Method for modifying pyrite to enhance microbial degradation of tetrachloroethylene and application thereof

Abstract

The application discloses a method for modifying pyrite to strengthen microbial degradation of tetrachloroethylene and application thereof, and adopts a coupling system of citric acid modified pyrite (C-FeS2) and desulfurization bacillus THU1 to synergistically degrade tetrachloroethylene (PCE) in water and soil under anaerobic conditions, so that the degradation rate of PCE reaches 98.7%, and the method is suitable for in-situ or ex-situ remediation of chlorinated hydrocarbon pollution in groundwater and soil and has a wide engineering application prospect.

Description

Technical Field

[0001] This invention belongs to the field of environmental microbial remediation technology, specifically relating to a method and application of modified pyrite-enhanced microbial degradation of tetrachloroethylene. Background Technology

[0002] Tetrachloroethylene (PCE), with the molecular formula C2Cl4, is a typical chlorinated volatile organic pollutant widely used in industries such as dry cleaning, metal degreasing, and electronic cleaning. Due to its chemical stability, density greater than water, and poor biodegradability, PCE exhibits strong persistence and mobility in soil and groundwater, making it one of the most common organohalides polluting groundwater globally. Long-term exposure to PCE can damage the liver, kidneys, and nervous system in humans and has potential carcinogenicity. The U.S. Environmental Protection Agency (USEPA) has listed PCE as a priority pollutant.

[0003] Currently, remediation technologies for PCE contamination mainly include physical extraction, chemical oxidation, thermal desorption, and bioremediation. Physical extraction and thermal desorption are costly and energy-intensive, and are not suitable for deep groundwater contamination. While chemical oxidation can rapidly degrade PCE, it consumes a large amount of oxidant and easily produces toxic byproducts such as chloroacetic acid, leading to secondary pollution. In contrast, bioreduction dechlorination technology has received widespread attention due to its environmental friendliness and strong sustainability.

[0004] Under anaerobic conditions, polyvinyl chloride (PCE) can be progressively degraded into trichloroethylene (TCE), dichloroethylene (DCE), and vinyl chloride (VC) through reductive dechlorination, ultimately transforming into harmless ethylene or ethane. This process relies on dehalogenating respiratory bacteria (such as *Dehalococcoides* and *Desulfitobacterium*), but the abundance of these bacteria in the natural environment is low, their metabolic activity is limited, and the high toxicity of PCE inhibits microbial growth, resulting in low degradation efficiency. For example, THU1, a desulfurizing bacillus (*Desulfitobacterium* sp.), has good reductive dechlorination capabilities, especially for high-chlorinated ethylenes such as PCE and TCE. However, THU1 exhibits a low degradation rate for PCE under solitary culture conditions and is easily inhibited by metabolites. Furthermore, the reductive dechlorination process requires sufficient electron donors and a suitable redox potential. Traditional bioremediation often adds lactic acid, hydrogen, or zero-valent iron as electron donors, but this presents problems such as unstable electron donor release, large pH fluctuations, and hydrogen escape due to iron corrosion.

[0005] In recent years, pyrite (FeS2) has been favored for its reducing properties and slow-release of Fe. 2+The ability to react with sulfides makes natural pyrite a potential material for enhancing the dechlorination process of anaerobic microorganisms. Natural pyrite can slowly oxidize and release ferrous ions and sulfides, which can act as electron donors or reducing equivalents, promoting the metabolic activity of dechlorinating bacteria. However, the small specific surface area and limited surface active sites of natural pyrite restrict its bioavailability.

[0006] Therefore, developing a PCE biodegradation method that stably provides electron donors, has high microbial activity, and achieves sufficient degradation is of great practical significance. Summary of the Invention

[0007] To overcome the shortcomings of the existing technology, the present invention aims to provide a method and application for modified pyrite-enhanced microbial degradation of tetrachloroethylene (PCE), solving the technical problems of insufficient electron donors, low microbial activity, and incomplete degradation in traditional bioremediation methods for PCE degradation.

[0008] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for modified pyrite-enhanced microbial degradation of tetrachloroethylene (PCE), comprising the following steps: S1. Preparation of citric acid modified pyrite material C-FeS2: The treated natural pyrite was added to a citric acid solution, stirred, filtered, washed and dried to obtain citric acid modified pyrite material C-FeS2. Preferably, the natural pyrite processed in step S1 is natural pyrite that has been crushed, sieved, and has a particle size of 100-200 mesh. Preferably, the concentration of the citric acid solution in step S1 is 0.1 ~ 0.3 mol / L; Preferably, the solid-liquid ratio of the treated natural pyrite and citric acid solution in step S1 is (1~5):10; Preferably, in step S1, the stirring conditions are stirring at room temperature for 12-36 h, the washing conditions are washing with deionized water until neutral, and the drying conditions are vacuum drying at 60℃-80℃. S2, Citric acid modified pyrite-enhanced microbial degradation of tetrachloroethylene (PCE): The C-FeS2 material from step S1 was added to the sterile anaerobic culture medium contaminated with PCE, and THU1 bacterial solution was inoculated. The medium was then allowed to stand for culture to degrade PCE.

[0009] Preferably, in step S2, the amount of C-FeS2 material added to the PCE-contaminated sterile anaerobic culture medium is 0.3~0.8 g / L; In step S2, the inoculation amount of THU1 in the PCE-contaminated sterile anaerobic culture medium is (3~5) mL / 25 mL, and the OD of THU1 is... 500The value is 0.1 to 0.2, more preferably OD. 500 The value is 0.15; In step S2, the pH value of the sterile anaerobic culture medium contaminated with PCE is 8.5~9.5, and the initial concentration is 1~3mM. The conditions for static culture in step S2 are: sealed, dark conditions, temperature of 25~35℃, and degradation time of 3~5 days; During the PCE degradation process in step S2, headspace gas is collected every 24 hours, and the PCE concentration is detected using GC-FID.

[0010] Secondly, this invention provides a method for enhancing the microbial degradation of tetrachloroethylene (PCE) using modified pyrite, which is applied to the bioremediation of chlorinated organic pollutants.

[0011] Preferably, the chlorinated organic pollutant is PCE-contaminated groundwater or PCE-contaminated soil; Preferably, the bioremediation is in-situ injection remediation or ex-situ reactor remediation.

[0012] This invention modifies natural pyrite with citric acid, effectively improving its dispersibility, surface functional group density, and electron transport capacity, enhancing its interfacial interaction with microorganisms, and simultaneously utilizing the modified pyrite to slowly release Fe under anaerobic conditions. 2+ The sulfides provide electron donors for the reduction and dechlorination reaction of desulfurizing bacteria THU1, stabilize the reduction environment of the system, enhance the microbial ability to dechlorinate and degrade PCE, and achieve the harmless degradation of PCE.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses a composite system of citric acid modified pyrite coupled with desulfurizing bacteria THU1. Compared with single microbial systems and natural pyrite coupled systems, the PCE degradation efficiency and dechlorination thoroughness are significantly improved. The PCE degradation rate of the present invention is as high as 98.7%.

[0014] 2. The modified pyrite of the present invention can stably and slowly release electron donors, solving the problems of unstable release, pH fluctuation and hydrogen escape of traditional electron donors, and the degradation system has high stability.

[0015] 3. The process conditions of this invention are mild, the operation is simple, the raw material cost is low, and no toxic byproducts are generated during the degradation process, resulting in no secondary pollution. It is suitable for in-situ or ex-situ remediation of chlorinated hydrocarbon pollution in groundwater and soil, and has broad engineering application prospects. Detailed Implementation

[0016] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0017] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0018] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±1℃.

[0019]

[0020] Based on a volume of 1 L of deionized water, the trace element composition includes: 10 mL of 25 w / w% HCl, 1.5 g of FeCl2·4H2O, 0.19 g of CoCl2·6H2O, 0.1 g of MnCl2·4H2O, 0.07 g of ZnCl2, 0.006 g of H3BO3, 0.036 g of Na2Mo4·4H2O, 0.024 g of NiCl2·6H2O, and 0.002 g of CuCl2·2H2O. Example 1

[0021] A method for enhancing the microbial degradation of PCE using modified pyrite, comprising the following steps: S1. Preparation of citric acid modified pyrite material C-FeS2: Natural pyrite was crushed and passed through a 200-mesh sieve to obtain treated natural pyrite. It was then added to a 0.1 mol / L citric acid solution and stirred at room temperature for 24 h. After filtration, it was washed with deionized water until neutral and dried under vacuum at 60 °C to obtain citric acid modified pyrite material C-FeS2. The solid-liquid ratio of the treated natural pyrite to the citric acid solution was 1:10. S2, Citric acid-modified pyrite-enhanced microbial degradation of PCE: Serum bottles, butyl rubber stoppers, aluminum caps, and sampling needles were pre-cleaned and sterilized. All operations were performed in an anaerobic incubator. 12.5 mg of C-FeS2 material was added to a 50 mL sterile serum bottle, followed by 22 mL of sterile anaerobic culture medium, and then 3 mL of activated THU1 bacterial suspension (OD200) was inoculated. 500 =0.15), shake the serum bottle to thoroughly mix the bacterial solution with the C-FeS2 material, and the total liquid volume of the system is 25 mL; Next, use a micropipette to add PCE standard solution to bring the initial concentration of contaminants to 1 mM (add 2.56 μL of PCE standard solution). Immediately after adding the standard solution, cap the serum bottle with a butyl rubber stopper, gently shake the bottle, and then quickly seal it with an aluminum cap to ensure that the system maintains an anaerobic environment. Transfer the bottle to a 30°C incubator and incubate in the dark for 3 days.

[0022] Example 2 (Low bacterial concentration experimental group) Adjusting the OD concentration of THU1 bacterial culture 500 The value was 0.1, and all other conditions remained the same as in Example 1.

[0023] Example 3 (High Bacterial Concentration Experimental Group) Adjusting the OD concentration of THU1 bacterial culture 500 The value was 0.2, and all other conditions remained the same as in Example 1.

[0024] Example 4 (C-FeS2 material low dosage experimental group) The amount of C-FeS2 material added in step S2 was adjusted to 7.5 mg, while other conditions remained the same as in Example 1.

[0025] Example 5 (Experimental group with high dosage of C-FeS2 material) The amount of C-FeS2 material added in step S2 was adjusted to 20 mg, while other conditions remained the same as in Example 1.

[0026] Comparative Example 1 (with addition of unmodified natural pyrite and bacterial solution) Natural pyrite of 200 mesh was selected, without citric acid modification, and all other conditions were kept the same as in Example 1.

[0027] Comparative Example 2 (only THU1 bacterial culture was added, without C-FeS2 material) A method for microbial degradation of PCE includes the following steps: Serum bottles, butyl rubber stoppers, aluminum caps, and sampling needles were pre-cleaned and sterilized. All operations were performed in an anaerobic incubator. 22 mL of sterile anaerobic culture medium was added to a 50 mL sterilized serum bottle, and 3 mL of activated THU1 bacterial suspension (OD100) was inoculated. 500 =0.15), shake the serum bottle, and the total liquid volume of the system is 25 mL; Next, use a micropipette to add PCE standard solution to bring the initial concentration of contaminants to 1 mM (add 2.56 μL of PCE standard solution). Immediately after adding the standard solution, cap the serum bottle with a butyl rubber stopper, gently shake the bottle, and then quickly seal it with an aluminum cap to ensure that the system maintains an anaerobic environment. Transfer the bottle to a 30°C incubator and incubate in the dark for 3 days.

[0028] Comparative Example 3 (only C-FeS2 material was added, without THU1 bacterial culture) A method for degrading PCE with modified pyrite includes the following steps: S1. Preparation of citric acid modified pyrite material C-FeS2: Natural pyrite was crushed and passed through a 200-mesh sieve to obtain treated natural pyrite. It was then added to a 0.1 mol / L citric acid solution and stirred at room temperature for 24 h. After filtration, it was washed with deionized water until neutral and dried under vacuum at 60 °C to obtain citric acid modified pyrite material C-FeS2. The solid-liquid ratio of the treated natural pyrite to the citric acid solution was 1:10. S2, Citric acid-modified pyrite-enhanced microbial degradation of PCE: The serum bottle, butyl rubber stopper, aluminum cap and sampling needle were cleaned and sterilized in advance. All operations were carried out in an anaerobic incubator. 12.5 mg of C-FeS2 material was added to 50 mL of sterilized serum bottle, followed by 22 mL of sterile anaerobic culture medium. The serum bottle was shaken and the total liquid volume of the system was 25 mL. Next, use a micropipette to add PCE standard solution to bring the initial concentration of contaminants to 1 mM (add 2.56 μL of PCE standard solution). Immediately after adding the standard solution, cap the serum bottle with a butyl rubber stopper, gently shake the bottle, and then quickly seal it with an aluminum cap to ensure that the system maintains an anaerobic environment. Transfer the bottle to a 30°C incubator and incubate in the dark for 3 days.

[0029] Comparative Example 4 (blank control group, without C-FeS2 material and THU1 bacterial culture) A method for enhancing the microbial degradation of PCE using modified pyrite, comprising the following steps: The serum bottles, butyl rubber stoppers, aluminum caps and sampling needles were cleaned and sterilized in advance. All operations were carried out in an anaerobic incubator. 25 mL of sterile anaerobic culture medium was added to 50 mL of sterilized serum bottles. Next, use a micropipette to add PCE standard solution to bring the initial concentration of contaminants to 1 mM (add 2.56 μL of PCE standard solution). Immediately after adding the standard solution, cap the serum bottle with a butyl rubber stopper, gently shake the bottle, and then quickly seal it with an aluminum cap to ensure that the system maintains an anaerobic environment. Transfer the bottle to a 30°C incubator and incubate in the dark for 3 days.

[0030] Performance testing: PCE degradation rate: At predetermined sampling time points (every 24 hours after the start of the reaction), headspace gas was collected, and the changes in headspace chlorinated hydrocarbon gas were detected by manual GC-FID injection, and the PCE degradation rate was calculated. Sampling method: Headspace gas is collected using a disposable syringe; each sample volume is 0.2 ml (approximately 0.8% of the headspace volume). After sampling, the syringe needle cap is replaced (to ensure that the gas sample in the syringe does not escape as much as possible), and the sample is transferred to the GC for injection.

[0031] GC-FID detection method: manual injection; split ratio of 10:1; temperature program starting at 45℃, increasing to 100℃ at 20℃ / min and holding for 2 minutes; high-purity nitrogen as carrier gas, column flow rate of 1ml / min.

[0032]

[0033] The results above show that, compared with Comparative Examples 1-4, Examples 1-5 achieved the highest PCE degradation rate of 98.7% through the synergistic effect of citric acid-modified pyrite and THU1, and the PCE degradation was complete. Further comparison of Examples 1-5 with Comparative Examples 1-4 reveals that: The results of the blank control group show that PCE itself has stable physicochemical properties and almost no natural degradation under anaerobic conditions. It can only be effectively degraded by artificial enhanced remediation systems. The results of the single microbial control group and the natural pyrite coupled control group showed that relying solely on THU1 microbial metabolism or using unmodified natural pyrite as an auxiliary remediation method both had the defects of low degradation efficiency and incomplete degradation, and could not meet the requirements of efficient remediation. The results of the control group of pure modified materials showed that citric acid modified pyrite only has a weak chemical reduction ability and cannot independently achieve efficient dechlorination of tetrachloroethylene. The efficient degradation effect of the present invention depends on the synergistic coupling effect of modified pyrite and desulfurizing bacteria THU1.

[0034] The above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for enhancing the microbial degradation of tetrachloroethylene (PCE) using modified pyrite, characterized in that, Includes the following steps: S1. Preparation of citric acid modified pyrite material C-FeS2: The treated natural pyrite was added to a citric acid solution, stirred, filtered, washed and dried to obtain citric acid modified pyrite material C-FeS2. S2, Citric acid modified pyrite enhances microbial degradation of PCE: Add the C-FeS2 material from step S1 to the sterile anaerobic culture medium contaminated with PCE, inoculate with THU1 bacterial solution, and incubate statically to degrade PCE.

2. The method for enhanced microbial degradation of tetrachloroethylene (PCE) using modified pyrite according to claim 1, characterized in that, The natural pyrite processed in step S1 is natural pyrite that has been crushed, sieved, and has a particle size of 100-200 mesh. The concentration of the citric acid solution in step S1 is 0.1 ~ 0.3 mol / L; The solid-liquid ratio of the treated natural pyrite and citric acid solution in step S1 is (1~5):10; In step S1, the stirring conditions are: stirring at room temperature for 12-36 hours; the washing conditions are: washing with deionized water until neutral; and the drying conditions are: vacuum drying at 60℃-80℃.

3. The method for enhanced microbial degradation of tetrachloroethylene (PCE) using modified pyrite according to claim 1, characterized in that, In step S2, the amount of C-FeS2 material added to the PCE-contaminated sterile anaerobic culture medium is 0.3~0.8 g / L; In step S2, the inoculation amount of THU1 in the PCE-contaminated sterile anaerobic culture medium is (3~5) mL / 25 mL, and the OD of THU1 is... 500 The value is 0.1 to 0.2; In step S2, the pH value of the sterile anaerobic culture medium contaminated with PCE is 8.5~9.5, and the initial concentration is 1~3mM. The conditions for static culture in step S2 are: sealed, dark conditions, temperature of 25~35℃, and degradation time of 3~5 days.

4. The application of the modified pyrite-enhanced microbial degradation method for tetrachloroethylene (PCE) as described in any one of claims 1 to 3 in the bioremediation of chlorinated organic pollutants.

5. The application according to claim 4, characterized in that, The chlorinated organic pollutants are PCE-contaminated groundwater or PCE-contaminated soil.

6. The application according to claim 4, characterized in that, The bioremediation is either in-situ injection remediation or ex-situ reactor remediation.

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