Compositions: coating or plastic – Coating or plastic compositions – Contains fireproofing or biocidal agent
Reexamination Certificate
1999-03-12
2001-05-01
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Contains fireproofing or biocidal agent
C106S727000, C106S808000, C106S823000, C424S617000, C514S185000
Reexamination Certificate
active
06224658
ABSTRACT:
FIELD OF ART
The present invention relates to a
Thiobacillus thiooxidans
growth inhibitor, a cement composition and a cement structure containing such growth inhibitor. In particular, the present invention relates to a growth inhibitor, a cement composition, and a cement structure which are capable of effectively inhibiting growth of
Thiobacillus thiooxidans
in its habitat, which can be used without causing environmental pollution even under acidic conditions, and which can be used for preventing deterioration of cement structures including a variety of concrete structures such as those in sewage treatment facilities, mortar structures, or concrete sewers that are brought into contact with sewage water.
BACKGROUND OF THE INVENTION
Cement structures such as concrete and mortar structures in sewage treatment facilities and the like conventionally have problems of becoming gypseous and deteriorated. This deterioration is ascribable to sulfur-oxidizing bacteria of the genus Thiobacillus that oxidize hydrogen sulfide to produce sulfuric acid. These bacteria usually live widely in soil or water, and grow by oxidation of sulfur compounds and assimilation of carbon dioxide. Some species of the sulfur-oxidizing bacteria of the genus Thiobacillus live in structures in contact with sewage water, yet some species of the bacteria live in structures exposed to the air and not in contact with sewage water in the sewage treatment facilities.
For preventing deterioration of such structures, various methods have hitherto been proposed. At present, practically employed methods include coating the structures with corrosion resisting materials. However, the coatings of the corrosion resisting materials are easily damaged from pinholes or scratches, and thus have problems in durability. In addition, it is difficult to coat the parts having complex configurations and fine parts such as joints of small-diameter tubes.
It is known that heavy metal ions could kill the sulfur-oxidizing bacteria of the genus Thiobacillus. Such bactericidal action is exhibited by direct action of heavy metal ions on the bacteria. Since heavy metals are dissolved and released in an ionized state, a large amount of heavy metals are required for achieving the bactericidal action. Released ions of some kinds of heavy metals have seriously harmful effect on environment, so that such metals cannot be used in sewage treatment facilities.
To overcome these problems, there is proposed and practiced a method for preventing deterioration of cement structures induced by sulfur-oxidizing bacteria of the genus Thiobacillus, wherein particular metals or metal oxides that are insoluble in water but soluble in sulfuric acid, such as nickel, are added to structures such as those of concrete (JP-A-4-149053). This method is excellent in that the particular metals completely prevent the sulfur-oxidizing activity, respiration, and carbon dioxide-fixation activity of the sulfur-oxidizing bacteria in the neutral pH range, resulting in sufficient prevention of deterioration of cement structures induced by sulfur-oxidizing bacteria.
However, inhibitory activities of nickel or its oxides against the bacteria of the genus Thiobacillus decrease toward the acidic pH range, and hardly exhibited at pH 3 or below. Therefore, the inhibitory activity of such metals can be maintained sufficiently in the area usually in contact with sewage water where the pH value is kept near neutrality, but hardly exhibited in acidic area not in direct contact with sewage water, or when sewage water is transiently acidified. In addition, when the metals that are insoluble in water but soluble in sulfuric acid, such as nickel, are exposed to strong acid, such metals are dissolved and released as metal ions, thus being unpreferable in the environmental point of view. The release of the metal ions also reduces the volume of the inhibitor itself, causing difficulty in maintaining the inhibitory activity against the bacteria of the genus Thiobacillus for a prolonged period of time.
Metals having inhibitory activities against the bacteria of the genus Thiobacillus other than nickel have also been under research. For example, it is known that a mixture of molybdenum, ammonium molybdate, or ammonium molybdate and tungsten activates growth of
Thiobacillus novellus,
whereas tungsten, when used alone, inhibits growth of the same bacteria (Journal of Bacteriology, Vol. 153, No. 2 (1983) William M. et al. “Sulfite Oxidase Activity in
Thiobacillus novellus”
p.941-944). It is also reported that molybdenum (Mo
4+
), which is known to activate growth of the above-mentioned
Thiobacillus novellus,
inhibits growth of
Thiobacillus thiooxidans
(Chemical Abstracts, Vol. 95, No. 1 (Jul. 6, 1981) p127 (1081a)).
Thus, even the sulfur-oxidizing bacteria of the same genus of Thiobacillus have different growth inhibitory mechanism. Therefore, even if a certain growth inhibitor is demonstrated to have an effect on
Thiobacillus novellus
viable in the neutral pH range of 6 to 8, such an inhibitor will not be used in the acidic pH range of 2 to 6, where
Thiobacillus novellus
is hardly viable. Further, it is not believed that a substance that inhibits growth of
Thiobacillus novellus
equally inhibits growth of
Thiobacillus thiooxidans
viable in the pH range of 2 to 6. Recent researches therefore indicate that the growth inhibitors proposed hitherto are not effective to all species of the sulfur-oxidizing bacteria of the genus Thiobacillus.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a
Thiobacillus thiooxidans
growth inhibitor which is capable of inhibiting effectively growth of
Thiobacillus thiooxidans
not only in the neutral pH range but also in the acidic pH range of 4 or below for a prolonged period of time.
It is another object of the present invention to provide a
Thiobacillus thiooxidans
growth inhibitor which can be added to a concrete material containing cement, water, and aggregates, or to a mortar material, and easily dispersed therein by mixing.
It is yet another object of the present invention to provide the growth inhibitor which can be used as a material for a cement structure to effectively prevent deterioration thereof induced by
Thiobacillus thiooxidans,
and which has excellent dispersibility when mixed in a ready-mixed concrete.
It is still another object of the present invention to provide a cement structure such as those of concrete or mortar that is effectively prevented from undergoing deterioration induced by
Thiobacillus thiooxidans
for a prolonged period of time even, for example, in sewage treatment facilities or in potentially acidic areas, and a cement composition that facilitates preparation of such cement structure.
The present inventors have confirmed that the conventional growth inhibitors for sulfur-oxidizing bacteria of the genus Thiobacillus containing nickel as an active component are capable of fully exhibiting their effect in cement structures that are maintained in the neutral pH range by, for example, direct contact with sewage water. The inventors have, however, also confirmed that such nickel-containing growth inhibitors exhibit decreased or almost no growth inhibitory activity particularly against
Thiobacillus thiooxidans
when the structure is in proximity to sewage treatment facilities, and the structure surface is not in direct contact with sewage water and kept in the acidic pH range of 4 or below by the action of hydrogen sulfide in the atmosphere.
The reason for the difference in the growth inhibitory effect on the same bacteria depending on the pH in the environment is not known. However, the conventional nickel-containing growth inhibitors do not act directly on the bacteria per se, but bind to the enzymes of the bacteria to exhibit the growth inhibitory activity. It is believed that the inhibitors do not bind to the enzymes sufficiently in the acidic pH range, resulting in lowered growth inhibitory activity. In view of the above, the inventors have made intensive studies searching for
Enokida Toshio
Maeda Terunobu
Negishi Atsunori
Tanaka Reiko
Uchida Hiromi
Darby & Darby
Green Anthony
Hazama Corporation
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