Restoring soil and preventing contamination of ground water

Details Restoring soil and preventing contamination of ground water Restoring soil and preventing contamination of ground water

2001-04-20

2003-05-27

Barry, Chester T. (Department: 1724)

Liquid purification or separation

Processes

Treatment by living organism

C210S747300, C435S174000, C435S262500, C435S289100

Reexamination Certificate

active

06569333

ABSTRACT:

TECHNICAL FIELD
The present invention relates to technology for restoring soil and preventing contamination of ground water by decomposing organic compounds by decomposing microorganisms in, for example, soil that has been contaminated by organic compounds such as agricultural chemicals. In particular, the present invention relates to technology for rapidly and efficiently accumulating and isolating only those decomposing microorganisms of a species that is capable of decomposing poorly degradable organic contaminants contained in soil, and to technology for restoring contaminated soil and preventing contamination of ground water by applying a retentive carrier for decomposing microorganisms that has accumulated those isolated decomposing microorganisms directly to contaminated soil.
BACKGOROUND ART
The restoration of soil contaminated by organic compounds such as agricultural chemicals by decomposing microorganisms along with the prevention of ground water contamination caused by those organic compounds has conventionally been considered to be a useful technology. For example, if decomposing microorganisms that decompose or detoxify organic compounds such as agricultural chemicals are present among microorganisms that thrive in soil, and the capabilities of these decomposing microorganisms is utilized, contaminants such as agricultural chemicals can be removed from soil.
However, in the natural state, due to the low density of decomposing microorganisms having the ability to decompose specific organic compounds, it has not been possible to effectively prevent the retention or diffusion of contaminants in the environment.
Consequently, if it were possible to accumulate only decomposing microorganisms able to decompose specific organic compounds at a higher density and in a state in which they possess decomposing activity, it would be possible to effectively realize restoration of contaminated soil and prevention of ground water contamination.
However, in the case of methods for culturing decomposing microorganisms carried out in the prior art, such as a method in which only a specific decomposing microorganism is inoculated into and grown in a liquid medium or solid medium that only uses a specific organic compound for its carbon source and nitrogen source, although only a specific decomposing microorganism can be cultured at high density, even if only that cultured decomposing microorganism is applied directly to an environment such as contaminated soil, that cultured decomposing microorganism hardly ever demonstrates its decomposing activity in a stable manner for a long period of time.
This is because, in the case of directly applying only a specific decomposing microorganism to contaminated soil, as a result of being subjected to the physiochemical properties of the contaminated soil, being preyed on by the large numbers of Protozoa and other organisms that thrive in the contaminated soil, or being unable to acquire a niche due to competition with other microorganisms, that specific decomposing microorganism is destroyed. In addition, this is also because, if the target organic compound to serve as the nutrient source (carbon source and nitrogen source) of a specific decomposing microorganism is adsorbed into a soil solid phase and is in a state that cannot be supplied to the specific decomposing microorganism, namely if it is in a state of low bioavailability, the decomposing activity of that specific decomposing microorganism cannot be demonstrated and maintained.
DISCLOSURE OF THE INVENTION
In consideration of these circumstances, the object of the present invention is to provide a technology for rapidly and efficiently accumulating a decomposing microorganism of a species that is capable of decomposing a specific organic compound in a state in which that decomposing activity is demonstrated in a stable manner for a long period of time, and for restoring contaminated soil and preventing contamination of ground water by using a decomposing microorganism retentive carrier that has accumulated that decomposing microorganism to decompose organic compounds present in contaminated soil.
The present invention is based on new findings obtained from research on an improved soil perfusion method previously proposed by the inventors of the present invention (Japanese Patent Application No. Hei 9-30176). The improved soil perfusion method proposed by the inventors of the present invention refers to using a porous material, which together with having a function that adsorbs a specific organic compound, also has a countless number of pores in a state that facilitates habitation by decomposing microorganisms having the ability to decompose that organic compound, to form an accumulation soil layer composed of this porous material and soil in which said decomposing microorganisms thrive, followed by continuously perfusing an inorganic salt medium having only the target organic compound for its carbon source and nitrogen source through this accumulation soil layer, thereby rapidly accumulating decomposing microorganisms in said porous material.
As a result, the inventors of the present invention considerably improved the accumulation and isolation rates of decomposing microorganisms to an extent that was unable to be realized with the soil perfusion method of the prior art. In other words, in this improved soil perfusion method, the porous material efficiently adsorbs carbon and nitrogen sources contained in the inorganic salt medium, namely the organic compound that is contaminating the soil, and due to the favorable conditions imparted by its pores, decomposing microorganisms grow and function actively by using the adsorbed organic compound as a nutrient source (carbon source and nitrogen source). As a result of effectively combining these factors, organic compounds that have been efficiently adsorbed into the pores are efficiently assimilated and decomposed by decomposing microorganisms within the pores, thereby realizing their rapid accumulation.
Decomposing microorganisms that accumulate in the porous material according to this improved soil perfusion method are in a state in which decomposing microorganisms of a species that has the ability to decompose a specific organic compound are selectively accumulated. However, the decomposing microorganisms that have accumulated in the porous material are actually in the state of a mixture with several species of bacteria not directly involved in decomposition.
Therefore, the inventors of the present invention attempted to apply the above improved soil perfusion method in order to accumulate only decomposing microorganisms of a species that is capable of decomposing a specific organic compound in a purified state. More specifically, according to the above improved perfusion method, a porous material that had accumulated a specific decomposing microorganism was first used as the inoculation source to inoculate a fresh porous material (in which decomposing microorganisms had not yet been accumulated) in a state of being mixed with several species of bacteria not directly involved in decomposition. By then perfusing an inorganic salt medium having for its carbon source and nitrogen source only the organic compound that serves as the nutrient source of that specific decomposing microorganism, only the specific decomposing microorganism was purified and accumulated in the fresh porous material.
Although it is possible that the decomposing microorganism accumulated in the porous material following the above purification is a single species of decomposing microorganism, since normally two to three species of decomposing microorganisms are present, in order to accumulate only those decomposing microorganisms that decompose a specific organic compound, the porous material in which decomposing microorganisms are accumulated following purification was crushed, mixed dilutions of the crushed porous material were prepared using phosphate buffer as diluent, those mixed dilutions were plated onto inorganic salt agar media that uses only the specific orga

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