Water treatment device and water treatment method

Abstract

The present invention provides a water treatment device (1) characterized by comprising: a first biological treatment tank (10) into which water to be treated containing ammoniacal nitrogen is continuously introduced and which biologically treats the water to be treated by autotrophic bacteria; a second biological treatment tank (12) into which the first treated water treated in the first biological treatment tank (10) continuously flows, and which biologically treats the first treated water by autotrophic bacteria; a bypass line (22) that bypasses and flows a part of the water to be treated into the second biological treatment tank (12) without passing through the first biological treatment tank (10); an ammoniacal nitrogen concentration meter (16) for measuring the ammoniacal nitrogen concentration of the second treated water treated in the second biological treatment tank (12); and a control unit (14) that controls the inflow amount of the water to be treated flowing through the bypass line (22) on the basis of the ammonia nitrogen concentration measured by the ammonia nitrogen concentration meter (16).

Description

Technical Field

[0001] The present invention relates to a water treatment device and a water treatment method for treating water containing ammonia nitrogen. Background Art

[0002] Conventionally, ammonia, nitric acid, and the like are used in semiconductor manufacturing processes such as integrated circuits (ICs), and wastewater containing nitrogen (ammonia, nitric acid), and the like is discharged as waste liquid from the process.

[0003] Biological denitrification is generally used to remove nitrogen from wastewater. This biological denitrification is a method of removing nitrogen by utilizing nitric acid respiration of denitrifying bacteria, which are facultative anaerobic bacteria, in an anaerobic state. In this biological denitrification, for example, wastewater is first subjected to nitrification treatment to convert ammonia nitrogen in the wastewater into nitrite nitrogen or nitrate nitrogen, and then a hydrogen donor such as methanol is added to convert the wastewater into an anaerobic state, thereby performing denitrification.

[0004] For nitrification of wastewater, for example, activated sludge method, biofilm method (e.g., fixed bed method, fluidized bed method), and granular method are used. Generally, in the activated sludge method, low load treatment (e.g., 0.1 to 0.3 kg-N / (m 3 ·d) In the biofilm method and particle method, high load treatment (e.g. 0.5 to 1.0 kg-N / (m 3 ·d)) (for example, refer to Patent Document 1).

[0005] Patent document 2 discloses the following technology: a unit is provided to measure the ammonia nitrogen concentration of nitrification-treated water in a nitrification tank, the measured ammonia nitrogen concentration is compared with a preset ammonia nitrogen concentration (1 to 10 mg / L), and when the measured value is below the set value, the nitrogen load of the nitrification tank is adjusted so that the measured value is above the set value.

[0006] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 4865211 Patent Document 2: Japanese Patent Application Laid-Open No. 08-126897 Summary of the invention

[0007] Technical problem to be solved by the invention An object of the present invention is to provide a water treatment device and a water treatment method which can stably obtain treated water with good water quality even if the concentration of water to be treated containing ammonia nitrogen fluctuates.

[0008] Technical solutions for solving technical problems A water treatment device according to one embodiment of the present invention is characterized in that it comprises: a first biological treatment tank, which allows treated water containing ammonia nitrogen to flow continuously, and at the same time, the treated water is biologically treated by autotrophic bacteria; a second biological treatment tank, which allows first treated water treated in the first biological treatment tank to flow continuously, and at the same time, the first treated water is biologically treated by autotrophic bacteria; a bypass line, which allows a part of the treated water to bypass and flow into the second biological treatment tank without passing through the first biological treatment tank; an ammonia nitrogen concentration measuring unit, which measures the ammonia nitrogen concentration of the second treated water treated in the second biological treatment tank; and a control unit, which controls the inflow of the treated water flowing in the bypass line based on the ammonia nitrogen concentration measured by the ammonia nitrogen concentration measuring unit.

[0009] In the water treatment apparatus, the control unit preferably controls the inflow rate of the water to be treated flowing through the bypass line so that the ammonia nitrogen concentration measured by the ammonia nitrogen concentration measuring unit is within a preset range.

[0010] In the water treatment device, the setting range is preferably 0.5 mg / L to 50 mg / L.

[0011] The water treatment device preferably includes a filtering unit for filtering the second treated water, and the ammonia nitrogen concentration measuring unit measures the ammonia nitrogen concentration of the filtered water filtered by the filtering unit.

[0012] Furthermore, a water treatment method according to one embodiment of the present invention is characterized in that it comprises the following steps: a first biological treatment step, in which treated water containing ammonia nitrogen is continuously flowed into a first biological treatment tank, and the treated water is biologically treated by autotrophic bacteria; a second biological treatment step, in which the first treated water treated in the first biological treatment tank is continuously flowed into a second biological treatment tank, and the first treated water is biologically treated by autotrophic bacteria; an inflow step, in which a portion of the treated water is bypassed and flows into the second biological treatment tank without passing through the first biological treatment tank; and an ammonia nitrogen concentration measuring step, in which the ammonia nitrogen concentration of the second treated water treated in the second biological treatment tank is measured, and in the inflow step, the inflow amount of the treated water flowing in the bypass is controlled based on the ammonia nitrogen concentration measured by the ammonia nitrogen concentration measuring step.

[0013] In the water treatment method, preferably, in the inflow step, the inflow rate of the water to be treated in the bypass inflow is controlled so that the ammonia nitrogen concentration measured in the ammonia nitrogen concentration measuring step is within a preset range.

[0014] In the water treatment method, the setting range is preferably 0.5 mg / L to 50 mg / L.

[0015] The water treatment method preferably includes a filtration step of filtering the second treated water, and in the ammonia nitrogen concentration measuring step, the ammonia nitrogen concentration of the filtered water after filtration in the filtration step is measured.

[0016] Effects of the Invention According to the present invention, it is possible to provide a water treatment apparatus and a water treatment method which can stably obtain treated water with good water quality even if the concentration of water to be treated containing ammonia nitrogen fluctuates. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram showing an example of the water treatment device according to the present embodiment.

[0018] Figure 2 It is a schematic structural diagram showing another example of the water treatment tank according to the present embodiment.

[0019] Figure 3 This is a graph showing daily changes in the bypass ratio of the treated water flowing to the second biological treatment tank relative to the flow rate of the treated water in the Example.

[0020] Figure 4 It is a graph showing the daily change in the ammonia nitrogen concentration of the second treated water obtained in the example and the comparative example. DETAILED DESCRIPTION

[0021] Hereinafter, an embodiment of the present invention will be described. This embodiment is an example for carrying out the present invention and does not limit the present invention.

[0022] Figure 1 It is a schematic structural diagram showing an example of the water treatment device according to the present embodiment. Figure 1 The water treatment apparatus 1 shown is an apparatus for biologically treating water to be treated containing ammonia nitrogen by biological treatment based on an activated sludge method, a biofilm method, a granular method, or the like. Figure 1 The water treatment device 1 shown in the figure comprises: a first biological treatment tank 10, a second biological treatment tank 12, a control device 14, an ammonia nitrogen concentration meter 16, a pump for treated water 18, an inflow line (20a, 20b), a bypass line 22, a treated water discharge line 24, and a flow control valve (26a, 26b). A diffuser 28 is provided at the bottom of the first biological treatment tank 10 and the second biological treatment tank 12. In addition, a screen 30 is provided in the first biological treatment tank 10 and the second biological treatment tank 12 so as to surround the treated water outlet.

[0023] An inflow pipeline 20a is connected to the inlet of the first biological treatment tank 10. In addition, a pump 18 for treated water and a flow control valve 26a are provided on the inflow pipeline 20a. One end of the inflow pipeline 20b is connected to the outlet of the first biological treatment tank 10, and the other end of the inflow pipeline 20b is connected to the inlet of the second biological treatment tank 12. One end of the bypass pipeline 22 is connected to the inflow pipeline 20a, and the other end of the bypass pipeline 22 is connected to the inflow pipeline 20b. In addition, a flow control valve 26b is provided on the bypass pipeline 22. A treated water discharge pipeline 24 is connected to the outlet of the second biological treatment tank 12. In addition, an ammonia nitrogen concentration meter 16 is provided on the treated water discharge pipeline 24.

[0024] The control device 14 is connected to the ammonia nitrogen concentration meter 16, the treated water pump 18, and the flow control valves 26a and 26b respectively through wired or wireless electrical connections. It should be noted that when a pH sensor, a water temperature sensor, etc. are provided in the first biological treatment tank 10 and the second biological treatment tank 12, the control device 14 can also be connected to these sensors, but the description is omitted in the figure.

[0025] The control device 14 is composed of, for example, a microcomputer and an electronic circuit, wherein the microcomputer is composed of a CPU for calculating a program, a ROM and a RAM for storing the program and the calculation results, and reads a given program stored in the ROM and the like and runs the program to control the operation of the raw water treatment device 1. For example, the operation of the treated water pump 18 is controlled, or the opening and closing degree of the flow control valves 26a and 26b are controlled.

[0026] The operation of the water treatment device 1 according to this embodiment will be described below.

[0027] The treated water pump 18 is operated by the control device 14, and the flow regulating valve 26a is opened to a predetermined opening, and the treated water containing ammonia nitrogen is supplied to the first biological treatment tank 10 through the inflow line 20a. At this time, the flow regulating valve 26b may be opened to a predetermined opening by the control device 14, so that a part of the treated water passing through the inflow line 20a bypasses the bypass line 22 and flows into the second biological treatment tank 12 (inflow process).

[0028] In the first biological treatment tank 10, oxygen-containing gas such as air is supplied through the diffuser 28, and the treated water is mixed with autotrophic bacteria. Then, in the first biological treatment tank 10, the treated water is biologically treated by autotrophic bacteria under aerobic conditions (first biological treatment process). Specifically, ammonia nitrogen in the treated water is nitrified by autotrophic bacteria to at least one of nitrite nitrogen and nitrate nitrogen. The treated water (first treated water) treated in the first biological treatment tank 10 is supplied to the second biological treatment tank 12 through the inflow pipeline 20b.

[0029] In the second biological treatment tank 12, oxygen-containing gas such as air is supplied through the diffuser 28, and the first treated water supplied from the inflow line 20b and the treated water flowing in from the bypass line 22 are mixed with autotrophic bacteria. In the second biological treatment tank 12, the first treated water and the treated water are biologically treated by autotrophic bacteria under aerobic conditions (second biological treatment process). The treated water (second treated water) treated in the second biological treatment tank 12 is discharged to the outside of the system through the treated water discharge line 24.

[0030] Here, the ammonia nitrogen concentration of the second treated water is measured by the ammonia nitrogen concentration meter 16 (ammonia nitrogen concentration measurement step). Then, the control device 14 controls the inflow of the treated water flowing in the bypass line 22 based on the ammonia nitrogen concentration in the second treated water measured by the ammonia nitrogen concentration meter 16. A specific example of the inflow control of the treated water is described below.

[0031] (Control Example 1) The ammonia nitrogen concentration of the second treated water flowing in the treated water discharge line 24 is detected by the ammonia nitrogen concentration meter 16, and the detected ammonia nitrogen concentration value is input to the control device 14. When the input ammonia nitrogen concentration is less than a predetermined value, the control device 14 controls the opening of the flow control valves 26a and 26b to increase the inflow of the treated water flowing in the bypass line 22. For example, when the treated water does not flow into the bypass line 22, the opening of the flow control valves 26a and 26b is controlled so that a predetermined inflow of the treated water flows into the bypass line 22. In addition, for example, when the treated water has already flowed into the bypass line 22, the opening of the flow control valves 26a and 26b is controlled so that an inflow of the treated water increased to a predetermined ratio relative to the inflow of the treated water at this time flows into the bypass line 22. In addition, when the input ammonia nitrogen concentration reaches a predetermined value or more, the control device 14 controls the opening of the flow control valves 26a and 26b to reduce the inflow of the treated water flowing in the bypass line 22. For example, the opening of the flow control valves 26a and 26b is controlled to stop the inflow of raw water into the bypass line 22. In addition, for example, the opening of the flow control valves 26a and 26b is controlled to allow the treated water to flow in the bypass line 22 with the inflow amount reduced to a predetermined ratio relative to the inflow amount of the treated water currently flowing in the bypass line 22. In order to perform stable treatment, the predetermined value is preferably set in the range of 0.6 times to 1 times the treatment target value.

[0032] Other examples of controlling the inflow of water to be treated will be described below.

[0033] (Control Example 2) The control device 14 controls the inflow of the treated water flowing in the bypass line 22 so that it is within the set range of the predetermined ammonia nitrogen concentration. For example, the set values ​​of the ammonia nitrogen concentration at two points, one large and one small, are predetermined (set value 1: the set value at the large end, set value 2: the set value at the small end). When the ammonia nitrogen concentration of the second treated water detected by the ammonia nitrogen concentration meter 16 is less than the set value at the small end (set value 2), the control device 14 controls the opening of the flow control valves 26a and 26b to increase the inflow of the treated water flowing in the bypass line 22. In addition, when the ammonia nitrogen concentration of the second treated water measured by the ammonia nitrogen concentration meter 16 is greater than the set value at the small end (set value 2) and less than the set value at the large end (set value 1), the control device 14 maintains the inflow of the treated water flowing in the bypass line 22. That is, the opening of the flow control valves 26a and 26b is maintained in the original state. In addition, when the ammonia nitrogen concentration in the second treated water measured by the ammonia nitrogen concentration meter 16 is equal to or higher than the set value (set value 1) at the larger end, the control device 14 controls the opening of the flow control valves 26a and 26b so as to reduce the inflow of the treated water flowing in the bypass line 22.

[0034] Considering the discharge water quality standard of the treated water discharged from the second biological treatment tank 12, the setting range (e.g., setting value 2 to setting value 1) is preferably set in the range of 0.5 mg / L to 50 mg / L, for example. Setting value 2 is preferably set in the range of 0.5 mg / L or more, and more preferably in the range of 0.5 mg / L to 5.0 mg / L. Setting value 1 is preferably set in the range of 50 mg / L or less, and more preferably in the range of 1.0 mg / L to 50 mg / L, for example.

[0035] The set value 1 can also be set based on the pH value in the second biological treatment tank 12. For example, a map (which can also be a relational expression, table, etc.) that specifies the relationship between the pH value and the set value is pre-stored in the control device 14. Then, the control device 14 applies the pH value in the second biological treatment tank 12 measured by the pH meter to the aforementioned map to calculate the set value. The control device 14 sets the calculated set value as the above-mentioned set value 1. By setting the set value 1 according to the pH value, the influence of free ammonia in the nitrification treatment can be suppressed, and the nitrification capacity can be improved. For example, in the case of pH 7 to 7.5 (water temperature 20°C), the set value 1 is preferably set to a range of 1.0 mg / L to 25 mg / L. In addition, since the water temperature is also affected by free ammonia, it is more preferable to set the set value 1 according to the pH and water temperature in the second biological treatment tank 12.

[0036] The amount of treated water flowing into the second biological treatment tank 12 by bypassing varies according to the measurement frequency of the ammonia nitrogen concentration of the second treated water, and its rate of change is preferably 0.1 to 20% relative to the overall treated water flow rate. In addition, considering the proliferation rate of microorganisms such as nitrifying bacteria, the amount of the increased portion of the inflow of treated water flowing into the second biological treatment tank 12 by bypassing is preferably set to less than 10%. When the measurement frequency of the ammonia nitrogen concentration of the second treated water is high, the above-mentioned rate of change is set to be small; when the measurement frequency is low, the above-mentioned rate of change is set to be large, thereby shortening the time required to achieve the target removal performance.

[0037] By carrying out biological treatment in two stages in series of the first biological treatment tank and the second biological treatment tank, the first stage is high-load roughing, that is, it is operated under the condition of high ammonia nitrogen concentration in the tank, and becomes a tank resistant to concentration changes in the tank. However, when the load of the treated water is reduced and the treatment is completed in the first stage biological treatment tank, the second stage biological treatment tank becomes no-load, and the treatment activity of the second stage biological treatment tank is reduced. Therefore, in the biological treatment tank of the second stage, it is necessary to make the ammonia nitrogen load more than a certain value, but if the ammonia nitrogen load of the biological treatment tank of the second stage is too high, the water quality of the treated water will deteriorate. Therefore, in the present embodiment, as described above, based on the ammonia nitrogen concentration of the treated water after treatment in the biological treatment tank of the second stage, the inflow of the treated water bypassed to the biological treatment tank of the second stage is controlled, thereby, even if the concentration of the treated water containing ammonia nitrogen changes, the load of the biological treatment tank of the second stage can be stabilized, and therefore, the reduction of the treatment activity caused by no load and the deterioration of the treated water quality caused by high load can be suppressed. That is, even if the concentration of the water to be treated containing ammonia nitrogen fluctuates, treated water with good water quality can be stably obtained.

[0038] exist Figure 2 In the water treatment device 2 shown in FIG. Figure 1 The same components of the water treatment device 1 shown are denoted by the same reference numerals, and the description thereof is omitted. Figure 2 The water treatment device 2 shown includes a filtering device 32 , and carriers 34 filled in the first biological treatment tank 10 and the second biological treatment tank 12 .

[0039] A part of the second treated water flowing in the treated water discharge pipeline 24 is supplied to the filtration device 32 through a branch pipeline 36a connected to the treated water discharge pipeline 24, and solid-liquid separation is performed by the filtration device 32. The filtered water obtained by the filtration device 32 is discharged to the outside of the system from the filtered water discharge pipeline 36b. At this time, the ammonia nitrogen concentration in the filtered water flowing in the filtered water discharge pipeline 36b is measured by an ammonia nitrogen concentration meter 16 provided in the filtered water discharge pipeline 36b. And as described above, based on the measured ammonia nitrogen concentration, the inflow rate of the water to be treated flowing in the bypass pipeline 22 is controlled.

[0040] By measuring the ammonia nitrogen concentration of the filtered water obtained by solid-liquid separation by the filtration device 32, the ammonia nitrogen concentration can be measured with high precision until it reaches a low concentration. In addition, since the filtered water obtained by solid-liquid separation by the filtration device 32 removes SS components and the like, the maintenance frequency of the ammonia nitrogen concentration meter 16 can be suppressed.

[0041] The ammonia nitrogen concentration meter 16 is not particularly limited as long as it can perform on-line measurement, and a coulometric titration type ammonia nitrogen analyzer is preferably used. The coulometric titration type ammonia nitrogen analyzer is based on the measurement of coulometric titration applied with coulometry. In principle, a calibration curve does not need to be made, and bromine having high selectivity and reactivity to ammonia can be used as a titrant. In addition, it has advantages such as the electrode part is not easily contaminated and cleaning with acid is relatively easy. Therefore, by using a coulometric titration type ammonia nitrogen analyzer, the man-hours for maintenance can be reduced. The measurement frequency of the ammonia nitrogen concentration meter 16 can be set arbitrarily, and it is preferably measured about once every 15 minutes.

[0042] The first biological treatment tank 10 and the second biological treatment tank 12 are not limited to only performing nitrification, and nitrification denitrification can also be performed simultaneously. There is no particular limitation on the form of the first biological treatment tank 10 and the second biological treatment tank 12, but from the viewpoint of maintaining as many nitrifying bacteria as possible in the tank and not having to provide a sedimentation tank, etc., a biofilm method is preferably used. In the biofilm method, for example, nitrifying bacteria attached to the carrier 34 and nitrifying bacteria floating in a large volume of water can be used for nitrification treatment and the like.

[0043] The carrier 34 is not particularly limited as long as it is a conventionally known carrier that can be used under aerobic conditions. As the carrier 34, for example, a plastic carrier, a sponge-like carrier, a gel-like carrier, etc. can be cited, but a sponge-like carrier with a good balance between cost and durability is preferably used.

[0044] Nutrient salts may be added to the first biological treatment tank 10 and the second biological treatment tank 12 from the viewpoint of culturing microorganisms, etc. Nutrient salts include essential nutrients such as nitrogen (N) and phosphorus (P), and 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).

[0045] From the viewpoint of culturing microorganisms, the pH in the first biological treatment tank 10 and the second biological treatment tank 12 is preferably adjusted to a pH range of, for example, 6 to 8, and more preferably adjusted to a pH range of 6.8 to 7.2 to suppress the inhibition of free ammonia.

[0046] The biological treatment in the first biological treatment tank 10 and the second biological treatment tank 12 is preferably performed under aerobic conditions, and the dissolved oxygen concentration in the first biological treatment tank 10 and the second biological treatment tank 12 is, for example, 0.5 mg / L or more, preferably 1 mg / L or more.

[0047] The water temperature of the first biological treatment tank 10 and the second biological treatment tank 12 is preferably maintained in the range of 15 to 40°C, for example.

[0048] The treated water as the treatment object may be, for example, wastewater containing ammonia nitrogen discharged in a semiconductor manufacturing process, etc. It should be noted that the water treatment method and water treatment device 1 according to the present embodiment can be well applied when the treated water contains calcium in a range of 100 mg / L or more, preferably 100 to 1000 mg / L.

[0049] Example Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[0050] <Example> use Figure 2 The water treatment device shown in the figure was subjected to a continuous water flow test under the following conditions. It should be noted that an acclimatization step was performed before the continuous water flow test was performed. Specifically, only the treated water was passed into the first biological treatment tank, and the ammonia nitrogen load was set to 0.6 kgN / (m 3 ·d) after which the first biological treatment and the second biological treatment were started. When the total ammonia nitrogen load reached 0.8 kgN / (m 3 The acclimatization step is completed in stage d), and then the verification of the continuous water flow test is carried out. Hereinafter, when referred to as a "biological treatment tank", it refers to both the first biological treatment tank and the second biological treatment tank.

[0051] [Test conditions] pH in biological treatment tank: 7.0-7.5 (adjusted with sodium hydroxide) Biological treatment tank volume: 2L Carrier: Sponge carrier made of hydrophobic polyurethane Carrier filling rate: 30% of the biological treatment tank (loose capacity / tank capacity) Temperature of treated water: 20℃ Ammonia nitrogen concentration in treated water: 25, 50 mg / L The composition of the treated water is as follows: ammonium chloride is added to the well water to reach the above-mentioned ammonium nitrogen concentration, and a solution containing sodium carbonate, phosphoric acid and trace elements is also added.

[0052] Ammonia nitrogen concentration meter: Coulometric titration ammonia nitrogen meter (manufactured by Central Kagaku Co., Ltd.) Treated water flow rate: fixed at 64L / d Overall ammonia nitrogen volume load: 0.4~0.8kgN / (m 3 d) ※ The total ammonia nitrogen volume load is calculated as follows: Total ammonia nitrogen volume load = ammonia nitrogen concentration in the treated water × treated water flow rate ÷ total tank volume of the first biological treatment tank and the second biological treatment tank In the continuous water flow test, after operating at an ammonia nitrogen concentration of 50 mg / L for 12 days, the ammonia nitrogen concentration of the treated water was changed to 25 mg / L for 3 days, and then the ammonia nitrogen concentration of the treated water was restored to 50 mg / L for operation. The bypass ratio of the treated water flowing to the second biological treatment tank relative to the treated water flow rate was set to 10% on the first day and 20% on the second day, so that the treated water bypassed and flowed into the second biological treatment tank. Then, starting from the third day, the ammonia nitrogen concentration of the second treated water was measured every 60 minutes using an ammonia nitrogen concentration meter, and the inflow of the treated water bypassing the second biological treatment tank was controlled so that the measured ammonia nitrogen concentration of the second treated water fell within the set ammonia nitrogen concentration range. Specifically, when the ammonia nitrogen concentration of the second treated water is less than 1.0 mg / L, the inflow of treated water bypassing into the second biological treatment tank is increased; when the ammonia nitrogen concentration of the second treated water is greater than 1.0 mg / L and less than 1.5 mg / L, the inflow of treated water bypassing into the second biological treatment tank is maintained; when the ammonia nitrogen concentration of the second treated water is greater than 1.5 mg / L, the inflow of treated water bypassing into the second biological treatment tank is reduced.

[0053] <Comparative Example> A continuous water flow test was conducted in the same manner as in Example except that the water to be treated was not bypassed and flowed into the second biological treatment tank.

[0054] Figure 3 The figure shows the daily change in the bypass ratio of the treated water to the second biological treatment tank relative to the treated water flow rate in the embodiment. Figure 4 The following table shows the daily changes in the ammonia nitrogen concentration of the second treated water obtained in the examples and comparative examples. Figure 3 The value of the bypass ratio of the treated water flowing to the second biological treatment tank plotted in the figure is the average value of five measurements per day. Figure 4 The ammonia nitrogen concentration of the second treated water plotted in the figure is the average of the values ​​measured by the ammonia nitrogen concentration meter for one day. In the comparative example, when the ammonia nitrogen concentration of the treated water is changed to 25 mg / L, Figure 4 As shown, the ammonia nitrogen concentration in the second treated water reached 0.1 mg / L, and very good water quality was obtained. However, after the ammonia nitrogen concentration of the treated water was restored to 50 mg / L, the ammonia nitrogen concentration in the second treated water deteriorated to 5.3 mg / L. Then, it took 3 days for the ammonia nitrogen concentration in the second treated water to reach 2 mg / L (target water quality). On the other hand, in the embodiment, when the ammonia nitrogen concentration in the treated water was changed to 25 mg / L, the ammonia nitrogen concentration in the second treated water became 1.1 mg / L, and the bypass ratio of the treated water at this time increased from about 20% to 38%. In addition, after the ammonia nitrogen concentration in the treated water was restored to 50 mg / L, the ammonia nitrogen concentration in the second treated water was also below 2 mg / L (target water quality). As shown in the embodiment, in the two-stage treatment of the first biological treatment tank and the second biological treatment tank, by controlling the inflow of the treated water bypassed to the second biological treatment tank based on the ammonia nitrogen concentration in the treated water obtained from the second biological treatment tank, even if the ammonia nitrogen concentration of the treated water fluctuates, treated water with good water quality can be stably obtained.

[0055] Description of Reference Numerals 1, 2: water treatment device; 10: first biological treatment tank; 12: second biological treatment tank; 14: control device; 16: ammonia nitrogen concentration meter; 18: pump for treated water; 20a, 20b: inflow pipeline; 22: bypass pipeline; 24: treated water discharge pipeline; 26a, 26b: flow regulating valve; 28: air diffuser; 30: screen; 32: filter device; 34: carrier; 36a: branch pipeline; 36b: filtered water discharge pipeline.

Claims

1. A water treatment device, characterized in that: have: A first biological treatment tank, which allows the treated water containing ammonia nitrogen to flow continuously, and simultaneously biologically treats the treated water by autotrophic bacteria; a second biological treatment tank, which allows the first treated water treated in the first biological treatment tank to flow continuously, and simultaneously biologically treats the first treated water by autotrophic bacteria; a bypass line for allowing a portion of the treated water to bypass the first biological treatment tank and flow into the second biological treatment tank; an ammonia nitrogen concentration measuring unit for measuring the ammonia nitrogen concentration of the second treated water treated in the second biological treatment tank; and A control unit controls the inflow rate of the water to be treated flowing through the bypass line based on the ammonia nitrogen concentration measured by the ammonia nitrogen concentration measuring unit.

2. The water treatment device according to claim 1, wherein: The control unit controls the inflow rate of the water to be treated flowing through the bypass line so that the ammonia nitrogen concentration measured by the ammonia nitrogen concentration measuring unit is within a preset range.

3. The water treatment device according to claim 2, wherein: The setting range is 0.5 mg / L to 50 mg / L.

4. The water treatment device according to any one of claims 1 to 3, wherein: The water treatment device includes a filtering unit for filtering the second treated water. The ammonia nitrogen concentration measuring unit measures the ammonia nitrogen concentration of the filtered water filtered by the filtering unit.

5. A water treatment method, characterized in that: have: A first biological treatment step, wherein the treated water containing ammonia nitrogen is continuously flowed into a first biological treatment tank, and the treated water is biologically treated by autotrophic bacteria; a second biological treatment step, wherein the first treated water treated in the first biological treatment tank is continuously flowed into the second biological treatment tank, and the first treated water is biologically treated by autotrophic bacteria; an inflow step of causing a portion of the water to be treated to bypass the first biological treatment tank and flow into the second biological treatment tank; and an ammonia nitrogen concentration measuring step, wherein the ammonia nitrogen concentration of the second treated water treated in the second biological treatment tank is measured, In the inflow step, the inflow amount of the water to be treated which flows in through the bypass is controlled based on the ammonia nitrogen concentration measured in the ammonia nitrogen concentration measuring step.

6. The water treatment method according to claim 5, wherein: In the inflow step, the inflow rate of the water to be treated that flows in through the bypass is controlled so that the ammonia nitrogen concentration measured in the ammonia nitrogen concentration measuring step is within a preset range.

7. The water treatment method according to claim 6, wherein: The setting range is 0.5 mg / L to 50 mg / L.

8. The water treatment method according to any one of claims 5 to 7, wherein: The water treatment method comprises a filtering step of filtering the second treated water, In the ammonia nitrogen concentration measuring step, the ammonia nitrogen concentration of the filtered water after filtering in the filtering step is measured.

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