JP2021171689A - Water treatment method and water treatment equipment - Google Patents

Abstract

The present invention provides a water treatment method and a water treatment device that can increase the water recovery rate in water treatment in which water to be treated containing suspended solids is subjected to membrane filtration treatment. [Solution] An inorganic flocculation treatment step of adding an inorganic flocculant to treated water containing suspended solids to perform inorganic flocculation treatment, and membrane filtration of the inorganic flocculated water obtained in the inorganic flocculation treatment step using a membrane. A membrane filtration step in which permeated water is obtained through treatment, a backwashing step in which the membrane is backwashed, and a polymer flocculant is added to the backwash wastewater obtained in the backwashing step to perform polymer flocculation treatment. a solid-liquid separation step of performing a solid-liquid separation treatment on the polymer flocculated water obtained in the polymer flocculation treatment step to obtain solid-liquid separated water; and at least one of the solid-liquid separated water. A water treatment method, comprising: a return step of returning the water to a stage before the membrane filtration step. [Selection diagram] Figure 1

Description

The present invention relates to a water treatment method and a water treatment apparatus for performing a membrane filtration treatment of water to be treated containing suspended solids.

Due to the increasing demand for water in recent years, there is an increasing demand for collecting and reusing wastewater. The higher the water recovery rate from the wastewater, the more desirable it is. On the other hand, for example, as in Patent Document 1, a method of membrane-filtering and reusing the solid-liquid separated water obtained by performing the solid-liquid separation treatment may be adopted.

Japanese Unexamined Patent Publication No. 2006-314974

In the method of membrane filtration and reusing the solid-liquid separated water obtained by performing the solid-liquid separation treatment on the backwash wastewater as in Patent Document 1, the solid-liquid separation cannot be sufficiently performed and water. It may not be possible to increase the recovery rate. An object of the present invention is to provide a water treatment method and a water treatment apparatus capable of increasing the water recovery rate in water treatment for performing a membrane filtration treatment of water to be treated containing a suspended substance.

In the present invention, an inorganic coagulation treatment step of adding an inorganic coagulant to water to be treated containing a suspended substance to perform the inorganic coagulation treatment, and a membrane filtration of the inorganic coagulation water obtained in the inorganic coagulation treatment step using a film. A film filtration step of performing treatment to obtain permeated water, a backwash step of backwashing the film, and a polymer flocculant treatment by adding a polymer flocculant to the backwash wastewater obtained in the backwash step. At least one of the polymer coagulation treatment step to be performed, the solid-liquid separation step of performing the solid-liquid separation treatment on the polymer coagulation water obtained in the polymer coagulation treatment step to obtain solid-liquid separation water, and the solid-liquid separation water. It is a water treatment method including a return step of returning the portion to the previous stage of the membrane filtration step.

In the return step in the water treatment method, it is preferable to return at least a part of the solid-liquid separated water to the step before the inorganic agglomeration treatment step or the inorganic agglomeration treatment step.

In the water treatment method, it is preferable to control the amount of the inorganic coagulant added in the inorganic coagulation treatment step based on the return flow rate of the solid-liquid separated water returned in the return step.

In the water treatment method, the polymer flocculant is preferably a nonionic polymer flocculant or a weak anionic polymer flocculant.

In the present invention, an inorganic aggregating treatment means for performing an inorganic aggregating treatment by adding an inorganic aggregating agent to water to be treated containing a suspended substance, and a membrane filtration of the inorganic agglomerating water obtained by the inorganic aggregating treatment means using a film. A polymer flocculant treatment is performed by adding a polymer flocculant to the membrane filtration means for performing treatment to obtain permeated water, the backwash means for backwashing the film, and the backwash wastewater obtained by the backwash means. At least one of the polymer coagulation treatment means to be performed, the solid-liquid separation means for obtaining solid-liquid separation water by performing a solid-liquid separation treatment on the polymer coagulation water obtained by the polymer coagulation treatment means, and the solid-liquid separation water. It is a water treatment apparatus including a return means for returning the unit to the previous stage of the membrane filtration means.

In the water treatment apparatus, it is preferable that the return means returns at least a part of the solid-liquid separated water to the inorganic agglomeration treatment means or the preceding stage of the inorganic agglomeration treatment means.

It is preferable that the water treatment apparatus further includes a control means for controlling the amount of the inorganic aggregating agent added to the inorganic aggregating treatment means based on the return flow rate of the solid-liquid separated water returned by the returning means.

In the water treatment apparatus, the polymer flocculant is preferably a nonionic polymer flocculant or a weak anionic polymer flocculant.

In the present invention, an inorganic aggregating treatment means for performing an inorganic aggregating treatment by adding an inorganic aggregating agent to water to be treated containing a suspended substance, and a membrane filtration of the inorganic agglomerating water obtained by the inorganic aggregating treatment means using a film. A method of modifying a treatment device including a membrane filtration means for performing treatment to obtain permeated water and a backwash means for backwashing the film, wherein the backwash wastewater obtained by the backwash means is made of a polymer. Solid-liquid separation to obtain solid-liquid separation water by performing solid-liquid separation treatment on the polymer-aggregated water obtained by the polymer-aggregating treatment means and the polymer-aggregating treatment means for performing the polymer-aggregating treatment by adding a flocculant. This is a method of modifying a processing apparatus, which comprises means and a return means for returning at least a part of the solid-liquid separated water to a stage before the membrane filtration means.

In the present invention, an inorganic aggregating treatment means for performing an inorganic aggregating treatment by adding an inorganic aggregating agent to water to be treated containing a suspended substance, and a membrane filtration of the inorganic agglomerating water obtained by the inorganic aggregating treatment means using a film. A water recovery device for recovering water from a treatment device including a membrane filtration means for performing treatment to obtain permeated water and a backwash means for backwashing the film, which was obtained by the backwash means. Solid-liquid separation is performed by solid-liquid separation treatment on the polymer coagulation treatment means that performs the polymer coagulation treatment by adding a polymer coagulant to the backwash wastewater and the polymer coagulation water obtained by the polymer coagulation treatment means. A water recovery device including a solid-liquid separating means for obtaining water and a returning means for returning at least a part of the solid-liquid separated water to a stage before the membrane filtration means.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a water treatment method and a water treatment apparatus capable of increasing the water recovery rate in water treatment for performing a membrane filtration treatment of water to be treated containing a suspended substance.

It is a schematic block diagram which shows an example of the water treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows the water treatment apparatus used in the comparative example 1. FIG.

Embodiments of the present invention will be described below. The present embodiment is an example of carrying out the present invention, and the present invention is not limited to the present embodiment.

<Water treatment equipment and water treatment method>
An outline of an example of the water treatment apparatus according to the embodiment of the present invention is shown in FIG. 1, and the configuration thereof will be described.

The water treatment apparatus 1 shown in FIG. 1 is obtained by an inorganic aggregating tank 12 and an inorganic aggregating treatment means as an inorganic aggregating treatment means for performing an inorganic aggregating treatment by adding an inorganic aggregating agent to water to be treated containing a suspended substance. A membrane filtration device 14 is used as a membrane filtration means for obtaining permeated water by performing a membrane filtration treatment on the inorganic aggregated water using a membrane, and a treated water tank 16 and a backwash means are used as a backwash means for backwashing the membrane. As the polymer coagulation treatment means for performing the polymer coagulation treatment by adding the polymer coagulant to the obtained backwash wastewater, the polymer coagulation tank 20 and the polymer coagulation water obtained by the polymer coagulation treatment means are solidified. A solid-liquid separation device 22 is provided as a solid-liquid separation means for obtaining solid-liquid separated water by performing a liquid separation treatment. The water treatment device 1 may include a water tank 10 to be treated for storing water to be treated and a backwash drainage tank 18 for storing backwash wastewater. The water treatment device 1 is a device that repeats an inorganic coagulation treatment, a membrane filtration treatment, and a backwash.

In the water treatment device 1 of FIG. 1, a pipe 36 is connected to the water inlet of the water tank 10 to be treated. The outlet of the water tank 10 to be treated and the inlet of the inorganic coagulation tank 12 are connected by a pipe 38 via a pump 24. The outlet of the inorganic coagulation tank 12 and the inlet on the primary side of the membrane filtration device 14 are connected by a pipe 40 via a pump 26. The permeation water outlet on the secondary side of the membrane filtration device 14 and the inlet of the treatment water tank 16 are connected by a pipe 42. A pipe 44 is connected to the treated water outlet of the membrane filtration device 14. The backwash water outlet of the treatment water tank 16 and the middle of the pipe 42 are connected by a pipe 46 via a pump 28. The backwash drainage outlet on the primary side of the membrane filtration device 14 and the inlet of the backwash drainage tank 18 are connected by a pipe 48. The outlet of the backwash drainage tank 18 and the inlet of the polymer coagulation tank 20 are connected by a pipe 50 via a pump 30. The outlet of the polymer coagulation tank 20 and the inlet of the solid-liquid separation device 22 are connected by a pipe 52. A pipe 54 is connected to the scum outlet of the solid-liquid separation device 22, and a pipe 56 is connected to the solid-liquid separation water outlet. The middle of the pipe 56 and the solid-liquid separated water inlet of the water tank 10 to be treated are connected by a pipe 58 which is a return means for returning at least a part of the solid-liquid separated water to the previous stage of the membrane filtration means. An inorganic coagulant addition pipe 60 is connected to the inlet of the inorganic coagulant tank 12 as an inorganic coagulant addition means. A polymer coagulant addition pipe 62 is connected to the polymer coagulant inlet of the polymer coagulant tank 20 as a means for adding the polymer coagulant. In the inorganic coagulation tank 12 and the polymer coagulation tank 20, stirring devices 32 and 34 are installed as stirring means having a rotation driving means such as a motor and stirring blades, respectively.

The water treatment method and the operation of the water treatment device 1 according to the present embodiment will be described.

The water to be treated containing suspended solids is stored in the water tank 10 to be treated as needed through the pipe 36, and then sent to the inorganic coagulation tank 12 through the pipe 38 by the pump 24. In the inorganic coagulation tank 12, the inorganic coagulant is added through the inorganic coagulant addition pipe 60 to perform the inorganic coagulation treatment (inorganic coagulation treatment step). The liquid in the inorganic coagulation tank 12 may be agitated by the agitator 32.

The inorganic agglomerated water obtained in the inorganic agglomeration treatment step is sent to the primary side of the membrane filtration device 14 through the pipe 40 by the pump 26. In the membrane filtration device 14, the inorganic aggregated water is subjected to a membrane filtration treatment using a membrane to obtain permeated water (membrane filtration step). The permeated water obtained by the membrane filtration treatment is sent from the secondary side of the membrane filtration device 14 to the treatment water tank 16 through the pipe 42 and stored. A part of the permeated water is discharged as treated water through the pipe 44, and is recovered by further performing reverse osmosis membrane treatment, ultraviolet (UV) irradiation treatment, activated carbon treatment, etc., if necessary.

As the membrane filtration process progresses, suspended solids and the like may accumulate on the surface of the membrane of the membrane filtration device 14, and filtration resistance may occur. When it becomes necessary to wash the membrane of the membrane filtration device 14, the membrane is backwashed. At least a part of the permeated water is introduced from the secondary side of the membrane filtration device 14 through the pipe 46 and the pipe 42 by the pump 28 as backwash water, and is discharged from the primary side to perform the backwash of the membrane (the membrane is backwashed). Backwash process). In this case, the treatment water tank 16, the pump 28, the pipe 46, and the pipe 42 function as backwashing means. The backwash drainage obtained in the backwash step is sent from the primary side of the membrane filtration device 14 to the backwash drainage tank 18 through the pipe 48, and is stored as needed. The backwashing step is performed, for example, on a regular basis, for example, once every 20 to 30 minutes to 2 to 3 hours. After the backwashing step is completed, the process may return to the inorganic coagulation treatment step and the membrane filtration step.

The backwash drainage obtained in the backwash step is sent to the polymer coagulation tank 20 through the pipe 50 by the pump 30. In the polymer coagulation tank 20, the polymer coagulant is added through the polymer coagulant addition pipe 62 to perform the polymer coagulation treatment (polymer coagulation treatment step). The liquid in the polymer coagulation tank 20 may be agitated by the agitator 34.

The polymer-aggregated water obtained in the polymer-aggregating treatment step is sent to the solid-liquid separator 22 through the pipe 52. In the solid-liquid separation device 22, solid-liquid separation treatment such as pressure flotation is performed on the polymer agglomerated water to obtain solid-liquid separated water (solid-liquid separation step). The scum obtained by the solid-liquid separation treatment is discharged through the pipe 54. The solid-liquid separated water obtained by the solid-liquid separation treatment is discharged through the pipe 56.

At least a part of the solid-liquid separated water is returned through the pipe 58 to, for example, the water tank 10 to be treated, which is the front stage of the membrane filtration device 14 (return step). At least a part of the solid-liquid separated water may be returned to the pre-stage of the membrane filtration device 14 (membrane filtration step), may be returned to the inorganic coagulation tank 12 (inorganic coagulation treatment step), or may be returned to the pipe 38 or the pipe. It may be returned to 40. As the return means, it is preferable to return at least a part of the solid-liquid separated water to the inorganic coagulation tank 12 or the previous stage of the inorganic coagulation tank 12. That is, in the return step, it is preferable that at least a part of the solid-liquid separated water is returned to the inorganic coagulation tank 12 or the previous stage of the inorganic coagulation tank 12.

The present inventors added a polymer flocculant to the backwash drainage of the membrane filtration apparatus 14, performed a polymer flocculant treatment, and partially or wholly separated the solid-liquid separated water by solid-liquid separation by precipitation, pressure levitation, or the like. It was found that the water recovery rate can be increased in the water treatment for performing the membrane filtration treatment of the water to be treated containing the suspended substance by returning the material to the pre-stage of the membrane filtration apparatus 14 (membrane filtration step).

By adding a polymer flocculant to the backwash wastewater, performing a polymer flocculation treatment, and separating the solids and liquids, the concentration ratio of the solid content can be increased, so that sludge can be discharged at a high concentration. The amount of water discharged to the outside of the system can be reduced, and the water recovery rate can be increased. Further, when a coagulant is added to the backwash wastewater to perform a solid-liquid separation treatment and the solid-liquid separated water is subjected to a membrane treatment again, if a polymer coagulant is used as the coagulant, it remains in the solid-liquid separated water. The polymer flocculant may block the membrane. A method of adding sand filtration after the solid-liquid separation is conceivable, but the equipment becomes large. In the present embodiment, the solid-liquid separated liquid portion (solid-liquid separated water) is further returned to the previous stage of the inorganic coagulation tank 12 (inorganic coagulation treatment step) or the inorganic coagulation tank 12 (inorganic coagulation treatment step) and is returned again. By adding the inorganic flocculant, the polymer flocculant remaining in the solid-liquid separated water is aggregated by the inorganic flocculant, and while suppressing the blockage of the film by the polymer flocculant remaining in the solid-liquid separated water, Clear water can be recovered and the water recovery rate can be further increased. Compared with the case where the inorganic coagulation treatment is performed and the membrane filtration is further performed without returning to the previous stage of the inorganic coagulation tank 12 (inorganic coagulation treatment step) or the inorganic coagulation tank 12 (inorganic coagulation treatment step), a further inorganic coagulation tank is formed. It becomes unnecessary.

According to the water treatment method and the water treatment apparatus according to the present embodiment, the water recovery rate can be increased to, for example, 95% or more, preferably 99% or more.

The inorganic agglutination treatment means and the polymer agglutination treatment means may be any as long as they carry out an agglutination reaction. A known configuration may be used.

The inorganic aggregating agent may be any inorganic aggregating agent that can be used for the inorganic aggregating treatment, and is not particularly limited. Examples of the inorganic flocculant include iron-based inorganic flocculants such as ferric chloride and polyferric sulfate, and aluminum-based inorganic flocculants such as aluminum sulfate and polyaluminum chloride (PAC). The type of inorganic flocculant to be used may be selected, for example, according to the properties of the water to be treated.

The amount of the inorganic flocculant added varies depending on the concentration of suspended solids in the water to be treated, the amount of the polymer flocculant added in the subsequent stage, and the like, but is preferably in the range of, for example, 5 to 200 mg / L. It is in the range of 5 to 50 mg / L.

In the water treatment method and the water treatment apparatus according to the present embodiment, it is preferable to control the amount of the inorganic coagulant added in the inorganic coagulation treatment step based on the return flow rate of the solid-liquid separated water returned in the return step. Thereby, the blockage of the membrane in the membrane filtration device 14 can be further suppressed. For example, a control device is provided as a control means for controlling the amount of the inorganic flocculant added based on the return flow rate of the solid-liquid separated water to be returned, and a return flow rate measuring means such as a flow meter is installed in the pipe 58 or the like to control the control device. And a flow meter, a pump that adjusts the amount of the inorganic flocculant added, etc. are connected by electrical connection, etc., and the control device controls the pump, etc. based on the return flow rate measured by the flow meter, and is inorganic. The amount of the flocculant added may be controlled.

The polymer flocculant may be any organic polymer flocculant that can be used for the polymer flocculation treatment, and is not particularly limited. The polymer flocculant is not particularly limited, such as a nonionic polymer flocculant, an anionic polymer flocculant, or a cationic polymer flocculant, but for example, polyacrylamide, sodium polyacrylate, acrylamide, and the like. Acrylate copolymers, sodium acrylamide propane sulfonate, chitosan, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, polyamidine and the like can be mentioned. The polymer flocculant may be used alone or in combination of two or more. The type of polymer flocculant to be used may be selected, for example, according to the properties of the water to be treated.

The water treatment method and the water treatment apparatus according to the present embodiment have high nonionic properties as a polymer flocculant, in which clogging of opaque membranes such as microfiltration membranes (MF membranes) and ultrafiltration membranes (UF membranes) is likely to occur. It is suitably applied when a molecular flocculant or an anionic polymer flocculant, particularly a nonionic polymer flocculant or a weak anionic polymer flocculant is used.

In the present specification, the nonionic polymer flocculant has a colloid equivalence value (charge amount of the colloidal substance contained in the flocculant) in the range of −1.0 meq / g or more and less than +1.0 meq / g. The weak anionic polymer flocculant has a colloid equivalence value of -2.0 meq / g or more and less than -1.0 meq / g, and the medium anionic polymer flocculant has a colloid equivalence value of -3. The range is .5 meq / g or more and less than -2.0 meq / g, the colloid equivalence value of the strong anionic polymer flocculant is less than -3.5 meq / g, and the cationic polymer flocculant is The colloid equivalence value is +1.0 meq / g or more. The colloid equivalent value can be measured by a method such as titration.

The amount of the polymer flocculant added varies depending on the concentration of suspended solids in the backwash wastewater, but is, for example, in the range of 0.5 to 5 mg / L, preferably in the range of 1 to 2 mg / L.

The pH may be adjusted by using a pH adjuster in the inorganic aggregation treatment step and the polymer aggregation treatment step. Examples of the pH adjuster include acids such as hydrochloric acid and sulfuric acid, and alkalis such as sodium hydroxide. The pH may be adjusted, for example, in the range of 4 to 11. The pH is measured, for example, by a pH meter, which is a pH measuring means installed in the inorganic coagulation tank 12 and the polymer coagulation tank 20.

The liquid temperature in the inorganic coagulation treatment and the polymer coagulation treatment is not particularly limited, and is, for example, in the range of 15 to 35 ° C. Since the separability changes depending on the viscosity and the like, it is desirable to adjust the liquid temperature so that it is as constant as possible.

As the membrane of the membrane filtration device 14, a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), or other opaque membrane can be used.

Examples of the solid-liquid separation device 22 include pressure flotation treatment, precipitation separation, and the like. The precipitation separation is not particularly limited, and examples thereof include a natural precipitation treatment using a precipitation tank, a sludge blanket type precipitation tank, and the like. Pressurized flotation treatment is preferable because the installation area is small.

The water to be treated is water containing suspended solids, etc., and is not particularly limited, but for example, river water, lake water, groundwater, urine, sewage, industrial wastewater such as semiconductor factory wastewater, etc. Can be mentioned. In addition, the water to be treated may contain other inorganic substances, ions and the like. The water treatment method and water treatment apparatus according to the present embodiment are applied to equipment that uses treated water obtained by treating water to be treated (for example, industrial wastewater such as semiconductor factory wastewater) as primary pure water. You can also do it.

The concentration of suspended solids in the water to be treated is, for example, in the range of 10 to 10000 mg / L. The concentration of suspended solids in the resulting treated water is, for example, in the range of 0.1 to 10 mg / L.

<How to modify the processing device>
The treatment apparatus including the inorganic agglomeration treatment means, the membrane filtration means, and the backwashing means may be modified to form the above water treatment apparatus.

The method for modifying the treatment apparatus according to the present embodiment is an inorganic coagulation treatment means for performing an inorganic coagulation treatment by adding an inorganic coagulant to the water to be treated containing a suspended substance, and an inorganic coagulation water obtained by the inorganic coagulation treatment means. This is a modification method of a treatment device including a membrane filtration means for obtaining permeated water by performing a membrane filtration treatment using a membrane and a backwash means for backwashing the membrane, and the reverse washing means obtained by the backwashing means. A polymer coagulation treatment means for performing a polymer coagulation treatment by adding a polymer flocculant to the washing water and a solid-liquid separation treatment for the polymer coagulation water obtained by the polymer coagulation treatment means are performed to obtain solid-liquid separation water. This is a method of modifying a processing apparatus, which is provided with a solid-liquid separating means for obtaining and a returning means for returning at least a part of the solid-liquid separated water to a stage before the membrane filtration means. As the return means, it is preferable to return at least a part of the solid-liquid separated water to the inorganic agglomeration treatment means or the stage before the inorganic agglomeration treatment means.

For example, as shown in FIG. 1, a film is formed on an inorganic aggregating tank 12 in which an inorganic aggregating agent is added to water to be treated containing a suspended substance to perform an inorganic aggregating treatment, and an inorganic aggregating water obtained in the inorganic aggregating tank 12. A treatment device including a membrane filtration device 14 for obtaining permeated water by performing a membrane filtration treatment using the treatment water tank 16, a pump 28, a pipe 46, a pipe 42, etc., which is a backwashing means for backwashing the membrane. Solid-liquid separation treatment is performed on the polymer coagulation tank 20 and the polymer coagulation water obtained in the polymer coagulation tank 20 in which the polymer coagulant is added to the backwash wastewater obtained by the backwash means to perform the polymer coagulation treatment. The treatment device may be modified by providing a solid-liquid separation device 22 for obtaining solid-liquid separation water, a pipe 58 or the like as a return means for returning at least a part of the solid-liquid separation water to the front stage of the membrane filtration device 14. As the return means, it is preferable to return at least a part of the solid-liquid separated water to the inorganic coagulation tank 12 or the previous stage of the inorganic coagulation tank 12.

<Water recovery device>
A water recovery device may be added to the treatment device including the inorganic agglomeration treatment means, the membrane filtration means, and the backwashing means to form the above water treatment device.

The water recovery device according to the present embodiment is a film for the inorganic agglomeration treatment means for performing the inorganic agglomeration treatment by adding an inorganic aggregating agent to the water to be treated containing a suspended substance, and the inorganic agglomeration water obtained by the inorganic agglomeration treatment means. A water recovery device for recovering water from a treatment device including a membrane filtration means for obtaining permeated water by performing a membrane filtration treatment using the water, and a backwash means for backwashing the membrane. A polymer coagulation treatment means for performing a polymer coagulation treatment by adding a polymer flocculant to the obtained backwash wastewater, and a solid-liquid separation treatment for the polymer agglomerated water obtained by the polymer coagulation treatment means to solidify. It is provided with a solid-liquid separation means for obtaining the liquid-separated water and a return means for returning at least a part of the solid-liquid separated water to the previous stage of the membrane filtration means. As the return means, it is preferable to return at least a part of the solid-liquid separated water to the inorganic agglomeration treatment means or the stage before the inorganic agglomeration treatment means.

For example, as shown in FIG. 1, the water recovery device includes an inorganic aggregating tank 12 in which an inorganic aggregating agent is added to water to be treated containing a suspended substance to perform an inorganic aggregating treatment, and an inorganic aggregating tank 12 obtained in the inorganic aggregating tank 12. A membrane filtration device 14 for obtaining permeated water by performing a membrane filtration treatment on agglomerated water using a membrane, and a treated water tank 16, a pump 28, a pipe 46, a pipe 42, etc., which are backwashing means for backwashing the membrane. A water recovery device that recovers water from the treatment device provided, and is a polymer coagulation tank 20 and a polymer coagulation tank that perform a polymer coagulation treatment by adding a polymer coagulant to the backwash wastewater obtained by the backwash means. A solid-liquid separation device 22 for obtaining solid-liquid separated water by performing a solid-liquid separation treatment on the polymer-aggregated water obtained in No. 20, and a return means for returning at least a part of the solid-liquid separated water to the previous stage of the membrane filtration device 14. A pipe 58 or the like is provided. As the return means, it is preferable to return at least a part of the solid-liquid separated water to the inorganic coagulation tank 12 or the previous stage of the inorganic coagulation tank 12.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Example 1>
Using the water treatment device shown in FIG. 1, a water flow test was conducted under the following treatment conditions. The entire amount of the solid-liquid separated water (pressurized floating treated water) obtained by the solid-liquid separation treatment was returned to the water tank to be treated. The concentration of suspended solids in the obtained treated water was 1 mg / L. The water recovery rate was about 99%.

[Processing conditions]
Water to be treated: Secondary treated sewage water (suspended solid concentration = 20 mg / L)
Inorganic flocculant: ferric chloride Inorganic flocculant addition amount: 100 mg / L
Water flow rate to be treated: 460 L / h
Decontamination Membrane: UNV-3003 (Asahi Kasei, UF Membrane)
Backwash frequency: Once every 28 minutes Backwash water amount: 18 L / min for 30 seconds Backwash drainage amount: 42 L / h
Polymer flocculant: Orfflock ON-1H (manufactured by Organo, nonionic polymer flocculant, colloid equivalence value is about -1.0 meq / g)
Amount of polymer flocculant added: 2 mg / L

<Comparative example 1>
As a comparative example, the water treatment apparatus shown in FIG. 2 was used. The water treatment device 3 shown in FIG. 2 includes a water tank 100 to be treated, an inorganic coagulation tank 102, a membrane filtration device 104, a treatment water tank 106, and a backwash drainage tank 108, and the backwash drainage is drained as it is for treatment. The concentration of suspended solids in the obtained treated water was 1 mg / L. The water recovery rate was about 90%.

In this way, by re-collecting the backwash wastewater, the water recovery rate as a system could be increased.

As described above, the water recovery rate could be increased in the water treatment for performing the membrane filtration treatment of the water to be treated containing the suspended substance by the water treatment apparatus and the water treatment method of the examples.

1,3 water treatment equipment, 10,100 water treatment tank, 12,102 inorganic coagulation tank, 14,104 membrane filtration equipment, 16,106 treatment water tank, 18,108 backwash drainage tank, 20 polymer coagulation tank, 22 solids Liquid separator, 24,26,28,30 pump, 32,34 stirrer, 36,38,40,42,44,46,48,50,52,54,56,58,60,62 piping.

Claims (10)

An inorganic coagulation treatment step in which an inorganic coagulant is added to water to be treated containing suspended solids to perform an inorganic coagulation treatment.
A membrane filtration step of obtaining permeated water by performing a membrane filtration treatment on the inorganic aggregated water obtained in the inorganic agglomeration treatment step using a membrane, and
The backwashing step of backwashing the membrane and
A polymer coagulation treatment step in which a polymer flocculant is added to the backwash wastewater obtained in the backwash step to perform a polymer coagulation treatment, and a polymer coagulation treatment step.
A solid-liquid separation step of obtaining solid-liquid separated water by performing a solid-liquid separation treatment on the polymer-aggregated water obtained in the polymer agglomeration treatment step.
A return step of returning at least a part of the solid-liquid separated water to the stage prior to the membrane filtration step,
A water treatment method comprising. The water treatment method according to claim 1.
A water treatment method comprising returning at least a part of the solid-liquid separated water to the step before the inorganic agglomeration treatment step or the inorganic agglomeration treatment step in the return step. The water treatment method according to claim 2.
A water treatment method characterized in that the amount of the inorganic coagulant added in the inorganic coagulation treatment step is controlled based on the return flow rate of the solid-liquid separated water returned in the return step. The water treatment method according to any one of claims 1 to 3.
A water treatment method, wherein the polymer flocculant is a nonionic polymer flocculant or a weak anionic polymer flocculant. Inorganic coagulation treatment means for performing inorganic coagulation treatment by adding an inorganic coagulant to water to be treated containing suspended solids,
A membrane filtration means for obtaining permeated water by performing a membrane filtration treatment on the inorganic aggregated water obtained by the inorganic agglomeration treatment means using a membrane.
A backwashing means for backwashing the membrane and
A polymer coagulation treatment means for performing a polymer coagulation treatment by adding a polymer flocculant to the backwash wastewater obtained by the backwash means, and a polymer coagulation treatment means.
A solid-liquid separation means for obtaining solid-liquid separated water by performing a solid-liquid separation treatment on the polymer-aggregated water obtained by the polymer agglomeration treatment means.
A return means for returning at least a part of the solid-liquid separated water to the previous stage of the membrane filtration means, and a return means.
A water treatment device characterized by comprising. The water treatment apparatus according to claim 5.
The water treatment apparatus is characterized in that at least a part of the solid-liquid separated water is returned to the inorganic agglomeration treatment means or a pre-stage of the inorganic agglomeration treatment means. The water treatment apparatus according to claim 6.
A water treatment apparatus further comprising a control means for controlling the addition amount of the inorganic coagulant in the inorganic coagulation treatment means based on the return flow rate of the solid-liquid separated water returned by the return means. The water treatment apparatus according to any one of claims 5 to 7.
A water treatment apparatus, wherein the polymer flocculant is a nonionic polymer flocculant or a weak anionic polymer flocculant. An inorganic aggregating treatment means for performing an inorganic aggregating treatment by adding an inorganic aggregating agent to water to be treated containing a suspended solid, and a membrane filtration treatment for the inorganic agglomerating water obtained by the inorganic aggregating treatment means using a membrane. A method of modifying a processing apparatus including a membrane filtration means for obtaining permeated water and a backwash means for backwashing the film.
A polymer coagulation treatment means for performing a polymer coagulation treatment by adding a polymer flocculant to the backwash wastewater obtained by the backwash means, and a polymer coagulation treatment means.
A solid-liquid separation means for obtaining solid-liquid separated water by performing a solid-liquid separation treatment on the polymer-aggregated water obtained by the polymer agglomeration treatment means.
A return means for returning at least a part of the solid-liquid separated water to the previous stage of the membrane filtration means, and a return means.
A method of modifying a processing device, which is characterized by providing. An inorganic coagulation treatment means for performing an inorganic coagulation treatment by adding an inorganic coagulant to water to be treated containing a suspended substance, and a membrane filtration treatment for the inorganic coagulation water obtained by the inorganic coagulation treatment means using a membrane. A water recovery device that recovers water from a treatment device including a membrane filtration means for obtaining permeated water and a backwash means for backwashing the film.
A polymer coagulation treatment means for performing a polymer coagulation treatment by adding a polymer flocculant to the backwash wastewater obtained by the backwash means, and a polymer coagulation treatment means.
A solid-liquid separation means for obtaining solid-liquid separated water by performing a solid-liquid separation treatment on the polymer-aggregated water obtained by the polymer agglomeration treatment means.
A return means for returning at least a part of the solid-liquid separated water to the previous stage of the membrane filtration means, and a return means.
A water recovery device comprising.

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