JP6961024B2 - Groundwater recharge system - Google Patents

Description

The present invention relates to a groundwater recharge system.

Generally, in underground excavation work, in order to appropriately suppress the water content of the excavation work part, the groundwater of the excavated part is pumped up near the ground surface in advance before excavation, and the excavation is performed in a state where the groundwater level is lowered. At this time, in order to reduce the sewage discharge rate and the influence of the water level drop around the site, a recharge method may be adopted in which the pumped groundwater is returned to the ground again.

However, in the conventional recharge method and groundwater treatment method, the ground clogging phenomenon near the screen of the recharge well (water injection well) is likely to occur, and it is difficult to maintain the water injection performance of the recharge well for a long period of time.

Therefore, various techniques have been proposed for removing clogging substances contained in groundwater pumped near the ground surface from the excavated portion in advance before excavation.
For example, Patent Document 1 discloses a clogging prevention device (recharge system) including a cylindrical hollow tube body and a tubular filter portion provided in a central portion of the hollow tube body. .. In this clogging prevention device, an annular space is formed between the inner circumference of the hollow tube and the outer circumference of the filter portion, and the discharged water (groundwater) containing construction-generated water, rainwater, groundwater, etc. is formed in the annular space. ) Is introduced into the annular space so that a swirling flow that faces downward from the tangential direction to the horizon occurs. Due to the centrifugal force and the difference in gravity, the heavy foreign matter in the discharged water falls downward, and the light foreign matter floats upward and passes through the filter part, 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 portion.

Japanese Patent No. 4379086

However, the clogging prevention device disclosed in Patent Document 1 described above has a main purpose of removing suspended solids (hereinafter referred to as SS) components such as clay particles, and thus is clogged. 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 for a long time in order to restore the water flow performance of the recharge well, the ground near the recharge well will be clogged, so the initial water injection performance will be reached. It was difficult to recover.

As a result of diligent studies, the present inventor has found that iron contributes significantly in addition to SS components such as clay particles to cause clogging of the ground near the recharge well. Normally, iron in groundwater exists in a divalent form (divalent iron), but as is done in conventional recharge systems, even if it is pumped to the ground surface through a closed pipe, it is a deep well. If it comes into contact with a small amount of air inside the (pumping well) or recharge well, it changes to a trivalent form (trivalent iron, that is, insoluble iron). In particular, ferric iron causes significant clogging of the ground on the water injection side and the screen and filter material of the recharge well, even at low concentrations. The present inventor has studied the configuration of a groundwater recharge system for preventing ferric iron from reaching the vicinity of the water injection portion of such a recharge well, and has 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 the present invention is a groundwater recharge system for performing a recharge method for injecting pumped groundwater into the ground, and is a closed pumping well for pumping the groundwater and pumping from the pumping well. It has been introducing the underground water, before Symbol locations present in sewage suspended solids components and removal unit for removing the metal oxide, and a reducing agent addition unit for adding a reducing agent to the ground water which has been treated by the removal unit, A detection unit for detecting the oxidation- reduction potential of the groundwater treated by the removal unit and a water injection well for injecting the groundwater to which the reducing agent is added into the ground are provided, and the detection unit detects the groundwater. The oxidative reduction potential is fed back to the reducing agent addition section.
The above-mentioned groundwater recharge system is a control unit that adjusts the amount of the reducing agent added to the groundwater treated by the removing unit in the reducing agent addition unit based on the redox potential fed back from the detection unit. May be further provided.
In the above-mentioned groundwater recharge system, the amount of the reducing agent added to the groundwater treated by the removal unit is such that the redox potential is equal to or less than a value indicating that the groundwater has completely lost its oxidizing power. May be adjusted to.

In the above-mentioned groundwater recharge system, the amount of the reducing agent added to the groundwater treated by the removing unit may be adjusted so that the redox potential is 200 mV or less.

According to the above configuration, the groundwater to which the reducing agent has been added by the reducing agent addition portion has sufficient and good clogging of the ground near the water injection well even if water is injected into the ground from the water injection well having the existing configuration. It becomes a state that can be prevented.

In the above-mentioned groundwater recharge system, the water level of the pumping well may be configured to be higher than the pumping position of the groundwater.

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

In the above-mentioned groundwater recharge system, the removing portion may be composed of a spring type filter.

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

In the above groundwater recharge system, the metal oxide may include insoluble valent iron.
In the above-mentioned groundwater recharge system, the insoluble iron may be trivalent iron obtained by oxidizing divalent iron in the groundwater pumped from the pumping well.
In the above-mentioned groundwater recharge system, the groundwater treated by the removing part in the reducing agent addition part so that the concentration of the ferric iron in the groundwater treated by the removing part is lower than 0.1 mg / L. The amount of the reducing agent to be added may be adjusted.
In the above-mentioned groundwater recharge system, the groundwater pumped from the pumping well may be guided to the water injection well through a closed water pipe.

According to the groundwater recharge system of the present invention, divalent iron contained in the groundwater pumped from the pumping well and which is the root cause of clogging of the filter of the water injection well and the ground near the water injection well is not oxidized as much as possible. Water is passed through a well-sealed water pipe, and the trivalent iron that is still slightly precipitated is removed by the filtration part, and the groundwater is brought into a reduced state by the reducing agent addition part. Therefore, when the groundwater pumped from the pumping well is injected into the ground, it is possible to bring the groundwater into a reduced state that can satisfactorily prevent clogging of the ground. As a result, the water flow performance of the groundwater recharge system can be maintained well, and clogging of the ground can be prevented.

It is the schematic (partial sectional view) which shows one Embodiment of the groundwater recharge system which concerns on this invention. It is a side view which shows the main part of the pumping well of the groundwater recharge system, (a) is related to a general pumping well, and (b) is related to 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 passed the water which adjusted the concentration of ferric iron with a constant head difference. It is a graph which shows the measurement result at the time of performing the column test which passed the water which adjusted the concentration of ferric iron with a constant head difference. It is a schematic diagram which shows the operation state in the spring type filter used for the spring type filter of the filtration part of the groundwater recharge system shown in FIG. 1, and (a) is the figure which shows the state at the time of a normal operation (recharge operation). Yes, (b) is a diagram showing a state during a backwash operation. It is a graph which shows an example of the filtration performance by the spring type filter used in 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 the groundwater recharge system according to the present invention will be described with reference to the drawings. The drawings used in the following description are schematic, and the length, width, thickness ratio, etc. are not always the same as the actual ones and can be changed as appropriate.

FIG. 1 is a schematic view showing the configuration of the groundwater recharge system 11 of 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, and the groundwater W pumped from the aquifer (ground) S2 by the pumping well 1 is sent to the water injection well 2. This is a system for guiding and injecting water from the water injection well 2 into the aquifer (ground) S3 by a recharge method.

The ground illustrated in FIG. 1 has a structure in which aquifers S1, S2, S3, ... And clay layers C1, C2, ... Are alternately repeated from the ground surface G along the depth direction J. If the recharge method can be applied, the ground structure, pumping position, and water injection position are not particularly limited.

As shown in FIG. 1, the groundwater recharge system 11 introduces a pumping well 1 for pumping the groundwater W and the groundwater W pumped from the pumping well 1, and the suspended substance component and the metal oxide existing in the groundwater W are introduced. The reducing agent Re is added to the removing unit 20 for removing the groundwater W, and the reducing agent Re is added to the groundwater W treated by the removing unit 20 until the oxidation-reduction potential of the groundwater W becomes equal to or less than a predetermined value. A water injection well 2 for injecting the groundwater W into the submerged layer (ground) S3 is provided, and the groundwater W pumped from the pumping well 1 is sealed with a pumping pipe (water flow pipe) 8A and a water flow pipe 8B, This is a system that leads to the water injection well 2 via 8C and 8D.

The pumping well 1 is a known drainage facility for pumping groundwater W in the aquifer S2, and specifically, a deep well (so-called so-called deep well) installed in an excavation area X partitioned by earth retaining D and D. , Deep well). A screen 1a buried in the ground deeper than the groundwater level (in FIG. 1, the aquifer S2) is formed near the lower end of the pumping well 1, and the groundwater W in the ground flows in from the screen 1a. Groundwater W is stored in the pumping well 1. Further, a lid is attached to the upper end of the pumping well 1, the upper end of the pumping well 1 is sealed by the lid, and the pumping well 1 has a closed structure.

In the groundwater W pumped from the pumping well 1, iron exists in a divalent state, that is, as soluble divalent iron. Divalent iron in groundwater W changes to trivalent iron when it comes into contact with air or the like even slightly during the process of pumping and subsequent treatment. In the groundwater recharge system 11 of the present embodiment, it is important to suppress the oxidation and precipitation of ferrous iron dissolved in the groundwater W as much as possible in the process from the pumping to the treatment by the removing unit 20. It is more important to suppress the oxidation and precipitation of ferrous iron in the groundwater W as the concentration of ferrous iron in the groundwater W increases.

FIG. 2A shows a state of pumping groundwater in a general pumping well, and FIG. 2B shows a state of 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 extent that the water 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. 2A, the water suction port Pa is exposed to the air environment in the pumping well 1, and not only the groundwater but also the air is sucked up from the water suction port Pa, and the groundwater W is oxidized and in the groundwater W. The oxidation of ferrous 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 suction port Pa of the pump P1. Further, from the viewpoint of more reliably preventing the oxidation of the groundwater W and the oxidation of the 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 view showing the configuration of a test apparatus when a column test is performed in which water having an adjusted concentration of ferric iron is passed through 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 set to 30 mm. Toyoura sand S assuming the soil in the ground was put in the bottom, and water WF'in which the concentration of ferric iron was adjusted while stirring in the water tank 52 was passed through the column 50. The water flow rate of the water WF at the initial stage of water flow was set from 15 mL / min to 16 mL / min. The water WF permeated through the column S was introduced into the water tank 54. In order to maintain a constant 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 ferric iron from 0.05 mg / L to 10 mg / L as shown in the graph. The measurement results when the above-mentioned column test is performed using tap water (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 shows the elapsed time of water passing through the column 50, and the vertical axis of the graph shows the amount of water WF passing 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). Become. As shown in FIG. 3, when the concentration of ferric iron in water is 0.1 mg / L or more, the Toyoura sand S is clogged in a short time, and the amount of water flow (that is, the amount of water injection) cannot be maintained. You can see that.
Therefore, in the groundwater recharge system 10, the concentration of ferric iron in the groundwater W is at least 0.1 mg / L in order for the groundwater W to be in a state where clogging of the ground near the water injection well can be sufficiently and satisfactorily prevented. It is important that it is smaller, preferably less than 0.05 mg / L, more preferably less than 0.01 mg / L.

As shown in FIG. 1, the pumping well 1 and the removing portion 20 are communicated with each other by a closed pumping 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 introduction port of the removing portion 20. One end of the pumping pipe 8A inserted into the pumping well 1 is connected to the discharge port of the pumping pump P1 arranged 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 removing section 20 through the inside of 8A.

The removal unit 20 introduces the groundwater W pumped into the filtration unit 20 through the pumping pipe 8A, and is caused by the SS component in the groundwater W and the air slightly mixed even if the water is pumped in a closed environment. It is a facility for removing metals such as iron and manganese and other oxides (that is, ferric iron and the like) in the precipitated groundwater W, and is equipped with a device composed of a spring type filter. Specifically, as the spring type filter, for example, the device exemplified by the liquid filtration filter element disclosed in Japanese Patent Application Laid-Open No. 8-196821, the spring type filter filtering device disclosed in Japanese Patent No. 1822317, and the like. Can be mentioned. A spring-type filter is made by processing stainless steel (SUS), which is made of a very rust-resistant material, into a special wire shape, and after attaching a precoat material to a spring-type filter in which this hard spring wire is wound into a coil. It 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 particularly excellent self-cleaning effect and backwash regeneration function, and has features and conditions suitable for filtering groundwater W in the present invention, such as almost no maintenance required.

The spring-type filter used in the spring-type filter of the removal unit 20 has conventionally been used mainly for wastewater (turbid water) treatment, but in the filtration treatment, the spring-type filter is coated at the first stage. By appropriately selecting the precoat material (that is, the filtration aid), the particle size (that is, the filtration accuracy) filtered by the spring type filter can be determined. Moreover, precise filtration can be realized at high speed and low pressure.

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

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

As shown in FIG. 6, assuming that cleaning is performed when the internal pressure of the spring-type filter reaches 200 kPa, when silica # 600H is used as the precoat material, cleaning is performed once every 60 minutes (that is, that is). It is equivalent to washing 24 times a day). Such cleaning frequency depends on the concentration of SS component and ferric iron in the water to be treated, but as can be seen from the cleaning frequency, when cleaning or replacing the removal material or filtration material that relies on human power, the treatment target It is difficult to maintain the concentration of SS component and ferric iron so that the ground is not clogged to the same extent as when a spring type filter is used. When the above-mentioned precoat material was used, the concentration of ferric iron contained in the filtered water was 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, as shown by "treated water" in FIG. 4, it was almost the same as tap water and hardly clogged. From this, it can be seen that the water filtered by the spring type filter is satisfactorily removed from the causative substance of clogging, and the water quality is such that long-term water injection is possible.

The configuration of the removing unit 20 is not limited to the spring type filter described above, and has the ability to remove SS components contained in the groundwater W introduced into the removing unit 20 and obstetric metals such as precipitated ferric iron. As long as it is a thing, it is not particularly limited. For example, the removing unit 20 may be any of a filter press, a belt press, a back filter, a centrifuge, a sand filter, and the like.

As shown in FIG. 1, the removing portion 20 and the filtered water tank 32 are communicated with each other by a closed water pipe 8B. One end of the water pipe 8B is connected to the outlet of the filtration unit 20, and the other end of the water pipe 8B is open to the inside of the filtered water tank 32. The groundwater W filtered by the filtration unit 20 is supplied to the inside of the filtered water tank 32 through the inside of the water pipe 8B.

The filtered water tank 32 is configured so that the groundwater W filtered by the removing unit 20 can be accommodated and taken out from a predetermined position. Further, a lid is attached to the upper end of the filtered water tank 32, the upper end of the filtered water tank 32 is sealed by the lid, and the filtered water tank 32 has a sealed structure. The filtered water tank 32 is not particularly limited as long as it is configured to be hermetically sealed as described above, and a known groundwater tank or the like can be applied.

Inside the filtered water tank 32, in addition to the other end of the water pipe 8B, one end of the sealed reducing agent supply pipe 8c is arranged. The other end of the reducing agent supply pipe 8c is connected to the reducing agent discharge port of the reducing agent adding device 15 of the reducing agent adding unit 14, and is filtered by the filtering unit 20 into the ground water W contained in the filtered 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 unit 14 is configured to bring the groundwater W filtered (treated) by the filtration unit 20 into a reducing state. In the present embodiment, the reducing agent adding unit 14 is reduced by the reducing agent adding device 15 for adding the reducing agent Re to the ground water W filtered by the filtering unit 20 and contained in the filtered water tank 32, and the reducing agent adding device 15. The reduction agent is detected by the first reduction potential detection unit 26 that detects the oxidation-reduction potential of the groundwater W before the agent Re is added and feeds back the detected oxidation-reduction potential to the reducing agent addition device 15, and the reducing agent addition device 15. At least one of the second reduction potential detection unit (detection unit) 27 that detects the oxidation-reduction potential of the groundwater W after Re is added and feeds back the detected oxidation-reduction potential to the reducing agent addition device 15. I have. The reducing agent addition unit 14 is configured to be able to adjust the addition amount of the reducing agent Re based on the information fed back from at least one of the first reduction potential detection unit 26 and the second reduction potential detection unit 27. There is.

The reducing agent adding 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 adding device 15 of the reducing agent adding unit 14 is not particularly limited as long as it contains a substance capable of reducing the groundwater W. Examples of such a substance include sodium thiosulfate, sodium sulfite, sodium hydrosulfide and the like. 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 can introduce a part of the groundwater W flowing in the water pipe 8B after being treated by the removal unit 20 and can detect the redox potential of the introduced groundwater W. .. The water pipe 8B is provided with a pump P2 for introducing a part of the groundwater W into the first reduction potential detection unit 26, if necessary. The detected redox potential of the ground water W is directly fed back to the reducing agent addition device 15, and the supply amount (addition amount) of the reducing agent Re in the reducing agent addition device 15 (reducing agent addition unit 14) based on the fed-back information. May be adjusted. In the present embodiment, the redox 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 introduced a part of the ground water W that was supplied with the reducing agent Re from the reducing agent adding device 15 and was led out to the water passage pipe 8C sealed from the filtered water tank 32, and introduced the ground water W. As long as the redox potential of the above can be detected, the present invention is not particularly limited. The water pipe 8C is provided with a pump P3 for introducing a part of the groundwater W into the second reduction potential detection unit 27, if necessary. The detected redox potential of the ground water W is directly fed back to the reducing agent addition device 15, and the supply amount (addition amount) of the reducing agent Re in the reducing agent addition device 15 (reducing agent addition unit 14) based on the fed-back information. May be adjusted. In the present embodiment, the redox 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.

The reducing agent addition unit 14 includes at least one of the first reduction potential detection unit 26 and the second reduction potential detection unit 27, but the oxidation-reduction potential of the groundwater W supplied to the water injection well 2 is set to a predetermined value or less. Both the first reduction potential detection unit 26 and the second reduction potential detection unit 27 are provided in order to more reliably bring the ground water W into a reducing state and to reliably prevent the excessive addition and insufficient addition of the reducing agent Re to the ground water W. It is preferable that it is. The first reduction potential detection unit 26 and the second reduction potential detection unit 27 may be integrated or may be shared with each other and configured as one detection unit.

Examples of the first reduction potential detection unit 26 and the second reduction potential detection unit 27 include an ORP (Oxidation-Reduction Potential) sensor, a dissolved oxygen sensor, and the like. An ORP sensor is preferable as the first reduction potential detection unit 26 and the second reduction potential detection unit 27 from the viewpoint of simple configuration and easy installation. When the ORP sensor is used, the ORP, which is a potential determined by the equilibrium state between the oxidant and the reducer coexisting in the groundwater W, is appropriately set. In a state where the groundwater W can sufficiently and satisfactorily prevent clogging of the water zone (ground) S3 near the water injection well, it is preferable that no oxidizing agent remains in the groundwater W after the reducing agent is added. The redox potential measured by the ORP sensors of the oxidant detection unit 26 and the dioxide agent detection unit 27 is at least 200 mV or less, preferably 100 mV or less, and more preferably 0 mV or less.

The remaining amount of the SS component in the groundwater W treated by the removing unit 20 can be measured using a turbidity meter or the like (not shown). For example, the concentration of the SS component in the groundwater W treated by the removing unit 20 is less than 1 mg / L from the viewpoint that clogging of the ground can be satisfactorily prevented when the groundwater W is injected into the ground. It is preferable to confirm that.

The groundwater recharge system 11 of the present embodiment includes a control unit 30. The control unit 30 supplies (addition amount) of 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 appropriately set and has a function of sending the signal S15 to the reducing agent adding device 15.
Examples of the control unit 30 include a computer, but the control unit 30 is not particularly limited as long as it has the above-mentioned functions.

The control unit 30 detected from the feedback of the second reduction potential detection unit 27 that the redox potential of the groundwater W derived from the filtered water tank 32 after the reducing agent Re was added was larger than the above-mentioned predetermined value. In this case, it is preferable to have a function of stopping the derivation of the groundwater W from the filtered water tank 32.
That is, it is preferable that the control unit 30 is composed of a computer having a built-in control program or the like. The above-mentioned control program is a procedure for capturing the redox potential of the groundwater W detected by the second reduction potential detection unit 27 into the computer, and if the redox potential of the groundwater W is equal to or less than a preset threshold value (predetermined value). , The procedure for connecting the outlet of the filtered water tank 32 and the water passage pipe 8C and the non-communication between the outlet of the filtered water tank 32 and the water passage pipe 8C if the redox potential of the groundwater W exceeds the threshold value. It is preferable that the procedure for making the state and the procedure for executing the state are performed.

The filtered 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 with each other by the sealed water pipe 8D. One end of the water pipe 8C is connected to the outlet of the filtered water tank 32, and the other end of the water pipe 8C is opened deeper than the predetermined water level of the water injection well 2B of the water injection well 2. On one end side of the water pipe 8C, a stirring device 24 for mixing the groundwater W and the reducing agent Re added to the groundwater W is provided. As the stirring device 24, for example, a static mixer having a small and simple structure can be used, but the stirring device 24 is not particularly limited as long as the groundwater W and the reducing agent Re can be mixed.

One end of the water pipe 8D is connected in the middle of the water pipe 8C, and the other end of the water pipe 8D is opened deeper than a predetermined water level of the water injection well 2A of the water injection wells 2. The groundwater W derived from the filtered 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 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 known water injection facilities (so-called recharge wells) for injecting the reduced groundwater W into the aquifer S3, and specifically, wells installed outside the excavation area X. Consists of. Screens 2a buried in the ground deeper than the groundwater level (in the aquifer S3 in FIG. 1) are formed in the water injection wells 2A and 2B, and the groundwater W in the water injection wells 2A and 2B flows out from the screen 2a. Then, the groundwater W is injected into the aquifer S3. Further, a lid is attached to the upper end of the water injection well 2, the upper end of the water injection well 2 is sealed by the lid, and the water injection well 2 has a closed 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 removing unit 20 via the sealed pumping pipe 8A. If there is a small amount of air or the like mixed in the closed pumping well 1 and the pumping pipe 8A, the divalent iron in the groundwater W is oxidized and the ferric iron is deposited. The precipitated metal oxide such as ferric iron and manganese can be removed from the groundwater W by passing through the removing unit 20 together with the SS component such as clay particles. That is, the removal unit 20 can remove the clogging-causing component in the groundwater W. Then, the reducing agent Re is added to the groundwater W filtered by the removing unit 20 by the reducing agent adding unit 14 until the redox potential becomes equal to or less than a predetermined value, and the groundwater W is sufficiently reduced. Therefore, the groundwater W pumped from the pumping well 1 can be brought into a reduced state by removing the components that cause clogging of the ground near the water injection well 2, so that the groundwater W can be brought into the ground from the water injection well 2. Even if water is injected into the water, it is possible to prevent clogging of the filter of the water injection well 2 and the ground near the water injection well 2 for a long period of time.
Due to the above-mentioned action and effect, the groundwater recharge system 11 of the present embodiment compares the groundwater W, that is, divalent iron, which conventionally increases the frequency of clogging of the screen and the filter provided in the ground on the water injection side and the water injection well. It is also possible to deal with groundwater W containing a large amount of target.

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 addition unit 14 has an existing configuration by setting the predetermined value of the oxidation-reduction potential of the groundwater to 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 configuration, the water level in the pumping well 1 is set to be higher than the water suction port Pa of the pump P1 which is the pumping position of the groundwater W, so that air is mixed and air is mixed in when the groundwater W is pumped. It is possible to more reliably suppress the oxidation of the groundwater W and the oxidation of the divalent iron in the groundwater W due to the mixing.

In the above configuration, since the groundwater W pumped from the pumping well 1 is filtered by the spring type filter, a small amount of metal oxide such as ferrous iron and 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 configuration, the metal oxide such as ferric 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 having an excellent self-cleaning effect and a small maintenance burden. In addition, the performance of the groundwater recharge system 11 can be easily maintained high.
Further, according to the groundwater recharge system 11 of the present embodiment, the oxidation and precipitation of ferrous iron dissolved in the groundwater W are suppressed as much as possible, the frequency of the backwash operation of the spring type filter is reduced, and the backwash operation is performed. (For example, the cost of precoating material, backwashing power, concentration treatment, etc.) can be suppressed. That is, the running cost can be remarkably suppressed by the groundwater recharge system 11 using the 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, at least one of the first reduction potential detection unit 26 and the second reduction potential detection unit 27 detects the oxidation-reduction potential of the ground water W and feeds it back to the reducing agent adding device 15. By doing so, it is possible to suppress the excessive addition or insufficient addition of the reducing agent Re, and to efficiently bring the ground water W into a reducing state that can satisfactorily prevent clogging when the water is injected into the ground. By using both the first reduction potential detection unit 26 and the second reduction potential detection unit 27, it is possible to bring the groundwater W into a reduced state that can more efficiently prevent clogging when water is injected into the ground. can.

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

For example, in the above-described embodiment, based on the fact that the water quality of the groundwater W can be grasped to some extent before the implementation of the recharge method, as shown in FIG. 7, the above-mentioned groundwater W pumped from the pumping well 1 is described above. A certain amount of reducing agent calculated from the water quality may be added. As a result, it is possible to more reliably prevent the oxidation of the groundwater W and the precipitation of ferric iron from the time of pumping to the time before being filtered by the removing unit 20, and it is possible to suppress the frequency of backwashing of the spring type filter.

Further, 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 closed notch tank or the like.

1 Pumping wells 2, 2A, 2B Water injection well 11 Groundwater recharge system 14 Reducing agent addition part 20 Removal part 26 First reduction potential detection part 27 Second reduction potential detection part Re Reducing agent W Groundwater

Claims (10)

It is a groundwater recharge system for performing a recharge method that injects pumped groundwater into the ground.
A closed pumping well for pumping the groundwater, and
A removal unit the said groundwater which is pumped from the pumping wells introduced, to remove suspended solids component and a metal oxide present in the prior SL groundwater,
A reducing agent addition part that adds a reducing agent to the groundwater treated in the removal part, and a reducing agent addition part.
A detector for detecting an oxidation-reduction potential of the ground water that has been treated by the removal unit,
A water injection well for injecting the groundwater to which the reducing agent has been added into the ground, and
With
The redox potential detected by the detection unit is fed back to the reducing agent addition unit.
Groundwater recharge system. The reducing agent addition unit further includes a control unit that adjusts the amount of the reducing agent added to the groundwater treated by the removal unit based on the redox potential fed back from the detection unit.
The groundwater recharge system according to claim 1. The amount of the reducing agent added to the groundwater treated by the removing portion is adjusted so that the redox potential is equal to or less than a value indicating that the groundwater has completely lost its oxidizing power.
The groundwater recharge system according to claim 1 or 2. The amount of the reducing agent added to the groundwater treated in the removing portion is adjusted so that the redox potential is 200 mV or less.
The groundwater recharge system according to claim 1 or 2. The water level of the pumping well is configured to be higher than the pumping position of the groundwater.
The groundwater recharge system according to any one of claims 1 to 4. The removing portion is composed of a spring-type filter.
The groundwater recharge system according to any one of claims 1 to 5. The metal oxide contains insoluble iron,
The groundwater recharge system according to any one of claims 1 to 6. The insoluble iron is trivalent iron obtained by oxidizing divalent iron in the groundwater pumped from the pumping well.
The groundwater recharge system according to claim 7. Addition of the reducing agent to be added to the groundwater treated by the removing part in the reducing agent addition part so that the concentration of the ferric iron in the groundwater treated by the removing part is lower than 0.1 mg / L. The amount is adjusted,
The groundwater recharge system according to claim 8. The groundwater pumped from the pumping well is guided to the water injection well through a closed water pipe.
The groundwater recharge system according to any one of claims 1 to 9.

Images