JP2004188406A - Anaerobic purifying method for soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anaerobic purifying method for soil to accelerate a decomposition of an organic hardly decomposable substance by anaerobic bacteria in a bio-remediation. <P>SOLUTION: When an organic solvent, oil and other hardly decomposable substance contained in soil or in a landfill site are decomposed and purified by anaerobic bacteria, a saponin-containing substance, nitrogen and phosphorus are supplied together with water. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention anaerobically or contaminates soil contaminated with mineral oil, such as the site of a gas station or an automobile dismantling plant, or the site of a factory, which is contaminated with hardly decomposable substances such as organic solvents and organochlorine compounds. Involved in the method of purifying the soil using the activity of anaerobic bacteria, especially saponin-containing materials and nutrients such as nitrogen and phosphorus mixed with water and bulking agent, and left in the soil, The present invention relates to a substance which decomposes hardly decomposable substances and purifies soil.
[0002]
[Prior art]
As a result of various economic activities, heavy metals and organic substances, which are discharged, accumulate in the soil, and these are detrimental to the environment, which has become a major social problem. At present, to remove these soil pollutants, the components dissolved in the pumped groundwater are removed by aeration or chemical treatment, or air is blown or sucked into the ground to remove pollutants in the air. Various methods have been used, such as removal of the soil and heat incineration of the contaminated soil itself.
[0003]
However, pumping groundwater cannot treat oils and hardly decomposable substances that do not dissolve in water, and suctioning air cannot treat other than volatile components. In addition, the heat incineration of the soil is troublesome and costly, and the disposal of the treated soil becomes a problem.
[0004]
Therefore, so-called bioremediation technology, in which microorganisms in the soil are used to decompose organic substances in the soil by its decomposing action, is being actively developed.
[0005]
[Problems to be solved by the invention]
By the way, there are two types of bioremediation in which the treatment is performed in an aerobic atmosphere using aerobic bacteria, and in the anaerobic atmosphere using an anaerobic bacteria. The former has a high processing speed, but requires labor and cost for air supply and the like. Also, there is a limit to the processing at the original position. On the other hand, if anaerobic bacteria that inhabit the soil are used, the treatment can be performed in situ in principle, and the soil can be purified at a low cost without relatively much effort.
[0006]
[Means for Solving the Problems]
However, an anaerobic bacterium generally has a slower growth rate than an aerobic bacterium, a slower rate of decomposing organic substances, and has a disadvantage that it takes a longer time for soil purification.
[0007]
The present invention is to add saponin to the soil in order to speed up the purification treatment by the anaerobic bacterium.In situ, cells and saponin-containing substances are added to the soil together with nutrients such as nitrogen and phosphorus in the soil. The greatest feature is that the soil is purified by pouring or mixing with the soil.
[0008]
That is, the contaminated soil targeted by the present invention is a soil of a gas station or a car dismantling plant, a petroleum complex, a coast, etc., which is contaminated with mineral oil such as gasoline, light oil, or heavy oil, an organic solvent, an organic chlorine-based compound. Soil such as a factory site contaminated with hard-to-decompose substances such as. Some of these contaminated soils, particularly those contaminated with mineral oil, have properties that appear oily and solidified with oil. When this happens, the soil receives very little water. Further, soil contaminated with an organic solvent or an organic chlorine compound also shows water repellency. This is because the soil itself has an oil absorbing function.
[0009]
Saponin acts on such water-repellent soil from two aspects. First, saponin has a surface-active effect and, depending on its concentration, acts to penetrate the water-repellent soil and eventually the cells into the soil. On the other hand, saponins, especially Kiraya saponins obtained from shabon trees, have a significant effect in wastewater treatment (activated sludge treatment) and sludge treatment, such as reducing generated sludge, decomposing oil, and promoting sludge decomposition. It has been made clear by the inventors. This is presumed to be due to the action of saponin to improve the biological activity of the microorganism.
[0010]
By the way, water is necessary for the inhabiting activity of microorganisms. Moisture in the soil includes chemical water, hygroscopic water, capillary water, and gravity water that moves freely due to gravity. Among them, the former two are said to be about 1 to 15%, depending on the type of soil, and do not evaporate even when heated to about 100 ° C., but bacteria can survive even with this much water. The oily soil also contains about 15 to 20% of water. However, it is said that about 30 to 50% of water is usually required for the propagation and diffusion of the cells. Therefore, in-situ soil purification requires water injection.
[0011]
Therefore, in the first method of the present invention, saponin is added to this water. In the second method, the water content of the soil is increased by sprinkling water later. On the other hand, the cells utilize those originally living in the soil. Bacteria (oil-decomposing bacteria) that assimilate the pollutants are present in the contaminated soil to a certain extent. However, if the number of microbial cells is small, it takes a long time to grow. Therefore, the microbial cells themselves may be supplied to the soil together with saponin. In this case, it is most preferable to culture and proliferate bacteria originally existing in the soil to be treated before use. Or you may make it use another kind of microbial cells adapted to the hardly decomposable substance in the contaminated soil.
[0012]
Examples of anaerobic bacteria and facultative anaerobic bacteria used include methane-producing bacteria, sulfate-reducing bacteria, acid-producing bacteria, oil-degrading bacteria, and Bacillus bacteria. It is said that the sulfate-reducing bacteria and the methane-producing bacteria are in a competitive relationship.
[0013]
By the way, in order for bacterial cells to propagate, it is generally necessary that C: N: P be present in a ratio of 100: 5: 1, in terms of C / N ratio. However, most of the pollutants targeted by the present invention are petroleum-derived, and N and P are low in contaminated soil. Therefore, it is necessary to supply nutrients such as nitrogen and phosphorus. The amount added depends on the type and concentration of the pollutant. Further, additives such as a pH adjuster are added as needed. In the case of bacteria requiring a silica content for growth, powdered horsetail powder or an extract thereof may be added, which contains a large amount of silicic acid. Various minerals such as iron and trace elements may be added.
[0014]
Next, saponin is a kind of glycoside contained in a plant, and is a general term for producing a colloid aqueous solution that is extremely whisker-like, and is found in many plants. In the present invention, the type of saponin used is not limited, but from the viewpoint of cost and stable supply, a saponin having a large content in a plant body, a large amount of the plant, and being stably available is preferred. From this viewpoint, saponin obtained from Kiraya saponin, yucca, squid, soybean, sugar beet, horsetail, and the like are preferable. Among them, particularly preferred is Kiraya saponin extracted from a soap tree (scientific name: Quiliaia saponaria Mol. Rosaceae) native to Chilly, Bolivia, Peru and the like in South America. This is a triterpene-based glycoside that uses quilayanic acid as an aglycone (the non-saccharide part of the glycoside), and is one of the few saponins whose structure and analytical techniques have been elucidated, and has a relatively high saponin-containing concentration. This is because an extract is obtained.
[0015]
As the saponin-containing agent, an extract (including a solvent) extracted from a plant body may be used as it is, or a purified per se may be used. The extraction may be carried out by a usual method, for example, by extraction with a lower alcohol such as ethanol. Furthermore, those obtained by processing purified products or extracts into powder, granules, or tablets are also used. Alternatively, a plant part containing saponin may be dried and ground. Currently available Kiraya saponin-containing substances contain about 4% as a natural saponin in the case of a liquid extract. In addition, a dried and ground plant material also contains about 4% of the same natural saponin.
[0016]
By the way, the present inventor has found that saponin is effective in the biological treatment process of sewage, but this is a nutrient for microorganisms because saponin is a glycoside, and in combination with the high oxygen content, microorganisms It is presumed that the treatment efficiency is improved as a result of helping breeding. Furthermore, the extract extracted from the plant contains a large amount of sugars and proteins, which also become nutrients of microorganisms.
[0017]
The concentration of saponin supplied to the soil increases or decreases depending on the concentration of contaminants in the soil. In the case of the above-mentioned wastewater treatment, it is considered that a soap tree extract (containing 4% as a natural saponin) is preferably about 10 to 20 ppm with respect to 500 ppm of the BOD component. On the other hand, the concentration of mineral oil collected at the site of an automobile dismantling plant can reach 20,000 to 60,000 ppm. Therefore, 1000 ppm or more is necessary, but unlike water, migration and diffusion are unlikely to occur in soil.
[0018]
Next, a method of supplying a saponin-containing substance or the like into contaminated soil will be described. The contaminants to be treated by the present invention are hardly decomposable substances such as mineral oils, organic solvents, and organochlorine compounds, and since these have a low specific gravity and are insoluble in water, they are used in relatively shallow parts of soil. It is likely to stay. Therefore, it seems that it is usually sufficient to purify the area up to about 2 to 3 m underground. In this case, it is preferable to inject the purified liquid obtained by mixing and dissolving the saponin-containing substance and the like into the soil under pressure and to diffuse the soil. When the contamination is limited to the surface layer, a powdery purifying agent obtained by mixing a saponin-containing substance or the like with a bulking agent may be mixed with the surface soil by stirring.
[0019]
In the former, a saponin-containing substance is added together with nutrients such as nitrogen and phosphorus, and, if necessary, a fungus body is added thereto. Do. First, an injection hole is excavated at the injection point using a boring machine, and the injection hole is press-fitted into the injection hole. The concentration, the injection amount, the number of injection ports, etc. of the purifying liquid are appropriately selected depending on the concentration of the pollutant, the depth of the contamination, and the land area.
[0020]
In the latter, a saponin-containing substance is added to nutrients such as nitrogen and phosphorus, and, if necessary, a bacterial purifier mixed with a bulking agent is added to the soil to be purified with a stirrer or the like. . However, the processing in this case is limited to about 50 cm from the ground surface. The use of the bulking agent is due to the fact that it is difficult to perform uniform stirring and mixing because the proportion of the cells is smaller than that of the soil. Normally, the stirring of the soil surface layer by the stabilizer is for mixing the cement or the like with the soil to stabilize the soil, and the cement or the like is used at about 10% with respect to the soil. In contrast, bacterial cells and saponin-containing substances are on the order of% or less. Therefore, it is necessary to increase these. Organic substances such as rice bran and coffee grounds, and inorganic substances such as talc can be used as the extender. It should be noted that since mixing by a stabilizer is usually performed in a dry state, it is desirable to sprinkle water after the mixing treatment.
[0021]
When it is desired to mix a powdery purifying agent into a deeper stratum that cannot be reached with a stabilizer or the like, it is possible to dig up the soil with a bulldozer or the like, and perform mixing and leveling.
[0022]
Since the state of contamination of the target soil, particularly the depth, can be determined by excavation, sampling of a sample core, etc., a construction method according to the depth may be employed. In the case of the present invention, it is considered that the depth of the contamination rarely exceeds 3 m. However, in the case where the contamination is carried out to a depth that cannot be accommodated by the injection of the purified liquid, it is preferable to cope with the depth mixing method. The deep mixing method is originally a simple pile forming method at a site, where soil and cement are mixed while drilling with a drill machine to form an underground pillar. When used in the present invention, the powdery purifying agent may be mixed instead of cement.
[0023]
(Experimental example)
Oil-contaminated soil (oil content: 3.1%) collected from an automobile scrap car factory was mixed with commercially available masa soil, and the oil content was adjusted to about 2%. In this experimental soil, total carbon: 77000 ppm, COD (manganese method): 6600 ppm, total nitrogen: 730 ppm, total phosphorus: 500 ppm, loss on ignition: 10%, and water content: 15.5 ppm. To this, a commercially available nitrogen fertilizer (ammonium sulfate, urea) was added so that the total nitrogen in the experimental soil was about 3850 ppm. This amount of addition yielded an experimental soil density of 2.25 g / cm ³ . Similarly, a commercially available phosphorus fertilizer (phosphate) was added so that the total phosphorus was 770 ppm.
[0024]
The blank was filled with the soil in a 2 L measuring cylinder, and the opening was covered so that air and moisture did not enter or leave. The saponin was added in such a manner that a substance containing Kiraya saponin (liquid, containing 4% of saponin) became 2500 and 3500 ppm with respect to soil. Further, 3500 ppm of oil-decomposing bacteria and 3500 ppm of Bacillus bacteria were added to a part of the saponin addition.
[0025]
Two months later, when the soil of each measuring cylinder containing blank, saponin, oil-degrading bacteria, and Bacillus bacteria was observed, the smell of the oil on the blank was more intense than at the beginning. did. On the other hand, in the others, the soil was smooth and the oily odor was less than at the beginning.
[0026]
And, very surprisingly, the oil content should have been about 2%, but increased to about 6% except for the blank. The blank also had an increased oil content. This is presumably because the oil initially impregnated and held in the micropores of the soil particles was eluted by the action of saponin and became ready for measurement. In the case of a blank, or by adding water or fertilizer, the action of the bacterial cells was improved, and as a result, it is considered that the elution of oil was caused.
[0027]
The addition ratio of the saponin-containing material in the present invention was determined based on the conventional experience of the present invention, but since the oil concentration was 2-3 times, the amount of the saponin-containing material considered to be necessary in the calculation was calculated. Will be insufficient. Therefore, in the present invention, when the oil concentration is re-measured 1 to 4 months after the addition of the saponin-containing substance, and the shortage of the saponin-containing substance is replenished, the processing is performed quickly and completely. Alternatively, about half of the initially calculated amount may be added, and the same amount of saponin-containing substance may be added several times.
[0028]
【Example】
Next, the present invention will be described in more detail based on examples.
(Example 1)
The site of a gas station (area 200 m ² ) was contaminated with petroleum products such as gasoline, kerosene, and light oil. At a contamination depth of 2-3 m, the concentration of the contaminants was 1000-3000 ppm depending on the location. Therefore, three injection holes are excavated by a boring machine at a place of 20 m ² at a place of 3000 ppm, and the processing liquid is injected by the injection machine. The treatment liquid was 3500 ppm of oil-degrading bacteria collected at the site of a gas station and grown to about 10 ⁹ / mg to 10 ¹¹ in a culture site where rice bran and quillaja saponin-containing material (liquid) were mixed. 3,500 ppm of nitrogen, 3.85 kg of nitrogen and 0.77 kg of phosphorus are dissolved in water to make the total amount 1 m ³ . 200 liters of this treatment liquid was injected into one place. With this injection, the treatment liquid permeated the soil evenly.
[0029]
As a result, the activity of the anaerobic microorganisms in the soil was promoted 4 to 5 times. Thereby, the decomposition of the hardly decomposable organic matter in the soil is promptly performed, the time required for the treatment is reduced, and the treatment cost is significantly reduced.
[0030]
(Example 2)
Similarly, select the place where the pollution depth is relatively shallow (40 cm) at the site of the gas station, and mix the bacterial cells and saponin-containing materials with rice bran as a bulking agent, along with nutrients such as nitrogen and phosphorus, to obtain a powdery purifying agent. The mixture was mixed with the soil with a stabilizer. The mixing ratio is about 10%. Then, it was left in a sprinkled state.
[0031]
【The invention's effect】
The present invention, as described in detail above, is to add saponin to soil in order to speed up the purification treatment by anaerobic bacteria, and in situ, saponin-containing substances together with nutrients such as nitrogen and phosphorus. Injection into the soil or mixing with the soil to achieve soil purification. Further, if necessary, cells grown or cultured or purified to be treated may be used together with the saponin-containing substance.
[0032]
Therefore, the processing takes longer time than when using anaerobic bacteria, but the processing is several times faster than when only anaerobic bacteria are used. In addition, it is characterized by extremely low processing costs, with only the operation of press-fitting the processing liquid and mixing of the powdery purifying agent at first.

Claims (8)

When purifying organic solvents, oils, and other hardly decomposable substances contained in soil using the activity of anaerobic or facultative anaerobic bacteria, the saponin-containing material was dissolved in water together with nutrients such as nitrogen and phosphorus. An anaerobic purification method for soil, wherein a purification liquid is injected into an appropriate portion of the soil to be purified with an injection machine. When purifying organic solvents, oils, and other hardly decomposable substances contained in soil using the activity of anaerobic or facultative anaerobic bacteria, mix saponin-containing substances with bulking agents together with nutrients such as nitrogen and phosphorus. Anaerobic purification method for soil, comprising mixing the powdered purification agent with the soil to be purified using a stirrer such as a stabilizer, and then watering the mixed portion. The soil anaerobic purification method according to claim 1 or 2, wherein a concentration of a contaminant contained in the soil to be purified is measured to determine a use concentration of the saponin-containing substance. The soil anaerobic according to claim 1 or 2, wherein the concentration of the contaminant contained in the soil to be purified is measured again after 1 to 4 months, and a saponin-containing substance is additionally added in accordance with the concentration. Purification method. The anaerobic purification method for soil according to claim 1 or 2, wherein the cells are mixed with the saponin-containing substance. The anaerobic purification method for soil according to claim 5, wherein the cells are used by multiplying cells collected from the target contaminated soil. The method for anaerobic purification of soil according to claim 5 or 6, wherein the cells are adapted to a hardly decomposable substance. The method for anaerobic purification of soil according to claim 1 or 2, wherein the saponin is Kiraya saponin.