Microbial remediation device and method for petroleum hydrocarbon contaminated soil

Abstract

The invention belongs to the technical field of soil remediation, and particularly discloses a microbial remediation device and method.The remediation device comprises a box body, a power source, a wire and plants, an air cathode counter electrode is arranged at the bottom of the box body, and the position, above the air cathode counter electrode, in the box body is filled with contaminated soil; a surface active agent and a carbon felt anode are arranged in the contaminated soil, plants are planted in the contaminated soil, the outer side of the carbon felt anode is coated with a gel water retention layer, and the carbon felt anode is connected with a power source after being connected with a wire through a titanium wire. According to the microbial remediation device and method for the petroleum hydrocarbon contaminated soil, microorganisms are combined with an external electric field and a solid electrode, so that the problems that electron acceptors in the soil are deficient and the utilization rate is low are solved; meanwhile, the diversity of petroleum hydrocarbon pollutant removal ways is increased through intervention of the remediation plants, the remediation distance is increased, and a new method is provided for remediation of the low-carbon petroleum hydrocarbon contaminated soil.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and particularly to a microbial remediation device and method for petroleum hydrocarbon-contaminated soil. Background Art

[0002] Petroleum plays an important role in the economic and social development of a country. However, due to immature extraction technologies, petroleum and its derivatives will inevitably enter the environment during exploration, extraction, transportation, and refining processes, thereby damaging the soil ecological environment. The main pollutants are petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAHs). The damage of petroleum hydrocarbons to the soil environment is mainly manifested as changing the structure and composition of the soil, affecting the growth of plants, poisoning the health of animals, and causing changes in the soil microbial community. Therefore, the remediation of petroleum-contaminated soil is extremely urgent.

[0003] At present, the remediation technologies for petroleum-contaminated soil at home and abroad involve bioremediation technologies. The microbial remediation technology composed of bioaugmentation and biostimulation, as a green remediation technology, has been widely studied due to its advantages of environmental friendliness, low disturbance to the environment, no secondary pollution, and stable effects. For the remediation of the contaminated soil surface layer, this technology can achieve the goals of simplicity, rapidity, and low cost. There are still several limiting factors in the traditional soil microbial remediation process: lack of electron acceptors in the soil, consumption of organic substrates by biological and abiotic competition, low quantity and activity of soil functional bacteria, low soil electron transfer efficiency, and accumulation of by-products. Therefore, how to supplement electron acceptors in the soil and directionally enrich functional microorganisms is a difficult point that needs to be broken through in the remediation of petroleum hydrocarbon-contaminated soil.

[0004] The microbial electrochemical system (MESs) based on electroactive microorganisms is a system that couples the advantages of biotechnology and electrochemical redox technologies. It can not only well provide electron acceptors ex-situ, but also directionally enrich electroactive microorganisms from the microbial community in the natural environment to achieve efficient and rapid degradation of pollutants. Under the current grand vision of carbon peak and carbon neutrality, the advantages of this technology in the field of low-carbon contaminated soil remediation are becoming more and more prominent.

[0005] Current research shows that the coupled system of MESs and phytoremediation technology (P-MES) can enhance the removal of petroleum hydrocarbons in soil. The novelty of P-MES lies in the unique relationship between plants and microorganisms in the rhizosphere: plants can use carbon dioxide through photosynthesis to produce a large amount of organic substances such as rhizosphere exudates and transport them to the soil, providing substrates for the microbial community in the root zone. At the same time, electroactive microorganisms can generate electrons by using these substrates and other organic pollutants in the rhizosphere with rhizosphere microorganisms and indigenous degradable microorganisms. In theory, the transpiration of plants can provide a driving force for the migration of water, resulting in the movement of substances with water. There is a positive correlation between the water content of the soil and the remediation performance of MESs. The increase in soil moisture can highly reduce the internal resistance and improve the activity and metabolic rate of microorganisms. By increasing the water content of the soil or reducing the evaporation of water, the pollutant removal efficiency can be effectively improved. Therefore, in addition to planting plants around the anode of MESs, a water retention layer is also set up, which is more conducive to increasing the water content of the soil, thereby maintaining biological activity and strengthening the degradation of petroleum hydrocarbon pollutants in the soil. Therefore, the present invention improves the overall water content of the system soil by setting up a water retention layer around the electrode and coupling the water retention function of plants, uses the hydrological driving force provided by the plant body to promote the migration of substances in the polluted soil, and stimulates the enrichment of functional microorganisms through an external electric field, ultimately realizing the enhancement of the remediation efficiency of petroleum hydrocarbon polluted soil and the increase of the remediation range of the remediation system. Summary of the Invention

[0006] The purpose of the present invention is to provide a microbial remediation device and method for petroleum hydrocarbon polluted soil, which is low-carbon, safe, green and efficient. By combining microorganisms with an external electric field and a solid electrode, the problems of lack and low utilization rate of electron acceptors in the soil are solved. At the same time, the intervention of remediation plants increases the diversity of petroleum hydrocarbon pollutant removal pathways and improves the remediation distance. While meeting the requirements of green, low-consumption, high-efficiency and stability, a new method for low-carbon remediation of petroleum hydrocarbon polluted soil is provided.

[0007] To achieve the above purpose, the present invention provides a microbial remediation device for petroleum hydrocarbon polluted soil, including a box body, a power supply, a wire, and a plant. An air cathode counter electrode is provided at the bottom of the box body. Polluted soil is filled above the air cathode counter electrode in the box body. A surfactant and a carbon felt anode are provided inside the polluted soil. The plant is planted in the polluted soil. A gel water retention layer is coated outside the carbon felt anode. The carbon felt anode is connected to the wire with a titanium wire and then connected to the power supply. The polluted soil also includes electricity-generating microorganisms, indigenous degradation microorganisms in the soil, and rhizosphere microorganisms. The voltage range provided by the power supply is set to 0.5 - 1.0V.

[0008] Preferably, the gel water-retaining layer is a mixture of polyacrylamide hydrogel and contaminated soil, and the mass ratio of polyacrylamide hydrogel to contaminated soil is 1:1 - 1:3, and the thickness of the gel water-retaining layer is 1 - 3 cm.

[0009] Preferably, the counter electrode of the air cathode is a carbon cloth air cathode. Both the carbon felt anode and the counter electrode of the air cathode need to be pretreated before use: First, cut the electrode material to reserve holes so that the roots of plants can pass through. Second, put the cut carbon felt or carbon cloth into acetone and soak it sealed for 12 - 18 h, and then ultrasonically clean it with ethanol and water in turn, and the ultrasonic time each time is not less than 10 min.

[0010] Preferably, the plant is one or more of Solanum nigrum, Mirabilis jalapa, Phragmites australis, Hylotelephium spectabile, Iris tectorum.

[0011] Preferably, the surfactant is one of biosurfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, non-ionic surfactants.

[0012] A microbial remediation method for petroleum hydrocarbon contaminated soil is realized through a remediation device, and includes the following steps:

[0013] S1. Add the surfactant to the contaminated soil and mix evenly;

[0014] S2. Bury the gel water-retaining layer and the carbon felt anode after cutting and designing into the contaminated soil;

[0015] S3. Fix the counter electrode of the air cathode at the bottom of the box, with one side facing the contaminated soil and the other side directly exposed to the air;

[0016] S4. Connect the wires to the carbon felt anode and the counter electrode of the air cathode with titanium wires respectively and then fix them;

[0017] S5. Plant the plants evenly in the contaminated soil to be remediated;

[0018] S6. Connect the wires to the power supply to provide a continuous and stable weak electric field for the remediation device.

[0019] Preferably, in step S1, the addition amount of the surfactant is 5 - 15 wt.%.

[0020] Preferably, in step S2, the depth of the carbon felt anode buried in the contaminated soil is 10 - 30 cm, and the horizontal distance from the center of the plant roots is 5 - 15 cm.

[0021] Preferably, in step S5, the planting density of the plants is 4 - 8 plants per square meter.

[0022] The advantages and beneficial effects of the present invention adopting the above-mentioned microbial remediation device and method for petroleum hydrocarbon-contaminated soil are as follows:

[0023] 1. The present invention introduces a weak electric field and solid electrodes into the plant-microbial remediation system, providing a continuous electron acceptor for the remediation of petroleum hydrocarbon contamination, and only requiring a small power input, having advantages in removing pollutants with low energy consumption and low carbon.

[0024] 2. The present invention can promote the migration and transformation of petroleum hydrocarbon pollutants in the soil by uniformly adding biosurfactants to the soil; utilize the hydrogeological driving force generated by plants to achieve the directional migration of petroleum hydrocarbon pollutants over a long distance, thereby improving the mass transfer ability of the system; use the weak electric field to stimulate the efficient enrichment of electrogenic microorganisms, rhizosphere microorganisms, and indigenous degradable microorganisms, and utilize the interaction between different microbial communities to promote the removal of refractory petroleum hydrocarbons; by arranging a water retention layer near the electrode and utilizing the water retention effect of plants, the water content of the soil in the system can be maximally increased, thereby improving the activity and metabolic rate of microorganisms and reducing the soil internal resistance; utilize the plants in the system to absorb, volatilize, root filter, degrade, and stabilize some of the petroleum hydrocarbon pollutants in the soil, thereby achieving degradation, providing more flexible pollutant removal performance.

[0025] 3. The present invention causes little disturbance to the original soil ecological environment, is green, low-consumption, highly efficient and stable, and has the ability to increase the effective remediation distance of the original technology.

[0026] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0027] Figure 1 is a schematic diagram of a microbial remediation device for petroleum hydrocarbon-contaminated soil according to the present invention;

[0028] Figure 2 is a graph showing the change in the content of total petroleum hydrocarbons (TPH) in the soil at different distances from the carbon felt anode at the end of the 30-day remediation cycle in Example 1 of the present invention and Comparative Examples 1-3;

[0029] Figure 3 is the change in the content of dissolved total organic carbon in the soil pore water near the carbon felt anode at the end of the 30-day remediation cycle in Example 1 of the present invention and Comparative Examples 1-3.

[0030] Reference Numerals

[0031] 1. Gel water retention layer; 2. Carbon felt anode; 3. Wire; 4. Air cathode counter electrode; 5. Power supply; 6. Plant; 7. Surfactant; 8. Box; 9. Electrogenic microorganism; 10. Indigenous degradable microorganism in the soil; 11. Rhizosphere microorganism. Detailed Embodiments

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. The terms such as "comprising" or "including" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left", "right" are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0034] Example 1

[0035] A microbial remediation device for petroleum hydrocarbon-contaminated soil, comprising a box body 8, a power source 5, a wire 3, and a plant 6. The plant 6 provides a hydrological driving force for the device. The roots of the plant 6 are dense and vigorous and the leaf area is large, and it has a certain tolerance to petroleum hydrocarbon pollutants. The material of the box body 8 should have the characteristics of strong toughness, low price, and easy machining, and is more preferably polymethyl methacrylate (plexiglass). An air cathode counter electrode 4 is provided at the bottom of the box body 8. Contaminated soil is filled above the air cathode counter electrode 4 in the box body 8. A surfactant 7 and a carbon felt anode 2 are provided inside the contaminated soil. The surfactant 7 promotes the migration and dissolution of petroleum hydrocarbons in the soil from the non-aqueous phase liquid or solid phase to the aqueous phase. The plant 6 is planted in the contaminated soil. A gel water retention layer 1 is coated outside the carbon felt anode 2. After connecting the carbon felt anode 2 to the wire 3 with a titanium wire and then connecting it to the power source 5, the contaminated soil also includes electricity-producing microorganisms 9, indigenous degradation microorganisms in the soil, and rhizosphere microorganisms 11. The voltage provided by the power source 5 is set to 0.7V.

[0036] The gel water retention layer 1 is a mixture of polyacrylamide hydrogel and contaminated soil. The mass ratio of polyacrylamide hydrogel to contaminated soil is 1:2, and the thickness of the gel water retention layer 1 is 2 cm.

[0037] The air cathode counter electrode 4 is a carbon cloth air cathode. Before use, both the carbon felt anode 2 and the air cathode counter electrode 4 need to be pretreated: First, the electrode material is cut to reserve holes so that the roots of the plant 6 can pass through. Second, the cut carbon felt or carbon cloth is sealed and soaked in acetone for 12 h, and then ultrasonically cleaned with ethanol and water in turn, and the ultrasonic time each time is not less than 30 min.

[0038] Plant 6 is Mirabilis jalapa.

[0039] Surfactant 7 is a biosurfactant.

[0040] A microbial remediation method for petroleum hydrocarbon contaminated soil, comprising the following steps:

[0041] S1. Add surfactant 7 to the contaminated soil and mix evenly; the addition amount of surfactant 7 is 10 wt.% of the contaminated soil.

[0042] S2. Bury the gel water retention layer 1 and the carbon felt anode 2 after cutting and designing into the contaminated soil; the depth of the carbon felt anode 2 buried in the contaminated soil is 15 cm, and the horizontal distance from the center of the root system of plant 6 is 10 cm.

[0043] S3. Fix the air cathode counter electrode 4 at the bottom end of the box 8, with one side facing the contaminated soil and the other side directly exposed to the air.

[0044] S4. Connect the wire 3 to the carbon felt anode 2 and the air cathode counter electrode 4 respectively with titanium wires and then fix them.

[0045] S5. Plant plant 6 evenly in the contaminated soil to be repaired; the planting density of plant 6 is 6 plants per square meter.

[0046] S6. Connect the wire 3 to the power supply 5 to provide a continuous and stable weak electric field for the repair device.

[0047] The treatment group of Example 1 is labeled as P-MES.

[0048] Place the above constructed soil repair device in an artificial greenhouse, maintain the greenhouse temperature at 22 - 24 °C, the humidity at 45 - 50% RH, and ensure the light condition is 12 h per day; the soil in the device initially operates under saturated conditions, and add an appropriate amount of water to the soil regularly to maintain the normal growth of plant 6; after the repair device operates for 40 days, collect soil samples at 10, 15, and 20 cm below the carbon felt anode 22 wrapped with the gel water retention layer 11 for testing and pore water at 15 cm for testing.

[0049] After the device has been running for 40 days, the total petroleum hydrocarbon content (TPHs) in the soil at different positions in the device is measured. The measurement method is the gravimetric method. Specifically: First, the petroleum hydrocarbon-contaminated soil sample is freeze-dried at -60 °C and 50 - 100 Pa for 48 h, and then ground through a 60-mesh sieve; 2 g is weighed and placed in a 50 mL Erlenmeyer flask, and an appropriate amount of dichloromethane is added and ultrasonically extracted repeatedly, and then poured into a 50 mL Erlenmeyer flask that has been weighed. It is then evaporated in a water bath at 42 °C until constant weight. The weight of the Erlenmeyer flask is weighed, and then the difference in the mass of the Erlenmeyer flask before and after evaporation is calculated, which is the total petroleum hydrocarbon content in the sample. The pore water in the soil (about 10 ml) is collected using a soil pore water collector with a membrane pore size of 0.60 μm, and then the content of soluble organic carbon in the collected pore water sample is tested using a total organic carbon analyzer.

[0050] Example 2

[0051] A microbial remediation device for petroleum hydrocarbon-contaminated soil, comprising a box body 8, a power supply 5, a wire 3, and a plant 6. An air cathode counter electrode 4 is provided at the bottom of the box body 8. Contaminated soil is filled above the air cathode counter electrode 4 in the box body 8. A surfactant 7 and a carbon felt anode 2 are provided inside the contaminated soil. The plant 6 is planted in the contaminated soil. A gel water retention layer 1 is coated outside the carbon felt anode 2. The carbon felt anode 2 is connected to the wire 3 using a titanium wire and then connected to the power supply 5. The contaminated soil also includes electricity-producing microorganisms 9, indigenous degradation microorganisms 10 in the soil, and rhizosphere microorganisms 11. The voltage range provided by the power supply 5 is set to 0.5 V.

[0052] The gel water retention layer 1 is a mixture of polyacrylamide hydrogel and contaminated soil. The mass ratio of polyacrylamide hydrogel to contaminated soil is 1:1, and the thickness of the gel water retention layer 1 is 3 cm.

[0053] The air cathode counter electrode 4 is a carbon cloth air cathode. Both the carbon felt anode 2 and the air cathode counter electrode 4 need to be pretreated before use: First, the electrode material is cut to reserve holes so that the roots of the plant 6 can pass through. Secondly, the cut carbon felt or carbon cloth is sealed and soaked in acetone for 16 h, and then ultrasonically cleaned with ethanol and water in turn, and the ultrasonic time each time is not less than 20 min.

[0054] The plant 6 is Solanum nigrum.

[0055] The surfactant 7 is an anionic surfactant.

[0056] A microbial remediation method for petroleum hydrocarbon-contaminated soil, comprising the following steps:

[0057] S1. Add the surfactant 7 to the contaminated soil and mix evenly. The addition amount of the surfactant 7 is 5 wt.%.

[0058] S2. Bury the gel water-holding layer 1 and the carbon felt anode 2 after cutting and designing into the contaminated soil. The depth of the carbon felt anode 2 buried in the contaminated soil is 10 cm, and the horizontal distance from the center of the root system of the plant 6 is 5 cm.

[0059] S3. Fix the air cathode counter electrode 4 at the bottom end of the box body 8, with one side facing the contaminated soil and the other side directly exposed to the air.

[0060] S4. Connect the wire 3 to the carbon felt anode 2 and the air cathode counter electrode 4 with titanium wires respectively and then fix them.

[0061] S5. Plant the plants 6 evenly in the contaminated soil to be repaired. The planting density of the plants 6 is 4 plants per square meter.

[0062] S6. Connect the wire 3 to the power supply 5 to provide a continuous and stable weak electric field for the repair device.

[0063] Example 3

[0064] A microbial remediation device for petroleum hydrocarbon contaminated soil, comprising a box body 8, a power supply 5, a wire 3, a plant 6. An air cathode counter electrode 4 is provided at the bottom of the box body 8. The contaminated soil is filled above the air cathode counter electrode 4 in the box body 8. A surfactant 7 and a carbon felt anode 2 are arranged inside the contaminated soil. The plant 6 is planted in the contaminated soil. A gel water-holding layer 1 is coated outside the carbon felt anode 2. Connect the carbon felt anode 2 to the wire 3 with a titanium wire and then connect it to the power supply 5. The contaminated soil also includes electricity-producing microorganisms 9, indigenous degradation microorganisms 10 in the soil, and rhizosphere microorganisms 11. The voltage range provided by the power supply 5 is set to 1.0 V.

[0065] The gel water-holding layer 1 is a mixture of polyacrylamide hydrogel and contaminated soil. The mass ratio of polyacrylamide hydrogel to contaminated soil is 1:3, and the thickness of the gel water-holding layer 1 is 1 cm.

[0066] The air cathode counter electrode 4 is a carbon cloth air cathode. Both the carbon felt anode 2 and the air cathode counter electrode 4 need to be pretreated before use: First, cut the electrode material to reserve holes so that the root system of the plant 6 can pass through. Second, put the cut carbon felt or carbon cloth into acetone and soak it sealed for 18 h. Then ultrasonically clean it with ethanol and water in turn, and the ultrasonic time each time is not less than 30 min.

[0067] The plant 6 is Iris tectorum.

[0068] The surfactant 7 is an amphoteric surfactant.

[0069] A microbial remediation method for petroleum hydrocarbon contaminated soil, comprising the following steps:

[0070] S1. Add surfactant 7 to the contaminated soil and mix evenly. The addition amount of surfactant 7 is 15 wt.%.

[0071] S2. Bury the gel water retention layer 1 and the carbon felt anode 2 after cutting and design into the contaminated soil. The depth of the carbon felt anode 2 buried in the contaminated soil is 30 cm, and the horizontal distance from the center of the root system of the plant 6 is 15 cm.

[0072] S3. Fix the air cathode counter electrode 4 at the bottom end of the box 8, with one side facing the contaminated soil and the other side directly exposed to the air.

[0073] S4. Connect the wire 3 to the carbon felt anode 2 and the air cathode counter electrode 4 with titanium wires respectively and then fix them.

[0074] S5. Plant the plants 6 evenly in the contaminated soil to be repaired. The planting density of the plants 6 is 8 plants per square meter.

[0075] S6. Connect the wire 3 to the power supply 5 to provide a continuous and stable weak electric field for the repair device.

[0076] Comparative Example 1

[0077] (1) Construction of the repair device in Comparative Example 1.

[0078] The rectangular box 8 providing a supporting role for the system is made of polymethyl methacrylate (plexiglass), with specific dimensions of 60 cm (length) × 50 cm (width) × 40 cm (height); in the present invention, the test soil is taken from an actual contaminated site. The test contaminated soil is pretreated (screened, ground, and sieved (10 mesh)) and mixed evenly with the biosurfactant at a ratio of 10 wt.% and then placed in the box 8; the carbon felt anode 2 is cut; the cut carbon felt anode 2 and the air cathode counter electrode 4 are pretreated. First, they are sealed and soaked in acetone for 12 h, and then ultrasonically cleaned with ethanol and water in turn, with each ultrasonic time being 30 min; the cut carbon felt anode 2 and the air cathode counter electrode 4 are connected to the wire 3 with titanium wires and then fixed; the gel water retention layer 1 for wrapping the anode is polyacrylamide hydrogel and is evenly mixed with the test contaminated soil at a ratio of 1:2; the cut carbon felt anode 2 and the polyacrylamide hydrogel water retention layer 1 are buried into the test contaminated soil in sequence as Figure 1 shown. The thickness of the gel water retention layer 1 is 2 cm, the depth buried in the soil is 15 cm, and the horizontal distance from the center of the root system of the plant 6 is 10 cm; the air cathode counter electrode 44 is fixed at the bottom end of the device, with one side facing the petroleum hydrocarbon contaminated soil and the other side directly exposed to the air. This treatment group is marked as Control.

[0079] (2) Operation of the repair device in Comparative Example 1.

[0080] Place the constructed soil remediation device in an artificial greenhouse, where the greenhouse temperature is maintained at 22 - 24 °C, the humidity is maintained at 45 - 50% RH, and the light condition is ensured to be 12 h / day; the soil in the device initially operates under saturated conditions, and an appropriate amount of water is added to the soil regularly to maintain the normal growth of plant 6; after the remediation device operates for 40 days, soil samples at 10, 15, and 20 cm below the carbon felt anode 2 wrapped with the gel water retention layer 1 are collected for testing, as well as pore water at 15 cm for testing.

[0081] (3) Testing of the remediation device in Comparative Example 1.

[0082] After the device operates for 40 days, the total petroleum hydrocarbon content (TPHs) in the soil at different positions in the device is measured. The measurement method is the gravimetric method. Specifically: First, the petroleum hydrocarbon - contaminated soil sample is freeze - dried at 48 h, - 60 °C, and 50 - 100 Pa, then ground and passed through a 60 - mesh sieve; 2 g is weighed and placed in a 50 - mL Erlenmeyer flask, and an appropriate amount of dichloromethane is added and repeatedly ultrasonically extracted, then poured into a pre - weighed 50 - mL Erlenmeyer flask, and continued to be evaporated in a water bath at 42 °C until constant weight. Weigh the Erlenmeyer flask, and then calculate the difference in the mass of the Erlenmeyer flask before and after evaporation, which is the total petroleum hydrocarbon content in the sample. A soil pore water collector with a membrane pore size of 0.60 μm is used to collect the pore water in the soil (about 10 ml), and then the content of soluble organic carbon in the collected pore water sample is tested with a total organic carbon analyzer.

[0083] Comparative Example 2

[0084] (1) Construction of the remediation device in Comparative Example 2.

[0085] The rectangular box 8 providing support for the system is made of polymethyl methacrylate (plexiglass), with specific dimensions of 60 cm (length) × 50 cm (width) × 40 cm (height); in the present invention, the test soil is taken from an actual contaminated site. After the test soil is pretreated (screened, ground, and passed through a sieve (10 - mesh)), it is mixed evenly with the biosurfactant 7 at 10 wt.%, and then placed in the box 8; Mirabilis jalapa is selected as the plant 6 providing the hydro - dynamic driving force, and the carbon felt anode 2 is cut according to the actual root diameter of Mirabilis jalapa so that its roots can pass through the carbon felt anode 2; the cut carbon felt anode 2 and the air cathode counter - electrode 4 are pretreated. First, they are sealed and soaked in acetone for 12 h, and then ultrasonically cleaned with ethanol and water in turn, with each ultrasonic time being 30 min; the cut carbon felt anode 2 and the air cathode counter - electrode 4 are connected to the wire 3 with titanium wire and fixed; the gel water retention layer 1 for wrapping the anode is a polyacrylamide hydrogel, which is evenly mixed with the test contaminated soil at a ratio of 1:2; the cut carbon felt anode 2 and the polyacrylamide hydrogel water retention layer 1 are arranged according to Figure 1The gel water retention layer 1 with a thickness of 2 cm is buried in the polluted soil as shown, and the depth of burial in the soil is 15 cm, and the horizontal distance from the center of the root system of the plant 6 is 10 cm; the air cathode counter electrode 4 is fixed at the bottom of the device, with one side facing the petroleum hydrocarbon polluted soil and the other side directly exposed to the air; the plant 6 Mirabilis jalapa, which provides the hydrological driving force for the device, is evenly planted in the petroleum hydrocarbon polluted soil to be repaired, and the planting density of the plant 6 that provides the hydrological driving force for the device is 6 plants per square meter; this treatment group is labeled as MES-C.

[0086] (2) Operation of the remediation device in Comparative Example 2.

[0087] Place the constructed soil remediation device in an artificial greenhouse, maintain the greenhouse temperature at 22 - 24 °C, the humidity at 45 - 50% RH, and ensure 12 h / day of light conditions; the soil in the device initially operates under saturated conditions, and an appropriate amount of water is added to the soil regularly to maintain the normal growth of the plant 6; after the remediation device operates for 40 days, collect soil samples at 10, 15, and 20 cm below the carbon felt anode 22 wrapped with the gel water retention layer 11 for testing and pore water at 15 cm for testing.

[0088] (3) Testing of the remediation device in Comparative Example 2.

[0089] After the device operates for 40 days, determine the total petroleum hydrocarbon content (TPHs) in the soil at different positions in the device. The measurement method uses the gravimetric method. Specifically: First, freeze-dry the petroleum hydrocarbon polluted soil sample taken at -60 °C and 50 - 100 Pa for 48 h, then grind it through a 60-mesh sieve; weigh 2 g and put it into a 50 mL Erlenmeyer flask, add an appropriate amount of dichloromethane, extract it by ultrasonic repeatedly, and then pour it into a pre-weighed 50 mL Erlenmeyer flask. Continue to evaporate it in a water bath at 42 °C until constant weight, weigh the weight of the Erlenmeyer flask, and then calculate the difference in the mass of the Erlenmeyer flask before and after evaporation as the total petroleum hydrocarbon content in the sample. Use a soil pore water collector with a membrane pore size of 0.60 μm to collect the pore water (about 10 ml) in the soil, and then use a total organic carbon analyzer to test the content of soluble organic carbon in the collected pore water sample.

[0090] Comparative Example 3

[0091] (1) Construction of the remediation device in Comparative Example 3.

[0092] The rectangular box 8 that provides support for the system is made of polymethyl methacrylate (plexiglass), with specific dimensions of 60 cm (length) × 50 cm (width) × 40 cm (height); in the present invention, the tested soil is taken from an actual contaminated site. After pretreatment (screening, grinding, sieving (10 mesh)), the tested soil is mixed evenly with the biosurfactant 7 at a ratio of 10 wt.%, and then placed in the box 8; the carbon felt anode 2 is cut; the cut carbon felt anode 2 and the air cathode counter electrode 4 are pretreated. First, they are sealed and soaked in acetone for 12 h, and then ultrasonically cleaned with ethanol and water in sequence, with each ultrasonic time being 30 min; the cut carbon felt anode 2 and the air cathode counter electrode 4 are connected to the wire 3 with titanium wire and then fixed; the gel water retention layer 1 for wrapping the anode is a polyacrylamide hydrogel and is evenly mixed with the tested contaminated soil at a ratio of 1:2; the cut carbon felt anode 2 and the polyacrylamide hydrogel water retention layer 1 are buried in the tested contaminated soil in sequence according to Figure 1 as shown. The thickness of the gel water retention layer 1 is 2 cm, and the depth of burial in the soil is 15 cm; the air cathode counter electrode 4 is fixed at the bottom of the device, with one side facing the petroleum hydrocarbon contaminated soil and the other side directly exposed to the air; the wire 3 for connecting the electrode and the power supply 5 is connected to the external power supply 5 that provides a stable weak electric field for the device to provide a continuous and stable weak electric field for the repair device. The power supply 5 that provides a stable weak electric field has a set voltage range of 0.7 V; this treatment group is labeled as P-C.

[0093] (2) Operation of the repair device in Comparative Example 3.

[0094] The constructed soil repair device is placed in an artificial greenhouse, where the greenhouse temperature is maintained at 22 - 24 °C, the humidity is maintained at 45 - 50% RH, and the light condition is ensured for 12 h / day; the soil in the device initially operates under saturated conditions, and an appropriate amount of water is added to the soil regularly to maintain the normal growth of the plant 6; after the repair device operates for 40 days, soil samples at 10, 15, and 20 cm below the carbon felt anode 2 wrapped with the gel water retention layer 1 are collected for testing, and the pore water at 15 cm is also tested.

[0095] (3) Testing of the repair device in Comparative Example 3.

[0096] After the device has been operating for 40 days, the total petroleum hydrocarbon content (TPHs) in the soil at different positions in the device is measured. The measurement method is the gravimetric method. Specifically: First, the petroleum hydrocarbon-contaminated soil sample is freeze-dried at -60 °C and 50 - 100 Pa for 48 h, and then ground through a 60-mesh sieve; 2 g is weighed and placed in a 50 mL Erlenmeyer flask, and an appropriate amount of dichloromethane is added and repeatedly ultrasonically extracted, then poured into a pre-weighed 50 mL Erlenmeyer flask, and the evaporation is continued in a water bath at 42 °C until constant weight. The weight of the Erlenmeyer flask is weighed, and then the difference in the mass of the Erlenmeyer flask before and after evaporation is calculated, which is the total petroleum hydrocarbon content in the sample. The pore water in the soil (about 10 ml) is collected using a soil pore water collector with a membrane pore size of 0.60 μm, and then the content of soluble organic carbon in the collected pore water sample is tested using a total organic carbon analyzer.

[0097] Comparative Example 4

[0098] (1) Construction of the remediation device for Comparative Example 4.

[0099] The rectangular box 8 that provides support for the system is made of polymethyl methacrylate (plexiglass), with specific dimensions of 60 cm (length) × 50 cm (width) × 40 cm (height); in the present invention, the test soil is taken from an actual contaminated site, and the test soil is placed in the box 8 after pretreatment (screening, grinding, sieving (10 mesh)); this treatment group is labeled as CK.

[0100] (2) Operation of the remediation device for Comparative Example 4.

[0101] The constructed soil remediation device is placed in an artificial greenhouse, the greenhouse temperature is maintained at 22 - 24 °C, the humidity is maintained at 45 - 50% RH, and the lighting conditions are ensured to be 12 h / day; the soil in the device initially operates under saturated conditions, and an appropriate amount of water is added to the soil regularly; after the remediation device has been operating for 40 days, soil samples and pore water at the same positions as in the examples are collected for testing.

[0102] (3) Testing of the remediation device for Comparative Example 4.

[0103] After the device has been running for 40 days, the total petroleum hydrocarbon content (TPHs) in the soil at different positions in the device is measured. The measurement method is the gravimetric method. Specifically: First, the petroleum hydrocarbon-contaminated soil sample is freeze-dried at -60°C and 50 - 100 Pa for 48 h, and then ground through a 60-mesh sieve; 2 g is weighed and placed in a 50 mL Erlenmeyer flask, and an appropriate amount of dichloromethane is added and ultrasonically extracted repeatedly, then poured into a pre-weighed 50 mL Erlenmeyer flask, and continued to be evaporated in a water bath at 42°C until constant weight. Weigh the Erlenmeyer flask, and then calculate the difference in the mass of the Erlenmeyer flask before and after evaporation, which is the total petroleum hydrocarbon content in the sample. The pore water in the soil (about 10 ml) is collected using a soil pore water collector with a membrane pore size of 0.60 μm, and then the content of soluble organic carbon in the collected pore water sample is measured using a total organic carbon analyzer.

[0104] Test Example 1

[0105] After the device in Example 1 and Comparative Examples 1 - 4 has been running for 40 days, soil samples at different positions (10, 15, and 20 cm) from the carbon felt anode 2 wrapped with the gel water retention layer 1 are sampled and tested for the total petroleum hydrocarbon content. The remaining total petroleum hydrocarbon content in the soil of each sample in Example 1 and Comparative Examples 1 - 4 is obtained (as Figure 2 shown). According to Figure 2 , after a 40-day repair cycle, the total petroleum hydrocarbon content at the same position in the repair devices of Example 1 (P-MES) and Comparative Examples 1 - 3 (P-C, MES-C, and Control) is the lowest for P-MES. This is because in P-MES, the stimulation of plants 6 and the weak electric field causes a large number of functional microorganisms (electricity-producing microorganisms 9, rhizosphere microorganisms 11, and indigenous degradable microorganisms 10) to accumulate near the roots, and because a large amount of organic matter is secreted and absorbed by the roots of plants 6, it provides sufficient energy substances for microbial activities. Similarly, the intervention of plants 6 provides a hydrogeological driving force for the migration of long-distance petroleum hydrocarbons, and the addition of the water retention layer also reduces the internal resistance of the soil. Therefore, through the interaction between highly active microorganisms and the absorption of some plant 6 roots, a large number of petroleum hydrocarbon compounds are removed. In the CK group of Comparative Example 4 (natural degradation), after 40 days of repair of the petroleum hydrocarbon pollution without any treatment, the remaining concentration of petroleum hydrocarbons at 15 cm is greater than that at the other two positions, which may be because the upper layer (10 cm) and the lower layer (20 cm) are in more intensive contact with air, and the oxygen content in the soil is higher than that in the middle layer.

[0106] Test Example 2

[0107] After running Example 1 and Comparative Examples 1-4 for 40 days, samples of the total petroleum hydrocarbon content in the soil pore water at a distance of 15 cm from the carbon felt anode 21 wrapped with the gel water retention layer 1 were sampled and tested to prove the migration and transformation of soluble organic matter in the soil pore water, and the dissolved organic carbon content in the soil of each sample of Example 1 and Comparative Examples 1-4 was obtained (as Figure 3 shown). According to Figure 3 , the soluble organic matter in the MES-C group that only planted plant 6 and the Control group that did not plant plant 6 but added the water retention layer and surfactant 7 decreased by 298 and 145 mg / L respectively compared with the CK group, which indicates that the addition of plant 6 and the water retention layer can promote the transfer of soluble organic matter in the soil pores. Compared with the water retention layer, the hydrogeological driving force provided by the life activities of plant 6 itself further drives the transfer of water and soluble organic matter in the soil. The lower content of soluble organic matter in the pore water of the P-C group than that of the Control group also proves the utilization of organic matter by the enrichment of functional microorganisms under weak electric field stimulation. The lowest soluble organic matter in the P-MES group successfully proves that weak electric field stimulation and the hydrogeological driving force of plant 6 can greatly promote the migration, transformation and degradation of petroleum hydrocarbons in contaminated soil.

[0108] Therefore, the present invention adopts the above-mentioned microbial remediation device and method for petroleum hydrocarbon-contaminated soil, which is low-carbon, safe, green and efficient. By combining microorganisms with an external electric field and a solid electrode, the problems of lack of electron acceptors and low utilization rate in the soil are solved. At the same time, the intervention of remediation plants increases the diversity of petroleum hydrocarbon pollutant removal pathways and improves the remediation distance. While meeting the requirements of green, low-consumption, high-efficiency and stability, it provides a new method for low-carbon remediation of petroleum hydrocarbon-contaminated soil.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A microbial remediation device for petroleum hydrocarbon contaminated soil, characterized in that: The invention comprises a box, a power source, a conductor and plants. An air cathode counter electrode is arranged at the bottom of the box, contaminated soil is filled above the air cathode counter electrode in the box, a surfactant and a carbon felt anode are arranged inside the contaminated soil, plants are planted in the contaminated soil, a gel water-retaining layer is coated on the outside of the carbon felt anode, the carbon felt anode is connected to the conductor with a titanium wire and then connected to a power source, the contaminated soil also comprises electricity-producing microorganisms, indigenous degradation microorganisms in the soil and rhizosphere microorganisms, and the voltage range provided by the power source is set to 0.5-1.0V.

2. The microbial remediation device for petroleum hydrocarbon contaminated soil according to claim 1 is characterized in that: The gel water-retaining layer is a mixture of polyacrylamide hydrogel and contaminated soil, the mass ratio of the polyacrylamide hydrogel to the contaminated soil is 1:1-1:3, and the thickness of the gel water-retaining layer is 1-3 cm.

3. The microbial remediation device for petroleum hydrocarbon contaminated soil according to claim 1 is characterized in that: The air cathode counter electrode is a carbon cloth air cathode, and the carbon felt anode and the air cathode counter electrode must be pretreated before use: first, the electrode material is cut to reserve holes so that the roots of the plant can pass through, and then the cut carbon felt or carbon cloth is sealed and soaked in acetone for 12-18 hours, and then ultrasonically cleaned with ethanol and water in turn, and the ultrasonic time each time is not less than 10 minutes.

4. The microbial remediation device for petroleum hydrocarbon contaminated soil according to claim 1 is characterized in that: The plants are one or more of Solanum nigrum, Mirabilis jalapa, Phragmites australis, Rhizoma Cyperi, and Iris.

5. The microbial remediation device for petroleum hydrocarbon contaminated soil according to claim 1 is characterized in that: The surfactant is one of a biosurfactant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant and a nonionic surfactant.

6. A microbial remediation method for petroleum hydrocarbon contaminated soil, characterized in that: The method is implemented by a repair device according to any one of claims 1 to 5, comprising the following steps: S1. Add the surfactant to the contaminated soil and mix well; S2, burying the gel water-retaining layer and the cut and designed carbon felt anode in the contaminated soil; S3. Fix the air cathode counter electrode at the bottom of the box, with one side facing the contaminated soil and the other side directly exposed to the air; S4, connecting the wires to the carbon felt anode and the air cathode electrodes with titanium wires and fixing them; S5. Planting the plants evenly in the contaminated soil to be remediated; S6. Connect the wire to the power source to provide a continuous and stable weak electric field for the repair device.

7. The microbial remediation method for petroleum hydrocarbon contaminated soil according to claim 6, characterized in that: In step S1, the amount of surfactant added is 5-15 wt.%.

8. The microbial remediation method for petroleum hydrocarbon contaminated soil according to claim 6, characterized in that: In step S2, the carbon felt anode is buried in the contaminated soil to a depth of 10-30 cm and a horizontal distance from the center of the plant root system of 5-15 cm.

9. The microbial remediation method for petroleum hydrocarbon contaminated soil according to claim 6, characterized in that: In step S5, the planting density of plants is 4-8 plants / square meter.

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