Method for reducing environmental load

Abstract

To provide a market solution for reducing environmental load by stabilizing the leaching concentration of contaminants from polluted soil or the concentration of contaminated groundwater below a certain level, which addresses a phenomenon previously overlooked in conventional pollution countermeasures including the variation in contaminant leaching rates depending on the amount of contaminated coexisting organic matter in the soil.SOLUTION: Immobilization materials and, as necessary, materials to reduce permeability to the subsurface structure are applied. The application of these immobilization materials initiates a series of operations by adsorbing organic pollutants onto the material surfaces, and subsequently promoting purification reactions involving NA and radical generation against the adsorbed organic pollutants. This is intended to regenerate the adsorption sites on the material surface through pollutant purification, thereby reducing the leaching concentration of contaminants from the contaminated soil or the concentration of contaminants in the groundwater. Furthermore, by applying materials that reduce permeability in conjunction with the above, it is intended to achieve a further reduction in the leaching concentration of contaminants or the concentration of contaminated groundwater.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for reducing environmental load by shifting soil contaminant elution concentrations and groundwater concentrations to a safer level through the application of materials to underground structures, which inhibit the adhesion of organic matter-metabolizing bacteria and the adsorption and elution of contaminants, followed by natural attenuation characterized by inhibiting protozoan predation, and the regeneration of the adsorption capacity of the materials through radical reactions mediated by electron acceptor precursors, etc. [Background technology]

[0002] Soil and groundwater contamination caused by organic halogen compounds, benzene, etc. has been found, for example, in surveys using Patent Document 1, to occur primarily by seeping from the surface into the ground, causing soil contamination, and then moving into perched water or groundwater, etc., and in some cases causing widespread groundwater contamination. Soil contamination by pollutants is generally regulated by elution concentrations, and groundwater standards are also regulated at concentrations equivalent to those elution concentrations. The elution concentration of soil contamination and groundwater contamination concentration are closely related to the contamination adsorption capacity of the soil, which is the contaminated medium. In general, the adsorption / elution of contaminants into soil is said to be strongly related to the carbon content in the soil (Non-Patent Document 1). Furthermore, it is expected that the concentration of such leached contaminants will decrease through natural attenuation, mainly by environmental microorganisms. However, in the natural environment, the number of environmental microorganisms is maintained at an extremely low concentration through predation by protozoa (Non-Patent Document 2), and therefore the decrease in the concentration of leached contaminants through natural attenuation has been extremely slow. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7423062 [Non-patent literature]

[0004] [Non-Patent Document 1] Adsorption and desorption of organohalogen compounds in soil, Water Pollution Research, Vol. 8, No. 5, pp. 282-288 (1985) [Non-patent document 2] Evaluation of the persistence of bacteria preyed on isolated and indigenous protozoa, Journal of the Japan Society of Civil Engineers, Vol. 75, No. 7, 2019, pp. III_395-III_402 Summary of the Invention [Problem to be solved by the invention]

[0005] At actual contaminated sites, what has a significant impact on the carbon content in the soil is organic matter that coexists with the contamination and exists in a mixed state with organic contamination (hereinafter referred to as coexisting organic matter). For example, organic chlorine compounds such as tetrachloroethylene are used for degreasing in metal processing and cleaning, and therefore are accompanied by contaminating organic matter, primarily oil / grease components. PFASs, the organic fluorine compounds contained in firefighting foams, are used to form flame-retardant foams and are accompanied by contaminating organic matter, primarily surfactant components. Furthermore, benzene is contained in some fuels, such as gasoline, and is accompanied by contaminating organic matter, primarily fuel components other than benzene. Thus, many pollutants were accompanied by contaminated organic matter and were eluted from the soil depending on the amount of organic matter present.

[0006] Incidentally, many of these pollutants are artificial compounds called xenobiotics that do not exist in nature in the first place, and contain many persistent substances that become less concentrated in the natural environment very slowly due to natural attenuation (NA; there are two types of NA, ENA and MNA, as will be described later) mainly through biodegradation. On the other hand, contaminated organic matter is often composed of general-purpose chemical products, etc., and is generally an easily decomposable substance that can be rapidly NA'd.

[0007] In this way, because the contaminated organic matter is mostly easily degradable while the contaminants are mostly difficult to degrade, the difference in the purification speed by NA, etc. between the two substances makes the leaching behavior of the contaminants from the soil quite unstable. In other words, even if the amount of contaminant remains the same, if the amount of coexisting contaminant organic matter decreases, the elution concentration of the contaminant increases. In actual implementation, soil contamination by organic halogen compounds, benzene, etc. is regulated by leaching concentration. However, the amount of leaching contamination varies depending on the amount of coexisting organic matter present, which may make predictions of the end point of purification in pollution purification projects and the two-year purification confirmation monitoring carried out after construction unstable.

[0008] In general, in response to the problem of the amount of contaminant leaching varying depending on the amount of contaminated organic matter present, a specific challenge is to provide a marketplace method for keeping the amount of contaminant leaching from contaminated soil stable at or below a certain concentration. Needless to say, new inventions that overcome these challenges will be technologies based on methodologies that contribute to the realization of a sustainable society. [Means for solving the problem]

[0009] The gist of the present invention for solving the above-mentioned problems resides in the following invention. For underground structures contaminated by organic pollutants consisting of pollutants and coexisting organic matter, (A) immobilization materials with hydrophobic sites that have the ability to adsorb organic pollutants and attract the attachment of organic matter-metabolizing bacteria are applied, and if necessary, materials that reduce permeability are also applied. (B) A method for reducing environmental loads, characterized by carrying out, in a series, activation on the surface of the immobilized material, which induces at least one of the following processes: (i) metabolic purification of organic pollutants, characterized by the inhibition of predation by protozoa of organic matter-metabolizing bacteria and the formation of aggregates; and (ii) purification by radical reactions driven by electron acceptors or electron acceptor precursors for organic matter-metabolizing bacteria, thereby regenerating adsorption sites on the surface of the immobilized material. [Effects of the Invention]

[0010] According to the method for reducing the environmental load of the present invention, the problem of unstable soil contamination elution behavior resulting from fluctuations in the amount of contaminated coexisting organic matter has been addressed. By applying immobilization materials or materials that reduce permeability to underground structures, not only can the contaminant elution concentration and groundwater concentration be suppressed / maintained below a certain concentration (for example, below the environmental standard value), but also, in order to restore the adsorption capacity of the immobilization material, radical reactions can be carried out via NA, which suppresses predation by protozoa and promotes the growth of organic matter-metabolizing bacteria characterized by aggregate formation, and appropriate transitions in the bacterial flora composition, or electron acceptor precursors, thereby making it possible to shift the soil contamination elution concentration and groundwater concentration to a safer side. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a micrograph showing the difference in aggregate formation under each culture condition, with respect to the formation of aggregates whose main constituents are organic matter-metabolizing bacteria, which is the present invention. [Figure 2] This figure shows a table summarizing the results of quantitative bacterial flora analysis using next-generation sequencing analysis, along with a diversity assessment, regarding the increase or decrease in the number of bacteria and specific protozoa under each culture condition in Figure 1. [Figure 3] FIG. 1 shows the results of an experiment on activation for regenerating adsorption sites on the surface of the immobilization material associated with the formation of aggregates of organic matter-metabolizing bacteria in the present invention. [Figure 4] FIG. 1 shows experimental results of the dechlorination reaction and microbially driven Fenton reaction by extracellular electron-transfer bacteria collected from an actual polluted site, which is the present invention. [Figure 5] FIG. 1 is a diagram summarizing the outline of the state before and after radical generation by electron acceptors and electron acceptor precursors involved in radical reactions in the activation operation for regenerating adsorption sites according to the present invention. [Figure 6] FIG. 1 is a diagram summarizing the mechanism of action and efficacy of each operation of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a representative embodiment of the present invention will be described based on the development history and practical examples.

[0013] This invention was developed with the aim of creating new technologies to combat soil and groundwater contamination in mind, in response to the Japanese government's goal of achieving carbon neutrality by 2050. Through such studies, a direction for technological development suited to the new era was found: "future soil and groundwater contamination countermeasure technologies will be environmentally friendly technologies that actively utilize recycled materials and circulative materials, or that minimize the use of constant fluid operations (for example, groundwater contamination countermeasures that require semi-permanent pumping and aeration), which lead to enormous energy consumption over the life cycle of contamination purification countermeasures." This led to the present invention, which has a background of low energy consumption and low environmental impact, such as reduced emissions of pollutants.

[0014] In order to implement such soil and groundwater contamination countermeasures, it is essential to apply appropriate immobilization materials or materials that reduce permeability to the source, which is the center of contamination where contamination moves from contaminated soil to groundwater, or to the contamination that flows down through groundwater, thereby reducing the concentration of soil leaching and groundwater contamination.

[0015] Furthermore, in such reduction treatment, it is important not only to adsorb the pollutants but also to adsorb the coexisting organic matter that causes instability in the elution of the contaminants.Furthermore, the present invention requires the immobilization of various substances, such as inducing the attachment of organic matter-metabolizing bacteria that are responsible for the NA of the contaminants to the surface of the immobilization material. In the present invention, an immobilization material having a hydrophobic site is used as a material that contributes to the adsorption and adhesion of such various substances. Specifically, organically modified minerals with carbon compounds arranged on the adsorption sites may be used, or if reducing the environmental load is particularly important, immobilization materials containing at least a portion of biologically derived activated carbon or biochar may be used.

[0016] In previous adsorption treatments for pollutants, activated carbon was often used in pollution treatment using land-based adsorption treatment plants, but new production of activated carbon involved multiple costly and heavy-duty steps, such as carbonization using organic materials as raw materials in the first stage and activation using energy, chemicals, etc. In light of this background, and taking into account the low environmental impact and cost-effectiveness, efforts were made to reuse not only new carbon but also recycled carbon.

[0017] In the application of immobilization materials to underground structures, particularly in the application of activated carbon to contaminated soil, the use of recycled carbon made from used activated carbon waste is preferred because it is difficult to recycle the activated carbon afterward. However, this does not preclude the use of virgin carbon if there is no other option.

[0018] While the final stage in the general life cycle of activated carbon is incineration, which releases carbon dioxide into the atmosphere, one of the features of the present invention is to achieve decarbonization by storing carbon components through underground burial of immobilization materials. Preferably, a negative emission state in which the balance of carbon dioxide emissions is on the fixed side, or at least a low emission state in which decarbonization is sufficiently achieved, can be achieved, which is not the best but is considered to be a better choice.

[0019] On the other hand, in order to aim for even lower-cost and lower-impact pollution control, it is also effective to use biochar produced by omitting the activation process in activated carbon production. Such biochar can be made from organic carbon such as wood charcoal (white charcoal, black charcoal, bamboo charcoal, powdered charcoal, sawdust charcoal), chicken manure charcoal, sludge charcoal, and smoked charcoal, which have been confirmed to be effective as adsorbents for pollutants. However, because the pollutant adsorption effect of biochar is extremely dependent on the material and lot, applicability tests must be conducted before use to confirm the appropriate application concentration. In addition, if a particularly high adsorption effect is required for a specific pollutant, the use of dedicated immobilization materials in combination with adsorbents such as organically modified minerals or other adsorbents should also be considered. [Example]

[0020] The applicability of the immobilization material in terms of its pollutant adsorption was assessed with reference to previous tests on the applicability of various pollutants to water treatment systems. Specifically, we selected 13 immobilization materials, including commercially available organically modified bentonite FLUORO-SORB (registered trademark / sold by Volclay Japan Co., Ltd.), which has hydrophobic regions that are capable of adsorbing organic pollutants and attracting organic matter-metabolizing bacteria, Rembind (registered trademark / sold by Rembind Co., Ltd.), which contains a portion of activated carbon, and various charcoal materials (white charcoal, black charcoal, bamboo charcoal, powdered charcoal, sawdust charcoal, livestock manure charcoal, sludge charcoal, smoked charcoal, recycled activated carbon, newly produced activated carbon, and charcoal made from organic waste). We adjusted the particle size to 5–10 mesh (with the addition of a stabilizer and subsequent granulation, if necessary), and packed each material into a 1-m-long, 50-mm diameter glass column. Assuming that the interstitial volume of the packed particles is 35% of the column volume, the elution volume equivalent to this 35% volume was counted as "1 elution volume," and a basic evaluation of the adsorption of each pollutant by various immobilization materials was conducted using a downward flow at a linear velocity of 0.1 m / h. The contaminants and concentrations in the water used for the evaluation were 17 types in total: 12 types of Class 1 specified hazardous substances specified in the Soil Contamination Countermeasures Act, PCB, 1,4-dioxane, and organic fluorine compounds (PFOA, PFOS, PFHxS). The concentrations of the 12 types of Class 1 specified hazardous substances and 1,4-dioxane were set at 0.1 mg / L, the PCB concentration at 10 μg / L, and the concentrations of the three organic fluorine compounds at 100 ng / L. The presence or absence of adsorption capacity was determined by analyzing the water passing through the column immediately after two elution volumes had been passed through.

[0021] As a result, in the analysis of the water passing through the columns of each of the 13 types of immobilization materials, all 17 types of pollutants were not detected, confirming that each of the 13 types of immobilization materials has the ability to adsorb the 17 types of pollutants evaluated (after which, this water treatment system experiment was continued, but needless to say, different results were obtained regarding the adsorption (flow) behavior of each pollutant on each immobilization material).

[0022] In construction, these immobilization materials may be applied singly or in combination. Chicken manure charcoal and sludge charcoal contain phosphorus components and are used not only as immobilization materials but also as a phosphorus source, a growth substrate for organic matter-metabolizing bacteria.

[0023] In the present invention, application of immobilization materials to underground structures is roughly divided into application to the contaminated core and application to the contaminated plume. When applied to the central part of the contamination, treatment to reduce leaching from the central part of the contamination is carried out by mixing the immobilization material into the contaminated soil using heavy soil improvement machinery such as backhoes and columnar improvement machines, or by injecting a slurry of the immobilization material into the soil pores using grout injection technology. On the other hand, when applied to contaminated plumes, immobilization materials that utilize the relevant soil improvement technology are applied to cover the contaminated plume, or a permeable wall structure is installed and immobilization materials are applied (filled) inside the structure to carry out permeation treatment of contaminated groundwater.

[0024] Furthermore, for immobilization materials used for application to underground structures, pH adjustment is carried out as necessary. Many charcoal-based immobilization materials in particular are alkaline, so mineral acids and buffers are used in combination to adjust the pH to the optimum for various purification reactions. Depending on the type of mineral acid or buffer, some may act as electron acceptors (respiration sources) or medium components that affect the growth of organic matter-metabolizing bacteria. Therefore, in consideration of the countermeasures to be implemented, applicability tests should be conducted in advance to select appropriate mineral acids and buffers for the series of purification work that constitutes the present invention.

[0025] In addition, if additional culture components or electron acceptors are required for the growth of organic matter-metabolizing bacteria, i.e., if enhanced natural attenuation (ENA) is to be implemented, the necessary components are added at the same time as the pH adjustment is carried out. Specifically, examples of culture components include nitrogen compounds, phosphorus compounds, potassium compounds, trace elements, vitamins, and the like. In addition, when supplying electron acceptors, an appropriate amount should be applied, taking into account the amount of contaminants and coexisting contaminated organic matter contained in the contaminated soil / groundwater. In particular, when aiming for a transition to a bacterial flora that includes extracellular electron transfer bacteria in the latter stage of construction, the type of electron acceptor supplied in the former stage may hinder the dominance of the extracellular electron transfer bacteria in the latter stage, so particular care should be taken with the amount applied.

[0026] Incidentally, it has been confirmed through experiments using microscope observations and quantitative bacterial flora analysis that applies next-generation sequencing analysis that after immobilization materials are applied to contaminated soil / groundwater, organic matter-metabolizing bacteria attach to the surface of the applied immobilization material and escape predation by protozoa, which promotes the assimilation and proliferation of coexisting contaminated organic matter, leading to the formation of aggregates (Figures 1 and 2). During actual construction work, it is advisable to conduct similar monitoring to check the construction status and make adjustments as necessary.

[0027] That is, C in Figure 1 10 As can be seen in the photographs of the AC-added culture (day 10), significant bacterial aggregate formation was observed only in the culture system to which activated carbon was added as an immobilization material. Furthermore, quantitative bacterial flora analysis evaluation using next-generation sequencing analysis of the number of bacteria and protozoa shown in Figure 2 also revealed a significant suppression of the number of protozoa (the number of mitochondrial 16S rRNA genes of protozoa) in the activated carbon-added system (B 10 and C 10 A significant increase in the relative bacterial count (comparison of the number of organic metabolizing bacteria and the relative bacterial 16S rRNA gene count) (B 10 and C 10 (comparison of the two) was confirmed. In other words, it is thought that by using activated carbon and other materials to treat contaminated soil / groundwater, organic matter-metabolizing bacteria attach to the activated carbon and then take on the role of ENA, which also serves to assimilate the contaminated coexisting organic matter adsorbed on the surface of the activated carbon, while also avoiding predation by protozoa, allowing them to multiply and grow into huge communities that form aggregates.

[0028] Protozoa, which are a few micrometers in size and live in underground structures (mainly in soil pores saturated with groundwater), consume bacteria by phagocytosis, directly ingesting bacteria from the cell surface through the cell membrane into their own cells (unicellular eukaryotes), which naturally limits the size of bacteria that can be ingested.The adhesion of organic matter-metabolizing bacteria to immobilized materials and the subsequent formation of aggregates both result in a substantial increase in size, which is thought to prevent them from being consumed by protozoa.

[0029] As shown in Non-Patent Document 2, the predatory pressure of protozoa on bacteria in the environment is extremely high. Even if bacteria are simply added to a system to attempt ENA of the target contaminant compound, it is extremely difficult to maintain the bacterial population in the system and effectively promote ENA of the target organic compound (Non-Patent Document 2 and Figure 2: B0 and B 10 comparison). Unfortunately, even in our industry, which deals with bioaugmentation technology that uses exogenous decomposition bacteria to purify soil and groundwater, the powerful predatory influence of protozoa in the natural world is largely unknown.

[0030] In this way, the mechanism by which protozoans avoid predation by attaching organic matter-metabolizing bacteria to immobilization materials and subsequently forming aggregates was clarified for the first time through quantitative evaluation of each microbial group in an experimental system simulating the saturated zone underground. By independently developing a methodology for maintaining the current bacterial abundance in the system, this led to the present invention, which enables the stable regeneration of adsorption sites on the surface of immobilization materials by utilizing ENA by organic matter-metabolizing bacteria for contaminated coexisting organic matter.

[0031] In addition to activated carbon, the ability to avoid predation by protozoans has been confirmed with a series of immobilization materials categorized as adsorbents with hydrophobic moieties, such as wood charcoal (white charcoal, black charcoal, bamboo charcoal, powdered charcoal, sawdust charcoal), chicken manure charcoal, sludge charcoal, smoked charcoal, carbonized food waste, and other materials such as FLUORO-SORB, an organically modified mineral, and Rembind, which partially contains activated carbon.The applicability of these immobilization materials can be investigated as necessary, and the most suitable immobilization material can be selected.

[0032] Incidentally, a simple evaluation shown in Example 2 was carried out regarding the phenomenon in which ENA by organic matter-metabolizing bacteria leads to the formation of aggregates and the regeneration of adsorption sites on the surface of the immobilized material. [Example]

[0033] Granular activated carbon was packed into a 10 cm column, and 0.1% potassium oleate solution was continuously passed through it as raw water. When the pH of the raw water and the pH of the water passing through the column became equal, it was determined that the breakthrough had reached saturation, and the water passage was stopped. Next, after the water was drained from the granular activated carbon in the column, the wet activated carbon was removed from the column, and 2 g was weighed out and placed in each of two 100 ml transparent vials with airtight stoppers. Furthermore, 10 ml of 5 mmol / L phosphate buffer (pH 7) prepared using groundwater was added to one vial (no medium added group), and 10 ml of a specified concentration of Daigo IMK medium (Fujifilm Wako Pure Chemical Industries, Ltd.) prepared based on 5 mmol / L phosphate buffer (pH 7) was added to the other (medium added group). Both vials were sealed with septa equipped with Teflon (registered trademark) liners and aluminum seals, and then a diluted solution of tetrachloroethylene was spiked into them so that the liquid phase concentration reached an equilibrium adsorption concentration with the activated carbon of approximately 1 mg / L or less. After shaking in a water bath at 15°C for 1 day in the dark, the tetrachloroethylene concentration in the headspace was measured by PID / GC to determine the tetrachloroethylene concentration in the liquid phase, which was used as the initial concentration. Thereafter, the water bath shaking culture was continued in the dark at 15°C, and after one month, the liquid phase concentration was determined from the headspace concentration in the same way, and the difference in tetrachloroethylene adsorption to activated carbon was observed depending on whether or not the microbial growth was due to the addition of Daigo IMK medium. As a result, in each vial after one month, in the medium-added group, it was observed that the activated carbon in the vial was covered with loose translucent flocs, and many flocs were floating in the medium, causing turbidity, but in the medium-free group, only slight turbidity occurred. Microscopic observation revealed that the flocs observed in the medium-added group were composed of bacteria, etc. The results of the tetrachloroethylene concentration in the vials after one month are shown in Figure 3. The amount of tetrachloroethylene adsorbed after one month was higher in the medium-added group than in the medium-free group. In general, the amount of tetrachloroethylene adsorbed onto activated carbon in a closed system increased due to the proliferation of bacteria and other organisms that used the oleic acid adsorbed onto the activated carbon as a carbon source. This suggests that the proliferation of bacteria and other organisms associated with the ENA of oleic acid that was present on the adsorption sites on the surface of the activated carbon resulted in the regeneration of these adsorption sites.

[0034] After the formation of aggregates primarily composed of organic matter-metabolizing bacteria, the bacterial flora undergoes a transition as electron acceptors such as oxygen and nitrate / sulfate ions used by the organic matter-metabolizing bacteria are depleted, and the bacteria become dominated by extracellular electron-transferring bacteria that use mainly carbonized materials mixed in the contaminated soil and metal oxides in the contaminated soil as electron acceptors (respiratory sources) and coexisting contaminated organic matter as electron donors (energy sources / carbon sources).

[0035] When excavating unsaturated soil in the center of a contaminated area, careful observation of the excavated surface often reveals areas where the soil color has changed from brown to blue in the contaminated areas. This change in the brown soil color to blue is caused by extracellular electron transfer bacteria. As the extracellular electron transfer bacteria grow by utilizing coexisting contaminated organic matter as a carbon and energy source, the trivalent iron that makes up the soil receives electrons from the electron transport chain of the extracellular electron transfer bacteria and changes to divalent iron, resulting in this blue coloring of the soil.

[0036] On the other hand, if we look from the unsaturated zone in the contamination center to the saturated zone, we can observe a phenomenon in which local maximums and minimums in underground microbial activity alternate along the contamination plume originating from the contamination center. This phenomenon of alternating microbial activity has been clarified by the surface gas survey method described in Patent Document 1, and is used to estimate the contamination center, the contamination plume, and the flow direction of contaminated groundwater.

[0037] Here, drilling surveys were conducted at five locations in the same contaminated plume at an untouched tetrachloroethylene-contaminated site: three maximum activity points (one at the edge of the maximum upstream of the groundwater flow, one at the center of the maximum, and one at the edge of the maximum downstream toward the minimum) and two minimum activity points before and after. As a result, both blue and brown layers were observed in the saturated zone strata. Furthermore, the depth at which the blue areas appeared was consistent across all drilling locations, appearing in roughly the same strata. This indicated that the blue areas, where NA of organic pollutants by extracellular electron-transporting bacteria was progressing, were distributed in a continuous band along the plume.

[0038] In addition, the composition of chlorinated ethylenes in the upstream and downstream areas of the maximum concentration at the same location showed that the dichloroethylene ratio increased as the water flowed downstream, while the monochloroethylene ratio decreased. Furthermore, a relatively more significant decrease in the total molar concentration of chlorinated ethylenes was observed at the maximum. Regarding the change in the composition of chlorinated ethylene contamination in the upstream and downstream areas of the former maximum, it is difficult to conclude anything more than that anaerobic dechlorination reactions are progressing at least in the blue area. However, regarding the decrease in the total molar concentration of chlorinated ethylenes in the latter maximum, it was suggested that two other concentration reduction mechanisms besides anaerobic dechlorination reactions may be involved.

[0039] First, one of the mechanisms for this concentration reduction is the stripping effect of metabolic gases such as carbon dioxide produced by the activation of microbial metabolism, which reduces the concentration of contaminants in groundwater. If the contaminants are volatile and metabolic gases are generated in the contaminated groundwater flow, it is obvious that the transition of the contaminants to gas will reduce the concentration of contaminants in the groundwater.

[0040] In fact, when the surface survey according to the aforementioned Patent Document 1 was carried out at a contaminated site where chlorinated ethylenes were detected, a simple measurement of the chlorinated ethylene concentration in the surface soil gas, converted into tetraethylene concentration, was carried out using a gas detection tube for tetraethylene at the same time as gas analysis to determine microbial activity.The results showed that the chlorinated ethylene concentration and carbon dioxide concentration in the soil gas were both maximum in almost all cases at the areas of maximum microbial activity, and it is therefore highly likely that this stripping effect makes a certain contribution to reducing the concentration of groundwater contamination.

[0041] However, while this stripping effect reduces groundwater concentrations, it can also be considered as a diffusion of contamination from underground to the atmosphere, which could be a concern in terms of human exposure at the surface when it comes to contamination management across the entire contaminated site. However, as will be described later, in a situation where peaks are scattered and widely distributed along the contamination plume, in order to effectively take measures to prevent exposure to contamination resulting from such stripping effects, the present invention aims to concentrate the locations where stripping occurs and prevent the diffusion and exposure of pollutants in the stripping gas to the ground surface by applying an appropriate immobilization material to the central part of the contamination, which is the source of the contamination.

[0042] On the other hand, considering the mechanism by which these maximum areas are formed, maximum and minimum areas of microbial metabolic activity are alternately arranged along the contaminated groundwater flow, and it is presumed that these maximum and minimum areas are induced by the diffusion of dissolved substances in the groundwater flow running parallel to the contaminated flow into the contaminated flow, and dissolved oxygen is cited as the main dissolved substance supplied by such diffusion and having the effect of increasing microbial metabolic activity.

[0043] When molecular oxygen is supplied to a bacterial flora dominated by extracellular electron transfer bacteria, the extracellular electron transfer bacteria are likely to exhibit a metabolic response that produces hydrogen peroxide. It is suggested that the Fenton reaction occurs between the ferrous iron derived from the ferric iron used as an electron acceptor by the extracellular electron transfer bacteria and the hydrogen peroxide produced. As a result, it was suggested that there exists another mechanism for the concentration decrease at the maximum point, in which hydroxyl radicals generated by this microbial-driven Fenton reaction cause an oxidation reaction accompanied by a decrease in the content of chlorinated ethylenes. To verify this, the confirmation test shown in Example 3 was carried out. [Example]

[0044] To verify the existence of a microbially driven Fenton reaction mechanism in this maximum area, drilling was carried out at the actual contaminated site at the center of the maximum area of ​​the repeating pattern of maximum and minimum microbial activity within the contaminated plume where slight amounts of monochloroethylene were detected. Core soil from the blue layer (1 cm of the core's outer periphery was discarded, leaving only the inner part) was collected and instantly frozen in liquid nitrogen in a Dewar vessel on site. This was then brought back to the lab, still immersed in liquid nitrogen, along with the collected groundwater. In the lab, the groundwater was first thoroughly boiled in a flask to degas it, then pure nitrogen gas (N2: 99.99999%) was passed through it and it was left to cool. A 5 mmol phosphate buffer solution was then prepared to a pH of 6.0, and the flask filled with pure nitrogen gas was then sealed and left to stand at ice temperature. Next, under a nitrogen atmosphere, 10 ml of pH-adjusted groundwater that had been chilled to ice temperature was placed into 15 30 ml brown vials that had been kept on ice and at ice temperature, and mannitol was added to 10 of the vials to make the final concentration 0.1 mmol. Furthermore, under a nitrogen atmosphere, the collected frozen blue soil samples were crushed using a pestle and mortar on ice that had been maintained at sub-zero temperatures after adding NaCl to crushed ice. After crushing, five sets of 5g of the crushed sample were weighed out and placed in five vials containing mannitol that had also been maintained at ice temperature under a nitrogen atmosphere. The vials were then sealed with septa fitted with Teflon (registered trademark) liners and aluminum seals, and were subsequently maintained at ice temperature (Figure 4: K to O in the table). Also, under the same nitrogen atmosphere, 10 sets of 5 g of the crushed sample were weighed out and placed in vials maintained at ice temperature: five with mannitol (F to J in the table in Figure 4) and five without (A to E in the table in Figure 4). These were then removed into an air atmosphere, and a 100 ml syringe fully filled with air was used to blow air into the gas phase of each vial to replace the gas phase with air. The vials were then sealed with a septum equipped with a Teflon (registered trademark) liner and an aluminum seal, and maintained at ice temperature on ice. Next, a tetrachloroethylene solution was spiked into all the vials using a microsyringe to give a liquid-phase equivalent concentration of 0.02 mg / L, and the vials were then kept at ice temperature. Next, the vials stored on ice were removed one by one every 10 minutes (GC analysis: 8 minutes + α) and immersed in a water bath shaker set to 15°C to achieve gas-liquid equilibrium within the vials at 15°C. After immersion for 60 minutes, gas was sampled from the headspace within the vials and subjected to PID / GC to measure the tetrachloroethylene concentration in the gas phase, and the initial concentration of tetrachloroethylene in the liquid phase was determined. The presence of other chlorinated ethylenes was also confirmed on the same analysis chart. After gas sampling, all vials were returned to the water bath shaker and continued to be shaken at 15°C. On the following day, 20 hours later, the tetrachloroethylene concentration in the liquid phase of all 15 vials in the water bath shaker was determined using the headspace method in the same manner as the previous day, and the presence of other chlorinated ethylenes was also confirmed.

[0045] The results are shown in Figure 4. The average tetrachloroethylene concentration after 20 hours under gas phase:air conditions differed depending on whether mannitol was added or not, and a significant decrease in tetrachloroethylene concentration was observed in the mannitol-free system. Furthermore, no other chlorinated ethylenes were detected in a series of PID / GC analyses under gas phase:air conditions. On the other hand, in a series of PID / GC analyses under gas phase: nitrogen conditions, the decrease in tetrachloroethylene concentration after 20 hours was slight, but trace amounts of dichloroethylene were found in the samples after 20 hours. These results suggest that under aerobic conditions, the presence or absence of mannitol, a hydroxyl radical scavenger, caused differences in the concentration of residual tetrachloroethylene, and that the Fenton reaction, which generates hydroxyl radicals, was induced by setting aerobic conditions.It is also considered that at actual contamination sites, there is a high probability that a microbial-driven Fenton reaction will occur due to the supply of molecular oxygen to areas where blue discoloration of the strata due to extracellular electron-transporting bacteria is observed. On the other hand, this experiment also verified that under anaerobic conditions, the dechlorination reaction proceeds, albeit slowly. It was therefore considered that, depending on the oxygen concentration gradient / distribution at the site, both the dechlorination reaction and the microbially driven Fenton reaction are likely to occur at the maximum level of microbial activity at untouched contaminated sites.

[0046] Generally, it is thought that such microbially driven Fenton reactions and the like occur mainly in the maximum areas of the countless microbial activities that occur in association with the contaminated plume in the saturated zone. However, it is easily conceivable that purification by the microbially driven Fenton reactions and the like can be more efficiently achieved by concentrating these countless maximum areas in one place with the coexisting contaminated organic matter using the immobilization material of the present invention. It is thought that groundwater rich in dissolved oxygen then flows downstream from the upstream groundwater flow area and comes into contact with the bacterial flora, mainly consisting of extracellular electron-transporting bacteria, on the surface of the immobilized material, thereby intensively inducing at least a microbially driven Fenton reaction and promoting the oxidative decomposition of pollutants by hydroxyl radicals.

[0047] In addition to such microbially driven ENA (assimilation metabolism and microbially driven Fenton reaction), there is a method for intentionally inducing radical reactions, which involves adding electron acceptors such as ferric iron, electron acceptor precursors such as ferrous iron, hydrogen peroxide, or persulfate, mainly to the saturated zone (Figure 5). [Example]

[0048] Regarding the intentional induction of radical reactions, a simple evaluation was carried out by simulating the addition of electron acceptor precursors mainly in the saturated zone.

[0049] The experiment was conducted in 100 ml brown serum vials containing 5 ml of reaction solution. The reaction solution contained tetrachloroethylene (final concentration 0.1 mg / L) as a contaminant, an alcohol cocktail (ethanol, tert-butyl alcohol, and mannitol: each 200 mM) as a radical scavenger, and either 0.1% persulfate or 0.1% hydrogen peroxide as an electron acceptor precursor, along with 5 g of activated carbon, as needed. Each vial was sealed and incubated overnight in a thermostatic shaker at 15°C under aerobic conditions. The contaminant concentration in the solution was then determined by headspace analysis.

[0050] To evaluate decomposition in the activated carbon-added system, the residual rate (%) was calculated from the residual contaminant concentration in each test plot relative to the residual contaminant concentration in the control plot after one day and one night, and then compared and considered. [Activated carbon addition system] (Control 1): Pollutant + activated carbon (Test area 1): Contaminant + persulfate + alcohol cocktail + activated carbon (Test area 2): Pollutant + persulfate + activated carbon (Test area 3): Contaminant + hydrogen peroxide + alcohol cocktail + activated carbon (Test area 4): Pollutant + hydrogen peroxide + activated carbon As a result, the survival rates in test plots 1 and 3, which contained an alcohol cocktail as a radical scavenger, were 85% and 93%, respectively, while the survival rates in test plots 2 and 4, which did not contain a radical scavenger, were 3% and 7%, respectively. The large change in survival rate depending on the presence or absence of a radical scavenger suggests that radical reactions contribute to the decomposition.

[0051] Next, an evaluation was carried out in the same way without the addition of activated carbon. The test system and results are as follows. The decomposition evaluation was carried out by calculating the residual rate (%) from the residual contaminant concentration in each test area relative to the residual contaminant concentration in the control area after one day and one night, and comparing and considering the results. [Activated carbon additive-free system] (Control area 2): Contaminants (Test area 5): Pollutant + persulfate + alcohol cocktail (Test area 6): Pollutant + persulfate (Test area 7): Contaminant + hydrogen peroxide + alcohol cocktail (Test area 8): Pollutant + hydrogen peroxide As a result, the survival rates in test plots 5 and 7, which contained radical scavengers, were 91% and 88%, respectively, while the survival rates in test plots 6 and 8, which did not contain radical scavengers, were 86% and 83%, respectively. Since the survival rate remained almost unchanged with or without radical scavengers, it was considered that radical generation was dependent on the presence of activated carbon.

[0052] Based on these results, similar experiments were conducted using other carbon-containing materials (white charcoal, black charcoal, bamboo charcoal, powdered charcoal, sawdust charcoal, livestock manure charcoal, sludge charcoal, smoked charcoal, recycled activated carbon, newly produced activated carbon, and carbonized food waste) as alternatives to activated carbon, as well as Rembind.The results suggested that, although the degree of effectiveness varied depending on the material, the decomposition of pollutants through radical reactions was at least somewhat promoted. In general, it was suggested that charcoal-containing materials in general have the effect of inducing radical reactions derived from electron carrier precursors, such as persulfuric acid and hydrogen peroxide.

[0053] In addition, the delivery of electron mediator precursors, etc. to the immobilization materials applied to underground structures is mainly carried out after soil improvement work / permeable wall installation, so injection wells are appropriately installed at the soil improvement work / permeable wall installation site after each work, and solutions of electron mediator precursors, etc. are injected through the wells.

[0054] The above-mentioned intentional induction of radical reactions is carried out when problems with the adsorption site occur, such as when adsorbent substances that are difficult to decompose with NA, such as humins contained in groundwater or secondary metabolites of contaminated organic matter, accumulate on the immobilization material and cause breakthrough, or when an excessive supply of the target contaminant (including contaminated organic matter) causes breakthrough of the immobilization material.

[0055] In this way, when breakthrough has occurred or is expected to occur, in addition to inducing purification reactions such as ENA and radical reactions as described above, construction work is carried out to reduce the permeability of the unsaturated zone in order to actively restrict the movement of contamination through rainfall infiltration and perched water flow through the unsaturated zone leading to the saturated zone where breakthrough is expected, thereby slowing the rate at which target pollutants are supplied to the saturated zone.

[0056] In this work to reduce permeability, impermeable materials such as fine minerals like bentonite or water glass, which are mainly used in grouting, can be mixed or injected into all or part of the contaminated soil to reduce permeability, or impermeable sheets, asphalt, mortar, etc. can be applied to the surface to prevent rainwater infiltration. Also, a method of preventing rainwater infiltration by erecting a building, whether temporary or permanent, on the site can be used.

[0057] The above-mentioned series of construction methods are primarily used to implement purification measures for relatively low concentrations of contamination over a short period of time and complete the pollution control measures, but in cases where extremely high concentrations of contaminants or coexisting organic matter are present, there may be situations where measures must be taken to achieve long-term NA after attempting to adsorb the contamination using immobilization materials. This long-term measure will use Monitored Natural Attenuation (MNA), which falls under the category of NA, to adopt measures that contribute to decarbonization. This "scientific natural attenuation" is actually more appropriately called "random natural attenuation," as it involves monitoring the reduction in pollution concentration over the long term through the slow decomposition of microorganisms by electron acceptors and the small amounts of nutrients supplied by groundwater and rainwater recharge, without making any changes to the target pollution.Although this is a passive method of pollution control, it has the lowest environmental impact and costs, as it consumes the least amount of energy.

[0058] In this way, in the method of reducing the environmental load of the present invention, it is possible to first adopt more aggressive methods such as ENA or radical reactions, and then transition to MNA as a subsequent step.It is important that stakeholders share the stance that the length of time required to purify the pollutant mass is not an issue, as long as the immobilization material continues to maintain the eluted pollutant concentration below the concentration level agreed upon by the stakeholders in the pollution control measure.

[0059] Incidentally, most pollutants can be decomposed by NA or radical reactions, but for some organic fluorine compounds such as PFOS, decomposition by these reactions is almost impossible. In such cases, the immobilization material of the present invention should be applied at least to the central part of the contamination, and the NA and radical reactions of the contaminated coexisting organic matter caused by the organic matter-metabolizing bacteria on the surface of the immobilization material should be promoted, thereby regenerating the adsorption sites on the surface of the immobilization material, further adsorbing the organic fluorine compounds, and maintaining low elution of organic fluorine compound contamination downstream from the contaminated layer.In addition, the application of materials that reduce permeability, which will help to reduce elution, should be considered. In addition, when implementing pollution control measures that do not involve the decomposition of target pollutants, it is essential to reach an agreement among stakeholders at the planning stage prior to construction.

[0060] The following inventive concept can be derived from the above-described embodiments and examples. (1) For underground structures contaminated by organic pollutants consisting of pollutants and coexisting organic matter, (A) apply immobilization materials with hydrophobic sites that have the ability to adsorb organic pollutants and attract the attachment of organic matter-metabolizing bacteria, and if necessary, also apply materials that reduce permeability. (B) The method is characterized by the sequential implementation of activation on the surface of the immobilized material, which induces at least one of the following processes: (i) metabolic purification of organic pollutants, characterized by the inhibition of predation by protozoa of organic matter-metabolizing bacteria and the formation of aggregates; and (ii) purification by radical reactions driven by the presence of electron acceptors or electron acceptor precursors for organic matter-metabolizing bacteria, thereby regenerating adsorption sites on the surface of the immobilized material.

[0061] (2) The underground structure is a water layer, and in addition to applying the immobilization material by the columnar improvement method or injection method, the immobilization material is applied to a permeable wall installed in a groundwater layer or a perched aquifer.

[0062] (3) The immobilization material is a carbonized material derived from waste.

[0063] (4) The contaminant is a halogen compound.

[0064] (5) After the activation, the pollution control measures are shifted to natural decay.

[0065] Next, the effects of the above-described inventive concept will be described. According to the method for reducing the environmental load relating to (1) of the present disclosure, a pollution control measure can be implemented by applying an immobilization material to underground structures containing pollutants, thereby reducing the elution concentration of pollutants from contaminated soil or the concentration of contaminated groundwater to a predetermined concentration or below (for example, below the environmental standard value).

[0066] Furthermore, by implementing work to reduce permeability in conjunction with the application of immobilization materials, the amount of contaminants leaching from the contaminated soil via recharge water, perched water, and groundwater can be reduced, thereby improving the retention of the various compounds that promote purification in the soil and reducing the concentration of contaminants leaching from the soil, as needed.

[0067] In addition, due to this effect of reducing leaching concentrations, even if there is soil containing high levels of contamination that may affect the growth of organic matter-metabolizing bacteria, the amount of contaminants leached from the contaminated soil can be reduced to avoid affecting the growth of organic matter-metabolizing bacteria, thereby efficiently achieving the purification effect of the present invention through the metabolism of organic pollutants by organic matter-metabolizing bacteria.

[0068] In addition, by reducing the permeability of contaminated soil, especially in the unsaturated zone, the amount of contamination that transfers to rainwater recharge and perched water, i.e., the amount of leaching, can be reduced, which can also contribute to reducing the concentration of contamination in groundwater, which is the final confluence of these.

[0069] Furthermore, by reducing the permeability of saturated zone contaminated soil, the amount of contamination that migrates into groundwater, i.e., the amount of leaching, can be reduced, which can also contribute to reducing the concentration of contamination in groundwater.

[0070] In general, the application of the immobilization materials and materials that reduce permeability has the dual effect of reducing the concentration of leaching contaminants, making it possible to implement soil and groundwater contamination countermeasures with ample leeway, even in cases where there is an extreme difference in the allowable contaminant concentration set in groundwater compared to the contaminant concentration in the unsaturated soil at the site.

[0071] In addition, the concentration of contaminants coexisting in the immobilized material can be further reduced by regenerating the adsorption sites using organic matter-metabolizing bacteria that are characterized by avoiding predation by protozoa.

[0072] Furthermore, by inducing NA and radical reactions derived from the provision of electron acceptors and electron acceptor precursors as needed, and purifying organic pollutants adsorbed on the adsorption sites on the surface of the immobilized material to regenerate the adsorption sites, it is possible to further reduce the leaching concentrations of pollutants that constitute Class 1 specified hazardous substances, as well as pollutants such as PCBs, 1,4-dioxane, and other PFASs (Figure 6).

[0073] Furthermore, with regard to human exposure due to the diffusion of metabolic gases derived from NA of organic pollutants above ground, which has been largely overlooked until now, by applying immobilization materials to the central part of the contamination, which is the source of the pollution, the areas where metabolic gases are generated by NA can be concentrated at the construction site, and furthermore, by concentrating the adsorption of the generated gaseous pollution by the applied immobilization materials, it is possible to avoid human exposure above ground.

[0074] The energy consumption in this countermeasure occurs mainly during the application of the immobilization material to the contaminated soil. After that, gravity injection of nutrients and monitoring are carried out only infrequently, and only as needed. Compared to energy-intensive pollution control methods that take decades, such as pumping and aeration treatment, which are often seen in conventional pollution remediation measures, this is an extremely low-cost and environmentally friendly countermeasure.

[0075] Furthermore, by concentrating and concentrating pollutants on the surface of the immobilized material, efficient purification can be achieved by accelerating NA and radical reactions, which are kinetically advantageous. Furthermore, this radical reaction can be induced from electron acceptor precursors using some immobilized materials as catalysts, allowing for more intensive purification on the surface of such materials, and the resulting electron acceptors can further promote the growth of organic matter-metabolizing bacteria.

[0076] In addition, when carbonized materials such as activated carbon are used as immobilization materials for PFAS contamination, it is expected that leaching can be suppressed by approximately 50 to 99% with an addition amount of less than 10% per unit soil weight. Furthermore, under similar conditions, when a mixed material containing a clay-based adsorbent other than carbonized material is used as the immobilization material, or when an organically modified clay-based adsorbent is used alone, it is expected that leaching can be suppressed by approximately 99 to 99.9%. In addition, by using immobilization materials containing carbonized materials that contain not only carbon but also a lot of phosphorus, such as livestock charcoal powder or sludge charcoal, under the conditions for adding the above-mentioned carbonized materials, the fertilizing effect of the phosphorus components can promote the growth of organic matter-metabolizing bacteria in the contaminated soil.

[0077] According to the method for reducing the environmental load relating to (2) of the present disclosure, the underground structure is a water layer, and by applying immobilization materials to a permeable wall installed in the groundwater layer or perched aquifer in addition to applying immobilization materials using the columnar improvement method or injection method, not only can contaminated water passing through the soil layer using the columnar improvement method or injection method be treated, but also more efficient contaminated water treatment can be achieved by bringing the granular material into contact with the contaminated water passing through the permeable wall without going through the soil.

[0078] According to the method for reducing the environmental burden related to (3) of the present disclosure, the immobilization material is a carbonized material derived from waste. Because it is waste, the carbon dioxide emissions required for raw material production are not counted, and the life cycle CO2 is particularly underestimated. This allows a series of pollution control projects to be counted negatively against carbon dioxide emissions, that is, it is possible to implement pollution control measures with an extremely low environmental impact, which promotes immobilization rather than carbon dioxide emissions.

[0079] According to the method for reducing the environmental load related to (4) of the present disclosure, the elution concentration of halogenated compounds, particularly extremely persistent PFASs such as PFOS, can be reduced by adsorption onto the surface of an immobilization material added to contaminated soil. In addition, the organic contaminants adsorbed to the adsorption sites on the surface of the material can be decomposed by NA or radical reactions caused by organic matter-metabolizing bacteria, thereby opening up new adsorption sites for persistent PFASs, thereby further reducing the elution of persistent PFAS contamination.

[0080] According to the method for reducing the environmental load related to (5) of the present disclosure, by shifting to pollution control measures based on natural attenuation after activation, pollution control measures can be implemented that have less environmental impact and are less costly.

[0081] The above has described the embodiments and examples of the present invention, but the specific configuration is not limited to the disclosure above, and it goes without saying that changes and additions that do not deviate from the gist of the present invention are also included in the present invention. [Industrial Applicability]

[0082] The method for reducing the environmental load according to the present invention is a technology that applies immobilization materials and, if necessary, materials that reduce permeability to contaminated underground structures, thereby stably suppressing the elution of pollutants, preferably to below the standard concentration level, and further promotes the suppression of protozoan predation and the regeneration of adsorption sites by NAs and radical reactions, which are characterized by aggregate formation, thereby further reducing the elution concentration of pollutants.The present invention can be used in pollution control projects that require the reduction of the environmental load caused by the elution of pollution from pollution sources.

Claims

1. For underground structures contaminated by organic pollutants consisting of pollutants and coexisting organic matter, (A) an immobilization material having a hydrophobic portion capable of adsorbing organic pollutants and attracting the attachment of organic matter-metabolizing bacteria is applied, and if necessary, a material for reducing permeability is also applied. (B) A method for reducing environmental loads, characterized by carrying out, in a series, activation on the surface of the immobilized material, which induces at least one of the following processes: (i) metabolic purification of organic pollutants, characterized by the inhibition of predation by protozoa of organic matter-metabolizing bacteria and the formation of aggregates; and (ii) purification by radical reactions driven by electron acceptors or electron acceptor precursors for organic matter-metabolizing bacteria, thereby regenerating adsorption sites on the surface of the immobilized material.

2. 2. The method for reducing environmental load according to claim 1, wherein the underground structure is a water layer, and the immobilization material is applied to a permeable wall installed in a groundwater layer or a perched aquifer in addition to application of the immobilization material by a columnar improvement method or an injection method.

3. 3. The method for reducing environmental load according to claim 1, wherein the immobilization material is a carbonized material derived from waste.

4. 3. The method for reducing environmental load according to claim 1, wherein the pollutant is a halogen compound.

5. 3. The method for reducing environmental load according to claim 1, further comprising the step of shifting to a pollution control measure based on natural attenuation after the activation.

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