JP7180310B2 - water treatment system - Google Patents

Description

The present invention relates to water treatment systems.

Sodium hypochlorite is used as a chlorine-based disinfectant to remove microorganisms in water treatment systems that perform membrane filtration processes using reverse osmosis membranes, in order to suppress biofilms derived from the growth of microorganisms. There is
For example, Patent Document 1 discloses a water generation method using a reverse osmosis membrane, in which sodium hypochlorite is allowed to flow into the reverse osmosis membrane in a water treatment system in order to suppress biofouling due to the generation of biofilms. It discloses a method of producing fresh water.

JP 2016-190214 A

However, if the sodium hypochlorite content in the feedwater flowing through the water treatment system is too high, the reverse osmosis membrane will deteriorate. Stabilizers are sometimes added to water treatment systems to prevent deterioration of reverse osmosis membranes. put away. Therefore, in order to prevent deterioration of the reverse osmosis membrane while suppressing biofilms, it is necessary to balance the content of sodium hypochlorite and the content of the stabilizer in the water supply.

In the water treatment system, the present invention relates to the content of sodium hypochlorite contained in the water supply for biofilm suppression and the content of the stabilizer contained in the water supply to prevent deterioration of the reverse osmosis membrane. To provide a water treatment system that can easily balance with

The present invention includes a filtration device that filters raw water to generate feed water, a raw water line that supplies raw water to the filtration device, and a reverse osmosis membrane that separates the feed water generated by the filtration device into permeated water and concentrated water. a module, a feed water line for supplying feed water to the reverse osmosis membrane module, a permeated water line for delivering permeated water separated by the reverse osmosis membrane module, and delivering concentrated water separated by the reverse osmosis membrane module. A concentrated water line, a concentrated waste water line that discharges all or part of the concentrated water to the outside of the system as concentrated waste water, a first chemical injection device that chemically injects a stabilizing agent into the water supply, and chemical injection of the stabilizing agent. a dosing controller that adjusts the amount to balance the molar ratio of chlorine-based oxidant and stabilizing agent in said water supply.

Further, a first chlorine concentration measuring device for measuring the chlorine concentration at the outlet of the filtering device is further provided, and the first chemical dosing device injects a stabilizing agent into the water supply downstream of the first chlorine concentration measuring device. Preferably, the chemical dosing control unit adjusts the chemical dosing amount of the stabilizer based on the chlorine concentration measured by the first chlorine concentration measuring device.

Further, downstream of the chlorine concentration measuring device, a second chemical injection device for chemically injecting a reducing agent into the water supply is further provided, and the chemical injection control unit is based on the chlorine concentration measured by the first chlorine concentration measuring device It is preferable to control the feeding amount of the reducing agent.

The reducing agent is preferably one or more of SBS (sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas.

Further, downstream of the first chlorine concentration measuring device, a third chemical injection device for chemically injecting a bromine compound into the water supply is further provided, and the chemical injection control unit controls the chlorine concentration measured by the first chlorine concentration measuring device Based on, it is preferable to control the dosing amount of the bromine compound.

Further, a fourth chemical injection device for chemically injecting a chlorine-based oxidant into the raw water and/or the feed water is further provided, and the chemical injection control unit controls the raw water based on the chlorine concentration measured by the first chlorine concentration measuring device. and/or to control the dosing of the chlorine-based oxidant into the water supply.

Further, a fifth chemical dosing device for dosing the stabilizing agent into the raw water is further provided, and the chemical dosing control unit is dosed into the raw water based on the chlorine concentration measured by the first chlorine concentration measuring device. It is preferred to control the dosing of both the stabilizing agent and the stabilizing agent dosed into the water supply.

Further comprising a second chlorine concentration measuring device for measuring the chlorine concentration in the concentrated water line or the concentrated wastewater line, the chemical dosing control unit, in addition to the chlorine concentration measured by the first chlorine concentration measuring device, 2 It is preferable to control the chemical injection based on the chlorine concentration measured by the chlorine concentration measuring device.

In addition, the present invention includes a filtration device that filters raw water to generate feed water, a raw water line that supplies raw water to the filtration device, and reverse osmosis that separates the feed water generated by the filtration device into permeated water and concentrated water. A membrane module, a feed water line for supplying feed water to the reverse osmosis membrane module, a permeated water line for sending permeated water separated by the reverse osmosis membrane module, and sending concentrated water separated by the reverse osmosis membrane module. a concentrated water line that discharges all or part of the concentrated water to the outside of the system as concentrated waste water, an outlet of the filtration device in the water supply line, and / or an oxidation-reduction potential in the concentrated waste water line a first chemical dosing device for dosing a stabilizing agent into the water supply downstream of the potential measuring device; and a stabilizing agent based on the oxidation-reduction potential measured by the potential measuring device. and a chemical dosing control unit that adjusts the molar ratio balance of the chlorine-based oxidant and the stabilizer in the water supply by controlling the dosing amount of the water treatment system.

Further, a second chemical injection device for chemically injecting a reducing agent into the water supply is further provided downstream of the potential measurement device, and the chemical injection control unit controls the reduction potential based on the oxidation-reduction potential measured by the potential measurement device. It is preferred to control the dosage of the agent.

The reducing agent is preferably one or more of SBS (sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas.

Further, a third chemical injection device for chemically injecting a bromine compound into the water supply is further provided downstream of the potential measurement device, and the chemical injection control unit detects bromine based on the oxidation-reduction potential measured by the potential measurement device. It is preferred to control the dosage of the compound.

Further, a fourth chemical injection device for chemically injecting a chlorine-based oxidant into the raw water and/or the feed water is further provided, and the chemical injection control unit controls the raw water and/or the feed water based on the oxidation-reduction potential measured by the potential measurement device. Alternatively, it is preferable to control the chemical injection of the chlorine-based oxidant into the water supply.

The chemical dosing controller further includes a fifth chemical dosing device for dosing the stabilizing agent into the raw water, and the chemical dosing control unit is configured to dope the stabilizing agent into the raw water based on the oxidation-reduction potential measured by the potential measuring device. It is preferable to control the dosing of both the agent and the stabilizing agent dosed into the water supply.

The reducing agent is preferably one or more of SBS (sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas.

Further, a water quality measuring means for measuring the water quality of the feed water is further provided, and the chemical dosing control unit determines the molar ratio of the chlorine-based oxidant and the stabilizer in the feed water based on the water quality measured by the water quality measuring means. It is preferable to adjust the balance and the amount of dosing.

In addition, it is preferable that the stabilizer contains a chelate component having sequestering and dispersing effects on metal ions, and/or a polymer.

According to the present invention, in the water treatment system, the content of sodium hypochlorite contained in the water supply for biofilm suppression and the stabilizer contained in the water supply to prevent deterioration of the reverse osmosis membrane It becomes possible to easily take balance with the content.

1 is an overall configuration diagram of a water treatment system according to an embodiment of the present invention; FIG. It is a flow chart explaining operation of a water treatment system concerning an embodiment of the present invention.

〔overall structure〕
Hereinafter, a water treatment system 1 that is an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a water treatment system 1 of the present invention.

As shown in FIG. 1, the water treatment system 1 includes a filtration device 3, a first chemical addition device 4, a second chemical addition device 5, a third chemical addition device 6, a fourth chemical addition device 7, A fifth chemical addition device 8, a first chlorine concentration sensor 9, a second chlorine concentration sensor 10, a water quality sensor 11, a pressure pump 12, an inverter 13, a reverse osmosis membrane module (hereinafter referred to as "RO membrane module ) 14 , a constant flow valve 15 , a proportional control drain valve 16 , and a controller 30 . The illustration of electrical connection lines between the control unit 30 and the device to be controlled is omitted.

The water treatment system 1 includes, as lines, a raw water line L1, a water supply line L2, a permeated water line L3, a concentrated water line L4, a circulating water line L5, and a concentrated waste water line L6. "Line" is a generic term for lines such as channels, routes, and pipelines through which fluid can flow. In addition, regardless of the origin (source) or quality of the water, the water flowing through the raw water line L1 is also referred to as "raw water", and the water flowing through the water supply line L2, the concentrated water line L4, or the circulating water line L5 is referred to as "water supply". , and the water flowing through the concentrated water line L4, the circulating water line L5, or the concentrated drainage line L6 is also referred to as "concentrated water."

The raw water line L1 is a line that supplies the raw water W10 toward the filtering device 3 . The upstream end of the raw water line L1 is connected to the water source 2 of the raw water W10. A downstream end of the raw water line L1 is connected to the filtering device 3 . A fourth chemical addition device 7 and a fifth chemical addition device 8 are provided in the raw water line L1.

The fourth chemical addition device 7 is a device that adds a fourth chemical to the raw water line L1. The fourth chemical addition device 7 is electrically connected to the controller 30 .
In the present embodiment, the fourth chemical addition device 7 adjusts the chlorine concentration in the raw water W10 by adding an oxidizing agent as the fourth chemical in order to suppress biofilm deposition in the reverse osmosis membrane module 14. . In the reverse osmosis membrane module 14, an example of the fourth chemical is a chlorine-based oxidizing agent such as sodium hypochlorite, since it can effectively suppress the adhesion of biofilms to the surface of the reverse osmosis membrane. . When the fourth chemical is sodium hypochlorite, the amount of sodium hypochlorite added is preferably such that the effective chlorine concentration in the water supply W21, which will be described later, is about 0.01 to 5 mgCl ₂ /L.
To simplify the description, an example in which the fourth chemical is sodium hypochlorite will be described below, but the present invention is not limited to this. As other chlorine-based oxidizing agents, for example, liquefied chlorine, bleaching powder, chlorinated isocyanuric acid, and the like may be used.

The fifth chemical addition device 8 is a device that adds a fifth chemical to the raw water line L1. The fifth chemical addition device 8 is electrically connected to the controller 30 .
In this embodiment, the fifth chemical addition device 8 adds a stabilizer as the fifth chemical in order to prevent deterioration of the reverse osmosis membrane provided in the reverse osmosis membrane module 14 . By adding the stabilizer, for example, the hypochlorous acid contained in the raw water W10 and the feed water W21 to be described later becomes stabilized hypochlorous acid. In the reverse osmosis membrane module 14, since deterioration of the reverse osmosis membrane can be effectively suppressed, examples of the fifth chemical include stabilizing agents such as amine-based compounds such as sulfamic acid. When the fifth chemical is sulfamic acid, the amount of sulfamic acid added is preferably such that the molar ratio of available chlorine derived from hypochlorous acid in the water supply W21 to sulfamic acid is about 1:1 to 20. , 1:1.5 to 10 is even better. This is because if sulfamic acid is less than 1 with respect to available chlorine 1, free chlorine is generated even if the reaction efficiency of both is assumed to be 100%.
For simplicity of explanation, an example in which the fifth drug is sulfamic acid will be described below, but the present invention is not limited to this.

In addition, the stabilizer may contain a chelating component and/or a polymer that sequesters and disperses metal ions.
When there is a transition metal on the surface of the permeated water W30 or the reverse osmosis membrane, even a substance with low oxidizing power, such as the stabilized hypobromous acid described later, coexists with the oxidizing agent, and the catalyst There is a concern that this action accelerates film deterioration. Therefore, in order to suppress film deterioration, a component having a chelating effect and a dispersing effect capable of sequestering transition metals is blended and added to the stabilizer.

The filtering device 3 is a device for preliminarily filtering the raw water W10, and may be an iron/manganese removing device, a sand filtering device, or the like.

The water supply line L2 is a line that supplies the water supply W21 to W22 toward the reverse osmosis membrane module . The water supply line L2 has a first water supply line L21 and a second water supply line L22 from upstream to downstream.

An upstream end of the first water supply line L21 is connected to the filtering device 3 . The downstream end of the first water supply line L21 is connected to the second water supply line L22 and the circulating water line L5 at the connection J1. A first chlorine concentration sensor 9, a first chemical addition device 4, a second chemical addition device 5, and a third chemical addition device 6 are provided in the first water supply line L21. In particular, the first chlorine concentration sensor 9 is provided upstream of the first chemical addition device 4 , the second chemical addition device 5 and the third chemical addition device 6 .

The first chlorine concentration sensor 9 is a device that measures the concentration of free chlorine in the feed water W21 at the outlet of the filtering device 3 . The first chlorine concentration sensor 9 is electrically connected to the controller 30 . The concentration of free chlorine in the feed water W21 measured by the first chlorine concentration sensor 9 is sent to the controller 30 as a detection signal.

The first chemical addition device 4 is a device that adds a first chemical to the water supply line L2. The first chemical addition device 4 is electrically connected to the controller 30 .
In this embodiment, the first chemical addition device 4 adds a stabilizer as the first chemical in order to prevent deterioration of the reverse osmosis membranes provided in the reverse osmosis membrane module 14 . By adding the stabilizer, for example, the hypochlorous acid contained in the feed water W21 becomes stabilized hypochlorous acid. In the reverse osmosis membrane module 14, since deterioration of the reverse osmosis membrane can be effectively suppressed, examples of the first chemical include stabilizers such as amine-based compounds such as sulfamic acid. When the first agent is sulfamic acid, the amount of sulfamic acid added is preferably such that the molar ratio of available chlorine derived from hypochlorous acid in the water supply W21 to sulfamic acid is about 1:1 to 20. , 1:1.5 to 10 is even better. This is because if sulfamic acid is less than 1 with respect to available chlorine 1, free chlorine is generated even if the reaction efficiency of both is assumed to be 100%.
To simplify the description, an example in which the first drug is sulfamic acid will be described below, but the present invention is not limited to this.

In addition, the stabilizer may contain a chelating component and/or a polymer that sequesters and disperses metal ions.

The second chemical addition device 5 is a device that adds a second chemical to the water supply line L2. The second chemical addition device 5 is electrically connected to the controller 30 .
In this embodiment, the second chemical addition device 5 adds a reducing agent as the second chemical in order to prevent deterioration of the reverse osmosis membranes provided in the reverse osmosis membrane module 14 . Addition of the reducing agent reduces the concentration of chlorine contained in the feed water W21 to an appropriate concentration. Examples of the second chemical include reducing agents such as SBS (NaHSO ₃ : sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas. To simplify the description, an example in which the second drug is SBS will be described below, but the present invention is not limited to this.

The third chemical addition device 6 is a device that adds the third chemical to the water supply line L2. The third chemical addition device 6 is electrically connected to the controller 30 .
In this embodiment, the third chemical addition device 6 adds a bromine compound in order to reduce damage to the reverse osmosis membranes provided in the reverse osmosis membrane module 14 . The addition of a bromine compound indirectly produces stabilized hypobromous acid, and the reaction of hypobromous acid with sulfamic acid finally produces a brominated sulfamic acid compound. Examples of third agents include bromine compounds such as sodium bromide. The amount of the bromine compound added is preferably such that the molar ratio of available chlorine derived from hypochlorous acid in the feed water W21 to the bromine compound is about 1:1 to 10, more preferably about 1:1 to 2. good.
To simplify the explanation, an example in which the third drug is sodium bromide will be described below, but the present invention is not limited to this.

The water quality sensor 11 measures the water quality of the feed water W21. The water quality sensor 11 is electrically connected to the controller 30 .
In this embodiment, the water quality sensor 11 detects TOC (Total Organic Carbon), COD (Chemical Oxygen Demand), BOD (Biochemical Oxygen Demand) as the water quality of the feed water W21. Any one or more of organic substances such as oxygen demand, AOC (Assimilable Organic Carbon), and microorganisms such as bacterial count and ATP count are measured. The control unit 30 receives these measurements from the water quality sensor 11, predicts the biofilm risk using the received measurements, and based on the predicted biofilm risk, stabilizes the chlorine-based oxidant in the water supply W21. In order to adjust the balance of the molar ratio of the chemical agent and the chemical feeding amount, the chemical feeding amount of the first chemical to the fifth chemical to the water supply W21 is set.

Alternatively, the water quality sensor 11 may measure the concentration of reducing substances contained in the feed water W21 as the water quality of the feed water W21. Specifically, the water quality sensor 11 detects the concentration of metal ions such as iron ions and manganese ions, which are reducing substances, the concentration of ions such as nitrite ions, the amount of ammonia nitrogen (nitrogen in ammonium ions), or SBS ( The concentration of sodium bisulfite: NaHSO ₃ ), etc. is measured. The control unit 30 receives the measured values of these reducing substance concentrations from the water quality sensor 11, and uses the received measured values to adjust the molar ratio balance between the chlorine-based oxidant and the stabilizer in the water supply W21. , to set the amounts of the first to fifth chemicals to be added to the water supply W21.

The upstream end of the second water supply line L22 is connected to the connection J1. The downstream end of the second water supply line L22 is connected to the primary inlet port of the reverse osmosis membrane module 14 . A pressure pump 12 is provided in the second water supply line L22.

The pressure pump 12 is a device that draws in the feed water W22 and pumps (discharges) it toward the reverse osmosis membrane module 14 . The pressurizing pump 12 is supplied with drive power whose frequency has been converted from the inverter 13 . The pressurizing pump 12 is driven at a rotational speed corresponding to the frequency of the supplied (input) driving power (hereinafter also referred to as "driving frequency").

The inverter 13 is an electric circuit (or a device having such a circuit) that supplies drive power whose frequency is converted to the pressure pump 12 . Inverter 13 is electrically connected to control unit 30 . A command signal is input to the inverter 13 from the control unit 30 . The inverter 13 outputs to the pressurizing pump 12 drive power having a drive frequency corresponding to the command signal (current value signal or voltage value signal) input from the control unit 30 .

The feed water W22 is supplied to the reverse osmosis membrane module 14 via the pressure pump 12 . Moreover, the water supply W22 consists of the water supply W21 and the circulating water W50 (described later).

The reverse osmosis membrane module 14 is a facility that separates feed water W22 into permeated water W30 and concentrated water W40. Specifically, the reverse osmosis membrane module 14 is a facility for membrane separation processing of the feed water W22 discharged from the pressurizing pump 12 into permeated water W30 from which dissolved salts have been removed and concentrated water W40 from which dissolved salts have been concentrated. is. The reverse osmosis membrane module 14 includes single or multiple reverse osmosis membrane elements (not shown). The reverse osmosis membrane module 14 performs a membrane separation process on the feed water W22 using these reverse osmosis membrane elements to produce a permeated water W30 and a concentrated water W40.

The permeated water line L3 is a line through which the permeated water W30 separated by the reverse osmosis membrane module 14 is delivered. The upstream end of the permeate line L3 is connected to the secondary port of the reverse osmosis membrane module 14 . A downstream end of the permeate line L3 is connected to a storage tank (not shown).

The concentrated water line L4 is a line through which the concentrated water W40 separated by the reverse osmosis membrane module 14 flows. The upstream end of the concentrated water line L4 is connected to the secondary port of the reverse osmosis membrane module 14 . Further, the downstream side of the concentrated water line L4 is branched into a circulating water line L5 and a concentrated drainage line L6 at the connection J2.

The circulating water line L5 is a line that is connected to the concentrated water line L4 and returns concentrated water (circulating water W50) as water supply to the water supply line L2. In this embodiment, the circulating water line L5 is a line that returns (circulates) the concentrated water W40 flowing through the concentrated water line L4 to the upstream side of the pressure pump 12 in the water supply line L2 as the circulating water W50. The upstream end of the circulating water line L5 is connected to the concentrated water line L4 at the connection J2. Further, the downstream end of the circulating water line L5 is connected to the water supply line L2 at the connection J1. A constant flow valve 15 is provided in the circulating water line L5.

The constant flow rate valve 15 is a device that adjusts the flow rate of the circulating water W50 flowing through the circulating water line L5 so as to maintain a predetermined constant flow rate value. The "constant flow rate value" held in the constant flow rate valve 15 is a concept that has a range of constant flow rate values, and is not limited to the target flow rate value of the constant flow rate valve. For example, considering the characteristics of the constant flow rate mechanism (for example, the temperature characteristics due to the material and structure), the constant flow rate valve may have an adjustment error of about ±10% with respect to the target flow rate value. The constant flow rate valve 15 maintains a constant flow rate value without requiring auxiliary power or external operation, and is, for example, one called a water governor. The constant flow rate valve 15 may be operated by auxiliary power or external operation to maintain a constant flow rate value.

The concentrated waste water line L6 is a line that is connected to the concentrated water line L4 and discharges the concentrated water as the concentrated waste water W60 to the outside of the system. In this embodiment, the concentrated water line L6 is connected to the concentrated water line L4 at the connection J2, and the concentrated water W40 separated by the reverse osmosis membrane module 14 is discharged outside the apparatus (outside the system) as concentrated water W60. is the line to A second chlorine concentration sensor 10 and a proportional control drain valve 16 are provided in the concentrated drain line L6.

The second chlorine concentration sensor 10 is a device that measures the combined chlorine concentration in the concentrated waste water W60 in the concentrated waste water line L6. The second chlorine concentration sensor 10 is electrically connected to the controller 30 . The combined chlorine concentration of the concentrated waste water W60 measured by the second chlorine concentration sensor 10 is transmitted to the control unit 30 as a detection signal.

The proportional control drain valve 16 is a valve that adjusts the flow rate of the concentrated waste water W60 discharged from the concentrated waste water line L6 to the outside of the apparatus. The proportional control drain valve 16 is electrically connected to the controller 30 . The valve opening degree of the proportional control drain valve 16 is controlled by a drive signal transmitted from the controller 30 . By transmitting a current value signal (eg, 4 to 20 mA) from the control unit 30 to the proportional control drain valve 16 to control the valve opening, the drain flow rate of the concentrated waste water W60 can be adjusted.

The control unit 30 is configured by a microprocessor (not shown) including a CPU and memory. In the control unit 30, the CPU of the microprocessor executes various controls related to the water treatment system 1 according to a predetermined program read from the memory. A part of the functions of the control unit 30 will be described below.

Based on the chlorine concentration measured by the first chlorine concentration sensor 9 and/or the second chlorine concentration sensor 10, the control unit 30 determines the dosage amount of the stabilizer added by the first chemical addition device 4, the second 2 Chemical injection amount of reducing agent added by chemical addition device 5 Chemical injection amount of bromine compound added by third chemical addition device 6 Chemical injection of chlorine-based oxidant added by fourth chemical addition device 7 As a chemical dosing control unit that adjusts the balance of the molar ratio of the chlorine-based oxidant and the stabilizer in the water supply W21 by adjusting the amount and the chemical dosing amount of the stabilizer added by the fifth chemical addition device 8 perform the functions of In this specification, the "concentration of free chlorine" measured by the first chlorine concentration sensor 9 and the "concentration of combined chlorine" measured by the second chlorine concentration sensor are collectively referred to as "chlorine concentration".

When the control unit 30 uses both the free chlorine concentration measured by the first chlorine concentration sensor 9 and the combined chlorine concentration measured by the second chlorine concentration sensor 10, for example, both Only the higher or lower chlorine concentration may be used.

In the present embodiment, for example, the chlorine concentration regions measured by the first chlorine concentration sensor 9 and/or the second chlorine concentration sensor 10 are sequentially changed from a low concentration region to a high concentration region. When the chlorine concentration is in the first region when the division is made into the second region, the third region, and the fourth region, the control unit 30 controls the fourth chemical addition device 7 to In order to increase the concentration of stabilized hypochlorous acid to an appropriate value, the amount of chlorine-based oxidizing agent injected is increased, and by controlling the first chemical addition device 4 and the fifth chemical addition device 8, The dosage of the stabilizing agent may be adjusted so as not to leave free chlorine in the water.

Further, when the chlorine concentration is in the second region, the control unit 30 controls the first chemical addition device 4 and the fifth chemical addition device 8 so as not to leave free chlorine in the water supply W21. The dosing amount of the agent may be adjusted.

Further, when the chlorine concentration is in the third region, the controller 30 controls the third chemical addition device 6 to reduce damage to the reverse osmosis membranes of the reverse osmosis membrane module 14. By increasing the chemical feeding amount of the bromine compound to and controlling the first chemical addition device 4 and the fifth chemical addition device 8, the chemical feeding amount of the stabilizer so as not to leave free chlorine in the water supply W21 may be adjusted.

Further, when the chlorine concentration is in the fourth region, the controller 30 controls the second chemical addition device 5 to lower the chlorine concentration in the feed water W21 to an appropriate value. At the same time, by controlling the first chemical addition device 4 and the fifth chemical addition device 8, the chemical injection amount of the stabilizer is adjusted so as not to leave free chlorine in the water supply W21 good.

It should be noted that the above control content is merely an example, and the present invention is not limited to this. For example, when the chlorine concentration is in any of the second to fourth regions, the controller 30 may control the fourth chemical addition device 7 to reduce the amount of chlorine-based oxidant to be fed. .

[Operation of the Invention]
Hereinafter, an operation example of the water treatment system 1 which is an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a flow chart showing the operation of the water treatment system 1 of the present invention.
In the following, the first region is defined as a region where the chlorine concentration is less than C 1, the second region is defined as a region where the chlorine concentration is C _{1 or} more and less than C ₂ , and the third region is defined as a region where the chlorine concentration is C _{The fourth} region is defined as a region having a chlorine concentration of _{C3 or} higher.

Table 1 below shows example settings for C ₁ -C ₃ . It is considered that the control concentration in the concentrated water is preferably 0.5 to 2.0 mg/L as effective chlorine concentration. The concentration in the water supply is the value obtained by dividing this value by the concentration ratio, and assuming a recovery rate of 50 to 80%, the concentration ratio will be 2 to 5 times. This is based on a formula of concentration ratio=1/(1-recovery).

In step S1, if the chlorine concentration measured by the first chlorine concentration sensor 9 and/or the second chlorine concentration sensor 10 is less than _C1 (S1: YES), the process proceeds to step S2. If the chlorine concentration measured by the first chlorine concentration sensor 9 or the second chlorine concentration sensor 10 is C1 _or higher (S1: NO), the process proceeds to step S3.

In step S2, the controller 30 controls the fourth chemical addition device 7 to increase the dosage of the chlorine-based oxidant, and controls the first chemical addition device 4 and the fifth chemical addition device 8. Thus, the amount of stabilizing agent to be injected is adjusted so as not to leave free chlorine in the feed water W21. After that, the process moves to step S1 (return).

In step S3, if the chlorine concentration measured by the first chlorine concentration sensor 9 or the second chlorine concentration sensor 10 is greater than or equal to _C1 and less than _C2 (S3: YES), the process proceeds to step S4. If the chlorine concentration measured by the first chlorine concentration sensor 9 or the second chlorine concentration sensor 10 is C2 _or higher (S3: NO), the process proceeds to step S5.

In step S4, the control unit 30 controls the first chemical addition device 4 and the fifth chemical addition device 8 to adjust the amount of stabilizing agent to be injected so as not to leave free chlorine in the water supply W21. After that, the process moves to step S1 (return).

In step S5, if the chlorine concentration measured by the first chlorine concentration sensor 9 and/or the second chlorine concentration sensor 10 is C2 _or more and less than _C3 (S5: YES), the process proceeds to step S6. . If the chlorine concentration measured by the first chlorine concentration sensor 9 or the second chlorine concentration sensor 10 is C3 _or higher (S5: NO), the process proceeds to step S7.

In step S6, the control unit 30 controls the third chemical addition device 6 to increase the chemical injection amount of the bromine compound to the water supply W21, and the first chemical addition device 4 and the fifth chemical addition device 8. By controlling, the dosage of the stabilizing agent is adjusted so as not to leave free chlorine in the feed water W21. After that, the process moves to step S1 (return).

In step S7, the control unit 30 controls the second chemical addition device 5 to start chemical injection of the reducing agent into the water supply W21, and controls the first chemical addition device 4 and the fifth chemical addition device 8. By doing so, the dosage of the stabilizing agent is adjusted so as not to leave free chlorine in the feed water W21. After that, the process moves to step S1 (return).

[Effect of this embodiment]
According to the water treatment system 1 according to the present embodiment described above, for example, the following effects are exhibited.
The water treatment system 1 of the present invention includes a filtration device 3 that filters raw water W10 to generate feed water W21, a raw water line L1 that supplies raw water W10 to the filtration device 3, and a feed water W21 generated by the filtration device 3. A reverse osmosis membrane module 14 that separates water W30 and concentrated water W40, a water supply line L2 that supplies feed water W22 to the reverse osmosis membrane module, and a permeated water line that delivers permeated water W30 separated by the reverse osmosis membrane module 14. L3, a concentrated water line L4 that delivers the concentrated water W40 separated by the reverse osmosis membrane module 14, a concentrated water line L6 that discharges all or part of the concentrated water W40 to the outside of the system as concentrated water W60, and water supply. The balance of the molar ratio between the chlorine-based oxidant and the stabilizer in the water supply W21 is adjusted by adjusting the first chemical addition device 4 for injecting the stabilizer into W21 and the amount of chemical injection of the stabilizer. A control unit 30 is provided.

When feed water filtered by the filtration device 3 is used as feed water to the reverse osmosis membrane module, fluctuations in residual chlorine concentration in the feed water after filtration become large. By adjusting the dosing of the stabilizer, it becomes possible to set the chlorine concentration in the upstream stage of the reverse osmosis membrane module to an appropriate value. Furthermore, compared to the method of removing free chlorine at a later stage than the filtering device, it is possible to simplify chemical feeding and reduce the amount of chemicals used in the entire system.

In addition, the water treatment system 1 further includes a first chlorine concentration sensor 9 that measures the chlorine concentration at the outlet of the filtration device 3, and the first chemical addition device 4 is added to the feed water W21 downstream of the first chlorine concentration sensor 9. A stabilizing agent is injected, and the controller 30 adjusts the amount of stabilizing agent injected based on the chlorine concentration measured by the first chlorine concentration sensor 9 .

By adjusting the chemical injection of the stabilizer based on the chlorine concentration at the filter outlet, the chlorine concentration in the upstream stage of the reverse osmosis membrane module can be adjusted to an appropriate value.

In addition, the water treatment system 1 further includes a second chemical addition device 5 that injects a reducing agent into the feed water W21 downstream of the first chlorine concentration sensor 9, and the control unit 30 measures by the first chlorine concentration sensor 9. Based on the determined chlorine concentration, the chemical feeding amount of the reducing agent is controlled.

When the chlorine concentration at the filter outlet is too high, by adding a reducing agent to the feed water, it becomes possible to supply the feed water containing a predetermined concentration of residual chlorine to the reverse osmosis membrane module.

The reducing agent is at least one of SBS (sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas.

By using one or more of SBS (sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas as a reducing agent, feedwater containing residual chlorine at a predetermined concentration can be supplied to the reverse osmosis membrane module. It becomes possible.

In addition, the water treatment system 1 further includes a third chemical addition device 6 that injects a bromine compound into the feed water W21 downstream of the first chlorine concentration sensor 9, and the control unit 30 measures by the first chlorine concentration sensor 9. Based on the determined chlorine concentration, the amount of bromine compound to be injected is controlled.

By chemically injecting a bromine compound to switch the stabilizer from a chlorine-based one to a bromine-based one, the oxidizing power of feed water is weakened, making it possible to reduce the degree of deterioration of the reverse osmosis membrane.

In addition, the water treatment system 1 further includes a fourth chemical addition device 7 that injects a chlorine-based oxidant into the raw water W10, and the control unit 30 controls the chlorine concentration measured by the first chlorine concentration sensor 9, Controls the chemical injection of the chlorine-based oxidant to the raw water W10.

If the chlorine concentration at the outlet of the filtration device is too high or too low, by controlling the chemical injection of the chlorine-based oxidant based on the chlorine concentration at the outlet of the filtration device, the release of free chlorine in the upstream stage of the reverse osmosis membrane module. It becomes possible to set the density to an appropriate value.

Further, the water treatment system 1 further includes a fifth chemical addition device 8 for injecting a stabilizer into the raw water W10, and the control unit 30 controls the raw water W10 based on the chlorine concentration measured by the first chlorine concentration sensor 9. It controls the dosing of both the stabilizing agent that is dosed into W10 and the stabilizing agent that is dosed into the water supply W21.

Since there are many pipes and tanks in the system, free chlorine volatilizes if the raw water stays for a long time. By converting free chlorine into a conjugate such as stabilized hypochlorous acid, it becomes possible to keep the inside of the system cleaner.

In addition, the water treatment system 1 further includes a second chlorine concentration sensor 10 that measures the chlorine concentration in the concentrated water line L4 or the concentrated wastewater line L6, and the control unit 30 controls the chlorine concentration measured by the first chlorine concentration sensor 9 In addition to , chemical feeding is controlled based on the chlorine concentration measured by the second chlorine concentration sensor 10 .

Not only the chlorine concentration measured by the first chlorine concentration sensor 9, but also the chemical addition device for reducing agents, stabilizers, and bromine compounds, and the concentrated water line L4 or the concentrated drainage line after the reverse osmosis membrane module 14 By controlling chemical injection based also on the chlorine concentration in L6, it becomes possible to more appropriately adjust the chemical injection amount balance of each chemical.

The stabilizing agent may also contain a chelate component that sequesters metal ions and disperses them, and/or a polymer.

It is thought that film deterioration can be reduced by increasing the amount of stabilizer added. By adding a component having the transition metal can be blocked, film deterioration can be further suppressed. In particular, when added at the same ratio as that of the stabilizer, as the amount added increases, the effect of blocking transition metals can be enhanced, and the complementary effects can reduce film deterioration.
In addition, the chelate component, which has sequestering and dispersing effects on metal ions, not only sequesters transition metals, but also plays a role in preventing metals from precipitating in excess of their solubility. This makes it possible to prevent membrane clogging due to the formation of metal scales while suppressing biofilms.
When biofilms and scales are formed in a composite manner, the biofilm structure tends to be strengthened by the scale portion acting as a binder. In combination with the biofilm inhibitory effect of stabilized hypobromous acid, a further biofilm inhibitory effect is expected.
In addition, the chelate component itself has a bactericidal effect and an antiseptic effect due to the action of depriving bacteria of essential metals necessary for living and the action of collapsing cells by reacting with metals in cells. It is expected to improve the storage stability in the water to be treated, and when added to the water to be treated, it is expected to have a further biofilm suppression effect by acting complementarily with the stabilized hypobromous acid.

[Modification]
Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various forms.

[Modification 1]
In the water treatment system 1, a first chlorine concentration sensor 9 and a second chlorine concentration sensor 10 are provided, and a control unit 30 as a chemical injection control unit performs chemical injection based on the chlorine concentration measured by these sensors. Control, but not limited to. For example, the water treatment system 1 includes a potential measuring device installed in the raw water line L1 instead of the first chlorine concentration sensor 9, and a potential installed in the concentrated wastewater line L6 instead of the second chlorine concentration sensor 10. A measuring device may be provided. Furthermore, the control unit 30 as a chemical injection control unit may control chemical injection based on the oxidation-reduction potentials measured by these potential measuring devices.

[Modification 2]
The water treatment system 1 may have a configuration different from the above embodiment. For example, although the circulating water line L5 is provided in the above description, the present invention is not limited to this, and a configuration without the circulating water line L5 may be employed. Moreover, the water treatment system 1 may be configured without the third chemical addition device 6 for chemical injection of the bromine compound. Moreover, the water treatment system 1 may be configured without the fifth chemical addition device 8 for injecting the stabilizer. Further, in the water treatment system 1, the fourth chemical addition device 7 for injecting the chlorine-based oxidant may be provided in the water supply line L2 instead of the raw water line L1. Moreover, the water treatment system 1 may be configured to have only one of the first chlorine concentration sensor 9 and the second chlorine concentration sensor 10 .

[Modification 3]
In addition, the water treatment systems 1 and 1A are more suitable if a chlorine-resistant membrane is used, since the influence of membrane deterioration is less likely to occur. By using together with the chemical injection adjustment method described above, the deterioration effect can be further reduced. As the chlorine resistant film, for example, there is a film manufactured using a polyamide-based material.

[Modification 4]
Further, in the water treatment systems 1 and 1A, it is preferable to use the water supply to which the chemical is added in the membrane cleaning step. The membrane cleaning process includes flushing and the like, and water may be supplied by connecting a water supply line to the concentrated water line.

[Modification 5]
Moreover, in the water treatment systems 1 and 1A, in order to reduce the amount of contact between chlorine and the membrane, from the viewpoint of deterioration prevention, the above chemical may be intermittently added only when biofilms are generated.

[Modification 6]
Moreover, in the water treatment systems 1 and 1A, in order to suppress the propagation of microorganisms during system suspension, it is preferable to add the above chemicals before suspension of the system.

1 water treatment system,
3 filtration device 4 first chemical addition device (first chemical injection device)
5 Second chemical addition device (second chemical injection device)
6 Third chemical addition device (third chemical injection device)
7 Fourth chemical addition device (fourth chemical injection device)
8 Fifth chemical addition device (fifth chemical injection device)
9 First chlorine concentration sensor (first chlorine concentration measuring device)
10 Second chlorine concentration sensor (second chlorine concentration measuring device)
11 water quality sensor (water quality measuring means)
12 pressurizing pump 14 reverse osmosis membrane module 30 control section (chemical dosing control section)
L1 raw water line L2 water supply line,
L3 permeate line L4 concentrate line,
L5 circulating water line L6 concentrated drainage line,
L21 First water supply line L22 Second water supply line

Claims (16)

a filtration device for filtering raw water to generate feed water;
a raw water line that supplies raw water to the filtration device;
a reverse osmosis membrane module that separates feedwater generated by the filtration device into permeated water and concentrated water;
a water supply line for supplying water to the reverse osmosis membrane module;
a permeated water line for sending permeated water separated by the reverse osmosis membrane module;
a concentrated water line for delivering concentrated water separated by the reverse osmosis membrane module;
A concentrated wastewater line that discharges all or part of the concentrated water to the outside of the system as concentrated wastewater;
a fourth chemical dosing device for dosing a chlorine-based oxidant into raw water and/or feed water;
a first chlorine concentration measuring device for measuring the free chlorine concentration in the feed water at the outlet of the filtering device;
a first chemical dosing device that, downstream of the first chlorine concentration measuring device, feeds a stabilizer that, when added to the feed water, generates stabilized hypochlorous acid through a chemical reaction with free chlorine in the feed water;
By adjusting the dosage of the stabilizing agent based on the free chlorine concentration at the outlet of the filtering device measured by the first chlorine concentration measuring device, the chlorine-based oxidant in the feed water and the stabilizing agent a chemical dosing control unit that adjusts the molar ratio balance of the agents to bring the concentration of free chlorine in the upstream stage of the reverse osmosis membrane module to an appropriate value . 2. The water treatment system of claim 1 , wherein said stabilizing agent comprises sulfamic acid . Downstream of the first chlorine concentration measuring device, further comprising a second chemical injection device for chemically injecting a reducing agent into the water supply,
3. The water treatment system according to claim 2, wherein said chemical dosing control unit controls the chemical dosing amount of the reducing agent based on the free chlorine concentration measured by said first chlorine concentration measuring device. 4. The water treatment system according to claim 3, wherein the reducing agent is one or more of SBS (sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas. Downstream of the first chlorine concentration measuring device, further comprising a third chemical injection device for chemically injecting a bromine compound into the water supply,
The water treatment according to any one of claims 2 to 4, wherein the chemical injection control unit controls the chemical injection amount of the bromine compound based on the free chlorine concentration measured by the first chlorine concentration measuring device. system. The chemical dosing control unit controls chemical dosing of the chlorine-based oxidant to raw water and/or feed water based on the free chlorine concentration at the outlet of the filtering device measured by the first chlorine concentration measuring device. The water treatment system according to any one of claims 2-5. Further comprising a fifth chemical dosing device for dosing the stabilizing agent into the raw water,
The chemical dosing control unit controls both the stabilizing agent that is chemically injected into the raw water and the stabilizing agent that is chemically injected into the feed water based on the concentration of free chlorine measured by the first chlorine concentration measuring device. The water treatment system according to any one of claims 2 to 6, which controls chemical injection of. Further comprising a second chlorine concentration measuring device for measuring the chlorine concentration in the concentrated water line or the concentrated wastewater line,
wherein the chemical dosing control unit controls chemical dosing based on the chlorine concentration measured by the second chlorine concentration measuring device in addition to the concentration of free chlorine measured by the first chlorine concentration measuring device; 8. The water treatment system according to any one of 7. a filtration device for filtering raw water to generate feed water;
a raw water line that supplies raw water to the filtration device;
a reverse osmosis membrane module that separates feedwater generated by the filtration device into permeated water and concentrated water;
a water supply line for supplying water to the reverse osmosis membrane module;
a permeated water line for sending permeated water separated by the reverse osmosis membrane module;
a concentrated water line for delivering concentrated water separated by the reverse osmosis membrane module;
A concentrated wastewater line that discharges all or part of the concentrated water to the outside of the system as concentrated wastewater;
a fourth chemical dosing device for dosing a chlorine-based oxidant into raw water and/or feed water;
a potential measuring device for measuring the oxidation-reduction potential at the outlet of the filtering device in the water supply line;
a first chemical dosing device for dosing, downstream of the potential measuring device, a stabilizing agent that is added to the feed water to generate stabilized hypochlorous acid through a chemical reaction with free chlorine in the feed water;
Based on the oxidation-reduction potential at the outlet of the filtration device measured by the potential measuring device, the molar ratio of the chlorine-based oxidant and the stabilizer in the water supply is controlled by controlling the chemical injection amount of the stabilizer. and a chemical dosing control unit that adjusts the balance of the reverse osmosis membrane module and adjusts the concentration of free chlorine in the upstream stage of the reverse osmosis membrane module to an appropriate value . Downstream of the potential measuring device, further comprising a second chemical injection device for injecting a reducing agent into the water supply,
10. The water treatment system according to claim 9, wherein said chemical dosing control unit controls the chemical dosing amount of the reducing agent based on the oxidation-reduction potential measured by said potential measuring device. 11. The water treatment system according to claim 10, wherein the reducing agent is one or more of SBS (sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas. Downstream of the potential measuring device, further comprising a third chemical injection device for injecting a bromine compound into the water supply,
The water treatment system according to any one of claims 9 to 11, wherein the chemical dosing control unit controls the chemical dosing amount of the bromine compound based on the oxidation-reduction potential measured by the potential measuring device. Any one of claims 9 to 12, wherein the chemical dosing control unit controls chemical dosing of the chlorine-based oxidant to raw water and/or feed water based on the oxidation-reduction potential measured by the potential measuring device. The water treatment system described in . Further comprising a fifth chemical dosing device for dosing the stabilizing agent into the raw water,
The chemical dosing control unit controls the dosing of both the stabilizing agent into the raw water and the stabilizing agent into the feed water based on the oxidation-reduction potential measured by the potential measuring device. is controlled, the water treatment system according to any one of claims 9 to 13. Further comprising water quality measuring means for measuring the water quality of the water supply,
Claims 1 to 14, wherein the chemical dosing control unit adjusts the balance of the molar ratio of the chlorine-based oxidant and the stabilizer in the water supply and the chemical dosing amount based on the water quality measured by the water quality measuring means. The water treatment system according to any one of . The water treatment system according to any one of claims 1 to 15, wherein the stabilizing agent contains a chelate component having a sequestering and dispersing action on metal ions and/or a polymer.

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