A method for removing and recovering dissolved organic matter in water

Abstract

The application provides a method for removing and recovering dissolved organic matter in water, which comprises sequentially adding a metal salt and an organic ligand into water to be treated, and recovering the dissolved organic matter by filtering after the dissolved organic matter is quickly wrapped to form a precipitate, wherein the metal salt comprises at least one of zinc acetate, zinc sulfate and zinc nitrate, and the organic ligand comprises a ligand containing an imidazole structure. The method of the application has the advantages of high DOM removal efficiency, low cost of raw materials, low production cost, simple preparation process, short preparation period, low requirement for equipment, good stability of DOM recovery and strong repeatability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage treatment, and particularly relates to a method for removing and recovering dissolved organic matter in water. BACKGROUND

[0002] Dissolved Organic Matter (DOM) is a complex heterogeneous mixture composed of large molecules such as phenols, quinones, olefins, amines, sulfides and heterocyclic groups, and widely exists in various water bodies, such as surface water, groundwater and sewage, wherein the concentration in surface water and groundwater is 1-10 mgC / L, and in sewage is 5-30 mgC / L. In the process of advanced oxidation of sewage, DOM can inhibit the removal of micro-pollutants through processes such as light shielding, consumption of active species and reduction of pollutant free radical intermediates. And in the process of disinfection of drinking water, DOM can react with disinfectants such as chlorine and chloramine to produce some disinfection by-products with carcinogenicity, such as trihalomethane and haloacetic acid. Therefore, the existence of DOM has a negative impact on the water treatment process.

[0003] In wastewater treatment, coagulation and sedimentation (adding a coagulant, which reacts and flocculates to form flocs that sink) and membrane treatment methods (ultrafiltration, microfiltration, nanofiltration, and reverse osmosis) are commonly used to reduce DOM in water. Coagulation and sedimentation methods are inefficient in removing DOM and cannot completely remove DOM from wastewater. Membrane treatment methods are expensive, time-consuming, space-consuming, and prone to membrane clogging. Common methods for recovering DOM include ion resins, ultrafiltration membranes, and solid-phase extraction. The ion resin method, based on the principle of ion exchange, adsorbs and removes DOM from water by exchanging ions in the water with ions on the resin. DOM is then eluted by changing the solution's pH. Disadvantages of this method include relatively high cost, increased operating costs due to frequent replacement or regeneration of the ion resin, and the formation of strong chemical bonds between some organic compounds and the ion resin, making regeneration more difficult. The effectiveness of ion resins is often affected by pH, requiring pH adjustment before use. Ultrafiltration membranes are a membrane separation technology commonly used to recover DOM. This method utilizes the micropores of ultrafiltration membranes to effectively retain organic molecules dissolved in water, enabling the recovery of organic matter. A disadvantage of this method is that the retention of organic matter can lead to membrane clogging, reducing permeability and requiring regular maintenance and cleaning. Ultrafiltration membranes are relatively expensive to prepare and maintain, and membrane replacement and maintenance can be costly, especially when processing large volumes of water. Appropriate equipment, such as high-pressure pumps, is usually required to ensure sufficient pressure when the water flows through the membrane. Solid-phase extraction (SPE) utilizes the specific adsorption of organic matter immobilized on an adsorbent to enrich and recover organic matter by adjusting conditions. SPE typically has certain limitations on the capacity of water samples and requires pretreatment and enrichment within a certain range, so it may not be able to process large quantities of water samples. The operation is relatively cumbersome, requiring accurate sample preparation and control of experimental conditions, and requiring high operator skills. The preparation costs of SPE columns and adsorbents are relatively high, and the solutions used for regeneration and maintenance may also increase operating costs.

[0004] In view of this, there is a need to develop a more efficient and cost-effective method to remove and recycle DOM. Summary of the Invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention provides a method for removing and recovering dissolved organic matter in water, which is more efficient and less expensive.

[0006] The first aspect of the present application provides a method for removing and recovering dissolved organic matter in water, the method comprising sequentially adding a metal salt and an organic ligand to water to be treated, and recovering the dissolved organic matter by filtration after the dissolved organic matter is wrapped to form a precipitate, wherein the metal salt comprises at least one of zinc acetate, zinc sulfate and zinc nitrate, and the organic ligand comprises a ligand comprising an imidazole structure.

[0007] The present application relates to a technical solution in a method for removing and recovering dissolved organic matter in water, and at least has the following beneficial effects:

[0008] In the method of the present application, metal ions in the metal salt are first coordinated with the dissolved organic matter (DOM), and are wrapped on the surface of the DOM, and then the organic ligand is coordinated with the metal ions in the metal salt wrapped on the surface of the DOM to form a precipitate, the precipitate is removed, and the chemical bond between the metal and the ligand can be destroyed by acidification to dissolve the precipitate, and finally the DOM is intercepted by filtration, thereby achieving the removal and recovery of the DOM in water.

[0009] Compared with ultrafiltration, the volume of water sample that needs to pass through for removing DOM by ultrafiltration is much larger than that of the present application, resulting in a large occupied space and a long required time. In the method of the present application, only the sample after acid dissolution of the precipitate needs to be filtered, so the sample volume is small and the required time is short.

[0010] The method of the present application has high DOM removal efficiency, low production cost, simple preparation process, short preparation period, low requirement for equipment, good DOM recovery stability and strong repeatability.

[0011] The method of the present application is a method for quickly removing DOM by coordination polymerization encapsulation, and then recovering the DOM. The ordinary coagulation precipitation method is to compress the organic matter by double electric layer, while the method of the present application is to wrap and adsorb.

[0012] The method of the present application is in-situ wrapping. If MOFs such as ZIF-8 that have been prepared or sold on the market are directly added to the water to be treated, the MOFs such as ZIF-8 perform adsorption on the DOM, rather than in-situ wrapping of the present application.

[0013] In the method of the present application, the metal ions in the metal salt adsorb the DOM, and after coordination in water, the coordination can be easily broken by acid dissolution.

[0014] According to some embodiments of the present application, the metal salt is zinc acetate, and the organic ligand is 2-methylimidazole.

[0015] Zinc acetate and 2-methyl imidazole can be replaced by other reagents, as long as the ligand of metal+imidazole structure coordinated with DOM is allowed, but it is considered that the material can be formed in water and easily released from coordination under acidic conditions. Such as zinc acetate, zinc sulfate, zinc nitrate, etc. The coordination is released in order to separate DOM and the surface metal+coordination, and the acid is released, and then filtered to obtain pure DOM.

[0016] According to some embodiments of the present application, the amount of metal salt added is 5-100 mmol / L.

[0017] According to some embodiments of the present application, the amount of metal salt added is 5 mmol / L, 20 mmol / L, 100 mmol / L or a range value formed by any two of them.

[0018] According to some embodiments of the present application, the amount of organic ligand added is 20-400 mmol / L.

[0019] According to some embodiments of the present application, the amount of organic ligand added is 20 mmol / L, 80 mmol / L, 400 mmol / L or a range value formed by any two of them.

[0020] According to some embodiments of the present application, after sequentially adding metal salt and organic ligand to the water to be treated, the solution is subjected to centrifugal treatment.

[0021] According to some embodiments of the present application, the centrifugal treatment is at a speed of 100-10000 rpm.

[0022] According to some embodiments of the present application, the centrifugal treatment is for a time of 0.1-2 h.

[0023] According to some embodiments of the present application, the method for recovering the dissolved organic matter includes: dissolving the precipitate in an acid solution and filtering using a dialysis membrane.

[0024] According to some embodiments of the present application, the pH of the acid solution is 3-6.

[0025] According to some embodiments of the present application, the molecular weight cut-off of the dialysis membrane is 100-500 Da.

[0026] According to some embodiments of the present application, the molecular weight cut-off of the dialysis membrane is 100 Da, 200 Da, 500 Da or a range value formed by any two of them.

[0027] According to some embodiments of the present application, the method comprises the following steps:

[0028] Step S1: removal of DOM: add metal salt to the solution containing DOM, then add organic ligand, put the solution in a centrifuge tube and centrifuge in a centrifuge, and the DOM is precipitated to the bottom of the centrifuge tube by the metal organic framework material;

[0029] Step S2: recovery of DOM: dissolve the precipitate in an acid solution, filter using a dialysis membrane, and the metal salt and organic ligand in the system can be completely filtered out, thereby recovering the DOM.

[0030] According to some embodiments of the present application, in step S1, the reaction temperature is 0-60℃.

[0031] According to some embodiments of the present application, in step S2, the acid solution includes dilute sulfuric acid, dilute hydrochloric acid or other dilute acid.

[0032] Zinc acetate and 2-methyl imidazole can pass through the membrane, and DOM cannot pass through, so that DOM can be intercepted. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The figure is a flowchart of the method of the present application.

[0034] Figure 2 The figure is the fluorescence spectrum test result of the complexation of zinc acetate and DOM in Example 1.

[0035] Figure 3 The figure is the Fourier infrared spectrum test result of the complexation of zinc acetate and DOM in Example 1.

[0036] Figure 4 The figure is a macroscopic morphology diagram of the ZIF-8@DOM precipitate recovered by the method of Example 1.

[0037] Figure 5 The figure is a microscopic morphology diagram of the ZIF-8@DOM precipitate recovered by the method of Example 1.

[0038] Figure 6 The figure is the removal and recovery effect of DOM in different actual water bodies by the method of Example 1.

[0039] Figure 7 The figure is the removal and recovery effect of DOM by the method of Example 1 and different processes. DETAILED DESCRIPTION

[0040] The following are specific embodiments of the present application, and the technical solutions of the present application are further described in conjunction with the embodiments, but the present application is not limited to these embodiments.

[0041] In some embodiments of the present application, a method for removing and recovering dissolved organic matter in water is provided, which comprises sequentially adding a metal salt and an organic ligand into water to be treated, and recovering the dissolved organic matter by filtration after the dissolved organic matter is wrapped to form a precipitate, wherein the metal salt comprises at least one of zinc acetate, zinc sulfate and zinc nitrate, and the organic ligand comprises a ligand containing an imidazole structure.

[0042] It should be noted that in the method of the present application, the metal ions in the metal salt are first coordinated with the dissolved organic matter (DOM) and wrapped on the surface of the DOM, and then the organic ligand is coordinated with the metal ions in the metal salt wrapped on the surface of the DOM to form a precipitate, and the DOM is intercepted by filtration, thereby achieving the removal and recovery of the DOM in water.

[0043] It should be noted that compared with ultrafiltration, the volume of water sample that needs to pass through for removing DOM by ultrafiltration is much larger than that of the present method, resulting in a large occupied space and a long required time. However, in the method of the present application, the sample that needs to be filtered is only the acid-dissolved sample after precipitation, so the sample volume is small and the required time is short.

[0044] It can be understood that the method of the present application has high removal efficiency of DOM, low production cost, simple preparation process, short preparation period, low requirement for equipment, good stability of DOM recovery, and strong repeatability.

[0045] It should be further noted that the method of the present application is a method of quickly removing DOM by coordination polymerization encapsulation, and then recovering the DOM. The ordinary coagulation precipitation method is to compress the organic matter by double electric layer, while the method of the present application is to wrap and adsorb.

[0046] It should be further noted that the method of the present application is in-situ wrapping. If MOFs such as ZIF-8 that have been prepared or sold on the market are directly added to the water to be treated, the MOFs such as ZIF-8 perform adsorption on the DOM, rather than in-situ wrapping of the present application.

[0047] In particular, in the method of the present application, the metal ions in the metal salt adsorb the DOM, and after coordination in water, the coordination can be easily broken by acid dissolution.

[0048] In some embodiments of the present application, the metal salt is zinc acetate, and the organic ligand is 2-methylimidazole.

[0049] Zinc acetate and 2-methyl imidazole can be replaced by other reagents, as long as the ligand of metal+imidazole structure coordinated with DOM is allowed, but it is considered that the material can be formed in water and easily released from coordination under acidic conditions. Such as zinc acetate, zinc sulfate, zinc nitrate, etc. The coordination is released in order to separate DOM and the surface metal+coordination, and the acid is released, and then filtered to obtain pure DOM.

[0050] In some embodiments of the present application, the amount of metal salt added is 5-100 mmol / L.

[0051] In some embodiments of the present application, the amount of metal salt added is 5 mmol / L, 20 mmol / L, 100 mmol / L or a range value formed by any two of them.

[0052] In some embodiments of the present application, the amount of organic ligand added is 20-400 mmol / L.

[0053] In some embodiments of the present application, the amount of organic ligand added is 20 mmol / L, 80 mmol / L, 400 mmol / L or a range value formed by any two of them.

[0054] In some embodiments of the present application, the metal salt and the organic ligand are sequentially added to the water to be treated, and then the solution is centrifuged.

[0055] In some embodiments of the present application, the centrifugal speed is 100-10000 rpm.

[0056] In some embodiments of the present application, the centrifugal time is 0.1-2h.

[0057] In some embodiments of the present application, the method for recovering the dissolved organic matter includes: dissolving the precipitate in an acid solution, and filtering using a dialysis membrane.

[0058] In some embodiments of the present application, the pH of the acid solution is 3-6.

[0059] In some embodiments of the present application, the molecular weight cut-off of the dialysis membrane is 100-500 Da.

[0060] In some embodiments of the present application, the molecular weight cut-off of the dialysis membrane is 100 Da, 200 Da, 500 Da or a range value formed by any two of them.

[0061] In some embodiments of the present application, the method of the present application can include the following steps:

[0062] Step S1: removal of DOM: add metal salt to the solution containing DOM, then add organic ligand, place the solution in a centrifuge tube and put it in a centrifuge for centrifugation, and the DOM is precipitated to the bottom of the centrifuge tube by the metal organic framework material;

[0063] Step S2: recovery of DOM: dissolve the precipitate in an acid solution, filter using a dialysis membrane, and completely filter out the metal salt and organic ligand in the system, thereby recovering the DOM.

[0064] In some embodiments of the present application, in step S1, the reaction temperature is 0-60°C.

[0065] In some embodiments of the present application, in step S2, the acid solution includes dilute sulfuric acid, dilute hydrochloric acid or other dilute acid.

[0066] Zinc acetate and 2-methylimidazole can pass through the membrane, and DOM cannot pass through, so that DOM can be intercepted.

[0067] The technical solutions of the present application will be better understood in combination with the specific embodiments below.

[0068] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods.

[0069] Example 1

[0070] A method for removing and recovering dissolved organic matter in water, the method comprising sequentially adding a metal salt and an organic ligand to the water to be treated, wrapping the dissolved organic matter to form a precipitate, removing the precipitate, and adding acid to acidify and break the chemical bond between the metal and the ligand, so that the precipitate is dissolved, and finally recovering the DOM by filtration, wherein the metal salt is zinc acetate and the organic ligand is 2-methylimidazole.

[0071] Specifically comprising the following steps:

[0072] (1) Take 100 mL of water sample, add 20 mmol / L of zinc acetate solution, and then add 80 mmol / L of 2-methylimidazole.

[0073] (2) Put it in a centrifuge at a speed of 10000 rpm for 5 min, and the ZIF-8@DOM precipitate to the bottom of the centrifuge tube.

[0074] (3) Take out the supernatant in the solution, add dilute sulfuric acid, adjust the pH of the solution to 3-6, and make up to 100 mL.

[0075] (4) Filter the solution with adjusted pH using a dialysis membrane with a size of 100 Da to obtain the solid DOM after reaction, marked as ZIF-8@DOM precipitate.

[0076] The initial concentration of DOM in the water sample was 10 mgC / L.

[0077] Combination Figure 1 The method of the present application can be better understood, steps (1) and (2) are as shown in (1) to (4) in Figure 1 , steps (3) and (4) are as shown in (5) to (8) in Figure 1 .

[0078] Example 2

[0079] The difference between this example and Example 1 is that the amount of zinc acetate solution added is 5 mmol / L, and the amount of 2-methylimidazole added is 20 mmol / L.

[0080] Example 3

[0081] The difference between this example and Example 1 is that the amount of zinc acetate solution added is 100 mmol / L, and the amount of 2-methylimidazole added is 400 mmol / L.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that the amount of zinc acetate solution added is 1 mmol / L, and the amount of 2-methylimidazole added is 1 mmol / L.

[0084] Experimental Test

[0085] The complexation of zinc ions and DOM in Example 1 was characterized by synchronous fluorescence spectroscopy, as shown in Figure 2 .

[0086] As can be seen from Figure 2 , after adding zinc acetate to the DOM solution, the characteristic fluorescence peak of DOM shifted from 344 nm to 384 nm, and the fluorescence intensity decreased, indicating that there was a strong interaction between Zn 2+ and DOM.

[0087] The complexation of zinc ions and DOM was characterized by synchronous Fourier infrared spectroscopy, as shown in Figure 3 .

[0088] As can be seen from Figure 3 , in the Fourier transform infrared spectrum, after Zn 2+ linked DOM (Zn 2+ -DOM), the C=O stretching vibration of the carboxyl group of DOM red-shifted from 1710 cm -1 to 1540 cm -1 , and a Zn-O stretching vibration absorption centered at 617 cm -1 appeared. This indicates that Zn 2+The coordination occurs between the carboxyl group of DOM, thereby weakening the electronic strength of the C=O bond and causing the Fourier transform infrared spectrum to red shift. 2+ As the amount of addition increases, the OH stretching vibration (range 3100-3600cm -1 ) gradually weakened, which indicated that there was a coordination interaction between Zn-carboxyl or Zn-hydroxyl groups.

[0089] The DOM powder was recovered by the method of Example 1 and the ZIF-8@DOM precipitate was obtained. Figure 4 shown.

[0090] from Figure 4 It can be seen that the ZIF-8@DOM precipitate recovered by the method of Example 1 has a regular morphology and uniform particle size in macroscopic terms.

[0091] The ZIF-8@DOM precipitate recovered by the method of Example 1 was characterized by scanning electron microscopy. Figure 5 As shown. Figure 5 It can be seen that the ZIF-8@DOM precipitate recovered by the method of Example 1 also has a regular morphology and uniform particle size at the microscopic level.

[0092] Using the same DOM solution, the DOM removal and recovery effects of Examples 1 to 3 and Comparative Example 1 were compared. The results showed that when the metal salt was added in an amount of 5-100 mmol / L and the organic ligand was added in an amount of 20-400 mmol / L, the DOM removal and recovery effects were better.

[0093] Furthermore, the removal and recovery of DOM in landfill leachate, sewage, surface water and DOM solution were tested by the method of Example 1. The results are shown in Table 1 and Figure 6 shown.

[0094] The initial concentration of DOM in the landfill leachate was 1181 mgC / L. The DOC of the initial DOM was measured using the NPOC method using a Shimadzu total organic carbon analyzer.

[0095] The initial concentration of DOM in the sewage was 52.3 mgC / L.

[0096] In surface water, the initial concentration of DOM was 3.3 mgC / L.

[0097] In the DOM solution, the initial concentration of DOM was 10 mgC / L.

[0098] Table 1

[0099] Landfill leachate Sewage Surface water DOM solution Removal rate 0.74 0.84 0.82 0.90 Recovery rate 0.59 0.72 0.76 0.77

[0100] The method of Example 1 was also compared to a common method of recovering DOM. As Figure 7

[0101] Figure 7 In this case, the process parameters for the ion exchange resin were: XAD-8 ion resin was used to isolate DOM from the actual water sample.

[0102] Data from the literature: Fujita, Y., Ding, W.-H. & Reinhard, M. Identification of wastewater dissolved organic carbon characteristics in reclaimed wastewater and recharged groundwater. Water Environ Res 68, 867-876, (1996).

[0103] Minor, E. C. et al. Structural characterization of dissolved organic matter: A review of current techniques for isolation and analysis. Environ Sci-Proc Imp 16, 2064-2079, (2014).

[0104] Maurice, P. A. et al. A comparison of surface water natural organic matter in raw filtered water samples, XAD, and reverse osmosis isolates. Water Res 36, 2357-2371, (2002).

[0105] Batra, S. et al. Adsorption of Bisphenol-A from aqueous solution using amberlite XAD-7 impregnated with aliquat 336: Batch, column, and design studies. Process Saf Environ 122, 232-246, (2019).

[0106] ​Hughes, D. D. et al. Rapid, Semi-automated fractionation of freshwater dissolved organic carbon using DAX 8 (XAD 8) and XAD 4 resins in tandem. Natural Science 8, 487-498, (2016).

[0107] Green, N. W. et al. An intercomparison of three methods for the large-scale isolation of oceanic dissolved organic matter. Mar Chem 161, 14-19, (2014).

[0108] The process parameters for ultrafiltration were: using 1 kDa ultrafiltration membrane, DOM in the actual water sample was separated.

[0109] Data from the literature: Minor, E. C. et al. Structural characterization of dissolved organic matter: A review of current techniques for isolation and analysis. Environ Sci-Proc Imp 16, 2064-2079, (2014).

[0110] Benner, R. et al. Abundance, size distribution, and stable carbon and nitrogen isotopic compositions of marine organic matter isolated by tangential-flow ultrafiltration. Mar Chem 57, 243-263, (1997).

[0111] Drouiche, M. et al. Economic study of the treatment of surface water by small ultrafiltration units. Water Sa 27, 199-204, (2001).

[0112] The process parameters of solid phase extraction are: using PPL-SPE chromatographic column to separate DOM in actual water samples.

[0113] The data comes from the literature: Minor, ECet al. Structural characterization of dissolved organic matter: A review of current techniques for isolation and analysis. Environ Sci-Proc Imp 16, 2064-2079, (2014).

[0114] Green, NWet al. An intercomparison of three methods for the large-scale isolation of oceanic dissolved organic matter. Mar Chem 161,14-19, (2014).

[0115] Dittmar, T. et al. Asimple and efficient method for the solid-phase extraction of dissolved organic matter (SPE-DOM) from seawater. Limnol Oceanogr-Meth 6, 230-235, (2008).

[0116] from Figure 7 It can be seen that the recovery efficiency of the method according to the embodiment of the present invention is the best.

[0117] The above examples illustrate that the method of the present invention, which utilizes a coordination polymerization encapsulation strategy to rapidly remove and recover DOM, has high DOM removal efficiency, readily available and inexpensive raw materials, low production costs, a simple preparation process, a short preparation cycle, low equipment requirements, and excellent DOM recovery stability and reproducibility, thus possessing great potential for practical application.

[0118] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that those skilled in the art may make several improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications are also included in the scope of protection of the claims of the present invention.

[0119] The application is described in detail above in connection with the embodiments, but the application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the application.

Claims

1. A method for removing and recovering dissolved organic matter in water, characterized in that: The method comprises sequentially adding a metal salt and an organic ligand to water to be treated, wrapping dissolved organic matter to form a precipitate, and then recovering the dissolved organic matter by filtration, wherein the metal salt comprises at least one of zinc acetate, zinc sulfate and zinc nitrate, and the organic ligand comprises a ligand containing an imidazole structure.

2. The method according to claim 1, characterized in that The metal salt is zinc acetate, and the organic ligand is 2-methylimidazole.

3. The method according to claim 1 or 2, characterized in that The added amount of the metal salt is 5-100 mmol / L.

4. The method according to claim 1 or 2, characterized in that The added amount of the organic ligand is 20-400 mmol / L.

5. The method according to claim 1 or 2, characterized in that After metal salt and organic ligand are sequentially added to the water to be treated, the solution is centrifuged.

6. The method according to claim 5, characterized in that The rotation speed of the centrifugal treatment is 100-10000 rpm.

7. The method according to claim 5, characterized in that The centrifugal treatment time is 0.1-2h.

8. The method according to claim 1 or 2, characterized in that The method for recovering the soluble organic matter by filtration comprises: dissolving the precipitate in an acid solution and filtering the solution using a dialysis membrane.

9. The method according to claim 8, characterized in that The pH of the acid solution is 3-6.

10. The method according to claim 8, characterized in that The molecular weight cut-off of the dialysis membrane is 80-500 Da.

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