Method for removing heavy metals in soil-underground water by using autotrophic microorganisms and application

Abstract

The embodiment of the invention discloses a method for removing heavy metal in soil-underground water through autotrophic microorganisms and application, relates to the technical field of soil-underground water heavy metal pollution treatment, and aims at solving the technical problem that the efficiency of reducing heavy metal through microorganisms in the existing oligotrophic condition is low. The method for removing the heavy metals in the soil-underground water comprises the following steps: carrying out long-term domestication and culture on mine polluted soil under an anaerobic condition to obtain autotrophic microorganisms; the autotrophic microorganisms are autotrophic microorganism strains capable of reducing hexavalent chromium into trivalent chromium; on the basis of the autotrophic microorganisms, iron / sulfur-containing semiconductor minerals existing in the mine contaminated soil serve as electron donors, and extracellular electron transfer of the autotrophic microorganisms is promoted so as to strengthen reduction and immobilize hexavalent chromium in soil-underground water.

Description

Technical Field

[0001] This application relates to the technical field of soil - groundwater heavy metal pollution treatment, and specifically relates to a method and application for removing heavy metals in soil - groundwater by autotrophic microorganisms. Background Art

[0002] During processes such as mining, smelting, and tailings stacking, the pollution problems caused by heavy metal residues in soil have attracted wide attention. Usually, it is a feasible strategy to repair heavy metal - contaminated soil through dissimilatory metal - reducing bacteria, such as reducing Cr(VI) and V(V) to reduce their toxicity. However, whether it is the dissimilatory iron reduction or humus reduction process, the heavy metal reduction mediated by microorganisms requires organic acids, sugars, etc. as carbon sources as electron donors. Due to heavy metal pollution, the mine - polluted soil environment usually shows characteristics such as oligotrophy, high heavy metals, high sulfates, and low pH, which lead to significant changes in the soil microbial community structure and lack of nutrient sources required for the typical extracellular electron transfer process of electroactive microorganisms. At the same time, the organic matter in soil and groundwater is difficult to maintain the energy metabolism of electroactive microorganisms, thus greatly limiting the process of microbial reduction of heavy metals. However, there are usually various semiconductor minerals rich in iron / sulfur in mine - polluted soil, which can serve as electron donors for microbial growth and metabolism, improve the extracellular electron transfer efficiency of microorganisms. Therefore, using inorganic electron donors such as iron / sulfur and their minerals existing in mine - polluted soil to enhance the reduction of heavy metals through microorganisms and achieve the remediation of heavy metal - polluted soil - groundwater is an important part of microbial technology in the field of soil - groundwater pollution remediation.

[0003] Under oligotrophic conditions, the electrons generated during the autotrophic microbial iron / sulfur cycle can be used for both the metabolic process of microorganisms and the reduction of high - valence, oxidized heavy metals. The iron / sulfur - containing semiconductor minerals (such as pyrite, marcasite, etc.) in mine - polluted soil - groundwater can serve as electron donors for autotrophic microbial growth, energy sources for heavy metal reduction, electron conductors between microbial cells, and electron storage media. These minerals can change electron flow, organic matter degradation, and the interaction between microbial species, and serve as an electron transfer channel between microbial flagella and electron acceptors to accelerate extracellular electron transfer. In the autotrophic / oligotrophic system, the extracellular electron transfer of electroactive microorganisms such as iron - oxidizing bacteria and sulfate - reducing bacteria can directly accelerate the electron flow to heavy metals and strengthen the iron / sulfur - mediated heavy metal reduction.

[0004] However, the efficiency of microbial reduction of heavy metals under the existing oligotrophic conditions is low. Therefore, a method for culturing heavy metal - reducing microorganisms under oligotrophic conditions from mine - polluted soil is proposed. At the same time, the cultured autotrophic microorganisms use the inherent semiconductor minerals in mine - polluted soil - groundwater as electron donors and CO 2It grows and reproduces using inorganic carbon sources, while reducing and immobilizing Cr(VI) to remove heavy metals in soil and groundwater. Summary of the Invention

[0005] The main purpose of this application is to provide a method for removing heavy metals in soil and groundwater, aiming to solve the technical problem of low efficiency of microbial reduction of heavy metals under oligotrophic conditions.

[0006] To achieve the above purpose, the technical solutions adopted in the embodiments of this application are as follows:

[0007] In a first aspect, an embodiment of this application provides a method for removing heavy metals in soil and groundwater, including the following steps:

[0008] Using mine-polluted soil, autotrophic microorganisms are obtained through long-term domestication under anaerobic conditions; the autotrophic microorganisms are autotrophic microbial strains capable of reducing hexavalent chromium to trivalent chromium.

[0009] Based on the autotrophic microorganisms, the iron / sulfur semiconductor minerals present in the mine-polluted soil are used as electron donors to promote the extracellular electron transfer of autotrophic microorganisms to strengthen the reduction and immobilization of hexavalent chromium in soil and groundwater.

[0010] As some optional embodiments of this application, the autotrophic microorganisms include anaerobic bacteria or facultative anaerobic bacteria.

[0011] As some optional embodiments of this application, the autotrophic microorganisms include Thiobacillus, Ferrovibrio, and Desulfovibrio.

[0012] As some optional embodiments of this application, after the mine-polluted soil is pre-treated by air-drying, removing impurities, sieving (<2 mm), etc., a culture solution is added, and target autotrophic microorganisms are obtained through long-term domestication under anaerobic conditions.

[0013] As some optional embodiments of this application, the culture solution includes the following concentration reagents: 0.5 g / L - 0.6 g / L NaHCO 3 , 0.2 g / L - 0.3 g / L CaCl 2 , 0.03 g / L - 0.04 g / L NH 4 Cl, 1.5 g / L - 1.6 g / L MgCl 2 ·6H 2 O, 0.4 g / L - 0.5 g / L NaCl, 0.02 g / L - 0.03 g / L KCl, and 0.02 g / L - 0.03 g / L KH 2 PO 4 .

[0014] In some alternative embodiments of the present application, the culture medium comprises the following concentration reagents: 0.504 g / L NaHCO 3 , 0.246 g / L CaCl 2 , 0.035 g / L NH 4 Cl, 1.507 g / L MgCl 2 ·6H 2 O, 0.445 g / L NaCl, 0.028 g / L KCl and 0.029 g / L KH 2 PO 4 .

[0015] In some alternative embodiments of the present application, when using the iron / sulfur semiconductor minerals present in the mine polluted soil as an electron donor based on the autotrophic microorganisms to promote the extracellular electron transfer of the autotrophic microorganisms to enhance the reduction and immobilization of hexavalent chromium in soil and groundwater, the inorganic carbon source dosage is 360 mg / L to 720 mg / L, the initial concentration of hexavalent chromium is 25 mg / L to 50 mg / L, and the dosage of the iron / sulfur semiconductor minerals is 2 g to 10 g.

[0016] In some alternative embodiments of the present application, when using the iron / sulfur semiconductor minerals present in the mine polluted soil as an electron donor based on the autotrophic microorganisms to promote the extracellular electron transfer of the autotrophic microorganisms to enhance the reduction and immobilization of hexavalent chromium in soil and groundwater, the inorganic carbon source dosage is 360 mg / L, the initial concentration of hexavalent chromium is 50 mg / L, and the dosage of the iron / sulfur semiconductor minerals is 10 g.

[0017] In a second aspect, the embodiments of the present application provide a bioelectrochemical device, using the autotrophic microorganisms described in the first aspect as the anode inoculum, and both the anode and cathode electrodes are carbon felts.

[0018] In some alternative embodiments of the present application, both the anode and cathode electrodes are circular carbon felts with a radius of 50 mm and a thickness of 3 mm.

[0019] Compared with the prior art, the present application uses cultured autotrophic microorganisms and proves the feasibility of FeS-mediated reduction of Cr(VI) in soil and groundwater by autotrophic electroactive microorganisms under the condition that FeS serves as an electron donor; that is, mine polluted soil is used, and after long-term domestication under anaerobic conditions, autotrophic microbial strains capable of reducing Cr(VI) to Cr(III) are cultured. During the domestication stage, the organic matter in the mine polluted soil decreased by 80.64%, and the remaining organic matter could not be utilized by microorganisms. Moreover, it was found that the decrease in the Cr(VI) concentration was mainly due to the action of anaerobic microorganisms in the system rather than the adsorption of the soil. The microorganisms cultured in the present application use sodium bicarbonate as an inorganic carbon source and FeS as an electron donor, and can significantly remove Cr(VI) in soil and groundwater (the removal rate is 97.0±0.5%). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram and a physical diagram of the microbial culture device involved in the embodiment of the present application;

[0021] Figure 2 It is a graph showing the change of Cr(VI) concentration with time involved in the embodiment of the present application;

[0022] Figure 3 It is a result diagram of the electron transfer ability of the semiconductor mineral FeS involved in the embodiment of the present application;

[0023] Figure 4 It is a graph showing the influence of the inorganic carbon source concentration on the removal of Cr(VI) involved in the embodiment of the present application;

[0024] Figure 5 It is a graph showing the influence of the initial Cr(VI) concentration on the removal of Cr(VI) involved in the embodiment of the present application;

[0025] Figure 6 It is a graph showing the influence of the initial FeS concentration on the removal of Cr(VI) involved in the embodiment of the present application;

[0026] Figure 7 It is a scanning electron microscope image of the precipitate in the autotrophic system involved in the embodiment of the present application (a is the control group, b is the experimental group) and the XPS spectra of the precipitate in the experimental group (c is the Fe2p spectrum, d is the Cr2p spectrum);

[0027] Figure 8 It is the microbial community structure (a phylum, b genus) and functional gene abundance (c functional gene, d functional protein) in the autotrophic system involved in the embodiment of the present application;

[0028] Figure 9 It is the bioelectrochemical device involved in the embodiment of the present application;

[0029] Figure 10Schematic flow chart of the method for removing heavy metals from soil - groundwater involved in the embodiments of the present application. Detailed implementation manners

[0030] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0031] Based on the technical problem that the efficiency of microbial reduction of heavy metals under oligotrophic conditions is relatively low in the prior art, the present application proposes a method for culturing heavy metal - reducing microorganisms under oligotrophic conditions from mine - polluted soil. At the same time, the autotrophic microorganisms after culturing are used to use the inherent semiconductor minerals in mine - polluted soil - groundwater as electron donors and NaHCO 3 as the inorganic carbon source to achieve growth and reproduction, and at the same time reduce and immobilize Cr(VI), so as to remove heavy metal Cr(VI) in soil - groundwater. This method can deepen the understanding of the mechanism of extracellular electron transfer coupling heavy metal reduction by autotrophic microorganisms using inorganic electron donors such as iron / sulfur, supplement and expand people's scientific understanding of the electron transfer mechanism of electroactive microorganisms, promote the application of soil bioelectrochemical technology in in - situ remediation of heavy metal pollution, and provide theoretical support and important scientific reference for major national needs such as the battle against soil pollution prevention and control and ecological civilization construction.

[0032] Specifically, the present application first cultivates autotrophic microorganisms based on mine - polluted soil, aiming to consume the original organic matter in the mine - polluted soil, so that the microorganisms cultured later only use the iron / sulfur semiconductor mineral (FeS) as the sole electron donor, and measure the change of organic matter in the mine - polluted soil during the microbial screening period. Secondly, explore the adsorption of Cr(Ⅵ) by the mine - polluted soil before cultivation, and the influence of pH on the adsorption of Cr(Ⅵ). Finally, use microbial technology to sequence and analyze the microorganisms cultured before and after the reaction, and determine the community characteristics of the domesticated autotrophic microorganisms. Secondly, the microorganisms used in the present application are the microorganisms cultured and domesticated in the first part, and use the iron / sulfur semiconductor mineral (FeS) as the sole electron donor and adopt NaHCO 3 as the carbon source of autotrophic microorganisms to study the reduction effect of Cr(Ⅵ). After the Cr(Ⅵ) reduction experiment, relevant technical analysis is carried out on the reduction products in the reactor to explore the action mechanism of FeS reducing Cr(Ⅵ); microbial analysis is carried out on the mine - polluted soil before and after the reaction by microbial analysis means, and the functional microorganisms and related functional genes and functional proteins are inferred.

[0033] That is, the method for removing heavy metals from soil - groundwater described in the present application, as Figure 10 shown, includes the following steps:

[0034] Step S10: Use mine polluted soil and cultivate autotrophic microorganisms through long-term domestication under anaerobic conditions; the autotrophic microorganisms are autotrophic microbial strains capable of reducing hexavalent chromium to trivalent chromium.

[0035] In a preferred embodiment, the autotrophic microorganisms include anaerobic bacteria or facultative anaerobic bacteria; the autotrophic microorganisms include Thiobacillus, Ferrovibrio, and Desulfovibrio. In another preferred embodiment, the mine polluted soil is used and target autotrophic microorganisms are screened through long-term domestication under anaerobic conditions. Among them, the culture medium includes the following concentration reagents: 0.5 g / L - 0.6 g / L NaHCO 3 、0.2 g / L - 0.3 g / L CaCl 2 、0.03 g / L - 0.04 g / L NH 4 Cl、1.5 g / L - 1.6 g / L MgCl 2 ·6H 2 O、0.4 g / L - 0.5 g / L NaCl、0.02 g / L - 0.03 g / L KCl, and 0.02 g / L - 0.03 g / L KH 2 PO 4 。In a further embodiment, the culture medium includes the following concentration reagents: 0.504 g / L NaHCO 3 、0.246 g / L CaCl 2 、0.035 g / L NH 4 Cl、1.507 g / L MgCl 2 ·6H 2 O、0.445 g / L NaCl、0.028 g / L KCl, and 0.029 g / L KH 2 PO 4 。

[0036] Step S20: Based on the autotrophic microorganisms, the iron / sulfur semiconductor minerals present in the mine polluted soil are used as electron donors to promote the extracellular electron transfer of autotrophic microorganisms to strengthen the reduction and immobilization of hexavalent chromium in soil and groundwater. In a further embodiment, when using iron / sulfur semiconductor minerals (FeS) as electron donors based on the autotrophic microorganisms to promote the autotrophic microorganisms to accept electrons and reduce hexavalent chromium in soil and groundwater, the dosage of inorganic carbon source is 360 mg / L - 720 mg / L, the initial concentration of hexavalent chromium is 25 mg / L - 50 mg / L, and the dosage of iron / sulfur semiconductor minerals (FeS) is 2 g - 10 g; furthermore, when using iron / sulfur semiconductor minerals (FeS) as electron donors based on the autotrophic microorganisms to promote the extracellular electron transfer of autotrophic microorganisms to strengthen the reduction and immobilization of hexavalent chromium in soil and groundwater, the dosage of inorganic carbon source is 360 mg / L, the initial concentration of hexavalent chromium is 50 mg / L, and the dosage of iron / sulfur semiconductor minerals (FeS) is 10 g. In addition, in order to further explore the electron transfer during the reduction of Cr(Ⅵ) by autotrophic microorganisms mediated by FeS, the present application also constructs a bioelectrochemical device based on domesticated autotrophic microorganisms and uses this device to remove Cr(VI) in groundwater. In the experiment, a bioelectrochemical system is constructed with carbon felt as the cathode and anode and titanium wire as the external circuit. The anode is covered with the cultivated microorganisms and FeS is added as an electron donor. Then the constructed bioelectrochemical system is connected to a data collector to detect electrochemical indexes such as the output voltage and current of the system, and combined with the removal rate of Cr(Ⅵ) to further analyze the reduction of Cr(Ⅵ) in the water body. The reaction products are characterized by materials, and the microbial community is further analyzed by microbial analysis means.

[0037] Next, the technical solutions of the present application and the technical effects they can produce will be described in more detail in combination with specific examples and experimental examples:

[0038] Example 1

[0039] In this example, through a long-term domestication process, autotrophic microorganisms capable of effectively using inorganic electron donors to reduce Cr(Ⅵ) are screened and cultivated.

[0040] First, a 110-day microbial domestication experiment is carried out. 50 g of mine polluted soil and 200 mL of solution (containing 50 mg / L Cr(VI) and a specific formula of culture solution, see Table 1) are placed in a 250 mL serum bottle, as Figure 1 shown, and stirred thoroughly to mix evenly. The culture medium consists of 200 mL of a specific formula of culture solution, 50 g of mine polluted soil, and 50 mg / L of Cr(Ⅵ). The ratio of the nutrient solution is shown in Table 1 in detail:

[0041] Table 1:

[0042]

[0043] To ensure an anaerobic environment inside the serum bottle, each time the culture medium containing Cr(Ⅵ) was replaced, high-purity nitrogen was flushed into the culture device for 60 minutes to expel dissolved oxygen and maintain the dissolved oxygen concentration inside the device at less than 0.2 mg / L. 5 mL of samples were taken from the culture device every day to measure the pH, oxidation-reduction potential (ORP), and the concentration of Cr(Ⅵ) in the samples. The acclimation process lasted for more than 110 days to ensure that the microorganisms were fully adapted to the environment and consumed the organic matter in the mine-contaminated soil. When the concentration of Cr(Ⅵ) in the culture device remained stable for three consecutive cycles, it indicated that the autotrophic microorganisms had been successfully acclimated for subsequent performance test experiments. The mine-contaminated soil without cultivation contained a certain amount of organic matter, which could serve as an electron donor for microorganisms to reduce Cr(Ⅵ). The long-term acclimation aimed to consume this organic matter to create conditions for the growth of autotrophic microorganisms. In subsequent experiments, the electron transfer efficiency during the reduction of Cr(Ⅵ) by autotrophic microorganisms could be clarified by adding an inorganic electron donor (such as FeS).

[0044] The change in the concentration of Cr(VI) during the culture process was measured, and the measurement results are as Figure 2 shown. Due to the presence of a certain amount of organic matter in the soil, the concentration of Cr(VI) rapidly decreased from 50 mg / L to about 1.0 mg / L under the action of heterotrophic microorganisms in the first 37 days. During the period from the 38th to the 91st day, as the content of organic matter decreased, the change in the concentration of Cr(VI) at the end of each cycle gradually became smaller. On the 91st day, the concentration of Cr(VI) decreased from the initial 44.46 mg / L to 34.53 mg / L. In the last three cycles, the concentration of Cr(VI) hardly changed with time and remained basically at about 46.0 mg / L. This indicates that the content of organic matter in the soil no longer changes and cannot be utilized by heterotrophic microorganisms, and the system has changed from a heterotrophic system to an autotrophic system.

[0045] Experimental Example 1

[0046] This experimental example was set up to measure the electron transfer ability of the semiconductor mineral FeS, and the results are as Figure 3 shown.

[0047] It can be seen from Figure 3 that obvious reduction peaks and oxidation peaks appeared in FeS at -0.62 V and -0.35 V. The electron acceptor capacity (EAC), electron donor capacity (EDC), and electron transfer capacity (ETC) of FeS were 0.38 μmol e - / g, 0.34 μmol e - / g, and 0.72 μmol e - / g, indicating that FeS has good electron transfer characteristics and electron exchange ability. Among them, Figure 3 Part a in it represents the cyclic voltammogram of FeS, and part b represents the electron transfer capacity diagram of FeS.

[0048] Experimental Example 2

[0049] This experimental example was set up to measure the effect of FeS-mediated autotrophic microorganism reduction of Cr(VI) and is divided into three parts; among them, the first part is the effect of the concentration of inorganic carbon source (the inorganic carbon source in this application is NaHCO 3 ) on the reduction of Cr(VI) by FeS-mediated autotrophic microorganisms; the second part is the effect of the initial Cr(VI) concentration on the reduction of Cr(VI) by FeS-mediated autotrophic microorganisms; the third part is the effect of the FeS concentration on the reduction of Cr(VI) by mediated autotrophic microorganisms. The results are as Figures 4 - 6 shown:

[0050] As Figure 4 shown, where Figure 4 Part a is the curve of the change in Cr(VI) concentration, and part b is the curve of the change in sulfate ion concentration; it can be seen that when no inorganic carbon source (0 mg / L) is added, a certain chemical reaction occurs between FeS and Cr(VI), so the concentration of Cr(VI) drops from the initial 48.68 mg / L to 15.64 mg / L, and the removal rate is 67.87%. When the initial concentration of NaHCO 3 increases from 180 mg / L to 540 mg / L, the concentration of Cr(VI) in groundwater is only 9.37 - 2.10 mg / L, and the removal rate of Cr(VI) significantly increases to 91.69%. When the concentration of NaHCO 3 continues to increase to 720 mg / L, the change in the removal rate of Cr(VI) is not obvious, only 95.68%. At the same time, the concentration of SO 4 2- continues to increase. When no inorganic carbon source is added, the concentration of SO 4 2- at the end of the experiment is only 57.04 mg / L, while the concentrations of SO 3 in the groups with added NaHCO 4 2- are 70.19, 76.40, 78.06, and 83.08 mg / L respectively. This is because when using NaHCO 3 as the carbon source and semiconductor mineral FeS as the electron donor, autotrophic microorganisms can oxidize S 2- in FeS to SO 4 2- , which is faster and more complete than the pure chemical reaction rate between FeS and Cr(VI).

[0051] As Figure 5 shown, even when the concentration of Cr(VI) in groundwater increases from 25 mg / L to 100 mg / L, the system still has a good removal effect on Cr(VI). The removal rate of Cr(VI) can exceed 80.34%, and can reach up to 99.80% at most. At the same time, the concentration of SO 4 2- increases from 41.57 mg / L to 171.58 mg / L. Among them, Figure 5 in part a shows the curve of the change in the concentration of Cr(VI), and part b shows the curve of the change in the concentration of sulfate ion.

[0052] As Figure 6 shown, when the initial concentration of FeS increases from 2 g / L to 10 g / L, the removal effect of the system on Cr(VI) is significantly enhanced. The removal rate of Cr(VI) increases from 27.21% to 97.99%, and the concentration of SO 4 2- increases from 18.79 mg / L to 69.70 mg / L. Among them Figure 6 in part a shows the curve of the change in the concentration of Cr(VI), and part b shows the curve of the change in the concentration of sulfate ion.

[0053] Experimental Example 3

[0054] This experimental example is set up to analyze the electron transfer and its products of FeS-mediated autotrophic microbial reduction of Cr(VI).

[0055] FeS as an electron donor can promote autotrophic microorganisms to reduce Cr(VI) to Cr(III). At the same time, Fe(II) in FeS is oxidized to Fe(III), and S(II) is oxidized to SO 4 2- , and a certain alkalinity is generated. At the end of the experiment, the average concentration of SO 4 2- increases to 69.70 mg / L. According to the reaction equation calculation shows that FeS can release 5.81 mM of electrons during the oxidation process of S(II). In the culture system, the concentration of Cr(VI) drops from 50 mg / L to about 2.6 mg / L, and 47.4 mg / L of Cr(VI) is reduced. This reduction process requires 1.23 mM of electrons, that is, about 21.1% of the electrons participate in the reduction process of Cr(VI). However, through theoretical calculation, the production amount of SO 4 2- should be 117.69 mg / L, while the actual detection result is 69.70 mg / L, which indicates that S(II) is not completely converted to SO 4 2-, it is also possible to generate other sulfides, such as S(0), or SO 4 2- will be reduced to S(II) again under anaerobic conditions.

[0056] When the experiment ended, the products in the system were characterized; the SEM images of the precipitates in the autotrophic system (a control group, b experimental group) and the XPS spectra of the precipitates in the experimental group (c Fe2p spectrum, d Cr2p spectrum) are as Figure 7 shown. The results showed that the FeS without adding NaHCO 3 was flaky with a smooth surface, and there were a large number of needle-like crystals around it (control group); due to the presence of mine polluted soil and NaHCO 3 , the surface of FeS became rough (experimental group). According to the X-ray spectrum (EDS), the mass proportion of Fe element in the control group was the highest (53.78%), while the Cr element was only 1.1%; the mass proportion of Cr element in the experimental group was 9.36%, which was 8.26% higher than that in the control group. This indicates that only a part of Cr in the control group existed in the precipitate in the form of flocs, while in the experimental group, most of the Cr existed in the form of precipitate under the action of FeS-mediated natural microbial reduction.

[0057] X-ray photoelectron spectroscopy (XPS) analysis found that an orbital peak of Fe2p1 / 2 appeared near 725.4 eV and an orbital peak of Fe2p3 / 2 appeared near 710.0 eV in the Fe2p spectrum, indicating that the iron element in the precipitate mainly existed in the form of Fe(III), that is, Fe(II) in FeS underwent an oxidation reaction and released electrons outward. An orbital peak of Cr2p3 / 2 appeared near 577.5 eV and an orbital peak of Cr2p1 / 2 was observed near 587.5 eV in the Cr2p spectrum, that is, the chromium element in the reaction product mainly existed in the form of Cr(III), and almost no spectrum of Cr(VI) was detected, indicating that Cr(VI) in the experimental group was almost completely reduced to Cr(III) and existed in the form of precipitate. The EDX quantitative analysis results of the precipitate are shown in Table 2.

[0058] Table 2 EDX quantitative analysis of the precipitate

[0059]

[0060] Experimental Example 4

[0061] This experimental example was set up to analyze the microbial community structure, functional genes, and protein abundances in the autotrophic system, and the results are as Figure 8 shown.

[0062] As Figure 8As shown, it is a diagram of the autotrophic system microbial community structure and functional gene abundances (part a in the figure represents the relative abundances of phyla, part b represents the relative abundances of genera, part c represents the relative abundances of functional genes, and part d represents the relative abundances of functional proteins).

[0063] It can be seen that the dominant bacteria at the class level before and after the reaction in the experimental group were mainly Alphaproteobacteria, Gammaproteobacteria, and Anaerolineae. Anaerolineae belongs to anaerobic or facultative anaerobic bacteria, and its relative abundance decreased by 4.01% after long-term cultivation. After cultivation, Geobacter and Desulfovibrio, which can reduce Cr(VI), were detected in this system. Their relative abundances were 3.66% and 5.28% respectively. Since the microorganisms in this system secrete approximately 4.71 mg / L of volatile fatty acids (such as acetic acid, butyric acid, valeric acid, etc.), which can provide organic carbon sources for some heterotrophic microorganisms such as Geobacter, their relative abundances are relatively high. In addition, Geobacter can form conductive pili to provide an extracellular electron transfer pathway for the reduction of Cr(VI). The relative abundance of Thiobacillus after cultivation was 1.25%, and it is an autotrophic microorganism that can oxidize sulfur elements. Ferrovibrio is an autotrophic microorganism that can oxidize Fe(II) in FeS to Fe(III), and its relative abundance increased significantly from 0.20% at the initial stage of the experiment to 1.40%. Correspondingly, the relative abundances of sulfur oxidation genes and iron oxidation genes were also up-regulated in this system, indicating that FeS was oxidized as an electron donor during the reaction, and intermediate products such as volatile fatty acids (VFA) were generated. The electrons generated were accepted by Cr(VI) and reduced to Cr(III). During the extracellular electron transfer process, due to the consumption of electron mediators such as flavins and quinones, the relative abundances of their functional genes and proteins decreased. This fully demonstrates that when FeS is added to this system, it strengthens the extracellular electron transfer process, improves the reduction of Cr(VI) by autotrophic microorganisms, and forms the precipitation and fixation of Cr(III), achieving the reduction and removal of Cr(VI) in groundwater by semiconductor minerals.

[0064] Example 2

[0065] This example constructs a bioelectrochemical device based on the following steps, namely:

[0066] The experimental device is a plastic cylinder with a radius of 50 mm and a height of 150 mm. The carbon felt is used as the anode and cathode respectively. The external circuit is connected with titanium wire and a 1000 Ω resistor is added. The microorganism used at the anode is the autotrophic microorganism cultured in Example 1. The cathode is placed on the surface of the solution, and nitrogen is filled into the reaction device to maintain anaerobic conditions (DO ≤ 0.2 mg / L). The device is as Figure 9 shown. The carbon felt of both the anode and cathode is a disc with a radius of 50 mm and a thickness of 3 mm.

[0067] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for removing heavy metals from soil and groundwater using autotrophic microorganisms, characterized in that: The following steps are involved: Using mine-contaminated soil, under anaerobic conditions, and culturing autotrophic microorganisms for a long time; the autotrophic microorganisms are autotrophic microbial strains that can reduce hexavalent chromium to trivalent chromium; Based on the autotrophic microorganisms, the iron / sulfur semiconductor minerals present in the mine-contaminated soil are used as electron donors to promote the extracellular electron transfer of the autotrophic microorganisms to strengthen the reduction and immobilization of hexavalent chromium in the soil and groundwater.

2. The method for removing heavy metals from soil and groundwater by autotrophic microorganisms according to claim 1, characterized in that: The autotrophic microorganisms include anaerobic bacteria or facultative anaerobic bacteria.

3. The method for removing heavy metals from soil and groundwater by autotrophic microorganisms according to claim 1, characterized in that: The autotrophic microorganisms include Thiobacillus, Ferrovibrio and Desulfovibrio.

4. The method for removing heavy metals from soil and groundwater by autotrophic microorganisms according to claim 1, characterized in that: The step of using the mine-contaminated soil to cultivate autotrophic microorganisms under anaerobic conditions for a long time comprises: The mine contaminated soil is pretreated, and then culture solution is added to the soil. The soil is domesticated for a long time under anaerobic conditions to screen and obtain target autotrophic microorganisms.

5. The method for removing heavy metals from soil and groundwater by autotrophic microorganisms according to claim 4, characterized in that: The culture solution includes the following concentration reagents: 0.5g / L-0.6g / L NaHCO3, 0.2g / L-0.3g / L CaCl2, 0.03g / L-0.04g / L NH4Cl, 1.5g / L-1.6g / L MgCl2·6H2O, 0.4g / L-0.5g / L NaCl, 0.02g / L-0.03g / L KCl and 0.02g / L-0.03g / L KH2PO4.

6. The method for removing heavy metals from soil and groundwater by autotrophic microorganisms according to claim 4, characterized in that: The culture solution includes the following concentration reagents: 0.504g / L NaHCO3, 0.246g / L CaCl2, 0.035g / L NH4Cl, 1.507g / LMgCl2·6H2O, 0.445g / L NaCl, 0.028g / L KCl and 0.029g / L KH2PO4.

7. The method for removing heavy metals from soil and groundwater by autotrophic microorganisms according to claim 1, characterized in that: Based on the autotrophic microorganisms, when the iron / sulfur semiconductor minerals present in the mine-contaminated soil are used as electron donors to promote the extracellular electron transfer of the autotrophic microorganisms to strengthen the reduction and immobilization of hexavalent chromium in the soil-groundwater, the dosage of the inorganic carbon source is 360 mg / L to 720 mg / L, the initial concentration of hexavalent chromium is 25 mg / L to 50 mg / L, and the dosage of the iron / sulfur semiconductor mineral is 2 g to 10 g.

8. The method for removing heavy metals from soil and groundwater by autotrophic microorganisms according to claim 1, characterized in that: Based on the autotrophic microorganisms, the iron / sulfur semiconductor minerals present in the mine-contaminated soil are used as electron donors to promote the extracellular electron transfer of the autotrophic microorganisms to enhance the reduction and immobilization of hexavalent chromium in the soil-groundwater. The dosage of the inorganic carbon source is 360 mg / L, the initial concentration of hexavalent chromium is 50 mg / L, and the dosage of the iron / sulfur semiconductor mineral is 10 g.

9. A bioelectrochemical device, characterized in that: A semiconductor mineral containing iron / sulfur is used as an electron donor, the autotrophic microorganism described in claim 1 is used as an anode inoculum, and both the cathode and cathode electrodes are carbon felt.

10. The bioelectrochemical device according to claim 9, characterized in that: The cathode and anode electrodes are both carbon felt discs with a radius of 50 mm and a thickness of 3 mm.

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