JP4483541B2 - Additives and methods for purifying contaminated soil and / or contaminated groundwater - Google Patents

Description

  The present invention relates to an additive used for the purification of soil and groundwater contaminated with an organic chlorine compound, and a purification method for purifying soil contaminated with an organic chlorine compound by the action of microorganisms by adding the additive.

  Conventionally, an anaerobic biomethod, which is a kind of bioremediation technology, is known as a method for purifying soil and groundwater contaminated with volatile organochlorine compounds such as trichlorethylene in situ. The anaerobic biomethod is a method in which an additive serving as a nutrient source for microorganisms is added to contaminated soil or the like, and an organic chlorine compound is reductively decomposed by the action of microorganisms. In the anaerobic biomethod, the activity of microorganisms that decompose organochlorine compounds differs depending on the type and amount of additives added to contaminated soil, etc. It has become.

  Accordingly, additives used in anaerobic biomethods have been studied. Conventionally, methods using saccharides such as lactose and sucrose as additives, organic acids such as citric acid and / or salts thereof, and / or salts thereof. Has been proposed (for example, Patent Document 1).

Citric acid and / or a salt thereof used as an additive in Patent Document 1 is a substance that is used as a food additive, has high safety, is easily available, and can reduce processing costs. Moreover, since citric acid and / or a salt thereof have a chelating ability for metal ions such as iron, precipitation of metal ions can be prevented when added to groundwater. Furthermore, since microorganisms involved in the decomposition of organochlorine compounds have a neutral pH range and an appropriate pH range, and citric acid and / or its salts have a pH buffering capacity in the neutral range, citric acid and By using the salt or / and its salt, an environment suitable for the activity of the microorganism can be adjusted without adding a pH adjuster.
JP 2002-1304 A

  By the way, the anaerobic biomethod uses microbial activity to decompose organochlorine compounds, so it is purified compared to the physicochemical method of removing contamination by injecting oxidizers, pumping groundwater, aeration, etc. Processing tends to take time. For this reason, in the anaerobic biomethod, it is required to promote the activity of microorganisms to improve the purification efficiency and to further shorten the period required for purification of the contaminated place. Accordingly, an object of the present invention is to provide an additive that can be used in anaerobic biomethods and that can promote the activity of microorganisms and shorten the treatment time. Another object of the present invention is to provide an additive that is highly safe, can be obtained inexpensively and easily, and can prevent an increase in processing cost.

  The present invention is an additive used in bioremediation to purify soil or groundwater contaminated with an organic chlorine compound by the action of microorganisms, and includes an organic acid-based substance and a protein-based substance, An additive capable of promoting the activity of anaerobic microorganisms is provided. More specifically, the present invention provides the following.

(1) An additive added to soil contaminated with organochlorine compounds and / or contaminated groundwater, wherein citric acid and / or a salt thereof and yeast extract are added at 1: 0.001 to 0.00. An additive comprising a concentration ratio of 1 (the concentration of the yeast extract is a concentration of a protein and a hydrolyzate thereof contained in the yeast extract).

(2) A method for purifying contaminated soil and / or contaminated groundwater in which additives are added to soil contaminated with organic chlorine compounds and / or contaminated groundwater, and the organic chlorine compounds are reductively decomposed by anaerobic microorganisms. The additive includes citric acid and / or a salt thereof and yeast extract, and the concentration of the citric acid and / or the salt in the contaminated place is 0.5 to 5 g / L, The concentration of the yeast extract in the contaminated place (the concentration of the yeast extract is the concentration of the protein and its hydrolyzate contained in the yeast extract) is 0.001 to 0.00 of the concentration of the citric acid and / or its salt. A method for purifying contaminated soil and / or contaminated groundwater to be multiplied by 1.

  Specific examples of the organic chlorine compound to be decomposed in the present invention include vinyl chloride, 1,1,1-trichloroethane, 1,2-dichloroethane, tetrachloroethylene (PCE), trichloroethylene (TCE), carbon tetrachloride, and dichloroethylene ( DCE) and the like, and polychlorinated biphenyls (PCB) containing dioxins are also included in the organochlorine compounds of the present invention.

  Examples of the organic acid and / or salt thereof include carboxylic acids such as citric acid, acetic acid, ascorbic acid, erythorbic acid, oxalic acid, tartaric acid, malonic acid, malic acid, and succinic acid, and / or salts thereof. Citric acid, ascorbic acid, erythorbic acid, oxalic acid, tartaric acid, malonic acid, malic acid, and succinic acid can be particularly suitably used as organic acids having chelating ability. Among these, citric acid, ascorbic acid, and salts thereof are particularly suitable because they have chelating ability, high safety, and pH buffering ability in a neutral range. Examples of organic acid salts include sodium salts, potassium salts, calcium salts, and ammonium salts.

  As protein and / or hydrolyzate thereof, one or more substances selected from the group consisting of yeast extract, malt extract, meat extract, fish extract and peptone that are highly safe and easily assimilated by microorganisms. Can be suitably used. In addition to these substances, bean extracts such as soybeans and peanuts, egg whites, plant proteins such as milk proteins, and animal proteins, as well as hydrolysates obtained by partially decomposing these proteins with proteases, pepsin, etc. And / or as a hydrolyzate thereof. The protein hydrolyzate preferably has an average molecular weight of about 1500 to 10,000.

  It is preferable that the additive is added to soil alone, groundwater alone, or both soil and groundwater (hereinafter referred to as “soil etc.”), and used in liquid form as an aqueous solution or water dispersion. When the additive is in liquid form, the organic acid and / or salt thereof and the protein and / or hydrolyzate thereof may be separately liquidized or a mixed liquid in which both are mixed. In the mixed solution, when the organic acid and / or salt thereof is 1, the ratio of protein and / or hydrolyzate thereof is 0.001 to 0.1, particularly 0.005 to 0.06 (weight ratio). It is preferable that it is contained.

  When the additive according to the present invention is liquid, the concentration of the organic acid and / or salt thereof in the contaminated soil or the like is 0.1 g / L or more, more specifically 0.5 to 5 g / L, and The organic acid and / or salt thereof, and the protein and / or salt thereof contained in the additive so that the concentration of the protein and / or salt thereof is 1 mg / L or more, more specifically 1 to 100 mg / L. It is preferable to adjust the concentration.

  The additive according to the present invention can be used in a so-called in-situ purification method that purifies contaminated soil or the like in situ without excavating soil and / or pumping groundwater. However, the present invention can also be used for processing by excavation and removal methods for excavating soil and the like, and in this case, an additive is added to the excavated and / or pumped soil and the like.

  Methods for adding additives in-situ include spraying the additive on contaminated soil, etc., or installing an injection tube that extends to the contaminated soil or groundwater layer and injecting the additive from this injection tube Etc. When spraying additives to soil, etc., liquid organic acid and / or salt thereof (hereinafter referred to as “organic acid liquid”) and liquid protein and / or hydrolyzate thereof (hereinafter referred to as “protein system”). May be sprayed separately, or a mixture of the two may be sprayed.

  When the organic acid solution and the protein solution are sprayed separately, the spraying order is not particularly limited, but it is preferable to spray the protein solution first. Moreover, when adding an additive to contaminated soil etc. from an injection tube, a liquid mixture may be used and an organic acid type | system | group liquid and a protein type | system | group liquid may be used. When the organic acid liquid and the protein liquid are injected separately, it is preferable to inject two kinds of liquids alternately.

  Examples of the method of adding an additive to excavated or pumped soil include a method of mixing an additive with excavated soil or the like and then backfilling the soil or the like to return it to the original position. Alternatively, the excavated soil may be put into a substantially cylindrical container to form a filter bed, and a liquid additive may be passed through the filter bed. The contaminated soil and groundwater can be purified together by alternately passing the additive and the treated liquid through the filter bed using the contaminated groundwater as the treated liquid.

  According to the present invention, the growth of anaerobic microorganisms involved in the decomposition of organochlorine compounds can be promoted by using an organic acid and / or salt thereof and a protein and / or hydrolyzate thereof in combination. . For this reason, according to the present invention, it is possible to increase the decomposition efficiency of soil contaminated with organochlorine compounds and shorten the time required for purification treatment.

  Hereinafter, the present invention will be described in detail as an embodiment of the present invention with reference to the drawings as an in-situ purification method in which an injection pipe is installed and an additive is injected and added to contaminated soil and groundwater.

  FIG. 1 is a schematic cross-sectional view of soil for explaining the in-situ purification method for contaminated soil and groundwater. In FIG. 1, reference numeral 21 denotes a saturated layer existing on the ground surface, 22 denotes an aquifer through which groundwater contaminated with an organic chlorine compound flows, and 23 denotes an impermeable layer in which clay or the like is deposited. In this embodiment, in order to purify contaminated groundwater and soil by the action of anaerobic microorganisms, the injection tube 11 is inserted into the ground from the surface, and the additive is injected from the injection tube 11 into the aquifer 22.

  Depending on the concentration of contaminants, a plurality of injection tubes 11 are preferably provided at intervals of 5 to 20 m where contaminated soil or the like is present. The injection pipe 11 is connected to the tank 12 via the pump 13, and the additive held in the tank 12 is added to the ground via the pump 12 and the injection pipe 11.

  The additive may be a mixed solution containing an organic acid and / or a salt thereof and a protein and / or a hydrolyzate thereof, or these may be added as separate liquids. When the organic acid-based solution and the protein-based solution are added separately, these two types of liquids are preferably added alternately in each of the plurality of injection tubes 11, but from one of the two adjacent injection tubes 11 It is not excluded from the scope of the present invention to inject the organic acid liquid and inject the protein liquid from the other side.

  In the present embodiment, the additive is a liquid material in which an organic acid and / or a salt thereof and a protein and / or a hydrolyzate thereof are mixed in advance and dispersed in water. It is added to the surrounding soil 23 (hereinafter referred to as “aquifer 22 etc.”). The concentration of the organic acid and / or salt thereof and the protein and / or hydrolyzate thereof contained in the additive is the flow rate of groundwater in the aquifer 22, the installation density of the injection pipe 11, the fluidity of the additive, etc. The concentration of the organic acid and / or salt thereof when added to the aquifer 22 or the like is 0.1 g / L or more, particularly 0.5 to 5 g / L, and the protein and The concentration of the hydrolyzate is adjusted to 1 mg / L or more, particularly 1 to 100 mg / L.

  When the concentration of the organic acid and / or salt thereof in the aquifer 22 or the like is less than 0.1 g / L, the supply of hydrogen is insufficient, so that the activity of microorganisms stagnate and the organic chlorine compound is efficiently decomposed. Not done. On the other hand, addition of an organic acid and / or salt thereof in an amount exceeding the above range is not preferable because there is no great difference in the decomposition efficiency of the organic chlorine compound and the treatment cost increases due to excessive addition of chemicals.

  In addition, when the concentration of the protein and / or the hydrolyzate thereof in the aquifer 22 or the like is less than 1 mg / L, the effect of promoting the dechlorination reaction cannot be obtained by using the protein or the like together with the organic acid or the like. On the other hand, even if a protein having a concentration exceeding 100 mg / L and / or a hydrolyzate thereof is added to the aquifer 22 or the like, an increase in effect commensurate with the amount added cannot be obtained.

  Proteins and / or hydrolysates thereof contained in the additive injected from the injection tube 11 are more easily degraded by microorganisms than organic acids and / or salts thereof. For this reason, by adding a small amount of protein of about 0.001 to 0.1 times (weight ratio) and / or a hydrolyzate thereof to the organic acid and / or salt thereof, the organic acid and / or It is possible to promote the growth of hydrogen producing bacteria that decompose the salt to produce hydrogen, and to promote the decomposition of organic acids and the like by the hydrogen producing bacteria. The dechlorinated bacterium decomposes an organic chlorine compound contained in the aquifer 22 and the like using hydrogen generated by the hydrogen-producing bacterium. Therefore, the purification period of contaminated groundwater or soil can be shortened by adding protein and / or its hydrolyzate and organic acid and / or its salt to the aquifer 22 or the like.

  In addition, in this invention, an additive may contain substances other than protein and / or its hydrolyzate, and organic acid and / or its salt. In addition, when the organic chlorine compound is not decomposed into ethylene or ethane in the aquifer 22 or the like and vinyl chloride, dichloroethylene or the like as an intermediate product accumulates, dichloroethylene as in the genus Dehalococoides. Microorganisms capable of decomposing etc. may be added from the injection tube 11.

  Hereinafter, the present invention will be described in more detail based on examples.

[Example 1]
Example 1 includes TCE, cis 1,2 dichloroethylene (cis-1,2-DCE), trans 1,2 dichloroethylene (trans-1,2-DCE), 1,1 dichloroethylene (1,1-DCE) and chloride. 100 ml of groundwater contaminated with vinyl monomer (VC) was placed in a 125 ml vial. To this vial, an additive containing sodium citrate as an organic acid salt and yeast extract as a protein was added, a rubber plug of butyl rubber was added, and nitrogen gas and carbon dioxide gas were mixed at a ratio of 7: 3. Purge with mixed gas. This was sealed with an aluminum cap and subjected to static culture at 30 ° C. as anaerobic conditions. The contents were periodically sampled from the vial, and the concentration of the organochlorine compound was measured using a gas chromatograph. The additive amount of sodium citrate added as an additive was 500 mg / L, and the additive concentration of yeast extract was 50 mg / L (the additive concentration of protein and its hydrolyzate was 14 mg / L).

[Comparative Example 1]
As Comparative Example 1, a vial containing groundwater to which only citric acid was added as an additive was prepared in the same manner as in Example 1 except that the yeast extract was not added. Table 1 shows the measurement results of the organochlorine compound concentration in Example 1 and Comparative Example 1 before addition of the additive and on the 20th, 40th, and 90th days after the addition. The unit of measured values is mg / L.

[Example 2]
As Example 2, an experiment was performed using a synthetic medium prepared by adding inorganic compounds such as nitrogen, phosphorus, potassium, calcium, sodium, magnesium, iron, and trace metals to pure water. The reason for using the synthetic medium is that the possibility that the groundwater used in Example 1 and Comparative Example 1 contains a substance that activates or inhibits some microbial activity is considered.

  The synthetic medium is placed in a vial similar to that used in Example 1, 500 mg / L of sodium citrate as the organic acid salt, and 50 mg / L of the yeast extract as the protein and its hydrolyzate (protein and its hydrolysis). As an additive, 14 mg / L) was added as an additive to the synthetic medium. The vial was then sealed with a rubber plug of butyl rubber and purged with a mixed gas in which nitrogen gas and carbon dioxide gas were mixed at a ratio of 7: 3. This was sealed with an aluminum cap for anaerobic conditions, and cis-1,2-DCE was added as a contaminant at a concentration of 20 mg / L. Furthermore, anaerobic microorganisms containing hydrogen-producing bacteria and dechlorinated bacteria are added by adding a culture solution obtained by culturing anaerobic microorganisms in a culture solution containing cis-1,2-DCE at a concentration of 0.05% by weight. The fungal group was inoculated and statically cultured at 30 ° C. The contents of the vial were periodically sampled, and the cis-1,2-DCE concentration was measured in the same manner as in Example 1.

[ Reference Examples 10-12 ]
As Reference Example 10 , in the same manner as in Example 2 except that 50 mg / L of malt extract (addition concentration of protein and its hydrolyzate was 3 mg / L) was used instead of yeast extract as the protein and its hydrolyzate. And experimented. Reference Example 11 was the same as Example 2 except that fish extract 50 mg / L (additional concentration of protein and hydrolyzate was 10 mg / L) was used instead of yeast extract as the protein and hydrolyzate thereof. . Reference Example 12 was carried out in the same manner as Example 2 except that 50 mg / L of casein peptone as a protein hydrolyzate (addition concentration as a protein hydrolyzate was 25 mg / L) was used instead of the yeast extract.

[Comparative Example 2]
As Comparative Example 2, an experiment was conducted in the same manner as in Example 2 except that vitamin was used instead of protein and sodium citrate and vitamin were added as additives. As a vitamin, a vitamin solution in Wolin medium (see The Journal of Biological Chemistry vol. 238, No. 8, August 1963) was used, and the addition concentration was 0.5 mg / L.

[Comparative Example 3]
As Comparative Example 3, an experiment was performed under the same conditions as in Example 2 except that the additive was only sodium citrate.

  Table 2 shows the measurement results of the cis-1,2-DCE concentrations at the start of the experiment (initial stage) and 20 days after the addition of the additives for Examples 2 to 5 and Comparative Examples 2 and 3. In the table, the additive concentration of additives other than citric acid is indicated by the additive concentration as a protein and / or its degradation product. Moreover, it means that the addition concentration of the vitamin indicated by * in Table 2 is the same as the concentration of the Wolin medium.

  As shown in Tables 1 and 2, even when sodium citrate alone or sodium citrate and vitamins are added as additives, organochlorine compounds are decomposed, but the protein or its hydrolyzate is dissolved in sodium citrate. When used together, the time required for decomposition can be reduced to half or less. As described above, according to the present invention, by using an organic acid substance such as sodium citrate and a protein substance such as yeast extract as additives, the decomposition rate of organochlorine compounds by microorganisms can be increased. Can be bigger.

  Furthermore, in order to examine the addition amount of an organic acid and / or a salt thereof, and a protein and / or a hydrolyzate thereof, an experiment was conducted using the synthetic medium used in Example 2 (Reference Examples 1 to 9). . In Reference Examples 1 to 9, sodium citrate or sodium L-ascorbate was used as the organic acid salt, yeast extract was used as the protein and its hydrolyzate, and the amount added was changed.

  Specifically, the synthetic medium was put into a vial as in Example 2, and for Reference Example 1, after adding only sodium citrate 500 mg / L as an additive to the synthetic medium, the same operation as in Example 2 was performed. And anaerobic conditions were added, cis-1,2-DCE was added as a contaminant at a concentration of 20 mg / L, and as in Example 2, anaerobic containing hydrogen-producing bacteria and dechlorinated bacteria The fungal group was inoculated and statically cultured at 30 ° C. The contents of the vial were periodically sampled, and the cis-1,2-DCE concentration was measured in the same manner as in Examples 1 and 2.

  Reference Example 2 was the same as Reference Example 1 except that sodium citrate 500 mg / L and yeast extract 1 mg / L (protein and its hydrolyzate concentration was 0.28 mg / L) were added as additives. . About Reference Examples 3-6, it carried out similarly to Reference Example 2 except having changed the addition amount of the yeast extract. Specifically, the amount of yeast extract added was 10 mg / L for Reference Example 3 (concentration as protein and its hydrolyzate was 2.8 mg / L), and 50 mg / L for Reference Example 4 (protein and its hydrolysis). The concentration as a product is 14 mg / L), Reference Example 5 is 100 mg / L (protein and its hydrolyzate concentration is 28 mg / L), and Reference Example 6 is 1000 mg / L (protein and its hydrolyzate concentration) 280 mg / L).

  In Reference Example 7, the additive was only yeast extract 50 mg / L (concentration as protein and its hydrolyzate was 14 mg / L), and Reference Example 8 was except that the additive was only 500 mg / L of sodium L-ascorbate. Same as Reference Example 1. Reference Example 9 was the same as Reference Example 1 except that 500 mg / L of sodium L-ascorbate and 50 mg / L of yeast extract (protein and its hydrolyzate concentration was 14 mg / L) were added as additives.

  Table 3 shows the measurement results of the cis-1,2-DCE concentration at the start of the experiment (initial stage) and 13 days after the addition of the additives for Reference Examples 1 to 9. In Table 3, symbol A indicates sodium citrate, symbol B indicates sodium L-ascorbate, “total” of the yeast extract addition amount indicates an addition concentration as a yeast extract, and “protein” indicates protein. And the addition density | concentration as its hydrolyzate is shown.

  As shown in Table 3, when only the organic acid salt or yeast extract was added, the degradation rate of cis-1,2-DCE remained at about 5% (Reference Examples 1, 7, and 8). On the other hand, in Reference Examples 3 to 6 and 9 in which the protein and its hydrolyzate were added together with the organic acid salt so as to be 1 mg / L or more, the degradation rate was doubled or more. In addition, in Reference Examples 4 and 5, the degradation rate could be doubled or more by doubling the amount of yeast extract added, but in Reference Example 6 in which 10 times the yeast extract of Reference Example 5 was added, The decomposition rate did not increase dramatically, and no improvement in the decomposition effect according to the increase in the amount added was confirmed. Furthermore, from the comparison between Reference Examples 4 and 9, it was found that, as the organic acid salt, a higher effect can be obtained by using sodium L-ascorbate than sodium citrate.

  The present invention can be used to purify soil and groundwater contaminated with an organic chlorine compound such as trichlorethylene.

It is a cross-sectional schematic diagram of the soil for demonstrating the in-situ purification method of soil and groundwater.

Explanation of symbols

11 Injection pipe 12 Tank 21 Saturated layer 22 Aquifer layer 23 Impermeable layer

Claims (2)

An additive added to soil contaminated with organochlorine compounds and / or contaminated groundwater,
Citric acid and / or salt thereof and yeast extract at a concentration ratio of 1: 0.001 to 0.1 (the concentration of the yeast extract is the concentration of the protein and the hydrolyzate contained in the yeast extract). Including additives. A method for purifying contaminated soil and / or contaminated groundwater, wherein an additive is added to soil contaminated with organochlorine compounds and / or contaminated groundwater, and the organochlorine compounds are reductively degraded by anaerobic microorganisms. ,
The additive seen contains citric acid and / or its salt, and yeast extract, and
The concentration of the citric acid and / or salt thereof in the contaminated place is 0.5-5 g / L,
The concentration of the yeast extract in the contaminated place (the concentration of the yeast extract is the concentration of the protein and its hydrolyzate contained in the yeast extract) is 0.001 to 0 of the concentration of the citric acid and / or its salt. .Contamination method for contaminated soil and / or contaminated groundwater.