Method for removing petroleum pollutants in soil in situ by applying ozone in cooperation with microorganisms

Abstract

The invention discloses a method for removing petroleum pollutants in soil in situ by using ozone in cooperation with microorganisms. According to the method, ozone gas with a certain concentration and air are intermittently and circularly injected into the soil containing the crude oil pollutants in situ for a specific duration, and biodegradation of the pollutants is achieved. According to the invention, ozone is injected to decompose organic pollutants which are difficult to degrade in petroleum into short-chain organic matters by utilizing relatively strong oxidability and penetrability of ozone, so that the bioavailability of the pollutants is improved; air injection creates a good aerobic environment in the soil, and promotes microorganisms to decompose refractory pollutants in the soil, so that in-situ harmless treatment of the polluted soil is realized.

Description

Technical Field

[0001] The invention belongs to the field of soil pollution control and relates to a method for removing petroleum pollutants in soil in situ by using ozone in collaboration with microorganisms. Background Art

[0003] There are three main remediation technologies for crude oil pollutants in soil: physical remediation, chemical remediation, and biological remediation. Biological remediation has the characteristics of no secondary pollution and low cost, and has become one of the most widely used methods for studying and applying organic contaminated soil. However, single biological remediation has poor degradation effect on petroleum substances with complex structure and tightly adsorbed in soil organic matter, and is also affected by multiple factors such as ambient temperature, soil pH, and nutrients during the remediation process, so the remediation effect is unstable. Single chemical oxidation technology has good remediation effect and short remediation time, but the addition of high concentration of oxidants will damage the soil environment and easily cause secondary pollution. How to improve the performance of microbial remediation of contaminated soil without causing secondary pollution has become an urgent problem to be solved in this field.

[0004] One of the current hot topics in soil remediation technology research is to use different composite remediation technologies according to the different pollution characteristics and soil conditions of the contaminated site, such as chemical oxidation combined with microbial remediation technology, which can not only solve the problem that microorganisms are difficult to degrade petroleum hydrocarbons with complex structures and long chains, but also improve the degradation efficiency. It is a soil remediation technology with research potential and application prospects. Chen et al. (Chen, T., Yavuz, BM, et al. (2019). Multicycle ozonation + bioremediation for soils containing residual petroleum. Environmental Engineering Science, 36 (12), 1443-1451.) analyzed the mechanism of action of ozone and residual crude oil pollutants in soil in the laboratory and found that ozone, as a strong oxidant, can attack aged petroleum hydrocarbon residues and produce soluble organic matter, which explains the feasibility of ozone coordinated bioremediation technology in principle, but the study did not conduct experimental verification of this technical route. Chen et al. (Chen, T., Delgado, AG, Yavuz, et al. (2017). Interpreting interactions between nozone and residual petroleum hydrocarbons in oil. Environmental science & technology, 51 (1), 506-513.) used ex situ ozone aeration + tillage to degrade petroleum hydrocarbons in the soil in a laboratory test. This experiment further verified the bio-enhancement ability of ozone on petroleum pollutants, but in terms of treatment method, it belongs to ex situ remediation, which is usually more expensive. Summary of the invention

[0005] In view of the low efficiency of existing microbial remediation of petroleum-contaminated soil, the high cost of chemical oxidation remediation and the secondary pollution, the present invention uses a method of using ozone to cooperate with microorganisms to remove petroleum pollutants in soil in situ, thereby achieving efficient in-situ remediation of petroleum-contaminated soil by microorganisms without causing secondary pollution.

[0006] The technical solution of the present invention is as follows:

[0007] The method for removing petroleum pollutants in soil in situ by using ozone and microorganisms comprises the following steps:

[0008] (1) Detect the concentration of petroleum pollutants in the contaminated land and determine the depth and scope of the contaminated soil;

[0009] (2) installing gas pressure injection wells in the contaminated land to form an injection grid, wherein the coverage of the gas injection system grid includes the contaminated soil range determined in step (1), and ensuring that the depth of the gas distribution grid coincides with the depth of the contaminated soil;

[0010] (3) Using an air compressor to pressurize the compressed air storage tank, using an electronically controlled three-way valve to control the high-pressure air to pass through the air humidifier and the ozone generator, and then inject it into the contaminated soil through the gas pressure injection well;

[0011] (4) controlling the opening of multiple electrically controlled three-way valves in batches through an automatic control system to alternately inject ozone and air into multiple grille gas injection wells;

[0012] (5) During the remediation process, the concentration of petroleum pollutants in the contaminated soil is regularly tested to determine the time required for treatment. The moisture content of the contaminated soil is monitored using an online soil moisture sensor, and the soil moisture content is adjusted to 5% to 10% using an air humidifier.

[0013] Preferably, in step (3), the total mass of ozone injected at a single time does not exceed 2.5 mg-ozone / g-organic pollutant.

[0014] Preferably, in step (3), during the gas injection process, the linear flow rate of the gas in the soil does not exceed 1 m / min.

[0015] Preferably, in step (4), the ozone gas concentration in the single ozone injection gas is 10-50 mg / L.

[0016] Preferably, in step (4), a single grille gas injection well is used and the air injection time is 7-14 days.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention prefers ozone gas as an oxidant, which can spread better in the soil and fully contact with pollutants compared to other advanced oxidants;

[0019] (2) The present invention adopts an ozone oxidation synergistic microbial treatment process. The ozone oxidation decomposes the refractory organic pollutants into small organic molecules, which serve as nutrients and carbon sources for microorganisms, effectively improving the biological effectiveness of refractory pollutants and expanding the application scope of bioremediation technology.

[0020] (3) The present invention creates a good aerobic soil environment by alternating ozone gas and air. During the normal growth of microorganisms, the organic small molecule pollutants formed by ozone oxidation can be used as nutrients and carbon sources for microorganisms, thereby reducing the concentration of pollutants in the soil. The gas circulation injection method is used to achieve alternating chemical remediation and biological remediation, and ultimately achieve the harmlessness of contaminated soil.

[0021] (4) The present invention utilizes the cost advantage of biological soil remediation technology and effectively reduces the cost of chemical oxidation soil remediation technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the implementation device for using ozone and microorganisms to remove petroleum pollutants in soil in situ.

[0023] Figure 2 Schematic diagram of the device for step (1) in Example 1.

[0024] Figure 3 The removal effect of ozone oxidation on segmented TPH when the mass concentration of the pollutant in step (1) in Example 1 is 1% and the oxidation time is 0.25, 0.5, 1, and 2 hours.

[0025] Figure 4 The removal effect of ozone oxidation on segmented TPH when the pollutant mass concentration in step S1 in Example 1 is 3% and the oxidation time is 0.25, 0.5, 1, and 2 hours.

[0026] Figure 5 Schematic diagram of the device in Example 2.

[0027] Figure 6 This is a comparison of the effects of petroleum pollutants in Example 2 before and after treatment under different treatment conditions. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with specific embodiments and drawings.

[0029] The present invention uses ozone in conjunction with microorganisms to remove petroleum pollutants in the soil in situ. Some large-molecule difficult-to-degrade organic pollutants in the soil undergo oxidation reactions, and the molecular chains are broken and converted into small-molecule organic matter. During the air injection period, the soil oxygen content increases, and the soil microorganisms regain activity. At the same time, degradable organic pollutants are used as carbon sources to perform aerobic decomposition, thereby reducing the content of organic pollutants in the soil. After accurately determining the contaminated area, an in-situ gas injection device is installed to achieve alternating and intermittent injection of ozone gas and air in the contaminated area, thereby gradually achieving the harmlessness of the pollutants.

[0030] The auxiliary effect of ozone on microbial degradation is that ozone's strong oxidizing property directly attacks organic matter to break aromatic rings to produce carboxylic acids or aldehydes. In addition, metal oxides in the soil can catalyze and promote ozone decay to produce free radicals, which have stronger oxidizing ability than ozone itself. It can attack saturated ring-structured organic molecules and certain non-carbon components. Ozone and the hydroxyl radicals (OH·) produced by ozone can react with all types of hydrocarbons to produce hydrophilic compounds, which makes ozone oxidation a very attractive method for contaminated soil remediation. Since ozone can be restored to oxygen in a short time, it will not have a great impact on soil microorganisms, allowing microorganisms to degrade short-chain organic matter while maintaining their activity, thereby improving the efficiency of microbial degradation of petroleum-contaminated soil.

[0031] Figure 1 This is a schematic diagram of the implementation device of the present invention for using ozone to cooperate with microorganisms to remove petroleum pollutants in the soil in situ, and the specific steps are as follows:

[0032] (1) Detect the concentration of petroleum pollutants in the contaminated land and determine the depth and scope of the contaminated soil;

[0033] (2) Preferably, a gas pressure injection well (8) is installed to form an injection grid, and the coverage of the gas injection system grid should include the contaminated soil range determined in step (1), and ensure that the depth of the gas distribution grid coincides with the depth of the contaminated soil;

[0034] (3) using an air compressor (1) to pressurize a compressed air storage tank (2), and using an electrically controlled three-way valve (3) to control the high-pressure air to pass through an air humidifier (5) and an ozone generator (6) and be injected into the soil;

[0035] (4) By controlling the multiple electrically controlled three-way valves (3) to open in batches through the automatic control system (4), ozone and air can be alternately injected into the multiple grille gas injection wells (7);

[0036] (5) During the remediation process, the concentration of petroleum pollutants in the contaminated soil is regularly tested to determine the time required for treatment. The moisture content of the contaminated soil is monitored using an online soil moisture sensor (9), and the soil moisture content is adjusted to 5% to 10% using an air humidifier.

[0037] Example 1

[0038] This example verifies the propagation advantage of ozone in oil-contaminated soil and its decomposition effect on crude oil pollutants, and demonstrates a method for optimizing ozone gas injection conditions.

[0039] (1) Taking petroleum as the target pollutant, contaminated soils with different pollutant mass fractions and different soil moisture contents were prepared. The pollutant concentration conditions were 0.5%, 1%, 2%, 3%, 4%, and 5% (mass fraction), and the soil moisture content conditions were 0%, 1%, 3%, and 5% (mass fraction).

[0040] (2) The experimental soil was loaded into a quartz column with a diameter of 1 cm and a length of 15 cm, and then connected to a homemade ozone soil oxidation experimental device. The schematic diagram of the device is shown in the figure. Figure 2 As shown; the device is mainly assembled from a soil column part (6), an ozone generator (2), an ozone detector (8) and an exhaust gas treatment device (9).

[0041] (3) Close the front valve (10), adjust the three-way valve (11) so that the gas does not pass through the soil column (6), and adjust the ozone generator (2) to an ozone concentration of 30 mg / L; after stabilization, open the soil column valve (10), adjust the three-way valve (11) so that the gas passes through the soil column (6) at a linear speed of 1 m / min, start timing, and use an ozone concentration detector (8) to monitor the ozone concentration.

[0042] (4) After the required treatment time is reached, close the soil column valve and adjust the three-way valve so that the gas does not pass through the soil column. After the soil is mixed evenly, retain the sample for testing.

[0043] Figure 3 The ozone penetration curves under different pollutant concentrations and water contents are shown. It can be seen from the figure that ozone gas has a good soil penetration effect. Under the condition of a gas linear velocity of 1m / min, the ozone outlet concentration can reach the inlet concentration level within 15 minutes of the experiment.

[0044] Figure 4 The results show that the residual concentration (mg / kg) of total petroleum hydrocarbons (TPH) in petroleum contaminated soils with different water contents after ozone treatment for 15min, 30min, 60min and 120min, respectively, when the mass concentration of pollutants is 1%. A, B, C and D represent the treatment groups with water contents of 0%, 1%, 3% and 5% (wt). The results show that the most drastic time period for the residual concentration of different petroleum hydrocarbons under ozone oxidation is 0-15min regardless of the reaction conditions. The removal of total petroleum hydrocarbons in this time period accounts for 61.64%-72.78% of the total removal. According to mass balance, the total ozone consumption in this stage is about 2.5mg-ozone / g-crude oil pollutants.

[0045] The results also show that soil moisture content has an important influence on the efficiency of ozone reaction. Compared with the group without added soil moisture (A), the decomposition efficiency of total TPH is the highest at a moisture content of 3%, reaching 81.98%. This is because ozone reacts with water under the catalysis of soil organic matter, metal oxides, etc. to generate hydroxyl radicals (·OH) with stronger oxidizing properties. Hydroxyl radicals (·OH) will react rapidly and non-selectively with organic pollutants to decompose them. Therefore, adding an appropriate amount of water to the reaction can promote the degradation of petroleum hydrocarbons.

[0046] The change of residual concentration (mg / kg) of segmented TPH shows that ozone has a decomposition effect on various components of petroleum pollutants. Taking soil with a moisture content of 3% as an example, after 15 minutes of treatment, the decomposition effects in diesel segments DRO1 (C10-C16), DRO2 (C16-C22) and DRO3 (C22-C28) and lubricating oil segments ORO1 (C28-C34) and ORO2 (C34-C40) can reach 42.4%, 48.5%, 50.9%, 60.2% and 72.6%, respectively, showing a rule that the larger the molecular weight, the more obvious the removal effect, indicating that ozone can effectively decompose large molecular pollutants into small molecular substances.

[0047] Example 2

[0048] This example demonstrates the effect of ozone and microorganisms in treating petroleum pollutants in soil in the laboratory. Figure 5 The specific experimental steps are as follows:

[0049] (1) Conditioning the soil containing petroleum pollutants to a moisture content of 5%-10% and a pH of 6.5-7.5;

[0050] (2) Filling the experimental soil into the experimental soil column container (1), the container has a diameter of 5 cm and a length of 25 cm;

[0051] (3) Adjust the rotor flowmeter 1 (3) to an air flow rate of (30 mL / min);

[0052] (4) adjusting the ozone generator (5) to generate ozone gas with a concentration of about 50 mg / L and a flow rate of 0.5 L / min;

[0053] (5) Adjust the three-way valve (7) so that the ozone gas is humidified by the washing bottle (6) and then introduced into the experimental column for 15 minutes;

[0054] (6) After the above step (5) is completed, the three-way valve (7) is adjusted so that the air gas is humidified by the washing bottle (8) and then introduced into the experimental column for 6 days;

[0055] (7) After completing step (6), repeat step (5) for a total of 5 cycles;

[0056] (8) After the above step (7) is completed, the contaminated soil is taken out from the experimental column in three layers: upper, middle and lower layers, and the concentration of petroleum pollutants in the soil is tested.

[0057] Figure 6 The changes in the concentration of petroleum pollutants at different depths of soil columns before and after ozone-assisted biological treatment are shown. When only air is introduced, the degradation capacity of microorganisms is very limited. On the 15th and 33rd days of the experiment, the average pollutant removal efficiency of the soil column is only about 11%. In the ozone-assisted microbial treatment experiment, the removal efficiency of petroleum pollutants in the soil has been significantly improved compared to the conditions of air only. On the 15th and 33rd days of the experiment, the pollutant removal rates reached 45.1% and 56.7%, respectively. This verifies that ozone-assisted microbial remediation of petroleum pollutants in soil has technical advantages in principle.

Claims

1. A method for removing petroleum pollutants in soil in situ by using ozone and microorganisms, characterized in that: The following steps are involved: (1) Detect the concentration of petroleum pollutants in the contaminated land and determine the depth and scope of the contaminated soil; (2) Installing gas pressure injection wells in the contaminated land to form an injection grid. The coverage of the gas injection system grid includes the contaminated soil range determined in step (1), and ensure that the depth of the gas distribution grid coincides with the depth of the contaminated soil; (3) Use an air compressor to pressurize the compressed air storage tank, and use an electronically controlled three-way valve to control the high-pressure air to pass through the air humidifier and ozone generator, and then inject it into the contaminated soil through the gas pressure injection well; (4) Controlling the opening of multiple electrically controlled three-way valves in batches through an automatic control system to alternately inject ozone and air into multiple grille gas injection wells; (5) During the remediation process, the concentration of petroleum pollutants in the contaminated soil is regularly tested to determine the time required for treatment. The moisture content of the contaminated soil is monitored using an online soil moisture sensor, and the soil moisture content is adjusted to 5%~10% using an air humidifier.

2. The method according to claim 1, characterized in that In step (3), the total mass of ozone injected at a single time shall not exceed 2.5 mg-ozone / g-organic pollutant.

3. The method according to claim 1, characterized in that In step (3), during the gas injection process, the linear flow velocity of the gas in the soil does not exceed 1 m / min.

4. The method according to claim 1, characterized in that In step (4), ozone is injected into the gas once, and the concentration of ozone gas is 10-50 mg / L.

5. The method according to claim 1, characterized in that In step (4), a single grille gas injection well is used and the air injection time is 7-14 days.

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