JP2014104416A - Water treatment apparatus and water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment apparatus and a water treatment method each capable of stably removing nitrogen components.SOLUTION: The provided apparatus includes: a heterotrophic bacterium denitrification tank 10 including heterotrophic denitrification bacteria 11 for denitrifying nitrous acid by using organic matters; a nitrification tank 20 configured at a step posterior to the heterotrophic bacterium denitrification tank 10 and including nitrification bacteria 21 for generating nitrous acid from ammonia; a denitrification tank 30 configured at a step posterior to the nitrification tank 20 and including autotrophic denitrification bacteria 31 for denitrifying ammonia and nitrous acid; and circulating means (40, 45) for circulating the treated water of the nitrification tank 20 into the heterotrophic bacterium denitrification tank 10.

Description

  The present invention relates to a water treatment apparatus and a water treatment method, and in particular, a water treatment apparatus and water for improving water quality by denitrifying nitrogen-containing raw water containing at least ammonia nitrogen with nitrifying bacteria and autotrophic denitrifying bacteria. It relates to the processing method.

  Wastewater (raw water) from ordinary households and business establishments may contain inorganic nitrogen such as ammonia, ammonium compounds, nitrite compounds, and nitrate compounds, and organic nitrogen such as amino acids and proteins. Nitrogen-containing raw water containing such nitrogen components causes eutrophication of the water environment and a decrease in dissolved oxygen, leading to deterioration of water pollution. Therefore, the amount of discharge to public water bodies is regulated based on wastewater standards. Yes. Therefore, denitrification treatment for nitrogen-containing raw water has been carried out mainly at large-scale business establishments and water treatment facilities.

  In general, as the denitrification treatment of low concentration nitrogen-containing raw water, chemical treatment such as a method of removing nitrate nitrogen using ion exchange or a method of oxidative decomposition using an oxidizing agent such as ozone is used. There are many cases. On the other hand, biological treatment using microorganisms is performed for denitrification treatment of high concentration nitrogen-containing raw water.

  In the conventional biological treatment of nitrogen-containing raw water, since most of the nitrogen components in the raw water exist as ammonia nitrogen, a combination of the nitrification process and the denitrification process is the mainstream. . Nitrosomonas bacteria, Nitrobacter bacteria and other nitrifying bacteria can be used in the nitrification process under the aerobic conditions, through ammonia nitrogen and nitrite nitrogen. The process of conversion to nitrate nitrogen is performed, and the subsequent denitrification process uses the reducing action of denitrifying bacteria such as Pseudomonas bacteria to harm the nitrate nitrogen under anaerobic conditions. The conversion to nitrogen gas is performed.

  However, it is difficult for the water treatment combining the nitrification step and the denitrification step to improve the nitrogen treatment rate, and a large-capacity treatment tank is required for treatment of the high concentration nitrogen-containing raw water. Moreover, since the denitrifying bacteria used in the denitrification step are generally heterotrophic, it is a treatment method that requires a relatively high operating cost, such as requiring supply of a carbon source (for example, methanol).

In recent years, water treatment using anaerobic ammonia oxidation has been promoted as an alternative treatment method that combines such a nitrification step and a denitrification step. Anaerobic ammonia oxidation is a method in which nitrite nitrogen is reduced with ammonia nitrogen and converted into nitrogen gas under anaerobic conditions by the action of a specific microorganism (autotrophic denitrifying bacterium described later). The reaction formula of this conversion is expressed as the following reaction formula (1).
_{^{1.00NH 4 + + 1.32NO 2 - +}} 0.066HCO 3 - + 0.13H +
→ 1.02N ₂ + 0.26NO ₃ ⁻ + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O (1)

  In the treatment by anaerobic ammonia oxidation, as shown in the reaction formula (1), ammonia nitrogen and nitrite nitrogen are simultaneously denitrified using ammonia as an electron donor and nitrous acid as an electron acceptor. For this reason, nitrite nitrogen is required as a substrate, and ammonia nitrogen and nitrite nitrogen are desirably contained in a ratio of 1.00: 1.32 for suitable denitrification. Therefore, a nitrite-type nitrification step for oxidizing a part of ammonia nitrogen in raw water to nitrite nitrogen is combined with the preceding stage of the autotrophic denitrification step using anaerobic ammonia oxidation.

  The water treatment that combines the nitrite type nitrification process and the autotrophic denitrification process can be configured to save space compared to the conventional water treatment that combines the nitrification process and the denitrification process. It is considered that the processing method can reduce the cost.

  As a water treatment method (denitrification method) that combines a nitrite-type nitrification step and an autotrophic denitrification step, Patent Document 1 (Patent No. 3899848) discloses raw water containing an ammonia source and organic matter, and organic matter as an electron. Heterotrophic denitrification process for contact with heterotrophic denitrification microorganisms using donor, nitrite ion and / or nitrate ion as electron acceptor, and ammonia oxidation of effluent of heterotrophic denitrification process Nitritation process that contacts with microorganisms and oxidizes ammonia ion mainly to nitrite ion, and effluent of nitritation process is autotrophic with ammonia ion as electron donor and nitrite ion as electron acceptor An autotrophic denitrification process that removes nitrite ions by contacting with denitrifying microorganisms and a return process that returns a part of the effluent of the autotrophic denitrification process to the heterotrophic denitrification process And Germany Denitrification process with a treated water discharge step of discharging another portion of the effluent as vegetative denitrification as treated water has been disclosed (see claim 1). By having such a configuration, the treated water of the autotrophic denitrification process is circulated to the heterotrophic denitrification process, and nitrate ions (nitrate state) generated by anaerobic ammonia oxidation of the autotrophic denitrification process are circulated. Nitrogen) is treated (denitrified) in a heterotrophic denitrification process.

Japanese Patent No. 3899848

  In the nitrite type nitrification step, ammonia nitrogen is oxidized to nitrite nitrogen, but in a normal nitrification reaction, oxidation is performed from nitrite nitrogen to nitrate nitrogen. In anaerobic ammonia oxidation in the autotrophic denitrification process, as shown in Reaction Formula (1), nitrite nitrogen is used as a substrate and nitrate nitrogen cannot be used. A technology to stop the reaction is required.

  Here, in the water treatment method (denitrification method) of Patent Document 1, the heterotrophic denitrification microorganisms in the heterotrophic denitrification step for treating nitrate ions (nitrate nitrogen) are nitrate ions (nitrate nitrogen). It is thought to have an enzyme that reduces to nitrite ions (nitrite nitrogen).

  However, the enzyme that reduces nitrate ion (nitrate nitrogen) to nitrite ion (nitrite nitrogen) and the enzyme that oxidizes nitrite ion (nitrite nitrogen) to nitrate ion (nitrate nitrogen) are the same. is there. When the heterotrophic denitrifying microorganisms in the heterotrophic denitrification process flow into the treatment tank in the subsequent nitrification process (nitrite nitrification process), nitrite ions (suboxide produced by the ammonia oxidizing microorganisms in the nitritation process) The reaction of heterotrophic denitrifying microorganisms that have flowed in (nitrate nitrogen) to nitrate ions (nitrate nitrogen) is promoted. For this reason, ammonia ions (ammonia nitrogen) are oxidized to nitrate ions (nitrate nitrogen), and the production of nitrite ions (nitrite nitrogen) in the nitritation process (nitrite type nitrification process) becomes unstable, There is a risk of a nitric acid type nitrification process.

  In this way, in the nitric acid type nitrification process, anaerobic ammonia oxidation uses nitrite nitrogen as a substrate and nitrate nitrogen cannot be used, so the denitrification performance of the autotrophic denitrification process becomes unstable, and the water treatment device Overall denitrification performance may be reduced.

  It has also been reported that autotrophic denitrifying bacteria in the autotrophic denitrification process are inactivated due to inhibition by nitrous acid used as a substrate. When the autotrophic denitrifying bacteria are deactivated, the denitrification performance of the autotrophic denitrification process may be reduced, and the denitrification performance of the entire water treatment apparatus may be reduced.

  In addition, these raw waters that are subject to water treatment often contain not only ammonia but also organic matter, and it is required to stably remove ammonia nitrogen and organic components to improve water quality. ing.

  Then, this invention makes it a subject to provide the water treatment apparatus and water treatment method which can remove a nitrogen component stably.

  In order to solve such a problem, the present invention is a subordinate denitrification tank having a heterotrophic denitrification bacterium that denitrifies nitrous acid using organic matter, and is disposed downstream of the subordinate denitrification tank. A nitrification tank having a nitrifying bacterium for producing nitric acid, a denitrification tank having an autotrophic denitrifying bacterium which is disposed downstream of the nitrification tank and denitrifies ammonia and nitrous acid, and treated water from the nitrification tank A water treatment device characterized by comprising a circulation means for circulation to a denitrification tank.

  The present invention also provides a heterotrophic denitrification treatment for denitrifying raw water from heterotrophic denitrification bacteria using organic matter with heterotrophic denitrification bacteria, and treated water treated by the heterotrophic denitrification treatment by nitrifying bacteria. A nitrite-type nitrification treatment for producing nitrite from ammonia, a circulation treatment for circulating a part of the treated water treated in the nitrite-type nitrification treatment to the heterotrophic denitrification treatment, and the nitrite-type nitrification A water treatment method comprising: an autotrophic denitrification treatment in which ammonia and nitrous acid are denitrified by autotrophic denitrifying bacteria in the remainder of the treated water treated in the treatment.

  ADVANTAGE OF THE INVENTION According to this invention, the water treatment apparatus and water treatment method which can remove a nitrogen component stably can be provided.

It is a block diagram of the water treatment device according to the first embodiment. It is a graph which shows an example of the relationship of the nitrogen concentration of the raw water in the water treatment apparatus which concerns on 1st Embodiment, the treated water of a nitrification tank, and the treated water of a denitrification tank. It is a block diagram of the water treatment apparatus according to the second embodiment. It is a block diagram of the configuration of a water treatment device according to a comparative example.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

<< First Embodiment >>
A water treatment apparatus 100 according to the first embodiment will be described with reference to FIG. FIG. 1 is a configuration block diagram of a water treatment apparatus 100 according to the first embodiment.

  The water treatment apparatus 100 according to the first embodiment includes a raw water pump 5 for feeding raw water, a dependent denitrification tank 10 having heterotrophic denitrifying bacteria 11, a nitrification tank 20 having nitrifying bacteria 21, and an autotrophic denitrification. A denitrification tank 30 having nitrifying bacteria 31, a circulation passage 40 for returning treated water from the nitrification tank 20 to the sub-denitrification tank 10, a circulation pump 45 provided in the circulation passage 40, and a control means 50. ing. The water treatment in the dependent denitrification tank 10 is referred to as heterotrophic denitrification treatment, the water treatment in the nitrification tank 20 is referred to as nitrite type nitrification treatment, and the water treatment in the denitrification tank 30 is referred to as autotrophic denitrification treatment.

  The raw water pump 5 can feed raw water to be treated by the water treatment apparatus 100 to the sub-denitrification tank 10. Here, the raw water to be treated by the water treatment apparatus 100 is nitrogen-containing raw water containing at least ammonia nitrogen. The raw water generally contains an organic substance. In addition, although the ammonia nitrogen concentration of raw | natural water is not limited, 10-2000 mg-N / L is preferable and especially 40-1000 mg-N / L is desirable. Further, the amount of organic matter in the raw water is not limited, and the organic matter may not be contained. Incidentally, the raw water may contain nutrient salts such as nitrogen, phosphorus, carbon, and heavy metals in addition to ammonia nitrogen.

  In the sub-denitrification tank 10, the raw water containing ammonia nitrogen and organic substances fed by the raw water pump 5 and the treated water of the nitrification tank 20 fed by the circulation pump 45 through the circulation passage 40 described later, Inflow. In FIG. 1, the raw water and the treated water in the nitrification tank 20 are illustrated as flowing into the dependent denitrification tank 10, but the present invention is not limited to this, and the nitrogen-containing raw water and the nitrification tank 20 The structure which flows into the dependent denitrification tank 10 separately with a treated water may be sufficient.

  The dependent denitrification tank 10 includes a heterotrophic denitrifying bacterium 11 and a stirring means 12 for stirring water in the dependent denitrification tank 10.

  The heterotrophic denitrifying bacterium 11 reacts nitrous acid by reacting nitrous acid contained in raw water or treated water of the nitrification tank 20 as an electron acceptor under anaerobic conditions, using an organic substance in the raw water as an electron donor. The nitrogen concentration of the water in the sub-denitrification tank 10 can be reduced by denitrifying the state nitrogen. The heterotrophic denitrifying bacteria 11 may be present in the activated sludge or may be present in the entrapping immobilization carrier, but is not limited thereto.

  In addition, when there are few organic substances contained in raw | natural water and the electron donor in the denitrification process of the subordinate denitrification tank 10 is insufficient, the organic substance input apparatus (not shown) which inputs an organic substance (for example, methanol) into the subordinate denitrification tank 10 is provided. In addition, the organic matter may be introduced into the sub-denitrification tank 10. Thereby, nitrite nitrogen can be suitably denitrified.

  The treated water treated in the dependent denitrification tank 10 flows out of the dependent denitrification tank 10 and flows into the nitrification tank 20.

  The nitrification tank 20 includes nitrifying bacteria 21, aeration means 22, dissolved oxygen concentration detection means 23, total nitrogen detection means 24, and ammonia nitrogen detection means 25.

Nitrifying bacteria 21 oxidize ammonia nitrogen to nitrite nitrogen under aerobic conditions. This reaction formula is expressed as the following reaction formula (2).
NH ₄ ⁺ + 1.5O ₂ → NO ₂ ⁻ + 2H ⁺ + H ₂ O (2)
The nitrifying bacteria 21 may be present in the activated sludge, may be present in the entrapping immobilization carrier, and is not limited thereto.

  The aeration means 22 can diffuse oxygen-containing gas containing oxygen into the water inside the nitrification tank 20. Moreover, the water in the nitrification tank 20 can be agitated by aeration.

  The dissolved oxygen concentration detection means 23 is a dissolved oxygen meter (DO meter), for example, and can detect the dissolved oxygen concentration of water inside the nitrification tank 20. The total nitrogen detection means 24 is a total nitrogen meter that measures light absorption based on, for example, potassium peroxodisulfide decomposition or catalytic pyrolysis, and can detect the total nitrogen concentration inside the nitrification tank 20. The ammonia nitrogen detection means 25 is, for example, an ion electrode type or absorbance measurement type measuring instrument, and can detect the ammonia nitrogen concentration inside the nitrification tank 20. The dissolved oxygen concentration detecting means 23, the total nitrogen detecting means 24, and the ammonia nitrogen detecting means 25 are desirably provided in the vicinity of the outflow side of the nitrification tank 20.

  The control means 50 can calculate the nitrite nitrogen concentration based on the difference between the total nitrogen concentration detected by the total nitrogen detection means 24 and the ammonia nitrogen concentration detected by the ammonia nitrogen detection means 25. It has become. Then, the control means 50 sets the dissolved oxygen concentration so that the ratio of the ammonia nitrogen concentration and the nitrite nitrogen concentration in the treated water flowing out from the nitrification tank 20 approaches a predetermined ratio (for example, 1.00: 1.32). Set the value. For example, when it is desired to increase the ratio of the nitrite nitrogen concentration to the ammonia nitrogen concentration, the set value is set higher than the current dissolved oxygen concentration. When it is desired to reduce the ratio of the nitrite nitrogen concentration to the ammonia nitrogen concentration, the set value is set lower than the current dissolved oxygen concentration. And the control means 50 controls the amount of aeration of the aeration means 22 so that the dissolved oxygen concentration detected by the dissolved oxygen concentration detection means 23 approaches the set value (DO control). The set value of the dissolved oxygen concentration is preferably about 0.1 to 4.0 mg / L.

In this way, by controlling the dissolved oxygen concentration, the reaction formula (2) can be controlled to control the ratio of the ammonia nitrogen concentration and the nitrite nitrogen concentration in the treated water flowing out from the nitrification tank 20. It is like that. Moreover, the reaction which oxidizes nitrite nitrogen represented by Reaction Formula (3) to nitrate nitrogen can be reduced by appropriately managing the dissolved oxygen concentration.
^{_{NO 2 - + 0.5O 2 → NO}} 3 - ··· (3)

  The treated water treated in the nitrification tank 20 flows out of the nitrification tank 20, a part of the treated water flows into the sub-denitrification tank 10 through the circulation channel 40 by the circulation pump 45, and the remaining treated water is dehydrated. It flows into the nitriding tank 30.

  The circulation pump 45 can feed the treated water from the nitrification tank 20 to the dependent denitrification tank 10 via the circulation flow path 40. In FIG. 1, the treated water in the nitrification tank 20 is shown as flowing into the dependent denitrification tank 10 via the circulation channel 40 after flowing out of the nitrification tank 20, but is not limited thereto. Further, one end of the circulation channel 40 may be connected to the nitrification tank 20, and the circulation pump 45 may be configured to suck in the treated water inside the nitrification tank 20 and send it to the dependent denitrification tank 10.

  The denitrification tank 30 includes an autotrophic denitrification bacterium 31, a stirring means 32 for stirring water in the denitrification tank 30, a dissolved oxygen concentration detection means 33, and a nitrogen detection means 34.

  The autotrophic denitrifying bacterium 31 reacts with ammonia as an electron donor and nitrous acid as an electron acceptor under anaerobic conditions (see the above reaction formula (1)), whereby ammonia nitrogen and nitrous acid are reacted. The nitrogen concentration of water in the denitrification tank 30 can be reduced by simultaneously denitrifying the nitrogen (anaerobic ammonia oxidation). In addition, the autotrophic denitrifying bacteria 31 may be present in activated sludge or may be present in the entrapping immobilization carrier, but is not limited thereto.

  The dissolved oxygen concentration detection means 33 can detect the dissolved oxygen concentration of water inside the denitrification tank 30. The nitrogen detection means 34 can detect the total nitrogen concentration inside the denitrification tank 30. The nitrogen detector 34 may be configured to detect the ammonia nitrogen concentration, the nitrite nitrogen concentration, and the nitrate nitrogen concentration. The dissolved oxygen concentration detection means 33 and the nitrogen detection means 34 are preferably provided in the vicinity of the outflow side of the denitrification tank 30.

  The control means 50 can operate the nitrification tank 20 by controlling the aeration means 22 as described above. Further, the control means 50 can control the operation of the raw water pump 5 and the circulation pump 45. Further, the state of the treated water treated by the water treatment apparatus 100 can be monitored based on the detection values of the dissolved oxygen concentration detecting means 33 and the nitrogen detecting means 34.

  Although not particularly limited, it is preferable to control the pH of each tank to be around 7. Moreover, the water flow method is not limited, For example, a continuous water flow type and a batch type may be sufficient.

<Action and effect>
The operation and effect of the water treatment apparatus 100 according to the first embodiment will be described using the example of FIG. FIG. 2 is a graph showing an example of the relationship between nitrogen concentration of raw water, treated water in the nitrification tank, and treated water in the denitrification tank in the water treatment apparatus 100 according to the first embodiment.

  Raw water having an ammonia concentration of about 700 mg-N / L (see the bar graph on the left side of FIG. 2) was allowed to flow into the sub-denitrification tank 10. Further, circulation from the nitrification tank 20 to the dependent denitrification tank 10 was performed. The circulation amount at this time was the same as the raw water amount. The result is shown in FIG.

  In the sub-denitrification tank 10, most of the nitrous acid derived from the nitrification tank 20 was removed, and a part of ammonia remained (not shown).

  Nitrification was performed in the nitrification tank 20 on the treated water in the sub-denitrification tank 10. As shown in the bar graph in the center of FIG. 2, about half of the nitrous acid was produced. On the other hand, production of nitric acid was not confirmed, and stable nitrite type nitrification performance was confirmed. A part of this treated water was circulated to the sub-denitrification tank 10 as needed, and the remaining part flowed into the denitrification tank 30.

  Anaerobic ammonia oxidation was performed on the treated water in the nitrification tank 20 in the denitrification tank 30. As shown in the bar graph on the right side of FIG. 2, the nitrogen component could be removed. The nitrogen removal rate of raw water and treated water in the denitrification tank 30 was about 85%, and this performance was stably obtained.

  Moreover, the concentration of nitrite nitrogen in the treated water in the nitrification tank 20 shown in the bar graph in FIG. 2, that is, the treated water flowing into the denitrification tank 30 is about 280 mg-N / L, and the autotrophic denitrifying bacteria 31 It was not affected by nitrous acid.

  Thus, according to the water treatment apparatus 100 according to the first embodiment, the treated water is circulated from the nitrification tank 20 to the dependent denitrification tank 10 via the circulation flow path 40, and nitrous acid is removed in the dependent denitrification tank 10. As a result, the concentration of the nitrogen component can be reduced. Moreover, when organic substance is contained in raw | natural water, an organic substance can also be removed with a nitrogen component with the subordinate denitrification tank 10. FIG.

  Here, in the example of FIG. 2, the difference (about 200 mg-N / L) between the total nitrogen concentration of the raw water on the left side of FIG. 2 and the total nitrogen concentration of the nitrification tank in the center of FIG. Corresponds to nitrite nitrogen concentration. Thus, by removing nitrous acid in the dependent denitrification tank 10, the total nitrogen concentration in the treated water flowing into the nitrification tank 20 can be reduced. The ratio of the ammonia nitrogen concentration and the nitrite nitrogen concentration in the treated water flowing out of the nitrification tank 20 is controlled to be a predetermined ratio (for example, 1.00: 1.32). The concentration of nitrite nitrogen in the treated water flowing out from the nitrification tank 20 (that is, the treated water flowing into the denitrification tank 30) is reduced by reducing the concentration of the nitrogen concentration and the nitrite nitrogen concentration). be able to. Thereby, it can reduce that autotrophic denitrification bacteria 31 receive inhibition by nitrous acid, and can be deactivated, and can obtain the stable autotrophic denitrification performance of the denitrification tank 30.

  Incidentally, by increasing the circulation flow rate by the circulation pump 45, the nitrite nitrogen removed in the dependent denitrification tank 10 increases, and the treated water flowing out from the nitrification tank 20 (that is, the treated water flowing into the denitrification tank 30). ) Nitrite nitrogen concentration can be reduced. Thus, the control means 50 controls the flow rate of the circulation pump 45 so that the nitrite nitrogen concentration calculated from the detection values of the total nitrogen detection means 24 and the ammonia nitrogen detection means 25 is within a predetermined range. Also good. The nitrite nitrogen concentration is desirably 50 to 280 mg-N / L. If the nitrite nitrogen concentration is less than 50 mg-N / L, the denitrification performance of the denitrification tank 30 is lowered, which is not desirable. Further, if the nitrite nitrogen concentration is higher than 280 mg-N / L, the autotrophic denitrifying bacteria 31 may be inactivated, which is not desirable.

  Moreover, since the nitrogen component which becomes object when removing nitrogen with the subordinate denitrification tank 10 is not nitric acid (refer patent document 1) but nitrous acid, in the nitrification tank 20, reaction in which nitrous acid is oxidized to nitric acid (Refer to the above-mentioned reaction formula (3)) is less influenced and stable nitrite type nitrification performance of the nitrification tank 20 can be obtained.

  As described above, according to the water treatment apparatus 100 according to the first embodiment, each reaction can be stably operated, the nitrogen component can be maintained at a low concentration, and an efficient denitrification treatment can be performed.

<Comparative example>
Here, the water treatment apparatus 100C according to the comparative example will be described with reference to FIG. FIG. 4 is a configuration block diagram of a water treatment apparatus 100C according to the comparative example. In addition, 100C of water treatment apparatuses which concern on a comparative example are equivalent to patent document 1 (patent 3899848 gazette), and the circulation flow path 40C returns the treated water of the denitrification tank 30 to the dependent denitrification tank 10C. It has become. That is, the water treatment apparatus 100 (see FIG. 1) according to the first embodiment returns the nitrite nitrogen to the dependent denitrification tank 10 by the circulation flow path 40, whereas the water treatment apparatus 100C according to the comparative example (see FIG. 4). ) Is configured to return nitrate nitrogen to the dependent denitrification tank 10C by the circulation channel 40C. For this reason, bacteria having an enzyme that reduces nitrate ions (nitrate nitrogen) to nitrite ions (nitrite nitrogen) exist in the dependent denitrification tank 10C. The bacterium and the heterotrophic denitrifying bacterium may be the same bacterium or different bacteria. In the following description, the heterotrophic denitrifying bacterium 11C will be described as having an enzyme that reduces nitrate ions (nitrate nitrogen) to nitrite ions (nitrite nitrogen).

  In the water treatment apparatus 100C according to the comparative example, when the heterotrophic denitrifying bacterium 11C of the dependent denitrification tank 10C flows into the nitrification tank 20 at the subsequent stage, the nitrite ions (nitrite nitrogen) generated by the nitrifying bacteria 21 are dependent. Since the enzyme of the nutritional denitrifying bacterium 11C is oxidized to nitrate ions (nitrate nitrogen), the production of nitrite ions (nitrite nitrogen) in the nitrification tank 20 may become unstable. Thus, when the production of nitrite ions (nitrite nitrogen) becomes unstable and nitrate ions (nitrate nitrogen) are produced, the denitrification tank 30 denitrifies nitrate ions (nitrate nitrogen). Therefore, the denitrification performance of the entire water treatment device 100C may be reduced.

  In the water treatment apparatus 100C according to the comparative example, it is difficult to reduce the concentration of nitrite nitrogen in the treated water flowing into the denitrification tank 30. For this reason, in order to prevent inactivation of the autotrophic denitrifying bacteria 31 in the denitrification tank 30, a process such as diluting the raw water is necessary, which may increase the operating cost.

<< Second Embodiment >>
A water treatment apparatus 200 according to the second embodiment will be described with reference to FIG. FIG. 3 is a configuration block diagram of a water treatment device 200 according to the second embodiment.

  Compared with the water treatment apparatus 100 (refer FIG. 1) which concerns on 1st Embodiment, the water treatment apparatus 200 which concerns on 2nd Embodiment, the organic substance removal tank 60, the deaeration tank 70, the nitric acid denitrification tank 80, Is further provided. Other configurations are the same as those of the water treatment apparatus 100 (see FIG. 1) according to the first embodiment, and a description thereof will be omitted.

  The organic substance removal tank 60 is, for example, a BOD oxidation tank, and includes a BOD oxidation bacterium 61, an aeration means 62 that diffuses oxygen-containing gas containing oxygen in water inside the organic substance removal tank 60, and a dissolved oxygen concentration detection means. 63. The BOD oxidizing bacteria 61 decomposes organic substances using oxygen. The BOD oxidizing bacteria 61 may be present in the activated sludge or may be present in the entrapping immobilization carrier, but is not limited thereto.

  As shown in FIG. 3, the attachment position of the organic substance removal tank 60 is desirably provided at the subsequent stage of the dependent denitrification tank 10. Since the dependent denitrification tank 10 denitrifies using organic matter as described above, excess organic matter that could not be treated in the dependent denitrification tank 10 can be treated in the organic matter removal tank 60, and the subsequent treatment ( The influence of the nitrification tank 20 and the denitrification tank 30) can be avoided. In addition, the attachment position of the organic matter removal tank 60 is not limited to this. For example, when a large amount of organic matter is contained in the raw water, the organic matter removal tank 60 is provided in the front stage of the sub-denitrification tank 10 to remove the organic matter. The structure which processes an excess part previously may be sufficient.

  The deaeration tank 70 includes a deaeration unit 72 and a dissolved oxygen concentration detection unit 73. The deaeration means 72 can reduce the dissolved oxygen concentration by aeration of oxygen-free oxygen-free gas in the water inside the deaeration tank 70. Moreover, the water in the nitrification tank 20 can be agitated by aeration. The deaeration tank 70 is disposed between the nitrification tank 20 under an aerobic condition and the denitrification tank 30 under an anaerobic condition, and can reduce the dissolved oxygen concentration of the treated water flowing into the denitrification tank 30.

  Here, as shown in FIG. 3, the circulation channel 40 circulates the treated water from a channel branched from the channel flowing into the deaeration tank 70 from the nitrification tank 20 (or directly from the nitrification tank 20). It is desirable to configure as follows. By comprising in this way, the usage-amount of oxygen-free gas can be reduced and an operating cost can be reduced. In addition, the attachment position of the circulation flow path 40 is not restricted to this, It processes from the flow path branched from the flow path which flows in from the deaeration tank 70 to the denitrification tank 30 (or directly from the deaeration tank 70). You may comprise so that water may be circulated. In this case, although the operating cost increases, an increase in the dissolved oxygen concentration in the sub-denitrification tank 10 under anaerobic conditions can be reduced.

  The nitric acid denitrification tank 80 includes denitrifying bacteria 81, stirring means 82, and dissolved oxygen concentration detecting means 83. The nitric acid denitrification tank 80 is disposed downstream of the denitrification tank 30 and denitrifies nitrate nitrogen generated by the treatment by anaerobic ammonia oxidation (see the above reaction formula (1)) to further reduce the nitrogen concentration. be able to. The denitrifying bacteria 81 may be present in the activated sludge, may be present in the entrapping immobilization carrier, and is not limited thereto. Moreover, the nitric acid denitrification tank 80 is not limited to the one that reduces organic matter by biological treatment, and may be configured to perform denitrification treatment by chemical treatment.

≪Modification≫
The water treatment apparatus (100, 200) according to the present embodiment is not limited to the configuration of the above embodiment, and various modifications can be made without departing from the spirit of the invention.

  The nitrogen-containing raw water to be treated by the water treatment apparatus (100, 200) according to the present embodiment is not limited to waste water from a general household or business establishment. For example, the water treatment apparatus for improving the water quality of the eutrophic water source may be used.

The agitation means 12, 32, and 82 are illustrated as being provided on the water side (see FIGS. 1 and 3), but are not limited thereto, and are provided, for example, on the tank bottom or the tank wall. It may be.
Moreover, although the nitrification tank 20 was demonstrated as what stirs an internal water when the aeration means 22 diffuses, it is not restricted to this, You may provide a stirring means (not shown) separately. The same applies to the organic matter removal tank 60 and the deaeration tank 70.

The aeration means 22 and 62 have been described as diffusing oxygen-containing gas into water, but the present invention is not limited to this. For example, a device (not shown) for mechanically stirring the water surface and mixing it with air. It may be.
Although the deaeration means 72 has been described as diffusing oxygen-free gas in water, the present invention is not limited to this. For example, a device for adsorbing oxygen (not shown) or a device for adding a deoxidizing material ( (Not shown).

  The nitrification tank 20 has been described as calculating the nitrite nitrogen concentration based on the difference between the total nitrogen concentration detected by the total nitrogen detector 24 and the ammonia nitrogen concentration detected by the ammonia nitrogen detector 25. However, it is not limited to this. For example, nitrite nitrogen detection means (not shown) may be further provided. In addition, a total nitrogen detection means 24 and a nitrite nitrogen detection means (not shown) are provided, and the total nitrogen concentration detected by the total nitrogen detection means 24 and the sub-phase detected by the nitrite nitrogen detection means (not shown). The ammonia nitrogen concentration may be calculated based on the difference from the nitrate nitrogen concentration.

100,200 Water treatment apparatus 5 Raw water pump 10 Subordinate denitrification tank 11 Heterotrophic denitrification bacteria 20 Nitrification tank 21 Nitrification bacteria 22 Aeration means 23 Dissolved oxygen concentration detection means 24 Total nitrogen detection means (nitrogen concentration detection means)
25 Ammonia nitrogen detection means (nitrogen concentration detection means)
30 Denitrification tank 31 Autotrophic denitrification bacteria 40 Circulation channel (circulation means)
45 Circulation pump (circulation means)
50 Control means 60 Organic substance removal tank 70 Deaeration tank 80 Nitric acid denitrification tank 81 Denitrifying bacteria

Claims (6)

A dependent denitrification tank having heterotrophic denitrifying bacteria for denitrifying nitrite using organic matter;
A nitrification tank that is disposed downstream of the sub-denitrification tank and has nitrifying bacteria that produce nitrous acid from ammonia;
A denitrification tank that is disposed downstream of the nitrification tank and has autotrophic denitrification bacteria that denitrify ammonia and nitrous acid;
Circulating means for circulating the treated water in the nitrification tank to the sub-denitrification tank. The water treatment apparatus according to claim 1, further comprising an organic substance removal tank that is disposed downstream of the sub-denitrification tank and in front of the nitrification tank and removes organic substances. The water treatment apparatus according to claim 1, further comprising a deaeration tank disposed downstream of the dependent nitrification tank and upstream of the denitrification tank and reducing a dissolved oxygen concentration. The water treatment apparatus according to claim 1, further comprising a nitric acid denitrification tank that is disposed downstream of the denitrification tank and denitrifies nitric acid. The circulation means has a circulation flow path for circulating the treated water of the nitrification tank to the sub-denitrification tank, and a circulation pump arranged in the circulation flow path,
Nitrogen concentration detection means for detecting the nitrite nitrogen concentration of the treated water of the nitrification tank;
Control means for controlling the flow rate of the circulation pump,
The control means includes
2. The water treatment apparatus according to claim 1, wherein the flow rate of the circulation pump is increased as the nitrite nitrogen concentration detected by the nitrogen concentration detection unit is higher. A heterotrophic denitrification treatment in which raw water is denitrified by heterotrophic denitrifying bacteria using organic matter and nitrite;
Nitrite-type nitrification treatment for producing nitrite from ammonia by nitrifying bacteria from the treated water treated by the heterotrophic denitrification treatment;
A circulation treatment for circulating a part of the treated water treated by the nitrite type nitrification treatment to the heterotrophic denitrification treatment;
A water treatment method, comprising: an autotrophic denitrification treatment in which ammonia and nitrous acid are denitrified by an autotrophic denitrifying bacterium in the remainder of the treated water treated by the nitrite type nitrification treatment.

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