Water treatment system and water treatment method

Abstract

To enable highly efficient water treatment by using an appropriate amount of oxidation accelerator. [Solution] The water treatment system according to the embodiment comprises a treatment tank into which the water to be treated is introduced, an oxidation accelerator injection unit for injecting an oxidation accelerator into the water to be treated, an ozone injection unit for injecting ozone into the water to be treated containing the oxidation accelerator flowing through the treatment tank, and a control unit. The control unit controls the amount of oxidation accelerator injected to a first amount if either the water quality information of the water to be treated or the amount of ozone injected is greater than a threshold set individually for the water quality information or the amount of ozone injected, and controls the amount of oxidation accelerator injected to a second amount which is less than the first amount if both the water quality information of the water to be treated and the amount of ozone injected are less than the threshold.

Description

Technical Field

[0001] Embodiments of the present invention relate to a water treatment system and a water treatment method.

Background Art

[0002] Conventionally, in the fields of tap water, sewage, industrial wastewater, pools, etc., for the treatment of oxidation decomposition, sterilization, deodorization, etc. of organic substances in water, water treatment using a combination of an oxidation promoter such as hydrogen peroxide and ozone has been studied. The highly oxidizing OH radicals generated from the oxidation promoter and ozone are said to be effective for the oxidative decomposition of hardly decomposable organic substances such as dioxins and 1,4-dioxane that cannot be mineralized by ozone alone. Also, the method of using hydrogen peroxide as an oxidation promoter is said to be effective for suppressing the generation of bromate ions, which are by-products of oxidative decomposition, due to the reducing action of hydrogen peroxide.

[0003] Therefore, in water treatment using a combination of ozone and hydrogen peroxide, many proposals have been made regarding the control method of the injection amounts of the oxidation promoter and ozone for the purpose of promoting the oxidative decomposition of organic substances and suppressing the generation of bromate ions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to provide a water treatment system and a water treatment method that enable highly efficient water treatment using an appropriate amount of oxidation accelerator. [Means for solving the problem]

[0006] The water treatment system according to the embodiment comprises a treatment tank into which water to be treated is introduced, an oxidation accelerator injection unit for injecting an oxidation accelerator into the water to be treated, an ozone injection unit for injecting ozone into the water to be treated containing the oxidation accelerator flowing through the treatment tank, and a control unit. The control unit controls the amount of oxidation accelerator injected to a first amount if either the water quality information of the water to be treated or the amount of ozone injected is greater than a threshold set individually for the water quality information or the amount of ozone injected, and controls the amount of oxidation accelerator injected to a second amount less than the first amount if both the water quality information of the water to be treated and the amount of ozone injected are less than the threshold. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram of a water treatment system according to an embodiment. [Figure 2] Figure 2 is an illustrative and schematic graph showing the relationship between the ratio of ozone and hydrogen peroxide injection amounts and the dissolved concentration of moldy odor substances. [Figure 3] Figure 3 is an illustrative and schematic graph showing the relationship between the ratio of ozone and hydrogen peroxide injection amounts and the bromate ion concentration. [Figure 4] Figure 4 is an illustrative and schematic graph showing the relationship between the amount of ozone injected and the dissolved concentration of moldy odor substances. [Figure 5] Figure 5 is an illustrative and schematic graph showing the relationship between the amount of ozone injected and the bromate ion concentration. [Figure 6] Figure 6 is an illustrative and schematic graph showing the relationship between the pH of the raw water and the bromate ion concentration of the treated water. [Figure 7]Figure 7 is an illustrative and schematic graph showing the relationship between the ratio of ozone and hydrogen peroxide injection amounts and the dissolved ozone and hydrogen peroxide concentrations in the treated water. [Figure 8] Figure 8 is an illustrative and schematic graph showing the relationship between the ratio of ozone and hydrogen peroxide injection amounts and the consumption and consumption rate of ozone and oxidation accelerators. [Figure 9] Figure 9 is a flowchart showing the water treatment flow according to the embodiment. [Figure 10] Figure 10 is a flowchart showing the water treatment process for the modified example. [Modes for carrying out the invention]

[0008] [Embodiment] The embodiments will be described below with reference to Figures 1 to 9.

[0009] Figure 1 is a schematic diagram of the water treatment system 1 according to an embodiment. The water treatment system 1 according to this embodiment is used, for example, in water purification treatment at a water treatment plant (hereinafter, water purification treatment may be referred to as "water treatment").

[0010] As shown in Figure 1, the water treatment system 1 of this embodiment comprises a treatment tank 2, an oxidation accelerator injection unit 3, an ozone injection unit 4, and a control device 11.

[0011] In the following explanation, the water to be treated is referred to as either "raw water" or "treated water." "Raw water" refers to the water to be treated before it is introduced into treatment tank 2, while "treated water" refers to the water to be treated before and after it is introduced into treatment tank 2. In particular, when referring to the water to be treated both before and after it is introduced into treatment tank 2, it is referred to as "treated water." The treated water contains moldy odor substances as substances to be treated. An example of a moldy odor substance is an organic substance called 2-MIB. In addition to moldy odor substances, the substances to be treated may also be trihalomethane precursors, etc.

[0012] The treatment tank 2 is a tank into which the water to be treated is introduced. The water to be treated in the present embodiment is, for example, the water from which turbidity components have been removed in the sedimentation tank of the water purification plant. The treatment tank 2 has an inlet part 2a into which the water to be treated flows in, an outlet part 2b from which the water to be treated flows out, two divided treatment tanks 2c, 2d, and a connecting flow path 2e between the two divided treatment tanks 2c, 2d. The connecting flow path 2e is partitioned from the divided treatment tanks 2c, 2d by a partition wall 2f. The water to be treated introduced into the treatment tank 2 from the inlet part 2a flows out of the treatment tank 2 to the outside from the outlet part 2b through the divided treatment tank 2c, the connecting flow path 2e, and the divided treatment tank 2d.

[0013] The hydrogen peroxide injection part 3 is installed near the inlet part 2a and injects hydrogen peroxide into the water to be treated (raw water) before it is introduced into the treatment tank 2. The hydrogen peroxide injection part 3 transmits the injection amount of hydrogen peroxide to the control device 11. Further, the hydrogen peroxide injection part 3 adjusts the injection amount of hydrogen peroxide with respect to the water to be treated (raw water) based on the instruction of the control device 11. Hydrogen peroxide is an example of an oxidation accelerator.

[0014] The ozone injection part 4 is installed in the treatment tank 2 and brings ozone into contact with the water to be treated containing hydrogen peroxide flowing in the treatment tank 2. Specifically, the ozone injection part 4 is installed below each of the two divided treatment tanks 2c, 2d, and introduces a gaseous bubble containing ozone into the water to be treated through a diffuser pipe, a diffuser plate, or an injector.

[0015] Also, the ozone injection part 4 is connected to an ozone generator 4b. The ozone generated by the ozone generator 4b is sent to the ozone injection part 4 through a pipe 4a. The ozone generator 4b adjusts the injection amount of ozone into the water to be treated by the ozone injection part 4 based on the instruction of the control device 11. Further, the ozone generator 4b transmits the injection amount of ozone to the control device 11.

[0016] With the configuration as described above, the water to be treated comes into contact with ozone in the divided treatment tank 2c and then comes into contact with ozone in the divided treatment tank 2d. As a result, in the water to be treated, hydrogen peroxide and ozone react to generate OH radicals.

[0017] Furthermore, in this embodiment, the time when the water to be treated first comes into contact with ozone in the divided treatment tank 2c is defined as the start of ozone contact, and the time when the water to be treated is no longer in contact with ozone in the divided treatment tank 2d is defined as the end of ozone contact.

[0018] The control device 11 includes a raw water measuring unit 14, a treated water measuring unit 15, a water quality measuring unit 90, and a control unit 16.

[0019] The raw water measurement unit 14 is a fluorescence analyzer capable of measuring the fluorescence intensity of the water to be treated (raw water) before hydrogen peroxide is injected. Fluorescence intensity is an indicator of the organic matter concentration in the water to be treated, for example, with an excitation wavelength of 320-360 nm and a fluorescence intensity of 400-450 nm. Specifically, the raw water measurement unit 14 is installed near the inlet 2a, upstream of the hydrogen peroxide injection unit 3, and is configured to determine the concentration of fulvic acid-like organic matter, a type of humic substance, in the water to be treated (raw water) before it is introduced into the treatment tank 2. Fulvic acid-like organic matter is easily decomposed by ozone treatment (hereinafter sometimes referred to as ozone treatment) or OH radical treatment (hereinafter sometimes referred to as accelerated oxidation treatment), and is one of the substances targeted by ozone treatment and accelerated oxidation treatment. Fulvic acid-like organic matter is an example of soluble organic matter.

[0020] The raw water measurement unit 14 transmits the measured fulvic acid-like organic matter concentration of the treated water (raw water) to the control unit 16. By installing the raw water measurement unit 14 near the inlet 2a, controllability can be improved when treating water with large fluctuations in influent water quality.

[0021] The treated water measurement unit 15 is a fluorescence analyzer capable of measuring the fluorescence intensity of the treated water. Specifically, the treated water measurement unit 15 is installed in the connecting channel 2e and is configured to identify the concentration of fulvic acid-like organic matter in the treated water flowing through the connecting channel 2e. The treated water measurement unit 15 transmits the identified fulvic acid-like organic matter concentration in the treated water to the control unit 16.

[0022] In this embodiment, absorbance may be used instead of fluorescence intensity. In this case, the raw water measurement unit 14 and the treated water measurement unit 15 are spectrophotometers. The measurement wavelength of the spectrophotometer is set to, for example, 250 to 270 nm.

[0023] The water quality measurement unit 90 is, for example, the pH measurement unit 91. The pH measurement unit 91 measures the pH of the raw water (hereinafter sometimes referred to as raw water pH). In the case of a water treatment plant, the range of raw water pH is often 6 to 8. As will be described in detail later using Figure 6, the higher the raw water pH in this range, the higher the concentration of bromate ions, a by-product of ozone treatment, in the treatment tank 2. Also, if bromate ions are easily generated, bromate is easily generated. In this specification, the ease with which bromate is generated in the water to be treated will be referred to as the bromate generation risk. For example, if the water to be treated is in a state where bromate is easily generated, such as when the raw water pH is high, the bromate generation risk is high, and if the water to be treated is in a state where bromate is not easily generated, the bromate generation risk is low. The pH measurement unit 91 transmits the raw water pH to the control unit 16.

[0024] Furthermore, the water quality measuring unit 90 may be, for example, a water temperature measuring unit 92 or an electrical conductivity measuring unit 93. Also, the water quality measuring unit 90 may consist of one of the pH measuring unit 91, water temperature measuring unit 92, or electrical conductivity measuring unit 93, or it may include two or more of them.

[0025] If the water quality measurement unit 90 is, for example, a water temperature measurement unit 92, the water temperature measurement unit 92 measures the temperature of the raw water before hydrogen peroxide is injected (hereinafter sometimes referred to as the raw water temperature). In the case of a water treatment plant, the range of the raw water temperature is often 0 to 30°C. Within this range, the higher the raw water temperature, the higher the concentration of bromate ions generated by ozone treatment in the treatment tank 2. In other words, the higher the raw water temperature, the easier it is for bromate ions to be generated, and therefore the risk of bromate generation is high. The water temperature measurement unit 92 transmits the raw water temperature to the control unit 16.

[0026] If the water quality measurement unit 90 is, for example, an electrical conductivity measurement unit 93, the electrical conductivity measurement unit 93 measures the electrical conductivity of the raw water. Electrical conductivity is higher the higher the concentration of ionic components contained in the raw water. That is, the higher the electrical conductivity, the higher the bromide ion concentration may be, and in this case, the risk of bromate formation increases. The electrical conductivity measurement unit 93 transmits the measured electrical conductivity of the raw water to the control unit 16. However, in the case of a water treatment plant, the composition and concentration of ionic components differ depending on the water source, so the electrical conductivity also differs depending on the water source.

[0027] The control unit 16 controls the injection amounts of ozone and hydrogen peroxide based on information obtained from each unit. Specifically, the control unit 16 determines the risk of bromate formation based on water quality information such as raw water pH, raw water temperature, and electrical conductivity obtained from the water quality measurement unit 90, and the amount of ozone injected received from the ozone generator 4b, and controls the injection amounts of ozone and hydrogen peroxide according to the risk of bromate formation. More specific operation of the control unit 16 will be described later in the explanation of the water treatment method.

[0028] Next, prior to explaining the water treatment method in the water treatment system 1 described above, we will explain the method for controlling the injection amounts of ozone and hydrogen peroxide using the research results by the inventors shown in Figures 2 to 7.

[0029] First, using Figures 2 and 3, we will explain the effect of reducing moldy odor substances in the treated water and suppressing the generation of bromate ions when the amount of ozone injected is constant and the amount of hydrogen peroxide injected is varied.

[0030] Figure 2 is an illustrative and schematic graph showing the relationship between the ratio of hydrogen peroxide injection to ozone injection and the dissolved concentration of moldy odor substances. In the graph shown in Figure 2, the horizontal axis corresponds to the hydrogen peroxide / ozone injection ratio (molar ratio), and the vertical axis corresponds to the dissolved concentration of moldy odor substances in the treated water.

[0031] Figure 3 is an illustrative and schematic graph showing the relationship between the ratio of hydrogen peroxide injection to ozone injection and the bromate ion concentration. In the graph shown in Figure 3, the horizontal axis corresponds to the hydrogen peroxide / ozone injection ratio (molar ratio), and the vertical axis corresponds to the bromate ion concentration in the treated water. In the examples in Figures 2 and 3, the ozone injection rate is kept constant at 1.5 mg / L.

[0032] As shown in Figure 2, in the range where the injection ratio of hydrogen peroxide to ozone is greater than 0.5, no significant difference is observed in the dissolved concentration of moldy odor substances. In other words, even when the injection amount of hydrogen peroxide is reduced to an injection ratio of around 0.5, a sufficient decomposition effect on moldy odor substances can be obtained.

[0033] However, as shown in Figure 3, increasing the injection ratio of hydrogen peroxide to ozone reduces the bromate ion concentration in the treated water. Increasing the amount of hydrogen peroxide injected can suppress the generation of bromate ions.

[0034] Next, using Figures 4 and 5, we will explain the effect of changing the amount of ozone injected on reducing moldy odor substances in the treated water and on suppressing the generation of bromate ions.

[0035] Figure 4 is an illustrative and schematic graph showing the relationship between the ozone injection rate (concentration) and the dissolved concentration of moldy odor substances. In the graph shown in Figure 4, the horizontal axis corresponds to the ozone injection amount, and the vertical axis corresponds to the dissolved concentration of moldy odor substances.

[0036] Figure 5 is an illustrative and schematic graph showing the relationship between the ozone injection rate (concentration) and the bromate ion concentration. In the graph shown in Figure 5, the horizontal axis corresponds to the ozone injection amount, and the vertical axis corresponds to the bromate ion concentration.

[0037] Furthermore, in Figures 4 and 5, the values ​​plotted with squares (□) represent the dissolved concentration of moldy odor substances and the bromate ion concentration, respectively, when both hydrogen peroxide and ozone are injected. For comparison, the values ​​plotted with diamonds (◇) represent the concentration of moldy odor substances and the bromate ion concentration, respectively, when only ozone is injected. Also, in Figures 4 and 5, the injection volume ratio (molar ratio) of ozone to hydrogen peroxide is kept constant at 1.

[0038] As shown in Figure 4, whether both ozone and hydrogen peroxide are injected, or only ozone is injected, it can be seen that increasing the amount of ozone injected reduces the dissolved concentration of moldy odor substances.

[0039] Furthermore, as shown in Figure 5, it can be seen that in both cases—when both ozone and hydrogen peroxide are injected, and when ozone is injected alone—the bromate ion concentration increases as the amount of ozone injected increases.

[0040] Based on the research results shown in Figures 2 to 5, the inventors found that it is preferable to control the injection of both ozone and hydrogen peroxide while maintaining a balance between the two injections in order to reduce the concentration of moldy odor substances, and to increase or decrease the injection balance of hydrogen peroxide according to the risk of bromate generation.

[0041] Next, we will explain how to control the injection amounts of ozone and hydrogen peroxide according to the risk of bromate formation. The specific method for determining the risk of bromate formation will be described later using Figure 6.

[0042] If the risk of bromate formation is low, it is advisable to control ozone injection to reduce the concentration of moldy odor substances. As shown in Figure 2, even if the injection ratio of hydrogen peroxide to ozone is increased to 0.5 or higher, the decomposition of moldy odor substances does not progress significantly, so it is desirable to control the injection so that the molar ratio is in the range of 0.3 to 0.5. The molar ratio range of 0.3 to 0.5 is an example of the second amount.

[0043] Now, let's discuss ozone injection control.

[0044] Ozone injection control is performed, for example, based on the fluorescence intensity obtained in the raw water measurement unit 14 and the fluorescence intensity obtained in the treated water measurement unit 15. The fluorescence intensity measured in the raw water measurement unit 14 indicates the concentration of fulvic acid-like organic matter. Part of the molecular structure of fulvic acid is decomposed by ozone and OH radicals, and the fluorescence intensity decreases. Specifically, for example, ozone injection control can be performed based on the remaining fluorescence intensity (fulvic acid-like organic matter) calculated by dividing the fluorescence intensity (concentration of fulvic acid-like organic matter) obtained in the treated water measurement unit 15 as a measurement of the water quality of the treated water by the fluorescence intensity (concentration of fulvic acid-like organic matter) obtained in the raw water measurement unit 14.

[0045] The control unit 16 controls the ozone generator 4b to control the amount of ozone injected so that the calculated remaining percentage reaches a predetermined target remaining percentage for fluorescence intensity.

[0046] Since the decomposition rate is similar to that of moldy odor substances by ozone and hydrogen peroxide, the amount of decomposition of moldy odor substances can be estimated by the change in fluorescence intensity indicating fulvic acid concentration. The target remaining percentage of fluorescence intensity can be set from the target remaining percentage of moldy odor substances, and it is desirable to set it so that the target remaining percentage of fluorescence intensity is equal to the target remaining percentage of moldy odor substances. However, depending on the water quality components of the raw water, the rate of change in fluorescence intensity that decreases due to ozone and OH radicals differs slightly from the remaining percentage of moldy odor substances. Therefore, it is preferable to pre-determine a table showing the relationship between the target remaining percentage of moldy odor substances and the target remaining percentage of fluorescence intensity for the raw water at each water treatment plant to which this control is applied.

[0047] The target retention rate of moldy odor substances is set by dividing the target concentration of moldy odor substances (often referred to as a control value or target value) by the maximum concentration of moldy odor substances that can be tolerated in the raw water to be treated. The reason for using the maximum concentration of moldy odor substances in the raw water as the division value is that it is difficult to measure the concentration of moldy odor substances in the raw water in real time, and it is common to measure it at a frequency of once a day, once a week, or once a month.

[0048] Furthermore, the control unit 16 may control the amount of ozone injected into the treatment tank 2 based on at least one of the fluorescence intensity measured as raw water quality in the raw water measurement unit 14 and the fluorescence intensity measured as treated water quality in the treated water measurement unit 15. For example, if the fluorescence intensity in the raw water measurement unit 14 fluctuates little, a value similar to the residual rate of fluorescence intensity (fulvic acid-like organic matter) described above can be obtained from the fluorescence intensity in the treated water measurement unit 15. Also, for example, by knowing in advance the correlation between the fulvic acid-like organic matter concentration in the raw water, the amount of ozone injected, and the fulvic acid-like organic matter concentration in the treated water after ozone injection, a value similar to the residual rate of fluorescence intensity (fulvic acid-like organic matter) can be obtained from the fluorescence intensity in the raw water measurement unit 14. This makes it possible to reduce the number of fluorescence analyzers that need to be installed.

[0049] Another method for controlling ozone injection when the risk of bromate generation is low is to pre-establish a table showing the relationship between the amount of ozone injected and the predetermined moldy odor concentration of the raw water, and the operator can manually set the injection amount based on that table.

[0050] Next, we will explain the case where the risk of bromate formation is judged to be high. When the risk of bromate formation is high, ozone injection control should be carried out in the same way as when the risk of bromate formation is low, and the injection ratio of hydrogen peroxide to ozone should be changed to a higher value. Specifically, when the risk of bromate formation is high, it is desirable to control the injection so that the injection ratio (molar ratio) of hydrogen peroxide to ozone is in the range of 1.0 to 5.0, and the higher the risk of bromate formation, the higher the injection ratio of hydrogen peroxide should be. The molar ratio range of 1.0 to 5.0 is an example of the first amount.

[0051] Here, we will explain how to assess the risk of bromate production, using Figure 6.

[0052] Figure 6 is an illustrative and schematic graph showing the relationship between the pH of the raw water and the bromate ion concentration of the treated water. More specifically, Figure 6 is a graph showing the bromate ion concentration when ozone is injected alone into treated water with different raw water pH levels. In the graph shown in Figure 6, the horizontal axis corresponds to the pH of the raw water, and the vertical axis corresponds to the bromate ion concentration dissolved in the treated water.

[0053] In the example shown in Figure 6, the ozone injection rate is kept constant at 1.5 mg / L. The pH is adjusted by adding sulfuric acid.

[0054] Figure 6 shows that in ozone treatment, the higher the pH of the raw water, the higher the concentration of bromate ions produced, even with the same amount of ozone injection. Therefore, the control unit 16 determines the risk of bromate generation based on the pH of the raw water to be treated. That is, for example, if the threshold pH is set to 7.5 to 8.0, the control unit 16 determines that the risk of bromate generation is high when the raw water pH exceeds the threshold pH of 7.5 to 8.0.

[0055] Although not shown in the diagram, in ozone treatment, the higher the raw water temperature, the higher the concentration of bromate ions produced, even with the same amount of ozone injection. Therefore, the control unit 16 determines the risk of bromate generation based on the raw water temperature of the water to be treated. That is, for example, if a threshold of 20°C is set, the control unit 16 determines that the risk of bromate generation is high when the raw water temperature exceeds the threshold of 20°C. However, the threshold for raw water temperature may be set for each water treatment plant.

[0056] Furthermore, the bromate ion generation reaction in ozone treatment involves the formation of bromide ions (Br) in the raw water. - The reaction between ozone and bromide ions produces bromate ions via an intermediate. Therefore, even with the same amount of ozone injection, a higher bromide ion concentration results in a greater production of bromate. In other words, a higher concentration of bromide ions increases the risk of bromate formation.

[0057] Since it is difficult to measure the bromide ion concentration in raw water in real time, one method is to use the electrical conductivity of the raw water as an alternative indicator. Because electrical conductivity correlates with the total amount of ions in water, it can be used as an indicator to judge the magnitude of the bromide ion concentration. In other words, it can be assumed that the higher the electrical conductivity of the raw water, the higher the concentration of bromate produced. Therefore, the control unit 16 judges the risk of bromate production based on the electrical conductivity of the water to be treated. That is, for example, a predetermined threshold is set for electrical conductivity, and if the electrical conductivity exceeds the threshold, the control unit 16 determines that the risk of bromate production is high.

[0058] However, since electrical conductivity also reacts to changes in the concentration of other ionic components, it may not be suitable for determining the risk of bromate ion generation if the correlation between bromide ion concentration and electrical conductivity is low at each water treatment plant.

[0059] As shown in Figure 5, the bromate ion concentration increases as the ozone injection rate increases. Therefore, the control unit 16 determines the risk of bromate generation based on the ozone injection rate. That is, for example, if the threshold is set at 2.0 g of ozone per 1 m3 of treated water (ozone injection rate = 2.0 mg / L), the control unit 16 determines that the risk of bromate generation is high when the ozone injection rate exceeds the threshold of 2.0 mg / L. It is desirable to set the threshold for the ozone injection rate for each water treatment plant.

[0060] The above examples illustrate several indicators that can be used to assess the risk of bromate formation, including raw water pH, raw water temperature, electrical conductivity, and ozone injection amount as water quality information. However, one of these indicators may be used to assess the risk of bromate formation, or two or more may be used in combination.

[0061] Furthermore, the operator may determine the risk of bromate generation based on raw water quality and the results of bromate ion analysis conducted during routine water quality management.

[0062] The following explains how the reaction between ozone and hydrogen peroxide proceeds depending on the injection ratio of hydrogen peroxide to ozone, using Figures 7 and 8.

[0063] Figure 7 is an illustrative and schematic graph showing the relationship between the ratio of ozone and hydrogen peroxide injection amounts and the dissolved ozone and hydrogen peroxide concentrations in the treated water. In the graph shown in Figure 7, the horizontal axis corresponds to the hydrogen peroxide / ozone injection ratio (molar ratio), the vertical axis (left) corresponds to the dissolved ozone concentration in the treated water, and the vertical axis (right) corresponds to the dissolved hydrogen peroxide concentration in the treated water.

[0064] In Figure 7, the values ​​plotted with black squares represent the dissolved ozone concentration, and the values ​​plotted with diamonds represent the hydrogen peroxide concentration. Furthermore, in the example in Figure 7, the ozone injection rate is kept constant at 1.5 mg / L.

[0065] As shown in Figure 7, increasing the injection ratio of hydrogen peroxide to ozone reduces the dissolved ozone concentration, approaching zero when the injection ratio exceeds 0.5. This is because the injected ozone reacts with hydrogen peroxide to generate OH radicals, which are consumed in the oxidative decomposition of moldy odor substances, etc.

[0066] Figure 8 shows the dissolved ozone concentration and hydrogen peroxide concentration values ​​shown in Figure 7 converted to their respective consumption amounts and consumption rates.

[0067] Figure 8 is an illustrative and schematic graph showing the relationship between the ratio of ozone and hydrogen peroxide injection amounts and the consumption and consumption rate of ozone and oxidation accelerators. In the graph shown in Figure 8, the horizontal axis corresponds to the hydrogen peroxide / ozone injection amount ratio (molar ratio), the vertical axis (left) corresponds to the consumption rate of ozone and hydrogen peroxide, and the vertical axis (right) corresponds to the consumption amount of ozone and hydrogen peroxide.

[0068] In Figure 8, the values ​​plotted with black diamonds (◇) represent the ozone consumption rate, the values ​​plotted with black squares (□) represent the ozone consumption amount, the values ​​plotted with diamonds (◇) represent the hydrogen peroxide consumption rate, and the values ​​plotted with squares (□) represent the hydrogen peroxide consumption amount. For both hydrogen peroxide and ozone, the consumption amount is calculated by subtracting the dissolved amount in the treated water from the injection amount, and the consumption rate is calculated by dividing the consumption amount by the injection amount. The dissolved amount in the treated water is calculated from the concentration.

[0069] As shown in Figure 8, increasing the injection ratio of hydrogen peroxide to ozone increases both the amount and rate of ozone consumption, and when the injection ratio exceeds 0.5, the consumption rate approaches 100%. As described above using Figure 7, the injected ozone is consumed in the generation of OH radicals, reactions with moldy odor substances in the treated water, and self-decomposition reactions.

[0070] Furthermore, increasing the ratio of hydrogen peroxide injection to ozone increases the consumption of hydrogen peroxide. However, the hydrogen peroxide consumption rate rises sharply from around 0.2 injection ratio, reaching a maximum around 0.5, and does not change significantly beyond 0.5.

[0071] Hydrogen peroxide injected into the treated water is consumed in the generation of OH radicals as long as ozone remains in the treated water. That is, as long as the hydrogen peroxide injection ratio does not exceed 0.5, the hydrogen peroxide is consumed in the generation of OH radicals. Therefore, for example, in the range where the hydrogen peroxide consumption rate changes significantly (for example, the range of injection ratio from 0.2 to 0.5 in Figure 7), it is thought that a large amount of hydrogen peroxide is consumed and a large amount of OH radicals are generated.

[0072] At this time, the concentration of hydrogen peroxide remaining in the treated water is 0.2 to 0.5 mg / L (Figure 7).

[0073] On the other hand, hydrogen peroxide injected into the treated water is consumed in the decomposition reaction of OH radicals, reactions with other radical components, and reduction reactions of reaction byproducts by ozone, provided that there is little ozone remaining in the treated water. This is because hydrogen peroxide in the treated water alone cannot promote the decomposition reaction of moldy odor substances in the treated water, and self-decomposition reactions do not proceed in a short time. In other words, in the range where the hydrogen peroxide injection ratio exceeds 0.5, hydrogen peroxide is consumed in reactions other than the generation of OH radicals. Therefore, in the range where there is no significant change in the amount of hydrogen peroxide consumed, it can be considered that the generation of OH radicals is not progressing.

[0074] Thus, by controlling the amount of hydrogen peroxide injected based on the hydrogen peroxide consumption rate, it becomes possible to efficiently generate OH radicals with a smaller amount of hydrogen peroxide injected. However, if there is no means to measure the hydrogen peroxide concentration of the treated water in real time, control based on the hydrogen peroxide consumption rate cannot be implemented. In this invention, the amount of hydrogen peroxide injected is controlled based on the risk of bromate generation determined from the water quality of the treated water, which can be measured in real time. This makes it possible to oxidize and decompose moldy odor substances and the like with an even smaller amount of hydrogen peroxide injected.

[0075] Next, using Figure 9, we will describe the water treatment method of the present invention that enables the above-described control.

[0076] Figure 9 is a flowchart showing the water treatment flow according to this embodiment. The water treatment method according to this embodiment performs the following steps: a bromate formation risk determination step, an injection amount determination step, an accelerated oxidation step, an organic matter measurement step, and a control step. The ozone injection amount in this embodiment is assumed to be 1.5 mg / L.

[0077] In the bromate generation risk assessment step, the control unit 16 acquires water quality information of the water to be treated, or the amount of ozone injected into the water to be treated, as indicators for determining the risk of bromate generation (S101). Specifically, the control unit 16 acquires raw water pH, raw water temperature, or raw water electrical conductivity, as well as the amount of ozone injected, as water quality information from the water quality measurement unit 90 and the ozone injection unit 4.

[0078] The control unit 16 determines whether either the acquired water quality information or the ozone injection amount exceeds a predetermined threshold set individually for each of the water quality information and the ozone injection amount (S102). Specifically, if the control unit 16 acquires, for example, the raw water pH as water quality information, it determines whether the raw water pH exceeds a first threshold set in advance. The control unit 16 also determines whether the acquired ozone injection amount exceeds a second threshold set in advance for the ozone injection amount. In this embodiment, the first threshold is, for example, pH 7.5 to 8.0, and the second threshold is, for example, 2.0 g.

[0079] If either the acquired water quality information or the ozone injection amount exceeds a predetermined threshold, for example, if the raw water pH exceeds the first threshold of pH 7.5 to 8.0 (S102: Yes), the control unit 16 determines that the risk of bromate formation is high. On the other hand, if neither the acquired water quality information nor the ozone injection amount exceeds a predetermined threshold (S102: No), the control unit 16 determines that the risk of bromate formation is low.

[0080] If the risk of bromate formation is determined to be high, in the injection amount determination step, the control unit 16 determines that the ratio (molar ratio) of the amount of hydrogen peroxide injected to the amount of ozone injected is in the range of 1.0 to 5.0 as the first amount (S103). On the other hand, if the risk of bromate formation is determined to be low, the control unit 16 determines that the ratio (molar ratio) of the amount of hydrogen peroxide injected to the amount of ozone injected is in the range of 0.3 to 0.5 as the second amount (S104).

[0081] Furthermore, if either the water quality information or the ozone injection amount is equal to a predetermined threshold set individually for each of the water quality information and ozone injection amount, the control unit 16 may determine whether the risk of bromate formation is high or low. For example, if either the water quality information or the ozone injection amount is equal to a predetermined threshold, the control unit 16 will determine that the risk of bromate formation is low.

[0082] In the accelerated oxidation step, the control unit 16 controls the oxidation accelerator injection unit 3 and injects hydrogen peroxide into the water to be treated (raw water) introduced from the inlet 2a into the treatment tank 2 in an injection amount (molar ratio) determined in the injection amount determination step (S105). The water to be treated with hydrogen peroxide injected is then injected from the inlet 2a of the treatment tank 2 into the divided treatment tank 2c.

[0083] Next, the control unit 16 controls the ozone generator 4b and injects ozone from the ozone injection unit 4 into the water to be treated flowing through the treatment tank 2 (S106). As a result, the water to be treated, which contains hydrogen peroxide and flows through the treatment tank 2, comes into contact with the ozone.

[0084] In the organic matter measurement step, the control unit 16 calculates the remaining percentage of fluorescence intensity (fulvic acid-like organic matter) from the fluorescence intensity obtained in the raw water measurement unit 14 and the treated water measurement unit 15, respectively (S107).

[0085] Next, in the control step, the control unit 16 determines the amount of ozone to be injected based on the remaining amount calculated in S107 and transmits this information to the ozone generator 4b. Thereafter, the processing of each of the steps described above is repeated.

[0086] [Summary] The water treatment system 1 of this embodiment controls the amount of hydrogen peroxide injected according to the risk of bromate formation in the water to be treated. That is, an appropriate amount of hydrogen peroxide can be injected depending on whether the risk of bromate formation is low or high. In this way, the amount of hydrogen peroxide injected is optimized according to the risk of bromate formation, so problems such as excessive hydrogen peroxide injection can be avoided, and highly efficient water treatment becomes possible.

[0087] [Differentiation] Modified examples of the embodiment will be described below with reference to Figure 10.

[0088] In the above-described embodiment, the risk of bromate generation was determined by comparing water quality information or the amount of ozone injected with a predetermined threshold for each. In contrast, the modified water treatment system differs from the above-described embodiment in that two thresholds are set in advance for each of the water quality information or the amount of ozone injected, and the two thresholds are used depending on the condition of the water to be treated. Note that in the following, the description of configurations similar to those in the above-described embodiment may be omitted.

[0089] Figure 10 is a flowchart showing the water treatment flow according to the modified example. In the modified water treatment method, the control unit 16 repeatedly performs the following steps: a bromate generation risk determination step, which performs a bromate generation risk determination step; an injection amount determination step; an accelerated oxidation step, which performs an oxidation accelerator injection process in which hydrogen peroxide is injected into the water to be treated by controlling the oxidation accelerator injection unit 3 and an ozone injection process in which ozone is injected into the water to be treated by controlling the ozone injection unit 4; an organic matter measurement step; and a control step.

[0090] In the bromate formation risk determination step, the control unit 16 acquires water quality information of the water to be treated, or the amount of ozone injected into the water to be treated, as indicators for determining the risk of bromate formation (S201). Also, in the bromate formation risk determination step, if the control unit 16 determines that the risk of bromate formation is low in the current water to be treated (S202: Yes), it sets a first value as the threshold for the next bromate formation risk determination process (S203). Specifically, if the current raw water pH of the water to be treated is, for example, 7.0 (low risk of bromate formation), the control unit 16 sets the first value as the threshold for the next bromate formation risk determination process.

[0091] If the raw water pH exceeds a first value of pH 7.7 (S204: Yes), the control unit 16 determines that there is a high risk of bromate formation and determines that the ratio (molar ratio) of hydrogen peroxide injection to ozone injection amount becomes the first amount (S207).

[0092] On the other hand, if the control unit 16 determines that there is a high risk of bromate formation in the current water to be treated (S202: No), it sets a second value as the threshold for the next process of determining the risk of bromate formation (S203). Specifically, if the pH of the raw water to be treated is, for example, 8.5 (high risk of bromate formation), the control unit 16 sets a second value, for example, 7.5, as the threshold for the next process of determining the risk of bromate formation.

[0093] The control unit 16 determines that the risk of bromate formation is small when the raw water pH falls below the second value of pH 7.5 (S206: Yes), and determines that the ratio (molar ratio) of hydrogen peroxide injection to ozone injection amount is the second amount (S208).

[0094] The processes in S209 to S212 correspond to the processes in S105 to S108 in Figure 9, so their explanation will be omitted.

[0095] Thus, different thresholds are used depending on whether the risk of bromate formation is judged to be low or low and the hydrogen peroxide injection ratio is increased, or whether the risk of bromate formation is judged to be high and the hydrogen peroxide injection ratio is decreased. This reduces the number of times the hydrogen peroxide injection ratio needs to be changed and allows for more reliable suppression of bromate formation.

[0096] [Other variations] In the above embodiment, the risk of bromate formation was determined by comparing water quality information or the amount of ozone injected with a predetermined threshold for each, but the method for determining the risk of bromate formation is not limited to this. For example, the risk of bromate formation may be determined in stages, and the hydrogen peroxide injection ratio may be changed in stages accordingly.

[0097] The water treatment system 1 in the above-described embodiment can be applied not only to the treatment of drinking water but also to the treatment of sewage, as well as to fields such as industrial wastewater and swimming pools.

[0098] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0099] 1...Water treatment system, 2...Treatment tank, 2c, 2d...Divided treatment tank, 2e...Connecting channel, 3...Oxidation accelerator injection unit, 4...Ozone injection unit, 11...Control device, 14...Raw water measurement unit, 15...Treatment water measurement unit, 16...Control unit, 90...Water quality measurement unit, 91...pH measurement unit, 92...Water temperature measurement unit, 93...Electrical conductivity measurement unit.

Claims

1. A treatment tank into which the water to be treated is introduced, An oxidation accelerator injection unit for injecting an oxidation accelerator into the water to be treated, An ozone injection unit for injecting ozone into the water to be treated, which contains the oxidation accelerator and flows through the treatment tank, It comprises a control unit and, The control unit, If either the water quality information of the water to be treated or the amount of ozone injected is greater than a threshold set individually for the water quality information or the amount of ozone injected, the amount of oxidation accelerator injected is controlled to a first amount. If both the water quality information of the water to be treated and the amount of ozone injected are smaller than the threshold, the amount of oxidation accelerator injected is controlled to be a second amount, which is less than the first amount. Water treatment system.

2. The aforementioned water quality information is, The pH value, water temperature, and electrical conductivity of the water to be treated are, The water treatment system according to claim 1.

3. The control unit, The amount of the oxidation accelerator injected is controlled in proportion to the amount of ozone injected. The water treatment system according to claim 1.

4. The first quantity is The ratio of the amount of oxidation accelerator injected to the amount of ozone injected is such that the molar ratio is between 1.0 and 5.

0. The water treatment system according to claim 1.

5. The second amount is The ratio of the amount of oxidation accelerator injected to the amount of ozone injected is such that the molar ratio is 0.3 to 0.

5. The water treatment system according to claim 1.

6. The system comprises at least one of the following: a raw water measuring unit for measuring the concentration of dissolved organic matter in the raw water, which is the water to be treated, before it is introduced into the treatment tank; and a treated water measuring unit for measuring the concentration of dissolved organic matter in the water to be treated from the time of ozone contact until the time of contact termination. The control unit, The amount of ozone injected into the treatment tank is controlled based on at least one of the raw water quality measurement value in the raw water measurement unit and the treated water quality measurement value in the treated water measurement unit. The water treatment system according to claim 1.

7. The control unit, The amount of ozone injected is controlled based on the ratio of the raw water quality measurement value to the water quality measurement value. The water treatment system according to claim 6.

8. At least one of the raw water measuring unit and the treated water measuring unit is A fluorescence analyzer capable of measuring the fluorescence intensity of the dissolved organic matter in the raw water and the water to be treated, The excitation wavelength of the fluorescence analyzer is in the range of 320 to 360 nm, and the fluorescence intensity is in the range of 400 to 450 nm. The water treatment system according to claim 6.

9. At least one of the raw water measuring unit and the treated water measuring unit is An absorbance meter capable of measuring absorbance proportional to the concentration of dissolved organic matter in the raw water and the water to be treated, The wavelength used for measuring the absorbance is within the wavelength range that includes 260 nm. The water treatment system according to claim 6.

10. The system includes a pH measuring unit capable of measuring the pH value of the treated water, The water treatment system according to claim 2.

11. The system includes a water temperature measuring unit capable of measuring the water temperature of the water to be treated. The water treatment system according to claim 2.

12. The system includes an electrical conductivity measuring unit capable of measuring the electrical conductivity of the water to be treated. The water treatment system according to claim 2.

13. A water treatment method performed in a water treatment system that includes a treatment tank into which water to be treated is introduced, The steps include injecting an oxidation accelerator into the water to be treated, The steps include injecting ozone into the water to be treated, which contains the oxidation accelerator and flows through the treatment tank, If either the water quality information of the water to be treated or the amount of ozone injected is greater than a threshold set individually for the water quality information or the amount of ozone injected, the amount of oxidation accelerator injected is controlled to be a first amount; if both the water quality information of the water to be treated and the amount of ozone injected are less than the threshold, the amount of oxidation accelerator injected is controlled to be a second amount less than the first amount. A water treatment method that includes [a specific component].

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