JP2023059384A - water treatment system - Google Patents

Abstract

To provide a water treatment system capable of preventing oxidative deterioration of reverse osmosis membranes and reducing a cost of chemical feed.SOLUTION: A water treatment system 1 has: a reverse osmosis membrane module 17; a feed water line for supplying water to the reverse osmosis membrane module 17; a permeated water line L2 for delivering permeated water W20 separated in the reverse osmosis membrane module 17; a concentrated wastewater line L5; first chemical feed means for executing chemical feed of either a stabilizer or a reducer into the water supplied to the reverse osmosis membrane module 17; a control part 30 for controlling a first chemical feed amount which is a chemical feed amount of either the stabilizer or the reducer by the first chemical feed means; and halogen detection means 6 for detecting a halogen concentration of the permeated water separated by the reverse osmosis membrane module 17, wherein the control part 30 controls the first chemical feed amount based on the halogen concentration detected by the halogen detection means 6.SELECTED DRAWING: Figure 1

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.

When water in which a halogen-based oxidizing agent such as sodium hypochlorite is added or in which halogen is present by electrolysis is treated with a reverse osmosis membrane, the reverse osmosis membrane is oxidatively deteriorated. For this reason, as disclosed in Patent Document 2, for example, a technique is known in which a reducing agent such as sodium hydrogen sulfite (SBS) or sodium sulfite is added in the upstream stage of a reverse osmosis membrane to remove halogen. In addition, a stabilizer may be added before the reverse osmosis membrane.

JP 2016-190214 A JP-A-7-308671

When a reducing agent or stabilizer is used in a water treatment system, poor mixing of the halogen with the reducing agent or stabilizer may occur. Also, the halogen concentration in the water supply of the water treatment system may become excessive. In the above case, there is a risk that halogen will leak into the reverse osmosis membrane, causing oxidative deterioration of the reverse osmosis membrane. On the other hand, in order to prevent oxidative deterioration of the reverse osmosis membrane, it is conceivable to excessively inject the reducing agent and the stabilizing agent into the water supply, but there is a problem that the cost of injecting the chemical increases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a water treatment system capable of preventing oxidative deterioration of a reverse osmosis membrane and reducing the cost of chemical dosing.

The present invention comprises a reverse osmosis membrane module, 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, and the reverse osmosis membrane module for separation. A concentrated waste water line for discharging part or all of the concentrated water to the outside of the system as concentrated waste water; 1 chemical injection means; chemical injection control means for controlling a first chemical injection amount which is an amount of one of the stabilizing agent and the reducing agent injected by the first chemical injection means; and the reverse osmosis membrane module. and a halogen detection means for detecting the halogen concentration of the permeated water separated by, and the chemical injection control means controls the first chemical injection amount based on the halogen concentration detected by the halogen detection means. to water treatment systems.

In the water treatment system described above, it is preferable that the chemical feeding control means increases the first chemical feeding amount when the halogen concentration detected by the halogen detecting means is equal to or higher than a predetermined value.

In the above water treatment system, the water supply line is provided with a second chemical injection means for chemically injecting hypohalous acid into the water supply, and the chemical injection control means is detected by the halogen detection means. When the halogen concentration is equal to or higher than a predetermined numerical value, it is preferable to perform control to reduce a second chemical injection amount, which is the chemical injection amount of the hypohalous acid by the second chemical injection means.

In the water treatment system described above, the chemical feeding control means controls the molar concentration of halogen in the water supply of the water supply line and the molar concentration of either the stabilizing agent or the reducing agent to be in a predetermined ratio. Furthermore, it is preferable to control the first chemical injection amount or the second chemical injection amount.

In the water treatment system described above, the halogen detection means is preferably colorimetric halogen detection means for measuring the absorbance of permeated water colored by the reaction between the halogen and the reagent.

In the water treatment system described above, the reverse osmosis membrane used in the reverse osmosis membrane module is preferably a halogen-resistant membrane.

1 is an overall configuration diagram of a water treatment system according to a first embodiment of the present invention; FIG. It is a functional block diagram of the control part with which the water treatment system concerning a 1st embodiment of the present invention is equipped. It is a whole lineblock diagram of a water treatment system concerning a 2nd embodiment of the present invention. It is a functional block diagram of the control part with which the water treatment system concerning a 2nd embodiment of the present invention is equipped.

[1 First Embodiment]
[1.1 Overall configuration]
Hereinafter, the water treatment system 1 which is 1st Embodiment of this invention is demonstrated, referring 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 an oxidant addition device 3 as a second chemical injection means, a stabilizer addition device 4 as a first chemical injection means, a scale dispersant addition device 5, Halogen detection means 6, pressure pump 15, inverter 16, reverse osmosis membrane module (hereinafter also referred to as "RO membrane module") 17, flow control valve 18, proportional control drain valve 19, and control unit 30 , a first flow sensor FM1, a second flow sensor FM2, and a third flow sensor FM3. 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 first water supply line L11 and a second water supply line L12, a permeated water line L2, a concentrated water line L3, a circulating water line L4, and a concentrated waste water line L5. "Line" is a generic term for lines such as channels, routes, and pipelines through which fluid can flow. In addition, water flowing through the water supply line L1, the concentrated water line L3, or the circulating water line L4, regardless of its origin (source) or water quality, is also referred to as "water supply", and is referred to as the concentrated water line L3, circulating water line L4, or concentrated The water flowing through the drain line L5 is also called "concentrated water".

The first water supply line L11 and the second water supply line L12 are lines that supply water supplies W11 and W12 toward the reverse osmosis membrane module 17, respectively.

The upstream end of the first water supply line L11 is connected to the water source 2 of the water supply W11. The downstream end of the first water supply line L11 is connected to the second water supply line L12 and the circulating water line L4 at the connection J1. For example, an oxidant addition device 3, a stabilizer addition device 4, and a scale dispersant addition device 5 are installed in the first water supply line L11 in this order from the upstream side to the downstream side. In addition to the above, a residual halogen concentration detection device capable of detecting the residual halogen concentration in the feed water W11 may be installed upstream of the oxidant addition device 3 in the first water supply line L11.

The feed water W11 may be treated water filtered by a filtering device (not shown) or water containing free halogens such as tap water.

The oxidizing agent addition device 3 as the second chemical injection means is a device for chemically injecting, for example, hypohalous acid as an oxidizing agent into the water supply W11 in the first water supply line L11. The oxidant addition device 3 is electrically connected to the controller 30 . The oxidant addition device 3 suppresses biofilm deposition in the RO membrane module 17 by adding an oxidant to the feed water W11. Examples of the hypohalous acid include sodium hypochlorite, sodium hypobromite, and the like. In addition to the above, liquefied chlorine, bleaching powder, chlorinated isocyanuric acid, and the like may be used as the oxidizing agent. The above oxidizing agents may be used singly or in combination of two or more.

A stabilizer addition device 4 as a first chemical injection means adds a stabilizer as a first chemical in order to prevent deterioration of the reverse osmosis membrane provided in the RO membrane module 17 . By adding the stabilizer, for example, the hypohalous acid contained in the feed water W11 becomes stabilized hypohalous acid. In the RO membrane module 17, since deterioration of the reverse osmosis membrane can be effectively suppressed, examples of stabilizers include stabilizers such as amine-based compounds such as sulfamic acid-based compounds.

When the feed water W11 contains hypochlorous acid, the stabilizer may further contain a bromine compound such as sodium bromide. A bromine compound first reduces hypochlorous acid and produces hypobromous acid. Next, the generated hypobromous acid reacts with a stabilizer such as a sulfamic acid-based compound to become stabilized hypobromous acid. This makes it possible to reduce damage to the reverse osmosis membrane provided in the RO module 17 as compared with the case of generating stabilized hypochlorous acid. When the feed water W11 contains a bromine source such as bromide ions, the stabilizing agent may not contain a bromine compound. Alternatively, hypochlorous acid and bromine compounds may be added separately.

Furthermore, the stabilizer may contain a halogen bonded to the sulfamic acid-based compound. That is, the stabilizing agent may contain a stabilized halogen-type component and a surplus of a sulfamic acid-based compound. This makes it possible to use a stabilized halogen salt as a disinfectant in addition to stabilized hypochlorous acid and stabilized hypobromous acid.

The scale dispersant addition device 5 adds a scale dispersant to the water supply W11 in the first water supply line L11 in order to suppress the formation of scale such as silica and hardness components in the RO module 17 . Examples of scale dispersants include sequestering metal ions, chelating agents having dispersing action, and/or low-molecular-weight polymers.

The upstream end of the second water supply line L12 is connected to the connection J1. A downstream end of the second water supply line L12 is connected to a primary inlet port of the RO module 17 . A pressure pump 15 is provided in the second water supply line L12.

The pressurizing pump 15 is a device that sucks the water supply W12 and pumps (discharges) it toward the RO module 17 . The pressurizing pump 15 is supplied with drive power whose frequency has been converted from the inverter 16 . The pressurizing pump 15 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 16 is an electric circuit (or a device having such a circuit) that supplies drive power whose frequency is converted to the pressure pump 15 . Inverter 16 is electrically connected to control unit 30 . A command signal is input to the inverter 16 from the control unit 30 . The inverter 16 outputs to the pressurizing pump 15 drive power having a drive frequency corresponding to the command signal (current value signal or voltage value signal) input from the control unit 30 .

Feed water W12 is supplied to the RO module 17 via the pressure pump 15 . Moreover, the water supply W12 is composed of the water supply W11 and the circulating water W40 described later.

The RO module 17 is equipment that separates the feed water W12 into the permeated water W20 and the concentrated water W30. Specifically, the RO module 17 is equipment for membrane separation treatment of the feed water W12 discharged from the pressure pump 15 into a permeated water W20 from which dissolved salts have been removed and a concentrated water W30 in which dissolved salts have been concentrated. . The RO module 17 comprises single or multiple reverse osmosis membrane elements (not shown). The RO module 17 performs a membrane separation process on the feed water W12 using these reverse osmosis membrane elements to produce a permeated water W20 and a concentrated water W30.

The reverse osmosis membrane in the RO module 17 is preferably a halogen-resistant membrane. As a result, even if halogen is detected in the permeated water W20 by the halogen detection means 6, which will be described later, deterioration of the reverse osmosis membrane is suppressed until control for reducing halogen in the feed water W11 is applied. be able to. Halogen-resistant films include, for example, those manufactured using materials such as polyamides and cellulose acetates. A commercially available product can be used as the halogen-resistant film. Examples of polyamide-based halogen-resistant films include TM720D-440 (trade name, manufactured by Toray Industries, Inc.). Examples of the cellulose acetate-based halogen-resistant film include HA3110 (trade name, manufactured by Toyobo) and SC4201 (trade name, manufactured by Toray Industries, Inc.). Since cellulose acetate-based halogen-resistant membranes have high halogen-resistant properties due to their material properties, the water treatment system 1 according to the present embodiment uses reverse osmosis polyamide-based halogen-resistant membranes, which require more attention in controlling the halogen concentration. It is more suitable when used as a membrane.

The permeated water line L2 is a line through which the permeated water W20 separated by the RO module 17 is delivered. The upstream end of the permeate line L2 is connected to the secondary port of the reverse osmosis membrane module 17 . A downstream end of the permeate line L2 is connected to a storage tank (not shown). A halogen detector 6 and a first flow rate sensor FM1 are installed in the permeated water line L2.

Halogen detection means 6 measures the halogen concentration in the permeated water W20. The halogen detection means 6 can measure, for example, the total amount of halogen including free halogen such as free chlorine and free bromine in the permeated water W20. When free halogen is contained in the feed water W12, the free halogen is consumed by combining with the biofilm formed on the RO module 17, thereby suppressing biofilm formation. However, if the total amount of free halogen contained in the feed water W12 is excessive with respect to the amount required to suppress the biofilm formation, the free halogen reaches the reverse osmosis membrane of the RO module 17 and reverse osmosis. Degradation of the membrane may occur. Excess free halogen reaching the reverse osmosis membrane permeates the reverse osmosis membrane due to its low molecular weight. Halogen detection means 6 can detect the total amount of halogen including free halogen that permeates the reverse osmosis membrane of RO module 17 . Therefore, it becomes possible to optimize the amount of the oxidizing agent and the first chemical added to the feed water W11.

A specific example of the halogen detection means 6 is preferably, for example, colorimetric halogen detection means for measuring the absorbance of permeated water colored by the reaction between the halogen and the reagent. Specifically, the colorimetric halogen detection means 6 intermittently collects a portion of the permeated water W20 from the permeated water line L2 at predetermined intervals, and adds a coloring reagent to the collected permeated water W20. The halogen concentration of the permeated water W20 is measured by adding it to develop a color and measuring the absorbance of the permeated water W20 that has developed the color. By applying a colorimetric halogen detection means as the halogen detection means 6, the halogen concentration can be accurately measured even for the permeated water W20 having a low electrical conductivity. In addition, the colorimetric halogen detection means is preferable because it can selectively measure the total amount of free halogen even when low-molecular-weight binding halogen such as chloramine is mixed in the permeated water W20. . As such colorimetric halogen detecting means, known means can be used. As the halogen detection means 6, it is possible to use a polarographic electrode, an oxidation-reduction potential meter (ORP meter), etc. in addition to the colorimetric halogen detection means, but it is difficult to be affected by the electrical conductivity of the permeated water W20. It is most preferable to use a colorimetric halogen detection means as the halogen detection means 6 because accurate measurement can be performed.

The first flow rate sensor FM1 is a device that detects the flow rate of the permeated water W20 flowing through the permeated water line L2 as a first detected flow rate value. The first flow rate sensor FM1 is electrically connected to the controller 30 . A first detected flow rate value of the permeated water W20 detected by the first flow rate sensor FM1 is transmitted to the control section 30 as a pulse signal. As the first flow rate sensor FM1, for example, a pulse transmission type flow rate sensor in which an axial flow impeller or a tangential impeller (not shown) is arranged in a flow path housing can be used.

The concentrated water line L3 is a line through which the concentrated water W30 separated by the RO module 17 flows. The upstream end of the concentrated water line L3 is connected to the secondary port of the RO module 17 . Further, the downstream side of the concentrated water line L3 is branched into a circulating water line L4 and a concentrated waste water line L5 at the connection J2.

The circulating water line L4 is a line that is connected to the concentrated water line L3 and returns concentrated water (circulating water W40) as water supply to the second water supply line L12. In this embodiment, the circulating water line L4 is a line that returns (circulates) the concentrated water W30 flowing through the concentrated water line L3 as circulating water W40 upstream of the pressure pump 15 in the second water supply line L12. be. The upstream end of the circulating water line L4 is connected to the concentrated water line L3 at a connection J2. In addition, the downstream end of the circulating water line L4 is connected to the second water supply line L12 at the connection J1. The circulating water line L4 is provided with a flow control valve 18 and a second flow sensor FM2.

The flow rate adjustment valve 18 is a valve that adjusts the flow rate of the circulating water W40 flowing through the circulating water line L4. The flow regulating valve 18 has a constant flow element that allows a substantially constant flow of circulating water W40 to flow regardless of the differential pressure in the flow regulating valve 18, and a and a proportional element that increases the flow rate of the circulating water W40. The differential pressure at the flow rate control valve 18 is specifically the differential pressure between the water pressures in the lines before and after the flow rate control valve 18 . A constant flow element maintains a constant flow value without the need for auxiliary power or external manipulation, and may be used, for example, under the name of a water governor. As the proportional element, for example, an element called an orifice may be used, and the flow rate of the circulating water W<b>40 flowing from the orifice is proportional to the differential pressure in the flow control valve 18 .

A constant flow valve may be used instead of the flow control valve 18 . The constant flow valve is a device that adjusts the flow rate of the circulating water W40 flowing through the circulating water line L4 so as to maintain a predetermined constant flow rate value. The "constant flow rate value" held in the constant flow valve is a concept that has a range of constant flow rate values, and is not limited to the target flow rate value in the constant flow 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. A constant flow valve maintains a constant flow rate value without the need for auxiliary power or external operation, and is, for example, known by the name of a water governor. The constant flow rate valve may be operated by auxiliary power or external operation to maintain a constant flow rate value.

The second flow rate sensor FM2 is a device that detects the flow rate of the circulating water W40 flowing through the circulating water line L4 as a second detected flow rate value. The second flow rate sensor FM2 is electrically connected to the controller 30 . A second detected flow rate value of the circulating water W40 detected by the second flow rate sensor FM2 is transmitted to the controller 30 as a pulse signal. As with the first flow rate sensor FM1, the second flow rate sensor FM2 can be, for example, a pulse transmission type flow rate sensor in which an axial flow impeller or a tangential impeller (not shown) is arranged in the flow path housing.

The concentrated waste water line L5 is a line that is connected to the concentrated water line L3 and discharges the concentrated water as the concentrated waste water W50 to the outside of the system. In this embodiment, the concentrated water line L5 is connected to the concentrated water line L3 at the connection part J2, and is a line that discharges the concentrated water W30 separated by the RO module 17 to the outside of the apparatus (outside the system) as the concentrated water W50. is. The concentrated drainage line L5 is provided with a proportional control drainage valve 19 and a third flow rate sensor FM3.

The proportional control drain valve 19 is a valve that adjusts the flow rate of the concentrated waste water W50 discharged from the concentrated waste water line L5 to the outside of the apparatus. The proportional control drain valve 19 is electrically connected to the controller 30 . The valve opening degree of the proportional control drain valve 19 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 19 to control the valve opening, the drain flow rate of the concentrated waste water W50 can be adjusted.

The third flow rate sensor FM3 is a device that detects the flow rate of the concentrated waste water W50 as a third detected flow rate value. The third flow rate sensor FM3 is electrically connected to the controller 30 . A third detected flow rate value of the concentrated waste water W50 detected by the third flow rate sensor FM3 is transmitted to the control section 30 as a pulse signal. Similar to the first flow rate sensor FM1, the third flow rate sensor FM3 may be, for example, a pulse transmission type flow rate sensor in which an axial flow impeller or a tangential impeller (not shown) is arranged in the flow path housing.

The control unit 30 as chemical feeding control means controls the first chemical feeding amount and the second chemical feeding amount for the water supply W11. 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.

FIG. 2 is a functional block diagram of the control section 30. As shown in FIG. The control unit 30 includes a stabilizer dosing control unit 301 , an oxidizing agent dosing control unit 302 , a dosing amount calculation unit 303 , and a dispersing agent dosing control unit 304 .

When the halogen concentration detected in the permeated water W20 by the halogen detection means 6 is equal to or greater than a predetermined value, the stabilizing agent dosing control unit 301 determines the first Perform control to increase the amount of chemical injection. That is, the stabilizer addition device 4 is controlled to increase the amount of the stabilizer added to the feed water W11. The predetermined halogen concentration detected in the permeated water W20 can be, for example, 0.002 mmol/L or less. In addition to the above, when it is estimated that the halogen concentration detected from the permeated water W20 is zero and the contamination of the reverse osmosis membrane of the RO module 17 is increasing, the stabilizer dosing control unit 301 Alternatively, control may be performed to reduce the dosage of the stabilizer within a predetermined range. Contamination of the reverse osmosis membrane is caused by a decrease in the temperature-corrected flow rate or permeation flux of the permeated water W20 detected by the first flow rate sensor FM1, or by an increase in the transmembrane pressure difference of the reverse osmosis membrane of the RO module 17. Presumed. The transmembrane pressure of the reverse osmosis membranes of the RO module 17 can be obtained, for example, by measuring the pressure of the feed water W12 at the primary side inlet of the RO module 17 and the pressure of the concentrated water W30 at the secondary side of the RO module 17 using a pressure sensor or the like. It can be calculated by measuring by

The stabilizing agent dosing control unit 301 controls the stabilizing agent addition device 4 to add the stabilizing agent to the feed water W11 so that the molar concentration of the stabilizing agent with respect to the molar concentration of halogen in the feed water W11 has a predetermined ratio. Control the injection volume. The molar concentration ratio can be, for example, 1 to 3 molar concentrations of the stabilizer with respect to 1 molar concentration of halogen. The molar concentration ratio may be 1.5-3. By setting the lower limit of the molar concentration ratio to 1.5, the halogen is stabilized and can be prevented from permeating the RO module 17, although it depends on the mixing state after the addition of the stabilizer. On the other hand, the lower limit of the molar concentration ratio can be set to less than 1 when halogen is not detected from the permeated water W20 by the halogen detecting means 6. As a result, the total amount of halogen in the feed water W11 is increased to such an extent that it does not permeate the reverse osmosis membrane, thereby suppressing biofilm formation in the RO module 17 and reducing the chemical injection amount of the stabilizer. be able to.

The stabilizing agent dosing control unit 301 may control the dosing amount of the stabilizing agent based on the increment of the stabilizer calculated by the dosing amount calculating unit 303 described below, and the halogen detection means When the halogen concentration in the permeated water W20 detected by 6 exceeds a predetermined threshold value, the amount of stabilizer added may be controlled such that a predetermined amount of stabilizer is added. .

Similar to the stabilizer injection control unit 301, the oxidant injection control unit 302 controls the oxidant addition device 3 so that the molar concentration of the stabilizer with respect to the molar concentration of halogen in the feed water W11 has a predetermined ratio. to control the dosage of hypohalous acid to the feed water W11. That is, when the halogen concentration detected in the permeated water W20 by the halogen detection means 6 is equal to or higher than a predetermined value, control is performed to reduce the second chemical feeding amount in the feed water W11 according to the halogen concentration in the permeated water W20. conduct. In addition to the above, the oxidant chemical injection control unit 302 presumes that the halogen concentration detected from the permeated water W20 is zero and that the contamination of the reverse osmosis membrane of the RO module 17 is increasing as described above. In this case, control may be performed to increase the dosage of hypohalous acid within a predetermined range.

The oxidant chemical dosing control unit 302 may control the chemical dosing amount of hypohalous acid based on the reduction amount of hypohalous acid calculated by the chemical dosing amount calculating unit 303, which will be described below. When the halogen concentration in the permeated water W20 detected by means 6 exceeds a predetermined threshold value, chemical injection of hypohalous acid is performed so as to reduce a predetermined amount of chemical injection of hypohalous acid. You can control the amount.

In the control unit 30, when the halogen concentration detected in the permeated water W20 is equal to or higher than a predetermined numerical value, the stabilizing agent chemical injection control unit 301 performs control to increase the first chemical injection amount in the feed water W11, It is optional whether the oxidant chemical injection control unit 302 performs control to reduce the second chemical injection amount in the water supply W11 or performs both in parallel. However, since the amount of chemical injection can be reduced, it is preferable to preferentially perform control to reduce the amount of second chemical injection in the water supply W11.

Based on the halogen concentration in the permeated water W20 detected by the halogen detection means 6, the chemical feeding amount calculator 303 calculates the chemical feeding amount of the stabilizer and hypohalous acid to be added to the feed water W11. The chemical injection amount calculation unit 303 calculates, for example, an increase amount of the stabilizer added to the feed water W11 or a decrease amount of hypohalous acid, based on the halogen concentration in the permeated water W20. Then, the increase amount of the stabilizer or the decrease amount of hypohalous acid relative to the feed water W11 is calculated so that the concentration of the stabilizer is in the range of 1 to 3 mol with respect to the halogen concentration of 1 mol in the feed water W11. do. The lower limit of the molar concentration range may be 1.5 or less than 1. The increase amount of the stabilizer or the decrease amount of hypohalous acid is calculated based on the flow rate of the feed water W11. The flow rate of the feed water W11 can be calculated, for example, as the total value of the flow rate of the permeated water W20 detected by the first flow sensor FM1 and the flow rate of the concentrated waste water W50 detected by the third flow sensor FM3. The flow rate of the circulating water W40 is detected by the second flow rate sensor FM2.

The dispersant chemical injection control unit 304 controls the chemical injection of the scale dispersant into the water supply W11 by the scale dispersant addition device 5 . The dispersant dosing control unit 304 may control the dosing amount of the scale dispersant according to, for example, the calcium concentration and silica concentration of the raw water. For example, when the calcium concentration or silica concentration in the raw water increases, the dispersant chemical dosing control unit 304 may perform control to increase the amount of scale dispersant added.

[1.2 Operation of the first embodiment]
The operation of the water treatment system 1 according to the first embodiment will be described below. When the water supply W11 is supplied from the water source 2 to the first water supply line L11, the oxidant addition device 3 as the second chemical injection means supplies sodium hypochlorite to the water supply W11 under the control of the oxidant chemical injection control unit 302. A halogen acid is dosed. Next, a stabilizer is injected from the stabilizer addition device 4 under the control of the stabilizer injection controller 301 into the feed water W11. At this time, the dosage of the hypohalous acid and the stabilizer is controlled based on the halogen concentration in the permeated water W20, and the molar concentration of the halogen in the feed water W11 and the molar concentration of the stabilizer is controlled to be a ratio within a predetermined range.

Next, a scale dispersant is chemically injected from the scale dispersant addition device 5 into the water supply W11 under the control of the dispersant chemical injection controller 304 . As a result, generation of scale such as silica and hardness components in the RO module 17 can be suppressed.

At the connecting portion J1, the water supply W11 flowing through the first water supply line L11 and the circulating water W40 flowing through the circulating water line L4 join and flow into the second water supply line L12 as the water supply W12. The feed water W12 is pressure-fed (discharged) toward the RO module 17 by the pressurizing pump 15 supplied with drive power whose frequency has been converted from the inverter 16 .

The feed water W12 pressure-fed (discharged) toward the RO module 17 undergoes a membrane separation process in the RO module 17 into permeated water W20 from which dissolved salts have been removed and concentrated water W30 from which dissolved salts have been concentrated. The permeated water W20 that has undergone membrane separation in the RO module 17 is sent out through a permeated water line L2 that is connected to the secondary side port of the RO module 17 .

On the other hand, the concentrated water W30 that has undergone membrane separation in the reverse osmosis membrane module 17 flows into the concentrated water line L3 that is connected to the secondary side port of the reverse osmosis membrane module 17 . The concentrated water W30 that has flowed into the concentrated water line L3 is separated at the connection J2 into circulating water W40 that flows through the circulating water line L4 and concentrated water W50 that flows through the concentrated water line L5.

The flow rate of the circulating water W40 flowing into the circulating water line L4 is adjusted to a predetermined flow rate value by the flow control valve 18 or the constant flow valve. The circulating water W40 is returned to the connecting portion J1. The flow rate of the concentrated waste water W50 flowing into the concentrated waste water line L5 is adjusted by the proportional control drain valve 19. Concentrated waste water W50 that has passed through the proportional control drain valve 19 is discharged outside the system.

When the halogen concentration in the permeated water W20 is excessive than the target value, when stopping the water treatment system 1 or replacing the water in the system, first, the hypohalous acid by the oxidant addition device 3 for the feed water W11 Stop the injection of Next, the inflow of the circulating water W40 into the circulating water line L4 is stopped, and all of the concentrated water W30 is discharged as the concentrated waste water W50. After a predetermined time has passed in this state, each device of the water treatment system 1 is stopped. This can prevent halogen from reaching the reverse osmosis membrane of the RO module 17 when the water treatment system 1 is stopped. Halogen contained in the feed water W11 may be removed by adding a reducing agent instead of stopping the chemical injection of hypohalous acid by the oxidizing agent addition device 3 .

[1.3 Effects of First 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 has a halogen detection means 6 for detecting the halogen concentration of the permeated water W20 separated by the RO module 17, and the control unit 30 detects the halogen concentration detected by the halogen detection means 6, and stabilizes the The amount of the stabilizing agent injected by the agent adding device 4 is controlled. When halogen permeates the RO module 17, it is evident that the halogen reaches the reverse osmosis membrane, and there is concern that the halogen may deteriorate the reverse osmosis membrane. However, with the above configuration, when halogen permeates the reverse osmosis membrane, the concentration of permeating halogen can be detected to control the amount of chemical injection. Therefore, it is possible to optimize the amount of chemical injection, suppress deterioration of the reverse osmosis membrane, and reduce the cost of chemical injection.

When the halogen concentration detected by the halogen detection means 6 is equal to or higher than a predetermined value, the controller 30 preferably performs control to increase the amount of stabilizer added by the stabilizer addition device 4 . As a result, when the halogen concentration of the permeated water W20 is equal to or higher than a predetermined value, the amount of the stabilizer injected can be increased to reduce the halogen concentration of the permeated water W20, thereby suppressing deterioration of the reverse osmosis membrane. can.

The first water supply line L11 of the water treatment system 1 is provided with an oxidant addition device 3 for chemically injecting hypohalous acid into the water supply W11. When the concentration is equal to or higher than a predetermined value, it is preferable to perform control to reduce the amount of hypohalous acid injected by the oxidant addition device 3 . As a result, when the halogen concentration of the permeated water W20 is equal to or higher than a predetermined value, the amount of hypohalous acid chemical injection can be reduced to reduce the halogen concentration of the permeated water W20, thereby preventing deterioration of the reverse osmosis membrane. can be suppressed. Also, the cost for chemical injection can be reduced.

The control unit 30 controls the dosage of the stabilizing agent so that the molar concentration of the halogen in the feed water W11 and the molar concentration of the stabilizing agent have a predetermined ratio. As a result, the halogen concentration in the feed water and the concentration of the stabilizer and the like are controlled within a preset range of appropriate molar ratios, so that the risk of leakage of halogen into the permeated water W20 can be reduced.

The halogen detection means 6 is preferably a colorimetric halogen detection means for measuring the absorbance of the permeated water colored by the reaction between the halogen and the reagent. Thereby, it is possible to accurately measure the halogen concentration of the permeated water W20, which has low electrical conductivity and may contain bonding halogen such as chloramine.

The reverse osmosis membrane used in the RO module 17 is preferably a halogen-resistant membrane. As a result, when halogen is detected in the permeated water W20, deterioration of the reverse osmosis membrane can be suppressed even if the operation of the water treatment system 1 is continued for a predetermined period of time.

[2 Second embodiment]
Hereinafter, the water treatment system 1A which is 2nd Embodiment of this invention is demonstrated, referring drawings. In the following description, among the components provided in the water treatment system 1A according to the second embodiment, the same reference numerals are used for the same components as the components provided in the water treatment system 1 according to the first embodiment. , and the description may be omitted.

FIG. 3 is an overall configuration diagram of the water treatment system 1A of the present invention. Unlike the water treatment system 1, the water treatment system 1A does not include the oxidant addition device 3 and the stabilizer addition device 4, but includes a reducing agent addition device 4A as the first chemical injection means.

A reducing agent addition device 4A as a first chemical injection means is a device for adding a reducing agent to the first water supply line L11. The reducing agent addition device 4A is electrically connected to the controller 30A. The reducing agent addition device 4A adds a reducing agent that reduces halogen in the feed water W11 in order to prevent deterioration of the reverse osmosis membrane provided in the RO module 17 . Examples of reducing agents include reducing agents such as SBS (NaHSO ₃ : sodium bisulfite), sodium sulfite, sodium thiosulfate, and sulfurous acid gas.

FIG. 4 is a functional block diagram of the control section 30A. The control unit 30A does not include the oxidant chemical injection control unit 302 included in the control unit 30, and has a reducing agent chemical injection control unit 301A instead of the stabilizer chemical injection control unit 301, and a chemical injection amount calculation unit 303 instead of the chemical injection amount calculation unit 303. 303 A of chemical injection amount calculation parts are each provided.

When the halogen concentration detected in the permeated water W20 by the halogen detection means 6 is equal to or greater than a predetermined value, the reducing agent chemical injection control unit 301A adjusts the concentration of halogen in the permeated water W20 to reduce the concentration of the first chemical in the feed water W11. Perform control to increase the injection amount. In other words, the reducing agent addition device 4A is controlled to increase the chemical feeding amount of the reducing agent to the feed water W11. The predetermined halogen concentration detected in the permeated water W20 can be, for example, 0.002 mmol/L or less. In addition to the above, when it is estimated that the halogen concentration detected from the permeated water W20 is zero and the contamination of the reverse osmosis membrane of the RO module 17 is increasing, the reducing agent injection control unit 301A Control may be performed to reduce the chemical feeding amount of the reducing agent within a predetermined range.

The reducing agent dosing control unit 301A controls the dosing amount of the reducing agent to the feed water W11 by the reducing agent addition device 4A so that the molar concentration of the reducing agent with respect to the molar concentration of halogen in the feed water W11 becomes a predetermined ratio. do. The molar concentration ratio can be, for example, 1 to 5 molar concentrations of the reducing agent with respect to 1 molar concentration of halogen. The molar concentration ratio may be 1.5-3. By setting the lower limit of the molar concentration ratio to 1.5, it is possible to prevent halogen from being reduced and permeating through the RO module 17, although this depends on the mixing state after the addition of the reducing agent. On the other hand, the lower limit of the molar concentration ratio can be set to less than 1 when halogen is not detected from the permeated water W20 by the halogen detecting means 6.

The reducing agent chemical injection control unit 301A may control the chemical injection amount of the reducing agent based on the amount of increase in the reducing agent calculated by the chemical injection amount calculation unit 303A described below, or may be detected by the halogen detection means 6. The chemical feeding amount of the reducing agent may be controlled so that a predetermined amount of the reducing agent is added when the halogen concentration in the permeated water W20 thus obtained exceeds a predetermined threshold value.

The chemical feeding amount calculation unit 303A calculates the chemical feeding amount of the reducing agent to be added to the feed water W11 based on the halogen concentration in the permeated water W20 detected by the halogen detection means 6 . The chemical feeding amount calculation unit 303A calculates an increased amount of the reducing agent added to the feed water W11, for example, based on the halogen concentration in the permeated water W20. Then, the amount of increase of the reducing agent with respect to the feed water W11 is calculated so that the concentration of the reducing agent is in the range of 1 to 5 mol with respect to the halogen concentration of 1 mol in the feed water W11. The lower limit of the molar concentration range may be 1.5 or less than 1. The amount of increase in the reducing agent is calculated based on the flow rate of the feed water W11.

As described above, in the water treatment system 1A using the reducing agent addition device 4A as the first chemical injection means, the same effects as in the water treatment system 1 can be obtained.

[3 Modifications]
[3.1 Modification 1]
In the water treatment systems 1 and 1A according to the above embodiments, the halogen detection means 6 detects the halogen concentration in the permeated water W20 downstream of the RO module 17 . Instead of the halogen detection means 6, a halogen detection means for detecting the halogen concentration in the rear stage of the stabilizer addition device 4 or the stabilizer addition device 4A in the first water supply line L11 may be provided. As a result, it is possible to control the chemical injection amount according to the detection result of the halogen concentration in the water supply in the upstream stage of the water treatment system, so that the chemical injection amount can be controlled with good responsiveness when halogen is detected. A reverse osmosis membrane is preferably provided upstream of the halogen detection means for separating binding halogens that interfere with the measurement.

[3.2 Modification 2]
In the water treatment systems 1 and 1A according to the above embodiments, instead of the halogen detection means 6, halogen detection means for detecting the halogen concentration in the concentrated waste water line L5 may be provided. As a result, even if a biofilm is formed in the RO module 17, the amount of chemical injection is controlled according to the detection result of the halogen concentration of the concentrated water in which the halogen is not consumed by combining with the biofilm. becomes possible. Thereby, the measurement accuracy of the halogen detecting means can be improved. It is preferable to provide a reverse osmosis membrane for separating the binding halogen that interferes with the measurement before the halogen detecting means.

[3.3 Modification 3]
Although the above-described first embodiment has been described as the water treatment system 1 in which hypohalous acid is chemically injected by the oxidant addition device 3 into the water supply W11 supplied from the water source 2, it is not limited to this. The water treatment system 1 does not need to chemically inject an oxidizing agent such as hypohalous acid into the water supply W11. Alternatively, a residual chlorine concentration meter may be provided upstream of the stabilizer addition device 4 when the residual halogen concentration in the raw water fluctuates. Also, a filtering device and/or a water softening device may be provided upstream of the oxidizing agent adding device 3 . This makes it possible to accurately grasp the halogen concentration in the feed water W11.

[3.4 Modification 4]
In the water treatment systems 1 and 1A according to the above embodiments, mixing means may be provided after the stabilizing agent addition device 4 or the reducing agent addition device 4A, which is the first chemical injection means. Since the mixing means promotes homogenization of the halogen and the stabilizer or reducing agent in the feed water W11, it is possible to reduce the dosage of the stabilizing agent or reducing agent. The mixing means is not particularly limited, but may be, for example, a device such as a mixer, or a device that generates a turbulent flow in the water supply W11 by providing a bent portion in a path such as a pipe that constitutes the water supply W11. There may be.

[3.5 Modification 5]
In the water treatment systems 1 and 1A according to the above embodiments, the stabilizer addition device 4 or the reducing agent addition device 4A as the first chemical injection means and the oxidant addition device 3 as the second chemical injection means At the start of injection and/or when increasing the amount of chemical injection, accelerated chemical injection that temporarily increases the discharge amount of the chemical injection amount may be performed. This promotes homogenization of the halogen and the stabilizer or reducing agent in the feed water W11, improves the response delay of chemical injection, and enables prompt injection of an appropriate amount of chemical.

[3.6 Modification 6]
In the water treatment systems 1 and 1A according to the above embodiments, the stabilizer addition device 4 or the reducing agent addition device 4A as the first chemical injection means and the oxidant addition device 3 as the second chemical injection means It may have an ejection amount checker for detecting an ejection failure.

[3.7 Modification 7]
Although the water treatment systems 1 and 1A according to the above embodiments have been described as having the circulating water line L4, the present invention is not limited to this. The water treatment systems 1 and 1A may not have a circulating water line and may discharge all of the concentrated water to the outside of the system as concentrated waste water.

[3.8 Modification 8]
In the water treatment systems 1 and 1A according to the above embodiments, measuring means for measuring at least one of the electrical conductivity and silica concentration of the permeated water W20 may be provided. When deterioration of the RO membrane progresses, the electrical conductivity and silica concentration of the permeated water W20 increase. Therefore, the deterioration state of the RO film can be grasped by the measuring means. Furthermore, depending on the state of deterioration of the RO membrane ascertained by the above measuring means, the amount of the oxidizing agent injected by the oxidizing agent adding device 3 and the chemical injection amount of the stabilizer by the stabilizing agent adding device 4 may be changed. good.

1, 1A water treatment system 3 oxidant addition device (second chemical injection means)
4 Stabilizer addition device (first chemical injection means)
4A reducing agent addition device (first chemical injection means)
6 Halogen detection means 17 Reverse osmosis membrane module 30, 30A Control section (Chemical injection control means)
L11 1st water supply line (water supply line)
L12 Second water supply line (water supply line)
L2 Permeate line L5 Concentrated wastewater line

Claims (6)

a reverse osmosis membrane module;
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 waste water line for discharging part or all of the concentrated water separated by the reverse osmosis membrane module to the outside of the system as concentrated waste water;
a first chemical injection means for injecting either a stabilizing agent or a reducing agent into the water supply supplied to the reverse osmosis membrane module;
chemical feeding control means for controlling a first chemical feeding amount, which is the chemical feeding amount of either the stabilizing agent or the reducing agent by the first chemical feeding means;
halogen detection means for detecting the halogen concentration of the permeated water separated by the reverse osmosis membrane module;
The water treatment system, wherein the chemical injection control means controls the amount of the first chemical injection based on the halogen concentration detected by the halogen detection means. 2. The water treatment system according to claim 1, wherein said chemical injection control means performs control to increase said first chemical injection amount when the halogen concentration detected by said halogen detection means is equal to or higher than a predetermined numerical value. The water supply line is provided with a second chemical injection means for chemically injecting hypohalous acid into the water supply,
The chemical-feeding control means provides a second chemical-feeding amount, which is the chemical-feeding amount of the hypohalous acid by the second chemical-feeding means, when the halogen concentration detected by the halogen-detecting means is equal to or higher than a predetermined numerical value. The water treatment system according to claim 1 or 2, wherein control is performed to reduce the The chemical injection control means controls the first chemical injection so that the molar concentration of halogen in the water supply of the water supply line and the molar concentration of one of the stabilizer and the reducing agent have a predetermined ratio. 4. The water treatment system according to claim 3, wherein the amount or said second chemical dosing amount is controlled. 5. The water treatment system according to any one of claims 1 to 4, wherein said halogen detection means is colorimetric halogen detection means for measuring the absorbance of permeated water colored by a reaction between halogen and a reagent. The water treatment system according to any one of claims 1 to 5, wherein the reverse osmosis membrane used in said reverse osmosis membrane module is a halogen-resistant membrane.

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