Water treatment method and water treatment device

Abstract

To provide a water treatment method and a water treatment device, storing concentrated water concentrated by an upstream separation membrane and further treating the concentrated water with a downstream separation membrane, capable of efficiently supplying the downstream separation membrane with a chemical of a specified concentration.SOLUTION: A water treatment method including an upstream membrane separation treatment step of intermittently injecting a chemical into water to be treated and subjecting the water to be treated into which a chemical is injected, to a membrane separation treatment, to obtain first concentrated water and first permeated water, and a downstream membrane separation treatment step of subjecting the first concentrated water delivered from an intermediate water tank 12 subsequent to storing the same in the intermediate water tank 12, to a membrane separation treatment to obtain second concentrated water and second permeated water, is characterized by controlling a chemical injecting time (Td), a chemical concentration rate (a) in the upstream membrane separation treatment step, and a retention time (Tr) in the intermediate water tank so that the maximum value of the concentration (C2) of the chemical flowing into the downstream membrane separation treatment step is controlled to be not lower than the concentration (C0) of the chemical flowing into the upstream membrane separation treatment step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment method and a water treatment device using multiple stages of separation membranes. [Background technology]

[0002] 2. Description of the Related Art In the operation of a separation membrane device using a separation membrane such as a reverse osmosis membrane, suppression of fouling, such as so-called biofouling, in which microorganisms and the like adhere to the separation membrane, is a major issue.

[0003] Furthermore, in a separation membrane device, in order to improve the recovery rate of treated water, it is common to temporarily store the concentrated water concentrated by a separation membrane placed upstream in an intermediate water tank, and then treat it further downstream to obtain treated water (see Patent Document 1).

[0004] As a method for suppressing fouling in a separation membrane device, a method has been proposed in which a chemical such as a bactericide is injected into the water to be treated as a fouling inhibitor (see Patent Document 2).

[0005] Furthermore, from the viewpoint of economy and the like, these chemicals are often intermittently injected into the water to be treated (see Patent Document 3). In this case, since the minimum concentration required to be effective varies depending on the type of chemical, the chemical is generally injected so that the chemical concentration in the water to be treated at the separation membrane remains at or above the minimum required concentration for a predetermined period of time or more.

[0006] In an apparatus in which concentrated water concentrated by a separation membrane (upstream separation membrane) arranged upstream as described above is temporarily stored in an intermediate water tank and then treated by a separation membrane (downstream separation membrane) arranged further downstream, when a chemical is intermittently injected into the inlet of the upstream separation membrane, the concentration of the chemical at the inlet of the downstream separation membrane may become lower than the concentration of the chemical at the inlet of the upstream separation membrane. To solve this problem, it is conceivable to inject the chemical again at the inlet of the downstream separation membrane, but this would increase the amount of chemical used and would be inefficient. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2020-065963 A [Patent Document 2] Patent No. 6401491 [Patent Document 3] JP 2020-142211 A Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a water treatment method and water treatment device in which concentrated water concentrated by an upstream separation membrane is stored in an intermediate water tank and then further treated by a downstream separation membrane, which can efficiently supply a predetermined concentration of chemicals to the downstream separation membrane. [Means for solving the problem]

[0009] The present invention includes a chemical injection step of intermittently injecting a chemical into water to be treated, an upstream separation membrane treatment step of performing separation membrane treatment using a first separation membrane on the water to be treated into which the chemical has been injected to obtain a first concentrated water and a first permeate, and a downstream separation membrane treatment step of storing the first concentrated water in an intermediate water tank and then performing separation membrane treatment using a second separation membrane on the first concentrated water sent from the intermediate water tank to obtain a second concentrated water and a second permeate, and the chemical injection time (T d ), the drug concentration ratio (a) in the upstream separation membrane treatment process, the retention time in the intermediate water tank (T r ) so that the maximum inflow concentration (C2) of the chemical into the downstream separation membrane treatment step is equal to or greater than the inflow concentration (C0) of the chemical into the upstream separation membrane treatment step.

[0010] In the water treatment method, the first separation membrane and the second separation membrane are preferably reverse osmosis membranes.

[0011] In the water treatment method, the drug concentration ratio (a) in the upstream separation membrane treatment step is preferably in the range of 1 to 10 times.

[0012] In the water treatment method, the agent is preferably a biofouling inhibitor.

[0013] In the water treatment method, the biofouling inhibitor preferably includes at least one of a stabilized hypobromous acid composition, chlorosulfamic acid, and DBNPA.

[0014] The present invention includes a chemical injection means for intermittently injecting a chemical into water to be treated, an upstream separation membrane treatment means for performing separation membrane treatment using a first separation membrane on the water to be treated into which the chemical has been injected, to obtain a first concentrated water and a first permeate, an intermediate water tank for storing the first concentrated water, a downstream separation membrane treatment means for performing separation membrane treatment using a second separation membrane on the first concentrated water sent from the intermediate water tank, to obtain a second concentrated water and a second permeate, and a time for injecting the chemical (T d ), the drug concentration ratio (a) in the upstream separation membrane treatment means, the retention time (T r ) so that the maximum value of the inflow concentration (C2) of the chemical into the downstream separation membrane treatment means is equal to or greater than the inflow concentration (C0) of the chemical into the upstream separation membrane treatment means.

[0015] In the water treatment device, the first separation membrane and the second separation membrane are preferably reverse osmosis membranes.

[0016] In the water treatment device, the drug concentration ratio (a) in the upstream separation membrane treatment means is preferably in the range of 1 to 10 times.

[0017] In the water treatment device, the agent is preferably a biofouling inhibitor.

[0018] In the water treatment device, the biofouling inhibitor preferably includes at least one of a stabilized hypobromous acid composition, chlorosulfamic acid, and DBNPA. Effect of the Invention

[0019] The present invention provides a water treatment method and water treatment apparatus in which concentrated water concentrated by an upstream separation membrane is stored in an intermediate tank and then further treated by a downstream separation membrane, which can efficiently supply a predetermined concentration of a chemical to the downstream separation membrane. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0022] An example of a water treatment apparatus according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0023] The water treatment device 1 in Figure 1 includes a pipe 28 as a chemical injection means for intermittently injecting a chemical into the water to be treated, an upstream separation membrane treatment device 10 as an upstream separation membrane treatment means for performing separation membrane treatment on the water to be treated to which the chemical has been injected using a first separation membrane to obtain a first concentrated water and a first permeate, an intermediate water tank 12 for storing the first concentrated water, and a downstream separation membrane treatment device 14 as a downstream separation membrane treatment means for performing separation membrane treatment on the first concentrated water sent from the intermediate water tank 12 using a second separation membrane to obtain a second concentrated water and a second permeate.

[0024] In the water treatment device 1 of Fig. 1, a pipe 16 is connected to the inlet of the upstream separation membrane treatment device 10. A pipe 18 is connected to the first permeate outlet of the upstream separation membrane treatment device 10. A pipe 20 connects the first concentrated water outlet of the upstream separation membrane treatment device 10 to the inlet of the intermediate water tank 12. A pipe 22 connects the outlet of the intermediate water tank 12 to the inlet of the downstream separation membrane treatment device 14. A pipe 24 is connected to the second permeate outlet of the downstream separation membrane treatment device 14, and a pipe 26 is connected to the second concentrated water outlet. A pipe 28 is connected to the pipe 16, so that a chemical can be intermittently injected into the water to be treated.

[0025] The water treatment method and the operation of the water treatment device 1 according to this embodiment will be described.

[0026] The water to be treated is sent to the upstream separation membrane treatment device 10 through piping 16. Here, a chemical is intermittently injected into the water to be treated in piping 16 through piping 28 (chemical injection step). A water tank to be treated may be provided upstream of the upstream separation membrane treatment device 10, and a chemical may be intermittently injected into the water to be treated in the water tank.

[0027] In the upstream separation membrane treatment device 10, the water to be treated into which the chemical has been injected is subjected to separation membrane treatment using a first separation membrane, and a first concentrated water and a first permeate are obtained (upstream separation membrane treatment step). The first permeate is discharged through a pipe 18. The first concentrated water is sent to the intermediate water tank 12 through a pipe 20 and temporarily stored in the intermediate water tank 12.

[0028] The first concentrated water is stored in the intermediate water tank 12, and then sent to the downstream separation membrane treatment device 14 through the pipe 22. In the downstream separation membrane treatment device 14, the first concentrated water sent from the intermediate water tank 12 is subjected to separation membrane treatment using a second separation membrane, and a second concentrated water and a second permeate are obtained (downstream separation membrane treatment step). The second permeate is discharged through the pipe 24, and the second concentrated water is discharged through the pipe 26.

[0029] In the water treatment method and water treatment device 1 according to this embodiment, the chemical is added to the water to be treated in the upstream separation membrane treatment device 10 (upstream separation membrane treatment step), but is not added to the first concentrated water which is the water to be treated in the downstream separation membrane treatment device 14. That is, the chemical is added only to the water to be treated in the upstream separation membrane treatment device 10 (upstream separation membrane treatment step).

[0030] In the water treatment method and the water treatment device 1 according to the present embodiment, the “chemical injection time (T d )," "the drug concentration ratio (a) in the upstream separation membrane treatment process (upstream separation membrane treatment device 10)," "the residence time in the intermediate water tank 12 (T r ) is adjusted so that the maximum inflow concentration (C2) of the drug to the downstream separation membrane treatment process (downstream separation membrane treatment device 14) is equal to or greater than the inflow concentration (C0) of the drug to the upstream separation membrane treatment process (upstream separation membrane treatment device 10).

[0031] That is, T d :Drug injection time T r : Intermediate tank retention time a: Drug concentration ratio in the upstream separation membrane C0: Drug inflow concentration to the upstream separation membrane C1: Drug effluent concentration from the upstream separation membrane C2: Drug inflow concentration to downstream separation membrane When C0≦C2 So that, T d (drug injection time), T r (residence time in intermediate tank) and a (drug concentration ratio in upstream separation membrane). In addition, C1 = C0 × a It is.

[0032] As described above, in water treatment in which concentrated water concentrated by an upstream separation membrane is stored in an intermediate water tank and then further treated by a downstream separation membrane, when a chemical is intermittently injected at the inlet of the upstream separation membrane, if the injection amount and injection time of the chemical are determined taking into consideration only the required concentration at the upstream separation membrane, the chemical concentration at the inlet of the downstream separation membrane may be lower than the chemical concentration at the inlet of the upstream separation membrane, and the specified amount of chemical may not be supplied to the downstream separation membrane. This is thought to be because the injected chemical is diluted in the intermediate water tank or consumed in the upstream separation membrane. Therefore, the "chemical injection time (T d )," "the drug concentration ratio (a) in the upstream separation membrane treatment process (upstream separation membrane treatment device 10)," "the residence time in the intermediate water tank (T r ) is adjusted so that the maximum concentration (C2) of the chemical at the inlet to the downstream separation membrane treatment process (downstream separation membrane treatment device 14) is equal to or greater than the concentration (C0) of the chemical at the inlet to the upstream separation membrane treatment process (upstream separation membrane treatment device 10). By making the chemical concentration (C2) at the downstream separation membrane inlet equal to or greater than the chemical concentration (C0) at the upstream separation membrane inlet, a predetermined concentration of chemical can also be supplied to the downstream separation membrane (following separation membrane) located downstream of the primary side of the upstream separation membrane (previous separation membrane). If a biofouling inhibitor is used as the chemical, both the upstream and downstream separation membranes can be efficiently sterilized.

[0033] Drug injection time (T d The drug injection time (T) can be adjusted, for example, by increasing or decreasing the operating time of the drug injection pump provided in the pipe 28 or by increasing or decreasing the opening and closing time of the valve provided in the pipe 28. d ) may be, for example, 1 to 300 minutes.

[0034] The "drug concentration ratio (a) in the upstream separation membrane treatment step" can be adjusted, for example, by changing the operating conditions of the upstream separation membrane or by using a drug with a different rejection rate in the upstream separation membrane. The drug concentration ratio (a) in the upstream separation membrane treatment step is, for example, in the range of 1 to 10 times, and preferably in the range of 1 to 5 times. If the drug concentration ratio (a) in the upstream separation membrane treatment step is less than 1 time, the effect of the drug in the downstream separation membrane treatment step may be insufficient, and if it exceeds 10 times, it may cause a decrease in the performance of the separation membrane.

[0035] "Retention time in the intermediate tank (T r The retention time (T) in the intermediate tank can be adjusted by changing the capacity of the intermediate tank 12 or the amount of the first concentrated water flowing into the intermediate tank 12. r ) may be, for example, 1 to 300 minutes.

[0036] Drug infusion time (T d ), the drug concentration ratio in the upstream separation membrane treatment process (a), and the retention time in the intermediate tank (T r ) so that the maximum concentration of the chemical inflow to the downstream separation membrane treatment process (C2) is equal to or greater than the concentration of the chemical inflow to the upstream separation membrane treatment process (C0). An example of a water treatment device having such a configuration is shown in Figure 2.

[0037] 2 may further include a control device 30 as the adjusting means, and an agent concentration measuring device 32 as an agent concentration measuring means for measuring the agent concentration at the inlet of the downstream separation membrane treatment process (downstream separation membrane treatment device 14). As an agent concentration measuring means for measuring the agent concentration at the inlet of the upstream separation membrane treatment process (upstream separation membrane treatment device 10), an agent concentration measuring device may be installed downstream of the connection point of pipe 28 in pipe 16.

[0038] In water treatment device 2, chemical concentration measuring device 32 is installed in piping 22. Control device 30 and chemical concentration measuring device 32, and control device 30 and chemical injection pumps, valves, etc. installed in piping 28 are connected by wired or wireless electrical connections, etc.

[0039] In the water treatment device 2, the control device 30 controls the “chemical injection time (T d )," "the drug concentration ratio (a) in the upstream separation membrane treatment process (upstream separation membrane treatment device 10)," "the residence time in the intermediate water tank (T r ) is adjusted so that the maximum inflow concentration (C2) of the drug to the downstream separation membrane treatment process (downstream separation membrane treatment device 14) is equal to or greater than the inflow concentration (C0) of the drug to the upstream separation membrane treatment process (upstream separation membrane treatment device 10), and so that the drug concentration (C2) at the downstream separation membrane inlet is equal to or greater than the drug concentration (C0) at the upstream separation membrane inlet.

[0040] The control device 30 is composed of a microcomputer and electronic circuits, which include, for example, a calculation means such as a CPU that executes a program, and storage means such as a ROM and a RAM that store the program and the calculation results, and controls the drug injection time (T d ), the drug concentration ratio in the upstream separation membrane treatment process (a), and the retention time in the intermediate tank (T r ) so that the maximum inflow concentration (C2) of the chemical to the downstream separation membrane treatment process is equal to or greater than the inflow concentration (C0) of the chemical to the upstream separation membrane treatment process.

[0041] The control device 30 controls, for example, the drug injection pump provided in the piping 28 to increase or decrease the operation time, thereby controlling the "drug injection time (T d The control device 30 can adjust the "chemical concentration ratio (a) in the upstream separation membrane treatment step" by, for example, controlling the opening of a valve provided in the pipe 20 of the upstream separation membrane. The control device 30 can adjust the "chemical concentration ratio (a) in the upstream separation membrane treatment step" by, for example, controlling a valve or the like provided in the pipe 20. r ) can be adjusted.

[0042] There are no particular limitations on the drug concentration measuring device as long as it is capable of measuring the drug concentration, and examples of such a device include a residual chlorine meter.

[0043] Methods for measuring the residual concentration of halogen-based chemicals include the DPD method and the polarographic method.

[0044] The chemical concentration at the inlet of the downstream separation membrane treatment step (downstream separation membrane treatment device 14) may be measured automatically or manually by a chemical concentration measuring device 32.

[0045] <Separation membrane> The first separation membrane used in the upstream separation membrane treatment device 10 and the second separation membrane used in the downstream separation membrane treatment device 14 are not particularly limited, and examples thereof include reverse osmosis membranes (RO membranes), nanofiltration membranes (NF membranes), microfiltration membranes (MF membranes), ultrafiltration membranes (UF membranes), etc. Among these, the target is essentially reverse osmosis membranes and nanofiltration membranes (NF membranes) that can concentrate ion components, i.e., where drug concentration occurs, and the water treatment method and water treatment device according to this embodiment are suitably applied to the reverse osmosis membrane.

[0046] As the reverse osmosis membrane, a composite membrane made of polyamide is generally used.

[0047] In each of the upstream separation membrane treatment device 10 and the downstream separation membrane treatment device 14, multiple stages of separation membrane treatment devices may be used in series or in parallel.

[0048] <Water to be treated> There are no particular limitations on the type of water to be treated, and examples of the water to be treated include environmental water (groundwater, river water, seawater, etc.) and wastewater.

[0049] <Drugs> The chemicals to be injected into the water to be treated are not particularly limited, and examples include biofouling inhibitors (bactericides), dispersants, etc. The water treatment method and water treatment device according to the present embodiment are preferably applied to the chemicals to be injected into the water to be treated, in the case of biofouling inhibitors that are effective even when injected intermittently.

[0050] Examples of biofouling inhibitors include a stabilized hypobromous acid composition containing a bromine-based oxidant and a sulfamic acid compound, a stabilized hypochlorous acid composition containing a chlorine-based oxidant and a sulfamic acid compound, a halocyanoacetamide compound such as 2,2-dibromo-3-nitrilopropionamide (DBNPA), hypochlorous acid, isothiazolinone, peracetic acid, and performic acid.

[0051] As the chemical, in particular, a chemical that hardly permeates the upstream separation membrane, i.e., a chemical injected into the water to be treated is almost transferred to the first concentrated water side (for example, a rejection rate of 95% or more in a separation membrane such as a reverse osmosis membrane) is preferable. Specific examples include a stabilized hypobromous acid composition, chlorosulfamic acid, and DBNPA, and a stabilized hypobromous acid composition having a high rejection rate in a separation membrane such as a reverse osmosis membrane is preferable.

[0052] The "stabilized hypobromous acid composition containing a bromine-based oxidizing agent and a sulfamic acid compound" may be a stabilized hypobromous acid composition containing a mixture of a "bromine-based oxidizing agent" and a "sulfamic acid compound", or may be a stabilized hypobromous acid composition containing a "reaction product of a bromine-based oxidizing agent and a sulfamic acid compound". The "stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound" may be a stabilized hypochlorous acid composition containing a mixture of a "chlorine-based oxidizing agent" and a "sulfamic acid compound", or may be a stabilized hypochlorous acid composition containing a "reaction product of a chlorine-based oxidizing agent and a sulfamic acid compound".

[0053] Examples of the bromine-based oxidizing agent include bromine (liquid bromine), bromine chloride, bromic acid, bromate, hypobromous acid, etc. Hypobromous acid may be produced by reacting a bromine compound such as sodium bromide with a chlorine-based oxidizing agent such as hypochlorous acid. When the bromine-based oxidizing agent is bromine, there is no chlorine-based oxidizing agent, and therefore the deterioration effect on separation membranes such as reverse osmosis membranes is significantly low.

[0054] Examples of chlorine-based oxidizing agents include chlorine gas, chlorine dioxide, hypochlorous acid or its salt, chlorous acid or its salt, chloric acid or its salt, perchloric acid or its salt, and chlorinated isocyanuric acid or its salt. Among these, examples of salts include alkali metal hypochlorite such as sodium hypochlorite and potassium hypochlorite, alkaline earth metal hypochlorite such as calcium hypochlorite and barium hypochlorite, alkali metal chlorite such as sodium chlorite and potassium chlorite, alkaline earth metal chlorite such as barium chlorite, other metal chlorite such as nickel chlorite, alkali metal chlorate such as ammonium chlorate, sodium chlorate, and potassium chlorate, alkaline earth metal chlorate such as calcium chlorate and barium chlorate, and the like. These chlorine-based oxidizing agents may be used alone or in combination of two or more. As the chlorine-based oxidizing agent, it is preferable to use sodium hypochlorite from the viewpoint of handling and the like.

[0055] Examples of the bromine compound include sodium bromide, potassium bromide, lithium bromide, ammonium bromide, hydrobromic acid, etc. Among these, sodium bromide is preferred from the viewpoint of formulation costs, etc.

[0056] The sulfamic acid compound is a compound represented by the following general formula (1). R2NSO3H (1) (In the formula, R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

[0057] Examples of the sulfamic acid compound include sulfamic acid (amidosulfuric acid) in which both R groups are hydrogen atoms, as well as sulfamic acid compounds in which one of the two R groups is a hydrogen atom and the other is an alkyl group having 1 to 8 carbon atoms, such as N-methylsulfamic acid, N-ethylsulfamic acid, N-propylsulfamic acid, N-isopropylsulfamic acid, and N-butylsulfamic acid, sulfamic acid compounds in which both of the R groups are alkyl groups having 1 to 8 carbon atoms, such as N,N-dimethylsulfamic acid, N,N-diethylsulfamic acid, N,N-dipropylsulfamic acid, N,N-dibutylsulfamic acid, N-methyl-N-ethylsulfamic acid, and N-methyl-N-propylsulfamic acid, sulfamic acid compounds in which one of the two R groups is a hydrogen atom and the other is an aryl group having 6 to 10 carbon atoms, such as N-phenylsulfamic acid, and salts thereof. Examples of sulfamic acid salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts, strontium salts and barium salts, other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts and nickel salts, ammonium salts and guanidine salts. Sulfamic acid compounds and their salts may be used alone or in combination of two or more. As the sulfamic acid compound, it is preferable to use sulfamic acid (amidosulfuric acid) from the viewpoint of environmental load and the like.

[0058] The stabilized hypobromous acid composition may further contain an alkali. Examples of the alkali include alkali hydroxides such as sodium hydroxide and potassium hydroxide. From the viewpoint of product stability at low temperatures, sodium hydroxide and potassium hydroxide may be used in combination. The alkali may be used as an aqueous solution instead of a solid.

[0059] Examples of the dispersant include polyacrylic acid, polymaleic acid, and phosphonic acid.

[0060] <How to inject the drug> The chemical is intermittently injected into the water to be treated in the upstream separation membrane treatment device 10 (upstream separation membrane treatment step). Intermittent injection refers to an injection in which an injection period during which the chemical is injected into the water to be treated is separated from an injection period during which the chemical is not injected into the water to be treated. The chemical may be automatically injected into the water to be treated by a chemical injection pump or the like. The chemical may be injected into the piping or into the water to be treated tank.

[0061] <Other configurations> At a stage subsequent to the downstream separation membrane treatment, at least one of a reverse osmosis membrane treatment device, a UV treatment device, or an ion exchange treatment device may be provided, and at least one of a reverse osmosis membrane treatment, a UV treatment, or an ion exchange treatment may be performed on the permeate of the separation membrane treatment. EXAMPLES

[0062] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0063] <Examples 1 and 2, Comparative Example 1> In the water treatment device 1 of Figure 1, a chemical was injected into the water to be treated in the upstream separation membrane treatment device, and the chemical concentration flowing into the downstream separation membrane treatment device was measured when the device was operated under the following operating conditions. The chemical concentration (mg-Cl / L) was measured by a total chlorine measurement method (DPD (N,N-diethyl-p-phenylenediamine) method) using a HACH multi-item water quality analyzer DR / 4000. The results are shown in Table 1.

[0064] [Operating conditions] -Retention time of intermediate tank (T r ):20 minutes - Concentration rate in the upstream separation membrane (a): 2 times Drug inflow concentration to upstream separation membrane (C0): 10mg-Cl / L Drug: Drug containing a stabilized hypobromous acid composition as an active ingredient - Intermittent infusion time of drug per 1440 minutes (T d ): 20 minutes (Example 1), 15 minutes (Example 2), 10 minutes (Comparative Example 1)

[0065] [Table 1]

[0066] In the examples, by setting the intermittent drug injection time to 15 minutes or more, the drug inflow concentration to the downstream separation membrane could be made equal to or higher than the drug inflow concentration to the upstream separation membrane.

[0067] <Reference examples 1~5> The rejection rate (%) of the active ingredients of various biofouling inhibitors in a reverse osmosis membrane was measured. The drug concentration was measured using the DPD method. The results are shown in Table 2. Rejection rate (%) = [1-(chemical concentration in permeate water / chemical concentration in raw water)] x 100

[0068] [Test conditions] Separation membrane: Polyamide polymer reverse osmosis membrane Operating pressure: 0.75MPa ·Raw water: Sagamihara well water (pH7.2, conductivity 240μS / cm) Chemicals: stabilized hypobromous acid composition (Reference Example 1), chlorosulfamic acid (Reference Example 2), DBNPA (Reference Example 3), sodium hypochlorite (Reference Example 4), chloramine (Reference Example 5)

[0069] [Medicines used] (Stabilized hypobromous acid composition) A stabilized hypobromous acid composition was prepared by mixing 16.9% by weight (wt%) liquid bromine, 10.7% by weight sulfamic acid, 12.9% by weight sodium hydroxide, 3.94% by weight potassium hydroxide, and the remainder of water under a nitrogen atmosphere. The stabilized hypobromous acid composition had a pH of 14 and a total chlorine concentration of 7.5% by weight.

[0070] (Chlorosulfamic acid) A stabilized hypochlorous acid composition (chlorosulfamic acid) was prepared by mixing 50% by weight of 12% sodium hypochlorite aqueous solution, 10% by weight of sulfamic acid, 8% by weight of sodium hydroxide, and the remainder of water. The pH of the stabilized hypochlorous acid composition was 14, and the total chlorine concentration was 6% by weight.

[0071] (DBNPA) 2,2-Dibromo-3-nitrilopropionamide (DBNPA) was used.

[0072] (Sodium hypochlorite) A 12% aqueous solution of sodium hypochlorite was used.

[0073] (Chloramine) A specified concentration of chloramine was generated in the water being treated by injecting and mixing sodium hypochlorite and ammonium chloride into the water being treated from the separation membrane at 10 mgCl / L and 11.3 mg / L in terms of available chlorine, respectively.

[0074] [Table 2]

[0075] It can be seen that the stabilized hypobromous acid composition (Reference Example 1), chlorosulfamic acid (Reference Example 2), and DBNPA (Reference Example 3) have a rejection rate of 95% or more in the reverse osmosis membrane.

[0076] As described above, in the method of the embodiment, in a water treatment process in which concentrated water concentrated by an upstream separation membrane is stored in an intermediate water tank and then further treated by a downstream separation membrane, a predetermined concentration of chemicals can be efficiently supplied to the downstream separation membrane as well. [Explanation of symbols]

[0077] 1, 2 water treatment device, 10 upstream separation membrane treatment device, 12 intermediate water tank, 14 downstream separation membrane treatment device, 16, 18, 20, 22, 24, 26, 28 piping, 30 control device, 32 drug concentration measuring device.

Claims

1. An agent injection step of intermittently injecting an agent into the water to be treated; an upstream separation membrane treatment step of performing a separation membrane treatment using a first separation membrane on the water to be treated into which the chemical has been injected, to obtain a first concentrated water and a first permeate; a downstream separation membrane treatment step of storing the first concentrated water in an intermediate water tank, and then performing a separation membrane treatment on the first concentrated water sent from the intermediate water tank using a second separation membrane to obtain a second concentrated water and a second permeate; Including, The injection time of the drug (T ｄ ), the drug concentration ratio in the upstream separation membrane treatment step (a), the residence time in the intermediate water tank (T ｒ ) to adjust the inflow concentration (C ２ ) is the inflow concentration (C ０ ) or more.

2. The water treatment method according to claim 1, The water treatment method, wherein the first separation membrane and the second separation membrane are reverse osmosis membranes.

3. The water treatment method according to claim 1 or 2, The water treatment method, wherein the drug concentration ratio (a) in the upstream separation membrane treatment step is in the range of 1 to 10 times.

4. The water treatment method according to any one of claims 1 to 3, The water treatment method, wherein the agent is a biofouling inhibitor.

5. The water treatment method according to claim 4, The water treatment method, wherein the biofouling inhibitor comprises at least one of a stabilized hypobromous acid composition, chlorosulfamic acid, and DBNPA.

6. A chemical injection means for intermittently injecting a chemical into the water to be treated; an upstream separation membrane treatment means for performing a separation membrane treatment using a first separation membrane on the water to be treated into which the chemical has been injected, to obtain a first concentrated water and a first permeate; An intermediate water tank for storing the first concentrated water; a downstream separation membrane treatment means for performing a separation membrane treatment using a second separation membrane on the first concentrated water sent from the intermediate water tank to obtain a second concentrated water and a second permeate; The injection time of the drug (T ｄ ), the drug concentration ratio in the upstream separation membrane treatment means (a), the residence time in the intermediate water tank (T ｒ ) to adjust the inflow concentration (C ２ ) is the inflow concentration (C ０ ) or more; and A water treatment device comprising:

7. The water treatment device according to claim 6, The water treatment device, wherein the first separation membrane and the second separation membrane are reverse osmosis membranes.

8. The water treatment device according to claim 6 or 7, A water treatment device, wherein the drug concentration ratio (a) in the upstream separation membrane treatment means is in the range of 1 to 10 times.

9. The water treatment device according to any one of claims 6 to 8, The water treatment device according to claim 1, wherein the chemical is a biofouling inhibitor.

10. The water treatment device according to claim 9, The water treatment device, wherein the biofouling inhibitor comprises at least one of a stabilized hypobromous acid composition, chlorosulfamic acid, and DBNPA.

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