Water treatment apparatus and water treatment method

Abstract

To provide a water treatment apparatus and a water treatment method, capable of reducing an aeration gas volume, a use amount of a pH adjustment agent, and a use amount of a hydrogen donor, with regard to a water treatment in which a nitrification treatment, a denitrification treatment and an oxidation treatment are applied to treatment-target water containing ammoniac nitrogen using a carrier carrying a microorganism.SOLUTION: A water treatment apparatus 1 includes: a first nitrification tank 10 configured to apply a first nitrification treatment to treatment-target water containing ammoniac nitrogen by an autotrophic germ; a first denitrification tank 12 configured to apply a first denitrification treatment to first nitrification-treated water under a presence of a hydrogen donor; a second nitrification tank 14 configured to apply a second nitrification treatment to first denitrification-treated water by an autotrophic germ; a second denitrification tank 16 configured to apply a second denitrification treatment to second nitrification-treated water under a presence of a hydrogen donor; and an oxidation tank 18 configured to apply an oxidation treatment to second denitrification-treated water. A carrier carrying a microorganism is packed into each of the first nitrification tank 10, the first denitrification tank 12, the second nitrification tank 14, the second denitrification tank 16 and the oxidation tank 18.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment apparatus and a water treatment method for performing nitrification and denitrification treatments on water to be treated that contains ammonia nitrogen. [Background technology]

[0002] Conventionally, ammonia, nitric acid, etc. have been used in the manufacturing process of semiconductors such as integrated circuits (ICs), etc. For this reason, wastewater containing nitrogen (ammonia, nitric acid, etc.) is discharged as waste liquid from the process.

[0003] The biological nitrogen treatment is generally used to remove nitrogen from wastewater. In this biological nitrogen treatment, for example, the wastewater is first nitrified to convert the ammonia nitrogen in the wastewater into nitrite nitrogen or nitrate nitrogen, and then a hydrogen donor such as methanol is added to the wastewater in an anoxic state to perform a denitrification treatment to remove nitrogen.

[0004] For example, activated sludge method, biofilm method (e.g., fixed bed method or fluidized bed method), granule method, etc. are used for nitrification treatment. In general, activated sludge method is a low-load treatment (e.g., 0.1 to 0.3 kg-N / (m 3 ·day) is used, and in the biofilm method and granular method, high load treatment (for example, 0.5 to 1.0 kg-N / (m 3 For example, see Patent Document 1.

[0005] Furthermore, the carrier method (fixed bed or fluidized bed) uses a microorganism-holding carrier to hold denitrifying bacteria in high concentrations on the carrier, allowing for higher load operation than the flotation method, and since there is no need to return the sludge separated from the solid-liquid in the settling tank, maintenance and management are easier. In particular, the method using a fluidized carrier allows for stable operation, since backwashing is not required. In particular, by optimizing the trace elements added, it is possible to achieve a concentration of, for example, 1.0 kg-N / (m 3High-load treatment is carried out for at least 1.5 hours (days) (see, for example, Patent Document 2). In this specification, unless otherwise specified, the term "denitrifying bacteria" refers to heterotrophic denitrifying bacteria that perform denitrification in the presence of a hydrogen donor.

[0006] On the other hand, biological nitrogen treatment requires high costs for the aeration volume required to supply the oxygen needed for nitrification, pH adjusters such as alkali for pH adjustment, and hydrogen donors needed for denitrification, and there is a demand for further reductions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4865211 [Patent Document 2] Patent No. 6461408 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a water treatment device and a water treatment method that can reduce the aeration air volume, the amount of pH adjuster used, and the amount of hydrogen donor used in water treatment that performs nitrification, denitrification, and oxidation treatments on water to be treated that contains ammonia nitrogen using a carrier that retains microorganisms. [Means for solving the problem]

[0009] The present invention is a water treatment device comprising a first nitrification tank in which a first nitrification treatment is performed by autotrophic bacteria on water to be treated that contains ammonia nitrogen; a first denitrification tank in which a first denitrification treatment is performed in the presence of a hydrogen donor on the first nitrification-treated water that has been subjected to the first nitrification treatment; a second nitrification tank in which a second nitrification treatment is performed by autotrophic bacteria on the first denitrification-treated water that has been subjected to the first denitrification treatment; a second denitrification tank in which a second denitrification treatment is performed in the presence of a hydrogen donor on the second nitrification-treated water that has been subjected to the second nitrification treatment; and an oxidation tank in which an oxidation treatment is performed on the second denitrification-treated water that has been subjected to the second denitrification treatment, wherein each of the first nitrification tank, the first denitrification tank, the second nitrification tank, the second denitrification tank, and the oxidation tank are filled with a carrier for retaining microorganisms.

[0010] It is preferable that the water treatment device further comprises a first nitrate ion concentration measuring means for measuring the nitrate ion concentration in the first denitrification tank, a second nitrate ion concentration measuring means for measuring the nitrate ion concentration in the second nitrification tank, and a control means for controlling the amount of hydrogen donor to be added to the first denitrification tank based on the first nitrate ion concentration obtained by measurement using the first nitrate ion concentration measuring means, and for controlling the amount of hydrogen donor to be added to the second denitrification tank based on the second nitrate ion concentration obtained by measurement using the second nitrate ion concentration measuring means.

[0011] In the water treatment device, it is preferable that the oxidized water that has been subjected to the oxidation treatment is circulated to the first nitrification tank.

[0012] The present invention is a water treatment method comprising: a first nitrification step in which a first nitrification treatment is performed by autotrophic bacteria on water to be treated that contains ammonia nitrogen; a first denitrification step in which a first denitrification treatment is performed in the presence of a hydrogen donor on the first nitrification-treated water that has been subjected to the first nitrification treatment; a second nitrification step in which a second nitrification treatment is performed by autotrophic bacteria on the first denitrification-treated water that has been subjected to the first denitrification treatment; a second denitrification step in which a second denitrification treatment is performed in the presence of a hydrogen donor on the second nitrification-treated water that has been subjected to the second nitrification treatment; and an oxidation step in which an oxidation treatment is performed on the second denitrification-treated water that has been subjected to the second denitrification treatment, wherein each of the first nitrification tank, the first denitrification tank, the second nitrification tank, the second denitrification tank and the oxidation tank is filled with a carrier for retaining microorganisms.

[0013] It is preferable that the water treatment process further includes a first nitrate ion concentration measurement process for measuring the nitrate ion concentration in the first denitrification tank, and a second nitrate ion concentration measurement process for measuring the nitrate ion concentration in the second nitrification tank, and that the amount of hydrogen donor to be added to the first denitrification tank is controlled based on the first nitrate ion concentration obtained by measurement in the first nitrate ion concentration measurement process, and the amount of hydrogen donor to be added to the second denitrification tank is controlled based on the second nitrate ion concentration obtained by measurement in the second nitrate ion concentration measurement process.

[0014] In the water treatment step, it is preferable that the oxidized water that has been subjected to the oxidation treatment is circulated to the first nitrification step. Effect of the Invention

[0015] The present invention provides a water treatment device and a water treatment method that use a carrier that retains microorganisms to perform nitrification, denitrification, and oxidation treatments on water to be treated that contains ammonia nitrogen, and that can reduce the aeration air volume, the amount of pH adjuster used, and the amount of hydrogen donor used. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. [Diagram 5] 1 is a graph showing the transition of the concentration (mg / L) of nitrite nitrogen (NO2-N), the concentration (mg / L) of nitrate nitrogen (NO3-N), and TOC (mg / L) in a tank in an embodiment. [Figure 6] 1 is a graph showing the change in concentration (mg / L) of ammonia nitrogen (NH4-N) in a tank in an ammonia addition system in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0018] An example of a water treatment apparatus according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0019] The water treatment device 1 includes a first nitrification tank 10 in which a first nitrification treatment is performed by autotrophic bacteria on water to be treated that contains ammonia nitrogen, a first denitrification tank 12 in which a first denitrification treatment is performed in the presence of a hydrogen donor on the first nitrification-treated water that has been subjected to the first nitrification treatment, a second nitrification tank 14 in which a second nitrification treatment is performed by autotrophic bacteria on the first denitrification-treated water that has been subjected to the first denitrification treatment, a second denitrification tank 16 in which a second denitrification treatment is performed in the presence of a hydrogen donor on the second nitrification-treated water that has been subjected to the second nitrification treatment, and an oxidation tank 18 in which an oxidation treatment is performed on the second denitrification-treated water that has been subjected to the second denitrification treatment. The first nitrification tank 10 is filled with a carrier 56 for holding microorganisms, the first denitrification tank 12 is filled with a carrier 58 for holding microorganisms, the second nitrification tank 14 is filled with a carrier 60 for holding microorganisms, the second denitrification tank 16 is filled with a carrier 62 for holding microorganisms, and the oxidation tank 18 is filled with a carrier for holding microorganisms (not shown).

[0020] In the water treatment device 1, a water to be treated pipe 36 is connected to the inlet of the first nitrification tank 10. The first nitrification treated water outlet of the first nitrification tank 10 and the first nitrification treated water inlet of the first denitrification tank 12 are connected by a first nitrification treated water pipe 38. The first denitrification treated water outlet of the first denitrification tank 12 and the first denitrification treated water inlet of the second nitrification tank 14 are connected by a first denitrification treated water pipe 40. The second nitrification treated water outlet of the second nitrification tank 14 and the second nitrification treated water inlet of the second denitrification tank 16 are connected by a second nitrification treated water pipe 42. The second denitrification treated water outlet of the second denitrification tank 16 and the second denitrification treated water inlet of the oxidation tank 18 are connected by a second denitrification treated water pipe 44. The oxidation treated water outlet of the oxidation tank 18 is connected to an oxidation treated water pipe 46. A first hydrogen donor supply pipe 48 is connected to the first denitrification tank 12 via a first pump 50. A second hydrogen donor supply pipe 52 is connected to the second denitrification tank 16 via a second pump 54 .

[0021] The first nitrification tank 10 is provided with a screen 22 for suppressing outflow of the carrier 56 into the first nitrification treated water pipe 38, and is provided with an aeration device 20 as an oxygen-containing gas supplying means for supplying oxygen-containing gas. The first denitrification tank 12 is provided with an agitation device 24 having a rotating drive means such as a motor and an agitation blade as an agitation means. The first denitrification tank 12 is provided with a screen 26 for suppressing outflow of the carrier 58 into the first denitrification treated water pipe 40. The second nitrification tank 14 is provided with a screen 30 for suppressing outflow of the carrier 60 into the second nitrification treated water pipe 42, and is provided with an aeration device 28 as an oxygen-containing gas supplying means for supplying oxygen-containing gas. The second denitrification tank 16 is provided with an agitation device 32 having a rotating drive means such as a motor and an agitation blade as an agitation means. The second denitrification tank 16 is provided with a screen 34 for suppressing outflow of the carrier 62 into the second denitrification treated water pipe 44.

[0022] The water treatment method and the operation of the water treatment device 1 according to this embodiment will be described.

[0023] In the water treatment device 1, the water to be treated that contains ammonia nitrogen is sent to the first nitrification tank 10 through the water to be treated piping 36. In the first nitrification tank 10, an oxygen-containing gas is supplied by the aeration device 20, and the water to be treated is subjected to a first nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 56 under aerobic conditions, and ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (first nitrification step).

[0024] The first nitrification treated water that has been subjected to the first nitrification treatment is sent to the first denitrification tank 12 through the first nitrification treated water piping 38. Here, in the first denitrification tank 12, a first hydrogen donor is supplied to the first nitrification treated water by the first pump 50 through the first hydrogen donor supply piping 48 (first hydrogen donor supply step). In the first denitrification tank 12, a first denitrification treatment is performed on the first nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and nitrite ions or nitrate ions are reduced to nitrogen gas (first denitrification step).

[0025] The first denitrification treated water that has been subjected to the first denitrification treatment is sent to the second nitrification tank 14 through the first denitrification treated water piping 40. In the second nitrification tank 14, oxygen-containing gas is supplied by the aeration device 28, and the first denitrification treated water is subjected to a second nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 60 under aerobic conditions, and the remaining ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (second nitrification step).

[0026] The second nitrification treated water that has been subjected to the second nitrification treatment is sent to the second denitrification tank 16 through the second nitrification treated water piping 42. Here, in the second denitrification tank 16, a second hydrogen donor is supplied to the second nitrification treated water through the second hydrogen donor supply piping 52 by the second pump 54 (second hydrogen donor supply step). In the second denitrification tank 16, a second denitrification treatment is performed on the second nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and the remaining nitrite ions or nitrate ions are reduced to nitrogen gas (second denitrification step).

[0027] The second denitrification treated water that has been subjected to the second denitrification treatment is sent to the oxidation tank 18 through the second denitrification treated water pipe 44. In the oxidation tank 18, the second denitrification treated water is subjected to oxidation treatment, and organic matter remaining in the second denitrification step is oxidized (oxidation step). The oxidation treated water that has been subjected to the oxidation treatment is discharged as treated water through the oxidation treated water pipe 46.

[0028] In the water treatment method and water treatment device according to this embodiment, water to be treated that contains ammoniacal nitrogen is treated in the following order: first nitrification tank 10 (first nitrification step), first denitrification tank 12 (first denitrification step), second nitrification tank 14 (second nitrification step), second denitrification tank 16 (second denitrification step), and oxidation tank 18 (oxidation step).This makes it possible to reduce the aeration air volume, the amount of pH adjuster used, and the amount of hydrogen donor used in water treatment that performs nitrification, denitrification, and oxidation treatments on water to be treated that contains ammoniacal nitrogen using a carrier that holds microorganisms.

[0029] The reason why the aeration air volume, the amount of pH adjuster used, and the amount of hydrogen donor used can be reduced by performing the treatment in the order of the first nitrification tank 10 (first nitrification process), the first denitrification tank 12 (first denitrification process), the second nitrification tank 14 (second nitrification process), the second denitrification tank 16 (second denitrification process), and the oxidation tank 18 (oxidation process) is thought to be as follows.

[0030] In the nitrification reaction, ammonia nitrogen (ammonium ion: NH4 + ) is converted to nitrite ion (NO2 - ) is converted to nitrite ions (NO2 - ) is converted to nitrate ion (NO3 - In the denitrification reaction, the nitrite or nitrate ions are reduced to nitrogen gas (N2) by denitrifying bacteria. Nitrification reaction: NH4 + →NO2 - (Ammonia oxidizing bacteria) NO2 - →NO3 - (Nitrite oxidizing bacteria) Denitrification reaction: NO3 - →NO2 - →NO→N2O→N2 (denitrifying bacteria)

[0031] Ammoniacal nitrogen is reduced to a certain degree in the first nitrification tank 10 (first nitrification step), and the remaining ammoniacal nitrogen is reduced as much as possible in the second nitrification tank 14 (second nitrification step), thereby stabilizing the treatment by mitigating load fluctuations, and space saving is possible by high-speed treatment in the first nitrification tank 10 (first nitrification step). In the case of one-stage treatment, treatment is performed under conditions where the ammoniacal nitrogen concentration in the nitrification tank is low, and it is easily affected by inhibition when the ammoniacal nitrogen concentration becomes high. By using two-stage treatment, ammoniacal nitrogen is reduced to a certain degree under high load conditions in the first nitrification tank 10 (first nitrification step), that is, the nitrification tank is operated under conditions where the ammoniacal nitrogen concentration in the nitrification tank is high, making the nitrification tank resistant to concentration fluctuations in the tank.

[0032] In the first nitrification tank 10 (first nitrification step), high-speed treatment is carried out under high-load conditions, resulting in a mixture of nitrate ions and nitrite ions. When nitrification treatment is carried out in the first nitrification tank 10 (first nitrification step) and then in the second nitrification tank 14 (second nitrification step), the remaining nitrite ions are nitrified to nitrate ions, which requires oxygen. On the other hand, by performing nitrification treatment in the first nitrification tank 10 (first nitrification step), then performing denitrification treatment in the first denitrification tank 12 (first denitrification step), and then performing nitrification treatment in the second nitrification tank 14 (second nitrification step), the nitrite ions remaining in the first nitrification tank 10 (first nitrification step) can be denitrified directly in the first denitrification tank 12 (first denitrification step) without being converted to nitrate ions, which makes it possible to reduce the amount of aeration required in the nitrification steps (first nitrification step and second nitrification step) and to reduce the amount of hydrogen donor added in the denitrification steps (first denitrification step and second denitrification step).

[0033] In the first denitrification tank 12 (first denitrification process), a portion of the ammoniacal nitrogen remaining in the first nitrification tank 10 (first nitrification process) can be utilized for bacterial cell synthesis. Therefore, compared to a case in which nitrification treatment is performed in the second nitrification tank 14 (second nitrification process) following the first nitrification tank 10 (first nitrification process), the ammoniacal nitrogen load on the second nitrification tank 14 (second nitrification process) can be reduced, and the amount of aeration required in the second nitrification tank 14 (second nitrification process) can be reduced, making it possible to reduce the amount of alkali added for pH adjustment.

[0034] In the water treatment method and water treatment device according to this embodiment, the first nitrate ion concentration in the first denitrification tank 12 and the second nitrate ion concentration in the second nitrification tank 14 may be measured, and the amount of hydrogen donor added to the first denitrification tank 12 may be controlled based on the first nitrate ion concentration, and the amount of hydrogen donor added to the second denitrification tank 16 may be controlled based on the second nitrate ion concentration. An example of a water treatment device of this type is shown in Figure 2.

[0035] The water treatment device 3 in Figure 2, in addition to the configuration of the water treatment device 1 in Figure 1, is equipped with a first nitrate ion concentration measuring device 64 as a first nitrate ion concentration measuring means for measuring the nitrate ion concentration in the first denitrification tank 12, a second nitrate ion concentration measuring device 66 as a second nitrate ion concentration measuring means for measuring the nitrate ion concentration in the second nitrification tank 14, and a first control device 68 and a second control device 70 as control means for controlling the amount of hydrogen donor to be added to the first denitrification tank 12 based on the first nitrate ion concentration obtained by measurement with the first nitrate ion concentration measuring device 64, and for controlling the amount of hydrogen donor to be added to the second denitrification tank 16 based on the second nitrate ion concentration obtained by measurement with the second nitrate ion concentration measuring device 66.

[0036] In the water treatment device 3, a first nitrate ion concentration measuring device 64 is installed in the first denitrification tank 12. A second nitrate ion concentration measuring device 66 is installed in the second nitrification tank 14. The first nitrate ion concentration measuring device 64 and the first control device 68, and the first pump 50 and the first control device 68 are each connected by wire or wirelessly so as to be able to communicate with each other. The second nitrate ion concentration measuring device 66 and the second control device 70, and the second pump 54 and the second control device 70 are each connected by wire or wirelessly so as to be able to communicate with each other.

[0037] In the water treatment device 3, the water to be treated that contains ammonia nitrogen is sent to the first nitrification tank 10 through the water to be treated piping 36. In the first nitrification tank 10, oxygen-containing gas is supplied by the aeration device 20, and the water to be treated is subjected to a first nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 56 under aerobic conditions, and ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (first nitrification step).

[0038] The first nitrification treated water that has been subjected to the first nitrification treatment is sent to the first denitrification tank 12 through the first nitrification treated water piping 38. Here, in the first denitrification tank 12, a first hydrogen donor is supplied to the first nitrification treated water by the first pump 50 through the first hydrogen donor supply piping 48 (first hydrogen donor supply step). In the first denitrification tank 12, a first denitrification treatment is performed on the first nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and nitrite ions or nitrate ions are reduced to nitrogen gas (first denitrification step).

[0039] The first denitrification treated water that has been subjected to the first denitrification treatment is sent to the second nitrification tank 14 through the first denitrification treated water piping 40. In the second nitrification tank 14, oxygen-containing gas is supplied by the aeration device 28, and the first denitrification treated water is subjected to a second nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 60 under aerobic conditions, and the remaining ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (second nitrification step).

[0040] The second nitrification treated water that has been subjected to the second nitrification treatment is sent to the second denitrification tank 16 through the second nitrification treated water piping 42. Here, in the second denitrification tank 16, a second hydrogen donor is supplied to the second nitrification treated water through the second hydrogen donor supply piping 52 by the second pump 54 (second hydrogen donor supply step). In the second denitrification tank 16, a second denitrification treatment is performed on the second nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and the remaining nitrite ions or nitrate ions are reduced to nitrogen gas (second denitrification step).

[0041] The second denitrification treated water that has been subjected to the second denitrification treatment is sent to the oxidation tank 18 through the second denitrification treated water pipe 44. In the oxidation tank 18, the second denitrification treated water is subjected to oxidation treatment, and organic matter remaining in the second denitrification step is oxidized (oxidation step). The oxidation treated water that has been subjected to the oxidation treatment is discharged as treated water through the oxidation treated water pipe 46.

[0042] Here, the nitrate ion concentration in the first denitrification tank 12 is measured by the first nitrate ion concentration measuring device 64 (first nitrate ion concentration measuring step), and the nitrate ion concentration in the second nitrification tank 14 is measured by the second nitrate ion concentration measuring device 66 (second nitrate ion concentration measuring step). The first control device 68 controls the amount of hydrogen donor added to the first denitrification tank 12 by the first pump 50 based on the first nitrate ion concentration obtained by measurement with the first nitrate ion concentration measuring device 64, and the second control device 70 controls the amount of hydrogen donor added to the second denitrification tank 16 by the second pump 54 based on the second nitrate ion concentration obtained by measurement with the second nitrate ion concentration measuring device 66 (control step).

[0043] In the first denitrification tank 12, organic matter is added as a hydrogen donor. However, if any organic matter remains, it will flow into the second nitrification tank 14 and coexist with fast-growing microorganisms that are responsible for the oxidation reaction of the organic matter, which raises concerns about a decrease in nitrification activity in the second nitrification tank 14.

[0044] It is desirable to add a hydrogen donor so that as little organic matter as possible remains in the first denitrification tank 12. Therefore, by determining the amount of hydrogen donor to be added to the first denitrification tank 12 based on the measured value of the nitrate ion concentration of the denitrification treated water in the first denitrification tank 12, it is possible to prevent excessive addition of the hydrogen donor, and by intentionally allowing nitrate ions to remain, it is possible to operate the tank in a state where almost no organic matter remains.

[0045] The first control device 68 and the second control device 70 are composed of, for example, a microcomputer and electronic circuits each consisting of a calculation means such as a CPU that calculates a program and storage means such as ROM and RAM that store the program and the calculation results, and have the function of controlling the flow rate of the first pump 50 and the second pump 54, or the opening and closing degree of the valves provided in the first hydrogen donor supply pipe 48 and the second hydrogen donor supply pipe 52.

[0046] The first control device 68 and the second control device 70 may be a single control device, or separate control devices may be used.

[0047] The first nitrate ion concentration measuring device 64 and the second nitrate ion concentration measuring device 66 are preferably capable of continuously measuring the nitrate ion concentration, and for example, an ion electrode type or optical type sensor can be used.

[0048] The nitrate ion concentration is preferably controlled to be in the range of, for example, 1 to 20 mg / L. In particular, since the measurement accuracy of the nitrate ion sensor may be low when the nitrate ion concentration is low, it is more preferable to control the concentration to be in the range of 5 to 20 mg / L.

[0049] On the other hand, since it is not necessary to leave nitrate ions in the second denitrification tank 16, it is sufficient to add an amount of hydrogen donor necessary for denitrification according to the second nitrate ion concentration measured by the second nitrate ion concentration measuring device 66 in the second nitrification tank 14. In the second nitrification tank 14, the carrier 60 is fluidized by aeration, which is expected to have a cleaning effect on the second nitrate ion concentration measuring device 66 that measures nitrate ions.

[0050] Regarding the amount of hydrogen donor required for denitrification, the following formula has been proposed as the amount of methanol required when methanol is used as the hydrogen donor. Methanol required = 2.47 x NO3-N + 1.53 x NO2-N + 0.87 x DO Here, DO is the dissolved oxygen that flows into the denitrification tank. Therefore, the amount of methanol that needs to be added is about 2.5 times the amount of nitrate nitrogen and about 1.5 times the amount of nitrite nitrogen.

[0051] The first denitrification tank 12 treats the nitrite ions and nitrate ions flowing in from the first nitrification tank 10, but as shown in the reaction pathway, the nitrite is denitrified first. As described above, an organic substance such as methanol may be added to the first denitrification tank 12 based on the nitrate ion concentration in the first denitrification tank 12 and so that it remains.

[0052] In the second nitrification tank 14, the remaining ammonia nitrogen is reduced as much as possible, so the remaining nitrogen becomes nitrate nitrogen. Therefore, the amount of hydrogen donor, such as organic matter such as methanol, added to the second denitrification tank 16 may be controlled based on the nitrate ion concentration in the second nitrification tank 14. In the case of methanol, the nitrate nitrogen concentration is calculated from the nitrate ion concentration, and the amount of nitrate nitrogen is calculated from the inflow amount to the second denitrification tank 16, and then the required amount of hydrogen donor may be determined. For example, the amount of methanol added in the second denitrification tank 16 may be calculated as the nitrate nitrogen concentration in the second nitrification tank 14 x the inflow amount to the second denitrification tank 16 x (2.5 to 3.0).

[0053] The hydrogen donor may be an organic substance contained in the water to be treated, or may be supplied from the outside when the hydrogen donor is insufficient, particularly in the case of inorganic wastewater. In this case, the supply amount of the hydrogen donor is determined based on the nitrogen concentration and the amount of water in the water to be treated, and the hydrogen donor may be continuously added based on the supply amount. Examples of the hydrogen donor supplied from the outside include, but are not limited to, one or more of alcohols such as methanol, ethanol, and isopropyl alcohol, organic acids such as acetic acid, hydrogen gas, acetone, glucose, ethyl methyl ketone, and tetramethylammonium hydroxide (TMAH). All hydrogen donors known in the art can be used.

[0054] In this way, by controlling the amount of hydrogen donor added to the first denitrification tank 12 based on the first nitrate ion concentration, and by controlling the amount of hydrogen donor added to the second denitrification tank 16 based on the second nitrate ion concentration, the amount of hydrogen donor used can be reduced.

[0055] In the water treatment method and water treatment device according to this embodiment, the oxidized water may be circulated to the first nitrification tank 10 (nitrification step). An example of a water treatment device of this type is shown in FIG.

[0056] In the water treatment device 5 of FIG. 3, in addition to the configuration of the water treatment device 3 of FIG. 2, a circulation pipe 72 branched off from the oxidized water pipe 46 is connected to the water to be treated pipe 36 .

[0057] In the water treatment device 5, the water to be treated that contains ammonia nitrogen is sent to the first nitrification tank 10 through the water to be treated piping 36. In the first nitrification tank 10, an oxygen-containing gas is supplied by the aeration device 20, and the water to be treated is subjected to a first nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 56 under aerobic conditions, and ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (first nitrification step).

[0058] The first nitrification treated water that has been subjected to the first nitrification treatment is sent to the first denitrification tank 12 through the first nitrification treated water piping 38. Here, in the first denitrification tank 12, a first hydrogen donor is supplied to the first nitrification treated water by the first pump 50 through the first hydrogen donor supply piping 48 (first hydrogen donor supply step). In the first denitrification tank 12, a first denitrification treatment is performed on the first nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and nitrite ions or nitrate ions are reduced to nitrogen gas (first denitrification step).

[0059] The first denitrification treated water that has been subjected to the first denitrification treatment is sent to the second nitrification tank 14 through the first denitrification treated water piping 40. In the second nitrification tank 14, oxygen-containing gas is supplied by the aeration device 28, and the first denitrification treated water is subjected to a second nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 60 under aerobic conditions, and the remaining ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (second nitrification step).

[0060] The second nitrification treated water that has been subjected to the second nitrification treatment is sent to the second denitrification tank 16 through the second nitrification treated water piping 42. Here, in the second denitrification tank 16, a second hydrogen donor is supplied to the second nitrification treated water through the second hydrogen donor supply piping 52 by the second pump 54 (second hydrogen donor supply step). In the second denitrification tank 16, a second denitrification treatment is performed on the second nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and the remaining nitrite ions or nitrate ions are reduced to nitrogen gas (second denitrification step).

[0061] The second denitrification treated water that has been subjected to the second denitrification treatment is sent to the oxidation tank 18 through the second denitrification treated water piping 44. In the oxidation tank 18, the second denitrification treated water is subjected to oxidation treatment, and organic matter remaining in the second denitrification step is oxidized (oxidation step). The oxidation treated water that has been subjected to the oxidation treatment is discharged as treated water through the oxidation treated water piping 46. At least a portion of the oxidation treated water is circulated to the first nitrification tank 10 (nitrification step) through the circulation piping 72 and the treated water piping 36 (circulation step).

[0062] By circulating the oxidized water to the first nitrification tank 10 (nitrification step), the rate of the first nitrification tank 10 (nitrification step) can be increased and the treatment performance can be stabilized.

[0063] The reason why circulating the oxidized water to the first nitrification tank 10 (nitrification process) can speed up the first nitrification tank 10 (nitrification process) and stabilize the treatment performance is believed to be as follows.

[0064] Nitrifying bacteria are autotrophic bacteria, and therefore utilize inorganic carbon (IC) in water for bacterial synthesis. Generally, low-load treatment such as activated sludge (e.g., 0.1-0.3 kg-N / (m 3 In the case of aeration, it is possible to secure the amount of inorganic carbon required for nitrifying bacteria by dissolving carbon dioxide in the treated water through aeration. However, in the case of biofilm methods (e.g., fixed bed and fluidized bed methods) in which a biological retention carrier is introduced into the treatment system and the bacteria are retained within the treatment system, high load treatment (e.g., 0.5 to 1.0 kg-N / (m3 Therefore, inorganic carbon necessary for the growth of nitrifying bacteria tends to be insufficient. For example, in Patent Document 1, the treatment speed is increased by supplying bicarbonate or carbonate.

[0065] On the other hand, in the oxidation tank 18 (oxidation step), the concentration of inorganic carbon in the oxidation tank 18 increases due to the treatment of organic matter remaining in the second denitrification tank 16 (second denitrification step) or due to the inorganic carbon remaining from the second denitrification tank 16 (second denitrification step). Therefore, by circulating the oxidized water to the first nitrification tank 10 (first nitrification step), inorganic carbon can be supplied to the first nitrification tank 10 (first nitrification step), which leads to the speedup and stabilization of the first nitrification tank 10 (first nitrification step). In addition, the alkalinity remaining in the oxidized water is supplied, which leads to a reduction in the amount of alkali used for pH adjustment in the first nitrification tank 10 (first nitrification step). Since the inorganic carbon remaining in the first denitrification tank 12 (first denitrification step) is supplied to the second nitrification tank 14 (second nitrification step), it is not necessary to circulate the oxidized water to the second nitrification tank 14 (second nitrification step).

[0066] In the water treatment method and water treatment device according to this embodiment, the water to be treated may be distributed to a first nitrification tank 10 (first nitrification step) and a second nitrification tank 14 (second nitrification step). An example of a water treatment device of this type is shown in FIG.

[0067] In the water treatment device 7 in FIG. 4, in addition to the configuration of the water treatment device 3 in FIG. 2, a pipe 74 for water to be treated branched off from the pipe 36 for water to be treated is connected to the first denitrification treated water pipe 40.

[0068] In the water treatment device 7, a portion of the water to be treated that contains ammonia nitrogen is sent to the first nitrification tank 10 through the water to be treated piping 36, and the remaining portion is sent to the second nitrification tank 14 through the water to be treated piping 36, the water to be treated piping 74, and the first denitrification treated water piping 40. In the first nitrification tank 10, oxygen-containing gas is supplied by the aeration device 20, and the water to be treated is subjected to a first nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 56 under aerobic conditions, and ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (first nitrification step).

[0069] The first nitrification treated water that has been subjected to the first nitrification treatment is sent to the first denitrification tank 12 through the first nitrification treated water piping 38. Here, in the first denitrification tank 12, a first hydrogen donor is supplied to the first nitrification treated water by the first pump 50 through the first hydrogen donor supply piping 48 (first hydrogen donor supply step). In the first denitrification tank 12, a first denitrification treatment is performed on the first nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and nitrite ions or nitrate ions are reduced to nitrogen gas (first denitrification step).

[0070] The first denitrification treated water that has been subjected to the first denitrification treatment is sent to the second nitrification tank 14 through the first denitrification treated water pipe 40. Meanwhile, as described above, a remaining part of the water to be treated is sent to the second nitrification tank 14 through the water to be treated pipe 36, the water to be treated pipe 74, and the first denitrification treated water pipe 40. In the second nitrification tank 14, oxygen-containing gas is supplied by the aeration device 28, and under aerobic conditions, the first denitrification treated water (including the water to be treated sent through the water to be treated pipe 36, the water to be treated pipe 74, and the first denitrification treated water pipe 40) is subjected to a second nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 60, and the remaining ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (second nitrification step).

[0071] The second nitrification treated water that has been subjected to the second nitrification treatment is sent to the second denitrification tank 16 through the second nitrification treated water piping 42. Here, in the second denitrification tank 16, a second hydrogen donor is supplied to the second nitrification treated water through the second hydrogen donor supply piping 52 by the second pump 54 (second hydrogen donor supply step). In the second denitrification tank 16, a second denitrification treatment is performed on the second nitrification treated water by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and the remaining nitrite ions or nitrate ions are reduced to nitrogen gas (second denitrification step).

[0072] The second denitrification treated water that has been subjected to the second denitrification treatment is sent to the oxidation tank 18 through the second denitrification treated water piping 44. In the oxidation tank 18, the second denitrification treated water is subjected to oxidation treatment, and organic matter remaining in the second denitrification step is oxidized (oxidation step). The oxidation treated water that has been subjected to the oxidation treatment is discharged as treated water through the oxidation treated water piping 46. At least a portion of the oxidation treated water is circulated to the first nitrification tank 10 (nitrification step) through the circulation piping 72 and the treated water piping 36 (circulation step).

[0073] By distributing the water to be treated between the first nitrification tank 10 (first nitrification process) and the second nitrification tank 14 (second nitrification process), the load can be distributed between the first nitrification tank 10 (first nitrification process) and the second nitrification tank 14 (second nitrification process).

[0074] The water to be treated in the water treatment method and water treatment device according to the present embodiment is nitrogen-containing water that contains ammoniacal nitrogen. Examples of the water to be treated include industrial wastewater such as wastewater from the electronics industry, wastewater from metal refining plants, and wastewater from power plants, and wastewater containing digested desorption water discharged during sludge treatment. Here, the wastewater from the electronics industry contains various chemicals, and the components in the wastewater vary greatly depending on the products manufactured. Examples of the nitrogen-containing water include wastewater from wafer cleaning. In addition to ammonia, this wastewater often contains tetramethylammonium hydroxide (TMAH), hydrogen peroxide, fluoride ions, isopropyl alcohol (IPA), and the like.

[0075] The concentration of ammonia nitrogen in the water to be treated is, for example, in the range of 10 to 1000 mg / L, and preferably in the range of 20 to 500 mg / L.

[0076] When phosphorus (P) and trace elements contained in the water to be treated are insufficient, phosphorus (P) and trace elements may be added externally. Phosphorus (P) may be supplied to the water to be treated, for example, as phosphoric acid, and the phosphorus (P) may be mixed with the water to be treated to supply the system. Trace elements may be supplied to the water to be treated, for example, as a trace element solution, and the trace elements may be mixed with the water to be treated to supply the system.

[0077] "Trace elements" refers to any or all of the following: sulfur (S), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and molybdenum (Mo).

[0078] As trace elements, salts containing each element may be added as powder to the water to be treated, but if there are multiple elements that are in short supply, the number of chemicals will increase accordingly, which may make handling and inventory management complicated. On the other hand, it is easier to handle and save space to supply a trace element solution in which multiple salts containing each element are mixed and dissolved in water, and the pH is acidic to suppress precipitation. For example, the composition of the trace element solution may be changed according to the elements that are in short supply in the water to be treated, taking into consideration the solubility of each salt in water, or a lineup of several different combinations may be prepared and determined according to the properties of the water to be treated. Unless otherwise specified, the term "trace element solution" refers to a liquid in which all or part of the types of trace elements shown above are dissolved in a solvent such as water. The content of trace elements in the water to be treated can be measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0079] The concentration of phosphorus (P) in the water to be treated varies depending on the ammonia nitrogen concentration of the water to be treated, and may be added in the range of 1 / 50 to 1 / 5 of the ammonia nitrogen concentration, for example, or may be added so that the phosphate ion concentration in the denitrification treatment water remains at about 0.5 to 1.0 mgP / L.

[0080] Regarding the location where phosphorus (P) and trace elements are added, they may be supplied in the treated water piping 36 through which the treated water flows into the first nitrification tank 10, or they may be supplied to a separate tank for temporarily storing the treated water, or they may be added directly to the first nitrification tank 10.

[0081] When circulating the oxidized water, the amount of the oxidized water circulated to the first nitrification tank 10 (first nitrification step) in the circulation process may be, for example, in the range of 10 to 100% by volume of the oxidized water relative to the water to be treated, and it is preferable to circulate the amount in the range of 20 to 50% by volume.

[0082] During periods when the ammonia nitrogen load is low, such as during start-up or regular factory inspections, the water to be treated is distributed, thereby applying a constant load to each tank and maintaining treatment performance. When distributing the water to be treated, the amount of water to be treated may be distributed to the second nitrification tank 14 (second nitrification step) in the range of 10 to 50% by volume of the water to be treated, for example.

[0083] The water temperature in the first nitrification tank 10 and the second nitrification tank 14 may be maintained in the range of, for example, 15 to 40° C. The pH in the first nitrification tank 10 and the second nitrification tank 14 may be maintained in the range of, for example, 6.0 to 8.5. If the pH in the first nitrification tank 10 and the second nitrification tank 14 fluctuates, the pH may be maintained within the above pH range by adding an acid such as hydrochloric acid or sulfuric acid or an alkali such as an aqueous sodium hydroxide solution.

[0084] The water temperature in the first denitrification tank 12 and the second denitrification tank 16 may be maintained in the range of, for example, 15 to 40° C. The pH in the first denitrification tank 12 and the second denitrification tank 16 may be maintained in the range of, for example, 6.0 to 8.5. If the pH in the first nitrification tank 10 and the second denitrification tank 16 fluctuates, the pH may be maintained within the above pH range by adding an acid such as hydrochloric acid or sulfuric acid or an alkali such as an aqueous sodium hydroxide solution.

[0085] The TN (Total Nitrogen) volumetric load in the first denitrification tank 12 and the second denitrification tank 16 is, for example, 0.1 to 3.0 kg-N / (m 3 ·day) ranges from 0.5 to 2.0 kg-N / (m 3 It is preferable that the range is 100-150 days.

[0086] The oxidation treatment in the oxidation tank 18 is an aerobic treatment.

[0087] The water temperature in the oxidation tank 18 may be maintained in the range of, for example, 15 to 40° C. The pH in the oxidation tank 18 may be maintained in the range of, for example, 6.0 to 8.5. If the pH in the oxidation tank 18 fluctuates, it may be maintained within the above pH range by adding an acid such as hydrochloric acid or sulfuric acid or an alkali such as an aqueous solution of sodium hydroxide.

[0088] In the first nitrification tank 10, the first denitrification tank 12, the second nitrification tank 14, the second denitrification tank 16, and the oxidation tank 18, carriers are introduced and the bacteria are retained on the floating carriers, thereby increasing the contact efficiency between the bacteria and at least one of ammoniacal nitrogen, nitrate nitrogen, and nitrite nitrogen, as well as organic matter, making it possible to operate at high loads and facilitating the management of sludge containing bacteria.

[0089] The means for retaining ammonia oxidizing bacteria, nitrite oxidizing bacteria, denitrifying bacteria, etc. is not limited to a fluidized bed method using a carrier, but may be any method such as a fixed bed method, a floating type, a membrane separation activated sludge method, or a USB method.

[0090] The carrier is not particularly limited as long as it is a carrier that has been conventionally used, and examples thereof include plastic carriers, sponge-like carriers, and gel-like carriers. In particular, in the first denitrification tank 12 (first denitrification step) and the second denitrification tank 16 (second denitrification step), a gel-like carrier is used as a fluidized carrier to suppress floating of the carrier due to nitrogen gas, and the carrier has high fluidity due to stirring, so that high-load treatment is possible compared to plastic carriers and sponge-like carriers. The gel-like carrier is not particularly limited, and examples thereof include water-absorbent polymer gel-like carriers containing polyvinyl alcohol, polyethylene glycol, polyurethane, and the like. In addition, methods for maintaining sludge in the carrier include a method of entrapping and immobilizing sludge inside the carrier in advance, and a method of putting the carrier and seed sludge into the tank and forming a biofilm on the carrier. The method of forming a biofilm on the carrier is preferable in terms of increasing the contact efficiency with the water to be treated and maintaining high activity.

[0091] The shape of the carrier is not particularly limited, but is preferably spherical, cubic, rectangular, cylindrical, or the like, about 1 to 10 mm. In particular, in the first denitrification tank 12 (denitrification step) and the second denitrification tank 16 (second denitrification step), a spherical or cylindrical gel-like carrier about 3 to 8 mm is preferred. To facilitate formation of a fluidized state inside the tank, the specific gravity of the carrier is at least greater than 1.0, and preferably a true specific gravity of 1.1 or more, or an apparent specific gravity of 1.01 or more.

[0092] As an agitation method in the first denitrification tank 12 (denitrification process) and the second denitrification tank 16 (second denitrification process), a draft tube that is installed approximately vertically inside the tank and is open at the top and bottom may be installed, and a vertical agitator or a submersible aerator may be used to form a downward flow inside the draft tube and an upward flow outside the draft tube.

[0093] The amount of carriers added to the first nitrification tank 10, first denitrification tank 12, second nitrification tank 14, second denitrification tank 16, and oxidation tank 18 is preferably in the range of 10 to 70% of the tank volume. If the amount of carriers added is less than 10% of the tank volume, the reaction rate may be slow, and if it exceeds 70%, the carriers become difficult to flow, and the treated water may short-pass due to clogging by sludge during long-term operation, resulting in a deterioration in treated water quality.

[0094] The soluble TN concentration of the treated water varies depending on the TN concentration of the water to be treated, but can be, for example, in the range of 0.5 to 10 mg / L, preferably in the range of 0.5 to 5 mg / L. EXAMPLES

[0095] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0096] <Example 1 and Comparative Example 1> An experiment was conducted to confirm that a portion of ammonia was removed in the denitrification tank in the presence of a hydrogen donor. Denitrification experiments were conducted in two systems: an ammonia-added system in which ammonia was added to the treated water, and a non-ammonia-added system in which ammonia was not added.

[0097] (Batch experiment conditions) Denitrification tank volume: 0.5L Microorganism retention carrier: Polyvinyl alcohol gel carrier (heterotrophic denitrifying bacteria attached to the carrier) Carrier filling rate: 10% (carrier bulk volume / tank volume) Test water: Well water to which sodium nitrate was added in an amount equivalent to a nitrate nitrogen concentration of 500 mg / L, as well as phosphoric acid and trace element solutions, was used to simulate wastewater. Ammonium chloride was added to the ammonia-added system in an amount equivalent to an ammonia nitrogen concentration of 60 mg / L. Hydrogen donor: Methanol was added in an amount equivalent to 450 mg / L in terms of TOC concentration. Tank pH: Controlled to pH 7.5 using a pH meter

[0098] The water quality in the tank was checked after a certain period of time had passed while stirring the tank with a stirrer. The water quality was measured after filtering through a 0.45μm filter.

[0099] (Batch experiment results) Figure 5 shows the trends in the concentration (mg / L) of nitrite nitrogen (NO2-N), nitrate nitrogen (NO3-N), and TOC (mg / L) in the tank. Figure 6 shows the trends in the concentration (mg / L) of ammonia nitrogen (NH4-N) in the tank in the ammonia addition system.

[0100] Heterotrophic denitrification occurred in both the ammonia-added and non-added systems, with little difference observed in denitrification activity. On the other hand, ammonia concentrations were reduced in the ammonia-added system, confirming that ammonia was partially processed in heterotrophic denitrification. Nitrite nitrogen remained below 1 mg / L in both systems.

[0101] These results show that in water treatment using a carrier that retains microorganisms to perform nitrification, denitrification, and oxidation processes on water containing ammonia nitrogen, the aeration air volume, the amount of pH adjuster used, and the amount of hydrogen donor used can be reduced. [Explanation of symbols]

[0102] 1,3,5,7 water treatment device, 10 first nitrification tank, 12 first denitrification tank, 14 second nitrification tank, 16 second denitrification tank, 18 oxidation tank, 20,28 aeration device, 22,26,30,34 screen, 24,32 agitation device, 36,74 treated water piping, 38 first nitrification treated water piping, 40 first denitrification treated water piping, 42 second nitrification treated water piping, 44 second denitrification treated water piping, 46 oxidation treated water piping, 48 first hydrogen donor supply piping, 52 second hydrogen donor supply piping, 50 first pump, 54 second pump, 56,58,60,62 carrier, 64 first nitrate ion concentration measuring device, 66 second nitrate ion concentration measuring device, 68 first control device, 70 second control device, 72 circulation piping.

Claims

1. a first nitrification tank in which a first nitrification treatment is performed on the water to be treated that contains ammonia nitrogen using autotrophic bacteria; a first denitrification tank for performing a first denitrification treatment on the first nitrification treated water in the presence of a hydrogen donor; a second nitrification tank in which a second nitrification treatment is performed on the first denitrification treated water by autotrophic bacteria; a second denitrification tank for performing a second denitrification treatment on the second nitrification treated water in the presence of a hydrogen donor; an oxidation tank for performing an oxidation treatment on the second denitrification treatment water that has been subjected to the second denitrification treatment; Equipped with A water treatment device comprising: a first nitrification tank, a first denitrification tank, a second nitrification tank, a second denitrification tank, and an oxidation tank, each of which is filled with a carrier for holding microorganisms.

2. The water treatment device according to claim 1, a first nitrate ion concentration measuring means for measuring the nitrate ion concentration in the first denitrification tank; A second nitrate ion concentration measuring means for measuring the nitrate ion concentration in the second nitrification tank; a control means for controlling an amount of a hydrogen donor to be added to the first denitrification tank based on the first nitrate ion concentration obtained by measurement using the first nitrate ion concentration measuring means, and for controlling an amount of a hydrogen donor to be added to the second denitrification tank based on the second nitrate ion concentration obtained by measurement using the second nitrate ion concentration measuring means; The water treatment device further comprising:

3. The water treatment device according to claim 1 or 2, The water treatment device according to claim 1, wherein the oxidized water is circulated to the first nitrification tank.

4. A first nitrification step in which a first nitrification treatment is performed on the water to be treated containing ammonia nitrogen using autotrophic bacteria; a first denitrification step of performing a first denitrification treatment on the first nitrification treated water in the presence of a hydrogen donor; A second nitrification process in which a second nitrification process is performed on the first denitrification treated water using autotrophic bacteria; a second denitrification step of subjecting the second nitrification treated water to a second denitrification treatment in the presence of a hydrogen donor; an oxidation step of performing an oxidation treatment on the second denitrification treated water that has been subjected to the second denitrification treatment; Including, A water treatment method comprising filling each of the first nitrification tank, the first denitrification tank, the second nitrification tank, the second denitrification tank and the oxidation tank with a carrier for holding microorganisms.

5. The water treatment method according to claim 4, a first nitrate ion concentration measuring step of measuring a nitrate ion concentration in the first denitrification tank; a second nitrate ion concentration measuring step of measuring the nitrate ion concentration in the second nitrification tank; Further comprising: A water treatment method comprising the steps of: controlling the amount of hydrogen donor to be added to the first denitrification tank based on a first nitrate ion concentration obtained by measurement in the first nitrate ion concentration measurement step; and controlling the amount of hydrogen donor to be added to the second denitrification tank based on a second nitrate ion concentration obtained by measurement in the second nitrate ion concentration measurement step.

6. The water treatment method according to claim 4 or 5, The water treatment method according to claim 1, wherein the oxidized water is circulated to the first nitrification step.

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