Efficient flocculation, ozone catalysis and membrane distillation combined process for purifying high-salinity wastewater

Abstract

The invention relates to an efficient flocculation, ozone catalysis and membrane distillation combined process which is suitable for treating high-salinity wastewater, especially desulfurization wastewater of a coal-fired power plant and coal chemical wastewater. According to the technology, efficient flocculation, ozone catalysis and membrane distillation technologies are ingeniously fused, a specially-made chitosan-based flocculant is added in the flocculation stage, and suspended solids and heavy metal ions in wastewater are effectively removed by means of the excellent adsorption and flocculation efficiency of the specially-made chitosan-based flocculant; in the ozone catalysis stage, an ozone decomposition process is accelerated by adding a self-developed ternary composite catalyst, so that organic pollutants are deeply purified; in the membrane distillation stage, a self-made antifouling and moisture-resistant composite membrane is used for efficient desalination and concentration, and finally efficient purification and recycling of the high-salinity wastewater are achieved. The process can significantly improve the wastewater treatment effect, reduce the concentration of salt and harmful substances in the wastewater, also reduce the operation cost, and is suitable for large-scale industrial wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of coal chemical wastewater treatment, and in particular to a method for preparing an anti-fouling and anti-humidity functional membrane for concentrating high-salt wastewater and a pretreatment+membrane concentration process. Technical Background

[0002] With the advancement of industrialization, a large amount of wastewater generated by coal-fired power plants, coal chemical industry and other industries has become a serious environmental problem. Especially in the treatment of desulfurization wastewater and coal chemical wastewater, these wastewaters contain high salt and organic pollutants. According to the 2023 coal chemical wastewater industry analysis report, the new coal chemical industry wastewater generation reached 4.745 billion tons / year, and the wastewater treatment technologies involved include organic and high-salt wastewater treatment processes. Conventional treatment methods are difficult to effectively remove harmful substances, resulting in low treatment efficiency and subsequent water quality that is difficult to meet standards. Traditional wastewater treatment methods cover physical, chemical and biological methods. However, these methods generally face challenges such as low treatment efficiency, high cost and difficulty in meeting the standards for treated water quality, such as traditional membrane distillation technology is susceptible to pollution, ozone catalytic reaction efficiency is low, and the removal rate of heavy metals by traditional flocculants is less than 60%. Therefore, there is an urgent need for a new wastewater treatment process that is efficient, low-cost and has a high treatment effect.

[0003] The sources of coal chemical brine are diverse, including the preparation of desalted water, repeated use of circulating water, boiler water and brine generated by adding chemicals in recycled water treatment. In addition to a small amount of brine enriched in the above process, the fresh water used in the project itself also contains salt. Especially in coal chemical projects, the Yellow River water is used as fresh water supply, and the salt brought in exceeds 50% of the salt content of the entire project system; at the same time, the chemical agents added in the production process and water system are also an important source of salt, and the amount of salt produced by them accounts for more than one-third of the total salt content. Therefore, even if a limited water-saving effect can be achieved by determining a reasonable circulation multiple and dosing method, it will eventually produce about 15% to 30% of the total volume of difficult-to-handle brine. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention proposes a high-efficiency flocculation + ozone catalysis + membrane distillation combined process design. The process significantly improves the treatment efficiency of high-salinity wastewater through the three-stage combined treatment of flocculation, ozone catalysis and membrane distillation, and is particularly suitable for the efficient treatment of desulfurization wastewater from coal-fired power plants and coal chemical wastewater.

[0005] The technical solution of the present invention includes the following key steps:

[0006] 1. Flocculation stage: Chitosan was dissolved in 1% acetic acid solution, thiocyanuric acid was added, and the reaction was carried out at 60°C for 6 hours under nitrogen protection. The product was precipitated with ethanol, dried, and crushed to 100 mesh to obtain a chitosan-based flocculant. The homemade chitosan-based flocculant was added to the wastewater. The chitosan-based flocculant showed excellent flocculation ability and could effectively remove suspended particles and some soluble organic matter in the wastewater. The flocculant can not only remove most of the suspended particles, but also create better conditions for subsequent treatment processes by improving water quality. The mass ratio of chitosan to thiocyanuric acid can be between 2:1 and 3:1, but when it is 3:1, the flocculation effect is the best, the suspended matter removal rate reaches 95%, and the heavy metal (As, Hg) removal rate reaches 90%.

[0007] 2. Ozone catalysis stage: After the fly ash is acid-washed (5% HNO3) and calcined (600°C), it is immersed in a mixed solution of Mn(NO3)2, Ce(NO3)3, and Bi(NO3)3 (Mn, Ce, Bi molar ratio 1:1:0.5), dried at 80°C, and calcined at 500°C for 3 hours to obtain a ternary composite catalyst. In the wastewater treatment process, the addition of specific reagents can significantly improve the decomposition efficiency of ozone, thereby accelerating the oxidative decomposition of organic pollutants. For example, by adding calcium ions or barium ions to the wastewater, the hydroxyl radical scavenger produced during the base-catalyzed ozone advanced oxidation process can be removed, thereby improving the utilization efficiency of ozone. In addition, the ozone catalytic oxidation method has also shown good results in treating COD in high-salinity concentrated water. The device operates stably and the effluent COD index is qualified. The molar ratio of Mn, Ce and Bi can be between 1:1:1 and 3:2:1, but the catalyst performance is best when it is 1:1:0.5. The ozone dosage is 50-100 mg / L, the reaction temperature is 40-60°C, the residence time is 30-60 minutes, and the COD after degradation is ≤50 mg / L.

[0008] 3. Membrane distillation stage: PVDF-HEP and SiO2 (mass ratio 8:2) are dissolved in DMAC and electrospun (voltage 18kV, flow rate 1mL / h) to form a base membrane; chitosan solution (2wt%) is electrosprayed onto the surface of the base membrane, with a coating thickness of 1-2μm to obtain a homemade composite membrane. The wastewater is treated by membrane distillation using a homemade composite membrane. Membrane distillation technology is a process that purifies wastewater by separating water vapor from salt in wastewater. At this stage, salt and other soluble pollutants in the wastewater can be effectively removed, and high-quality purified water is ultimately produced. The composite membrane material is able to maintain high-efficiency processing capabilities during long-term use due to its excellent membrane flux and outstanding anti-pollution properties.

[0009] The combined process of the present invention comprises the following key components: a high-efficiency flocculation reaction component, which adds a chitosan-based flocculant and finely controls the pH value of wastewater within the range of 6.5 to 7.5; an ozone catalytic reaction component, which has a built-in Mn-Ce-Bi ternary composite catalyst, the catalyst is carefully proportioned, and the molar ratio of Mn, Ce, and Bi is accurate to 1:1:0.5; a membrane distillation component, which uses a composite membrane with PVDF-HEP and super-hydrophobic SiO2 as the basic membrane; the outlet of the high-efficiency flocculation reaction component is connected to the inlet of the ozone catalytic reaction component, and the outlet of the ozone catalytic reaction component is connected to the inlet of the membrane distillation component.

[0010] The high-efficiency flocculation reaction component comprises a flocculation reaction device, a water sample collection device and a circulation pump; when working, the high-salt wastewater flows through the flocculation reaction device and the water sample collection device in sequence, and enters the ozone catalytic reaction component through the circulation pump.

[0011] The ozone catalytic reaction component includes an ozone generator, an ozone detector, an ozone catalytic reactor, and a water quality detector; the ozone generated by the ozone generator enters the ozone catalytic reactor through the ozone detector, and the ozone detector can control the ozone flow; the water quality detector is connected to the ozone catalytic reactor to regularly detect water quality.

[0012] The membrane distillation component includes a feed side system, a flow controller, a membrane distillation device, an osmotic side system, a conductivity monitor, a water production monitoring device and a circulation pump; when working, water enters the membrane distillation device from the feed side system through the circulation pump and the flow controller, and the treated clean water enters the water production monitoring device from the osmotic side system through the circulation pump.

[0013] The beneficial effects brought by the present invention are:

[0014] The technical solution of the present invention can effectively remove suspended matter, organic pollutants and salts in wastewater through the three-stage combined treatment of flocculation, ozone catalysis and membrane distillation. Compared with traditional wastewater treatment methods, this process has the following advantages:

[0015] 1. High efficiency: The three-stage combined treatment process complements each other and can significantly improve the treatment efficiency of high-salinity wastewater and remove a variety of pollutants in the water.

[0016] 2. Low cost: The use of homemade chitosan-based flocculants, ternary composite catalysts and composite membrane materials reduces the cost of raw materials in the wastewater treatment process.

[0017] 3. Environmental protection: This process can not only treat high-salt wastewater, but also recycle purified water to achieve the purpose of wastewater resource utilization, with good environmental benefits.

[0018] 4. Simple operation: The operation process of each stage is simple, easy for industrial application and promotion.

[0019] 5. The flocculation stage removes suspended matter and colloids, reduces membrane pore blockage, and increases membrane flux by more than 30%; the ozone catalysis stage degrades macromolecular organic matter to prevent it from forming a gel layer on the membrane surface, thereby extending the membrane life. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the technical description of the present invention.

[0021] In the attached picture:

[0022] Figure 1 It is a flow chart of the high-efficiency flocculation+ozone catalysis+membrane distillation process design of the present invention.

[0023] Figure numerals: 1. flocculation reaction device; 2. water sample collection device; 3. circulation pump; 4. ozone generator; 5. ozone detector; 6. ozone catalytic reactor; 7. water quality detector; 8. feed side system; 9. flow control meter; 10. membrane distillation device; 11. osmosis side system; 12. conductivity monitor; 13. water production monitoring device. Specific implementation methods

[0025] During the specific implementation process, the wastewater first goes through the flocculation stage, where an appropriate amount of chitosan-based flocculant is added to flocculate and settle the suspended matter and heavy metal pollutants in the water. Subsequently, the wastewater enters the ozone catalysis stage, where a homemade ternary composite catalyst is added to promote ozone decomposition under catalytic action and oxidatively degrade organic pollutants in the wastewater. Finally, the wastewater enters the membrane distillation stage, where the water is distilled through a composite membrane to remove salt and dissolved pollutants, and obtain purified water that meets emission standards.

[0026] (1) High-efficiency flocculation stage: The wastewater to be treated is mixed with a chitosan-based flocculant, which is a graft copolymer of chitosan and thiocyanate in a mass ratio of 3:1. After mixing, the pH is adjusted to 6.5-7.5 and the reaction time is 20-30 minutes. The suspended solids and heavy metal ions are effectively removed by reducing turbidity, reducing chemical oxygen demand (COD) and biochemical oxygen demand (BOD), improving color removal rate, and reducing heavy metal ion content.

[0027] (2) Ozone catalysis stage: The flocculated wastewater is sent to a reaction device containing a ternary composite catalyst, wherein the catalyst is loaded on a fly ash carrier in a molar ratio of 1:1:0.5 with manganese (Mn), cerium (Ce), and bismuth (Bi), and the specific surface area of ​​the carrier is ≥300m 2 / g, catalyst specific surface area ≥150m 2 / g, ozone dosage is 50-100mg / L, reaction temperature is 40-60℃, residence time is 30-60 minutes, COD is degraded to ≤50mg / L;

[0028] (3) Membrane distillation stage: The catalytic wastewater is passed through an anti-fouling and anti-wetting composite membrane. The composite membrane is made of PVDF-HEP and super-hydrophobic SiO2 through electrospinning to form a base membrane, and the surface is electrosprayed with chitosan coating. The membrane pore size is 0.1-0.3 μm, the operating temperature is 60-80°C, the transmembrane pressure difference is 10-20 kPa, and the desalination rate is ≥99.5%.

[0029] Embodiment 1:

[0030] The treatment parameters of a coal chemical wastewater (salinity 15,000mg / L, COD 500mg / L) are as follows:

[0031] (1) High-efficiency flocculation stage: the wastewater to be treated is mixed with a chitosan-based flocculant made of chitosan grafted copolymerized with thiocyanate in a mass ratio of 3:1, the flocculant dosage is 0.5%-1% of the wastewater volume, the pH is adjusted to 6.5-7.5 after mixing, and the reaction time is 25 minutes;

[0032] (2) Ozone catalysis stage: The flocculated wastewater is sent to a reaction device containing a ternary composite catalyst. The catalyst is composed of manganese (Mn), cerium (Ce), and bismuth (Bi) loaded on a fly ash carrier in a molar ratio of 1:1:0.5. Ozone is continuously added through an ozone generator at a dosage of 75 mg / L, a reaction temperature of 50 °C, and a residence time of 45 minutes.

[0033] (3) Membrane distillation stage: The catalytic wastewater is passed through an anti-fouling and anti-wetting composite membrane with an operating temperature of 70°C and a transmembrane pressure difference of 15 kPa.

[0034] After this process:

[0035] Flocculation stage: suspended solids removal rate 95%, heavy metal (As, Hg) removal rate ≥ 90%;

[0036] Ozone catalysis stage: COD drops to 45mg / L; the activity retention rate of the catalyst after 5 cycles is ≥85%;

[0037] Membrane distillation stage: produced water conductivity ≤50μS / cm, desalination rate 99.8%.

[0038] Compared with traditional processes, such as single membrane distillation, the energy consumption is 2.5kWh / m 3 The energy consumption of the present invention is 1.8 kWh / m 3 After the suspended solids are removed by flocculants, the membrane fouling rate is reduced by about 70%. After the membrane distillation module is continuously operated for 100 hours, the membrane flux is ≥18L / m 2 ·h(initial flux 20L / m 2 h, after 100 hours).

[0039] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A high-efficiency flocculation + ozone catalysis + membrane distillation combined process for high-salinity wastewater purification, characterized in that: The system includes the following key components: (1) a high-efficiency flocculation reaction component, which adds chitosan-based flocculants and adjusts the wastewater pH to 6.5-7.5; (2) an ozone catalytic reaction component, which has a built-in Mn-Ce-Bi ternary composite catalyst, and the molar ratio of Mn, Ce, and Bi in the catalyst is 2:1:1; (3) a membrane distillation component, which uses a composite membrane based on PVDF-HEP and super-hydrophobic SiO2; The outlet of the high-efficiency flocculation reaction component is connected to the inlet of the ozone catalytic reaction component, and the outlet of the ozone catalytic reaction component is connected to the inlet of the membrane distillation component.

2. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 1 is characterized in that: The high-efficiency flocculation reaction component comprises a flocculation reaction device, a water sample collection device and a circulation pump; when working, the high-salt wastewater flows through the flocculation reaction device and the water sample collection device in sequence, and enters the ozone catalytic reaction component through the circulation pump.

3. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 1 is characterized in that: The ozone catalytic reaction component includes an ozone generator, an ozone detector, an ozone catalytic reactor, and a water quality detector; the ozone generated by the ozone generator enters the ozone catalytic reactor through the ozone detector, and the ozone detector can control the ozone flow; the water quality detector is connected to the ozone catalytic reactor to regularly detect water quality.

4. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 1 is characterized in that: The membrane distillation component includes a feed side system, a flow controller, a membrane distillation device, an osmotic side system, a conductivity monitor, a water production monitoring device and a circulation pump; when working, water enters the membrane distillation device from the feed side system through the circulation pump and the flow controller, and the treated clean water enters the water production monitoring device from the osmotic side system through the circulation pump.

5. A high-efficiency flocculation + ozone catalysis + membrane distillation combined process for high-salinity wastewater purification, characterized in that: The following steps are involved: (1) High-efficiency flocculation stage: the wastewater to be treated is mixed with a chitosan-based flocculant, which is made by graft copolymerization of chitosan and trithiocyanate at a mass ratio of 3:

1. The amount of flocculant added is 0.5%-1% of the wastewater volume. After mixing, the pH is adjusted to 6.5-7.

5. The reaction time is 20-30 minutes. The removal rate of suspended solids is ≥95%, and the removal rate of heavy metals (As, Hg) is ≥90%; (2) Ozone catalysis stage: The flocculated wastewater is sent to a reaction device containing a ternary composite catalyst, wherein the catalyst is loaded on a modified fly ash carrier in a molar ratio of 1:1:0.5 of manganese (Mn), cerium (Ce), and bismuth (Bi), and the specific surface area of ​​the carrier is ≥300m 2 / g, ozone dosage is 50-100mg / L, reaction temperature is 40-60℃, residence time is 30-60 minutes, COD after degradation is ≤50mg / L; (3) Membrane distillation stage: The catalytic wastewater is passed through an anti-fouling and anti-wetting composite membrane. The composite membrane is made of PVDF-HEP and super-hydrophobic SiO2 through electrospinning to form a base membrane, and the surface is electrosprayed with chitosan coating. The membrane pore size is 0.1-0.3 μm, the operating temperature is 60-80°C, the transmembrane pressure difference is 10-20 kPa, and the desalination rate is ≥99.5%.

6. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 5 is characterized in that: The high-efficiency flocculant is a flocculant prepared by graft copolymerization of chitosan and an appropriate amount of heavy metal scavenger thiocyanate through free radical polymerization in a laboratory.

7. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 5, characterized in that: The ozone catalytic reaction device adopts an ozone generator and a catalyst to work together, wherein the catalyst is manganese (Mn), cerium (Ce), and bismuth (Bi) loaded on a fly ash carrier through an impregnation-calcination method to form a ternary composite catalyst.

8. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 5, characterized in that: The membrane distillation device adopts a combination of membrane distillation and gas permeation to concentrate wastewater through temperature polarization.

9. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 5, characterized in that: The composite membrane uses PVDF-HEP and super-hydrophobic SiO2 as spinning liquid to prepare a base membrane through electrostatic spinning; and obtains a final composite membrane through electrospraying a chitosan flocculant.

10. The high-efficiency flocculation + ozone catalysis + membrane distillation combined process according to claim 5, characterized in that: The wastewater treatment efficiency of the process is above 50%, the salt concentration of the treated wastewater is ≤100 mg / L, COD is ≤30 mg / L, and the energy consumption is reduced by more than 20% compared with the existing single treatment method.

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