Integrated water treatment process coupling pollutant mineralization and adsorbent preparation

Abstract

The invention discloses an integrated water treatment process for coupling pollutant mineralization and adsorbent preparation. The integrated water treatment process comprises the following steps: 1) removing dissolved pollutants from wastewater through a PCPs-based carbon material adsorption layer; 2) discharging purified water from an outlet; 3) after adsorption saturation, regenerating the PCPs-based carbon material by using the regeneration solution, and discharging high-concentration pollutants along with the regeneration solution; (4) adding an organic ligand and a metal solution into the regeneration solution, generating PCPs through coordination polymerization, adsorbing dissolved pollutants, packaging the pollutants into the PCPs, and enabling the pollutants to enter a sedimentation tank; (5) circulating effluent of the sedimentation tank as a regeneration solution, and collecting PCPs (Personal Computer Products) containing pollutants through a funnel; and 6) drying and pyrolyzing the collected PCPs, mineralizing pollutants and converting the pollutants into a PCPs-based carbon material which can be repeatedly used as an adsorbent. The invention provides a novel water treatment process concept, and the method has a wide application prospect in treatment of refractory organic pollutants in wastewater.

Description

Technical Field

[0001] The present invention relates to the field of water treatment, and more particularly to an integrated water treatment process that couples pollutant mineralization and adsorbent preparation. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are difficult to be naturally degraded due to the extremely stable C-F bonds in their molecules and are called "forever chemicals". PFAS entering the water environment pose a great risk to human health, and more and more researchers have begun to focus on the treatment technologies for PFAS in water. The adsorption method can effectively remove PFAS from water, but the adsorbent saturated with adsorption only transfers PFAS from the aqueous phase. Even if the solvent regeneration is carried out on the saturated adsorbent, the regenerated solvent containing high-concentration PFAS needs to be further treated and disposed of. These practices do not completely solve the health risks brought by PFAS and need further treatment to completely mineralize PFAS. However, if the heat treatment is directly carried out on the regeneration reagent, there are disadvantages such as high energy consumption and large resource consumption.

[0003] Pyrolysis treatment of the adsorbent saturated with adsorption is currently recognized as an effective and stable degradation technology for PFAS. However, there are also potential drawbacks in the pyrolysis process, such as mass loss of the adsorbent, collapse of the pore structure, and deterioration of the adsorption performance. Porous coordination polymers (PCPs) are an excellent precursor of porous carbon materials. During the pyrolysis process, they form a porous carbon skeleton, which not only loads metal sites but also has a developed microporous structure and defects, and is particularly suitable for the deep removal of PFAS in water. It is worth noting that if the formation site of PCPs is set in the regenerated waste liquid to be treated, PFAS in the regeneration solution can be adsorbed and encapsulated into the interior of PCPs during the formation process of PCPs. Then, the PCPs containing high-concentration PFAS are collected for pyrolysis, and the mineralization of PFAS and the preparation of PCPs-based carbon materials can be completed simultaneously. This approach is more economical and effective compared with the traditional method of adding the finished carbon material adsorbent to the wastewater and then pyrolyzing and regenerating it, and can avoid the negative impact of frequent pyrolysis and regeneration on the pore structure of the adsorbent. Summary of the Invention

[0004] The object of the present invention is to provide an integrated water treatment process that couples pollutant mineralization and adsorbent preparation, so as to solve the problem that the existing technology lacks a low-cost and effective wastewater treatment process for refractory organic pollutants.

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

[0006] An integrated water treatment process coupling pollutant mineralization and adsorbent preparation is provided, including the following steps: 1) Wastewater enters the adsorption tower through the inlet, flows through the adsorption layer with PCPs-based carbon material as the adsorbent, and removes the dissolved pollutants in the wastewater through adsorption; 2) The wastewater flows out from the purified water outlet after being purified by the PCPs-based carbon material layer; 3) The PCPs-based carbon material is regenerated by adding a regeneration solution, and the regeneration solution carries high-concentration pollutants and flows out from the regeneration solution outlet; 4) An organic ligand solution and a metal solution are added to the flowing regeneration solution simultaneously or successively, and a coordination polymerization reaction occurs to generate PCPs, adsorb the dissolved pollutants in the regeneration solution and encapsulate them into the interior of PCPs, and after full reaction, it enters the sedimentation tank; 5) The effluent from the sedimentation tank is reused as the regeneration solution again; meanwhile, the PCPs containing high-concentration organic pollutants are collected through the lower funnel; 6) The collected PCPs pass through a dryer and a pyrolyzer, and a pore-forming agent or an activator beneficial to the formation of pore structure is added, and the adsorbed organic pollutants are mineralized into inorganic small molecules during the pyrolysis process, and at the same time, PCPs-based carbon material is formed as the adsorbent of the adsorption tower.

[0007] Preferably, in step 3), the regeneration solution is regenerated by using a mixed solution of water and an organic solvent with adjusted acidity and alkalinity, the volume ratio of the organic solvent = 0-80%, and the acidity and alkalinity adjustment range is from neutral to alkaline.

[0008] Preferably, in step 4), 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.

[0009] 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.

[0010] Preferably, the dosage of the metal salt and the organic ligand is 0.01 g / L - 10 g / L.

[0011] Preferably, the molar ratio of the metal to the organic ligand is metal∶organic ligand = 1∶1 - 1∶8.

[0012] Preferably, the combinations of the metal salt and the organic ligand can be selected from: trimesic acid + iron nitrate, 2-methylimidazole + copper sulfate.

[0013] Preferably, in step 6), pyrolysis is carried out at 400-1000 °C for 1 h - 3 h to achieve the mineralization and decomposition of organic pollutants.

[0014] According to a preferred embodiment of the present invention, in step 6), the collected PCPs can be pyrolyzed into granular carbon, and then added to the adsorption tower for use as an adsorbent.

[0015] Preferably, the pore-forming agent or activator can be selected from ammonium bicarbonate or potassium hydroxide.

[0016] Preferably, the organic pollutant is a perfluoro- and polyfluoroalkyl compound. By way of example and not limitation, the perfluoro- and polyfluoroalkyl compound is perfluorooctanoic acid (PFOA).

[0017] It should be understood that the purpose of the present invention is to provide an integrated water treatment process that couples pollutant mineralization and adsorbent preparation. The embodiments particularly relate to a recycling treatment idea for refractory organic pollutants: that is, the PCPs-based carbon material in the adsorption tower adsorbs and removes organic pollutants in water, and a regeneration solution containing a high concentration of organic matter is generated during its regeneration; the organic pollutants in the regeneration solution then enter the PCPs solid phase through in-situ adsorption and encapsulation during the formation of PCPs; finally, by pyrolyzing the PCPs, while mineralizing the organic pollutants, a PCPs-based carbon material is formed and reused as an adsorbent in the adsorption tower. However, the present invention is not limited to the recycling treatment of refractory organic pollutants and can also be extended to other types of wastewater treatment.

[0018] Based on the in-situ adsorption and encapsulation characteristics of pollutants during the formation of PCPs, the main idea of the present invention is to provide a wastewater treatment process. However, considering that the in-situ adsorption and encapsulation process of pollutants during the formation of PCPs may result in unsatisfactory performance due to the complex composition of the wastewater, and incomplete coordination reaction may cause secondary pollution. Therefore, the present invention creatively provides an integrated water treatment process that couples pollutant mineralization and adsorbent preparation for the first time. By setting the PCPs formation process in the regeneration solution containing pollutants, the treated regeneration solution and unreacted reagents can be recycled. Moreover, this process is particularly targeted at PFAS, such refractory organic pollutants, and has successfully achieved its stable removal and degradation at a relatively low cost.

[0019] Specifically, the present invention uses PCPs-based carbon materials as adsorbents in the adsorption tower for the advanced treatment of refractory organic pollutants such as PFAS in water. After the PCPs-based carbon materials are saturated with adsorption, they are regenerated, and high-concentration refractory organic pollutant waste liquid is desorbed. Subsequently, the dissolved pollutants in the regeneration solution are adsorbed during the PCPs formation process and encapsulated into the interior of the PCPs. The PCPs containing high-concentration pollutants are pyrolyzed to complete the preparation of the PCPs-based carbon materials while mineralizing the pollutants. Finally, the PCPs-based carbon materials are used to fill the adsorption tower. The present invention couples and synchronizes the mineralization of pollutants and the preparation of adsorbents, enhancing the economy of the PCPs-based carbon materials during the adsorption process and having great application potential in the field of treating refractory organic wastewater.

[0020] An integrated water treatment process coupling pollutant mineralization and adsorbent preparation provided by the present invention has the following beneficial effects compared with the prior art:

[0021] 1) By combining the in-situ adsorption and encapsulation characteristics of pollutants during the PCPs formation process with reliable pyrolysis technology, the present invention not only reduces the treatment cost but also achieves good PFAS degradation effects.

[0022] 2) By first adsorbing, then regenerating and eluting, and then using the PCPs formation process to in-situ adsorb and encapsulate pollutants, compared with directly pyrolyzing and disposing of the regeneration solution, the treatment volume and energy consumption cost are greatly reduced.

[0023] 3) The present invention fully realizes resource recycling and is more environmentally friendly.

[0024] 4) The present invention is not limited to the effective and low-cost treatment of PFAS, but also applicable to various other wastewater treatment situations.

[0025] In summary, for an integrated water treatment process coupling pollutant mineralization and adsorbent preparation provided by the present invention, the core lies in utilizing the adsorption capacity of the PCPs-based carbon materials. First, the PCPs-based carbon materials are used to remove pollutants in the wastewater through adsorption, and then the pollutants in the regeneration solution are removed through in-situ adsorption and encapsulation during the PCPs formation process. Subsequently, the newly obtained PCPs-based carbon materials are supplemented to the PCPs-based carbon material layer of the previous adsorption tower, achieving both the degradation of organic pollutants and the resource utilization of pyrolysis products. Through one-time pyrolysis energy input, the purposes of pollutant mineralization and adsorbent preparation are simultaneously achieved, successfully realizing the low-cost and effective treatment of refractory organic pollutants in wastewater. Description of the Drawings

[0026] Figure 1Shows a process flow diagram of an integrated water treatment process that couples pollutant mineralization and adsorbent preparation according to the present invention;

[0027] Figure 2 Shows the adsorption performance of the in-situ encapsulation adsorption of trimellitic acid + iron nitrate during the formation of PCPs on a simulated regenerated solution containing a high concentration of PFOA;

[0028] Figure 3 Shows the adsorption performance of the in-situ encapsulation adsorption of 2-methylimidazole + copper sulfate during the formation of PCPs on a simulated regenerated solution containing a high concentration of PFOA. Specific embodiments

[0029] The following further illustrates 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.

[0030] Please refer to Figure 1 , Figure 1 The present invention provides a process flow diagram of an integrated water treatment process that couples pollutant mineralization and adsorbent preparation. As shown in the figure, the method includes the following steps:

[0031] 1) Wastewater enters the core treatment unit through the water inlet at the top of the adsorption tower. The packing here is PCPs-based carbon material, and the pollutants in the wastewater are adsorbed and removed by adsorption. After the wastewater is purified by the PCPs-based carbon material layer, it flows out from the purified water outlet.

[0032] 2) When the system operates for a period of time and the PCPs-based carbon material has reached the adsorption saturation amount, the PCPs-based carbon material is regenerated through the regenerated solution inlet, and then the regenerated solution flows out from the upper end.

[0033] In this step 2), for example, to regenerate and elute PFOA, a mixed solution of methanol and deionized water can be used.

[0034] 3) The regenerated solution flowing out from the upper end serves as the inlet water for the in-situ encapsulation adsorption unit during the formation of PCPs, and often contains a high concentration of organic pollutants. The steps of in-situ encapsulation adsorption during the formation of PCPs are taken as examples rather than limitations. Organic ligand solution and metal solution can be added to the wastewater in sequence, so that metal ions and organic ligands undergo a coordination polymerization reaction to generate PCPs, adsorbing the organic pollutants in the wastewater. After sufficient adsorption, it enters the sedimentation tank. Among them, the dosage of metal salt and organic ligand is preferably 0.01 g / L - 10 g / L.

[0035] It should be understood that the organic ligand solution and the metal solution can be added to the wastewater sequentially, or the order can be swapped, or the organic ligand solution and the metal solution can be added simultaneously. The present invention does not limit the addition order of the two. However, their performances may vary because the process of forming PCPs crystals by their reaction is affected by the concentrations of the metal and the ligand, as well as other factors. The optimal effect needs to be explored and optimized according to the actual situation. In addition, the organic ligand solution and the metal solution can be mixed and reacted first, and then added to the wastewater to prevent the low concentrations of the organic ligand solution and the metal solution from affecting the coordination reaction, or to avoid interference from other components in the wastewater.

[0036] 4) The effluent from the sedimentation tank is collected and reused as the regeneration solution or the backwashing solution; meanwhile, the PCPs containing high-concentration organic pollutants are collected through the lower funnel.

[0037] 5) The collected PCPs first enter a dryer to remove moisture, and then enter a pyrolyzer. During the pyrolysis process, the organic pollutants are mineralized and decomposed, and at the same time, the PCPs are carbonized and activated into porous carbon materials. The PCPs-based carbon materials prepared after pyrolysis can be formed and used in an adsorption tower to achieve resource recycling.

[0038] The pyrolysis conditions are based on the conditions that can completely mineralize the adsorbed target pollutants. For example, the PFOA studied here can completely mineralize the pollutants after pyrolysis at 600 °C for 2 h. If there are other types of pollutants, the mineralization temperature and time of these pollutants need to be tested first, and then the pyrolysis conditions are determined according to the test results.

[0039] As an example, in the following embodiments of the present invention, ferric nitrate and copper sulfate are selected as metal salts, trimesic acid and 2-methylimidazole are selected as organic ligands, and PFOA is selected as the dissolved pollutant. The in-situ encapsulation adsorption performances of the two combinations of trimesic acid + ferric nitrate and 2-methylimidazole + copper sulfate in the process of forming PCPs are tested, as well as the removal performance for the regeneration solution simulating the solution containing high-concentration PFOA with 20% methanol content and 200 μg / L of PFOA. Secondly, the PCPs after adsorbing the high-concentration PFOA solution are collected, subjected to pyrolysis treatment, and then the PFOA content in the eluate is eluted and detected.

[0040] Example 1

[0041] Removal Performance of In-situ Encapsulation Adsorption during the Formation of PCPs for PFOA in the Regenerated Solution: Add 20 mL of methanol into a 100 mL PP beaker, then add 10 mL of PFOA solution (2 mg / L), and add 70 mL of deionized water. Then stir for 5 min and take a sample as the initial value. Then pour out the solution, wash it, and re-add 20 mL of methanol and 10 mL of PFOA solution (2 mg / L). Take another two 50 mL beakers, dissolve the same mass of ferric nitrate and trimesic acid (0.108, 0.216, 0.432, 0.864 g) in 35 mL of deionized water respectively. After dissolution, mix and stir in a 100 mL glass beaker for 30 min to generate PCPs. Then pour the generated PCPs into the system under stirring conditions, continue to stir for 60 min, and take a sample from the supernatant for detection.

[0042] The experimental results are as Figure 2 shown. When the dosage of metal and organic ligand is 1.08 g / L, the removal rate of PFOA can reach 94.2%. With the increase of the dosage, the removal rate tends to 100%, verifying the feasibility of in-situ encapsulation adsorption during the formation of PCPs for the removal of high-concentration PFOA in the regenerated solution.

[0043] Example 2

[0044] Removal Performance of In-situ Encapsulation Adsorption during the Formation of PCPs for PFOA in the Regenerated Solution: Add 20 mL of methanol into a 100 mL PP beaker, then add 10 mL of PFOA solution (2 mg / L), and add 70 mL of deionized water. Then stir for 5 min and take a sample as the initial value. Then pour out the solution, wash it, and re-add 20 mL of methanol and 10 mL of PFOA solution (2 mg / L). Take another two 50 mL beakers, dissolve the same mass of copper sulfate and 2-methylimidazole (0.108, 0.216, 0.432, 0.864 g) in 35 mL of deionized water respectively. After dissolution, mix and stir in a 100 mL glass beaker for 30 min to generate PCPs. Then pour the generated PCPs into the system under stirring conditions, continue to stir for 60 min, and take a sample from the supernatant for detection.

[0045] The experimental results are as Figure 3 shown. 2-Methylimidazole + copper sulfate achieved similar results to trimesic acid + ferric nitrate. With the increase of the dosage, the removal rate tends to 100%, verifying the feasibility of other combinations for the removal of high-concentration PFOA in the regenerated solution.

[0046] Example 3

[0047] Feasibility of pyrolytic mineralization of PFOA: Add 10 mL of PFOA solution (2 mg / L) to a 100 mL PP beaker, then add 40 mL of deionized water, and dissolve trimellitic acid (0.054 g) at the same time. In another beaker, add 50 mL of deionized water and dissolve 0.054 g of iron nitrate. Then add the iron nitrate solution under stirring conditions and continue stirring for 60 min. Subsequently, centrifuge the solution, and then dry and grind to obtain the original PCPs product containing PFOA. Pyrolyze the product in a tube furnace at 600 °C for 2 h. Take the pyrolysis product and place it in an ion tube, add 50 mL of 20% methanol solution, centrifuge, and sample and detect the supernatant.

[0048] It was found that PFOA could not be detected in the eluted supernatant, confirming that pyrolysis had a good mineralization effect on PFOA.

[0049] As described above, it is only the preferred embodiment of the present invention and is not intended 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. Those not described in detail in the present invention are all conventional technical contents.

Claims

1. An integrated water treatment process for coupled pollutant mineralization and adsorbent preparation, characterized in that: The following steps are involved: 1) Wastewater enters the adsorption tower through the water inlet and flows through the adsorption layer with PCPs-based carbon material as adsorbent, removing dissolved pollutants in the wastewater through adsorption; 2) The wastewater flows out from the purified water outlet after being purified by the PCPs-based carbon material layer; 3) regenerating the PCPs-based carbon material by adding a regeneration solution, and the regeneration solution carries a high concentration of dissolved pollutants and flows out from the regeneration solution outlet; 4) Adding organic ligand solution and metal solution to the outflowing regeneration solution simultaneously or successively, a coordination polymerization reaction occurs to generate PCPs, which adsorb the dissolved pollutants in the regeneration solution and encapsulate them into the PCPs, and then enter the precipitation tank after sufficient reaction; 5) The effluent from the sedimentation tank is reused as the regeneration solution; at the same time, PCPs containing high concentrations of organic pollutants are collected through the lower funnel; 6) The collected PCPs are passed through a dryer and a pyrolysis machine, and a pore-forming agent or activator that is beneficial to the formation of a pore structure is added. During the pyrolysis process, the adsorbed organic pollutants are mineralized into inorganic small molecules, and PCPs-based carbon materials are formed and used as adsorbents for adsorption towers.

2. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: In step 3), the regeneration solution is regenerated by using a mixed solution of water and an organic solvent with adjusted acidity and alkalinity, the volume proportion of the organic solvent is 0-80%, and the acidity and alkalinity are adjusted in the range of neutral to alkaline.

3. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: In step 4), 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, and manganese chloride.

4. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: In step 4), the organic ligand includes: 2-methylimidazole, terephthalic acid, 2-aminoterephthalic acid, 2,5-dihydroxyterephthalic acid, 5-methylisophthalic acid, 4,4'-biphenyldicarboxylic acid, trimesic acid, and pyridine derivatives.

5. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: The dosage of metal salt and organic ligand is 0.01g / L-10g / L.

6. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: The molar ratio of metal to organic ligand is metal:organic ligand=1:1-1:

8.

7. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: The combination of organic ligand and metal salt can be selected from: trimesic acid + ferric nitrate, trimesic acid + ferrous acetate, 2-methylimidazole + ferric nitrate, 2-methylimidazole + ferrous sulfate, 2-methylimidazole + ferrous acetate, 2-methylimidazole + cupric sulfate, trimesic acid + zinc nitrate, 2-methylimidazole + zinc nitrate.

8. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: In step 6), pyrolysis is performed at 400-1000° C. for 1-3 hours to achieve mineralization and decomposition of organic pollutants.

9. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 1, characterized in that: The dissolved pollutants are perfluoro and polyfluoroalkyl compounds.

10. The integrated water treatment process for coupled pollutant mineralization and adsorbent preparation according to claim 9, characterized in that: The perfluoro and polyfluoroalkyl compounds include perfluorooctanoic acid.

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