JP2020006332A - Water treatment apparatus and water treatment method - Google Patents

Abstract

To provide a water treatment apparatus capable of performing control to enhance a flux without irreversible clogging of a filtration membrane in the case of using water to be treated of which the quality fluctuates with time.SOLUTION: A water treatment apparatus 41 includes: water quality measuring means 11 for measuring the COD of water to be treated 2 of which the quality fluctuates with time; coagulation treatment means 13 for adding a coagulant to the water to be treated 2 downstream of the water quality measuring means 11 to obtain coagulation-treated water 3; a filtration membrane 22 for subjecting the coagulation-treated water 3 to membrane filtration to obtain treated water 4; and flux controlling means 14 for controlling a flux of the filtration membrane 22 based on the COD value measured by the water quality measuring means 11. The filtration membrane 22 is a microfiltration membrane or an ultrafiltration membrane. A water treatment method uses the water treatment apparatus.SELECTED DRAWING: Figure 1

Description

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

  Water treatment for purifying water using a reverse osmosis membrane (RO membrane) is generally increasing. Specifically, it is used for desalination of seawater, production of drinking water, makeup water for cooling towers, production of process water, pretreatment of boiler feedwater, and the like. Here, in the case of using organic matter-containing wastewater, it is known to perform biological treatment or membrane treatment with an ultrafiltration membrane (UF membrane) as pretreatment of water treatment using a reverse osmosis membrane (Patent Document 1 and 2).

  Patent Literature 1 discloses a coagulation separation step of adding a coagulant to raw water containing an organic substance and performing coagulation separation to obtain coagulation separation treatment water, a filtration treatment step of filtering coagulation separation treatment water to obtain filtration treatment water, In a method for producing a reverse osmosis membrane permeated water comprising a reverse osmosis membrane separation step of separating filtered water into a reverse osmosis membrane permeated water and a reverse osmosis membrane concentrated water by a reverse osmosis membrane, the coagulation separation step is performed at a pH of 3 to 6. A method for producing reverse osmosis permeated water in an acidic region is described.

  Patent Document 2 discloses a biological treatment means for biologically treating organic wastewater, a filtration device into which at least a part of biologically treated water from the biological treatment means is introduced, and a reverse osmosis membrane separation device into which filtered water from the filtration device is introduced. And a return means for returning at least one of the backwash wastewater of the filtration device, the chemical wash wastewater of the filtration device, and the concentrated water of the reverse osmosis membrane separation device to the raw water introduction side of the biological treatment means. An organic waste water recovery treatment device having a coagulation treatment means for solid-liquid separation after coagulation treatment of at least a part of water returned to the raw water introduction side of the biological treatment means by the return means, and a solid-liquid separation means Also, there is described an organic wastewater recovery treatment apparatus in which treated water of a solid-liquid separation means is supplied to a biological treatment means.

JP 2013-244468 A JP 2013-08983 A

  Here, it is known that, since the water quality of the general wastewater of a pulp and paper mill fluctuates with time, clogging of a filtration membrane occurs in generally assumed pretreatment, and the pretreatment becomes unstable (Patent Reference 1).

When treated water whose water quality fluctuates with time, when the flux (flux) or the amount of filtered water is controlled to be constant, stable operation (filtration) is performed for the treated water with low COD (chemical oxygen demand). This is a safe operation in which the membrane is irreversibly blocked, but there is a problem that the amount of recovered water is reduced. At this time, there is a problem that the filtration membrane is irreversibly blocked for wastewater having a high COD.
However, Patent Documents 1 and 2 do not describe a method for solving these problems. In particular, [0013] of Patent Document 2 describes that the problem of the film flux cannot be solved by the pretreatment by the aggregation treatment.

  The problem to be solved by the present invention is to provide a water treatment apparatus that can control so as to increase the flux without causing irreversible clogging of a filtration membrane when using water to be treated whose water quality fluctuates with time. It is.

  In the present invention, by measuring the COD of the water to be treated whose water quality fluctuates with time, and controlling the flux of the filtration membrane based on the value of the measured COD, when the water to be treated whose water quality fluctuates with time is used. The inventors have found that the flux can be controlled to be high without causing irreversible clogging of the filtration membrane, and the above-mentioned problem has been solved.

The configuration of the present invention, which is a specific means for solving the above problems, and a preferred configuration of the present invention will be described below.
[1] Water quality measuring means for measuring the COD of the water to be treated whose quality varies with time,
Coagulation treatment means to obtain coagulation treatment water by adding a coagulant to the water to be treated downstream of the water quality measurement means,
A filtration membrane that obtains treated water by membrane filtration of the coagulation treated water,
A flux control unit that controls the flux of the filtration membrane based on the value of COD measured by the water quality measurement unit,
A water treatment device, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.
[2] The water treatment apparatus according to [1], further including a pH adjusting unit for adjusting the pH of the water to be treated to 5 to 7 between the water quality measuring unit and the aggregation treatment unit.
[3] The water treatment apparatus according to [1] or [2], wherein the coagulant is an inorganic coagulant.
[4] The water treatment apparatus according to any one of [1] to [3], further comprising a backwashing unit for backwashing the filtration membrane.
[5] When the value of COD measured by the water quality measurement means is 200 mg / L or less, the flux satisfies the following formula 1,
When the value of COD measured by the water quality measurement means exceeds 200 mg / L, the flux control means is controlled so that the flux becomes 0.28 ± 0.05 m / day. Any one of [1] to [4] A water treatment apparatus according to item 1.
Equation 1
−0.0045 × COD + 1.08 ≦ flux ≦ −0.0039 × COD + 1.08
(In the formula 1, the unit of COD is mg / L, and the unit of flux is m / day.)
[6] The water treatment apparatus according to any one of [1] to [5], wherein the flux control means is a water supply pump that supplies the coagulated water from the primary side of the filtration membrane.
[7] A coagulant addition amount control unit that controls the coagulant addition amount based on the COD value measured by the water quality measurement unit,
When the value of COD measured by the water quality measurement means is 200 mg / L or less, the amount of the coagulant added satisfies the following formula 2,
When the value of COD measured by the water quality measurement means exceeds 200 mg / L, the control means for controlling the addition amount of the flocculant is controlled so that the addition amount of the flocculant becomes 100 ± 10 mg / L [1] to [6]. The water treatment apparatus according to any one of the above.
Equation 2
0.4 × COD ≦ addition amount of flocculant ≦ 0.6 × COD
(In Formula 2, the unit of COD is mg / L, and the unit of the amount of the coagulant added is mg / L.)
[8] a fungicide addition amount control means for controlling the fungicide addition amount based on the COD value measured by the water quality measurement means,
When the value of COD measured by the water quality measuring means is 200 mg / L or less, the amount of the fungicide added satisfies the following formula 3,
When the value of COD measured by the water quality measuring means exceeds 200 mg / L, the controlling means for controlling the amount of fungicide to be added is controlled so that the amount of fungicide to be added is 200 ± 10 mg / L [1] to [7]. The water treatment apparatus according to any one of the above.
Equation 3
0.9 × COD ≦ addition amount of fungicide ≦ 1.1 × COD
(In Formula 3, the unit of COD is mg / L, and the unit of the amount of the fungicide added is mg / L.)
[9] a disinfectant addition amount control means for controlling the disinfectant addition amount based on the COD value measured by the water quality measurement means,
The flocculant addition amount control means is a flocculant pump,
The water treatment apparatus according to [7] or [8], wherein the disinfectant addition amount control means is a disinfectant pump.
[10] A biological treatment tank is provided upstream of the water quality measuring means, and
The water treatment apparatus according to any one of [1] to [9], wherein the water to be treated is obtained by biologically treating at least one of wastewater from a pulp and paper mill and wastewater from a cardboard factory.
[11] The water treatment apparatus according to any one of [1] to [10], further including a solid-liquid separation unit between the aggregation treatment unit and the filtration membrane.
[12] The water treatment apparatus according to any one of [1] to [11], wherein the COD of the water to be treated fluctuates with time including at least a range of 200 mg / L or less.
[13] a water quality measuring step of measuring the COD of the water to be treated whose water quality fluctuates with time;
A coagulation treatment step of adding a coagulant to the water to be treated downstream of the water quality measurement step to obtain coagulation treatment water,
A membrane filtration step of subjecting the coagulated water to membrane filtration with a filtration membrane to obtain treated water;
Comprising a flux control step of controlling the flux of the filtration membrane based on the value of COD measured in the water quality measurement step,
A water treatment method, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.

  ADVANTAGE OF THE INVENTION According to this invention, when using the to-be-processed water whose water quality fluctuates with time, the water treatment apparatus which can be controlled so that flux may be increased without causing irreversible clogging of a filtration membrane can be provided.

FIG. 1 is a flowchart of an example of a water treatment method using the water treatment device of the present invention. FIG. 2 is a flowchart of another example of the water treatment method using the water treatment device of the present invention. FIG. 3 is a flowchart of another example of the water treatment method using the water treatment device of the present invention.

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

[Water treatment equipment]
The water treatment apparatus of the present invention comprises a water quality measuring means for measuring the COD of the water to be treated whose water quality fluctuates with time, and a coagulation treatment means for adding a coagulant to the water to be treated downstream of the water quality measuring means to obtain coagulated water. And a filtration membrane for obtaining treated water by membrane filtration of the coagulated water, and a flux control means for controlling the flux of the filtration membrane based on the value of COD measured by the water quality measurement means, wherein the filtration membrane is a microfiltration membrane or It is an ultrafiltration membrane.
ADVANTAGE OF THE INVENTION According to this invention, when using the to-be-processed water whose water quality fluctuates with time, it can control (preferably automatic control) to raise a flux without causing irreversible blockage of a filtration membrane. As a result, the water treatment device of the present invention can continue stable operation for a long time. Further, according to the present invention, wastewater can be used for industrial water for factories, and the cost of purchasing industrial water at factories can be reduced.
Hereinafter, preferred embodiments of the water treatment apparatus of the present invention will be described.

<Overall configuration of water treatment device>
Preferred embodiments of the overall configuration of the water treatment apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart of an example of a water treatment method using the water treatment device of the present invention.
The water treatment apparatus 41 shown in FIG. 1 includes a water quality measuring unit 11 for measuring the COD of the water 2 to be treated, and a coagulant added to the water 2 to be treated downstream of the water quality measuring unit 11 to obtain the coagulated water 3. Coagulation treatment means 13, filtration membrane 22 for subjecting coagulation treatment water 3 to membrane filtration to obtain treatment water 4, and flux control means 14 for controlling the flux of filtration membrane 22 based on the value of COD measured by water quality measurement means 11. Is provided. In the water treatment apparatus 41 shown in FIG. 1, the coagulation treatment means 13 is arranged so that a coagulant can be added to the water 2 to be treated in the coagulation stirring tank 21.

FIG. 2 is a flowchart of another example of the water treatment method using the water treatment device of the present invention. The water treatment device 41 shown in FIG. 2 is a more preferable embodiment of the water treatment device shown in FIG. In addition to the water treatment device shown in FIG. 1, the water treatment device 41 shown in FIG. 2 includes a coagulant addition amount control unit 13a and a bactericide addition amount control unit 13b as coagulation treatment units.
In the water treatment apparatus 41 shown in FIG. 2, a pH adjustment unit 12 is provided between the water quality measurement unit 11 and the coagulation treatment unit 13. The pH adjusting means 12 is arranged so that an acid or an alkali can be added to the water 2 to be treated in the coagulation stirring tank 21.
The water treatment apparatus 41 shown in FIG. 2 includes the back washing means 15 for back washing the filtration membrane 22. The reverse cleaning means 15 is arranged so that the cleaning fluid 6 or gas (not shown) can be passed from the secondary side to the primary side of the filtration membrane 22.

FIG. 3 is a flowchart of another example of the water treatment method using the water treatment device of the present invention. The water treatment device 41 shown in FIG. 3 is a more preferable embodiment of the water treatment device shown in FIG.
The water treatment device 41 shown in FIG. 3 includes a biological treatment tank 24 upstream of the water quality measurement unit 11. It is preferable that the biological treatment tank 24 can biologically treat the raw water 1 that is the wastewater from the factory 51 to obtain the water 2 to be treated. In addition, only a part of the biologically treated water from the biological treatment tank 24 may be used as the water to be treated 2, and the remaining biologically treated water may be discharged to sewage or the like (not shown).
The water treatment apparatus 41 shown in FIG. 3 includes a reverse osmosis membrane 23 that obtains permeated water 5 by subjecting treated water 4 to reverse osmosis membrane treatment. It is preferable that the permeated water 5 be supplied to, for example, a factory 51 as service water.
Hereinafter, preferred embodiments of each part constituting the water treatment apparatus of the present invention will be described.

<Raw water>
Raw water used in the water treatment apparatus is not particularly limited, and various types of wastewater such as sewage and factory wastewater can be used as the raw water. It is preferable to use raw water whose COD varies with time. It is more preferable to use raw water that has a COD that fluctuates with time and contains a hardly decomposable organic substance that is difficult to treat biologically. Examples of the hardly decomposable organic substance include an organic substance containing phosphoric acid. Examples of such wastewater include wastewater from a paper mill. Wastewater from paper mills contains hardly decomposable organic matter, the amount of chemicals used increases and decreases due to brand changes during the papermaking process, and the organic matter in the wastewater is recycled because the wastewater is reused and circulated in the system. As a result, water quality fluctuates over time. Of the wastewater from a paper mill, the wastewater from a pulp and paper mill and the wastewater from a cardboard factory are used as raw water. Examples of the wastewater from the pulp and paper mill include general wastewater from pulp and paper and white water (filtrate generated in the dewatering step of the pulp manufacturing process). It is particularly preferable to use white water. As the white water, water having a COD of 200 mg / L or more can be preferably used.
The pH of the raw water is preferably from 5.0 to 7.0, and more preferably from 5.0 to 6.0.
It is preferable to use, as the water to be treated, water which has been appropriately pretreated as needed with respect to the raw water. Biological treatment can be mentioned as pretreatment.

<Biological treatment tank>
The water treatment apparatus of the present invention preferably includes a biological treatment tank from the viewpoint of obtaining the water to be treated in which the COD of the raw water is reduced. Although the position of the biological treatment tank is not particularly limited, a biological treatment tank is preferably provided upstream of the coagulation treatment means, and more preferably a biological treatment tank is provided upstream of the water quality measurement means. The biological treatment tank is not particularly limited, but is preferably provided with at least an aeration tank and capable of performing activated sludge treatment. When raw water whose COD fluctuates with time is biologically treated, naturally biologically treated water whose COD fluctuates with time can be obtained.

<Water to be treated>
In the water treatment apparatus of the present invention, treated water whose water quality fluctuates with time is used. In the present invention, the water to be treated is preferably obtained by biologically treating at least one of wastewater from a pulp and paper mill and wastewater from a cardboard factory.
COD in the present specification is preferably COD _Mn (chemical oxygen demand by potassium permanganate). The value of COD _Mn in the present specification is a value determined in accordance with JIS K 0102: 2013 “Oxygen consumption by potassium permanganate at 100 ° C. (COD _Mn )”. However, COD depending on the type of other oxidizing agent such as COD _Cr (chemical oxygen demand by potassium dichromate) may be used.
The water to be treated preferably has COD _Mn (chemical oxygen demand by potassium permanganate) of 10 to 300 mg / L, more preferably 30 to 200 mg / L, and 50 to 200 mg / L. Is particularly preferred. In the present invention, the COD _{Mn of the} water to be treated preferably fluctuates with time including at least a range of 200 mg / L or less, and more preferably fluctuates with time including at least a range of 50 to 200 mg / L.
In the present invention, the water to be treated may contain a hardly decomposable organic substance. The water to be treated preferably has a phosphoric acid concentration of 0.1 to 100 mg / L, more preferably 0.1 to 50 mg / L, and particularly preferably 0.1 to 10 mg / L.
Further, in the present invention, the water to be treated may contain calcium at a high concentration. The water to be treated preferably has a calcium concentration of 0.1 to 1000 mg / L, more preferably 0.1 to 500 mg / L, and particularly preferably 0.1 to 100 mg / L.

<Water quality measurement means>
The water treatment apparatus of the present invention includes a water quality measurement unit that measures the COD of the water to be treated. There is no particular limitation on the water quality measuring means, and a known COD meter or UV meter (ultraviolet absorbance meter) can be used. It is known that the absorbance of the water to be treated and the COD in the water to be treated, which are measured by a UV meter, have a high correlation. Therefore, the correlation data of both is obtained in advance, and the treatment is performed based on the correlation data of both. The COD in the water to be treated can be obtained from the absorbance of the water. Correlation data between absorbance and COD may be stored in an arbitrary control unit, and the COD in the water to be treated may be obtained by comparing the absorbance obtained by the control unit with the correlation data between the two.
The water quality measuring means may include means for transmitting the measured COD value to the flux control means. The water quality measuring means may further include a means for transmitting the measured COD value to the flocculant addition amount control means and the bactericide addition amount control means. Examples of these transmitting means include an electromagnetic wave transmitting means, and the measured COD value can be transmitted to the electromagnetic wave receiving means of each portion via a wire or wirelessly. Thus, it is possible to automatically control, for example, increasing the flux without causing irreversible blockage of the filtration membrane.
On the other hand, the water quality measuring means may have means for transmitting the measured COD value to the control unit. The control unit includes a storage unit, a calculation unit, and the like, and can perform predetermined functions by executing a computer program stored in the storage unit. It is preferable that the control unit controls the flux control unit, the coagulant addition amount control unit, and the disinfectant addition amount control unit to be in an appropriate state.
The water quality measuring means may not include a flux control means, a flocculant addition amount control means, a disinfectant addition amount control means, or a means for transmitting the measured COD value to the control unit. In this case, the water quality measuring means is provided with a means for displaying the value of the COD measured, and based on the display of the measured COD value, the flux controlling means, the adding quantity controlling means for the flocculant and the adding quantity controlling means for the disinfectant are provided. May be controlled by an administrator.

<PH adjustment means>
The water treatment device preferably includes a pH adjusting unit. The position of the pH adjusting means is not particularly limited, but it is preferable to provide a pH adjusting means between the water quality measuring means and the coagulation treatment means. Although a pH adjusting unit may be provided downstream of the aggregating unit, it is preferable that no pH adjusting unit is provided downstream of the aggregating unit. In particular, it is preferable not to add an alkali downstream of the aggregation treatment means from the viewpoint of preventing scale from being generated by the addition of the alkali. In particular, when the raw water contains a large amount of hardness (calcium), it is preferable to prevent calcium scale from being generated by adding an alkali.
In the pH adjusting means, the pH of the water to be treated is preferably adjusted to 5.0 to 7.0, more preferably to 5.0 to 6.0.
In the case where the pH of the raw water is 5.0 to 6.0 and the pH of the raw water is within the coagulation range of the inorganic coagulant, the pH adjusting means may not be provided.

<Aggregation treatment means>
The water treatment apparatus of the present invention includes a coagulation treatment means for obtaining a coagulation treatment water by adding a coagulant to water to be treated downstream of the water quality measurement means. It is preferable to form flocs in the obtained coagulated water by the coagulation treatment means.
Examples of the flocculant include an inorganic flocculant and a polymer flocculant. Examples of the inorganic coagulant include aluminum sulfate (sulfuric acid band), polyaluminum chloride (PAC), ferric chloride, ferrous sulfate, polyiron sulfate, and polysilica iron. Among these, a sulfate band and PAC are preferable, and PAC is more preferable. Examples of the polymer flocculant include an amphoteric polymer flocculant, a nonionic polymer flocculant, an anionic polymer flocculant, and a cationic polymer flocculant. In the present invention, the coagulant is preferably an inorganic coagulant.

In the present invention, the coagulation treatment means may include a disinfectant addition means for adding a disinfectant to the water to be treated downstream of the water quality measurement means. The order in which the disinfectant adding means and the flocculant adding means are installed is not particularly limited, and any one may be provided first, and the disinfectant and the flocculant may be added substantially simultaneously.
The fungicide is not particularly limited, and includes an oxidizing agent, a slime control agent, and an alkali agent.
Examples of the oxidizing agent include a chlorine-based oxidizing agent, a bromine-based oxidizing agent, and ozone. In particular, by sterilizing the water to be treated with a chlorine-based oxidizing agent, it is possible to suppress biofouling on the membrane surface of the filtration membrane (and / or the reverse osmosis membrane). This is preferable from the viewpoint of suppressing the frequency of chemical cleaning. However, an optimum bactericide can be selected according to the conditions of the water treatment.
Examples of the chlorine-based oxidizing agent include chlorine dioxide, hypochlorous acid, and sodium hypochlorite, and sodium hypochlorite is more preferable.

(Means for controlling the amount of coagulant added)
The water treatment apparatus of the present invention preferably includes a coagulant addition amount control unit that controls the coagulant addition amount based on the COD value measured by the water quality measurement unit. In particular, it is preferable to control the amount of the flocculant to be added so that a floc having a particle diameter capable of removing the floc by the filtration membrane can be formed without using a solid-liquid separation means other than the filtration membrane.
In the present invention, when the COD value measured by the water quality measuring means is 200 mg / L or less, the amount of the coagulant added satisfies the following formula 2, and the COD value measured by the water quality measuring means exceeds 200 mg / L. It is preferable to control the means for controlling the amount of coagulant added so that the amount of coagulant added is 100 ± 10 mg / L.
Equation 2
0.4 × COD ≦ addition amount of flocculant ≦ 0.6 × COD
(In Formula 2, the unit of COD is mg / L, and the unit of the amount of the coagulant added is mg / L.)
In particular, when the COD value measured by the water quality measurement means is 200 mg / L or less, the amount of the coagulant added satisfies the following formula 2A, and when the COD value measured by the water quality measurement means exceeds 200 mg / L, the coagulation is performed. It is more preferable to control the coagulant addition amount control means so that the addition amount of the agent is 100 ± 5 mg / L.
Equation 2A
0.45 × COD ≦ the amount of coagulant added ≦ 0.55 × COD
(In Formula 2A, the unit of COD is mg / L, and the unit of the amount of the coagulant added is mg / L.)
As other control methods, for example, when the COD is less than 120 mg / L, when the COD is 120 to 150 mg / L, when the COD is 150 to 180 mg / L, and when the The addition amount of the coagulant may be determined in advance, and the addition amount of the coagulant may be automatically or manually controlled based on the COD value measured by the water quality measuring means.
In the present invention, the coagulant addition amount control means is preferably a coagulant pump, and may be a coagulant pump capable of automatically controlling the coagulant addition amount based on the COD value measured by the water quality measurement means. More preferred.

(Means for controlling the amount of fungicide added)
The water treatment apparatus of the present invention preferably includes a disinfectant addition amount control unit that controls the disinfectant addition amount based on the COD value measured by the water quality measurement unit. In particular, it is preferable to control the addition amount of the bactericide so that biofouling of the filtration membrane can be suppressed without using a solid-liquid separation means other than the filtration membrane.
In the present invention, when the COD value measured by the water quality measuring means is 200 mg / L or less, the amount of the fungicide added satisfies the following formula 3, and when the COD value measured by the water quality measuring means exceeds 200 mg / L. It is preferable to control the disinfectant addition amount control means so that the disinfectant addition amount is 200 ± 10 mg / L.
Equation 3
0.9 × COD ≦ addition amount of fungicide ≦ 1.1 × COD
(In Formula 3, the unit of COD is mg / L, and the unit of the amount of the fungicide added is mg / L.)
In particular, when the COD value measured by the water quality measuring means is 200 mg / L or less, the amount of the fungicide added satisfies the following formula 3A, and when the COD value measured by the water quality measuring means exceeds 200 mg / L, sterilization is performed. It is more preferable to control the disinfectant addition amount control means so that the addition amount of the agent is 200 ± 5 mg / L.
Equation 3A
0.95 × COD ≦ addition amount of fungicide ≦ 1.05 × COD
(In Formula 3A, the unit of COD is mg / L, and the unit of the amount of the fungicide added is mg / L.)
As other control methods, for example, when the COD is less than 120 mg / L, when the COD is 120 to 150 mg / L, when the COD is 150 to 180 mg / L, and when the The value of the amount of the disinfectant may be determined in advance, and the amount of the disinfectant may be automatically or manually controlled based on the COD value measured by the water quality measuring means.
In the present invention, the disinfectant addition amount control means is preferably a disinfectant pump, and may be a disinfectant pump capable of automatically controlling the disinfectant addition amount based on the COD value measured by the water quality measuring means. More preferred.

<Filtration membrane>
The water treatment apparatus of the present invention includes a filtration membrane that obtains treated water by membrane-filtrating coagulated treated water. In the present invention, the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.
The opening diameter of the microfiltration membrane is not particularly limited, and is preferably 0.1 to 0.5 μm, and more preferably 0.1 to 0.2 μm. The opening diameter of the ultrafiltration membrane is not particularly limited, but is preferably 0.01 to 0.05 μm, and more preferably 0.01 to 0.02 μm.
The shape of the filtration membrane is not particularly limited, and examples thereof include a hollow fiber membrane, a spiral membrane, a pleated membrane, and a flat membrane. Preferably, the filtration membrane is a hollow fiber membrane.

<Flux control means>
The water treatment apparatus of the present invention includes a flux control unit that controls the flux of the filtration membrane based on the value of COD measured by the water quality measurement unit.
In the present invention, when the COD value measured by the water quality measuring means is 200 mg / L or less, the flux satisfies the following formula 1, and when the COD value measured by the water quality measuring means exceeds 200 mg / L, the flux is 0. It is preferable to control the flux control means so as to be .28 ± 0.05 m / day.
Equation 1
−0.0045 × COD + 1.08 ≦ flux ≦ −0.0039 × COD + 1.08
(In the formula 1, the unit of COD is mg / L, and the unit of flux is m / day.)
In particular, when the COD value measured by the water quality measurement means is 200 mg / L or less, the flux satisfies the following formula 1A. When the COD value measured by the water quality measurement means exceeds 200 mg / L, the flux is 0.28 / L. It is more preferable to control the flux control means so as to be ± 0.02 m / day.
Formula 1A
−0.0041 × COD + 1.08 ≦ flux ≦ −0.0039 × COD + 1.08
(In Formula 1A, the unit of COD is mg / L, and the unit of flux is m / day.)
As other control methods, for example, when the COD is less than 120 mg / L, when the COD is 120 to 150 mg / L, when the COD is 150 to 180 mg / L, and when the The value of the flux may be determined, and the flux of the filtration membrane may be automatically or manually controlled based on the value of the COD measured by the water quality measuring means.
In the present invention, the flux control means is preferably a water supply pump that supplies coagulated water from the primary side of the filtration membrane, and a water supply pump that can automatically control the flux based on the value of COD measured by the water quality measurement means. More preferably, there is.

<Backwashing means>
It is preferable that the water treatment apparatus of the present invention includes a backwashing unit for backwashing the filtration membrane. For the reverse cleaning, air, a cleaning fluid, or the like can be used, and it is preferable to use a cleaning fluid.

<Chemical cleaning>
The water treatment apparatus of the present invention preferably has means for performing CIP (cleaning-in-place cleaning) cleaning using a chemical. In the CIP cleaning using a chemical, it is preferable to stop the water treatment and circulate the chemical in the system of the water treatment apparatus.
The chemical used for the CIP cleaning using the chemical is preferably an acid, an alkali, or a cleaning agent. When the water to be treated contains a large amount of minerals, acids are preferred. Examples of the acid include hydrochloric acid, sulfuric acid, nitric acid, citric acid, oxalic acid, and EDTA. When the water to be treated contains a large amount of organic substances, it is preferably alkali. Further, the chemical is preferably a cleaning agent having resistance to the ultrafiltration membrane. Examples of the detergent having resistance to an alkali or an ultrafiltration membrane include hypochlorous acid or a salt thereof, sodium hydroxide, hydrogen peroxide, and the like, and sodium hypochlorite is preferable.

<Treatment water>
The treated water that has passed through the filtration membrane can be supplied to the reverse osmosis membrane as it is because suspended solids (SS) are sufficiently removed.

<Reverse osmosis membrane>
It is preferable that the water treatment apparatus includes a reverse osmosis membrane capable of permeating treated water to obtain permeated water.
The opening diameter of the reverse osmosis membrane is not particularly limited, and is preferably 0.001 to 0.005 μm, and more preferably 0.001 to 0.002 μm.
The material of the reverse osmosis membrane is not particularly limited, and for example, a polyamide membrane or the like can be used.

<Permeated water>
The treated water can be subjected to reverse osmosis membrane treatment, recovered as permeated water (also referred to as recovered water), and reused. For example, wastewater from a factory can be collected as permeated water having a quality similar to that of industrial water, and can be reused as service water (industrial water). The permeated water can be reused as sterile water.

<Other devices>
The water treatment device may include a portion having another function.
Further, the water treatment apparatus may be provided with a solid-liquid separation means such as a settling tank, a floating tank, and a centrifugal separator between the biological treatment tank and the filtration membrane. In particular, an embodiment in which a solid-liquid separation means is provided between the aggregation treatment means and the filtration membrane can be mentioned. However, since the water treatment apparatus of the present invention can be continuously operated without a solid-liquid separation means upstream of the filtration membrane, the cost can be reduced by not providing the solid-liquid separation means between the biological treatment tank and the filtration membrane. It is preferable from the viewpoint of doing. In particular, it is more preferable that no solid-liquid separation means is provided between the aggregation treatment means and the filtration membrane. By performing solid-liquid separation in the membrane filtration step, the equipment scale can be reduced. In addition, since the flocculant can be used in the solid-liquid separation means as a subsequent stage of the flocculation treatment means, the possibility of leakage due to excessive use is reduced, or depending on the type of the flocculant, adsorption of the flocculent floc to the separation membrane is performed. In order to reduce the possibility of separation membrane contamination or filtration performance deterioration due to the promotion, it is preferable not to provide a solid-liquid separation means.
Further, when the polymer flocculant is not used in the solid-liquid separation means, no leak occurs due to excessive addition of the polymer flocculant, and the polymer flocculant does not adhere to the filtration membrane and irreversible blocking does not occur.

[Water treatment method]
The water treatment method of the present invention comprises a water quality measurement step of measuring the COD of the water to be treated whose water quality fluctuates with time, and a coagulation treatment step of adding a coagulant to the water to be treated downstream of the water quality measurement step to obtain coagulated water. And a membrane filtration step of obtaining treated water by membrane filtration of the coagulation-treated water with a filtration membrane, and a flux control step of controlling the flux of the filtration membrane based on the COD value measured in the water quality measurement step. It is a microfiltration membrane or an ultrafiltration membrane.
The preferred embodiment of the water treatment method of the present invention is the same as the preferred embodiment of the water treatment apparatus of the present invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Materials, usage amounts, ratios, processing contents, processing procedures, and the like shown in the following examples can be appropriately changed 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 described below.

[Example 1]
Using the water treatment apparatus shown in FIG. 3, the following water treatment was performed using wastewater from a paper mill (white water from a pulp and paper mill) as raw water. The pH of the raw water was 5.0 to 6.0.
First, the raw water 1 from the factory 51 was subjected to activated sludge treatment in the biological treatment tank 24, and the obtained biologically treated water was used as the water 2 to be treated. When the COD _Mn of the water 2 to be treated was measured by the water quality measuring means 11 including a COD meter, the COD _Mn concentration was 78 to 200 mg / L. In addition, since the water 2 to be treated had a phosphoric acid concentration of 5 to 20 mg / L, it was considered that the raw water and the water to be treated contained a hardly decomposable organic substance that was difficult to biologically treat. The water 2 to be treated had a calcium concentration of 100 to 500 mg / L.

The water to be treated 2 is introduced into the coagulation and stirring tank 21, and sodium hydroxide is added as a pH adjuster from the pH adjusting means 12 to automatically adjust the pH in the coagulation and stirring tank 21 to 6.0 to 6.5. did. Further, for the coagulation and stirring tank 21, the coagulation treatment means 13 including the coagulant pump having the coagulant addition amount control means 13a and the bactericide pump having the bactericide addition amount control means 13b are used. The agent was added.
PAC was used as an inorganic flocculant. The addition amount of the coagulant was controlled according to the value of COD _Mn (mg / L) measured by the COD meter, and the addition amount (mg / L) of the coagulant was determined by the following conversion formula. PAC used a stock solution concentration of 10% by mass.
Equation 2B
Amount of coagulant added = 0.5 × COD _Mn
Sodium hypochlorite was used as a bactericide. Control of the amount of the fungicide was performed in accordance with the value of COD _Mn (mg / L) measured by the COD meter, and the amount of the fungicide added (mg / L) was determined by the following conversion formula. Sodium hypochlorite used was a stock solution having a concentration of 12% by mass.
Equation 3B
Disinfectant addition = 1.0 x COD _Mn

The coagulation treatment water 3 was supplied from the coagulation stirring tank 21 to the primary side of the filtration membrane 22 by the flux control means 14 comprising a water pump, and the treatment water 4 was obtained by membrane filtration.
In the membrane filtration, an ultrafiltration membrane, OJI-MENBRANE (registered trademark) was used as the filtration membrane 22, and the membrane was treated with a previously set flux. The control of the flux of the filtration membrane 22 is performed according to the value of COD _Mn (mg / L) measured by the COD meter, and the flux (unit is the amount of filtered water per day per 1 m ^{2 of} membrane area) m ³ / (m ² · day), that is, m ³ / day), that is, m / day) was determined.
Equation 1B
Flux = −0.004 × COD _Mn + 1.08

  Up to the membrane filtration process under the above conditions, backwashing using a cleaning fluid (processed water 4 stored in a process water tank, not shown) once per 10 minutes, and hypochlorous acid twice per day Chemical cleaning using a sodium solution was performed. As a result, the ultrafiltration membrane was able to maintain the differential pressure of the filtration membrane at 40 to 60 kPa immediately after the backwash for about half a year.

[Example 2]
White water from a pulp and paper mill different from that in Example 1 (different chemicals in the paper making process for producing paper of another brand) was used as raw water. The pH of the raw water was 5.0 to 6.0.
Activated sludge treatment was performed on the raw water 1 from the factory 51 in the biological treatment tank 24, and the obtained biologically treated water was used as the water to be treated 2. When the COD _Mn of the water 2 to be treated was measured by the water quality measuring means 11 including a COD meter, the COD _Mn concentration always fluctuated within a range exceeding 200 mg / L. In addition, since the water 2 to be treated had a phosphoric acid concentration of 5 to 20 mg / L, it was considered that the raw water and the water to be treated contained a hardly decomposable organic substance that was difficult to biologically treat. The water 2 to be treated had a calcium concentration of 100 to 500 mg / L.
Using this water to be treated, water treatment was carried out in the same manner as in Example 1 except that the amount of addition of the flux, the coagulant, and the amount of the bactericide were changed as follows.
Flux = 0.28m / day
Addition amount of flocculant = 100 mg / L
Fungicide addition = 200 mg / L
The steps up to the membrane filtration step were performed under the above conditions, and one reverse washing was performed once every 10 minutes and two chemical washings using a sodium hypochlorite solution were performed per day. As a result, the ultrafiltration membrane was able to maintain the differential pressure of the filtration membrane at 40 to 60 kPa immediately after the backwash for about half a year.

[Comparative Example 1]
White water from a different pulp and paper mill from Examples 1 and 2 (different chemicals in the papermaking process to produce different brands of paper) was used as raw water. The pH of the raw water was 5.0 to 6.0.
Activated sludge treatment was performed on the raw water 1 from the factory 51 in the biological treatment tank 24, and the obtained water to be treated was used as the water to be treated 2. When the COD _Mn of the water to be treated 2 was measured by the water quality measuring means 11 including a COD meter, the COD _Mn concentration always fluctuated with time in a range including both a range of 150 to 200 mg / L and a range exceeding 200 mg / L. Was. In addition, since the water 2 to be treated had a phosphoric acid concentration of 5 to 20 mg / L, it was considered that the raw water and the water to be treated contained a hardly decomposable organic substance that was difficult to biologically treat. The water 2 to be treated had a calcium concentration of 100 to 500 mg / L.
Using this water to be treated, the same as in Example 1 except that the flux, the added amount of the flocculant and the added amount of the bactericide were determined as described below without controlling according to the value of COD _Mn of the water to be treated. To perform water treatment.
Flux = 0.5m / day
Addition amount of flocculant = 100 mg / L
Fungicide addition = 200 mg / L
Up to the membrane filtration step under the above conditions, and once backwashing for 10 minutes and twice for chemical cleaning using sodium hypochlorite solution per day were performed, but stable operation was not possible. Immediately after the washing, the differential pressure of the filtration membrane could not be maintained at 40 to 60 kPa. Thereafter, even if the frequency of the back washing and the chemical washing was further increased, the differential pressure did not recover, and water was not allowed to pass after about one month.

As described above, according to the water treatment apparatus of the present invention, it has been found that when using the water to be treated whose time fluctuates, the flux can be controlled to be high without causing irreversible blockage of the filtration membrane.
From Comparative Example 1, when the flux is set to a fixed value without being based on the value of COD measured by the water quality measuring means, irreversible blocking of the filtration membrane may be caused when the water to be treated whose water quality varies with time is used. all right.

REFERENCE SIGNS LIST 1 raw water 2 treated water 3 flocculated treated water 4 treated water 5 permeated water 6 cleaning fluid 11 water quality measuring means 12 pH adjusting means 13 flocculating processing means 13a flocculant addition amount control means 13b disinfectant addition amount control means 14 flux control Means 15 Reverse washing means 21 Coagulation stirring tank 22 Filtration membrane 23 Reverse osmosis membrane 24 Biological treatment tank 41 Water treatment device 51 Factory

Claims (13)

Water quality measuring means for measuring the COD of the water to be treated whose quality varies with time,
Coagulation treatment means to obtain coagulation treatment water by adding a coagulant to the water to be treated downstream of the water quality measurement means,
A filtration membrane to obtain treated water by membrane filtration of the coagulated water,
Flux control means for controlling the flux of the filtration membrane based on the value of COD measured by the water quality measurement means,
The water treatment device, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.   The water treatment apparatus according to claim 1, further comprising a pH adjusting unit that adjusts a pH of the water to be treated to 5 to 7 between the water quality measuring unit and the aggregation treatment unit.   The water treatment apparatus according to claim 1, wherein the coagulant is an inorganic coagulant.   The water treatment apparatus according to any one of claims 1 to 3, further comprising a backwashing unit that backwashes the filtration membrane. When the value of COD measured by the water quality measuring means is 200 mg / L or less, the flux satisfies the following formula 1,
The method according to any one of claims 1 to 4, wherein when the COD value measured by the water quality measurement means exceeds 200 mg / L, the flux control means is controlled so that the flux becomes 0.28 ± 0.05 m / day. The water treatment device according to claim 1.
Equation 1
−0.0045 × COD + 1.08 ≦ flux ≦ −0.0039 × COD + 1.08
(In the formula 1, the unit of COD is mg / L, and the unit of flux is m / day.)   The water treatment device according to any one of claims 1 to 5, wherein the flux control unit is a water supply pump that supplies the coagulated water from a primary side of the filtration membrane. The apparatus further includes a coagulant addition amount control unit that controls an addition amount of the coagulant based on a value of COD measured by the water quality measurement unit,
When the value of COD measured by the water quality measuring means is 200 mg / L or less, the amount of the coagulant added satisfies the following formula 2,
2. The method according to claim 1, wherein when the COD value measured by the water quality measurement means exceeds 200 mg / L, the addition amount control means for the coagulant is controlled so that the addition amount of the coagulant is 100 ± 10 mg / L. The water treatment device according to any one of claims 6 to 6.
Equation 2
0.4 × COD ≦ addition amount of flocculant ≦ 0.6 × COD
(In Formula 2, the unit of COD is mg / L, and the unit of the amount of the coagulant added is mg / L.) A disinfectant addition amount control unit that controls an addition amount of the disinfectant based on the value of COD measured by the water quality measurement unit,
When the value of COD measured by the water quality measuring means is 200 mg / L or less, the amount of the fungicide added satisfies the following formula 3,
2. The disinfectant addition amount control means is controlled such that when the COD value measured by the water quality measurement means exceeds 200 mg / L, the disinfectant addition amount is 200 ± 10 mg / L. The water treatment apparatus according to any one of claims 7 to 7.
Equation 3
0.9 × COD ≦ addition amount of fungicide ≦ 1.1 × COD
(In Formula 3, the unit of COD is mg / L, and the unit of the amount of the fungicide added is mg / L.) A disinfectant addition amount control unit that controls an addition amount of the disinfectant based on the value of COD measured by the water quality measurement unit,
The flocculant addition amount control means is a flocculant pump,
9. The water treatment apparatus according to claim 7, wherein the disinfectant addition amount control means is a disinfectant pump. A biological treatment tank is provided upstream of the water quality measuring means, and
The water treatment apparatus according to any one of claims 1 to 9, wherein the water to be treated is obtained by biologically treating at least one of wastewater from a pulp and paper plant and wastewater from a cardboard plant.   The water treatment apparatus according to any one of claims 1 to 10, further comprising a solid-liquid separation unit between the coagulation treatment unit and the filtration membrane.   The water treatment apparatus according to any one of claims 1 to 11, wherein the COD of the water to be treated fluctuates with time including at least a range of 200 mg / L or less. A water quality measuring step of measuring the COD of the water to be treated whose water quality fluctuates with time,
A coagulation treatment step of adding a coagulant to the water to be treated downstream of the water quality measurement step to obtain coagulation treatment water,
A membrane filtration step of subjecting the coagulated water to membrane filtration with a filtration membrane to obtain treated water;
A flux control step of controlling the flux of the filtration membrane based on the value of COD measured in the water quality measurement step,
The water treatment method, wherein the filtration membrane is a microfiltration membrane or an ultrafiltration membrane.