Pipe cleaning method

Abstract

To remove PFAS adhering to the inside of pipes and reduce the amount of PFAS-containing waste generated as a result. [Solution] A method for cleaning a pipe, comprising: an estimation step of estimating the amount of eluted PFAS, which is the amount of PFAS adhering to the inside of the pipe to be cleaned; a preparation step of preparing an adsorbent with a capacity capable of adsorbing and removing the amount of PFAS based on the amount of eluted PFAS; a peeling step of peeling off the adhering material inside the pipe; a cleaning step of cleaning the inside of the pipe with cleaning water simultaneously with or after the peeling step; and a removal step of removing solid matter from the used cleaning water and removing PFAS using the adsorbent, wherein the cleaning water from which the solid matter and PFAS have been removed is reused in the cleaning step.

Description

Technical Field

[0001] The present invention relates to a method for cleaning pipes.

Background Art

[0002] Patent Document 1 describes a pipe cleaning apparatus that puts a cleaning liquid in a cleaning liquid storage tank, sucks up the cleaning liquid through a filter with a high-pressure water pump, sends it to a pipe connection part (pipe connection assembly cylinder) on the cleaning liquid supply side, passes the cleaning target pipe of the object to be processed (object to be cleaned) through a flexible pipe, and further returns it to a pipe connection part (pipe connection assembly cylinder) on the cleaning liquid receiving side through the flexible pipe and collects it in the cleaning liquid storage tank.

[0003] In the same document, the pipe cleaning apparatus is said to repeat circulation in the above-mentioned flow to clean the cleaning target pipe, and the filter removes scale and dust contained in the recovered cleaning liquid so as not to circulate it back to the cleaning target pipe again.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] PFAS (perfluoroalkyl compounds and polyfluoroalkyl compounds) are hardly decomposable and remain for a long time, so they are pointed out as causative substances that cause environmental problems, and at the same time, regulations are being strengthened in recent years. PFAS has been used in various applications so far, and one of those applications is as a fire extinguishing agent in case of fire. Therefore, foam fire extinguishing agents containing PFAS have been used in the past for foam fire extinguishing equipment installed in commercial facilities, parking lots, airports, military facilities and other large facilities.

[0006] PFAS may adhere to and remain inside the piping used in such facilities. Although PFAS is generally water-soluble, PFAS that has adhered to the inside of piping that has been in use for many years is difficult to remove by simple washing. This is because layers of deposits such as scale, formed by precipitated inorganic salts, may form inside the piping, and PFAS that is incorporated into such deposits or adsorbed into the gaps cannot be removed by washing and remains. Even if the pipes are washed and the foam fire extinguishing agent is replaced with one that does not contain PFAS, the PFAS remaining in the deposits inside the pipes will slowly dissolve from the surface of the deposit layer and continue to contaminate the water passing through the inside of the pipes for a long period of time.

[0007] Furthermore, PFAS remaining in the deposits inside pipes poses a problem when replacing equipment piping. This is because the pipes removed during replacement have absorbed PFAS, making them difficult to dispose of as general waste. Therefore, in order to dispose of pipes removed from equipment as waste, it is necessary to remove the deposits inside using mechanical means such as wire brushes, and then wash them with water to remove the PFAS and make them clean. However, this process generates not only scale debris containing PFAS, but also a large amount of wastewater in which PFAS has dissolved.

[0008] Naturally, this wastewater cannot be released into the environment, so it must be stored in some kind of storage facility and then treated appropriately. However, accumulating large amounts of wastewater each time the pipes are cleaned, and then performing PFAS decomposition treatment on that large amount of wastewater, for example using a high-temperature furnace, is far too costly in terms of both work efficiency and energy consumption, and is not very practical.

[0009] The same applies not only to piping used in fire extinguishing systems, but also to piping used in other equipment where PFAS may adhere to its interior. For example, similar problems can occur in piping used in factories that handle fluorine compounds.

[0010] This invention has been made in view of these circumstances, and its purpose is to remove PFAS adhering to the inside of pipes and to reduce the amount of PFAS-containing waste generated as a result. [Means for solving the problem]

[0011] The invention disclosed in this application, which aims to solve the above-mentioned problems, has various aspects, and a summary of some of the most representative aspects is as follows.

[0012] (1) A method for cleaning a pipe, comprising: an estimation step of estimating the amount of eluted PFAS, which is the amount of PFAS adhering to the inside of the pipe to be cleaned; a preparation step of preparing an adsorbent with a capacity capable of adsorbing and removing the amount of PFAS eluted based on the amount of eluted PFAS; a peeling step of peeling off the adhering material inside the pipe; a cleaning step of cleaning the inside of the pipe with cleaning water simultaneously with or after the peeling step; and a removal step of removing solid matter from the used cleaning water and removing PFAS using the adsorbent, wherein the cleaning water from which the solid matter and PFAS have been removed is reused in the cleaning step.

[0013] (2)(1) The removal step is a method of cleaning a pipe, which is carried out in parallel with the cleaning step.

[0014] (3)(1) A method for cleaning a pipe, wherein the estimation step includes an elution amount measurement step for measuring the amount of PFAS eluted per unit amount of deposits inside the pipe, and a total amount estimation step for estimating the total amount of deposits inside the pipe.

[0015] (4)(3) A method for cleaning a pipe, wherein the total amount estimation step includes a first thickness measurement step of measuring the thickness of the deposit inside the pipe by non-destructive testing.

[0016] (5)(1) A method for cleaning a pipe, comprising a confirmation step after the cleaning step to confirm that the amount of PFAS adhering to the inside of the pipe is less than or equal to a predetermined amount.

[0017] (6)(5) In the above, the confirmation step includes a second thickness measurement step of measuring the thickness of the deposits inside the pipe by non-destructive inspection, a method for cleaning a pipe.

Brief Description of the Drawings

[0018] [Figure 1] It is a piping diagram of a cleaning facility used when implementing the pipe cleaning method according to an embodiment of the present invention. [Figure 2] It is a flowchart for explaining the procedure of the pipe cleaning method according to an embodiment of the present invention. [Figure 3] It is a flowchart showing an example of the estimation step. [Figure 4] It is a diagram showing an example of the relationship between the thickness of the deposits inside the pipe and the peak frequency detected as the frequency response. [Figure 5] It is an example of an adsorption curve obtained by an adsorption capacity confirmation test. [Figure 6] It is a flowchart showing an example of the confirmation step.

Embodiments for Carrying Out the Invention

[0019] Figure 1 is a piping diagram of a cleaning facility 100 used when implementing the pipe cleaning method according to an embodiment of the present invention. The cleaning facility 100 has, as main facilities, a peeling station 1, a cleaning water tank 2, and a purification facility 3.

[0020] The peeling station 1 is equipment for cleaning the pipe P by peeling off the PFAS and adherences attached to the inside of the pipe P to be cleaned and then washing it with water. At the peeling station 1, the pipe P mechanically scrapes off the adherences such as scale attached to its inside, and the original inner surface of the exposed pipe P is also washed off by water washing, and the PFAS is removed to be cleaned. The peeling method may be arbitrary. For example, it may be done by scraping the inside of the pipe P with a motor-rotating wire brush 11 or grinding it with a router. The adherences inside the pipe P are finely crushed into adherent pieces and peeled off from the inner surface of the pipe P. Also, at this time, the old lining applied to the inner surface of the pipe P may be peeled off simultaneously.

[0021] Also, simultaneously with or after the peeling of the adherences, washing water is supplied to the inside of the pipe P to wash away the adherent pieces and wash the original inner surface of the exposed pipe P with water. The washing water stored in the washing water tank 2 is pumped and supplied by the pump 20. In the example shown in Fig. 1, while the inner surface of the pipe P is being cleaned with the wire brush 11, the washing water is simultaneously supplied from one side of the pipe P. The solid substances such as the crushed adherent pieces and the old lining, and the PFAS attached to the inner surface of the pipe P are washed away by the washing water and flow out from the other side of the pipe P.

[0022] The stripping area 1 is equipped with a washing tank 10, and the stripping and washing of adhering material from the pipe P is performed inside this washing tank 10. Therefore, the washing water used and solid materials such as pieces of adhering material stripped from the pipe P are collected in the washing tank 10 without scattering into the surroundings and are transferred to the purification equipment 3. The washing tank 10 is a concave-shaped workspace with an opening at the top, and its side walls and bottom are impermeable to prevent the collected washing water and solid materials from being released into the surrounding environment. The washing tank 10 may be a permanently installed facility, for example, constructed of lined concrete walls, or it may be a temporarily installed facility, for example, an open container made of FRP (fiber-reinforced plastic) simply placed on the ground, or a frame that is easy to assemble and disassemble is installed on the ground, and the bottom and side walls of the water storage tank are constructed inside with an impermeable resin sheet such as polyethylene sheet (so-called blue sheet / tarpaulin).

[0023] The stripping equipment, such as the wire brush 11, installed in the stripping area 1 may be an automatic tool, a manual tool, or a combination of both. For example, for straight pipes P, an automatic tool can be used to automatically clean the inside of the pipe once it is set in a predetermined position. For curved pipes, branched pipes, joints, and other pipes P whose internal shape is not necessarily uniform, a wire brush 11 can be attached to an electric manual tool (e.g., an electric drill), and a worker can perform the cleaning inside the stripping area 1.

[0024] The wastewater from the stripping area 1 consists of wash water in which PFAS has dissolved, mixed with solid matter containing attached material fragments. The purification equipment 3 is a device that removes the solid matter and PFAS from this wastewater, purifying it so that it can be reused as wash water. In this embodiment, the purification equipment 3 comprises a sedimentation tank 30, a filter 31, and an adsorbent 32.

[0025] The sedimentation tank 30 removes relatively large solid particles that can be separated by sedimentation from the wastewater, i.e., the wash water after use. The structure of the sedimentation tank 30 is not particularly limited, but in the simplified example shown in Figure 1, a mesh screen 33 prevents the movement of suspended solid particles, while a pump 35 pumps up the supernatant liquid overflowing from the separator 34 and sends it to the filter 31. The solid particles that have settled in the sedimentation tank 30 slide down the inclined surface 36 and are discharged from the drain 37.

[0026] The filter 31 is a filter that removes fine solid matter that is not completely separated by sedimentation in the sedimentation tank 30 and remains suspended in the wastewater. By passing the wastewater through the filter media, the solid matter in the wastewater is trapped and removed by the filter media. The shape of the filter 31 and the filter media used can be those commonly used and are not particularly limited. For example, it may consist of a filter housing with cartridge-type filter media attached, and any type of filter media such as wound type, span type, or pleated type may be used.

[0027] The wastewater that has passed through filter 31 is water containing soluble components, including PFAS, with solid matter removed. The adsorbent 32 uses an adsorbent packed inside to adsorb and remove the soluble components from the passing water. Specifically, the adsorbent 32 may be a treatment column packed with ion exchange resin. In Figure 1, a single treatment column is shown as the adsorbent 32, but multiple treatment columns connected in parallel or in series may be used as the adsorbent 32. Note that the adsorbent used to remove PFAS from the wastewater in the adsorbent 32 does not necessarily have to be ion exchange resin; other materials such as activated carbon or zeolite may be used, or a combination of these materials may be used.

[0028] Furthermore, a flow regulator 38 is provided in the inlet piping to the adsorbent 32 to control the flow rate of wastewater flowing into the adsorbent 32. In addition, a drain valve 39 is provided in the discharge piping from the adsorbent 32 to allow for appropriate maintenance, such as the removal of residual water in the piping. In addition, to monitor and manage whether the purification system 3 is operating normally, appropriate instruments such as flow meters and pressure gauges (not shown) may be provided, and additional drain valves for maintenance may be added.

[0029] In this embodiment, the wastewater treatment system 3 is shown to include both a sedimentation tank 30 and a filter 31, but it may be replaced with a system that includes only one of these. Furthermore, the equipment for removing solid matter from wastewater is not necessarily limited to a sedimentation tank 30 or a filter 31, and other types of equipment may be used. For example, a centrifugal separator (cyclone) can also be used.

[0030] The wastewater that has passed through the purification equipment 3 is clean water from which solid matter and PFAS have been removed, so it is returned to the washing water tank 2 and reused as washing water. The solid matter in the wastewater has PFAS adsorbed on its surface or has incorporated PFAS into its interior. Therefore, when pipe P is washed using the washing equipment 100, the PFAS-containing waste generated after washing consists of the settled solid matter discharged from the drain 37 of the sedimentation tank 30, the used filter media of the filter 31 that trapped the suspended solid matter in the wastewater, and the adsorbent that fills the inside of the adsorbent 32 and adsorbs PFAS. The large amount of wastewater generated during washing is purified by the purification equipment 3 and collected in the washing water tank 2, so the amount of PFAS-containing waste requiring proper treatment after pipe P is washed is significantly reduced.

[0031] In this way, by properly using the cleaning equipment 100 to clean the pipe P, the large amount of wastewater generated during the cleaning of the pipe P can be purified, and the amount of PFAS-containing waste generated during the cleaning can be significantly reduced. Furthermore, since the cleaning water used during the cleaning process is purified as it is being reused, the amount of water used is also significantly reduced, and the environmental burden and labor costs associated with the cleaning work are also reduced. If there are no plans for reuse, or if it is necessary to empty the cleaning water tank 2 for maintenance purposes, the cleaning water stored in the cleaning water tank 2 may simply be disposed of.

[0032] However, such effects can only be obtained if the wastewater is properly purified by passing it through the purification facility 3, and any remaining PFAS is completely removed or reduced to below the standard value. At this time, as mentioned above, PFAS is a persistent and chemically stable substance, which presents a problem in that it is difficult to detect or measure it in situ.

[0033] In other words, it is not possible to immediately confirm whether the wastewater that has passed through the purification facility 3 has been properly purified. Furthermore, measuring the concentration of PFAS in the water requires analysis by a specialized analytical institution, which takes several days to a week. This means that even if a large amount of PFAS is released from pipe P during the cleaning process using the purification facility 3, exceeding the adsorption capacity of the adsorber 32 of the purification facility 3, and causing breakthrough of the adsorber 32, this cannot be immediately detected.

[0034] Therefore, the adsorption capacity of the adsorbent 32 must be sufficient to adsorb the PFAS released during the cleaning of the pipe P, and when installing the purification equipment 3, the adsorption capacity of the adsorbent 32 must exceed the amount of PFAS released. However, if the adsorption capacity of the adsorbent 32 is set too high, the amount of adsorbent that needs to be prepared and the amount of PFAS-containing waste that requires proper treatment will increase, leading to unnecessary cost increases. Moreover, no matter how the adsorption capacity is set, there is no guarantee that it will exceed the amount of PFAS released, so it cannot fundamentally solve the risk of breakthrough of the adsorbent 32.

[0035] In other words, the adsorption capacity of the adsorbent 32 must be properly designed when the purification equipment 3 is installed. The pipe cleaning method according to this embodiment uses the cleaning equipment 100 described above to clean the pipe P, rationally designing the adsorption capacity of the adsorbent 32, preventing breakthrough of the adsorbent 32 during the cleaning operation, purifying the large amount of wastewater generated during the cleaning of the pipe P, and ensuring that the advantageous effects of significantly reducing the amount of PFAS-containing waste generated during cleaning are reliably achieved.

[0036] Figure 2 is a flowchart illustrating the procedure for cleaning the pipe according to this embodiment. The procedure will be described below in accordance with the flowchart.

[0037] <Quotation Process> (ST1) In this process, prior to cleaning the pipe P, the amount of eluted PFAS, which is the amount of PFAS adhering to the inside of the pipe P to be cleaned that will dissolve, is estimated. That is, after the cleaning operation, some of the PFAS adhering to the inside of the pipe P will detach and dissolve in the cleaning water, while other parts will be adsorbed onto the surface of the adsorbent fragments detached from the pipe P or trapped inside. Of these, the PFAS that should be adsorbed and removed by the adsorbent 32 is the detached and dissolved in the cleaning water, i.e., eluted. Therefore, if the total amount of this eluted PFAS can be estimated, the adsorption capacity required by the adsorbent 32 can be designed.

[0038] Figure 3 is a flowchart showing an example of the estimation process. The estimation process broadly includes an elution amount measurement process, which measures the amount of PFAS eluted per unit amount of deposits inside pipe P, and a total amount estimation process, which estimates the total amount of deposits inside pipe P.

[0039] <Elution amount measurement process> (ST1-1) In the elution measurement process, a portion of the adhering material is actually peeled off from pipe P, and the obtained adhering material fragment is mixed with washing water. The amount of PFAS dissolved in the washing water is then measured to determine the amount of PFAS eluted per unit amount of adhering material. More specifically, first, a sample of the adhering material is taken (ST1-1a).

[0040] Sampling of the adhering material is performed by peeling off the adhering material from a portion of pipe P and obtaining a fragment of the adhering material. The volume of the obtained fragment is determined. The volume may be determined from the measured mass and specific gravity of the obtained fragment. The amount of adhering material to be sampled is small; for example, peeling off several tens of centimeters of adhering material from the end of pipe P and obtaining about 0.1 to a few grams is sufficient.

[0041] The obtained deposit fragments are thoroughly mixed with a predetermined amount (e.g., 100 ml) of washing water to dissolve the PFAS detached from the deposit fragments into the washing water. This washing water is then analyzed by a specialized analytical laboratory to measure the concentration of PFAS contained in the washing water, thereby determining the amount of PFAS leached from the deposit (ST1-1b). The amount of PFAS leached into the washing water per unit volume of the deposit can be determined from the volume of the deposit fragments used, the amount of washing water, and the concentration of PFAS contained in the washing water.

[0042] Furthermore, when sampling the deposited material, a wire brush of the same type as that used in the purification equipment 3 will be used for removal. This is because the amount of PFAS leached from the deposited material fragments is thought to depend on the size, shape, and distribution of the fragments, and therefore it is desirable to remove the deposited material under the same conditions as the actual cleaning operation of pipe P. For example, larger removed fragments are thought to have incorporated PFAS internally, resulting in less leaching into the liquid, while finer fragments are thought to result in a larger amount of PFAS leaching.

[0043] <Total volume measurement process> (ST1-2) In the previous elution measurement step, the amount of PFAS eluted per unit amount of the adhering material, in this case per unit volume, was obtained. Therefore, if the total volume of adhering material inside the pipe P to be cleaned is known, the total amount of PFAS eluted into the cleaning water during the cleaning of pipe P can be determined. The total amount measurement step estimates the total volume of adhering material inside all pipes P involved in the cleaning process.

[0044] In the total amount measurement process, the thickness of the deposit inside pipe P is measured (ST1-2a). Hereafter, this measurement process will be referred to as the first thickness measurement process. The reason for adding "first" here is to distinguish it from the verification process described later, in which the thickness of the deposit inside pipe P may be measured again.

[0045] The thickness of the deposits inside pipe P is considered to be almost constant throughout the entire pipe P, with no significant differences. Therefore, if this thickness is known, the total volume of deposits inside pipe P can be estimated from the geometric dimensions of pipe P. For example, if pipe P contains a straight pipe with an inner diameter of r and a total length of L, and the measured thickness of the deposits is t, then the volume of deposits inside such a straight pipe can be estimated by πt(2r-t)L. Similarly, the volume of deposits inside a curved pipe with an inner diameter of r, a radius of curvature of the centerline of R, and a central angle of θ can be estimated by πθt(2r-t)R. Likewise, if formulas for estimating the volume of deposits inside various pipes and fittings contained in pipe P are determined in advance, the total volume of deposits inside pipe P can be easily estimated using the specific geometric dimensions and the measured thickness of the deposits.

[0046] The method for measuring the thickness of the deposits inside the pipe P in the first thickness measurement step is not necessarily limited and can be any method. For example, the pipe P may be cut at any position and the thickness of the deposit layer exposed on the cut surface may be measured directly. However, considering the ease of the work and the fact that new waste requiring disposal, such as cutting dust, is generated, it is desirable to measure the thickness of the deposits by non-destructive testing.

[0047] Non-destructive testing methods are not limited to any specific type, but examples include those using ultrasound, gamma rays, X-rays, and other forms of radiation.

[0048] In the case of inspection using ultrasound, as an example, an ultrasonic vibrator and vibration detector are attached to arbitrary positions in pipe P, and the frequency response to the application of ultrasonic vibrations by the vibrator is detected. Figure 4 shows an example of the relationship between the thickness of the deposit inside pipe P and the peak frequency detected as a frequency response. As shown in the figure, there is a correlation between the thickness of the deposit inside pipe P and the detected peak frequency. Therefore, if the relationship between the thickness of the deposit and the peak frequency is measured in advance for pipes of the same type as pipe P, which have scale or other deposits fixed inside, the thickness of the deposit inside pipe P can be detected non-destructively.

[0049] Alternatively, the thickness of the deposits can be measured using the Time of Flight (ToF) method, taking advantage of the fact that the acoustic impedance of the pipe body (e.g., steel) and the deposits such as scale fixed inside are different, and ultrasonic waves are reflected at the interface between them. The speed of sound in the pipe body and the speed of sound in the deposits such as scale should be measured in advance.

[0050] Other applicable methods include measuring the thickness of the deposit from the transmittance of gamma rays using radioactive isotopes, and measuring the thickness of the deposit by obtaining cross-sectional images using X-ray tomography.

[0051] The thickness of the deposit can be measured at any point in pipe P, but the reliability of the measurement will be higher if measurements are taken at multiple locations and the average value is adopted as the representative value. In the total amount measurement process, after the thickness of the deposit is measured, the total amount of deposit inside pipe P that is being cleaned is calculated and estimated using the calculation formulas already described, etc., and the geometric dimensions of pipe P and the measured thickness of the deposit (ST1-2b).

[0052] <Estimation of eluted PFAS amount> (ST1-3) The amount of PFAS leached per unit amount of adhering material is obtained in the leaching amount measurement step, and the total amount of adhering material is obtained in the total amount measurement step. By multiplying these two amounts, the amount of leached PFAS, which is the amount of PFAS adhering to the inside of the entire pipe P that dissolves into the washing water, is estimated.

[0053] <Preparation process> (ST2) Returning to Figure 2, preparations are made for the cleaning equipment 100 for cleaning pipe P. This process includes the installation of the equipment included in the cleaning equipment 100, namely the stripping area 1, the cleaning water tank 2, and the purification equipment 3, as well as the connection of necessary piping. Installation of the stripping area 1 includes the installation of the cleaning tank 10 if it is not a permanent facility, and the preparation of stripping equipment such as wire brushes 11. Installation of the cleaning water tank 2 includes installing the cleaning water tank 2 itself, replenishing the cleaning water if necessary, and preparing the pump 20. Installation of the purification equipment 3, in this embodiment, includes the preparation and installation of the sedimentation tank 30, filter 31, and adsorbent 32.

[0054] Here, the adsorbent 32 is prepared to have a capacity (adsorption capacity) sufficient to adsorb the amount of PFAS estimated in the estimation process. In other words, the size and number of processing columns included in the adsorbent 32 are arranged so that the adsorption capacity of the adsorbent 32 exceeds the amount of eluted PFAS.

[0055] This preparation is carried out according to the amount of eluted PFAS. For example, the amount of eluted PFAS may be multiplied by a safety factor of 1.2, and the necessary number of processing columns may be arranged so that the total volume of processing columns, each with a fixed capacity, exceeds this value. Alternatively, categories (e.g., three categories: large, medium, and small) may be defined according to the amount of eluted PFAS, and pre-designed adsorbents 32 may be arranged for each corresponding category. In any case, in this process, at least an adsorbent 32 with a capacity capable of adsorbing and removing the amount of PFAS eluted is prepared based on the amount of eluted PFAS.

[0056] Incidentally, when determining the capacity that the adsorbent 32 should have, it is desirable to conduct an adsorption capacity confirmation test to confirm the adsorption capacity of the adsorbent itself used in the adsorbent 32 for PFAS. This is because the solute contained in the washing water is not necessarily only PFAS, but also contains other dissolved ions, and the adsorption capacity of the ion exchange resin and other adsorbents used in the processing column of the adsorbent 32 for PFAS depends on the properties of the washing water. This adsorption capacity confirmation test can be performed in the elution amount measurement step of the estimation step by stirring with the adsorbent fragments and using a portion of the washing water from which PFAS and other dissolved ions have eluted from the adsorbent fragments as a sample. This is because the properties of such washing water are considered to be almost identical to the used washing water generated when washing pipe P in the stripping field 1 of the washing equipment 100.

[0057] Figure 5 shows an example of an adsorption curve obtained through an adsorption capacity confirmation test. By dividing a sample of washing water into multiple portions, adding different amounts of adsorbent to each, and measuring the concentration of PFAS in the washing water after reaching equilibrium (equilibrium concentration), the amount of PFAS adsorbed per unit weight by the adsorbent at that equilibrium concentration (equilibrium adsorption amount) can be determined from the difference between the PFAS concentration before adsorption and the amount of adsorbent added (dry weight), and furthermore, an adsorption curve showing the relationship between the two can be obtained from multiple measurement results. There are no particular restrictions on the units of equilibrium concentration and equilibrium adsorption amount, but in Figure 5, ng / L and ng / mg-dry (dry weight) are used, respectively. In addition, it is generally known that the obtained adsorption curve becomes a straight line when the equilibrium concentration is plotted on a logarithmic scale, as shown in the figure, in the region of low equilibrium concentration. The black diamond marks in the figure show examples of measured values.

[0058] Once such an adsorption curve is obtained, the target concentration of PFAS to be achieved after removing PFAS from the washing water is given by ρ d Therefore, the equilibrium adsorption amount m shown by the adsorbent at that time. d This is obtained. The minimum amount of adsorbent required (dry weight) is the amount of eluted PFAS estimated in the estimation process plus the equilibrium adsorption amount m d It can be found by dividing by .

[0059] <Peeling process, cleaning process, removal process> (ST3) Once the cleaning equipment 100 is properly prepared and the pipes P to be cleaned are brought into the cleaning equipment 100, the pipes P are cleaned using the cleaning equipment 100. This cleaning of the pipes P consists of a peeling step performed in the peeling area 1 to peel off the adhering material inside the pipes P, a cleaning step also performed in the peeling area 1 to clean the inside of the pipes P using cleaning water, and a removal step using the purification equipment 3 to remove solid matter from the used cleaning water and to remove PFAS using the adsorbent 32.

[0060] Here, it is preferable that the removal process be carried out in parallel with the washing process. This is because, as already explained, the washing water from which solid matter and PFAS have been removed is intended to be reused in the washing process. By simultaneously using the washing water in the washing process and purifying the washing water in the removal process, the washing water can be recycled, and the overall amount of washing water used can be reduced.

[0061] <Confirmation process> (ST4) If the pipe P subjected to the peeling and washing processes has had its internal deposits removed and has been thoroughly washed with washing water, it is considered that the PFAS adhering to its interior has been completely or almost completely removed and the pipe P is in a clean state. On the other hand, if some deposits remain inside the pipe P that have not been completely removed, there is a possibility that PFAS remains on its surface or inside. Therefore, in the confirmation process, it is confirmed that the amount of PFAS adhering to the inside of the pipe P is below a predetermined amount.

[0062] Figure 6 is a flowchart showing an example of the verification process. In the verification process, first, the thickness of the deposits inside pipe P is remeasured (ST4-1). Hereafter, this measurement process will be referred to as the second thickness measurement process. The reason for adding "second" here is to distinguish it from the measurement process of the thickness of the deposits inside pipe P in the estimation process, which has already been explained. This second thickness measurement process may be carried out in the same manner as the first thickness measurement process, and it is preferable that the measurement is performed by non-destructive testing, but this is not necessarily required.

[0063] Since the estimation process provides the amount of PFAS leached into the washing water per unit volume of the deposited material, the amount of PFAS remaining inside pipe P can be estimated from the thickness of the remaining deposited material obtained in the second thickness process. This amount does not necessarily have to be determined as a total amount; it may also be determined as the amount of PFAS leached per unit area of ​​the inner surface of pipe P. If this amount of PFAS leached per unit area of ​​the inner surface of pipe P is zero or below the standard value, then pipe P subjected to the verification process can be judged to be clean.

[0064] If, as a result of the second thickness measurement process, a pipe P is determined to have been insufficiently cleaned, that is, if residual deposits have not been sufficiently removed, it is sent back to the degreasing and cleaning process for re-cleaning. This verification process is performed for each pipe P being cleaned, thereby preventing any insufficiently cleaned pipes P from being overlooked. Herein, the second thickness measurement process does not require analysis by a specialized institution, so it can be performed on-site (in situ).

[0065] The verification process may be completed with only the second thickness measurement process. However, when cleaning pipe P, it may be necessary to provide proof that PFAS has been sufficiently removed from the inside of pipe P before discarding or reusing the pipe P after cleaning. Therefore, in the verification process, a prescribed inspection, such as an inspection of the inner surface, is performed on part or all of the pipe P that has passed through the second thickness measurement process (ST4-2). This inspection may be carried out by a method determined by the business operator that cleans the pipe P, or by the business operator that disposes of or reuses the pipe P, or by a public institution such as an administrative organization. As an example, this inspection may be performed on a certain area inside the pipe P (for example, 100 cm²). 2 This may be done by wiping the pipe P with a designated special cloth, having a specialized institution analyze the amount of PFAS adhering to the cloth, and measuring the amount of residual PFAS per unit area of ​​the inner surface of the pipe P.

[0066] Since pipes P that pass this inspection are clean, they can be disposed of as regular pipe material in the usual disposal process, and can also be reused as pipe material after applying lining or other treatments as needed.

[0067] <Post-processing steps> Returning to Figure 2, once all pipes P have been cleaned, the cleaning equipment 100 is removed. At this time, the inner surface of the stripping area 1 and the wire brush 11, etc., should be thoroughly washed with water to remove any PFAS that may be adhering to their surfaces, and then purified by the purification equipment 3. The sedimented material fragments and residual water in the sedimentation tank 30 of the purification equipment 3 are removed from the drain 37, the filter media of the filter 31 and the adsorbent of the adsorbent 32 are recovered and properly disposed of as PFAS-containing waste. After replacing the filter media of the filter 31 and the adsorbent of the adsorbent 32 with new ones, the entire cleaning equipment 100 is dismantled and removed, and all processes are complete. The cleaning water stored in the cleaning water tank 2 is either kept in the cleaning water tank 2 in preparation for the next pipe cleaning, or if there are no plans to use it, it is disposed of as normal wastewater.

[0068] The specific configurations shown in describing the embodiments of the pipe cleaning method described above are illustrative examples, and those skilled in the art can change the number and arrangement of the equipment used, or replace them with similar equipment, as long as their function is not impaired. The present invention, as shown through these embodiments, is not limited to the specific configurations illustrated. [Explanation of Symbols]

[0069] 1. Stripping area, 2. Washing water tank, 3. Purification equipment, 10. Washing tank, 11. Wire brush, 20. Pump, 30. Sedimentation tank, 31. Filter, 32. Adsorber, 33. Mesh screen, 34. Separator, 35. Pump, 36. Inclined surface, 37. Drain, 38. Flow regulator, 39. Drain valve, 100. Washing equipment, P pipe.

Claims

1. An estimation step to estimate the amount of eluted PFAS (perfluoroalkyl substances and polyfluoroalkyl compounds) that are attached to the inside of the pipe to be cleaned, A preparation step of preparing an adsorbent with a capacity capable of adsorbing and removing the amount of PFAS eluted, based on the amount of PFAS eluted, A peeling step to remove the adhering material inside the pipe, Simultaneously with or after the stripping step, a cleaning step is performed in which the inside of the pipe is cleaned using cleaning water. A removal step is performed to remove solid matter from the used washing water and to remove PFAS using the adsorbent, It has, The washing water from which the solid matter and the PFAS have been removed is reused in the washing process. Methods for cleaning pipes.

2. The removal step is carried out in parallel with the washing step. The method for cleaning a pipe according to claim 1.

3. The estimation process described above is: A step of measuring the amount of PFAS eluted per unit amount of deposit inside the tube, A total amount estimation step for estimating the total amount of deposits inside the pipe, including, The method for cleaning a pipe according to claim 1.

4. The total amount estimation step includes a first thickness measurement step of measuring the thickness of the deposit inside the pipe by non-destructive testing. The method for cleaning a pipe according to claim 3.

5. The process includes a confirmation step after the cleaning step to confirm that the amount of PFAS adhering to the inside of the pipe is less than or equal to a predetermined amount. The method for cleaning a pipe according to claim 1.

6. The verification step includes a second thickness measurement step of measuring the thickness of the deposit inside the pipe by non-destructive testing. The method for cleaning a pipe according to claim 5.

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