A high-efficiency flocculation + ozone catalysis + membrane distillation combined process for high-salinity wastewater purification

Abstract

The present application relates to a kind of high-efficiency flocculation+ozone catalysis+membrane distillation combined process, it is applicable to the treatment of high-salinity wastewater, especially coal-fired power plant desulfurization wastewater and coal chemical wastewater.The process ingeniously combines high-efficiency flocculation, ozone catalysis and membrane distillation technology, add special chitosan-based flocculant in flocculation stage, with its excellent adsorption and flocculation efficiency, effectively remove suspended solids and heavy metal ions in wastewater;Ozone catalysis stage is through the addition of self-developed ternary composite catalyst, accelerates the process of ozone decomposition, thereby deeply purifying organic pollutants;In the membrane distillation stage, use self-made antifouling and anti-wetting composite membrane for efficient desalination and concentration, finally reach the efficient purification and reuse of high-salinity wastewater.The process can significantly improve the treatment effect of wastewater, reduce the concentration of salt and harmful substances in wastewater, also reduce the operating cost, suitable for large-scale industrial wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of coal chemical wastewater treatment technology, and in particular to a method for preparing an antifouling and moisture-proof functional membrane for high-salt wastewater concentration and a pretreatment + membrane concentration process. Technical Background

[0002] With the advancement of industrialization, the large amounts of wastewater generated by coal-fired power plants and coal chemical industries have become a serious environmental problem. This is particularly true in the treatment of desulfurization wastewater and coal chemical wastewater, which contain high levels of salt and organic pollutants. According to a 2023 analysis report on coal chemical wastewater, the annual wastewater generation from the emerging coal chemical industry reached 4.745 billion tons, involving wastewater treatment technologies for organic and high-salinity wastewater. Conventional treatment methods are insufficient to effectively remove harmful substances, resulting in low treatment efficiency and failure to meet subsequent water quality standards. Traditional wastewater treatment methods encompass physical, chemical, and biological methods; however, these methods generally face challenges such as low treatment efficiency, high costs, and difficulty in achieving acceptable water quality standards. For example, traditional membrane distillation technology is susceptible to fouling, ozone catalytic reaction efficiency is low, and traditional flocculants achieve less than 60% removal rate of heavy metals. Therefore, there is an urgent need for a new wastewater treatment process that is efficient, low-cost, and has high treatment effectiveness.

[0003] The sources of concentrated brine in coal chemical projects are diverse, including demineralized water preparation, repeated use of circulating water, boiler water carryover, and concentrated brine generated from the addition of chemicals during recycled water treatment. Besides the small portion of concentrated brine accumulated during these processes, the fresh water used in the project itself also contains salt. Particularly in coal chemical projects using Yellow River water as fresh water replenishment, the salt carried over from Yellow River water accounts for more than 50% of the total salt content of the entire project system. Simultaneously, the chemical agents added during production and in the water system are also significant sources of salt, contributing more than one-third of the total salt content. Therefore, even if limited water-saving effects can be achieved by determining reasonable circulation ratios and chemical dosing methods, approximately 15% to 30% of the total volume will ultimately be generated as difficult-to-treat concentrated brine. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention proposes a combined process design of high-efficiency flocculation + ozone catalysis + membrane distillation. This process significantly improves the treatment efficiency of high-salinity wastewater through the combined treatment of flocculation, ozone catalysis, and membrane distillation in three stages, 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 this invention includes the following key steps:

[0006] 1. Flocculation Stage: Chitosan was dissolved in a 1% acetic acid solution, and trithiocyanate was added. The mixture was reacted at 60°C for 6 hours under nitrogen protection. The product was precipitated with ethanol, dried, and then pulverized to 100 mesh to obtain a chitosan-based flocculant. Adding this self-made chitosan-based flocculant to wastewater demonstrated its excellent flocculation ability, effectively removing suspended particles and some dissolved organic matter. This flocculant not only removes most suspended particles but also improves water quality, creating better conditions for subsequent treatment processes. The mass ratio of chitosan to trithiocyanate can be between 2:1 and 3:1, but a ratio of 3:1 yields the best flocculation effect, with a suspended solids removal rate of 95% and a heavy metal (As, Hg) removal rate of 90%.

[0007] 2. Ozone Catalytic Stage: Fly ash is acid-washed (5% HNO3), calcined (600℃), and then impregnated in a mixed solution of Mn(NO3)2, Ce(NO3)3, and Bi(NO3)3 (Mn, Ce, Bi molar ratio 1:1:0.5). After drying at 80℃, it is calcined at 500℃ for 3 hours to obtain a ternary composite catalyst. In wastewater treatment, adding specific reagents can significantly improve the decomposition efficiency of ozone, thereby accelerating the oxidative decomposition of organic pollutants. For example, by adding calcium or barium ions to wastewater, hydroxyl radical scavengers generated during alkaline catalytic ozone advanced oxidation can be removed, thus improving ozone utilization efficiency. Furthermore, ozone catalytic oxidation has also shown good results in treating COD in high-salinity concentrated water; the device operates stably, and the effluent COD index meets the requirements. 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 the ratio is 1:1:0.5. The ozone dosage is 50-100 mg / L, the reaction temperature is 40-60℃, 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; a chitosan solution (2wt%) is electrosprayed onto the base membrane surface, with a coating thickness of 1-2μm, to obtain a self-made composite membrane. The self-made composite membrane is used for membrane distillation treatment of wastewater. Membrane distillation technology is a process that purifies wastewater by separating water vapor from salts in the wastewater. In this stage, salts and other dissolved pollutants in the wastewater are effectively removed, ultimately producing high-quality purified water. This composite membrane material, with its excellent membrane flux and outstanding antifouling properties, maintains high-efficiency treatment capacity during long-term use.

[0009] The combined process of this invention includes the following key components: a high-efficiency flocculation reaction component, which adds chitosan-based flocculant and finely controls the pH of the wastewater within the range of 6.5 to 7.5; an ozone catalytic reaction component, which incorporates a Mn-Ce-Bi ternary composite catalyst, the catalyst being carefully formulated with a molar ratio of Mn, Ce, and Bi accurate to 1:1:0.5; a membrane distillation component, which uses a composite membrane based on PVDF-HEP and superhydrophobic 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.

[0010] The high-efficiency flocculation reaction component includes a flocculation reaction device, a water sample collection device, and a circulation pump; during operation, high-salt wastewater flows sequentially through the flocculation reaction device and the water sample collection device, and then enters the ozone catalytic reaction component through the circulation pump.

[0011] The ozone catalytic reaction assembly includes an ozone generator, an ozone detector, an ozone catalytic reactor, and a water quality analyzer. The ozone generated by the ozone generator enters the ozone catalytic reactor through the ozone detector, which can control the ozone flow rate. The water quality analyzer is connected to the ozone catalytic reactor and monitors the water quality at regular intervals.

[0012] The membrane distillation assembly includes a feed-side system, a flow meter, a membrane distillation unit, a permeate-side system, a conductivity monitor, a permeate flow monitoring device, and a circulation pump. During operation, water enters the membrane distillation unit from the feed-side system via the circulation pump and the flow meter, and the treated purified water enters the permeate flow monitoring device from the permeate-side system via the circulation pump.

[0013] The beneficial effects of this invention are:

[0014] The technical solution of this invention utilizes a three-stage combined treatment process of flocculation, ozone catalysis, and membrane distillation to effectively remove suspended solids, organic pollutants, and salts from wastewater. Compared to traditional wastewater treatment methods, this process has the following advantages:

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

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

[0017] 3. Environmental friendliness: This process can not only treat high-salt wastewater, but also recycle and purify water, achieving the goal of wastewater resource utilization and having good environmental benefits.

[0018] 4. Simple operation: The operation process at each stage is simple and easy to apply and promote in industrial applications.

[0019] 5. The flocculation stage removes suspended solids and colloids, reducing membrane pore blockage and increasing membrane flux by more than 30%; the ozone catalysis stage degrades macromolecular organic matter, preventing the formation of a gel layer on the membrane surface and extending membrane life. Attached Figure Description

[0020] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the technical description of the present invention will be briefly introduced below.

[0021] In the attached diagram:

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

[0023] Reference numerals in the attached figures: 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 analyzer; 8. Feed-side system; 9. Flow controller; 10. Membrane distillation device; 11. Permeate-side system; 12. Conductivity monitor; 13. Product water monitoring device. Specific implementation methods

[0024] In the specific implementation process, the wastewater first undergoes a flocculation stage, where an appropriate amount of chitosan-based flocculant is added to cause suspended solids and heavy metal pollutants in the water to flocculate and settle. Subsequently, the wastewater enters an ozone catalysis stage, where a self-made ternary composite catalyst is added to promote ozone decomposition and oxidize and degrade organic pollutants in the wastewater. Finally, the wastewater enters a membrane distillation stage, where a composite membrane is used to distill the water, removing salts and dissolved pollutants to obtain purified water that meets emission standards.

[0025] (1) High-efficiency flocculation stage: The wastewater to be treated is mixed with chitosan-based flocculant, which is composed of chitosan and trithiocyanate graft copolymerized at 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. By reducing turbidity, reducing chemical oxygen demand (COD) and biochemical oxygen demand (BOD), increasing color removal rate, and reducing heavy metal ion content, suspended solids and heavy metal ions are effectively removed.

[0026] (2) Ozone catalytic stage: The flocculated wastewater is fed into a reaction device containing a ternary composite catalyst. The catalyst consists of manganese (Mn), cerium (Ce), and bismuth (Bi) in a molar ratio of 1:1:0.5 supported on a fly ash carrier, with a specific surface area ≥300 m². 2 / g, catalyst specific surface area ≥150m² 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;

[0027] (3) Membrane distillation stage: The catalytic wastewater is passed through an antifouling and antiwetting composite membrane. The composite membrane is made of PVDF-HEP and superhydrophobic SiO2 by electrospinning to form a base membrane, and the surface is coated with a chitosan coating by electrospraying. The membrane pore size is 0.1-0.3μm, the operating temperature is 60-80℃, the transmembrane pressure difference is 10-20kPa, and the desalination rate is ≥99.5%.

[0028] Example 1:

[0029] The treatment parameters for a certain coal chemical wastewater (salt content 15,000 mg / L, COD 500 mg / L) are as follows:

[0030] (1) High-efficiency flocculation stage: The wastewater to be treated is mixed with chitosan-based flocculant made by graft copolymerization of chitosan and trithiocyanate at a mass ratio of 3:1. The flocculant dosage is 0.5%-1% of the wastewater volume. After mixing, the pH is adjusted to 6.5-7.5 and the reaction time is 25 minutes.

[0031] (2) Ozone catalytic stage: The flocculated wastewater is sent into a reaction device containing a ternary composite catalyst. The catalyst is composed of manganese (Mn), cerium (Ce), and bismuth (Bi) in a molar ratio of 1:1:0.5 on a fly ash carrier. Ozone is continuously added through an ozone generator at a dosage of 75 mg / L. The reaction temperature is 50°C and the residence time is 45 minutes.

[0032] (3) Membrane distillation stage: The catalytic wastewater is passed through an antifouling and antiwetting composite membrane at an operating temperature of 70℃ and a transmembrane pressure difference of 15kPa.

[0033] After processing using this process:

[0034] Flocculation stage: suspended solids removal rate 95%, heavy metal (As, Hg) removal rate ≥90%;

[0035] Ozone catalysis stage: COD reduced to 45 mg / L; catalyst activity retention rate ≥ 85% after 5 cycles;

[0036] Membrane distillation stage: product water conductivity ≤50μS / cm, desalination rate 99.8%.

[0037] Compared to traditional processes, such as single membrane distillation with an energy consumption of 2.5 kWh / m³, 3 The energy consumption of this invention is 1.8 kWh / m³. 3 Furthermore, after removing suspended solids with flocculants, the membrane fouling rate is reduced by approximately 70%. After 100 hours of continuous operation, the membrane flux of the membrane distillation unit is ≥18 L / m³. 2 ·h (initial flux 20 L / m) 2 • h, after 100 hours).

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A highly efficient combined process of flocculation + ozone catalysis + membrane distillation for the purification of high-salinity wastewater, characterized in that, Includes the following steps: (1) High-efficiency flocculation stage: Add a flocculant made of chitosan and trithiocyanate by free radical polymerization graft copolymerization at a mass ratio of 3:1 to the wastewater to be treated. The flocculant dosage is 0.5%-1% of the wastewater volume. After mixing, adjust the pH to 6.5-7.5 and react for 20-30 minutes. The suspended solids removal rate is ≥95%, and the heavy metals As and Hg removal rate is ≥90%. (2) Ozone catalytic stage: The flocculated wastewater is sent to a reaction device containing a Mn-Ce-Bi ternary composite catalyst. The molar ratio of manganese (Mn), cerium (Ce), and bismuth (Bi) in the catalyst is 1:1:0.

5. The catalyst is manganese (Mn), cerium (Ce), and bismuth (Bi) loaded on a modified fly ash carrier by impregnation-calcination method. The specific surface area of ​​the carrier is ≥300 m² / g. The ozone dosage is 50-100 mg / L. The reaction temperature is 40-60℃. The residence time is 30-60 minutes. The COD of the effluent after degradation is ≤50 mg / L. (3) Membrane distillation stage: The catalytic wastewater is passed through an antifouling and antiwetting composite membrane. The composite membrane is made of PVDF-HEP and superhydrophobic SiO2 by electrospinning to form a base membrane, and a chitosan coating is electrosprayed onto the surface to obtain the final composite membrane. The membrane pore size is 0.1-0.3μm, the operating temperature is 60-80℃, the transmembrane pressure difference is 10-20 kPa, and the desalination rate is ≥99.5%.

2. The process according to claim 1, characterized in that, The support for the Mn-Ce-Bi ternary composite catalyst is fly ash that has been acid-washed and calcined.

3. The process according to claim 1, characterized in that, The activity retention rate of the catalyst in the ozone catalysis stage is ≥85% after being recycled 5 times.

4. The process according to claim 1, characterized in that, The process produces wastewater with a salt concentration ≤100 mg / L and COD ≤30 mg / L, and energy consumption is reduced by more than 20% compared to existing single treatment methods.

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