JP7567218B2 - Water treatment device and water treatment method - Google Patents

Description

The present invention relates to a water treatment device and a water treatment method.

Membrane filtration using filtration membranes is used in the fields of pure water production and wastewater recovery as a means of separating and removing inorganic matter (turbid matter, colloidal components) and organic matter in the water being treated. Microfiltration membranes (MF membranes) and ultrafiltration membranes (UF membranes) are used as filtration membranes. MF membranes with a pore size of about 1 μm are generally used, and UF membranes with a pore size of 0.005 to 0.5 μm are generally used. In membrane filtration using these filtration membranes, if the water being treated contains a large amount of inorganic or organic matter, the filtration membrane is likely to become clogged. For this reason, before the water being treated is subjected to membrane filtration, a coagulant is added to the water being treated to coagulate the inorganic and organic matter contained in the water to form coarse particles (coagulated flocs), which are then separated and removed by membrane filtration.

Patent Document 1 describes a water treatment device capable of generating coarse flocculated flocs, which includes a mixing means for mixing a flocculant with the water to be treated, a flocculation means for introducing the water to be treated so that a swirling flow is generated, and a solid-liquid separation means for separating the water to be treated from solid-liquid, and in which the mixing means and the flocculation means are in a state in which the water to be treated is not released to the atmosphere (sealed type). In the water treatment device described in Patent Document 1, the solid-liquid separation means is capable of performing solid-liquid separation processes such as precipitation, pressurized flotation, filtration, and membrane separation to remove flocs such as turbidity.

International Publication No. 2011/122658

In the water treatment device described in Patent Document 1, a mixing means, a flocculation means, and a solid-liquid separation means are connected in series. For this reason, for example, when a membrane filtration treatment device is used as the solid-liquid separation means, water treatment cannot be performed while the filtration membrane is being cleaned. For this reason, it is difficult to continuously and stably treat a large amount of water to be treated.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a water treatment device and a water treatment method that can continuously and stably treat a large amount of water to be treated.

In order to solve the above problems, the present invention employs the following configuration.
[1] a flocculation treatment unit for producing flocculated treated water containing flocs ;
a membrane filtration treatment unit provided downstream of the coagulation treatment unit and into which the coagulation-treated water flows ;
A connecting flow path connecting the flocculation treatment unit and the membrane filtration treatment unit;
A control unit,
The flocculation treatment unit includes a plurality of flocculation treatment devices arranged in parallel with respect to the flow path of the water to be treated, and a confluence flow path that merges the flocculated water that has been flocculated by the plurality of flocculation treatment devices and sends it to the connecting flow path.
The membrane filtration treatment unit is provided with a plurality of membrane filtration treatment devices arranged in parallel with the flow path of the coagulation treatment water and having a greater number of membrane filtration treatment devices than the coagulation treatment devices, and a diversion flow path that diverts the coagulation treatment water sent from the connection flow path and supplies it to the plurality of membrane filtration treatment devices.
The control unit controls the flow of the coagulated treated water in the diversion flow path so as to put at least one of the multiple membrane filtration treatment devices into a paused state in which the coagulated treated water is not passed through, and to make it possible to switch between the membrane filtration treatment devices to be put into a paused state.

[2] Further, a raw water tank in which the water to be treated is retained;
a treated water supply flow path having a branch portion connecting the raw water tank and each of the plurality of coagulation treatment devices;
a pump disposed upstream of the branch portion of the water supply flow path,
The water treatment device according to [1], wherein the treated water supply flow path, the plurality of coagulation treatment devices, the confluence flow path, the connection flow path, and the branch flow path are each sealed.
[3] The water treatment device according to [1] or [2], further comprising a filtration membrane cleaning agent adding device for each of the membrane filtration treatment devices.

[4] A water treatment method using the water treatment device according to any one of [1] to [3],
A flocculation treatment step of flocculating the water to be treated in each of the plurality of flocculation treatment devices provided in the flocculation treatment unit;
A confluence process in which the flocculated water that has been flocculated by the multiple flocculation treatment devices is merged in the confluence flow path and sent to the connection flow path;
A diversion process in which the flocculated treated water sent from the connecting flow path is diverted in the diversion flow path, and at least one of the plurality of membrane filtration treatment devices is put into a dormant state in which the flocculated treated water is not passed through the control unit, and the remaining membrane filtration treatment devices are put into an operating state in which the flocculated treated water is passed through the control unit;
A membrane filtration treatment step of performing membrane filtration treatment on the coagulation treated water using the membrane filtration treatment device in operation.

[5] The water treatment method described in [4], in the diversion process, the control unit switches the membrane filtration treatment device to be put into a suspended state based on the operating time, water flow rate, or operating pressure of the membrane filtration treatment device.
[6] The water treatment method according to [4] or [5], further comprising a filtration membrane cleaning step of adding a filtration membrane cleaning agent to the membrane filtration treatment device in a suspended state to clean the filtration membrane.
[7] A water treatment method described in any one of [4] to [6], wherein in the diversion process, the control unit adjusts the flow rate of the coagulation treatment water passed through each of the multiple membrane filtration treatment devices so that the ratio of the flow rate of each of the membrane filtration treatment devices to the average flow rate of the multiple membrane filtration treatment devices is within the range of 80% or more and 120% or less.

According to the water treatment device of the present invention, the coagulation treatment unit is provided with multiple coagulation treatment devices, so that a large amount of water to be treated can be treated. In addition, the coagulation-treated water that has been coagulated by multiple coagulation treatment devices is merged in a merging flow path, so that the coagulation-treated water can be membrane-filtered by one membrane filtration treatment unit. This makes it possible to reduce the size of the device and save energy. The membrane filtration treatment unit is provided with multiple membrane filtration treatment devices, the number of which is greater than the number of coagulation treatment devices, and the control unit can put at least one of the multiple membrane filtration treatment devices into a pause state in which the coagulation-treated water is not passed through, and can switch between the membrane filtration treatment devices that are in a pause state, so that the number of membrane filtration treatment devices in operation in the entire membrane filtration treatment unit can be kept constant, and the amount of membrane filtration treatment can be stabilized. As described above, according to the water treatment device of the present invention, a large amount of water to be treated can be continuously and stably treated.

The water treatment device of the present invention further includes a treated water supply device, and the pump of the treated water supply device is arranged upstream of the branch of the treated water supply flow path, and the treated water supply flow path, the multiple coagulation treatment devices, the merging flow path, the connecting flow path, and the diversion flow path are each configured to be sealed, so that the water conveying force of the pump is less likely to be released to the outside compared to when the flow path from the raw water tank to the diversion flow path is open to the atmosphere. This allows the pump's water conveying capacity to be efficiently utilized, making it possible to efficiently supply treated water from the raw water tank to the membrane filtration treatment device. This allows a large amount of treated water to be continuously and stably treated, while also saving energy.

In addition, according to the water treatment device of the present invention, each membrane filtration treatment device is further configured to include a filtration membrane cleaning agent adding device, so that the filtration membrane of the membrane filtration treatment device in a dormant state can be cleaned and the filtration efficiency of the filtration membrane can be restored. This makes it possible to more reliably treat the coagulation treatment water continuously and stably.

According to the water treatment method of the present invention, since multiple coagulation treatment devices are used in the coagulation treatment process, a large amount of water to be treated can be treated. In addition, since the coagulation-treated water prepared in each coagulation treatment device is combined in the confluence process, it is possible to perform membrane filtration treatment in one membrane filtration treatment unit. This makes it possible to reduce the size of the device and save energy. In addition, in the diversion process, at least one of the multiple membrane filtration treatment devices, which is greater in number than the coagulation treatment devices, is in a suspended state in which the coagulation-treated water is not passed through, and the remaining membrane filtration treatment devices are in an operating state in which the coagulation-treated water is passed through, so that the membrane filtration treatment amount in the entire membrane filtration treatment unit is stable. As described above, according to the water treatment method of the present invention, a large amount of water to be treated can be continuously and stably treated.

In addition, according to the water treatment method of the present invention, in the diversion process, the control unit switches the membrane filtration treatment device to be in a suspended state based on the operating time, water flow rate, or operating pressure of the membrane filtration treatment device, so that it is possible to switch to a membrane filtration treatment device with high filtration efficiency before the filtration efficiency of the filtration membrane of the membrane filtration treatment device significantly decreases. Therefore, it is possible to more reliably treat a large amount of water to be treated continuously and stably.

In addition, the water treatment method of the present invention further includes a filtration membrane cleaning process in which a filtration membrane cleaning agent is added to a suspended membrane filtration treatment device to clean the filtration membrane, thereby allowing the membrane filtration treatment device with reduced filtration efficiency to be regenerated and reused. This makes it possible to more reliably treat a large amount of water to be treated continuously and stably.

In addition, according to the water treatment method of the present invention, in the diversion process, the control unit adjusts the flow rate of the coagulated treated water passed through each of the multiple membrane filtration treatment devices so that the ratio of the flow rate of each membrane filtration treatment device to the average flow rate of the multiple membrane filtration treatment devices is within a range of 80% to 120%, thereby making it possible to keep the membrane filtration processing rate of each of the multiple membrane filtration treatment devices constant, thereby stabilizing the filtration efficiency of the membrane filtration treatment device. This makes it possible to more reliably treat a large amount of water to be treated stably.

FIG. 1 is a schematic diagram illustrating a water treatment device according to an embodiment of the present invention. FIG. 2 is a flow diagram illustrating a water treatment method according to an embodiment of the present invention.

A water treatment device and a water treatment method according to an embodiment of the present invention will be described.
FIG. 1 is a schematic diagram illustrating a water treatment device according to an embodiment of the present invention.
As shown in Figure 1, the water treatment device 1 of this embodiment has a treated water supply device 10, a coagulation treatment unit 20, a membrane filtration treatment unit 40, a connecting flow path 60 connecting the coagulation treatment unit 20 and the membrane filtration treatment unit 40, and a control unit 70.

The treated water supply device 10 is a device for supplying the treated water W1 to the coagulation treatment unit 20. The treated water supply device 10 is equipped with a raw water tank 11, a treated water supply flow path 12, and a pump 14. The raw water tank 11 is a tank for temporarily storing the treated water W1. The treated water supply flow path 12 is equipped with a branch section 13 that connects the raw water tank 11 to each of the three coagulation treatment devices 21 provided in the coagulation treatment unit 20. The pump 14 is disposed upstream of the branch section 13 of the treated water supply flow path 12. The treated water W1 is supplied to the coagulation treatment unit 20 by this pump 14, and the coagulation treatment water W2 generated in the coagulation treatment unit 20 is supplied to the membrane filtration treatment unit 40.

The flocculation treatment unit 20 is installed downstream of the treated water supply device 10. The flocculation treatment unit 20 includes three flocculation treatment devices 21 and a confluence flow path 26. Each of the three flocculation treatment devices 21 is connected to a flocculant addition device 30.

The three flocculation treatment devices 21 (first flocculation treatment device 21a, second flocculation treatment device 21b, and third flocculation treatment device 21c) are arranged in parallel with respect to the flow path of the water to be treated W1. The flocculation treatment device 21 is a device that performs flocculation treatment, that is, a process in which a flocculating agent is added to the water to be treated W1 to flocculate inorganic matter (turbidity substances, colloidal components) and organic matter in the water to be treated W1, thereby generating flocculated treated water W2 containing flocculated flocs. Note that the number of flocculation treatment devices is not limited to three. There is no particular limit to the number of flocculation treatment devices as long as it is multiple (two or more), but it is preferable that the number is within the range of two to five.

It is preferable that the three coagulation treatment devices 21 have little variation in the amount of water W1 passing through them when they are in operation. When the three coagulation treatment devices 21 are in operation, the ratio of the amount of water W1 passing through each of the three coagulation treatment devices 21 may be adjusted to be within a range of 80% to 120% of the average amount of water passing through the three coagulation treatment devices 21, for example. By adjusting the amount of water passing through the three coagulation treatment devices 21 as described above, it becomes possible to uniformly coagulate the water W1 to be treated in each of the three coagulation treatment devices 21, and the water W1 to be treated can be coagulated more reliably and continuously in a stable manner.

The three flocculation treatment devices 21 are configured to include, for example, a treated water inlet section 22, a flocculant addition section 23, a mixing section 24, and a flocculated treated water retention section 25. The treated water inlet sections 22 of the three flocculation treatment devices 21 are each connected to the treated water supply flow path 12. The configuration of the flocculation treatment devices 21 is not limited to the above configuration. For example, the treated water inlet sections 22 of each flocculation treatment device do not have to be connected to the treated water supply flow path 12. That is, different treated water may be introduced into each of the first flocculation treatment device 21a, the second flocculation treatment device 21b, and the third flocculation treatment device 21c. Two or more flocculant addition sections 23 may be provided.

The treated water introduction section 22 introduces the treated water W1 supplied through the treated water supply flow path 12. The flocculant addition section 23 adds the flocculant supplied from the flocculant addition device 30. The mixing section 24 mixes the treated water W1 with the flocculant to prepare the flocculated treated water W2. For example, a line mixer can be used as the mixing section 24. The flocculated treated water retention section 25 temporarily retains the flocculated treated water W2, flocculating inorganic and organic matter in the flocculated treated water W2 to generate flocculated flocs. A pH adjuster addition device may be installed in the mixing section 24 and/or the flocculated treated water retention section 25 to adjust the pH of the flocculated treated water W2 to a value suitable for the flocculant.

The flocculant addition device 30 is equipped with a flocculant tank 31 in which the flocculant is stored, and pumps 32a, 32b, and 32c that supply the flocculant to the first flocculant treatment device 21a, the second flocculant treatment device 21b, and the third flocculant treatment device 21c, respectively. There are no particular limitations on the type of flocculant, and known flocculants used as flocculants for water treatment, such as inorganic flocculants and polymer flocculants, can be used according to conditions such as the type and content of inorganic and organic substances contained in the water to be treated W1. Examples of inorganic flocculants that can be used include aluminum chloride, polyaluminum chloride, aluminum sulfate, aluminum salts such as aluminum hydroxide or aluminum oxide dissolved in hydrochloric acid or sulfuric acid, ferric chloride, ferric sulfate, and ferrous sulfate. Examples of polymer flocculants that can be used include nonionic polymer flocculants such as polyacrylamide, polyethylene oxide, and urea-formaldehyde resin; cationic polymer flocculants such as polyaminoalkyl methacrylate, polyethyleneimine, halogenated polydiallylammonium, and chitosan; and anionic polymer flocculants such as sodium polyacrylate, partial hydrolyzates of polyacrylamide, partially sulfomethylated polyacrylamide, and poly(2-acrylamide)-2-methylpropane sulfur salt. These flocculants may be used alone or in combination of two or more. In addition to these flocculants, an oxidizing agent such as sodium hypochlorite may be added.

The confluence flow path 26 is a flow path for confluence of the flocculated treated water W2 that has been flocculated by the three flocculation treatment devices 21 and sending it to the connecting flow path 60. The confluence flow path 26 is connected to the flocculated treated water retention section 25 of the three flocculation treatment devices 21.

The membrane filtration processing unit 40 is installed after the coagulation processing unit 20. The membrane filtration processing unit 40 is equipped with four membrane filtration processing devices 41 and a diversion flow path 44. Each of the four membrane filtration processing devices 41 is equipped with a filtration membrane cleaning agent addition device 50.

The four membrane filtration treatment devices 41 (first membrane filtration treatment device 41a, second membrane filtration treatment device 41b, third membrane filtration treatment device 41c, and fourth membrane filtration treatment device 41d) are arranged in parallel with respect to the flow path of the coagulation-treated water W2. The membrane filtration treatment device 41 is a device that performs a process of membrane filtering the coagulation-treated water W2 using a filtration membrane (not shown) to separate and remove coagulated flocs in the coagulation-treated water W2 to generate membrane-filtered water W3. The number of membrane filtration treatment devices 41 is set to be greater than the number of coagulation treatment devices 21. It is preferable that the number of membrane filtration treatment devices 41 is in the range of N+1 or more and 2×N or less, where N is the number of coagulation treatment devices 21.

It is preferable that the four membrane filtration treatment devices 41 have little variation in the amount of flocculated treated water W2 passing through them when they are in operation. When the four membrane filtration treatment devices 41 are in operation, the ratio of the amount of flocculated treated water W2 passing through each of the four membrane filtration treatment devices 41 may be adjusted to be within a range of 80% to 120% of the average amount of water passing through the membrane filtration treatment device 41, for example. By adjusting the amount of water passing through the four membrane filtration treatment devices 41 as described above, it is possible to uniformly membrane filter the flocculated treated water W2 in each of the four membrane filtration treatment devices 41, and the flocculated treated water W2 can be more reliably and continuously membrane filtered in a stable manner.

Each of the four membrane filtration treatment devices 41 is configured to include, for example, a coagulation-treated water inlet 42 and a filtration membrane (not shown). The coagulation-treated water inlet 42 of each membrane filtration treatment device 41 is used to introduce the coagulation-treated water. As the filtration membrane of the membrane filtration treatment device 41, a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) can be used.

The filtration membrane cleaning agent adding device 50 is a device for adding a filtration membrane cleaning agent to the membrane filtration treatment device 41 to clean the filtration membrane when the membrane filtration treatment device 41 is in a stopped state (a state in which the coagulation treatment water to be treated is not passed through). By cleaning the membrane filtration treatment device 41 in a stopped state, the filtration efficiency can be improved when the membrane filtration treatment device 41 is in an operating state (a state in which the coagulation treatment water to be treated is passed through). The filtration membrane cleaning agent adding device 50 is equipped with two adding devices, a first adding device 51a and a second adding device 51b. The first adding device 51a is equipped with a first cleaning agent tank 52a in which the first cleaning agent is stored, and a pump 53a that supplies the first cleaning agent to the membrane filtration treatment device. The first adding device 51a is equipped with a second cleaning agent tank 52b in which a second cleaning agent different from the first cleaning agent is stored, and a pump 53b that supplies the second cleaning agent to the membrane filtration treatment device. There is no particular limit to the type of filtration membrane cleaner, and known cleaners used as filtration membrane cleaners, such as acidic or alkaline agents, can be used according to conditions such as the composition of the flocs separated and removed by the filtration membrane and the amount of flocs attached to the filtration membrane. As the filtration membrane cleaner, for example, an acid solution with a pH of 2 or less, an alkaline solution with a pH of 12 or more, or a solution containing sodium hypochlorite at a concentration of 10 mg/L can be used. The number of addition devices is not limited to two. There is no particular limit to the number of addition devices as long as it is one or more.

The diversion flow path 44 diverts the coagulated treated water W2 sent from the connecting flow path 60 so that it can be supplied to the membrane filtration treatment device 41. That is, the first membrane filtration treatment device 41a is connected to the connecting flow path 60 via the first diversion flow path 44a. Similarly, the second membrane filtration treatment device 41b is connected to the connecting flow path 60 via the second diversion flow path 44b, the third membrane filtration treatment device 41c is connected to the connecting flow path 60 via the third diversion flow path 44c, and the fourth membrane filtration treatment device 41d is connected to the connecting flow path 60 via the fourth diversion flow path 44d.

The control unit 70 controls the flow of the coagulation-treated water W2 through the diversion flow path 44 so that at least one of the membrane filtration treatment devices 41 is in a paused state in which the coagulation-treated water W2 is not passed through, and the membrane filtration treatment device 41 to be in a paused state can be switched. For example, an opening/closing valve can be used as the control unit 70.

The control unit 70 is provided in each of the diversion channels 44 at a position upstream of the membrane filtration treatment device 41. That is, the first control unit 70a is provided in a position upstream of the first membrane filtration treatment device 41a in the first diversion channel 44a. Similarly, the second control unit 70b is provided in a position upstream of the second membrane filtration treatment device 41b in the second diversion channel 44b, the third control unit 70c is provided in a position upstream of the third membrane filtration treatment device 41c in the third diversion channel 44c, and the fourth control unit 70d is provided in a position upstream of the fourth membrane filtration treatment device 41d in the fourth diversion channel 44d.

In the water treatment device 1 of this embodiment, the fourth control unit 70d closes the flow of the flocculated treated water W2 in the fourth branch flow path 44d, thereby putting the fourth membrane filtration treatment device 41d in a suspended state. Meanwhile, the first control unit 70a opens the flow of the flocculated treated water W2 in the first branch flow path 44a, thereby putting the first membrane filtration treatment device 41a in an operating state. Similarly, the second control unit 70b and the third control unit 70c open the flow of the flocculated treated water W2 in the second branch flow path 44b and the third branch flow path 44c, thereby putting the second membrane filtration treatment device 41b and the third membrane filtration treatment device 41c in an operating state.

When the control unit 70 switches the membrane filtration treatment device 41 in operation to the suspended state, the suspended membrane filtration treatment device 41 is put into operation, and the number of membrane filtration treatment devices 41 in operation in the entire membrane filtration treatment unit 40 is fixed. For example, when any of the first diversion flow path 44a, the second diversion flow path 44b, and the third diversion flow path 44c in operation is suspended, the suspended fourth membrane filtration treatment device 41d is put into operation. By keeping the number of membrane filtration treatment devices 41 in operation in the entire membrane filtration treatment unit 40 constant, it is possible to reduce fluctuations in the amount of water passing through the treated water W1 in the entire membrane filtration treatment unit 40. This makes it possible to more reliably perform continuous and stable membrane filtration treatment of the coagulated treated water W2.

The control unit 70 may, for example, switch the membrane filtration treatment device 41 to be put into a suspended state based on the operating time, water flow rate, or operating pressure of the membrane filtration treatment device 41. That is, when the operating time of the membrane filtration treatment device 41 has elapsed for a predetermined time, the control unit 70 switches the membrane filtration treatment device 41 in an operating state to a suspended state. Alternatively, when the water flow rate of the membrane filtration treatment device 41 falls below a predetermined value, the control unit 70 switches the membrane filtration treatment device 41 with the reduced water flow rate to a suspended state. Alternatively, when the operating pressure of the membrane filtration treatment device 41 rises above a predetermined value, the control unit 70 switches the membrane filtration treatment device with the increased operating pressure to a suspended state.

In the water treatment device 1 of this embodiment, the treated water supply flow path 12, the junction flow path 26, the connecting flow path 60, and the branch flow path 44 are, for example, pipes. In addition, each of the treated water supply flow path 12, the coagulation treatment device 21, the junction flow path 26, the connecting flow path 60, and the branch flow path 44 is configured to be sealed. Note that a portion of each flow path may be open to the atmosphere.

In addition, the three coagulation treatment devices 21 of the coagulation treatment unit 20 and the four membrane filtration treatment devices 41 of the membrane filtration treatment unit 40 may be configured to have the same water flow rate in each operating state. In this case, by making the number of coagulation treatment devices 21 and membrane filtration treatment devices 41 in the operating state the same, the water to be treated W1 can be continuously and stably treated. This simplifies the configuration of the water treatment device 1 and reduces the size of the device. For example, the ratio of the water flow rate of each of the coagulation treatment device 21 and the membrane filtration treatment device 41 to the average of the water flow rate of the water to be treated W1 of the coagulation treatment device 21 in the operating state and the water flow rate of the coagulated treated water W2 of the membrane filtration treatment device 41 in the operating state is adjusted to be within a range of 80% to 120%.

Next, a water treatment method according to this embodiment using the water treatment apparatus shown in FIG. 1 will be described.
FIG. 2 is a flow diagram illustrating a water treatment method according to an embodiment of the present invention.
As shown in FIG. 2, the water treatment method of this embodiment includes a to-be-treated water supply step S01, a coagulation treatment step S02, a confluence step S03, a division step S04, and a membrane filtration treatment step S05.

In the treated water supply S01, the treated water W1 stored in the raw water tank 11 provided in the treated water supply device 10 is supplied by the pump 14 via the treated water supply passage 12 to the treated water inlet 22 of each of the three coagulation treatment devices 21 in the coagulation treatment unit 20.

In the flocculation treatment step S02, flocculation treatment is performed using each of the three flocculation treatment devices 21 (first flocculation treatment device 21a, second flocculation treatment device 21b, third flocculation treatment device 21c) provided in the flocculation treatment unit 20. That is, the water to be treated W1 introduced from the water to be treated inlet section 22 of the flocculation treatment device 21 and the flocculant added from the flocculant addition section 23 are mixed in the mixing section 24 to prepare flocculated treated water W2, and the flocculated treated water W2 is retained in the flocculated treated water retention section 25. Then, inorganic and organic matter in the flocculated treated water W2 is flocculated in the flocculated treated water retention section 25 to generate coarse flocculated flocs.

In the confluence process S03, the flocculated treated water W2 that has been flocculated by the three flocculation treatment devices 21 is merged in the confluence flow path 26. The merged flocculated treated water W2 is then sent to the connecting flow path 60.

In the diversion step S04, the coagulated treated water W2 sent from the connecting flow path 60 is diverted through the diversion flow path 44 provided in the membrane filtration processing unit 40, and the control unit 70 places one of the four membrane filtration processing devices 41 (fourth membrane filtration processing device 41d) in a suspended state in which the coagulated treated water W2 is not passed through. Meanwhile, the remaining membrane filtration processing devices 41 (first membrane filtration processing device 41a, second membrane filtration processing device 41b, and third membrane filtration processing device 41c) are placed in an operating state in which the coagulated treated water is passed through.

In the membrane filtration process S05, the flocculated treated water W2 is subjected to membrane filtration treatment using the membrane filtration treatment devices (first membrane filtration treatment device 41a, second membrane filtration treatment device 41b, and third membrane filtration treatment device 41c) in operation. That is, the flocculated flocs in the flocculated treated water W2 are separated and removed by the filtration membrane.

The fourth membrane filtration treatment device 41d, which is in a suspended state, has a filtration membrane cleaning agent added to it using a filtration membrane cleaning agent adding device 50, and the filtration membrane is cleaned (filtration membrane cleaning process). This improves the filtration efficiency that has been reduced due to clogging caused by the adhesion of coagulated flocs. In order to maintain a high level of filtration efficiency in each membrane filtration treatment device, in the second diversion process S05, the membrane filtration treatment device that is suspended without supplying the coagulated treated water W2 may be switched based on, for example, the operating time or operating water volume or operating pressure of the membrane filtration treatment device.

In addition, the membrane filtration treatment device 41 may reduce variation in the amount of water passing through it during operation in order to perform the membrane filtration treatment stably. For example, the control unit 70 adjusts the amount of coagulated treated water W2 passed through each of the membrane filtration treatment devices 41 in operation so that the ratio of the amount of water passing through each membrane filtration treatment device 41 to the average amount of water passing through the membrane filtration treatment device 41 is within a range of 80% to 120%.

As described above, according to the water treatment device 1 of this embodiment, the coagulation treatment unit 20 is equipped with three coagulation treatment devices 21 (first coagulation treatment device 21a, second coagulation treatment device 21b, third coagulation treatment device 21c), so that a large amount of water to be treated W1 can be treated. In addition, the coagulation-treated water W2 that has been coagulated by the three coagulation treatment devices 21 is merged in the merging flow path 26, so that the coagulation-treated water W2 can be membrane-filtered by a single membrane filtration treatment unit 40. This allows for a reduction in the size of the device and energy savings. The membrane filtration treatment unit 40 is equipped with four membrane filtration treatment devices 41 (first membrane filtration treatment device 41a, second membrane filtration treatment device 41b, third membrane filtration treatment device 41c, fourth membrane filtration treatment device 41d), which is more than the coagulation treatment device, and one of the four membrane filtration treatment devices 41 (fourth membrane filtration treatment device 41d) is put into a pause state in which the coagulation treatment water W2 is not passed through, and the membrane filtration treatment device to be put into a pause state can be switched by the control unit 70, so that the number of membrane filtration treatment devices 41 in operation in the entire membrane filtration treatment unit 40 can be kept constant, and the membrane filtration treatment amount is stabilized. As described above, according to the water treatment device of this embodiment, a large amount of water to be treated can be continuously and stably treated.

In addition, according to the water treatment device 1 of this embodiment, it further has a treated water supply device 10, and the pump 14 of the treated water supply device 10 is arranged upstream of the branching portion 13 of the treated water supply flow path 12, and the treated water supply flow path 12, the coagulation treatment device 21, the merging flow path 26, the connecting flow path 60, and the diversion flow path 44 are each sealed, so that the water conveying force of the pump 14 is less likely to be released to the outside compared to when the flow path from the raw water tank 11 to the diversion flow path 44 is open to the atmosphere. Therefore, the water conveying capacity of the pump 14 can be efficiently exerted, and it is possible to efficiently supply the treated water W1 from the raw water tank 11 to the membrane filtration treatment device 41. Therefore, a large amount of treated water W1 can be continuously and stably treated, and energy saving can be achieved.

Furthermore, according to the water treatment device 1 of this embodiment, each of the membrane filtration treatment devices 41 is configured to include a filtration membrane cleaning agent addition device 50, so that the filtration membrane of the membrane filtration treatment device 41 in a dormant state can be cleaned to restore the filtration efficiency of the filtration membrane. This makes it possible to more reliably treat the coagulation treatment water W2 continuously and stably.

According to the water treatment method of this embodiment, since multiple coagulation treatment devices 21 are used in the coagulation treatment step S02, a large amount of the water to be treated W1 can be treated. In addition, in the confluence step S03, the coagulation-treated water W2 prepared by each coagulation treatment device 21 is combined, so that it is possible to perform membrane filtration treatment with one membrane filtration treatment unit 40. This makes it possible to reduce the size of the device and save energy. In addition, in the diversion step S03, one of the four membrane filtration treatment devices 41, which is more than the coagulation treatment device 21, is put into a suspended state in which the coagulation-treated water W2 is not passed through, and the remaining membrane filtration treatment devices 41 are put into an operating state in which the coagulation-treated water W2 is passed through, so that the membrane filtration treatment amount of the entire membrane filtration treatment unit 40 is stable. As described above, according to the water treatment method of this embodiment, a large amount of the water to be treated W1 can be continuously and stably treated.

In addition, according to the water treatment method of this embodiment, in the diversion step S04, the control unit 70 switches the membrane filtration treatment device 41 to a suspended state based on the operating time, water flow rate, or operating pressure of the membrane filtration treatment device 41, so that it can be switched to a membrane filtration treatment device with high filtration efficiency before the filtration efficiency of the filtration membrane of the membrane filtration treatment device 41 drops significantly. Therefore, a large amount of the water to be treated W1 can be treated continuously and stably more reliably.

In addition, according to the water treatment method of this embodiment, a filtration membrane cleaning process is further included in which a filtration membrane cleaning agent is added to the suspended membrane filtration treatment device to clean the filtration membrane, so that the membrane filtration treatment device with reduced filtration efficiency can be regenerated and reused. Therefore, a large amount of the water to be treated W1 can be treated continuously and stably more reliably.

In addition, according to the water treatment method of this embodiment, in the diversion process, the control unit 70 adjusts the flow rate of the coagulated treated water W2 passed through each of the three membrane filtration treatment devices 41 (first membrane filtration treatment device 41a, second membrane filtration treatment device 41b, and third membrane filtration treatment device 41c) in operation so that the ratio of the flow rate of each membrane filtration treatment device to the average flow rate of the three membrane filtration treatment devices 41 is within the range of 80% to 120%. This makes it possible to keep the membrane filtration processing rate of each of the three membrane filtration treatment devices 41 constant, thereby stabilizing the filtration efficiency of the membrane filtration treatment device 41. Therefore, a large amount of treated water W1 can be more reliably treated stably.

[Example 1]
A water treatment device having the same configuration as the water treatment device shown in Figure 1 was prepared, except that the coagulation treatment unit was equipped with two coagulation treatment devices (a first coagulation treatment device and a second coagulation treatment device) and the membrane filtration treatment unit was equipped with three membrane filtration treatment devices (a first membrane filtration treatment device, a second membrane filtration treatment device, and a third membrane filtration treatment device).The water to be treated was treated for 30 days using a water treatment device having the same configuration as the water treatment device shown in Figure 1.

In each flocculation treatment device of the flocculation treatment unit, ferric chloride (concentration: 38%) was used as the flocculating agent in the flocculating agent addition section. The amount of flocculating agent added was 100 mg/L. In the mixing section, the treated water and the flocculating agent were mixed using a static mixer (Noritake Co., Ltd.). The obtained flocculated treated water was retained in the retention section for 5 minutes and then supplied to the membrane filtration treatment unit.

The membrane filtration treatment device of the membrane filtration treatment unit used a UF membrane made of polyvinylidene fluoride as a filtration membrane. The membrane filtration treatment unit was supplied with coagulated water at a flow rate of 2 ^m3 /h, and the first and second membrane filtration treatment devices were operated and the third membrane filtration treatment device was stopped during the first 15 days, and membrane filtration treatment of the coagulated water was performed. During the last 15 days, the second and third membrane filtration treatment devices were operated and the first membrane filtration treatment device was stopped, and membrane filtration treatment of the coagulated water was performed.

After 30 days of water treatment, the water treatment was stopped. Next, to evaluate the performance (water permeability) of each membrane filtration treatment device, the differential pressure (transmembrane pressure difference, the difference between the inlet pressure and the permeate outlet pressure) was measured when pure water was filtered. The results are shown in Table 1 below.

[Example 2]
Water treatment was performed in the same manner as in Example 1, except that the suspended membrane filtration treatment device was switched to the third membrane filtration treatment device, the first membrane filtration treatment device, the second membrane filtration treatment device, and the third membrane filtration treatment device in this order every 7 days, and the filtration membrane was washed for the suspended membrane filtration treatment device. The filtration membrane was washed by washing with water after performing chemical washing for 1.5 days. The chemical washing was performed by acid washing with oxalic acid in the first half, and alkaline washing with an alkaline solution containing sodium hypochlorite in the second half. After performing water treatment for 30 days, the water treatment was stopped, and the performance (water permeability) of each membrane filtration treatment device was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[Example 3]
When the differential pressure of the membrane filtration treatment device in operation rose to exceed 50 kPa, the membrane filtration treatment device with the increased differential pressure was switched to a suspended state, and the suspended membrane filtration treatment device was switched to an operating state, and the suspended membrane filtration treatment device was chemically cleaned of the filtration membrane in the same manner as in Example 2 above. Water treatment was performed in the same manner as in Example 1. In addition, when the differential pressure of the membrane filtration treatment device in operation exceeded 50 kPa during the chemical cleaning of the filtration membrane, the operation was continued with the differential pressure exceeding 50 kPa until the chemical cleaning of the filtration membrane was completed. After performing water treatment for 30 days, the water treatment was stopped, and the performance (water permeability) of each membrane filtration treatment device was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[Example 4]
Water treatment was carried out in the same manner as in Example 3, except that the flow rate of the coagulation-treated water through the membrane filtration treatment device in operation was adjusted to 0.8 to 1.2 m ³ /h by adjusting the opening of the control unit (on-off valve). Note that in Examples 1 to 3, the amount of coagulation-treated water introduced into the membrane filtration treatment device was not adjusted as in Example 4. After performing water treatment for 30 days, the water treatment was stopped, and the performance (water permeability) of each membrane filtration treatment device was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[Comparative Example 1]
A water treatment device was prepared in which the first flocculation treatment device and the first membrane filtration treatment device were directly connected, and the second flocculation treatment device and the second membrane filtration treatment device were directly connected. Water treatment was performed in the same manner as in Example 1, except that this water treatment device was operated continuously for 30 days. After the water treatment was performed for 30 days, the water treatment was stopped, and the performance (water permeability) of each membrane filtration treatment device was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

The reason why the pressure difference increases when filtrating with pure water is because the flocculated flocs adhere to the filtration membrane and cause clogging. In Comparative Example 1, the first membrane filtration treatment device and the second membrane filtration treatment device were continuously operated without switching the membrane filtration treatment device, so the amount of flocculated flocs adhered to the filtration membrane increased, and the pressure difference when filtrating with pure water increased. In contrast, in Example 1, the first membrane filtration treatment device and the third membrane filtration treatment device were switched and operated, so the amount of flocculated flocs adhered to the filtration membrane was reduced compared to Comparative Example 1, and the first membrane filtration treatment device and the third membrane filtration treatment device had a lower pressure difference when filtrating with pure water. Furthermore, in Examples 2 and 3, the cycle of switching the membrane filtration treatment device was shortened, and the membrane filtration treatment device in the suspended state washed the filtration membrane, so the amount of flocculated flocs adhered to the filtration membrane was reduced, and the pressure difference when filtrating with pure water was further reduced. Furthermore, in Example 4, the flow rate of the coagulated treated water through the membrane filtration treatment device in operation was adjusted to 0.8 to 1.2 ^m3 /h, so that the amount of coagulated flocs adhering to the filtration membrane was further reduced, and the differential pressure when filtration was performed with pure water was further reduced.

1...water treatment device, 10...water to be treated supply device, 11...raw water tank, 12...water to be treated supply flow path, 13...branching section, 14...pump, 20...coagulation treatment unit, 21...coagulation treatment device, 21a...first coagulation treatment device, 21b...second coagulation treatment device, 21c...third coagulation treatment device, 22...water to be treated introduction section, 23...coagulant addition section, 24...mixing section, 25...coagulation treatment water retention section, 26...confluence flow path, 30...coagulant addition device, 31...coagulant tank, 32a, 32b, 32c...pump, 40...membrane filtration treatment unit, 41...membrane filtration treatment device, 41a...first membrane filtration treatment device, 41b...second membrane filtration treatment device 41c...third membrane filtration treatment device, 41d...fourth membrane filtration treatment device, 42...flocculation treated water inlet, 44...diversion flow path, 44a...first diversion flow path, 44b...second diversion flow path, 44c...third diversion flow path, 44d...fourth diversion flow path, 50...filter membrane cleaning agent addition device, 51a...first addition device, 51b...second addition device, 52a...first cleaning agent tank, 52b...second cleaning agent tank, 53a, 53b...pump, 60...connection flow path, 70...control device, 70a...first control device, 70b...second control device, 70c...third control device, 70d...fourth control device, W1...water to be treated, W2...flocculation treated water, W3...membrane filtration treated water

Claims (7)

a flocculation treatment unit for producing flocculated treated water containing flocs ;
a membrane filtration treatment unit provided downstream of the coagulation treatment unit and into which the coagulation-treated water flows ;
A connecting flow path connecting the flocculation treatment unit and the membrane filtration treatment unit;
A control unit,
The flocculation treatment unit includes a plurality of flocculation treatment devices arranged in parallel with respect to the flow path of the water to be treated, and a confluence flow path that merges the flocculated water that has been flocculated by the plurality of flocculation treatment devices and sends it to the connecting flow path.
The membrane filtration treatment unit is provided with a plurality of membrane filtration treatment devices arranged in parallel with the flow path of the coagulation treatment water and having a greater number of membrane filtration treatment devices than the coagulation treatment devices, and a diversion flow path that diverts the coagulation treatment water sent from the connection flow path and supplies it to the plurality of membrane filtration treatment devices.
The control unit controls the flow of the coagulated treated water in the diversion flow path so as to put at least one of the multiple membrane filtration treatment devices into a paused state in which the coagulated treated water is not passed through, and to make it possible to switch between the membrane filtration treatment devices to be put into a paused state. Furthermore, a raw water tank in which the water to be treated is retained;
a treated water supply flow path having a branch portion connecting the raw water tank and each of the plurality of coagulation treatment devices;
a pump disposed upstream of the branch portion of the water supply flow path,
The water treatment device according to claim 1 , wherein the untreated water supply flow path, the plurality of coagulation treatment devices, the confluence flow path, the connection flow path, and the branch flow path are each sealed. The water treatment device according to claim 1 or 2, further comprising a filter membrane cleaning agent adding device for each of the membrane filtration treatment devices. A water treatment method using the water treatment device according to any one of claims 1 to 3,
A flocculation treatment step of flocculating the water to be treated in each of the plurality of flocculation treatment devices provided in the flocculation treatment unit;
A confluence process in which the flocculated water that has been flocculated by the multiple flocculation treatment devices is merged in the confluence flow path and sent to the connection flow path;
A diversion process in which the flocculated treated water sent from the connecting flow path is diverted in the diversion flow path, and at least one of the plurality of membrane filtration treatment devices is put into a dormant state in which the flocculated treated water is not passed through the control unit, and the remaining membrane filtration treatment devices are put into an operating state in which the flocculated treated water is passed through the control unit;
A membrane filtration treatment step of performing membrane filtration treatment on the coagulation treated water using the membrane filtration treatment device in operation. The water treatment method according to claim 4, wherein in the diversion step, the control unit switches the membrane filtration treatment device to be put into a suspended state based on the operation time, water flow rate, or operation pressure of the membrane filtration treatment device. The water treatment method according to claim 4 or 5 further includes a filtration membrane cleaning step of adding a filtration membrane cleaning agent to the membrane filtration treatment device in a suspended state to clean the filtration membrane. The water treatment method according to any one of claims 4 to 6, wherein in the diversion step, the control unit adjusts the flow rate of the coagulated water passed through each of the plurality of membrane filtration treatment devices so that the ratio of the flow rate of each of the membrane filtration treatment devices to the average flow rate of the plurality of membrane filtration treatment devices is within a range of 80% to 120%.

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