JP2020039993A - Water treatment method and water treatment facility - Google Patents

Abstract

To provide a water treatment method capable of efficiently suppressing biofouling in a first membrane separation part for subjecting water to be treated to membrane separation with a reverse osmosis membrane and a second membrane separation part for subjecting concentrated water separated in the membrane separation part to membrane separation with a reverse osmosis membrane.SOLUTION: A water treatment method includes a membrane separation step of subjecting water to be treated to membrane separation in a first membrane separation part having a reverse osmosis membrane to obtain concentrated water and subjecting the concentrated water obtained in the first membrane separation part to membrane separation in a second membrane separation part having a reverse osmosis membrane, wherein the membrane separation step includes subjecting the water to be treated containing a chlorine-based oxidant and a slime control agent to the membrane separation in the first membrane separation part, and the slime control agent is at least one selected from the group consisting of 5-chloro-2-methyl-4-isothiazoline-3-one (CMIT), 2-methyl-4-isothiazoline-3-one (MIT), 2,2-dibromo-3-nitropropionamide (DBNPA), and 2-bromo-2-nitropropane-1,3-diol (bronopol).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water treatment method and a water treatment facility configured to perform the water treatment method.

  2. Description of the Related Art Conventionally, there is known a water treatment method in which a water to be treated to which a chlorine-based oxidizing agent such as sodium hypochlorite is added is subjected to membrane separation using a membrane separation unit having a reverse osmosis membrane. As this type of water treatment method, for example, a method is known in which water to be treated to which a chlorine-based oxidizing agent and a sulfamic acid compound are added is subjected to membrane separation by a reverse osmosis membrane in a membrane separation unit (Patent Document 1).

  In the water treatment method described in Patent Literature 1, a chlorine-based oxidizing agent reacts with a sulfamic acid compound to produce a stable compound in the water to be treated. Since the microorganisms can be prevented from adhering to the reverse osmosis membrane by the bactericidal action of such a compound, biofouling of the reverse osmosis membrane can be suppressed to some extent. However, the ability of the chlorine-based oxidant to suppress biofouling due to the oxidizing power of the chlorine-based oxidant is reduced by the amount consumed by the above reaction. Therefore, in the water treatment method described in Patent Literature 1, the biofouling suppressing ability inherent in the chlorine-based oxidizing agent cannot be used efficiently because the chlorine-based oxidizing agent is consumed. In addition, although the above-mentioned stable compounds have a bactericidal action, biofouling cannot always be suppressed efficiently unless the concentration is increased.

JP 2006-263510 A

  By the way, in the water treatment method, for example, concentrated water that has been subjected to membrane separation in the upstream membrane separation unit may be further subjected to membrane separation in the downstream membrane separation unit. In such a water treatment method, biofouling is more likely to occur in an upstream membrane separation unit that membrane-separates water to be treated containing a component serving as a nutrient source of microorganisms than in a downstream membrane separation unit. On the other hand, when a chlorine-based oxidizing agent and a sulfamic acid compound are added to the water to be treated as in the method described in Patent Document 1, for example, the stable compound mainly causes the upstream membrane separation section and the downstream Biofouling will be suppressed in both of the membrane separation parts on the side. As described above, the above-mentioned stable compound cannot suppress biofouling, particularly in the upstream membrane separation unit, unless inefficient such as increasing the concentration in the water to be treated. Therefore, biofouling is efficiently performed in the upstream membrane separation unit for separating the water to be treated with a reverse osmosis membrane and the downstream membrane separation unit for separating the concentrated water in the membrane separation unit with a reverse osmosis membrane. There is a need for a water treatment method that can be well controlled.

  In view of the above problems and demands, the present invention provides an upstream first membrane separation unit that performs membrane separation of water to be treated with a reverse osmosis membrane, and membrane separation of concentrated water in the membrane separation unit with a reverse osmosis membrane. It is an object of the present invention to provide a water treatment method capable of efficiently suppressing biofouling in a downstream second membrane separation section. Another object is to provide a water treatment facility configured to perform the water treatment method.

In order to solve the above-mentioned problems, a water treatment method according to the present invention is characterized in that a concentrated water obtained by membrane-separating water to be treated in a first membrane separation unit having a reverse osmosis membrane is converted into a second membrane having a reverse osmosis membrane. A membrane separation step for separating the membrane in the separation unit is provided,
The membrane separation step includes performing membrane separation of the water to be treated containing the chlorine-based oxidizing agent and the slime control agent in the first membrane separation unit,
Slime control agents include 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), 2-methyl-4-isothiazolin-3-one (MIT), 2,2-dibromo-3-nitropropionamide (DBNPA) and at least one selected from the group consisting of 2-bromo-2-nitropropane-1,3-diol (bronoball).

In the above water treatment method, in a state where the chlorine-based oxidizing agent and the slime control agent are mixed in the water to be treated, the chlorine-based oxidizing agent having a high reaction rate can oxidize microorganisms and be consumed relatively quickly. A slime control agent having a slow reaction rate requires a relatively long time to act on microorganisms and be consumed. Accordingly, the oxidizing power of the chlorine-based oxidizing agent having relatively high biofouling suppressing ability can efficiently suppress biofouling in the first membrane separation unit where biofouling is likely to occur. Further, the membrane separation in the first membrane separation unit increases the concentration of the slime control agent in the concentrated water separated in the second membrane separation unit. Even with a slime control agent having a relatively low biofouling suppression ability, the increased concentration can efficiently suppress biofouling in the second membrane separation unit.
Therefore, according to the above-mentioned water treatment method, the first membrane separation unit for separating the water to be treated with the reverse osmosis membrane, and the second membrane separation unit for separating the concentrated water of the membrane separation unit with the reverse osmosis membrane are provided. In the above, biofouling can be efficiently suppressed.

In the above water treatment method, the membrane separation step has a concentration control step of controlling the concentration of the chlorine-based oxidizing agent or the slime control agent in the water to be treated or the concentrated water,
The concentration control step may include controlling a concentration of the chlorine-based oxidizing agent in the concentrated water.
Thereby, biofouling can be efficiently suppressed while suppressing deterioration of the reverse osmosis membrane due to the oxidizing power of the chlorine-based oxidizing agent.

In the above water treatment method, the membrane separation step has a concentration control step of controlling the concentration of the chlorine-based oxidizing agent or the slime control agent in the water to be treated or the concentrated water,
The concentration control step may include controlling the concentration of the slime control agent in the water to be treated. Thereby, biofouling can be more efficiently and efficiently suppressed.

  In the above-mentioned water treatment method, the membrane separation step includes, depending on the amount of biofouling generated in the first membrane separation unit or the second membrane separation unit, a chlorine-based oxidizing agent or a slime control agent in the water to be treated or the concentrated water. It may have a density control step of controlling the density. Thereby, biofouling can be efficiently suppressed without using a chlorine-based oxidizing agent or a slime controlling agent more than necessary.

The water treatment facility of the present invention includes a first membrane separation unit having a reverse osmosis membrane and a second membrane separation unit having a reverse osmosis membrane,
Concentrated water obtained by subjecting the water to be treated containing a chlorine-based oxidizing agent and a slime control agent to membrane separation in the first membrane separation unit can be subjected to membrane separation in the second membrane separation unit,
Slime control agents include 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), 2-methyl-4-isothiazolin-3-one (MIT), 2,2-dibromo-3-nitropropionamide (DBNPA) and at least one selected from the group consisting of 2-bromo-2-nitropropane-1,3-diol (bronoball).

  The water treatment method and the water treatment equipment according to the present invention include a first membrane separation unit for separating the water to be treated with a reverse osmosis membrane, and a second membrane separation unit for separating the concentrated water of the membrane separation unit with a reverse osmosis membrane. In this case, there is an effect that biofouling can be efficiently suppressed.

The schematic diagram showing the outline of the water treatment equipment of this embodiment.

  Hereinafter, an embodiment of a water treatment facility according to the present invention will be described in detail with reference to the drawings.

For example, as shown in FIG. 1, the water treatment equipment 1 of the present embodiment includes a first upstream membrane separation unit 10 having a reverse osmosis membrane and a second downstream membrane separation unit 20 having a reverse osmosis membrane. Is provided. The water treatment equipment 1 of the present embodiment further includes a third membrane separation unit 30 disposed downstream of the second membrane separation unit 20.
The water treatment equipment 1 according to the present embodiment includes a water storage unit 4 for storing the water to be treated, a pressure pump P for pressurizing the water to be treated supplied from the water storage unit 4, and a first membrane separation unit 10 from the water storage unit 4. And a treated water supply path 8 for supplying treated water. The first membrane separation unit 10 is arranged at the most upstream side among the membrane separation units.

The water treatment equipment 1 of the present embodiment is configured to store the water to be treated in the water storage unit 4. In addition, the water to be treated stored in the water storage unit 4 is supplied to the first membrane separation unit 10 via the water supply passage 8, and the supplied water to be treated is subjected to membrane separation by the first membrane separation unit 10. Then, the first concentrated water and the first permeated water are obtained. In addition, the obtained first concentrated water is subjected to membrane separation in the second membrane separation unit 20 to obtain a second concentrated water and a second permeated water. The second concentrated water obtained by membrane separation in the second membrane separation unit 20 is further membrane-separated in the third membrane separation unit 30 on the downstream side.
In the water treatment equipment 1 of the present embodiment, microorganisms may adhere to the reverse osmosis membrane with the water treatment and clogging (biofouling) of the reverse osmosis membrane may occur.

  The water to be treated is not particularly limited, and for example, factory wastewater discharged from an electronic component manufacturing factory or the like, or seawater, industrial water, tap water, well water, river water, or the like is used.

The third concentrated water B that has passed through the first membrane separation unit 10, the second membrane separation unit 20, and the third membrane separation unit 30, for example, has its moisture evaporated and the residue is discarded. Alternatively, the third concentrated water B is discharged to, for example, sewage or mixed with other treated water and discharged to a river. Alternatively, the third concentrated water B may be reprocessed and used.
On the other hand, the permeated water A obtained in each of the first membrane separation unit 10, the second membrane separation unit 20, and the third membrane separation unit 30 is collected, for example, pure water, production water, drinking water, and industrial water. Used for applications such as washing water.

  The water storage unit 4 has a water tank to be treated. As shown in FIG. 1, the water storage unit 4 is configured to store the water to be treated inside the water tank to be treated so as to supply the water to be treated to the first membrane separation unit 10 through the water supply passage 8. Have been. The water storage unit 4 is configured to be capable of storing therein water to be treated including a chlorine-based oxidizing agent (first agent) and a slime control agent (second agent) to be described later.

The treated water supply path 8 is configured to supply treated water from the water storage unit 4 to the first membrane separation unit 10.
A pressure pump P for pressurizing the water to be treated is attached to the water supply passage 8 as shown in FIG. 1, for example. The pressurized pump P can supply pressurized water to be treated to the first membrane separation unit 10.

Each of the first membrane separation unit 10, the second membrane separation unit 20, and the third membrane separation unit 30 has a membrane unit having a reverse osmosis membrane. The membrane unit is configured so that the water to be treated supplied from the water to be treated supply path 8 is separated into concentrated water and permeated water by a reverse osmosis membrane. As the membrane unit, a conventionally known general unit is employed. In each membrane separation unit, for example, a plurality of membrane units are connected in parallel.
The reverse osmosis membrane can be degraded by a chlorine-based oxidizing agent, depending on the concentration. When the material of the reverse osmosis membrane is polyamide, it is relatively susceptible to deterioration by a chlorine-based oxidizing agent. In the water treatment equipment 1 of the present embodiment, the material of the reverse osmosis membrane may be polyamide, as described later, since the degradation of the reverse osmosis membrane due to the chlorine-based oxidizing agent can be suppressed.

The water treatment equipment 1 of the present embodiment further includes a concentration control unit 5 that controls the concentrations of the chlorine-based oxidant and the slime control agent in the water to be treated.
As shown in FIG. 1, the concentration control unit 5 includes a first chemical addition unit 51 that can add a chlorine-based oxidizing agent (first chemical) to the water to be treated before membrane separation, and a slime to the water to be treated before membrane separation. A second drug addition section 52 to which a control agent (second drug) can be added. In the water treatment equipment 1 of the present embodiment, the water to be treated including the chlorine-based oxidizing agent and the slime control agent can be supplied to the first membrane separation unit 10 by the first chemical addition unit 51 and the second chemical addition unit 52. Is configured. The water treatment equipment 1 of the present embodiment is configured to be capable of performing water treatment for membrane-separating water to be treated that does not contain any of a chlorine-based oxidizing agent and a slime control agent.

The concentration control unit 5 includes a free chlorine measurement unit 53 that measures the free chlorine concentration in the first concentrated water obtained by the first membrane separation unit 10. Then, the water treatment equipment 1 of the present embodiment, for example, when the free chlorine concentration in the first concentrated water obtained in the first membrane separation unit 10 is less than the predetermined concentration, by the first chemical addition unit 51, It is configured to increase the amount of chlorine-based oxidizing agent added.
Further, the concentration control unit 5 includes a pressure loss measuring unit 54 that measures a pressure loss of the first membrane separation unit 10. In the water treatment equipment 1 of the present embodiment, for example, clogging of the reverse osmosis membrane occurs due to microorganisms attached to the reverse osmosis membrane, and the pressure loss of the first membrane separation unit 10 measured by the pressure loss measurement unit 54 is used as a reference. When the value becomes equal to or more than the value, the first chemical addition section 51 is configured to start adding a chlorine-based oxidant to the water to be treated or increase the amount of the chlorine-based oxidant added.

  The first chemical addition unit 51 is configured to be able to add a chlorine-containing oxidant-containing liquid to the water to be treated. The first chemical adding section 51 is configured to be able to adjust the concentration of the chlorine-based oxidant in the water to be treated by changing the amount of the chlorine-based oxidant-containing liquid added. The first chemical addition unit 51 may be configured to add the chlorine-containing oxidant-containing liquid into the water tank to be treated of the water storage unit 4. In some cases, the first chemical addition unit 51 does not add the chlorine-based oxidizing agent to the water to be treated.

The chlorine-based oxidizing agent is, for example, an oxoacid salt of chlorine. The oxoacid salt of chlorine is, for example, at least one selected from the group consisting of hypochlorite, chlorite, chlorate, and perchlorate.
Examples of the hypochlorite include calcium hypochlorite (bleach), sodium hypochlorite, potassium hypochlorite, and the like. As the hypochlorite, sodium hypochlorite is preferred.

The water treatment equipment 1 according to the present embodiment uses, for example, the concentration of free chlorine in the first concentrated water obtained in the first membrane separation unit 10 as an index to determine the concentration of the chlorine-based oxidant in the water to be treated before membrane separation. May be configured to be controlled. For example, the water treatment equipment 1 according to the present embodiment includes a chlorine-based oxidizing agent added to the water to be treated so that the free chlorine concentration in the first concentrated water is in the range of 0.01 mg / L to 0.10 mg / L. May be configured to adjust the amount.
In addition, the water treatment equipment 1 of this embodiment sets the concentration of free chlorine in the first concentrated water to be 0.01 mg / L or more and 0.10 mg / L or less, preferably 0.05 mg / L or less. The amount of the chlorine-based oxidizing agent to be added may be adjusted to suppress the deterioration of the reverse osmosis membrane in the second membrane separation unit 20.

  The second chemical addition section 52 is configured to be able to add the slime control agent-containing liquid to the water to be treated. The second chemical addition section 52 is configured to adjust the concentration of the slime control agent (second chemical) in the water to be treated by changing the amount of the slime control agent-containing liquid to be added. The second chemical addition unit 52 may be configured to add the slime control agent-containing liquid into the water tank to be treated of the water storage unit 4. In some cases, the second chemical addition unit 52 does not add the slime control agent to the water to be treated.

  The slime control agent includes 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) and 2-methyl-4-isothiazolin-3-one (MIT) as thiazoline-based compounds, and organic bromine. It is at least one selected from the group consisting of 2,2-dibromo-3-nitropropionamide (DBNPA) and 2-bromo-2-nitropropane-1,3-diol (bronobol) as a system compound. .

In the water treatment equipment 1 of the present embodiment, in a state where the chlorine-based oxidizing agent and the slime control agent are mixed in the water to be treated, the chlorine-based oxidizing agent (first agent) having a high reaction rate oxidizes microorganisms. While the slime control agent (second agent) having a slow reaction rate can be consumed relatively quickly, it takes a relatively long time before it is consumed by acting on microorganisms. Since the chlorine-based oxidizing agent has oxidizing power, the ability to suppress biofouling is relatively high. Therefore, the biofouling in the first membrane separation unit 10 where biofouling easily occurs due to the oxidizing power of the chlorine-based oxidizing agent can be efficiently suppressed. In particular, when the chlorine-based oxidizing agent and the slime controlling agent are mixed, the chlorine-based oxidizing agent has higher reactivity than the slime controlling agent, and therefore, the chlorine-based oxidizing agent is preferentially used in the first membrane separation unit 10. The concentration of the chlorine-based oxidizing agent is sufficiently reduced. In addition, the concentration of the slime control agent in the first concentrated water separated by the membrane in the second membrane separation unit 20 is increased by the amount of the permeated water obtained by the membrane separation in the first membrane separation unit 10. That is, the concentration of the slime control agent is higher in the first concentrated water than in the water to be treated. Because of the increased concentration, even a slime control agent having a relatively low biofouling suppression ability can efficiently suppress biofouling in the second membrane separation unit 20. On the other hand, since the chlorine-based oxidizing agent has a sufficiently low concentration, the chlorine concentration in the first concentrated water is reduced to a concentration that does not deteriorate the membrane in the second membrane separation unit 20 and the third membrane separation unit 30. Reduced. In the first membrane separation unit 10, the oxidizing power of the chlorine-based oxidizing agent acts preferentially on sterilization, rather than on degradation of the reverse osmosis membrane, and weakens. The deterioration of the reverse osmosis membrane can be suppressed to the extent that the oxidizing power is weakened.
Therefore, in the water treatment equipment 1 of the present embodiment, the chlorine-containing oxidizing agent and the slime control agent in the reverse osmosis membrane treatment equipment are simply added to the water to be treated before passing through the reverse osmosis membrane. Biofouling can be efficiently suppressed in the first membrane separation unit 10 for separating water with a reverse osmosis membrane and the second membrane separation unit 20 for separating concentrated water in the membrane separation unit with a reverse osmosis membrane. In addition, the degradation of the reverse osmosis membrane in the first membrane separation unit 10 and the second membrane separation unit 20 can be suppressed.

  The water treatment equipment 1 of the present embodiment is configured to control the concentration of the slime control agent (second chemical) in the water to be treated before being subjected to membrane separation to 3 ppm or more and 50 ppm or less, preferably 5 ppm or more and 25 ppm or less. Is also good. The slime control agent can suppress biofouling at a concentration of usually 10 ppm or more and 50 ppm or less, preferably 15 ppm or more and 35 ppm or less, but as described above, the water to be treated is separated by the membrane separation of the first membrane separation unit 10. Since the concentration of the slime control agent in the first concentrated water and the second concentrated water is higher than that in the first concentrated water and the second concentrated water, the second membrane separation unit 20 and the third membrane separation Biofouling in the section 30 can be efficiently suppressed. As described below, the concentration of the slime control agent in the water to be treated may be controlled according to the amount of biofouling generated in the first membrane separation unit 10 or the second membrane separation unit 20.

In the water treatment equipment 1 of the present embodiment, the concentration control unit 5 includes the second membrane separation unit 20 and the second membrane separation unit 20 in order to predict the amount of biofouling generated in the second membrane separation unit 20 and the third membrane separation unit 30. The three-membrane separation unit 30 includes a reagent addition unit 55 that can add a reagent that reacts with microorganisms attached to the reverse osmosis membrane to the first concentrated water. The reagent changes into a detection substance by reacting with the microorganism.
Further, the concentration control unit 5 includes a detection substance measuring unit 56 that measures the concentration of the detection substance in the second concentrated water or the third concentrated water.
The water treatment equipment 1 of the present embodiment may be configured, for example, when the total amount of the water to be treated separated by membrane reaches a predetermined amount, when the operation time reaches a predetermined time, or when the first permeated water to the third When the conductivity of any of the permeated water exceeds the set value, the reagent is added to the first concentrated water by the reagent adding section 55, and the first concentrated water containing the reagent is subjected to membrane separation in the second membrane separation section 20. Meanwhile, the detection substance is generated by reacting the microorganism adhered to the reverse osmosis membrane with the reagent, and the concentration of the detection substance in the second concentrated water or the third concentrated water is measured by the detection substance measuring unit 56. It is configured.

  The reagent adding section 55 is configured so that a reagent-containing liquid containing a reagent can be added to the first concentrated water.

  The reagent is not particularly limited as long as it reacts with a microorganism growing in water to generate a detection substance. Examples of the reagent include a fluorescent reagent that generates a detection substance that emits fluorescence by reacting with a microorganism. As the reagent, a fluorescent reagent such as resazurin is preferable because the detection substance emits fluorescence to facilitate detection.

  Next, an embodiment of the water treatment method according to the present invention will be described.

The water treatment method of the present embodiment converts the concentrated water obtained by membrane-separating the water to be treated in the upstream first membrane separation unit 10 having the reverse osmosis membrane into the downstream second membrane having the reverse osmosis membrane. A membrane separation step for separating the membrane in the separation unit 20 is provided.
The membrane separation step includes separating the water to be treated containing the chlorine-based oxidizing agent (first agent) and the slime control agent (second agent) by the first membrane separation unit 10.
The membrane separation step may include separating the water to be treated that does not contain any of the chlorine-based oxidizing agent (first agent) and the slime control agent (second agent) by membrane.

  The water treatment method of the present embodiment can be carried out, for example, using the above-described water treatment equipment 1.

  In the water treatment method of the present embodiment, in the membrane separation step, the water to be treated including the chlorine-based oxidizing agent (first agent) and the slime control agent (second agent) is supplied to the first upstream membrane separation unit 10. Thus, membrane separation can be performed. On the other hand, in the membrane separation step, the water to be treated that does not contain a chlorine-based oxidizing agent or a slime control agent can be supplied to the first upstream membrane separation unit 10 to perform membrane separation. In the water treatment method of the present embodiment, microorganisms adhere to the reverse osmosis membrane of the first membrane separation unit 10 in particular, as the water to be treated containing neither the chlorine-based oxidizing agent nor the slime control agent is subjected to membrane separation. Thus, clogging of the reverse osmosis membrane (biofouling) may occur.

The water treatment method of the present embodiment includes a concentration control step of controlling the concentration of a chlorine-based oxidizing agent (first agent) or a slime control agent (second agent) in the water to be treated or the concentrated water (first concentrated water or the like). Prepare.
The concentration control step includes controlling the concentration of the chlorine-based oxidizing agent in the first concentrated water, or controlling the concentration of the slime controlling agent in the water to be treated.

  In the concentration control step, the concentration of the chlorine-based oxidizing agent in the first concentrated water can be controlled by changing the amount of the chlorine-based oxidizing agent added from the first chemical adding section 51 to the water to be treated. In the concentration control step, the concentration of the chlorine-based oxidizing agent in the first concentrated water is in the range of 0.01 mg / L or more and 0.10 mg / L or less, preferably 0.05 mg / L or less in terms of free chlorine concentration (that is, It is preferable to control the free chlorine concentration in one concentrated water to 0.01 mg / L or more and 0.10 mg / L or less, preferably 0.05 mg / L or less. Since the chlorine-based oxidizing agent has an oxidizing power, it has a relatively high biofouling suppressing ability, but may deteriorate the reverse osmosis membrane. Since the chlorine-based oxidizing agent is preferentially consumed to remove microorganisms attached to the membrane, a low concentration of the chlorine-based oxidizing agent rarely deteriorates the reverse osmosis membrane. Therefore, when the concentration of free chlorine is within the above range, biofouling can be efficiently suppressed while suppressing degradation of the reverse osmosis membrane due to the oxidizing power of the chlorine-based oxidizing agent.

  For example, in the concentration control step, when the free chlorine concentration in the first concentrated water becomes less than a predetermined concentration (for example, in the range of 0.01 mg / L to 0.10 mg / L, preferably 0.01 mg / L to 0.1 mg / L). (When the concentration becomes lower than one predetermined concentration in the range of not more than 05 mg / L), the concentration of free chlorine in the first concentrated water can be controlled by increasing the amount of the chlorine-based oxidizing agent added to the water to be treated. .

In the concentration control step, the concentration of the chlorine-based oxidizing agent in the first concentrated water can be controlled within a predetermined range according to the amount of biofouling generated in the first membrane separation unit 10. For example, in the concentration control step, the pressure loss of the first membrane separation unit 10 measured by the pressure loss measurement unit 54 is a first reference value (for example, the pressure loss of the first membrane separation unit 10 is used as an index of the amount of biofouling generated). When the difference from the initial pressure rises to one reference value of 0.10 MPa or more, the amount of the chlorine-based oxidizing agent added to the water to be treated can be increased. After the amount of the chlorine-based oxidizing agent is increased, when the above-mentioned pressure loss decreases to a second reference value (for example, one reference value whose difference from the initial pressure is less than 0.10 MPa), the pressure loss is added to the water to be treated. The amount of chlorine-based oxidizing agent used can be reduced or the addition can be stopped. Note that the first reference value is larger than the second reference value. The difference between the first reference value and the second reference value may be 0.10 MPa or less.
In the concentration control step, it is preferable to change the free chlorine concentration in the first concentrated water according to the pressure difference (the difference from the above initial value) in the first membrane separation unit 10. For example, when the differential pressure is 0.10 MPa or more and less than 0.20 MPa, the concentration of free chlorine in the first concentrated water is controlled to be 0.01 mg / L or more and less than 0.05 mg / L. Further, for example, when the differential pressure becomes 0.20 MPa or more, the control is performed such that the free chlorine concentration in the first concentrated water becomes 0.05 mg / L or more and less than 0.10 mg / L. If the differential pressure is high, the amount of organic substances (such as microorganisms) attached to the film is large, and therefore, even if the concentration of free chlorine is set high, the film is less likely to be deteriorated by the chlorine-based oxidizing agent. On the other hand, when the differential pressure is low, the amount of organic substances (such as microorganisms) attached to the film is small. Therefore, by setting the free chlorine concentration to be low, the deterioration of the film can be suppressed. For example, in this way, the concentration of free chlorine in the first concentrated water can be controlled to 0.01 mg / L or more and 0.10 mg / L or less, preferably 0.05 mg / L or less. By controlling in this manner, biofouling can be efficiently suppressed without using a chlorine-based oxidizing agent more than necessary.

In the concentration control step, the concentration of the slime control agent (second chemical) in the water to be treated can be controlled by changing the amount of the slime control agent (second chemical) added to the water to be treated from the second chemical addition unit 52. .
In the concentration control step, it is preferable to control the concentration of the slime control agent (second chemical) in the water to be treated within the range of 3 ppm to 50 ppm, preferably 5 ppm to 25 ppm. Thereby, biofouling can be more efficiently and efficiently suppressed.

  In the concentration control step, as described below, a chlorine-based oxidizing agent or a slime controlling agent in the water to be treated or the concentrated water according to the amount of biofouling generated in the first membrane separation unit 10 or the second membrane separation unit 20. May be controlled.

  For example, in the concentration control step, in order to know the amount of biofouling generated in the second membrane separation unit 20 and the third membrane separation unit 30, a reagent is added from the reagent addition unit 55 to the first concentrated water, and the reagent is added. The added first concentrated water can be subjected to membrane separation in the second membrane separation unit 20 and the third membrane separation unit 30. Then, the concentration of the detection substance in the third concentrated water obtained by the membrane separation in the third membrane separation section 30 can be measured by the detection substance measurement section 56. For example, if the measured concentration of the detection substance is increasing, the amount of the slime control agent added by the second chemical addition section 52 is increased, while the measured concentration of the detection substance is decreasing. For example, the amount of the slime control agent added by the second drug addition section 52 is reduced. By controlling in this manner, biofouling can be efficiently suppressed without using a slime control agent more than necessary.

  In the water treatment method of the present embodiment, the chlorine-based oxidation is performed in the membrane separation step in accordance with the amount of biofouling generated in the first membrane separation unit 10, or the second membrane separation unit 20 or the third membrane separation unit 30. Of water to be treated containing at least one of an agent or a slime control agent in the first membrane separation unit 10 and water to be treated containing neither the chlorine-based oxidizing agent nor the slime control agent in the first membrane separation unit 10 Can be alternately repeated. Thereby, use of the chlorine-based oxidizing agent and the slime controlling agent more than necessary is suppressed, and the usage of the chlorine-based oxidizing agent and the slime controlling agent can be suppressed. Since the amount of use of the chlorine-based oxidizing agent and the slime control agent (particularly, the amount of the slime control agent) can be suppressed, the cost required for implementing the water treatment method can be suppressed.

  In the present embodiment, the amount of the slime control agent added is controlled according to the amount of biofouling generated, but the present invention is not limited to such an embodiment. As described below, the amount of the slime control agent added may be controlled based on the amount of viable bacteria in the concentrated water or the biological activity.

  For example, in another embodiment, the amount of ATP in the concentrated water that has been subjected to membrane separation in the most downstream membrane separation unit may be measured, and the amount of the slime control agent added may be controlled according to the measured value. Specifically, when the measured value of the ATP amount in the above-mentioned concentrated water is high, it can be determined that microorganisms are present (or there is a trace thereof) in the concentrated water, and thus the amount of the slime control agent added is increased. On the other hand, when the measured value of the ATP amount is low, it can be determined that the number of microorganisms in the concentrated water is small, and therefore, the amount of the slime control agent to be added is reduced.

  For example, in another embodiment, a relational expression between the number of viable bacteria and the amount of the slime control agent added in each season is acquired in advance, and the number of viable bacteria becomes, for example, 0 based on the relational expression of the corresponding season. The amount of the slime control agent may be determined. In addition, using the same wastewater, the relational expression between the number of viable bacteria at each temperature and the amount of the slime control agent added is obtained in advance, and the optimum amount of addition at each temperature is determined. May be determined.

The amount of the slime control agent to be added can be controlled as described below. The concentration of the slime control agent in the last concentrated water (third concentrated water B in the present embodiment) that has been subjected to membrane separation in the most downstream membrane separation unit (the third membrane separation unit 30 in the present embodiment) is determined at the time of addition. The concentration of the slime control agent is calculated based on the concentration and the concentration ratio so that the concentration of the slime control agent in the final concentrated water (third concentrated water B) is 10 ppm or less, preferably higher than 0 ppm and 5 ppm or less. It is more preferable to control the amount added. Specifically, in the present embodiment, it is preferable to control the addition amount so that the concentration of the slime control agent in the concentrated water after the membrane separation in the third membrane separation unit falls within the above range.
By controlling the concentration of the slime control agent in the final-stage concentrated water to be 10 ppm or less, the amount of the slime control agent added can be reduced (for example, 2/5 or less) as compared with the conventional case.
When the water treatment equipment 1 includes only the first membrane separation unit 10 and the second membrane separation unit 20 as the membrane separation units, the most downstream membrane separation unit is the second membrane separation unit 20, and the last stage. The concentrated water is the second concentrated water.

  In the water treatment method of the present embodiment, in order to reduce the degree of clogging of the reverse osmosis membrane, for example, an inorganic alkali such as NaOH or KOH, or an inorganic acid such as hydrochloric acid or sulfuric acid is added to the water to be treated. Thereby, the water to be treated can be made strongly alkaline (for example, higher than pH 10) or strongly acidic (for example, lower than pH 4). Thereby, at least a part of the microorganisms attached to the reverse osmosis membrane can be removed from the membrane.

Although the water treatment equipment and the water treatment method of the embodiment are as described above, the present invention is not limited to the water treatment equipment and the water treatment method described above.
In addition, various aspects used in general water treatment facilities and water treatment methods can be adopted as long as the effects of the present invention are not impaired.

1: Water treatment equipment,
10: first membrane separation unit, 20: second membrane separation unit, 30: third membrane separation unit,
4: Water storage,
5: concentration control unit,
51: a first drug addition section (chlorine oxidant addition section), 52: a second drug addition section (slime control agent addition section),
53: free chlorine measuring section, 54: pressure loss measuring section,
55: reagent adding section, 56: detecting substance measuring section,
8: treatment water supply route,
P: Pressurizing pump,
A: Permeated water, B: Third concentrated water.

Claims (5)

A membrane separation step of membrane-separating concentrated water obtained by membrane-separating water to be treated in a first membrane separation unit having a reverse osmosis membrane in a second membrane separation unit having a reverse osmosis membrane,
The membrane separation step includes performing membrane separation of the water to be treated including a chlorine-based oxidizing agent and a slime control agent in the first membrane separation unit,
The slime control agent includes 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), 2-methyl-4-isothiazolin-3-one (MIT), 2,2-dibromo-3-nitropropion A water treatment method, which is at least one selected from the group consisting of amide (DBNPA) and 2-bromo-2-nitropropane-1,3-diol (bronoball). The membrane separation step has a concentration control step of controlling the concentration of the chlorine-based oxidizing agent or the slime control agent in the water to be treated or the concentrated water,
The water treatment method according to claim 1, wherein the concentration control step includes controlling a concentration of the chlorine-based oxidizing agent in the concentrated water. The membrane separation step has a concentration control step of controlling the concentration of the chlorine-based oxidizing agent or the slime control agent in the water to be treated or the concentrated water,
The water treatment method according to claim 1, wherein the concentration control step includes controlling a concentration of the slime control agent in the water to be treated.   In the membrane separation step, depending on the amount of biofouling generated in the first membrane separation unit or the second membrane separation unit, the chlorine-based oxidizing agent or the slime control agent in the water to be treated or the concentrated water. The water treatment method according to any one of claims 1 to 3, further comprising a concentration control step of controlling a concentration. A first membrane separation unit having a reverse osmosis membrane and a second membrane separation unit having a reverse osmosis membrane;
Concentrated water obtained by membrane-separating water to be treated containing a chlorine-based oxidizing agent and a slime control agent in the first membrane separation unit can be membrane-separated in the second membrane separation unit. ,
The slime control agent includes 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), 2-methyl-4-isothiazolin-3-one (MIT), 2,2-dibromo-3-nitropropion A water treatment facility, which is at least one selected from the group consisting of amide (DBNPA) and 2-bromo-2-nitropropane-1,3-diol (bronoball).

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