Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Destruction of hazardous or toxic waste
Reexamination Certificate
2001-07-09
2004-12-07
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Destruction of hazardous or toxic waste
C435S262000, C210S610000, C210S757000
Reexamination Certificate
active
06828141
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for purifying matter such as soil, sediment, sludge and water contaminated with halogenated organic compounds, particularly a chlorinated organic compound. The present invention particularly relates to a method for purifying contaminated matter by reductive dehalogenation combining a chemical reaction with a biological reaction, thereby decomposing the halogenated organic compound.
RELATED ART
Recently, halogenated organic compounds such as tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, and dichloroethylene are wide used as a degreasing agent for electronic components and mechanical metal components and a cleaning agent for dry cleaning. Halogenated organic compounds are contaminants in soil and ground water. These halogenated organic compounds do not readily decompose in the natural world and are hardly soluble in water, and therefore tend to accumulate in soil and to penetrate into ground water. Moreover, halogenated organic compounds are known to induce hepatic disorders and cancer. Therefore, it is desirable to decompose halogenated organic compounds such as chlorinated organic compounds in soil and so on.
In these days, bioremediation has been receiving attention to purify soil, ground water and so on contaminated with halogenated organic compounds. Bioremediation is safe and has improved costs to effects. However, the bioremediation requires a long period of time to be effective and there are limits on the kinds and concentrations of substances that can be decomposed. Therefore, we may not necessarily be satisfied with the bioremediation
The bioremediation includes aerobic decomposition of trichloroethylene with methane assimilating microorganism, toluene/phenol decomposing microorganism, ammonia oxidizing microorganism and alkene assimilating microorganism, and there are numerous reports on the aerobic decomposition. However, the aerobic decomposition has disadvantages as follows: decomposition reactions are unstable; the range of substances able to be decomposed is very limited; and highly chlorinated compounds such as tetrachloroethylene and carbon tetrachloride cannot be decomposed.
On the other hand, many anaerobic microorganisms have specificity to decompose a wide range of highly chlorinated compounds such as tetrachloroethylene, trichloroethylene, carbon tetrachloride and so on. However, the anaerobic microorganisms have disadvantages in that growth thereof is very slow; and anaerobic microorganisms produce and thus accumulate strongly toxic intermediate metabolites in the process of the anaerobic decomposition (see H. Uchiyama and S. Yagi; Bioscience and industry, Vol. 52, No. 11, pp. 879-884, 1994).
On the other hand, it has been reported that halogenated organic compounds can be decomposed by chemical reactions, and reductive treatment of chlorinated organic compounds with metallic iron has been disclosed (see T. Senzaki; Treatment of Ground Water Contaminated with Chlorinated Organic Compounds—treatment technique with activated carbon carrying metal iron at low temperatures; “PPM” Vol. 26, No. 5, pp. 64-70, 1995). In view of the foregoing, the present inventors tried dechlorination tests wherein metallic iron is added to soil in the absence of a carbon source for a microorganism. However, under conditions that microorganism is not cultivated and particularly conditions that a reductive atmosphere and a neutral condition are not maintained, the present inventors did not observe any dechlorination reaction. Moreover, the addition of an iron salt such as FeCl
2
, FeCl
3
and FeSO
4
instead of the metallic iron did not produce the dechlorination reaction, either.
It has been reported that metallic iron and high-pressure air can be injected into soil for reacting iron powder with halogenated organic compounds in the soil to convert into inorganic compounds, thereby detoxifying the same (see Japanese Patent Application Laid Open No. 8-257570). However, the method has disadvantages concerning equipment for injecting air and there is a chance that the halogenated organic compounds may diffuse. Moreover, the use of high-pressure air increases costs, and therefore is not practical.
It has been reported that chlorinated organic compounds contaminating soil and ground water can be removed by combining a natural compound having catalytic activity for dehalogenation with microorganism treatment (see “Nikkei Biotech” published by Nikkei BP Inc., Oct. 7, 1996, No. 361, pp. 14-15). However, the document does not disclose specific natural compounds and the microorganism at all.
U.S. Pat. No. 5,411,664 discloses a method for decomposing halogenated organic compounds by adding fibrous organic matter and multivalent metal particles to a contaminated matter. However, the U.S. patent does not disclose a reducing agent such as reduced iron, cast iron, alloy, a water soluble reducing agent and so on. Moreover, the U.S. patent does not disclose maintaining the contaminated matter in a reductive atmosphere or a specific pH subsequent to adding the reducing agent.
Moreover, depending on the composition of a nutritional source added, biological reductive reactions such as sulfate reduction and methane fermentation may occur, and sulfur-containing noxious gases such as hydrogen sulfide and mercaptan are produced and a combustible gas such as a methane gas may be generated. Moreover, the production of iron sulfide may change color of soil into black. A reaction of metallic powder and water may produce a combustible hydrogen gas.
In a laboratory scale, it is easy to homogeneously mix a reducing agent and a nutritional source with a contaminated matter. However, in order to purify contaminated matter such as soil, in reality, a large amount of reducing agent and the nutritional source would be required, which may warrant engineering works. Moreover, it is not easy to homogeneously mix the contaminated matter in such a large scale. Furthermore, it is expected that mixing conditions may affect a decomposition rate of halogenated organic compounds. Particularly, a special technique is required to purify the contaminated matter having a volume of not less than 1 m
3
and particularly not less than 10 m
3
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for purifying matter contaminated with a halogenated organic compound by combining chemical reaction with a biological reaction, thereby decomposing the halogenated organic compound.
The first aspect of the present invention has an object of decomposing the halogenated organic compounds by reductive dehalogenation reaction.
The second aspect of the present invention has an object of decomposing the halogenated organic compounds by a chemical dehalogenation reaction.
The third aspect of the present invention has an object of preventing the generation of sulfur-containing noxious gas and combustible gas as well as the excessive decoloration of contaminated matter such as soil, which may occur as a result of by-products of the reductive dehalogenation reaction.
The fourth aspect of the present invention has an object of mixing the reducing agent and the nutritional source with the contaminated matter when the contaminated matter has a large volume.
The first aspect of the present invention is characterized by adding a prescribed reducing agent, thereby promoting the reductive dehalogenation reaction.
The second aspect of the present invention is characterized by adding a prescribed reducing agent, thereby promoting the chemical reductive dehalogenation reaction. Contrary to the first aspect of the present invention, the second aspect need not involve the use of a biological reaction. Use of the prescribed reducing agent allows to decompose halogenated organic compounds solely by chemical reactions.
In the third aspect of the present invention, a nutritional source containing an organic carbon and 20 to 50 percent by weight, based on the organic carbon, of an oxidized form of nitrogen is used so as to change a group of microorganis
Kataoka Naoaki
Kitajima Nobumitsu
Seki Naoki
Shimomura Tatsuo
Shinmura Hiroshi
Beisner William H.
Ebara Corporation
Wenderoth Lind & Ponack LLP
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