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

Abstract

The invention discloses a microbubble stripping device and application of the microbubble stripping device in ammonia-nitrogen wastewater treatment. Comprising a microbubble dispersion device, an absorption device and a gas-liquid separation device which are sequentially connected through pipelines, the microbubble dispersing device is filled with a Janus hollow fiber membrane; the inner diameter of the steel wire rope is 0.1-2.0 mm; the thickness of the wall ranges from 0.05 mm to 0.6 mm; the pore diameter is 0.05 to 2.0 [mu] m; the water contact angle of the hydrophilic layer is smaller than 65 degrees, and the water contact angle of the hydrophobic layer is larger than 110 degrees. Air is dispersed into microbubbles to be in contact with ammonia-nitrogen wastewater, and the advantages of large specific surface area, high mass transfer efficiency and long gas-liquid contact time of the microbubbles are utilized, so that mass transfer of ammonia nitrogen in water to a gas phase is enhanced, the gas-liquid ratio is reduced, the energy consumption in the air stripping process is reduced, and the equipment investment and operation cost in the air stripping process are reduced.

Description

Technical Field

[0001] The present application relates to a microbubble stripping device and its application in ammonia nitrogen wastewater treatment, belonging to the technical field of chemical separation. Background Art

[0002] Ammonia nitrogen has always been a difficult problem in wastewater treatment. Since ammonia nitrogen was used as a binding pollutant control indicator, industries that produce high ammonia nitrogen wastewater urgently need technologies that can treat wastewater at a cost acceptable to enterprises while meeting treatment efficiency. According to the latest "Annual Report on Environmental Statistics", the total amount of wastewater discharged nationwide is 73.53 billion tons, and the amount of ammonia nitrogen discharged in wastewater is 2.299 million tons. Among them, the amount of ammonia nitrogen discharged from industrial sources is 217,000 tons, the amount of ammonia nitrogen discharged from agricultural sources is 726,000 tons, and the amount of ammonia nitrogen discharged from urban life is 1.341 million tons.

[0003] The discharge of ammonia nitrogen wastewater mainly comes from the chemical raw materials and chemical products manufacturing industry, agricultural and sideline food processing industry, petroleum processing, coking and nuclear fuel processing industry, textile industry, etc. Due to the complex chemical composition and poor biodegradability of these ammonia nitrogen wastewaters, the traditional biological denitrification process has poor denitrification effect. The removal of ammonia nitrogen to meet the standards often becomes a bottleneck in the treatment of such wastewater. Moreover, with the increasing severity of water eutrophication and people's in-depth understanding of the harm of ammonia nitrogen to the quality of water environment, the treatment standards for ammonia nitrogen in wastewater treatment are becoming increasingly stringent. For this reason, the economical and effective removal of ammonia nitrogen in wastewater has become one of the urgent problems to be solved in the treatment of ammonia nitrogen wastewater.

[0004] The stripping method is a widely used method in current research and engineering applications. The principle of the stripping method is that under alkaline conditions, the ammonia nitrogen in the wastewater mainly exists in the form of free ammonia. According to the concentration difference of volatile substances such as ammonia nitrogen in the gas and liquid phases, the 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] The essence of ammonia nitrogen stripping is a mass transfer process, which is related to the difference in equilibrium partial pressure of ammonia concentration in the gas and liquid phases, 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 (NH 4+ ) and free ammonia (NH3) exist in a state of equilibrium.

[0006] Compared with the large floor space and low treatment efficiency of the stripping pool, the stripping tower has the advantages of high stripping efficiency, simple operation, and small floor space, and is widely used in industrial applications. The most significant defects of the stripping process in industrial applications are that the device has poor treatment effect, high gas-liquid ratio, poor mass transfer efficiency of NH3 during the stripping process, easy scaling and clogging of the equipment, and high alkali consumption. These problems lead to high equipment investment and operating costs during the stripping process, which restricts the application of the stripping method in the treatment of ammonia nitrogen in wastewater. Therefore, it is urgent to develop new stripping processes and integrated technologies to further improve the removal efficiency of ammonia nitrogen and reduce investment and operating costs.

[0007] The gas in the traditional stripping tower is milli-centimeter-level bubbles or airflow, and its gas-liquid contact area is small, resulting in low mass transfer efficiency. Compared with milli-centimeter-level bubbles, micron-level bubbles have better mass transfer performance. The advantages of micron-level bubbles in the ammonia nitrogen stripping process are as follows;

[0008] (1) High gas partial pressure

[0009] For micron-sized bubbles, due to the small radius of curvature and the liquid phase tension on its outer surface, the pressure inside the bubble is higher than the pressure of the liquid at the location. The higher pressure P follows the Young-Laplace equation:

[0010] Gas pressure in microbubbles P = 2σ / r(1)

[0011] In formula (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 gas partial pressure inside the bubble, an increase in the driving force of the gas film mass transfer, and an enhancement of the mass transfer of NH3;

[0012] (2) Reduction of the thickness of the gas film and liquid film

[0013] According to the double-membrane theory that describes gas-liquid mass transfer, there is a stable gas film and a stable liquid film at the junction of gas and liquid. Compared with traditional large bubbles, the shape of micron-sized bubbles is closer to a rigid sphere, and the thickness of the liquid film becomes thinner. That is, the smaller the diameter of the microbubble, the thinner its liquid film, which strengthens the gas-liquid mass transfer of the microbubble;

[0014] (3) Increased mass transfer coefficient

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

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

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

[0018] Due to the introduction of microbubbles, the gas-liquid contact area is greatly increased. Therefore, the gas-liquid contact area enhancement factor, A, can be added to the gas film and liquid film mass transfer equation. We preliminarily believe that the range of A is between 50-100.

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

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

[0021] (5) Microbubbles have a carrying effect, improving operational stability

[0022] As the bubble diameter decreases, the probability of bubble aggregation decreases, the buoyancy of the bubbles in the absorption liquid decreases, and the bubbles and the absorption liquid are in a stable foam fluid state. Bubbling, flooding and other phenomena in the absorption tower will not occur, and the operating stability is greatly increased.

[0023] The preparation of microbubbles is the key to increasing the gas-liquid contact area and strengthening the gas-liquid reaction. The existing methods for preparing microbubbles mainly include: pressurized dissolved gas release method, dispersed air method, electrolysis method, microporous dispersion method, etc. The pressurized dissolved gas-release method is a process in which gas is pressurized in a liquid to form a supersaturated solution, and then released under reduced pressure to form tiny bubbles. It can be used to prepare uniform microbubbles with a size of 20 to 100 μm, but the current technology has low working efficiency and gas-liquid ratio, high energy consumption and technical requirements. The size of microbubbles prepared by the electrolysis of water is between 20 and 60 μm, but the electrolysis process consumes a lot of energy and has low working efficiency. The gas production of the air-induction-dispersion method is large and the energy consumption is low, but the bubble particle size produced is uneven. The gas-liquid ratio of ammonia nitrogen stripping is relatively high, and the number of microbubbles required is large, which puts forward high requirements on the energy consumption of microbubble preparation. Compared with the above-mentioned microbubble preparation method, the micropore dispersion method is a process in which gas forms tiny bubbles under the shear force of liquid. This method can achieve low energy consumption preparation of micron-sized bubbles with different sizes and gas-liquid ratios by optimizing the operating conditions. The preparation methods of various microbubbles are shown in the table below.

[0024] Preparation methods and performance comparison of microbubbles

[0025]

[0026] In the aeration process of microporous dispersion method, microporous membrane is a commonly used aeration device. Compared with the existing microbubble preparation device, microporous membrane has the advantages of simple preparation, large porosity and low preparation cost. However, the hydrophilicity / hydrophobicity of the microporous membrane has an important influence on the preparation of microbubbles. The membrane pores of the hydrophobic membrane are highly hydrophobic and difficult to wet with water, so bubbles can be prepared stably. However, the interaction between the bubbles and the membrane material is large, and it is difficult for small bubbles to desorb, and the particle size of the prepared bubbles is still at the millimeter level. The interaction between the bubbles and the hydrophilic membrane is small, and small bubbles are easy to desorb, and the particle size of the prepared bubbles can reach the micron level. However, during use, the membrane pores of the hydrophilic membrane are easily wetted by liquid, resulting in clogging of the membrane pores and difficulty in continuous gas production. Therefore, neither hydrophobic membranes nor hydrophilic membranes can prepare microbubbles in a long-lasting and stable manner.

[0027] In recent years, Janus membranes with both hydrophilic and hydrophobic properties have attracted extensive attention from scholars. Under the synergistic effect of the differences in microstructure and surface chemical properties on both sides of the Janus membrane, an "intrinsic" driving force can be provided for the transport of gas and liquid in the membrane. This characteristic makes Janus membranes show unique advantages over traditional separation membranes in terms of unidirectional liquid transmission, mist collection, directional oil-water separation, membrane distillation, and nanofiltration. Some researchers use Janus membranes to aerate and supply oxygen to water. The hydrophilic layer of the Janus membrane can produce microbubbles, while the hydrophobic layer can inhibit the wetting of the membrane pores, achieving the purpose of long-term and stable preparation of microbubbles. Compared with hydrophilic membranes, the pressure of gas production after using Janus membranes is reduced from 0.2MPa to 0.02MPa. Compared with hydrophobic membranes, the oxygen supply rate of Janus membranes is greatly accelerated. During the aeration process, the hydrophilic layer of the Janus membrane can produce microbubbles, while the hydrophobic layer can inhibit water from wetting the membrane pores and maintain continuous gas production. Therefore, Janus membranes can produce microbubbles at low cost, continuously, and stably. Summary of the invention

[0028] The principle of the stripping method is that under alkaline conditions, ammonia nitrogen in wastewater mainly exists in the form of free ammonia. According to the concentration difference of volatile substances such as ammonia nitrogen in the gas and liquid phases, the 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, the bubble particle size in the existing stripping tower is relatively large, mostly millimeter and centimeter bubbles, and the gas-liquid mass transfer performance is poor, resulting in a large amount of gas required to complete the stripping of ammonia nitrogen in the wastewater.

[0029] To solve this problem, the present application utilizes the hydrophilicity / hydrophobicity of the Janus separation membrane to achieve continuous and low-cost preparation of microbubbles, and achieves efficient removal of ammonia nitrogen in the wastewater treatment process through the strengthening effect of microbubbles.

[0030] According to one aspect of the present application, there is provided a microbubble stripping device, 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 to 2.0 mm;

[0033] The wall thickness of the Janus hollow fiber membrane is 0.05-0.6 mm;

[0034] The pore size of the Janus hollow fiber membrane is 0.05 to 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 wall thickness of the Janus hollow fiber membrane is 0.2-0.3 mm;

[0039] The pore size of the Janus hollow fiber membrane is 0.3-1.0 μm;

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

[0041] The stripping gas is introduced into the hydrophobic inner cavity of the Janus hollow fiber membrane. After the stripping gas passes through the membrane, it contacts the ammonia nitrogen wastewater in the hydrophilic outer cavity of the Janus hollow fiber membrane to form micron-sized bubbles. The ammonia nitrogen wastewater is stripped using micron-sized bubbles; the Janus hollow fiber membrane has a hydrophobic inner layer and a hydrophilic outer layer. The gas enters the membrane assembly from the hydrophobic layer inside the membrane, contacts the ammonia nitrogen-containing wastewater in the outer hydrophilic layer, and forms micron-sized bubbles. It can be an organic membrane material and / or an inorganic membrane material.

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

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

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

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

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

[0047] The 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 through a 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 packing density of the Janus hollow fiber membrane is 5 to 60%.

[0056] Optionally, the packing density of the Janus hollow fiber membrane is 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 1-2, ensuring that the liquid fully flushes the outer surface of the Janus hollow fiber membrane to avoid flow dead zones.

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

[0059] The inner layer membrane-making liquid and the outer layer membrane-making liquid are introduced into the spinning core liquid by using a double-channel nozzle, and co-extruded to obtain a double-layer hollow fiber membrane, and the modified monomer is grafted to obtain the Janus hollow fiber membrane;

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

[0061] The outer layer film-making solution contains a film-forming polymer B, an outer layer additive, an organic solvent B and an 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 polymer contains a hydrophilic structure and a hydrophobic structure. One of the amphiphilic polymers contains a hydroxyl group and a hydrophobic group, and is named as amphiphilic polymer I. The other amphiphilic polymer is named as amphiphilic polymer II. The amphiphilic polymer is synthesized by free radical polymerization, and a hydrophilic monomer and a hydrophobic monomer are selected, and the monomer contains an olefin structure.

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

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

[0066] The hydrophilic monomer I is selected from an olefin monomer containing a hydroxyl group, specifically selected 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 vinyl pyrrolidone;

[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 the 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 polyvinyl pyrrolidone;

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

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

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

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

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

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

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

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

[0081] The polymerization time is 40 to 600 minutes;

[0082] Optionally, the polymerization time is any value of 40 min, 60 min, or any range between the two.

[0083] The polymerization is carried out in the presence of a catalyst;

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

[0085] The grafting modification monomer comprises the following steps:

[0086] immersing the double-layer hollow fiber membrane in a solvent solution containing a modified monomer;

[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, 0.15:1, or a range value between any two of them.

[0090] The inner layer film-making liquid is stirred I;

[0091] The stirring temperature is 10-120°C;

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

[0093] The stirring time I is 1 to 20 hours.

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

[0095] The outer film-making liquid is stirred II;

[0096] The stirring temperature of II is 10 to 120° C.

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

[0098] The stirring time II is 1 to 20 hours.

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

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

[0101] The mass concentration of the aqueous solution containing ethanol, methanol or an organic solvent is 10-80 wt %.

[0102] The total extrusion rate of the inner film-forming liquid and the outer film-forming liquid is 3 to 20 mL / min;

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

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

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

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

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

[0108] The mass concentration of the aqueous solution containing ethanol, methanol or an organic solvent is 10-80 wt %.

[0109] The Janus hollow fiber membrane is washed, solvent exchanged, and dried;

[0110] The washing is water washing;

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

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

[0113] By changing the composition, flow rate, core liquid and gel bath composition of the inner and outer membrane-making liquids, Janus hollow fiber membranes with different hydrophilic / hydrophobic layer thicknesses, hydrophilicity and hydrophobicity, and pore structures can be prepared.

[0114] According to another aspect of the present application, a method for treating ammonia nitrogen wastewater is provided, using the above-mentioned microbubble stripping device.

[0115] The temperature of the ammonia nitrogen wastewater is 5-90°C.

[0116] Optionally, the temperature of the ammonia nitrogen wastewater is 30 to 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 to 500:1

[0119] The beneficial effects of this application include:

[0120] The present application adopts Janus separation membrane as a microbubble dispersion device to disperse air into microbubbles to contact ammonia nitrogen wastewater, and utilizes the advantages of large specific surface area, high mass transfer efficiency and long gas-liquid contact time of microbubbles to enhance the mass transfer of ammonia nitrogen in water to the gas phase, reduce the gas-liquid ratio, reduce the energy consumption of the stripping process, and reduce the equipment investment and operating costs of the stripping process.

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

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

[0123] (3) The ammonia nitrogen wastewater treatment method provided by the present application can significantly reduce the volume of the stripping equipment, save floor space, the microbubbles are highly stable in the liquid and are not easy to aggregate, and the absorption equipment can be placed flat, which is particularly suitable for applications where the tower height is limited;

[0124] (4) The ammonia nitrogen wastewater treatment method provided by the present application can significantly reduce the gas consumption during the stripping process, reduce the energy consumption of the blower, and reduce the operating cost. At the same time, the volume of the stripping equipment is reduced, which can significantly reduce the investment cost of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0128] Device example 1

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

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

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

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

[0134] 6. The gas-liquid separator (i.e., the gas-liquid separation device) is connected to 8. the acid absorption device via 6b. the 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, the outlet III-2 pipeline.

[0136] Preparation Example 1

[0137] Take 8g of acryl alcohol and 2g of styrene, dissolve them in 415g of dimethylacetamide, add 0.1g of azobisisobutyronitrile, introduce nitrogen, heat and stir at 50°C 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 an inner layer membrane solution.

[0138] Take 20g of vinyl pyrrolidone and 5g of styrene, dissolve them in 350g of dimethylacetamide, add 0.5g of azobisisobutyronitrile, 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 an outer layer film-making solution.

[0139] The inner film-making liquid and the outer film-making liquid are added to the inner film-making liquid spinning tank and the outer film-making liquid spinning tank respectively, and vacuum degassing is carried out for 24 hours. The outer film-making liquid and the inner film-making liquid are respectively injected into the double-channel nozzle, and ethanol is used as the core liquid and deionized water is used as the outer gel bath to spin a double-layer hollow fiber membrane. The flow rate of the outer film-making liquid is 5ml / min, and the inner film-making liquid is 0.5ml / min to obtain a double-layer hollow fiber membrane. The obtained double-layer hollow fiber membrane is immersed in the grafting modification solution, and the grafting reaction is carried out for 24 hours. The composition of the grafting modification solution is 1g of hexafluorohexyltriethoxysilane and 100g of n-hexane. The grafted double-layer membrane is rinsed in deionized water for 48 hours, and ethanol-n-hexane is replaced and dried successively to obtain a Janus hollow fiber membrane. The Janus membrane has a hydrophobic inner layer and a hydrophilic outer layer structure.

[0140] Example 1

[0141] The device described in Device Example 1 was used.

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

[0143] Take 0.1m3 of ammonia nitrogen wastewater 3 (ammonia nitrogen content is 1500ppm, COD content is 500ppm), heated to 40℃, the solution pH is adjusted to 11.2, and the ammonia nitrogen wastewater is 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, and the air contacts the ammonia nitrogen wastewater on the outer surface to form micron-sized bubbles.

[0144] Gas flow rate is 2m 3 / h, the ammonia nitrogen wastewater flow rate is 2m 3 / h, gas phase pressure is 40KPa, liquid phase pressure before membrane is 25KPa, and liquid phase pressure after membrane is 10KPa. The ammonia nitrogen removal effect is as follows:

[0145] Blow-off time (h) Removal rate (%) Gas-Liquid Ratio 1 24.3 20:1 2 44.1 40:1 3 56.4 60:1 4 66.3 80:1 5 73.8 100:1 6 79.9 120:1 7 84.2 140:1 8 89.6 160:1 9 94.1 180:1 10 95.2 200:1

[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, introduce nitrogen, heat and stir at 70°C 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 an outer layer film-forming solution.

[0148] Take 40g of polyethylene glycol acrylate and 10g of methyl acrylate, dissolve them in 360g of dimethylacetamide, add 0.5g of azobisisobutyronitrile, and heat and stir the mixture at 60°C for 400min to obtain a solution containing amphiphilic polymer II. Add 70g of polyethersulfone and 20g of anhydrous lithium chloride to the solution to obtain an inner layer film-forming solution.

[0149] The inner film-making liquid and the outer film-making liquid are added to the inner film-making liquid spinning tank and the outer film-making liquid spinning tank respectively, and vacuum degassing is carried out for 24 hours. The outer film-making liquid and the inner film-making liquid are respectively injected into the double-channel nozzle, and water is used as the core liquid and propanol is used as the outer gel bath to spin a double-layer hollow fiber membrane. The flow rate of the outer film-making liquid is 1.5ml / min, and the inner film-making liquid is 3.5ml / min to obtain a double-layer hollow fiber membrane. The obtained double-layer hollow fiber membrane is immersed in the grafting modification solution, and the grafting reaction is 24 hours. The composition of the grafting modification solution is 5g hexafluorohexyltriethoxysilane and 95g toluene. The grafted double-layer membrane is rinsed in deionized water for 48 hours, and ethanol-n-hexane is replaced and dried successively to obtain a Janus hollow fiber membrane. The Janus membrane has a hydrophobic outer layer and a hydrophilic inner layer structure.

[0150] Example 2

[0151] The device described in Device Example 1 was used.

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

[0153] Take 0.1m3 of ammonia nitrogen wastewater 3 (ammonia nitrogen content is 1500ppm, COD content is 500ppm), heated to 40℃, the solution pH is adjusted to 11.3, and the ammonia nitrogen wastewater is 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, and the air contacts the ammonia nitrogen wastewater on the outer surface to form micron-sized bubbles.

[0154] Gas flow rate is 5m 3 / h, the ammonia nitrogen wastewater flow rate is 5m 3 / h, gas phase pressure is 45KPa, liquid phase pressure before membrane is 30KPa, and liquid phase pressure after membrane is 10KPa. The ammonia nitrogen removal effect is as follows:

[0155] Blow-off time (h) Removal rate (%) Gas-Liquid Ratio 1 51.4 50:1 2 76.3 100:1 3 88.4 150:1 4 95.4 200:1

[0156] Example 3

[0157] The device described in Device Example 1 was used.

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

[0159] Take 0.1m3 of ammonia nitrogen wastewater 3 (ammonia nitrogen content is 1500ppm, COD content is 500ppm), heated to 50℃, the solution pH is adjusted to 11.2, and the ammonia nitrogen wastewater is 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, and the air contacts the ammonia nitrogen wastewater on the outer surface to form micron-sized bubbles.

[0160] Gas flow rate is 5m 3 / h, the ammonia nitrogen wastewater flow rate is 5m 3 / h, gas phase pressure is 45KPa, liquid phase pressure before membrane is 33KPa, and liquid phase pressure after membrane is 10KPa. The ammonia nitrogen removal effect is as follows:

[0161] Blow-off time (h) Removal rate (%) Gas-Liquid Ratio 1 55.4 50:1 2 81.2 100:1 3 93.3 150:1 4 98.3 200:1

[0162] Comparative Example 1

[0163] The device described in Device Example 1 was used.

[0164] Ammonia nitrogen wastewater treatment is carried out using a traditional stripping tower. Take 1m 3 (ammonia nitrogen content is 1500ppm, COD content is 500ppm), heated to 50℃, adjusted the solution pH to 11.4, pumped ammonia nitrogen wastewater and compressed air into the absorption tower, the gas flow rate is 500m 3 / h, the ammonia nitrogen wastewater flow rate is 1m 3 / h, gas phase pressure is 5KPa. The ammonia nitrogen removal effect is as follows:

[0165] Blow-off time (h) Removal rate (%) Gas-Liquid Ratio 1 24.3 500:1 2 45.5 1000:1 3 62.3 1500:1 4 77.3 2000:1 5 84.1 2500:1 6 88.2 3000:1

[0166] Comparative Example 2

[0167] The device described in Device Example 1 was used.

[0168] PVDF hydrophobic hollow fiber membrane is used as the membrane material, the water contact angle is 135°, the inner diameter of the hollow fiber membrane is 0.8 mm, the outer diameter is 1.3 mm, and the pore size of the Janus membrane is 0.4 μm. 300 hollow fiber membranes are taken to make a hollow fiber membrane assembly, the membrane fiber packing density is 55%, and the effective length is 100 cm.

[0169] Take 0.1m3 of ammonia nitrogen wastewater 3 (ammonia nitrogen content is 1500ppm, COD content is 500ppm), heated to 50℃, adjusted the solution pH to 11.3, and pumped the ammonia nitrogen wastewater into the outer surface of the PVDF hydrophobic hollow fiber membrane module. Pumped compressed air into the inner surface of the PVDF hydrophobic hollow fiber membrane module, the air contacts the ammonia nitrogen wastewater on the outer surface, forming millimeter-level bubbles.

[0170] Gas flow rate is 30m 3 / h, the ammonia nitrogen wastewater flow rate is 5m 3 / h, gas phase pressure is 45KPa, liquid phase pressure before membrane is 33KPa, and liquid phase pressure after membrane is 10KPa. The ammonia nitrogen removal effect is as follows:

[0171] Blow-off time (h) Removal rate (%) Gas-Liquid Ratio 1 35.4 300:1 2 56.2 600:1 3 71.3 900:1 4 81.3 1200:1 5 87.2 1500:1 6 92.3 2000:1

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

[0173] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A microbubble stripping device, characterized in that: It includes a micro bubble dispersion device, an absorption device, and a gas-liquid separation device which are sequentially connected 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 to 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 to 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°.

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

3. The microbubble stripping device according to claim 2, characterized in that: The outlet I is connected to the inlet II pipeline; The outlet II is connected to the inlet III through a pipeline.

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

5. The microbubble stripping 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 pipeline of the acid absorption device.

6. The microbubble stripping 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 stripping device according to claim 1, characterized in that: In the microbubble dispersion device, the packing density of the Janus hollow fiber membrane is 5 to 60%.

8. The microbubble stripping device according to claim 1, characterized in that: The Janus hollow fiber membrane is prepared by the following steps: The inner layer membrane-making liquid and the outer layer membrane-making liquid are introduced into the spinning core liquid by using a double-channel nozzle, and co-extruded to obtain a double-layer hollow fiber membrane, and the modified monomer is grafted to obtain the Janus hollow fiber membrane; The inner layer film-making solution contains a film-forming polymer A, an inner layer additive, an organic solvent A and an amphiphilic polymer A; The outer layer film-making solution contains a film-forming polymer B, an outer layer additive, an organic solvent B and an amphiphilic polymer B; The amphiphilic polymer A and the amphiphilic polymer B are independently selected from amphiphilic polymer I and amphiphilic polymer II; The amphiphilic polymer I is obtained by polymerizing a hydrophilic monomer I and a hydrophobic monomer I; The amphiphilic polymer II is obtained by polymerizing a hydrophilic monomer II and a hydrophobic monomer II; The hydrophilic monomer I is selected from at least one of allyl alcohol and butenol; The hydrophilic monomer II is selected from at least one of polyethylene glycol acrylate and vinyl pyrrolidone; 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 at least one of polyethylene glycol, anhydrous lithium chloride and polyvinyl pyrrolidone; The outer layer additive is selected from at least one of polyethylene glycol, anhydrous lithium chloride and polyvinyl pyrrolidone; The organic solvent A and the organic solvent B are independently selected from at least one of dimethylacetamide, dimethylformamide, N-methylpyrrolidone and tetrahydrofuran; The mass concentration of the film-forming polymer A in the inner layer film-forming solution is 10-25wt%, the mass concentration of the inner layer additive is 5-20wt%, and the mass concentration of the amphiphilic polymer A is 1-20wt%; The mass concentration of the film-forming polymer B in the outer layer film-forming solution is 10-25 wt %, the mass concentration of the outer layer additive is 5-20 wt %, and the mass concentration of the amphiphilic polymer B is 1-20 wt %.

9. A method for treating ammonia nitrogen wastewater, characterized in that: A microbubble stripping device as claimed in any one of claims 1 to 7 is used.

10. The method for treating ammonia nitrogen wastewater according to claim 8, characterized in that: The temperature of the ammonia nitrogen wastewater is 5 to 90° C. The gas-liquid ratio during the treatment process is 100-2000:1.

Images