Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2001-07-19
2004-01-20
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S757000, C210S170050
Reexamination Certificate
active
06679992
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a purification method and a purification apparatus capable of effectively purifying a contaminated object containing halogenated organic compounds. More particularly, the invention relates to a purification method and a purification apparatus capable of purifying a contaminated object containing chlorinated organic compounds, such as soil, sediment, sludge, or water, e.g., interstitial water of sludge or groundwater, by a chemical reaction or a reductive dehalogenation reaction comprising a combination of a chemical reaction and a biological reaction, to degrade the halogenated organic compounds efficiently.
RELATED ART
The entire disclosure of an international application PCT/JP/98/00363, filed with the Japanese Patent Office on Jan. 29, 1998, entitled “A Method for Purifying Object Contaminated with Halogenated Organic Compounds,” is cited in the present patent application.
In recent years, there have been one report after another on contamination of soil and groundwater with halogenated organic compounds, such as tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, and dichloroethylene, which are widely used as degreasing agents for metal components of electronic equipment, and cleaning agents for dry cleaning. Recently, in particular, attention has been attracted to contamination with dioxins discharged from incineration facilities, PCB, etc. These halogenated organic compounds are not easily degraded in the natural world, and sparingly soluble in water. Thus, they tend to be accumulated in the soil and penetrated into groundwater in the contaminated area. The halogenated organic compounds are also known to cause hepatic damage and have carcinogenicity. It is desired, therefore, that halogenated organic compounds, such as chlorinated organic compounds, contained in the soil, etc. be degraded and rendered harmless.
Recently, bioremediation has attracted attention as a method of purifying soil, groundwater, etc. contaminated with halogenated organic compounds. The bioremediation method is highly cost-effective and has high safety. Bioremediation, however, has the problems that treatment requires a long time, and the types and concentrations of substances which can be degraded are restricted, as will be described below.
Aerobic degradation of trichloroethylene by methane assimilating organisms, toluene or phenol degrading organisms, ammonia oxidizing bacteria, or alkene assimilating organisms is known as an example of bioremediation. However, this method has the following drawbacks: 1) Degradation reaction is unstable. 2) The scope of substances to be degraded is very narrow. 3) It has no degrading action on highly chlorinated substances such as tetrachloroethylene and carbon tetrachloride.
Many anaerobic microorganisms, on the other hand, can degrade highly chlorinated organic compounds, such as tetrachloroethylene, trichloroethylene, and carbon tetrachloride, and have a broad range of applications. However, they are defective, for example, in that 1) growth of the microorganisms is very slow, and 2) strongly toxic intermediary metabolites are formed and accumulated during the anaerobic degradation process (Uchiyama HIROO and Yagi OSAMI, Bioscience and Industry, 1994, Vol. 52, No. 11, 879-884).
As a technique for decomposing halogenated organic compounds by a chemical reaction, reductive treatment of chlorinated organic compounds with metallic iron has been reported (Yazaki TETSUO, Treatment of Organochlorine Compound Contaminated Groundwater—Technology for Treatment at Low Temperatures with Metallic Iron Deposited Activated Carbon, “PPM”, 1995, Vol. 26, No. 5, 64-70). Thus, the inventor of the present invention attempted to conduct dechlorination experiments by adding metallic iron into the soil in the absence of a carbon source for microorganisms. However, no dechlorination reaction was observed under conditions under which no microorganisms were cultured, particularly when a reductive atmosphere and neutral conditions were not maintained. Nor was any dechlorination reaction noted when an iron salt, such as FeCl
2
, FeCl
3
or FeSO
4
, was added instead of metallic iron.
Furthermore, there is a report of a method for treating halogenated organic compounds to become harmless, which comprises injecting metallic iron and high pressure air into contaminated soil to react the halogenated organic compounds with an iron powder to make it inorganic (Japanese Unexamined Patent Publication No. 1996-257570). This method involves a problem about air injection facilities, and a risk of vaporization of the halogenated organic compounds. The method is also impractical, since the use of high pressure air causes the problem of cost.
There is also a report of a method for removing organochlorine compounds, which have contaminated soil or groundwater, by combining a natural substance having a dehalogenation catalytic action and bioremediation (“Nikkei Biotech” (Nikkei BP), published Oct. 7, 1996, No. 361, 14-15). However, this report is silent on concrete natural substances and microorganisms.
U.S. Pat. No. 5,411,664 describes a method for degradation of halogenated organic compounds by addition of a fibrous organic material and polyvalent metal particles, e.g., iron, to a contaminated object. However, this U.S. patent does not describe a reducing agent, such as reduced iron, cast iron, an alloy, or a water-soluble reducing agent. Nor does this patent describe that the contaminated object is held in a reducing atmosphere after addition of a reducing agent.
In the laboratory, it is easy to mix a reducing agent, a nutrient source, and a contaminated object uniformly. To purify a contaminated object, such as soil, actually in situ, on the other hand, large amounts of a reducing agent and a nutrient source are mixed, thus requiring construction work. Moreover, uniform mixing is not necessarily easy. In addition, the conditions during kneading may affect the degradation ratio of halogenated organic compounds. To purify a contaminated object of a volume of 1 m
3
or more, particularly, a volume of 10 m
3
or more, an ingenious idea is needed for the kneading method.
Besides, to purify a contaminated object, such as soil, in situ, it has been common practice to perform a small amount of pumping downstream from a contaminated aquifer, apply purification treatment for the contaminated object to the pumped groundwater, then dissolve a nutrient source for microorganisms, which degrade the contaminant, in the treated groundwater, and inject the groundwater again into an upstream unsaturated soil or aquifer. With this method, however, the pumped contaminated water cannot be reinjected unless it is purified below the concentration complying with the ban on the permeation of effluent into the ground. Thus, it is necessary to install purification facilities on the ground, posing the problem of an increased cost. Also, the injected normal water brings about a phenomenon of a detour formed in the flow of the contaminated groundwater. This phenomenon poses the problem that the injected nutrient source does not thoroughly mix with the groundwater.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a contaminated object purification method and purification apparatus which can efficiently and easily purify a contaminated object containing halogenated organic compounds. Particularly, its object is to provide a purification method and a purification apparatus which can efficiently and easily purify a contaminated object containing halogenated organic compounds, especially soil and groundwater, in situ.
According to one aspect of the present invention, water is circulated so as to pass through the contaminated object, for example, the contaminated object in the soil. According to another aspect of the present invention, circulation of water in this manner is not required.
According to an aspect of the present invention, there is provided a purification method for purifying a contaminated object containing
Kitagawa Masayoshi
Oya Shunji
Shimomura Tatsuo
Barry Chester T.
Ebara Corporation
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