gas; 3. a water pump; 4. a Janus hollow fiber membrane module (i.e., a microbubble dispersion device); 4a. inlet I-1; 4b. inlet I-2; 4c. outlet I; 5. an absorption pipeline (i.e., an absorption device); 5a. inlet II; 5b. outlet II; 6. a gas-liquid separator (i.e., a gas-liquid separation device); 6a. inlet III; 6b. outlet III-1; 6c. outlet III-2; 7. a gas flow meter; and 8. an acid absorption device.

[0130] 1. The ammonia nitrogen wastewater tank is connected to 4. Janus hollow fiber membrane module (i.e., microbubble dispersion device) via 3. water pump and 4b. inlet I-2 pipeline;

[0131] 2. The stripping gas is connected to the Janus hollow fiber membrane module (i.e., the microbubble dispersion device) via a pressure gauge and the inlet I-1 pipeline (4a).

[0132] 4. The Janus hollow fiber membrane module (i.e., the microbubble dispersion device) and 5. the absorption pipeline (i.e., the absorption device) are connected via 4c, outlet I and 5a, inlet II pipelines.

[0133] 5. The absorption pipeline (i.e., the absorption device) and 6. the gas-liquid separator (i.e., the gas-liquid separation device) are connected via pipelines 5b, outlet II and 6a, inlet III.

[0134] 6. The gas-liquid separator (i.e., the gas-liquid separation device) is connected to 8. the acid absorption device via 6b, outlet III-1 and 7. the gas flow meter pipeline;

[0135] 6. The gas-liquid separator (i.e., the gas-liquid separation device) is connected to 1. the ammonia nitrogen wastewater tank via 6c, outlet III-2 pipeline.

[0136] Preparation Example 1

[0137] Dissolve 8g of allyl alcohol and 2g of styrene in 415g of dimethylacetamide, add 0.1g of azobisisobutyronitrile, purge with nitrogen gas, and heat and stir at 50℃ for 40min to obtain a solution containing amphiphilic polymer I. Add 50g of PVDF and 25g of polyethylene glycol 400 to this solution to obtain the inner layer film-forming solution.

[0138] Take 20g of vinylpyrrolidone and 5g of styrene, dissolve them in 350g of dimethylacetamide, add 0.5g of azobisisobutyronitrile, and heat and stir at 60℃ for 80min to obtain a solution containing amphiphilic polymer II. Add 100g of PVDF and 25g of polyethylene glycol 400 to this solution to obtain the outer layer film-forming solution.

[0139] The inner and outer layer film-forming solutions were added to the inner and outer layer film-forming solution spinning tanks, respectively, and vacuum degassing was performed for 24 hours. The outer and inner layer film-forming solutions were then fed into a dual-channel nozzle, using ethanol as the core solution and deionized water as the outer gel bath, to spin a double-layer hollow fiber membrane. The flow rate of the outer layer film-forming solution was 5 ml / min, and the flow rate of the inner layer film-forming solution was 0.5 ml / min, resulting in a double-layer hollow fiber membrane. The obtained double-layer hollow fiber membrane was immersed in a grafting modification solution, and the grafting reaction was carried out for 24 hours. The grafting modification solution consisted of 1 g of hexafluorohexyltriethoxysilane and 100 g of n-hexane. The grafted double-layer membrane was rinsed in deionized water for 48 hours, and then dried using a successive ethanol-n-hexane displacement process to obtain a Janus hollow fiber membrane. This Janus membrane has a hydrophobic inner layer and a hydrophilic outer layer structure.

[0140] Example 1

[0141] The apparatus described in Example 1 is used.

[0142] The Janus separation membrane prepared in Preparation Example 1 has an outer hydrophilic layer with a water contact angle of 35° and an inner hydrophobic layer with a water contact angle of 135°. The hollow fiber membrane has an inner diameter of 0.7 mm and an outer diameter of 1.2 mm, and the pore size of the Janus membrane is 0.3 μm. 200 hollow fiber membranes were used to prepare a hollow fiber membrane module with a fiber packing density of 40% and an effective length of 100 cm.

[0143] Take 0.1m of ammonia nitrogen wastewater. 3 (Ammonia nitrogen content is 1500ppm, COD content is 500ppm), heated to 40℃, and the solution pH is adjusted to 11.2. The ammonia nitrogen wastewater is then pumped into the outer surface of the Janus hollow fiber membrane module. Compressed air is pumped into the inner surface of the Janus hollow fiber membrane module, where the air comes into contact with the ammonia nitrogen wastewater on the outer surface, forming micron-sized bubbles.

[0144] The gas flow rate is 2m. 3 / h, ammonia nitrogen wastewater flow rate 2m 3 The flow rate was [h], the gas phase pressure was 40 kPa, the pre-membrane liquid phase pressure was 25 kPa, and the post-membrane liquid phase pressure was 10 kPa. The ammonia nitrogen removal effect is as follows:

[0145] Stripping time (h) Removal rate (%) Gas-liquid ratio 124.3 20:1244.1 40:1356.4 60:1466.3 80:1573.8 100:1679.9 120:1784.2 140:1889.6 160:1994.1 180:11095.2 200:1 surface

[0146] Preparation Example 2

[0147] Take 30g of butenol and 10g of methyl methacrylate, dissolve them in 350g of dimethylacetamide, add 0.1g of azobisisobutyronitrile, purge with nitrogen gas, and heat and stir at 70℃ for 200min to obtain a solution containing amphiphilic polymer I. Add 100g of polyethersulfone and 20g of anhydrous lithium chloride to this solution to obtain the outer layer film-forming solution.

[0148] 40g of polyethylene glycol acrylate and 10g of methyl acrylate were dissolved in 360g of dimethylacetamide. 0.5g of azobisisobutyronitrile was added, and the mixture was heated and stirred at 60℃ for 400min to obtain a solution containing amphiphilic polymer II. 70g of polyethersulfone and 20g of anhydrous lithium chloride were added to this solution to obtain the inner layer film-forming solution.

[0149] The inner and outer layer film-forming solutions were added to the inner and outer layer film-forming solution spinning tanks, respectively, and vacuum degassing was performed for 24 hours. The outer and inner layer film-forming solutions were then fed into a dual-channel nozzle, using water as the core liquid and propanol as the outer gel bath, to spin a double-layer hollow fiber membrane. The flow rate of the outer layer film-forming solution was 1.5 ml / min, and that of the inner layer film-forming solution was 3.5 ml / min, resulting in a double-layer hollow fiber membrane. The obtained double-layer hollow fiber membrane was immersed in a grafting modification solution, and the grafting reaction was carried out for 24 hours. The grafting modification solution consisted of 5 g of hexafluorohexyltriethoxysilane and 95 g of toluene. The grafted double-layer membrane was rinsed in deionized water for 48 hours, and then dried using a successive ethanol-n-hexane displacement process to obtain a Janus hollow fiber membrane. This Janus membrane has a hydrophobic outer layer and a hydrophilic inner layer structure.

[0150] Example 2

[0151] The apparatus described in Example 1 is used.

[0152] The Janus separation membrane prepared in Preparation Example 2 has an outer hydrophilic layer with a water contact angle of 25° and an inner hydrophobic layer with a water contact angle of 125°. The hollow fiber membrane has an inner diameter of 0.5 mm and an outer diameter of 1.0 mm, and the pore size of the Janus membrane is 0.5 μm. 400 hollow fiber membranes were used to prepare a hollow fiber membrane module with a fiber packing density of 50% and an effective length of 100 cm.

[0153] Take 0.1m of ammonia nitrogen wastewater. 3 (Ammonia nitrogen content is 1500ppm, COD content is 500ppm), heated to 40℃, and the solution pH is adjusted to 11.3. The ammonia nitrogen wastewater is then pumped into the outer surface of the Janus hollow fiber membrane module. Compressed air is pumped into the inner surface of the Janus hollow fiber membrane module, where the air comes into contact with the ammonia nitrogen wastewater on the outer surface, forming micron-sized bubbles.

[0154] The gas flow rate is 5m. 3 / h, ammonia nitrogen wastewater flow rate 5m3 The flow rate was [h], the gas phase pressure was 45 kPa, the pre-membrane liquid phase pressure was 30 kPa, and the post-membrane liquid phase pressure was 10 kPa. The ammonia nitrogen removal effect is as follows:

[0155] Stripping time (h) Removal rate (%) Gas-liquid ratio 151.4 50:1276.3 100:1388.4 150:1495.4 200:1 surface

[0156] Example 3

[0157] The apparatus described in Example 1 is used.

[0158] The Janus separation membrane prepared in Preparation Example 1 has an outer hydrophilic layer with a water contact angle of 35° and an inner hydrophobic layer with a water contact angle of 135°. The hollow fiber membrane has an inner diameter of 0.7 mm and an outer diameter of 1.2 mm, and the pore size of the Janus membrane is 0.3 μm. 200 hollow fiber membranes were used to prepare a hollow fiber membrane module with a fiber packing density of 40% and an effective length of 100 cm.

[0159] Take 0.1m of ammonia nitrogen wastewater. 3 (Ammonia nitrogen content 1500ppm, COD content 500ppm), heated to 50℃, pH adjusted to 11.2, and the ammonia nitrogen wastewater was pumped into the outer surface of the Janus hollow fiber membrane module. Compressed air was pumped into the inner surface of the Janus hollow fiber membrane module, and the air came into contact with the ammonia nitrogen wastewater on the outer surface, forming micron-sized bubbles.

[0160] The gas flow rate is 5m. 3 / h, ammonia nitrogen wastewater flow rate 5m 3 The flow rate was [h], the gas phase pressure was 45 kPa, the pre-membrane liquid phase pressure was 33 kPa, and the post-membrane liquid phase pressure was 10 kPa. The ammonia nitrogen removal efficiency was as follows:

[0161] Stripping time (h) Removal rate (%) Gas-liquid ratio 155.4 50:1281.2 100:1393.3 150:1498.3 200:1 surface

[0162] Comparative Example 1

[0163] The apparatus described in Example 1 is used.

[0164] A traditional stripping tower is used to treat ammonia nitrogen wastewater. 1 m³ of ammonia nitrogen wastewater is taken. 3 (Ammonia nitrogen content is 1500 ppm, COD content is 500 ppm), heated to 50℃, pH adjusted to 11.4, ammonia nitrogen wastewater and compressed air are pumped into the absorption tower, gas flow rate is 500 m / s. 3 / h, ammonia nitrogen wastewater flow rate 1m 3 / h, gas phase pressure 5 kPa. Ammonia nitrogen removal effect is as follows:

[0165] Stripping time (h) Removal rate (%) Gas-liquid ratio 124.3 500:1245.5 1000:1362.3 1500:1477.3 2000:1584.1 2500:1688.2 3000:1 surface

[0166] Comparative Example 2

[0167] The apparatus described in Example 1 is used.

[0168] PVDF hydrophobic hollow fiber membrane was used as the membrane material, with a water contact angle of 135°. The inner diameter of the hollow fiber membrane was 0.8 mm, the outer diameter was 1.3 mm, and the pore size of the Janus membrane was 0.4 μm. 300 hollow fiber membranes were used to fabricate a hollow fiber membrane module with a fiber packing density of 55% and an effective length of 100 cm.

[0169] Take 0.1m of ammonia nitrogen wastewater. 3 (Ammonia nitrogen content is 1500ppm, COD content is 500ppm), heat to 50℃, adjust the pH of the solution to 11.3, and pump the ammonia nitrogen wastewater into the outer surface of the PVDF hydrophobic hollow fiber membrane module. Compressed air is pumped into the inner surface of the PVDF hydrophobic hollow fiber membrane module, and the air comes into contact with the ammonia nitrogen wastewater on the outer surface, forming millimeter-sized bubbles.

[0170] The gas flow rate is 30m. 3 / h, ammonia nitrogen wastewater flow rate 5m 3 The flow rate was [h], the gas phase pressure was 45 kPa, the pre-membrane liquid phase pressure was 33 kPa, and the post-membrane liquid phase pressure was 10 kPa. The ammonia nitrogen removal efficiency was as follows:

[0171] Stripping time (h) Removal rate (%) Gas-liquid ratio 135.4 300:1256.2 600:1371.3 900:1481.3 1200:1587.2 1500:1692.3 2000:1 surface

[0172] It can be seen that when using a traditional stripping tower for ammonia nitrogen stripping, the stripping effect is poor due to the large size of the bubbles and insufficient gas-liquid contact area. A large gas-liquid ratio (2000:1 to 3000:1) is required to achieve a removal effect of 88 to 92%, which is far less than the removal effect of microbubbles prepared by Janus membrane.

[0173] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A microbubble blowing device, characterized in that, The device comprises a microbubble dispersion device, an absorption device, and a gas-liquid separation device connected in sequence by pipelines; the microbubble dispersion device is filled with a Janus hollow fiber membrane; the inner diameter of the Janus hollow fiber membrane is 0.1–2.0 mm; the wall thickness of the Janus hollow fiber membrane is 0.05–0.6 mm; the pore size of the Janus hollow fiber membrane is 0.05–2.0 μm; the water contact angle of the hydrophilic layer of the Janus hollow fiber membrane is less than 65°, and the water contact angle of the hydrophobic layer is greater than 110°; the Janus hollow fiber membrane is prepared by the following steps: the inner layer film-forming solution and the outer layer film-forming solution are co-extruded through a dual-channel nozzle with a spinning core solution to obtain a double... Janus hollow fiber membrane is obtained by grafting modified monomers onto a hollow fiber membrane. The inner layer film-forming solution contains film-forming polymer A, inner layer additive, organic solvent A, and amphiphilic polymer A. The outer layer film-forming solution contains film-forming polymer B, outer layer additive, organic solvent B, and amphiphilic polymer B. Amphiphilic polymer A and amphiphilic polymer B are independently selected from amphiphilic polymer I and amphiphilic polymer II. Amphiphilic polymer I is obtained by polymerizing hydrophilic monomer I and hydrophobic monomer I. Amphiphilic polymer II is obtained by polymerizing hydrophilic monomer II and hydrophobic monomer II. Hydrophilic monomer I is selected from at least one of allyl alcohol and butenol. Hydrophilic monomer II is selected from at least one of allyl alcohol and butenol. At least one of polyethylene glycol acrylate and vinylpyrrolidone; the hydrophobic monomer I and the hydrophobic monomer II are independently selected from at least one of styrene, methyl acrylate, acrylonitrile, and hexafluorobutyl acrylate; the amphiphilic polymer A in the inner layer film-forming solution and the amphiphilic polymer B in the outer layer film-forming solution are different from each other; the modified monomer is selected from at least one of hexafluorohexyltriethoxysilane and tridecafluorooctyltriethoxysilane; the film-forming polymer A and the film-forming polymer B are independently selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, polymethyl methacrylate, polyvinyl chloride, and polyacrylonitrile; the inner layer additive is selected from polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone. The outer layer additive is selected from at least one of ketones; the outer layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride, and polyvinylpyrrolidone; the organic solvent A and organic solvent B are independently selected from at least one of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran; the inner layer film-forming polymer A in the inner layer film-forming solution has a mass concentration of 10-25 wt%, the inner layer additive has a mass concentration of 5-20 wt%, and the amphiphilic polymer A has a mass concentration of 1-20 wt%; the outer layer film-forming polymer B in the outer layer film-forming solution has a mass concentration of 10-25 wt%, the outer layer additive has a mass concentration of 5-20 wt%, and the amphiphilic polymer B has a mass concentration of 1-20 wt%.

2. The microbubble blowing device according to claim 1, characterized in that, The microbubble dispersion device is provided with inlet I-1, inlet I-2, and outlet I; inlet I-1 is the stripping gas inlet; inlet I-2 is the liquid inlet; the absorption device is provided with inlet II and outlet II; the gas-liquid separation device is provided with inlet III, outlet III-1, and outlet III-2; outlet III-1 is the gas outlet; outlet III-2 is the liquid outlet.

3. The microbubble blowing device according to claim 2, characterized in that, Outlet I is connected to inlet II; outlet II is connected to inlet III.

4. The microbubble blowing device according to claim 2, characterized in that, The outlet III-2 is connected to the inlet I-2 pipeline.

5. The microbubble blowing device according to claim 2, characterized in that, The microbubble stripping device includes an acid absorption device; the outlet III-1 is connected to the acid absorption device via pipeline.

6. The microbubble blowing device according to claim 2, characterized in that, The stripping gas entering from the inlet I-1 is selected from at least one of oxygen, nitrogen, carbon dioxide, helium, and argon.

7. The microbubble blowing device according to claim 1, characterized in that, In the microbubble dispersion device, the Janus hollow fiber membrane has a packing density of 5-60%.

8. A method for treating ammonia nitrogen wastewater, characterized in that, The microbubble blowing device according to any one of claims 1 to 7 is used.

9. The ammonia nitrogen wastewater treatment method according to claim 8, characterized in that, The temperature of the ammonia nitrogen wastewater is 5~90℃; the gas-liquid ratio during the treatment process is 100~2000:1.

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