KR101298600B1 - Permeable Reactive Barrier restoring system and method for preventing pollutant dispersion through auto-injection of chemical and microorganism - Google Patents

Abstract

The present invention relates to a system and method for regenerating permeable reactive walls through automatic chemical spraying for preventing the spread of pollution, and more particularly, to increase the filler treatment efficiency in permeable reactive walls reduced as the purification of contaminated groundwater continues. The present invention relates to a permeable reactive wall regeneration system and method for automating pollution measurement detection system and chemical injection system to enable reactivity recovery and life extension.

Description

Permeable Reactive Barrier restoring system and method for preventing pollutant dispersion through auto-injection of chemical and microorganism}

The present invention relates to a system and method for regenerating permeable reactive walls through automatic injection of chemicals for preventing the spread of pollution, and more particularly, to improve the efficiency of fillers in permeable reactive walls reduced as the purification of contaminated groundwater continues. The present invention relates to a permeable reactive wall regeneration system and method for automating pollution measurement detection system and drug injection system to enable reactivity recovery and life extension.

Permeable Reactive Barrier (PRB) is a technology that can replace the method of continuously extracting and purifying contaminated ground water. It is installed in the flow path of contaminated ground water and reacts when contaminated ground water passes through the wall. It is a method of inducing chemical reaction between media and pollutants and purifying pollutants using physicochemical and biological mechanisms such as precipitation, volatilization, biodegradation, adsorption and oxidation / reduction. In the past decades, research and technology development of oil contaminated soil / groundwater purification methods have been actively conducted. The water permeable reaction wall introduced by McMurthy and Elton in 1985 is excellent in its economic efficiency and treatment effect. As a result, it has been spotlighted as an alternative technology to reduce costs compared to the existing pollution restoration method.

Permeable reactive walls can be classified into continuous and funnel and gate depending on their shape (Vidic et al., 1996). Since continuous reaction walls do not change the flow and flow rates of groundwater contaminants, contaminants can be removed while maintaining a similar flow rate in underground aquifers. Therefore, it is relatively easy to construct and does not affect the existing groundwater flow, but considering the groundwater flow of the site, it is necessary to make contact with the reaction wall with sufficient cross section and size. Since the wall must be manufactured, the economy can be reduced. On the other hand, inductively attached reactive walls are economically advantageous because they can reduce the reaction area by directing and treating the flow of groundwater contaminated zones to the gates by using funnels with low permeability. Since the contact time of the reaction medium is short, the thickness of the wall should be increased so that sufficient contact can occur. The funnel uses a slurry wall such as a soil-bentonite slurry wall, a cement-bentonite slurry wall, a plastic concrete, a steel sheet pile, a synthetic resin sheet pile, a wooden sheet pile, or the like.

Major mechanisms of permeable reactive walls include redox chemical reactions, adsorption, and precipitation with contaminants in groundwater. Chlorine-based organic compounds (TCE, PCE, cDCE, tDCE, VC, CCl4, etc.), chromium , Uranium, and the like.

Young's iron is the most researched and used filler in permeable reaction wall, and continuous research on materials such as Fe (II) iron oxide, Al, Zn, Limestone, Zeolite, Pyrite, Sn, Mg, Cu, etc. Is being performed. Filled media has a problem that the efficiency of pollutant treatment decreases with time. The surface area that can cause chemical reactions decreases or the adsorption of contaminants accumulates and the adsorptive surface area decreases, and eventually into the permeable reaction wall. The pollutants flow into the groundwater, making it difficult to effectively treat the contaminants in the groundwater. In the end, the service life is terminated because the pollutants are not treated at all. Thus, recent studies have been conducted to extend the service life of permeable reactive walls. As part of this, when using oil adsorbent as a filler for the treatment of groundwater contaminated with oil recently, microorganisms or highly oxidizing agents are injected to decompose the oil pollutants adsorbed on the adsorbent to recover the adsorption capacity which decreases with time. Research to restore adsorption capacity is underway.

As a prior art, Korean Patent No. 10-0529301 discloses a method for restoring the reducing ability of iron to hexavalent chromium by iron oxide reduction using microorganisms. have. However, the applicant has further converged the contaminant detection technology and the contaminant disintegrator injection technology to 'automate' the entire system, so that the permeable reaction wall containing a common adsorbent as a filler is a permeant with an oxidizing agent as a filler. Iron Reducing Bacteria (IRB) is applied to sexually reactive walls to restore the reactivity of fillers that are less reactive over time through chemical or biological mechanisms to maintain treatment efficiency for contaminants. A system and method for regenerating permeable reactive wall through automatic chemical injection for preventing diffusion have been proposed.

The present invention has been made to solve the above-mentioned conventional problems, the chemicals that can automatically recover the treatment capacity of the filler when the concentration of the contaminants in the groundwater through a treatment water concentration change monitoring system exceeds a certain value It is an object of the present invention to provide a system and method for prolonging the life of a permeable reaction wall by spraying to restore the filler performance.

In order to achieve the above object, the water permeable reaction wall regeneration system through automatic chemical spraying to prevent contamination diffusion according to the present invention is installed in the water permeable reaction wall (1), the water permeable reaction wall (1) and contaminated Automatic injection control (2) for the detection of substances and injection of chemicals, the chemical tank (4) for storing the chemicals for regenerating the permeable reaction wall, and whether or not the injection of chemicals depending on the contaminant concentration detected in the automatic injection control It is composed of a control unit 3 for determining and transmitting a control signal to the chemical tank.

According to one aspect of the invention, the water-permeable reaction wall (1) is filled with iron or iron and / and the adsorbent, the chemical tank (4) stores the oxidizing agent when the iron reducing bacteria, the filler is adsorbent when the filling is zero iron. In the case of a permeable reaction wall using a combination of ductile iron and an adsorbent, the iron reducing bacteria and the oxidizing agent are separately stored and sprayed.

According to another aspect of the present invention, a plurality of automatic injection wells (2) installed in the permeable reaction wall (1) is a cylindrical body portion (2-0), an underground water pollution sensor for monitoring the concentration of pollutants (2-1), a chemical injection pipe (2-2) for receiving the medicine from the chemical tank and injecting it into the injection well, the groundwater contamination sensor and the medicine injection pipe passes through and packing (2-3) ), And the injection hole (2-4) is provided in the chemical injection pipe for injecting the chemical.

A method for regenerating permeable reaction walls through automatic chemical injection for preventing pollution diffusion according to the present invention is to operate the chemical injection and injection system automatically according to the set concentration value, and the concentration of the pollutant in the groundwater pollution sensor 2-1. Detecting; Transmitting the concentration detected by the groundwater pollution sensor 2-1 to the controller 3; When the detected concentration is greater than or equal to the set concentration value, a control signal is transmitted from the control unit to the chemical tank 4 to operate the metering pump 4-1 connected to the chemical tank; And injecting the medicine through the injection hole (2-4) by injecting the medicine from the medicine tank (4) into the medicine injection pipe (2-2) of the automatic injection well by the operation of the metering pump; The drug consists of reacting with the permeable reaction wall.

The water permeable reaction wall regeneration system and method through the automatic chemical injection for preventing the diffusion of the present invention, first, by converging the pollution detection technology and injection technology of the permeable reactive wall regeneration material and automating them, the concentration of contaminants in the groundwater If exceeds a certain value, it automatically sprays the drug to restore the filler performance to provide an effect of extending the life of the permeable reaction wall.

Therefore, the present invention can perform the regeneration of the filler in a timely manner by the set concentration value, and above all, it is possible to prevent the source of contamination diffusion, Control The system that can log the set concentration value periodically enables accurate and effective monitoring, and can also minimize the number of workers in the field by unmanned automation, thereby providing an economical permeable reactive wall regeneration system by reducing labor costs and expenses. have.

In addition, it is possible to determine the location of the permeable reaction wall by grasping the location of the pollutant and the groundwater flow in case of soil groundwater contamination or underground tank contamination due to oil leakage, etc., thereby preventing the spread of contamination. Subsequently, it is possible to reduce the trouble of periodic sampling and injection timing, and the recorder can record pollutant concentrations periodically so that the concentration change over time can be used to systematically operate the system.

1 is a process flow diagram of a water permeable reaction wall regeneration system through automatic chemical injection for preventing contamination diffusion according to the present invention.
2 is a block diagram of a permeable reaction wall regeneration system through automatic chemical injection for preventing the spread of contamination according to the present invention.
Figure 3 is a perspective view of the automatic injection well of the permeable reaction wall regeneration system through the automatic chemical injection for preventing pollution diffusion according to the present invention.
4 (a) and 4 (b) are tables and graphs showing a regeneration effect of a water permeable reaction wall that adsorbs oil materials during chemical oxidant injection.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

It is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Throughout the specification, the same reference numerals are used for the same names.

Furthermore, terms used herein are for the purpose of illustrating embodiments and are not intended to limit the present invention. In this specification, the singular forms include plural forms as the case may be, unless the context clearly indicates otherwise. &Quot; comprises "and / or" comprising "used in the specification do not exclude the presence or addition of one or more other elements other than the stated element. Unless defined otherwise, all terms used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. In addition, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

Other advantages and features of the present invention, and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings.

1 is a process flow diagram of a water permeable reaction wall regeneration system through automatic chemical injection for preventing contamination diffusion according to the present invention. In the present invention, the 'drug' automatically injected is defined as the oxidant and microorganisms collectively.

Referring to FIG. 1, when (a) the permeable reaction wall 1 starts operation of the equipment to treat contaminated water, (b) the groundwater contamination sensor 2 of the automatic injection well 2 installed in the permeable reaction wall 2 -1) monitor the concentration of contaminants in groundwater; (c) As a result of analyzing the concentration of pollutants detected by the groundwater pollution sensor, monitoring is continued when the concentration of pollutants in the treated water is lower based on the set concentration value, and (d) the signal of the controller is higher than the set concentration value. By the drug is delivered to the drug injection pipe (2-2) inside the automatic injection well (2) from the chemical tank (4) proceeds to the process of spraying.

More specifically, the method for regenerating the permeable reaction wall through automatic spraying for preventing the diffusion of pollution according to the present invention includes: detecting the concentration of the pollutant in the groundwater pollution sensor 2-1;

Transmitting the concentration detected by the groundwater pollution sensor 2-1 to the controller 3;

When the detected concentration is greater than or equal to the set concentration value, a control signal is transmitted from the control unit to the chemical tank 4 to operate the metering pump 4-1 connected to the chemical tank; And

Injecting the medicine from the chemical tank (4) to the chemical injection pipe (2-2) of the automatic injection well by the operation of the metering pump is injected by the injection port (2-4); And

The drug consists of reacting with the permeable reaction wall.

In particular, the step of reacting the drug with the permeable reaction wall is the step of dispersing the drug via the groundwater inside the automatic injection well (2) when the drug injection; Chemicals dispersed in the groundwater exit through holes drilled in the screen of the bottom of the automatic injection well and move between the permeable reactive wall filler voids; The chemicals and the fillers of the permeable reaction wall are reacted and regenerated. At this time, if the filler of the permeable reaction wall is zero iron, the iron reducing bacteria, which are microorganisms, are injected as a medicine to reduce the iron oxide of the filler, and if the filler is an adsorbent, chemical oxidants are injected to decompose the pollutants adsorbed on the adsorbent. The sex reaction wall is regenerated.

2 is a block diagram of a permeable reaction wall regeneration system through automatic chemical injection for preventing the spread of contamination according to the present invention. Referring to FIG. 2, the water-permeable reactive wall regeneration system according to the present invention includes a water-permeable reactive wall (1), an automatic injection well (2) installed in the water-permeable reactive wall (1), a controller (3), and It consists of a chemical tank (4).

The permeable reaction wall (1) can be selected as a filler, such as iron or iron and / or adsorbent, the iron reducing bacteria when the filler is zero iron, the oxidant is automatically sprayed as a chemical to regenerate the permeable reaction wall when the filler is adsorbent. . In complex contaminated sites, two types of fillers (iron particles, adsorbents) can be applied together. The adsorbent may be selected from peat, compost, or activated carbon.

As the permeable reactive wall is changed over time as the reactant (ferrous iron) processes the contaminant, the surface of the permeable reactant gradually decreases due to the decrease in the surface area of the non-ferrous iron that comes into contact with the contaminant. The following formula is a chemical formula indicating the decomposition mechanism of TCE, a representative substance that can be processed by iron particles.

Fe ⁰ + RCl + H ⁺ → RH + X

^{2Fe 2 + + RCl + H +} → 2Fe 3 + + RH + X -

RCl + H ₂ → RH + H ⁺ + X ^-

As Fe ⁰ is oxidized to divalent iron and trivalent iron oxide, the ability to give electrons out of the iron surface gradually decreases the reactivity of permeable reaction walls filled with zero iron, which reduces the ability to treat contaminants, thus reducing the lifetime of the system. This is done. Therefore, in order to regenerate the reactivity of the surface of the iron particles oxidized with Fe3 +, Fe3 + should be reduced to Fe2 +. For this, iron reducing bacteria (Iron Reducing Bacteria; IRB) are typically used.

Representative species used as iron-reducing bacteria include Shewanella Oneidensis MR-1 (Bose et al., 2009; McLean et al., 2008), Shewanella alga BrY (Shin et al., 2007), Shewanella Putrefaciens CN32 (Haas and Dichristina, 2002; Liu et al., 2001) and Geobacter Sulfurreducens (Yan et al., 2008). All of these bacteria are readily available to those skilled in the art. The iron-reducing bacterium undergoes anaerobic respiration and metabolism while receiving trivalent iron ions as electron acceptors and reducing them to divalent iron ions. By supplying the appropriate carbon source and electron donor to maintain metabolic activity, iron reactivity can be restored by reducing trivalent iron as follows.

On the other hand, even when the adsorbent is filled in the permeable reaction wall, its reactivity decreases with time. Therefore, the permeable reaction wall regeneration system and method through the automatic injection to prevent contamination diffusion according to the present invention uses an oxidizing agent such as hydrogen peroxide as an injection chemical to recover the treatment efficiency. In particular, Fenton's reagent using hydrogen peroxide and iron ions is a representative oxidant applied to the in-situ chemical oxidation technology. In 1894, tartaric acid was decomposed when iron salt and hydrogen peroxide were mixed. Fenton reported for the first time. In the Fenton reaction, iron ions act as a catalyst to generate hydroxyl radicals (OH) by hydrogen peroxide, and the reactor is represented by the following chemical formula.

^{_{Fe 2 + + H 2 O 2}} → OH + OH - + Fe 3 +

Hydrogen peroxide used in this process is naturally friendly and easy to operate because it is decomposed into oxygen and water in the natural state, iron is abundant in nature as a non-toxic element, and has the advantage of generating less harmful by-products than other high oxidation processes. Fenton reaction is used a lot. The reaction rate is considerably fast, but in the region of pH 5 or more, iron ions precipitate with iron salts, thereby greatly reducing the oxidation reaction power, and sludge occurs after the reaction, which causes some disadvantages in the application of soil and groundwater.

In order to overcome this pH problem, the modified Fenton technique is a technique in which a complex is combined with iron ions to form a complex ion so that iron ions do not precipitate with iron salt even in the neutral region. EDTA, oxalate, citrate, etc., are used to form complexes with iron ions, allowing oxidation to occur. One of the further variation of the Fenton reaction (perhydroxyl radical) peroxide radical species, chemistry reactivity by injecting an excess of hydrogen peroxide (HO ₂₎ and superoxide radical _{(superoxide radical anion) (O 2} -), hydroperoxide anion (hydroperoxide anion) (HO _2- ), which is shown below.

OH + H ₂ O ₂ → HO ₂ + H ₂ O

Fe ^{3 +} + H ₂ O ₂ → Fe ^{2 +} + HO ₂ + H ⁺

^{_{HO 2 → O 2 - + H}} + (pKa = 4.8)

_{^{HO 2 + Fe 2 + → Fe}} 3 + + HO 2 -

As such, by injecting hydrogen peroxide or Fenton reagent as a chemical advanced oxidant or using modified Fenton technique, oil pollutants adsorbed on the adsorbent can be decomposed to restore the adsorptive capacity of the permeable reaction wall.

In the permeable reaction wall regeneration system in which iron reduction bacteria and / or oxidants are automatically sprayed according to the filling, the permeable reaction wall 1 for effectively purifying the contaminated groundwater is flowed into the permeable reaction wall. Installed in the direction perpendicular to the, adjust the interval of the injection well (2) in accordance with the internal permeability. In the case of high permeability, the interval between injection wells is narrowed because the injected chemical is effectively moved and dispersed between the soil voids, and about 1-2 m can be regarded as the general design range. The injection wells are installed from the surface to the depth of the filling zone of the permeable reaction wall, and like the permeable reaction wall, it is preferable to install them in a grid shape at regular intervals in the permeable reaction wall in a direction perpendicular to the flow of contaminated groundwater. . Injection well material is a commonly used well material that has no permeability of the material itself, but the outer circumferential surface of the tubular body portion is provided with a plurality of slits to penetrate the inside can pass through the contaminated water without passing through the soil. The injection well has a tubular body portion (2-0), such as a cylindrical and polygonal tubular shape, both ends of which are open, the upper end of which is closed with a packing (2-3), and the lower end has a screen and is perforated on the screen. Through the holes or slits on the outer circumferential surface of the injection well, the injection chemicals are dispersed from the inside of the injection well into the filler in the permeable reaction wall, and the reaction takes place.

The control unit 3 which operates the drug injection and injection system based on the set concentration value for the contamination level can effectively monitor the pollution level and permeable reactive wall regeneration ability through a system capable of periodically logging the concentration value. The control unit 3 may further include any one or more of a dashboard or a recorder for recording the pollutant concentration to enable monitoring of the pollutant concentration. The recorder allows you to record pollutant concentrations periodically so you can see how concentrations change over time so you can operate your system systematically.

Figure 3 is a perspective view of the automatic injection well of the permeable reaction wall regeneration system through the automatic chemical injection for preventing pollution diffusion according to the present invention. Referring to FIG. 3, a plurality of automatic injection wells 2 installed in the permeable reaction wall 1 have a cylindrical body portion 2-0, a groundwater pollution sensor 2-1, and a chemical injection pipe ( 2-2), packing 2-3, and injection hole 2-4.

The groundwater pollution sensor 2-1 is a pollutant sensor commonly used to monitor the concentration of contaminants in the contaminated water or the treated water according to the present invention. Groundwater contamination sensor is preferably installed inside the injection well for convenience of construction, it may be located outside the injection well as needed.

The chemical injection pipe (2-2) is a device for injecting the drug, that is, iron reducing bacteria or / and oxidant transferred from the chemical tank (4) into the injection well (2), the contamination of the pollutants detected by the groundwater pollution sensor When the concentration is higher than the set concentration value, the metering pump 4-1 is operated by the control signal of the control unit and the chemical is sent from the chemical tank to the chemical injection tube.

The packing (2-3) is fixed to the groundwater contamination sensor (2-1) and the chemical injection pipe (2-2), and when the medicine is injected in a state in which the injection well closed by the packing, the groundwater in the injection well Dispersion of the drug is achieved through the media. If the drug is continuously injected, the drug is discharged to the injection hole (2-4) provided in the chemical injection pipe is made to be dispersed between the permeable reaction wall filler filler voids. The jets 2-4 are preferably screens for multiple drilling or effective dispersion.

Figure 4 (a), (b) is a table and graph showing the regeneration effect of the permeable reaction wall that adsorbs oil material during chemical oxidant injection, 5.3m × 1.6 by selecting a specific oil pollution site inside the oil bag After the permeable reaction wall having the m-scale chemical treatment zone and the biological treatment zone and the permeable reaction wall regeneration system through the automatic injection of the present invention, BTEX (benzene, toluene, ethylbenzene, xylene), which are representative pollutants ), The effect was tested. Injecting hydrogen peroxide and iron / oxalate solutions simultaneously as chemical oxidants produced highly reactive Hydroxyl Radicals. The injected amount was 1 ton of iron / oxalate solution and 1 ton of hydrogen peroxide solution. Chemical oxidant was injected to be uniformly diffused in the wall through the injection wells installed at regular intervals in the permeable reaction wall. According to FIG. 4, before injecting the oxidant according to the present invention, the reactivity of the permeable reaction wall decreased 2.75 ppm of benzene in the treated water, but 0.07 ppm was measured after 3 days of injecting the oxidant. Toluene is 3.32 before oxidant injection, 0.00 after 3 days of injection, ethylbenzene is 0.04 before oxidant injection, 0.00 after 3 days of injection, xylene is 3.21 before injection of oxidant, and 3 days after injection Afterwards, it was confirmed that the amount of adsorption fixed in the permeable reaction wall was greatly reduced to 0.77 to restore the adsorption capacity. This shows the elevated effect of the water permeable reaction wall regeneration system according to the present invention.

1: permeable reactive wall 2: automatic injection well
2-0: Body 2-1: Groundwater Pollution Degree Sensor
2-2: Chemical injection pipe 2-3: Packing
2-4: injection hole 3: control unit
4: Chemical tank 4-1: Metering pump

Claims (8)

In the regeneration system of permeable reaction wall for the purification of contaminated groundwater,
A cylindrical body portion (2-0), the ground water pollution sensor (2-1) is installed in contact with the contaminated water in the body portion to monitor the concentration of pollutants, the drug is transferred from the chemical tank to the body portion A chemical injection pipe (2-2) to be injected into the interior, the packing (2-3) formed so as to penetrate the ground water pollution sensor and the chemical injection pipe while closing the upper end of the body portion, the chemical injection pipe is provided to spray the medicine An automatic injection well (2) having injection holes (2-4) and installed in the permeable reaction wall (1), respectively;
A chemical tank (4) for storing a chemical for regenerating the permeable reaction wall; And
Automatic injection of chemicals for preventing the contamination of the diffusion, characterized in that it comprises a control unit (3) to determine whether the chemical input according to the pollutant concentration detected by the groundwater pollution sensor of the automatic injection well and transmits a signal to the chemical tank Permeable reactive wall regeneration system through The method of claim 1,
The body part (2-0) has a plurality of slits, water permeable reaction wall regeneration system through the automatic injection of chemicals to prevent contamination diffusion. The method of claim 1,
The chemicals stored in the chemical tank 4 are permeable through automatic spraying of chemicals to prevent contamination diffusion, characterized in that it comprises an iron oxidizing agent or reducing the oxidant or the filler of the permeable reaction wall from trivalent iron oxide to divalent iron oxide. Sex Reactive Wall Regeneration System. The method of claim 1,
The chemical tank 4,
Through the automatic injection of medicine to prevent contamination diffusion, characterized in that it comprises a metering pump (4-1) for transferring the medicine to the medicine injection pipe (2-2) according to the control signal transmitted from the control unit (3) Permeable Reactive Wall Regeneration System. The method of claim 1,
The control unit 3,
A permeable reactive wall regeneration system using automatic spraying of chemicals for preventing contamination, characterized in that it comprises at least one of an instrument panel for monitoring the concentration of pollutants or a recorder for recording the concentration of pollutants. In order to automatically regenerate the permeable reaction wall according to the pollutant concentration,
Detecting the concentration of pollutant in the groundwater pollution sensor 2-1;
Transmitting the concentration detected by the groundwater pollution sensor 2-1 to the controller 3;
When the detected concentration is greater than or equal to the set concentration value, a control signal is transmitted from the control unit to the chemical tank 4 to operate the metering pump 4-1 connected to the chemical tank;
Injecting the medicine through the injection port (2-4) by injecting the medicine from the chemical tank (4) to the chemical injection pipe (2-2) of the automatic injection well by the operation of the metering pump; And
A method for regenerating a permeable reactive wall through automatic spraying of a chemical for preventing pollution diffusion, characterized in that the step of reacting the medicine and the filler of the permeable reactive wall is regenerated. The method according to claim 6,
The drug,
A method for regenerating a permeable reactive wall through automatic spraying of a chemical to prevent contamination diffusion, comprising: an oxidizing agent for regenerating a packed substance by decomposing contaminants adsorbed on an adsorbent, which is a filler of the permeable reactive wall. The method according to claim 6,
The drug,
A method for regenerating a permeable reactive wall through automatic chemical spraying for preventing the diffusion of pollution, characterized in that it comprises iron reducing bacteria to reduce the filling of the permeable reactive wall from trivalent iron oxide to divalent iron oxide.

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