Treatment system for purifying high-salinity wastewater

Abstract

The utility model relates to a treatment system for purifying high-salinity wastewater, which is suitable for treating high-salinity wastewater, particularly desulfurization wastewater of a coal-fired power plant and coal chemical wastewater. By combining efficient flocculation, ozone catalysis and membrane distillation technologies, a self-made chitosan-based flocculant is added in a flocculation stage, and suspended solids and heavy metal ions in wastewater are removed by utilizing good adsorption performance and flocculation capacity of the self-made chitosan-based flocculant; in the ozone catalysis stage, a self-made ternary composite catalyst is added, ozone decomposition is promoted, and organic pollutants are further removed; 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] 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. Particularly in the treatment of desulfurization wastewater and coal chemical wastewater, these wastewaters contain high levels of salt and organic pollutants. As of 2023, the wastewater generated by my country's new coal chemical industry reached 4.745 billion tons per year. 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 include physical, chemical, and biological methods, but most suffer from low treatment efficiency, high costs, and failure to meet discharge standards for treated water. For example, traditional membrane distillation is prone to fouling, ozone catalysis has low efficiency, and traditional flocculants have a heavy metal removal rate of less than 60%. 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, brine carried over from boiler water, and concentrated brine generated from the addition of chemicals during recycled water treatment. Besides the small portion of water enriched in the aforementioned processes, the fresh water used in the project itself also contains a certain amount of salt. For example, in coal chemical projects, the amount of salt introduced by using Yellow River water as fresh water replenishment exceeds 50% of the total salt content of the entire project system. Furthermore, the salt content generated by chemical agents added throughout the production process and water system accounts for 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 volume of difficult-to-treat concentrated brine will still be generated. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention proposes a treatment system design for purifying high-salinity wastewater. This process, through a three-stage combined treatment of flocculation, ozone catalysis, and membrane distillation, significantly improves the treatment efficiency of high-salinity wastewater, 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 utility model 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. When this self-made chitosan-based flocculant was added to wastewater, it exhibited excellent flocculation capabilities, efficiently 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%. 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 range from 1:1:1 to 3:2:1, but the catalyst performance is optimal at a ratio of 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. 3. Membrane distillation stage: PVDF-HEP and SiO2 (mass ratio 8:2) are dissolved in DMAC and electrospun (voltage 18 kV, flow rate 1 mL / h) to form a base membrane; chitosan solution (2 wt%) is electrosprayed onto the surface of the base membrane, with a coating thickness of 1–2 μm, to obtain a self-made composite membrane. The self-made composite membrane is used to treat wastewater by membrane distillation. Membrane distillation technology is a process of purifying wastewater by separating water vapor from salts in 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 maintains high-efficiency processing capacity during long-term use thanks to its excellent membrane flux and outstanding antifouling properties.

[0007] The treatment system of this utility model includes the following key components: a high-efficiency flocculation reaction component, which adds 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 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] The beneficial effects of this invention are:

[0012] 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:

[0013] 1. High Efficiency: The three-stage combined treatment process complements each other, significantly improving the treatment efficiency of high-salinity wastewater and removing various pollutants from the water. 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. 3. Environmental Friendliness: This process not only treats high-salinity wastewater but also recycles purified water, achieving the goal of wastewater resource utilization and demonstrating good environmental benefits. 4. Simple Operation: The operation process of each stage is simple, facilitating industrial application and promotion. 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

[0014] 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.

[0015] In the attached diagram:

[0016] Figure 1 This is a flowchart of the high-salt wastewater purification treatment system design of this utility model.

[0017] 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. Detailed Implementation

[0018] In the specific implementation process, the wastewater first goes through the flocculation stage, and an appropriate amount of chitosan-based flocculant is added to make the suspended solids and heavy metal pollutants in the water flocculate and settle. Then, the wastewater enters the ozone catalysis stage, and a self-made ternary composite catalyst is added to promote ozone decomposition under catalysis and oxidize and degrade the organic pollutants in the wastewater. Finally, the wastewater enters the membrane distillation stage, and the water is distilled through the composite membrane to remove salt and dissolved pollutants, and purified water that meets the discharge standards is obtained. (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 the color removal rate, and reducing the content of heavy metal ions, suspended solids and heavy metal ions are effectively removed. (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) in a molar ratio of 1:1:0.5 loaded on a fly ash carrier. The specific surface area of ​​the carrier is ≥300 m² / g, the specific surface area of ​​the catalyst is ≥150 m² / g, the ozone dosage is 50–100 mg / L, the reaction temperature is 40–60℃, the residence time is 30–60 minutes, and the COD is degraded to ≤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. The surface is coated with a chitosan coating by electrospraying. The membrane pore size is 0.1–0.3 μm, the operating temperature is 60–80℃, the transmembrane pressure difference is 10–20 kPa, and the desalination rate is ≥99.5%. Example

[0019] The treatment parameters for a certain coal chemical wastewater (salt content 15,000 mg / L, COD 500 mg / L) are as follows:

[0020] (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.

[0021] (2) Ozone catalytic 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) 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℃ and the residence time is 45 minutes.

[0022] (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 15 kPa.

[0023] After processing using this process:

[0024] Flocculation stage: Suspended solids removal rate 95%, heavy metal (As, Hg) removal rate ≥90%;

[0025] Ozone catalysis stage: COD reduced to 45 mg / L; catalyst activity retention rate ≥85% after 5 cycles;

[0026] Membrane distillation stage: product water conductivity ≤50 μS / cm, desalination rate 99.8%.

[0027] Compared to traditional processes, such as single membrane distillation consuming 2.5 kWh / m³, this invention consumes only 1.8 kWh / m³. 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 module is ≥18 L / m²·h (initial flux 20 L / m²·h, after 100 hours).

[0028] 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 treatment system for purifying high-salinity wastewater, characterized in that, The key components include: (1) a high-efficiency flocculation reaction component, which adds chitosan-based flocculant and adjusts the pH of the wastewater to 6.5–7.5; (2) an ozone catalytic reaction component, which incorporates a Mn-Ce-Bi ternary composite catalyst with a Mn, Ce, and Bi molar ratio of 2:1:1; and (3) a membrane distillation component, which uses a composite membrane based on PVDF-HEP and superhydrophobic SiO2. The outlet of the high-efficiency flocculation reaction unit is connected to the inlet of the ozone catalytic reaction unit, and the outlet of the ozone catalytic reaction unit is connected to the inlet of the membrane distillation unit.

2. The high-salinity wastewater purification system according to claim 1, characterized in that, 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.

3. The high-salinity wastewater purification system according to claim 1, characterized in that, 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.

4. The high-salinity wastewater purification system according to claim 1, characterized in that, 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.

5. The high-salinity wastewater purification system according to claim 1, characterized in that, The composite membrane is prepared by electrospinning using PVDF-HEP and superhydrophobic SiO2 as spinning solutions to form the base membrane; the final composite membrane is obtained by electrospraying chitosan flocculant.

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