Water treatment device and water treatment method

Abstract

To provide a water treatment apparatus which reduces manpower required when starting up the apparatus and enables the apparatus to be started up automatically, in water treatment where treated water containing ammonia nitrogen is nitrated by biological treatment.SOLUTION: A water treatment apparatus 1 includes: a biological treatment tank 12 in which treated water containing ammonia nitrogen is nitrated by autotrophic bacteria; a pump 18 for treated water that supplies the treated water to the biological treatment tank 12; and an ammonia nitrogen concentration meter 16 that measures the ammonia nitrogen concentration in the treated water treated by the biological treatment tank 12; and a control unit 14 that controls the supply and suspension of the treated water by the pump 18 for treated water based on the ammonia nitrogen concentration measured by the ammonia nitrogen densitometer 16.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a water treatment device and a water treatment method for treating water to be treated that contains ammonia nitrogen. [Background technology]

[0002] Conventionally, hydrofluoric acid, ammonia, nitric acid, etc. are used in the manufacturing process of semiconductors such as integrated circuits (ICs), and wastewater containing fluorine (hydrofluoric acid), nitrogen (ammonia, nitric acid), etc. is discharged from these processes.

[0003] Fluorine in wastewater is generally removed physicochemically, for example, by adding calcium to form calcium fluoride. To fully remove fluorine from wastewater, it is desirable to add a significant amount of calcium ions. Generally, the target fluoride concentration in fluoride-removed water is about 10 mg / L or less. In this case, it is desirable to keep the residual calcium concentration in the fluoride-removed water at about 100 to 1000 mg / L.

[0004] Biological denitrification is commonly used to remove nitrogen. This method utilizes nitrate respiration in an anaerobic environment by denitrifying bacteria, which are facultative anaerobic bacteria. In this biological denitrification process, for example, wastewater is first nitrified to convert ammonia nitrogen into nitrite nitrogen or nitrate nitrogen, and then a hydrogen donor such as methanol is added to create an anaerobic environment for denitrification.

[0005] Fluorine and nitrogen in wastewater are removed by combining fluoride removal and nitrogen removal as described above. Since wastewater containing a large amount of fluorine has an adverse effect on biological treatment using bacteria, biological denitrification treatment is carried out after the fluorine in the wastewater is removed. Therefore, wastewater that is the target of biological denitrification treatment often contains a large amount of calcium (see, for example, Patent Document 1).

[0006] Nitrification treatment of wastewater can be carried out using, for example, the activated sludge method, the biofilm method (for example, the fixed bed method or the fluidized bed method), or the granular method. Generally, the activated sludge method is used for low-load treatment (for example, 0.1 to 0.3 kg-N / (m 3 ·d)) is used, and in the biofilm method and granular method, high load treatment (e.g., 0.5 to 1.0 kg-N / (m 3 d)) is carried out (see, for example, Patent Document 1).

[0007] When starting up such a nitrification treatment system, it is common to sample treated water from the biological treatment tank once or several times a day, measure the ammonia nitrogen concentration by manual analysis, and once it is determined that the ammonia nitrogen concentration has dropped sufficiently, apply a load to increase the nitrification activity. However, this method requires manual labor during the start-up period for analysis and load adjustment. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4865211 [Patent Document 2] Japanese Patent Application Publication No. 08-126897 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-036558 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present disclosure aims to provide a water treatment device and a water treatment method that can reduce the manpower required to start up the device and enable the device to be started up automatically in water treatment in which water to be treated containing ammonia nitrogen is nitrified by biological treatment. [Means for solving the problem]

[0010] A water treatment device according to one aspect of the present disclosure includes a biological treatment tank in which water to be treated containing ammonia nitrogen is nitrified by autotrophic bacteria, a water supply means for supplying the water to be treated to the biological treatment tank, and an ammonia nitrogen concentration measuring means for measuring the ammonia nitrogen concentration in the treated water treated in the biological treatment tank. a nutrient salt supplying means for supplying nutrients to the biological treatment tank; Controlling start and stop of supply of the untreated water by the untreated water supply means and controlling the amount of nutrient salts supplied by the nutrient salt supply means. and a control means for controlling the supply of the water to be treated when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or higher than a first threshold value, and for controlling the water to be treated when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or lower than a second threshold value after the supply of the water to be treated is stopped. and controlling the amount of nutrients supplied by the nutrient supply means based on the amount of ammonia nitrogen loaded in the biological treatment tank. It is characterized by:

[0011] A water treatment device according to one aspect of the present disclosure includes a biological treatment tank in which water to be treated containing ammonia nitrogen is nitrified by autotrophic bacteria, a water to be treated supply means for supplying the water to be treated to the biological treatment tank, an ammonia nitrogen concentration measuring means for measuring the ammonia nitrogen concentration in the treated water treated in the biological treatment tank, and a control means for controlling the supply and stop of the water to be treated by the water to be treated supply means, wherein the control means controls the water to be treated supply means to stop the supply of the water to be treated when the ammonia nitrogen concentration measured by the ammonia nitrogen concentration measuring means becomes equal to or greater than a first threshold, and controls the water to be treated supply means to resume the supply of the water to be treated when the ammonia nitrogen concentration measured by the ammonia nitrogen concentration measuring means becomes equal to or less than a second threshold after the stop. The first threshold value is set based on the pH in the biological treatment tank. A water treatment device characterized by:

[0012] In the water treatment device, the second threshold value is preferably less than 1 mg / L.

[0013] Furthermore, it is preferable that the water treatment device includes a filtration means for filtering the treated water treated in the biological treatment tank, and the ammoniacal nitrogen concentration measuring means measures the ammoniacal nitrogen concentration in the filtered water filtered by the filtration means.

[0015] In the water treatment device, the water to be treated preferably contains 100 mg / L or more of calcium.

[0017] Furthermore, a water treatment method according to one aspect of the present disclosure includes a biological treatment process in which water to be treated containing ammoniacal nitrogen is nitrified using autotrophic bacteria in a biological treatment tank; a water to be treated supply process in which the water to be treated is supplied to the biological treatment tank using a water to be treated supply means; an ammoniacal nitrogen concentration measurement process in which the ammoniacal nitrogen concentration in the treated water treated in the biological treatment tank is measured using an ammoniacal nitrogen concentration measurement means; and a control process in which the control means controls the water to be treated supply means to start and stop supplying the water to be treated, wherein in the control process, when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measurement means becomes equal to or greater than a first threshold value, the control means controls the water to be treated supply means to stop supplying the water to be treated, and when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measurement means becomes equal to or less than a second threshold value after the stoppage, the control means controls the water to be treated supply means to resume supplying the water to be treated.

[0018] Furthermore, a water treatment method according to one aspect of the present disclosure includes a biological treatment step of nitrifying water containing ammonia nitrogen in a biological treatment tank using autotrophic bacteria; a water-to-be-treated supply step of supplying the water-to-be-treated to the biological treatment tank using a water-to-be-treated supply means; and an ammonia nitrogen concentration measurement step of measuring the ammonia nitrogen concentration in the treated water treated in the biological treatment tank using an ammonia nitrogen concentration measurement means. a nutrient salt supplying step of supplying nutrients to the biological treatment tank by a nutrient salt supplying means; a control step of controlling start and stop of supply of the water to be treated by the water to be treated supply means by a control means; A, and a control step B of controlling the amount of nutrient salts supplied by the nutrient salt supply means and the control step AIn the case where the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or higher than a first threshold value, the control means controls the untreated water supply means to stop the supply of the untreated water, and when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or lower than a second threshold value after the stop, the control means controls the untreated water supply means to resume the supply of the untreated water. In the control step B, the control means controls the amount of nutrients supplied by the nutrient supply means based on the amount of ammonia nitrogen loaded in the biological treatment tank. A water treatment method comprising: [Effects of the Invention]

[0019] According to the present disclosure, in water treatment in which water to be treated containing ammonia nitrogen is nitrified by biological treatment, it is possible to provide a water treatment device and a water treatment method that can reduce the manpower required for starting up the device and automatically start up the device and restore nitrification activity. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic configuration diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Figure 2] 4 is a flowchart showing an example of a control flow by a control device. [Figure 3] 10 is a flowchart showing another example of a control flow by the control device. [Figure 4] FIG. 2 is a schematic configuration diagram showing another example of a water treatment device according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following describes an embodiment of the present disclosure. The embodiment is an example of implementing the present disclosure and does not limit the present disclosure.

[0022] Fig. 1 is a schematic diagram showing an example of a water treatment device according to the present embodiment. The water treatment device 1 shown in Fig. 1 is a device that performs nitrification treatment on water to be treated that contains ammonia nitrogen through biological treatment such as activated sludge, biofilm, or granule processes.

[0023] The water treatment device 1 shown in Figure 1 includes a water tank 10 to be treated, a biological treatment tank 12, a control device 14, an ammonia nitrogen concentration meter 16, a pump 18 for water to be treated, a pump 20 for an ammonia nitrogen source, pipes 21a, 21b, 21c, and 21d, a tank 22, and a pH meter 23. An aeration device 24 is installed at the bottom of the biological treatment tank 12. A screen 26 is installed in the biological treatment tank 12 to surround the treated water outlet. The ammonia nitrogen concentration meter 16 and the pH meter 23 are installed in the biological treatment tank 12. The ammonia nitrogen concentration meter 16 is used to measure the concentration of the treated water treated in the biological treatment tank 12. As shown in Figure 1, the ammonia nitrogen concentration meter 16 is preferably installed near the outlet of the biological treatment tank 12.

[0024] A pipe 21a is connected to the inlet of the water tank 10 to be treated. One end of a pipe 21b is connected to the outlet of the water tank 10 to be treated, and the other end of the pipe 21b is connected to the inlet of the biological treatment tank 12. A pump 18 for water to be treated is installed in the pipe 21b. A pipe 21c is connected to the outlet of the biological treatment tank 12. One end of a pipe 21d is connected to the water tank 10 to be treated, and the other end of the pipe 21d is connected to the tank 22. A pump 20 for an ammoniacal nitrogen source is installed in the pipe 21d. An ammonium salt or an ammonium salt solution or the like is stored in the tank 22 as an ammoniacal nitrogen source. Examples of ammonium salts include ammonium chloride and ammonium sulfate.

[0025] The control device 14 is connected to the ammoniacal nitrogen concentration meter 16, pH meter 23, pump 18 for the water to be treated, and pump 20 for the ammoniacal nitrogen source by wired or wireless electrical connections, etc. Although not shown in the drawings, if a water temperature sensor is installed in the biological treatment tank 12, the control device 14 may be connected to the water temperature sensor.

[0026] Control device 14 is composed of, for example, a microcomputer and electronic circuitry, which is composed of a CPU that executes programs and ROM and RAM that store the programs and calculation results, and reads out a predetermined program stored in ROM or the like, and executes the program to control the operation of water treatment device 1. For example, based on the ammoniacal nitrogen concentration measured by ammoniacal nitrogen concentration meter 16, control is made to control the operation of pump 18 for treated water and control the operation of pump 20 for ammoniacal nitrogen source.

[0027] The operation of the water treatment device 1 according to this embodiment will be described.

[0028] Raw water (e.g., water to be treated containing ammoniacal nitrogen) passes through pipe 21a and is stored in tank 10 for water to be treated. Control device 14 operates pump 20 for ammoniacal nitrogen source as needed to add the ammoniacal nitrogen source in tank 22 to tank 10 for water to be treated through pipe 21d. When starting up the apparatus (starting up nitrification treatment), for example, when the flow rate or ammoniacal nitrogen concentration of water to be treated discharged from the factory is unstable, or when early start-up of the apparatus is required, it is desirable to add the ammoniacal nitrogen source.

[0029] The control device 14 operates the water pump 18 to supply the water to be treated, which contains ammonia nitrogen, from the water tank 10 to the biological treatment tank 12 through pipe 21b. In the biological treatment tank 12, an oxygen-containing gas such as air is supplied by an aeration device 24, and the water to be treated is mixed with autotrophic bacteria. Then, in the biological treatment tank 12, the ammonia nitrogen in the water to be treated is nitrified by biological treatment (nitrification treatment) using autotrophic bacteria under aerobic conditions. The ammonia nitrogen is nitrified by the autotrophic bacteria to at least one of nitrite nitrogen and nitrate nitrogen. The nitrified treated water is discharged to the outside of the system through pipe 21c.

[0030] FIG. 2 is a flowchart showing an example of a control flow by the control device. In step S10, the control device 14 operates the water-to-be-treated pump 18 to perform nitrification treatment while supplying water-to-be-treated containing ammoniacal nitrogen to the biological treatment tank 12, as described above, and then discharges the treated water. In step S12, the ammoniacal nitrogen concentration meter 16 measures the ammoniacal nitrogen concentration in the treated water that has been nitrified in the biological treatment tank 12. The control device 14 stores a preset first threshold value, and the control device 14 compares the measured ammoniacal nitrogen concentration with the first threshold value. If the measured ammoniacal nitrogen concentration is less than the first threshold value, the process returns to step S10. On the other hand, if the measured ammoniacal nitrogen concentration is equal to or greater than the first threshold value, the process proceeds to step S14, where the control device 14 stops operation of the water-to-be-treated pump 18 to stop the supply of water-to-be-treated to the biological treatment tank 12. Note that, from the time the ammoniacal nitrogen concentration becomes equal to or greater than the first threshold value until the operation of the water-to-be-treated pump 18 is stopped, treated water with a high ammoniacal nitrogen concentration is discharged from the pipe 21c. Therefore, while this control flow is being performed, it is desirable to provide a pipe to return the treated water flowing through pipe 21c to the treated water tank 10, or to dilute the treated water so that the ammonia nitrogen concentration in the treated water flowing through pipe 21c is below the discharge standard.

[0031] Next, in step S16, the supply of water to the biological treatment tank 12 is stopped while nitrification treatment in the biological treatment tank 12 continues. Therefore, the ammoniacal nitrogen concentration in the biological treatment tank 12 decreases over time. In step S18, the ammoniacal nitrogen concentration meter 16 measures the ammoniacal nitrogen concentration in the treated water that has been nitrified in the biological treatment tank 12. A preset second threshold value is stored in the control device 14, and the control device 14 compares the measured ammoniacal nitrogen concentration with the second threshold value. If the measured ammoniacal nitrogen concentration exceeds the second threshold value, the process returns to step S16. On the other hand, if the measured ammoniacal nitrogen concentration is equal to or less than the second threshold value, the process proceeds to step S20, where the control device 14 operates the water pump 18 to resume the supply of water to be treated that contains ammoniacal nitrogen to the biological treatment tank 12. That is, nitrification treatment is performed while water to be treated that contains ammoniacal nitrogen is supplied to the biological treatment tank 12, and the treated water is discharged. 2, for the sake of convenience, the control is ended after the supply of the water to be treated containing ammoniacal nitrogen to the biological treatment tank 12 is resumed, but during the start-up period of the apparatus, the process returns to step S10 after the supply of the water to be treated containing ammoniacal nitrogen to the biological treatment tank 12 is resumed. In other words, during the start-up period of the apparatus, the flow from step S10 to step S20 constitutes one cycle, and this cycle is repeated.

[0032] The start-up period of the apparatus is then determined to end, for example, after a predetermined time has elapsed since the start-up of the apparatus or when the ammoniacal nitrogen removal rate reaches a predetermined value. The determination of the end of the start-up period of the apparatus may be made by the control device 14 or by an operator. That is, the control device 14 or an operator may determine the end of the start-up period of the apparatus by, for example, measuring the start-up time of the apparatus or the ammoniacal nitrogen removal rate. After the start-up period of the apparatus ends, for example, the treated water containing ammoniacal nitrogen is continuously supplied to the biological treatment tank 12 to perform continuous nitrification treatment. At this time, the flow rate of the treated water containing ammoniacal nitrogen may be increased to increase the ammoniacal nitrogen load in the biological treatment tank 12. If the flow rate of the treated water needs to be finely adjusted, the treated water pump 18 may be inverter-controlled.

[0033] When an ammoniacal nitrogen source is supplied, the supply and stop of the ammoniacal nitrogen source may be controlled based on the ammoniacal nitrogen concentration in the treated water treated in the biological treatment tank 12. This will be explained in detail below.

[0034] FIG. 3 is a flowchart showing another example of a control flow by the control device. In step S30, the control device 14 operates the ammoniacal nitrogen source pump 20 to supply the ammoniacal nitrogen source to the water tank 10 and add the ammoniacal nitrogen source to the water to be treated. In step S32, the control device 14 operates the water pump 18 to perform nitrification treatment while supplying the water to be treated containing ammoniacal nitrogen to the biological treatment tank 12, and then discharges the treated water. In step S34, the ammoniacal nitrogen concentration meter 16 measures the ammoniacal nitrogen concentration in the treated water that has been nitrified in the biological treatment tank 12. The control device 14 then compares the measured ammoniacal nitrogen concentration with a preset first threshold. If the measured ammoniacal nitrogen concentration is less than the first threshold, the process returns to step S32. On the other hand, if the measured ammoniacal nitrogen concentration is equal to or greater than the first threshold, the process proceeds to step S36, where the control device 14 stops the operation of the ammoniacal nitrogen source pump 20 and stops the supply of the ammoniacal nitrogen source.

[0035] Next, in step S38, the supply of the ammoniacal nitrogen source to the water tank 10 is stopped, and the water to be treated is continued to be supplied to the biological treatment tank 12, thereby continuing nitrification treatment in the biological treatment tank 12 and discharge of the treated water. In step S40, the ammoniacal nitrogen concentration meter 16 measures the ammoniacal nitrogen concentration in the treated water that has been nitrified in the biological treatment tank 12. The control device 14 then compares the measured ammoniacal nitrogen concentration with a second threshold. If the measured ammoniacal nitrogen concentration exceeds the second threshold, the process returns to step S36. On the other hand, if the measured ammoniacal nitrogen concentration is equal to or less than the second threshold, the process proceeds to step S42, where the control device 14 operates the ammoniacal nitrogen source pump 20 to resume supplying the ammoniacal nitrogen source to the water tank 10. Then, nitrification treatment is performed while supplying the water to be treated containing ammoniacal nitrogen to the biological treatment tank 12, and the treated water is discharged. 3, for the sake of convenience, the control is ended after the supply of the ammoniacal nitrogen source to the tank 10 is resumed. However, during the start-up period of the apparatus, the supply of the ammoniacal nitrogen source to the tank 10 is resumed, and the process returns to step S30. That is, the flow from step S30 to step S42 constitutes one cycle, and this cycle is repeated. Then, for example, the start-up period of the apparatus is ended after a predetermined time has elapsed since the start-up of the apparatus or when the removal rate of ammoniacal nitrogen reaches a predetermined value. The end of the start-up period of the apparatus is as described above.

[0036] In step S36, even if the operation of the ammoniacal nitrogen source pump 20 continues to be stopped, the ammoniacal nitrogen concentration may not become equal to or less than the second threshold value. In other words, steps S36 to S40 may be repeated without proceeding to step S42. To avoid such a case, for example, the control device 14 may measure the stop time of the ammoniacal nitrogen source pump 20, and if the measured time exceeds a predetermined time, in step S36, while continuing the stop of the ammoniacal nitrogen source pump 20, stop the operation of the water to be treated pump 18 to stop the supply of water to be treated to the biological treatment tank 12. Then, in step S38, nitrification treatment in the biological treatment tank 12 is continued while the supply of the ammoniacal nitrogen source to the water to be treated tank 10 and the supply of water to be treated to the biological treatment tank 12 are stopped. This operation makes it easier for the ammoniacal nitrogen concentration in the biological treatment tank 12 to become equal to or less than the second threshold value, making it easier to proceed to step S42.

[0037] By operating in the manner described above, the labor required for starting up the apparatus can be reduced and the apparatus can be started up automatically.

[0038] The second threshold is preferably set in the range of less than 1 mg / L, and more preferably in the range of 0.1 mg / L to 0.8 mg / L, in order to enable quick start-up of the apparatus.

[0039] The first threshold is preferably set in the range of 5 to 50 mg / L, for example, taking into consideration the water quality of the treated water discharged from the biological treatment tank 12. Alternatively, the first threshold is preferably set based on the pH value in the biological treatment tank 12. For example, the control device 14 stores a map (which may be a relational expression or a table) that defines the relationship between the pH value and the threshold. The control device 14 then receives the pH value in the biological treatment tank 12 measured by the pH meter 23 and calculates the threshold by applying the pH value to the map. The control device 14 sets the calculated threshold as the first threshold. Setting the first threshold based on the pH value makes it possible to suppress the influence of free ammonia during nitrification treatment and improve digestion capacity. For example, when the pH is 7 to 7.5 (water temperature 20°C), the first threshold is preferably set in the range of 10 to 25 mg / L. Furthermore, because free ammonia is also affected by water temperature, it is more preferable to set the first threshold based on the pH and water temperature in the biological treatment tank 12.

[0040] The ammoniacal nitrogen concentration meter 16 is not particularly limited as long as it is capable of online measurement, but a coulometric titration ammoniacal nitrogen meter is preferable. A coulometric titration ammoniacal nitrogen meter measures by coulometric titration, which applies coulometry. In principle, a calibration curve does not need to be created, and bromine, which has high selectivity and reactivity with ammonia, can be used as the titrant. Other advantages include the electrode being less susceptible to contamination and being relatively easy to clean with acid. Therefore, using a coulometric titration ammoniacal nitrogen meter reduces the number of maintenance personnel required.

[0041] The measurement frequency by the ammoniacal nitrogen concentration meter 16 can be set arbitrarily, but it is preferable to perform measurements at least once every 15 minutes while the water to be treated is being supplied to the biological treatment tank, and it is preferable to perform measurements at least once every hour while the supply of the water to be treated is stopped. It is also preferable to set a transition time of about several minutes from when the measured ammoniacal nitrogen concentration becomes equal to or greater than the first threshold value until the supply of the water to be treated is stopped, and a transition time of about several minutes from when the measured ammoniacal nitrogen concentration becomes equal to or less than the second threshold value until the supply of the water to be treated is resumed.

[0042] In the water treatment device 1 of FIG. 1, the ammoniacal nitrogen concentration is measured by measuring the ammoniacal nitrogen concentration of the treated water in the biological treatment tank 12, but this is not limiting. For example, the ammoniacal nitrogen concentration may be measured in filtrate obtained by solid-liquid separation of the treated water in the biological treatment tank 12 using a filtration device. By using filtrate obtained by solid-liquid separation using a filtration device, the ammoniacal nitrogen concentration can be measured accurately even at low concentrations. Furthermore, since SS components and the like have been removed from the filtrate obtained by solid-liquid separation using a filtration device, the maintenance frequency of the ammoniacal nitrogen concentration meter 16 can be reduced. An example of a water treatment device with such a configuration is shown in FIG. 4.

[0043] In the water treatment device 2 shown in Fig. 4, the same components as those in the water treatment device 1 shown in Fig. 1 are denoted by the same reference numerals, and their description will be omitted. The water treatment device 2 shown in Fig. 4 has a filtration device 28 and a carrier 30 packed in a biological treatment tank 12.

[0044] The treated water extracted from pipe 21e installed near the outlet of biological treatment tank 12 is subjected to solid-liquid separation by filtration device 28 to obtain filtrate. The obtained filtrate is discharged to the outside of the system from pipe 21f. An ammoniacal nitrogen concentration meter 16 is installed in pipe 21f. The ammoniacal nitrogen concentration meter 16 measures the ammoniacal nitrogen concentration in the filtrate flowing through pipe 21f. If a treated water tank is installed to store the filtrate discharged from pipe 21f, the ammoniacal nitrogen concentration meter 16 may be installed in the treated water tank to measure the ammoniacal nitrogen concentration in the filtrate stored in the treated water tank.

[0045] The type of biological treatment tank 12 is not particularly limited, but it is preferable to use a biofilm method, which allows as many nitrifying bacteria as possible to be retained in the tank and eliminates the need for a settling tank. The biofilm method is a method of nitrification using nitrifying bacteria attached to carriers 30. If a large amount of ammonia nitrogen remains in the biological treatment tank 12, the toxicity of free ammonia increases, affecting the nitrifying bacteria. However, biofilms attached to the carriers 30 have the advantage of being more resistant to toxicity than ordinary suspended sludge. Therefore, the biofilm method using the carriers 30 is suitable for operations in which the ammonia nitrogen concentration in the biological treatment tank 12 temporarily increases, such as during the start-up of the water treatment device of this embodiment.

[0046] The carrier 30 is not particularly limited as long as it is a conventionally known carrier used under aerobic conditions. Examples of the carrier 30 include plastic carriers, sponge-like carriers, and gel-like carriers, but sponge-like carriers are preferred because they offer a good balance between cost and durability.

[0047] The water treatment device of this embodiment may adjust the amount of nutrients added to the biological treatment tank 12 based on the ammoniacal nitrogen load in the biological treatment tank 12. The ammoniacal nitrogen load in the biological treatment tank 12 is calculated from the ammoniacal nitrogen concentration in the biological treatment tank 12 and the volume of the biological treatment tank 12.

[0048] For example, the control device 14 may store a map or the like that defines the ammoniacal nitrogen load amount and the amount of nutrient salt to be added to the biological treatment tank 12. The control device 14 then calculates the amount of nutrient salt to be added by applying the map to the calculated ammoniacal nitrogen load amount to the biological treatment tank 12. The control device 14 may add the calculated amount of nutrient salt to be added from the nutrient salt supply pipe to the biological treatment tank 12, for example, by controlling a pump, a valve, or the like that is provided in a nutrient salt supply pipe that supplies nutrients to the biological treatment tank 12 as nutrient salt supply means.

[0049] Nutrients 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).

[0050] The pH in the biological treatment tank 12 during nitrification treatment is preferably adjusted to a range of, for example, pH 6 to 8 from the viewpoint of microbial growth, and more preferably adjusted to a range of pH 6.8 to 7.2 to suppress inhibition by free ammonia.

[0051] Nitrification treatment is preferably carried out under aerobic conditions, and the dissolved oxygen concentration in the biological treatment tank 12 is, for example, 0.5 mg / L or more, preferably 1 mg / L or more.

[0052] The water temperature in the biological treatment tank 12 is preferably maintained in the range of 15 to 40°C, for example.

[0053] The water to be treated may be, for example, wastewater containing ammoniacal nitrogen discharged from semiconductor manufacturing processes, etc. When the water to be treated contains calcium at a concentration of 100 mg / L or more, preferably in the range of 100 to 1000 mg / L, the water treatment method and water treatment device according to this embodiment can be suitably applied. [Example]

[0054] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the following examples.

[0055] Example 1 The water treatment device shown in FIG. 4 was used and started up under the conditions shown below. [Test conditions] pH in biological treatment tank: 7.2 (adjusted with caustic soda) Biological treatment tank volume: 2L Carrier: Hydrophobic polyurethane sponge carrier Carrier filling rate: 30% of the biological treatment tank (bulk volume / tank volume) Temperature of treated water: 20℃ Ammonia nitrogen concentration in treated water: 500 mg / L Composition of treated water: Ammonium chloride was added to well water in an amount equivalent to an ammonium nitrogen concentration of 500 mg / L, and a solution containing sodium carbonate, phosphoric acid, and trace elements was also added. Ammonia nitrogen concentration meter: Coulometric titration type ammonia nitrogen meter (manufactured by Central Scientific)

[0056] After seed sludge was added to the biological treatment tank to achieve an MLSS of 500 mg / L, the water to be treated was supplied and nitrification treatment was carried out under aerobic conditions. During this process, the water nitrified in the biological treatment tank was discharged from the biological treatment tank. While the supply of water to be treated was continued, the ammonia nitrogen concentration in the filtrate, obtained by filtering the water treated in the biological treatment tank through a filtration device, was periodically measured. When the measured ammonia nitrogen concentration reached a first threshold of 25 mg / L, the supply of water to be treated was stopped. Even after the supply of water to be treated was stopped, nitrification treatment continued under aerobic conditions in the biological treatment tank. Then, every 15 minutes, the ammonia nitrogen concentration in the filtrate, obtained by filtering the water treated in the biological treatment tank through a filtration device, was measured. When the measured ammonia nitrogen concentration decreased to a second threshold of 1.5 mg / L, the supply of water to be treated was resumed. This cycle, from the start of the supply of water to be treated to the resumption of the supply of water to be treated, was considered one cycle, and four such cycles were performed. After completing four cycles of operation, the second threshold was changed to 0.8 mg / L, and operation was performed from the fifth cycle onwards, for a total of seven cycles of operation.

[0057] Table 1 summarizes the ammonia nitrogen concentration in the filtrate (after the supply of water to be treated was stopped and after the supply of water to be treated was restarted), the ammonia nitrogen load in the biological treatment tank, the time from the stoppage of the supply of water to be treated to the restart of the supply, and the ammonia nitrogen removal rate in the biological treatment tank. The ammonia nitrogen load in the biological treatment tank is a value calculated from the ammonia nitrogen concentration in the filtrate after the supply of water to be treated was stopped and the volume of the biological treatment tank. The ammonia nitrogen removal rate in the biological treatment tank is a value (ammonia nitrogen removal rate per hour) calculated from the value obtained by subtracting the ammonia nitrogen concentration in the filtrate when the supply of water to be treated was restarted from the ammonia nitrogen concentration in the filtrate after the supply of water to be treated was stopped, the volume of the biological treatment tank, and the time from the stoppage of the supply of water to be treated to the restart of the supply.

[0058] [Table 1]

[0059] Between cycles 1 and 4, the ammonia nitrogen removal rate was 0.024 kg-N / (m 3 The nitrification rate remained constant at 0.8 mg / L (-tank volume·d), and stable nitrification was achieved. After the water treatment device was put into operation, nitrification proceeded automatically without operator intervention. These results suggest that automatic startup is possible, reducing the labor required for system startup in water treatment that uses biological treatment to nitrify ammonia-containing water. While it was possible to start up the system by continuing the test under the test conditions for cycles 1 to 4, the ammonia-nitrogen removal rate could be increased by setting the second threshold to 0.8 mg / L (from 1.5 mg / L to 0.8 mg / L) from cycle 5 onward. Thus, setting the second threshold to a lower value improves the ammonia-nitrogen removal rate and allows for faster system startup.

[0060] <Example 2> Except for setting the second threshold to 0.6 mg / L, four cycles of operation were performed under the same conditions as in Example 1. Table 2 summarizes the ammoniacal nitrogen concentration in the filtrate (after the supply of water to be treated was stopped and after the supply of water to be treated was restarted), the ammoniacal nitrogen load in the biological treatment tank, the time from the stoppage of the supply of water to be treated to the restart of the supply, and the ammoniacal nitrogen removal rate in the biological treatment tank.

[0061] [Table 2]

[0062] In Example 2, the ammonia nitrogen removal rate increased during operation, reaching 0.030 kg-N / (m 3 -tank volume·d). From this result, it can be seen that in Example 2, in which the second threshold value is set to a lower value than in Example 1, the device can be started up more quickly than in Example 1. [Explanation of symbols]

[0063] 1, 2 water treatment device, 10 treated water tank, 12 biological treatment tank, 14 control device, 16 ammonia nitrogen concentration meter, 18 treated water pump, 20 ammonia nitrogen source pump, 21a to 21f piping, 22 tank, 23 pH meter, 24 aeration device, 26 screen, 28 filtration device, 30 carrier.

Claims

1. a biological treatment tank in which the water to be treated containing ammonia nitrogen is nitrified by autotrophic bacteria; a water-to-be-treated supply means for supplying the water-to-be-treated to the biological treatment tank; an ammonia nitrogen concentration measuring means for measuring the ammonia nitrogen concentration in the treated water treated in the biological treatment tank; a nutrient salt supplying means for supplying nutrients to the biological treatment tank; a control means for controlling start and stop of supply of the water to be treated by the water to be treated supply means and for controlling the amount of the nutrients to be supplied by the nutrient salt supply means; The control means controls the untreated water supply means to stop the supply of the untreated water when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or higher than a first threshold, and after the stoppage, controls the untreated water supply means to resume the supply of the untreated water when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or lower than a second threshold, and controls the supply amount of the nutrients by the nutrient supply means based on the ammoniacal nitrogen load in the biological treatment tank.

2. a biological treatment tank in which the water to be treated containing ammonia nitrogen is nitrified by autotrophic bacteria; a water-to-be-treated supply means for supplying the water-to-be-treated to the biological treatment tank; an ammonia nitrogen concentration measuring means for measuring the ammonia nitrogen concentration in the treated water treated in the biological treatment tank; a control means for controlling start and stop of supply of the water to be treated by the water to be treated supply means, The control means controls the water to be treated supply means to stop the supply of the water to be treated when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or higher than a first threshold value, and after the stoppage, controls the water to be treated supply means to resume the supply of the water to be treated when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or lower than a second threshold value, and the first threshold value is set based on the pH in the biological treatment tank.

3. 3. The water treatment device according to claim 1, wherein the second threshold value is less than 1 mg / L.

4. A filtration means is provided for filtering the treated water treated in the biological treatment tank, 4. The water treatment device according to claim 1, wherein the ammoniacal nitrogen concentration measuring means measures the ammoniacal nitrogen concentration in the filtered water filtered by the filtering means.

5. 5. The water treatment device according to claim 1, wherein the water to be treated contains 100 mg / L or more of calcium.

6. a biological treatment step in which the water to be treated containing ammonia nitrogen is nitrified by autotrophic bacteria in a biological treatment tank; a water-to-be-treated supply step of supplying the water to be treated to the biological treatment tank by a water-to-be-treated supply means; an ammoniacal nitrogen concentration measuring step of measuring the ammoniacal nitrogen concentration in the treated water treated in the biological treatment tank by an ammoniacal nitrogen concentration measuring means; a nutrient salt supplying step of supplying nutrients to the biological treatment tank by a nutrient salt supplying means; A control step A controls the supply and stop of the water to be treated by the water to be treated supply means by a control means, and a control step B controls the supply amount of the nutrients by the nutrient salt supply means, In the control step A, when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or higher than a first threshold value, the control means controls the water to be treated supply means to stop the supply of the water to be treated, and when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or lower than a second threshold value after the stoppage, the control means controls the water to be treated supply means to resume the supply of the water to be treated; and in the control step B, the control means controls the amount of nutrients supplied by the nutrient salt supply means based on the ammoniacal nitrogen load in the biological treatment tank.

7. a biological treatment step in which the water to be treated containing ammonia nitrogen is nitrified by autotrophic bacteria in a biological treatment tank; a water-to-be-treated supply step of supplying the water to be treated to the biological treatment tank by a water-to-be-treated supply means; an ammoniacal nitrogen concentration measuring step of measuring the ammoniacal nitrogen concentration in the treated water treated in the biological treatment tank by an ammoniacal nitrogen concentration measuring means; a control step of controlling start and stop of supply of the water to be treated by the water to be treated supply means by a control means, In the control step, when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or higher than a first threshold value, the control means controls the water to be treated supply means to stop the supply of the water to be treated, and when the ammoniacal nitrogen concentration measured by the ammoniacal nitrogen concentration measuring means becomes equal to or lower than a second threshold value after the stoppage, the control means controls the water to be treated supply means to resume the supply of the water to be treated, and the first threshold value is set based on the pH in the biological treatment tank.

Images