WO2003022748A1 - System and method for water treatment - Google Patents

Abstract

A system and a method for water treatment, the system comprising a multi-stage arresting device having two or more stages of arresting devices for arresting arrested matters in raw material with arresting agent, a membrane separating device for removing solid matters in the raw water by the membrane separation of the raw material and an arresting agent phase device for moving the arresting agent used in the arresting device on the rear stage of the multi-stage arresting devices to the arresting device on the front stage; the method for water treatment using the system, whereby the solid matters such as microorganisms in the raw water can be removed by arresting on the surface of a membrane and, when the arrested matters hard to be removed by the membrane separation are arrested with the arresting agent and removed, and the solid matters can be efficiently treated at a low cost without producing a large amount of used arresting agent.

Description

 Title of invention

 Water treatment system and water treatment method

 Technical field

 The present invention relates to a water treatment system and a water treatment method used for treating wastewater such as domestic wastewater and industrial wastewater.

 Background art

 Wastewater such as domestic wastewater and industrial wastewater contains organic substances represented by BOD and nitrogen-containing substances typified by ammonia nitrogen. Examples of such wastewater treatment include biological treatment using microorganisms for anaerobic treatment and aerobic treatment, and solid matter in raw water captured by membranes in such biological treatment. Methods that combine membrane separation for removal are being implemented.

 Recently, in addition to this method, a sewage treatment system that combines a process that captures an object such as phosphorus and ammoniacal nitrogen in raw water that is difficult to remove by membrane separation with a trapping agent such as an adsorbent and a membrane separation Are also being considered.

 However, in order to sufficiently capture an object in raw water with a capturing agent such as an adsorbent, a large amount of the capturing agent had to be used, and the cost of the capturing agent tended to increase. After such treatment, there was also a problem of waste treatment that a large amount of used trapping agent was generated.

 The present invention has been made in view of the above circumstances, and captures and removes solid substances such as microorganisms in raw water by a membrane surface, and removes an object which is difficult to remove by membrane separation such as phosphorus and ammonia nitrogen in raw water. It is an object of the present invention to provide a water treatment system and a water treatment method that can efficiently treat low-cost and efficient treatment without generating a large amount of used trapping agent when the treatment is performed by capturing with a trapping agent.

 Disclosure of the invention

The water treatment system of the present invention includes a multi-stage capturing device including two or more capturing devices that capture an object in raw water with a capturing agent, and a membrane component that separates the raw water into membranes to remove solids in the raw water. It has a separating device, and a capturing agent transfer device that transfers the capturing agent used in the capturing device on the downstream side of the multi-stage capturing device to the capturing device on the upstream side.

 It is preferable that the capturing agent transfer device transfers the capturing agent used in each of the capturing devices in the second and subsequent stages to the capturing device in the immediately preceding stage.

 It is preferable that each of the capturing devices includes a treatment water tank that brings the raw water into contact with the capturing agent, and the membrane separation device is provided after the multi-stage capturing device.

 Alternatively, each of the capturing devices includes a treatment water tank for bringing the raw water into contact with the capture agent, and the membrane treatment device is a submerged membrane separation device, and is provided in a last stage treatment water tank. Is preferred.

 The water treatment method of the present invention includes a multi-stage capturing step including two or more capturing steps of capturing an object in raw water with a capturing agent, and a membrane separation device that performs membrane separation of the raw water to remove solids in the raw water. And a capturing agent transporting step of transporting the capturing agent used in the capturing step on the subsequent stage to the capturing device on the upstream side, wherein the capturing agent used in the capturing step on the subsequent side is removed. It is characterized in that it is reused in the former stage.

 In the capturing agent transferring step, it is preferable to transfer the capturing agent used in each of the capturing steps of the second and subsequent stages to the capturing step of the immediately preceding stage.

 In each of the capturing steps, the raw water and the capturing agent are brought into contact in a treated water tank, and the membrane separation step is performed after the multi-stage capturing step, and the solid in the raw water and the capturing are performed. It is preferable to remove the agent.

 The scavenger is preferably at least one selected from the group consisting of activated carbon, zeolite, inorganic flocculant, chelating resin, hydroxyapatite, titanium oxide, activated alumina, and titanium silicate, and sodium, calcium, magnesium, and potassium. It is particularly preferable to use a zeolite carrying any one of the above cations.

 Further, in the water treatment method of the present invention, at least one object selected from the group consisting of ammoniacal nitrogen, nitrate nitrogen, phosphorus, heavy metals, heavy metal hydroxides, fluorine, and boron can be suitably removed.

According to the water treatment system and the water treatment apparatus having the above-described configuration, the capturing step is multi-stage, combined with the membrane treatment, and the capturing agent used in the subsequent side is reused in the previous side. Therefore, it is possible to effectively capture targets such as ammonia, phosphorus, and heavy metals with a smaller amount of capture agent used, and remove the used capture agent together with solids such as microorganisms contained in raw water. It can be easily removed. 'Thus, it is possible to remove the target object and solid matter such as microorganisms at low cost and with a small amount of trapping agent waste. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a flowchart illustrating the water treatment system of the present invention.

 FIG. 2 is a schematic configuration diagram showing one example of the water treatment system of the present invention.

 FIG. 3 is a schematic configuration diagram showing another example of the water treatment system of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the present invention will be described in detail.

 FIG. 1 is a flow chart schematically illustrating one embodiment of the water treatment system of the present invention for treating raw water such as industrial wastewater and domestic wastewater. This water treatment system captures an object in raw water with a capturing agent. It has a multi-stage capture device with two stages of capture devices, and a membrane separation device that separates solids in raw water by membrane separation of raw water. And this water treatment system is equipped with a trapping agent transfer device that transfers the trapping agent used in the trapping device at the rear stage of the multi-stage trapping device to the trapping device at the front stage, and is used in the trapping device at the rear stage. The trapping agent was made reusable by the pre-stage trapping device.

 Note that, in this example, an example in which two stages are provided as a multi-stage trapping device, but the number of stages of the multi-stage trapping device may be two or more, and the type of raw water and the obtained treated water The number of stages can be appropriately designed according to the concentration of the target object required in the above.

In this example, the trapping device has two stages, so the trapping agent used in the second stage trapping device is used as the trapping agent transfer device in the previous stage, the first stage trapping device. However, when the multi-stage capturing device has a configuration in which three or more capturing devices are provided, the capturing agent transfer device uses the capturing agent used in the downstream capturing device, There is no particular limitation as long as it is transported to the upstream capturing device. For example, in the case of a multi-stage capture device equipped with an n-stage capture device, the (n-1) th stage from the nth stage and the (n-1) th stage The trapping agent is effective if the trapping agent is sequentially transferred to the previous stage from the (n−2) th stage to the (n−2) th stage to the (n−3) th stage. It is particularly preferable for efficient use. However, the trapping agent used in the n-th capturing device is transferred to the (η-2) -th capturing device, or the capturing agent used in the n-th capturing device is captured in the (n-1) -th capturing device. It may be in the form of distribution to the device and the (n-2) th stage capture device, and it can be determined as required.

 FIG. 2 is a specific example of the water treatment system 10 of the present invention. In the water treatment system 10 of this example, a multistage trapping device 11 includes three-stage trapping devices 11a, llb, and 11c. Is used. Each of these three-stage capturing devices 11a, llb, and 1.1c has a processing water tank 13a, 13b, and 13c provided with a stirring device 12a, 12b, and 1c, respectively. Raw water comes into contact with the trapping agents 14a, 14b, 14c in 13a, 13b, 13c, and the target in raw water is trapped by these trapping agents 14a, 14b, 14c. .

 In addition, the multi-stage capturing device 11 includes a processing water tank 13a of the first-stage capturing device 11a (hereinafter, referred to as a first processing water tank) and a processing water tank 13b of the second-stage capturing device 11b (hereinafter, referred to as a first processing water tank). Below, it is referred to as the second treated water tank.) The first liquid sending means 15a for sending the raw water to the second treated water tank, and the treated water tank 13c of the third-stage capturing device 11c from the second treated water tank 13b ( Hereinafter, it is referred to as a third treatment tank.) A second tank 15b for sending raw water to the tank is provided. Therefore, the raw water treated by the upstream capturing device is sequentially sent to the downstream treated water tank, and the remaining objects that are not captured by the upstream capturing device remain and are captured by the downstream capturing device. It has become possible to be caught in. Here, as the first and second liquid sending means 15a, 15b, for example, a normal liquid sending pump can be used.

 Capture agents 14a, 1b, and 14c include adsorbents such as activated carbon and zeolite, as well as inorganic flocculants such as PAC (polyaluminum chloride), chelating resins, hydroxyapatite, titanium oxide, activated alumina, and titanium silicate. There is no particular limitation as long as it is a powder capable of capturing an object by utilizing an adsorption action, an ion exchange action, a chelate formation action, an electrostatic neutralization action and the like.

Among these scavengers 14a, 14b and 14c, for example, activated carbon was used. In this case, ammonia nitrogen, nitrate nitrogen, phosphorus, arsenic, heavy metals, etc. can be effectively trapped, and when zeolite is used, ammonia nitrogen, lead, boron, calcium, etc. Can be captured. When zeolite is used, the cation carried by natural or synthetic zeolite can be exchanged for any of sodium, calcium, magnesium, and potassium, and the pore size of zeolite can be controlled, and the target object can be used. It is possible to obtain a scavenger having optimal removal performance according to the conditions.

 In addition, when inorganic coagulants are used, phosphorus, arsenic, and hydroxides of heavy metals are used; when chelate resin is used, boron is used; when hydroxyapatite is used, fluorine and lead are used. When titanium oxide or diverted activated alumina is used, phosphorus and arsenic can be effectively trapped, and when titanium silicate is used, lead and arsenic can be trapped effectively.

 The particle size of the scavengers 14a, 14b, and 14c used here is not particularly limited, but the smaller the particle size, the larger the surface area and the more efficiently the target is trapped. And can be. In the case of zeolites, activated carbon, activated alumina, titanium oxide, etc., which adsorb the target by the adsorption action, the smaller the particle diameter, the higher the surface area to be covered, and therefore the higher the target adsorption speed. Therefore, in these cases, it is preferable to use those having an average particle diameter of 20 or less. However, if the average particle diameter is too small, the handling property is reduced, so that it is preferably 1 m or more. Further, the pore size of the filtration membrane used for solid-liquid separation preferably has a large average particle size.

 Then, in the water treatment system 10 of the example of FIG. 2, the immersion type membrane separator 16 is provided as a membrane separator in the third treated water tank 13c. Therefore, the raw water from which the target substances have been removed by the trapping agents 14a, 14b, and 14c in the first processing water tank 13a to the third processing water tank 13c is separated by membrane, and the raw water Solid matter such as microorganisms originally contained in the water and the trapping agent 14c in the third treatment water tank are removed on the membrane surface, so that purified treated water can be taken out.

The immersion type membrane separator 16 used in this example is a hollow fiber membrane module 17 And a suction pump 18 connected to the hollow fiber membrane module 17.

 The hollow fiber membrane module 17 includes a plurality of hollow fiber membranes 17 a arranged in a substantially parallel sheet shape, and two hollow fiber membranes 17 a supporting both ends of the hollow fiber membranes 17 a while maintaining their openings. And a tubular support 17b. Then, a suction pump 18 is connected to the tubular support 17 b, and by operating the suction pump 18, the raw water in the third treatment water tank 13 c displaces the hollow fiber membrane 17 a. The solids such as micro-organisms in the raw water and the trapping agent 14 c are trapped and removed on the membrane surface, thereby obtaining treated water.

 Here, the hollow fiber membrane 17a may be made of various materials such as polyolefin, polysulfone, polyamide, cell mouth, polyvinylidene fluoride, polyvinyl alcohol, and PMMA. Can be used. Further, those having an outer diameter of 200 to 400 urn, a film thickness of 50 to 300 m, and a porosity of about 40 to 89% can be preferably used. Further, the blocking hole diameter of the hollow fiber membrane 17a may be formed in a size that can reliably remove the trapping agent 14c used in the third treatment water tank 13c together with the solid matter in the raw water. It is determined according to the size of the target solid and the particle size of the scavenger 14c, but the blocking pore size is preferably 0.01 to 5 m, more preferably 0.1 to 1.0 m. Is set in the range. Here, if the blocking hole diameter is 0.2 m or less, microorganisms in the raw water can be almost completely captured on the membrane surface.

 Below the hollow fiber membrane module 17 in the third treated water tank 13c, an air diffuser tube 19 having an air diffusion hole (not shown) on the lower surface or side surface is arranged. Then, a gas such as compressed air is sent from the blower 20 to generate this gas from the diffused holes, so that the membrane surface of the hollow fiber membrane 17a can be air-scrubbed so that the membrane surface can be cleaned. ing.

As described above, the water treatment system 10 in FIG. 2 includes the multi-stage capture device 11 including the three-stage capture devices 11 a, 11 b, and 11 c, and the third treated water tank 13 Although the hollow fiber membrane module 17 of the immersion type membrane separation device 16 is provided in the c, the water treatment system 10 further includes the trapping device used in the trapping device in the subsequent stage. The agent is A trapping agent transfer device 21 for transferring the trapping agent to the trapping device is provided so that the trapping agent used in the trapping device in the subsequent stage can be reused in the prestage.

 The trapping agent transfer device 21 in the example of FIG. 2 is a first trapping agent transfer device that transfers the trapping agent 14 b used in the second treated water tank 1.3 b to the first treated water tank 13 a. 2 1a and a second trapping agent transfer device 2 1b for transferring the trapping agent 14c used in the third treatment tank 13c to the second treatment tank 13b. As a specific example of the first and second trapping agent transfer devices 21a and 21b, the trapping agents 14b and 14c in the treated water tanks 13b and 13c are taken together with some raw water. For example, a screw pump, a snake pump, a gear pump, a cascade pump, a tube pump, and the like for suctioning and transferring can be exemplified, and are appropriately selected according to the viscosity, concentration, amount, and the like of the transfer target.

 Next, a water treatment method using the water treatment system 10 of this example will be described. At the start of operation of this system, first, a trapping agent 14a is charged into the first treated water tank 13a, and then raw water such as industrial wastewater and domestic wastewater is introduced intermittently or continuously. The raw water and the trapping agent 14a are brought into contact in the first treated water tank 13a by operating the stirring device 12a provided in the first treated water tank 13a.

 Then, the first liquid sending means 15a is operated, and in the first treated water tank 13a, the raw water from which the target substance has been removed to some extent by the action of the capturing agent 14a is previously collected as the capturing agent 14a. The solution is sent to the second treated water tank 13 b into which b has been charged. Then, also in the second treated water tank 13b, as in the case of the first treated water tank 13a, the provided stirring device 12b is operated to separate the raw water and the trapping agent 14b. The contact is made in the second treated water tank 13b.

 Next, the second liquid sending means 15b is operated, and the raw water in which the object is further reduced is sent to the third treated water tank 13c in the second treated water tank 13b. Then, the raw water is brought into contact with the trapping agent 14c in the third treatment water tank 13c.

Thereafter, the suction pump 18 connected to the tubular support 17 b of the immersion type membrane separation device 16 provided in the third treatment water tank 13 c is operated, and the immersion type membrane separation device 16 is operated. You. Then, the raw water in the third treated water tank 13c is sucked through the hollow fiber membrane 17a, and together with solids such as microorganisms in the raw water 13 is placed in the third treated water tank 13c. Thrown in The trapping agent 14c is trapped on the surface of the hollow fiber membrane 17a. As a result, the treated water from which the solids and the trapping agent 14c have been separated and removed can be obtained through the hollow portion of the hollow fiber membrane 17a and the hollow portion of the tubular support 17b.

 Here, each residence time of the raw water in each of the first to third treated water tanks 13a, 13b, and 13c is determined by the degree of contamination of the raw water, the volume of the treated water tanks 13a, 13b, and 13c. What is necessary is just to determine suitably according to various conditions, such as the quantity of the used capture agent 14a, 14b, 14c. The residence time of the raw water in each of the treated water tanks 13a, 13b, and 13c depends on the supply speed of the raw water to the first treated water tank 13a, the first and second liquid sending means 15a, 15b. It can be arbitrarily controlled by appropriately adjusting the liquid sending speed and the suction speed of the treated water by the suction pump 18.

 Thus, the raw water is supplied to the first treated water tank 13a, and then the raw water and the trapping agents 14a, 14b, 1 are sequentially supplied to the first to third treated water tanks 13a, 13b, 13c. 4) Contact with c to perform the capture step. As described above, by using the plurality of treatment water tanks 13a, 13b, and 13c to perform a multi-stage trapping step including a plurality of trapping steps, the trapping action reaches an equilibrium state in the first treatment water tank 13a. Even if the capturing does not progress, the capturing step can be performed by bringing the raw water into contact with the capturing agents 14b and 14c in the second treated water tank 13b and the third treated water tank 13c. Therefore, the concentration of the target substance in the raw water can be reduced more efficiently than in a single-stage capturing step. In addition, according to such a multi-stage capturing process, as a result, compared to a case where the target is captured to the same extent in a single capturing process, a smaller amount of the capturing agent 14a, 14b, and 14c is used. An object can be captured.

 For example, when treating raw water containing ammonia at a high concentration of 100 Omg / L or more, use zeolite as the scavenger 14a, 14b, 14c, and use At a zeolite concentration of 20000-4000 Omg / L, ammonia can be captured efficiently. Also, under such conditions, even if the number of multi-stage capture processes is two, the ammonia concentration can be finally reduced to 1 Omg / L or less.

Further, in such a water treatment system 10, removal of the trapping agent 14c is performed by membrane separation. Separation is more effective than solid-liquid separation compared to the treatment using sedimentation of the capture agents 14a, 14b, and 14c, and other methods such as centrifugation, sand filtration, and filter-press treatment. Operation can be performed. In particular, in this example, the immersion type membrane separation device 16 is used as the membrane separation device, and the hollow fiber membrane module 17 is provided in the third treatment water tank 13 c. The configuration is very compact.

 In this way, the multi-stage capture process and the membrane separation process are performed continuously and constantly, and solid matter such as microorganisms, an object that is difficult to remove by membrane separation represented by ammonia, phosphorus, etc., and a capture agent 1 While effectively removing 4c, the first scavenger transfer device 21a and the second scavenger transfer device 21b were operated and used in the second treated water tank 13b. The scavenger 14b is supplied to the first treated water tank 13a, and the scavenger 14c used in the third treated water tank 13c is supplied to the second treated water tank 13b. Perform the transfer process. Then, a new trapping agent is supplied to the third treatment water tank 13 c at the last stage as necessary, while the first treatment water tank 13 a at the front stage is supplied as necessary. Take out the used scavenger 14a.

 The capture agent transfer speed by the first and second capture agent transfer devices 21a and 21b depends on the degree of contamination of raw water, the number of stages of the multi-stage capture device 11, the treatment tanks 13a, 13b, It can be set appropriately according to various conditions such as the residence time in 13 c. Also, transfer of the trapping agents 14b, 14c to the first and second treatment water tanks 13a, 13b, withdrawal of the trapping agent 14a from the first treatment water tank 13a, and The supply of the new capturing agent to the third treated water tank 13 may be performed continuously, intermittently, or periodically.

In this way, the trapping agent used in the subsequent capturing step is supplied to the preceding step, and is reused in the preceding capturing step, whereby each of the treated water tanks 13 a, 13 Since b and 13c are supplied with a capturing agent that still retains the capturing ability, it is possible to reuse the capturing agent very efficiently. That is, the capture equilibrium amount of the capture agent has a positive correlation with the concentration of the target substance, and increases as the concentration of the target substance increases. Therefore, even if the capture agent has reached the capture equilibrium on the downstream side where the concentration of the target is lower, if it is introduced into the former stage where the concentration of the target is higher, the capture equilibrium will be restored. Since it does not reach the equilibrium amount at the concentration of the target substance, it can be used further.

 Therefore, by performing such a trapping agent transfer step, the trapping agents 14a, 14b, and 14c can be more effectively used than in the method using a new trapping agent in each of the treated water tanks 14a, 14b, and 14c. It can be used and reduces the cost of scavengers 14a, 14b, and 14c, and reduces the amount of waste.

 In addition to the method of using a screw pump to carry out the trapping agent transfer process, openable and closable outlets are provided at the bottom of the treatment tanks 13b and 13c, etc. It may be carried out by extracting the water and supplying it to the treatment water tank on the preceding stage.

 In the above description, each of the trapping devices 11a, 11b, and 11c is provided with a treated water tank 13a, 13b, and 13c for bringing raw water into contact with the trapping agents 14a, 14b, and 14c. As an example of the membrane separation device, the immersion type membrane separation device 16 provided in the treatment water tank 13c of the capturing device 11c at the last stage is exemplified, but the form is not particularly limited.

 For example, as shown in FIG. 3, as each of the capturing devices 11a, lib, and 11c, a device provided with a treatment water tank 13a, 13b, and 13c as in the case of FIG. 2 is used. Examples include a mode in which the pressurized membrane separation device 22 is used. Here, the pressurized membrane separation device 22 is provided with a hollow fiber membrane module (not shown) in a housing, and feeds raw water to the housing under pressure, from the outside to the inside of the hollow fiber membrane surface. It removes solids from raw water by passing through. In the configuration shown in FIG. 3, although the energy cost tends to increase as compared with the case where the immersion type membrane separation device 16 is used as the membrane separation device, as in the case of the configuration in FIG. However, the solid substances originally contained in the raw water and the used scavengers 14a, 14b, 14c can be simultaneously removed.

As another example, although not shown in the figure, as each of the capturing devices lla, llb, and 11c for bringing the raw water into contact with the capturing agent, a column (not shown) filled with the capturing agent is used. Through which the raw water and the scavenger are brought into contact. In such a case, by connecting and using multiple columns, a multi-stage capture device

One can make up one. After the treatment for a certain period of time, the latter column is used as the former column as appropriate, and the latter column is used in the latter capturing step by using a column filled with a new capturing agent. The trapping agent transfer step of reusing the trapping agent thus reused in the former stage can be performed.

 Furthermore, by using a plurality of columns each filled with a capture agent as the multi-stage capture device 11 as described above, while using the pressurized membrane separator 22 used in FIG. It is also possible to carry out a multi-stage capture step after the separation step. That is, since the capture agent used in this form is packed in the column and not dispersed in the raw water, the membrane separation step is performed after the multi-stage capture step to remove the capture agent from the raw water. There is no need, and there is no problem if a multi-stage capture step is performed after the membrane separation step.

 Further, even when the immersion type membrane separation device 16 is used, in addition to the hollow fiber membrane module 17, a flat membrane filter module, a tubular membrane filter module, a ceramic filter module, and a metal membrane filter are used. Various separation membrane modules such as modules may be used.

 Furthermore, when using a submerged membrane separator 16 as a membrane separator, the raw water is subjected to membrane treatment using a suction pump 18 in Fig. 2, but for example, a hollow fiber membrane module 17 is submerged. In this mode, the water separation tank 23 is provided below the third processing water tank 13 c, and the separation of the membrane and the sending of the processing water to the storage tank 23 are performed by utilizing the gravity and the siphon effect. Is also possible. With this configuration, it is possible to obtain treated water with lower energy cost without using the suction pump 18 as shown in FIG.

 Example

 Hereinafter, the present invention will be described specifically with reference to examples.

 Using a water treatment system 10 having the form shown in FIG. 2, industrial wastewater containing ammonia as an object was treated. However, the number of stages of the multi-stage capturing device 11 was two, and a device provided with the immersion type membrane separation device 16 in the second treatment water tank 13b was used.

As the scavengers 14a and 14b, zeolite (average) having an action of absorbing ammonia is used. An average particle size of 20 urn) was used.

 Various experimental conditions are as follows.

 (1) Ammonia concentration in industrial wastewater: l OOOmgZL

 (2) Supply rate of industrial wastewater to the first treated water tank: 100 L / hr

 (3) Retention time of raw water in the first and second treated water tanks 13a and 13b: 2 hours each

 (4) Zeolite concentration in the first and second treated water tanks 13a and 13b: 32,000 Omg / L each

 (5) Zeolite transfer speed by the first and second scavenger transfer devices 21a and 21b: 6.3 kg / hr for each

 (6) Speed of extracting used zeolite from the first treated water tank 13a: 6.3 kg / hr

 (7) Feed rate of fresh zeolite to the second treated water tank 13b: 6.3 kg / r

 Under the above conditions, when the water treatment system 10 was operated steadily, treated water was obtained in which the ammonia concentration was reduced from the initial value of 100 Omg / L to 8.5 mgZL.

Claims

The scope of the claims  1. A multi-stage capture device having two or more capture devices for capturing an object in raw water with a capture agent, a membrane separation device for separating the raw water by membrane to remove solids in the raw water, and the multi-stage capture device A water treatment system, comprising: a trapping agent transfer device that transfers a trapping agent used in a trapping device at a subsequent stage to a trapping device at a preceding stage. .  2. The water capturing device according to claim 1, wherein the capturing agent transfer device transfers the capturing agent used in each of the second and subsequent capturing devices to the capturing device of the immediately preceding stage. Processing system.  3. Each of the capturing devices includes a treated water tank for bringing the raw water and the capturing agent into contact with each other,  2. The water treatment system according to claim 1, wherein the membrane separation device is provided after the multi-stage capturing device.  4. Each of the capturing devices includes a treated water tank for bringing the raw water and the capturing agent into contact with each other, and the membrane separation device is provided after the multi-stage capturing device. A water treatment system according to claim 1.  5. Each of the capturing devices includes a treated water tank for bringing the raw water and the capturing agent into contact with each other,  2. The water treatment system according to claim 1, wherein the membrane treatment device is an immersion type membrane separation device, and is provided in a last treatment water tank.  6. Each of the capturing devices includes a treated water tank for bringing the raw water into contact with the capturing agent,  3. The water treatment system according to claim 2, wherein the membrane treatment device is a submerged membrane separation device, and is provided in a last treatment water tank.  7.A multi-stage capturing step including two or more capturing steps of capturing an object in raw water with a capturing agent; a membrane separating step of membrane-separating the raw water to remove solids in the raw water; and the multi-stage capturing step. The capture agent used in the subsequent capture step, capture agent transfer step of transferring to the capture device of the previous stage, The capturing agent used in the capturing step of the latter stage is reused in the former stage. Water treatment method.  8. The capturing agent transferring step according to claim 7, wherein the capturing agent used in each of the capturing steps in the second and subsequent stages is transferred to the capturing step in the immediately preceding stage, respectively. Water treatment method.  9. In each of the capturing steps, the raw water and the capturing agent are brought into contact in a treated water tank,  8. The water treatment method according to claim 7, wherein the membrane separation step is performed after the multi-stage trapping step to remove the solids in the raw water and the trapping agent.  10. In each of the capturing steps, the raw water and the capturing agent are brought into contact in a treated water tank,  9. The water treatment method according to claim 8, wherein the solid separation in the raw water and the trapping agent are removed by performing the membrane separation step after the multi-stage trapping step.  11. The scavenger is at least one selected from the group consisting of activated carbon, zeolite, inorganic coagulant, chelating resin, hydroxyapatite, titanium oxide, activated alumina, and titanium silicate. The water treatment method according to any one of ranges 7 to 10.  12. The water treatment method according to any one of claims 7 to 10, wherein the scavenger comprises a zeolite that carries one of sodium, calcium, magnesium, and potassium cations.  13. The object according to claim 7, wherein the object is at least one selected from the group consisting of ammonium nitrogen, nitrate nitrogen, phosphorus, heavy metals, heavy metal hydroxides, fluorine, and boron. 10. The water treatment method according to any one of items 1 to 10.  14. The object according to claim 1, wherein the object is at least one selected from the group consisting of ammoniacal nitrogen, nitrate nitrogen, phosphorus, heavy metals, heavy metal hydroxides, fluorine, and boron. The water treatment method according to 1.  15. The object is at least one selected from the group consisting of ammoniacal nitrogen, nitrate nitrogen, phosphorus, heavy metals, heavy metal hydroxides, fluorine, and boron. The water treatment method according to 1.