Pure water production method and pure water production device

Abstract

To provide a method of producing pure water by treating oxidatively treated water containing urea oxidatively decomposed by hypohalous acid using biological activated carbon, capable of suppressing an ion load increase in a pure water production process, improving the efficiency of the biological treatment, and reducing the amount of dust coal being generated, and a device of producing pure water.SOLUTION: A method of producing pure water comprises an oxidative treatment step of adding hypohalous acid to water to be treated containing urea to apply an oxidative treatment to urea in an oxidative treatment device 10, and a biological treatment step comprising measuring a residual chlorine concentration in the oxidatively treated water, adding hydrogen peroxide to the oxidatively treated water according to the measured residual chlorine concentration, and biologically treating the water with hydrogen peroxide added thereto, in a biological treatment device 12 using biological activated carbon.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for producing pure water, and more particularly to a method and apparatus for producing pure water that can remove urea. [Background technology]

[0002] Conventionally, pure water such as ultrapure water, from which organic matter, ionic components, fine particles, bacteria, etc. have been highly removed, has been used as washing water in processes such as those for manufacturing semiconductor devices and liquid crystal display devices. In particular, when manufacturing electronic components, including semiconductor devices, a large amount of pure water is used in the cleaning process, and the quality of this water is becoming increasingly important. Pure water used in the cleaning process of electronic component manufacturing is required to have an extremely low total organic carbon (TOC) concentration, which is one of the water quality control items, in order to prevent organic matter contained in the pure water from carbonizing in the subsequent heat treatment process and causing insulation defects, and urea in particular has been attracting attention as an organic matter.

[0003] One inexpensive and efficient method for treating urea involves treating treated water with biological activated carbon after oxidative decomposition using hypobromous acid, which is generated by combining bromide salts such as sodium bromide with an oxidizing agent such as sodium hypochlorite (see Patent Document 1). The method described in Patent Document 1 aims to stably treat urea by combining physicochemical and biological treatments. However, the oxidizing agent remaining after the oxidative decomposition process may flow into the biological activated carbon. While the oxidizing agent is removed by the activated carbon, issues remain regarding the impact of the oxidizing agent on biological treatment performance and the impact of the generation of pulverized coal on downstream treatment. While the above effects can be mitigated by adding a reducing agent prior to biological treatment, depending on the type of reducing agent, there are concerns about increased ion load in the subsequent pure water production process, resulting in increased treatment costs and reduced treatment efficiency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-183275 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a pure water production method and apparatus that can suppress an increase in ion load in the pure water production process, improve the efficiency of biological treatment, and reduce the amount of pulverized coal generated in a method for treating oxidized water obtained by oxidatively decomposing urea with hypohalous acid using biological activated carbon. [Means for solving the problem]

[0006] The present invention includes an oxidation treatment step of adding hypohalous acid to water to be treated that contains urea to perform an oxidation treatment of the urea, a hydrogen peroxide addition step of measuring the residual chlorine concentration of the oxidized water obtained in the oxidation treatment step and adding hydrogen peroxide to the oxidized water in accordance with the measured residual chlorine concentration, and a biological treatment step of biologically treating the hydrogen peroxide-added water to which hydrogen peroxide has been added using biological activated carbon. The hydrogen peroxide addition step includes a first hydrogen peroxide addition step of measuring a first residual chlorine concentration of the oxidized treated water at a position close to the oxidation treatment step and adding hydrogen peroxide to the oxidized treated water in accordance with the measured first residual chlorine concentration, and a second hydrogen peroxide addition step of measuring a second residual chlorine concentration of the oxidized treated water at a position close to the biological treatment step and adding hydrogen peroxide to the oxidized treated water in accordance with the measured second residual chlorine concentration. Yes, this is a method for producing pure water.

[0007] In the above-described method for producing pure water, it is preferable that the biological treatment step uses a plurality of activated carbon towers filled with biological activated carbon carrying microorganisms, and the plurality of activated carbon towers are arranged in parallel.

[0008] In the method for producing pure water, the hypohalous acid is preferably hypobromous acid.

[0010] In the above-described pure water production method, it is preferable to measure the dissolved oxygen concentration of the hydrogen peroxide-added water or the biologically treated water obtained in the biological treatment step, and to add additional hydrogen peroxide to the oxidized treated water according to the measured dissolved oxygen concentration.

[0011] The present invention comprises an oxidation treatment means for adding hypohalous acid to water to be treated that contains urea to perform an oxidation treatment of the urea, a residual chlorine concentration measuring means for measuring the residual chlorine concentration of the oxidized water obtained by the oxidation treatment means, a hydrogen peroxide adding means for adding hydrogen peroxide to the oxidized water in accordance with the residual chlorine concentration measured by the residual chlorine concentration measuring means, and a biological treatment means for performing a biological treatment using biological activated carbon on the hydrogen peroxide-added water to which hydrogen peroxide has been added. The residual chlorine concentration measuring means comprises a first residual chlorine concentration measuring means for measuring a first residual chlorine concentration of the oxidized treated water at a position close to the oxidation treatment means, and a second residual chlorine concentration measuring means for measuring a second residual chlorine concentration of the oxidized treated water at a position close to the biological treatment means, and the hydrogen peroxide adding means comprises a first hydrogen peroxide adding means for adding hydrogen peroxide to the oxidized treated water in accordance with the first residual chlorine concentration measured by the first residual chlorine concentration measuring means, and a second hydrogen peroxide adding means for adding hydrogen peroxide to the oxidized treated water in accordance with the second residual chlorine concentration measured by the second residual chlorine concentration measuring means. It is a pure water production device.

[0012] In the pure water production system, it is preferable that the biological treatment means comprises a plurality of activated carbon towers filled with biological activated carbon carrying microorganisms, and the plurality of activated carbon towers are arranged in parallel.

[0013] In the pure water producing apparatus, the hypohalous acid is preferably hypobromous acid.

[0015] It is preferable that the pure water manufacturing apparatus further includes a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration of the hydrogen peroxide-added water or the biologically treated water obtained by the biological treatment means, and that the hydrogen peroxide-adding means adds additional hydrogen peroxide to the oxidized treated water in accordance with the measured dissolved oxygen concentration. [Effects of the Invention]

[0016] The present invention provides a method and apparatus for producing pure water that uses biological activated carbon to treat oxidized water obtained by oxidatively decomposing urea with hypohalous acid, thereby suppressing the increase in ionic load in the pure water production process, improving the efficiency of biological treatment, and reducing the amount of pulverized coal generated. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic configuration diagram showing an example of a pure water producing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic configuration diagram showing another example of a pure water manufacturing apparatus according to an embodiment of the present invention. [Figure 3]FIG. 2 is a schematic configuration diagram showing another example of a pure water manufacturing apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0019] An example of a pure water production system according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0020] The pure water manufacturing system 1 shown in Figure 1 includes an oxidation treatment device 10 and hypohalous acid addition pipe 42 as oxidation treatment means that adds hypohalous acid to water to be treated that contains urea to perform an oxidation treatment of the urea, a residual chlorine concentration measuring device 24 as residual chlorine concentration measuring means that measures the residual chlorine concentration of the oxidized water obtained by the oxidation treatment device 10, a hydrogen peroxide addition pipe 44 as hydrogen peroxide addition means that adds hydrogen peroxide to the oxidized water in accordance with the residual chlorine concentration measured by the residual chlorine concentration measuring device 24, and a biological treatment device 12 as biological treatment means that performs biological treatment using biological activated carbon on the hydrogen peroxide-added water to which hydrogen peroxide has been added.

[0021] The pure water producing system 1 may include a first ion exchange treatment device 14 as first ion exchange treatment means for performing a first ion exchange treatment on the biologically treated water obtained in the biological treatment device 12, a reverse osmosis membrane treatment device 16 as reverse osmosis membrane treatment means for performing reverse osmosis membrane treatment on the first ion exchange treated water obtained in the first ion exchange treatment device 14 to obtain RO permeate and RO concentrated water, an ultraviolet irradiation treatment device 18 as ultraviolet irradiation treatment means for performing ultraviolet irradiation treatment (ultraviolet oxidation treatment) on the RO permeate obtained in the reverse osmosis membrane treatment device 16, a second ion exchange treatment device 20 as second ion exchange treatment means for performing a second ion exchange treatment on the ultraviolet-irradiated water obtained in the ultraviolet irradiation treatment device 18, and a degassing treatment device 22 for degassing the second ion exchange treated water obtained in the second ion exchange treatment device 20. A filtration device (not shown) may be provided upstream of the biological treatment device 12 as filtration means for filtering the water to be treated.

[0022] In the pure water production system 1 of FIG. 1 , a pipe 26 is connected to the inlet of the oxidation treatment device 10. The outlet of the oxidation treatment device 10 and the inlet of the biological treatment device 12 are connected by a pipe 28. The outlet of the biological treatment device 12 and the inlet of the first ion exchange treatment device 14 are connected by a pipe 30. The outlet of the first ion exchange treatment device 14 and the inlet of the reverse osmosis membrane treatment device 16 are connected by a pipe 32. The RO permeate outlet of the reverse osmosis membrane treatment device 16 and the inlet of the ultraviolet irradiation treatment device 18 are connected by a pipe 34. The outlet of the ultraviolet irradiation treatment device 18 and the inlet of the second ion exchange treatment device 20 are connected by a pipe 36. The outlet of the second ion exchange treatment device 20 and the inlet of the degassing treatment device 22 are connected by a pipe 38. A pipe 40 is connected to the outlet of the degassing treatment device 22. A hypohalous acid addition pipe 42 is connected to the pipe 26. A residual chlorine concentration measuring device 24 is installed in the pipe 28, and a hydrogen peroxide addition pipe 44 is connected downstream of the residual chlorine concentration measuring device 24.

[0023] The operation of the pure water producing method and pure water producing apparatus 1 according to this embodiment will be described.

[0024] The pure water production system 1 (primary system) constitutes an ultrapure water production system together with an upstream pretreatment system and a downstream subsystem (secondary system). The raw water produced in the pretreatment system (hereinafter referred to as "water to be treated") contains organic matter including urea.

[0025] The water to be treated, which contains urea, is pressurized by a pump (not shown) and then sent to the oxidation treatment device 10 through the pipe 26. Here, in the pipe 26, hypohalous acid is added to the water to be treated through the hypohalous acid addition pipe 42 (hypohalous acid addition step). In the oxidation treatment device 10, the water to be treated is subjected to oxidation treatment with the hypohalous acid (oxidation treatment step). Through the oxidation treatment, urea and the like in the water to be treated are oxidized and decomposed.

[0026] The oxidized water obtained in the oxidation treatment device 10 is sent to the biological treatment device 12 through piping 28. Here, in piping 28, the residual chlorine concentration of the oxidized water is measured by the residual chlorine concentration measuring device 24 (residual chlorine concentration measuring step), and hydrogen peroxide is added to the oxidized water through the hydrogen peroxide addition piping 44 in accordance with the measured residual chlorine concentration (hydrogen peroxide addition step). The hydrogen peroxide reduces the hypohalous acid remaining in the oxidized water.

[0027] In the biological treatment device 12, the hydrogen peroxide-added water to which hydrogen peroxide has been added is subjected to biological treatment using biological activated carbon (biological treatment process). By the biological treatment, high molecular weight organic matter and the like are removed from the hydrogen peroxide-added water. The biologically treated water that has undergone the biological treatment is sent to the first ion exchange treatment device 14 through piping 30.

[0028] In the first ion exchange treatment device 14, the biologically treated water is subjected to a first ion exchange treatment (first ion exchange treatment step). The first ion exchange treatment device 14 has, for example, a cation tower (not shown) filled with a cation exchange resin, a decarbonation tower (not shown), and an anion tower (not shown) filled with anion exchange resin, which are arranged in series in this order from upstream to downstream. By the first ion exchange treatment, cationic components are removed from the biologically treated water in the cation tower, carbonates in the decarbonation tower, and anionic components in the anion tower. The first ion exchange treated water that has undergone the first ion exchange treatment is sent to the reverse osmosis membrane treatment device 16 through piping 32.

[0029] In the reverse osmosis membrane treatment device 16, reverse osmosis membrane treatment is performed on the first ion-exchange treated water, and RO permeate water and RO concentrated water are obtained (reverse osmosis membrane treatment step). Ion components and the like are removed from the first ion-exchange treated water by the reverse osmosis membrane treatment. The RO permeate water obtained by the reverse osmosis membrane treatment is sent to the ultraviolet irradiation treatment device 18 through piping 34.

[0030] The RO permeate water is subjected to ultraviolet irradiation treatment in the ultraviolet irradiation treatment device 18 (ultraviolet irradiation treatment step). The ultraviolet irradiation treatment device 18 includes, for example, a stainless steel reaction tank and a tubular ultraviolet lamp installed in the reaction tank. As the ultraviolet lamp, for example, an ultraviolet lamp that generates ultraviolet light containing at least one of the wavelengths of 254 nm and 185 nm, or a low-pressure ultraviolet lamp that generates ultraviolet light having wavelengths of 254 nm, 194 nm, and 185 nm, is used. The ultraviolet irradiation treatment decomposes TOC (total organic carbon) components and the like in the RO permeate water. The ultraviolet-irradiated water obtained by the ultraviolet irradiation treatment is sent to the second ion exchange treatment device 20 through piping 36.

[0031] In the second ion exchange treatment device 20, the ultraviolet irradiated water is subjected to a second ion exchange treatment (second ion exchange treatment step). The second ion exchange treatment device 20 is, for example, a regenerative ion exchange resin tower filled with anion exchange resin and cation exchange resin. The second ion exchange treatment device removes decomposition products (carbon dioxide, organic acids, etc.) of organic matter and the like that are generated in the ultraviolet irradiated water by the ultraviolet irradiation treatment. The second ion exchange treatment water that has undergone the second ion exchange treatment is sent to the degassing treatment device 22 through piping 38.

[0032] In the degassing device 22, the second ion-exchange treated water is degassed (degassing process). The degassing process removes dissolved oxygen and the like from the second ion-exchange treated water. The degassed water is sent to the next process (e.g., a subsystem (secondary system)) through a pipe 40.

[0033] In the pure water production method and pure water production apparatus according to this embodiment, in a method in which oxidized water obtained by oxidatively decomposing urea with hypohalous acid is treated with biological activated carbon, a step of adding hydrogen peroxide to the oxidized water is provided to reduce the hypohalous acid and perform biological treatment, thereby suppressing an increase in ionic load in the pure water production process, making it possible to improve the efficiency of biological treatment and reduce the amount of pulverized coal generated.

[0034] The oxidative decomposition process uses hypohalous acid to treat urea, and the remaining hypohalous acid is then reduced with hydrogen peroxide to prevent the oxidizing agent from remaining. In terms of efficiency, the oxidative decomposition process results in residual halogens being released, and because residual halogens have a higher redox potential than hydrogen peroxide, hydrogen peroxide functions as a reducing agent. While sodium sulfite and sodium bisulfite are examples of reducing agents other than hydrogen peroxide, there are concerns that they could increase the ionic load on downstream treatment processes.

[0035] For example, the reduction reaction between sodium hypochlorite and hydrogen peroxide is shown in the following formula: NaClO+H2O2 →NaCl+H2O+O2

[0036] The remaining hydrogen peroxide is decomposed by the reduction reaction represented by the following formula when it comes into contact with activated carbon in the subsequent biological treatment process. 2H2O2 → 2H2O + O2

[0037] The amount of hydrogen peroxide to be added may be determined depending on the residual chlorine concentration of the hypohalous acid. The residual chlorine can be measured by a residual chlorine concentration measuring device 24.

[0038] Furthermore, by carrying out reduction treatment with hydrogen peroxide, it is possible to suppress corrosion of metals due to residual hypohalous acid.

[0039] In biological treatment, the treatment performance of residual urea is improved by suppressing the inflow of hypohalous acid, an oxidizing agent. Urea is organic nitrogen, and in the biological treatment process, for example, in the case of nitrifying bacteria, it is decomposed into ammonia and carbon dioxide by decomposing enzymes, and the ammonia is further decomposed into nitrite and nitrate. In the case of heterotrophic bacteria, urea is decomposed into ammonia during the process of decomposing organic matter, which is then used to synthesize bacterial cells. The presence of hypohalous acid, an oxidizing agent, in the biological treatment process reduces the activity of the bacterial cells, resulting in a decrease in the treatment performance of the biological treatment.

[0040] Hydrogen peroxide is a hypohalous acid with a lower redox potential than the oxidizing agent remaining after oxidative decomposition treatment. Furthermore, the added hydrogen peroxide is consumed by the oxidizing agent, so it has little effect on activated carbon in the biological treatment process and reduces the amount of pulverized coal generated. Because pulverized coal can cause blockages in downstream treatment processes, such as reverse osmosis membrane treatment, adding hydrogen peroxide can help reduce fouling.

[0041] Biological treatment requires oxygen, and if the oxygen concentration is low after oxidation treatment, the oxygen produced by the reaction between hydrogen peroxide and activated carbon can be used in the biological treatment. By checking the DO (dissolved oxygen) concentration consumed in biological treatment in advance, the threshold DO concentration can be determined. For example, if the DO concentration of the oxidation-treated water is 2 mg / L and the DO concentration after biological treatment is 1 mg / L, 1 mg / L of DO will be consumed in the biological treatment. Therefore, if the DO concentration in the oxidation-treated water is below 1 mg / L, the shortage can be compensated for by adding hydrogen peroxide. A DO meter can be used to monitor the DO concentration. Alternatively, the DO concentration after biological treatment can be monitored and the amount of hydrogen peroxide added can be adjusted to maintain the DO concentration above a specified value.

[0042] [About hypohalous acids] Examples of hypohalous acid include hypobromous acid, hypochlorous acid, and hypoiodous acid, with hypobromous acid being preferred due to its urea removal ability. The hypohalous acid addition means may include, for example, a sodium bromide (NaBr) storage tank (sodium bromide supply means), a sodium hypochlorite (NaClO) storage tank (sodium hypochlorite supply means), a stirring tank for sodium bromide and sodium hypochlorite (sodium bromide and sodium hypochlorite mixing means), and a transfer pump. Because hypobromous acid is difficult to store for long periods of time, it can be produced by mixing sodium bromide and sodium hypochlorite according to the timing of use. For example, the hypobromous acid produced in the stirring tank (mixing means) is pressurized by a transfer pump and added to the water being treated that passes through piping 26 before the oxidation treatment. Alternatively, sodium bromide and sodium hypochlorite may be directly supplied to piping 26 and stirred by the flow of water being treated in piping 26 to produce hypobromous acid.

[0043] [About hydrogen peroxide] The hydrogen peroxide adding means includes, for example, a hydrogen peroxide storage tank and a transfer pump. For example, hydrogen peroxide is pressurized by the transfer pump and added to the oxidation-treated water passing through pipe 28 between the oxidation treatment and biological treatment. A reduction tank (not shown) may be provided after the addition of hydrogen peroxide, or hydrogen peroxide may be supplied directly to pipe 28, and the flow of oxidation-treated water in pipe 28 may agitate the hydrogen peroxide and reduce the oxidant.

[0044] The amount of hydrogen peroxide to be added may be determined according to the concentration of residual chlorine, which is an oxidizing agent. The residual chlorine can be measured by a residual chlorine concentration measuring device 24.

[0045] Since it is possible to supply DO during biological treatment, a DO meter may be installed before or after biological treatment, and the amount of hydrogen peroxide added may be controlled according to the DO concentration in addition to the value from the residual chlorine concentration measuring device 24. A pure water production system with such a configuration is shown in Figure 2.

[0046] 2 further includes a dissolved oxygen concentration measuring device 46 as a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration of hydrogen peroxide-added water or the dissolved oxygen concentration of biologically treated water obtained by biological treatment device 12, in addition to the configuration of pure water manufacturing system 1 shown in Fig. 1. In pure water manufacturing system 3, dissolved oxygen concentration measuring device 46 is installed in pipe 30. Dissolved oxygen concentration measuring device 46 may also be installed in pipe 28 downstream of the connection point of hydrogen peroxide-added pipe 44.

[0047] In the pure water production system 3, the residual chlorine concentration of the oxidized water is measured in the piping 28 by the residual chlorine concentration measuring device 24 (residual chlorine concentration measuring step), and hydrogen peroxide is added to the oxidized water through the hydrogen peroxide addition piping 44 in accordance with the measured residual chlorine concentration (hydrogen peroxide adding step). The hydrogen peroxide reduces the hypohalous acid remaining in the oxidized water. In the piping 30, the dissolved oxygen concentration of the biologically treated water obtained in the biological treatment device 12 is measured by the dissolved oxygen concentration measuring device 46 (dissolved oxygen concentration measuring step), and additional hydrogen peroxide is added to the oxidized water through the hydrogen peroxide addition piping 44 in accordance with the measured dissolved oxygen concentration (additional hydrogen peroxide adding step). In other words, a sufficient amount of hydrogen peroxide required for reduction may be added in accordance with the residual chlorine concentration, and then additional hydrogen peroxide may be added to maintain the DO concentration of the biological treatment device 12 at or above a predetermined value.

[0048] Because metal piping and pumps are installed between the oxidation treatment device 10 and the biological treatment device 12, the effects of corrosion can be minimized by reducing the oxidizing agent with hydrogen peroxide. The hydrogen peroxide can be added to a position close to the oxidation treatment device 10 or to a position close to the biological treatment device 12.

[0049] If hydrogen peroxide is added near the oxidation treatment device 10, the impact on metal piping and pumps can be minimized, but slime may be more likely to occur in the subsequent piping. If hydrogen peroxide is added near the biological treatment device 12, slime generation can be suppressed, but the impact on metal piping and pumps may be greater. The installation location should be selected depending on the degree of these impacts.

[0050] Alternatively, residual chlorine concentration measuring devices 24 can be installed in two locations, one near the oxidation treatment device 10 and the other near the biological treatment device 12, and hydrogen peroxide can be added in two locations after each residual chlorine concentration measuring device, allowing for two-stage injection of hydrogen peroxide, thereby controlling the residual chlorine concentration to a predetermined value. A pure water production system with this configuration is shown in Figure 3.

[0051] The pure water production system 5 shown in Figure 3 includes a first residual chlorine concentration measuring device 48 as a first residual chlorine concentration measuring device that measures a first residual chlorine concentration of the oxidized treated water at a position close to the oxidation treatment device 10, and a second residual chlorine concentration measuring device 50 as a second residual chlorine concentration measuring device that measures a second residual chlorine concentration of the oxidized treated water at a position close to the biological treatment device 12. The pure water production system 5 also includes a first hydrogen peroxide addition pipe 52 as a first hydrogen peroxide addition means that adds hydrogen peroxide to the oxidized treated water in accordance with the first residual chlorine concentration measured by the first residual chlorine concentration measuring device 48, and a second hydrogen peroxide addition pipe 54 as a second hydrogen peroxide addition means that adds hydrogen peroxide to the oxidized treated water in accordance with the second residual chlorine concentration measured by the second residual chlorine concentration measuring device 50. The remaining configuration is the same as that of the pure water production system 1 shown in Figure 1.

[0052] In the pure water production system 5, the oxidized water obtained in the oxidation treatment device 10 is sent to the biological treatment device 12 through piping 28. Here, in piping 28, a first residual chlorine concentration of the oxidized water is measured by a first residual chlorine concentration measuring device 48 at a position close to the oxidation treatment device 10 (first residual chlorine concentration measuring step), hydrogen peroxide is added to the oxidized water through a first hydrogen peroxide addition piping 52 in accordance with the measured first residual chlorine concentration (first hydrogen peroxide addition step), a second residual chlorine concentration of the oxidized water is measured by a second residual chlorine concentration measuring device 50 at a position close to the biological treatment device 12 (second residual chlorine concentration measuring step), and hydrogen peroxide is added to the oxidized water through a second hydrogen peroxide addition piping 54 in accordance with the measured second residual chlorine concentration (second hydrogen peroxide addition step). The hydrogen peroxide reduces the hypohalous acid remaining in the oxidized water.

[0053] For example, hydrogen peroxide is added near the oxidation treatment device 10 so that the residual chlorine concentration is 1 mg / L, and for example, hydrogen peroxide is added near the biological treatment device 12 so that no residual chlorine remains, thereby making it possible to both inhibit corrosion of metal piping and pumps and prevent slime in the piping.

[0054] The above is just one example, and if the distance between the oxidation treatment device 10 and the biological treatment device 12 is long, the set points and set values ​​can be changed arbitrarily to accommodate this.

[0055] [Biological treatment equipment] The biological treatment device 12 will be described in more detail. The biological treatment device 12 has, for example, a biological activated carbon tower, which is filled with carriers supporting microorganisms. The microorganisms may flow through the biological activated carbon tower, but to prevent the outflow of microorganisms, it is preferable that they are supported on a bioretention carrier, and it is particularly preferable to use a fixed bed type which has a large carrier capacity. Types of carriers include plastic carriers, sponge-like carriers, gel-like carriers, zeolite, ion exchange resins, activated carbon, etc., but activated carbon is used because it is inexpensive, has a large specific surface area, and has a large retention capacity. The oxidized water is passed through the biological activated carbon tower in a downward flow which reduces the outflow of microorganisms, but the oxidized water may also be passed in an upward flow. The water passing rate through the biological activated carbon tower is, for example, 4 to 20 h -1 The temperature of the oxidation treated water is, for example, in the range of 15 to 35°C, and if the temperature of the oxidation treated water is outside this range, a heat exchanger (not shown) may be provided upstream of the biological activated carbon tower.

[0056] The microorganisms are not particularly limited as long as they contain an enzyme with urease activity that decomposes urea, and either autotrophic or heterotrophic bacteria can be used. Because heterotrophic bacteria are preferred for providing organic matter as nutrients, autotrophic bacteria are preferred from the perspective of their impact on water quality, etc. Preferred examples of autotrophic bacteria include nitrifying bacteria. Urea, which is organic nitrogen, is decomposed into ammonia and carbon dioxide by the decomposition enzyme (urease) of nitrifying bacteria, and the ammonia is further decomposed into nitrite and nitrate. When heterotrophic bacteria are used, urea is decomposed into ammonia by the decomposition enzyme (urease) of nitrifying bacteria, just like nitrifying bacteria, and the generated ammonia is used for bacterial cell synthesis during the process of decomposing the organic matter. Commercially available microorganisms may be used, but microorganisms contained in sludge (seed sludge) from sewage treatment plants, for example, may also be used.

[0057] In the case of a fixed-bed system, the proliferation of microorganisms in or between the carriers can clog the flow path, reducing the contact efficiency between the microorganisms and the oxidized water and potentially reducing treatment performance. Backwashing is preferably performed to prevent such clogging. The backwash water can be the raw water supplied to the water purification system or the treated water (pure water) produced by the water purification system. By passing the backwash water in the opposite direction to the flow of the oxidized water, the microorganisms that have proliferated in or between the carriers can be detached by the water flow, preventing clogging. Backwashing is typically performed approximately once or twice a week, but if clogging persists, the frequency can be increased to approximately once a day.

[0058] The number of biological activated carbon towers is not particularly limited. From the viewpoint of ease of maintenance, it is preferable to provide multiple biological activated carbon towers and arrange the multiple biological activated carbon towers in parallel. It is desirable to periodically replace the activated carbon in the biological activated carbon towers, and the microorganisms may be reloaded in conjunction with the activated carbon replacement. It takes, for example, several tens of days for the microorganisms to become activated and enable efficient urea removal. By sequentially replacing the activated carbon and reloading the microorganisms in multiple biological activated carbon towers, the overall urea removal rate of the biological activated carbon towers can be maintained at a predetermined level. In other words, even if the urea removal rate of one biological activated carbon tower is low, the urea removal rates of the other biological activated carbon towers are maintained high, so the urea concentration in the treated water can be kept at a predetermined level. Alternatively, the biological activated carbon tower where the activated carbon replacement and microorganism reloading are performed may be isolated from the pure water production system and connected to the pure water production system when the urea removal rate reaches a predetermined level. Either method enables continuous operation of the pure water production system. [Example]

[0059] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0060] The simulated treated water was prepared by adding reagent urea to pure water to a urea concentration of 100 μg / L and adding trace elements necessary for biological treatment. This simulated treated water was then subjected to oxidation treatment using hypobromous acid, selected as the hypohalous acid. The hypobromous acid was generated by mixing NaBr and NaClO and added.

[0061] The concentration of hypobromous acid was measured by adding glycine to the sample water to convert free chlorine to combined chlorine, and then using a free chlorine reagent and a residual chloride concentration meter (HANNA). This method makes it possible to measure the concentration of hypobromous acid. The free residual chlorine concentration was measured using the DPD method.

[0062] To confirm the urea treatment performance, 6.4 mg / L of hypobromous acid was added to the simulated treated water, and the reaction pH was adjusted to 5.0 using diluted hydrochloric acid. The reaction time was 10 minutes, and after 10 minutes the urea concentration in the treated water was approximately 30 μg / L, and the free residual chlorine concentration was approximately 2 mg / L. The pH of the oxidized treated water was adjusted to 7.5 using NaOH, and the water was passed through a biological treatment device to evaluate the treatment performance.

[0063] The biological treatment tank was a 1.5 L cylindrical column packed with 1.0 L of granular activated carbon (Orbeez QHG, manufactured by Organo) to form a fixed bed. After adding 200 mg / L of nitrification / denitrification sludge and allowing it to soak, the flow of oxidized water downflow was started.

[0064] The water temperature during the test period was 20°C, and the water flow rate was SV5hr. -1 The value was calculated as (water flow rate ÷ activated carbon filling amount).

[0065] Backwashing was performed once every three days for 10 minutes at a time using treated water in an upward flow at a rate of LV25m / h (flow rate divided by the cross-sectional area of ​​the cylindrical column). The urea concentration was measured using an ORUREA (Organo).

[0066] [Water flow conditions] <Comparative Example 1> The oxidized water was passed through without being subjected to reduction treatment.

[0067] <Comparative Example 2> Sodium bisulfite was added to the oxidized water, and reduction treatment was performed before the water was passed through. To achieve the concentration required for reduction, 6 mg / L of sodium bisulfite was injected into the line leading to the biological treatment device, and reduction treatment was performed. It was confirmed in advance that no free residual chlorine concentration was detected, and if detected, the amount of sodium bisulfite injected was increased to adjust the concentration. The addition of sodium bisulfite increases the ionic load of the sodium sulfate in the downstream treatment compared to Comparative Example 1 and Example 1.

[0068] Example 1 Hydrogen peroxide was added to the oxidized water, and reduction treatment was carried out before the water was passed through. To achieve the concentration required for reduction, 2 mg / L of hydrogen peroxide was injected into the line leading to the biological treatment device, and reduction treatment was carried out. It was confirmed beforehand that no residual chlorine concentration was detected, and if it was detected, the amount of hydrogen peroxide injected was increased to adjust the amount. In the case of hydrogen peroxide, oxygen is produced, but there is almost no increase in the ion load.

[0069] [result] After 50 days of water flow under each condition as an acclimation period, water quality analysis was carried out. The results of the water quality analysis are shown in Table 1. These are the average values ​​for 20 days of water flow after acclimation.

[0070] [Table 1]

[0071] In the case of Comparative Example 1, the urea concentration remained at 19 μg / L, but in the cases of Comparative Example 2 and Example 1, the removal performance was improved.

[0072] The SS concentration in the backwash water was as high as 5 mg / L in Comparative Example 1, and was comparable to that in Example 1 and Comparative Example 2, confirming that the generation of pulverized coal could be suppressed.

[0073] Compared to Comparative Example 1, the DO consumption concentration in Comparative Example 2 increased due to the consumption of oxygen by sodium bisulfite, while in Example 1 it decreased due to the oxygen generated from hydrogen peroxide, confirming that the addition of hydrogen peroxide contributes to the supply of oxygen.

[0074] From the above, it was found that the urea treatment performance can be increased by reducing the oxidizing agent, and that the pulverized coal treatment can be suppressed. Furthermore, compared to the addition of sodium bisulfite, the addition of hydrogen peroxide has the advantage of causing almost no ionic load in the subsequent treatment and contributing to oxygen supply, so the addition of hydrogen peroxide is desirable as a reduction treatment after the oxidation treatment.

[0075] In this way, in the method of treating oxidized water obtained by oxidative decomposition of urea with hypohalous acid using biological activated carbon, it has become possible to suppress the increase in ionic load in the pure water production process, improve the efficiency of biological treatment, and reduce the amount of pulverized coal generated. [Explanation of symbols]

[0076] 1, 3, 5 pure water production apparatus, 10 oxidation treatment apparatus, 12 biological treatment apparatus, 14 first ion exchange treatment apparatus, 16 reverse osmosis membrane treatment apparatus, 18 ultraviolet irradiation treatment apparatus, 20 second ion exchange treatment apparatus, 22 degassing treatment apparatus, 24 residual chlorine concentration measuring apparatus, 26, 28, 30, 32, 34, 36, 38, 40 piping, 42 hypohalous acid addition piping, 44 hydrogen peroxide addition piping, 46 dissolved oxygen concentration measuring apparatus, 48 ​​first residual chlorine concentration measuring apparatus, 50 second residual chlorine concentration measuring apparatus, 52 first hydrogen peroxide addition piping, 54 second hydrogen peroxide addition piping.

Claims

1. an oxidation treatment step of adding hypohalous acid to the urea-containing water to be treated to perform an oxidation treatment of the urea; a hydrogen peroxide addition step of measuring the residual chlorine concentration of the oxidized water obtained in the oxidation treatment step and adding hydrogen peroxide to the oxidized water in accordance with the measured residual chlorine concentration; a biological treatment step in which the hydrogen peroxide-added water is biologically treated using biological activated carbon; Including, The hydrogen peroxide addition process is characterized by including: a first hydrogen peroxide addition process for measuring a first residual chlorine concentration of the oxidized treated water at a position close to the oxidation treatment process and adding hydrogen peroxide to the oxidized treated water in accordance with the measured first residual chlorine concentration; and a second hydrogen peroxide addition process for measuring a second residual chlorine concentration of the oxidized treated water at a position close to the biological treatment process and adding hydrogen peroxide to the oxidized treated water in accordance with the measured second residual chlorine concentration.

2. 2. The method for producing pure water according to claim 1, A method for producing pure water, characterized in that the biological treatment step uses a plurality of activated carbon towers filled with biological activated carbon carrying microorganisms, and the plurality of activated carbon towers are arranged in parallel.

3. 3. The method for producing pure water according to claim 1 or 2, 10. A method for producing pure water, wherein the hypohalous acid is hypobromous acid.

4. The method for producing pure water according to any one of claims 1 to 3, A method for producing pure water, characterized by measuring the dissolved oxygen concentration of the hydrogen peroxide-added water or the biologically treated water obtained in the biological treatment step, and adding additional hydrogen peroxide to the oxidized treated water in accordance with the measured dissolved oxygen concentration.

5. an oxidation treatment means for adding hypohalous acid to the water to be treated that contains urea to perform an oxidation treatment of the urea; a residual chlorine concentration measuring means for measuring the residual chlorine concentration of the oxidation-treated water obtained by the oxidation treatment means; a hydrogen peroxide adding means for adding hydrogen peroxide to the oxidized water in accordance with the residual chlorine concentration measured by the residual chlorine concentration measuring means; a biological treatment means for biologically treating the hydrogen peroxide-added water to which hydrogen peroxide has been added using biological activated carbon; Equipped with The residual chlorine concentration measuring means comprises a first residual chlorine concentration measuring means for measuring a first residual chlorine concentration of the oxidation treated water at a position close to the oxidation treatment means, and a second residual chlorine concentration measuring means for measuring a second residual chlorine concentration of the oxidation treated water at a position close to the biological treatment means, The hydrogen peroxide addition means of the pure water manufacturing apparatus is characterized in that it comprises: a first hydrogen peroxide addition means that adds hydrogen peroxide to the oxidized treated water in accordance with the first residual chlorine concentration measured by the first residual chlorine concentration measuring means; and a second hydrogen peroxide addition means that adds hydrogen peroxide to the oxidized treated water in accordance with the second residual chlorine concentration measured by the second residual chlorine concentration measuring means.

6. The pure water producing apparatus according to claim 5, The pure water production apparatus is characterized in that the biological treatment means comprises a plurality of activated carbon towers filled with biological activated carbon carrying microorganisms, and the plurality of activated carbon towers are arranged in parallel.

7. The water purifying apparatus according to claim 5 or 6, 1. A pure water producing apparatus, wherein the hypohalous acid is hypobromous acid.

8. The pure water producing apparatus according to any one of claims 5 to 7, The pure water producing apparatus further comprises a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration of the hydrogen peroxide-added water or the biologically treated water obtained by the biological treatment means, and the hydrogen peroxide adding means adds additional hydrogen peroxide to the oxidized treated water in accordance with the measured dissolved oxygen concentration.

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