JP6907353B2 - 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 discharge rate of sewage and the influence of the drop in the water level 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 from the excavated portion to the vicinity of the ground surface in advance before excavation.
For example, Patent Document 1 discloses a clogging prevention device (recharge system) including a tubular 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, deep wells can be pumped to the surface through closed pipes. 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 of injecting pumped groundwater into the ground, and is a groundwater recharge system for pumping the groundwater and the pumping well pumped from the pumping well. An oxidant addition part that adds an oxidant to the groundwater, a removal part that introduces the groundwater to which the oxidant is added, and removes suspended substance components and metals oxide existing in the groundwater after the addition of the oxidant. The detection unit includes a detection unit that detects the amount of the oxidant in the groundwater treated by the removal unit, and a water injection well for injecting the groundwater treated by the removal unit into the ground. The amount of the oxidant detected in is fed back to the oxidant addition portion, and the metal oxide contains insoluble iron .
Further, the insoluble iron may be trivalent iron obtained by precipitating divalent iron in the groundwater pumped from the pumping well by the oxidizing agent.
Further, the oxidant added to the groundwater pumped from the pumping well in the oxidant addition section so that the concentration of the ferric iron in the groundwater treated by the removal section is lower than 0.1 mg / L. The amount of the addition may be adjusted.
The above-mentioned groundwater recharge system controls the addition amount of the oxidant to be added to the groundwater pumped from the pumping well in the oxidant addition unit based on the amount of the oxidant fed back from the detection unit. Further units may be provided.
In the above-mentioned groundwater recharge system, the detection unit may calculate the amount of the oxidant based on the redox potential of the groundwater from which the suspended solids component and the metal oxide have been removed.

In the above-mentioned groundwater recharge system, the amount of the oxidant may be adjusted so that the redox potential is 200 mV or less.

In the above groundwater recharge system, the removal portion may Tei is a spring type filter.

In the groundwater recharge system described above, the oxidizing agent may contain sodium hypochlorite.

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 intentionally used as trivalent iron. It is precipitated, and this ferric iron is removed by the removing 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 satisfactorily prevent clogging of the ground. As a result, the water flow performance of the recharge system can be maintained well, and clogging of the ground can be prevented.

It is the schematic which shows one Embodiment of the groundwater recharge system which concerns on this invention. 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 and the water treated by a spring type filter 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 and the water treated by a spring type filter 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 removal 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 for the spring type filter of the removal 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 10 of the present embodiment.
As shown in FIG. 1, the groundwater recharge system 10 is installed at a site where excavation work or the like is performed, and the groundwater W pumped from the aquifer (ground) S2 is fed to the water injection well 2 by the pumping well 1. 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.

FIG. 1 is a schematic view showing the groundwater recharge system 10 of the present embodiment.
As shown in FIG. 1, the groundwater recharge system 10 includes a pumping well 1 for pumping groundwater W, an oxidizing agent adding unit 12 for adding an oxidizing agent Ox to the groundwater W pumped from the pumping well 1, and an oxidizing agent. The removal unit 20 that introduces the groundwater W to which Ox is added and removes the SS component existing in the groundwater, and the remaining amount of the oxidizing agent Ox in the groundwater W (of the groundwater W) in the groundwater W treated by the removal unit 20. The reducing agent adding section 14 to which the reducing agent Re is added until the oxidation-reduction potential) becomes equal to or less than a predetermined value, and the water injection well 2 for injecting the groundwater W to which the reducing agent Re is added into the submerged layer (ground) S3. And have.

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.

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.

FIG. 2 is a schematic view showing the configuration of a test apparatus when a column test is performed in which water having an adjusted trivalent iron concentration is passed through with a constant head difference H (that is, H shown in FIG. 2). In the test apparatus shown in FIG. 2, 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. 3 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 water flow rate (that is, the water injection amount) 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 pumping pipe 9A. One end of the pumping pipe 9A is inserted into the pumping well 1 from the upper end of the pumping well 1, and the other end of the pumping pipe 9A is connected to the introduction port of the removing portion 20. One end of the pumping pipe 9A 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 9A.

One end of the oxidant supply pipe 9a is connected in the middle of the pumping pipe 9A. The other end of the oxidant supply pipe 9a is connected to the oxidant discharge port of the oxidant addition portion 12, and the oxidant supply pipe 9a is provided with respect to the ground water W that is pumped from the pumping well 1 and flows in the pumping pipe 9A. It is said that the oxidant Ox can be supplied from the oxidant addition unit 12 via the above.

The oxidant addition unit 12 includes an oxidant supply device (not shown). The configuration of the oxidant addition section 12 is not particularly limited as long as the oxidant Ox can be discharged to the other end of the oxidant supply pipe 9a.
The oxidizing agent Ox supplied from the oxidizing agent adding unit 12 is not particularly limited as long as it contains a substance capable of oxidizing ferrous iron generally contained in groundwater W and precipitating trivalent iron. Examples of substances capable of oxidizing ferric iron in groundwater W and precipitating ferric iron include oxidizing agents such as sodium hypochlorite, hydrogen peroxide, sodium chlorite, ozone, and chlorine. The type and material of the oxidant Ox can be used as long as it is a highly reactive oxidant, but manganese, like iron, can cause clogging of the ground even at a relatively low concentration. The oxidizing agent Ox preferably contains, in addition to ferrous iron generally contained in groundwater W, a substance capable of oxidizing soluble manganese and precipitating ferric iron and hydrated manganese dioxide.

As described above, the oxidizing agent Ox preferably contains sodium hypochlorite. Sodium hypochlorite reacts with at least divalent iron in groundwater W instantly and reliably, and precipitates as ferric iron. Hypochlorous acid is superior not only in its quick reactivity but also in its safety such as being used for disinfecting tap water. In addition, the high oxidation rate means that the reaction for eliminating the oxidizing power can be performed quickly. Furthermore, the deactivation method such as passing through activated carbon can be easily performed.

A stirring device 22 for mixing the groundwater W and the oxidant Ox added to the groundwater W is located in the middle of the pumping pipe 9A and downstream of the position where one end of the oxidant supply pipe 9a is connected. It is provided. As the stirring device 22, for example, a static mixer or the like having a blade plate arranged in the pipe and automatically stirring by the flow of water can be used, but groundwater W and the oxidant Ox can be mixed. If there is, there is no particular limitation.

The removing unit 20 introduces the groundwater W pumped into the removing unit 20 through the pumping pipe 9A, and introduces the SS component in the groundwater W and metals such as iron and manganese oxidized by the oxidizing agent Ox. It is a facility for removing (that is, ferric iron, etc.) 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. 4A 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. 4B 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. 4A, 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 filter, as shown in FIG. 4 (b), the spring filter is clogged with SS components and metals such as iron and manganese (that is, ferric iron, etc.) and filtered. When the efficiency drops below the predetermined efficiency, backwash air and water are press-fitted through the water injection pipe 9b (see FIG. 1) connected to the outlet side of the spring-type filter of the removal unit 20. 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 recovered and discarded as a concentrated liquid through a drain pipe or the like (not shown in FIG. 1).

FIG. 5 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 dayrcy, manufacturer: Chuo Silica Co., Ltd.) was used.

As shown in FIG. 5, 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 keep 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. 2, it was found that, as shown by "treated water" in FIG. 3, 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 removal unit 20 is not limited to the above-mentioned spring type filter or one having a similar structure, and the metal oxide generated by the SS component and the oxidizing agent Ox contained in the groundwater W introduced into the removal unit 20. There is no particular limitation as long as it has the ability to remove. 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 water pipe 9B. One end of the water pipe 9B is connected to the lead-out portion of the removing portion 20, and the other end of the water pipe 9B is open to the inside of the filtered water tank 32. The groundwater W filtered by the removing unit 20 is supplied to the inside of the filtered water tank 32 through the inside of the water pipe 9B.

The filtered water tank 32 is configured to accommodate the groundwater W in which the oxidant Ox remains and can be derived from a predetermined position, and is not particularly limited, and a known tank or the like can be applied. A drainage pump P4 for discharging the groundwater W is provided in the outlet portion of the filtered water tank 32.

Inside the filtered water tank 32, one end of the reducing agent supply pipe 9c is arranged in addition to the other end of the water pipe 9B. The other end of the reducing agent supply pipe 9c is connected to the reducing agent discharge port of the reducing agent adding device 15 of the reducing agent adding unit 14, and is treated by the removing unit 20 into the groundwater 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 9c.

The reducing agent adding unit 14 is configured to remove the oxidizing agent Ox remaining in the groundwater W filtered (treated) by the removing unit 20 to bring the groundwater W into a reducing state. In the present embodiment, the reducing agent adding unit 14 is reduced by the reducing agent adding device 15 that is treated by the removing unit 20 and adds the reducing agent Re to the ground water W contained in the filtered water tank 32, and the reducing agent adding device 15. The first oxidant detector (detection ) that detects the amount of oxidant Ox in the ground water W before the agent Re is added by the oxidative reduction potential of the ground water W and feeds back the detected oxidative reduction potential to the reducing agent adding device 15. Part) 16 and the reducing agent addition device 15 detect the oxidation-reduction potential of the ground water W after the reducing agent Re is added, and feed back the detected oxidation-reduction potential to the reducing agent addition device 15. It comprises at least one of 17. The reducing agent adding unit 14 is configured to be able to adjust the amount of the reducing agent Re added based on the information fed back from at least one of the first oxidizing agent detecting unit 16 and the first dioxide agent detecting unit 17. ..

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 reducing agent supply pipe 9c.
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 is a substance capable of removing the oxidizing agent Ox remaining in 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 oxidant detecting unit 16 is not particularly limited as long as it can introduce a part of the groundwater W flowing in the water pipe 9B after being treated by the removing unit 20 and can detect the redox potential of the introduced groundwater W. .. The water pipe 9B is provided with a pump P2 for introducing a part of the groundwater W into the first oxidizing agent detection unit 16 as needed. The detected oxidation-reduction potential 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) is adjusted based on the fed back information. You may. In the present embodiment, the redox potential of the groundwater W detected by the first oxidant detection unit 16 is sent to the control unit 30 as a signal S16.

The second dioxide agent detecting unit 17 introduced a part of the groundwater W led out from the filtered water tank 32 to the water passage pipe 9C by supplying the reducing agent Re from the reducing agent adding device 15, and introduced the redox potential of the introduced groundwater W. Is not particularly limited as long as it can detect. The water pipe 9C is provided with a pump P3 for introducing a part of the groundwater W into the nitrogen dioxide detection unit 17 as needed. The detected oxidation-reduction potential of the ground water W is directly fed back to the reducing agent addition device 15, and based on the fed-back information, the supply amount (addition amount) of the reducing agent Re in the reducing agent addition device 15 (reducing agent addition unit 14). May be adjusted. In the present embodiment, the amount of the redox potential of the groundwater W detected by the dioxide agent detecting unit 17 is also sent to the control unit 30 as a signal S17.

The reducing agent adding unit 14 includes at least one of the first oxidizing agent detecting unit 16 and the first dioxide agent detecting unit 17, but the oxidation-reduction potential of the groundwater W supplied to the water injection well 2 is more reliably equal to or less than a predetermined value. In addition, in order to reliably prevent the excessive addition and insufficient addition of the reducing agent Re to the groundwater W, it is preferable that both the first oxidizing agent detecting unit 16 and the second dioxide agent detecting unit 17 are provided. Since the measurement target of the first oxidant detection unit 16 and the second dioxide agent detection unit 17 is the oxidant Ox in common, they may be integrated and shared with each other as one detection unit. It may be configured.

Examples of the first oxidant detection unit 16 and the second dioxide agent detection unit 17 include an ORP (Oxidation-Reduction Potential) sensor, a dissolved oxygen sensor, and the like. An ORP sensor is preferable as the first oxidizing agent detecting unit 16 and the second dioxide agent detecting unit 17 from the viewpoint of simple configuration and easy installation. When using the ORP sensor, 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 16 and the dioxide agent detection unit 17 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 10 of the present embodiment includes a control unit 30. The control unit 30 appropriately sets the supply amount (addition amount) of the reducing agent Re in the reducing agent adding device 15 based on the information fed back from the first oxidizing agent detecting unit 16 and the second dioxide agent detecting unit 17, and reduces the reducing agent Re. It has a function of sending as a signal S15 to the 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.

When the control unit 30 detects from the feedback of the dioxide agent detection unit 17 that the redox potential of the groundwater W derived from the filtered water tank 32 after the reducing agent Re is added is higher than the above-mentioned predetermined value. Preferably has 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 captures the redox potential of the groundwater W detected by the dioxide agent detection unit 17 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 9C and the non-communication state between the outlet of the filtered water tank 32 and the water passage pipe 9C if the redox potential of the groundwater W exceeds the threshold value. It is preferable that the procedure is configured to execute.

Further, the control unit 30 appropriately sets the supply amount (addition amount) of the oxidant Ox in the oxidant addition unit 12 based on the information fed back from the first oxidant detection unit 16 and the second dioxide agent detection unit 17. It is preferable to have a function of correcting and sending the signal S12 to the oxidizing agent addition unit 12. As a result, if the supply amount (addition amount) of the oxidant Ox in the oxidant addition unit 12 is adjusted according to the amount of the oxidant Ox remaining in the groundwater W derived from the filtered water tank 32, the oxidant Ox Excessive addition or insufficient addition of

The filtered water tank 32 and the water injection well 2 are communicated with each other by a water pipe 9C and a water pipe 9D that branches from the middle of the water pipe 9C. One end of the water pipe 9C is connected to the outlet of the filtered water tank 32, and the other end of the water pipe 9C is opened deeper than the predetermined water level of the water injection well 2B of the water injection well 2. A stirring device 24 for mixing the groundwater W and the reducing agent Re added to the groundwater W is provided on one end side of the water pipe 9C. 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 9D is connected in the middle of the water pipe 9C, and the other end of the water pipe 9D is opened deeper than the predetermined water level of the water injection well 2A of the water injection well 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 9C and 9D.

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 groundwater W in a reduced state into the aquifer S3 with the contained oxidizing agent Ox being equal to or less than a predetermined value. Consists of wells installed outside the excavation area X. 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 10 of the present embodiment, the oxidant Ox is added to the groundwater W pumped from the pumping well 1 by the oxidant addition unit 12, and the divalent iron in the groundwater W is oxidized. Then, it is precipitated as ferric iron. The precipitated metal oxide such as ferric iron and manganese is removed from the groundwater W by filtering with the SS component such as clay particles in the removing unit 20. That is, the clogging-causing component contained in the groundwater W can be removed by the removing unit 20. Then, the groundwater W is reduced until the amount of the oxidizing agent Ox remaining in the groundwater W filtered by the removing unit 20 becomes equal to or less than a predetermined value by the reducing agent adding unit 14. Therefore, the groundwater W pumped from the pumping well 1 can be in a good state with the components causing clogging of the ground near the water injection well removed.

As described above, according to the groundwater recharge system 10 of the present embodiment, it is contained in the groundwater W pumped from the pumping well 1, and is a root cause of clogging of the ground near the screen 2a of the water injection well 2 and the water injection well 2. The ferrous iron to be used is intentionally precipitated as ferric iron, and the ferric iron can be removed by the removing unit 20 and the groundwater W can be brought into a reduced state by the reducing agent adding unit 14. Therefore, when the groundwater W pumped from the pumping well 1 is injected into the ground, it is possible to satisfactorily prevent clogging of the ground. As a result, the water flow performance of the groundwater recharge system 10 can be maintained well, and clogging of the screen 2a of the water injection well 2 and the ground can be prevented.

Further, according to the groundwater recharge system 10 of the present embodiment, the groundwater W to which the reducing agent Re is added by the reducing agent addition unit 14 has a predetermined amount of the oxidizing agent Ox contained, that is, the oxidation-reduction potential of the groundwater W is appropriate. Since it is set to a value, even if water is injected into the ground from the water injection well 2 having the existing configuration, clogging of the ground near the water injection well 2 can be sufficiently and satisfactorily prevented.

Further, according to the groundwater recharge system 10 of the present embodiment, since the removal unit 20 is composed of a spring type filter, the oxidant Ox is added by the oxidant addition unit 12, and the oxidant Ox positively uses the oxidant Ox. Oxidized and precipitated metals such as ferric iron and manganese are captured by the spring filter of the spring filter, and even if clogging occurs, backwash air is added to the spring filter to control the pressure. Then, the metal oxide such as ferric iron and manganese and the SS component trapped in the spring type filter can be easily and substantially automatically removed and discharged. Therefore, it is possible to construct the groundwater recharge system 10 which has an excellent self-cleaning effect and a small maintenance burden.

Further, according to the groundwater recharge system 10 of the present embodiment, at least one of the first oxidant detection unit 16 and the first dioxide agent detection unit 17 detects the amount of oxidant Ox in the groundwater W, and the reducing agent addition device 15 By feeding back to, the excessive addition or insufficient addition of the reducing agent Re can be suppressed, and the groundwater W can be efficiently made into a state in which clogging can be satisfactorily prevented when the water is injected into the ground. By using both the first oxidant detection unit 16 and the second dioxide agent detection unit 17, it is possible to make the groundwater W more efficient and to be in a state where clogging can be satisfactorily prevented when water is injected into the ground. Further, by feeding back the amount of the oxidant Ox in the groundwater W detected by the first oxidant detection unit 16 and the second dioxide agent detection unit 17 to the oxidant addition unit 12, the excessive addition or insufficient addition of the oxidant Ox can be prevented. It can also be suppressed.

Further, according to the groundwater recharge system 10, sodium hypochlorite is added as an oxidant Ox to the groundwater W pumped from the pumping well, so that divalent iron in the groundwater W is instantly hypochlorite. It can be reacted with sodium and more quickly and reliably precipitated as ferric iron. As a result, the accuracy of removing ferric iron in the groundwater W in the removing unit 20 can be improved.

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, the device for adding the reducing agent Re as the reducing agent adding device 15 of the reducing agent adding unit 14 has been described, but as the reducing agent adding device 15, as shown in FIG. 6, the oxidizing agent Ox An activated charcoal tank having a function of reducing the amount of water may be used. In such a configuration, the groundwater W treated by the removing unit 20 can be passed through the activated carbon tank, and the groundwater W after passing the water can be guided to the water injection well 2.

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 known notch tank or the like.

1 Pumping wells 2, 2A, 2B Water injection wells 10 Groundwater recharge system 12 Oxidizing agent addition part 14 Reducing agent addition part 20 Removal part Ox Oxidizing agent Re Reducing agent W Groundwater

Claims (8)

It is a groundwater recharge system for performing a recharge method that injects pumped groundwater into the ground.
A pumping well for pumping the groundwater and
An oxidant addition part that adds an oxidant to the groundwater pumped from the pumping well,
A removal unit that introduces the groundwater to which the oxidizing agent has been added and removes suspended solids and metals present in the groundwater after the addition of the oxidizing agent.
A detection unit that detects the amount of the oxidant in the groundwater treated by the removal unit, and a detection unit.
A water injection well for injecting the groundwater treated in the removal section into the ground, and
With
The amount of the oxidant detected by the detection unit is fed back to the oxidant addition unit, and the amount is fed back to the oxidant addition unit .
The metal oxide contains insoluble iron,
Groundwater recharge system. The insoluble iron is trivalent iron obtained by precipitating divalent iron in the groundwater pumped from the pumping well by the oxidizing agent.
The groundwater recharge system according to claim 1. Addition of the oxidant to be added to the groundwater pumped from the pumping well in the oxidant addition section so that the concentration of the ferric iron in the groundwater treated in the removal section is lower than 0.1 mg / L. The amount is adjusted,
The groundwater recharge system according to claim 2. The oxidant addition unit further includes a control unit that adjusts the amount of the oxidant to be added to the groundwater pumped from the pumping well based on the amount of the oxidant fed back from the detection unit.
The groundwater recharge system according to any one of claims 1 to 3. The detection unit calculates the amount of the oxidant based on the redox potential of the groundwater from which the suspended solids component and the metal oxide have been removed.
The groundwater recharge system according to any one of claims 1 to 4. The amount of the oxidant added to the groundwater pumped from the pumping well is adjusted so that the redox potential is 200 mV or less.
The groundwater recharge system according to claim 5. The removing portion is composed of a spring type filter.
The groundwater recharge system according to any one of claims 1 to 6. The oxidizing agent contains sodium hypochlorite,
The groundwater recharge system according to any one of claims 1 to 7.

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