Method for strengthening natural attenuation of dichloromethane and synchronously fixing hexavalent chromium through electrical stimulation

Abstract

A method for strengthening natural attenuation of dichloromethane through electrical stimulation and synchronously fixing hexavalent chromium comprises the following steps that a micro electric field reactor is constructed according to a reaction bottle, electrode plates are constructed in the micro electric field reactor, the electrode plates are connected with a direct-current power source, and the electrode plates form an anode and a cathode of the micro electric field reactor; groundwater and soil containing pollutants are added into the micro electric field reactor; wherein the ratio of the soil to the underground water is 1: 9; the pollutants are dichloromethane and hexavalent chromium; starting the micro-electric field reactor under a shading condition, and domesticating microorganisms in the micro-electric field reactor for a plurality of cycles to construct a micro-electric field reaction system with a stable microbial community; wherein one period is at least eight days; and applying voltage to the micro electric field reaction system to purify pollutants of the underground water and the soil, so that natural attenuation of dichloromethane is enhanced by electrical stimulation, and hexavalent chromium is synchronously fixed.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, in particular to a method for electrically stimulating and strengthening the natural decay of dichloromethane and synchronously fixing hexavalent chromium. Background Art

[0002] Chromium is an essential metal element in my country's industrialization process and is widely used in electroplating, leather making, and the steel and chemical industries. The production process generates a large amount of chromium-containing wastewater and waste residue, causing serious environmental chromium pollution. Chromium has multiple valence states in the natural environment, while trivalent chromium and hexavalent chromium are relatively stable, while other oxidation states are often unstable as intermediate products. Among them, hexavalent chromium (Cr(VI)) is a highly toxic heavy metal ion that poses serious hazards to humans and the environment. In comparison, trivalent chromium (Cr(III)) is less toxic and has a low solubility. Hexavalent chromium has a high solubility in water and is highly biologically toxic. Therefore, how to reduce and fix Cr(VI) is a key challenge in remediating environmental chromium pollution. Summary of the Invention

[0003] In view of the above problems, the embodiments of this specification provide a method for electrically enhancing the natural decay of dichloromethane and synchronously fixing hexavalent chromium. By constructing a micro-electric field, the environment can be enhanced, which can significantly reduce hexavalent chromium pollution in the environment.

[0004] In the first aspect, the embodiments of the present invention provide a method for electrically stimulating and enhancing the natural decay of dichloromethane and synchronously fixing hexavalent chromium, comprising the following steps: constructing a micro-electric field reactor based on a reaction bottle, and constructing an electrode plate in the micro-electric field reactor, connecting the electrode plate to a DC power supply so that the electrode plate constitutes the anode and cathode of the micro-electric field reactor; adding groundwater and soil containing pollutants to the micro-electric field reactor; wherein the ratio of the soil to groundwater is 1:9; the pollutants are dichloromethane and hexavalent chromium; starting the micro-electric field reactor under light-shielding conditions, and acclimating the microorganisms in the micro-electric field reactor for multiple cycles to construct a micro-electric field reaction system with a stable microbial community; wherein one cycle is at least eight days; applying voltage to the micro-electric field reaction system to purify the pollutants in the groundwater and soil, and realizing electrically stimulating and enhancing the natural decay of dichloromethane and synchronously fixing hexavalent chromium.

[0005] In this embodiment, hexavalent chromium (Cr(VI)) is a highly toxic pollutant, which can be efficiently reduced to trivalent chromium (Cr(III)) with low toxicity through the synergistic effect of electrical stimulation and microorganisms. Trivalent chromium has a low solubility and weak biological toxicity, so it exists stably in the environment, reducing the harm of chromium to the human body and the ecosystem. Dichloromethane is a toxic organic pollutant that is usually difficult to decay naturally. Enhancing the degradation ability of microorganisms through electrical stimulation helps to accelerate the removal of dichloromethane and reduce its pollution to water bodies and soil. The construction of the micro-electric field reactor not only promotes electrochemical reactions, but also further enhances the removal efficiency of pollutants through the adaptation and stability of the microbial community. The effect of the electric field provides a favorable growth environment for microorganisms and improves the metabolic capacity of microorganisms. Compared with traditional chemical remediation methods, this method has low cost, does not rely on a large amount of chemical agents, and reduces the risk of secondary pollution. At the same time, the combination of electrical stimulation and natural decay is in line with the concept of sustainable development and has strong environmental protection characteristics. This technical solution is suitable for different types of soil and groundwater pollution scenarios. By adjusting the intensity of the electric field and the cycle of microbial acclimation, it can flexibly respond to pollutants of different concentrations and has strong adaptability. The effect of electrical stimulation is not limited to the reduction of pollutants, but can also promote the growth and activity of microbial communities, further improving the efficiency of pollutant degradation. This synergistic effect can significantly improve the remediation effect, especially in complex environments containing multiple pollutants. In short, this method combines the advantages of electrical stimulation, microbial acclimation and natural attenuation, can effectively repair chromium-contaminated environments, and has good application prospects and environmental benefits.

[0006] In a possible embodiment, the material of the electrode plate includes any one or more of carbon felt, graphite felt, graphite plate, and stainless steel plate.

[0007] In a possible implementation manner, the distance between the electrode plates is 4 cm.

[0008] In a possible embodiment, the electrode plate is in a rectangular parallelepiped configuration and is vertically placed in the micro-electric field reactor.

[0009] In one possible embodiment, the applied DC voltage is 0-0.9V.

[0010] In one possible implementation, the applied DC voltage is 0.6-0.9V.

[0011] In one possible implementation, the applied DC voltage is 0.6V.

[0012] In one possible embodiment, the concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 1 mg / L-10 mg / L, respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:2.5-10.

[0013] In one possible embodiment, the concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 5 mg / L-7.5 mg / L, respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:2.5-5.

[0014] In one possible embodiment, the concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 5 mg / L respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:5.

[0015] In one possible embodiment, the reaction bottle is a reagent bottle coated with aluminum foil.

[0016] In one possible embodiment, the microorganisms in the micro-electric field reactor are Pseudomonadota (Proteobacteria, 26.5%), Bacteroidota (Bacteroidetes, 18.3%), and Chloroflexota (Chloroflexi, 12.1%) at the phylum level.

[0017] In a second aspect, the embodiments of this specification also provide a device for electrically stimulating and enhancing the natural decay of dichloromethane and synchronously fixing hexavalent chromium, which is applied to the method described above, including a micro-electric field reactor, an electrode plate, and a DC power supply. The micro-electric field reactor contains groundwater and soil containing pollutants, wherein the ratio of the soil to the groundwater is 1:9; the pollutants are dichloromethane and hexavalent chromium; the micro-electric field reactor is started under light-shielding conditions, and the microorganisms in the micro-electric field reactor are acclimated for multiple cycles to construct a micro-electric field reaction system with a stable microbial community; wherein one of the cycles is at least eight days; a voltage is applied to the micro-electric field reaction system to purify the pollutants in the groundwater and soil, thereby achieving electrically stimulating and enhancing the natural decay of dichloromethane and synchronously fixing hexavalent chromium.

[0018] The present invention proposes an innovative, low-cost, and environmentally friendly remediation method for hexavalent chromium (Cr(VI)) and dichloromethane pollution in the environment by constructing a micro-electric field reactor and combining electrical stimulation with the synergistic effect of microorganisms. The method can effectively treat hexavalent chromium and dichloromethane pollution in the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 The changing trends of dichloromethane and Cr(VI) over time in the micro-electric field reactor are shown;

[0021] Figure 2 SEM images of four electrode materials are shown, including (a) graphite felt, (b) carbon felt, (c) graphite plate, and (d) stainless steel plate.

[0022] Figure 3 The electrochemical properties of different electrode materials in the bioelectrochemical system are shown, where (a) is the CV curve and (b) is the EIS spectrum;

[0023] Figure 4 Shows the XPS (Cr 2p) spectra of carbon felt and graphite plate;

[0024] Figure 5 The graphite plate is used as the electrode material, and under the condition of Cr(VI)-DCM composite pollution at 0.6V, (a) the change of DCM concentration over time; (b) the change of Cr(VI) concentration over time;

[0025] Figure 6 SEM images of the reactor precipitate are shown;

[0026] Figure 7 Shown are (a) XPS spectrum of Cr(2p) in the reactor precipitate, (b) XRD pattern in the reactor precipitate, and (c) TOC degradation and methyl chloride generation in the reactor;

[0027] Figure 8 The time-varying trends of dichloromethane and Cr(VI) under different voltage conditions in the micro-electric field reactor are shown;

[0028] Figure 9 The time-varying trends of dichloromethane and Cr(VI) at different concentrations in the micro-electric field reactor are shown;

[0029] Figure 10 Shown are (a) DCM removal efficiency; (b) Cr(VI) removal efficiency at different concentration (DCM:Cr(VI)) ratios;

[0030] Figure 11The distribution characteristics of microorganisms in the reactor sediment, anode, and cathode are shown (a) OUT level Venn diagram;

[0031] Figure 12 Shown are (a) phylum-level microbial community column stacking diagram and (b) genus-level microbial community heat map;

[0032] Figure 13 Shown are the phylogenetic tree constructed from the reactor sediment metagenomic samples (a); and the gene abundance heat map (b). DETAILED DESCRIPTION

[0033] It should be understood that the scope of protection of the present application is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present application are for the purpose of describing specific embodiments rather than for the purpose of limiting the scope of protection of the present application; in the specification and claims of the present application, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0034] When the embodiments provide numerical ranges, it should be understood that, unless otherwise specified herein, both endpoints of each numerical range and any numerical value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of this application, any method, equipment, and material of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present application can also be used to realize this application.

[0035] The "room temperature" mentioned in the examples of this application has a meaning well known in the art, generally referring to 24-28°C.

[0036] Hexavalent chromium (Cr(VI)), a typical environmental pollutant, is widely used and released in industrial activities such as metallurgy, electroplating, leather processing, and dye manufacturing due to its strong oxidizing properties and high toxicity, attracting widespread attention. Compared with trivalent chromium (Cr(III)), hexavalent chromium has stronger mobility and higher biotoxicity. It is efficiently absorbed by organisms and can easily induce physiological effects such as DNA damage, cell mutations, and carcinogenesis. Therefore, it is of great significance in ecological risk assessment and pollution control.

[0037] Dichloromethane (CH2Cl2) is a volatile organic compound (VOC) widely used in organic synthesis, as a cleaning agent, and as an extractant. It has good solubility and a low boiling point. In surface environmental samples (such as surface or shallow media such as soil, water, and vegetation), dichloromethane is highly volatile and mobile, entering environmental systems through atmospheric deposition, water infiltration, and soil adsorption. Due to its volatility, poor degradation, and toxicity to organs such as the central nervous system and the liver and kidneys, dichloromethane is considered an environmental pollutant with potential health risks.

[0038] The present application first screens the electrode materials and then uses electrical stimulation to enhance the natural decay and hexavalent chromium reduction fixation. More specifically, the method provided in the embodiment of the present application for electrically stimulating the natural decay of dichloromethane and simultaneously fixing hexavalent chromium includes the following steps:

[0039] (1) constructing a micro-electric field reactor based on the reaction bottle, constructing an electrode plate in the micro-electric field reactor, and connecting the electrode plate to a direct current power supply so that the electrode plate constitutes the anode and cathode of the micro-electric field reactor;

[0040] (2) adding groundwater and soil containing pollutants into the micro-electric field reactor; wherein the ratio of the soil to the groundwater is 1:9; and the pollutants are dichloromethane and hexavalent chromium;

[0041] (3) starting the micro-electric field reactor under light-shielding conditions, and acclimating the microorganisms in the micro-electric field reactor for multiple cycles to construct a micro-electric field reaction system with a stable microbial community; wherein one cycle is at least eight days;

[0042] (4) adding contaminated groundwater and soil to the micro-electric field reaction system, and applying voltage to the micro-electric field reaction system to purify the pollutants in the groundwater and soil, thereby achieving electrical stimulation to enhance the natural attenuation of dichloromethane and synchronously fix hexavalent chromium.

[0043] This invention aims to effectively reduce hexavalent chromium (Cr(VI)) pollution in the environment through the synergistic effect of electrical stimulation and microbial communities. The specific working principle is as follows:

[0044] Construction and working principle of micro electric field reactor:

[0045] A micro-electric field reactor is constructed in a reaction flask and connected to a DC power supply via electrode plates, forming an anode and cathode. The electrode plates form a micro-electric field within the micro-electric field reactor, applying voltage to pollutants in the soil and groundwater. The formation of this micro-electric field promotes electrolysis and electrochemical reactions, enhancing the reduction reaction of pollutants. The micro-electric field can effectively accelerate the reduction process of hexavalent chromium in the environment, reducing highly toxic Cr(VI) to less toxic Cr(III). It also promotes the fixation of hexavalent chromium through the interaction between the electric field and the microbial community, reducing its solubility and bioavailability in water.

[0046] Natural decay of dichloromethane:

[0047] Dichloromethane is a common organic pollutant that is generally difficult to degrade under natural conditions. In this technical solution, electrical stimulation is used to enhance the natural decay of dichloromethane. The electric field promotes the activity of microbial communities, indirectly accelerating the degradation of dichloromethane. Electrical stimulation helps promote microbial metabolic activity, thereby enhancing their degradation capacity.

[0048] Microbial Acclimation and Community Stability: In this method, through multiple cycles of acclimation (at least eight days), the microbial community gradually adapts to the presence of the electric field and forms a stable microbial community. Under the influence of the micro-electric field, these microorganisms help improve the reduction and fixation efficiency of hexavalent chromium and enhance their ability to degrade dichloromethane. The microbial activity helps fix minerals and form biofilms, thereby stabilizing chromium and other pollutants in soil and water, reducing their harm to the environment and organisms.

[0049] Voltage application and pollutant purification:

[0050] Applying a certain voltage to the micro-electric field reaction system can enhance the electrochemical reaction system and the metabolic activity of the microorganisms, thereby accelerating the reduction and degradation of the pollutants (hexavalent chromium and dichloromethane). Through this process, hexavalent chromium is reduced to trivalent chromium and fixed in the soil, while dichloromethane is removed through microbial degradation.

[0051] Based on the above content, the technical solution of this application is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments.

[0052] Example 1

[0053] Micro-electric field electrode material performance experiment

[0054] Micro-electric fields can enhance the natural attenuation of various pollutants in the environment by oxidizing (anode) and reducing (cathode) pollutants, providing unlimited clean electron donors / acceptors, and regulating microbial populations, dehydrogenase activity, and community structure, ultimately achieving the goal of degrading organic matter and reducing the environmental hazards of toxic heavy metals. The electrode material in the micro-electric field system provides an electron transmission channel, reacting with substances in the solution at the electrode surface.

[0055] Different electrode materials have distinct properties that can influence the electrochemical performance of the electrodes in a system. Carbon-based materials are often used as electrode materials due to their excellent conductivity, chemical stability, and abundant surface functional groups. Furthermore, stainless steel, with its corrosion resistance, plasticity, and high mechanical strength, possesses stable electrochemical properties, making it a promising candidate for electrode materials in electric field systems.

[0056] In this implementation, dichloromethane and hexavalent chromium were selected as target pollutants based on the characteristics of the pollutants in the demonstration site. Based on previous literature research, carbon felt, graphite felt, graphite plate, and stainless steel plate were determined as alternative materials to build a micro-electric field reactor for electrode material screening and microbial acclimation of the target demonstration site, and regular monitoring of pollutant concentrations and changes in microbial communities was carried out.

[0057] The experimental setup is as follows:

[0058] A 250 mL blue-capped reagent bottle was used as a carrier to construct a micro-electric field reaction system. 30 g of soil and 270 mL of simulated groundwater containing pollutants (soil-water ratio 1:9) were added to the reagent bottle.

[0059] ·Cr(VI) was added to simulated groundwater (0.1557 g / L NH4Cl, 0.2464 g / LCaCl2, 1.0572 g / L MgCl2·6H2O, 0.4459 g / L NaCl, 0.0283 g / L KCl, 0.8082 g / L NaHCO3, 0.0299 g / L KH2PO4) in the form of potassium dichromate, and the initial concentrations of Cr(VI) and dichloromethane were 5 mg / L.

[0060] Seal the bottle mouth with a rubber stopper to prevent the escape of dichloromethane. Insert the corresponding electrode plates from the bottle mouth, with a uniform distance of 4 cm between the electrodes. Ensure that the electrode plates are submerged below the liquid surface and wrap the entire reagent bottle with tin foil. The control group reactor settings are the same as those of the experimental group: 30g of soil and 270mL of simulated groundwater containing contaminants (soil-water ratio of 1:9). The initial concentrations of Cr(VI) and dichloromethane are 5mg / L, but no external power stimulation is applied.

[0061] A DH1766-1 DC power supply applied a stable voltage of 0.6V to the experimental reactor. A long-term acclimation cycle was performed, lasting eight days. Samples were taken every other day to measure dichloromethane and Cr(VI) concentrations. Seven acclimation cycles were run, and two cycles, after stabilization, were selected for electrode material screening.

[0062] Figure 1 The figure shows the changing trend of dichloromethane and Cr(VI) in the micro-electric field reactor over time. Figure 1 (a) shows the time variation of DCM concentration under different electrode materials; Figure 1 (b) shows the time variation of Cr(VI) concentration under different electrode materials. Figure 1 As shown, Figure 1 (a) shows the time-dependent changes in dichloromethane (DCM) concentration using different electrode materials during two cycles. It can be seen that the concentration of DCM gradually decreases during each reaction cycle, with the carbon felt and graphite plate electrode materials achieving the best DCM removal results. During the 8-day sixth cycle, the DCM removal rates for the carbon felt and graphite plate electrode materials were 96% and 96.5% respectively. In the unpowered control group, DCM was also removed through natural decay, achieving a removal rate of 63%. During the 8-day seventh cycle, the DCM removal rates for the carbon felt and graphite plate electrode materials were 97.8% and 95.4% respectively. In the unpowered control group, DCM was also removed through natural decay, achieving a removal rate of 62%. The above comparison demonstrates that, through electric field enhancement, the enhanced natural decay rate of DCM organic pollutants is increased by over 30% compared to the natural decay rate. Figure 1 (b) is a graph showing the change of hexavalent chromium concentration over time under different electrode materials. In each cycle, hexavalent chromium can be gradually removed. Among them, the hexavalent chromium removal performance of carbon felt and graphite plate electrode materials is the highest, which are 95.44% and 97.78% respectively, both exceeding 95%. It can be seen that micro-electric field assisted enhancement can effectively remove heavy metals.

[0063] Through the above analysis, it can be seen that the micro-electric field assisted strengthening function of the two electrode materials, carbon felt and graphite plate, is the most excellent. Compared with the natural attenuation rate, the enhanced natural attenuation rate of dichloromethane organic pollutants can be increased by 30%, and the stabilization rate of heavy metal hexavalent chromium can be achieved by more than 95%.

[0064] Example 2

[0065] Micro-electric field electrode material characterization

[0066] Based on the above performance test results, four stabilized electrode materials (graphite felt, carbon felt, graphite plate, and stainless steel plate) were selected for material characterization. The optimal electrode material was preliminarily screened based on the material characterization and performance test results. The electrode materials were characterized by mineralogical methods such as SEM (Scanning Electron Microscopy), XRD (X-ray Diffraction), XPS (X-ray Photoelectron Spectroscopy), and infrared spectroscopy, and analyzed by electrochemical characterization methods such as CV (Cyclic Voltammetry) and EIS (Electrochemical Impedance Spectroscopy).

[0067] In this embodiment, the material is first characterized using a scanning electron microscope (SEM, JEOL JAX840, Hitachi, Japan) equipped with an energy dispersive X-ray spectrometer (EDS). The scale of each image is 25.0 μm, which can be used to analyze the structural differences, contamination, or loading of the material.

[0068] Figure 2 Shows SEM images of four electrode materials, where (a) is graphite felt, (b) is carbon felt, (c) is graphite plate, and (d) is stainless steel plate. Figure 2 , Figure 2 (a) shows the state of graphite felt electrode material, e.g. Figure 2 As shown in (a), it can be observed that the material is composed of uniform and neatly arranged fibers, with a smooth fiber surface and no particles or impurities attached. Figure 2 (b) is a carbon felt electrode material, which also has a fibrous structure. However, compared with Figure (a), a small amount of particles or sediments appear on its surface, indicating that the electrode material has absorbed some pollutants or precursor particles after undergoing some initial reactions in the performance experiment. This may change its surface activity and electrochemical properties. High-magnification SEM images show that the surfaces of the two materials have shallow grooves along the long axis and have a discontinuous stripe structure. The gaps between the carbon fibers of the two materials are large, and each fiber is cylindrical with high porosity. Graphite plate electrode material Figure 2The surface of (c) is composed of a large number of tiny particles forming a raised platform, showing a completely different morphology, showing a structure with densely packed particles. There are a large number of pores between these tiny particles, which gives it a large specific surface area and porosity. This may be because the electrode surface is loaded with a large amount of nanopowder materials, such as activated carbon, metal oxides, or deposition products. The stainless steel plate also has a large number of pores between the tiny particles, but its carbon fiber diameter is larger than that of the carbon fiber in carbon felt and graphite felt. Figure (d) shows a stainless steel plate electrode material, which returns to a fiber-supported structure, but the fiber surface can be seen to be partially covered or coated, and irregular particles or flaky materials are attached to the surface, indicating that it has undergone a relatively obvious modification or reaction process, such as electrodeposition, chemical reduction deposition, or pollutant adsorption. This structure retains the original mechanical support properties while forming a reactive area on the surface.

[0069] The above is an analysis of the appearance characterization of the four electrode materials, and we will continue to explore the electrochemical properties of the four electrode materials. Figure 3 The electrochemical properties of different electrode materials in bioelectrochemical systems are shown, where (a) is the CV curve and (b) is the EIS spectrum. Figure 3 , Figure 3 It includes two important electrochemical characterization graphs, namely the cyclic voltammetry (CV) curve on the left (a) and the electrochemical impedance spectroscopy (EIS) on the right (b), which are used to evaluate the electrochemical performance of the four electrode materials. Specifically, in-depth analysis can be conducted from the aspects of reaction activity, charge transfer ability and electrode interface impedance.

[0070] It should be noted that the cyclic voltammetry curve is used to reflect the reversibility, electrochemical activity and capacitance performance of electrode materials. Figure 3 (a) shows the CV curves of four materials, with a scanning voltage range of -0.5V to 1.0V (vs.Ag / AgCl). The graphite plate (blue line) shows a significantly higher current response, especially in the oxidation peak and reduction peak regions, indicating that it has higher electrochemical activity. The area enclosed by the CV curve is directly related to the capacitance of the material. The larger the area, the stronger the charge storage capacity. The graphite plate electrode material has the largest area, indicating that its surface has more active sites or a larger specific surface area, which can provide more charge transfer channels. All materials show a certain degree of quasi-symmetric redox peaks during the scanning process, indicating that the electrode reaction has a certain reversibility. Electrochemical impedance spectroscopy (EIS) is used to analyze the interface resistance, charge transfer resistance and capacitance characteristics of electrode materials. As Figure 3 As shown in (b), the stainless steel plate shows the largest arc, indicating that its charge transfer resistance is the highest and electron transfer is limited; the arcs of graphite felt, carbon felt and graphite plate decrease in turn, among which the arc of graphite plate is the smallest, indicating that its charge transfer resistance is the smallest and the interfacial reaction kinetics is the best. Figure 3(b) The angle of the oblique line in the medium and low frequency bands reflects the diffusion process. The graphite plate shows a straight line that is close to vertical, indicating that the ion diffusion is faster and the mass transfer at the electrolyte-electrode interface is smooth. In contrast, the straight line of the stainless steel plate deviates more from the vertical direction, indicating that its ion diffusion is hindered and the interface diffusion resistance is larger.

[0071] Figure 4 The carbon felt XPS (Cr 2p) spectrum and the graphite plate XPS (Cr 2p) spectrum are shown. Figure 4 As shown in Figure 2, the carbon felt and graphite plate electrode materials were characterized by XPS. Figure 4 Figures (a) and (b) show the results of X-ray photoelectron spectroscopy (XPS) analysis of carbon felt and graphite plates, used to investigate the chemical composition and elemental valence states of the materials' surfaces, particularly the presence of chromium (Cr). Two key chromium species can be identified: Cr(III)-oxide (blue), with a peak at approximately 578–580 eV, representing the trivalent chromium oxidation state typically associated with Cr2O3; and Cr(VI) (red), with a peak at approximately 580–582 eV, representing hexavalent chromium, commonly found in CrO3 or Cr2O72-. In the graphite felt electrode material on the right, two peaks are primarily identified: Cr(III)-hydrogen oxide and Cr(III)-oxide. Both Cr(III) and Cr(VI) are present on the carbon felt surface, with the Cr(III) peak being more pronounced. The presence of Cr(III) on the graphite plate surface indicates that trivalent chromium is the predominant species. Hexavalent chromium is generally highly toxic, while trivalent chromium is relatively more stable. This valence distribution may indicate that the graphite plate and carbon felt surfaces have a certain Cr(VI) reduction ability or stability, making them suitable for Cr(VI) reduction electrodes.

[0072] Overall, carbon felt and graphite sheets, with their outstanding performance in performance experiments and material characterization, are undeniably the best electrode materials selected in this screening. Their enormous potential in organic pollutant degradation and heavy metal stabilization provides new directions and strong support for innovation in pollution control technologies.

[0073] Example 3

[0074] Micro-electric field-assisted enhancement of natural attenuation and directional migration

[0075] In this embodiment, combining the results of Example 2, we developed micro-electric field-assisted enhancement technology using graphite plates, the optimal electrode material. The experimental setup was similar to that of Example 1. The central experimental group was operated at 0.6V, with 5mg / L dichloromethane and 5mg / L hexavalent chromium added to the reactor. A control group with no voltage applied, a control group with hexavalent chromium contamination alone, and a control group with dichloromethane contamination alone were also set up. Three replicates were set up for each group to minimize sampling errors.

[0076] Figure 5 The graphite plate is used as the electrode material, and under the condition of 0.6V Cr(VI)-DCM composite pollution, (a) DCM concentration changes with time; (b) Cr(VI) concentration changes with time. Figure 5 As shown in Figure 2, during the stable operation of one cycle (8 days), the steady removal of dichloromethane and hexavalent Cr was observed. Figure 5 (a) The removal efficiency of DCM in the composite pollution (red line) is 95.15% ± 0.53%, which is 35.31% higher than the natural decay without power supply and 18.15% higher than the single control. Figure 5 (b) Combined pollution (red line) hexavalent chromium removal efficiency was 95.03 ± 2.62%. Compared to natural decay without power, the Cr(VI) removal efficiency increased significantly by 57.25%, and compared to the hexavalent chromium control group alone, the efficiency increased by 51.7%. This further demonstrates the excellent treatment capabilities of graphite plate as an electrode material.

[0077] Figure 6 Figure 2 shows the SEM image of the reactor precipitate. Figure 6 As shown, the sediment in the bioelectrochemical reactor was sampled and analyzed for Cr(VI) reduction products and dichloromethane degradation products. SEM combined with EDS spectroscopic analysis revealed that SEM images showed flocculent and flaky precipitates related to Cr in the reactor sediment. EDS spectra also indicated the formation of Cr in the sediment.

[0078] In order to study the chemical composition and element valence state of the sample surface, XPS technology was used to analyze its surface. Figure 7 Shown are (a) the XPS spectrum of Cr(2p) in the reactor precipitate, (b) the XRD pattern in the reactor precipitate, and (c) the degradation of TOC and the generation of methyl chloride in the reactor. Figure 7 (a) XPS spectrum shows that Cr(Ⅲ) and Cr(Ⅵ) are identified at 579eV, 575.05eV and 576eV respectively. Figure 7 (b) shows the formation of trivalent chromium in the reactor precipitate, primarily composed of CrO₃ and Cr₂O₃. TOC measurements within the reactor revealed a significant downward trend in the system. Since no carbon source was added to the system, this decrease in TOC indirectly suggests that the microorganisms were utilizing the carbon source. The formation of monochloromethane was also observed during this process, likely a product of dechlorination of the dichloromethane in the system.

[0079] Example 4

[0080] Influencing Factor Experiment-Voltage Screening

[0081] Figure 8 The figure shows the time-varying trends of dichloromethane and Cr(VI) under different voltage conditions in the micro-electric field reactor. Figure 8 As shown in the figure, in this embodiment, the selected graphite plate is selected to build a micro-electric field reactor for voltage optimization, providing the optimal voltage data for actual repair, wherein the voltage is set to 0.3V, 0.6V, and 0.9V, and the optimal voltage is preliminarily screened based on the performance test results. The concentration changes of dichloromethane and Cr(VI) under three voltages are shown in the figure. Figure 8 As shown in Figure 2, the voltage has a significant effect on the degradation of DCM and the reduction of Cr(VI). Figure 8 It is clear that there are significant differences in DCM degradation and Cr(VI) reduction rates under different voltage conditions. As the voltage increases, the DCM degradation and Cr(VI) reduction rates and final removal rates generally show a trend of first increasing and then slightly changing (rather than continuously improving with increasing voltage).

[0082] 0.6V is the optimal voltage: At 0.6V, both DCM degradation and Cr(VI) reduction achieved optimal results, with Cr(VI) removal rates reaching 97.7% and 95.4% for DCM. DCM degradation was nearly complete on day 8, and Cr(VI) reduction was close to 100%. This demonstrates that a voltage of 0.6V provides optimal energy conditions for the microorganisms and electrochemical reactions in the bioelectrochemical system, promoting DCM degradation and Cr(VI) reduction. In summary, under the voltage conditions set in this experiment, 0.6V is the most optimal voltage for dichloromethane degradation and hexavalent chromium reduction.

[0083] Example 5

[0084] Influencing Factor Experiment-Pollutant Concentration Screening

[0085] Taking into account the cost and feasibility of field application, the selected graphite plates were selected to build a micro-electric field reactor for pollutant concentration optimization. Among them, the pollutant concentrations were set to 1mg / L-10mg / L, and the concentration ratio of dichloromethane and Cr(VI) in the pollutants was 1:1. In some embodiments, the pollutant concentrations were set to 5mg / L-7.5mg / L, and the concentration ratio of dichloromethane and Cr(VI) in the pollutants was 1:1. In a specific embodiment, the pollutant concentrations were set to 1mg / L, 2.5mg / L, 5mg / L, 7.5mg / L, and 10mg / L, and the concentration ratio of dichloromethane and Cr(VI) in the pollutants was 1:1.

[0086] Figure 9The figure shows the time-varying trends of dichloromethane and Cr(VI) at different concentrations in the micro-electric field reactor. Figure 9 (a) shows the time-varying trend of dichloromethane at different concentrations in the micro-electric field reactor; Figure 9 (b) shows the time-varying trend of Cr(VI) at different concentrations in the micro-electric field reactor. Figure 9 As shown in the figure, using graphite plates as the electrode material and operating at a voltage of 0.6V, the concentrations of dichloromethane and Cr(VI) were selected at 1, 2.5, 5, 7.5, and 10 mg / L (fixed ratio 1:1). The removal efficiency of each pollutant at different concentrations was investigated, and the results showed that both dichloromethane and Cr(VI) were stably removed over an 8-day experimental period. The removal rates of dichloromethane and Cr(VI) gradually decreased with increasing initial concentrations, reaching a 95% removal rate for Cr(VI) at 5 mg / L.

[0087] Figure 10 The following table shows the (a) DCM removal efficiency and (b) Cr(VI) removal efficiency at different concentrations (DCM:Cr(VI)). Figure 10 As shown, in this embodiment, the degradation rate of the combined pollution of dichloromethane (DCM) and hexavalent chromium (Cr(VI)) was also explored at different concentration ratios. The concentration range of hexavalent chromium was changed while the concentration of dichloromethane was kept at 5 mg / L. The results are as follows Figure 10 As shown in (a) and (b), under different concentrations of DCM:Cr(VI) ratio, the removal efficiency of hexavalent chromium is the highest when the initial concentration of the two pollutants is 5mg / L:5mg / L (i.e. 1:1), and the different initial hexavalent chromium concentrations have no significant effect on the removal efficiency of DCM. These two bar graphs show the removal rates of DCM (dichloromethane) and Cr(VI) (hexavalent chromium) at different ratios (5:2.5, 5:5, 5:7.5, 5:10). Figure 10 (a) DCM removal efficiency chart: The removal rates corresponding to the four different ratios are all high, approaching or exceeding 90%. The removal rates for the 5:2.5, 5:5, and 5:10 ratios are relatively close, all exceeding 95%. The removal rate for the 5:7.5 ratio is slightly lower, but still remains above 90%. This indicates that under these experimental conditions, the different ratios have relatively little effect on DCM removal, and the overall removal effect is relatively ideal. Figure 10The Cr(VI) removal rate graph (b) shows even more pronounced differences. The removal rate at a 5:2.5 ratio is relatively low, around 78%. The 5:5 ratio achieves the highest removal rate, approaching 97%. The 5:7.5 ratio decreases slightly, reaching approximately 62%. The 5:10 ratio achieves the lowest removal rate, approximately 54%. This indicates that different ratios significantly affect Cr(VI) removal, with a 5:5 ratio likely being the optimal choice, achieving the highest removal efficiency.

[0088] Overall, Figure 10 Figures a and b in the figure compare the removal rates at different ratios, intuitively demonstrating the influence of the ratio factor on the removal effects of DCM and Cr(VI), and providing a reference for the selection of ratios in practical applications.

[0089] Example 6

[0090] Microbial community analysis

[0091] Microbial analysis helps to gain a deeper understanding of the removal mechanism of DCM and Cr(VI). By studying the types, numbers and metabolic activities of the microorganisms involved in the reaction, it can be revealed how microorganisms remove these pollutants through biotransformation, adsorption and other processes. Microbial analysis was performed on the sediments from the stable dichloromethane and hexavalent chromium composite pollution electrochemical system of the central experimental group to further clarify the composition of the microbial community in the treatment system. Different microbial species play different roles in the pollutant removal process, and understanding the community structure helps to identify key functional microorganisms. Estimating the functional diversity of the microbial community can understand the system's comprehensive treatment capacity for pollutants. Functionally diverse microbial communities can more effectively cope with complex environmental changes and pollutant types, and improve the stability and removal efficiency of the system.

[0092] Table 1 Alpha diversity index of reactor anode, cathode and sediment

[0093]

[0094] Table 1 shows the alpha diversity index derived from 16S rRNA sequencing. The observed species (Observed Species) represent the number of different microbial species detected. The number was 1953 for the Sediment sample, 1253 for the Anode sample, and 776 for the Cathode sample, indicating that the sediment had the highest number of detected microbial species and the cathode had the lowest. The Chao1 index, used to estimate the total number of species in a sample, is an estimate of species richness. Higher values ​​indicate a higher potential species richness. The Sediment sample had the highest Chao index (no specific Chao1 estimate is given, but the trend suggests a relatively high potential species richness), reflecting a potentially richer microbial population in the sediment. The Shannon index comprehensively considers species richness and evenness. Higher values ​​indicate greater diversity and evenness in the microbial community. The Shannon index for the three samples was relatively close (5.35-5.37), indicating similarities in microbial community diversity and evenness. The Simpson index measures species dominance within a community. Smaller values ​​indicate more dominant species and lower diversity, while larger values ​​indicate a more even distribution of species and higher diversity. The Simpson index for all three samples was low (0.015-0.025), indicating that some relatively dominant microbial species may exist within each sample.

[0095] Figure 11 (a) OUT level Venn diagram showing the distribution characteristics of microorganisms in the reactor sediment, anode, and cathode. Figure 11 , Figure 11 A Venn diagram shows the number of shared and unique OTUs (Operational Taxonomic Units) for the sediment, cathode, and anode communities at the OTU (Operational Taxonomic Unit) level. It should be noted that in phylogenetic or population genetics studies, an OTU is an artificially assigned identifier to a taxonomic unit (strain, genus, species, group, etc.) to facilitate analysis. To understand the number of bacterial species and genera in a sample's sequencing results, sequences must be clustered. Clustering groups sequences based on their similarity, with each cluster being an OTU. All sequences can be assigned OTUs based on different similarity levels, typically using a 97% similarity level for bioinformatic statistical analysis. A Venn diagram displays the distribution of microbial OTUs.

[0096] Further OUT-level analysis of the microbial community revealed that the number of unique OTUs in the sediment community was 1,346, the number of unique OTUs in the cathode community was 252, and the number of unique OTUs in the anode community was 544. The sediment had the most unique OTUs (1,346), indicating that its microbial community was highly diverse and unique. The anode and cathode also had a large number of unique OTUs, 544 and 252, respectively, indicating that specific microorganisms may be screened in the electrode environment. The intersection between the cathode and anode (011) was relatively large, indicating that the electrochemical environments of the two poles may be similar (such as electron donor and acceptor structures, etc.), with 172 OUTs. Micro-electric field-assisted enhanced natural attenuation technology has an impact on the core microbial community.

[0097] Figure 12 Shown are (a) a phylum-level microbial community column stacking diagram and (b) a genus-level microbial community heat map. Figure 12 , in the door level diagram Figure 12 In (a), Chloroflexota, Bacteroidetes, Acidobacteriota, and Verrucomicrobiota were enriched in the sediment. Chloroflexota was the most abundant, accounting for 8.36% of the microbial community. Acidobacteriota, Verrucomicrobiota, and Gemmatimonadota were enriched at the cathode, accounting for 44.29% of the microbial community. Chloroflexota and Bacteroidota were enriched at the anode, accounting for 10.6% of the phylum-level microbial community.

[0098] At the genus level, Rhodoeyelaceae and Pseudomonas were enriched at the anode; the dominant bacteria at the cathode were Hydrogenophaga and Rhodoeyelaceae, among which the methylotrophic bacteria Hydrogenophaga was involved in the degradation of DCM.

[0099] Figure 13 Shown is a phylogenetic tree constructed from the reactor sediment metagenomic sample (a); and a gene abundance heat map (b). Figure 13 , perform metagenomic sequencing on the samples and analyze the microbial community in the reactor at the genetic level, Figure 12(a) shows the results of metagenomic sequencing and binning analysis of three samples, and a total of 32 high-quality MAGs (Metagenome-Assembled Genomes) with at least 70% completeness and less than 10% contamination were retrieved. It should be noted that MAGs are obtained by assembling and binning metagenomic sequencing data (such as Illumina, PacBio, Nanopore, etc.). These genomes can represent one or more microbial species and have high completeness and low contamination. Completeness refers to whether the genes contained in the MAG are complete enough to represent the genome of the species; contamination refers to whether genes from other species are mixed in the MAG.

[0100] Phylogenetic tree analysis showed that the microbial communities in the samples were mainly composed of Pseudomonadota (Proteobacteria, 26.5%), Bacteroidota (Bacteroidetes, 18.3%), and Chloroflexota (Chloroflexi, 12.1%). More importantly, all MAGs carried at least one gene involved in the reduction of hexavalent chromium (Cr(VI)) and a gene related to dichloromethane degradation. In this embodiment, a total of 16 functional genes were identified, of which chrA, yieF, and NfsA have been identified as being capable of Cr(VI) reduction. The enzymes encoded by these genes have the ability to reduce hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)]. Enzymes involved in hexavalent chromium reduction, such as yieF, are NAD(P)H-dependent reductases that can use intracellular reducing equivalents (such as NADH or NADPH) to reduce Cr(VI) to Cr(III). This indicates that microorganisms have formed a set of efficient energy acquisition and utilization strategies when utilizing electron donors in the microelectric field environment. They can produce reducing equivalents such as NADH or NADPH through metabolic processes and use this energy for the reduction reaction of pollutants, thus achieving efficient energy utilization. In addition, studies have also found that other oxidoreductases such as chrA, iron reductase, and quinone reductase are also involved in the reduction process of Cr(VI). The activity of these enzymes may be affected by electron donors, cofactors, and environmental conditions, thereby regulating the reduction efficiency of Cr(VI). Therefore, the chrA and yieF genes play an important role in microbial Cr(VI) reduction and bioremediation. dhlA and dehA are genes encoding dichloromethane (DCM) dehalogenase in bacteria, which have the ability to convert dichloromethane into metabolizable intermediates. These genes are widely present in multiple MAGs.

[0101] Based on the scheme described above, an embodiment of the present invention specification provides a method for electrically stimulating and enhancing the natural decay of dichloromethane and synchronously fixing hexavalent chromium, comprising the following steps: constructing a micro-electric field reactor based on a reaction bottle, and constructing an electrode plate in the micro-electric field reactor, connecting the electrode plate to a DC power supply so that the electrode plate constitutes the anode and cathode of the micro-electric field reactor; adding groundwater and soil containing pollutants to the micro-electric field reactor; wherein the ratio of the soil to groundwater is 1:9; the pollutants are dichloromethane and hexavalent chromium; starting the micro-electric field reactor under light-shielding conditions, and acclimating the microorganisms in the micro-electric field reactor for multiple cycles to construct a micro-electric field reaction system with a stable microbial community; wherein one cycle is at least eight days; adding contaminated groundwater and soil to the micro-electric field reaction system, and applying voltage to the micro-electric field reaction system to purify the pollutants in the groundwater and soil, thereby achieving electrically stimulating and enhancing the natural decay of dichloromethane and synchronously fixing hexavalent chromium.

[0102] In a possible embodiment, the material of the electrode plate includes any one or more of carbon felt, graphite felt, graphite plate, and stainless steel plate.

[0103] Furthermore, the material of the electrode plate can be carbon felt or graphite plate.

[0104] In a possible implementation manner, the distance between the electrode plates is 4 cm.

[0105] In a possible embodiment, the electrode plate is in a rectangular parallelepiped configuration and is vertically placed in the micro-electric field reactor.

[0106] In one possible embodiment, the applied DC voltage is 0-0.9V.

[0107] In one possible implementation, the applied DC voltage is 0.6-0.9V.

[0108] In one possible implementation, the applied DC voltage is 0V, 0.3V, 0.6V, or 0.9V.

[0109] In one possible embodiment, the concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 1 mg / L-10 mg / L, respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:2.5-10.

[0110] In one possible embodiment, the concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 5 mg / L-7.5 mg / L, respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:2.5-5.

[0111] In one possible embodiment, the concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 1 mg / L, 2.5 mg / L, 5 mg / L, 7.5 mg / L and 10 mg / L, respectively; wherein the concentration ratio of dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants is 5:5.

[0112] In one possible embodiment, the reaction bottle is a reagent bottle coated with aluminum foil.

[0113] In one possible embodiment, the microorganisms in the micro-electric field reactor are Pseudomonadota (Proteobacteria, 26.5%), Bacteroidota (Bacteroidetes, 18.3%), and Chloroflexota (Chloroflexi, 12.1%) at the phylum level.

[0114] The embodiments of this specification also provide a device for electrically stimulating and strengthening the natural decay of dichloromethane and synchronously fixing hexavalent chromium, which is applied to the method as described above, including a micro-electric field reactor, an electrode plate, and a DC power supply. Wherein, the micro-electric field reactor contains groundwater and soil containing pollutants, wherein the ratio of the soil to the groundwater is 1:9; the pollutants are dichloromethane and hexavalent chromium; the micro-electric field reactor is started under light-shielding conditions, and the microorganisms in the micro-electric field reactor are acclimated for multiple cycles to construct a micro-electric field reaction system with a stable microbial community; wherein one of the cycles is at least eight days; contaminated groundwater and soil are added to the micro-electric field reaction system, and a voltage is applied to the micro-electric field reaction system to purify the pollutants in the groundwater and soil, thereby achieving electrically stimulating and strengthening the natural decay of dichloromethane and synchronously fixing hexavalent chromium.

[0115] The present invention proposes an innovative, low-cost, and environmentally friendly remediation method and device for hexavalent chromium (Cr(VI)) and dichloromethane pollution in the environment by constructing a micro-electric field reactor and combining electrical stimulation with the synergistic effect of microorganisms. The method and device can effectively treat hexavalent chromium and dichloromethane pollution in the environment.

[0116] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical concepts disclosed in this application shall be covered by the claims of this application.

Claims

1. A method for synchronously fixing hexavalent chromium by electrically enhancing the natural decay of dichloromethane, characterized in that: The following steps are involved: Constructing a micro-electric field reactor based on the reaction bottle, constructing an electrode plate in the micro-electric field reactor, and connecting the electrode plate to a direct current power supply so that the electrode plate constitutes the anode and cathode of the micro-electric field reactor; Adding groundwater and soil containing pollutants into the micro-electric field reactor; wherein the ratio of the soil to the groundwater is 1:9; and the pollutants are dichloromethane and hexavalent chromium; Starting the micro-electric field reactor under light-shielding conditions, and acclimating the microorganisms in the micro-electric field reactor for multiple cycles to construct a micro-electric field reaction system with a stable microbial community; wherein one cycle is at least eight days; Contaminated groundwater and soil are added to the micro-electric field reaction system, and voltage is applied to the micro-electric field reaction system to purify the pollutants in the groundwater and soil, thereby achieving electrical stimulation to enhance the natural attenuation of dichloromethane and synchronously fix hexavalent chromium.

2. The method according to claim 1, characterized in that The material of the electrode plate includes any one or more of carbon felt, graphite felt, graphite plate, and stainless steel plate.

3. The method according to claim 1, characterized in that The distance between the electrode plates is 4 cm.

4. The method according to any one of claims 1 to 3, characterized in that The applied DC voltage was 0-0.9V.

5. The method according to claim 4, characterized in that The applied DC voltage was 0.6-0.9V.

6. The method according to claim 5, characterized in that The applied DC voltage was 0.6V.

7. The method according to any one of claims 1 to 3, characterized in that The concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 1 mg / L-10 mg / L respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:2.5-10.

8. The method according to claim 7, characterized in that The concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 5 mg / L-7.5 mg / L respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:2.5-5.

9. The method according to claim 8, characterized in that The concentrations of dichloromethane, dichloromethane and hexavalent chromium (Cr(VI)) in the pollutants are set to 5 mg / L respectively; wherein the concentration ratio of dichloromethane to hexavalent chromium (Cr(VI)) in the pollutants is 5:

5.

10. The method according to any one of claims 1 to 3, characterized in that The reaction bottle is a reagent bottle coated with aluminum foil.

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