Urea treatment device and urea treatment method

Abstract

The present application provides a urea treatment device and a urea treatment method, which can inhibit the increase of the TOC value of the treatment water supplied to the use point. The urea treatment device for treating urea in treatment water comprises: a first reaction tank for treating urea in the treatment water; a first adding unit connected with the first reaction tank or connected with a first pipe connected with the first reaction tank and supplying the treatment water to the first reaction tank, and adding bromide salt and chlorine-based oxidizing agent to the treatment water; a second reaction tank for treating urea remaining in the first treatment water treated by the first reaction tank; and a second adding unit connected with the second reaction tank or connected with a second pipe connected with the second reaction tank and supplying the first treatment water to the second reaction tank, and adding at least one of chlorine-based oxidizing agent or inorganic acid to the first treatment water. The device is used for a urea treatment method.

Description

Technical Field

[0001] This application is based on Japanese Patent Application No. 2021-23654, filed on February 17, 2021, and claims priority based on that application. That application is incorporated herein by reference in its entirety.

[0002] This invention relates to a urea treatment apparatus and a treatment method, and more particularly to a urea treatment apparatus and a urea treatment method in a pure water manufacturing process. Background Technology

[0003] Pure water production equipment, used to produce pure water from raw water sources such as tap water, groundwater, and industrial water, typically combines reverse osmosis membrane devices, ion exchange devices, and ultraviolet oxidation devices. When the raw water contains urea, which is difficult to remove by reverse osmosis membrane devices, ion exchange devices, and ultraviolet oxidation devices, the TOC (total organic carbon) concentration of the produced pure water increases due to residual urea. In the production of ultrapure water, which requires exceptionally high purity for applications such as semiconductor manufacturing, the upper limit of the TOC concentration in the resulting ultrapure water is strictly set, necessitating a process to remove urea from the raw water.

[0004] JP Patent Application Publication No. 9-94585 discloses a method in which a reagent for generating hypobromide is added to raw water and supplied to a reaction tank, and urea is decomposed and removed in the reaction tank using hypobromide.

[0005] Generally, the urea decomposition reaction takes time, thus requiring a long residence time in the reaction tank. In such urea treatment methods (treatment devices), the following problem exists: if urea is not completely decomposed in the reaction tank and flows to the downstream stage, even if additional agents for hypobromite formation are added to the raw water at that point, a time lag occurs until treated water with urea removed is obtained. During this period, there is a problem of supplying treated water with an increased TOC value to the point of use.

[0006] Therefore, the object of the present invention is to provide a urea treatment apparatus and a urea treatment method that can suppress the supply of treated water with an increased TOC value to the point of use. Summary of the Invention

[0007] The present invention covers the following [1] to

[10] configurations.

[0008] [1] A urea treatment device for treating urea in water to be treated, the urea treatment device comprising:

[0009] The first reaction tank treats the urea in the water to be treated;

[0010] The first addition unit is connected to the first reaction tank or to a first pipe connected to the first reaction tank and supplying the water to be treated to the first reaction tank, and adds bromide salt and chlorine-based oxidant to the water to be treated.

[0011] A second reaction tank treats any residual urea in the first treated water after it has been treated by the first reaction tank; and

[0012] The second addition unit is connected to the second reaction tank or to a second pipe connected to the second reaction tank and supplying the first treated water to the second reaction tank, and adds at least one of a chlorine-based oxidant or an inorganic acid to the first treated water.

[0013] [2] Based on the urea treatment device described in [1] above, the residence time of the first treated water in the second reaction tank is shorter than the residence time of the treated water in the first reaction tank.

[0014] [3] Based on the urea treatment device described in [1] or [2] above, the urea treatment device has:

[0015] A TOC meter or urea meter, installed downstream of the second reaction tank, monitors the TOC or urea concentration in the second treated water after treatment by the second reaction tank; and

[0016] A unit that controls the amount of material added from the first addition unit and / or the second addition unit based on the TOC concentration or urea concentration in the second treated water.

[0017] [4] Based on the urea treatment device described in any of [1] to [3] above, the urea treatment device includes a reducing agent addition unit, which is located after the second reaction tank, and the reducing agent reduces the oxidant components contained in the second treated water.

[0018] [5] A pure water production system, comprising:

[0019] The urea treatment device described in any of [1] to [4] above;

[0020] An ion exchange unit, located downstream of the urea treatment unit, is supplied with water treated by the urea treatment unit; and

[0021] A reverse osmosis membrane device is installed downstream of the ion exchange device and is supplied with water treated by the ion exchange device.

[0022] [6] A urea treatment method is a method for treating urea in water to be treated, the urea treatment method comprising:

[0023] The first treatment step involves adding bromide salts and chlorine-based oxidants as urea decomposition agents to the water to be treated to treat the urea; and

[0024] The second treatment step involves adding at least one of a chlorine-based oxidant or an inorganic acid as a urea decomposition agent to the first treated water obtained from the first treatment step to treat the residual urea in the first treated water.

[0025] [7] Based on the urea treatment method described in [6] above, the treatment time of the second treatment step is shorter than that of the first treatment step.

[0026] [8] Based on the urea treatment method described in [6] or [7] above, the urea treatment method includes:

[0027] The measurement process involves measuring the TOC or urea concentration in the second treated water obtained from the second treatment process; and

[0028] The dosage control step involves controlling the amount of urea decomposing agent added in the first treatment step and / or the second treatment step based on the TOC or urea concentration in the second treated water.

[0029] [9] Based on any of the urea treatment methods described in [6] to [8] above, the urea treatment method includes: a reduction step, which reduces the oxidant components contained in the second treated water.

[0030]

[10] A method for producing pure water, comprising the urea treatment method described in any one of [6] to [9] above as a pretreatment step.

[0031] According to the present invention, a urea treatment apparatus and a urea treatment method can be provided to suppress the supply of treated water with an increased TOC value to the point of use.

[0032] The above and other objectives, features and advantages of this application will become clear from the detailed description below, which is illustrated with reference to the accompanying drawings. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating an example of the urea treatment apparatus of the present invention.

[0034] Figure 2 This is a schematic diagram illustrating another example of the urea treatment apparatus of the present invention.

[0035] Figure 3The figures are schematic representations of embodiments 1 to 3 and comparative example 3.

[0036] Figure 4 The diagram schematically illustrates the embodiments of Comparative Examples 1 and 2.

[0037] Figure 5 This is a diagram illustrating an example of a pure water production system. Detailed Implementation

[0038] The inventors of this invention, through their explorations to solve the aforementioned problems, have obtained the following insights.

[0039] That is, the urea treatment process, which generates hypobromite ions to decompose urea in the treated water to obtain treated water, is set up in two steps. If urea tends to flow out in the first step, a urea decomposing agent (chlorinated oxidant or acid) is injected in the second step to remove urea, thereby ensuring that the treated water after urea removal is always supplied with the optimal dosage. Hereinafter, regarding the present invention, firstly, the urea treatment method will be described, and then, the urea treatment apparatus capable of implementing this treatment method will be described.

[0040] The urea treatment method of the present invention relates to a method for treating urea in water to be treated. This urea treatment method comprises the following two steps.

[0041] • First treatment step: The step of adding bromide salts and chlorine-based oxidants as urea decomposition agents to the urea-containing water to treat the urea.

[0042] • Second treatment step: A step of adding at least one of a chlorine-based oxidant or an inorganic acid as a urea decomposition agent to the first treated water obtained from the first treatment step to treat the residual urea in the first treated water.

[0043] In this invention, it is important to perform two treatment steps, which can be continuous or discontinuous. Furthermore, between the two treatment steps, as long as no equipment consuming hypobromic acid (such as an activated carbon tower) is installed, a water filtration step can also be included, for example, the filtration step based on a dual-layer sand filter (multi-media filter: MMF) described later.

[0044] In the first treatment step, a urea-decomposing agent (hereinafter referred to simply as "agent") that generates hypobromic acid is added to the water to be treated. The water to be treated can, as appropriate, contain urea; for example, it can be raw water used for pure water production, such as industrial water, tap water, or well water. The water to be treated contains, for example, approximately 2–500 μg / L of urea. A bromide salt and a chlorine-based oxidant are added as the agent for generating hypobromic acid. The bromide salt is preferably water-soluble; for example, sodium bromide (NaBr) is used. As the chlorine-based oxidant, hypochlorite is used, especially sodium hypochlorite (NaClO).

[0045] If the above-mentioned reagent is added to the water to be treated containing urea, the urea in the water to be treated will be removed by a selective oxidation urea decomposition reaction, resulting in the first treated water.

[0046] The urea decomposition reaction is based on the following reaction.

[0047] NaBr + NaClO → NaBrO + NaCl

[0048] CO(NH2)2+3NaBrO→3NaBr+N2+2H2O+CO2

[0049] The first treatment process can be carried out by adjusting the water to be treated to normal temperature (e.g., around 20°C), normal pressure (e.g., around 1 atmosphere), and pH 7, and allowing the reaction to proceed for approximately 0.5 to 24 hours.

[0050] The amount of bromide salt and chlorine-based oxidant added is appropriately set according to the concentration of urea in the water to be treated, without any particular limitation. However, it is preferred to add them to make the concentration of urea in the first water to be treated less than 1 μg / L, usually about 1 to 5 mg / L of bromide salt and about 1 to 10 mg / L of chlorine-based oxidant.

[0051] As a method of adding bromide salts or chloride-based oxidants, there are no particular restrictions as long as the form promotes the generation of hypobromite ions. Methods such as adding various injection pipes to the water supply piping of the water being treated, or using a mixer that also functions as a pipeline mixer or mixing reaction tank are all acceptable.

[0052] Next, in the second treatment step, a chlorine-based oxidant or an inorganic acid is added as a reagent to the first-treated water obtained from the first treatment step. Only one of the chlorine-based oxidant and the inorganic acid needs to be added; either one or both can be added. As the chlorine-based oxidant, hypochlorite, especially sodium hypochlorite (NaClO), is used, similar to that used in the first treatment step. As the acid, hydrochloric acid (HCl), nitric acid (HNO3), phosphoric acid (H3PO4), and sulfuric acid (H2SO4) are used, for example.

[0053] In the case where sodium hypochlorite (NaClO) is added to the first treated water as a chlorine-based oxidant, the residual urea in the first treated water is removed based on the same reaction as in the first treated water, thus obtaining the second treated water.

[0054] In addition, when HCl is added as an inorganic acid to the first treated water, and when chlorine-based oxidants and inorganic acids are added, only the pH of the first treated water changes. Based on the same reaction as the first treatment process, the residual urea in the first treated water is removed to obtain the second treated water.

[0055] Chlorine-based oxidants and / or inorganic acids are added to the first treated water as urea decomposition agents to obtain the second treated water.

[0056] The second treatment step is carried out by adding chlorine-based oxidants and / or inorganic acids to the first-treated water, which has been adjusted to normal temperature (e.g., around 20°C) and normal pressure (e.g., around 1 atmosphere).

[0057] When adding a chlorine-based oxidant to the first-treated water in the second treatment step, it is preferable to add it in such a way that the concentration of free residual chlorine is 1 to 10 mg / L.

[0058] Furthermore, when adding inorganic acid to the first-treated water in the second treatment step to adjust the pH, it is preferable to carry out the process under conditions of pH 4 to 6. If the pH of the treated water is less than 4, there is a disadvantage that hypobromite ions may be vaporized due to the addition of the aforementioned reagent. Conversely, if the pH of the treated water exceeds 10, although the treatment capacity of urea will be improved, the salt load will increase, which is not preferred. Therefore, the above-mentioned range is set.

[0059] Furthermore, when using both chlorine-based oxidants and inorganic acids in the second processing step, it is preferable to add them such that the amounts of the chlorine-based oxidant and inorganic acid are respectively within the aforementioned ranges. That is, it is preferable to add chlorine-based oxidants so that the free residual chlorine concentration is 1 to 10 mg / L, and to add inorganic acids so that the pH is between 4 and 6.

[0060] As a method for adding chlorine-based oxidants and / or acids, similar to the first treatment step, methods such as installing and adding injection pipes in the water supply piping of the water to be treated, or using a mixer that combines a pipeline mixer and a mixing reaction tank, can be used.

[0061] In the urea treatment method of the present invention, it is preferable that the processing time of the second treatment step is shorter than the processing time of the first treatment step. By making the processing time of the second treatment step shorter than the processing time of the first treatment step, treated water after rapid removal of urea can be supplied.

[0062] Specifically, it is preferable to set the processing time of the first processing step to the processing time of the second processing step to a ratio of 2:1 to 60:1.

[0063] Furthermore, in the urea treatment method of the present invention, it is preferable to control the amount of reagent added in the first treatment step and / or the second treatment step by monitoring the TOC or urea concentration in the treated water. Specifically,

[0064] Preferably, it includes: a measurement step for measuring the TOC or urea concentration in the second treated water obtained from the second treatment step; and an addition control step for controlling the addition amount of urea decomposing agent in the first treatment step and / or the second treatment step based on the TOC or urea concentration in the second treated water.

[0065] In this case, at least in the subsequent stage of the second treatment process, in the process of measuring and monitoring the TOC concentration or urea concentration in the second treated water, a TOC meter or urea meter (measuring device) is installed to measure and monitor the changes in the TOC concentration or urea concentration in the treated water. This allows the amount of reagent added in the second treatment process to be controlled based on the TOC or urea concentration in the second treated water, thereby controlling the amount of reagent added in the first treatment process.

[0066] In cases where a process is to be set up to monitor changes in TOC or urea concentration in the second treated water based on a TOC meter or urea meter, as mentioned above, it is necessary to set up the process at least after the second treatment process. However, from the perspective of being able to detect urea leakage earlier and quickly add the reagent to the filter or filtration tank (the equipment performing the second treatment process), it is preferable to set up the process not only after the second treatment process but also after the first treatment process.

[0067] Not only does it treat residual urea in the water, but the reagents that generate hypobromic acid also put a load on the pure water production system; therefore, the amount of reagent added should be as small as possible. According to the invention of this embodiment, the necessity of urea treatment can be determined by quantitatively measuring the urea concentration in the treated water, and an appropriate amount of reagent can be added when treatment is required. Therefore, urea leakage from the reaction tank can be suppressed while reducing the load on the pure water production system. Furthermore, the processing time of the second treatment step can be set to be shorter, making outlet management control easier to follow. The outlet management control in the second treatment step is as follows, for example.

[0068] (1) Detect the upward trend (change / slope over time) of TOC concentration or urea concentration, and input the data related to the upward trend of TOC concentration or urea concentration into the learning algorithm of the machine learning device.

[0069] (2) The learning algorithm uses machine learning to determine whether it is necessary to add a drug in order to not exceed the given concentration based on the input data. The machine learning device outputs data indicating whether the drug needs to be added.

[0070] (3) If it is determined that the drug needs to be added based on the judgment of machine learning, the amount of drug to be added is calculated. In addition to outputting the data indicating whether the drug needs to be added, the machine learning device will also output the data indicating the amount of drug to be added.

[0071] Based on the above, in the second processing step, the amount of reagent added can be controlled before the TOC concentration or urea concentration reaches the management value.

[0072] Furthermore, a reduction treatment step is preferably provided after the second treatment step to reduce the residual oxidant components in the treated water. The reduction treatment step is preferably provided either before or after the step that monitors the TOC or urea concentration in the treated water; however, from the viewpoint of TOC or urea concentration detection accuracy, it is preferable to provide it before the step that monitors the TOC or urea concentration in the treated water. Here, hydrogen peroxide or the like can be used as the reducing agent.

[0073] Hereinafter, an example of a urea treatment apparatus for implementing the urea treatment method of the present invention will be described using the accompanying drawings. Furthermore, although in Figure 1 The invention describes a urea treatment apparatus in which the urea treatment method of the present invention is implemented in a series of systems, but is not limited thereto. The urea treatment method of the present invention can also be implemented in multiple series of urea treatment apparatuses (systems).

[0074] Figure 1The treatment apparatus 10 shown has two reaction tanks arranged in series. The upstream reaction tank (first reaction tank 20) ​​and the downstream reaction tank (second reaction tank 25) are connected by a second pipe 23. At the inlet of the first reaction tank 20, a first pipe (raw water supply pipe) 22 is connected to supply water to be treated to the first reaction tank 20. A first addition unit 21 for adding bromide salt and chlorine-based oxidant to the water is connected to the first pipe 22. The first addition unit 21 can be configured to add a mixture of bromide salt and chlorine-based oxidant to the water, or it can be configured to add bromide salt and chlorine-based oxidant separately to the water. Examples of bromide salts include sodium bromide (NaBr), and examples of chlorine-based oxidants include sodium hypochlorite (NaClO). The first reaction tank 20 and the second reaction tank 25 are connected by the second pipe 23, which supplies the treated water from the first reaction tank to the second reaction tank 25. A second addition unit 24 for adding at least one of a chlorine-based oxidant or an inorganic acid is connected to the second piping 23. A third piping 26 for discharging treated water is connected to the second reaction tank 25.

[0075] The treated water, after bromide salt and chlorine-based oxidant are added by the first addition unit 21, is supplied to the first reaction tank 20 through the first piping 22, where the urea in the treated water is treated. The resulting treated water is discharged from the first reaction tank 20 through the second piping 23.

[0076] In the process of supplying the treated water discharged from the first reaction tank 20 via the second pipe 23 to the second reaction tank 25, at least one of a chlorine-based oxidant or an inorganic acid is added from the second addition unit 24. Within the second reaction tank 25, residual urea in the treated water after treatment by the first reaction tank 20 is treated, and the treated water is discharged from the second reaction tank 25 via the third pipe 26.

[0077] Additionally, a stirring mechanism (not shown) may be installed in each reaction tank as appropriate. The stirring mechanism consists of a mixer, a water pump, or an aeration device, etc.

[0078] In the downstream stage of the second reaction tank 25, a TOC meter or urea meter 28 is installed to monitor the TOC concentration or urea concentration in the treated water. The meter controls the addition unit 21 of the first reaction tank and / or the addition unit 24 of the second reaction tank based on the TOC concentration or urea concentration (see reference). Figure 1 The single-dot dash (in the image) can control the amount of medicine added.

[0079] Furthermore, downstream of the second reaction tank 25, there is a reducing agent addition unit 27 for reducing oxidant components contained in the treated water, such as hydrogen peroxide. Hydrogen peroxide, sodium sulfite, etc., can be used as the reducing agent. Hydrogen peroxide is preferred because it can reduce oxidant components without increasing the ion load on downstream equipment. The reducing agent addition unit 27 can be configured either before or after the TOC meter or urea meter 28, but from the viewpoint of improving the detection accuracy of TOC or urea concentrations and preventing the deterioration of the pretreatment device before TOC or urea concentration detection, it is preferable to configure it before the TOC meter or urea meter.

[0080] The residence time of the water being treated in the second reaction tank 25 (the treatment time in the second treatment step) is preferably shorter than the residence time of the water being treated in the first reaction tank 20 (the treatment time in the first treatment step). The residence time of the water being treated in the reaction tank can be adjusted, for example, by making the capacity of the second reaction tank 25 smaller than the capacity of the first reaction tank 20. In this case, it is preferable to set the ratio of the capacity of the first reaction tank 20 to the capacity of the second reaction tank 25 to be 2:1 to 60:1. Furthermore, the second reaction tank 25 can utilize an existing filter or a raw water tank; either of these can be used as long as the urea decomposition reaction proceeds, and a plug flow can also be employed.

[0081] like Figure 2 As shown in (a) to (c), a dual-layer sand filter (multi-media filter: MMF) can be installed downstream of the first reaction tank 20 to filter out turbid components. Backwashing and rinsing are performed periodically in the MMF33. The backwash water used in the backwashing process and the rinsing water used in the rinsing process can be supplied by high-quality water from the second reaction tank 25 onwards (not shown). The water quality of the water discharged from the MMF33 after the rinsing process (rinsing wastewater) is determined using a water quality meter (not shown), such as... Figure 2 As shown in (a), water of good quality (rinsing wastewater) is returned to the first reaction tank 20 as rinsing return water via return piping (fourth piping) 29, while water of poor quality is discarded via piping not shown. Furthermore, the flow rate of the rinsing return water is obtained by a flow meter not shown. Bromine salts and chlorine-based oxidants, such as sodium bromide (NaBr) and sodium hypochlorite (NaClO), can be added to the rinsing return water flowing in the fourth piping 29. The mixing of the rinsing return water containing the chemicals can be achieved, for example, using a line mixer not shown. The amount of chemicals added (dosage) can be determined by a residual salt meter (not shown) installed on the fourth piping 29. That is, when the treated water supplied from piping 22 to the first reaction tank 20 does not flow into piping 22, the dosage can be controlled solely by the flow rate of the rinsing return water; conversely, when the water flows into piping 22, the dosage can be controlled by the flow rate from piping 22 in addition to the rinsing return water.

[0082] In addition, such as Figure 2 As shown in (a), inorganic acids and / or hypochlorous acids, such as hydrochloric acid (HCl) and / or sodium hypochlorite (NaClO), can be added either at the pre-stage of MMF33 or at both the pre-stage of MMF33 and the pre-stage of the second reaction layer 25.

[0083] In addition, such as Figure 2 As shown in (b), a portion of the piping from the first reaction tank 20 to the MMF33 can be branched off to form a return piping (fifth piping 30) to the first reaction tank 20.

[0084] Considering malfunctions and maintenance, multiple MMF33 units are typically installed downstream of the first reaction tank 20, and there may be instances where an MMF33 unit is not in operation. In this case, a branch pipe from the piping connecting the first reaction tank 20 to the MMF33, which branches off from the piping connecting the first reaction tank 20 to the non-operational MMF33, can be designated as a return pipe (fifth piping 30) to the first reaction tank 20. Chemicals can also be added to this fifth piping. The mixing of the flushing water containing the chemical can be achieved, for example, using a line mixer (not shown). The dosage can be determined by installing a residual salt meter (not shown) in the fifth piping. In other words, the dosage can be controlled in conjunction with the flow rate of flushing return water, etc.

[0085] By setting up such a fifth piping 30, the chemicals can be added even when no flushing water is generated due to the backwashing process performed by MMF33.

[0086] In addition, such as Figure 2 As shown in (b), inorganic acids and / or hypochlorous acids, such as hydrochloric acid (HCl) and / or sodium hypochlorite (NaClO), can be added either at the pre-stage of MMF33 or at both the pre-stage of MMF33 and the pre-stage of the second reaction layer 25.

[0087] Furthermore, such as Figure 2 As shown in (c), the chemical is added to the aforementioned fourth pipe 29 or fifth pipe 30, and then merged with the first pipe 22 that transports the water to be treated, thereby ensuring reliable chemical injection when the water to be treated flows into the first reaction tank 20. Regarding the dosage, a residual salt meter (not shown) can be installed in the fourth pipe 29 or fifth pipe 30 to determine the dosage. In other words, the dosage can be controlled in conjunction with the flow rate of flushing return water, etc.

[0088] In addition, such as Figure 2As shown in (c), inorganic acids and / or hypochlorous acids, such as hydrochloric acid (HCl) and / or sodium hypochlorite (NaClO), can be added either at the pre-stage of MMF33 or at both the pre-stage of MMF33 and the pre-stage of the second reaction layer 25.

[0089] Furthermore, such as Figure 2 As shown in (a) to (c), preferably, an activated carbon tower 34 is provided separately from the reducing agent addition unit for reducing the oxidant components described above, downstream of the second reaction tank 25, as a unit for removing the oxidant components contained in the second treated water. By providing the activated carbon tower 34, deterioration of the downstream RO membrane can be prevented.

[0090] In the case of the MMF33 described above, it is explained that a portion of the flushing drainage is used as a form of return flushing water, but... Figure 2 In (a) to (c), the urea treatment method of the present invention is implemented using a series of systems, thus requiring the timing of the flushing start to coincide with the timing of the raw water supply. In this case, it is preferable to store water in the reaction tank until the flushing is completed (until the injection is completed) without allowing it to flow to subsequent stages. Furthermore, when the urea treatment method of the present invention is implemented using multiple series of systems, flushing water obtained from other series can be used, thus eliminating the need to coincide the timing of the flushing start with the timing of the raw water supply.

[0091] In the processing apparatus of the present invention, the timing of the addition (injection) of reagents into the first reaction tank 20 can also be linked to the opening and closing of an automatic valve (not shown) installed in the raw water supply pipe (first pipe) 22. For example, when raw water flows in (when the raw water inflow pump is turned on), the injection of bromide salt and chlorine oxidant can begin, and when the raw water inflow stops (when the raw water inflow pump is turned off), the injection of bromide salt and chlorine oxidant can be stopped.

[0092] The processing apparatus and processing method of the present invention described above are suitable not only as pretreatment methods and processing apparatus in pure water production systems for producing pure water from raw water such as tap water, groundwater, and industrial water, but also as processing apparatus and systems for removing TOC from wastewater recycled for purposes such as reducing water consumption.

[0093] (Pure water production system)

[0094] The processing apparatus based on the present invention can be used as a pretreatment device for pure water production.

[0095] Figure 5A pure water production system incorporating a urea treatment device based on the present invention is shown. The illustrated pure water production system produces primary pure water from raw water and includes: heat exchangers (HEX) 51 and 52, which are supplied with raw water and are configured in series as two stages; a urea treatment device 10, which is supplied with raw water discharged from the downstream heat exchanger 52 as treated water; a filter 53; an activated carbon (ACF) device 54; an ion exchange device 55; and a reverse osmosis (RO) membrane device 56. For example, the urea treatment device 10 may be... Figure 1 The urea treatment unit 10 is shown. A filter 53, an activated carbon unit 54, and an ion exchange unit 55 are connected to the outlet of the urea treatment unit 10 in this order. The ion exchange unit 55 has a cation exchange resin column (CER), a decarbonation column (DG), and an anion exchange resin column (AER) arranged from its inlet side. Water discharged from the ion exchange unit 55 is supplied to an upstream heat exchanger 51 as a heat source to heat the raw water, and then supplied to a reverse osmosis membrane unit 56. Primary purified water is discharged from the reverse osmosis membrane unit 56. As a result, in Figure 5 In the pure water production system shown, a urea treatment device 10 is provided as a pretreatment device for the pure water production system consisting of filter 53, activated carbon device 54, ion exchange device 55 and reverse osmosis membrane device 56.

[0096] In addition, in such Figure 5 In the pure water production system shown, the filter device 53 connected to the downstream of the urea treatment device 10 can be used as the second reaction layer 25.

[0097] Of course, the composition of the pure water production system installed after the urea treatment unit 10 is not limited to... Figure 5 The structure shown.

[0098] The heat exchangers 51 and 52 will be described. At higher reaction temperatures, the decomposition reaction of urea based on hypobromic acid proceeds more rapidly. Therefore, heat exchangers 51 and 52 are provided to heat the water being treated. Water discharged from the ion exchange unit 55 is supplied to the upstream heat exchanger 51 as a heat source. The water discharged from the ion exchange unit 55 is obtained by passing treated water from the urea treatment unit 10 through the filter 53, the activated carbon unit 54, and the ion exchange unit 55, and is heated upstream of the urea treatment unit 10, thus increasing its temperature. However, this alone is insufficient to raise the temperature of the water supplied to the urea treatment unit 10 to a given temperature. Therefore, a heat medium from a higher-temperature heat source is supplied to the downstream heat exchanger 52, thereby raising the temperature of the raw water supplied to the urea treatment unit 10 as the water being treated to a given temperature.

[0099] exist Figure 5In the pure water production system shown, although the water discharged from the ion exchange unit 55 and supplied to the reverse osmosis membrane unit 56 is used as a heat source to supply the heat exchanger 51, the specific part of the pure water production system downstream of the urea treatment unit 10 from which the water is supplied to the heat exchanger 51 can be determined according to the configuration of the pure water production system. For example, if an activated carbon unit is provided in the pure water production system, and the configuration is such that water flowing downstream of the activated carbon unit is supplied to the heat exchanger 51, the water supplied to the activated carbon unit is in a heated state, thus improving the activity of the biological activated carbon. Conversely, if the configuration is such that water flowing upstream of the activated carbon unit is supplied to the heat exchanger 51, the water temperature at the inlet of the activated carbon unit decreases, thus increasing the adsorption capacity in the activated carbon unit. If a coagulation tank is provided in the pure water production system, the heated water discharged from the urea treatment unit 10 is supplied to the coagulation tank, thereby suppressing poor coagulation caused by low water temperature.

[0100] In a pure water production system that generates pure water from raw water, a temporary storage tank for raw water is typically installed at the inlet to smooth the supply of raw water to the pure water production system. Figure 5 In the pure water production system shown, the reaction tank 20 in the treatment device 10 also functions as a tank for temporary storage of raw water, so there is no need to set up a separate tank for temporary storage of raw water.

[0101] Example

[0102] The present invention will now be described in more detail through examples and comparative examples.

[0103] (Example 1)

[0104] assembled Figure 3 The treatment apparatus 11 shown was prepared by adding urea to tap water from Sagamihara to a concentration of 50 μg / L, and this was used as the water to be treated.

[0105] The water to be treated was adjusted to pH 7 and temperature 20°C, and supplied to the first reaction tank 20 with a capacity of 300L at a flow rate of 75L / hr. Sodium bromide 2mg / L and sodium hypochlorite 2.2mg / L were added to the front of the first reaction tank 31 to carry out urea decomposition for 4 hours. The treated water was then supplied to the second reaction tank 32 with a capacity of 75L. Hydrochloric acid was added to the front of the second reaction tank 32 to adjust the pH to 6, and urea decomposition was carried out for 1 hour.

[0106] 100 ml of water was taken from the outlet of the first reaction tank 31 and hydrogen peroxide was added until the oxidant was completely removed. The urea concentration in the treated water was then analyzed, and the result showed that the urea concentration in the treated water at this point was 3.8 μg / L. Similarly, 100 ml of water was taken from the outlet of the second reaction tank 32 and hydrogen peroxide was added. The result showed that the urea concentration in the treated water at this point was <1 μg / L.

[0107] In addition, the treated water and the concentration of urea in the treated water were quantified by LC-MS analysis.

[0108] (Example 2)

[0109] Sodium hypochlorite was added in place of hydrochloric acid at the pre-stage of the second reaction tank 31, and the same experiments as in Example 1 were performed. Regarding the addition of sodium hypochlorite at the pre-stage of the second reaction tank 32, 4 mg / L of sodium hypochlorite was added to achieve a residual chlorine concentration of 4.4 mg / L in the treated solution. The urea concentration in the treated water discharged from the first reaction tank 31 was 3.8 μg / L. The urea concentration in the treated water discharged from the second reaction tank 32 was 1.4 μg / L.

[0110] (Example 3)

[0111] Hydrochloric acid and sodium hypochlorite were added upstream of the second reaction tank 32, and the same tests as in Example 1 were performed. Regarding the addition of hydrochloric acid and sodium hypochlorite upstream of the second reaction tank 32, after adjusting the pH to 6 by adding hydrochloric acid, 4 mg / L of sodium hypochlorite was added to achieve a residual chlorine concentration of 4.4 mg / L in the treated solution. The urea concentration in the treated water discharged from the first reaction tank 31 was 3.8 μg / L. The urea concentration in the treated water discharged from the second reaction tank 32 was <1 μg / L.

[0112] (Comparative Example 1)

[0113] assembled Figure 4 The treatment apparatus 12 shown is used to prepare water by adding urea to tap water from Sagamihara to a concentration of 50 μg / L, and this water is used as the treated water.

[0114] The water to be treated was adjusted to pH 7 and the water temperature was adjusted to 20°C. It was then supplied to a reaction tank 40 with a capacity of 375L at a flow rate of 75L / h. Sodium bromide 2mg / L and sodium hypochlorite 2.2mg / L were added to the front of the reaction tank 40 to carry out urea decomposition for 5 hours.

[0115] Take 100 ml of water from the outlet of reaction tank 40 and add hydrogen peroxide until the oxidant is gone. Analyze the urea concentration in the treated water. The result is that the urea concentration in the treated water at this time is 2.0 μg / L.

[0116] (Comparative Example 2)

[0117] Four hours after the urea decomposition reaction began, 4 mg / L of sodium hypochlorite was added to the reaction tank 40 to make the residual chlorine concentration 4.4 mg / L. Otherwise, the same test as Comparative Example 1 was performed.

[0118] Five hours after the start of the urea decomposition reaction (one hour after the addition of sodium hypochlorite), 100 ml of water was taken from the outlet of reaction tank 40, and hydrogen peroxide was added until the oxidant was exhausted. The urea concentration in the treated water was then analyzed, and the result was that the urea concentration in the treated water at this time was 2.0 μg / L.

[0119] (Comparative Example 3)

[0120] Except that 2 mg / L of sodium bromide was added instead of hydrochloric acid in the pre-stage of the second reaction tank 30, the same experiment as in Example 1 was performed. The urea concentration in the treated water discharged from the first reaction tank 20 was 3.8 μg / L. The urea concentration in the treated water discharged from the second reaction tank 30 was 3.8 μg / L.

[0121] The results of Examples 1 to 3 and Comparative Examples 1 to 3 above are summarized in Table 1.

[0122] [Table 1]

[0123]

[0124] The results above confirm the following fact: In the process of decomposing urea by adding bromide salts and chlorine-based oxidants, the urea decomposition reaction is carried out in two steps. In the second step, chlorine-based oxidants and / or acids are added to adjust the reaction pH and residual chlorine concentration, thereby enabling stable urea decomposition treatment.

[0125] Although some preferred embodiments of the invention have been shown and described in detail, it should be understood that various changes and modifications can be made without departing from the spirit or scope of the claims.

[0126] (Label Explanation)

[0127] 10. Urea treatment apparatus of the present invention

[0128] 11. Urea treatment apparatus of Examples 1-3 and Comparative Example 3

[0129] 12 Urea treatment devices of Comparative Examples 1 and 2

[0130] 20 First Reaction Tank

[0131] 21 First Added Unit

[0132] 22 First Pipeline

[0133] 23 Second Pipeline

[0134] 24 Second Added Unit

[0135] 25 Second Reaction Tank

[0136] 26 Third Pipe

[0137] 27 Reducing agent addition unit

[0138] 28TOC meter or urea meter

[0139] 29 Fourth Pipe

[0140] 30 Fifth Pipe

[0141] 31 First Reaction Tank

[0142] 32 Second Reaction Tank

[0143] 33MMF

[0144] 34 Activated Carbon Tower

[0145] 40 reaction tanks

[0146] 51, 52 heat exchangers

[0147] 53 filter

[0148] 54 Activated Carbon Device

[0149] 55 Ion Exchange Unit

[0150] 56. Reverse osmosis membrane unit.

Claims

1. A urea treatment device for treating urea in water, the urea treatment device comprising: The first reaction tank treats the urea in the water to be treated; A first addition unit is connected to the first reaction tank or to a first pipe connected to the first reaction tank and supplying the water to be treated to the first reaction tank. The first addition unit adds bromide salt and chlorine-based oxidant to the water to be treated. The second reaction tank treats the urea remaining in the first treated water after it has been treated by the first reaction tank. as well as A second additive unit is connected to the second reaction tank or to a second piping connected to the second reaction tank and supplying the first treated water to the second reaction tank. The second additive unit adds at least one of a chlorine-based oxidant or an inorganic acid to the first treated water. The chlorine-based oxidant is hypochlorite, and the inorganic acid is hydrochloric acid, nitric acid, phosphoric acid, or sulfuric acid.

2. The urea treatment device according to claim 1, wherein, The residence time of the first treated water in the second reaction tank is shorter than the residence time of the treated water in the first reaction tank.

3. The urea treatment device according to claim 1 or 2, wherein, The urea treatment device has the following features: A measuring device, which is installed after the second reaction tank, measures the TOC concentration or urea concentration in the second treated water after it has been treated by the second reaction tank. as well as A unit that controls the amount of material added from the first addition unit and / or the second addition unit based on the TOC concentration or urea concentration in the second treated water.

4. The urea treatment device according to claim 3, wherein, The urea treatment device includes a reducing agent addition unit, which is located after the second reaction tank. The reducing agent reduces the oxidizing agent components contained in the second treated water.

5. A pure water production system, comprising: The urea treatment apparatus according to any one of claims 1 to 4; An ion exchange unit, located downstream of the urea treatment unit, is supplied with water treated by the urea treatment unit; and A reverse osmosis membrane device is installed downstream of the ion exchange device and is supplied with water treated by the ion exchange device.

6. A urea treatment method, comprising the method of treating urea in water to be treated, the urea treatment method comprising: In the first treatment step, bromide salts and chlorine-based oxidants are added to the water to be treated as urea decomposition agents to treat the urea. as well as In the second treatment step, at least one of a chlorine-based oxidant or an inorganic acid is added to the first treated water obtained from the first treatment step as a urea decomposition agent to treat the residual urea in the first treated water. The chlorine-based oxidant is hypochlorite, and the inorganic acid is hydrochloric acid, nitric acid, phosphoric acid, or sulfuric acid.

7. The urea treatment method according to claim 6, wherein, The processing time of the second processing step is shorter than that of the first processing step.

8. The urea treatment method according to claim 6 or 7, wherein, The urea treatment method includes: The measurement process involves measuring the TOC or urea concentration in the second treated water obtained from the second treatment process; and The dosage control step involves controlling the amount of urea decomposing agent added in the first treatment step and / or the second treatment step based on the TOC or urea concentration in the second treated water.

9. The urea treatment method according to claim 8, wherein, The urea treatment method includes a reduction step, which reduces the oxidant components contained in the second treated water.

10. A method for producing pure water, comprising the urea treatment method according to any one of claims 6 to 9 as a pretreatment step.

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