JP2019147137A - Differential pressure reducing method of membrane module, water treatment method and water treatment device - Google Patents

Abstract

To provide a differential pressure reducing method of a membrane module capable of performing forward washing of a filtration membrane by circulating chemicals and capable of recovering a differential pressure of the membrane module as compared to periodical backward washing and chemical washing upon a normal operation.SOLUTION: A differential pressure reducing method of a membrane module as the differential pressure reducing method of the membrane module provided with at least one side of a fine filtration membrane and an ultrafiltration membrane causes circulation water containing chemicals to pass through a circulation channel and the membrane module and performs forward washing of the membrane module while providing the circulation channel which connects at least one of channels of the downstream side of the membrane module. Further, water treatment method and a water treatment device are provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for reducing a differential pressure of a membrane module, a water treatment method, and a water treatment apparatus.

In general, as a method for separating and removing pollutants in treated water in various types of water treatment systems such as water treatment systems, sewage treatment systems, industrial water treatment systems, wastewater treatment systems, seawater desalination systems, filtration by membrane modules There is known a water treatment method using water.
In the water treatment method using membrane filtration, as filtration continues, contaminants in the water to be treated adhere to the filtration membrane, causing clogging (fouling) of the filtration membrane, and the differential pressure of the filtration membrane increases ( Filtration performance is reduced). Therefore, it is necessary to eliminate clogging by periodically back-washing the filtration membrane (washing while passing water from the downstream to the upstream during filtration of the filtration membrane) or washing with chemicals.
As a method for cleaning the membrane module, various back-washing, chemical cleaning, and forward cleaning (cleaning while passing water from upstream to downstream during filtration of the filtration membrane) are known (see Patent Documents 1 to 3). ).

  In Patent Literature 1, a membrane filtration unit that is divided into a primary side and a secondary side by a filtration membrane, filters the treated water supplied to the primary side through a filtration membrane, and permeates the filtrate water to the secondary side; A backwash water discharge line connected to the primary side of the membrane filtration unit via a backwash water discharge valve, and a backwash water supply line connecting the secondary side of the membrane filtration unit and the backwash water tank via a backwash pump A backwash preparation step of closing the backwash water discharge valve and operating the backwash pump to increase the pressure applied to the filtration membrane to a predetermined pressure, and backwashing After the pressure applied to the filtration membrane in the preparatory step reaches a predetermined pressure, the backwashing water discharge valve is opened, and the backwashing step of flowing backwash water from the secondary side to the primary side of the membrane filtration unit, An apparatus backwashing method is described.

  In Patent Document 2, in a method for cleaning an outside-type membrane module that has been treated with raw water containing scale components, a cleaning chemical solution is allowed to flow along the secondary side surface of the membrane without backwashing. A method for cleaning a membrane module is described which includes a first cleaning step for cleaning only the secondary side, and a second cleaning step for backwashing the membrane after the first cleaning step.

  Patent Document 3 discloses that a separation membrane that has been contaminated and deteriorated by operation and whose blocking performance is reduced is washed with an acid or alkali or both, and then water containing an organic substance containing polyphenol is passed through under pressure to block the separation membrane. A method for recovering the performance of a separation membrane that restores performance is described.

JP 2011-183320 A JP2015-229146A JP 2006-224049 A

Patent Documents 1 and 2 are methods for back-washing a filtration membrane using water to which a drug is added.
Patent Document 3 is a method of circulating the chemicals and sequentially washing the filtration membrane.

  The problem to be solved by the present invention is that the membrane can be sequentially washed by circulating the drug, and the difference in the membrane module that can recover the differential pressure of the membrane module more than regular backwashing and chemical washing during normal operation. It is to provide a pressure reduction method.

  As a result of intensive studies to solve the above problems, the present inventors have provided a circulation channel that connects at least one of the channels on the downstream side of the membrane module to the upstream side of the membrane module. By passing the circulating water containing the medicine through the circulation channel and the membrane module and washing the membrane module, the filtration membrane can be washed in order by circulating the medicine, and regular backwashing and medicine during normal operation It has been found that the differential pressure of the membrane module can be recovered rather than cleaning, and the present invention has been completed.

Specifically, the configurations of the present invention and preferred embodiments of the present invention are as follows.
[1] A method for reducing a differential pressure of a membrane module including at least one of a microfiltration membrane and an ultrafiltration membrane,
With a circulation channel connecting at least one of the channels on the downstream side of the membrane module to the upstream side of the membrane module,
A method for reducing a differential pressure of a membrane module, wherein circulating water containing a chemical is passed from the upstream side to the downstream side of the filtration membrane through the filtration membrane and the circulation channel to wash the membrane module.
[2] The method for reducing the differential pressure of the membrane module according to [1], wherein the drug is at least one of an acid and an alkali.
[3] The channel on the downstream side of the membrane module includes a branch portion,
The method for reducing the differential pressure of the membrane module according to [1] or [2], further comprising a step of switching a flow path on the downstream side of the membrane module from a flow path other than the circulation flow path to the circulation flow path.
[4] The treated water is passed through a membrane module including at least one of a microfiltration membrane and an ultrafiltration membrane to obtain treated water, and the membrane module is regularly backwashed and / or chemically washed. With normal operation;
A water treatment method including the method for reducing a differential pressure of a membrane module according to any one of [1] to [3].
[5] The channel on the downstream side of the membrane module includes a branch portion,
In normal operation, the channel on the downstream side of the membrane module is a channel other than the circulation channel,
[4] The water treatment method according to [4], including a step of switching a flow path on the downstream side of the membrane module from a flow path other than the circulation flow path to a circulation flow path after the normal operation until the method for reducing the pressure difference of the membrane module. .
[6] The flux when circulating water is passed through the membrane module is increased from 1.2 times to 10.0 times the flux when water to be treated is passed through the membrane module. [4] or [5] Water treatment method.
[7] The water treatment method according to any one of [4] to [6], wherein treated water obtained by normal operation is used as circulating water.
[8] A membrane module comprising at least one filtration membrane of a microfiltration membrane and an ultrafiltration membrane that obtains treated water by passing the treated water;
A pump for water to be treated which sends the water to be treated to the membrane module;
Including a branch located in the flow path downstream of the membrane module;
At least one of the branch outlets can discharge treated water,
At least one of the outlets of the branch part can be connected to a circulation channel upstream of the membrane module to circulate the circulating water,
A water treatment apparatus comprising means for adding chemicals to circulating water.
[9] The water treatment apparatus according to [8], further including a treated water pump that feeds treated water upstream of the branch portion.
[10] The water treatment apparatus according to [8] or [9], including a water tank to be treated that can store the water to be treated.
[11] The water treatment apparatus according to any one of [8] to [10], which includes a treated water tank capable of storing treated water.
[12] The water treatment apparatus according to any one of [8] to [11], wherein the branch portion is a three-way valve.
[13] The water treatment apparatus according to any one of [8] to [11], wherein the outlet of the branch portion connected to the circulation flow path includes a circulating water pump.

  According to the present invention, there is provided a method for reducing a differential pressure of a membrane module that can circulate a drug in order to sequentially wash the filtration membrane, and can recover the differential pressure of the membrane module more than regular backwashing and chemical cleaning during normal operation. Can be provided.

FIG. 1 is a schematic cross-sectional view showing an example of the water treatment apparatus of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the water treatment apparatus of the present invention.

  Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Differential pressure reduction method of membrane module]
The membrane module differential pressure reduction method of the present invention is a membrane module differential pressure reduction method comprising at least one filtration membrane of a microfiltration membrane and an ultrafiltration membrane, and includes at least a flow path downstream of the membrane module. With the circulation channel connecting one to the upstream side of the membrane module, the circulating water containing the drug is passed through the filtration membrane and the circulation channel from the upstream side to the downstream side of the filtration membrane to pass the membrane module. Wash.
With this configuration, the filtration membrane can be washed in order by circulating the drug, and the differential pressure of the membrane module can be recovered more than regular backwashing and drug washing during normal operation. In particular, the differential pressure that could not be reduced by physical cleaning using chemicals that was performed during conventional normal operation can be reduced, and effective physical cleaning can be performed in the membrane module (housing). Without being bound by any theory, the dirt adhering to the surface of the filtration membrane with continuous pores can be removed by physical cleaning using a chemical agent that has been performed in the conventional normal operation. On the other hand, the dirt clogged inside the pores of the filtration membrane cannot be removed by physical cleaning using a drug that has been performed in the conventional normal operation, and the differential pressure cannot be sufficiently reduced. On the other hand, according to the method for reducing the differential pressure of the membrane module of the present invention, dirt clogged inside the pores of the filtration membrane can be removed, and the differential pressure can be sufficiently reduced.
In a preferred embodiment of the present invention, the frequency of washing can be reduced and the amount of drug used can be suppressed.
In the present invention, backwashing may or may not be performed, but if backwashing is not performed, a backwash pump is not required, and equipment costs can be suppressed.
In a preferred embodiment of the present invention, the drainage amount can be suppressed by providing a circulation channel (circulation washing line) and returning the circulation water upstream of the membrane module.
In a preferred embodiment of the present invention, it is preferable that the flux can be efficiently recovered as a result of reducing the differential pressure of the membrane module.
Hereinafter, preferred embodiments of the present invention will be described.

<Filtration membrane>
The filtration membrane is a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane).
Examples of the form of the filtration membrane include a hollow fiber and a flat membrane, and a hollow fiber is preferable.
Examples of hollow fibers include an external pressure type (method in which treated water enters from the outside to the inside and the inner treated water is discharged from the end; a dead end method) and an internal pressure type (cross flow method). The external pressure type is preferable.
By adopting an ultrafiltration membrane or a microfiltration membrane, bacteria such as Escherichia coli can be completely removed from the water to be treated in the normal operation described later, and treated water that is aseptic water can be obtained. The treated water can be treated as it is with a nanofiltration membrane (NF membrane) or a reverse osmosis membrane (RO membrane), and demineralized water can be easily obtained.
The filtration membrane is preferably an ultrafiltration membrane. There is no restriction | limiting in particular as an ultrafiltration membrane, A well-known ultrafiltration membrane etc. can be used. A commercially available ultrafiltration membrane may be used. For example, OJI-MEMBRANE (registered trademark) manufactured by Oji Engineering Co., Ltd. can be preferably used.
In the ultrafiltration membrane, the lower limit value of the pore diameter is preferably 0.001 μm or more, more preferably 0.05 μm or more, and particularly preferably 0.01 μm or more. The upper limit value of the pore diameter is preferably 0.05 μm or less, more preferably 0.04 μm or less, and particularly preferably 0.03 μm or less.
The material of the filtration membrane is an organic polymer such as polyvinylidene fluoride (PVDF), cellulose acetate (CA), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyethylene (PE), polyethersulfone (PES), etc. Alternatively, inorganic materials such as ceramics can be used.

<Circulating water>
Circulating water is circulating water containing chemicals.
The circulating water is preferably a liquid that provides a higher flux than the water to be treated (raw water) during normal operation when passing through the filtration membrane.
In this invention, it is preferable to use the treated water (membrane filtration water) obtained by the below-mentioned normal driving | operation as circulating water. The amount of waste water can be reduced by circulating the treated water obtained in the normal operation through the circulation channel.

(Drug)
There are no particular restrictions on the drug.
In the present invention, the drug is preferably an acid, an alkali, or a cleaning agent.
When the filter membrane contains dirt (adhered matter), that is, the component contained in the water to be treated is a mineral, it is preferably an acid. Examples of the acid include hydrochloric acid, sulfuric acid, nitric acid, citric acid, oxalic acid, EDTA and the like, and sulfuric acid is preferable. When forming aggregated flocs using an inorganic flocculant such as sulfuric acid band (aluminum sulfate) as the pretreatment in normal operation, mineral components (positively charged on the surface of negatively charged filth) using acid are used. The differential pressure can be effectively reduced by dissolving the adhering dirt.
When the dirt (adhered matter) to the filtration membrane, that is, the component contained in the water to be treated is an organic substance, an alkali is preferable. Moreover, it is preferable that a chemical | medical agent is a cleaning agent which has the tolerance to an ultrafiltration membrane. Examples of the detergent having resistance to alkalis and ultrafiltration membranes include hypochlorous acid or a salt thereof, sodium hydroxide, hydrogen peroxide, and the like, and sodium hypochlorite is preferable. By using hypochlorous acid or its salt, the surface of the circulating water can be treated even when the differential pressure is high enough to prevent the flow rate (flow velocity) or flux (flux) from increasing in the treated water during normal operation. By reducing the tension, a shearing force is applied to the pores of the filtration membrane, and the differential pressure can be effectively reduced.

<Circulation channel>
The circulation channel connects at least one of the channels on the downstream side of the membrane module to the upstream side of the membrane module.
The specific structure of the circulation channel will be described later in the description of the water treatment apparatus.

(Branch part)
In the present invention, it is preferable that the flow path on the downstream side of the membrane module includes a branch portion.
In this invention, it is preferable to have the step which switches the flow path downstream of a membrane module from flow paths other than a circulation flow path to a circulation flow path.
The specific structure of the branch portion will be described later in the description of the water treatment apparatus.

<Washing>
In this invention, the circulating water containing a chemical | medical agent is passed through a filtration membrane and a circulation flow path toward the downstream from the upstream of a filtration membrane, and a membrane module is wash | cleaned.
Although there is no restriction | limiting in particular as washing | cleaning time, It is preferable that it is 1 to 60 minutes, It is more preferable that it is 3 to 40 minutes, It is especially preferable that it is 3 to 30 minutes.

[Water treatment method]
In the water treatment method of the present invention, treated water is passed through a membrane module including at least one of a microfiltration membrane and an ultrafiltration membrane to obtain treated water, and the membrane module is regularly backwashed and And / or a normal operation for cleaning the chemical and a method for reducing the differential pressure of the membrane module of the present invention.

<Normal operation>
In normal operation, the treated water is passed through a membrane module equipped with at least one of a microfiltration membrane and an ultrafiltration membrane to obtain treated water, and the membrane module is regularly backwashed and / or chemically washed. To do.

(Filtration)
In normal operation, the water to be treated is passed through a membrane module including at least one of a microfiltration membrane and an ultrafiltration membrane to obtain treated water. This stage is sometimes called filtration.

-Treated water-
There is no restriction | limiting in particular as to-be-processed water, River water, well water, lake water, high turbidity water, etc. can be used. The present invention can be applied to a wide range of systems such as water treatment, sewage treatment, drinking water production, industrial water production, wastewater advanced treatment, wastewater recovery treatment, and seawater desalination.
There is no restriction | limiting in particular in the organic substance density | concentration of to-be-processed water.
The chemical oxygen demand (COD) of the water to be treated is preferably 500 mg / L or less, more preferably 100 mg / L or less as a potassium permanganate COD measurement method (CODMn). 20 mg / L or less is particularly preferable. The lower limit value of CODMn is not particularly limited.

-Flocculant-
The water to be treated is preferably pretreated by adding a flocculant or the like.
Examples of the flocculant include inorganic flocculants and organic flocculants (for example, polymer flocculants), and inorganic flocculants are preferable.
Inorganic flocculants include aluminum flocculants such as polyaluminum chloride (PAC) and aluminum sulfate (sulfuric acid band), or iron flocculants of polyiron, ferrous chloride, ferric chloride and polysilica iron. The aluminum flocculant is more preferable, and the sulfuric acid band is particularly preferable. There is no restriction | limiting in particular in the addition amount of an inorganic flocculant, It can adjust suitably.

-Flux of water to be treated-
In the normal operation filtration of the water treatment method of the present invention, the flux for allowing the water to be treated to pass through the membrane module is not particularly limited, and the lower limit is preferably 0.5 m / day or more, preferably 1.0 m / day or more. It is more preferable that it is 1.5 m / day or more. In normal operation filtration, the upper limit value of the flux that allows the water to be treated to pass through the membrane module is not particularly limited, and is preferably 8 m / day or less, and more preferably 1.8 m / day or less.

-Flow rate of treated water-
In the method for reducing the differential pressure of the membrane module of the present invention, the flow rate (flow velocity) for passing the water to be treated through the membrane module is not particularly limited, and the lower limit is preferably 0.5 m ³ / h or more, and 1.5 m ³ / h or more is more preferable, and 2.5 m ³ / h or more is particularly preferable. In normal operation filtration, the upper limit value of the flow rate for allowing the water to be treated to pass through the membrane module is not particularly limited, and is preferably, for example, 13 m ³ / h or less, and more preferably 3 m ³ / h or less.

(Reverse cleaning, chemical cleaning)
In normal operation, the membrane module is periodically backwashed and / or drug washed. Although either reverse cleaning or chemical cleaning may be performed, it is preferable to perform both reverse cleaning and chemical cleaning. There is no restriction | limiting in particular as a backwashing apparatus, A well-known backwashing apparatus can be used.
Water treatment using a filtration membrane has a potential fouling problem due to suspended flocs and microbial growth on the membrane surface.
The normal operation is preferably performed once every time the differential pressure increases by 3 to 7 kPa, more preferably once every time the differential pressure increases by 4 to 6 kPa, and the differential pressure increases by 5 kPa. It is particularly preferred to carry out once each time.
In normal operation, it is desirable to perform chemical cleaning of the filter membrane once every 1 to 48 hours, for example using sodium hypochlorite, and more desirably once every 6 to 36 hours. Most preferably, it is performed once every 12 to 24 hours.

<Step to switch to circulation channel>
In the present invention, the flow path on the downstream side of the membrane module includes a branch portion,
In normal operation, the channel on the downstream side of the membrane module is a channel other than the circulation channel,
It is preferable to have a step of switching the flow path on the downstream side of the membrane module from the flow path other than the circulation flow path to the circulation flow path after the normal operation until the method for reducing the pressure difference of the membrane module.
The shorter the time from the normal operation to the method for reducing the differential pressure of the membrane module, the better. In a preferred embodiment of the present invention, when treated water obtained in a normal operation is used as the circulating water, the time from the normal operation to the method for reducing the differential pressure of the membrane module can be shortened.
A method for switching from a flow path other than the circulation flow path to the circulation flow path is not particularly limited, and can be switched according to the shape of the branch portion.
When the branch portion includes a valve such as a three-way valve, the valve can be appropriately opened and closed to switch to the circulation flow path.
When the branch portion includes a circulating water pump, the circulating water pump can be appropriately started to switch to the circulation flow path.

<Flux of circulating water>
In the present invention, the flux when circulating water passes through the membrane module is preferably 1.0 times or more than the flux when water to be treated passes through the membrane module, and is 1.2 to 10.0 times the flux. More preferably, it is 1.5 to 5 times, particularly preferably 1.5 to 3 times. By passing water through the filtration membrane with a higher flux in the differential pressure reduction method of the membrane module than during normal operation filtration, the deposits on the surface of the filtration membrane can be washed more, and the differential pressure can be further reduced.
In the present invention, circulating water containing the drug is circulated and washed in order to decompose dirt clogged inside the pores of the filtration membrane or to remove clogs due to shear stress. It is possible to increase the flux when circulating water passes through the membrane module than the flux during normal operation.
Further, in the method for reducing the differential pressure of the membrane module, the temperature of the circulating water may be temporarily increased to lower the viscosity, and the flux when circulating water passes through the membrane module may be higher than the flux during normal operation.
In addition, the surfactant may be used alone or in combination with other chemicals to lower the viscosity of the circulating water and increase the flux when passing the circulating water through the membrane module than the flux during normal operation. .
In the method for reducing the differential pressure of the membrane module, the flux for allowing the circulating water to pass through the membrane module is not particularly limited, and the lower limit value is preferably 1.8 m / day or more, more preferably 2.5 m / day or more. Preferably, it is 3.5 m / day or more. The upper limit of the flux for allowing the circulating water to pass through the membrane module is not particularly limited, and can be, for example, 18 m / day or less, preferably 9 m / day or less, and preferably 5.4 m / day or less. More preferred.

<Flow rate of circulating water>
Instead of controlling the circulating water flux, the circulating water flow rate may be controlled. The flow rate when circulating water passes through the membrane module is preferably 1.0 times or more than the flow rate when water to be treated is passed through the membrane module, and is preferably 1.2 times to 10.0 times. More preferably, it is particularly preferably 1.5 to 5 times, and more preferably 1.5 to 3 times.
In difference pressure reduction method of the membrane module, the flow rate passing the circulating water to the membrane module (flow rate) is not particularly limited, it is preferable that the lower limit is 3m 3 ^{/ h} or more, is 3.6 m 3 / ^h or more More preferably, it is particularly preferably 6 m ³ / h or more. It circulating water upper limit of the flow rate passing through a membrane module is not particularly limited, for example, it is a 30 m 3 / ^h or less, preferably 15 m 3 / ^h or less, or less 9m 3 / ^h Is more preferable.

[Water treatment equipment]
The water treatment device of the present invention is a membrane module comprising at least one filtration membrane among a microfiltration membrane and an ultrafiltration membrane that allows the treated water to pass through to obtain treated water;
A pump for water to be treated which sends the water to be treated to the membrane module;
Including a branch located in the flow path downstream of the membrane module;
At least one of the branch outlets can discharge treated water,
At least one of the outlets of the branch part can be connected to a circulation channel upstream of the membrane module to circulate the circulating water,
A means for adding chemicals to the circulating water is provided.

<Configuration of water treatment device>
First, the configuration of the water treatment apparatus will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing an example of the water treatment apparatus of the present invention. The water treatment apparatus shown in FIG. 1 is an example in the case of newly installing equipment as a branch part.
In the water treatment apparatus shown in FIG. 1, in normal operation, the discharge valve 31 and the water valve 33 to be treated are opened, the circulation valve 32 is closed, and the water 1 to be treated is introduced into the water tank 11 to be treated. The treated water 1 is sent to the membrane module 12 by the treated water pump 21, filtered through the membrane, and sent to the treated water tank 13 as treated water 2. The treated water 2 is discharged out of the water treatment apparatus as discharged water 5 from the discharge valve 31 by the treated water pump 22.
In the water treatment apparatus shown in FIG. 1, in the method for reducing the pressure difference of the membrane module, the discharge valve 31 and the water valve 33 to be treated are closed, the circulation valve 32 is opened, and the treated water 2 is treated from the circulation channel 41. It returns to the water tank 11, and the chemical | medical agent 4 is added to the treated water 2 returned by the chemical | medical agent addition means 14, and it is set as the circulating water 3. FIG. The circulating water 3 is sent to the membrane module 12 by the pump 21 for treated water, the filtration membrane is washed in order, sent to the treated water tank 13, and returned to the treated water tank 11 from the circulation channel 41 again. Is repeated to circulate in the water treatment apparatus.

FIG. 2 is a schematic cross-sectional view showing another example of the water treatment apparatus of the present invention. The water treatment apparatus shown in FIG. 2 is an example when a circulating water pump is added to an existing facility as a branching portion.
In the water treatment apparatus shown in FIG. 2, in normal operation, the discharge valve 31 and the treated water valve 33 are opened, the operation of the circulating water pump 23 is stopped, and the treated water 1 is introduced into the treated water tank 11. . The treated water 1 is sent to the membrane module 12 by the treated water pump 21, filtered through the membrane, and sent to the treated water tank 13 as treated water 2. The treated water 2 is discharged out of the water treatment apparatus as discharged water 5 from the discharge valve 31 by the treated water pump 22.
In the water treatment apparatus shown in FIG. 2, in the method for reducing the differential pressure of the membrane module, the discharge valve 31 and the water valve 33 to be treated are closed, the operation of the circulating water pump 23 is started, and the treated water 2 is passed through the circulation flow path. 41 is returned to the water tank 11 to be treated. In the water tank 11 to be treated, the chemical 4 is added to the treated water 2 returned by the chemical addition means 14 to obtain the circulating water 3. The circulating water 3 is sent to the membrane module 12 by the pump 21 for treated water, the filtration membrane is washed in order, sent to the treated water tank 13, and returned to the treated water tank 11 from the circulation channel 41 again. Is repeated to circulate in the water treatment apparatus.
Hereinafter, a preferable aspect is demonstrated about the detail of a structure of the water treatment apparatus of this invention.

<Treatment tank>
The water treatment apparatus of the present invention preferably includes a water tank to be treated that can store the water to be treated.
It is preferable that the water treatment apparatus includes means for adding a flocculant or the like in the water tank to be treated or upstream of the water tank to be treated.

<Pump for treated water>
The water treatment device of the present invention includes a pump for water to be treated that feeds water to be treated to the membrane module.
There is no restriction | limiting in particular as a pump for to-be-processed water, A well-known pump can be used. The pump for water to be treated is preferably capable of adjusting the flow rate (flow rate) with an inverter or the like.

<Membrane module>
The membrane module includes at least one filtration membrane of a microfiltration membrane and an ultrafiltration membrane that obtains treated water through the treated water.
A preferred embodiment of the membrane module is as described in the above-described method for reducing the differential pressure of the membrane module.

<Pump for treated water>
The water treatment apparatus of the present invention preferably includes a treated water pump that feeds treated water upstream of the branch portion. There is no restriction | limiting in particular as a pump for treated water, A well-known pump can be used.

<Treatment water tank>
The water treatment apparatus of the present invention preferably includes a treated water tank that can store treated water.

<Circulation channel>
In the circulation channel, at least one of the outlets of the branch portions is connected to the circulation channel upstream of the membrane module. In particular, it is preferable that at least one of the channels on the downstream side of the membrane module is connected to the upstream side of the membrane module.
The piping of the circulation channel is not particularly limited as long as circulating water can be fed.
Although there is no restriction | limiting in particular as an upstream of the membrane module which a circulation channel connects, It is preferable that it is a to-be-processed water tank.

(Branch part)
The water treatment apparatus of the present invention includes a branch portion located in the flow path on the downstream side of the membrane module.
In the water treatment apparatus of the present invention, at least one of the outlets of the branch part can discharge the treated water, and at least one of the outlets of the branch part can be connected to a circulation channel upstream of the membrane module to circulate the circulating water.
It is preferable that at least one of the outlets of the branch portion is connected to a circulation flow path upstream of the membrane module so that at least a part of the treated water can be returned as circulating water.
The branching section is not particularly limited, and may be a branched pipe, a combination of a discharge valve and a circulation valve, a three-way valve in which the discharge valve and the circulation valve are integrated, or a circulating water pump. .

-Three-way valve-
In the first aspect of the water treatment apparatus of the present invention, the branching section is preferably a three-way valve. There is no restriction | limiting in particular as a three-way valve, A well-known three-way valve can be used. The three-way valve is preferably a valve in which a discharge valve and a circulation valve are integrated. In the three-way valve in which the discharge valve and the circulation valve are integrated, the discharge valve and the circulation valve may be opened and closed independently, or may be opened and closed in conjunction with each other.

−Circulating water pump−
In the 2nd aspect of the water treatment apparatus of this invention, it is preferable that the exit of the branch part by the side connected to a circulation flow path is equipped with the pump for circulating water.
There are no particular restrictions on the location where the circulating water pump is installed. For example, the circulating water pump may be installed in the pipe between the membrane module and the treated water tank, in the treated water tank, or in the pipe downstream of the treated water tank. You may install in. It is preferable to install the circulating water pump in the treated water tank from the viewpoint of omitting the installation area.
There is no restriction | limiting in particular as a pump for circulating water, A well-known pump can be used. When the circulating water pump is installed in the treated water tank, the circulating water pump is preferably a submersible pump from the viewpoint of reducing the installation area.

<Mechanical addition to circulating water>
The water treatment apparatus of the present invention includes a chemical addition means for circulating water.
There is no restriction | limiting in particular as a chemical | medical agent addition means to circulating water, A well-known thing can be used.
The drug addition means may have a stirring part in addition to the drug addition part.
There is no restriction | limiting in particular as a position of the chemical | medical agent addition means to circulating water, Any position of a to-be-treated water tank, a treated water tank, a circulation flow path, and piping which connects them may be sufficient, and it is preferable that it is a to-be-treated water tank.

<Other devices>
The water treatment device may include other known devices.
For example, a pH adjusting device may be provided at an arbitrary place.
For example, a temperature control device may be provided at an arbitrary place.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[Comparative Example 1]
A water treatment apparatus having the configuration shown in FIG. 1 was produced. In the water treatment apparatus, a three-way valve in which the discharge valve 31 and the circulation valve 32 are integrated is used.

As water to be treated, pond water having an organic substance concentration of 20 mg / L for CODMn was used.
In the water to be treated, a predetermined amount of sulfuric acid band and hypochlorous acid was added as a flocculant to the water to be treated to perform a coagulation reaction.

<Normal operation>
The treated water after the coagulation reaction is introduced into a membrane module equipped with an ultrafiltration membrane having a pore diameter of 0.02 μm, and the treated water pump is adjusted at a flow rate (flow rate) of 3.0 m ³ / h. The membrane was continuously processed. The treated water obtained after the membrane treatment was introduced into the treated water tank. With the circulation valve 32 closed and the discharge valve 31 opened, the treated water was continuously fed by the treated water pump and discharged to the outside of the water treatment apparatus as discharged water. Backwashing was performed at each stage where the differential pressure increase exceeded 5 kPa. Furthermore, the sodium hypochlorite solution washing | cleaning was performed once per day.
In normal operation, the differential pressure of the ultrafiltration membrane was continuously measured, and the maximum value of the differential pressure and the minimum value of the differential pressure were measured. The obtained results are shown in Table 1 below.
In the normal operation of Comparative Example 1, the maximum value of the differential pressure of the ultrafiltration membrane increased to about 41 kPa.

[Example 1]
<Normal operation>
In the same manner as in Comparative Example 1, normal operation was performed at a flow rate (flow rate) of 3.0 m ³ / h until the maximum value of the differential pressure of the ultrafiltration membrane reached about 41 kPa.

<Differential pressure reduction method for membrane module>
When the maximum value of the differential pressure of the ultrafiltration membrane rises to about 41 kPa, the treated water valve 33 is closed, the inflow of treated water is stopped, the discharge valve 31 is closed, and the circulation valve 32 is opened. Water is circulated as circulating water 3, and sodium hypochlorite solution is added as chemical 4 from chemical addition means 14 to circulating water 3 to a predetermined concentration, and the water to be treated is adjusted to 3.0 m. Forward washing was performed by continuously filtering and circulating at a flow rate (flow rate) of ³ / h for 30 minutes.
The flow rate was measured with an electromagnetic flow meter installed on the downstream side.
The flux was calculated by dividing the flow rate per day by the membrane area, and is shown in Table 1 below.

<Normal operation after differential pressure reduction method for membrane module>
Thereafter, the water to be treated 33 is opened to resume the inflow of water to be treated, the circulation valve 32 is closed and the discharge valve 31 is opened to return to the normal operation at a flow rate (flow velocity) of 3.0 m ³ / h. Backwashing was performed at each stage where the differential pressure increase exceeded 5 kPa. Furthermore, the sodium hypochlorite solution washing | cleaning was performed once per day.
In the normal operation after the method for reducing the differential pressure of the membrane module, the differential pressure of the ultrafiltration membrane was continuously measured, and the maximum value of the differential pressure and the minimum value of the differential pressure were measured. The obtained results are shown in Table 1 below.

[Example 2]
In Example 1, except that the flow rate (flow velocity) of the circulating water in the method for reducing the differential pressure of the membrane module was doubled from 3.0 m ³ / h to 6.0 m ³ / h, the same as in Example 1, A method for reducing the differential pressure of the membrane module was performed.
Then, it returns to normal operation similarly to Example 1, and in the normal operation after the method for reducing the differential pressure of the membrane module, the differential pressure of the ultrafiltration membrane is continuously measured, and the maximum differential pressure of the ultrafiltration membrane is measured. The minimum value and differential pressure were measured. The obtained results are shown in Table 1 below.

From Table 1 above, according to the method for reducing the differential pressure of the membrane module of the present invention, the filtration membrane can be washed in order by circulating the drug, and the membrane module can be washed more than regular backwashing and chemical washing during normal operation. It was found that the differential pressure can be recovered.
In Example 1, the maximum value of the differential pressure in only normal operation can be lowered from 41 kPa to 38 kPa and the minimum value of the differential pressure can be lowered from 37 kPa to 34 kPa by the method for reducing the pressure difference of the membrane module for about 30 minutes following the normal operation. I understood it.
In Example 2, the maximum value of the differential pressure in only normal operation can be lowered from 41 kPa to 37 kPa and the minimum value of the differential pressure can be lowered from 37 kPa to 33 kPa by the method for reducing the pressure difference of the membrane module for about 30 minutes following the normal operation. I understood it.
When Examples 1 and 2 were compared, the change in the recovery amount of the differential pressure due to the change in the flow rate (flow velocity) of the membrane module was not so large. This is because sodium hypochlorite contributes to the decomposition of organic matter, but the organic matter concentration CODMn of the treated water used in Examples 1 and 2 was as low as 20 mg / L.
Furthermore, by adding the chemical to the treated water and circulating it, the time to shift from the normal operation to the method for reducing the pressure difference of the membrane module is very short, so that the treated water is not wasted, the amount of drainage can be suppressed, and the chemical is wasted. It was found that it can be reused for 30 minutes of chemical cleaning.
In Comparative Example 1 and Examples 1 and 2, when the normal operation was performed until the maximum value of the differential pressure reached 50 kPa, the method for reducing the differential pressure of the membrane module was also started. And the trend of the results of 2 was not different.
In Comparative Example 1 and Examples 1 and 2, when the water treatment apparatus shown in FIG. 2 was used instead of the water treatment apparatus shown in FIG. 1, the results of Comparative Example 1, Examples 1 and 2 were also obtained. It was the same as the trend.
In Comparative Example 1, when the method for reducing the differential pressure of the membrane module is performed in the same manner as in Example 1 except that the chemical is not added to the circulating water from the chemical addition means, there is no effect of reducing the differential pressure, and the filter membrane is not effective. The problem of clogging arises.

[Comparative Example 101]
In Comparative Example 1, normal operation is performed until the maximum value of the differential pressure reaches about 52 kPa (including backwashing at each stage where the differential pressure increase exceeds 5 kPa and washing with sodium hypochlorite solution once a day) A normal operation was performed in the same manner as in Comparative Example 1 except that the above operation was continued.
In normal operation, the differential pressure of the ultrafiltration membrane was continuously measured, and the maximum value of the differential pressure and the minimum value of the differential pressure were measured. The obtained results are shown in Table 2 below.

[Example 101]
<Normal operation>
In the same manner as in Comparative Example 101, normal operation was performed at a flow rate (flow rate) of 3.0 m ³ / h until the maximum value of the differential pressure of the ultrafiltration membrane reached about 52 kPa.

<Differential pressure reduction method for membrane module>
When the maximum value of the differential pressure of the ultrafiltration membrane rises to about 52 kPa, the treated water valve 33 is closed, the inflow of treated water is stopped, the discharge valve 31 is closed, and the circulation valve 32 is opened. Water is circulated as circulating water 3, and a sulfuric acid solution is added as drug 4 from the drug addition means 14 to the circulating water 3 to a predetermined concentration, and the water to be treated is adjusted to 3.0 m ³ / h. Normal washing was performed by continuously filtering and circulating at a flow rate (flow rate) for 30 minutes.

<Normal operation after differential pressure reduction method for membrane module>
Thereafter, the water to be treated 33 is opened to resume the inflow of water to be treated, the circulation valve 32 is closed and the discharge valve 31 is opened to return to the normal operation at a flow rate (flow velocity) of 3.0 m ³ / h. Backwashing was performed at each stage where the differential pressure increase exceeded 5 kPa. Furthermore, the sodium hypochlorite solution washing | cleaning was performed once per day.
In the normal operation after the method for reducing the differential pressure of the membrane module, the differential pressure of the ultrafiltration membrane was continuously measured, and the maximum value of the differential pressure and the minimum value of the differential pressure were measured. The obtained results are shown in Table 2 below.

[Example 102]
In Example 101, except that the flow rate (flow velocity) of circulating water in the method for reducing the differential pressure of the membrane module was doubled from 3.0 m ³ / h to 6.0 m ³ / h, the same as in Example 101, A method for reducing the differential pressure of the membrane module was performed.
Thereafter, the normal operation is restored in the same manner as in Example 101, and in the normal operation after the method for reducing the differential pressure of the membrane module, the differential pressure of the ultrafiltration membrane is continuously measured, and the maximum differential pressure of the ultrafiltration membrane is measured. The minimum value and differential pressure were measured. The obtained results are shown in Table 2 below.

From Table 2 above, according to the method for reducing the differential pressure of the membrane module of the present invention, the filtration membrane can be washed in order by circulating the drug, and the membrane module can be washed more than the regular backwash and the drug wash during normal operation. It was found that the differential pressure can be recovered.
In Example 101, the maximum value of the differential pressure only in the normal operation can be lowered from 52 kPa to 38 kPa and the minimum value of the differential pressure can be lowered from 43 kPa to 34 kPa by the method for reducing the differential pressure of the membrane module for about 30 minutes following the normal operation. I understood it.
In Example 102, the maximum value of the differential pressure in normal operation alone can be reduced from 52 kPa to 33 kPa and the minimum value of the differential pressure can be decreased from 43 kPa to 31 kPa by the method for reducing the differential pressure of the membrane module for about 30 minutes following the normal operation. I understood it.
Comparing Examples 101 and 102, it was found that the differential pressure of the ultrafiltration membrane was further reduced by about 5 kPa due to the fact that the flow rate (flow rate) of the membrane module was doubled. In normal operation, aggregated flocs are formed by using a sulfuric acid band (aluminum sulfate) on the water to be treated as a pretreatment, and in Examples 101 and 102, aluminum components ( It adheres to the surface of the negatively charged filth and is covered with a positive charge. In the case of comparing the examples 101 and 102 using sulfuric acid in the method for reducing the differential pressure of the membrane module, dirt is more likely to fall from the surface of the membrane module. Therefore, the flow rate of the membrane module is higher than that in the case of comparing the examples 1 and 2. The effect of increasing the (flow velocity) by 2 times becomes remarkable.
Furthermore, by adding the chemical to the treated water and circulating it, the time to shift from the normal operation to the method for reducing the pressure difference of the membrane module is very short, so that the treated water is not wasted, the amount of drainage can be suppressed, and the chemical is wasted. It was found that it can be reused for 30 minutes of chemical cleaning.

1 treated water 2 treated water 3 circulating water 4 chemical 5 discharged water 11 treated water tank 12 membrane module 13 treated water tank 14 chemical adding means 21 treated water pump 22 treated water pump 23 circulating water pump 31 discharge valve 32 circulating Valve 33 Water valve to be treated 41 Circulating flow path 42 Branching portion

Claims (13)

A method for reducing the differential pressure of a membrane module comprising at least one filtration membrane of a microfiltration membrane and an ultrafiltration membrane,
With a circulation channel connecting at least one of the channels on the downstream side of the membrane module to the upstream side of the membrane module,
A method for reducing the differential pressure of a membrane module, wherein circulating water containing a chemical is passed through the filtration membrane and the circulation channel from the upstream side to the downstream side of the filtration membrane to wash the membrane module.   The method for reducing a differential pressure of a membrane module according to claim 1, wherein the chemical is an acid, an alkali, or a cleaning agent. The flow path on the downstream side of the membrane module includes a branch part,
The method for reducing a differential pressure of a membrane module according to claim 1 or 2, further comprising a step of switching a flow path downstream of the membrane module from a flow path other than the circulation flow path to the circulation flow path. Normal operation in which treated water is passed through a membrane module having at least one of a microfiltration membrane and an ultrafiltration membrane to obtain treated water, and the membrane module is regularly backwashed and / or chemically washed. When;
The water treatment method including the differential pressure | voltage reduction method of the membrane module as described in any one of Claims 1-3. The flow path on the downstream side of the membrane module includes a branch part,
In the normal operation, the channel on the downstream side of the membrane module is a channel other than the circulation channel,
5. A step of switching a flow path on the downstream side of the membrane module from a flow path other than the circulation flow path to the circulation flow path after the normal operation and before the method for reducing the differential pressure of the membrane module. The water treatment method as described in any one of.   The flux when the circulating water is passed through the membrane module is 1.2 to 10.0 times the flux when the treated water is passed through the membrane module. Water treatment method.   The water treatment method according to any one of claims 4 to 6, wherein the treated water obtained in the normal operation is used as the circulating water. A membrane module comprising at least one of a microfiltration membrane and an ultrafiltration membrane that obtains treated water by passing the treated water;
A pump for water to be treated which sends the water to be treated to the membrane module;
Including a branch portion located in a flow path on the downstream side of the membrane module,
At least one of the outlets of the branch part can discharge the treated water,
At least one of the outlets of the branching section can be connected to a circulation channel upstream of the membrane module to circulate circulating water,
A water treatment apparatus comprising means for adding a chemical to the circulating water.   The water treatment apparatus of Claim 8 provided with the pump for treated water which sends the said treated water upstream of the said branch part.   The water treatment apparatus of Claim 8 or 9 provided with the to-be-treated water tank which can store the said to-be-treated water.   The water treatment apparatus according to any one of claims 8 to 10, comprising a treated water tank capable of storing the treated water.   The water treatment apparatus according to any one of claims 8 to 11, wherein the branch portion is a three-way valve.   The water treatment apparatus according to any one of claims 8 to 11, wherein an outlet of the branch portion on a side connected to the circulation flow path includes a circulating water pump.

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