Water treatment method and apparatus

Abstract

To provide a method and apparatus for preventing leakage of chlorine and deterioration of a separation membrane in a water treatment method and apparatus in which a chlorine-based oxidizing agent is added to ammonia nitrogen-containing raw water so as to apply chlorination treatment, and a reducing agent is added to chlorine-treated water so as to perform membrane separation.SOLUTION: When a chlorine-based oxidizing agent is added to ammonia nitrogen-containing raw water so as to oxidize and decompose oxidizable substances containing ammoniacal nitrogen through discontinuous point chlorination treatment in a chlorination treatment apparatus 1, residual chlorine is removed by adding a reducing agent to chlorine-treated water in a residual chlorination apparatus 2, and membrane separation is performed in an RO membrane separation apparatus 4, the water treatment method is configured to calculate the combined chlorine concentration (C-Cl) from a difference between the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl), and calculate an addition amount of the reducing agent according to the formula [1] so as to perform control. [1]: Reducing agent concentration=(fs)x[((C-Cl)×m×a)+((F-Cl×m)] (In the formula, (fs) represents a safety factor and ranges from 1 to 1.2, (m) represents a molecular weight ratio between the reducing agent in the reaction equivalent and Cl2, and (a) represents a combined chlorine coefficient and ranges from 1.2 to 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment method and apparatus for chlorinating raw water containing ammonia nitrogen by adding a chlorine-based oxidizing agent, and then adding a reducing agent to the chlorinated water to perform membrane separation. More specifically, the present invention relates to a water treatment method and apparatus for chlorinating raw water containing ammonia nitrogen by a discontinuous point chlorination method by adding a chlorine-based oxidizing agent, and then adding a reducing agent to the chlorinated water to remove residual chlorine and perform membrane separation. [Background technology]

[0002] In water and wastewater treatment, a chlorine-based oxidizing agent such as sodium hypochlorite is added to raw water for the purpose of sterilization and oxidation within the system. Patent Document 1 (JP Patent Publication 104310 / 1999) proposes a method in which a free chlorine agent is added as a disinfectant for RO membranes to sterilize, and then ammonium ions are added to generate chloramines. Since the widely used free chlorine agents such as chlorine and sodium hypochlorite deteriorate RO membranes as oxidizing agents and reduce their performance, ammonium ions are added to reduce the oxidizing properties, and the combined chlorine agent (chloramine) is brought into contact with the RO membrane in a form with low oxidizing properties.

[0003] Patent Document 2 (WO2011 / 125764) describes a method in which free or combined chlorine is added to the water to be treated in the presence of free chlorine, and pretreatment such as coagulation, solid-liquid separation, and activated carbon treatment is performed, a reducing agent such as sodium hydrogen sulfite is added to remove the free or combined chlorine, and then a new combined chlorine agent is added to perform RO membrane treatment. The reason for adding the free or combined chlorine agent during pretreatment is to prevent slime problems in the pretreatment process, and the reason for adding the reducing agent is said to be to add an appropriate amount of slime prevention agent suitable for membrane treatment after removing the remaining free or combined chlorine.

[0004] Patent Document 3 (WO2012 / 133620) describes a method of adding a free chlorine agent to the water to be treated to sterilize it, then adding one or more sulfamic acid compounds selected from sulfamic acid, combined chlorine type sulfamic acid, and their salts to the water to be treated containing free chlorine to convert the free chlorine contained in the water to be treated to combined chlorine, then adding a reducing agent to the water to be treated to reduce the free chlorine concentration, and then supplying the water to a membrane separation device for membrane separation. Here, the method describes a method of measuring the free chlorine concentration of the water to be treated after adding the sulfamic acid compound, and adjusting the amount of the sulfamic acid compound and / or the reducing agent to be added so that the free chlorine concentration of the water to be treated is 0.4 mg / L or less.

[0005] Patent Document 4 (WO2019 / 031430) describes a water treatment method and apparatus in which a chlorine-based oxidizing agent is added to raw water to perform pretreatment, a reducing agent is added to the pretreated water to remove residual chlorine, and a slime inhibitor is further added to perform membrane separation. The method and apparatus describe measuring the free chlorine or total chlorine in the chlorine-treated water, adding a reducing agent required to reduce them, and then removing the residual chlorine, followed by membrane separation.

[0006] However, when a combined chlorine agent is added during pretreatment, or when a free chlorine agent is added, if the raw water contains ammonia nitrogen, combined chlorine such as chloramine is formed, weakening the oxidizing power, and there are cases where sterilization and oxidation cannot be performed sufficiently. Also, when groundwater is used as the raw water and a free chlorine agent is added to oxidize and remove iron, manganese, etc., if the raw water contains ammonia nitrogen, combined chlorine is formed, weakening the oxidizing power, and there are cases where oxidation of iron, manganese, etc. cannot be performed sufficiently. Furthermore, if there is an excess of combined chlorine in chlorine measurement, it becomes an interference substance in the chlorine analysis, and there are cases where chlorine cannot be measured accurately. Furthermore, if combined chlorine is present when a reducing agent is added, it is difficult to control the amount of reducing agent added to make the combined chlorine zero. There are also problems such as the combined chlorine, which is a combination of ammonia nitrogen and chlorine, easily affecting the separation membrane.

[0007] When raw water contains ammonia nitrogen, the breakpoint chlorination method is known as a method for removing such ammonia nitrogen. In this method, as the amount of chlorine-based oxidizing agent added to raw water containing ammonia nitrogen is increased, the amount of combined chlorine increases and reaches a maximum value, but as the amount of chlorine agent is further increased, the amount of combined chlorine decreases and reaches a minimum point, and as the amount is further increased, free residual chlorine increases. The minimum value is the breakpoint, and the breakpoint chlorination is a treatment method for removing ammonia nitrogen by adding a chlorine-based oxidizing agent so that the chlorine concentration exceeds the breakpoint.

[0008] However, in such a breakpoint chlorination treatment, it is required to control the amount of chlorine-based oxidizing agent added so that the chlorine concentration is in a region slightly exceeding the breakpoint, but it is difficult to detect the breakpoint, and combined chlorine may be detected even in the region exceeding the breakpoint, and if combined chlorine remains, it becomes difficult to control the amount of reducing agent added. In general, the amount of chlorine-based oxidizing agent or reducing agent added is controlled by measuring the total chlorine concentration, free chlorine concentration, redox potential, etc., but it is difficult to detect the breakpoint even if these are used as indicators alone. In addition, even if the amount of reducing agent required to remove chlorine is calculated using the measured total chlorine concentration, free chlorine concentration, redox potential, etc., it may not be possible to prevent chlorine leakage. In such cases, the amount of reducing agent is usually calculated by multiplying it by a safety factor, but there are problems such as the fact that chlorine leakage cannot be prevented and deterioration of the separation membrane may occur. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 1-104310 [Patent Document 2] WO2011 / 125764 [Patent Document 3] WO2012 / 133620 [Patent Document 4] WO2019 / 031430 Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to provide a water treatment method and apparatus which, in treating raw water containing ammoniacal nitrogen by adding a chlorine-based oxidizing agent, can properly add the chlorine-based oxidizing agent to remove ammoniacal nitrogen and oxidize remaining oxidizable substances, and can properly add a reducing agent to reduce remaining chlorine, thereby preventing chlorine leakage and deterioration of a separation membrane. [Means for solving the problem]

[0011] The present invention relates to the following water treatment method and apparatus. (1) A chlorination process in which a chlorine-based oxidant is added to raw water containing ammonia nitrogen and ammonia nitrogen is removed by breakpoint chlorination; a residual chlorine removal step of removing residual chlorine by adding a reducing agent to the chlorinated water; a membrane separation step of separating the residual chlorine-removed water using a separation membrane; A water quality measurement process for measuring the total chlorine concentration and free chlorine concentration of the chlorinated water; A control step of controlling the amount of reducing agent added based on the measured values ​​of the total chlorine concentration and the free chlorine concentration of the chlorine-treated water, The control step is configured to calculate a combined chlorine concentration (C-Cl) from the difference between the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl), and to calculate and control the amount of reducing agent to be added by the following formula [1]. Reducing agent concentration = fs × [((C-Cl) × m × a) + ((F-Cl) × m)] 〔1〕 (In the formula, fs is a safety factor of 1 to 1.2, and m is the reaction equivalent of the reducing agent and Cl 2 The molecular weight ratio of 1.2 to 2 is a combined chlorine coefficient. (2) The reducing agent is sodium bisulfite (SBS). The water treatment method according to the above (1), wherein the control step is configured to control the amount of the reducing agent added according to the following formula [2]: SBS concentration=fs×[((C-Cl)×1.5×a)+((F-Cl)×1.5)]...[2] (In the formula, fs is a safety factor of 1 to 1.2, and a is a combined chlorine coefficient of 1.2 to 2.) (3) The water treatment method according to (1) or (2) above, wherein the membrane separation step is configured to add a slime inhibitor to the residual chlorine-removed water and then perform membrane separation. (4) A chlorine treatment device that adds a chlorine-based oxidizing agent to raw water containing ammonia nitrogen and removes ammonia nitrogen through discontinuous point chlorination; A residual chlorine removal device that removes residual chlorine by adding a reducing agent to chlorinated water; A membrane separation device that separates the residual chlorine removed water using a separation membrane; A water quality measuring device for measuring the total chlorine concentration and free chlorine concentration of chlorinated water; and A control device is provided for controlling the amount of reducing agent added based on the measured values ​​of the total chlorine concentration and the free chlorine concentration of the chlorine-treated water, The control device is configured to calculate the combined chlorine concentration (C-Cl) from the difference between the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl), and to calculate and control the amount of reducing agent to be added using the following formula [1]. Reducing agent concentration = fs × [((C-Cl) × m × a) + ((F-Cl) × m)] 〔1〕 (In the formula, fs is a safety factor of 1 to 1.2, and m is the reaction equivalent of the reducing agent and Cl 2 The molecular weight ratio of 1.2 to 2 is a combined chlorine coefficient. (5) The reducing agent is sodium bisulfite (SBS). The water treatment device according to (4) above, wherein the control device is configured to control the amount of reducing agent added according to the following formula (2): SBS concentration=fs×[((C-Cl)×1.5×a)+((F-Cl)×1.5) 〕 ..〔2〕 (In the formula, fs is a safety factor of 1 to 1.2, and a is a combined chlorine coefficient of 1.2 to 2.) (6) The water treatment device according to (4) or (5) above, wherein the membrane separation device is configured to add a slime inhibitor to the residual chlorine-removed water and perform membrane separation.

[0012] The raw water containing ammoniacal nitrogen that is supplied to the water treatment method and apparatus of the present invention for treatment is raw water containing ammoniacal nitrogen. Examples of such raw water containing ammoniacal nitrogen include general water containing ammoniacal nitrogen, such as natural water such as river water and groundwater that contain ammoniacal nitrogen, industrial water, wastewater, and wastewater treatment water. Such raw water containing ammoniacal nitrogen may be raw water contained in a treatment system in operation, such as a circulating cooling water system or a circulating cleaning water system. The content of ammoniacal nitrogen in the raw water containing ammoniacal nitrogen is not particularly limited. Furthermore, the raw water may not contain ammoniacal nitrogen at first, but may be raw water from a system in which ammoniacal nitrogen is mixed in midway.

[0013] The chlorination process is a process in which a chlorine-based oxidizing agent is added to raw water containing ammoniacal nitrogen, and ammoniacal nitrogen is removed by discontinuous point chlorination. Such a chlorination process may be performed as a process dedicated to chlorination, or may be performed in a pretreatment process. Pretreatment processes that do not adversely affect the chlorination process are preferred, such as pretreatments for removing impurities from raw water, such as coagulation, filtration, and activated carbon treatment, and pretreatments for oxidizing and removing oxidizable substances such as iron and manganese.

[0014] Examples of chlorine-based oxidizing agents include chlorine gas, hypochlorous acid or its salts, trichloroisocyanuric acid, electrolytic chlorine, and the like, which are generally used as bactericides, disinfectants, oxidizing agents, and the like. When a chlorine-based oxidizing agent is added to raw water containing ammoniacal nitrogen and chlorine-based oxidizing agent is used for chlorination, the ammoniacal nitrogen and the chlorine-based oxidizing agent combine to form combined chlorine such as chloramine. In Patent Documents 1 to 4, chlorination is performed with an amount of chlorine-based oxidizing agent added that is sufficient to form such combined chlorine, but when combined chlorine is formed, the oxidizing power is weakened, and there are cases in which the sterilization of fungi and the oxidation of iron, manganese, and the like cannot be sufficiently performed. In contrast, in the present invention, discontinuous chlorination is performed with a high amount of chlorine-based oxidizing agent added, which decomposes combined chlorine and removes ammoniacal nitrogen.

[0015] Breakpoint chlorination is a chlorination treatment that is performed by adding a chlorine-based oxidizing agent so that the residual chlorine concentration exceeds a breakpoint. In the chlorination method, as the amount of chlorine-based oxidizing agent added to raw water containing ammonia nitrogen is increased, the amount of combined chlorine generated increases and reaches a maximum value, but as the amount of chlorine agent added is further increased, the amount of combined chlorine decreases and reaches a minimum. If the amount is further increased, free chlorine increases and total chlorine increases. The minimum value is the breakpoint, and by performing chlorination by adding a chlorine-based oxidizing agent so that the residual chlorine concentration exceeds this breakpoint, oxidizable substances including ammonia nitrogen are decomposed and removed.

[0016] The residual chlorine removal step is a step in which a reducing agent is added to the chlorinated water obtained from the above chlorination step to remove residual chlorine. Residual chlorine contained in the chlorinated water causes deterioration of the separation membrane used in the membrane separation step, so the chlorinated water after removing the residual chlorine (residual chlorine removed water) is sent to the membrane separation step to prevent deterioration of the separation membrane. To remove the residual chlorine, a reducing agent is added to the chlorinated water to react with the chlorine and remove the residual chlorine. Examples of reducing agents include bisulfite, thiosulfate, sulfurous acid, thioglycolic acid, erythorbic acid, ascorbic acid, and salts thereof, with water-soluble salts such as sodium salts being preferred, and sodium hydrogen sulfite (SBS) being particularly preferred.

[0017] The amount of reducing agent added in the residual chlorine removal process is preferably the same as or equal to the amount required to remove the residual chlorine contained in the chlorinated water, but since leakage of residual chlorine causes deterioration of the separation membrane, it is necessary to control the amount of reducing agent added so as to prevent leakage of residual chlorine. In such a case, the amount of reducing agent is usually calculated by multiplying the amount by a safety factor, but even this cannot prevent leakage of chlorine, and may lead to deterioration of the separation membrane. The amount of reducing agent added is controlled based on the water quality measurement results in the water quality measurement process, but it is difficult to measure the amount of combined chlorine in the residual chlorine, and variations are likely to occur. If the amount of reducing agent added is calculated based on the measurement results of the amount of combined chlorine, which is likely to vary, the amount of reducing agent added will also vary, making it difficult to control the amount of reducing agent added. For example, if the amount of combined chlorine is measured to be less than the actual amount, a correspondingly small amount of reducing agent will be added, but this will result in insufficient removal of residual chlorine and leakage of chlorine. In order to prevent chlorine leakage due to such measurement value variations, the amount of reducing agent to be added is calculated by multiplying the measured amount of combined chlorine by the combined chlorine coefficient in addition to the normal safety factor, thereby preventing leakage of residual chlorine.

[0018] The membrane separation process is a process in which the residual chlorine-removed water sent from the residual chlorine removal process is supplied to a separation membrane and separated by membrane. Examples of the separation membrane include membranes that allow the solution to permeate by membrane separation, such as UF membranes, MF membranes, and RO membranes. In particular, RO membranes, especially RO membranes made of polymer membranes having nitrogen-containing groups such as polyamide and aramid, which are easily deteriorated by chlorine, are suitable. Since residual chlorine has been removed from the chlorine-removed water, the cause of deterioration of the separation membrane is eliminated. Since such chlorine-removed water is prone to slime problems, it is preferable to add a slime inhibitor to the chlorine-removed water and perform membrane separation. Examples of slime inhibitors include combined chlorine agents in which chlorine is combined with sulfamic acid (salt), isothiazolinone-based bactericides, and organic bromine-based bactericides. Among these, it is preferable to use combined chlorine agents in which chlorine is combined with sulfamic acid (salt), since it is possible to remove the reducing agent added in excess in the residual chlorine removal process.

[0019] The water quality measurement process is a process for measuring the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorinated water. The water quality measurement process is configured to measure the total chlorine concentration and free chlorine concentration of the chlorinated water in order to determine the amount of reducing agent to be added in the chlorine removal process. The total chlorine concentration and free chlorine concentration are measured using a colorimetric method based on the DPD method or an electrode-type measuring device. The total chlorine concentration (T-Cl), free chlorine concentration (F-Cl) and combined chlorine concentration (C-Cl) are measured according to JIS K 0400-33-10:1999, and the Cl 2 The value is expressed as: Total chlorine concentration (T-Cl) is measured as the sum of (free chlorine concentration (F-Cl) + combined chlorine concentration (C-Cl)).

[0020] The control process is a process for controlling the amount of reducing agent added based on the measured values ​​of the total chlorine concentration and free chlorine concentration of the chlorinated water measured in the water quality measurement process. The control process is configured to calculate the combined chlorine concentration (C-Cl) from the difference between the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl), and to calculate and control the amount of reducing agent added by the following formula [1]. Reducing agent concentration = fs × [((C-Cl) × m × a) + ((F-Cl) × m)] 〔1〕 (In the formula, fs is a safety factor of 1 to 1.2, and m is the reaction equivalent of the reducing agent and Cl 2 and a is a combined chlorine coefficient of 1.2 to 2, preferably 1.3 to 1.8. m is Cl 2 Reactive equivalents of reducing agent and Cl to reduce 2 The molecular weight ratio of Cl is 1. If the reducing agent is sodium hydrogen sulfite (SBS), 2 When is 1 mole, the reaction equivalent SBS for reducing it is 1 mole. Therefore, the molecular weight ratio is 104 / 71, which is rounded up to 1.5.

[0021] The reducing agent is preferably sodium hydrogen sulfite (SBS). In this case, the control step can control the amount of reducing agent added according to the following formula (2). SBS concentration=fs×[((C-Cl)×1.5×a)+((F-Cl)×1.5) 〕 ..〔2〕 (In the formula, fs is a safety factor of 1 to 1.2, and a is a combined chlorine coefficient of 1.2 to 2, preferably 1.3 to 1.8.)

[0022] The control step is provided for controlling the amount of reducing agent added in the residual chlorine removal step in claims 1 and 2, but can also be configured to control the amount of chlorine-based oxidizing agent added in the chlorination step. When controlling the amount of chlorine-based oxidizing agent added in the chlorination step, the control step can be configured to control the amount of chlorine-based oxidizing agent added in the chlorination step so that the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl) of the chlorine-treated water maintain the relationship of the following formula [3]. (T-Cl)≒(F-Cl)...[3]

[0023] In formula [3], (T-Cl) ≒ (F-Cl) means that the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl) are almost equal, and indicates that the area is near the discontinuous point and that the combined chlorine is essentially zero. The difference between (T-Cl) and (F-Cl) in "(T-Cl) ≒ (F-Cl)" is 0.1 to 0.5 mg (Cl 2 ) / L, preferably 0.1 to 0.3 mg (Cl 2 ) / L of concentration difference.

[0024] In the discontinuous chlorination method, when the amount of chlorine-based oxidizing agent added to raw water containing ammonia nitrogen is increased, combined chlorine (C-Cl) increases until it reaches a maximum value, but if the amount of chlorine-based oxidizing agent added is further increased, combined chlorine is decomposed and reaches a discontinuous minimum value. During this period, free chlorine (F-Cl) shows a value close to zero, and if the amount of chlorine-based oxidizing agent is further increased, free chlorine (F-Cl) increases, but combined chlorine (C-Cl) maintains its minimum value or even decreases. Therefore, it is difficult to accurately measure the discontinuity by measuring only either total chlorine (T-Cl) or free chlorine (F-Cl).

[0025] In order to perform discontinuous chlorination, a chlorine-based oxidizing agent is added to raw water containing ammonia nitrogen in the chlorination process, the total chlorine (T-Cl) and free chlorine (F-Cl) of the chlorinated water are measured in the water quality measurement process, and the amount of chlorine-based oxidizing agent added can be controlled based on the measured values ​​of total chlorine and free chlorine in the chlorinated water in the control process so that (T-Cl) ≒ (F-Cl) in formula [3] is satisfied. Since total chlorine (T-Cl) is (free chlorine (F-Cl) + combined chlorine (C-Cl)), as the amount of chlorine-based oxidizing agent added is increased, total chlorine (T-Cl) increases, decreases from the maximum value, and reaches a discontinuous point (minimum value), and as the amount of chlorine-based oxidizing agent added is further increased, total chlorine (T-Cl) increases. In contrast, free chlorine (F-Cl) shows a value close to zero when combined chlorine is present, even if the amount of chlorine-based oxidizing agent is added and increased, but when combined chlorine is decomposed and approaches the discontinuous point, free residual chlorine (F-Cl) begins to increase. Therefore, by controlling the amount of chlorine-based oxidizing agent added so that (T-Cl) ≒ (F-Cl) in equation (3) holds, chlorine-treated water from which ammonia nitrogen has been removed can be obtained.

[0026] The water treatment device of the present invention is constructed by a combination of devices for performing the operations of each step in the water treatment method. First, the chlorination device can have a reaction section into which raw water containing ammonia is introduced or passes, and a chemical feed section equipped with a chemical tank, an injection path, an injection pump, a control valve, etc. for adding a chlorine-based oxidizing agent to the raw water containing ammoniacal nitrogen, so that a chlorination process is performed to remove ammoniacal nitrogen by discontinuous point chlorination. Such a chlorination device can also serve as a pretreatment device or other devices. Examples of pretreatment devices include pretreatment devices for removing impurities such as coagulation, filtration, and activated carbon treatment of raw water, and pretreatment devices for oxidizing and removing oxidizable substances such as iron and manganese. By combining such a pretreatment device with a chemical feed section, it can be used as a chlorination device.

[0027] The residual chlorine removal device is configured to remove residual chlorine by adding a reducing agent to the chlorinated water obtained from the chlorine treatment device. This residual chlorine removal device can be configured to add a reducing agent to the chlorinated water to cause a reaction, and reduce and remove the residual chlorine through an oxidation-reduction reaction, so that the residual chlorine can be removed with high accuracy. In this case, the amount of reducing agent to be added can be calculated from the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) measured by the water quality measurement device using the above formulas [1] and [2].

[0028] The membrane separation device is equipped with a separation membrane and is configured to perform membrane separation of the residual chlorine-removed water sent from the residual chlorine removal device. Examples of the separation membrane include membranes that allow the solution to permeate by membrane separation, such as UF membranes, MF membranes, and RO membranes, but in particular, RO membranes, especially RO membranes made of polymer membranes having nitrogen-containing groups such as polyamide and aramid, are suitable. Since the residual chlorine is removed from the residual chlorine-removed water, the cause of deterioration of the separation membrane is eliminated, but if the situation is such that slime problems are likely to occur, it is preferable to provide a chemical injection section for adding a slime inhibitor. Examples of slime inhibitors include those mentioned above, but a combined chlorine agent in which chlorine is combined with sulfamic acid (salt) is preferable.

[0029] The water quality measuring device is a measuring device that measures the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorinated water obtained from the chlorination treatment device, and a colorimetric method using the DPD method, an electrode type, etc. Such a water quality measuring device is preferably installed between the chlorination treatment device and the residual chlorine removal device and is capable of measuring both the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl), but separate measuring devices may also be used for the measurements.

[0030] The control device is a device that calculates and controls the amount of reducing agent to be added using the above formula [1] or [2] based on the measured values ​​of the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorinated water measured by the water quality measuring device, and calculates and controls the amount of chlorine-based oxidizing agent to be added using the above formula [3].It includes an arithmetic device such as a computer that outputs a control signal for the amount to be added by calculation, and is configured to control the amount of liquid delivered by the injection pump of the chemical injection section and the opening degree of the control valve, etc., using the control signal.

[0031] The water treatment device performs chlorination to remove ammonia nitrogen by discontinuous chlorination by adding a chlorine-based oxidizing agent to raw water containing ammonia nitrogen according to each step of the water treatment method. At this time, the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorinated water are measured by a water quality measuring device, and the control device can control the amount of chlorine-based oxidizing agent added by the above formula [3] based on the measured values ​​of the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorinated water measured by the water quality measuring device. This makes it possible to remove ammonia nitrogen from the raw water, thereby increasing the oxidizing power, and enabling the sterilization of remaining fungi and the oxidizing removal of oxidizable substances such as iron and manganese.

[0032] The chlorinated water obtained from the chlorine treatment device is added with a reducing agent in a residual chlorine removal device to remove residual chlorine, and the residual chlorine-removed water sent from the residual chlorine removal device is separated by a separation membrane in a membrane separation device to become treated water. In the residual chlorine removal device, the control device calculates and controls the amount of reducing agent to be added using the above formula [1] or [2] based on the measured values ​​of the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorinated water measured by the water quality measurement device. As a result, even if combined chlorine is detected in the area beyond the discontinuous point, the residual chlorine is effectively reduced and removed to prevent chlorine leakage, and deterioration of the separation membrane in the membrane separation device can be prevented. When a slime inhibitor is added to the membrane separation device to perform membrane separation, the slime inhibitor is added from the chemical injection section to prevent slime formation in the separation membrane, thereby enhancing the membrane separation effect.

[0033] In the breakpoint chlorination, it is required to control the amount of chlorine-based oxidizing agent added so that the chlorine concentration is in a region slightly exceeding the breakpoint, but it is difficult to detect the breakpoint when combined chlorine is present. Combined chlorine may also be detected in the region exceeding the breakpoint, and if combined chlorine remains, it becomes difficult to control the amount of reducing agent added. In general, the amount of chlorine-based oxidizing agent or reducing agent added is controlled by measuring the total chlorine concentration, free chlorine concentration, redox potential, etc., but it is difficult to detect the breakpoint even if these are used as indicators alone. Even if the amount of reducing agent required to remove chlorine is calculated and added using the measured total chlorine concentration, free chlorine concentration, redox potential, etc., there are cases where chlorine leakage cannot be prevented. In such cases, the amount of reducing agent is usually calculated by multiplying it by a safety factor, but even with this, chlorine leakage cannot be prevented and deterioration of the separation membrane may occur.

[0034] When the cause was investigated, it was found that when combined chlorine remains, the reactivity with DPD reagent and reducing agent varies depending on the composition and reactivity of combined chlorine, so that the measured value of total chlorine concentration varies, and it was presumed that the variation would be further increased if the amount of reducing agent added was calculated based on the measured value and an oxidation-reduction reaction was performed. In order to prevent chlorine leakage even if such variation occurs, it is possible to prevent chlorine leakage by controlling it using the above formula [1] or [2], which introduces a combined chlorine coefficient that is applied only to combined chlorine in addition to the safety factor of the entire reaction including free chlorine. Effect of the Invention

[0035] In the present invention, when a chlorine-based oxidizing agent is added to raw water containing ammoniacal nitrogen for treatment, the chlorine-based oxidizing agent can be appropriately added to remove ammoniacal nitrogen and further oxidize remaining oxidizable substances, and a reducing agent can be appropriately added to reduce residual chlorine, preventing chlorine leakage and deterioration of the separation membrane. [Brief description of the drawings]

[0036] [Figure 1]FIG. 1 is a flow diagram illustrating a water treatment method and apparatus according to an embodiment of the invention. [Diagram 2] 1 is a graph showing the measured values ​​after 30 minutes in Reference Example 1 of the Examples. [Diagram 3] 1 is a graph showing the measured values ​​after 60 minutes in Reference Example 1 of the Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] FIG. 1 shows a water treatment method and apparatus according to an embodiment of the present invention, in which 1 is a chlorination treatment device, 2 is a residual chlorine removal device, 3 is a safety filter, 4 is an RO membrane separation device, 5 is a chlorine-based oxidizing agent tank, 6 is a reducing agent tank, 7 is a slime prevention agent tank, and 8 is a control device. The chlorination treatment device 1 is configured to perform chlorination treatment to remove ammonia nitrogen by discontinuous point chlorination by adding a chlorine-based oxidizing agent to raw water containing ammonia nitrogen. The residual chlorine removal device 2 is configured to remove residual chlorine by adding a reducing agent to the chlorine-treated water. The RO membrane separation device 4 is partitioned into a concentrated liquid chamber 4b and a permeated liquid chamber 4c by an RO membrane module 4a, and is configured to perform RO membrane separation. The detector C1 is configured to measure free chlorine (F-Cl) and total chlorine (T-Cl) on the path L2 and send a free / total chlorine detection signal D1 to the control device 8, the detector C2 is configured to measure free chlorine (F-Cl) and total chlorine (T-Cl) on the path L3 and send a free / total chlorine detection signal D2 to the control device 8, and the detector C3 is configured to measure the slime inhibitor on the path L4 and send a slime inhibitor signal D3 to the control device 8. The control device 8 is configured to control the pump P1 by a control signal S1 obtained from the free / total chlorine detection signal D1 of the detector C1, control the pump P2 by a control signal S2 obtained from the free / total chlorine detection signal D1 of the detector C1, correct the control signal S2 by the free / total chlorine detection signal D2 of the detector C2, and control the pump P3 by a control signal S3 obtained from the slime inhibitor signal D3.

[0038] The water treatment method using the above-mentioned device is carried out as follows. First, when raw water containing ammoniacal nitrogen is supplied to the chlorination treatment device 1 from the raw water channel L1, the pump P1 is controlled by a control signal S1 from the control device 8, and a chlorine-based oxidant is added from the chlorine-based oxidant tank 5 through the path L7 and supplied to the chlorination treatment device 1. As a result, in the chlorination treatment device 1, chlorination of the raw water containing ammoniacal nitrogen is carried out as a chlorination process, and oxidizable substances containing ammoniacal nitrogen in the raw water are oxidized and decomposed. The chlorination treatment device 1 may be a device dedicated to chlorination, but it is preferable that it also serves as a pretreatment device such as coagulation, filtration, and activated carbon treatment, in which case pretreatment and chlorination can be carried out simultaneously.

[0039] In the process of sending the chlorine-treated water from the chlorine treatment device 1 to the residual chlorine removal device 2 through the path L2, the free chlorine concentration (F-Cl) and total chlorine concentration (T-Cl) are measured by the detector C1, and the resulting free / total chlorine detection signal D1 is sent to the control device 8. In the control device 8, a control signal S1 is sent to control the amount of chlorine-based oxidizing agent added in the chlorination process so that the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl) maintain the relationship of the above formula [3] based on the free / total chlorine detection signal D1, and the pump P1 is controlled.

[0040] In order to control the amount of chlorine-based oxidant added to perform discontinuous chlorination in the chlorination process, the total chlorine (T-Cl) and free chlorine (F-Cl) in the chlorinated water are measured by the detector C1, and a free / total chlorine detection signal D1 is sent to the control device 8. The control device 8 then sends a control signal S1 to the pump P1 so that (T-Cl) ≒ (F-Cl) in formula [3] is satisfied, and controls the addition of chlorine-based oxidant to the raw water containing ammonia nitrogen. At this time, the difference between (T-Cl) and (F-Cl) is set to 0.1 to 0.5 mg (Cl 2 ) / L, preferably 0.1 to 0.3 mg (Cl 2 ) / L. In this case, the difference between (T-Cl) and (F-Cl) is 0.5 mg (Cl 2) / L or more, there is a chlorine deficiency, so increase the amount of chlorine-based oxidizing agent added. Also, if the difference between (T-Cl) and (F-Cl) is less than 0.1 mg (Cl 2 ) / L or less, there is an excess of chlorine, so reduce the amount of chlorine-based oxidizing agent added.

[0041] As a result, in the chlorination process in the chlorination treatment device 1, raw water containing ammoniacal nitrogen is chlorinated, and oxidizable substances containing ammoniacal nitrogen in the raw water are oxidized and decomposed, with the substances that are most easily oxidized being decomposed in order. In the present invention, by performing discontinuous point chlorination, a chlorine-based oxidizing agent is added to raw water containing ammoniacal nitrogen to oxidize and decompose ammoniacal nitrogen, and chlorination is performed so as to further sterilize the water and oxidize and decompose iron, manganese, etc.

[0042] The chlorinated water obtained from the chlorine treatment device 1 is sent to the residual chlorine removal device 2 after adding a reducing agent through the path L2, and residual chlorine is removed by an oxidation-reduction reaction. At this time, the control device 8 calculates the combined chlorine concentration (C-Cl) from the difference between the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl) of the free / total chlorine detection signal D1, and calculates the amount of reducing agent to be added using the above formula [1] or formula [2] to generate a control signal S2. Then, the pump P2 is controlled by this control signal S2, and the chlorinated water to which the reducing agent has been added is sent from the reducing agent tank 6 through the path L8 to the residual chlorine removal device 2, where the residual chlorine is removed by reacting with the reducing agent. Formula [1] is a formula that is generally applicable to reducing agents, while formula [2] is a formula specific to the reducing agent being sodium hydrogen sulfite (SBS). In the control device 8, the amount of reducing agent to be added is calculated and controlled by the above formula [1] or [2] based on the measured values ​​of the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorine-treated water measured by the detector C1. Even when combined chlorine is detected in the area beyond the discontinuity point, the residual chlorine is effectively reduced and removed, preventing chlorine leakage and preventing deterioration of the separation membrane in the membrane separation device.

[0043] In the process of the residual chlorine-removed water being sent to the safety filter 3 from the path L3, the detector C2 measures free chlorine (F-Cl) and total chlorine (T-Cl), and the control signal S2 can be corrected by the obtained free / total chlorine detection signal D2. That is, when free chlorine (F-Cl) or total chlorine (T-Cl) is detected, the amount of the reducing agent added can be increased. In addition, in the process of adding the slime inhibitor from the slime inhibitor tank 7 through the path L9 and supplying the water to the RO membrane separation device 4 from the path L4, the pump P3 is controlled by the control signal S3 obtained from the slime inhibitor signal D3 of the detector C3 to control the amount of the slime inhibitor added. In the RO membrane separation device 4, the slime inhibitor-added water enters the concentrated liquid chamber 4b, the solvent permeates through the RO membrane module 4a and is separated by membrane, the permeated liquid in the permeated liquid chamber 4c is taken out from the path L5, and the concentrated liquid remaining in the concentrated liquid chamber 4b is discharged from the path L6.

[0044] In this way, in the control of the amount of chlorine-based oxidizing agent added by the control device 8, when the pump P1 is controlled by the control signal S1 obtained from the free / total chlorine detection signal D1 of the detector C1, the control according to the above formula [3] is performed to perform discontinuous chlorination, and the chlorine-based oxidizing agent is appropriately added to remove ammonia nitrogen for oxidation treatment, and sterilization and oxidation removal of iron, manganese, etc. are possible. In addition, by removing ammonia nitrogen from the chlorine-treated water and removing residual chlorine in a state where total chlorine (T-Cl) and free chlorine (F-Cl) are low, the amount of reducing agent can be calculated easily and accurately, and residual chlorine can be removed efficiently. Furthermore, since RO membrane separation can be performed in a state where there is little residual chlorine, deterioration of the RO membrane can be prevented and membrane separation can be performed efficiently.

[0045] In the residual chlorine removal device 2, the amount of reducing agent to be added is calculated and controlled by the control device 8 using the above formula [1] or [2] based on the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) of the chlorinated water measured by the detector C1, thereby effectively preventing chlorine leakage, thereby preventing deterioration of the separation membrane and making it possible to continue efficient membrane separation for a long period of time. EXAMPLES

[0046] Examples and comparative examples of the present invention will be described below. In each example, % is mass %.

[0047] [Reference example 1]: (1) Sample preparation 1) Ammonium sulfate 0.184% solution: Ammonium sulfate ((NH 4 ) 2 SO 4 0.368 g of this compound was weighed out and dissolved in 200 g of pure water to prepare 200 ml of a 0.184% ammonium sulfate solution. 2) Sodium hypochlorite 0.1 (Cl 2 )% solution: Dilute approximately 12% sodium hypochlorite 100 times, then dilute it again 100 times, measure the chlorine concentration, measure the effective chlorine concentration, and add 0.1(Cl 2 )% solution was prepared. 2 )% solution is 0.5ml / 500ml (Cl 2 )1mg / L. 3) Base water: Tap water was treated with activated carbon and dechlorinated to prepare base water.

[0048] (2) Test method In a 500 mL beaker containing (499-A) mL of base water, 1 mL of 0.184% ammonium sulfate solution was added and stirred for 1 minute. Then, 0.1% sodium hypochlorite (Cl 2 A mL of % solution was added and stirred (A is the (Cl) 2 ) is a unitless value that corresponds to the amount added. Sodium hypochlorite 0.1 (Cl 2 Total chlorine (T-Cl), free chlorine (F-Cl), oxidation-reduction potential (ORP), and ammonia nitrogen (NH 4 The results after 30 minutes are shown in Table 1 and FIG. 2, and the results after 60 minutes are shown in Table 2 and FIG. 3. In FIG. 2 and FIG. 3, the vertical dashed lines indicate the control target values ​​in the discontinuous point treatment. NH 4-N was measured according to the JIS K0102 indophenol blue method.

[0049] [Results after 30 minutes] [Table 1]

[0050] [Results after 60 minutes] [Table 2]

[0051] From the above results, the amount of combined chlorine ((T-Cl)-(F-Cl)) increases as the amount of chlorine-based oxidizing agent added to raw water containing ammonia nitrogen increases. Until the total chlorine (T-Cl) reaches a maximum value, the amount of ammonia nitrogen remains essentially unchanged, but in the region beyond the maximum value, the total chlorine (T-Cl) decreases and the ammonia nitrogen decreases until it reaches a minimum point (discontinuity point). At the discontinuity point, the ammonia nitrogen becomes essentially zero and the free chlorine (F-Cl) begins to increase, but even in the region beyond the discontinuity point, ammonia nitrogen is detected and combined chlorine is formed. In this region, the difference between the total chlorine (T-Cl) and the free chlorine (F-Cl) is large, indicating the presence of oxidizable substances in the chlorine-treated water. Furthermore, by increasing the amount of chlorine agent added, the state of (T-Cl) ≒ (F-Cl) is reached, indicating that the oxidizable substances are decomposed.

[0052] Example 1 In the same manner as in the test method of Reference Example 1, 1 mL of 0.184% ammonium sulfate solution was added to a 500 mL beaker containing (499-A) mL of base water, and the mixture was stirred for 1 minute. Then, 0.1 (Cl 2 A mL of )% solution was added and stirred (A is the (Cl) 2 ) is a unitless value that corresponds to the amount added. Sodium hypochlorite 0.1 (Cl 2)% solution was added, 30 minutes later, the total chlorine concentration (T-Cl) and free chlorine concentration (F-Cl) were measured, and sodium hydrogen sulfite (SBS) was added as a reducing agent according to the following formula [2.1] (fs = 1.1, a = 2 in the above formula [2]) to remove residual chlorine, and the total chlorine concentration (T-Cl) was measured. Sodium hypochlorite was then added at 1 (Cl 2 ) mg / L to remove excess SBS, and the residual total chlorine concentration (T-Cl)* (+1) was measured. This residual total chlorine concentration corresponds to the complement of excess SBS, and is 1 (Cl 2 The part exceeding 100 mg / L indicates the leaked chlorine concentration. The results are shown in Table 3. SBS concentration = 1.1× [((C-Cl)×1.5×2)+((F-Cl)×1.5)]...[2.1]

[0053] Example 2 In Example 1, sodium hydrogen sulfite (SBS) was added according to the following formula [2.2] (fs=1.1, a=1.3 in the above formula [2]). The results are shown in Table 3. SBS concentration = 1.1× [((C-Cl)×1.5×1.3)+((F-Cl)×1.5)]...[2.2]

[0054] Comparative Example 1 In Example 1, sodium hydrogen sulfite (SBS) was added according to the following formula [2.3]. The results are shown in Table 3. SBS concentration = 1.1 x ((T-Cl) x 1.5)... [2.3]

[0055] [Table 3]

[0056] From the above results, in Comparative Example 1, in which the amount of sodium hydrogen sulfite (SBS) added was controlled according to formula [2.3], Cl 2 Added amount 7.5mg (Cl 2 ) / L, the residual total chlorine concentration (T-Cl)* (+1) is 1(Cl 2) mg / L, indicating that residual chlorine is leaking from the residual chlorine removal device. In contrast, in Examples 1 and 2, in which the amount of sodium hydrogen sulfite (SBS) added was controlled according to formula [2.1] or formula [2.2], it can be seen that there is no residual chlorine leakage from the residual chlorine removal device. In this case, the amount of sodium hydrogen sulfite (SBS) added is small, and there is little excessive addition. In particular, in Example 2, in which the amount of sodium hydrogen sulfite (SBS) added was controlled according to formula [2.2], it can be seen that there is no residual chlorine leakage, and the excessive addition of sodium hydrogen sulfite (SBS) can be controlled to a smaller amount. [Industrial Applicability]

[0057] INDUSTRIAL APPLICABILITY The present invention can be used in a water treatment method and apparatus for chlorinating raw water containing ammoniacal nitrogen by adding a chlorine-based oxidizing agent, removing residual chlorine in the chlorinated water, and performing membrane separation. [Explanation of symbols]

[0058] 1 Chlorine treatment device, 2 Residual chlorine removal device, 3 Safety filter, 4 RO membrane separation device, 4a RO membrane module, 4b Concentrate chamber, 4c Permeate chamber, 5 Chlorine-based oxidant tank, 6 Reducing agent tank, 7 Slime prevention agent tank, 8 Control device, P1, P2, P3 Pump, C1, C2, C3 Detector, S1, S2, S3 Control signal, D1, D2 Free / total chlorine detection signal, D3 Slime prevention agent signal.

Claims

1. a chlorination process in which a chlorine-based oxidant is added to the raw water containing ammonia nitrogen, and ammonia nitrogen is removed by discontinuous point chlorination; a residual chlorine removal step of removing residual chlorine by adding a reducing agent to the chlorinated water; a membrane separation step of separating the residual chlorine-removed water using a separation membrane; A water quality measurement process for measuring the total chlorine concentration and free chlorine concentration of the chlorinated water; A control step of controlling the amount of reducing agent added based on the measured values ​​of the total chlorine concentration and the free chlorine concentration of the chlorine-treated water, The control step is configured to calculate a combined chlorine concentration (C-Cl) from the difference between the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl), and to calculate and control the amount of reducing agent to be added by the following formula [1]. Reducing agent concentration = fs x [((C-Cl) x m x a) + ((F-Cl) x m)] ... [1] (In the formula, fs is a safety factor of 1 to 1.2, and m is the reaction equivalent of the reducing agent and Cl ２ The molecular weight ratio of a is 1.2 to 2, and a is the combined chlorine coefficient.

2. The reducing agent is sodium bisulfite (SBS), 2. The water treatment method according to claim 1, wherein the control step is configured to control the amount of the reducing agent added according to the following formula [2]: SBS concentration = fs × [((C-Cl) × 1.5 × a) + ((F-Cl) × 1.5)] ... [2] (In the formula, fs is a safety factor of 1 to 1.2, and a is a combined chlorine coefficient of 1.2 to 2.)

3. 3. The water treatment method according to claim 1, wherein the membrane separation step is configured to add a slime inhibitor to the residual chlorine-removed water and then perform membrane separation.

4. A chlorine treatment device that adds a chlorine-based oxidizing agent to raw water containing ammonia nitrogen and removes ammonia nitrogen by discontinuous point chlorination; A residual chlorine removal device that removes residual chlorine by adding a reducing agent to chlorinated water; A membrane separation device that separates the residual chlorine removed water using a separation membrane; A water quality measuring device for measuring the total chlorine concentration and free chlorine concentration of chlorinated water; and A control device is provided for controlling the amount of reducing agent added based on the measured values ​​of the total chlorine concentration and the free chlorine concentration of the chlorine-treated water, The control device is configured to calculate a combined chlorine concentration (C-Cl) from the difference between the total chlorine concentration (T-Cl) and the free chlorine concentration (F-Cl), and to calculate and control the amount of reducing agent to be added using the following formula [1]. Reducing agent concentration = fs x [((C-Cl) x m x a) + ((F-Cl) x m)] ... [1] (In the formula, fs is a safety factor of 1 to 1.2, and m is the reaction equivalent of the reducing agent and Cl ２ The molecular weight ratio of a is 1.2 to 2, and a is the combined chlorine coefficient.

5. The reducing agent is sodium bisulfite (SBS), 5. The water treatment device according to claim 4, wherein the control device is configured to control the amount of the reducing agent added according to the following formula [2]: SBS concentration = fs × [((C-Cl) × 1.5 × a) + ((F-Cl) × 1.5)] ... [2] (In the formula, fs is a safety factor of 1 to 1.2, and a is a combined chlorine coefficient of 1.2 to 2.)

6. 6. The water treatment apparatus according to claim 4, wherein the membrane separation device is configured to add a slime inhibitor to the residual chlorine-removed water and perform membrane separation.

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