Method for electrically enhancing bioremediation of halogenated hydrocarbon contaminated sites in stages and application thereof

Abstract

The application provides a method and application of electrically powered staged enhanced microbial remediation, and belongs to the technical field of organic contaminated site remediation. The staged method comprises the following steps: providing a persistent high-intensity electric field in a pre-incubation stage to accelerate the reduction of the oxidation-reduction potential and the in-situ competitive electron acceptor content of the soil in-situ environment; providing a persistent medium-intensity electric field in a bacterial agent implantation stage to input suitable enriched culture into the bacterial agent implantation well, promote the migration of active functional microorganisms to the cathode, and form active functional groups in a larger range of soil; and providing an intermittent low-intensity electric field in a contaminant remediation stage to transport the contaminant to the functional group area through the low-intensity electric dialysis effect, prolong the overflow time, and make the contaminant be completely degraded under the biological reduction dehalogenation effect. The synergistic effect of the three stages greatly reduces the start-up time and the remediation time required for site remediation, improves the utilization rate of nutrient agents, the utilization rate of bacterial agents and the utilization rate of electric energy, and simultaneously realizes the efficient degradation of the contaminant.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic contaminant site remediation, and particularly relates to a method for electrically enhanced staged remediation of halogenated hydrocarbon contaminated sites and application. BACKGROUND

[0002] Among groundwater pollution, organic pesticides, petroleum hydrocarbons, aromatic hydrocarbons and halides have strong carcinogenic, teratogenic and mutagenic properties, and have caused serious pollution in the soil and groundwater environment worldwide. For petroleum hydrocarbon aromatic hydrocarbon and other pollutants, degrading bacteria are commonly present in soil, so it is relatively easy to achieve remediation of pollutants; for halogenated organic pollutants, their ecological niche is between iron reduction and sulfate reduction, on the one hand, they are disturbed by environmental electron acceptors, on the other hand, the ecological niche of dehalogenating microorganisms is too narrow, and their competition ability in soil is extremely weak, so they are rarely present in contaminated sites, which makes it difficult for halogenated organic pollutants to be utilized and mineralized. In addition, organic pollutants often infiltrate into the low-permeability aquifer boundary in the form of DNAPL, and infiltrate into low-permeability media to form a long-term slow-release underground pollution source. Limited by material transport and the rarity of degrading microorganisms, the natural attenuation process of halogenated hydrocarbons in low-permeability media is very slow, and the half-life often takes decades, making it extremely difficult to remediate and restore. Therefore, in the field of remediation of halogenated hydrocarbons in low-permeability aquifers, there is a need to develop green, economic and effective in-situ groundwater remediation technologies.

[0003] In recent years, the remediation technology for aquifer organic pollutants has developed rapidly, and soil thermal remediation, solidification / stabilization, in-situ chemical / oxidation, soil leaching, and multiphase extraction processes have been verified and popularized. However, the demand for fine, green and efficient technology research and application is increasing, especially low-cost, green, efficient and sustainable coupling technology. Among them, microbial remediation technology has the characteristics of in-situ implementation, low energy consumption, complete degradation of pollutants, and green environmental protection, and is considered one of the most promising directions for removing soil and groundwater organic pollutants; electric remediation technology has high controllability and is considered one of the most promising control methods for groundwater pollution control technology. Due to the high controllability of electric technology, in recent years, a small number of studies have focused on electric combined technology, such as electric-biological, electric-leaching, electric-oxidation combined remediation. Existing in-situ electrically enhanced microbial remediation technology for halogenated hydrocarbon contaminated sites is mainly based on biological stimulation and biological enhancement to promote microbial reduction and dehalogenation of pollutants under constant voltage and stable voltage electric field. In the case of biological stimulation, a remediation time of more than 300 days is usually required, and there is a serious accumulation of intermediate toxic by-products dichloroethylene and chloroethylene, which can usually reach 50% or more; in the case of biological enhancement of engineered bacteria implantation, the abundance of the core functional microorganism Dehalococcoides can only reach 10 2 -10 4The current remediation method based on the stage-by-stage electrokinetic enhancement of microorganisms has not been paid attention to, mainly because the control effect of the electric field intensity on the site environment and the degradation activity of microorganisms is not clear, and the stage-by-stage method and mode lack guidance. SUMMARY

[0004] The present application aims at the above-mentioned deficiencies of the prior art, and provides an electrokinetic stage-by-stage enhanced bioremediation method and application, which has the characteristics of high efficiency, low cost and environmental friendliness in treating organic pollutants in low permeability media.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The first object of the present application is to provide an electrokinetic stage-by-stage enhanced bioremediation method, which comprises the following steps:

[0007] Step S1, arranging a well pipe, a bacterial agent fermentation tank and a buffer tank in a halogenated hydrocarbon contaminated low permeability area, the well pipe comprising at least one anode well, one cathode well, one bacterial agent implantation well, one bacterial agent fermentation tank and one circulating buffer tank; the anode well and the cathode well are respectively communicated with the circulating buffer tank, and the bacterial agent fermentation tank is communicated with the bacterial agent implantation well;

[0008] Step S2, pre-incubation stage, applying a high-intensity direct current electric field to the soil in the halogenated hydrocarbon contaminated low permeability aquifer area, supplementing microbial nutrients to the soil through high electromigration efficiency under the high-intensity electric field to promote the reduction of the soil oxidation-reduction potential to the ecological niche suitable for dehalogen functional microorganisms;

[0009] Step S3, simultaneously carrying out site adaptability culture of the engineering bacterial agent in the pre-incubation stage, carrying out site adaptability culture of the microbial agent in the bacterial agent fermentation tank to adapt to the biogeochemical environment of the site in advance; the microbial agent comprises dehalogen engineering bacterial agent;

[0010] The adaptability culture is the enrichment culture by adding the site soil suspension liquid to the bacterial agent and then carrying out anaerobic dehalogen fermentation again until the adaptability culture standard is met, so that the bacterial agent adapts to the biogeochemical environment of the site in advance;

[0011] Step S4, bacterial agent implantation stage, circulating the microbial agent meeting the adaptability standard to the bacterial agent implantation well, applying a medium-low intensity direct current electric field to the soil, and transporting the functional microorganisms in the bacterial agent implantation well to the cathode area through the appropriate electro-osmosis force;

[0012] Step S5, contaminant degradation stage, applying an intermittent low intensity electric field to the soil, transmitting the halogenated hydrocarbon contaminant to the active microbial functional group region by the effect of slow electroosmosis flow, reducing the byproduct dichloroethylene and chloroethylene produced in the microbial reductive dehalogenation process of halogenated hydrocarbon contaminant by prolonging the contaminant flow time.

[0013] Further, the electrodes in the cathode well and the anode well are both net-shaped or plate-shaped TiMMO electrodes.

[0014] Further, in step S2, the average voltage gradient between the anode and cathode electrodes in the pre-incubation stage is 2-4 V / cm.

[0015] Further, in step S3, the bacteria agent fermentation tank improves the suitability of the mixed bacteria agent in the field in the pre-incubation stage, and continuously provides the enriched culture in the bacteria agent implantation stage, the standard of the adaptive culture is that the Dehalococcoides dehalogenans in the enriched culture reaches at least 20% relative abundance and 10 9 million cells / mL.

[0016] Further, in step S4, the average voltage gradient between the electrodes in the bacteria agent implantation stage is 1-2 V / cm.

[0017] Further, in step S5, the average voltage gradient between the electrodes in the contaminant degradation stage is 0.1-1.0 V / cm.

[0018] Further, the voltage supply cycle of the contaminant degradation stage is 7-14 days / month.

[0019] Further, the microbial nutrient agent contains sodium propionate and vitamin B 12 .

[0020] Further, the yield of the byproduct chloroethylene is less than 30%.

[0021] The third object of the present application is to provide the application of the above-mentioned electrically enhanced staged bioremediation method in the in-situ remediation of organic contaminated soil, and the applicable site background conditions are: the site is a porous water-containing medium, the water content is greater than 50%, the average permeability coefficient is less than 10 -4 cm / s, or a non-homogeneous aquifer containing low permeability medium, and the pH is between 6 and 9.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) The application provides a method and application of electrically enhanced staged microbial remediation. The application involves three stages. The pre-incubation stage is used to reduce the oxidation-reduction potential and the content of in-situ competitive electron acceptors in the soil in-situ environment, thereby shortening the start-up time for the functional microorganisms to initiate the reduction dehalogenation; the pre-incubation stage is also used to culture the engineering bacterial agent in-situ to promote the bacterial agent to adapt to the in-situ biogeochemical environment in advance; the bacterial agent implantation stage promotes the active functional microorganisms in the bacterial agent bed to migrate to the cathode through the electro-osmosis effect, thereby promoting a larger range of soil to form an active functional group and improving the pollutant degradation potential; and the pollutant degradation stage transports the pollutants to the active microbial functional group area through the electro-osmosis effect, and completes the degradation under the action of biological reduction dehalogenation. Through the synergistic effect of the three stages, the start-up time required for the site remediation is greatly reduced, the implantation rate of the bacterial agent is accelerated, the utilization rate of the nutrient agent, the utilization rate of the bacterial agent and the utilization rate of the electric energy are improved, and the efficient degradation of the pollutants is realized.

[0024] The electric mass transfer system created by the direct current field in the low-permeability medium is used to regulate the migration of the nutrient agent, the functional microorganisms and the pollutants in the aquifer and the pollutant degradation process, thereby improving the distribution range of the microbial functional group in the aquifer and the degradation effect of the pollutants: 1. The supply of organic carbon required for the consumption of competitive electron acceptors by the microorganisms is regulated, thereby creating a suitable soil niche for the microbial dehalogenation; 2. The migration of the active functional microorganisms is controlled, thereby improving the range and abundance of the dehalogenation functional microorganisms in the soil without causing excessive migration of the microorganisms, and thereby improving the degradation potential of the soil microbial functional group to the pollutants; and 3. The migration of the pollutants is controlled, thereby promoting the contact between the pollutants and the active microbial functional group while reducing the migration of the microorganisms, fully exerting the reduction dehalogenation degradation capacity of the microorganisms, and thereby promoting the step-by-step dehalogenation reduction degradation of the halogenated hydrocarbon pollutants.

[0025] Compared with the constant-voltage electrically enhanced microbial remediation method, the staged variable-voltage electrically enhanced microbial remediation technology has staged targetability and targeted implantation position, greatly improves the utilization efficiency of the bacterial agent and the nutrient agent, and is a more environmentally friendly and economical remediation method. In the staged enhanced microbial remediation method, the abundance of the core functional microorganism Dehalococcoides dehalogenans can reach 10 6 -10 7 times / mL, which is increased by 3-4 orders of magnitude.

[0026] (2) The staged method greatly reduces the start-up time of the biological enhancement and the amount of the bacterial agent used, and greatly improves the implantation efficiency of the bacterial agent.

[0027] (3) The present application divides the inoculation of the microbial agent and the degradation of the pollutants into stages, reduces the loss caused by the high-intensity electric transmission of the microbial agent, prolongs the contact time of the pollutants with the microorganisms in the degradation stage, reduces the content of the intermediate by-products dichloroethylene and chloroethylene in the process of the dehalogenation and degradation of the pollutants by the microorganisms, and can realize more complete harmless degradation.

[0028] (4) The method provided by the present application does not add harmful chemical agents, has no secondary pollution risk, is more green and environmentally friendly, and has low cost.

[0029] (5) The present application combines the electrokinetics, which is an effective technology for promoting the migration of solutes in low-permeability water-containing media, with the microbial remediation technology, and strengthens the electrokinetic remediation / microbial remediation effect.

[0030] (6) The remediation method provided by the present application maintains the acidity and alkalinity in the anode and cathode wells, and does not cause a sharp change in the pH of the in-situ aquifer.

[0031] (7) The present application reduces the soil oxidation-reduction potential in the pre-incubation stage in advance, creates a suitable ecological niche for the dehalogenation microorganisms, and improves the survival rate and inoculation efficiency of the microbial agent. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a principle diagram of electrokinetic remediation of halogenated hydrocarbon organic pollutants by the microbial remediation in the embodiment of the present application;

[0033] Figure 2 is a device structure schematic diagram of the electrokinetic staged remediation provided by the present application;

[0034] Figure 3 is an experimental device diagram of the simulation of low-permeability media in the embodiment of the present application;

[0035] Figure 4 is a structure schematic diagram of the electrokinetic remediation column divided into five stages in the present application;

[0036] Figure 5 is a soil oxidation-reduction potential diagram of each region of the soil after the operation for 28 days under different electric field conditions;

[0037] Figure 6 is a soil degradation capacity diagram of trichloroethylene of the soil in each region after the operation for 28 days under different electric field conditions;

[0038] Figure 7 is a trichloroethylene degradation effect diagram after the operation for 28 days under different electric field conditions. DETAILED DESCRIPTION

[0039] In order to make the objects, technical solutions and advantages of the present application clearer, the embodiments of the present application are described in detail below, and the examples of the embodiments are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0040] Reference Figure 1 A mechanism diagram of an electrically powered staged enhanced microbial remediation method provided by the present application. The stages include a pre-incubation stage, a bacteria agent implantation stage and a pollutant degradation stage; the enhancement includes biological stimulation by adding nutrient agents and biological enhancement by adding engineered bacteria agents; the nutrient agents are injected at multiple points of the electrode well and the bacteria agent bed well, and the bacteria agents are added at multiple bacteria agent bed wells at a distance from the anode; a high-intensity direct current electric field is applied to the soil in the pre-incubation stage, and high electric migration efficiency under the high-intensity electric field is used to supplement microbial nutrient agents to the soil to promote the reduction of the soil oxidation-reduction potential to a suitable dehalogen functional microorganism; high-concentration and high-activity microbial bacteria agents are circulated to the bacteria agent bed well in the bacteria agent implantation stage, and a low-to-medium intensity direct current electric field is applied to the soil, and the functional microorganisms in the bacteria agent bed well are transported to the cathode region by suitable electro-osmosis force, while the loss of the bacteria agents caused by excessive transport is avoided, and the formation of an effective active microbial functional group in the contaminated soil is promoted; an intermittent low-intensity electric field is applied to the soil in the pollutant degradation stage, and the halogenated hydrocarbon pollutants are transported to the active microbial functional group region by the slow electro-osmosis flow, and the by-products generated in the process of incomplete reduction and dehalogen of the halogenated hydrocarbon pollutants by the microorganisms are greatly reduced by prolonging the flow time of the pollutants.

[0041] Reference Figure 2 A device structure schematic diagram of an electrically powered staged enhanced microbial remediation provided by the present application, which comprises a well pipe, a bacteria agent fermentation tank and a buffer tank, the well pipe comprises at least one anode well, one cathode well, one bacteria agent bed well, one bacteria agent fermentation tank and one buffer tank, the cathode well and the anode well are connected with the buffer tank, the bacteria agent bed well is connected with the bacteria agent fermentation tank, the cathode well is electrically connected with a cathode electric control device, and the anode well is electrically connected with an anode electric control device.

[0042] In the implementation process of the device, the bacteria agents are supplied to the contaminated aquifer in stages, and the direct current electric fields of different intensities are controlled to enhance the microbial degradation of the organic halogenated pollutants in the aquifer of the site, and the specific steps include the following steps:

[0043] (1) According to the hydrogeological conditions, the soil apparent resistivity and the pollutant occurrence of the aquifer of the contaminated site, the anode well, the cathode well and the bacteria agent circulation well layout scheme are set, and the wells are drilled.

[0044] (2) In the field, build a bacteria agent fermentation tank and an underground water circulation buffer tank. Mix the underground water in the cathode electrode well and the anode electrode well in the buffer tank, and adjust the pH to be neutral in real time, and maintain a certain concentration of nutrient agent in the underground water in real time.

[0045] (3) In the pre-incubation stage, high-intensity direct current is applied to the soil. Through the characteristics of the negatively charged organic acid nutrient component under high-intensity electric field, it migrates to the anode, and the soil in-situ microorganisms are supplemented with organic carbon source from the cathode to the anode, which stimulates the in-situ microorganisms to consume the soil in-situ electron acceptor. The whole process reduces the oxidation-reduction potential of the soil, and incubates a good space for the dehalogenation active microorganisms.

[0046] (4) In the pre-incubation stage, the field suitability culture of the engineering bacteria agent is carried out at the same time. The soil suspension liquid is added to the fermentation tank of the bacteria agent for anaerobic dehalogenation fermentation again, and the mixed bacteria enrichment culture suitable for the field is obtained through enrichment culture. The bacteria agent suitability culture standard is that the core species Dehalococcoides pseudogranulatus reaches 20% relative abundance and 10 9 individuals / mL of cell number at the same time.

[0047] It should be noted that the mixed bacteria agent is a reduction dehalogenation bacteria agent obtained by enrichment culture from the actual chlorinated hydrocarbon contaminated soil. The enrichment culture method is referred to in the paper (Dechlorination and organohalide-respiring bacteria dynamics in sediment samples of the Yangtze Three Gorges Reservoir, Environmental Science and Pollution Research, 2013, 20: 7046-7056, doi: 10.1007 / s11356-013-1545-9)

[0048] (5) In the bacteria agent implantation stage, a medium-low intensity direct current is applied to the soil, and the bacteria agent with the suitability culture standard is circulated in the bacteria agent implantation well. Through the electro-osmosis force under the medium-intensity electric field, the microorganisms without electricity and with weak electricity move from the bacteria agent implantation well to the cathode. Since the suitable living space has been created in S1, the bacteria agent can be successfully implanted, and the concentration of the nutrient agent in the anode and cathode wells is maintained during the process to promote the implanted bacteria agent to maintain activity.

[0049] (6) The pollutant degradation stage applies a low-intensity direct current electric field to the soil, and under the electric osmosis force, the uncharged component halogenated hydrocarbon is transported from the anode to the cathode, and is gradually reduced and mineralized by the reduction dehalogenation of the functional group of the already-implanted microorganism. In the halogenated pollutant degradation process, the concentration of the nutrient agent is lower than the preset value, and a small amount of nutrient agent is added again until the concentration of the organic pollutant in the aquifer reaches the treatment requirement.

[0050] It should be noted that the low-permeability aquifer region of the halogenated hydrocarbon pollution in the present application refers to an aquifer with a permeability coefficient less than 10 -4 cm / s or a non-homogeneous aquifer containing low-permeability medium structures.

[0051] Example 1

[0052] To investigate the degradation effect of the electromotion-enhanced microbial remediation technology on halogenated hydrocarbon pollutants, a case test was carried out by taking trichloroethylene widely stored in the boundary of low-permeability medium as the target pollutant.

[0053] Reference Figure 3 A plexiglass column was used to construct a simulated low-permeability medium aquifer, the electromotion-enhanced column has a diameter of 7 cm and a length of 20 cm, fluororubber flanges are used to connect the cathode and anode electrode chambers at both ends of the soil column, and the electrode chambers are used to simulate the anode well and cathode well (diameter: 8 cm, length: 4 cm). The anode and cathode electrode chambers are connected with a circulating water pump and a 500 mL circulating tank, a 2 L gas bag is connected to the upper part of the circulating tank to detect the operating state. TiMMO mesh coated with IrO2 and Ta2O5 is used as the electrode (diameter: 7.8 cm, thickness: 0.2 cm) of the electrode chamber. The simulated soil is taken from the low-permeability aquifer (3-5 m underground) of a contaminated site. The left side of the experimental column body from 0 to 9 cm and from 11 to 20 cm is filled with low-permeability soil, and quartz sand (10-20 mesh) is filled in 9-11 cm to simulate the bacteria agent implantation well. 1.1 L of simulated groundwater is injected into the simulated electrode well and circulating tank, the composition of the simulated groundwater is 5 mmol / L sodium bicarbonate aqueous solution, 15 mmol of sodium lactate is added to the simulated groundwater as the simulated microbial nutrient agent, and 200 μmol of trichloroethylene is added to the simulated groundwater as the simulated pollutant. The simulated groundwater is mixed uniformly under the action of a peristaltic pump at a rate of 20 mL / min along the cathode-anode-circulating tank-cathode. The input voltage of the column experiment is set to 0, 20, 40, 55 and 70 V, which corresponds to an average voltage gradient of 0, 1.00, 2.00, 2.75 and 3.50 V / cm applied to the soil. The concentration of the nutrient agent sodium lactate is maintained at about 15 mmol / L, and the concentration of trichloroethylene is about 100 μmol / L during the operation of all column experiment groups. The bacteria agent is subjected to soil suitability culture, and the culture method is as follows: 5 g / L of anaerobic soil suspension is added to the primary dehalogenation engineering bacteria solution, 15 mmol / L of sodium lactate, 0.001 mmol / L of vitamin B12 and 250 μmol / L TCE in anaerobic fermentor, and the enrichment fermentation was repeated 4 times with 10% suspension inoculation. After the enrichment fermentation, the relative abundance of the core species Dehalococcoides sp. reached 20% and the cell number reached 10 9 After the field suitability culture, the community composition of the enrichment culture was shown in Table 1 as follows:

[0054] Table 1. Composition of the microbial inoculant after the suitability culture

[0055]

[0056] To study the effect of the implementation of the pre-incubation stage on the shaping of the soil dehalogenation environment, as shown in Figure 4 , the electrokinetic column was divided into 5 segments every 4 cm from the anode to the cathode after the pre-incubation. The results are shown in Figure 5 . As can be seen from the figure, the soil redox potential in the electrokinetic column operated for 28 days under the condition of a voltage gradient of 3.50 V / cm decreased from the initial soil of-225.8 mV to-411 to-624 mV, which indicated that the soil niche gradually changed from the iron-reducing niche to the sulfate-reducing and hydrogen-producing fermentation niche suitable for dehalogenation, and the high-intensity electric field did not affect the formation of a suitable dehalogenation redox potential in the anode region.

[0057] As shown in Figure 6 , to study the enhancement law of the soil microbial community degradation effect after the electrokinetic microbial inoculation, the soil was divided into 5 segments every 4 cm from the anode to the cathode after 28 days of operation, and was inoculated into simulated groundwater at 100 g / L, and the trichloroethylene degradation effect was monitored. As shown in Figure 6 (a), all the soil from the anode to the cathode had the ability to completely degrade trichloroethylene to cis-dichloroethylene, and the activity of the cathode region V was higher than that of the anode region I. As can be seen from Figure 6 (a), the dehalogenation activity in the anode region increased more significantly when the voltage gradient increased from 1.00 V / cm to 3.50 V / cm, so the high-intensity (i.e., a voltage gradient of 3.50 V / cm) electric field was used as the electric field in the pre-incubation stage to accelerate the formation of a suitable dehalogenation biogeochemical environment in the in-situ field, and to provide more favorable conditions for the inoculation of the microbial inoculant.

[0058] In the microbial inoculation stage, from Figure 6(b and c) It can be seen that the bacteria mainly migrated from the bacteria inoculation well to the III-V region under the effect of electro-osmotic flow which is mainly from the anode to the cathode. When a low intensity electric field was applied (i.e. a voltage gradient of 1.00 V / cm), the bacteria remained in the inoculation well; while when a high intensity and medium-high intensity electric field was applied (i.e. a voltage gradient of 2.75-3.50 V / cm), the bacteria over-diffused, which resulted in a low activity remaining in the III-V region. Only when a medium-low intensity electric field was applied (i.e. 2.00 V / cm), the bacteria migrated to the cathode successfully and effectively remained. Therefore, it is concluded that a medium-low intensity electric field should be applied during the bacteria implantation stage, which can maximize the migration of the bacteria while ensuring that the bacteria will not over-migrate and be lost.

[0059] As shown in Figure 7 , in order to study the electric field intensity selection during the pollutant degradation stage, the components in the gas bag were tested by interval sampling and cumulative gas collection during the operation of the electrokinetic enhanced column system. The recovered ethylene is the harmless end product of the reduction dehalogenation of trichloroethylene by the implanted bacteria. Under a high intensity electric field (i.e. a voltage gradient of 3.50 V / cm), less than 50% of the trichloroethylene was degraded, and only 30% of the harmless product ethylene was obtained. As the electric field intensity decreased from 3.50 V / cm to 1.00 V / cm, the proportion of the harmless product ethylene increased to 60%, and the complete harmless effect of the pollutant reached the best. Therefore, it is concluded that a low intensity electric field should be applied during the pollutant degradation stage, which can maximize the time of the pollutant in the active microorganism region under the condition of effective nutrition supply, so as to achieve a better complete dehalogenation effect.

[0060] Example 2: A contaminated site of a chemical plant

[0061] The TCE in the aquifer was treated by using the device as shown in Figure 2 , and the specific steps were as follows:

[0062] Step S1: Drill wells in a low-permeability TCE-contaminated aquifer (5-10 meters underground) within the saturation zone. Each treatment unit is 4m x 8m. Within each unit, drill wells 10m deep at points (0,0) and (0,4) as anode electrode wells; drill wells 10m deep at points (0,4), (2,4), and (4,4) as inoculum loading wells; and drill wells 10m deep at points (0,8) and (4,8) as cathode electrode wells. Install an anaerobic inoculum fermenter near point (0,4) and a circulating buffer tank near point (4,4). Install permeable sidewall pipes (20cm diameter) in the cathode, anode, and inoculum loading wells. Install a water pump at the bottom of the inoculum loading well, followed by the laying of quartz sand (2-4mm particle size) as the inoculum loading bed. Connect the water pump to the fermenter. Install water pumps at the bottom of the cathode and anode electrode wells, connecting them to the circulating tank. TiMMO mesh electrodes are fixed at a depth of 6-9 meters in the anode and cathode wells, and the electrode plates are connected to the electrical control equipment outside the wells via wires.

[0063] Step S2: Start the power supply to create a 3200V (4V / cm) DC electric field between the anode and cathode. A water pump mixes and circulates the nutrient solution and groundwater in the anode, cathode, and circulation tank at a rate of 1L / min, neutralizing the acidic / alkaline environment in the electrode well and maintaining the groundwater within a neutral pH range of 6-8. The concentration of the nutrient solution, sodium lactate, is maintained at 15mmol / L, and vitamin B1 is added. 12 Concentration greater than 0.001 mmol / L. Microbial nutrients are replenished to the soil via electromigration. When the redox potential of the low-permeability aquifer is below -300 mV (Ag / AgCl) and the competitive electron acceptor Fe(III) no longer decreases, the high-voltage electric field power supply during the pre-incubation stage is stopped, and the circulation of the electrode well water pump is stopped.

[0064] Step S3: Add 5 g / L of anaerobic soil suspension to the primary engineered bacterial culture in an anaerobic fermenter. Enrichment fermentation is then carried out in an anaerobic fermenter containing 15 mmol / L sodium lactate, 0.001 mmol / L vitamin B12, and 250 μmol / L LTCE. The enrichment fermentation is repeated four times with a 10% suspension inoculation ratio. The qualified criteria for enrichment fermentation are: a relative abundance of the core species *Dehalococcoides* reaching 20% ​​and a cell count reaching 10-1. 9 per mL.

[0065] Step S4: The water pump exchanges the groundwater in the inoculant injection well with the fermenter at a rate of 1 L / min, maintaining this for 10 minutes. 9core species Dehalococcoides concentration at 10 6 / mL level. Circulating the enrichment culture of suitability standard from the inoculum well to the electrode well, restarting the power supply, creating 1600V (2V / cm) direct current field between the anode and cathode, transporting the functional microorganism in the inoculum well to the cathode area by the electro-osmotic force. The water pump mixes and circulates the nutrient solution and groundwater in the anode, cathode and circulation tank at 1L / min, so that the acidic / alkaline environment in the electrode well can be neutralized, and the groundwater is kept in the neutral pH range of 6-8, the concentration of sodium lactate nutrient is maintained at 15mmol / L, and the concentration of vitamin B 12 When the Dehalococcoides implantation is detected from the inoculum well to the cathode electrode well, stop the power supply, stop the electrode well water pump circulation, and stop the inoculum well water pump circulation.

[0066] Step S5, intermittently creating 400V (0.5V / cm) power supply between the anode and cathode, slowly transmitting the TCE pollutants from the anode to the cathode to the inoculum bed area, gradually dehalogenating and reducing the by-products dichloroethylene and chloroethylene produced in the process of microbial reduction dehalogenation of halogenated hydrocarbon pollutants.

[0067] Results: At 0 days, the soil suspension from the site is added to the anaerobic fermentation tank and mixed with YUAN-Lab-TCE and the enrichment fermentation culture is started, and at 60 days, the enrichment culture reaches the suitability standard; At 30 days, the nutrient solution is circulated from the buffer tank to the cathode and anode electrode wells, and then the electric control device is started to apply high-voltage direct current to the contaminated site during the pre-incubation stage, and at 45 days, the competitive electron acceptor Fe(III) capacity in the aquifer is reduced by 40%, and the ORP is reduced to -415mV (Ag / AgCl), and at 55-60 days, the competitive electron acceptor Fe(III) in the aquifer is no longer reduced and is maintained at 50μmol / g, which meets the implantation conditions of dehalogenating inoculum, and at 60 days, the power is turned off; At 60 days, the enrichment culture of site suitability standard is circulated to the inoculum well, and then the electric control device is started to apply continuous medium-voltage direct current to the site to transport the inoculum, and at 75 days, the implantation of core species Dehalococcoides is detected at 1 / 2 sampling point in the aquifer, and at 85 days, the implantation of Dehalococcoides is observed at all detection points from the inoculum well to the cathode well, so the power is turned off at 90 days; From 90 days, the electric control device applies indirect low-voltage direct current to the site for 7 days per month during the pollutant degradation stage, and within 90-120 days, 95% of the TCE in the site is completely degraded to harmless product ethylene.

[0068] The above not involved, applicable to the prior art.

[0069] Although some specific embodiments of the present application have been described in detail by way of example with reference to the drawings, it is to be understood that the above examples are intended to be illustrative only and are not intended to limit the scope of the present application, and that various modifications and changes can be made by those skilled in the art to the particular embodiments described without departing from the spirit and scope of the present application. It is intended that the scope of the present application be limited only by the broadest interpretation of the appended claims to be accorded under 35 U.S.C. § 112.

Claims

1. A method for electrodynamic phased enhanced bioremediation, characterized in that, The specific steps include the following: S1. In a low-permeability area contaminated with halogenated hydrocarbons, a well casing, a microbial agent fermentation tank, and a buffer tank are arranged. The well casing includes at least one anode well, one cathode well, one microbial agent implantation well, one microbial agent fermentation tank, and one circulating buffer tank. The anode well and the cathode well are respectively connected to the circulating buffer tank, and the microbial agent fermentation tank is connected to the microbial agent implantation well. The electrodes in the cathode well and the anode well are mesh or plate-shaped titanium-plated iridium-tantalum TiMMO electrodes. S2. In the pre-incubation stage, a high-intensity DC electric field is applied to the soil in the low-permeability area contaminated with halogenated hydrocarbons. The high electromigration efficiency under the high-intensity electric field is used to supplement the soil with microbial nutrients to promote the reduction of soil redox potential and the consumption of competitive electron acceptors until the dehalogenated microorganisms reach a suitable ecological niche. The average voltage gradient between the anode and cathode electrodes in the pre-incubation stage is 4 V / cm. S3. During the pre-incubation stage, the microbial agents are simultaneously cultured in the fermentation tank to adapt to the site's biogeochemical environment in advance; the microbial agents include dehalogenation engineered microbial agents; S4. In the microbial agent implantation stage, suitable microbial agents that meet the standards are circulated into the implantation well, and a medium-to-low intensity DC electric field is applied to the soil. Through appropriate electrodialysis force, the functional microorganisms in the implantation well are transported to the cathode area. The average voltage gradient between the electrodes in the microbial agent implantation stage is 2 V / cm. S5. In the pollutant degradation stage, an intermittent low-intensity electric field is applied to the soil. The halogenated hydrocarbon pollutants are transported to the functional area of ​​active microorganisms through a slow electrodialysis flow. By extending the pollutant flow time, the byproducts dichloroethylene and vinyl chloride generated during the microbial reduction and dehalogenation process of the halogenated hydrocarbon pollutants are reduced. The average voltage gradient between electrodes in the pollutant degradation stage is 1 V / cm.

2. The method as described in claim 1, characterized in that, In step S3, the microbial fermentation tank improves the suitability of the dehalogenation engineering microbial agent in the site during the pre-incubation stage, and continuously provides enrichment cultures during the microbial agent implantation stage. The standard for the adaptive culture is the concentration of microbial agents in the enrichment culture. Dehalococcoides Dehalogenated Bacteroides simultaneously achieved a relative abundance of at least 20% and 10 9 Cell count per mL.

3. The method as described in claim 1, characterized in that, The voltage supply cycle for the pollutant degradation stage is 7-14 days / month.

4. The method as described in claim 1, characterized in that, The microbial nutrient contains sodium propionate and vitamin B. 12 .

5. The method as described in claim 1, characterized in that, The yield of the byproducts vinyl chloride and dichloroethylene is less than 30%.

6. The application of the electrodynamic staged enhanced bioremediation method as described in any one of claims 1-5 in the in-situ remediation of organically contaminated soil, characterized in that, The applicable site conditions are: the site is a porous, water-saturated medium with an average permeability coefficient of less than 10. -4 cm / s or heterogeneous aquifers containing low-permeability media, with a pH between 6 and 9.

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