KR100750596B1 - Soil purification method using microwave radiation and microbe and purification system - Google Patents

Abstract

A system for remediating contaminated soil in an economical and efficient manner, which can be applied when remediating the soil by digging soil contaminated with petroleum-based organic contaminants at high concentration, and a method for remediating the contaminated soil by using the system are provided. A system for remediating contaminated soil comprises: a remediator(10) having a reactor(1) into which contaminated soil is injected, and a microwave generator(2) for heating the reactor; a discharge pump(30) for discharging vapor generated in the reactor; a gas-liquid separator(20) for cooling the vapor discharged from the reactor to separate liquid and gas from the vapor; a gas treating unit(40) for treating the gas separated in the gas-liquid separator; a liquid storage tank(50) for storing the liquid separated in the gas-liquid separator; a microorganism culture medium(60) for injecting a microorganism culture media into the reactor; and a water tank(70) for supplying water into the reactor. The reactor further has a porous distributor(4) formed in an upper portion thereof, and a porous filter(3) formed in a lower portion thereof.

Description

Soil Purification Method using Microwave Radiation and Microbe and Purification System

1 is a schematic diagram of a contaminated soil purification system of the present invention.

<Description of the code used in the main part of the drawing>

1: reactor 2: microwave generator 3: porous filter 4: porous distributor

10: purifier 20: gas-liquid separator 30: discharge pump 40: gas treatment device

50: liquid reservoir 60: microbial incubator 70: water tank 80: pump

The present invention relates to a method and system for significantly purifying contaminated soil using microwaves and microorganisms.

Human activities have contaminated the soil with various compounds such as pesticides, gunpowder and petroleum compounds, and techniques for purifying the contaminated soil have been developed in various developed countries. Physicochemical treatments include soil washing, incineration, solidification and stabilization, vitrification, soil vapor extraction (SVE), and thermal desorption, and biological treatments include bioventing, bioopile, landfarming, and in situ. And in-situ and ex-situ bioremediation, phytoremediation, and the like, and methods of combining and treating each of these methods with a complex treatment method have been developed. Among the treatment methods developed, economical and efficient methods are selected and used for soil purification, taking into account the characteristics of pollutants, the degree of pollution, the topography, and the characteristics of the soils to be cleaned. Although various soil purification methods have been developed so far, the cost of soil purification is so high that there is still a need to develop economic and efficient soil purification techniques.

In Korea, the 1995 Enactment of the Soil Environment Conservation Act enacted an interest in the purification of polluted soils, and while investing in the development of purification technology, it was still in the early stage of introduction. Currently, most of the technologies used for domestic soil purification are unfortunately not the technologies of domestic development but the fact that they are used by adopting technologies developed in foreign countries. In other words, the technology developed by research and investment in developed countries is imported and used. One of the major soil purification projects in Korea is the purification of the Munheung Oil Pollution Area in Busan. The thermal desorption technology used here was imported from Canada. This is an example showing the weakness of domestic soil purification environmental technology.

Thermal desorption is a method of excavating soil and heating the soil to a high temperature (100 ~ 550 ℃) in a heat dryer to desorb volatile and semivolatile organic contaminants to purify the soil. Purification efficiency for volatile and semi-volatile organic pollutants is higher than other purification techniques because the final concentration of pollutants can be treated to 5 mg / kg or less, but there is a limit to the removal of non-volatile organic pollutants. In addition, the high energy cost of heating requires the development of efficient heating methods.

Soil vapor extraction method is a technique that induces desorption and removes desorbed organic contaminants by volatilizing volatile and semi-volatile contaminants from the soil by using a vacuum pump to the contaminated unsaturated soil layer. Semi-volatile contaminants are difficult to desorb, lengthen the soil cleanup process and increase maintenance costs. In order to compensate for this disadvantage, a system for accelerating volatilization by adding air is added, and a system for accelerating evaporation and volatilization by heating the soil by injecting steam or hot air is added. Injecting steam or hot air is an indirect soil heating method, which is low in energy efficiency due to heat loss to the surroundings, and thus requires a more efficient heating method because of high energy consumption costs. In addition, the addition of these air injection or heating systems is not easy to remove non-volatile and non-desorbable contaminants.

Bioventing is a system that increases the activity of aerobic microorganisms by blowing air into unsaturated soil layers to biodegrade and remove organic contaminants in the soil. Bioventing is mainly applied to large areas with low concentrations and is difficult to apply at high concentrations. Most biological treatment methods, including bioventing, can cause odors due to volatilization of contaminants when applied at high concentrations, and are difficult to degrade by microorganisms due to the toxicity of the contaminants.

The present invention was developed to overcome the limitations of the prior art in the purification system and method of contaminated soil, petroleum-based organic contaminants (gasoline, diesel, bunker oil, engine oil, polycyclic aromatic compounds, etc.) are contaminated at a high concentration It is an object of the present invention to provide an economical and efficient polluted soil purification apparatus and a method for treating polluted soil using the same in the case of digging and purifying existing soil.

In the present invention, the contaminated soil purification system includes a microwave generator for soil heating, a purifier having a reactor for desorption and microbial decomposition of soil contaminants, a discharge pump used for steam extraction, and microorganisms for culturing bacteria that can decompose contaminants. It consists of an incubator. Contaminated soil purification method removes volatile and semi-volatile pollutants preferentially through the process of heat desorption and steam extraction, and the volatile, semi-volatile and non-volatile pollutants remaining in the soil are sequentially injected with microbial fluid. The process is further removed through microbial degradation.

In order to achieve the above object, the present invention uses microwaves to remove volatile and semi-volatile substances in the soil first, to lower the concentration of contaminants, and to purify the soil by injecting microbial culture medium in the second, so that the conventional treatment of the soil is not performed. Compared with the high concentration of contaminants, the amount of microbial culture solution (or concentration) can be reduced, the purification time by microorganisms can be shortened, and microwaves can be used to efficiently remove nonvolatile organic materials that are not removed during the first treatment. The present invention was found to be able to be removed by the present invention, thereby achieving an excellent purification effect.

In the present invention, petroleum-based organic contaminants (volatile, semi-volatile and non-volatile) can be quickly removed by heating or extracting soil contaminated with high concentration simultaneously or sequentially, and are not easily removed even by heating and extraction. Contaminants can additionally decompose and remove contaminants adsorbed on the soil through microbial injection.

First, the purification method of the present invention is as follows.

a) introducing contaminated soil into the reactor;

b) raising the temperature inside the reactor by the microwave generator;

c) recovering and separating the volatile organic compounds and the quasi-volatile organic compounds in the heated reactor;

d) purifying the microorganism culture solution in a reactor in which the volatile organic compound and the semi-volatile organic compound have been removed;

In addition, the present invention may repeat the steps b) to d) one or more times as necessary.

In the present invention, microwave (2.45 GHz) is used for soil heating. In conventional conventional kiln rotary kiln, furnace heating or hot air or steam injection method heat transfer to the soil through the heating medium is low heat transfer efficiency. On the other hand, when using ultrashort waves, the soil can be heated in a short time by directly irradiating the wave to the soil (subject) to be heated, and the heat transfer efficiency is superior to that through the heating medium by selectively irradiating only the soil (subject). There is this. In addition, the microwave is economically competitive in terms of initial facility cost and maintenance because the heating device is simple and easy to operate.

When injecting liquid microorganisms, some of the contaminants adsorbed in the soil are desorbed into the liquid phase, and the contaminants dissolved in the liquid phase are decomposed by the microorganisms. The microbial fluid contains organic substances (biosurfactants, microbial metabolites, enzymes, etc.) secreted by the microorganisms, so that the solubility of the adsorptive and non-desorbable organic contaminants increases, so the desorption of these contaminants increases when the microbial fluid is injected. Contaminants that are not dissolved and adsorbed on the soil organic matter or surface are contaminated by the microbial membrane when the microorganisms are attached to the soil contaminant, and then degraded due to contaminant transfer into the microorganism. Belonging to wild microorganisms such as Pseudomonas sp., Agrobacterium sp., Clostridium sp., Sphingomonas sp., And Ralstonia sp. Microbes have chemotaxis and mobility for organic contaminants. Because of their chemotaxis and mobility, these microorganisms do not dissolve but migrate toward the adsorbed contaminants and degrade the contaminants through close contact or direct contact.

High molecular weight non-volatile contaminants are not only readily soluble in aqueous solutions, but also difficult to be directly degraded by microorganisms. These contaminants are decomposed by extracellular enzymes, and the partially decomposed contaminants have a relatively small molecular weight, are easily dissolved in aqueous solutions, and the dissolved substances are further decomposed by direct decomposition of the microorganisms. Proceeds. Pseudomonas sp., Agrobacterium sp., Clostridium sp., Ralstonia sp., Thiobacillus sp., Acinetobacker (Acinetobacter sp.), Mycobacterium sp., Arthrobacter sp., Flavoacterium sp., Achromobacter sp., Genus Gomonas Microorganisms such as Sphingomonas sp. Secrete enzymes that can degrade organic contaminants.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described based on an accompanying drawing.

The contaminated soil purification system of the present invention uses microwaves during soil heating, and removes residual contaminants after steam extraction using microorganisms.

Figure 1 is a schematic diagram for explaining the configuration and the process by the soil purification apparatus of the present invention. As shown in FIG. 1, the contaminated soil purification system of the present invention includes a purifier 10 equipped with a reactor 1 for placing contaminated soil and a microwave generator 2 for heating the reactor 1;

A discharge pump 30 for discharging steam generated in the reactor 1;

A gas-liquid separator 20 for separating the vapor discharged from the reactor 1 into a liquid and a gas;

A gas treatment device 40 for treating the gas separated from the gas-liquid separator 20;

A liquid reservoir (50) for storing the liquid separated from the gas-liquid separator (20);

A microbial incubator 60 for introducing a microbial culture liquid into the reactor 1; And

A water tank 70 for supplying water to the reactor 1;

Disclosed is a contaminated soil purification system equipped with.

In addition, the top of the reactor (1), that is, the inlet of the contaminated soil may be further provided with a porous distributor (4) to be evenly sprayed when water or microbial culture liquid injection, the lower end of the reactor is generated A porous filter 3 for discharging volatile and semivolatile organic compounds may be further provided.

In addition, the present invention may be further provided with a thermometer, a pressure gauge, a soil moisture meter and the like optionally inside the reactor.

Hereinafter, the above apparatus will be described in more detail.

In the present invention, the purifier 10 is provided with a reactor (1) and a microwave generator (2) that can put the soil to remove the contaminants.

 In the present invention, the microwave generator 2 generates microwaves having a frequency of 2.45 GHz. At this time, the microwave wavelength is about 1.2 cm.

In the present invention, the reactor (1) is decontamination or decomposition of soil contaminants occur, it is selected from materials that can transmit microwave, that is, polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE) It is preferred to be at least one resin or high heat treated glass (Pyrex).

The soil inside the reactor 1 is preferably a soil having an initial moisture of 20% or more, and is preferably heated to 80 to 150 ° C. with microwaves. The heating temperature depends on the amount of microwave generation, the type of soil and the moisture content of the soil. When the moisture content of the soil introduced into the reactor 1 is less than 20%, it is preferable to replenish moisture arbitrarily before and after adding the soil to the reactor 1. At this time, it is preferable to further include a soil moisture meter (not shown) in the reactor (1) as needed to measure the moisture content of the soil in the reactor, when the water in the soil is less than 20%, the water tank 70 It is good to supply water from

Moisture in the soil helps to heat the soil due to its excellent ability to absorb electromagnetic waves due to its high dielectric constant and generates heat, and also helps to desorb and volatilize organic pollutants by increasing the dissolution of highly soluble pollutants. Do it.

In the present invention, the reactor (1) is preferably provided with a porous distributor (4) to evenly spray the liquid injected from the water tank (70) or microbial incubator 60 in the inlet for introducing contaminated soil. The porous distributor 4 means using a material that transmits water or air but does not pass particulate matter.

In addition, in order to easily discharge the volatile and semi-volatile vapor generated when heating the contaminated soil in the reactor (1) using the microwave generator (2), that is, the discharge port has a porous filter on the opposite side of the porous distributor (4). (3) is provided. The porous filter (3) uses a material that can pass only water and air so that the soil does not escape down, the vapor discharged from the porous filter (3) is a gas-liquid separator 20 by the discharge pump (30) And is separated into a gas and a liquid and processed or stored in the gas treatment device 40 and the liquid storage tank 50, respectively. At this time, it is preferable that a vacuum of 5 to 20 mmHg is formed at the top of the soil in the reactor 1 during steam extraction to move the air flow in the reactor toward the gas-liquid separator. Therefore, it is preferable to further include a pressure gauge (not shown) in the reactor to check the pressure state. The soil water content after steam extraction is preferably 10% or less. The extracted steam or water is separated into gas and liquid in the gas-liquid separator 20. The gas-liquid separator 20 is preferably a water-cooled or air-cooled device.

Next, after the volatile and semivolatile vapors of the contaminated soil are discharged by the microwave generator 2, the remaining nonvolatile contaminants are purified by the microorganisms. At this time, as a device for providing a microbial culture liquid used, the microbial culture device 60 is provided.

The microorganism incubator 60 cultures microorganisms that degrade organic contaminants in a liquid phase, and microorganisms that can be used at this time include Pseudomonas sp., Agrobacterium sp., And Crostridium genus. sp.), Ralstonia sp., Thiobacillus sp., Acinetobacter sp., Mycobacterium sp., Arthrobacter sp. ), Flavoacterium sp., Achromobacter sp., Sphingomonas sp.

In the microorganism incubator 60, the microorganisms are preferably cultured to have a concentration of about 108 microorganisms per ml. The microbial fluid cultured in the microbial incubator 60 is injected into the reactor 1 through the pump 80. At this time, the amount of the microbial fluid to be injected is preferably injected by the amount corresponding to the weight of the soil in the reactor (1). That is, the amount of microbial fluid injected into the soil is preferably in the range of 1: 1 to 1: 2 by weight. After injecting the microbial fluid into the soil, it is desirable to have a aging period of 24 hours or more. At this time, the injected microbial fluid penetrates into the soil by gravity and also penetrates into the pores of the soil by capillary action. As microbial fluid penetrates the entire soil, microorganisms that break down contaminants also penetrate. The infiltrated microorganisms decompose and dissolve the contaminants that are desorbed from the soil, and the insoluble contaminants are additionally decomposed by the attached microorganisms or enzymes secreted by the microorganisms. Wild type microbes are chemotactic and mobile. The chemotaxis and mobility of these microorganisms allow the microbes to move to the point where the contaminants are adsorbed, effectively removing the contaminants. In addition, decomposition of adsorbed pollutants also occurs by enzymes secreted by microorganisms. After removal of contaminants, the microbial culture liquid is introduced into the liquid storage tank 50 through the gas-liquid separator 20 by opening a valve at the bottom of the reactor 1.

As in the present invention, the combination of microwave irradiation, steam extraction, and microbial treatment in contaminated soils increases the removal efficiency of organic contaminants, and in particular, the removal efficiency of non-volatile and adsorptive contaminants.

Hereinafter, the present invention will be described with reference to Examples for the specific description of the present invention, but the present invention is not limited to the following Examples.

[Preparation for experiment]

The uncontaminated soil was collected and contaminated with toluene (volatile) 83000ppm, naphthalene (semi-volatile) 11000ppm, and pinanesrene (non-volatile) 5600ppm. The organic carbon content of soil was 13%.

If only soil vapor extraction was used (Comparative Example 1), microwave heating (irradiated at 2.54 GHz) and soil vapor extraction were performed in parallel (Comparative Example 2), only microorganisms were treated (Comparative Example 3), microwave When the microorganisms (Pseudomonas sp.) Treatment was applied to the heating and soil vapor extraction (Example), the results were seen.

[Measurement method for pollutants]

After the soil was treated by each treatment method, 10g of soil samples were transferred to a 20ml glass vial, 10ml of methanol was injected, and the mixture was extracted with methanol by rotation mixing 9 times per minute for 2 days. The extracted samples were analyzed by using high performance liquid chromatography (HPLC). 15 cm x 4.6 mm (5 um) of Supelcosil LC-PAH was used as a column in HPLC, and UV / VIS 254 nm was used as a detector.

Comparative Example 1

Put 12g of the contaminated soil into the reactor and use the discharge pump 30 for 10 minutes After steam extraction, 10g of soil was taken as a sample, the concentration of the pollutants remaining in the soil was measured according to the method of measuring the above pollutants, and the concentrations of the pollutants remaining in the soil were shown in Table 1 below. .

Comparative Example 2

Put 12g of the contaminated soil into the reactor and operate the microwave generator (irradiated at 2.54 GHz), heat it at 80 ° C for 1 minute, extract the steam for 10 minutes, take 10g of the soil as a sample, Extracting the remaining pollutants to measure the concentration, the results of calculating the concentration of the pollutants remaining in the soil are shown in Table 1 below.

Comparative Example 3

Put 12g of the contaminated soil into the reactor, add microbial culture solution (Pseudomonas sp.) To the same weight as the soil, and leave it for 24 hours, remove the microbial culture solution and take 10g of soil as a sample to measure the above contaminants. By measuring the concentration by extracting the remaining contaminants in the soil, the results of calculating the concentration of the contaminants remaining in the soil are shown in Table 1 below.

EXAMPLE

12 g of the contaminated soil was placed in a reactor, and the microwave generator (irradiated at 2.54 GHz) was heated at 80 ° C. for 1 minute, followed by steam extraction for 10 minutes, and then the microbial culture medium (Pseudomonas sp. After adding by weight, it is left for 24 hours, and then microbial culture solution is removed, 10g of soil is taken as a sample, and the concentration of contaminants remaining in the soil is measured according to the measurement method of the above contaminants. The results of calculating the concentration of the substance are shown in Table 1 below.

TABLE 1

As shown in the table, it can be seen that the comparative example 1 which carried out only steam extraction is very effective in removing toluene, which is a volatile compound, and is relatively ineffective in removing naphthalene or pinanthrene. In Comparative Example 2 in which microwave heating and steam extraction were performed in parallel, it can be seen that it is very effective for removing toluene and naphthalene, which is a semi-volatile substance, but it can be confirmed that it is relatively ineffective for removing evacuation. In other words, by heating and steam extraction it was very difficult to remove the highly adsorptive and nonvolatile evacuation styrene from the soil. In addition, in the case of Comparative Example 3 using only the microbial culture medium, toxicity was added to the microorganisms due to the initial high concentration of contaminants, and the degradation of contaminants by the microorganisms was very low due to the inhibition of microorganism activity. Removal was minimal.

In the embodiment according to the present invention, the microbial treatment in addition to microwave heating and steam extraction resulted in additional removal of toluene and naphthalene, as well as removal of the highly adsorptive and nonvolatile material, fenanthrene, which was remarkably surprising compared to the respective methods. Indicated.

As described above, in the present invention, unlike the conventional thermal desorption method, the present invention adopts the direct soil heating method for directly irradiating the microwaves directly to the soil, rather than the indirect heating method for heating the soil through the heating medium. Only selectively heatable, good heat transfer efficiency can save energy, increase the temperature of the soil in a short time, and has the advantages of easy operation.

In addition, the present invention induces the dissolution of contaminants by injecting microbial fluid to the residual and non-desorbable contaminants that were difficult to remove in the conventional thermal desorption and steam extraction method, or took a long time to remove, decompose and adsorb the dissolved contaminants. It is possible to remove the pollutants directly by microorganisms or by enzymes, thereby increasing the soil pollutant removal rate and shortening the soil purification time.

In the present invention, in the early stage of soil purification, thermal desorption and soil vapor extraction processes are applied simultaneously or sequentially to remove volatile and semivolatile contaminants, and sequentially, microbial decomposition processes are applied to residual and nonvolatile contaminants. And the non-desorbable contaminants are additionally treated by microbial decomposition to remove contaminants at lower concentrations than conventional thermal desorption and soil vapor extraction apparatuses and methods. Applicable to the purification.

Claims (8)

As a contaminated soil purifier to clean contaminated soil, A purifier equipped with a reactor for contaminating soil and a microwave generator for heating the reactor; A discharge pump for discharging steam generated in the reactor; Gas-liquid separator for cooling the steam discharged from the reactor to separate the liquid and gas; A gas treatment device for treating the gas separated by the gas-liquid separator; A liquid storage tank for storing the liquid separated from the gas-liquid separator; A microbial incubator for injecting a microbial culture liquid into the reactor; And A water tank for supplying water to the reactor; Soil purification apparatus characterized in that it is provided. delete The method of claim 1, The reactor further comprises a porous distributor for evenly spraying water or microbial culture liquid injection and a porous filter to facilitate the discharge of volatile, semi-volatile vapor or microbial culture liquid generated during heating. The method of claim 1, The reactor is a contaminated soil purification apparatus, characterized in that using at least one resin selected from polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE) or high heat treated glass (Pyrex). delete delete delete delete

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