JP3564573B2 - Biological remediation methods for contaminated soil and groundwater - Google Patents

Description

【００２１】
表２に前述の要領で作成したミクロコスムを６０日間、培養した場合の有機塩素化合物濃度を示す。表中のＴＣＡはトリクロロエタン、ＴＣＥはトリクロロエチレン、ＰＣＥはテトラクロロエチレンをそれぞれ示す。有機塩素化合物濃度はガスクロマトグラフで測定した。３種類いずれの地下水の場合においても、電子供与体を添加したミクロコスム中の有機塩素化合物濃度は、電子供与体を添加していないミクロコスムに比べて低い。これは、電子供与体の添加がミクロコスム内の微生物による有機塩素化合物の脱ハロゲン化を促進していることを示す。有機塩素化合物の還元的脱ハロゲン化が最も顕著に現れているのは，電子供与体を添加したＮｏ．３のミクロコスムである。このミクロコスムでは、初期ＴＣＥ濃度が比較的高いにも関わらず、ハロゲン呼吸による減少が顕著である。酵母エキスを電子供与体として添加したミクロコスム（Ｎｏ．３、６、９）において、底層の地下水で形成したＮｏ．３とＮｏ．６は、表層のＮｏ．９に比べて有機塩素化合物の除去効果が高いが、これは、採取した地下水の深さに起因すると考えられ（一般的に表層の地下水は、底層の地下水に比べ、化学的に酸化されている）、表層地下水の除去効率の低さは、土着微生物が地質化学的条件に順応するのに要する時間を反映している。
【００２２】
【表２】

【００２３】
【発明の効果】
本発明によれば、有機ハロゲン化合物により汚染された土壌及び地下水の修復において、電子供与体の添加により土壌・地下水を嫌気性雰囲気とし、嫌気性微生物による還元的脱ハロゲン化によって効果的な汚染の除去が実現できる。また、安価な電子供与体を選択することで、低コストの修復工事が可能となる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for biologically remediating soil or groundwater contaminated by an organohalogen compound and an additive used in the method.
[0002]
[Prior art]
At present, physical treatment methods such as pumping of contaminated groundwater, adsorption of activated carbon or resin, and volatilization and removal of air by drying the contaminated soil are considered to be effective as restoration techniques for soil and groundwater contaminated by organic halogen compounds. However, neither of these technologies has high initial capital investment and power costs and is not a fundamental measure because it is not a technology that completely detoxifies pollutants. Therefore, development of a bioremediation technology that decomposes hard-to-decompose harmful substances contained in soil or groundwater using microorganisms to remove contamination is expected.
[0003]
Bioremediation is a technology that breaks down harmful organic compounds biologically and converts them into harmless substances such as carbon dioxide, methane, water, inorganic salts, and biomass. More recently, the concept of bioremediation has been extended to techniques for repairing hazardous waste, contaminated soil and groundwater. Under such circumstances, research and development using aerobic microorganisms have been performed for bioremediation of chlorocarbon contamination in Japan.
Biostimulation is to promote the decomposition and removal of pollution by growing and activating specific aerobic microorganisms living in the pollution site, so that carbon source materials such as methane, air or pure oxygen, This is a method of supplying necessary substances such as nutrients.
Bioaugmentation, also known as a biological addition method, is a method of cultivating and activating a large number of single microorganisms with excellent resolution and injecting this together with an oxidizing agent into the basement of the contamination site to decompose and remove the contamination. It is.
[0004]
[Problems to be solved by the invention]
These methods have a problem that introduction of an oxidizing agent or a large amount of air requires a large amount of capital investment and repair cost. In addition, there is a problem that the resolution of microorganisms depends on the environment of the injected contaminated area, and there is also a problem that the capabilities of the injected microorganisms are not always sufficiently exhibited.Moreover, in order to utilize anaerobic microorganisms having the resolution of organic halogen compounds. There was a problem that means for making the restoration target area anaerobic was not considered. As described above, all of the bioremediation technologies developed so far have problems therein, and there is a need for the development of a repair technology for solving them.
[0005]
The present invention has been made in view of the above-mentioned problems in the prior art, and is capable of reproducing a remediation effect at contaminated sites nationwide and enabling low-cost remediation work to be performed on organic halogen compound-contaminated soil or contaminated groundwater. It is intended to provide a biological repair method and an additive applied thereto.
[0006]
[Means for Solving the Problems]
The biological restoration method for contaminated soil and groundwater according to the first invention of the present application is to supply a yeast extract to soil and groundwater contaminated with an organic halogen compound to activate and proliferate indigenous aerobic bacteria. It is characterized by comprising a step of setting the environment to an anaerobic atmosphere, and a step of subsequently decomposing the organic halogen compound by reductive dehalogenation using yeast extract which is also an electron donor .
[0011]
When an electron donor is added to soil or groundwater in a region contaminated with an organic halogen compound, indigenous microorganisms consume oxygen as an electron acceptor together with the electron donor, and make the soil or groundwater an anaerobic atmosphere. Thereafter, the anaerobic microorganism uses the organic halogen compound as an electron acceptor in the absence of oxygen. For example, tetrachloroethylene is converted to trichloroethylene and further to dichloroethylene by successive reductive dechlorination reactions, and is finally decomposed to a stable inorganic salt. As described above, since an organic halogen compound is used as an electron acceptor, dehalogenation is promoted if an appropriate electron donor is present. Hydrogen molecules, organic matter in soil in the natural world, and hydrocarbons for fuel may be electron donors.
[0012]
The present invention is characterized in that, when repairing an organic halogen compound-contaminated soil and groundwater, an indigenous bacterium is activated and proliferated by supplying an appropriate electron donor to make the contaminated soil and / or groundwater anaerobic. Having. The electron donor is selected from yeast waste, humic acid, organic waste from food factories, etc. based on the results of microcosm experiments, and is used to remove contamination.
[0013]
The restoration target in the present invention is soil or groundwater contaminated with an organic halogen compound. An organic halogen compound is a substance in which hydrogen of an aliphatic or aromatic hydrocarbon is substituted with a halogen (eg, fluorine or chlorine). For example, aliphatic organic chlorine compounds such as trichlorethylene (hereinafter referred to as TCE), tetrachloroethylene (same as above, PCE) and trichloroethane (same as above, TCA) correspond thereto.
[0014]
As an electron donor, sodium benzoate and the like are used, but they are expensive, and when these are used as additives, the repair cost increases. Therefore, as the electron donor, yeast extract, organic wastes from food factories, beer factories, sugar factories and the like, extracts thereof, humic acid, and the like are preferable because they are inexpensive and easily available.
[0015]
The electron donor selected in the laboratory-scale microcosm experiment is added to the contaminated area, and the soil and groundwater are made anaerobic by oxygen respiration of indigenous microorganisms. Thereafter, the anaerobic microorganism decomposes to an inorganic halogen salt by dehalogenation using an organic halogen compound as an electron acceptor to detoxify the salt and restore the polluted environment. Since microorganisms used for restoration are anaerobic, there is no need to supply an oxidizing agent or air, and the cost of restoration work is low because the electron donor itself is inexpensive.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
In the present invention, a microcosm study on a laboratory scale selects an appropriate electron donor according to the microorganisms native to the contaminated area. Microcosms are formed from soil and groundwater collected from contaminated areas. Electron donors such as yeast extract, humic acid, organic waste from food factories, beer factories, sugar factories, etc. are added to the microcosm. Soil and water are sampled periodically from microcosms to monitor the concentrations of organic halides, sulfates, nitrates, methane and inorganic halides, BOD, COD, dissolved oxygen and redox potential. Based on these results, the optimal combination of electron donors for the contaminated area to be repaired is selected.
[0017]
Electron donors are injected into the soil or groundwater to be repaired from injection wells drilled into the contaminated area. The interval between injections depends on the results of analysis of soil and groundwater samples collected from monitoring wells, but it is considered that about once a month is sufficient.
[0018]
The indigenous microorganisms use the injected electron donor to consume oxygen in the soil and groundwater, and make the soil and groundwater in the restoration target area an anaerobic atmosphere. Then, the indigenous anaerobic microorganism decomposes an organic halogen compound as an electron acceptor by reductive dehalogenation using the injected electron donor in the created anaerobic atmosphere. Decomposition of organic halogen compounds by dehalogenation of anaerobic microorganisms occurs sequentially from compounds having a high halogen number, and eventually decomposes to inorganic halogen salts.
[0019]
【Example】
An embodiment of the present invention will be described below.
Example 1
A laboratory-scale microcosm experiment was performed to verify the effect of the addition of the electron donor on the restoration of groundwater contaminated by organic halogen compounds. Microcosms were formed in ground water collected from an area contaminated with an organochlorine compound in a 500 mL glass container sterilized in advance. Groundwater was collected from the surface and two bottom layers using aseptic techniques. The collection instrument was subjected to aseptic removal of particles with a phosphorus-free detergent and washed in the order of tap water, distilled water, alcohol, chlorine bleach, and demineralized water. From the collected samples, three types of microcosms were formed: one in which indigenous bacteria were sterilized by adding 0.5 g of mercuric chloride, one in which nothing was added, and one in which yeast extract was added as an electron donor. As the yeast extract, 0.3% m / v of BACTO yeast extract (DIFCO Research Institute product code 0127) was used. BACTO is a registered trademark owned by Difco Laboratories. Mercury chloride and yeast extract were added at the time of sample collection to minimize loss due to volatilization of organochlorine compounds when opening the sample bottle. Table 1 shows the total amount of aliphatic organochlorine compounds, the oxidation-reduction potential, and the dissolved oxygen concentration in the collected groundwater. The total aliphatic organic chlorine compound concentration was measured by gas chromatography. The prepared microcosm was cultured at 20 ° C. for 60 days so that a head space was not formed. The pH was between 6.5 and 6.7 during the culture period in all microcosms. As is clear from Table 1, No. collected from groundwater in the bottom layer. The microcosms of 4 to 6 have a high total organic chlorine compound concentration, are chemically reduced and have a low oxidation-reduction potential, and have low dissolved oxygen and are anaerobic.
[0020]
[Table 1]

[0021]
Table 2 shows the organochlorine compound concentration when the microcosm prepared as described above was cultured for 60 days. In the table, TCA indicates trichloroethane, TCE indicates trichlorethylene, and PCE indicates tetrachloroethylene. The organic chlorine compound concentration was measured by gas chromatography. In any of the three types of groundwater, the concentration of the organochlorine compound in the microcosm containing the electron donor is lower than that in the microcosm containing no electron donor. This indicates that the addition of the electron donor promotes the dehalogenation of organochlorine compounds by microorganisms in the microcosm. The most remarkable occurrence of the reductive dehalogenation of the organochlorine compound was caused by the addition of an electron donor to the No. 3 compound. 3 microcosms. In this microcosm, the decrease due to halogen respiration is significant, despite the relatively high initial TCE concentration. In microcosms (Nos. 3, 6, and 9) to which yeast extract was added as an electron donor, No. 3 formed in groundwater in the bottom layer. 3 and No. No. 6 is No. of the surface layer. Although the removal effect of organochlorine compounds is higher than that of No. 9, it is thought that this is due to the depth of the collected groundwater (generally, surface groundwater is chemically oxidized compared to bottom groundwater). ) The low efficiency of surface groundwater removal reflects the time it takes for indigenous microorganisms to adapt to geochemical conditions.
[0022]
[Table 2]

[0023]
【The invention's effect】
According to the present invention, in the restoration of soil and groundwater contaminated by an organic halogen compound, the soil and groundwater are converted to an anaerobic atmosphere by the addition of an electron donor, and the effective contamination is reduced by reductive dehalogenation by anaerobic microorganisms. Removal can be realized. In addition, by selecting an inexpensive electron donor, low-cost restoration work becomes possible.

Claims (1)

The soil or ground water contaminated with organohalogen compounds supplying yeast extract, a step of the soil and groundwater environment anaerobic atmosphere by activity and proliferation of the indigenous aerobic bacteria, a yeast extract is also the subsequent electron donor Using a reductive dehalogenation to decompose an organic halogen compound .