Water treatment method

Abstract

To provide a rational water treatment method capable of sufficiently maintaining the PFAS concentration in water requiring treatment stored within a reservoir at a sufficiently low level, even when a storage compartment is not isolated.SOLUTION: A water treatment method includes the steps of: measuring the amount of water requiring treatment stored in a storage compartment and a pre-treatment PFAS concentration, which is the PFAS (perfluoroalkyl and polyfluoroalkyl substances) concentration in the water requiring treatment; selecting an adsorbent cartridge and calculating an effective period thereof based on the amount, the pre-treatment PFAS concentration, and a target PFAS concentration; immersing a water treatment apparatus, which has an integrated submersible pump attached to an intake or a discharge port of the selected adsorbent cartridge, into the water requiring treatment in the storage compartment, and operating the submersible pump; and replacing the adsorbent cartridge upon expiration of the effective period.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment method. [Background technology]

[0002] Patent Document 1 discloses a mobile system and method for PFAS (perfluoroalkyl compounds and polyfluoroalkyl compounds) wastewater treatment. The system described in this document is installed on a portable platform such as a trailer, and PFAS wastewater is pumped up through a hose by a pump, passed through a sediment filter, granular activated carbon (GAC), and ion exchange resins (IX) to purify the water, and then stored in a treated water holding tank.

[0003] Patent document 2 describes a water treatment method in which information is collected about mold odor-causing substances that cause mold odors in a reservoir through measurements using a mobile body (measurement drone) that can move on the water surface or underwater, and measures to suppress the generation of the mold odor-causing substances are determined based on the information about the mold odor-causing substances, and the determined measures are implemented by a mobile body (measurement drone) that can move in the air, on the water surface or underwater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0322951 [Patent Document 2] Patent Publication No. 2021-90910 Summary of the Invention [Problem to be solved by the invention]

[0005] PFAS are persistent and remain for long periods of time, which has led to them being identified as substances causing environmental problems. At the same time, regulations have been strengthened in recent years. This has created a need for water treatment to remove PFAS from water containing PFAS and purify it.

[0006] PFAS are water-soluble, and some of the PFAS released into the environment in the past remain dissolved in stored water. Such water containing dissolved PFAS can be stored in a variety of forms, including underground water storage tanks (pits) used to store firewater, and artificial or natural reservoirs. In the remainder of this specification, the water from which dissolved PFASs are to be removed is referred to as "treated water," and the area storing the treated water is referred to as "storage area."

[0007] Because PFAS are chemically stable, their removal from water requiring treatment is primarily achieved by adsorption treatment using ion exchange resins, activated carbon, zeolites, etc. For the same reason, there is no known technology for easily measuring PFAS concentrations in water requiring treatment, and measurement of PFAS concentrations must be performed by specialized analytical laboratories, making it currently impossible to know the PFAS concentration in water requiring treatment in real time. For these reasons, when attempting to remove PFAS from water requiring treatment, the PFAS concentration in the water must be measured in advance, the total amount of PFAS to be removed must be estimated, and then the amount of adsorbent required and treatment conditions, such as the treatment period, must be determined.

[0008] The above-mentioned method is effective when the storage compartment is isolated, i.e., when it is believed that the PFAS in the water requiring treatment in the storage compartment is not exchanged with the outside. However, depending on the configuration of the storage compartment, there are cases where the storage compartment is not isolated, i.e., PFAS is added to the water requiring treatment from the outside. In such cases, if the PFAS concentration in the water requiring treatment is controlled to a certain upper limit, referred to as the upper limit concentration, in such cases, the PFAS concentration in the water requiring treatment may not be sufficiently reduced to the upper limit concentration, or even if it is reduced to the upper limit concentration, the PFAS concentration may rise again. Due to the difficulty of measuring PFAS concentrations as mentioned above, there is a high risk that such situations may be overlooked.

[0009] A storage compartment may not be isolated, for example, if a certain amount of PFAS is adsorbed to the walls of a storage tank or to the mud at the bottom, and the dissolution of PFAS into the water requiring treatment and the adsorption of PFAS to the walls are in equilibrium. In this case, even if the PFAS in the water requiring treatment is removed, the PFAS adsorbed to the walls will continue to dissolve in the water requiring treatment, resulting in a continuous supply of PFAS to the water requiring treatment. Alternatively, if the storage compartment is a reservoir, PFAS contained in the surrounding soil may flow in via rainwater or groundwater, or new PFAS may be supplied due to some kind of human activity or accident.

[0010] However, it is generally not possible to predict the amount of PFAS that may be supplied from outside. Therefore, if a storage compartment is not considered isolated, it is unknown how to maintain the PFAS concentration in the water requiring treatment below the upper limit. For example, even if an attempt is made to allow for the dissolution of PFAS adsorbed on the wall surface into the water requiring treatment, there are no design guidelines for how much of a margin to use. Therefore, no matter what margin is set, there is no guarantee that the PFAS concentration in the water requiring treatment will be maintained below the upper limit, and the costs required for this are not reasonable.

[0011] The present invention was made in consideration of these circumstances, and its purpose is to provide a rational water treatment method that can maintain a sufficiently low PFAS concentration in water requiring treatment stored in a water tank, even when the storage compartment is not isolated. [Means for solving the problem]

[0012] The invention disclosed in this application to solve the above problems has various aspects, and representative aspects thereof are outlined below.

[0013] (1) A water treatment method comprising the steps of: measuring the amount of water requiring treatment stored in a storage compartment and the pre-treatment PFAS concentration, which is the concentration of PFASs (perfluoroalkyl compounds and polyfluoroalkyl compounds) contained in the water requiring treatment; selecting an adsorbent cartridge and calculating its effective period based on the amount, the pre-treatment PFAS concentration, and the target PFAS concentration; immersing a water treatment device having a submersible pump integrally attached to the intake or outlet of the selected adsorbent cartridge in the water requiring treatment in the storage compartment and operating the submersible pump; and replacing the adsorbent cartridge every time the effective period expires.

[0014] (2) In (1), the adsorbent cartridge is selected by selecting, from among a plurality of adsorbent cartridge candidates loaded with different adsorbent amounts, an adsorbent cartridge candidate loaded with an adsorbent amount exceeding the minimum adsorbent amount required to adsorb the amount of PFAS to be removed, which is calculated based on the amount, the pre-treatment PFAS concentration, and the target PFAS concentration, and the effective period is calculated as the period required for the PFAS concentration in the water to be treated to reach the target PFAS concentration when the adsorbent with the minimum adsorbent amount is used, assuming that the storage compartment is isolated.

[0015] (3) In (1), the water treatment method includes the steps of: re-measuring the PFAS concentration of the water requiring treatment every time the effective period elapses; if the re-measured PFAS concentration exceeds the pre-treatment PFAS concentration, re-selecting an adsorbent cartridge and recalculating the effective period based on the amount, the re-measured PFAS concentration, and the target PFAS concentration; immersing a water treatment device having a submersible pump integrally attached to the intake or outlet of the re-selected adsorbent cartridge in the water requiring treatment in the storage compartment and operating the submersible pump; and replacing the adsorbent cartridge every time the recalculated effective period elapses.

[0016] (4) The water treatment method according to any one of (1) to (3), wherein the water treatment device is provided with a measure to prevent it from falling over.

[0017] (5) In the water treatment method according to (4), the anti-tip measure is suspension support using a flexible string-like member.

[0018] (6) In the water treatment method according to (1), the water treatment device is placed sideways on the floor of the storage compartment.

[0019] (7) In (6), the adsorbent cartridge has a cartridge tank and an intrusion pipe extending from the top of the cartridge tank to the bottom of the cartridge tank, and the intrusion pipe is connected to the water intake.

[0020] (8) In the water treatment method according to (7), a tilting support is attached to the adsorbent cartridge, which supports the adsorbent cartridge in an inclined state on the floor surface at an angle greater than 0 degrees and less than 90 degrees. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram schematically illustrating a state in which a first embodiment of a water treatment method according to the present invention is carried out. [Figure 2] 1A and 1B are diagrams illustrating an example of the structure of a water treatment device. [Figure 3] FIG. 1 is a flow diagram of a water treatment method according to a first embodiment of the present invention. [Figure 4] FIG. 1 shows adsorption isotherms. [Figure 5] FIG. 1 shows the relationship between the ratio of the PFAS concentration in water requiring treatment to the target PFAS concentration and time. [Figure 6] FIG. 1 is a diagram showing an example of the change over time in the PFAS concentration of water to be treated when the water treatment method according to the first embodiment of the present invention is carried out. [Figure 7] FIG. 2 is a diagram schematically illustrating a state in which a second embodiment of the water treatment method according to the present invention is carried out. [Figure 8] FIG. 4 is a flow diagram of a water treatment method according to a second embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing an example of the change over time in the PFAS concentration of water to be treated when a water treatment method according to a second embodiment of the present invention is carried out. [Figure 10] FIG. 10 is a diagram showing a modified example of the water treatment device used in the first or second embodiment of the water treatment method according to the present invention. [Figure 11] FIG. 10 is a top view showing an example of the structure of a water treatment device according to a modified example, which is laid on its side on the floor surface in a water storage tank. [Figure 12] FIG. 10 is a partial cross-sectional side view showing an example of a water treatment device in which an inclined support is attached to the top of an adsorbent cartridge. [Figure 13] FIG. 10 is a perspective view showing an example of the structure of an inclined support. DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 1 is a diagram illustrating a first embodiment of a water treatment method according to the present invention. The diagram illustrates a schematic cross-sectional view of a water tank 1, a typical water storage compartment containing treatment-requiring water W to be treated. The water tank 1 is located underground, below ground level GL, and its floor 10 and four side surfaces 11 are covered with walls to prevent water leakage. A ceiling 12 is provided above the water tank 1 to prevent foreign objects such as fallen leaves and dust from falling into the water tank 1 and also serves as a floor on which mechanical equipment such as a fire pump 2 is installed.

[0023] An access opening 13 is provided in the ceiling 12, allowing an operator to enter the interior of the water tank 1 for maintenance or the like. The access opening 13 is a so-called manhole, and is large enough for one person to enter and exit, but is not particularly large. In normal times, the access opening 13 may be closed with an appropriate lid. A ladder 14 is provided on the wall so that an operator can descend into the water tank 1 from the access opening 13. In FIG. 1, for simplicity of illustration, the ladder 14 is not shown submerged in the water to be treated W, but the ladder 14 is provided at a position that allows the operator to reach the floor 10.

[0024] A building 3 is provided above the water tank 1 to protect the fire pump 2 and the access opening 13 from wind and rain. The building 3 may also be used as a warehouse to store accessories for the fire pump 2, such as a water discharge hose and replacement parts for maintenance.

[0025] A water treatment device 4 is installed in the water tank 1. The water treatment device 4 is installed so as to be immersed in the water to be treated W, submerged below the water surface, and its bottom surface is in contact with the floor surface 10. A fixing device 50 such as an eyebolt is attached to the top of the water treatment device 4, and the water treatment device 4 is suspended by a flexible string-like member 51 such as a wire or rope, thereby providing a tip-over prevention measure 5. The flexible string-like member 51 is fixed in an appropriate position by an appropriate method. In this example, the flexible string-like member 51 is fixed to the ladder 14 by a hook 52 provided at the end of the flexible string-like member 51, preventing the water treatment device 4 from tipping or moving due to the water flow of the water to be treated W. Note that the tip-over prevention measure 5 does not necessarily have to be a suspension support by the flexible string-like member 51, and any method that can prevent the water treatment device 4 from tipping and maintain its function can be used. Suspension support was selected because it is simple and reliable and makes maintenance such as replacing the adsorbent cartridge 40 of the water treatment device 4, which will be described later, easy to perform.

[0026] The water treatment device 4 has a submersible pump 41 integrally attached to the water intake or discharge port of the adsorbent cartridge 40, and in this embodiment, is carried into the water storage tank 1 through the access opening 13. The submersible pump 41 is supplied with power from a power source (not shown) via a cable 6, and is driven by the power of the submersible pump 41 as indicated by the arrow F in the figure. in As shown by arrow F in the figure, the water to be treated W is sent into the adsorbent cartridge 40. out As shown in FIG. 1, the submersible pump 41 is attached to the water intake of the adsorbent cartridge 40, but it may alternatively be attached to the water outlet.

[0027] A predetermined amount of adsorbent is loaded into the adsorbent cartridge 40, and as the water to be treated W sent by the submersible pump 41 passes through the adsorbent cartridge 40, the PFAS in the water to be treated W is adsorbed by the adsorbent and removed. The adsorbent may be a porous adsorbent such as activated carbon or zeolite, an ion exchange resin, or a mixture of these. Furthermore, as the submersible pump 41 operates, the PFAS in the water to be treated W is adsorbed by the adsorbent, as indicated by the arrow F in the figure. in and arrow Fout A water flow indicated by is generated in the water requiring treatment W, and by stirring the water requiring treatment W, after a sufficient amount of time has passed, PFAS removal treatment will be performed on the entire water requiring treatment W in the water tank 1.

[0028] Figure 2 is a diagram showing an example of the structure of water treatment device 4. The diagram shows a partial cross-sectional view of the internal structure of adsorbent cartridge 40 of water treatment device 4. Adsorbent cartridge 40 has a structure in which adsorbent 43 is filled inside a cylindrical cartridge tank, and water taken in through a water intake port of intake / discharge port 42 provided at the top of the cartridge tank passes through adsorbent 43 and is then discharged through a discharge port. In Figure 2, the right side of intake / discharge port 42 is the water intake port and the left side is the discharge port, and the arrows indicate the flow of water when submersible pump 41 is operating.

[0029] Furthermore, at the intake port on the right side of the intake / discharge port 42, a submersible pump 41 is fixed directly to the adsorbent cartridge 40 via a pipe joint 44. The pipe joint 44 may be of the general screw-in type or a so-called one-touch type. The adsorbent cartridge 40 and the submersible pump 41 can be separated as needed by removing this pipe joint 44, allowing them to be replaced as appropriate. In addition, a stand 45 is attached to the bottom of the cartridge tank of the adsorbent cartridge 40 to support the adsorbent cartridge 40 in an upright position. The stand 45 may have a flange-like enlarged diameter portion as shown in the figure, or may have support legs that protrude radially outward.

[0030] 3 is a flow diagram of the water treatment method according to this embodiment. Note that the flow shown in the figure is for explaining a typical procedure, and some steps that may be performed in any order may be interchanged or performed simultaneously.

[0031] To carry out the water treatment method, first, in step ST1, the amount of water requiring treatment W stored in the water storage tank 1 and the pre-treatment PFAS concentration, which is the PFAS concentration in the water requiring treatment W, are measured. The amount of water requiring treatment W can be easily determined from the water level of the water requiring treatment W in the water storage tank 1, and the pre-treatment PFAS concentration can be measured by sampling a portion of the water requiring treatment W and having an analytical laboratory perform component analysis. This measurement usually takes about half a day to several days.

[0032] In the next step, ST2, an adsorption capacity confirmation test is conducted. In this test, the water requiring treatment W collected from the water storage tank 1 is brought into contact with a predetermined amount of adsorbent on a trial basis, and the change in PFAS concentration before and after is measured to determine the amount of PFAS adsorbed per unit amount of the adsorbent to be used for the water requiring treatment W (this is called the adsorption capacity).

[0033] It is believed that not only PFAS but also other ionic substances and other solutes are dissolved in the water requiring treatment W, and the composition and concentration of these solutes differ for each water requiring treatment W. Furthermore, since the adsorbent does not selectively adsorb only PFAS but also adsorbs these other solutes at the same time, the adsorption capacity of the adsorbent for PFAS differs depending on the properties of the water requiring treatment W, and it is desirable to confirm this experimentally.

[0034] In the next step ST3, an adsorbent cartridge 40 is selected and its effective period is calculated. The adsorbent cartridge 40 is selected by selecting, from among multiple adsorbent cartridge candidates each containing a different amount of adsorbent, a candidate adsorbent cartridge containing an amount of adsorbent that exceeds the minimum amount of adsorbent required to adsorb the amount of PFAS to be removed, which is calculated based on the amount of water to be treated W, the pre-treatment PFAS concentration, and the target PFAS concentration.

[0035] Specifically, the target PFAS concentration of the treated water W is the target PFAS concentration ρ d From the adsorption isotherm shown in Figure 4, the target PFAS concentration ρ dThe adsorption capacity c of the adsorbent at the time of reaching the target value is determined. Here, as shown in Figure 4, when both the vertical and horizontal axes are scaled logarithmically, the adsorption isotherm often takes on a shape that is roughly close to a straight line. The specific shape of the adsorption isotherm differs depending on the adsorbent used and the properties of the water W to be treated, so the detailed shape of this adsorption isotherm is determined in advance by an adsorption capacity confirmation test carried out in step ST2.

[0036] In addition, the target PFAS concentration ρ d is the upper limit of PFAS concentration ρ th Set a smaller value than the upper limit concentration ρ th is the standard value for continuously managing the PFAS concentration in the treated water W to a value below this upper limit. d is the upper concentration limit ρ th For example, the upper concentration limit ρ th It shall be set at 50% of the above.

[0037] The amount of PFAS to be removed (m) that must be adsorbed from the PFAS dissolved in the water to be treated (W) can be calculated using the following formula (1).

number

[0038] From this, the minimum amount of adsorbent M required to adsorb the amount of PFAS to be removed m is given by the following equation (2).

number

[0039] Then, from among the candidates for the adsorbent cartridge 40 that have different adsorbent amounts, a candidate that has an adsorbent amount that exceeds the minimum adsorbent amount M is selected as the adsorbent cartridge 40. To give a specific example, if the candidate adsorbent cartridges have adsorbent amounts of 20 L, 40 L, and 60 L, and the minimum adsorbent amount M is calculated to be 42 L, the 60 L candidate is selected as the adsorbent cartridge 40.

[0040] The effective period is the period when the PFAS concentration in the treated water W reaches the target PFAS concentration ρ when the minimum amount of adsorbent M is used, assuming that the storage compartment is isolated. d In other words, the target PFAS concentration ρ is calculated as the period required to reach the target PFAS concentration ρ when there is no inflow or outflow of PFAS dissolved in the water to be treated W other than adsorption to the adsorbent in the water treatment device 4. d The time it takes to reach it is the validity period.

[0041] The effective period is calculated based on the target PFAS concentration ρ shown in Figure 5 as an example. d The relationship between the ratio of the PFAS concentration ρ of the water requiring treatment W to the PFAS concentration ρ of the water requiring treatment W and time t is used. This relationship will have different curves depending on the capacity of the submersible pump 41, but here, to make the capacity of the submersible pump 41 dimensionless, we use the ratio (V / Q) of the amount V of the water requiring treatment W divided by the volumetric flow rate Q achieved by the submersible pump 41. V / Q has the dimension of time and indicates the time it takes for the submersible pump 41 to move all of the water in the water storage tank 1 with a volume equal to the water requiring treatment W. The smaller the value of V / Q, the higher the capacity of the submersible pump 41, and therefore the shorter the time required for water treatment to be completed. Therefore, Figure 5 shows three cases where V / Q is 12 [h], 24 [h], and 36 [h]. The smaller the V / Q and the better the mixing ability, the steeper the slope of the curve and the quicker ρ / ρ d approaches 1, indicating that the PFAS concentration ρ decreases rapidly.

[0042] Here, the effective period T is ρ / ρ when any V / Q curve is selected. d is its initial value ρ0 / ρ dIt can be calculated as the time it takes for the value of ρ0 to reach 1. For example, ρ0 / ρ d If we assume that V / Q = 3, and select the curve of V / Q = 12, the effective period T will be T 12 Similarly, if you select the curve of V / Q=24, the effective period T is T 24 , V / Q=36, the effective period T is T shown in the figure. 36 It is required that:

[0043] Alternatively, instead of manually reading a diagram such as that shown in FIG. 5, the effective period T may be determined using a computer simulation.

[0044] The submersible pump 41 is selected and Q is determined so that the effective period T obtained in this way is close to a realistic water treatment period. Such a period may be from a few days to a few months, for example, around one month. By specifically determining Q, the effective period T is determined.

[0045] It should be noted that the minimum adsorbent amount M and the effective period T are both values ​​determined assuming that the storage compartment is isolated. In other words, if the storage compartment, specifically, the water tank 1 in this embodiment, is not isolated and, for example, PFAS adsorbed on its wall surface elutes, the decrease in the PFAS concentration ρ of the treatment-requiring water W due to operation of the water treatment device 4 is thought to be more gradual than that of the V / Q curve shown in Figure 5.

[0046] Returning to FIG. 3, in the next step ST4, the submersible pump 41 is integrally attached to the selected adsorbent cartridge 40 to assemble the water treatment device 4. In the next step ST5, the assembled water treatment device 4 is immersed in the water tank 1, and tip-over prevention measures 5 are applied.

[0047] In the subsequent step ST6, the underwater pump 41 is operated to perform the removal treatment of PFAS from the water to be treated W. This removal treatment continues until the expiration of the effective period T as shown in step ST7. When the effective period T has elapsed, the process proceeds to step ST8, where the underwater pump 41 is stopped and the removal treatment of PFAS from the water to be treated W is temporarily stopped.

[0048] Furthermore, in step ST9, the water treatment device 4 is once lifted from the water storage tank 1, the adsorbent cartridge 40 is replaced with a new one, and then the process returns to step ST5 to continue the immersion of the water treatment device 4 and the operation of the underwater pump 41. This replacement of the adsorbent cartridge 40 is performed every time the effective period T elapses.

[0049] Referring to FIG. 6, the technical meaning of the flow shown in FIG. 3 will be described. FIG. 6 is a diagram showing an example of the temporal change in the PFAS concentration ρ of the water to be treated W when the water treatment method according to the present embodiment is implemented.

[0050] Assuming that the time point of t = 0 is the time when the underwater pump 41 is first operated, that is, the time when the removal treatment of PFAS from the water to be treated W is started, the PFAS concentration ρ of the water to be treated W at that time is equal to the PFAS concentration ρ0 before treatment. Thereafter, in the period of 0 ≦ t < T until the first effective period T elapses, the PFAS concentration ρ decreases as shown by the solid line in the figure.

[0051] At this time, the V / Q curve shown in FIG. 5, that is, the ideal change in the PFAS concentration ρ when it is assumed that the storage section is isolated, is shown by the dashed line in the period of 0 ≦ t < T in the graph of FIG. 6. As is clear from the figure, in the actual water storage tank 1, the storage section is not isolated and there is an inflow of PFAS into the water to be treated W from the outside. Therefore, the change in the actual PFAS concentration ρ shown by the solid line is gentler than the ideal change shown by the dashed line.

[0052] Thereafter, the adsorbent cartridge 40 is replaced whenever the effective period T elapses, i.e., whenever t = T, 2T, 3T, .... This timing is indicated in the figure by adding a filled triangle on the curve showing the PFAS concentration ρ. In this way, by replacing the adsorbent cartridge 40 every time the effective period T elapses, even if the storage compartment is not isolated, the adsorption capacity of the water treatment device 4 will not reach its limit and become unable to treat the water (i.e., breakthrough of the adsorbent cartridge 40 will occur), and the PFAS removal capacity of the water treatment device 4 can be reasonably maintained.

[0053] Here, even if PFAS adsorbed on, for example, the wall surface of the water tank 1 is eluted into the water requiring treatment W, the rate of such elution is considered to have been in equilibrium with the rate of adsorption onto the wall surface, etc., at the time when the PFAS concentration ρ of the water requiring treatment W was the pre-treatment PFAS concentration ρ0, and therefore, an increase in the PFAS concentration ρ due to such elution will not cause the PFAS concentration ρ of the water requiring treatment W to increase above the pre-treatment PFAS concentration ρ0. In other words, as long as the water treatment device 4 continues to operate, the PFAS concentration ρ of the water requiring treatment W will monotonically decrease, and the upper limit concentration ρ th The target PFAS concentration ρ can be maintained at a lower value and, over a sufficient period of time, d to reach.

[0054] Therefore, according to the water treatment method of this embodiment, the PFAS concentration ρ of the water to be treated W can be calculated by the upper limit concentration ρ without estimating the amount of PFAS adsorbed on, for example, the wall surface of the water storage tank 1. th Since the pressure can be kept lower and an unnecessarily large adsorption cartridge 40 or an underwater pump 41 with excessive performance is not used, the water treatment device 4 itself can be selected and operated in a compact and rational manner.

[0055] In the first embodiment described above, the inflow of PFAS from outside into the water requiring treatment W in the water storage compartment was considered to be in equilibrium at a pre-treatment PFAS concentration ρ0, such as through the elution of PFAS adsorbed on the wall surface of the water storage tank 1. The second embodiment described next assumes, in addition to this, a situation in which new PFAS may be supplied unexpectedly, in some cases, due to some kind of human activity or accident.

[0056] 7 is a diagram showing a schematic cross section of a water treatment device 4 installed in a reservoir 7 as a water storage compartment containing water W to be treated, the water W being the target of water treatment, so as to be immersed in the water W.

[0057] Thus, when the storage section is a section such as an artificial or natural reservoir 7, the mooring section for the measure 5 to prevent the water treatment device 4 from tipping over may not be located directly above the water treatment device 4. Therefore, in this embodiment, the measure 5 to prevent tipping over is implemented by floating a buoy 53 on the surface of the water to be treated W and connecting it to the fixing device 50 of the water treatment device 4 with a flexible string-like member 51 for suspension support. It is desirable to fix the buoy 53 to the ground surface GL with a wire rope 54 or the like to prevent it from being carried away by wind or waves.

[0058] For ease of explanation, in this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant explanations will be omitted. Therefore, unless otherwise specified, the explanations given in the first embodiment regarding the components already explained will also be applied to this embodiment.

[0059] In the present embodiment, external inflow of PFAS into the water requiring treatment W can occur not only through elution of PFAS adsorbed on the mud at the bottom of the reservoir 7, but also through inflow from surrounding soil during rainfall, or through human activity in the surrounding area, i.e., the inflow of wastewater containing PFAS or the inflow of PFAS-containing chemicals, such as fire extinguishing agents, due to accidents, etc. Such inflows can periodically or irregularly cause sudden increases in the PFAS concentration of the water requiring treatment W in the reservoir 7.

[0060] 8 is a flow diagram of the water treatment method according to this embodiment. The flow shown in the figure also explains a typical procedure, and some steps that may be performed in any order may be interchanged or performed simultaneously.

[0061] In carrying out the water treatment method according to this embodiment, steps ST1 to ST7 are the same as those in the first embodiment.

[0062] If it is determined in step ST7 that the valid period T has elapsed, the process proceeds to step ST10, where the submersible pump 41 is stopped and the water treatment device 4 is withdrawn. Then, in step ST11, the current PFAS concentration ρ of the treatment-requiring water W stored in the reservoir 7 is measured again.

[0063] Since this re-measurement usually takes half a day to several days, the stopping of the submersible pump 41 and the withdrawal of the water treatment device 4 in step ST10 may be postponed until the measurement results are obtained, and the operation of the submersible pump 41 may continue.

[0064] In step ST12, the measured PFAS concentration ρ is compared with the pre-treatment PFAS concentration ρ0 to determine whether ρ > ρ0. If the determination is negative, i.e., ρ ≦ ρ0, this means that even if there is a new inflow of PFAS from the outside into the treatment-requiring water W in the reservoir 7, the amount of the inflow will remain at an amount that can be sufficiently removed by continuing water treatment using the selected adsorbent cartridge 40 and the calculated effective period T. Therefore, proceed to step ST13, simply replace the adsorbent cartridge 40 with a new one, return to step ST5, and continue immersing the water treatment device 4 and operating the submersible pump 41 to reduce the PFAS concentration ρ of the treatment-requiring water W and reduce the upper limit concentration ρ th It is believed that the value can be maintained at a lower level.

[0065] On the other hand, if ρ > ρ0 in step ST12, that is, the remeasured PFAS concentration ρ is greater than the pre-treatment PFAS concentration ρ0, it is considered that the amount of adsorbent in the selected adsorbent cartridge 40 will not be sufficient to quickly adsorb and remove the PFAS newly introduced into the water to be treated W. Therefore, the remeasured PFAS concentration ρ is set as the new pre-treatment PFAS concentration ρ0, and the process returns to step ST3, where the selection of the adsorbent cartridge 40 and the calculation of the effective period T are redone. That is, the remeasured PFAS concentration ρ and the target PFAS concentration ρ d Based on this, the adsorbent cartridge 40 is reselected and the validity period T is recalculated.

[0066] The subsequent steps are the same as those already described. That is, in step ST4, the water treatment device 4 is assembled, that is, the reselected submersible pump 41 is attached integrally to the water intake or discharge port of the reselected adsorbent cartridge 40 to assemble the water treatment device 4, in step ST5, the water treatment device 4 is immersed in the water to be treated W in the reservoir 7, which is the storage compartment, in step ST6, the submersible pump 41 is operated, and the subsequent steps are repeated.

[0067] FIG. 9 is a diagram showing an example of the change over time in the PFAS concentration ρ of the water W to be treated when the water treatment method according to this embodiment is carried out.

[0068] In FIG. 9, time 0≦t <t acc The period from t to t is exactly the same as that shown in FIG. 6. In this example, the time t=t acc At this point, for some reason, PFAS newly flows into the water requiring treatment W in the reservoir 7, and the concentration of PFAS increases to ρ acc (>ρ0).

[0069] time t=t acc At this point, the PFAS concentration ρ is acc The increase in PFAS concentration ρ can be determined by re-measuring the current PFAS concentration ρ of the water requiring treatment W at time t = 2T. At this time, the PFAS concentration ρ is accAlthough there is thought to be a slight decrease from ρ0, it is still above ρ0. Obtaining such measurement results allows us to determine that PFAS has newly flowed into the treatment-requiring water W in the reservoir 7 due to some external factor, and we then reselect the adsorbent cartridge 40 and recalculate the validity period T. The water treatment device 4 is assembled based on the reselected adsorbent cartridge 40, and the removal of PFAS from the treatment-requiring water W continues.

[0070] Since PFAS is removed from the treatment-requiring water W using the reselected adsorbent cartridge 30, the PFAS concentration ρ of the treatment-requiring water W quickly decreases to the standard value ρ after time t = 2T, as shown in FIG. th If the concentration falls below the target PFAS concentration ρ and there is no new PFAS inflow, d gradually approaches .

[0071] If the reselected effective period is written as T', the point in time t=2T when ρ>ρ0 was detected is newly set as t=0 (shown in parentheses in Figure 9), and for the new effective period T', the adsorbent cartridge 40 is replaced every time t=T', 2T', 3T', ... passes, and water treatment continues thereafter.

[0072] According to the water treatment method of this embodiment, even if the storage compartment is not isolated and new PFASs periodically or irregularly flow into the treatment-requiring water W, the PFAS concentration ρ of the treatment-requiring water W can be increased to the upper limit concentration ρ without estimating the amount of PFASs adsorbed, for example, to the mud deposited on the bottom of the reservoir 7 or predicting the amount of new PFASs that flow in. th Since the pressure can be kept lower and an unnecessarily large adsorption cartridge 40 or an underwater pump 41 with excessive performance is not used, the water treatment device 4 itself can be selected and operated in a compact and rational manner.

[0073] 10 is a diagram showing a modified example of the water treatment device 4 used in the first or second embodiment of the water treatment method according to the present invention. In this modified example, the water treatment device 4 is not suspended, but is placed sideways on the floor surface 10 so as to be completely submerged in the water to be treated W in the water storage tank 1.

[0074] Similar to the previous embodiment, the water treatment device 4 comprises an adsorbent cartridge 40 and a submersible pump integrally attached to the adsorbent cartridge's intake or discharge port. Because the adsorbent cartridge 40 does not need to stand on the floor 10 underwater, no stand or other component for upright support is attached to the bottom of the adsorbent cartridge 40. A mooring line 8, such as a wire or rope, is attached to a fixture 50, such as an eyebolt, at the top of the water treatment device 4, and a hook 80 attached to the other end of the mooring line 8 allows the water treatment device 4 to be moored to a structure such as a ladder 14. The mooring line 8 does not provide any support for the water treatment device 4 in the water tank 1; rather, it allows the water treatment device 4 to be easily lifted out of the water by pulling on the mooring line 8 when, for example, replacing the adsorbent cartridge 40. The water treatment device 4 lies freely lying on its side on the floor 10.

[0075] Figure 11 is a top view showing an example of the structure of a water treatment device 4 according to a modified example, lying on its side on the floor 10 inside a water storage tank 1. Similar to Figure 2, Figure 11 also shows a partial cross-sectional view of the internal structure of the adsorbent cartridge 40 of the water treatment device 4. The adsorbent cartridge 40 is similar in structure to the adsorbent cartridge 40, with a cylindrical cartridge tank filled with adsorbent 43. Water taken in through the intake port of the intake / discharge port 42 at the top of the cartridge tank passes through the adsorbent 43 and then is discharged through the discharge port. A submersible pump 41 is directly attached to the adsorbent cartridge 40 via a pipe joint 44. As in Figure 2, Figure 11 shows the intake port on the right side of the intake / discharge port 42 and the discharge port on the left side. The submersible pump 41 is attached to the intake port on the right side, but it is also possible to attach the submersible pump 41 to the discharge port on the left side. Also, arrows in Figure 11 indicate the flow of water during operation.

[0076] The adsorbent cartridge 40 is structured with a penetration pipe 46 that extends from the top to the bottom of the cartridge tank, allowing water passing through the interior of the cartridge tank to pass through the entire cartridge tank. Strainers 47, 48 are attached to the end of the penetration pipe 46 and the top of the cartridge tank, respectively, to prevent the adsorbent 43 contained inside the cartridge tank from leaking out of the cartridge tank. The figure also shows that a mooring line 8 is attached to a fixture 50 provided at the top of the water treatment device 4, and that power is supplied to the submersible pump 41 via a cable 6.

[0077] In the water treatment device 4 according to this modification, the intrusion pipe 46 is connected to the water intake. That is, the water to be treated W that flows in from the water intake / discharge port 42 passes through the intrusion pipe 46, is released into the cartridge tank near the bottom of the cartridge tank, flows toward the top while coming into contact with the adsorbent 43 contained inside the cartridge tank, and flows out from the discharge port of the intrusion pipe 46.

[0078] Generally, the adsorbent 43 is granular, and the filling rate relative to the capacity of the cartridge tank is about 70 to 80%, not 100%, so there are gaps inside the cartridge tank. Therefore, unless an external force such as a water flow acts on the adsorbent 43, it settles vertically downward due to its own weight. Therefore, when the adsorbent cartridge 40 is placed on its side as in this modified example, the adsorbent 43 accumulates on the vertically lower side, and gaps are created inside the cartridge tank along the opposite, vertically upper side.

[0079] The water flow passing through the inside of the cartridge tank tends to flow through a path with low resistance to passage (such a water flow path will hereinafter be referred to as a "short-circuit path"), so if such a gap is created, the water to be treated W will flow through this gap inside the cartridge tank, and there is a risk that the water to be treated W will not come into sufficient contact with the adsorbent 43 contained inside the cartridge tank. In contrast, if the particles of the adsorbent 43 are stirred by the water flow inside the cartridge tank and are suspended inside the cartridge tank, no specific gap will be created, so it is thought that the water to be treated W can come into sufficient contact with the adsorbent 43.

[0080] Because the cross-sectional area of ​​the outlet of the intrusion pipe 46 is typically smaller than the cross-sectional area of ​​the outlet at the top of the cartridge tank, when the intrusion pipe 46 is connected to the water intake and the water to be treated W is introduced into the cartridge tank through the intrusion pipe 46, the introduced water to be treated W is forcefully ejected from the intrusion pipe 46, vigorously stirring the adsorbent 43. As a result, the internal gaps formed when the adsorbent cartridge 40 is placed on its side are thought to immediately disappear, and the adsorbent 43 particles become evenly suspended inside the cartridge tank. Furthermore, the water to be treated W ejected from the intrusion pipe 46 collides with the bottom of the cartridge tank immediately after ejection, creating turbulence, which efficiently stirs the adsorbent 43 particles. Therefore, compared to when the intrusion pipe 46 is connected to a drainage outlet, this is thought to be more effective at stirring the adsorbent 43 particles.

[0081] In this modified example, in order to prevent gaps from being created inside the cartridge tank that could create a short-circuit path, an inclined support 49 is attached to the top of the adsorbent cartridge 40, so that when the water treatment device 4 is placed sideways on the floor 10 of the water tank 1, the adsorbent cartridge 40 does not lie completely horizontally, but is instead inclined at a certain angle with the bottom of the cartridge tank facing downwards.

[0082] 12 is a partial side cross-sectional view showing an example of a water treatment device 4 in which a tilting support 49 is attached to the top of the adsorbent cartridge 40. In this example, the tilting support 49 is a large-diameter ring-shaped member attached to the upper side of the cartridge tank, and as shown in the figure, when the water treatment device 4 is placed on a floor surface 10, the bottom of the cartridge tank and the outer periphery of the tilting support 49 come into contact with the floor surface 10, and the adsorbent cartridge 40 is tilted at an angle greater than 0 degrees and less than 90 degrees.

[0083] At this time, the side of the intake / discharge port 42 to which the submersible pump 41 is attached faces downward as shown in the figure due to the weight of the submersible pump 41. The other configurations of the water treatment device 4 are as already described, so the same components are given the same symbols and redundant explanations will be omitted.

[0084] At this time, the granular adsorbent 43 inside the cartridge tank settles under its own weight and, as shown, accumulates at the bottom of the cartridge tank with a surface that is generally parallel to the floor surface 10. Since the cartridge tank is not parallel to the floor surface 10 but is inclined at an angle greater than 0 degrees and less than 90 degrees, as is clear from Figure 12, no continuous gap is formed from the bottom to the top, and therefore no short-circuit path is created.

[0085] In this state, when the submersible pump 41 is operated and the water to be treated W is introduced into the cartridge tank from the water intake, the adsorbent 43 accumulated at the bottom of the cartridge tank is blown up and sufficiently stirred inside the cartridge tank, preventing the formation of short-circuit paths inside the cartridge tank and allowing the water to be sufficiently brought into contact with the adsorbent 43. Furthermore, even when the amount of adsorbent 43 is reduced depending on the amount of PFAS to be removed, short-circuit paths are less likely to form inside the cartridge tank, making it possible to operate the water treatment device 4 without impairing its adsorption capacity.

[0086] FIG. 13 is a perspective view showing an example of the structure of the tilting support 49. The tilting support 49 may be made of a rigid material such as metal or synthetic resin, and may have an inner ring 49a fixed to the outer periphery of the cartridge tank and an outer ring 49b that contacts the floor 10 of the water tank 1 and supports the water treatment device 4 in an inclined position, connected by appropriate spokes 49c. Alternatively, although not shown, the tilting support 49 may be an inflatable type made of flexible synthetic resin, or a life-ring-shaped device made of hard porous resin, such as hard polystyrene foam. In this case, the buoyancy generated by the tilting support 49 partially offsets the weight of the water treatment device 4, but is not sufficient to prevent the water treatment device 4 itself from sinking into the water W to be treated.

[0087] Generally, the diameter of access opening 13 for accessing the inside of water tank 1 is about 600 mm. Therefore, inclined support 49 is designed to have an outer diameter of less than 600 mm so as not to hinder the transport of water treatment device 4 into the inside through access opening 13.

[0088] The above-described embodiments and modifications have been prepared to specifically illustrate and explain various aspects of the inventions disclosed in this specification, and are not intended to limit the inventions to the specific shapes, dimensions, numbers, etc. shown in the embodiments and modifications. In implementing the inventions disclosed in this specification, the designs shown in the embodiments and modifications can be modified, combined, or partially omitted as necessary, and the disclosure of this specification includes such modifications. [Explanation of symbols]

[0089] 1 water tank, 2 fire pump, 3 building, 4 water treatment device, 5 fall prevention measures, 6 cable, 7 reservoir, 8 mooring line, 10 floor, 11 side, 12 ceiling, 13 access opening, 14 ladder, 40 absorbent cartridge, 41 submersible pump, 42 intake / discharge port, 43 absorbent, 44 pipe joint, 45 stand, 46 penetration pipe, 47 strainer, 48 strainer, 49 tilt support, 50 fixing device, 51 flexible string-like member, 52 hook, 53 buoy, 54 wire rope, 80 hook, F in ,F out Water flow, GL ground surface, W water requiring treatment.

Claims

1. measuring the amount of water requiring treatment stored in the storage compartment and the pre-treatment PFAS concentration, which is the concentration of PFAS (perfluoroalkyl substances and polyfluoroalkyl compounds) contained in the water requiring treatment; selecting a sorbent cartridge and calculating a useful life based on the amount, the pre-treatment PFAS concentration, and the target PFAS concentration; a step of immersing a water treatment device having a submersible pump integrally attached to the water intake or discharge port of the selected adsorbent cartridge in the water to be treated in the storage compartment and operating the submersible pump; replacing the sorbent cartridge after each expiration of the validity period; A water treatment method comprising the steps of:

2. The selection of the adsorbent cartridge is performed by selecting, from among a plurality of adsorbent cartridge candidates loaded with different adsorbent amounts, an adsorbent cartridge candidate loaded with an adsorbent amount exceeding a minimum adsorbent amount required to adsorb the amount of PFAS to be removed, which is calculated based on the amount, the pre-treatment PFAS concentration, and the target PFAS concentration; The effective period is calculated as a period required for the PFAS concentration of the water to be treated to reach the target PFAS concentration when the minimum amount of adsorbent is used, assuming that the storage compartment is isolated. The water treatment method according to claim 1 .

3. a step of re-measuring the PFAS concentration of the water to be treated every time the effective period elapses; If the remeasured PFAS concentration is higher than the pre-treatment PFAS concentration, reselecting an adsorbent cartridge and recalculating a validity period based on the amount, the remeasured PFAS concentration, and a target PFAS concentration; a step of immersing a water treatment device having a submersible pump integrally attached to the water intake or discharge port of the reselected adsorbent cartridge in the water to be treated in the storage compartment and operating the submersible pump; replacing the sorbent cartridge every time the recalculated expiration date elapses; The water treatment method according to claim 1, comprising:

4. The water treatment device is provided with a fall prevention measure. The water treatment method according to any one of claims 1 to 3.

5. The fall prevention measure is a suspension support using a flexible string-like member. The water treatment method according to claim 4.

6. The water treatment device is placed sideways on the floor of the storage compartment. The water treatment method according to claim 1 .

7. the sorbent cartridge includes a cartridge tank and an intrusion pipe extending from the top of the cartridge tank to the bottom of the cartridge tank, the intrusion pipe being connected to the water intake; The water treatment method according to claim 6.

8. an inclined support device is attached to the adsorbent cartridge, the inclined support device supporting the adsorbent cartridge on the floor surface at an angle greater than 0 degrees and less than 90 degrees; The water treatment method according to claim 7.

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