KR101196987B1 - Method for Ex-situ Restoration of Contaminated Soil - Google Patents

Abstract

PURPOSE: A method for restoring polluted soil is provided to shorten times needed for treating the polluted soil by improving the reduction rate of pollutants. CONSTITUTION: A method for restoring polluted soil includes the following steps: soil polluted with oils is excavated and arranged on the ground, or moisture is supplied into the excavated place; 100 parts by weight of a 5-35% hydrogen peroxide aqueous solution and 5.0-10.0 parts by weight of sodium persulfate or calcium peroxide as a solid oxidant are injected into the pollute soil with moisture to be oxidized; 0.05-2.0 parts by weight of iminodisuccinic acid as a catalyst is injected into the polluted soil; and the soil is mixed by an excavator. [Reference numerals] (AA) Ridge; (BB) Polluted soil; (CC) Bank; (DD) Entrance

Description

Method for Ex-situ Restoration of Contaminated Soil

The present invention relates to a method for restoring the contaminated soil by ground treatment to purify soil contaminated with various oils, and more particularly, to excavate the contaminated soil with an excavator and lay it on the surface or excavate the hydrogen peroxide as an oxidant in the ground. And a method of purifying and restoring contaminated soil by oxidizing oil contained in contaminated soil using a mixture of solid sodium persulfate and the like.

   As the modernization and diversification of the industry is accelerating, the consumption of oil as an energy source and raw materials of various chemical products is increasing exponentially. As a result of the increase of oil storage facilities and transportation handling, oil is a secondary problem caused by it. Soil pollution is a serious environmental problem.

   Soil pollution is one of the serious environmental pollution that can cause wide area pollution such as primary pollution of soil itself, secondary pollution to surrounding rivers and groundwater. Currently, 12,917 gas stations and 7,347 oil storage industry facilities in Korea Etc., which are managed as oil-related soil pollution causing facilities. In recent years, however, leaked oil contaminates a significant amount of soil and groundwater due to aging and inadequate handling of these facilities.

   Fuel stored in these facilities is hydrophobic, insoluble in water, and once spilled into the soil, it can form strong adsorption with the soil or remain non-aqueous phase liquids (NAPL) for a long time. In addition, since they are composed of very complex petroleum hydrocarbons and contain a lot of harmful components to human body and soil organisms, it is necessary to properly treat the contaminated soil.

   In Korea, the Soil Environment Conservation Act has been in force since 1996 to classify more than a certain scale of petroleum and toxic substance manufacturing and storage facilities as specific soil contamination facilities, and periodically conduct soil contamination tests within three years. In case of non-compliance, 16 substances including petroleum and toxic substances are regulated and controlled as soil pollution regulations by issuing a corrective order to improve the contaminated soil.

   The technology to purify soil contaminated with oil is classified into In-situ and Ex-situ by treatment location, and physical methods (excavation removal, shielding, pumping, vacuum extraction, Solidification, hydraulic fracturing, pyrolysis, plasma, etc.), chemical methods (oxidation, neutralization, ion exchange, soil washing, surfactant washing, freezing, vitrification, etc.), biological methods (decomposition, aeration, soil cultivation, etc.) are known. Among them, the chemical oxidation method, that is, the technique of using hydrogen peroxide as the representative oxidant and contacting with oil pollutants in the ground to decompose them into carbon dioxide and water, can decompose and treat oil pollutants in the place faster than other technologies. This method is most commonly used due to its advantages that can be easily realized in the market. However, this method is not economically economical in a wide range of low-contaminated areas, and increases the processing cost due to the introduction of excess hydrogen peroxide and iron catalysts. And problems that have a big impact on the ecosystem.

As a specific example of the prior art, Korean Patent Publication No. 10-0476134 (Mar. 14., 2005) discloses a method for restoring soil contaminated soil and groundwater by sequential merging of hydrogen peroxide, ultraviolet rays and oil decomposition microorganisms. This method combines oil permeation by chemical reaction of hydrogen peroxide with biological oil decomposition by microorganisms to take advantage of each method and eliminates the disadvantages that can occur in combination use.However, as the underground treatment technology, the restoration period is long and the process is complicated. There is a problem that management is difficult. In addition, Korean Patent Laid-Open Publication No. 10-2010-0090506 (August 16, 2010) discloses desorption by increasing the solubility and vapor pressure of organic pollutants by heating the soil through steam injection and increasing the moisture content, and steam After removing the contaminants in the soil through extraction, microorganisms are added to the remaining organic contaminants to further decompose and remove them, and finally, heavy metals are removed by acid washing. This long, complex process is difficult to manage. In addition, Korean Patent Publication No. 10-1146785 discloses contaminated soil with an excavator and places it on the surface of the earth or excavates hydrogen peroxide as an oxidizing agent and ferrous chloride as a catalyst (FeCl ₂ ) or ferrous sulfate (FeSO ₄ ). Although a method of purifying and restoring contaminated soil by oxidizing oil contained in contaminated soil is disclosed, the reduction rate after treatment of contaminated soil is not satisfactory.

   On the other hand, when biological processes are linked after treatment by chemical methods, microbial growth and oil degradation activity are often inhibited by residual chemicals, and after treatment by biological methods, treatment by chemical methods is linked. In the case of making the initial purification efficiency slightly lowered, such problems remain.

Therefore, the present inventors have studied the technology of effectively linking the chemical method and the biological method applied to the ground treatment technology, unlike the ground treatment technology, to overcome the disadvantages of each unit process and ground the soil contaminated with oil that can take advantage only Invented a method of restoration.

The present invention has been made in order to solve the above problems, and excavated soil contaminated with various oils with an excavator to spread on the ground surface or to supply moisture in the excavated ground and then mixed with hydrogen peroxide and solid sodium persulfate, etc. The problem is to provide a method for clarifying and restoring contaminated soil from the ground by oxidizing oil contained in the contaminated soil.

   The present invention is a method for restoring contaminated soil by surface treatment,

1) a water supply step of excavating soil contaminated with oil with an excavator and laying it on the surface or supplying water in the excavated site;

2) 100 to 5 parts by weight of aqueous solution of 5 to 35% hydrogen peroxide and 5.0 to 10.0 parts by weight of sodium persulfate or calcium peroxide, which are solid oxidants, to oxidize the contaminated soil supplied with water in the water supply step. Oxidation step;

3) a soil oxidation step of inverting and stirring the contaminated soil in which the hydrogen peroxide aqueous solution and the solid state oxidant are injected in the oxidizing step with an excavator; and provides a method for surface treatment of the contaminated soil, characterized in that it comprises.

   In another aspect, the present invention provides a method for restoring the contaminated soil by ground treatment, characterized in that the catalyst is further injected 0.05 ~ 2.0 parts by weight in the soil oxidation step.

Finally, the present invention provides a method for restoring the contaminated soil by surface treatment, characterized in that the imino disuccinic acid (Imino disuccinic acid).

In the method for restoring the soil treatment according to the present invention, the soil contained in the contaminated soil is excavated by using an excavator and spread on the ground or using excavated soil using hydrogen peroxide and solid sodium persulfate or calcium peroxide. Unlike the underground treatment method, it is possible to significantly reduce the treatment period by improving the reduction rate of pollutants unlike the underground treatment method by oxidizing the polluted soil by oxidizing it, and the process is simple and can be applied if it is secured enough without additional facilities. There is such a remarkable effect.

1 is a schematic diagram of a soil oxidation farm in accordance with the present invention.

   A method of restoring the contaminated soil by ground treatment according to the present invention will be described in detail with reference to the accompanying drawings.

   The water supply step of supplying water to the soil contaminated with oil, which is the first step of the present invention, is a preparatory step of the present invention, and it is generally known that the water content of the contaminated soil is 5 to 18 wt%. In order to apply the soil surface restoration method, appropriate moisture is required in the soil, and the appropriate moisture content of the contaminated soil is preferably in the range of 20-25 wt%.

   Soils with high moisture content can block the flow of air between the soil pores, disrupting the oxygen supply, and inhibiting the activity of microorganisms when the soil is dry.

In general, the moisture content of the excavated contaminated soil of contaminated soil is less than 18wt%, so the water is slightly lacking in applying the present invention, and water can be solved by spraying water on the contaminated soil with an injector periodically to solve the water shortage. In addition, in case of excessive moisture due to rainfall, installation of rainwater inflow blocking facilities such as houses should be considered in order to reduce treatment efficiency.

   In the second step of the present invention, the oxidation step is a step of injecting hydrogen peroxide and solid sodium persulfate or calcium peroxide into the contaminated soil supplied with moisture in the water supplying step, and injecting the oxidant at an appropriate concentration into the contaminated soil. It forms a hydroxyl radical to react with the oil present in the contaminated soil.

The hydrogen peroxide used in the oxidation step is discharged from the hydrogen peroxide tank, diluted to an appropriate concentration, mixed with the solid phase oxidant, and then supplied to the contaminated soil to generate radical hydroxide (OH?) As in Scheme 1 below.

H ₂ O ₂ → 2? OH------(Scheme 1)

Radical hydroxide (OH?) Generated from hydrogen peroxide as described above may decompose the oil by reacting with the oil present in the contaminated soil as in Scheme 2 below.

OH + M (oil) → decomposition products------(Scheme 2)

However, hydrogen peroxide is a material having an unstable structure, and has a property of reacting with other media in the soil or decomposing itself as shown in Scheme 3 below.

2H ₂ O ₂ + X (soil) → O ₂ + 2H ₂ O------(Scheme 3)

As described above, part of the hydrogen peroxide injected into the contaminated soil reacts with oil, and another part reacts with other media in the soil. Therefore, in order to effectively decompose the oil, an appropriate amount of hydrogen peroxide is finally considered in consideration of the loss from the reaction with the soil. Adjust the supply of hydrogen peroxide to allow oil to react with the oil. At this time, a method of checking the treatment rate of hydrogen peroxide and contaminated soil is needed to find the optimal injection amount.In general, since the above reaction occurs firstly, a reaction rate constant is obtained by using a first-order reaction equation such as the following Equation 4 and the Optimal conditions are derived by comparing the rate constant versus the dose.

dC / dt = kC------(Scheme 4)

In the above scheme, C is the concentration of contaminated oil.

   In the restoration method of the present invention according to Scheme 4, it is preferable to use hydrogen peroxide aqueous solution in the range of 5 to 35%. When the concentration is less than 5%, the oxidizing power is weak and almost no oxidation occurs, and more than 35%. In this case, the oxidative power may increase, but the stability may be insufficient and an explosion may occur.

In this case, when the liquid hydrogen peroxide is administered to the contaminated soil, it is preferable to use a mixture of hydrogen peroxide and solid oxidant rather than to use hydrogen peroxide alone. As a solid oxidant which can be mixed with the hydrogen peroxide, granular or powdered sodium persulfate (Na2S2O8) or calcium peroxide (Calcium Peroxide, CaO ₂ ) may be used, and the mixing ratio of hydrogen peroxide and solid oxidant is 100: 5.0. It is preferable that it is the range of -10.0 weight part.

   On the other hand, the use of a catalyst with a solid phase oxidant can further increase the oxidizing power, the kind of imino disuccinic acid (Imino Disuccinic Acid) is preferred as a white solid.

   The hydrogen peroxide containing the solid oxidant is sprayed directly onto the surface of the contaminated soil, and when spraying, the hydrogen peroxide solution can be spread evenly over the soil surface so that the hydrogen peroxide solution naturally flows into the soil contaminated by gravity. do. At this time, when the mixing ratio of hydrogen peroxide and the solid state oxidant is less than 5.0 parts by weight, the oxidation reaction does not occur actively, and when it exceeds 10.0 parts by weight, the increase in oxidizing power is insignificant and the cost increases due to the overuse of the solid state oxidant. When the catalyst is further used, the mixing of the hydrogen peroxide and the catalyst is preferably in a ratio of 100: 0.05 to 2.0 parts by weight. At this time, when the mixing ratio is less than 0.05 parts by weight, the oxidation reaction is weakly occurred. There is a disadvantage in that the increase in oxidizing power is insignificant and the cost increases due to the use of the overcatalyst.

   The soil oxidation step, which is the last step of the present invention, is a step of inverting the soil contaminated with hydrogen peroxide and solid oxidant in the oxidation step with an excavator, and turning the soil contaminated in the soil oxidation farm as an excavator periodically as shown in FIG. It is a finishing step to increase the treatment efficiency by promoting the oxidation reaction of the contaminated soil by forming the gyrus while stirring and flipping.

Furthermore, the soil oxidation cultivation field needs additional sites to install barriers and access roads in order to prevent the spread of additional pollutants. The layout of the soil oxidation cultivation site is based on the site conditions, ease of access, and the shortest distance from the excavation area. It can be located and installed in single and plural depending on the purification period. The cultivation cycle of the contaminated soil is determined by the time required per one time based on the removal rate derived through the removal efficiency test of the pollutants. The cultivation frequency is determined by the total purification period and the cultivation cycle. Decide For example, if the total purification period is within 48 hours and the tilling cycle is 12 hours, the number of tillages is four. Separately, even in the case of treating soil contaminated with highly volatile oil species, it is not necessary to install an exhaust gas treatment device using a volatile organic compound in a soil oxidation farm.

[Preparation for experiment]

From the site where the oil storage tank was located, excavated 100㎥ of contaminated soil with an excavator up to about 2m in depth of about 50m2, and collected 500g of it and measured the moisture of the contaminated soil. It was confirmed that, after spraying water on the contaminated soil with an injector, the moisture was measured and found to contain 23% by weight of water was used as a sample.

[Component Analysis of Soil Contamination]

Analyze the content of benzene, toluene, ethylbenzene, xylene, total petroleum hydrocarbon (TPH) by soil process test using gas chromatography (HP 6890 Plus) to analyze the contaminated soil component of the sample. The results are shown in Table 1 below.

Analysis of ingredients before treatment of contaminated soil pollutant benzene toluene Ethylbenzene xylene TPH Concentration (ppm) 0.019 0.018 0.009 0.048 573

In the present embodiment, 10 ml of contaminated soil laid in a soil oxidative farm was 750 kg of 17% aqueous hydrogen peroxide solution and 60 kg of white crystalline powder, sodium persulfate, were mixed in advance and mixed by an excavator. Thereafter, the oxidized soil of the soil cultivation plant was stirred four times with an excavator and turned over, while hydrogen peroxide oxidized the contaminated soil for 48 hours, and 500 g of contaminated soil was recovered and sampled.

The sample was obtained by performing the restoration of contaminated soil in the same manner as in Example 1, except that 30 kg of sodium persulfate was mixed instead of 60 kg of sodium persulfate as a solid oxidizing agent.

In Example 1, except that 80kg instead of 60kg of sodium persulfate as a solid oxidizing agent was carried out in the same manner to carry out the restoration of contaminated soil samples were obtained.

Except for additionally adding 10 kg of the iminodisuccinic acid catalyst in Example 1 was carried out in the same manner to perform a sample of the restoration of contaminated soil.

A sample was obtained after performing contaminated soil restoration work in the same manner except that 0.3 kg was added in place of 10 kg of iminodisuccinic acid as a catalyst in Example 4.

A sample was obtained after performing contaminated soil restoration work in the same manner except that 16 kg was added in place of 10 kg of iminodisuccinic acid as a catalyst in Example 4.

Comparative Example 1

Except for mixing 60kg of sodium persulfate in Example 1 except ferrous sulfate (FeSO ₄ ) 7H ₂ O 20kg was mixed in the same manner to perform a restoration of contaminated soil samples were obtained.

Comparative Example 2

In Comparative Example 1, except that 10 kg of ethylenediamine tetraacetic acid was further mixed as a cocatalyst, the same procedure was followed to restore the contaminated soil.

[Component Analysis after Treatment of Polluted Soil]

Benzene, toluene, ethylbenzene and xylene by soil process test using gas chromatography (HP 6890 Plus) to analyze the contaminated soil components of the samples collected in Examples 1 to 6 and Comparative Examples 1 and 2, respectively. The results of analyzing the content of total petroleum-based hydrocarbon (TPH) are shown in the following [Table 2], and the results were compared with the analysis results before the treatment of contaminated soil.

 Component analysis before and after treatment of contaminated soil (ppm) benzene toluene Ethylbenzene xylene TPH TPH Reduction (%) Before processing 0.019 0.018 0.009 0.048 573 - Example 1 0.005 0.007 0.005 0.008 97 83.1 Example 2 0.007 0.009 0.007 0.010 106 81.5 Example 3 0.006 0.008 0.006 0.009 100 82.6 Example 4 0.004 0.006 0.004 0.007 85 85.0 Example 5 0.006 0.007 0.006 0.008 99 82.7 Example 6 0.005 0.006 0.006 0.007 97 83.0 Comparative Example 1 0.007 0.011 0.006 0.020 203 64.6 Comparative Example 2 0.005 0.008 0.005 0.009 153 73.3

Example 1 and Example 4 belonging to the numerical limitation range of the present invention from Table 2 above are compared with Examples 2, 3, 5, 6, and before the components of the contaminated soil are outside the numerical limitation range of the present invention. It can be seen that the pollutants were reduced and the TPH reduction rate was significantly improved than Examples 1 and 2.

Claims (3)

delete delete In the method of restoring contaminated soil by surface treatment,
1) a water supply step of excavating soil contaminated with oil with an excavator and laying it on the surface or supplying water in the excavated site;
2) 100 to 5 parts by weight of aqueous solution of 5 to 35% hydrogen peroxide and 5.0 to 10.0 parts by weight of sodium persulfate or calcium peroxide (calcium peroxide) are injected into the contaminated soil supplied with water in the water supply step. Oxidation step;
3) the soil oxidation step of injecting a 0.05 ~ 2.0 parts by weight of imino disuccinic acid as a catalyst to the contaminated soil in which the hydrogen peroxide aqueous solution and the solid state oxidant are injected in the oxidation step, and then inverts by stirring with an excavator. Method of restoring the soil treated by the ground treatment, characterized in that.

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