Method for removing vinyl chloride pollutants by promoting dehalogenation bacteria to perform reductive dechlorination under oxidizing condition by using MOFs (Metal-Organic Frameworks) material

Abstract

The invention belongs to the technical field of microbial remediation of halogenated organic pollutants, and particularly relates to a method for removing vinyl chloride pollutants by promoting dehalogenation bacteria to perform reductive dechlorination under an oxidizing condition by using an MOFs material. According to the method, a functional MOFs material is added in the reaction process of carrying out reductive dechlorination on vinyl chloride by anaerobic dehalogenation bacteria under the aerobic condition, the anaerobic dehalogenation bacteria are coated by the MOFs material, and oxidative substances are catalytically decomposed, so that the dehalogenation bacteria are protected from being damaged by the oxidative substances in the environment, and finally complete dechlorination of vinyl chloride under the oxidative condition is realized. And converting into ethylene. Meanwhile, depending on the protection effect of the MOFs material, the problem of competitive elimination of indigenous microorganisms to anaerobic bacteria in the actual soil and underground water remediation process can be relieved or even eliminated. In conclusion, the method can effectively solve the core problems of'oxygen inactivation 'and'competitive elimination' of anaerobic microorganisms in the in-situ bioremediation application, and obviously improves the in-situ remediation efficiency of halogenated organic matters.

Description

Technical Field

[0001] This invention belongs to the field of microbial remediation technology for halogenated organic pollutants, specifically relating to a method for using MOFs materials to promote the reduction and dechlorination of vinyl chloride pollutants by dehalogenating bacteria under oxidizing conditions. Background Technology

[0002] The widespread application and emission of halogenated organic compounds (HOCs) in various fields have seriously threatened the environment, ecology, and human health. Among them, trichloroethylene (TCE) and monochloroethylene (VC) are HOCs requiring special attention. Vinyl chloride, chloromethane, and chloroethane are also included in the regulatory scope, demonstrating that HOC pollution remediation remains a key focus of environmental pollution prevention and control. Vinyl chloride compounds (mainly including tetrachloroethylene, PCE; trichloroethylene, TCE; dichloroethylene, DCE, etc.) are typical HOCs, possessing lipophilic and hydrophobic properties and a density greater than water. Once these substances are released into the soil environment, they permeate into aquifers under gravity, then form pollution plumes driven by water flow, adsorbing onto the surfaces of soil and sediment particles. More alarmingly, under the combined action of soil minerals and microorganisms, vinyl chloride undergoes a natural dechlorination reaction, generating more volatile and toxic low-chlorinated products (such as monochloroethylene, VC). This process not only hinders land development and use but also poses a significant threat to groundwater safety and human health. Therefore, exploring and developing green, safe, and efficient technologies for the remediation of vinyl chloride-contaminated soil and groundwater is both necessary and urgent. This work is of paramount importance for advancing the battles to protect blue skies, clear waters, and clean soil to higher standards, and for improving the quality of the ecological environment and the level of public health protection.

[0003] Microbial reductive dehalogenation is one of the most promising methods for in-situ remediation of halogenated organic pollution. This is mainly because: (1) Halogenated organic matter mainly accumulates in anaerobic or facultative anaerobic media such as soil, sediments and groundwater, which just meets the growth requirements of anaerobic dehalogenating bacteria; (2) Compared with traditional physical and chemical methods, microbial reductive dehalogenation has the advantages of low cost, no secondary pollution and little interference to the original environment; (3) Microbial reductive dehalogenation has a wide range of substrates and can remediate different halogenated organic pollutants; (4) There are already successful cases of microbial reductive dehalogenation remediation (Wu R, Shen R, Liang Z, et al. Improve niche colonization and microbial interactions for organohalide-respiring-bacteria-mediated remediation of chloroethene-contaminated sites[J]. Environmental Science & Technology, 2023, 57(45):17338-17352.). Among them, organic halogen-respiring bacteria (OHRB) are the core microbial group in the remediation of halogenated organic matter. However, these dehalogenating bacteria have three major limitations, which limit their practical application effectiveness: (1) slow growth and reproduction rate, and harsh growth conditions; (2) strict anaerobic, losing activity upon contact with trace amounts of oxygen; and (3) easily eliminated by competition from other native microorganisms. These limitations directly result in the generally low abundance and activity of dehalogenating bacteria in actual contaminated sites, making it difficult to achieve efficient dehalogenation remediation of halogenated organic matter. Therefore, improving the adaptability and resilience of dehalogenating bacteria to complex environments is the core approach to improving their on-site survival status and increasing the efficiency of dehalogenation remediation. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides a method for promoting the dehalogenation and dechlorination of vinyl chloride pollutants by MOFs materials under oxidizing conditions. By coating the dehalogenation bacteria with functional MOFs materials, their resistance to environmental and indigenous microorganisms is enhanced, thereby achieving efficient removal of halogenated organic pollutants.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a method for promoting the reduction and dechlorination of vinyl chloride pollutants by dehalogenating bacteria under oxidizing conditions using MOFs materials. Specifically, in the process of reducing and dechlorinating vinyl chloride pollutants using anaerobic dehalogenating bacteria under aerobic conditions, functional MOFs materials are added. The anaerobic dehalogenating bacteria are coated with MOFs materials and catalyzed to decompose oxidizing substances, thereby promoting the reduction and dechlorination of vinyl chloride pollutants by dehalogenating bacteria under oxidizing conditions. The preparation method of the functional MOFs material is as follows: Zirconium chloride (ZrCl4) and 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB) are dissolved in a mixed solvent of N,N-dimethylformamide (DMF), formic acid (HCOOH) and water (H2O), and then kept at 100-130℃ for 36-48 h. After cooling to room temperature, a white MOFs precipitate is obtained by centrifugation. After washing, the precipitate is redispersed in hydrochloric acid (HCl) and heated at 60-80℃ for 10-14 h to remove the formate ligands, thus obtaining the MOFs material.

[0006] Preferably, the concentration of the functional MOF material is 15-30 mg / L.

[0007] Preferably, the vinyl chloride contaminants include tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cis-DCE), and monochloroethylene (VC).

[0008] Preferably, the anaerobic dehalogenating bacteria are a mixed culture of dehalogenating bacteria, obtained by enrichment culture according to the method described in Chinese Invention Patent CN111676147A, containing at least one of dehalogenating cocci, dehalogenating monoclonal bacteria, and dehalogenating bacilli. The dehalogenating bacteria enrichment can effectively and completely dechlorinate PCE, TCE, cis-DCE, and VC to form non-toxic ethylene.

[0009] Preferably, the mass ratio of ZrCl4 to H3BTB is 10-15:13-18.

[0010] Preferably, the volume ratio of DMF, HCOOH and H2O in the mixed solvent is 7-8:1-2:0.4-0.7.

[0011] Preferably, the insulation temperature is 120-130℃ and the time is 40-48 h.

[0012] Preferably, the temperature for removing the formate ligand is 70-80°C and the time is 12-14 hours.

[0013] Preferably, the washing involves repeatedly washing the white MOF precipitate by centrifugation with DMF and water 3-5 times each.

[0014] The second aspect of this invention also provides the application of the method described in the first aspect of using MOFs materials to promote dehalogenation bacteria to remove vinyl chloride contaminants under oxidative conditions in the actual site remediation of halogenated organic compounds, wherein the halogenated organic compounds are vinyl chloride.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention discloses a method for promoting the reduction and dechlorination of vinyl chloride contaminants by dehalogenating bacteria under oxidizing conditions using MOFs (Metal-Oxide-Flavors). The method involves adding functional MOFs to the anaerobic dehalogenating bacteria's reduction and dechlorination of vinyl chloride under aerobic conditions. The MOFs encapsulate the anaerobic dehalogenating bacteria and catalyze the decomposition of oxidizing substances, thus protecting the bacteria from damage by environmental oxidizing agents. Ultimately, this achieves complete dechlorination of vinyl chloride under oxidizing conditions, converting it into ethylene. This invention effectively protects the anaerobic dehalogenating bacteria from the complex environment of contaminated sites by encapsulating them with MOFs, reducing competition with native microorganisms. This method significantly enhances the survival ability of anaerobic dehalogenating bacteria under aerobic conditions, thereby ensuring the successful completion of the complete dechlorination reaction of vinyl chloride. Furthermore, this invention provides an efficient and feasible technical path for in-situ microbial remediation of sites contaminated with halogenated organic compounds, and also provides a practical reference for the protection schemes of microbial agents used in actual remediation. Attached Figure Description

[0016] Figure 1 Scanning electron microscope (a) and transmission electron microscope (b) images of functional MOF materials.

[0017] Figure 2 Scanning electron microscope (a), transmission electron microscope (b), and elemental distribution map (c) of microorganisms coated with functional MOFs materials are shown; wherein, Figure (c) is the line scan image of the white box in Figure (b).

[0018] Figure 3 The kinetics of the reduction and dechlorination of tetrachloroethylene by anaerobic dehalogenating bacteria coated with functional MOFs materials in an oxidizing environment are shown in (a) and the growth curve of the dehalogenating bacteria is shown in (b).

[0019] Figure 4 (a) Kinetic diagram of the reduction dechlorination of tetrachloroethylene by anaerobic dehalogenating bacteria without MOFs material under oxidizing conditions and (b) Growth curve of dehalogenating bacteria. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0022] Example 1: Preparation of functional MOF materials Accurately weigh 12 mg of zirconium chloride (ZrCl4) and 15 mg of 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB), and dissolve them in a mixed solvent of 7.2 mL N,N-dimethylformamide (DMF), 1.5 mL formic acid (HCOOH), and 0.45 mL ultrapure water (H2O). After shaking until completely dissolved, transfer the solution to a 25 mL reaction vessel. Place the reaction vessel in an oven and keep it at 130 °C for 48 h. After cooling naturally to room temperature, centrifuge to obtain a white MOF precipitate. Wash the precipitate three times each with DMF and water by centrifugation, then redisperse it in 0.1 M hydrochloric acid (HCl). Finally, heat at 80 °C for 14 h to remove the formate ligands, thus obtaining the functionalized MOF material.

[0023] The prepared MOF materials were tested using scanning electron microscopy and transmission electron microscopy. The test results are as follows: Figure 1 As shown, the prepared MOFs material has a two-dimensional layered structure, which can effectively encapsulate dehalogenated bacteria.

[0024] Example 2: Using MOFs materials to promote the reduction and dechlorination of vinyl chloride contaminants by dehalogenating bacteria under oxidizing conditions. 1. Experimental Methods The prepared MOFs material was dispersed in an anaerobic dehalogenated bacteria culture serum bottle (100 mL) at a concentration of 20 mg / L. Then, 1 mmol / L tetrachloroethylene (PCE) was added to the dehalogenated bacteria culture serum bottle, and the culture was carried out in a constant temperature shaker at 100 rpm and 30 °C for 3 days. Then, oxygen with a volume ratio (based on the volume of the serum bottle) of 21% was added to the serum bottle, and the culture was continued in a constant temperature shaker. The PCE reduction and dechlorination and the growth of dehalogenated bacteria were monitored.

[0025] The operation of culturing anaerobic dehalogenated bacteria in serum bottles was carried out according to the method described in Chinese invention patent CN111676147A, specifically as follows: urban tetrachloroethylene-contaminated sediment samples (mainly underground sediments containing tetrachloroethylene pollutants from chemical plants, pesticide factories, etc.) were collected, and 5 mL was inoculated into 500 mL at a concentration of 1... In anaerobic liquid medium containing DL-lactic acid sodium (mainly containing salt, trace element donors, pH adjusters, buffers, oxygen indicators, organic reducing agents, vitamins, DL-lactic acid sodium, and L-cysteine) with mmol / L tetrachloroethylene as the sole electron acceptor, the culture was carried out under anaerobic conditions at 30°C in the dark until the tetrachloroethylene was completely dechlorinated. Then, the culture was passaged under the same conditions. After three passages, there were no solid residues of the original sediment in the culture medium. The resulting culture medium is a mixed culture of anaerobic dehalogenated bacteria, which mainly contains dehalococcoides, as well as a small amount of dehalogenated monoclonal bacteria and dehalobacter.

[0026] The growth of PCE-reducing dechlorination and dehalogenation bacteria was determined using gas chromatography and real-time fluorescence quantitative PCR, respectively. Specifically: PCE reduction dechlorination test: Gas chromatography (Agilent 7890B) equipped with a flame ionization detector (FID) and a GS-GasPro capillary column (30 m0.32 mm, Agilent J&W Scientific, USA) was used to test for vinyl chloride contaminants. The injection port and detector temperatures were 220℃ and 250℃, respectively. The column oven program was as follows: initial temperature 80℃, hold for 0.2 min, then increase to 190℃ at 45℃ / min and hold for 1 min.

[0027] Growth of dehalogenated bacteria: The growth of dehalogenated bacteria was monitored using real-time quantitative PCR. First, DNA was extracted from the collected biological samples using the FastDNA® Spin kit (MP Biomedicals). The specific extraction procedure was described in the kit's instructions. Then, real-time quantitative PCR was performed on the dehalogenated bacteria using specific primers DhcF / DhcR (DhcF: 5'-GGTAATACGTAGGGAAGCAAGCG-3'; DhcR: 5'-CCGGTTAAGCCGGGAAATT-3'). Simultaneously, full-length 16S rRNA was used as a template and amplified using universal primers (8F / 1541R) (8F: 5'-AGAGTTTGATCMTGGCTCAG-3'; 1541R: 5'-AAGGAGGTGATCCAGCCGCA-3'). The amplified rRNA was then quantified using real-time quantitative PCR to construct the growth curve of the dehalogenated bacteria.

[0028] 2. Experimental Results MOFs material coating dehalogenation status, such as Figure 2 As shown, the PCE reduction dechlorination and dehalogenation bacteria growth are as follows: Figure 3 As shown in the figure. The results indicate that, under oxidizing conditions, through the coating and protection of MOF materials, anaerobic dehalogenating bacteria still have a high efficiency in dechlorinating 1 mmol / L PCE, and can completely convert it into ethylene in about 45 days. Furthermore, the dehalogenating bacteria cells also show a significant growth trend.

[0029] Comparative Example 1: This comparative example is the same as Example 2, except that MOFs were not added to the anaerobic dehalogenated bacteria culture serum bottle (100 mL). It was also cultured at 100 rpm and 30°C for 3 days in a constant-temperature shaker. Then, oxygen (21% by volume) was added to the serum bottle, and the culture continued in a constant-temperature shaker. The reduction and dechlorination of tetrachloroethylene and the growth of the dehalogenated bacteria were monitored. Figure 4 As shown, the results revealed that without the protection of MOFs materials under oxidizing conditions, dehalogenating bacteria could not grow and reductively dechlorinate.

[0030] In summary, the method for promoting the reductive dechlorination of vinyl chloride pollutants using MOFs materials provided by this invention can effectively encapsulate anaerobic dehalogenating bacteria and protect them from damage by oxidizing substances, enabling continued growth and reductive dechlorination under oxidizing conditions. Simultaneously, relying on the protective effect of MOFs materials, it can also alleviate or even eliminate the problem of competition and elimination of anaerobic bacteria by indigenous microorganisms in actual soil and groundwater remediation processes. Therefore, this invention can effectively solve the core problems of "aerobic inactivation" and "competitive elimination" of anaerobic microorganisms in in-situ bioremediation applications, significantly improving the in-situ remediation efficiency of halogenated organic matter.

[0031] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for removal of vinyl chloride pollution by dechlorination under oxidative conditions using MOFs material to promote dehalogenating bacteria, characterized in that, In the reaction process of reducing dechlorination of vinyl chloride pollutants by anaerobic dehalogenating bacteria under aerobic conditions, functional MOFs materials are added, which coat the anaerobic dehalogenating bacteria and catalytically decompose oxidative substances, thereby promoting the dehalogenating bacteria to reduce dechlorination and remove vinyl chloride pollutants under oxidative conditions. The preparation method of the functional MOFs material is as follows: dissolving zirconium chloride and 1,3,5-tris(4-carboxylphenyl) benzene in a mixed solvent of N,N-dimethylformamide, formic acid and water, then placing it in 100-130℃ for 36-48 h, then cooling to room temperature, then obtaining white MOFs precipitate by centrifugation, washing the precipitate, then dispersing the precipitate in hydrochloric acid again, and heating at 60-80℃ for 10-14 h to remove formate ligand.

2. The method of claim 1, wherein the MOFs material promotes the dehalogenating bacteria to remove the vinyl chloride pollutants under the oxidative conditions. The addition concentration of the functional MOFs material is 15-30 mg / L.

3. The method of claim 1, wherein the MOFs material promotes the dehalogenating bacteria to remove the vinyl chloride pollutants under the oxidative conditions, and the method is characterized in that, The vinyl chloride pollutants include tetrachloroethylene, trichloroethylene, cis-dichloroethylene and monochloroethylene.

4. The method of claim 1, wherein the MOFs material promotes the dehalogenating bacteria to remove the vinyl chloride pollutants under the oxidative conditions, and the method is characterized in that, The anaerobic dehalogenating bacteria are a mixed culture of dehalogenating bacteria, which are enriched and cultured according to the method described in Chinese invention patent CN111676147A, and contain at least one of Dehalococcoides, Dehalococcus and Dehalobacter.

5. The method of claim 1, wherein the MOFs material promotes the removal of vinyl chloride pollutants by dechlorinating bacteria under oxidative conditions. The mass ratio of zirconium chloride to 1,3,5-tris(4-carboxylphenyl) benzene is 10-15:13-18.

6. The method of claim 1, wherein the MOFs material promotes the removal of vinyl chloride pollutants by dechlorinating bacteria under oxidative conditions. In the mixed solvent, the volume ratio of N,N-dimethylformamide, formic acid and water is 7-8:1-2:0.4-0.

7.

7. The method of claim 1, wherein the MOFs material promotes the dehalogenating bacteria to remove the vinyl chloride pollutants under the oxidative conditions. The temperature of the heat preservation is 120-130℃, and the time is 40-48 h.

8. The method of claim 1, wherein the MOFs material promotes the dehalogenating bacteria to remove the vinyl chloride pollutants under the oxidative conditions, and the method further comprises: The temperature for removing formate ligand by heating is 70-80℃, and the time is 12-14 h. ​ 9. The method of claim 1, wherein the MOFs material promotes the dehalogenating bacteria to remove the vinyl chloride pollutants under the oxidative conditions, and the method further comprises: The washing is repeated washing 3-5 times by centrifugation of the white MOFs precipitate with DMF and water. ​ 10. Use of the method for removal of vinyl chloride pollution by dechlorination under oxidative conditions using MOFs material promoting dehalogenating bacteria according to any of claims 1-9 for real site remediation of halogenated organic compounds, characterized in that, The halogenated organic compound is vinyl chloride.

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