JP3020145B2 - Methods for treating mercury contaminants and microorganisms particularly useful therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating mercury in sediment or soil contaminated with mercury and a microorganism useful for the method. In the present invention, mercury-decomposing bacteria capable of converting mercury compounds into volatile mercury vapor are used, and mercury sulfide (HgS) and divalent mercury present in the bottom of Minamata Bay and mercury-contaminated soil contaminated with mercury are used. Ion (Hg
²⁺ ), and a new mercury treatment method capable of simultaneously removing mercury compounds such as methylmercury (CH ₃ Hg ⁺ ).

[0002]

2. Description of the Related Art In recent years, environmental pollution due to the emission of mercury from the chemical industry has caused Minamata disease, which has become a major social problem. Mercury is currently used in industrial products such as batteries, thermometers, fluorescent lamps and amalgams used in dentistry, and is eventually concentrated in sludge at sewage treatment plants. Also, Brazil,
In many world countries, such as China, Iraq, Tanzania,
Mercury pollution to the environment has become serious at various business sites and gold mining sites. Furthermore, as a result of the use of mercury as a pesticide and the like, in many countries, contamination with organic mercury such as methylmercury and phenylmercury acetate has also become a problem. Sediment and soil contaminated with mercury are treated by physical treatment methods such as dredging, containment, and overheating.
These methods are not fundamental solutions because they are expensive and do not remove mercury. On the other hand, in an environment contaminated with mercury, bacteria that convert and decompose various mercury compounds into volatile mercury vapor inhabit. A method for removing divalent mercury using these bacteria has been proposed, but most of the mercury in the environment exists as insoluble mercury sulfide, and bacteria capable of decomposing this mercury sulfide have been discovered. Therefore, these methods cannot be applied to the treatment of mercury-contaminated sediment in the environment.

[0003]

As described above, at present, there is no method of fundamentally treating mercury in a large amount of sediment or soil, and there is no technology using microorganisms. , Because it exists as insoluble mercury sulfide,
Bacteria cannot be used directly to treat mercury sulfide, and most known mercury-degrading bacteria are
It can only decompose mercury compounds of high valency and cannot decompose organic mercury compounds such as methylmercury and phenylmercury acetate.

[0004] Under the circumstances, the present invention provides a method for effectively treating mercury contaminants such as sediment and soil containing mercury using microorganisms, and provides a particularly useful microorganism therefor. It is the purpose.

[0005]

Means for Solving the Problems As a result of diligent studies, the present inventor has found that in treating mercury contaminants using microorganisms, mercury in the contaminants is converted to Hg ²⁺ and thiol compounds are present. The present inventors have found that it is effective to perform the treatment, and found a microorganism that is particularly useful for the treatment method, leading to the present invention.

That is, the present invention relates to (1) a method for treating mercury contaminants, in which insoluble inorganic mercury compounds in mercury contaminants are oxidized under acidic conditions, converted to Hg ²⁺ , and then thiol after pH adjustment. compound and in the presence of a mercury reducing microorganisms by reducing Hg ²⁺ treatment of mercury contaminants and converting punished <br/> sense to mercury vapor, (2) reducing mercury microorganisms Shudoaru Telomonas (P
(3) The method for treating a mercury contaminant according to (1), which is a microorganism belonging to the genus pseudoalteromonas; (3) The method for treating a mercury contaminant according to (1) or (2), wherein the mercury contaminant is a mercury-contaminated soil or sediment. (4) The method for treating mercury contaminants according to any one of (1) to (3), wherein the thiol compound is a thioglycolate salt, (5) Mercury-reducing pseudo-Alteromonas M-1 ( Biotechnology Industrial Technology Research Institute accession number FERM P-1604
9).

In the sediment and the like, most of the mercury contained therein exists as insoluble mercury sulfide. In the present invention, when the mercury contaminant contains mercury sulfide,
It is important to oxidize this under acidic conditions to convert it to water-soluble divalent mercury ions. In this case, hydrochloric acid is preferable as an acid to be used, and ferric chloride is preferable as an oxidizing agent. By converting mercury sulfide into water-soluble divalent mercury ions in this way, it becomes possible to convert and remove mercury sulfide in the environment as mercury vapor using microorganisms.

Sulfuric acid and nitric acid may be used as the acid used in the above-mentioned method of converting mercury sulfide to Hg ²⁺ conversion. However, these acids are too strong to coexist with a neutralized substance produced by the microorganism treatment at a later stage. Adversely affect As the oxidizing agent, there are Ag ⁺ , Cu ⁺ , Cd ^2+, etc. in addition to Fe ³⁺ , but the use of these is also not preferable because the subsequent microbial treatment does not proceed.

The present invention is also effective for removing not only inorganic mercury compounds but also organic mercury compounds such as methylmercury and phenylmercury acetate.

As the microorganism used in the method for treating mercury of the present invention, any known bacteria that can reduce Hg ²⁺ and convert it into mercury vapor can be used. These bacteria can be collected and isolated from, for example, sediment in Minamata Bay by methods well known to those skilled in the art. However, sodium chloride generated at the time of pH adjustment hinders the reaction of converting Hg ²⁺ into mercury and volatilizing and removing it from many bacteria. Therefore, it is preferable to use a new bacterium of the present invention which requires sodium chloride for the mercury volatilization reaction. This new bacterium is Pseudoalteromonas (Pseudoalteromonas) belonging to the genus Pseudoalteromonas, and is already a FERM P-160 strain at the National Institute of Biotechnology and Industrial Technology.
Deposited as No. 49.

The fungus according to the present invention was collected, cultured and isolated as follows.

In October 1985, from the seawater of Minamata Bay,
30 ° C. on a ZoBell 2216E agar medium containing mercuric chloride (HgCl ₂ ) at a rate of 50 μg / ml.
After aerobic culture for 4 hours, colonies were formed and isolated.

ZoBell 2216E medium is prepared by adding 30 g of NaCl, 0.7 KCl to 1 liter of distilled water.
g, MgCl ₂ .6H ₂ O 10.8 g, MgSO ₄ .7
_{H 2 O5.4g, CaCl 2 · 2H} 2 O 1g, containing yeast extract 1g and peptone 5 g, pH is are adjusted to 7.6.

Next, the morphological characteristics and mycological characteristics of the fungus of the present invention will be described.

Gram-negative rods Growth temperature (ZoBell 2216E) Growth from 10 ° C. to 37 ° C., growth not possible at 45 ° C. Yellowish orange pigment production in catalase + oxidase + DNase medium Indole production Acid from glucose arginine de hydrolase, urease - gelatin hydrolyzate mannose, mannitol, N-acetyl-gluco the amine decomposition cytochrome oxidase + amylase - DNase + arginine, lysine, ornithine decarboxylase - the nature of the above, the bacteria of the present invention Pseudoalte
Probably the closest to Romanas halopranktis . However, Pseudoalteromon
The bacteria of the present invention are clearly distinguishable in that nitrate is not available to the bacteria of the present invention, whereas ashalopranktis is able to utilize nitrate.

In addition, the bacterium of the present invention can decompose mercuric chloride, methylmercury chloride, ethylmercury chloride, phenylmercuric acetate, thimerosal, mercury parachlorobenzoate, and mercury fluorescein acetate and convert them to mercury vapor. it can. The minimum inhibitory concentrations for mercuric chloride and methylmercury chloride were 50 μg / ml and 0.5 μg / ml at 30 ° C. for 24 hours in a ZoBell 2216E liquid medium.
g. NaCl resistance can be developed in peptone water containing 1% to 7% NaCl, and cannot be developed without NaCl.

As already mentioned, in the present invention,
By adding hydrochloric acid and ferric chloride to soil and sediment contaminated with mercury, the contained inorganic mercury such as mercury sulfide is oxidized and eluted as divalent mercury ions. It is intended to treat mercury contaminants by converting them into air and releasing them into the air.

In the present invention, in particular, when the above-mentioned new bacteria are used, since the organic mercury compound can be directly decomposed and reduced to mercury vapor, the above-mentioned pretreatment necessary for the insoluble inorganic compound is required. Is basically unnecessary. However, when these are mixed, by performing the above pretreatment, inorganic mercury and organic mercury can be treated simultaneously, which is more effective. In addition, the pretreatment can elute the organic mercury adsorbed in the soil and sediment, and promotes the reduction reaction. Therefore, the pretreatment is also effective from this point.

In the present invention, the treatment is carried out in the presence of a thiol compound in order to promote the mercury volatilization reaction. As such a thiol compound, for example, sodium thioglycolate, cysteine, mercaptoethanol and the like are preferable.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the following examples.

Example of Pretreatment 0.5 g of Minamata Bay sediment was placed in a 100 ml Erlenmeyer flask, 100 ml of hydrochloric acid was added at each concentration, and iron chloride (F) was added thereto.
(eCl ₃ .6H ₂ O) was added and left at room temperature for 24 hours to elute mercury from the bottom. On the next day, 50 ml of distilled water was added to the Erlenmeyer flask to wash the sediment, and a mouthpiece (No.
Filtered in 1). The sediment was dried overnight at room temperature, and the amount of mercury in the sediment was measured with an atomic absorption spectrophotometer. Table 1 shows the results of the elution of mercury from the sediment with each concentration of hydrochloric acid.

[0022]

[Table 1]

EXAMPLE 1 A 200 ml Erlenmeyer flask was charged with 20 g of Minamata Bay sediment, 100 ml of 3N HCl was added, and iron chloride (Fe) was added thereto.
2 g of Cl ₃ .6H ₂ O) is added and left at room temperature for 24 hours to elute mercury from the bottom. The next day, the supernatant was collected with a Komagome pipette. 5 ml of this solution was placed in a 50 ml impinger, and about 5 ml of 3N NaOH was added to adjust the pH to 7.0. In this solution, a 1 M phosphate buffer (pH 7.0) containing 1 mM sodium thioglycolate was added.
30) was added to prepare a volatile reaction solution. Pseu
doortelomonas M-1 strain at 10 μg / m
After culturing for 17 hours at 30 ° C. in a ZoBell2216E artificial seawater medium containing 1 l of mercuric chloride, the mixture was collected by a centrifuge, and 8 mg was added per 40 ml of the volatilization reaction solution. The mercury volatilization reaction by the bacteria was performed in a thermostat at 30 ° C. for 24 hours by feeding air with an air pump to stir sediment and to send generated mercury vapor to a trap. Table 2 shows the mercury removal over time for this reaction.

[0024]

[Table 2]

As shown in the above Reference Example and Example 1, it is clear that most of the mercury sulfide in the sediment is eluted by hydrochloric acid and iron chloride, converted to mercury vapor by bacteria, and removed.

Example 2 1 g of field soil was put into a 50 ml impinger, methylmercury chloride was added thereto, 5 ml of 3N HCl and 0.05 g of iron chloride were mixed, and the mixture was allowed to stand at room temperature for 24 hours.
About 5 ml of 3N NaOH was added thereto to adjust the pH to 7.0, and the same operation as in Example 2 was performed to remove methylmercury from the soil. Table 3 shows the removal of methylmercury over time in this reaction.

[0027]

[Table 3]

As shown in Example 2 above, it is clear that most of the methyl mercury in the soil is converted to mercury vapor by bacteria and removed.

[0029]

As described above, according to the present invention,
Contaminants including insoluble inorganic mercury compounds, such as mercury sulfide, and organic mercury compounds, such as methylmercury, for which there has been no effective treatment method, can be simultaneously treated. Further, the present invention provides a novel microorganism particularly useful for the treatment method.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an experimental apparatus used in an example of the present invention.

[Explanation of symbols]

 1. 1. air pump, Constant temperature bath 3. Impinger 4. 4. Mercury vapor trap 5. Silicon tube

Continuation of the front page (51) Int.Cl. ⁷ identification code FI C02F 3/34 C02F 11/02 ZAB 11/02 ZAB B09B 3/00 ZABE (58) Investigation field (Int.Cl. ⁷ , DB name) C12N 1/20 A62D 3/00 B09C 1/10 C02F 3/34 C02F 11/02 BIOSIS (DIALOG) CA (STN) WPIDS (STN)

Claims (5)

(57) [Claims] 1. A method for treating mercury contaminants, wherein insoluble inorganic mercury compounds in the mercury contaminants are oxidized under acidic conditions, and Hg ²⁺
After the pH is adjusted, Hg ²⁺ is reduced in the presence of a thiol compound and a mercury-reducing microorganism to produce mercury vapor.
A method for treating mercury contaminants, which comprises converting into mercury. 2. The method for treating mercury contaminants according to claim 1, wherein the mercury-reducing microorganism is a microorganism belonging to the genus Pseudoalteromonas. 3. The method for treating mercury contaminants according to claim 1, wherein the mercury contaminants are mercury contaminated soil or sediment. 4. The method for treating mercury contaminants according to claim 1, wherein the thiol compound is a thioglycolate. 5. A mercury-reducing pseudo-Alteromonas M-
1 (Biotechnological Research Institute accession number FERM P-1
6049).