Polluted soil treatment method

Abstract

The invention relates to the field of soil treatment, and discloses a treatment method of contaminated soil. The method comprises the following steps: (1) carrying out first mixing on polluted soil, water and an oxidizing agent; (2) drying the first mixed material obtained in the step (1) until the water content is 15-30wt%, and carrying out second mixing on a solid phase and organic matter degrading bacteria; (3) maintaining the material after the second mixing; optionally, the method further comprises the step (4) of conducting heat treatment on the materials treated in the step (3). According to the method, pollutants in the polluted soil can be fully removed under the condition that energy consumption is obviously low, secondary pollution is not prone to being generated, and practical application is better facilitated.

Description

Technical Field

[0001] The present invention relates to the field of soil treatment, and in particular to a method for treating contaminated soil. Background Art

[0002] Thermal desorption technology is frequently used in fields such as soil remediation. Thermal desorption is primarily categorized as in-situ and ex-situ. In-situ treatment involves treating contaminated soil in its original location through methods such as heating and chemical injection. Heating elevates the temperature of the contaminated area, altering the physicochemical properties of pollutants and promoting their desorption into the gas phase. Extraction of the gas phase removes pollutants from the underground environment, resulting in high energy consumption. Chemical coupling, however, is less effective and can easily lead to secondary contamination. In general, in-situ thermal desorption is limited to small treatment volumes and low pollutant vaporization temperatures. Ex-situ thermal desorption involves excavating the pollutants and, after pretreatment, incinerating them at high temperatures to remove harmful components from the contaminated soil. The resulting gases are then discharged through processes such as cyclone dust removal, secondary combustion, spray towers, quenching towers, and heat exchangers. The advantages of thermal desorption technology include a wide range of pollutants, high treatment rates, and large treatment volumes. However, despite these advantages, ex-situ thermal desorption still has room for improvement in treatment efficiency and energy consumption, as well as further improvements in energy consumption control to achieve energy conservation and carbon reduction. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a method for treating contaminated soil. The method can fully remove pollutants in contaminated soil with significantly lower energy consumption, is less likely to cause secondary pollution, and is more conducive to practical application.

[0004] In order to achieve the above object, the present invention provides a method for treating contaminated soil, the method comprising:

[0005] (1) first mixing the contaminated soil, water and oxidant;

[0006] The first mixing is performed so that the water content of the material after the first mixing is 45-65 wt % and the content of the oxidant is 4-12 wt %;

[0007] (2) The first mixed material obtained in step (1) is dried to a moisture content of 15-30 wt%, and the solid phase and the organic matter-degrading bacteria are mixed for a second time, so that the initial content of the organic matter-degrading bacteria in the second mixed material is not less than 0.5×10 5 cfu / g;

[0008] (3) maintaining the second mixed material;

[0009] Optionally, the method further comprises:

[0010] (4) The material treated in step (3) is subjected to heat treatment.

[0011] Through the above technical solution, the method can fully remove pollutants in contaminated soil with significantly lower energy consumption (for example, heat treatment only takes a relatively short time), with better treatment effect, less likely to cause secondary pollution, and more conducive to practical application. DETAILED DESCRIPTION

[0012] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0013] The present invention provides a method for treating contaminated soil, the method comprising:

[0014] (1) first mixing the contaminated soil, water and oxidant;

[0015] The first mixing is performed so that, in the first mixed material, the water content is 45-65 wt % (for example, 45, 48, 50, 52, 55, 58, 60, 62, 65, and any range formed by any two of the above values, and a value within the range) and the content of the oxidant is 4-12 wt % (for example, 4, 5, 6, 7, 8, 9, 10, 11, 12, and any range formed by any two of the above values, and a value within the range) wt %;

[0016] (2) The first mixed material obtained in step (1) is dried to a moisture content of 15-30 wt% (for example, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, and a range formed by any two of the above values ​​and a value within the range), and the solid phase and the organic matter-degrading bacteria are mixed for a second time, so that the initial content of the organic matter-degrading bacteria in the second mixed material is not less than 0.5×10 5 cfu / g;

[0017] (3) maintaining the second mixed material;

[0018] Optionally, the method further comprises:

[0019] (4) The material treated in step (3) is subjected to heat treatment.

[0020] The inventors of the present invention have discovered that if the contaminated soil is treated ex situ (rather than in situ) according to the above, the contaminants can be effectively removed in step (3). In the case of low contaminant content, step (4) can be omitted, thus avoiding the need for heat treatment. Even if step (4) is required, the heat treatment can be completed in a relatively short time, thus significantly reducing costs and being more suitable for practical applications. It is understandable that heat treatment requires a relatively high temperature, which results in higher treatment costs, especially when the amount of contaminated soil to be treated is large. Such costs can be quite high.

[0021] According to the present invention, preferably, the contaminated soil is soil contaminated by organic pollutants.

[0022] According to the present invention, preferably, the weight content of organic pollutants in the contaminated soil is 1-3 (for example, it can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 and the range formed by any two of the above values ​​and the value within the range) wt%.

[0023] The present invention does not particularly limit the specific types of organic pollutants. They may be petroleum hydrocarbons, polycyclic aromatic hydrocarbons, benzene series, etc.

[0024] According to the present invention, preferably, in the first mixing, the particle size of the contaminated soil is no greater than 8 cm. The contaminated soil can be crushed to meet the above conditions before mixing.

[0025] According to the present invention, preferably, the first mixing is performed so that, in the material after the first mixing, the water content is 50-60 (for example, it can be 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60 and the range formed by any two of the above values ​​and the value within the range) wt%, and the content of the oxidant is 5-10 (for example, it can be 5, 6, 7, 8, 9, 10 and the value within the range formed by any two of the above values) wt%.

[0026] According to the present invention, preferably, the first mixing is maintained for 6-8 hours. After the mixing is completed, the above time is maintained.

[0027] According to the present invention, preferably, the oxidant is selected from at least one of hydrogen peroxide, potassium permanganate and sodium persulfate.

[0028] Preferably, in step (2), the drying method includes: performing a third mixing of the first mixed material and the flocculant, separating a portion of the liquid phase, and performing a first drying. The third mixing can be performed in a screw stacker, and the liquid phase can be removed during the operation of the screw stacker. Generally, the water content of the solid phase after processing by the screw stacker is about 35-55 wt%.

[0029] Preferably, the mass ratio of the first mixed material to the flocculant is 100:(5-10).

[0030] Preferably, the flocculant is selected from at least one of an inorganic flocculant and an organic flocculant.

[0031] Preferably, the inorganic flocculant is selected from polyaluminium sulfate and / or polyferric sulfate, and the organic flocculant is selected from at least one of polyacrylamide, lignosulfonate and acrylic acid.

[0032] Among them, when adding flocculants, heavy metal capture agents can also be selectively added according to the conditions of the polluted soil, such as some hydroxides, sulfides, carbonates, etc. that can form precipitation. They can generally react with Cu in wastewater at room temperature and a wide pH value range. 2+ 、Hg 2+ Wait for various heavy metal ions to undergo chemical reactions to remove them.

[0033] Preferably, the drying method further comprises: mixing the material after the first drying with a desiccant for a fourth time, and then performing a second drying until the moisture content in the material is 15-30 wt %. The desiccant can generally be lime powder (to avoid the generation of other pollutants). The amount of desiccant used is such as to achieve the above moisture content.

[0034] According to the present invention, preferably, in step (2), the initial content of organic matter degrading bacteria in the second mixed material is 1×10 5 -1×10 7 cfu / g. Under the above content conditions, the treatment effect can be further guaranteed.

[0035] Among them, the present invention has no particular restrictions on the specific types of organic matter degrading bacteria, and can select suitable bacterial groups for treatment according to the specific types of pollutants in the contaminated soil. By adopting the scheme of the present invention, in combination with organic matter degrading bacteria, such a coupled microbial treatment method can obtain a better treatment effect on the contaminated soil, and there is no particular restriction on the type of microorganism itself. Generally, bacteria suitable for organic matter degradation can be applied to the scheme of the present invention. However, preferably, in step (2), at least one of the organic matter degrading bacteria Acinetobacter, Pseudomonas, Candida tropicalis, Bacillus cereus and Alcaligenes faecalis can be used. Among them, any one, any two, or any multiple of the above organic matter degrading bacteria can be used, and the present invention has no particular restrictions on this. As long as their total amount meets the above range, better treatment effect can be guaranteed.

[0036] Preferably, the method further comprises: removing materials with a particle size greater than 5 cm from the second mixed materials.

[0037] According to the present invention, preferably, the second mixing lasts for 2-4 minutes.

[0038] According to the present invention, preferably, the second mixing temperature is 25-35 (for example, it can be 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 and the range formed by any two of the above values ​​and the value within the range) °C.

[0039] According to the present invention, preferably, the second mixing is carried out in a drum screen. The screen of the drum screen can also simultaneously remove materials with a particle size greater than 5 cm.

[0040] According to the present invention, preferably, in step (3), the temperature maintained is 28-32 (for example, 28, 29, 30, 31, 32) °C.

[0041] According to the present invention, preferably, in step (3), the maintenance time is 1-2 days.

[0042] According to the present invention, preferably, in step (4), the heat treatment time is 3-5 min (for example, 3, 3.5, 4, 4.5, 5, and any range formed by any two of the above values, and any value within the range). Even if step (4) is required, the treatment can be completed in a shorter time, which can significantly reduce energy consumption.

[0043] According to the present invention, preferably, the temperature of the heat treatment is 100-700 (for example, it can be 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700 and the range formed by any two of the above values ​​and the values ​​within the range) °C.

[0044] Through the above method, pollutants in contaminated soil can be fully removed with significantly lower energy consumption.

[0045] The present invention will be described in detail below through examples.

[0046] In the following examples and comparative examples, unless otherwise specified, the standards after treatment are as follows: in accordance with the provisions of the "Guidelines for Establishing Target Values ​​for Soil Pollution Remediation of Construction Land" (Trial).

[0047] For contaminated soil, after purification, extraction, heating and separation, the content of organic pollutants in it is detected and analyzed by gas chromatography.

[0048] In addition, the qualified rate is detected in the following manner: randomly taking samples from different positions of the processed material, taking 100 positions as an example, if the samples corresponding to n positions are qualified, the qualified rate is 100%×(n / 100).

[0049] Example 1

[0050] The contaminated soil is soil contaminated by organic pollutants, wherein the weight content of the organic pollutants is 2 wt %, and the organic pollutants are specifically petroleum hydrocarbons.

[0051] (1) Take the contaminated soil, sieve it, and take the part with a particle size of no more than 8 cm. Mix it with water and potassium permanganate for a first time. The water content of the mixed material is 60 wt % and the content of the oxidant is 5 wt %. Maintain for 6 hours.

[0052] (2) The material and polyaluminum sulfate are mixed for a third time, in such an amount that the mass ratio of the material to the flocculant after the first mixing is 100:5. The material is first partially dehydrated in a spiral press and dried to a moisture content of 40 wt%. The material is then removed and mixed with lime powder to a moisture content of 30 wt% in the contaminated soil.

[0053] The soil treated as above was fed into a drum screen together with organic matter degrading bacteria (Acinetobacter, Pseudomonas, Candida tropicalis, Bacillus cereus and Alcaligenes faecalis) for a second mixing at 25°C for 3 min. The amount of organic matter degrading bacteria was such that the total initial content of organic matter degrading bacteria in the soil was 1×10 5 cfu / g, and mix thoroughly. During this process, the drum screen will screen out stones with a particle size greater than 5 cm.

[0054] (3) Maintain the material treated in step (2) at 30°C for 1.5 days.

[0055] (4) After the treatment in step (3), the content of organic pollutants was detected. If it was found that the content did not meet the post-treatment standard, the material was heat-treated at 600°C for 3 minutes.

[0056] After the heat treatment, the organic pollutant content in the soil was tested and it was found that the pollutant treatment pass rate was 96%.

[0057] Example 2

[0058] The contaminated soil is soil contaminated by organic pollutants, wherein the weight content of the organic pollutants is 1.5 wt %, and the organic pollutants are specifically petroleum hydrocarbons.

[0059] (1) Contaminated soil was screened and the portion with a particle size of no greater than 8 cm was taken for a first mixing with water and sodium persulfate. The first mixing had a water content of 58 wt% and an oxidant content of 7 wt%. The mixture was maintained for 7 hours.

[0060] (2) The material and polyaluminum sulfate are mixed for a third time, in such an amount that the mass ratio of the material to the flocculant after the first mixing is 100:6. The material is first partially dehydrated in a spiral press and dried to a moisture content of 38 wt%. The material is then removed and mixed with lime powder to a moisture content of 28 wt% in the contaminated soil.

[0061] The soil treated as above was fed into a drum screen together with organic matter degrading bacteria (Acinetobacter, Pseudomonas, Candida tropicalis, Bacillus cereus and Alcaligenes faecalis) for a second mixing at 30°C for 3 min. The amount of organic matter degrading bacteria was such that the initial total content of organic matter degrading bacteria in the soil was 1×10 6 cfu / g, and mix thoroughly. During this process, the drum screen will screen out stones with a particle size greater than 5 cm.

[0062] (3) Maintain the material treated in step (2) at 28°C for 1.2 days.

[0063] (4) After the treatment in step (3), the content of organic pollutants was detected and it was found that it still did not meet the post-treatment standard, so the material was heat-treated at 450°C for 3 minutes.

[0064] After the heat treatment, the organic pollutant content in the soil was tested and it was found that the pollutant treatment pass rate was 97%.

[0065] Example 3

[0066] The contaminated soil is soil contaminated by organic pollutants, wherein the weight content of the organic pollutants is 2.5 wt %, and the organic pollutants are specifically petroleum hydrocarbons.

[0067] (1) Take the contaminated soil, sieve it, and take the part with a particle size of no more than 8 cm. Mix it with water and potassium permanganate for a first time. The water content of the material after the first mixing is 52 wt % and the content of the oxidant is 5.5 wt %. Maintain it for 8 hours.

[0068] (2) The material and polyaluminum sulfate are mixed for a third time, with the amount being such that the mass ratio of the material to the flocculant after the first mixing is 100:8. The material is first partially dehydrated in a spiral press and dried to a moisture content of 42 wt%. The material is then removed and mixed with lime powder to achieve a moisture content of 25 wt% in the contaminated soil.

[0069] The soil treated as above was fed into a drum screen together with organic matter degrading bacteria (Acinetobacter, Pseudomonas, Candida tropicalis, Bacillus cereus and Alcaligenes faecalis) for a second mixing at 35°C for 3.5 min. The amount of organic matter degrading bacteria was such that the initial total content of organic matter degrading bacteria in the soil was 1×10 7 cfu / g, and mix thoroughly. During this process, the drum screen will screen out stones with a particle size greater than 5 cm.

[0070] (3) Maintain the material treated in step (2) at 32°C for 1.8 days.

[0071] (4) After the treatment in step (3), the content of organic pollutants was detected and it was found that it still did not meet the post-treatment standard. Therefore, the material was heat-treated at 300°C for 3.5 minutes.

[0072] After the heat treatment, the organic pollutant content in the soil was tested and it was found that the pollutant treatment pass rate was 97%.

[0073] Comparative Example 1

[0074] The same soil as in Example 1 was treated according to the method of Example 1, except that the amount of organic matter-degrading bacteria used was such that the content of organic matter-degrading bacteria in the second mixed material was 1×10 4 cfu / g.

[0075] After the treatment in step (3), it was found that the content of organic pollutants did not meet the standard. During the heat treatment, the target temperature was 650° C. and the qualified rate reached 96% after 4 minutes of treatment.

[0076] Comparative Example 2

[0077] The same soil as in Example 1 was treated according to the method of Example 1, except that the contaminated soil with a water content of 30 wt% obtained in step (2) was directly heat-treated at 700° C. A qualified rate of 96% was achieved after 4 minutes of heat treatment.

[0078] In actual industrial treatment, especially for large-scale soil treatment, every 50°C increase in heat treatment temperature or every 0.5 minute increase in heat treatment time results in significant industrial costs. The method provided by the present invention can effectively remove pollutants from contaminated soil while consuming significantly less energy.

[0079] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for treating contaminated soil, characterized in that: The method includes: (1) first mixing the contaminated soil, water and oxidant; The first mixing is performed so that the water content of the material after the first mixing is 45-65 wt % and the content of the oxidant is 4-12 wt %; (2) The first mixed material obtained in step (1) is dried to a moisture content of 15-30 wt%, and the solid phase and the organic matter-degrading bacteria are mixed for a second time, so that the initial content of the organic matter-degrading bacteria in the second mixed material is not less than 0.5×10 5 cfu / g; (3) maintaining the second mixed material; Optionally, the method further comprises: (4) The material treated in step (3) is subjected to heat treatment.

2. The method according to claim 1, wherein The contaminated soil is soil contaminated by organic pollutants; Preferably, the weight content of organic pollutants in the contaminated soil is 1-3 wt%.

3. The method according to claim 1, wherein In the first mixing, the particle size of the contaminated soil is no larger than 8 cm.

4. The method according to claim 1, wherein The first mixing is performed so that the water content of the material after the first mixing is 50-60 wt % and the content of the oxidant is 5-10 wt %; Preferably, the first mixing is maintained for 6-8 hours.

5. The method according to claim 1 or 4, wherein The oxidant is selected from at least one of hydrogen peroxide, potassium permanganate and sodium persulfate.

6. The method according to claim 1 or 2, wherein: In step (2), the drying method includes: performing a third mixing of the first mixed material and the flocculant, and separating a portion of the liquid phase; Preferably, the mass ratio of the first mixed material to the flocculant is 100:(5-10); Preferably, the flocculant is selected from at least one of an inorganic flocculant and an organic flocculant; Preferably, the inorganic flocculant is selected from polyaluminium sulfate and / or polyferric sulfate, and the organic flocculant is selected from at least one of polyacrylamide, lignosulfonate and acrylic acid; Preferably, the drying method further comprises: performing a fourth mixing of the material after separation of a portion of the liquid phase and a desiccant until the water content in the material is 15-30 wt%.

7. The method according to claim 1, wherein In step (2), the initial content of organic matter degrading bacteria in the second mixed material is 1×10 5 -1×10 7 cfu / g; Preferably, in step (2), the organic matter-degrading bacteria include at least one of Acinetobacter, Pseudomonas, Candida tropicalis, Bacillus cereus and Alcaligenes faecalis.

8. The method according to claim 1 or 7, wherein In step (2), the method further comprises: removing material having a particle size greater than 5 cm from the second mixed material; Preferably, the second mixing lasts for 2-4 minutes; Preferably, the temperature of the second mixing is 25-35°C; Preferably, the second mixing is performed in a trommel.

9. The method according to any one of claims 1 to 3, wherein: In step (3), the temperature is maintained at 28-32°C; Preferably, in step (3), the maintenance time is 1-2 days.

10. The method according to any one of claims 1 to 3, wherein: In step (4), the heat treatment time is 3-5 minutes; Preferably, the temperature of the heat treatment is 100-700°C.