Water treatment apparatus and water treatment method

Abstract

To provide a water treatment apparatus and a water treatment method, capable of stabilizing a treatment performance in a denitrification treatment, 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 nitrification tank 10 configured to apply a nitrification treatment to treatment-target water containing ammoniac nitrogen by an autotrophic germ; a denitrification tank 12 configured to apply a denitrification treatment to nitrification-treated water under a presence of a hydrogen donor; and an oxidation tank 14 configured to apply an oxidation treatment to denitrification-treated water. A carrier carrying a microorganism is packed into each of the nitrification tank 10, the denitrification tank 12 and the oxidation tank 14. A trace element is added to each of the nitrification tank 10 and the denitrification tank 12.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, hydrofluoric acid, ammonia, nitric acid, etc. have been used in semiconductor manufacturing processes, etc. For this reason, wastewater containing fluorine (hydrofluoric acid, etc.), nitrogen (ammonia, nitric acid, etc.), etc. is discharged as waste liquid from these processes.

[0003] Fluorine in wastewater is generally removed physicochemically, for example, by adding calcium to form calcium fluoride. In order to sufficiently remove fluorine from wastewater, it is desirable to create conditions in which a significant amount of calcium ions remain. In general, the target fluorine concentration in fluoride-removed water is set to about 10 mg / L or less, and in this case, the residual calcium concentration in the fluoride-removed water is set to about 100 to 1000 mg / L.

[0004] 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.

[0005] 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.

[0006] 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 3 High-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.

[0007] In addition, typical nutrients used in biological treatment, including nitrification and denitrification, include the essential nutrients nitrogen (N) and phosphorus (P), as well as trace elements such as 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). If there is a shortage of these elements in the wastewater, it is desirable to add them comprehensively. In particular, in wastewater from semiconductor factories and other sources where trace elements are likely to be lacking, it is often the case that any or all of these elements are added.

[0008] In the method of Patent Document 2, when nitrification is performed first and then denitrification is performed, high-speed treatment in the denitrification tank is achieved by adding molybdenum to the water to be treated that flows into the nitrification tank as a trace element that is insufficient. Molybdenum is added to the water to be treated that flows into the nitrification tank in an amount necessary not only for nitrifying bacteria but also for denitrifying bacteria.

[0009] The method of nitrogen treatment in which the necessary amounts of nitrifying bacteria and denitrifying bacteria are added together to the water to be treated flowing into the nitrification tank, as in the method of Patent Document 2, had the problem that the treatment performance of the downstream denitrification tank became unstable. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 4865211 [Patent Document 2] Patent No. 6461408 Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a water treatment device and a water treatment method that can stabilize the treatment performance in denitrification treatment, in which nitrification treatment, denitrification treatment, and oxidation treatment are performed on water to be treated that contains ammonia nitrogen using a carrier that retains microorganisms. [Means for solving the problem]

[0012] The present invention provides a water treatment device comprising a nitrification tank in which autotrophic bacteria are used to perform nitrification treatment on water to be treated that contains ammonia nitrogen, a denitrification tank in which denitrification treatment is performed on the nitrification-treated water in the presence of a hydrogen donor, and an oxidation tank in which oxidation treatment is performed on the denitrification-treated water, wherein each of the nitrification tank, denitrification tank, and oxidation tank is filled with a carrier for retaining microorganisms, and trace elements are added to each of the nitrification tank and denitrification tank.

[0013] In the water treatment device, it is preferable that the water to be treated contains 100 mg / L or more of calcium, and that phosphorus is added to each of the nitrification tank and the denitrification tank.

[0014] In the water treatment device, it is preferable that the oxidized water that has been subjected to the oxidation treatment is circulated to the nitrification tank.

[0015] The present invention is a water treatment method comprising a nitrification step in which autotrophic bacteria are used to nitrify water to be treated that contains ammonia nitrogen, a denitrification step in which denitrification is performed on the nitrification-treated water in the presence of a hydrogen donor, and an oxidation step in which oxidation is performed on the denitrification-treated water, in which a carrier for retaining microorganisms is used in each of the nitrification step, the denitrification step, and the oxidation step, and trace elements are added to each of the nitrification tank and the denitrification tank.

[0016] In the water treatment step, it is preferable that the water to be treated contains 100 mg / L or more of calcium, and that phosphorus is added in each of the nitrification step and the denitrification step.

[0017] In the water treatment step, it is preferable that the oxidized water obtained by the oxidation treatment is circulated to the nitrification step. Effect of the Invention

[0018] The present invention provides a water treatment device and a water treatment method that can stabilize the treatment performance in the denitrification treatment in water treatment that uses a carrier that retains microorganisms to perform nitrification treatment, denitrification treatment, and oxidation treatment on water to be treated that contains ammonia nitrogen. [Brief description of the drawings]

[0019] [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] 1 is a graph showing the TN volume load in a denitrification tank and the TN concentration of treated water in the denitrification tank from 210 to 280 days after the start of operation in Comparative Example 1 and Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] 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.

[0021] 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.

[0022] The water treatment device 1 comprises a nitrification tank 10 in which the water to be treated containing ammonia nitrogen is nitrified using autotrophic bacteria, a denitrification tank 12 in which the nitrification-treated water is denitrified in the presence of a hydrogen donor, and an oxidation tank 14 in which the denitrification-treated water is oxidized. The nitrification tank 10 is filled with carriers 42 for holding microorganisms, the denitrification tank 12 is filled with carriers 44 for holding microorganisms, and the oxidation tank 14 is filled with a carrier (not shown) for holding microorganisms.

[0023] In the water treatment device 1, a water to be treated pipe 24 is connected to the water to be treated inlet of the nitrification tank 10. A nitrification-treated water outlet of the nitrification tank 10 and a nitrification-treated water inlet of the denitrification tank 12 are connected by a nitrification-treated water pipe 26. A denitrification-treated water outlet of the denitrification tank 12 and a denitrification-treated water inlet of the oxidation tank 14 are connected by a denitrification-treated water pipe 28. An oxidation-treated water outlet of the oxidation tank 14 is connected to an oxidation-treated water pipe 30. A first trace element supply pipe 32 is connected to the water to be treated pipe 24. A hydrogen donor supply pipe 34 and a second trace element supply pipe 36 are connected to the nitrification-treated water pipe 26.

[0024] The nitrification tank 10 is equipped with a screen 18 for preventing the carriers 42 from flowing out into the nitrification treated water pipe 26, and is equipped with an aeration device 16 as an oxygen-containing gas supplying means for supplying an oxygen-containing gas. The denitrification tank 12 is equipped with an agitator 20 as an agitating means, for example, having a rotation driving means such as a motor and an agitating blade. The denitrification tank 12 is equipped with a screen 22 for preventing the carriers 44 from flowing out into the denitrification treated water pipe 28.

[0025] The water treatment method and the operation of the water treatment device 1 according to this embodiment will be described.

[0026] In the water treatment device 1, the water to be treated that contains ammonia nitrogen is sent to the nitrification tank 10 through the water to be treated piping 24. Here, in the water to be treated piping 24, a first trace element is supplied to the water to be treated through the first trace element supply piping 32 (first trace element supply step). In the nitrification tank 10, an oxygen-containing gas is supplied by the aeration device 16, and under aerobic conditions, the water to be treated is subjected to nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 42, and ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (nitrification step).

[0027] The nitrification-treated water that has been subjected to the nitrification treatment is sent to the denitrification tank 12 through the nitrification-treated water pipe 26. Here, in the nitrification-treated water pipe 26, a second trace element is supplied to the nitrification-treated water through the second trace element supply pipe 36 (second trace element supply step). Also, in the nitrification-treated water pipe 26, a hydrogen donor is supplied to the nitrification-treated water through the hydrogen donor supply pipe 34 (hydrogen donor supply step). In the denitrification tank 12, the nitrification-treated water is denitrified by denitrifying bacteria (heterotrophic bacteria) in the presence of the hydrogen donor, and nitrite ions or nitrate ions are reduced to nitrogen gas (denitrification step).

[0028] The denitrification treated water that has been subjected to the denitrification treatment is sent to the oxidation tank 14 through the denitrification treated water pipe 28. In the oxidation tank 14, the denitrification treated water is subjected to an oxidation treatment, and organic matter remaining in the 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 30.

[0029] In the water treatment method and water treatment device according to this embodiment, a carrier for retaining microorganisms is used in each of the nitrification tank 10 (nitrification step), the denitrification tank 12 (denitrification step), and the oxidation tank 14 (oxidation step). Trace elements are added to each of the nitrification tank 10 (nitrification step) and the denitrification tank 12 (denitrification step). By adding trace elements to each of the nitrification tank 10 (nitrification step) and the denitrification tank 12 (denitrification step), it is possible to stabilize the treatment performance in the denitrification step in water treatment in which the carrier for retaining microorganisms is used to perform nitrification, denitrification, and oxidation treatments on water to be treated that contains ammonia nitrogen.

[0030] The reason why the treatment performance in the denitrification treatment can be stabilized by adding trace elements to both the nitrification tank 10 (nitrification step) and the denitrification tank 12 (denitrification step) is believed to be as follows.

[0031] 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)

[0032] In the nitrification tank 10, oxygen is required to oxidize ammonia nitrogen to nitrite or nitrate. If all trace elements necessary for nitrifying bacteria (ammonia oxidizing bacteria, nitrite oxidizing bacteria) and denitrifying bacteria are added to the water to be treated that flows into the nitrification tank 10, it is expected that some of the added trace elements will be oxidized in the nitrification tank 10 and will be in a form that is difficult for the denitrifying bacteria to utilize in the downstream denitrification tank 12. As a result, it is thought that the treatment performance and stability in the denitrification tank 12 will decrease.

[0033] In contrast, by adding trace elements to both the nitrification tank 10 and the denitrification tank 12, for example by adding a portion of the trace elements to the denitrification tank 12 without changing the total amount of trace elements added, each element of the trace elements will be utilized by denitrifying bacteria in the subsequent denitrification tank 12 without going through the oxidation process in the nitrification tank 10, and it is believed that the treatment performance of the denitrification tank 12 will be improved.

[0034] "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).

[0035] As the trace elements, salts containing each element may be added as powder to the nitrification tank 10 and the denitrification tank 12, respectively. However, if there are multiple elements that are in short supply, the number of chemicals increases accordingly, which may make handling and inventory management complicated. On the other hand, it is better in terms of handling and installation space to mix and dissolve multiple salts containing each element in water, etc., and supply them as a trace element solution with an acidic pH 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, etc., or several lineups with different combinations may be prepared and determined according to the properties of the water to be treated. The same trace element or trace element solution may be added as the first trace element and the second trace element, or different trace elements or trace element solutions may be added. The content of trace elements in the water to be treated can be measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0036] Hereinafter, unless otherwise specified, the term "trace element solution" refers to a liquid in which all or some of the types of trace elements shown above are dissolved in a solvent such as water.

[0037] In the water treatment method and water treatment device according to this embodiment, phosphorus (P) may be added to both the nitrification tank 10 (nitrification step) and the denitrification tank 12 (denitrification step). An example of a water treatment device of this type is shown in FIG.

[0038] In the water treatment device 3 of Figure 2, in addition to the configuration of the water treatment device 1 of Figure 1, a first phosphorus supply pipe 38 is connected to the treated water pipe 24, and a second phosphorus supply pipe 40 is connected to the nitrification treatment water pipe 26.

[0039] In the water treatment device 3, the water to be treated that contains ammonia nitrogen is sent to the nitrification tank 10 through the water to be treated pipe 24. Here, in the water to be treated pipe 24, a first trace element is supplied to the water to be treated through a first trace element supply pipe 32 (first trace element supply step). Also, in the water to be treated pipe 24, a first phosphorus is supplied to the water to be treated through a first phosphorus supply pipe 38 (first phosphorus supply step). In the nitrification tank 10, an oxygen-containing gas is supplied by the aeration device 16, and under aerobic conditions, the water to be treated is subjected to nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 42, and ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (nitrification step).

[0040] The nitrification-treated water that has been subjected to the nitrification treatment is sent to the denitrification tank 12 through the nitrification-treated water pipe 26. Here, in the nitrification-treated water pipe 26, a second trace element is supplied to the nitrification-treated water through the second trace element supply pipe 36 (second trace element supply step). In addition, in the nitrification-treated water pipe 26, a hydrogen donor is supplied to the nitrification-treated water through the hydrogen donor supply pipe 34 (hydrogen donor supply step). In addition, in the nitrification-treated water pipe 26, a second phosphorus is supplied to the nitrification-treated water through the second phosphorus supply pipe 40 (second phosphorus supply step). In the denitrification tank 12, the nitrification-treated water is denitrified by denitrifying bacteria (heterotrophic bacteria) in the presence of a hydrogen donor, and nitrite ions or nitrate ions are reduced to nitrogen gas (denitrification step).

[0041] The denitrification treated water that has been subjected to the denitrification treatment is sent to the oxidation tank 14 through the denitrification treated water pipe 28. In the oxidation tank 14, the denitrification treated water is subjected to an oxidation treatment, and organic matter remaining in the 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 30.

[0042] By adding phosphorus (P) to both the nitrification tank 10 (nitrification process) and the denitrification tank 12 (denitrification process), the risk of calcium phosphate precipitation in the nitrification tank 10 (nitrification process) can be reduced and the treatment performance in the denitrification tank 12 (denitrification process) can be stabilized, even when the water to be treated contains a high concentration of calcium, for example, 100 mg / L or more.

[0043] The reason why adding phosphorus (P) to both the nitrification tank 10 and the denitrification tank 12 reduces the risk of calcium phosphate precipitation in the nitrification tank 10 and stabilizes the treatment performance in the denitrification tank 12 is believed to be as follows.

[0044] Phosphorus is an essential nutrient for both nitrifying bacteria and denitrifying bacteria, but nitrifying bacteria are autotrophic bacteria and require only about one-tenth the amount of phosphorus required by heterotrophic denitrifying bacteria.

[0045] For example, in the case of treated water with a high calcium concentration, there is a risk of calcium phosphate precipitation in the nitrification tank 10, and there is a concern that inorganic matter such as precipitated calcium phosphate may accumulate in the organism retention carrier (carrier 42). If the amount of inorganic matter accumulated in the carrier increases, it may lead to a decrease in the fluidity of the carrier and a deterioration in treatment. Therefore, this risk is usually reduced by lowering the pH or keeping the pH within a specified range.

[0046] If all of the phosphorus required for the nitrification tank 10 and the denitrification tank 12 is added to the water to be treated flowing into the nitrification tank 10, there will be an increased risk of calcium phosphate precipitation and a corresponding shortage of phosphorus required by the denitrification bacteria. Therefore, it is desirable to increase the amount of phosphorus added to the denitrification tank 12.

[0047] Therefore, by adding the phosphorus required for the denitrifying bacteria in the denitrification tank 12 to the nitrification treatment water flowing into the denitrification tank 12 rather than to the water to be treated flowing into the nitrification tank 10, it is possible to reduce the risk of calcium phosphate precipitation in the nitrification tank 10 and contribute to stabilizing the treatment in the denitrification tank 12.

[0048] In the water treatment method and water treatment device according to this embodiment, the oxidized water may be circulated to the nitrification tank 10 (nitrification step). An example of a water treatment device of this type is shown in FIG.

[0049] In the water treatment device 5 of Figure 3, in addition to the configuration of the water treatment device 3 of Figure 2, a circulation pipe 46 branched off from the oxidized water pipe 30 is connected to the upstream side of the connection point of the first trace element supply pipe 32 and the connection point of the first phosphorus supply pipe 38 in the treated water pipe 24. The above is one example, and it is sufficient that the oxidized water is circulated to the nitrification tank 10.

[0050] In the water treatment device 5, the water to be treated that contains ammonia nitrogen is sent to the nitrification tank 10 through the water to be treated pipe 24. Here, in the water to be treated pipe 24, a first trace element is supplied to the water to be treated through a first trace element supply pipe 32 (first trace element supply step). Also, in the water to be treated pipe 24, a first phosphorus is supplied to the water to be treated through a first phosphorus supply pipe 38 (first phosphorus supply step). In the nitrification tank 10, an oxygen-containing gas is supplied by the aeration device 16, and under aerobic conditions, the water to be treated is subjected to nitrification treatment by nitrifying bacteria (autotrophic bacteria) such as ammonia oxidizing bacteria and nitrite oxidizing bacteria held in the carrier 42, and ammonium ions are nitrified to nitrite ions (nitrite nitrogen) and then to nitrate ions (nitrate nitrogen) (nitrification step).

[0051] The nitrification-treated water that has been subjected to the nitrification treatment is sent to the denitrification tank 12 through the nitrification-treated water pipe 26. Here, in the nitrification-treated water pipe 26, a second trace element is supplied to the nitrification-treated water through the second trace element supply pipe 36 (second trace element supply step). In addition, in the nitrification-treated water pipe 26, a hydrogen donor is supplied to the nitrification-treated water through the hydrogen donor supply pipe 34 (hydrogen donor supply step). In addition, in the nitrification-treated water pipe 26, a second phosphorus is supplied to the nitrification-treated water through the second phosphorus supply pipe 40 (second phosphorus supply step). In the denitrification tank 12, the nitrification-treated water is denitrified by denitrifying bacteria (heterotrophic bacteria) in the presence of a hydrogen donor, and nitrite ions or nitrate ions are reduced to nitrogen gas (denitrification step).

[0052] The denitrification treated water that has been subjected to the denitrification treatment is sent to the oxidation tank 14 through the denitrification treated water pipe 28. In the oxidation tank 14, the denitrification treated water is subjected to an oxidation treatment, and organic matter remaining in the denitrification process is oxidized (oxidation process). The oxidation treated water that has been subjected to the oxidation treatment is discharged as treated water through the oxidation treated water pipe 30. At least a portion of the oxidation treated water is circulated to the nitrification tank 10 (nitrification process) through the circulation pipe 46 and the treated water pipe 24 (circulation process).

[0053] By circulating the oxidized water to the nitrification tank 10 (nitrification step), the nitrification tank 10 (nitrification step) can be accelerated and the treatment performance can be stabilized.

[0054] The reason why circulating the oxidized water to the nitrification tank 10 (nitrification step) can speed up the nitrification tank 10 (nitrification step) and stabilize the treatment performance is believed to be as follows.

[0055] 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 3In 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 / (m 3 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.

[0056] On the other hand, since the concentration of inorganic carbon in the oxidation tank 14 (oxidation process) increases due to the treatment of organic matter remaining in the denitrification tank 12 (denitrification process) or due to the inorganic carbon remaining from the denitrification tank 12 (denitrification process), by circulating the oxidized water to the nitrification tank 10 (nitrification process), inorganic carbon can be supplied to the nitrification tank 10 (nitrification process), which leads to the speedup and stabilization of the nitrification tank 10 (nitrification process). In addition, it also supplies the alkalinity remaining in the oxidized water, which leads to a reduction in the amount of alkali used to adjust the pH in the nitrification tank 10 (nitrification process).

[0057] 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.

[0058] 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.

[0059] When the water to be treated contains calcium, the concentration of calcium in the water to be treated is, for example, 100 mg / L or more, and preferably in the range of 100 to 500 mg / L.

[0060] When phosphorus (P) and trace elements contained in the water to be treated and the nitrification treatment water are insufficient, phosphorus (P) and trace elements may be added externally. Phosphorus (P) may be supplied, for example, as phosphoric acid, to the water to be treated and the nitrification treatment water through the first phosphorus supply pipe 38 and the second phosphorus supply pipe 40, respectively, and the phosphorus (P) may be mixed with the water to be treated, thereby supplying the system. Trace elements may be supplied, for example, as a trace element solution, to the water to be treated and the nitrification treatment water through the first trace element supply pipe 32 and the second trace element supply pipe 36, respectively, and the trace elements may be mixed with the water to be treated, thereby supplying the system.

[0061] The concentrations of trace elements in the water to be treated, i.e., the concentrations of each trace element required for nitrification / denitrification treatment, vary depending on the ammonia nitrogen concentration in the water to be treated, but the required concentrations as a guide are as follows: The sulfur (S) concentration may be, for example, 0.1 to 10 mg / L, the potassium (K) concentration may be, for example, 0.1 to 10 mg / L, the sodium (Na) concentration may be, for example, 0.1 to 10 mg / L, the calcium (Ca) concentration may be, for example, 0.02 to 2 mg / L, the magnesium (Mg) concentration may be, for example, 0.05 to 5 mg / L, the iron (Fe) concentration may be, for example, 0.05 to 5 mg / L, and the manganese (Mg) concentration may be, for example, 0.05 to 5 mg / L. The concentration of Mn may be, for example, 0.01 to 1 mg / L, the concentration of cobalt (Co) may be, for example, 0.005 to 0.5 mg / L, the concentration of nickel (Ni) may be, for example, 0.005 to 0.5 mg / L, the concentration of copper (Cu) may be, for example, 0.01 to 1 mg / L, the concentration of zinc (Zn) may be, for example, 0.01 to 1 mg / L, and the concentration of molybdenum (Mo) may be, for example, 0.01 to 1 mg / L. If the concentration of each trace element in the water to be treated is less than the lower limit, the treatment performance may decrease, and if the concentration exceeds the upper limit, depending on the type of trace element, the treatment may be inhibited.

[0062] The distribution ratio of the trace elements added may be, for example, nitrification tank 10 (nitrification process):denitrification tank 12 (denitrification process)=10:1 to 1:10, preferably 1:2 to 1:5, relative to the total amount of trace elements added calculated from the required concentrations of the trace elements shown above. If the distribution ratio of the trace elements added in the nitrification tank 10 (nitrification process) is less than 1:10, the nitrification treatment performance may decrease, whereas if it is more than 10:1, the denitrification treatment performance may decrease.

[0063] The phosphorus (P) concentration in the water to be treated, i.e., the concentration of phosphorus (P) required for nitrification-denitrification treatment, 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.

[0064] The phosphorus addition distribution ratio may be, for example, nitrification tank 10 (nitrification process):denitrification tank 12 (denitrification process)=10:1 to 1:10 relative to the total phosphorus addition amount shown above, and is preferably 1:5 to 1:10. If the phosphorus addition distribution ratio in the nitrification tank 10 (nitrification process) is less than 1:10, the nitrification treatment performance may decrease, whereas if it is more than 10:1, the denitrification treatment performance may decrease.

[0065] Phosphorus (P) and trace elements may be added to the treated water piping 24 through which the treated water flows into the nitrification tank 10, and to the nitrification treated water piping 26 through which the nitrification treated water flows into the denitrification tank 12, or to a separate tank for temporarily storing the treated water and a separate tank for temporarily storing the nitrification treated water, or to the nitrification tank 10 and the denitrification tank 12.

[0066] When circulating the oxidized water, the amount of the oxidized water circulated to the nitrification tank 10 (nitrification step) in the circulation step 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 preferably in the range of 20 to 50% by volume.

[0067] The water temperature in the nitrification tank 10 may be maintained in the range of, for example, 15 to 40° C. The pH in the nitrification tank 10 may be maintained in the range of, for example, 6.0 to 8.5. If the pH in the nitrification tank 10 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.

[0068] The water temperature in the denitrification tank 12 may be maintained in the range of, for example, 15 to 40° C. The pH in the denitrification tank 12 may be maintained in the range of, for example, 6.0 to 8.5. If the pH in the nitrification tank 10 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.

[0069] 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.

[0070] 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 amount of dissolved oxygen flowing into the denitrification tank. Therefore, the amount of methanol required to be added is about 2.5 times the amount of nitrate nitrogen and about 1.5 times the amount of nitrite nitrogen.

[0071] The TN (Total Nitrogen) volume load in the denitrification tank 12 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.

[0072] The oxidation treatment in the oxidation tank 14 is an aerobic treatment.

[0073] The water temperature in the oxidation tank 14 may be maintained in the range of, for example, 15 to 40° C. The pH in the oxidation tank 14 may be maintained in the range of, for example, 6.0 to 8.5. If the pH in the oxidation tank 14 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.

[0074] In the nitrification tank 10, denitrification tank 12 and oxidation tank 14, carriers are introduced and the bacteria are retained on the floating carriers, thereby increasing the efficiency of contact between the bacteria and at least one of ammoniacal nitrogen, nitrate nitrogen and nitrite nitrogen, and organic matter, enabling high-load operation and facilitating the management of sludge containing bacteria.

[0075] 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.

[0076] 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 denitrification tank 12 (denitrification step), by using a gel-like carrier as a fluidized carrier, floating of the carrier due to nitrogen gas is suppressed, and the fluidity of the carrier due to stirring is also high, 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.

[0077] The shape of the carrier is not particularly limited, but is preferably a sphere, a cube, a rectangle, a cylinder, or the like, about 1 to 10 mm in size. Particularly in the denitrification tank 12 (denitrification step), a gel-like carrier having a sphere or cylinder of about 3 to 8 mm in size 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 has a true specific gravity of 1.1 or more, or an apparent specific gravity of 1.01 or more.

[0078] As an agitation method in the denitrification tank 12 (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.

[0079] The amount of carriers added to the nitrification tank 10, denitrification tank 12, and oxidation tank 14 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, while if it exceeds 70%, the carriers become difficult to flow, and during long-term operation, the treated water may short-pass due to clogging by sludge, resulting in a deterioration in treated water quality.

[0080] 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

[0081] 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.

[0082] <Example 1 and Comparative Example 1> [Confirmation of trace element distribution effect in denitrification tank] Using the water treatment device shown in FIG. 3, a continuous water flow experiment was carried out on the water to be treated shown below.

[0083] (Composition of treated water) The simulated wastewater was prepared by adding ammonium chloride to pure water in an amount equivalent to an ammonia nitrogen concentration of 150 mg / L and calcium chloride to a calcium concentration of 300 mg / L.

[0084] (Phosphorus Addition) Phosphate was added to the water to be treated and the nitrification treated water so that the amount was 0.3 mg-P / L in the nitrification tank and 3.0 mg-P / L in the denitrification tank.

[0085] (Addition of trace elements) A trace element solution was used in which sulfur (S), potassium (K), magnesium (Mg), iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and molybdenum (Mo) were dissolved in pure water. The amounts of trace elements required for nitrification and denitrification in the trace element solution used this time were determined in advance in independent experimental systems for the nitrification tank and denitrification tank. Of the aforementioned "trace elements," sodium (Na) is supplied by using a sodium hydroxide solution to adjust the pH of the nitrification tank, and calcium (Ca) is included in the simulated wastewater, so it was not included in the trace element solution used this time.

[0086] In the initial stage of the continuous water flow experiment, the total amount of trace element solution necessary for nitrification and denitrification, which was confirmed in advance, was added to the water to be treated (simulated wastewater) (Comparative Example 1), and was distributed to the denitrification tank from the middle of the experiment (Example 1). During the period when the solution was distributed to the denitrification tank, the amount of trace element solution added to the water to be treated (simulated wastewater) was subtracted from the amount required for addition.

[0087] (nitrification tank) Tank volume: 3L Microorganism retention carrier: Hydrophobic polyurethane sponge carrier, aeration and agitation Carrier filling rate: 30% (carrier bulk volume / tank volume) Tank water temperature: 20℃ Tank pH: 7.5 (adjusted with sodium hydroxide solution)

[0088] (Denitrification tank) Tank volume: 1L Microorganism retention carrier: Polyvinyl alcohol gel carrier, stirred with a stirring device Carrier filling rate: 20% (carrier bulk volume / tank volume) Tank water temperature: 20℃ Tank pH: 7.0 (adjusted with hydrochloric acid) Hydrogen donor: Methanol was added in an amount equivalent to 100 mg / L in terms of TOC concentration.

[0089] (Oxidation tank) Tank volume: 1L Microorganism retention carrier: Hydrophobic polyurethane sponge carrier, agitated by aeration Carrier filling rate: 20% (carrier bulk volume / tank volume) Tank water temperature: 20℃ Tank pH: 7.5 (adjusted with hydrochloric acid) Amount of oxidized water circulated: 50% by volume of the oxidized water is circulated to the nitrification tank.

[0090] The above phosphorus and methanol concentrations are determined based on the amount of water passed, taking into account the amount of circulating oxidized water.

[0091] Water quality was measured after filtration through a 0.45 μm filter.

[0092] [Experimental Results] FIG. 4 shows the TN (Total Nitrogen) volume load in the denitrification tank and the TN concentration of the treated water in the denitrification tank from 210 to 280 days after the start of operation.

[0093] From day 210 to day 251, the total amount of the trace element solution necessary for nitrification and denitrification was added to the water to be treated (simulated wastewater) (Comparative Example 1), and distribution of the trace element solution to the denitrification tank started from day 252 onwards (Example 1). The distribution ratio to the denitrification tank was set to 1:2 (water to be treated: denitrification tank) from day 252 to day 268, and 1:5 (water to be treated: denitrification tank) thereafter.

[0094] During this experimental period, the TN concentration of the treated water from the nitrification tank was entirely nitrate nitrogen, and no residual ammonia nitrogen was observed in the nitrification tank.

[0095] The TN volumetric load of the denitrification tank was calculated from the TN concentration of the nitrification treated water, the inflow volume of the nitrification treated water into the denitrification tank, and the tank volume of the denitrification tank.

[0096] During the period of Comparative Example 1 in which trace elements were not distributed to the denitrification tank, the TN volumetric load was 1.5 to 2.0 kgN / (m 3 The plant was operated on a 24-hour cycle (days), and the TN concentration of the treated water was as high as 20 mg / L. Nitrogen remained in the treated water, and the treated water alternated between good and bad conditions, making the treatment unstable.

[0097] On the other hand, in the period of Example 1 from 252 days after the trace element solution was distributed to the denitrification tank, the treated water TN concentration remained below 4 mg / L, and nitrogen was treated well despite the different distribution ratio of the trace element solution (treated water: denitrification tank).

[0098] Thus, in Example 1, in a water treatment process in which nitrification, denitrification, and oxidation processes are performed on the treated water containing ammonia nitrogen using a carrier that retains microorganisms, the treatment performance in the denitrification process was stabilized. [Explanation of symbols]

[0099] 1, 3, 5 water treatment device, 10 nitrification tank, 12 denitrification tank, 14 oxidation tank, 16 aeration device, 18, 22 screen, 20 agitator, 24 treated water piping, 26 nitrification treated water piping, 28 denitrification treated water piping, 30 oxidation treated water piping, 32 first trace element supply piping, 34 hydrogen donor supply piping, 36 second trace element supply piping, 38 first phosphorus supply piping, 40 second phosphorus supply piping, 42, 44 carrier, 46 circulation piping.

Claims

1. a nitrification tank for performing nitrification treatment on the treated water containing ammonia nitrogen using autotrophic bacteria; a denitrification tank for performing a denitrification treatment on the nitrification-treated water in the presence of a hydrogen donor; an oxidation tank for performing oxidation treatment on the denitrification treatment water; Equipped with The nitrification tank, the denitrification tank, and the oxidation tank are each filled with a carrier for retaining microorganisms; A water treatment device comprising: a nitrification tank and a denitrification tank, each of which is configured to add trace elements.

2. The water treatment device according to claim 1, 2. A water treatment apparatus comprising: said water to be treated containing 100 mg / L or more of calcium; and adding phosphorus to each of said nitrification tank and said denitrification tank.

3. The water treatment device according to claim 1 or 2, The water treatment device is characterized in that the oxidized water that has been subjected to the oxidation treatment is circulated to the nitrification tank.

4. a nitrification step in which the treated water containing ammonia nitrogen is nitrified by autotrophic bacteria; a denitrification step of performing a denitrification treatment on the nitrification-treated water in the presence of a hydrogen donor; an oxidation step of performing an oxidation treatment on the denitrification treated water; Including, A carrier for retaining microorganisms is used in each of the nitrification step, the denitrification step, and the oxidation step, A water treatment method comprising adding trace elements to both the nitrification tank and the denitrification tank.

5. The water treatment method according to claim 4, A water treatment method, characterized in that the water to be treated contains 100 mg / L or more of calcium, and phosphorus is added in both the nitrification step and the denitrification step.

6. The water treatment method according to claim 4 or 5, The water treatment method according to the present invention is characterized in that the oxidized water is circulated to the nitrification step.

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