A kind of enhanced coagulation water treatment method based on in-situ PCP generation

Abstract

The application discloses a kind of based on in-situ generation PCPs's reinforced coagulation water treatment method, including the following steps: 1) pre-preparation metal salt solution;2) pre-preparation organic ligand solution;3) metal salt solution and organic ligand solution are added to the wastewater to be treated under stirring condition;4) PCPs is generated under the action of coordination reaction, and it is adsorbed and encapsulated to its inside in the process of crystallization;5) PCPs and its inside pollutant start to settle under the action of gravity after stopping stirring;6) PCPs and pollutant are accumulated in the bottom of container after settling, so as to achieve the purpose of removing dissolved pollutants in wastewater.The application removes pollutants by in-situ synthesis of PCPs in pollutant solution, which not only has significant removal effect on PFOA, but also shows application potential in the adsorption of other types of pollutants, has cost advantage and broad application prospect.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and more specifically to a method for treating coagulated water based on in-situ generation of PCPs. Background Technology

[0002] In recent years, perfluorinated and polyfluoroalkyl compounds (PFAS) have become a hot topic in water treatment due to their widespread presence in the global aquatic environment and their difficulty in natural degradation, posing a significant potential health risk to humans. Adsorption is the most common method for removing PFAS from water, and porous coordination polymers (PCPs), as a novel adsorbent, offer significant advantages in terms of high efficiency, selectivity, and designability, making them particularly suitable for the deep removal of PFAS from water. However, the use of PCPs suffers from drawbacks such as demanding synthesis conditions, high cost, and low yield, highlighting the urgent need to develop low-cost methods for using PCPs.

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

[0004] The purpose of this invention is to overcome the drawbacks of high energy consumption, cumbersome preparation, and high cost in the process of using PCPs for wastewater adsorption treatment. For the first time, it provides a similar enhanced coagulation water treatment method based on in-situ generation of PCPs. This method can effectively solve the defects of existing technologies and provide a new approach for the application of PCPs in water treatment and the treatment of various water pollutants.

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

[0006] A method for treating wastewater based on in-situ generation of PCPs is provided, comprising the following steps: 1) pre-preparing a metal salt solution; 2) pre-preparing an organic ligand solution; 3) adding the metal salt solution and the organic ligand solution to the wastewater to be treated under stirring conditions; 4) generating PCPs through coordination reaction, which adsorb and encapsulate dissolved pollutants in the water during crystallization; 5) after stirring is stopped, the PCPs and the pollutants inside begin to settle under gravity; 6) after settling, the PCPs and pollutants accumulate at the bottom of the container, thereby achieving the purpose of removing dissolved pollutants from the wastewater.

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

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

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

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

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

[0012] Preferably, the dissolved contaminant is a perfluorinated compound or the like. By way of example, and not limitation, the target contaminant is perfluorooctanoic acid (PFOA).

[0013] According to the present invention, a method for treating water using a type of enhanced coagulation is provided for the first time. The technical principle involves adding two or more agents to wastewater under stirring conditions. At least one agent reacts with another in solution to generate PCPs, typically containing a metal salt and an organic ligand. After the prepared solution is added to the wastewater, PCPs are generated through a coordination reaction. During the generation process, the PCPs adsorb dissolved pollutants in the wastewater in situ and encapsulate them within the PCPs. After the reaction is stopped for a period of time, the PCPs carry the pollutants to the bottom of the container, thereby achieving effective removal of dissolved pollutants. While the core mechanisms of enhanced coagulation and reinforced coagulation in generating flocs with adsorption properties differ, they are two parallel technologies. However, enhanced coagulation is similar to reinforced coagulation in terms of the dosing step (liquid agent), reaction appearance (large amounts of precipitable flocs), and application (removal of dissolved pollutants from water). Therefore, this invention names it enhanced coagulation.

[0014] This invention employs a combination of PCPs capable of reacting at room temperature to form crystals, with the crystallization reaction occurring directly in the pollutant solution. By utilizing the transition states of amorphous gel and metastable crystals during the nucleation and growth of PCPs, it overcomes the mass transfer resistance caused by the fixed pore size distribution of the formed PCP crystals, thereby enabling in-situ adsorption and encapsulation removal of dissolved pollutants in the solution. This invention is similar in operation to enhanced coagulation technology, with low energy consumption, simplicity, and effectiveness, and has broad application prospects in the field of water treatment.

[0015] Compared with the enhanced coagulation method, the enhanced coagulation method provided by the present invention produces flocculent precipitates with superior adsorption effects, and its application does not require the presence of suspended solids or colloids in the water. Compared with the addition of prepared PCPs, this method avoids the cumbersome and high-cost synthesis process. Therefore, the enhanced coagulation method has a strong cost advantage and application potential.

[0016] The advantages of this invention will be analyzed below, using the enhanced coagulation method and the room temperature stirring method for preparing PCPs adsorption as existing technologies.

[0017] Compared with enhanced coagulation methods:

[0018] 1) Water treatment performance:

[0019] The enhanced coagulation method of the present invention produces flocculent precipitates (PCPs) with superior performance in removing dissolved pollutants. Moreover, the enhanced coagulation method of the present invention can generate a large amount of flocculent precipitates to remove pollutants without the presence of suspended solids or colloids.

[0020] 2) Cost and process complexity:

[0021] Enhanced coagulation methods often fail to achieve ideal treatment results when suitable suspended matter or colloids are unavailable. In some cases, increasing coagulant dosage or adjusting reaction conditions may be necessary, but these measures may still fall short of treating complex pollutants and can lead to higher costs and increased operational complexity. The enhanced coagulation method of this invention is an in-situ adsorption and encapsulation method that works simply by mixing two solutions, avoiding the complex condition adjustment processes of enhanced coagulation. It also offers cost advantages and is simpler to operate.

[0022] Compared with PCPs adsorption methods:

[0023] 1) Cost aspect:

[0024] While PCPs materials perform well as adsorbents, their high preparation cost hinders mass production. The enhanced coagulation method of this invention, however, involves in-situ adsorption and encapsulation of two solutions to remove pollutants, avoiding the cumbersome preparation process of PCPs materials, reducing costs, improving economic feasibility, and making it more suitable for large-scale water treatment applications.

[0025] 2) Regeneration and resource utilization potential:

[0026] In PCPs adsorption methods, the treatment of saturated PCPs materials is relatively complex, and the regeneration cost can be high. The precipitate formed by the enhanced coagulation method of this invention can be degraded and mineralized through subsequent pyrolysis, and the pyrolysis products have the potential for resource utilization.

[0027] In summary, compared with the two methods mentioned above, the enhanced coagulation method provided by this invention can generate a large number of flocs to remove pollutants without the need for suspended matter, and the flocs are essentially PCPs, exhibiting good adsorption and encapsulation effects. Furthermore, this method is an in-situ pollutant removal process that simply mixes two solutions, avoiding the cumbersome preparation process of high-adsorption-performance PCPs materials and reducing usage costs.

[0028] This invention differs significantly from existing pollutant treatment methods by directly adding organic ligand solutions and metal salt solutions to pollutant solutions, utilizing in-situ formation of PCPs for adsorption and encapsulation. This innovative approach has the potential to transform existing water treatment processes and methods, offering numerous advantages such as improved treatment efficiency or reduced treatment costs.

[0029] It should be understood that, following this approach, there are many known and unknown reagent schemes, or various factors can be modified to optimize the performance of enhanced coagulation, or water treatment processes incorporating enhanced coagulation can be created. According to the definition of enhanced coagulation, the methods mentioned above involving the in-situ generation of porous coordination polymers in water using coordination interactions to adsorb and encapsulate pollutants all fall under the category of the enhanced coagulation water treatment method proposed in this invention.

[0030] Currently, we have experimentally verified the effectiveness of enhanced coagulation-like water treatment methods for PFOA removal. Enhanced coagulation-like methods have multiple advantages for treating recalcitrant organic pollutants like PFOA, such as the relatively low-cost formation of PCPs for effective adsorption and encapsulation of pollutants. The precipitate formed after encapsulation and adsorption facilitates solid-liquid separation of pollutants, and the PCPs precipitate containing pollutants can be degraded and mineralized through subsequent pyrolysis. Furthermore, the pyrolysis products have the potential for resource utilization. Enhanced coagulation-like methods also have application potential in the adsorption of other pollutants.

[0031] In summary, the enhanced coagulation water treatment method based on in-situ PCP generation provided by this invention focuses on utilizing the adsorption and encapsulation capabilities of PCPs during their formation process to remove pollutants by synthesizing PCPs in situ within the pollutant solution. This in-situ synthesis and treatment approach breaks with the conventional thinking of synthesizing PCPs before using them for adsorption and pollutant removal, thus pioneering a new water treatment method. This method not only demonstrates significant removal efficiency for PFOA but also shows application potential in the removal of other pollutants, offering cost advantages and broad application prospects. Attached Figure Description

[0032] Figure 1A flowchart of a method for treating coagulated water based on in-situ generation of PCPs, according to the present invention, is shown.

[0033] Figure 2 The performance comparison between enhanced coagulation and similar enhanced coagulation is shown;

[0034] Figure 3 The performance comparison between enhanced coagulants and corresponding PCPs is shown. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the techniques used in the embodiments are conventional practices in the art, or experimental methods recommended by the instrument manufacturer. Unless otherwise specified, the reagents and materials used in the embodiments are commercially available.

[0036] Please see Figure 1 , Figure 1 A flowchart of a method for treating coagulated water based on in-situ generation of PCPs, provided by this invention, is 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) Metal salt solution A and organic ligand solution B are added to the wastewater to be treated under stirring. PCPs can be generated through coordination reaction between the two.

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

[0041] 5) The downward arrow here represents the effect of gravity. After stirring is stopped, the PCPs and the contaminants inside them begin to settle under the influence of gravity.

[0042] 6) After settling, PCPs and pollutants accumulate at the bottom of the container, thereby achieving the purpose of removing dissolved pollutants from wastewater.

[0043] As an example, this embodiment of the invention selects PFOA as the dissolved pollutant. Three enhanced coagulation schemes were combined (polyaluminum chloride alone, cationic polyacrylamide alone, and PAC+PAM), and six enhanced coagulation schemes were developed (triphenyl phthalic acid + ferric nitrate, triphenyl phthalic acid + ferrous acetate, 2-methylimidazole + ferric nitrate, 2-methylimidazole + ferrous sulfate, 2-methylimidazole + ferrous acetate, and 2-methylimidazole + copper sulfate). An additional blank control group was also established. The PCPs formed by the six enhanced coagulation combinations were isolated, and their removal performance for PFOA was tested.

[0044] Example 1

[0045] PAC / PAM alone: ​​At room temperature, first add 10 mL of PFOA (2 mg / L) solution to a 100 mL polypropylene (PP) beaker, then add 40 mL of deionized water. In another beaker, add 50 mL of deionized water and 0.054 g of PAC / PAM. Adjust the initial pH of the PFOA solution to 8-9 using 0.1 mol / L NaOH solution. Then, add the coagulant solution to the PFOA solution under stirring, first stirring rapidly for 5 min, then stirring slowly and continuously for 1 h, and allowing it to stand until the supernatant is clear. Take a sample from the supernatant for analysis.

[0046] PAC+PAM: First, add 10 mL of PFOA (2 mg / L) solution to a 100 mL PP beaker, then add 40 mL of deionized water. In a second beaker, add 40 mL of deionized water and 0.054 g of PAC. In a 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 while stirring. After 1-2 minutes, add the PAM solution. Stir rapidly for 5 minutes, then stir slowly for 1 hour. Let it stand until the supernatant is clear, then take a sample from the supernatant for analysis.

[0047] Enhanced coagulation: First, add 10 mL of PFOA (2 mg / L) solution to a 100 mL PP beaker, then add 40 mL of deionized water and dissolve the organic ligand (0.054 g). In another beaker, add 50 mL of deionized water and dissolve 0.054 g of the metal salt. Then, add the metal salt solution under stirring conditions, stir rapidly for 5 min, then stir slowly and continuously for 1 h, and let stand until the supernatant is clear. Take a sample of the supernatant for testing.

[0048] Experimental results are as follows Figure 2As shown, the five enhanced coagulation combinations achieved better removal effects than enhanced coagulation. Among them, pyromellitic acid + ferric nitrate and 2-methylimidazole + copper sulfate had the best effects, with a maximum PFOA removal rate of 93.6%.

[0049] Example 2

[0050] First, 50 mL of deionized water and 0.054 g of metal salt were dissolved in six beakers respectively. In another six beakers, 50 mL of deionized water and 0.054 g of organic ligand were dissolved. The metal salt solution was added while stirring the organic ligand solution. The mixture was first stirred rapidly for 5 min, then slowly and continuously stirred for 1 h. The solutions were then centrifuged, and the precipitate was dried overnight at 60°C in an oven, then ground for later use. Next, 100 mL of PFOA (200 μg / L) solution was prepared in 100 mL PP beakers. After thorough mixing, a sample was taken as the initial value. Then, powdered PCPs prepared from the six groups of enhanced coagulation combinations were added to each beaker. After stirring for 60 min and allowing to stand, samples were taken again from the supernatant for analysis.

[0051] Experimental results are as follows Figure 3 As shown, the removal effect of the six types of enhanced coagulation combinations is far superior to that of the corresponding PCPs materials. Among them, pyromellitic acid + ferric nitrate and 2-methylimidazole + copper sulfate have the best effects.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. All simple and equivalent changes and modifications made in accordance with the claims and description of this application fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A method for treating coagulated water based on in-situ generation of PCPs, characterized in that, Includes the following steps: 1) Prepare the metal salt solution in advance; 2) Prepare organic ligand solutions in advance; 3) The metal salt solution and the organic ligand solution are added to the wastewater to be treated under stirring conditions; 4) The metal salt solution and the organic ligand solution undergo a coordination reaction in the wastewater to generate PCPs in situ. During the crystallization process, the PCPs adsorb and encapsulate dissolved pollutants in the water in situ. 5) After stirring is stopped, the PCPs and adsorbed pollutants begin to settle under the influence of gravity; 6) After settling, PCPs and pollutants accumulate at the bottom of the container, achieving the purpose of removing dissolved pollutants from the wastewater; The combination of metal salt and organic ligand is selected from: ferric nitrate and pyromellitic acid, copper sulfate and 2-methylimidazole.

2. The enhanced coagulation water treatment method according to claim 1, characterized in that, The dosage of both metal salts and organic ligands ranged from 0.01 g / L to 10 g / L.

3. The enhanced coagulation water treatment method according to claim 2, characterized in that, The molar ratio of metal to organic ligand is metal:organic ligand = 1:1 to 1:

8.

4. The enhanced coagulation water treatment method according to claim 1, characterized in that, The dissolved contaminants are perfluorinated and polyfluorinated alkyl compounds.

5. The enhanced coagulation water treatment method according to claim 4, characterized in that, The perfluorinated and polyfluoroalkyl compounds include perfluorooctanoic acid.

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