Method for optimizing and regulating reduction efficiency of in-situ biological sulfurized zero-valent iron on trichloroethylene

Abstract

The invention provides a method for optimally regulating and controlling the reduction efficiency of in-situ bio-sulfurized zero-valent iron on trichloroethylene, which comprises the following steps: selecting zero-valent iron with the particle size of 2 mu m, 7 mu m and 23 mu m, and the dosage of 10 g; the preparation method comprises the following steps: selecting xanthan gum modified micron iron slurry with the mass of 1.5 g, 3.0 g and 6.0 g respectively; the method comprises the following steps: collecting a water-containing medium with the burial depth of 2-3 m, enriching and domesticating in-situ microorganisms which are resistant to trichloroethylene and have a SO4 < 2-> reduction function, and after collecting a water-containing medium sample, performing microorganism domestication within 24 hours; and injecting the xanthan gum modified zero-valent iron slurry and the domesticated bacterial liquid into an underground water in-situ remediation simulation device. According to the technical scheme, through the synergistic effect of various microorganisms, the dechlorination degree of trichloroethylene in the presence of a natural electron acceptor NO3 <-> is improved, the influence of toxic by-products is reduced, the electron selectivity is enhanced, the long-term performance of zero-valent iron is enhanced, and finally a reduction path of chemical dechlorination and biological denitration is realized; good application prospects are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of groundwater in-situ remediation, in particular, and particularly relates to a method for optimizing and controlling the reduction efficiency of in-situ bio-sulfidized zero-valent iron on trichloroethylene. BACKGROUND

[0002] Trichloroethylene, a typical chlorinated hydrocarbon, is widely used in modern industry as a cleaning agent for electronic components, a solvent for other organic substances, and an important chemical raw material. Trichloroethylene is slightly soluble in water and is a heavy non-aqueous phase liquid, which has strong vertical migration ability in the aeration zone and can easily enter groundwater and accumulate in the aquiclude to form a continuously expanding pollution plume, greatly affecting the water quality of the surrounding groundwater. Trichloroethylene has low biodegradability, with a half-life of 0.5-1.5 years in soil and 1-4.5 years in groundwater, thus posing a long-term threat to human health. Currently, groundwater trichloroethylene pollution has become a key problem faced by many regions (especially industrial sites), with 48.42% of samples detecting volatile organic pollutant content exceeding the standard, and trichloroethylene being one of the main pollution components. Therefore, exploring cost-effective trichloroethylene-contaminated groundwater remediation technology is a necessary requirement and important prerequisite for risk control and management of contaminated sites.

[0003] Micro-scale zero-valent iron (mZVI) is a highly efficient remediation material, and the injected in-situ reaction zone technology constructed by mZVI has good engineering application prospects. Sulfidation modification has been proven to effectively improve the target effectiveness of mZVI on chlorinated hydrocarbon pollutants (especially trichloroethylene). When the sulfate content in groundwater is sufficient, organic matter can stimulate the growth of sulfate-reducing bacteria (SRB), and the respiration of SRB leads to the formation of reduced iron sulfide minerals (FeS and FeS2) from naturally occurring Fe(III) oxide / hydroxide minerals in sediments, promoting the biogeochemical reductive dechlorination of chlorinated alkenes. In recent years, some studies have directly or indirectly proven that in-situ bio-sulfidized zero-valent iron can promote trichloroethylene dechlorination, improve electron transfer efficiency, and reduce hydrogen evolution rate.

[0004] However, the pH, temperature, initial concentration of trichloroethylene, dissolved oxygen, and other inorganic or organic coexisting components in the actual groundwater environment can adversely affect the removal of target pollutants. For example, the presence of natural electron acceptor NO3 - may drive nitrate-reducing-sulfur-oxidizing bacteria to re-oxidize S 2- to SO4 2- , affecting the bio-sulfidation effect of ZVI, and driving denitrifying bacteria to inhibit SRB by competing for substrates and producing toxic denitrification intermediates. At the same time, NO3 -As a highly competitive coexisting electron acceptor, it can affect electron flow in the system, hindering its long-term dechlorination performance. Furthermore, the impact of different zero-valent iron properties on the reactivity of in situ biosulfurization systems remains unclear. Therefore, it is imperative to develop a method to optimize and regulate the reduction efficiency of trichloroethylene by in situ biosulfurized zero-valent iron in the presence of a natural electron acceptor. This is crucial for ensuring the long-term and stable dechlorination of the biosulfurized mZVI system during actual site remediation, reducing remediation costs, and comprehensively optimizing remediation results. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a method for optimizing and regulating the reduction efficiency of trichloroethylene by in-situ biosulfurized zero-valent iron. In view of the problems of poor reduction selectivity and low dechlorination efficiency of zero-valent iron due to the presence of natural electron acceptors in actual groundwater environments, as well as the unclear effect of different conditions and parameters on the remediation of trichloroethylene-contaminated groundwater by in-situ biosulfurized zero-valent iron, the present invention provides a method for optimizing and regulating the reduction efficiency of trichloroethylene by in-situ biosulfurized zero-valent iron. In the presence of nitrate (NO3 - ) in the presence of natural electron acceptors represented by zero-valent iron, by changing the mobility and particle size of zero-valent iron to regulate the growth of in situ microorganisms (sulfate-reducing bacteria, nitrate-reducing bacteria, etc.), the in situ generation of pyrite minerals is promoted, the selectivity of N2 is enhanced, and the efficiency, long-term effect and stability of trichloroethylene removal are enhanced, providing technical theoretical support for the in situ remediation of contaminated groundwater.

[0006] The present invention is achieved through the following technical solution: a method for optimizing and regulating the reduction efficiency of trichloroethylene by in situ biosulfurized zero-valent iron, specifically comprising the following steps: Step S1, selecting zero-valent iron with particle sizes of 2 μm, 7 μm, and 23 μm, respectively, and adding an amount of 10 g; Step S2, selecting xanthan gum modified micron iron slurry with masses of 1.5 g, 3.0 g, and 6.0 g respectively; Step S3: Collect water-containing medium with a burial depth of 2-3 m, enrich and acclimate the water-containing medium with trichloroethylene tolerance and SO4 2- For the in situ microorganisms with reducing function, the microorganisms were acclimated within 24 hours after the aqueous medium sample was collected: 10 g of aqueous medium was added to a 500 mL serum bottle, filled with simulated groundwater with a dissolved oxygen concentration of less than 0.5 mg / L, and 2 mL / L of sodium lactate was added as a carbon source; the culture was carried out in a shaker at 25°C and 120 rpm, and the SO4 content in the sample was measured regularly. 2- concentration, the solution was observed to become obviously black with a pungent odor, and SO4 2- The concentration dropped to 28.9-86.7 mg / L, indicating successful microbial acclimation. In addition, the simulated groundwater was replaced weekly to maintain microbial activity. Step S4: inject the xanthan gum modified zero-valent iron slurry and the bacterial solution after acclimation in step S3 into the groundwater in-situ remediation simulation device. The specific steps are as follows: the groundwater in-situ remediation simulation device includes a seepage column, the side wall of the seepage column is The 100-cm opening was used for the injection of xanthan gum modified zero-valent iron slurry. The inside of the seepage column consisted of an upper silk cloth, a 3-cm thick glass bead buffer layer, 6-layered quartz sand, a 3-cm thick glass bead buffer layer, and a lower silk cloth. Ultrapure water was added simultaneously when filling the quartz sand. After each layer of quartz sand was filled, it was compacted and bubbles were removed. A syringe was used to evenly inject 10 mL of the acclimated bacterial solution on the surface to allow it to naturally penetrate into the matrix. The bottom and top of the seepage column were closed with three-way valves, and a post-treatment column was connected to the top. During the filling process, N2 was continuously introduced to maintain an anaerobic environment. The xanthan gum modified zero-valent iron slurry was introduced into the seepage column from the openings every 5 cm on the side wall and the bottom of the seepage column using a multi-point injection method. The xanthan gum modified zero-valent iron slurry was introduced at a flow rate of 50.18 µL / min for 1 h, followed by high-speed stirring for 0.5 h. Then, 10 mL of the acclimated bacterial solution was introduced at a flow rate of 26.18 µL / min. h, and stirred again for 0.5 h; this process was repeated until 2 L of slurry was completely injected; The simulated groundwater was placed in a sterile sampling bag and continuously injected into the seepage column from bottom to top at a flow rate of 96.00µL / min. When preparing the simulated groundwater, N2 was added to ensure that the dissolved oxygen content was lower than 0.5 mg / L.

[0007] As a preferred embodiment, the preparation steps of xanthan gum-modified micron iron slurry, i.e., mZVI slurry, are as follows: 1 L of ultrapure water is added to a conical flask, and nitrogen is introduced to ensure that the dissolved oxygen concentration in the water is less than 0.5 mg / L; xanthan gum XG is added to the conical flask, and while keeping the bottle mouth sealed, it is stirred at high speed for 1 hour using a mechanical stirrer until the xanthan gum is completely dissolved; then, 10 g of mZVI is added, and the sealed stirring is continued for 1 hour to obtain a uniformly dispersed mZVI slurry.

[0008] As a preferred solution, the bottom diameter of the seepage column is 4 cm and the height is 36 cm.

[0009] As a preferred solution, the seepage column is filled with 6 layers of quartz sand, each layer is 5 cm.

[0010] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects compared with the prior art: (1) The present invention improves the dechlorination degree of trichloroethylene through the synergistic action of multiple microorganisms, reduces the impact of toxic by-products, enhances electron selectivity, strengthens the long-term performance of zero-valent iron, and ultimately realizes the reduction path of "chemical dechlorination and biological denitrification", which has a good application prospect.

[0011] (2) The zero-valent iron migration and particle size optimization and control method adopted in the application realizes rapid and complete dechlorination of trichloroethylene, and can maintain a high trichloroethylene removal rate after running for 4 months, thereby enhancing the long-term effectiveness and stability of efficient removal of trichloroethylene in groundwater.

[0012] (3) The in-situ biological sulfidation zero-valent iron method for repairing trichloroethylene contaminated groundwater adopted in the application has simple preparation process and low cost, and will not affect the soil and groundwater environment.

[0013] (4) The in-situ biological sulfidation zero-valent iron method for repairing trichloroethylene contaminated groundwater adopted in the application can be applied to actual groundwater, and since there are rich sulfate and sulfate-reducing bacteria that can be activated in the actual groundwater layer, the application will provide a good application background. Additional aspects and advantages of the application will become apparent from the following description section or through practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0014] The above and / or additional aspects and advantages of the application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which: Figure 1 It is an in-situ groundwater remediation indoor experimental simulation device; Figure 2 It is a settling curve of different mZVI slurries in application example 1; Figure 3 It is a rheological curve of different mZVI slurries in application example 1; Figure 4 It is the trichloroethylene content in the effluent of different systems in application example 2 changes with time and the cumulative removal amount; Figure 5 It is a dechlorination product distribution diagram after reaction of different systems in application example 2 is completed; Figure 6 It is a cumulative diagram of denitrogenation products of different systems in application example 2; Figure 7 It is the microbial sample in each layer after reaction of different systems in application example 2 is completed, at the genus level. DETAILED DESCRIPTION

[0015] In order to more clearly understand the above-mentioned purposes, features and advantages of the application, the application will be further described in detail below in combination with the drawings and specific embodiments. It should be noted that the embodiments of the application and the features in the embodiments can be combined with each other without conflict.

[0016] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can be practiced in other manners different from those described herein, and therefore, the scope of the present application is not limited to the specific embodiments disclosed below.

[0017] The following description is made in conjunction with Figures 1 to 7 The method for optimizing and regulating the in-situ bio-sulfidized zero-valent iron to repair the efficiency of trichloroethylene is specifically explained.

[0018] In Figure 1 Based on the device shown in the description, the present application proposes a method for optimizing and regulating the in-situ bio-sulfidized zero-valent iron to reduce the efficiency of trichloroethylene, which specifically includes the following steps: Step S1, the particle size of zero-valent iron is selected to be 2 μm, 7 μm and 23 μm, and the dosage is 10 g; Step S2, xanthan gum modified micron iron slurry with a mass of 1.5 g, 3.0 g and 6.0 g is selected; the preparation steps of xanthan gum modified micron iron slurry, namely mZVI slurry, are as follows: 1 L of ultrapure water is added to a conical flask, and N2 is introduced to ensure that the dissolved oxygen concentration in the water is lower than 0.5 mg / L; xanthan gum XG is added to the conical flask, and a mechanical stirrer is used for high-speed stirring under the condition that the bottle opening is sealed, for 1 h, until the xanthan gum is completely dissolved; then, 10 g of mZVI is added, and the sealed stirring is continued for 1 h to ensure that the mZVI is uniformly dispersed and modified, so that the uniformly dispersed mZVI slurry is obtained.

[0019] Step S3, the aqueous medium with a burial depth of 2~3 m is collected, and the sampling point is located in a high SO4 2- Concentration area (coordinates: 36°20′33″N, 120°8′18″E) of groundwater in Jiaozhou City, Shandong Province. In order to enrich and domesticate the in-situ microorganisms which are tolerant to trichloroethylene and have SO4 2- reduction function, the aqueous medium sample is collected and sent to the laboratory within 24 hours, and the microorganisms are domesticated: 10 g of the aqueous medium is added to a 500 mL serum bottle, which is filled with simulated groundwater (Table 1) with a dissolved oxygen concentration lower than 0.5 mg / L, and 2 mL / L of sodium lactate is added as a carbon source; the sample is cultured in a shaking bed at 25℃ and 120 rpm, and the SO4 2- concentration in the sample is determined at regular time intervals; it is observed that the solution becomes obviously black and is accompanied by a pungent odor, and at the same time, the SO4 2- concentration decreases to 28.9~86.7 mg / L, which indicates that the microorganisms are successfully domesticated; in addition, the simulated groundwater is replaced once a week to maintain the activity of the microorganisms, so that they can be used for subsequent experiments; Step S4, the xanthan gum modified zero-valent iron slurry and the bacteria solution after domestication in step S3 are injected into the groundwater in-situ remediation simulation device. The specific steps are as follows: the groundwater in-situ remediation simulation device comprises a seepage column, the side wall of the seepage column is opened every 5 cm for injection of the xanthan gum modified zero-valent iron slurry, and the inside of the seepage column is provided with, from bottom to top, an upper layer of silk cloth, a 3 cm thick glass bead buffer layer, quartz sand filled in 6 layers (5 cm per layer), a 3 cm thick glass bead buffer layer, and a lower layer of silk cloth; wherein, during filling of the quartz sand, ultrapure water is synchronously added, after filling of each layer of quartz sand, compaction is performed and air bubbles are removed, and 10 mL of the domesticated bacteria solution is uniformly injected on the surface using a syringe to allow natural penetration into the matrix; the bottom and the top of the seepage column are closed by three-way valves, and the top is connected to a post-treatment column to reduce environmental pollution caused by experimental wastewater; during the filling process, N2 is continuously introduced to maintain an anaerobic environment; the xanthan gum modified zero-valent iron slurry is introduced into the seepage column through the openings every 5 cm on the side wall and the bottom of the seepage column in a multi-point injection manner, and the xanthan gum modified zero-valent iron slurry is introduced at a flow rate of 50.18 µL / min for 1 h, followed by high-speed stirring for 0.5 h; then, the xanthan gum modified zero-valent iron slurry is introduced at a flow rate of 26.18 µL / min for 1 h, followed by stirring for 0.5 h again; this process is repeated until 2 L of the slurry is completely injected; The xanthan gum modified zero-valent iron slurry is introduced into the seepage column in a multi-point injection manner to ensure uniform distribution of the slurry in the seepage column. Specifically, three-way valves are connected to the openings on the side and bottom of the seepage column, and the slurry is introduced through a pump pipe; the slurry is introduced at a flow rate of 50.18 µL / min for 1 h, followed by high-speed stirring for 0.5 h to prevent the zero-valent iron from sinking; then, the slurry is introduced at a flow rate of 26.18 µL / min for 1 h, followed by stirring for 0.5 h again; this process is repeated until 2 L of the slurry is completely injected. To improve the injection efficiency, two bottles of the slurry can be prepared and introduced alternately.

[0020] The simulated groundwater is placed in a sterile sampling bag, and continuously injected into the seepage column from bottom to top at a flow rate of 96.00 µL / min (equivalent to a groundwater flow rate of 11.01 cm / d); to prevent O2 from entering, when the simulated groundwater is prepared, sufficient N2 is filled to ensure that the dissolved oxygen content is less than 0.5 mg / L. In addition, the simulated groundwater should be replaced regularly.

[0021] Table 1 Composition of simulated groundwater Example 1 The effects of different masses of xanthan gum on the mobility of zero-valent iron with different particle sizes were studied. 1.5 g, 3.0 g, and 6.0 g of xanthan gum (XG) were used to modify mZVI with particle sizes of 2 μm, 7 μm, and 23 μm, respectively. The slurries with different formulations were named: XG1.5+ZVI2, XG3.0+ZVI2, XG1.5+ZVI7, XG3.0+ZVI7, XG1.5+ZVI23, XG3.0+ZVI23, and XG6.0+ZVI23. The rest of the experimental procedures remained the same.

[0022] The sedimentation curves of different mZVI slurries obtained in the present invention are as follows: Figure 2 As shown in the figure, for the 23 μm mZVI particle size group, at a xanthan gum concentration of 1.5 g / L, the relative absorbance decreased to 0.193 after 10 minutes. When the xanthan gum concentration increased to 3 g / L, the relative absorbance gradually decreased, reaching 0.3497 at 240 minutes, indicating that xanthan gum can effectively alleviate the sedimentation of ZVI. When the xanthan gum concentration was further increased to 6 g / L, there was almost no sedimentation within 4 hours. This indicates that for the same mZVI particle size, a higher xanthan gum concentration results in better stability and worse sedimentation performance.

[0023] The rheological curves of different mZVI slurries obtained in the present invention are as follows: Figure 3 As shown. At the same xanthan gum concentration, mZVI slurries of different particle sizes exhibited similar viscosities, indicating no significant correlation between slurry viscosity and mZVI particle size. At the same particle size and shear rate, the corresponding viscosity range for a xanthan gum concentration of 1.5 g / L was 0–111 mPa•s. When the xanthan gum concentration increased to 3 g / L, the corresponding viscosity ranged from 76–396 mPa•s. When the xanthan gum concentration increased to 6 g / L, the corresponding viscosity range reached 100–999 mPa•s, indicating that the slurry viscosity increased significantly with increasing xanthan gum concentration. Higher slurry viscosity increases flow resistance and increases slurry injection energy consumption. Therefore, higher concentrations are not necessarily better. Based on the sedimentation properties and viscosity of xanthan gum-modified mZVI slurries, 3 g / L xanthan gum was ultimately selected for mZVI modification.

[0024] Example 2 The influence of the optimal quality of xanthan gum obtained in research example 1 on the dechlorination performance of in-situ bio-sulfidized zero-valent iron was studied, and a bio-sulfidized system of 2 mu mZVI without adding xanthan gum was set as a control group, named BS2, which was injected into the seepage column from the side opening by a manual syringe; 3.0 g of xanthan gum (XG) was used to modify the bio-sulfidized system of 2 mu mZVI, 7 mu mZVI and 23 mu mZVI respectively, and the bio-sulfidized systems were named XG-BS2, XG-BS7 and XG-BS23 respectively, and the remaining experimental operation steps were kept consistent.

[0025] The content of trichloroethylene in the effluent of different systems obtained by the present application changes with time, as shown in Figure 4 At the initial stage of the experiment, the particle size has a greater influence on the removal rate of trichloroethylene, and the reaction rate of mZVI with smaller particle size is faster; in the middle stage, xanthan gum has an influence on the persistence of trichloroethylene removal, and the group containing xanthan gum can prolong the reaction time by 12 d, indicating that the addition of xanthan gum effectively slows down the passivation process of mZVI. Finally, the cumulative trichloroethylene removal amount of the XG-BS7 group is the highest (64.58 mgC), followed by the XG-BS23 group (62.86 mgC), the XG-BS2 group (29.99 mgC) and the BS2 group (28.84 mgC). This shows that the bio-sulfidized mZVI system with larger particle size exhibits higher dechlorination degree in the trichloroethylene dechlorination process.

[0026] The distribution diagram of dechlorination products after the reaction of different systems obtained by the present application is shown in Figure 5 After the reaction is completed, the proportion of products in the BS2 and XG-BS2 groups shows similar characteristics in various indicators, indicating that the addition of xanthan gum does not have a significant influence on the reduction and dechlorination pathways of trichloroethylene. Compared with the 2 mu group, the content of chlorinated by-products in the XG-BS7 and XG-BS23 groups is lower, especially in the XG-BS7 group, the proportion of DCE is 14.48%, and in the XG-BS23 group, it is 12.18%. In these two groups, the generation amount of ethylene continues to rise linearly, and the proportion of ethylene is 59.48% (XG-BS7) and 51.37% (XG-BS23) respectively. These results show that the bio-sulfidized mZVI system with larger particle size exhibits higher dechlorination degree in the trichloroethylene dechlorination process.

[0027] The cumulative diagram of denitrification products of different systems obtained by the present application is shown in Figure 6 The smaller particle size mZVI (such as 2 mu) has a faster removal rate of NO3 - in the initial stage, but the long-term effect is poor; the xanthan gum modified 2 mu mZVI (XG-BS2 group) has improved removal persistence, indicating that the xanthan gum modification alleviates the rapid consumption of iron particles to some extent and improves the stability. The cumulative NO3- The highest removal rate was 274.4 mgN, followed by the XG-BS7 group (272.4 mgN), the XG-BS2 group (245.7 mgN), and the BS2 group (238.4 mgN). Furthermore, the introduction of large-particle mZVI not only promoted the stability of the denitrification process but also increased the efficiency of N2 production, demonstrating the unique advantage of large-particle zero-valent iron in promoting the activity of denitrifying bacteria.

[0028] The community abundance of each layer of microbial samples at the genus level after the reaction of different systems obtained in the present invention is as follows: Figure 7 In the XG-BS7 and XG-BS23 groups, SRB bacteria are as follows. Desulfobulbus 、 Desulfomicrobium The relative abundance of SRB was higher (29.07%~39.74%), and the relative abundance of dsrA gene in the DSR process was higher (1.31%). This result shows that the xanthan gum modified biosulfurization mZVI system with larger particle size provides a more suitable environment for the growth of SRB and promotes SO4 2- bioreduction effect. Azospira 、 Pseudomonas 、 Thauera 、 Stutzerimonas and Azoarcus The relative abundance of denitrifying bacteria was ranked second (13.13%~26.78%), which effectively reduced NO3 - content.

[0029] The research results of the above application examples show that under the regulation of an appropriate amount of xanthan gum (3 g) and larger particle size (23 μm) zero-valent iron, the abundance of sulfate-reducing bacteria and denitrifying bacteria was increased, the reaction activity of sulfate-reducing bacteria in reducing sulfate was promoted, the influence of natural electron acceptors was reduced, and the remediation efficiency of zero-valent iron for trichloroethylene-contaminated groundwater was significantly improved.

[0030] Throughout this specification, terms such as "one embodiment," "some embodiments," and "specific embodiments" mean that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0031] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for optimizing and regulating the reduction efficiency of trichloroethylene by in situ biosulfurized zero-valent iron, characterized in that: The specific steps include: Step S1, selecting zero-valent iron with particle sizes of 2 μm, 7 μm, and 23 μm, respectively, and adding an amount of 10 g; Step S2, selecting xanthan gum modified micron iron slurry with masses of 1.5 g, 3.0 g, and 6.0 g respectively; Step S3: Collect water-containing medium with a burial depth of 2-3 m, enrich and acclimate the water-containing medium with trichloroethylene tolerance and SO4 2- For the in situ microorganisms with reducing function, the microorganisms were acclimated within 24 hours after the aqueous medium sample was collected: 10 g of aqueous medium was added to a 500 mL serum bottle, filled with simulated groundwater with a dissolved oxygen concentration of less than 0.5 mg / L, and 2 mL / L of sodium lactate was added as a carbon source; the bottle was cultured in a shaker at 25°C and 120 rpm, and the SO4 content in the sample was measured regularly. 2- concentration, the solution was observed to become obviously black with a pungent odor, and SO4 2- The concentration dropped to 28.9-86.7 mg / L, indicating successful microbial acclimation. In addition, the simulated groundwater was replaced weekly to maintain microbial activity. Step S4: inject the xanthan gum modified zero-valent iron slurry and the bacterial solution after acclimation in step S3 into the groundwater in-situ remediation simulation device. The specific steps are as follows: the groundwater in-situ remediation simulation device includes a seepage column, the side wall of the seepage column is The 3 cm opening was used for the injection of xanthan gum modified zero-valent iron slurry. The inside of the seepage column was composed of an upper silk cloth, a 3 cm thick glass bead buffer layer, 6 layers of quartz sand, a 3 cm thick glass bead buffer layer and a lower silk cloth from bottom to top. Ultrapure water was added simultaneously when filling the quartz sand. After each layer of quartz sand was filled, it was compacted and bubbles were removed. A syringe was used to evenly inject 10 mL of the acclimated bacterial solution on the surface to allow it to naturally penetrate into the matrix. The bottom and top of the seepage column were closed with three-way valves, and a post-treatment column was connected to the top. During the filling process, N2 was continuously introduced to maintain an anaerobic environment. The xanthan gum modified zero-valent iron slurry was introduced into the seepage column from the openings every 5 cm on the side wall and the bottom of the seepage column using a multi-point injection method. The xanthan gum modified zero-valent iron slurry was introduced at a flow rate of 50.18 µL / min for 1 h, and then stirred at high speed for 0.5 h; then, the solution was introduced at a flow rate of 26.18 μL / min for 1 h and stirred again for 0.5 h; this process was repeated until 2 L of slurry was completely injected; The simulated groundwater was placed in a sterile sampling bag and continuously injected into the seepage column from bottom to top at a flow rate of 96.00µL / min. When preparing the simulated groundwater, N2 was added to ensure that the dissolved oxygen content was lower than 0.5 mg / L.

2. The method for optimizing and controlling the reduction efficiency of trichloroethylene by in situ biosulfurized zero-valent iron according to claim 1, characterized in that The preparation steps of the xanthan gum modified micron iron slurry, i.e., mZVI slurry, are as follows: 1 L of ultrapure water is added to a conical flask, and N2 is introduced to ensure that the dissolved oxygen concentration in the water is lower than 0.5 mg / L; xanthan gum XG is added to the conical flask, and while keeping the bottle mouth sealed, a mechanical stirrer is used to stir at high speed for 1 hour until the xanthan gum is completely dissolved; then, 10 g of mZVI is added, and the sealed stirring is continued for 1 hour to obtain a uniformly dispersed mZVI slurry.

3. The method for optimizing and controlling the reduction efficiency of trichloroethylene by in-situ biosulfurized zero-valent iron according to claim 1, characterized in that: The bottom diameter of the seepage column is 4 cm and the height is 36 cm.

4. The method for optimizing and controlling the reduction efficiency of trichloroethylene by in-situ biosulfurized zero-valent iron according to claim 1, characterized in that: The seepage column is divided into 6 layers of quartz sand, each layer is 5 cm.

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