Remediation methods for petroleum hydrocarbon-contaminated soil

Abstract

This invention provides a method for remediating petroleum hydrocarbon-contaminated soil, comprising the following steps: (1) pretreating the petroleum hydrocarbon-contaminated soil; (2) separating the pretreated petroleum hydrocarbon-contaminated soil into high-concentration contaminated soil and low-concentration contaminated soil; (3) adding a first treatment agent to the high-concentration contaminated soil, mixing and separating to obtain slurry, the first treatment agent comprising sodium alkyl sulfonate, quicklime and water; (4) mixing the slurry and low-concentration contaminated soil, adding a second treatment agent, mixing, spreading and planting alfalfa seeds and maintaining regularly, the second treatment agent comprising petroleum hydrocarbon-degrading bacteria, enzyme preparations, nutrients and bulking agents. This remediation method is simple and effective, the remediation process is environmentally friendly, and the remediated soil can be reused.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and more particularly to a soil remediation method, and even more particularly to a method for remediating petroleum hydrocarbon-contaminated soil. Background Technology

[0002] Because petroleum is highly hydrophobic and has a strong viscosity, it tends to stick to the soil when it comes into contact with it during the oil extraction process. This not only reduces the soil's aeration and water permeability, but also causes soil pollution when the substances in the petroleum exceed a certain content. These pollutants are usually petroleum hydrocarbons.

[0003] When petroleum hydrocarbons enter the soil, they first impact and harm the soil environment, such as reducing soil permeability and negatively affecting soil microbial diversity and plant growth. Secondly, petroleum hydrocarbons, absorbed by plants, remain in various parts of crops, affecting crop quality. Thirdly, components of petroleum hydrocarbons that are not easily adsorbed by the soil can seep into the ground with precipitation, polluting shallow groundwater and thus affecting groundwater quality. Petroleum hydrocarbons in contaminated soil can enter the human or animal body through respiration, skin contact, and ingestion. Substances such as benzene, toluene, and phenols in petroleum hydrocarbons, if exposed to high concentrations over a prolonged period, can cause symptoms such as nausea, headache, and dizziness. Polycyclic aromatic hydrocarbons (PAHs) in petroleum hydrocarbons can affect the normal function of organs such as the liver and kidneys, and may even cause cancer. Therefore, petroleum hydrocarbon contamination of soil poses a potentially serious threat to the ecological environment, food safety, and human health, requiring close attention.

[0004] Given the unique location of oil well sites, green and sustainable remediation methods are needed for soil contaminated during oil extraction. Currently used methods such as gas-phase extraction, extraction elution, and thermal desorption suffer from drawbacks including high energy consumption, large equipment requirements, and complex operation and maintenance. Chemical oxidation technology is prone to secondary pollution and hinders subsequent land reclamation and revegetation. Furthermore, the effectiveness of biomass remediation technology is significantly affected by the initial concentration of pollutants in the soil.

[0005] Therefore, there is an urgent need for a robust approach to address the remediation of petroleum hydrocarbon-contaminated soils. Summary of the Invention

[0006] The purpose of this invention is to provide a method for remediating petroleum hydrocarbon-contaminated soil. This remediation method is simple and effective, the remediation process is environmentally friendly, and the remediated soil can be reused.

[0007] To achieve the above objectives, the present invention provides a method for remediating petroleum hydrocarbon-contaminated soil, comprising the following steps:

[0008] (1) Pre-treat the soil contaminated with petroleum hydrocarbons;

[0009] (2) The pretreated petroleum hydrocarbon contaminated soil is divided into high-concentration contaminated soil and low-concentration contaminated soil, wherein the petroleum hydrocarbon content of the high-concentration contaminated soil is above 5000 mg / kg and the petroleum hydrocarbon content of the low-concentration contaminated soil is less than 5000 mg / kg.

[0010] (3) Add a first treatment agent to the high-concentration contaminated soil, mix and separate to obtain mud, wherein the first treatment agent includes sodium alkyl sulfonate, quicklime and water;

[0011] (4) Mix the mud and the low-concentration contaminated soil, add the second treatment agent, mix, spread and plant alfalfa seeds and maintain regularly. The second treatment agent includes petroleum hydrocarbon degrading bacteria, enzyme preparations, nutrients and bulking agents.

[0012] The technical solution adopted in this invention has at least the following technical effects.

[0013] (1) Due to the high hydrophobicity and strong viscosity of petroleum hydrocarbons, soils contaminated by them exhibit significant heterogeneity and are prone to compaction. Therefore, pretreatment of petroleum hydrocarbon-contaminated soil by crushing and screening can remove oil-coated soil particles that are bound to petroleum. On the one hand, this can remove difficult-to-treat petroleum pollution sources and reduce the concentration of pollutants in the soil. On the other hand, it can make the distribution of pollutants in the soil more uniform and reduce the volume of petroleum hydrocarbon-contaminated soil to be treated.

[0014] (2) Since high concentrations of petroleum hydrocarbon pollutants threaten the survival of microorganisms and plants, the pretreated petroleum hydrocarbon contaminated soil is divided into high-concentration contaminated soil and low-concentration contaminated soil. A first treatment agent including sodium alkyl sulfonate, quicklime and water is added to the high-concentration contaminated soil. The petroleum hydrocarbon contaminated soil is classified and treated according to the pollutant concentration, which helps to reduce the amount of first treatment agent used, save costs, reduce the concentration of pollutants in the soil, and improve the survival rate of microorganisms and plants.

[0015] (3) The first treatment agent includes sodium alkyl sulfonate, quicklime, and water. Sodium alkyl sulfonate has good surfactant and solubilizing effects, transferring petroleum hydrocarbon pollutants from the soil to the liquid phase. Quicklime generates a large amount of heat upon contact with water, accelerating the volatilization of some low-boiling-point pollutants in the petroleum hydrocarbons. Additionally, calcium is an important signal transduction substance in plants, participating in the transmission of drought signals. The Ca in the first treatment agent... 2+This method can improve the water absorption capacity of alfalfa seeds, promote radicle growth, and enhance the drought resistance of alfalfa. Therefore, even under drought conditions, the remediation method of this invention can achieve good remediation effects on petroleum hydrocarbon-contaminated soil. By treating highly contaminated soil with the first treatment agent, the petroleum hydrocarbon content in the highly contaminated soil can be reduced, thereby improving the feasibility of achieving remediation standards for highly contaminated soil. Furthermore, the resulting filtrate can be reused after treatment, saving resources.

[0016] (4) The second treatment agent includes petroleum hydrocarbon-degrading bacteria, enzyme preparations, nutrients, and a leavening agent. Enzyme preparations assist petroleum hydrocarbon-degrading bacteria in degrading pollutants and provide a carbon source for plant growth. Nutrients provide alfalfa with nitrogen, phosphorus, and potassium nutrients; root exudates during alfalfa growth co-metabolize with petroleum hydrocarbon-degrading bacteria to mineralize and degrade petroleum hydrocarbon pollutants. The leavening agent improves the permeability and water retention of contaminated soil, creating a favorable growth environment for petroleum hydrocarbon-degrading bacteria and alfalfa. Through the synergistic effect of petroleum hydrocarbon-degrading bacteria, enzyme preparations, and alfalfa, the degradation of petroleum hydrocarbons can be enhanced, thereby reducing the amount of petroleum hydrocarbons in the soil and thus remediating the soil.

[0017] (5) The first treatment agent is used first, followed by the second treatment agent. The sodium alkyl sulfonate in the first treatment agent, in addition to its excellent surfactant and solubilizing effects, also possesses permeability and wettability, making the pollutants more homogeneous in the soil. This improves soil structure, enhances soil water and fertilizer retention capacity, increases the absorption and utilization rate of nutrients by alfalfa, and promotes alfalfa growth. Furthermore, it strengthens the co-metabolism between alfalfa root exudates and petroleum hydrocarbon-degrading bacteria, mineralizing and degrading petroleum hydrocarbon pollutants. This also facilitates the subsequent absorption and utilization of pollutants by petroleum hydrocarbon-degrading bacteria and alfalfa, improving remediation efficiency.

[0018] Preferably, the pretreatment includes crushing and screening the petroleum hydrocarbon-contaminated soil and removing oil-bearing soil particles from the soil.

[0019] Preferably, when the first treatment agent treats the highly polluted soil, the sodium alkyl sulfonate is first added to the highly polluted soil, then water is added and stirred for 1.5 to 4.0 hours, and quicklime is added every 0.5 hours.

[0020] Preferably, the sodium alkyl sulfonate accounts for 3-7 wt.% of the highly polluted soil, the water accounts for 90-110 wt.% of the highly polluted soil, and the amount of quicklime added each time is 0.1-2.0 wt.% of the highly polluted soil.

[0021] Preferably, the mud and the low-concentration contaminated soil are mixed and then dried until the moisture content is below 40 wt.% before the second treatment agent is added and mixed.

[0022] Preferably, the second treatment agent comprises 0.001 to 0.002 wt.% petroleum hydrocarbon degrading bacteria, 0.003 to 0.006 wt.% enzyme preparation, 0.4 to 0.8 wt.% nutrient agent and 1.5 to 3.5 wt.% leavening agent.

[0023] Preferably, the leavening agent includes soybean meal, crushed green waste, or straw.

[0024] Preferably, the thickness of the mixture of mud and low-concentration contaminated soil after spreading is 30-50 cm.

[0025] Preferably, the planting amount of alfalfa seeds is 0.5–3.0 g / m². 2 .

[0026] Preferably, the alfalfa seeds are regularly watered and sprayed with plant nutrient solution for maintenance, and the alfalfa can be harvested once every 3 to 4 months, for a total of 3 to 4 harvests. Detailed Implementation

[0027] The method for remediating petroleum hydrocarbon-contaminated soil of the present invention classifies petroleum hydrocarbon-contaminated soil into different grades according to the different contents of petroleum hydrocarbons, and pre-treats high-concentration contaminated soil to reduce its petroleum hydrocarbon content, and then performs degradation treatment together with low-concentration contaminated soil to carry out soil remediation. The specific remediation process may include the following steps (1) to (4).

[0028] (1) Pre-treat the soil contaminated with petroleum hydrocarbons.

[0029] (2) The pretreated petroleum hydrocarbon contaminated soil was divided into high-concentration contaminated soil and low-concentration contaminated soil. The petroleum hydrocarbon content of the high-concentration contaminated soil was more than 5000 mg / kg, and the petroleum hydrocarbon content of the low-concentration contaminated soil was less than 5000 mg / kg.

[0030] (3) Add the first treatment agent to the high-concentration contaminated soil, mix and separate to obtain mud. The first treatment agent includes sodium alkyl sulfonate, quicklime and water.

[0031] (4) Mix mud and low-concentration contaminated soil, add the second treatment agent, spread it out and plant alfalfa seeds and maintain it regularly. The second treatment agent includes petroleum hydrocarbon degrading bacteria, enzyme preparations, nutrients and bulking agents.

[0032] The pretreatment process includes crushing and screening the petroleum hydrocarbon-contaminated soil, and removing oil-coated soil particles. These oil-coated particles can be sent to an oil sludge treatment plant for resource utilization. When treating high-concentration contaminated soil with the first treatment agent, sodium alkyl sulfonate is added first, followed by water and stirring for 1.5–4.0 hours, with quicklime added every 0.5 hours. After stirring, the mixture is allowed to stand for 20–50 minutes, then separated. The supernatant is input into the wastewater treatment system, and after treatment to meet standards, it can be used or discharged. The resulting sludge is then mixed with low-concentration contaminated soil. After mixing, the sludge and low-concentration contaminated soil are first dried until the moisture content is below 40 wt.% before adding the second treatment agent. Drying before treatment reduces the treatment volume.

[0033] Sodium alkyl sulfonate constitutes 3–7 wt.% of the highly contaminated soil, water constitutes 90–110 wt.% of the highly contaminated soil, and quicklime is added in amounts of 0.1–2.0 wt.% of the highly contaminated soil each time. As examples, the content of sodium alkyl sulfonate may be, but is not limited to, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, and 7 wt.%. The content of water may be, but is not limited to, 90 wt.%, 92 wt.%, 94 wt.%, 96 wt.%, 98 wt.%, 100 wt.%, 102 wt.%, 104 wt.%, 106 wt.%, 108 wt.%, and 110 wt.%. The content of quicklime may be, but is not limited to, 0.1 wt.%, 0.3 wt.%, 0.5 wt.%, 0.7 wt.%, 0.9 wt.%, 1.0 wt.%, 1.2 wt.%, 1.4 wt.%, 1.6 wt.%, 1.8 wt.%, 1.1 wt.%, 1.3 wt.%, 1.5 wt.%, 1.7 wt.%, 1.9 wt.%, and 2.0 wt.%.

[0034] The second treatment agent comprises 0.001–0.002 wt.% petroleum hydrocarbon-degrading bacteria, 0.003–0.006 wt.% enzyme preparation, 0.4–0.8 wt.% nutrient agent, and 1.5–3.5 wt.% leavening agent. The content of petroleum hydrocarbon-degrading bacteria may be, but is not limited to, 0.0010 wt.%, 0.0011 wt.%, 0.0012 wt.%, 0.0013 wt.%, 0.0014 wt.%, 0.0015 wt.%, 0.0016 wt.%, 0.0017 wt.%, 0.0018 wt.%, 0.0019 wt.%, and 0.0020 wt.%. The content of enzyme preparation may be, but is not limited to, 0.003 wt.%, 0.004 wt.%, 0.005 wt.%, and 0.006 wt.%. The content of nutrients may be, but is not limited to, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, and 0.8 wt.%. The content of leavening agents may be, but is not limited to, 1.5 wt.%, 1.8 wt.%, 2.0 wt.%, 2.2 wt.%, 2.5 wt.%, 2.8 wt.%, 3.0 wt.%, 3.2 wt.%, and 3.5 wt.%. Nutrients may be compound nitrogen, phosphorus, and potassium fertilizers, and leavening agents may include soybean meal, crushed green waste, or straw.

[0035] The mixture of mud and low-concentration contaminated soil, after being spread, should be 30–50 cm thick. The thickness can be, but is not limited to, 30cm, 32cm, 34cm, 36cm, 38cm, 40cm, 42cm, 44cm, 46cm, 48cm, and 50cm. The planting rate of alfalfa seeds is 0.5–3.0 g / m². 2 As an example, the planting amount can be, but is not limited to, 0.5 g / m². 2 0.7g / m 2 0.9g / m 2 1.0g / m 2 1.2g / m 2 1.4g / m 2 1.6g / m 2 1.8g / m 2 2.0g / m 2 2.2g / m 2 2.4g / m 2 2.6g / m 2 2.8g / m 2 3.0g / m 2 Alfalfa seeds should be watered and sprayed with plant nutrient solution regularly. Alfalfa can be harvested every 3 to 4 months, for a total of 3 to 4 harvests.

[0036] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0037] Example 1

[0038] The remediation method of this invention was used to remediate contaminated soil at an abandoned well site in Northwest China, which may include the following steps.

[0039] (1) Excavators were used to excavate the petroleum hydrocarbon contaminated area in sections and layers. The soil was initially crushed and screened to remove oil-coated soil particles. The oil-coated soil particles were collected and sent to the oil sludge treatment plant for resource utilization. The screened contaminated soil was kept for later use.

[0040] (2) The soil after pretreatment was tested for petroleum hydrocarbon content. Soil with a content of more than 5000 mg / kg was considered high-concentration polluted soil, and soil with a content of less than 5000 mg / kg was considered low-concentration polluted soil.

[0041] (3) Add 5 wt.% sodium alkyl sulfonate to the highly contaminated soil, and add clean water at a soil-to-water mass ratio of 1:1. Stir rapidly and shake for 2 hours. Add 1% quicklime to the mud solution every 0.5 hours. After shaking, let the mud solution stand for 30 minutes, separate it, and send the supernatant into the wastewater treatment system. The treated wastewater can be reused, and the sediment at the bottom is reserved for later use.

[0042] (4) After mixing the mud and low-concentration contaminated soil, allow it to dry slightly to control the soil moisture content to around 40%. Then, add 0.0015 wt.% petroleum hydrocarbon degrading bacteria and 0.005 wt.% petroleum hydrocarbon degrading bacteria to the mixed contaminated soil. 3 An enzyme preparation, 0.7 wt.% nutrient agent, 2.0 wt.% soybean meal, and crushed green waste in equal mass ratios were mixed evenly and then spread evenly. An impermeable membrane was laid under the spread area, and the thickness of the spread layer of contaminated soil was 30 cm. At the same time, a layer of alfalfa seeds was sown on the soil surface at a rate of 1.5 g / m². 2 Regularly water and spray plant nutrient solution to maintain the soil. Harvest the plants every 3 months. After 3 harvests, the petroleum hydrocarbon content in the soil can reach the remediation target value of 500mg / kg.

[0043] 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 the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for remediating petroleum hydrocarbon-contaminated soil, characterized in that, Including the following steps: (1) Pre-treat the soil contaminated with petroleum hydrocarbons; (2) The pretreated petroleum hydrocarbon contaminated soil is divided into high-concentration contaminated soil and low-concentration contaminated soil, wherein the petroleum hydrocarbon content of the high-concentration contaminated soil is above 5000 mg / kg and the petroleum hydrocarbon content of the low-concentration contaminated soil is less than 5000 mg / kg. (3) A first treatment agent is added to the highly polluted soil and mixed to obtain a slurry. The first treatment agent includes sodium alkyl sulfonate, quicklime and water. When the first treatment agent treats the highly polluted soil, the sodium alkyl sulfonate is added to the highly polluted soil first, then water is added and stirred for 1.5 to 4.0 hours, and quicklime is added every 0.5 hours. The sodium alkyl sulfonate accounts for 3 to 7 wt.% of the highly polluted soil, the water accounts for 90 to 110 wt.% of the highly polluted soil, and the amount of quicklime added each time is 0.1 to 2.0 wt.% of the highly polluted soil. (4) Mix the mud and the low-concentration contaminated soil, add the second treatment agent, mix, spread and plant alfalfa seeds and maintain regularly. The second treatment agent includes petroleum hydrocarbon degrading bacteria, enzyme preparations, nutrients and bulking agents.

2. The method for remediating petroleum hydrocarbon-contaminated soil according to claim 1, characterized in that, The pretreatment includes crushing and screening the petroleum hydrocarbon-contaminated soil, and removing oil-bearing soil particles from the soil.

3. The method for remediating petroleum hydrocarbon-contaminated soil according to claim 1, characterized in that, The mud and the low-concentration contaminated soil are mixed and then dried until the moisture content is below 40 wt.% before the second treatment agent is added and mixed.

4. The method for remediating petroleum hydrocarbon-contaminated soil according to claim 1, characterized in that, The second treatment agent comprises 0.001–0.002 wt.% petroleum hydrocarbon degrading bacteria, 0.003–0.006 wt.% enzyme preparation, 0.4–0.8 wt.% nutrient agent, and 1.5–3.5 wt.% leavening agent.

5. The method for remediating petroleum hydrocarbon-contaminated soil according to claim 1, characterized in that, The leavening agent includes soybean meal, crushed green waste, or straw.

6. The method for remediating petroleum hydrocarbon-contaminated soil according to claim 1, characterized in that, The thickness of the mixture of mud and low-concentration contaminated soil, after being spread, is 30-50 cm.

7. The method for remediating petroleum hydrocarbon-contaminated soil according to claim 1, characterized in that, The planting rate of alfalfa seeds is 0.5–3.0 g / m². 2 .

8. The method for remediating petroleum hydrocarbon-contaminated soil according to claim 1, characterized in that, The alfalfa seeds are regularly watered and sprayed with plant nutrient solution for maintenance. The alfalfa can be harvested every 3 to 4 months, for a total of 3 to 4 harvests.