Strengthening-like coagulation water treatment technology based on in-situ generation of PCPs

Abstract

The invention discloses a similar reinforced coagulation water treatment technology based on in-situ generation of PCPs (Personal Computer Products). The technology comprises the following steps: 1) preparing a metal salt solution in advance; 2) preparing an organic ligand solution in advance; 3) adding the metal salt solution and the organic ligand solution into the wastewater to be treated under a stirring condition; (4) generating PCPs (Personal Computer Products) under the action of coordination reaction, and adsorbing and packaging dissolved pollutants in water into the PCPs in a crystallization process; (5) after stirring is stopped, PCPs and pollutants in the PCPs start to settle under the action of gravity; and (6) accumulating the settled PCPs and pollutants at the bottom of the container so as to achieve the purpose of removing the dissolved pollutants in the wastewater. According to the method, pollutants are removed by in-situ synthesis of PCPs in a pollutant solution, so that the method has a remarkable removal effect on PFOA (perfluorooctanoic acid), also shows application potential in adsorption of other types of pollutants, and has a cost advantage and a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and more particularly to a coagulation-like water treatment technology based on in-situ generation of PCPs. Background Art

[0002] In recent years, per- and polyfluoroalkyl substances (PFAS) have become a hot topic in the field of water treatment due to their widespread presence in the global water environment and their resistance to natural degradation, posing a huge potential health risk to humans. Adsorption is the most commonly used method for removing PFAS from water. As a new type of adsorbent, porous coordination polymers (PCPs) have outstanding advantages in terms of high efficiency, selectivity, and designability, and are particularly suitable for the deep removal of PFAS in water. However, the use of PCPs has the disadvantages of harsh synthesis conditions, high cost, and low yield, and there is an urgent need to develop low-cost methods for using PCPs.

[0003] The preparation of PCPs by room-temperature stirring synthesis has great practical application potential due to its simple synthesis conditions and low cost. However, the formed PCPs still need to be filtered, dried, and washed before use, which brings a series of costs and makes the synthesis steps more cumbersome. Therefore, it is necessary to continue to develop more simple and effective methods for using PCPs. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of high energy consumption, cumbersome preparation, and high cost in the process of using PCPs for wastewater adsorption treatment. For the first time, a coagulation-like water treatment technology based on in-situ generation of PCPs is provided. This method can effectively solve the defects of the existing technology and provide a new idea for the water treatment application of PCPs and the treatment of various water pollutants.

[0005] To solve the above problems, the present invention adopts the following technical solutions:

[0006] Provide a coagulation-like water treatment technology based on in-situ generation of PCPs, including the following steps: 1) Prepare a metal salt solution in advance; 2) Prepare an organic ligand solution in advance; 3) Add the metal salt solution and the organic ligand solution to the wastewater to be treated under stirring conditions; 4) The two react under the action of coordination reaction to generate PCPs, which adsorb and encapsulate the dissolved pollutants in the water into their interiors during the crystallization process; 5) After stopping stirring, the PCPs and the pollutants inside them start to settle under the action of gravity; 6) The settled PCPs and pollutants accumulate at the bottom of the container, thereby achieving the purpose of removing the dissolved pollutants in the wastewater.

[0007] Preferably, the metal salts include: zinc nitrate, zinc acetate, copper sulfate, copper nitrate, iron nitrate, ferric chloride, ferrous sulfate, iron acetate, cobalt nitrate, cobalt acetate, nickel nitrate, nickel acetate, manganese nitrate, manganese chloride, etc.

[0008] Preferably, the organic ligands include: 2-methylimidazole, terephthalic acid, 2-aminoterephthalic acid, 2,5-dihydroxyterephthalic acid, 5-methylisophthalic acid, 4,4'-biphenyldicarboxylic acid, trimesic acid, pyridine derivatives, etc.

[0009] Preferably, the dosage of the metal salt and the organic ligand is both 0.01 g / L - 10 g / L.

[0010] Preferably, the molar ratio of the metal to the organic ligand is metal∶organic ligand = 1∶1 - 1∶8.

[0011] Preferably, the combination of the metal salt and the organic ligand can be selected from: trimesic acid + iron nitrate, trimesic acid + ferrous acetate, 2-methylimidazole + iron nitrate, 2-methylimidazole + ferrous sulfate, 2-methylimidazole + ferrous acetate, 2-methylimidazole + copper sulfate, trimesic acid + zinc nitrate, 2-methylimidazole + zinc nitrate.

[0012] Preferably, the dissolved pollutants are perfluorinated compounds, etc. By way of example and not limitation, the target pollutant is perfluorooctanoic acid (PFOA).

[0013] According to the present invention, a kind of enhanced coagulation-like water treatment technology is provided for the first time. Its technical principle is that by adding two or more kinds of medicaments to the wastewater under stirring conditions, at least one of the medicaments can react with another in the solution to generate PCPs, usually including a metal salt and an organic ligand. After the prepared solution is added to the wastewater, PCPs can be generated through a coordination reaction. During the generation process of PCPs, the dissolved pollutants in the wastewater are adsorbed in-situ and encapsulated inside the PCPs. After stirring is stopped for a period of time, the PCPs carry the pollutants and precipitate to the bottom of the container, thereby effectively removing the dissolved pollutants. The mechanism core of enhanced coagulation-like is different from that of enhanced coagulation which generates flocs with adsorption performance, so they are two parallel technologies. However, enhanced coagulation-like is similar to enhanced coagulation in terms of the dosing step (liquid medicament), reaction appearance (a large amount of precipitable flocs), and use (removing dissolved pollutants in water body), so the present invention names it enhanced coagulation-like.

[0014] The present invention adopts a combination that can react at room temperature to form PCPs, and directly carries out the crystallization reaction in the pollutant solution. Utilizing the transition states such as amorphous gel and metastable crystal form experienced during the nucleation and growth process of PCPs, it breaks through the mass transfer resistance caused by the fixed pore size distribution of the formed PCPs crystals, thereby adsorbing and encapsulating and removing the dissolved pollutants in the solution in-situ. The operation form of the present invention is similar to that of the enhanced coagulation technology, with low process energy consumption, simple and effective, and has broad application prospects in the field of water treatment.

[0015] Compared with the enhanced coagulation technology provided by the present invention, the flocculent precipitate produced has a more excellent adsorption effect, and the application does not require the presence of suspended solids or colloids in water; compared with adding the prepared PCPs, this technology avoids the cumbersome and high cost in the synthesis process. Therefore, the enhanced coagulation-like technology has strong cost advantages and application potential.

[0016] The following mainly takes the enhanced coagulation technology and the PCPs adsorption technology prepared by the room temperature stirring method as the prior art to analyze the advantages of the present invention.

[0017] Compared with the enhanced coagulation technology:

[0018] 1) Water treatment performance:

[0019] The flocculent precipitate (PCPs) produced by the enhanced coagulation-like technology of the present invention has a more excellent performance in removing dissolved pollutants, and the enhanced coagulation-like technology of the present invention can generate a large amount of flocculent precipitate to play the role of pollutant removal without the presence of suspended solids or colloids.

[0020] 2) Cost and process complexity:

[0021] When there are no suitable suspended substances or colloids, it is difficult for the enhanced coagulation technology to achieve an ideal treatment effect. And in some cases, it may be necessary to increase the dosage of the coagulant, adjust the reaction conditions and other means, but it may still not meet the treatment requirements of complex pollutants, and may bring higher costs and more operation complexity. The enhanced coagulation-like technology of the present invention is an in-situ adsorption and encapsulation technology, which can play a role by simply mixing two solutions, avoiding the complex condition adjustment process in enhanced coagulation, and having cost advantages and more convenient operation.

[0022] Compared with the PCPs adsorption technology:

[0023] 1) In terms of cost:

[0024] Although the PCPs material as an adsorbent has good effects, the material preparation cost is high, and it is difficult to achieve mass production and application. The enhanced coagulation-like technology of the present invention is an in-situ adsorption and encapsulation process for removing pollutants by simply mixing two solutions, avoiding the cumbersome preparation process like the PCPs material, reducing the use cost, improving the economic feasibility, and being more suitable for large-scale water treatment applications.

[0025] 2) Regeneration and resource utilization potential:

[0026] In the PCPs adsorption technology, the treatment of the PCPs material saturated with adsorption is relatively complex, and the regeneration cost may be high. The precipitate formed by the enhanced coagulation-like technology of the present invention can achieve the degradation and mineralization of pollutants through subsequent pyrolysis, and the products after pyrolysis have the potential for resource utilization.

[0027] In summary, compared with the above two technologies, the enhanced coagulation technology provided by the present invention can generate a large number of flocs to remove pollutants without the need for suspended matter, and the essence of the flocs is PCPs, which has good adsorption and encapsulation effects. At the same time, the technology is an in-situ pollutant removal process of simply mixing two solutions, avoiding the cumbersome preparation process of high-adsorption PCPs materials and reducing the cost of use.

[0028] The present invention directly adds organic ligand solution and metal salt solution into pollutant solution, and utilizes the technical idea of ​​in-situ formation of PCPs for adsorption and encapsulation, which is significantly different from the existing pollutant treatment technology. This technological innovation has many potential advantages, such as changing the existing water treatment process and methods, improving treatment efficiency or reducing treatment costs.

[0029] It should be understood that under the concept of this technology, there are many proven or unproven pharmaceutical solutions, or changing various factors to optimize the performance of quasi-enhanced coagulation, or creating some water treatment processes that include quasi-enhanced coagulation. According to the definition of quasi-enhanced coagulation, the above methods involving the use of coordination to generate porous coordination polymers in situ in water to adsorb and encapsulate pollutants all belong to the quasi-enhanced coagulation water treatment technology proposed by the present invention.

[0030] At present, we have verified the effectiveness of enhanced coagulation water treatment technology for PFOA removal through experiments. Enhanced coagulation has multiple advantages in treating difficult-to-degrade organic pollutants such as PFAS, such as the formation of PCPs at a relatively low cost to effectively adsorb and encapsulate pollutants. The precipitate formed after encapsulation and adsorption is easy to achieve solid-liquid separation of pollutants. The PCPs precipitate containing pollutants can be degraded and mineralized through subsequent pyrolysis. At the same time, the products after pyrolysis also have the potential to be used as resources. Enhanced coagulation also has application potential in the adsorption of other pollutants.

[0031] In summary, the core of the quasi-enhanced coagulation water treatment technology based on in-situ generation of PCPs provided by the present invention is to utilize the ability of PCPs materials to adsorb and encapsulate dissolved pollutants in water during their formation process, and to remove pollutants by in-situ synthesis of PCPs in pollutant solutions. This idea of ​​in-situ synthesis and treatment breaks the conventional thinking that traditional PCPs materials are synthesized and then used for adsorption and removal of pollutants, and opens up a new water treatment method. This technology not only has a significant removal effect on PFOA, but also shows application potential in the removal of other pollutants, with cost advantages and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1Shows a flow chart of a coagulation-like water treatment technology based on in-situ generation of PCPs provided by the present invention;

[0033] Figure 2 Shows the performance comparison between enhanced coagulation and coagulation-like;

[0034] Figure 3 Shows the performance comparison between coagulation-like and the corresponding PCPs. Specific embodiments

[0035] The following further describes the present invention in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional operations in the art or experimental methods recommended by instrument equipment manufacturers. The reagents and materials used in the embodiments can be obtained from commercial sources unless otherwise specified.

[0036] Please refer to Figure 1 , Figure 1 , which is a flow chart of a coagulation-like water treatment technology based on in-situ generation of PCPs provided by the present invention. As shown in the figure, the method includes the following steps:

[0037] 1) Prepare metal salt solution A in advance;

[0038] 2) Prepare organic ligand solution B in advance;

[0039] 3) Add metal salt solution A and organic ligand solution B to the wastewater to be treated under stirring conditions. Under the action of coordination reaction, PCPs can be generated;

[0040] 4) The circular symbols in the figure represent dissolved pollutants in the wastewater, which can be encapsulated and adsorbed after the generation of PCPs;

[0041] 5) The downward arrow here represents the action of gravity. After stopping stirring, PCPs and the pollutants inside them start to settle under the action of gravity;

[0042] 6) The settled PCPs and pollutants accumulate at the bottom of the container, thereby achieving the purpose of removing dissolved pollutants in the wastewater.

[0043] For example, in the embodiments of the present invention, PFOA is selected as the dissolved pollutant. Three enhanced coagulation schemes are combined (single polyaluminum chloride (PAC), single cationic polyacrylamide (PAM), PAC + PAM), six types of enhanced coagulation schemes (trimellitic acid + iron nitrate, trimellitic acid + ferrous acetate, 2-methylimidazole + iron nitrate, 2-methylimidazole + ferrous sulfate, 2-methylimidazole + ferrous acetate, 2-methylimidazole + copper sulfate), and an additional blank control group is set up. The PCPs formed by six types of enhanced coagulation combinations are separated, and their removal performance for PFOA is tested.

[0044] Example 1

[0045] Single PAC / PAM: At room temperature, first add 10 mL of PFOA (2 mg / L) solution into a 100 mL polypropylene (PP) beaker, and then add 40 mL of deionized water. In another beaker, add 50 mL of deionized water and 0.054 g of PAC / PAM. Use 0.1 mol / L NaOH solution to adjust the initial pH of the PFOA solution to 8 - 9. Then, under stirring conditions, add the coagulant solution into the PFOA solution, stir rapidly for 5 min first, then stir slowly and continuously for 1 h and let it stand. After the supernatant is clarified, take a sample from the supernatant for detection.

[0046] PAC + PAM: First add 10 mL of PFOA (2 mg / L) solution into a 100 mL PP beaker, and then add 40 mL of deionized water. In the second beaker, add 40 mL of deionized water and 0.054 g of PAC, and in the third beaker, add 10 mL of deionized water and 0.054 g of PAM. Adjust the pH of the PFOA solution to 8 - 9, then add the PAC solution under stirring conditions, and add the PAM solution 1 - 2 min later. Stir rapidly for 5 min first, then stir slowly and continuously for 1 h and let it stand. After the supernatant is clarified, take a sample from the supernatant for detection.

[0047] Enhanced coagulation of a certain type: First add 10 mL of PFOA (2 mg / L) solution into a 100 mL PP beaker, then add 40 mL of deionized water, and simultaneously add the organic ligand for dissolution (0.054 g). In another beaker, add 50 mL of deionized water and 0.054 g of metal salt for dissolution. Then, under stirring conditions, add the metal salt solution, stir rapidly for 5 min first, then stir slowly and continuously for 1 h and let it stand. After the supernatant is clarified, take a sample from the supernatant for detection.

[0048] The experimental results are as Figure 2 shown. Five types of enhanced coagulation combinations achieved better removal effects than enhanced coagulation. Among them, trimellitic acid + iron nitrate and 2-methylimidazole + copper sulfate had the best effects, with a maximum PFOA removal rate of up to 93.6%.

[0049] Example 2

[0050] First, add 50 mL of deionized water and 0.054 g of metal salt to six beakers respectively for dissolution, and add 50 mL of deionized water and 0.054 g of organic ligand to another six beakers for dissolution. While stirring the organic ligand solution, add the metal salt solution. First, stir rapidly for 5 min, and then stir slowly and continuously for 1 h. Then centrifuge the solution, separate the precipitate, dry it overnight in an oven at 60 °C, and then grind it for standby. Subsequently, prepare 100 mL of PFOA (200 μg / L) solution in 100 mL PP beakers respectively. After mixing evenly, take samples as the initial values, and then add the powdered PCPs prepared by six groups of enhanced coagulation combinations respectively. After stirring for 60 min, let it stand, and take samples again for detection in the supernatant respectively.

[0051] The experimental results are as Figure 3 shown. The removal effects of the six groups of enhanced coagulation combinations are far better than those of the corresponding PCPs materials. Among them, trimesic acid + ferric nitrate and 2-methylimidazole + copper sulfate have the best effects.

[0052] The above-mentioned are only the preferred embodiments of the present invention, and are not used to limit the scope of the present invention. Various changes can be made to the above embodiments of the present invention. All simple, equivalent changes and modifications made according to the claims and the content of the specification of the present invention application fall within the scope of the claims of the present invention patent. The content not described in detail in the present invention is all conventional technical content.

Claims

1. A kind of enhanced coagulation-like water treatment technology based on in-situ generation of PCPs, characterized in that, It includes the following steps: 1) Prepare a metal salt solution in advance; 2) Prepare an organic ligand solution in advance; 3) Add the metal salt solution and the organic ligand solution to the wastewater to be treated under stirring conditions; 4) The metal salt solution and the organic ligand solution react coordinatively to form PCPs, which adsorb and encapsulate the dissolved pollutants in water into their interiors during the crystallization process; 5) After stopping stirring, the PCPs and the adsorbed pollutants start to settle under the action of gravity; 6) The settled PCPs and pollutants accumulate at the bottom of the container, achieving the purpose of removing the dissolved pollutants in the wastewater.

2. The enhanced coagulation-like water treatment technology according to claim 1, wherein The metal salts include: zinc nitrate, zinc acetate, copper sulfate, copper nitrate, iron nitrate, iron chloride, ferrous sulfate, iron acetate, cobalt nitrate, cobalt acetate, nickel nitrate, nickel acetate, manganese nitrate, manganese chloride.

3. The enhanced coagulation-like water treatment technology according to claim 1, characterized in that, The organic ligands include: 2-methylimidazole, terephthalic acid, 2-aminoterephthalic acid, 2,5-dihydroxyterephthalic acid, 5-methylisophthalic acid, 4,4'-biphenyldicarboxylic acid, trimesic acid, pyridine derivatives.

4. The enhanced coagulation-like water treatment technology according to claim 1, wherein, The dosage of both the metal salt and the organic ligand is 0.01 g / L - 10 g / L.

5. The enhanced coagulation-like water treatment technology according to claim 1, characterized in that, The molar ratio of the metal to the organic ligand is metal∶organic ligand = 1∶1 - 1∶8.

6. The enhanced coagulation-like water treatment technology according to claim 1, wherein The combinations of the metal salt and the organic ligand are selected from: trimesic acid + iron nitrate, trimesic acid + ferrous acetate, 2-methylimidazole + iron nitrate, 2-methylimidazole + ferrous sulfate, 2-methylimidazole + ferrous acetate, 2-methylimidazole + copper sulfate, trimesic acid + zinc nitrate, 2-methylimidazole + zinc nitrate.

7. The enhanced coagulation-like water treatment technology according to claim 1, characterized in that, The dissolved pollutants are per- and polyfluoroalkyl substances.

8. The enhanced coagulation-like water treatment technology according to claim 7, characterized in that, The per- and polyfluoroalkyl substances include perfluorooctanoic acid.

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