JP2017186772A - Groundwater recharge system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a groundwater recharge system, in which water flow efficiency in the recharge system is maintained and clogging of ground near a water injection well may be prevented.SOLUTION: A groundwater recharge system 11 comprises a closed drawn water well 1 for drawing groundwater W, a removal part 20 into which the groundwater W drawn from the drawn water well 1 is introduced and in which floating substance component and metal oxide contained in the groundwater W are removed, a reducing agent supplementation part 14 in which groundwater W filtrated at a filtration part 20 is supplied with reducing agent Re at a level where the oxidation-reduction potential of the groundwater W is reduced to a predetermined value or less, a water injection well 2 for injecting the groundwater W supplied with the reducing agent Re into the ground. The groundwater W drawn from the drawn water well 1 is led to the water injection well 2 via closed water pipes.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a groundwater recharge system.

  In general, in underground excavation work, in order to moderate moisture in the excavation work part, excavation is performed in a state in which the groundwater in the excavation part is pumped up near the ground surface in advance and the groundwater level is lowered before excavation. At this time, in order to reduce the sewage discharge flow and the effects of lowering the water level around the site, a recharge method may be employed in which the pumped groundwater is returned to the ground again.

  However, in the conventional recharge method and groundwater treatment method, the ground in the vicinity of the screen of the recharge well (water injection well) is likely to be clogged, and it has been difficult to maintain the water injection performance of the recharge well for a long time.

In view of this, various techniques have been proposed for removing clogging substances contained in groundwater pumped from the excavated portion near the surface before excavation on the surface.
For example, Patent Document 1 discloses a clogging prevention device (recharge system) including a cylindrical hollow tube and a cylindrical filter provided at the center of the hollow tube. . In this clogging prevention device, an annular space is formed between the inner periphery of the hollow tube body and the outer periphery of the filter portion, and the discharged water (groundwater) containing construction-generated water, rainwater, groundwater, etc. is contained in the annular space. ) Is introduced into the annular space so that a swirling flow that faces downward from the tangential direction with respect to the horizontal line occurs. Large foreign matter in the discharged water falls downward due to the centrifugal force and the difference in gravity, and the small foreign matter floats upward and passes through the filter portion, so that the solid content in the discharged water is filtered. . Then, the treated water after filtration is taken out from the inner peripheral side of the filter unit.

Japanese Patent No. 4379086

  However, since the clogging prevention device disclosed in the above-mentioned Patent Document 1 is mainly intended to remove suspended solids (hereinafter referred to as SS) components such as clay particles, clogging occurs. There was a problem that the occurrence of the phenomenon could not be fundamentally suppressed. In addition, even if the recharge is stopped and the recharge well is backwashed over time in order to restore the water charge performance of the recharge well, the ground near the recharge well will be clogged. It was difficult to recover.

  As a result of intensive studies, the present inventor has found that iron contributes significantly in addition to SS components such as clay particles as the cause of clogging of the ground near the recharge well. Normally, iron in groundwater exists in a divalent form (bivalent iron), but even if it is pumped to the ground surface through a sealed pipe, as in a conventional recharge system, deep well If a slight amount of air is touched inside the (pumped well) or the recharge well, it changes to a trivalent form (trivalent iron, ie, insoluble iron). In particular, trivalent iron causes significant clogging in the ground and recharge well screen and filter material on the water injection side even at low concentrations. The present inventor studied the configuration of a groundwater recharge system for preventing trivalent iron from reaching the vicinity of the water injection portion of the recharge well, and completed the present invention.

  The present invention has been made in view of the above circumstances, and provides a groundwater recharge system capable of maintaining the water flow performance of the recharge system and preventing clogging of the ground near the water injection well.

  The groundwater recharge system according to claim 1 is a groundwater recharge system for performing a recharge method for pouring the pumped groundwater into the ground, and includes a sealed pumping well for pumping the groundwater, and the pumped well. A removal unit that introduces the pumped groundwater and removes suspended solid components and metal oxides present in the groundwater, and a redox potential of the groundwater is equal to or lower than a predetermined value in the groundwater treated by the removal unit. A reductant addition part for adding a reductant to and a water injection well for pouring the groundwater to which the reductant is added into the ground, and the groundwater pumped from the water well is sealed It guide | induces to the said water injection well through a water pipe.

According to the above-described configuration, the groundwater pumped from the pumping well is introduced into the filtration unit through the sealed water pipe. If air or the like is slightly mixed in the sealed water pipe, divalent iron in the groundwater is oxidized and trivalent iron is deposited. At this time, manganese that can affect the clogging of the ground although having less influence than iron can also be deposited as hydrated manganese dioxide. Slightly precipitated metal oxides such as trivalent iron are removed from the groundwater by passing through the removal section together with SS components such as clay particles. That is, the clogging cause component in the groundwater is removed by the removing unit. Then, the reducing agent is added to the groundwater treated by the removing unit until the oxidation-reduction potential becomes a predetermined value or less, and the groundwater is sufficiently reduced. Therefore, the groundwater pumped from the pumping well is freed from components that cause clogging of the ground in the vicinity of the pumping well and is reduced, so even if this groundwater is injected into the ground from the pumping well, Clogging of the ground in the vicinity of the filter and the water injection well almost disappears.
The above-mentioned predetermined value is a redox potential that indicates the allowable amount of oxidant remaining in the groundwater that can satisfactorily prevent clogging of the ground when water is poured into the ground by a water injection well. Is the amount that completely loses oxidizing power.

  In the groundwater recharge system according to claim 2, the predetermined value is 200 mV or less.

  According to the above-described configuration, the groundwater to which the reducing agent is added by the reducing agent addition unit is sufficiently and well clogged in the ground in the vicinity of the water injection well even when water is injected into the ground from the water injection well having the existing configuration. It will be in a state that can be prevented.

  The groundwater recharge system according to claim 3, wherein a water level of the pumping well is configured to be higher than a pumping position of the groundwater.

  According to the above-described configuration, in the pumping well, the mixing of air during the pumping of groundwater, the oxidation of groundwater due to the mixing of air, and the oxidation of divalent iron in the groundwater can be more reliably suppressed.

  The groundwater recharge system according to claim 4 is characterized in that the removing unit is constituted by a spring type filter.

  According to the above configuration, since groundwater pumped from the pumping well is filtered by the spring filter, a slight amount of metal oxide such as trivalent iron deposited in the groundwater is captured by the spring filter of the spring filter. Even if clogging occurs, backwash air is added to the spring filter and the pressure is controlled, so that the metal oxide such as trivalent iron and SS components can be removed easily and almost automatically. Discharged. Therefore, a groundwater recharging system having an excellent self-cleaning effect and a low maintenance burden can be obtained.

  The groundwater recharge system according to claim 5, wherein the reducing agent addition unit adds the reducing agent to the groundwater treated by the removing unit, and the reducing agent is added by the reducing agent addition device. A first reduction potential detector that detects the oxidation-reduction potential of the groundwater before being discharged, and feeds back the detected oxidation-reduction potential to the reducing agent addition device, and the reducing agent is added by the reducing agent addition device. At least one of a second reduction potential detector that detects the oxidation-reduction potential of the groundwater after the detection and feeds back the detected oxidation-reduction potential to the reducing agent addition device. The reducing agent addition amount is configured to be adjustable based on information fed back from at least one of a potential detection unit and the second reduction potential detection unit. It is characterized in.

  According to the above-described configuration, the ground water oxidation-reduction potential is detected by at least one of the first oxidant detecting unit and the second dioxide agent detecting unit, and fed back to the reducing agent addition device, whereby excessive addition or addition of reducing agent is performed. Shortage is suppressed, groundwater is efficient, and when it is poured into the ground, it becomes a reduced state that can well prevent clogging.

  According to the groundwater recharge system of the present invention, the ferrous iron contained in the groundwater pumped from the pumping well and causing the clogging of the ground in the vicinity of the filter and the water injection well is not oxidized as much as possible. The trivalent iron that is still slightly deposited is removed by the filtration unit, and the groundwater is reduced by the reducing agent addition unit. Therefore, when the groundwater pumped from the pumping well is poured into the ground, it can be brought into a reduced state that can well prevent clogging of the ground. Thereby, the water flow performance of a groundwater recharge system can be kept favorable and clogging of the ground can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic (partial sectional drawing) which shows one Embodiment of the groundwater recharge system which concerns on this invention. It is a side view which shows the principal part of the pumping well of a groundwater recharge system, Comprising: (a) is related with a general pumping well, (b) is related with the pumping well of the groundwater recharge system shown in FIG. It is a schematic diagram which shows the structure of the test apparatus at the time of performing the column test which watered the water which adjusted the density | concentration of trivalent iron with the fixed head difference. It is a graph which shows the measurement result at the time of performing the column test which watered the water which adjusted the density | concentration of trivalent iron with the fixed head difference. It is the schematic which shows the mode of operation in the spring type filter used for the spring type filter of the filtration part of the groundwater recharge system shown in Drawing 1, and (a) is a figure showing the mode at the time of normal operation (recharge operation). Yes, (b) is a diagram showing a state during the backwash operation. It is a graph which shows an example of the filtration performance by the spring type filter used for the spring type filter of the filtration part of the groundwater recharge system shown in FIG. It is the schematic which shows the modification of the groundwater recharge system which concerns on this invention.

  Hereinafter, an embodiment of a groundwater recharge system according to the present invention will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the ratios of length, width, and thickness are not necessarily the same as actual ones, and can be changed as appropriate.

FIG. 1 is a schematic diagram illustrating a configuration of a groundwater recharge system 11 according to the present embodiment.
As shown in FIG. 1, the groundwater recharge system 11 is installed at a site where excavation work or the like is performed. The groundwater W pumped from the aquifer (ground) S2 by the pumping well 1 is supplied to the water injection well 2. It is a system for conducting a recharge method for guiding water from the water injection well 2 into the aquifer (ground) S3.

  The ground illustrated in FIG. 1 has a structure in which aquifers S1, S2, S3,... And clay layers C1, C2,. In addition, if a recharge construction method is applicable, the structure of a ground, a pumping position, and a water pouring position will not be specifically limited.

  As shown in FIG. 1, a groundwater recharge system 11 introduces a pumping well 1 for pumping up groundwater W, and groundwater W pumped from the pumping well 1, so that suspended matter components and metal oxides present in the groundwater W are introduced. The reducing unit 20 for removing the reducing agent, the reducing agent adding unit 14 for adding the reducing agent Re to the groundwater W treated by the removing unit 20 until the oxidation-reduction potential of the groundwater W becomes a predetermined value or less, and the reducing agent Re are added. Water injection well 2 for injecting the groundwater W into the aquifer (ground) S3, and a pumping pipe (water pipe) 8A and a water pipe 8B in which the groundwater W pumped from the pumping well 1 is sealed. This is a system that leads to the water injection well 2 through 8C and 8D.

  The pumping well 1 is a well-known drainage facility for pumping up groundwater W in the aquifer S2, and specifically, a deep well (so-called so-called deep well) installed in an excavation region X partitioned by earth retainings D and D. , Deep well). Near the lower end of the pumping well 1, a screen 1a embedded in the ground deeper than the groundwater level (the aquifer S2 in FIG. 1) is formed, and groundwater W in the ground flows from the screen 1a. Groundwater W is stored in the pumping well 1. Moreover, the lid | cover is attached to the upper end of the pumping well 1, the upper end of the pumping well 1 is sealed with the lid | cover, and the pumping well 1 has a sealed structure.

  In the groundwater W pumped from the pumping well 1, iron exists in a divalent state, that is, as divalent iron having solubility. The divalent iron in the groundwater W changes to trivalent iron when it is exposed to air or the like even during the process of pumping, or during the subsequent treatment. In the groundwater recharge system 11 of the present embodiment, it is important to suppress as much as possible oxidation and precipitation of divalent iron dissolved in the groundwater W in the process from after pumping up to being treated by the removing unit 20. It is more important to suppress the oxidation and precipitation of divalent iron in the groundwater W as the concentration of divalent iron in the groundwater W increases.

2A shows a state when pumping groundwater in a general pumping well, and FIG. 2B shows a state when pumping groundwater W in the pumping well 1 of the groundwater recharge system 11. ing. In FIGS. 2A and 2B, the screen 1a is omitted. In a general pumping well, the groundwater W is sucked up to the limit whether or not the suction port (pumping position) Pa of the pumping pump P1 is exposed to the air environment in the pumping well 1. Then, as shown in FIG. 2 (a), the water inlet Pa is exposed to the air environment in the pumping well 1, and not only groundwater but also air is sucked up together from the water inlet Pa, and oxidation of the groundwater W and in the groundwater W The oxidation of divalent iron was promoted.
Therefore, in the pumping well 1 of the groundwater recharge system 11, the water level in the well is kept higher than the water inlet Pa of the pumping pump P1. In addition, from the viewpoint of more reliably preventing oxidation of the groundwater W and oxidation of divalent iron in the groundwater W, the pumping well 1 is preliminarily filled with an inert gas such as helium, nitrogen, or argon. preferable. The inert gas is not particularly limited, but nitrogen is preferable from the viewpoint of cost and the like.

  FIG. 3 is a schematic diagram showing a configuration of a test apparatus when a column test is performed in which water adjusted in the concentration of trivalent iron is passed with a constant head difference H (that is, H shown in FIG. 3). In the test apparatus shown in FIG. 3, the inner diameter D of the column 50 was 30 mm. The Toyoura sand S which assumed the soil in the ground was put in the bottom part, and water WF 'which adjusted the density | concentration of trivalent iron, stirring in the water tank 52 was flowed through the column 50. FIG. The water flow rate of the water WF at the initial stage of water flow was set to 15 mL / min to 16 mL / min. The water WF that passed through the column S was introduced into the water tank 54. In order to maintain a constant water head difference H, the water tank 54 is provided with a mechanism for discharging the groundwater WF higher than a predetermined position in the water tank 54 and a water tank 56 for storing the discharged groundwater WF.

FIG. 4 is a graph showing the measurement results when the above-mentioned column test was performed by changing the concentration of trivalent iron from 0.05 mg / L to 10 mg / L as indicated by the numerical values shown in the graph. The measurement results when the above-described column test is performed using tap water (the concentration of iron and its compound is 0.01 mg / L to 0.02 mg / L) used in the experiment are also shown. The horizontal axis of the graph indicates the elapsed time of water flow to the column 50, and the vertical axis of the graph indicates the amount of passing water WF from the column 50 to the water tank 54. If the Toyoura sand S is not clogged, in the graph, the relationship between the elapsed time of water flow to the column 50 and the amount of water WF passed to the column 50 is linear (the (linear) straight line shown in FIG. 3) and Become. As shown in FIG. 3, when the concentration of trivalent iron in water is 0.1 mg / L or more, clogging occurs in Toyoura sand S in a short time, and the amount of water flow (that is, the amount of water injection) cannot be maintained. I understand that.
Therefore, in the groundwater recharge system 10, in order for the groundwater W to be in a state that can sufficiently and satisfactorily prevent clogging of the ground near the water injection well, the concentration of trivalent iron in the groundwater W is at least 0.1 mg / L. It is important that it is smaller, preferably smaller than 0.05 mg / L, more preferably smaller than 0.01 mg / L.

  As shown in FIG. 1, the pumped well 1 and the removing unit 20 are communicated with each other by a sealed pumped-up pipe 8A. One end of the pumping pipe 8A is inserted into the pumping well 1 from the upper end of the pumping well 1, and the other end of the pumping pipe 8A is connected to the inlet of the removing unit 20. One end of a pumping pipe 8A inserted into the pumping well 1 is connected to a discharge port of a pumping pump P1 disposed in the pumping well 1, and the groundwater W in the pumping well 1 is pumped by the pumping pump P1. It is pumped into the removal section 20 through the inside of 8A.

  The removal unit 20 introduces the groundwater W that has been pumped into the filtration unit 20 through the pumping pipe 8A, and the SS component in the groundwater W or air slightly mixed even when pumped in a sealed environment. It is equipment for removing metal oxides (ie, trivalent iron and the like) including iron and manganese in the precipitated groundwater W, and is equipped with a device composed of a spring filter. Specific examples of the spring filter include a liquid filter element disclosed in Japanese Patent Laid-Open No. Hei 8-196211, a spring filter apparatus disclosed in Japanese Patent No. 1822317, and the like. Is mentioned. The spring type filter is made of stainless steel (SUS) made of a very rust-resistant material into a special wire shape, and after applying this pre-coating material to a spring type filter with this hard spring wire wound in a coil shape, This is based on the concept of removing the residue adhering to the precoat material together with the precoat material. Such a spring type filter has a particularly excellent self-cleaning effect and a backwashing regeneration function, and has features and conditions suitable for filtering the groundwater W in the present invention, such as making maintenance substantially unnecessary. .

  Conventionally, the spring type filter used in the spring type filter of the removing unit 20 has been used mainly for drainage (turbid water) treatment. However, in the filtration process, the spring type filter is coated at the first stage. By appropriately selecting the precoat material (i.e., filter aid), the particle size (i.e., filtration accuracy) filtered by the spring filter can be determined. In addition, precise filtration can be realized at high speed and low pressure.

Further, the spring filter of the removing unit 20 does not require an additive such as a flocculant.
FIG. 5A is a schematic diagram showing a state of normal operation (recharge operation) in the spring filter of the spring filter of the removing unit 20, and FIG. 5B is a clogging component of the spring filter. It is the schematic which shows the mode at the time of the backwash operation for removing. During normal operation, as shown in FIG. 5 (a), groundwater W containing an SS component and metal oxide is introduced into the spring filter, and the filtered groundwater W flows out from the outlet of the spring filter. . As a self-cleaning effect of the spring type filter, as shown in FIG. 5B, the spring type filter is clogged with SS components and metal oxides such as iron and manganese (that is, trivalent iron, etc.). When the efficiency falls below a predetermined efficiency, backwash air is press-fitted through a sealed water injection pipe 8b (see FIG. 1) connected to the outlet side of the spring-type filter of the removing unit 20 and the like. Thus, the pressure from the inside to the outside of the spring type filter is automatically applied and controlled. As a result, so-called backwashing is performed, and the clogging component captured by the spring filter can be collected and discarded as a concentrated liquid via a drain pipe (not shown in FIG. 1).

  FIG. 6 is a graph showing an example of filtration performance by a spring filter when a spring filter device (manufacturer: Monobe Engineering Co., Ltd.) is used as a spring filter used in the spring filter of the removing unit 20. is there. In this filtration performance measurement, the flow rate per spring of the spring type filter was made constant at 1 L / min, and the concentration of trivalent iron in the water flow was set to 2 mg / L. Under such conditions, the pressure change in the spring type filter was measured. As the precoat material, silica # 600H (average particle diameter: 38 μm, pass rate: 2.2 darcy, manufacturer: Chuo Silica Co., Ltd.) was used.

  As shown in FIG. 6, assuming that the cleaning is performed when the internal pressure of the spring filter reaches 200 kPa, when silica # 600H is used as the precoat material, the cleaning is performed once every 60 minutes (ie, Equivalent to washing 24 times a day). The frequency of such washing depends on the concentration of SS components and trivalent iron in the water to be treated. However, as can be seen from the frequency of washing, cleaning and replacement of removal materials or filtration materials that rely on human power are subject to treatment. It is difficult to keep the concentration of SS water and the concentration of trivalent iron so that the ground is not clogged to the same extent as when using a spring-type filter. In addition, when the above-mentioned precoat material was used, the density | concentration of the trivalent iron contained in the water after filtration became 0.05 mg / L or less. As a result of passing the filtered water through the column test apparatus shown in FIG. 3, it was found that clogging was almost the same as tap water as shown by “treated water” in FIG. 4. This also shows that the water filtered with the spring filter has a water quality that allows the long-term water injection to be successfully removed from the substances causing clogging.

  In addition, the structure of the removal part 20 is not limited to the spring-type filter mentioned above, It has the capability which can remove obstetric metals, such as SS component contained in the groundwater W introduce | transduced into the removal part 20, and the precipitated trivalent iron. If it is a thing, it will not specifically limit. For example, the removing unit 20 may be any one of a filter press, a belt press, a back filter, a centrifuge, a sand filter, and the like.

  As shown in FIG. 1, the removal unit 20 and the filtrate water tank 32 are communicated with each other by a sealed water pipe 8B. One end of the water conduit 8 </ b> B is connected to the outlet of the filtration unit 20, and the other end of the water conduit 8 </ b> B is open to the inside of the filtrate water tank 32. The groundwater W filtered by the filtration unit 20 is supplied into the filtrate water tank 32 through the water pipe 8B.

  The filtrate water tank 32 is configured so as to accommodate the groundwater W filtered by the removing unit 20 and to be derived from a predetermined position. Moreover, the lid | cover is attached to the upper end of the filtrate water tank 32, the upper end of the filtrate water tank 32 is sealed by the lid | cover, and the filtrate water tank 32 has a sealing structure. The filtered water tank 32 is not particularly limited as long as it can be sealed as described above, and a known underground water tank or the like can be applied.

  Inside the filtrate water tank 32, one end of a sealed reducing agent supply pipe 8c is arranged in addition to the other end of the water pipe 8B. The other end of the reducing agent supply pipe 8 c is connected to the reducing agent discharge port of the reducing agent addition device 15 of the reducing agent addition unit 14. The ground water W is filtered by the filtration unit 20 and accommodated in the filtrate water tank 32. On the other hand, the reducing agent Re can be supplied from the reducing agent addition unit 14 via the reducing agent supply pipe 8c.

  The reducing agent addition part 14 is a structure for making the groundwater W filtered (processed) by the filtration part 20 into a reduced state. In the present embodiment, the reducing agent adding unit 14 is reduced by the reducing agent adding device 15 that adds the reducing agent Re to the groundwater W that is filtered by the filtering unit 20 and accommodated in the filtrate water tank 32, and is reduced by the reducing agent adding device 15. The reducing agent is detected by the first reducing potential detector 26 that detects the redox potential of the groundwater W before the agent Re is added, and feeds back the detected redox potential to the reducing agent adding device 15. And a second reduction potential detector 27 that detects the oxidation-reduction potential of the groundwater W after the addition of Re and feeds back the detected oxidation-reduction potential to the reducing agent addition device 15. The reducing agent addition unit 14 is configured to be able to adjust the addition amount of the reducing agent Re based on information fed back from at least one of the first reduction potential detection unit 26 and the second reduction potential detection unit 27. Yes.

The reducing agent addition device 15 is not particularly limited as long as the reducing agent Re can be discharged to the other end of the sealed reducing agent supply pipe 8c.
The reducing agent Re supplied from the reducing agent addition device 15 of the reducing agent addition unit 14 is not particularly limited as long as it contains a substance capable of reducing the groundwater W. Examples of such substances include sodium thiosulfate, sodium sulfite, and sodium hydrosulfide. Sodium thiosulfate is suitable because it is a highly safe substance such as being used as a material for dechlorination of ornamental fish.

  The first reduction potential detection unit 26 is not particularly limited as long as it introduces a part of the groundwater W flowing in the water pipe 8B after being processed by the removal unit 20 and can detect the oxidation-reduction potential of the introduced groundwater W. . The water pipe 8B is provided with a pumping pump P2 for introducing a part of the groundwater W to the first reduction potential detector 26 as necessary. The detected oxidation-reduction potential of the groundwater W is directly fed back to the reducing agent adding device 15, and the supply amount (adding amount) of the reducing agent Re in the reducing agent adding device 15 (reducing agent adding unit 14) based on the fed back information. May be adjusted. In the present embodiment, the oxidation-reduction potential of the groundwater W detected by the first reduction potential detection unit 26 is sent to the control unit 30 as a signal S26.

  The second reduction potential detection unit 27 is supplied with the reducing agent Re from the reducing agent addition device 15, introduces a part of the groundwater W led out from the filtrate water tank 32 to the water flow pipe 8 </ b> C, and introduces the introduced groundwater W There is no particular limitation as long as the oxidation-reduction potential of can be detected. The water pipe 8C is provided with a pumping pump P3 for introducing a part of the groundwater W to the second reduction potential detector 27 as necessary. The detected oxidation-reduction potential of the groundwater W is directly fed back to the reducing agent adding device 15, and the supply amount (adding amount) of the reducing agent Re in the reducing agent adding device 15 (reducing agent adding unit 14) based on the fed back information. May be adjusted. In the present embodiment, the oxidation-reduction potential of the groundwater W detected by the second reduction potential detection unit 27 is also sent to the control unit 30 as a signal S27.

  Although the reducing agent addition part 14 is provided with at least one of the 1st reduction potential detection part 26 and the 2nd reduction potential detection part 27, the oxidation reduction potential of the groundwater W supplied to the water injection well 2 is made into predetermined value or less. In order to make the groundwater W more reliably reduced and to reliably prevent excessive addition and insufficient addition of the reducing agent Re to the groundwater W, both the first reduction potential detection unit 26 and the second reduction potential detection unit 27 are provided. It is preferable that In addition, the 1st reduction potential detection part 26 and the 2nd reduction potential detection part 27 may be integrated, and may mutually be comprised as one detection part.

  Examples of the first reduction potential detection unit 26 and the second reduction potential detection unit 27 include an ORP (Oxidation-Reduction Potential) sensor and a dissolved oxygen sensor. From the viewpoint of simple configuration and easy installation, the first reduction potential detection unit 26 and the second reduction potential detection unit 27 are preferably ORP sensors. When using the ORP sensor, an ORP that is a potential determined by an equilibrium state between an oxidant and a reductant coexisting in the groundwater W is appropriately set. As a state in which the groundwater W can sufficiently and satisfactorily prevent clogging of the aquifer (ground) S3 in the vicinity of the injection well, it is preferable that no oxidant remains in the groundwater W after the addition of the reducing agent. The oxidation-reduction potential measured by the ORP sensor of the oxidant detection unit 26 and the second dioxide detection unit 27 is at least 200 mV or less, preferably 100 mV or less, and more preferably 0 mV or less.

  In addition, the residual amount of SS component in the groundwater W processed by the removal part 20 can be measured using the turbidimeter etc. which are not shown in figure. From the point that the clogging of the ground can be satisfactorily prevented when the groundwater W is poured into the ground, for example, the concentration of the SS component in the groundwater W treated by the removing unit 20 is less than 1 mg / L. It is preferable that this is confirmed.

The groundwater recharge system 11 of this embodiment includes a control unit 30. The control unit 30 supplies the reducing agent Re in the reducing agent addition device 15 based on the signals (information) S26 and S27 fed back from the first reduction potential detection unit 26 and the second reduction potential detection unit 27. Is set appropriately and sent to the reducing agent adding device 15 as a signal S15.
An example of what constitutes the control unit 30 is a computer, but is not particularly limited as long as it has the above-described function.

The control unit 30 detects from the feedback of the second reduction potential detection unit 27 that the redox potential of the groundwater W derived from the filtrate water tank 32 after the addition of the reducing agent Re is larger than the predetermined value described above. In the case, it is preferable to have a function of stopping the derivation of the groundwater W from the filtrate water tank 32.
That is, it is preferable that the control unit 30 is configured by a computer in which a control program or the like is built. The above-described control program is a procedure in which the computer captures the redox potential of the groundwater W detected by the second reduction potential detector 27 and the redox potential of the groundwater W is equal to or less than a preset threshold value (predetermined value). If the outlet of the filtrate water tank 32 and the water pipe 8C are in communication with each other, and if the oxidation-reduction potential of the groundwater W exceeds the threshold, the outlet of the filtrate water tank 32 and the water pipe 8C are not in communication. It is preferable to be configured to execute the procedure for setting the state.

  The filtrate water tank 32 and the water injection well 2 are branched from the middle of the sealed water pipe 8C and the water pipe 8C, and are communicated by a sealed water pipe 8D. One end of the water conduit 8 </ b> C is connected to the outlet of the filtrate water tank 32, and the other end of the water conduit 8 </ b> C is opened deeper than a predetermined water level of the water injection well 2 </ b> B in the water injection well 2. A stirrer 24 for mixing the ground water W and the reducing agent Re added to the ground water W is provided on one end side of the water pipe 8C. As the stirring device 24, for example, a static mixer having a small and simple configuration can be used, but is not particularly limited as long as the ground water W and the reducing agent Re can be mixed.

  One end of the water pipe 8D is connected to the middle of the water pipe 8C, and the other end of the water pipe 8D is opened in a deep portion from the predetermined water level of the water injection well 2A in the water injection well 2. Groundwater W derived from the filtrate water tank 32 and having an oxidation-reduction potential of a predetermined value or less is supplied to the water injection wells 2A and 2B through the water pipes 8C and 8D.

The water injection well 2 includes the two water injection wells 2A and 2B as described above. However, the number of wells provided in the water injection well 2 is not particularly limited.
The water injection wells 2A and 2B are well-known water injection facilities (so-called recharge wells) for injecting the groundwater W in a reduced state into the aquifer S3, specifically, wells installed outside the excavation region X Consists of. In the water injection wells 2A and 2B, a screen 2a embedded in the ground deeper than the groundwater level (the aquifer S3 in FIG. 1) is formed, and the groundwater W in the water injection wells 2A and 2B flows out from the screen 2a. Then, groundwater W is injected into the aquifer S3. Moreover, the lid | cover is attached to the upper end of the water injection well 2, the upper end of the water injection well 2 is sealed with the lid | cover, and the water injection well 2 has a sealed structure.

As described above, in the groundwater recharge system 11 of the present embodiment, the groundwater W pumped from the pumping well 1 is introduced into the removal unit 20 via the sealed pumping pipe 8A. If there is air or the like slightly mixed even in the sealed pumping well 1 and the pumping pipe 8A, divalent iron in the groundwater W is oxidized and trivalent iron is deposited. Precipitated metal oxides such as trivalent iron and manganese can be removed from the groundwater W by passing through the removal section 20 together with SS components such as clay particles. That is, the clogging cause component in the groundwater W can be removed by the removing unit 20. And the reducing agent Re is added by the reducing agent addition part 14 to the groundwater W filtered by the removal part 20 until the oxidation-reduction potential becomes below a predetermined value, and the groundwater W is fully reduced. Accordingly, the groundwater W pumped from the pumping well 1 can be brought into a reduced state by removing components that cause clogging of the ground near the water injection well 2. Even when water is poured into the water, clogging of the filter of the water injection well 2 and the ground near the water injection well 2 can be prevented over a long period of time.
Due to the effects described above, the groundwater recharge system 11 according to the present embodiment has compared the groundwater W, that is, the divalent iron, in which the clogging of screens and filters provided in the ground or water injection well on the water injection side is high. It is possible to cope with groundwater W including a large amount.

  According to the groundwater recharge system 11 of the present embodiment, the groundwater W to which the reducing agent Re is added by the reducing agent adding unit 14 has an existing configuration by setting the groundwater oxidation-reduction potential to a predetermined value of 200 mV or less. Even if water is injected into the ground from the water injection well 2, clogging of the ground near the water injection well 2 can be sufficiently and satisfactorily prevented.

  According to the above-described configuration, the water level in the pumping well 1 is configured to be higher than the water inlet Pa of the pumping pump P1 that is the pumping position of the groundwater W. Oxidation of groundwater W and oxidation of divalent iron in groundwater W due to contamination can be more reliably suppressed.

In the above-described configuration, since the groundwater W pumped from the pumping well 1 is filtered by the spring type filter, a slight amount of metal oxide such as trivalent iron or manganese deposited in the groundwater W is spring type of the spring type filter. Even if the filter is trapped and clogged, backwash air is added to the spring filter to control the pressure. Therefore, according to the above-described configuration, the metal oxide such as trivalent iron and manganese and the SS component can be easily and substantially automatically removed and discharged. Therefore, it is possible to construct the groundwater recharge system 11 that has an excellent self-cleaning effect and has a small maintenance burden. Moreover, the performance of the groundwater recharge system 11 can be easily maintained high.
Moreover, according to the groundwater recharge system 11 of the present embodiment, the oxidation and precipitation of divalent iron dissolved in the groundwater W is suppressed as much as possible, the frequency of backwashing operation of the spring filter is reduced, and the backwashing operation is performed. Costs (for example, costs for precoat materials, backwashing power, concentrate processing, etc.) can be reduced. That is, the running cost can be remarkably suppressed by the groundwater recharge system 11 using a spring-type filter as compared with the conventional groundwater recharge system using a filter for wastewater treatment or the like.

  Further, according to the groundwater recharge system 11 of the present embodiment, the redox potential of the groundwater W is detected by at least one of the first reduction potential detection unit 26 and the second reduction potential detection unit 27 and is fed back to the reducing agent addition device 15. By doing so, excessive addition or insufficient addition of the reducing agent Re can be suppressed, and the groundwater W can be efficiently brought into a reduced state in which clogging can be well prevented when poured into the ground. By using both the first reduction potential detection unit 26 and the second reduction potential detection unit 27, the groundwater W can be more efficiently brought into a reduction state that can prevent clogging well when water is poured into the ground. it can.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications are possible within the scope of the gist of the present invention described in the claims. It can be changed.

  For example, in the above-described embodiment, the water quality of the groundwater W can be grasped to some extent before the recharge method is carried out, and the above-described groundwater W pumped from the pumping well 1 as shown in FIG. A certain amount of reducing agent calculated from the water quality may be added. Thereby, the oxidation of the ground water W and the precipitation of trivalent iron from after pumping up to before being filtered by the removing unit 20 can be more reliably prevented, and the backwash frequency of the spring filter can be suppressed.

  For example, in order to observe the state of the groundwater W pumped from the pumping well 1, the pumped groundwater W may be temporarily stored in a sealed notch tank or the like.

DESCRIPTION OF SYMBOLS 1 Pumping well 2,2A, 2B Injection water well 11 Groundwater recharge system 14 Reductant addition part 20 Removal part 26 First reduction potential detection part 27 Second reduction potential detection part Re Reductant W Groundwater

Claims (5)

A groundwater recharge system for performing a recharge method for pouring pumped groundwater into the ground,
A sealed pumping well for pumping the groundwater;
A removal unit that introduces the groundwater pumped from the pumping well and removes suspended solid components and metal oxides present in the groundwater;
A reducing agent addition unit for adding a reducing agent to the groundwater treated in the removal unit until a redox potential of the groundwater becomes a predetermined value or less;
A water injection well for pouring the groundwater to which the reducing agent is added into the ground;
With
A groundwater recharging system, wherein the groundwater pumped from the pumping well is guided to the water injection well through a sealed water pipe.   The groundwater recharge system according to claim 1, wherein the predetermined value is 200 mV or less.   The groundwater recharging system according to claim 1 or 2, wherein a water level of the pumping well is configured to be higher than a pumping position of the groundwater.   The groundwater recharging system according to any one of claims 1 to 3, wherein the removing unit is configured by a spring-type filter. The reducing agent addition part is
A reducing agent addition device for adding the reducing agent to the groundwater treated in the removal unit;
A first reduction potential detection unit that detects the redox potential of the groundwater before the reducing agent is added by the reducing agent addition device, and feeds back the detected oxidation / reduction potential to the reducing agent addition device; and At least one of a second reduction potential detection unit that detects a redox potential of the groundwater after the reducing agent is added by a reducing agent addition device and feeds back the detected redox potential to the reducing agent addition device. When,
With
The reductant addition amount is configured to be adjustable based on information fed back from at least one of the first reduction potential detection unit and the second reduction potential detection unit. The groundwater recharge system according to claim 4.

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