JP2008012497A - Water treatment apparatus and water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment apparatus and a water treatment method capable of reducing an amount of chlorine used, in a chlorine oxidation treatment of ammonia contained in raw water. <P>SOLUTION: The water treatment apparatus and water treatment method can reduce an amount of chlorine used, by controlling pH of the raw water within a given range, converting ammonia in the raw water to monochloramine by adding a chlorine agent, then decomposing monochloramine by irradiating the chlorine-treated water with ultraviolet ray, in a chlorine oxidation treatment of ammonia contained in raw water. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water treatment apparatus and a water treatment method for treating ammonia contained in raw water in water purification, environmental purification, industrial water treatment, sewage treatment, wastewater treatment, and the like.

  When ammonia is present in drinking raw water or waste water, the treatment method includes oxidation treatment with a chlorinating agent (chlorine oxidation treatment), biological oxidation treatment, stripping treatment, and the like. In addition, a method is known in which an oxidizing agent such as hydrogen peroxide is added to waste water and irradiated with ultraviolet rays to oxidize ammonia to nitric acid (see, for example, Patent Document 1).

Among them, chlorination treatment represented by the following formula using sodium hypochlorite or the like is often used, but in order to completely decompose and decompose ammonia into nitrogen, ammonia and Chlorine having a concentration ratio with chlorine of about 1:10 is necessary.
2NH ₃ + 3NaOCl → N ₂ + 3HCl + 3NaOH

Further, it is known that when ammonia and chlorine are reacted at a concentration ratio of about 1: 5, chloramine (monochloramine: NH ₂ Cl and dichloramine: NHCl ₂ ) is generated.
NH ₃ + NaOCl → NH ₂ Cl + NaOH
NH ₃ + 2NaOCl → NHCl ₂ + 2NaOH

JP-A-7-155773

  As described above, in order to completely oxidize ammonia with chlorine, a large amount of chlorine, which is about 10 times the ammonia concentration, is required, and there is a problem that the chloride ion concentration in the treated water increases. On the other hand, when the amount of chlorine used for the chlorination treatment was reduced, chloramine was produced, and ammonia could not be completely decomposed.

  The present invention is a water treatment apparatus and a water treatment method capable of reducing the amount of chlorine used in the chlorination treatment of ammonia contained in raw water.

  The present invention is a water treatment apparatus for treating ammonia contained in raw water, comprising a reaction tank equipped with pH adjusting means for adjusting the pH of the raw water to a range of 7.5 to 8.6, and a pH within the above range. A chlorine agent adding means for adding a chlorine agent to the adjusted pH-adjusted raw water; and an ultraviolet irradiation means for irradiating the chlorinated water to which the chlorine agent is added with ultraviolet rays.

  Moreover, it is preferable that the water treatment apparatus further includes a return means for returning a part of the ultraviolet treated water irradiated with the ultraviolet rays to the reaction tank.

  The present invention is also a water treatment method for treating ammonia contained in raw water, wherein the pH of the raw water is adjusted to a range of 7.5 to 8.6, and the pH is adjusted to the above range. a chlorine agent addition step of adding a chlorine agent to the pH-adjusted raw water, and an ultraviolet irradiation step of irradiating the chlorinated water to which the chlorine agent is added with ultraviolet rays.

  The water treatment method preferably further includes a returning step of returning a part of the ultraviolet-treated water irradiated with the ultraviolet rays to the chlorinating agent adding step.

  In the present invention, in the chlorination treatment of ammonia contained in the raw water, the pH of the raw water is adjusted to a predetermined range, and after adding a chlorinating agent to make the ammonia in the raw water monochloramine, ultraviolet rays are applied to the chlorinated water. By irradiating and decomposing monochloramine, it is possible to provide a water treatment device and a water treatment method capable of reducing the amount of chlorine used.

  Hereinafter, embodiments of the present invention will be described.

When ammonia in raw water is treated by chlorine oxidation, chloramines (monochloramine: NH ₂ Cl and dichloramine: NHCl ₂ ) are produced when the amount of chlorine used is reduced. Therefore, if the chloramine is decomposed by any method, ammonia can be completely decomposed while reducing the amount of chlorine to be used. It is known that chloramine is decomposed by ultraviolet rays, and the present inventors examined the decomposition of chloramine by ultraviolet rays after chlorination treatment, but the pH during the chlorination reaction, the wavelength of ultraviolet rays, the irradiation efficiency, etc. It was found that chloramine remained.

  Therefore, further examination revealed that when chloramine is produced by reacting chlorine with ammonia, the production ratio of monochloramine and dichloramine differs depending on the pH at the time of reaction, whereas dichloramine is produced slightly at around pH 7.0, It was found that almost all monochloramine was produced in the pH range of 7.5 to 8.6. In addition, it is known that monochloramine is decomposed mainly by irradiating with ultraviolet rays around 250 nm, and dichloramine is irradiated with ultraviolet rays around 220 nm or 290 nm (for example, Otsuki et al. "Summary", September 1990, p.900-901). Therefore, the pH of the raw water containing ammonia is adjusted to the range of 7.5 to 8.6, the amount of added chlorine is reduced and the chlorine oxidation reaction is performed, and the generated monochloramine has a wavelength at which monochloramine is easily decomposed. It was found that ammonia can be almost completely decomposed by reducing the amount of chlorine used by decomposing with.

  An example of the water treatment apparatus according to the embodiment of the present invention is shown in FIG. The water treatment apparatus 1 according to the present embodiment includes a raw water tank 10, a reaction tank 12, a pH adjusting apparatus 14 (pH adjusting agent injection pump 38, pH adjusting agent storage tank 40) and a pH measuring apparatus 16 that are pH adjusting means. A chlorine agent addition device 18 (chlorine agent injection pump 34, chlorine agent storage tank 36) as a chlorine agent addition unit, an ultraviolet irradiation device 20 as an ultraviolet irradiation unit, and a control unit 22 as a pH control unit.

  In the water treatment apparatus 1, one end of a pipe 24 is connected to the upper part of the raw water tank 10, and the other end is connected to a raw water source 28 such as a deep well through a pumping pump 26. One end of the raw water inflow pipe 30 is connected to the lower part of the raw water tank 10 via a raw water pump 32, and the other end is connected to the lower part of the reaction tank 12. A chlorine agent storage tank 36 is connected to the upper part of the reaction tank 12 via a chlorine agent injection pump 34, and a pH adjustment agent storage tank 40 is connected via a pH adjustment agent injection pump 38. The reaction vessel 12 is provided with a stirrer 42 and a pH measuring device 16. The lower part of the reaction tank 12 is connected to the inlet of the ultraviolet irradiation apparatus 20 by a chlorinated water outflow pipe 44, and the outlet of the ultraviolet irradiation apparatus 20 is connected to a processing water tank (not shown) by a treated water outflow pipe 46. A chlorine agent storage tank 36 is connected to the treated water outflow pipe 46 via a chlorine agent injection pump 34. The controller 22 is connected to the pH measuring device 16 and the pH adjusting agent injection pump 38, respectively.

  Next, the operation of the water treatment apparatus 1 and the water treatment method according to this embodiment will be described. Raw water (treated water) such as deep well water is pumped from a raw water source 28 by a pumping pump 26 and sent to the raw water tank 10. Further, the raw water is sent from the raw water tank 10 to the reaction tank 12 by the raw water pump 32.

  Next, the pH adjusting agent is injected from the pH adjusting agent storage tank 40 into the raw water in the reaction tank 12 by the pH adjusting agent injection pump 38 and is stirred by the stirrer 42, while the pH of the raw water is 7.5 to 8.6. The range is adjusted (pH adjustment step). At this time, the pH of the raw water is measured by the pH measuring device 16, and the injection amount by the pH adjusting agent injection pump 38 is controlled by the control unit 22 based on the measured value. Here, the pH adjusting agent is added to the raw water in the reaction tank 12, but it may be injected into the raw water inflow pipe 30 or the like.

  In the method according to the present embodiment, the pH of the raw water is adjusted to a range of 7.5 to 8.6, and a predetermined amount of chlorinating agent is added according to the ammonia nitrogen concentration of the raw water, whereby the ammonia in the raw water is reduced. Monochloramine with chlorine. If the pH is less than 7.5, the production rate of dichloramine increases. Further, if the pH exceeds 8.6, the pH adjustment step is required again later in order to make the pH of the treated water near neutral. Moreover, since the production | generation ratio of a monochloramine becomes high, the said pH has the preferable range of 7.5-8.5, and the range which is 8.0-8.5 is more preferable.

  Examples of the pH adjuster include known alkalis such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide, potassium carbonate, and calcium hydroxide when the raw water is acidic, but sodium hydroxide is preferable. The alkali is preferably added in the form of an aqueous solution in order to make it uniform quickly. Moreover, when raw | natural water is alkaline, well-known acids, such as a sulfuric acid, hydrochloric acid, phosphoric acid, are mentioned, A sulfuric acid is preferable. Moreover, in order to avoid a rapid neutralization reaction, it is preferable to add an alkali or an acid as an aqueous solution of 5% to 30%, preferably 10% to 20%. When the pH of the raw water is in the range of 7.5 to 8.6, it is not necessary to add a pH adjuster here. When the raw water is deep well water, the pH is usually about 6.5 to 7.0, and therefore an alkaline aqueous solution such as an aqueous sodium hydroxide solution is used as a pH adjuster.

  After the pH adjustment of the raw water, the chlorine agent is injected from the chlorine agent storage tank 36 into the pH-adjusted raw water adjusted in the reaction tank 12 by the chlorine agent injection pump 34 and stirred by the stirrer 42 while the raw water is subjected to chlorination treatment. Performed (chlorine agent addition step). The reaction time for the chlorination treatment may be about 5 to 60 minutes, preferably about 15 to 20 minutes.

  As the chlorinating agent, chlorine gas, sodium hypochlorite, liquefied chlorine, chloramine, chlorine dioxide and the like can be used, but sodium hypochlorite and liquefied chlorine are preferably used, and sodium hypochlorite is used. It is more preferable. The chlorine injection rate in the chlorine agent addition process using sodium hypochlorite or the like may be adjusted so that the residual chlorine concentration is 0.1 mg / L to 1.0 mg / L at the exit of the ultraviolet irradiation device 20. preferable.

  Also in the chlorinating agent addition step, the pH of the chlorinated water is measured by the pH measuring device 16, and the pH adjusting agent injection pump 38 injects the pH adjusting agent by the control unit 22 as necessary based on the measured value. The raw water may be adjusted to have a pH of 7.5 to 8.6, preferably 7.5 to 8.5.

  Next, the chlorinated water subjected to the chlorination treatment is sent to the ultraviolet irradiation device 20, and an ultraviolet irradiation treatment is performed (ultraviolet irradiation process). In the ultraviolet irradiation step, the chlorinated water is irradiated with ultraviolet rays, and chloramine and the like generated by the chlorination treatment are decomposed.

  The wavelength of the ultraviolet rays to be irradiated is not particularly limited as long as it includes a wavelength at which chloramine, particularly monochloramine is easily decomposed, but as described above, one having a wavelength around 250 nm at which monochloramine is easily decomposed is preferable.

  As the ultraviolet lamp, for example, a mercury lamp, an amalgam lamp, a xenon lamp or the like can be used. Mercury lamps are classified into low pressure, medium pressure, and high pressure depending on the mercury vapor sealing pressure in the lamp, and the wavelength distribution of ultraviolet rays is different. As the ultraviolet lamp used for ultraviolet irradiation in the present embodiment, a low-pressure mercury lamp whose main emission wavelength is around 250 nm is preferable. The low-pressure mercury lamp has features such as low lamp power consumption and long lamp life.

Dose of ultraviolet rays irradiated by the ultraviolet irradiation device 20, as long as it can decompose chloramine is not particularly ^limited, is preferably in the range of ^{10mJ / cm 2 ~200mJ / cm 2} , 50mJ / cm 2 More preferably, it is in the range of ˜100 mJ / cm ² .

  The treated water (ultraviolet treated water) that has been subjected to the ultraviolet irradiation treatment is discharged to the treated water tank or the like through the treated water outflow pipe 46. In addition, a chlorine agent may be added from the chlorine agent storage tank 36 by the chlorine agent injection pump 34 connected to the treated water outflow pipe 46 as needed before discharge to the treated water tank or the like. Thereby, when undecomposed ammonia remains in treated water, ammonia can be decomposed reliably.

  As described above, with the water treatment apparatus and the water treatment method according to the present embodiment, the amount of chlorine to be used is reduced and ammonia is almost completely decomposed (the concentration of ammonia nitrogen in the treated water is, for example, 0. 05 mg / L or less).

  An example of the water treatment apparatus according to another embodiment of the present invention is shown in FIG. The water treatment apparatus 3 according to the present embodiment includes a return pipe 48 and a return pump 50 that are return means in addition to the configuration of the water treatment apparatus 1.

  In the water treatment device 3, one end of a return pipe 48 is connected to the treated water outflow pipe 46, and the other end is connected to the upper part of the reaction layer 12 via a return pump 50.

  In the water treatment device 3, a part of the treated water subjected to the ultraviolet irradiation treatment is returned to the reaction tank 12 by the return pump 50 through the return pipe 48 (return process). The return amount may be determined according to the quality of the treated water. As a result, the ammonia remaining in the treated water can be reliably converted into chloramine, and the amount of chlorine used can be further reduced. Further, chloramine can be more reliably decomposed by subjecting undecomposed chloramine remaining in the treated water to ultraviolet treatment again.

  The water treatment apparatus and the water treatment method according to the present embodiment are used for water treatment facilities, sewage treatment facilities, industrial wastewater treatment facilities, industrial water treatment facilities, etc. It can be used for the treatment of water, river water, lake water, coagulation sediment supernatant water, various process intermediate water, various recovered water, various waste water, and the like.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

<Example 1>
Ammonia contained in the groundwater was decomposed at an amount of treated water of 1200 m ³ / day using the apparatus shown in FIG. Deep well water having an ammonia nitrogen concentration of 8.0 mg / L, pH = 6.9, and water temperature of 18.0 ° C. was sent to the raw water tank 10 at 50 m ³ / hr using a pumping pump 26. Further, the raw water pump 32 is sent from the raw water tank 10 to the reaction tank (effective capacity 15 m ³ ) 12, and the liquid in the reaction tank 12 is stirred by the stirrer 42 so that pH = 8.0 ± 0.2. After adding 20% aqueous sodium hydroxide solution to the reaction tank 12, 11% (Cl ₂ equivalent) sodium hypochlorite is adjusted to a chlorine concentration of 40 mg / L (5 times the ammonia nitrogen concentration). Added to. The reaction time in the reaction vessel 12 was 15 minutes. The chlorinated water flowing out from the reaction tank 12 was irradiated with ultraviolet rays (main wavelength: 250 nm) with an ultraviolet irradiation device (12 low-pressure mercury lamps, rated power of 1.4 kW) 20. The amount of ultraviolet irradiation was 50 mJ / cm ² , the amount of treated water in the ultraviolet irradiation device 20 was 60 m ³ / hr, of which 10 m ³ / hr was returned to the reaction vessel 12. In order to completely oxidatively decompose ammonia, additional chlorine was required, and an additional 5.0 mg / L of 11% sodium hypochlorite was added to the treated water outflow pipe 46. According to this example, the total chlorine addition rate required for decomposing ammonia was 45 mg / L. The water quality of the treated water was ammonia nitrogen concentration <0.01 mg / L, pH = 8.2, and residual chlorine concentration was 0.5 mg / L. Table 1 summarizes the results. In addition, the measuring method followed the water supply test method (2001).

<Comparative Example 1>
Ammonia was treated by the conventional chlorination treatment method (without ultraviolet irradiation). Using the same raw water as in Example 1, 11% sodium hypochlorite was added to a chlorine concentration of 85 mg / L (10.6 times the amount of ammonia nitrogen concentration), and the reaction time was 30 minutes. Processed. The water quality of the treated water was ammonia nitrogen concentration 0.5 mg / L, pH = 7.5, and residual chlorine concentration was 0.05 mg / L. Table 1 summarizes the results.

<Comparative example 2>
Further, as Comparative Example 2, 11% sodium hypochlorite was added at a chlorine concentration of 40 mg / L (5% with respect to the ammonia nitrogen concentration) without adjusting pH with an aqueous sodium hydroxide solution in the reaction tank 12 of Example 1. The reaction water was treated for 15 minutes, and the treated water was irradiated with ultraviolet rays under the same conditions as in Example 1. As additional chlorine for complete oxidative decomposition of ammonia, an additional 24 mg / L of chlorine was required, and the total chlorine addition rate required for decomposing ammonia was 64 mg / L. The water quality of the treated water was ammonia nitrogen concentration <0.01 mg / L, pH = 7.4, and residual chlorine concentration was 0.7 mg / L. Table 1 summarizes the results.

  When ammonia was decomposed by the method of Example 1, (45 [mg / L] / 85 [mg / L]) × 100 = 53% compared to the conventional chlorine oxidation method of Comparative Example 1, It was possible to treat with a chlorine addition amount of 53%. Further, even in the case of the treatment method using the chlorinating agent treatment and the ultraviolet irradiation treatment, compared with the case of performing the reaction with sodium hypochlorite without adjusting the pH as in Comparative Example 2, (45 mg / L] / 64 [mg / L]) × 100 = 70%, and treatment was possible with a chlorine addition amount of 70% when pH was not adjusted.

  Thus, when ammonia was oxidized as in Example 1, the amount of chlorine added could be reduced to about ½ of the conventional chlorine oxidation method. Since the amount of chlorine added can be greatly reduced compared to conventional methods, water quality items such as chloride ion concentration (reference value 200 mg / L or less), evaporation residue (reference value 500 mg / L or less), etc. for drinking water use. Also improved.

It is a figure which shows schematic structure of an example of the water treatment apparatus which concerns on embodiment of this invention. It is a figure which shows schematic structure of the other example of the water treatment apparatus which concerns on embodiment of this invention.

Explanation of symbols

1,3 Water treatment device, 10 Raw water tank, 12 Reaction tank, 14 pH adjustment device, 16 pH measurement device, 18 Chlorine agent addition device, 20 Ultraviolet irradiation device, 22 Control unit, 24 Piping, 26 Pumping pump, 28 Raw water source , 30 Raw water inflow pipe, 32 Raw water pump, 34 Chlorine agent injection pump, 36 Chlorine agent storage tank, 38 pH adjustment agent injection pump, 40 pH adjustment agent storage tank, 42 Stirrer, 44 Chlorine treatment water outflow pipe, 46 Treatment water outflow pipe 48 return pipes, 50 return pumps.

Claims (4)

A water treatment apparatus for treating ammonia contained in raw water,
A reaction vessel equipped with pH adjusting means for adjusting the pH of the raw water to a range of 7.5 to 8.6;
A chlorinating agent adding means for adding a chlorinating agent to the pH-adjusted raw water whose pH has been adjusted to the above range;
Ultraviolet irradiation means for irradiating ultraviolet rays to chlorinated water to which the chlorinating agent is added;
A water treatment apparatus comprising: The water treatment device according to claim 1,
The water treatment apparatus further comprising a returning means for returning a part of the ultraviolet treated water irradiated with the ultraviolet rays to the reaction tank. A water treatment method for treating ammonia contained in raw water,
A pH adjustment step of adjusting the pH of the raw water to a range of 7.5 to 8.6,
A chlorinating agent adding step of adding a chlorinating agent to the pH-adjusted raw water adjusted to the above-mentioned range;
An ultraviolet irradiation step of irradiating the chlorinated water to which the chlorinating agent is added with ultraviolet rays;
A water treatment method comprising: The water treatment method according to claim 3,
The water treatment method characterized by further including the return process which returns a part of ultraviolet-treated water irradiated with the said ultraviolet-ray to the said chlorine agent addition process.

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