Urea treatment device and treatment method

Abstract

To provide a urea treatment device and a urea treatment method capable of suppressing elevation of TOC value of treated water to be supplied to a use point.SOLUTION: Disclosed are a urea treatment device for treatment of urea in water to be treated and a urea treatment method using the device. The urea treatment device is assembled with: a first reaction tank to treat urea in water to be treated; a first addition means connected to the first reaction tank or a first piping connecting with the first reaction tank to supply the water to be treated to the first reaction tank to add a bromide salt and a chlorine-based oxidant to the water to be treated; a second reaction tank to treat urea remaining in a first treated water having been treated in the first reaction tank; and a second addition means connected to the second reaction tank or a second piping connecting with the second reaction tank to supply the first treated water to the second reaction tank to add at least one of a chlorine-based oxidant or a mineral acid to the first treated water.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a urea treatment device and a treatment method, and more particularly to a urea treatment device and a treatment method for a pure water production process. [Background technology]

[0002] Pure water production systems used to produce pure water from raw water such as tap water, groundwater, or industrial water are composed of, for example, a combination of a reverse osmosis membrane device, an ion exchange device, and an ultraviolet oxidation device. When urea is contained in the raw water, it is a substance that is difficult to remove using any of the reverse osmosis membrane device, the ion exchange device, and the ultraviolet oxidation device. The urea remaining in the produced pure water increases the TOC (total organic carbon) concentration of the pure water. When producing particularly pure water with a high purity for applications such as semiconductor manufacturing, i.e., ultrapure water, a strict upper limit is set for the TOC concentration in the resulting ultrapure water, and therefore a process for removing urea from the raw water is required.

[0003] Patent Document 1 discloses a method in which a chemical that generates hypobromite is added to raw water and supplied to a reaction tank, and urea is decomposed and removed by the hypobromite in the reaction tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-94585 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, the urea decomposition reaction takes time, so it is necessary to ensure a long residence time in the reaction tank. In such a urea treatment method (treatment device), if urea is not completely decomposed in the reaction tank and flows out to the rear of the reaction tank, even if additional chemicals that generate hypobromite are added to the raw water at that point, there will be a time lag before treated water with urea removed is obtained. During that time, there is a problem that treated water with an elevated TOC value will be supplied to the point of use. Therefore, an object of the present invention is to provide a urea treatment device and a urea treatment method that can prevent treated water with an elevated TOC value from being supplied to a point of use. [Means for solving the problem]

[0006] The present invention comprises the following components [1] to

[10] . [1] A urea treatment device for treating urea in water to be treated, a first reaction tank in which urea in the water to be treated is treated; a first adding means connected to the first reaction tank or a first pipe connected to the first reaction tank and supplying the water to be treated to the first reaction tank, for adding a bromide salt and a chlorine-based oxidizing agent to the water to be treated; a second reaction tank in which urea remaining in the first treated water treated in the first reaction tank is treated; a second adding means connected to the second reaction tank or a second pipe connected to the second reaction tank and supplying the first treated water to the second reaction tank, the second adding means adding at least one of a chlorine-based oxidizing agent or a mineral acid to the first treated water; A urea treatment device comprising: [2] The urea treatment device according to [1], wherein a residence time of the first treated water in the second reaction tank is shorter than a residence time of the water to be treated in the first reaction tank. [3] A TOC meter or a urea meter provided downstream of the second reaction tank for monitoring the TOC concentration or the urea concentration in the second treated water treated in the second reaction tank; a means for controlling the amount of addition from the first addition means and / or the second addition means in accordance with the TOC concentration or the urea concentration in the second treated water; The urea treatment device according to [1] or [2] above, [4] The urea treatment device according to any one of [1] to [3], further comprising a reducing agent adding means provided downstream of the second reaction tank for reducing an oxidizing agent component contained in the second treated water. [5] The urea treatment device according to any one of [1] to [4] above, an ion exchange device provided downstream of the urea treatment device and supplied with the water treated by the urea treatment device; a reverse osmosis membrane device provided downstream of the ion exchange device and supplied with water treated by the ion exchange device. [6] A urea treatment method for treating urea in water to be treated, comprising: a first treatment step of treating the urea by adding a bromide salt and a chlorine-based oxidizing agent as urea decomposition agents to the water to be treated; a second treatment step of adding at least one of a chlorine-based oxidizing agent and a mineral acid as a urea decomposing agent to the first treated water obtained in the first treatment step to treat urea remaining in the first treated water; A urea treatment method comprising the steps of: [7] The urea treatment method according to [6], wherein the treatment time of the second treatment step is shorter than the treatment time of the first treatment step. [8] a measuring step of measuring the TOC or urea concentration in the second treated water obtained in the second treatment step; an addition amount control step of controlling the addition amount of a urea decomposition agent in the first treatment step and / or the second treatment step according to the TOC or urea concentration in the second treated water; The urea treatment method according to [6] or [7] above, [9] The urea treatment method according to any one of [6] to [8], further comprising a reduction step of reducing an oxidizing agent component contained in the second treated water.

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

[0007] According to the present invention, it is possible to provide a urea treatment device and a urea treatment method that can prevent treated water with an elevated TOC value from being supplied to a point of use. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating an example of a urea treatment device according to the present invention. [Figure 2] FIG. 2 is a schematic view showing another example of a urea treatment device of the present invention. [Figure 3] 1 is a diagram schematically illustrating embodiments of Examples 1 to 3 and Comparative Example 3. FIG. [Figure 4] 1 is a diagram schematically illustrating embodiments of Comparative Examples 1 and 2. FIG. [Figure 5] FIG. 1 is a diagram illustrating an example of a pure water production system. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present inventors have conducted research to solve the above problems and have come to the following findings. It has been discovered that by installing two urea treatment processes in which hypobromite ions are generated to decompose urea in the water to be treated and obtain treated water, and if urea tends to flow out in the first process, an additional urea decomposing agent (a chlorine-based oxidizing agent or an acid) is further injected in the second process to remove the urea, it is possible to constantly supply treated water from which urea has been removed with an optimal amount of chemical. Hereinafter, the present invention will first be described with respect to a urea treatment method, and then with respect to a urea treatment apparatus that can implement the treatment method.

[0010] The urea treatment method of the present invention relates to a urea treatment method for treating urea in water to be treated, and the urea treatment method includes the following two steps. First treatment step: A step of treating the urea by adding a bromide salt and a chlorine-based oxidizing agent as a urea decomposing agent to the water to be treated. Second treatment step: A step of adding at least one of a chlorine-based oxidizing agent and a mineral acid as a urea decomposition agent to the first treated water obtained in the first treatment step, thereby treating the urea remaining in the first treated water. In the present invention, it is important to perform two treatment steps, and the two treatment steps may or may not be continuous. Furthermore, a step of filtering the treated water, for example, a filtration step using a double-layer sand filter (multimedia filter: MMF) described below, may be included between the two treatment steps, as long as no equipment that consumes hypobromous acid (such as an activated carbon tower) is installed.

[0011] In the first treatment step, a urea decomposing agent (hereinafter simply referred to as "chemical") that generates hypobromous acid is added to the water to be treated in the preliminary stage. Water containing urea can be used as the water to be treated, and raw water for producing pure water, such as industrial water, city water, or well water, can be used as appropriate. The water to be treated contains urea at a concentration of, for example, approximately 2 to 500 μg / L. A bromide salt and a chlorine-based oxidizing agent are added as the chemical that generates hypobromous acid. The bromide salt is preferably water-soluble, such as sodium bromide (NaBr). The chlorine-based oxidizing agent can be, for example, a hypochlorite, particularly sodium hypochlorite (NaClO). When the chemical agent is added to the water to be treated that contains urea, the urea in the water to be treated is selectively oxidized and removed by a ureolysis reaction, and the first treated water is obtained. The urea decomposition reaction is based on the following reaction: NaBr+NaClO→NaBrO+NaCl CO(NH2)2+3NaBrO→3NaBr+N2+2H2O+CO2 The first treatment step can be carried out by adjusting the water to be treated to room temperature (for example, about 20° C.), normal pressure (for example, about 1 atmosphere), and pH of about 7, and reacting for about 0.5 to 24 hours. The amounts of bromide salt and chlorine-based oxidizing agent added are set appropriately depending on the concentration of urea in the treated water and are not particularly limited, but it is preferable to add them so that the concentration of urea in the first treated water is 1 μg / L or less, and typically the amount of bromide salt is about 1 to 5 mg / L and the amount of chlorine-based oxidizing agent is about 1 to 10 mg / L.

[0012] The method of adding the bromide salt and the chlorine-based oxidizing agent is not particularly limited as long as it is in a form that promotes the production of hypobromite ions. For example, a method in which the respective injection pipes are installed in the water supply pipe for the water to be treated and the oxidizing agent is added, or a method in which a mixer such as a line mixer or a mixing reaction tank is used in combination, can be used.

[0013] In the subsequent second treatment step, a chlorine-based oxidizing agent or a mineral acid is added as a chemical to the first treated water obtained in the first treatment step. It is sufficient to add at least one of the chlorine-based oxidizing agent and the mineral acid, and it is also possible to add either one or both. As in the first treatment step, the chlorine-based oxidizing agent may be, for example, a hypochlorite, particularly sodium hypochlorite (NaClO). Examples of acids that may be used include hydrochloric acid (HCl), nitric acid (HNO), phosphoric acid (HPO), and sulfuric acid (HSO).

[0014] When sodium hypochlorite (NaClO) is added to the first treated water as a chlorine-based oxidizing agent, as in the first treatment step, the remaining urea in the first treated water is removed by a reaction similar to that in the first treatment step, and the second treated water is obtained. Furthermore, when HCl is added as a mineral acid to the first treated water, or when a chlorine-based oxidizing agent and a mineral acid are added, the pH of the first treated water changes, and the remaining urea in the first treated water is removed by a reaction similar to that in the first treatment step, and second treated water is obtained.

[0015] The second treated water is obtained by adding a chlorine-based oxidizing agent and / or a mineral acid as a urea decomposition agent to the first treated water. The second treatment step is carried out by adding a chlorine-based oxidizing agent and / or a mineral acid to the first treated water adjusted to room temperature (for example, about 20° C.) and atmospheric pressure (for example, about 1 atmosphere). In the second treatment step, when a chlorine-based oxidizing agent is added to the first treated water, it is added so that the free residual chlorine concentration is preferably 1 to 10 mg / L. Furthermore, in the second treatment step, when adjusting the pH by adding a mineral acid to the first treated water, it is preferable to keep the pH at 4 to 6. If the pH of the water to be treated is less than 4, the hypobromite ions will gasify due to the addition of the chemicals described above. Conversely, if the pH of the water to be treated exceeds 10, the urea treatment capacity will improve, but this will result in an increased salt load, which is not desirable, so the pH is set to the above range. Furthermore, when a chlorine-based oxidizing agent and a mineral acid are used in combination in the second treatment step, it is preferable to add the chlorine-based oxidizing agent and the mineral acid in amounts within the above-mentioned ranges, respectively. That is, it is preferable to add the chlorine-based oxidizing agent so that the free residual chlorine concentration is 1 to 10 mg / L, and add the mineral acid so that the pH is 4 to 6.

[0016] As a method for adding the chlorine-based oxidizing agent and / or acid, similar to the first treatment step, a method in which the respective injection pipes are installed in the water supply pipe for the water to be treated and the chlorine-based oxidizing agent and / or acid are added, or a method in which a mixer such as a line mixer or a mixing reaction tank is used in combination, can be used.

[0017] In the urea treatment method of the present invention, the treatment time of the second treatment step is preferably shorter than the treatment time of the first treatment step. By making the treatment time of the second treatment step shorter than the treatment time of the first treatment step, treated water from which urea has been quickly removed can be supplied. Specifically, it is preferable that the ratio of the treatment time in the first treatment step to the treatment time in the second treatment step is 2:1 to 60:1.

[0018] In the urea treatment method of the present invention, it is preferable to control the amount of chemicals added in the first treatment step and / or the second treatment step by monitoring the TOC or urea concentration in the treated water. a measuring step of measuring the TOC or urea concentration in the second treated water obtained in the second treatment step; and an addition amount control step of controlling the addition amount of the urea decomposition agent in the first treatment step and / or the second treatment step according to the TOC or urea concentration in the second treated water. It is preferred that the compound has the following structure: At least after the second treatment step, a step of measuring and monitoring the TOC concentration or urea concentration in the second treated water is provided. For example, a TOC meter or urea meter (measuring device) is provided after the second treatment step, and changes in the TOC concentration or urea concentration in the treated water are measured and monitored. This allows the amount of chemicals added in the second treatment step, and further the amount of chemicals added in the first treatment step, to be controlled according to the TOC or urea concentration in the second treated water. As mentioned above, the process of monitoring changes in the TOC concentration or urea concentration in the second treated water by installing a TOC meter or urea meter must be installed at least after the second treatment process. However, it is preferable to install it not only after the second treatment process but also after the first treatment process, as this allows for early detection of urea leaks and allows for rapid addition of chemicals in the filter or filtration tank (the equipment that carries out the second treatment process).

[0019] Not only the residual urea in the treated water, but also the chemicals that generate hypobromous acid are a burden on the pure water production system, so the less chemicals added, the better. According to the present embodiment of the invention, the urea concentration in the treated water is quantified to determine the need for urea treatment, and if treatment is necessary, an appropriate amount of chemicals can be added, thereby reducing the burden on the pure water production system while suppressing urea leakage from the reaction tank. Furthermore, the treatment time of the second treatment step can be set short, making it easy to follow the outlet management control. The outlet management control in the second treatment step is, for example, as follows. (1) The increasing trend (change / slope over time) of the TOC concentration or urea concentration is detected, and data on the increasing trend of the TOC concentration or urea concentration is input into a learning algorithm provided in the machine learning device. (2) Based on the input data, the learning algorithm uses machine learning to determine whether or not it is necessary to add a drug to prevent the concentration from exceeding a specified level, and the machine learning device outputs data indicating whether or not it is necessary to add a drug. (3) If it is determined based on machine learning that a drug needs to be added, the amount of drug to be added is calculated, and the machine learning device outputs data indicating the amount of drug to be added in addition to data indicating whether or not a drug needs to be added. As a result, in the second treatment step, the amount of chemical agent added can be controlled before the TOC concentration or urea concentration reaches the control value.

[0020] Furthermore, a reduction treatment step is preferably provided after the second treatment step to reduce the oxidizing agent components remaining in the treated water. The reduction treatment step may be provided either before or after the step of monitoring the TOC or urea concentration in the treated water, but from the viewpoint of the detection accuracy of the TOC or urea concentration, it is preferable to provide it before the step of monitoring the TOC or urea concentration in the treated water. The reducing agent used here may be hydrogen peroxide or the like.

[0021] An example of a urea treatment apparatus for carrying out the urea treatment method of the present invention will be described below with reference to the drawings. Note that, although Fig. 1 and other figures illustrate a urea treatment apparatus in which the urea treatment method of the present invention is carried out in a single-line system, the present invention is not limited thereto, and the urea treatment method of the present invention may be carried out in a urea treatment apparatus (system) with multiple lines. The treatment apparatus 10 shown in FIG. 1 includes 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. A first pipe (raw water supply pipe) 22, which supplies water to be treated to the first reaction tank 20, is connected to the inlet of the first reaction tank 20. The first pipe 22 is connected to a first addition means 21, which adds a bromide salt and a chlorine-based oxidizing agent to the water to be treated. The first addition means 21 may be configured to add a mixture of the bromide salt and the chlorine-based oxidizing agent to the water to be treated, or may be configured to add the bromide salt and the chlorine-based oxidizing agent separately to the water to be treated. Examples of bromide salts include sodium bromide (NaBr), and examples of chlorine-based oxidizing agents include sodium hypochlorite (NaClO). The first reaction tank 20 and the second reaction tank 25 are connected by a second pipe 23, which supplies treated water treated in the first reaction tank to the second reaction tank 25. A second addition means 24 for adding at least one of a chlorine-based oxidizing agent and a mineral acid is connected to the second pipe 23. A third pipe 26 for discharging the treated water is connected to the second reaction tank 25. The treated water to which the bromide salt and the chlorine-based oxidizing agent have been added by the first adding means 21 is supplied to the first reaction tank 20 through the first pipe 22, and the urea in the water to be treated is treated in the first reaction tank 20. The resulting treated water is discharged from the first reaction tank 20 through the second pipe 23. At least one of a chlorine-based oxidizing agent or a mineral acid is added from the second adding means 24 to the treated water discharged from the first reaction tank 20 through the second pipe 23 before being supplied to the second reaction tank 25. In the second reaction tank 25, the urea remaining in the treated water treated in the first reaction tank 20 is treated, and the treated water is discharged from the second reaction tank 25 through the third pipe 26. Each reaction tank may be provided with an agitation mechanism (not shown) as appropriate, which is composed of a stirrer, a submerged pump, an aeration device, or the like.

[0022] A TOC meter or urea meter 28 is provided downstream of the second reaction tank 25 to monitor the TOC concentration or urea concentration in the treated water, and the amount of chemical added can be controlled by controlling the addition means 21 of the first reaction tank and / or the addition means 24 of the second reaction tank (see the dashed dotted line in Figure 1) according to the TOC concentration or urea concentration. Furthermore, downstream of the second reaction tank 25, there is provided a means 27 for adding a reducing agent, such as hydrogen peroxide, that reduces the oxidizing agent components contained in the treated water. Examples of reducing agents that can be used include hydrogen peroxide and sodium sulfite. Hydrogen peroxide is preferred because it can reduce the oxidizing agent components without increasing the ionic load on downstream equipment. The reducing agent adding means 27 may be placed either upstream or downstream of the TOC meter or urea meter 28, but from the perspectives of improving the detection accuracy of the TOC concentration or urea concentration and preventing deterioration of pretreatment equipment prior to detection of the TOC concentration or urea concentration, it is preferable to place it upstream of the TOC meter or urea meter.

[0023] The residence time of the water to be treated in the second reaction tank 25 (treatment time in the second treatment step) is preferably shorter than the residence time of the water to be treated in the first reaction tank 20 (treatment time in the first treatment step). The residence time of the water to be treated in the reaction tanks 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, the ratio of the capacity of the first reaction tank 20 to the capacity of the second reaction tank 25 is preferably 2:1 to 60:1. The second reaction tank 25 may be an existing filter or a raw water tank, or both, and may be a plug flow as long as the urea decomposition reaction proceeds.

[0024] As shown in Figures 2(a) to 2(c), a two-layer sand filter (multimedia filter: MMF) may be installed downstream of the first reaction tank 20 to filter turbid components. Backwashing and rinsing processes are periodically performed in the MMF 33. The backwash water used in the backwashing process and the rinse water used in the rinse process can be supplied from a source (not shown) of good quality water from the second reaction tank 25 onward. The quality of the water (rinse wastewater) discharged from the MMF 33 during the rinse process is determined using a water quality meter (not shown). Relatively good quality water (rinse wastewater) is returned to the first reaction tank 20 via a return pipe (fourth pipe) 29 as rinse return water, as shown in Figure 2(a). Water with poor quality is discarded via a pipe (not shown). The flow rate of the rinse return water is measured using a flow meter (not shown). Chemicals such as bromide salts and chlorine-based oxidizing agents, for example, sodium bromide (NaBr) and sodium hypochlorite (NaClO), can be added to the rinse return water flowing through the fourth pipe 29. In this case, a line mixer (not shown) can be used, for example, to mix the rinse return water containing the chemicals. The amount of chemical to be added (chemical dosage) can be determined by installing a residual salt meter (not shown) in the fourth pipe 29. In other words, when the water to be treated supplied from pipe 22 to the first reaction tank 20 does not flow in from pipe 22, the chemical dosage can be controlled in accordance with the amount of the rinse return water alone. Conversely, when the water flows in from pipe 22, the chemical dosage can be controlled in accordance with the flow rate from pipe 22 in addition to the rinse return water. As shown in FIG. 2(a), chemicals such as mineral acid and / or hypochlorous acid, e.g., hydrochloric acid (HCl) and / or sodium hypochlorite (NaClO), may be added before the MMF, or before both the MMF and the second reaction layer.

[0025] 2(b), a part of the pipe leading from the first reaction vessel 20 to the MMF 33 may be branched to form a return pipe (fifth pipe 30) to the first reaction vessel 20. In consideration of breakdowns, maintenance, and the like, multiple MMFs 33 are typically installed downstream of the first reaction tank 20, and some MMFs 33 may be out of operation. In this case, among the pipes branching off from the pipe feeding from the first reaction tank 20 to the MMFs 33 and connecting to the first reaction tank 20, the pipe branching off from the pipe feeding from the first reaction tank 20 to the out-of-operation MMFs 33 can be used as a return pipe (fifth pipe 30) to the first reaction tank 20. A chemical agent can also be added to this fifth pipe. In this case, the chemical-containing rinse water can be mixed using, for example, a line mixer (not shown). The chemical feed amount can be determined by installing a residual salt meter (not shown) in the fifth pipe. In other words, the chemical feed amount can be controlled according to the amount of water, such as rinse return water. By providing such a fifth pipe 30, even when the backwashing process using the MMF 33 does not generate rinse water, the chemical agent can be added. Also, as shown in FIG. 2(b), chemicals such as mineral acid and / or hypochlorous acid, e.g., hydrochloric acid (HCl) and / or sodium hypochlorite (NaClO), may be added before the MMF 33, or before both the MMF and the second reaction layer.

[0026] Furthermore, as shown in Figure 2(c), by adding a chemical to the fourth pipe 29 or fifth pipe 30 and then merging them with the first pipe 22 that transports the water to be treated, it is possible to reliably administer the chemical when the water to be treated flows into the first reaction tank 20. The amount of chemical to be administered can be determined by installing a residual salt meter (not shown) in the fourth pipe or fifth pipe. In other words, it is possible to control the chemical administration in accordance with the amount of water, such as rinse return water. As shown in FIG. 2(c), chemicals such as mineral acid and / or hypochlorous acid, e.g., hydrochloric acid (HCl) and / or sodium hypochlorite (NaClO), may be added before the MMF 33, or before both the MMF 33 and the second reaction layer 25.

[0027] 2(a) to 2(c), an activated carbon tower 34 is preferably provided downstream of the second reaction tank as a means for removing oxidizing agents contained in the second treated water, in addition to the means for adding a reducing agent that reduces the oxidizing agents. By providing the activated carbon tower 34, deterioration of the downstream RO membrane can be prevented.

[0028] In the above, when the MMF 33 is provided, a portion of the rinse wastewater is used as return rinse water. However, since the urea treatment method according to the present invention is carried out in a single-line system in Figures 2(a) to 2(c), it is necessary to synchronize the timing of the start of rinse with the timing of the supply of raw water. In this case, it is preferable to store water in the reaction tank until the rinse is completed (until the chemical supply is completed) and not to discharge it to the subsequent stage. Note that when the urea treatment method according to the present invention is carried out in a system with multiple lines, rinse water obtained in another line can be used, so it is not necessary to synchronize the timing of the start of rinse with the timing of the supply of raw water.

[0029] In the treatment apparatus of the present invention, the timing of chemical addition (chemical dosing) to the first reaction tank 20 can be linked to the opening and closing of an automatic valve (not shown) provided in the raw water supply pipe (first pipe) 22. For example, the chemical dosing of the bromide salt and chlorine-based oxidizing agent can be started when raw water flows in (when the raw water inflow pump is turned on), and can be stopped when the raw water inflow stops (when the raw water inflow pump is turned off).

[0030] The treatment device and treatment method of the present invention described above are suitable as a pretreatment method and treatment device in a pure water production system used to produce pure water from raw water such as tap water, groundwater, or industrial water. They can also be applied to treatment devices and systems that remove TOC from recycled wastewater, which are used for purposes such as reducing water consumption.

[0031] (Pure water production system) The treatment device according to the present invention can be used as a pretreatment device for producing pure water. FIG. 5 shows a pure water production system incorporating a urea treatment device according to the present invention. The illustrated pure water production system produces primary pure water from raw water and includes two heat exchangers (HEX) 51 and 52 arranged in series to which raw water is supplied, a urea treatment device 10 to which raw water discharged from the downstream heat exchanger 52 is supplied as water to be treated, a filter 53, an activated carbon treatment device (ACF) 54, an ion exchange device 55, and a reverse osmosis membrane device (RO) 56. The urea treatment device 10 shown in FIG. 1 can be used, for example. The filter 53, the activated carbon treatment device 54, and the ion exchange device 55 are connected, in this order, to the outlet of the urea treatment device 10. The ion exchange device 55 is configured with a cation exchange resin tower (CER), a decarbonation tower (DG), and an anion exchange resin tower (AER) arranged from the inlet side. The water discharged from the ion exchange device 55 is supplied to the upstream heat exchanger 51 and used as a heat source to heat the raw water, and then supplied to the reverse osmosis membrane device 56. Primary pure water is discharged from the reverse osmosis membrane device 56. In summary, in the pure water producing system shown in FIG. 5, the urea treatment device 10 is provided as a pretreatment device for the pure water producing system consisting of the filter 53, the activated carbon device 54, the ion exchange device 55, and the reverse osmosis membrane device 56. In the pure water production system shown in FIG. 5, the filtration device 53 connected to the downstream of the urea treatment device 10 can be used as a second reaction tank. Of course, the configuration of the pure water producing system provided downstream of the urea treatment device 10 is not limited to that shown in FIG.

[0032] The heat exchangers 51 and 52 will now be described. The decomposition reaction of urea by hypobromous acid proceeds more quickly when the reaction temperature is increased. Therefore, the heat exchangers 51 and 52 are provided to heat the water to be treated. Water discharged from an ion exchanger 55 is supplied to the upstream heat exchanger 51 as a heat source. The water discharged from the ion exchanger 55 is water obtained by passing treated water from the urea treatment device 10 through a filter 53, an activated carbon device 54, and an ion exchanger 55. The water discharged from the ion exchanger 55 has been heated in the upstream stage of the urea treatment device 10, and thus its temperature is increased. However, this alone is not enough to raise the temperature of the water to be treated supplied to the urea treatment device 10 to a predetermined 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 to be supplied to the urea treatment device 10 to a predetermined temperature.

[0033] In the pure water production system shown in FIG. 5 , water discharged from the ion exchanger 55 before being supplied to the reverse osmosis membrane device 56 is supplied as a heat source to the heat exchanger 51. However, which part of the pure water production system downstream of the urea treatment device 10 the water flows through can be supplied to the heat exchanger 51 as appropriate, depending on the configuration of the pure water production system. For example, if the pure water production system includes an activated carbon device, supplying the water flowing downstream of the activated carbon device to the heat exchanger 51 increases the activity of the biological activated carbon because the water is heated. Conversely, if the pure water production system includes a water flowing upstream of the activated carbon device to the heat exchanger 51, the water temperature at the inlet of the activated carbon device is lowered, allowing for a larger adsorption capacity in the activated carbon device. If a coagulation tank is provided in the pure water production system, supplying the heated water discharged from the urea treatment device 10 to the coagulation tank can suppress poor coagulation due to low water temperature.

[0034] In a pure water production system that produces pure water from raw water, a tank for temporarily storing the raw water is generally placed at the inlet to smooth the amount of raw water supplied to the pure water production system. In the pure water production system shown in Figure 5, the reaction tank 20 in the treatment device 10 also functions as a tank for temporarily storing the raw water, eliminating the need to provide a separate tank for temporarily storing the raw water. [Example]

[0035] The present invention will be described in more detail below with reference to examples and comparative examples.

[0036] Example 1 The treatment device 11 shown in Fig. 3 was assembled. Urea was added to Sagamihara city water to adjust the concentration to 50 µg / L, and this was used as the water to be treated. The water to be treated was adjusted to pH 7 and a water temperature of 20°C and supplied to a first reaction tank 20 having a capacity of 300 L at a flow rate of 75 L / hr. 2 mg / L of sodium bromide and 2.2 mg / L of sodium hypochlorite were added upstream of the first reaction tank 31 to perform urea decomposition for 4 hours. The treated water was supplied to a second reaction tank 32 having a capacity of 75 L, and hydrochloric acid was added upstream of the second reaction tank 32 to adjust the pH to 6, and urea decomposition was performed for 1 hour. 100 ml of the outlet water from the first reaction tank 31 was sampled, and hydrogen peroxide was added until the oxidant was consumed. The urea concentration in the treated water was analyzed, and the urea concentration in the treated water at this time was found to be 3.8 μg / L. Similarly, 100 ml of the outlet water from the second reaction tank 32 was sampled, and hydrogen peroxide was added. The urea concentration in the treated water at this time was found to be <1 μg / L. The urea concentrations in the untreated water and treated water were quantified by LC-MS analysis.

[0037] Example 2 A test similar to that in Example 1 was carried out, except that sodium hypochlorite was added instead of hydrochloric acid upstream of the second reaction tank 31. 4 mg / L of sodium hypochlorite was added upstream of the second reaction tank 32 so that the residual chlorine concentration in the treated solution would be 4.4 mg / L. 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.

[0038] Example 3 A test similar to that in Example 1 was carried out, except that both hydrochloric acid and sodium hypochlorite were added upstream of the second reaction tank 32. The hydrochloric acid and sodium hypochlorite were added upstream of the second reaction tank 32 by adding hydrochloric acid to adjust the pH to 6, and then adding 4 mg / L of sodium hypochlorite so that the residual chlorine concentration in the treated liquid was 4.4 mg / L. 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.

[0039] (Comparative Example 1) The treatment device 12 shown in Fig. 4 was assembled. Urea was added to Sagamihara city water to adjust the concentration to 50 µg / L, and this was used as the water to be treated. The water to be treated was adjusted to pH 7 and water temperature 20°C, and supplied to a reaction tank 40 having a capacity of 375 L at a flow rate of 75 L / h. 2 mg / L of sodium bromide and 2.2 mg / L of sodium hypochlorite were added upstream of the reaction tank 40, and urea decomposition was carried out for 5 hours. 100 ml of the outlet water from the reaction tank 40 was taken, and hydrogen peroxide was added until the oxidant was gone. The urea concentration in the treated water was analyzed, and the urea concentration in the treated water at this time was found to be 2.0 μg / L.

[0040] (Comparative Example 2) A test similar to that of Comparative Example 1 was carried out, except that after 4 hours had elapsed since the urea decomposition reaction, an additional 4 mg / L of sodium hypochlorite was added to the reaction tank 40 so that the residual chlorine concentration became 4.4 mg / L. Five hours after the start of the urea decomposition reaction (one hour after the addition of sodium hypochlorite), 100 ml of the outlet water from the reaction tank 40 was taken, and hydrogen peroxide was added until all the oxidant was gone. The urea concentration in the treated water was analyzed, and the urea concentration in the treated water at this time was found to be 2.0 μg / L.

[0041] (Comparative Example 3) A test similar to that in Example 1 was carried out, except that 2 mg / L of sodium bromide was added instead of hydrochloric acid upstream of the second reaction tank 30. 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. The results of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1.

[0042] [Table 1]

[0043] From the above results, it can be concluded that in the treatment of decomposing urea by adding bromide salt and chlorine-based oxidizing agent, It was confirmed that stable urea decomposition treatment can be achieved by carrying out the urea decomposition reaction in two steps, adding a chlorine-based oxidizing agent and / or acid in the second step and adjusting the reaction pH and residual chlorine concentration. [Explanation of symbols]

[0044] 10. Urea treatment device of the present invention 11 Urea treatment devices of Examples 1 to 3 and Comparative Example 3 12 Urea treatment devices of Comparative Examples 1 and 2 20 First Reactor 21 First adding means 22 First Pipe 23 Second Pipe 24 Second Addition Method 25 Second Reactor 26 Third Pipe 27 Means of adding reducing agent 28 TOC meter or urea meter 29 Fourth Pipe 30 Fifth Pipe 31 First Reactor 32 Second Reactor 33MMF 34 Activated carbon tower 40 Reaction Tank 51, 52 Heat exchanger 53 Filter 54 Activated carbon device 55 Ion exchange device 56 Reverse osmosis membrane equipment

Claims

1. A urea treatment device for treating urea in water to be treated, a first reaction tank in which urea in the water to be treated is treated; a first adding means connected to the first reaction tank or a first pipe connected to the first reaction tank and supplying the water to be treated to the first reaction tank, for adding a bromide salt and a chlorine-based oxidizing agent to the water to be treated; a second reaction tank in which urea remaining in the first treated water treated in the first reaction tank is treated; a second adding means connected to the second reaction tank or a second pipe connected to the second reaction tank and supplying the first treated water to the second reaction tank, the second adding means adding at least one of a chlorine-based oxidizing agent or a mineral acid to the first treated water; A urea treatment device comprising:

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

3. a measuring device provided downstream of the second reaction tank, for measuring a TOC concentration or a urea concentration in the second treated water treated in the second reaction tank; a means for controlling the amount of addition from the first addition means and / or the second addition means in accordance with the TOC concentration or the urea concentration in the second treated water; The urea treatment device according to claim 1 or 2, further comprising:

4. 4. The urea treatment device according to claim 3, further comprising a reducing agent adding means provided downstream of the second reaction tank for reducing an oxidizing agent component contained in the second treated water.

5. The urea treatment device according to any one of claims 1 to 4, an ion exchange device provided downstream of the urea treatment device and supplied with the water treated by the urea treatment device; a reverse osmosis membrane device provided downstream of the ion exchange device and supplied with water treated by the ion exchange device.

6. A urea treatment method for treating urea in water to be treated, comprising: a first treatment step of treating the urea by adding a bromide salt and a chlorine-based oxidizing agent as urea decomposition agents to the water to be treated; a second treatment step of adding at least one of a chlorine-based oxidizing agent and a mineral acid as a urea decomposing agent to the first treated water obtained in the first treatment step to treat urea remaining in the first treated water; A urea treatment method comprising the steps of:

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

8. a measuring step of measuring a TOC or urea concentration in the second treated water obtained in the second treatment step; an addition amount control step of controlling the addition amount of a urea decomposition agent in the first treatment step and / or the second treatment step according to the TOC or urea concentration in the second treated water; The method for treating urea according to claim 6 or 7, comprising:

9. The urea treatment method according to claim 8 , further comprising a reduction step of reducing an oxidizing agent component 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.

Images