JP2005246237A - Treatment method for contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method for contaminated soil which method prevents the expansion of contamination by reducing the moisture holding capacity of contaminated soil by utilizing the working of nature without installing highly expensive special equipment and which method can perform a thermal melting treatment for making contaminated soil harmless at a low fuel expense. <P>SOLUTION: The treatment method comprises the following steps: a growing step wherein a variety of plant from which a vegetable oil is produced is planted or is sowed and raised; an excavation step wherein the surface layer of contaminated soil in which the plant has grown is excavated; a separation step wherein a matter unsuitable for melting is separated and removed from the excavated soil yielded in the excavation step; and a thermal melting step wherein the excavated soil after the separation step is made harmless with a melting furnace 6. A fuel oil prepared by purifying a vegetable oil produced from the plant having grown in the growing step is used as the fuel oil used in the thermal melting step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for treating contaminated soil in which industrial waste, incinerated ash, municipal waste, or the like is dumped, or contaminated soil contaminated with a chemical substance.

  In unmanaged landfills of industrial waste, incineration ash, municipal waste, and other waste, environmental pollution caused by discarded waste, that is, hazardous substances such as chemical substances, heavy metals, and dioxins contained in the discarded waste There is a problem that secondary particles such as particles scattered by strong winds may be scattered by polluting the surrounding soil, flowing out due to rain, etc., contaminating the surrounding soil, and flowing into the groundwater to contaminate the groundwater. It was.

Therefore, in order to prevent outflow of contaminated water to the surroundings due to an increase in the amount of inflow water to the contaminated soil due to rain, the contaminated soil is covered with a water shielding vent sheet to reduce the inflow water or to prevent the outflow of contaminated water. It has been proposed to take measures to prevent the spread of environmental pollution around the treatment plant, such as providing a wastewater treatment facility for purifying contaminated water at the plant, or to detoxify the contaminated soil by heating.
JP 2001-334231 A

  However, even if the contaminated soil is covered with a water-impervious air-permeable sheet, there is a problem that the evaporation effect does not increase so much in autumn and winter when the temperature is low, and the water retention amount increases, especially on sloping land due to rainwater flowing from the surrounding soil. There was a problem that it was difficult to avoid the rise in In addition, when a wastewater treatment facility is provided, there is a problem that a large-scale facility for purifying contaminated water that is sometimes generated in large quantities is required, and not only the initial cost but also the maintenance cost increases.

  Furthermore, in the technology to detoxify the contaminated soil by heating and melting it in a heating furnace or melting furnace to repair the contaminated soil or reduce the volume of waste, A crushing / sorting process is required as a pretreatment process to dig up and crush to a particle size suitable for heat treatment or to remove unsuitable materials. Contaminated soil adheres to the inside of equipment used in pretreatment processes such as conveyor devices that transport soil, crushers that crush contaminated soil, sorting machines that remove inappropriate materials, and storage tanks that store before heat treatment. Therefore, a drying process for reducing the amount of water retained in the soil is further required in order to frequently cause a blockage accident in the conveyance path in the apparatus and a breakdown accident in the drive unit in the apparatus. In addition, when fossil fuels are used as a heat source for drying and heat melting, there is a problem that fuel costs increase.

  The present invention has been made in view of the above-described conventional problems, and prevents the spread of pollution by reducing the amount of water retained in contaminated soil by utilizing natural activities without providing costly separate facilities. At the same time, the present invention is to provide a method for treating contaminated soil that can be detoxified by heating and melting at a low fuel cost.

  In order to achieve the above-mentioned object, the characteristic configuration of the method for treating contaminated soil according to the present invention is that, as described in claim 1 of the document of the claims, planted varieties that produce vegetable oil in the contaminated soil are planted or planted. A sowing and growing process, a drilling process for excavating the surface soil of the contaminated soil on which the plant has grown, a separating process for separating and removing unsuitable molten material from the excavated soil by the drilling process, and the excavated soil that has been separated and removed It consists of a heating and melting step for detoxification treatment by heating and melting, and fuel oil refined from a vegetable oil collected from a plant grown in the growing step is used as a fuel in the heating and melting step.

  In the process of excavating the contaminated soil on the surface layer, the contaminated soil is captured by the roots of the plant, so that the excavation process can be performed while suppressing the scattering of the particles to which the pollutants adhere, and the heating process is contaminated. Since the amount of water retained in the soil is kept low, it is possible to detoxify contaminated soil in a state where the total amount of heat required for the heat treatment is reduced to improve energy efficiency. Furthermore, the drying step that has been conventionally required is no longer necessary, and even if a drying step is required, the amount of water retained in the soil is reduced in advance due to the evapotranspiration of the plant. In addition to being able to reduce the amount of fuel consumption required for transportation, conveyor devices that transport contaminated soil, crushers that crush contaminated soil, sorting machines that remove unsuitable materials, storage tanks that store before heat treatment, etc. Thus, it is possible to prevent obstruction of the equipment used in the pretreatment process and damage to the drive section in the equipment.

  In addition to the first characteristic configuration described above, the second characteristic configuration is the average of the specific period in the contaminated soil area, in addition to the first characteristic configuration described above. The varieties are more than or almost equal to precipitation.

  In other words, the amount of water retained in the soil is rapidly reduced by evapotranspiration from plants grown in the contaminated soil, so that the drainage from the contaminated soil is suppressed and the contamination of the surrounding soil is reduced during rainfall. In addition, it is possible to prevent the outflow of contaminated water due to rainfall throughout the specified period and to keep the amount of water retained in the soil low.

  In addition to the first or second characteristic configuration described above, the third characteristic configuration is the same as that described in claim 3, and the plant has a total amount of evapotranspiration during a specific period in the contaminated soil region. It is a combination of two or more varieties that are greater than or approximately equal to the average precipitation during the specific period.

  By combining the varieties in this way, it is possible to expand the variety selection flexibility of the cultivated plants to complement each other according to the difference in the growth period of the cultivated varieties in the specific period and the difference in the amount of evapotranspiration.

  In addition to any one of the first to third feature configurations described above, the fourth feature configuration is the Brassicaceae, Gramineae, Palm, Legume, It is in the point that it is selected from any of the aceae.

  The plant from which the above-described vegetable oil can be collected is preferably selected from any of the Brassicaceae, Gramineae, Palm, Leguminous, Spiraceae, and particularly, the ground cover plants such as Brassicaceae, Gramineae, Legumes. Or, if it is a shallow root plant, the water retention amount can be greatly reduced from the surface soil to the middle soil, so that the root soil is spread on the surface soil and middle soil of the contaminated soil, especially the ground cover plant with roots on the surface soil. If so, it is possible to effectively suppress the situation where the surface soil capture capability is enhanced, and particles attached with harmful substances such as heavy metals and dioxin contained in the dumped waste are scattered by strong winds and contaminate the surrounding soil. It becomes.

  In addition to any one of the first to third characteristic configurations described above, the fifth characteristic configuration is the rapeseed, corn, sesame, oil palm, coconut, sunflower, It is in the point selected from either soybean or olive.

  As described above, according to the present invention, it is possible to reduce the water retention amount of the contaminated soil by using natural activities and prevent the spread of contamination without providing additional expensive facilities, and also by heating and melting. It has become possible to provide a method for treating contaminated soil that can be detoxified at low fuel costs.

  Embodiments of the present invention will be described below. As shown in FIG. 1, industrial waste, incinerated ash, municipal waste, and other wastes, and soil covered with those wastes are mixed with contaminated soil 1 contaminated with heavy metals or dioxins. It is deposited in the treatment plant 2 excavated in the area. The surface soil of the contaminated soil 1 is planted with rapeseed of the Brassicaceae, which is a ground cover plant rooting in the surface layer portion, and the water retention amount of the contaminated soil is adjusted by evapotranspiration. The rapeseed is sown at the beginning of autumn and dies around April and May. However, it can grow most during the rainy season from June to August or heavy rainfall by double cropping, so that the evapotranspiration can be enhanced most. . In particular, during this period, the amount of water retained in the soil by evapotranspiration is much lower than in bare land.

  In the treatment plant 2, a reservoir 3 for storing overflow from contaminated soil caused by rainfall is excavated and a pump for irrigating contaminated drainage collected in the reservoir 3 to the rape grown in the contaminated soil, An irrigation facility 4 made of piping or the like is provided. Therefore, without requiring an external water source for irrigation, it is possible to avoid the spread of contamination outside the system by circulating drainage generated from contaminated soil as irrigation for plant growth in a closed system It is configured. The sewage drainage collected in the reservoir 3 can be sent to the wastewater treatment plant 7 as necessary to be purified and discharged into the river.

  After the plant is grown and seeded, the top soil of the treatment plant 2 is excavated and sorted, and then melted by the melting furnace 6, and the soil after the melt treatment is backfilled in the treatment plant 2, or concrete aggregate, Used as roadbed material.

  The rape grown in the treatment plant 2 described above is harvested and collected after fruiting, further prepared or refined as fuel oil, and part or all of it is used as fuel for melting in the melting furnace described later. Unlike mineral oil-based fuels, edible oils have problems of high viscosity, low volatility or ignitability. In order to solve these problems, terpene compounds are mixed with vegetable oil, used as fuel oil blended with heavy oil, triglyceride or free fatty acid, which is the main component of vegetable oil, and alcohol such as methanol with supercritical state or sublimation. By transesterification and dehydration in a critical state, it can be converted into a monoesterified product and recovered as a fuel oil.

  If the plant-derived fuel used in this way is used, the amount of carbon dioxide discharged to the natural world can be reduced and the consumption of fossil fuel can be suppressed. According to the Kyoto Protocol to the United Nations Framework Convention on Climate Change, Japan needs to reduce carbon dioxide emissions by 6 percent over the five years from 2008 to 2012, with 1990 as the base year. In this regard, based on the “Guidelines for Calculation of Greenhouse Gas Emissions from Business Operators” issued in July 2003 by the Global Environment Bureau of the Ministry of the Environment, a portion of heavy oil can be calculated as shown in the trial calculation table shown in FIG. By using the above-mentioned plant-derived fuel oil, a remarkable effect that it can be reduced by about 1.8% can be obtained.

  Below, the detoxification process of contaminated soil is demonstrated. When the contaminated soil 1 is accumulated over a depth of 3 m or more from the surface layer portion and treated for a long period of time, as shown in FIG. 2 (a), the surface layer divided into blocks with a substantially constant area is divided into blocks. Excavate to a depth of about 2 m and perform the detoxification process described later, and seed rape on the surface after excavation. While the seeded rapeseed germinates and grows, the adjacent block or the block separated from the already excavated block is similarly excavated to a depth of about 2 m and subjected to the detoxification treatment. The block after excavation is seeded with rapeseed in the same manner as described above. By repeating the above treatment in sequence, the water retention rate of the soil to be excavated is kept low by utilizing the evapotranspiration function by plants, and the long-term detoxification treatment process is completed while avoiding the outflow of contaminated water to the surroundings. In addition, as a procedure for excavation, it is preferable to excavate a block that is separated from the excavated block rather than excavating a block adjacent to the excavated block because the influence of an increase in the water retention amount due to rainfall can be reduced. . Here, the excavation depth is set to 2 m, which corresponds to the depth at which the effect of reducing the water retention amount of the soil by the ground cover plant or the shallow root plant is obtained.

  When the contaminated soil 1 is accumulated over a depth of 3 m or less from the surface layer portion and can be processed in a short period of several months, as shown in FIG. 2B, the surface layer is divided into blocks with a substantially constant area. Are sequentially excavated to the ground in units of blocks and subjected to the detoxification process described below. If there was rain during excavation of a block, after the plant that had grown in that block was excavated and removed, the remaining water was not excavated until the water content was 20% or less. Allow to dry, during which time proceed to the next block excavation process.

  The detoxification process described above will be described in detail below. As shown in FIG. 3, after seeding the grown rapeseed (S1), the excavation process of the contaminated soil is performed (S2), and the contaminated soil is put into a crusher such as a biaxial shear crusher by a conveyor mechanism. Large waste is crushed to a particle size of several tens of millimeters (S3), and then metals are separated and collected using a metal sorter such as a magnetic sorter (S4). The soil and plants are stored in a storage tank, and the stored processed materials are sequentially put into a surface melting furnace to vitrify them, so that thermal decomposition treatment of harmful substances such as dioxin and containment of heavy metals in glass crystals are performed. (S5) Used as concrete aggregate or roadbed material (S6) A series of processing is performed on-site. In the above detoxification process, the moisture content is adjusted to 20% or less by the evapotranspiration action of the plants grown on the contaminated soil, so that the drying process of the excavated soil becomes unnecessary, and the consumption of drying energy associated therewith In addition, various inconveniences such as damage to the equipment, etc., have been solved. Further, as a molten fuel to be supplied to the heating burner of the surface melting furnace, by providing a step S7 for extracting oil from the rapeseed cultivated in step S1 and refining it into fuel oil, and using the generated plant-derived fuel oil It can save fossil fuels and reduce carbon dioxide generation.

  In the above-described embodiment, the plant that uses the rapeseed of the Brassicaceae family has been described as the plant grown in the treatment plant. It is possible to grow by selecting a single plant or a plurality of plants. Specifically, in addition to rapeseed, corn, sesame, oil palm, coconut, sunflower, soybean, olive and the like can be selected.

  As shown in FIG. 5, a gravel layer 7 is provided at the bottom of a 1 / 2000a Wagner pot 6 surrounded by a heat insulating material 14, and contaminated soil 8 is packed on the bottom via cotton cloth. In addition to installing a copper-constantan thermocouple 9 in the middle of the depth direction for measurement, prepare a plurality of test pots with a 3-wire TDR probe 10 installed in the middle of the depth direction for measuring the moisture content, Each was installed on the electronic balance 11. From the bottom of each pot 6, the overflow water that was not retained in the soil was installed so as to flow into the graduated cylinder 13 through the silicon tube 12. Experiments for confirming the amount of evapotranspiration of plants were conducted using the above-described experimental apparatus.

  One of the Wagner pots mentioned above is left bare, and the other pots are planted with cruciferous rapeseed rapeseed, oilseed rape, and tanashikibu, respectively, once a day for all, a decrease from the pot weight of the previous day The amount was irrigated. Pot weight and graduated cylinder weight were continuously measured with an electronic balance and converted to mm units, and evapotranspiration from mid-July to October was recorded.

  As a result, as shown in FIG. 6, the average evapotranspiration rate of 3 mm / d (maximum of about 4.8 mm / d) in bare land is about 5 mm / d (maximum of about 9.6 mm / d) by growing plants. It was found that the amount of evapotranspiration increased by 57% in Akasano rape compared to the case of bare land. Plant evapotranspiration is high when soil moisture content is high (> 20 percent) and low when soil moisture content is low (<20 percent), so water content decreases rapidly when soil moisture content is high The effect of stabilizing at a low water content contributes more than the figure of 57 percent.

Explanatory drawing of the processing method of contaminated soil by this invention Illustration of detoxification method for contaminated soil Flow chart of detoxification treatment method for contaminated soil Trial calculation of carbon dioxide emissions Illustration of test equipment Graph showing test results

Explanation of symbols

1: Contaminated soil 2: Treatment site 3: Reservoir 4: Irrigation equipment 5: Ground 6: Melting furnace

Claims (5)

  A planting process for planting or sowing a variety of plants that produce vegetable oil in the contaminated soil, a drilling process for excavating the surface soil of the contaminated soil on which the plant has grown, and a melting inappropriate material from the excavated soil by the drilling process A separation process for separating and removing, and a heating and melting process for detoxifying the separated excavated soil by heating and melting, and the fuel oil purified from the vegetable oil collected from the plant grown in the growing process is the heating and melting process Of contaminated soil used as a fuel in Japan.   2. The method for treating contaminated soil according to claim 1, wherein the plant is a cultivar having an average evapotranspiration during a specific period that is greater than or substantially equal to an average precipitation during the specific period in the contaminated soil region.   2. The treatment of contaminated soil according to claim 1, wherein the plant is a combination of two or more varieties whose total amount of average evapotranspiration during a specific period is greater than or substantially equal to the average precipitation during the specific period in the contaminated soil region. Method.   The method for treating contaminated soil according to any one of claims 1 to 3, wherein the plant is selected from any of the Brassicaceae, Gramineae, Coconut, Leguminous, and Spiraceae families.   The method for treating contaminated soil according to any one of claims 1 to 3, wherein the plant is selected from rapeseed, corn, sesame, oil palm, coconut, sunflower, soybean, and olive.

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