Wastewater treatment method, wastewater treatment device, and wastewater treatment carrier

Abstract

To provide a wastewater treatment method, a wastewater treatment apparatus, and a carrier for wastewater treatment capable of performing stable nitrogen treatment.SOLUTION: Disclosed is a wastewater treatment method for denitrification treatment of wastewater by bringing ammonia-containing wastewater into contact with a carrier for wastewater treatment 12 in a reaction tank 14 accommodating the carrier for wastewater treatment 12 containing ammonia oxidation bacterium and anamox bacterium, wherein dissolved oxygen concentration of wastewater in the reaction tank 14 is controlled to 0.5 mg / L or over and 4.0 mg / L or under, and wastewater in the reaction tank 14, or, ammonia concentration of treatment water discharged from the reaction tank 14 is controlled to 10 mg / L or over and 500 mg / L or under. Also, a wastewater treatment apparatus for executing this wastewater treatment method, and, a carrier for wastewater treatment used for this wastewater treatment method are disclosed.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a wastewater treatment method, a wastewater treatment device, and a wastewater treatment carrier, and more particularly to a wastewater treatment method, a wastewater treatment device, and a wastewater treatment carrier that utilize anammox bacteria. [Background technology]

[0002] Removal of ammonia contained in wastewater is an issue from the perspective of environmental conservation. Biological treatment methods are often used for nitrogen treatment, and in recent years, a new nitrogen treatment method using the anammox reaction caused by anammox bacteria has been developed.

[0003] The anammox reaction converts ammonia and nitrite into nitrogen gas. Therefore, approximately half of the ammonia in the raw water is oxidized to nitrite, and the ammonia and the resulting nitrite are denitrified by the anammox reaction. The oxidation of ammonia to nitrite is carried out by ammonia-oxidizing bacteria, which are aerobic bacteria, while the anammox reaction is carried out by anaerobic anammox bacteria. Therefore, it is preferable that the oxidation of ammonia to nitrite and the anammox reaction be carried out in separate reaction tanks.

[0004] Meanwhile, a single-tank system is known that can utilize ammonia-oxidizing bacteria and anammox bacteria in a single tank (aerobic layer) (see Patent Document 1 below). With a single-tank system, two reactions can be carried out in a single tank, making it simple and easy to maintain. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2006 / 035885 Summary of the Invention [Problem to be solved by the invention]

[0006] In a single-tank system, it is necessary to maintain the activity of opposing organisms, aerobic and anaerobic bacteria, in a single reactor. In particular, to achieve a high treatment speed, it is necessary to inject a large amount of oxygen, and operation at a high dissolved oxygen concentration (DO) is required. However, there is a problem in that high dissolved oxygen concentrations cause the inactivation of anammox bacteria.

[0007] Furthermore, when nitrite-oxidizing bacteria grow in the reaction tank, the nitrite used by the anammox bacteria is oxidized by the nitrite-oxidizing bacteria to nitrate, and the nitrate is not processed by the anammox bacteria, resulting in a decrease in the nitrogen removal rate.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a wastewater treatment method, a wastewater treatment device, and a carrier for wastewater treatment that can maintain the activity of ammonia-oxidizing bacteria and anammox bacteria and perform stable nitrogen treatment. [Means for solving the problem]

[0009] In order to achieve the object of the present invention, the wastewater treatment method of the present invention is a wastewater treatment method in which wastewater containing ammonia is brought into contact with the wastewater treatment carrier in a reaction tank containing a wastewater treatment carrier having ammonia-oxidizing bacteria and anammox bacteria attached thereto, or a wastewater treatment carrier having a mixture of ammonia-oxidizing bacteria-attached carriers having ammonia-oxidizing bacteria attached thereto and anammox bacteria-attached carriers having anammox bacteria attached thereto, and the method controls the dissolved oxygen concentration of the wastewater in the reaction tank to between 0.5 mg / L and 4.0 mg / L, and controls the ammonia concentration of the wastewater in the reaction tank or the treated water discharged from the reaction tank to between 10 mg / L and 500 mg / L.

[0010] According to one embodiment of the present invention, the dissolved oxygen concentration is preferably controlled by controlling the aeration volume of air supplied into the reaction tank.

[0011] According to one embodiment of the present invention, the ammonia concentration is preferably controlled by controlling at least one of the aeration volume of air supplied into the reaction tank and the inflow rate of raw water before wastewater treatment.

[0012] According to one embodiment of the present invention, it is preferable to control the pH of the wastewater in the reaction tank or the treated water discharged from the reaction tank to 6.5 or more and 8.5 or less.

[0013] According to one embodiment of the present invention, the nitrogen load on the reaction vessel is 0.5 kg-N / m 3 / day or more 3.0kg-N / m 3 It is preferable that it is / day or less.

[0014] According to one embodiment of the present invention, when the ammonia concentration or total nitrogen concentration of raw water before wastewater treatment is A, the ammonia concentration of the wastewater from the reaction tank or the treated water discharged from the reaction tank is B, and the nitric acid concentration of the wastewater from the reaction tank or the treated water discharged from the reaction tank is C, a control value D, which is the ratio of the produced nitric acid to the amount of ammonia treated, is calculated by D=C / (AB), and it is preferable to control the control value D to be 0.05 or more and 0.25 or less.

[0015] According to one aspect of the present invention, the carrier is preferably polyvinyl alcohol.

[0016] In order to achieve the object of the present invention, the wastewater treatment device of the present invention comprises a reaction tank containing a wastewater treatment carrier having ammonia-oxidizing bacteria and anammox bacteria attached thereto, or a mixture of ammonia-oxidizing bacteria-attached carriers having ammonia-oxidizing bacteria attached thereto and anammox bacteria-attached carriers having anammox bacteria attached thereto; a raw water supply pipe for supplying raw water before treatment to the reaction tank; a treated water discharge pipe for discharging treated water treated in the reaction tank; an air supply means for supplying air into the reaction tank; a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration of the wastewater in the reaction tank; an ammonia concentration measuring means for measuring the ammonia concentration of the wastewater or the treated water in the reaction tank; and a control means for controlling the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means to be between 0.5 mg / L and 4.0 mg / L, and controlling the ammonia concentration measured by the ammonia concentration measuring means to be between 10 mg / L and 500 mg / L.

[0017] According to one aspect of the present invention, the control means preferably controls the dissolved oxygen concentration by controlling the aeration air volume of the air supply means.

[0018] According to one aspect of the present invention, the control means preferably controls the ammonia concentration by controlling at least one of the aeration air volume by the air supply means and the inflow rate of the raw water.

[0019] According to one embodiment of the present invention, it is preferable to provide a pH measurement means for measuring the pH of the wastewater or treated water in the reaction tank, and a pH control means for controlling the pH measured by the pH measurement means to be 6.5 or more and 8.5 or less.

[0020] According to one embodiment of the present invention, the nitrogen load on the reaction vessel is 0.5 kg-N / m 3 / day or more 3.0kg-N / m 3 It is preferable that it is / day or less.

[0021] According to one embodiment of the present invention, when the ammonia concentration or total nitrogen concentration of raw water is A, the ammonia concentration of wastewater from the reaction tank or treated water discharged from the reaction tank is B, and the nitrate concentration of wastewater from the reaction tank or treated water discharged from the reaction tank is C, a calculation unit is provided that calculates a control value D, which is the ratio of the generated nitric acid to the amount of ammonia treated, by D=C / (AB), and it is preferable that the control means controls the control value D to be 0.05 or more and 0.25 or less.

[0022] In order to achieve the object of the present invention, the wastewater treatment carrier according to the present invention is a wastewater treatment carrier used in the wastewater treatment method described above, in which ammonia oxidizing bacteria and anammox bacteria are attached to the carrier.

[0023] In order to achieve the object of the present invention, the wastewater treatment carrier of the present invention is a mixture of an ammonia-oxidizing bacteria-attached carrier in which ammonia-oxidizing bacteria are attached to a carrier and an anammox bacteria-attached carrier in which anammox bacteria are attached to a carrier. [Effects of the Invention]

[0024] According to the wastewater treatment method, wastewater treatment device, and wastewater treatment carrier of the present invention, the activity of ammonia-oxidizing bacteria and anammox bacteria can be maintained, the growth of nitrite-oxidizing bacteria can be suppressed, and stable denitrification treatment can be performed. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a conceptual diagram of a wastewater treatment device according to a first embodiment. [Figure 2] FIG. 10 is a conceptual diagram of a wastewater treatment device according to a second embodiment. [Figure 3] FIG. 1 shows an experimental apparatus used to manufacture an anammox bacteria-attached carrier. [Figure 4] FIG. 1 is a diagram showing an experimental apparatus used for producing ammonia-oxidizing bacteria-attached carriers. [Figure 5] FIG. 1 is a diagram showing water quality data of Experimental Example 1. [Figure 6] FIG. 1 is a graph showing the nitrogen treatment rate in Experimental Example 1. [Figure 7] FIG. 10 is a diagram showing water quality data of Experimental Example 2. [Figure 8] FIG. 10 is a diagram showing water quality data of Experimental Example 2. [Figure 9] FIG. 1 is a graph showing the time course of nitrogen load (NLR) and nitrogen treatment rate (NCR) in Experimental Example 2. [Figure 10] FIG. 10 is a diagram showing water quality data of Experimental Example 2. [Figure 11] FIG. 10 is a graph showing changes in FA and ΔNO3 / ΔNH4 in Experimental Example 2. [Figure 12] FIG. 10 is a diagram showing water quality data of Experimental Example 3. [Figure 13] FIG. 10 is a diagram showing water quality data of Experimental Example 3. [Figure 14] FIG. 10 is a graph showing the time course of nitrogen load (NLR) and nitrogen treatment rate (NCR) in Experimental Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0026] The wastewater treatment method, wastewater treatment device, and wastewater treatment carrier according to the present invention will be described below with reference to the accompanying drawings. In this specification, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower and upper limits.

[0027] First Embodiment [Wastewater treatment equipment] 1 is a conceptual diagram of a wastewater treatment device 10 according to a first embodiment. The wastewater treatment device 10 includes a reaction tank 14 containing a wastewater treatment carrier 12, a raw water supply pipe 16 for supplying raw water to the reaction tank 14 before treatment, a treated water discharge pipe 18 for discharging treated water treated in the reaction tank 14, and an air diffuser plate 20 and a blower 22 that function as air supply means for supplying air to the reaction tank 14. The wastewater treatment device 10 also includes a dissolved oxygen concentration measuring means 24 for measuring the dissolved oxygen concentration of the wastewater in the reaction tank 14, an ammonia concentration measuring means 26 for measuring the ammonia concentration of the wastewater in the reaction tank 14, and a control means 28 for controlling the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means 24 and the ammonia concentration measured by the ammonia concentration measuring means 26 within predetermined ranges.

[0028] The reaction tank 14 is a tank in which denitrification treatment is performed by bringing the wastewater treatment carrier 12, to which ammonia-oxidizing bacteria and anammox bacteria are attached, into contact with wastewater containing ammonia. By containing the wastewater treatment carrier 12 to which ammonia-oxidizing bacteria and anammox bacteria are attached, the reaction tank 14 can be used as a reaction tank used in a one-tank system in which the nitrification reaction of ammonia contained in the wastewater and the anammox reaction can be performed in one tank. The shape and size of the reaction tank 14 are not particularly limited and are selected appropriately depending on the amount of wastewater to be treated, etc. An agitator 30 is provided in the reaction tank 14, and the wastewater and wastewater treatment carrier 12 in the reaction tank 14 are agitated by rotating the agitator 30 using a motor 32.

[0029] The raw water supply pipe 16 is a pipe through which raw water before wastewater treatment is supplied to the reaction tank 14. The raw water supply pipe 16 is connected to a raw water tank (not shown) in which raw water is stored, and supplies raw water from the raw water tank to the reaction tank 14. The raw water supply pipe 16 has a valve 34, which controls the inflow rate of the raw water. The treated water discharge pipe 18 is a pipe through which treated water treated in the reaction tank 14 is discharged.

[0030] An air diffuser plate 20 is disposed at the bottom of the reaction tank 14 to diffuse air into the reaction tank 14. A blower 22 is connected to the air diffuser plate 20, and compressed air is supplied from the blower 22 to the air diffuser plate 20. As a result, air is supplied to the ammonia-oxidizing bacteria and anammox bacteria in the wastewater treatment carrier 12, and the diffused air causes the wastewater treatment carrier 12 to flow within the reaction tank 14, bringing the wastewater into contact with the wastewater treatment carrier 12. Therefore, nitrogen in the wastewater is biologically treated, and denitrification treatment is carried out.

[0031] The dissolved oxygen concentration measuring means 24 may be, but is not limited to, a diaphragm type DO meter, a fluorescent type DO meter, or the like.

[0032] The ammonia concentration measuring means 26 may be, but is not limited to, an ammonia ion electrode, an automatic ammonia measuring device, or the like. Although the ammonia concentration measuring means 26 is provided in the reaction tank 14 to measure the ammonia concentration of the wastewater in FIG. 1 , the ammonia concentration measuring means 26 may also be provided in the treated water discharge pipe 18 to measure the ammonia concentration of the treated water. Because the wastewater in the reaction tank 14 is continuously denitrified, there is a large amount of wastewater in the reaction tank 14 relative to the inflow of raw water. Therefore, there is almost no difference between the ammonia concentration of the wastewater in the reaction tank 14 and the ammonia concentration of the treated water. Therefore, measuring the ammonia concentration of the treated water allows for control that is substantially the same as measuring the ammonia concentration of the wastewater.

[0033] The control means 28 controls the dissolved oxygen concentration measured by the dissolved oxygen concentration measurement means 24 to be between 0.5 mg / L and 4.0 mg / L. The dissolved oxygen concentration can be controlled by controlling the blower 22 that supplies air into the reaction tank 14 and controlling the aeration air volume. Because the reaction tank 14 contains ammonia-oxidizing bacteria, which are aerobic bacteria, and anammox bacteria, which are anaerobic bacteria, it is important to control the dissolved oxygen concentration in the reaction tank 14 to maintain the activity of both. By maintaining the dissolved oxygen concentration in the above range, the nitrification reaction can be promoted and the anammox bacteria can be prevented from being inactivated.

[0034] Furthermore, the control means 28 controls the ammonia concentration measured by the ammonia concentration measurement means 26 to be between 10 mg / L and 500 mg / L. By controlling the ammonia concentration, the proliferation of nitrite-oxidizing bacteria in the reaction tank can be suppressed. The activity of nitrite-oxidizing bacteria to oxidize nitrite to nitrate can be inhibited by setting the ammonia concentration to a predetermined concentration or higher. The ammonia concentration of the wastewater in the reaction tank 14 is preferably controlled between 30 mg / L and 400 mg / L, and more preferably between 50 mg / L and 300 mg / L.

[0035] The ammonia concentration can be controlled by controlling at least one of the blower 22 to control the aeration air volume and the valve 34 to control the inflow rate of the raw water supplied into the reaction tank 14.

[0036] The wastewater treatment device 10 further includes a pH measurement means 36 for measuring the pH of the wastewater in the reaction tank 14 and a pH control means 38 for controlling the pH measured by the pH measurement means 36 within a predetermined range. Because anammox bacteria are deactivated at high alkalinity, pH control is preferred. The pH of the wastewater in the reaction tank 14 is preferably controlled to between 6.5 and 8.5. Setting the pH to 8.5 or less can prevent the anammox bacteria from being deactivated. On the other hand, because the activity of anammox bacteria decreases even at low pH, a pH of 6.5 or higher is preferred. The pH of the wastewater is more preferably controlled to between 7.0 and 8.0, and even more preferably to 7.5. Note that the pH does not need to be strictly controlled to 7.5; it is sufficient to adjust the pH to approximately 7.5, for example, within a range of 7.5 ±0.2.

[0037] The pH can be controlled by adding chemicals such as hydrochloric acid (HCl) and sodium hydroxide (NaOH) stored in the chemical tank 40. Note that the pH in the reaction tank 14 tends to decrease due to the nitrification reaction, so it is preferable to increase the pH by adding chemicals such as sodium hydroxide (NaOH).

[0038] As in the case of measuring the ammonia concentration described above, the pH may be measured by measuring the pH of the treated water instead of measuring the pH of the wastewater in the reaction tank 14.

[0039] In the wastewater treatment device of this embodiment, the nitrogen load in the reaction tank 14 is set to 0.5 kg-N / m 3 / day or more 3.0kg-N / m 3 / day or less. More preferably, it is 1.0 kg-N / m 3 / day or more 3.0kg-N / m 3 / day or less, more preferably 1.0 kg-N / m 3 / day or more 2.5kg-N / m 3 / day or less. When the nitrogen load increases, the aeration air volume must be increased to oxidize the ammonia using ammonia-oxidizing bacteria. Increasing the aeration air volume increases the oxygen concentration in the reaction tank 14, which may reduce the activity of the anammox bacteria. By controlling the dissolved oxygen concentration and ammonia concentration in the wastewater as described above, denitrification can be performed without reducing the nitrogen treatment rate, even under reaction conditions with a higher nitrogen load than before.

[0040] [Wastewater treatment carriers] Next, the wastewater treatment carrier 12 used in the wastewater treatment device of the present invention will be described. The wastewater treatment carrier 12 is a wastewater treatment carrier 12 used for the anammox reaction in a single-tank system. The wastewater treatment carrier 12 can be produced by attaching ammonia oxidizing bacteria and anammox bacteria to a carrier. Alternatively, the wastewater treatment carrier 12 can be produced by mixing an ammonia oxidizing bacteria-attached carrier in which ammonia oxidizing bacteria are attached to a carrier, and an anammox bacteria-attached carrier in which anammox bacteria are attached to a carrier.

[0041] <Ammonia-oxidizing bacteria> The ammonia-oxidizing bacteria can be attached to the carrier using activated sludge with ammonia-oxidizing activity. For example, activated sludge collected from a sewage treatment plant can be used. The method for attaching the ammonia-oxidizing bacteria to the carrier is not particularly limited.

[0042] <Anammox bacteria> The anammox bacteria can be attached to the carrier using accumulated sludge, which is preferably capable of undergoing the anammox reaction using ammonia and nitrite. The method for attaching the anammox bacteria to the carrier is not particularly limited.

[0043] <Carrier> Examples of carriers include gel carriers such as polyvinyl alcohol, alginic acid, polyethylene glycol, and acrylamide; plastic carriers such as cellulose, polyester, polypropylene, vinyl chloride, and polyurethane; and inorganic carriers such as activated carbon, diatomaceous earth, and zeolite. The carrier may be in the form of a fluidized bed using a floating carrier molded into an appropriate shape such as a sphere, cylinder, column, cube, or rectangular parallelepiped; or a fixed bed in which a carrier filter material such as a sponge, nonwoven fabric, or hollow fiber is arranged in a honeycomb, wave, lattice, fiber, or chrysanthemum shape. For fluidized beds, the size of the floating carrier is preferably in the range of 1 mm to 10 mm, and the packing rate is preferably in the range of 10% to 40% by volume relative to the capacity of the culture vessel. For fixed beds, the packing rate is preferably in the range of 10% to 50% by volume in terms of the apparent volume occupied by the culture vessel, and the void ratio is preferably 80% or more.

[0044] The carrier used in the present invention preferably has pores (communicating pores) that communicate from the surface to the interior. Here, "communicating pores" means that the pores do not exist independently, but that the pores communicate with each other. The communicating pores can be confirmed by observing the carrier using an electron microscope.

[0045] The pore size of the interconnected pores is preferably such that only bacteria can live inside the carrier. The pore size near the surface of the carrier is preferably 0.1 to 100 μm. If the pore size is less than 0.1 μm, bacteria may not be able to enter the carrier. The pore size near the surface is more preferably 0.5 μm or more. On the other hand, if the pore size near the surface exceeds 100 μm, large organisms other than bacteria may enter, which may result in a decrease in the nitrification rate and denitrification rate. The pore size is more preferably 50 μm or less. The pore size of the interconnected pores can be measured by methods such as observation using an electron microscope.

[0046] The type of carrier used in the present invention is not particularly limited. Because of its high affinity for bacteria and excellent bacterial habitat, the carrier is preferably a polymer gel carrier, and more preferably a polyvinyl alcohol gel carrier (PVA gel carrier). Since a large number of bacteria can be attached to a PVA gel carrier, stable treatment is possible with a short hydraulic retention time (HRT). Among these, a PVA gel carrier having interconnecting pores is preferably used.

[0047] Unlike foams such as sponges, PVA gel carriers do not easily release moisture even when deformed by external force, providing an environment suitable for bacterial habitation. The water content of the PVA gel carrier is preferably 70% by mass or more. The water content is more preferably 80% by mass or more, and even more preferably 90% by mass or more. On the other hand, if the water content exceeds 98% by mass, the strength of the PVA gel carrier may decrease. The water content is more preferably 96% by mass or less.

[0048] The equivalent sphere diameter of the carrier is preferably 1 to 10 mm. If the equivalent sphere diameter is small, when a screen is installed in a reaction vessel to prevent the carrier from flowing out, the mesh size of the screen must be made small, which may cause clogging. The equivalent sphere diameter is more preferably 2 mm or more. On the other hand, if the equivalent sphere diameter exceeds 10 mm, the fluidity of the carrier may decrease. The equivalent sphere diameter is more preferably 6 mm or less. Here, the equivalent sphere diameter is the diameter of a sphere having a volume equal to the volume of the particle.

[0049] The shape of the carrier is not particularly limited, and may be any shape such as a cube, rectangular parallelepiped, cylinder, sphere, macaroni shape, etc. Among these, a spherical shape is preferred in consideration of the contact efficiency with bacteria.

[0050] The specific gravity of the carrier is preferably slightly greater than that of water, and is such that the carrier can be swung in the reaction tank without being washed away from the reaction tank. In the treatment method of the present invention, by using a carrier having a specific gravity slightly greater than that of water, wastewater can be treated more stably without the carrier being washed away. From this perspective, the specific gravity of the carrier is preferably 1.001 or more, more preferably 1.005 or more. On the other hand, the specific gravity is preferably 1.2 or less, more preferably 1.1 or less, and even more preferably 1.05 or less.

[0051] The PVA gel carrier of the present invention may be an acetalized PVA gel carrier, from the viewpoint of being able to increase the amount of bacteria that can be retained and ensuring durability in repeated use.

[0052] [Wastewater treatment method] Next, a wastewater treatment method according to a first embodiment will be described. The wastewater treatment method according to the first embodiment can be carried out, for example, using a wastewater treatment device 10 shown in FIG. 1. A wastewater treatment carrier 12 is housed in the reaction tank 14. The carrier 12 contains a wastewater treatment carrier 12 with ammonia-oxidizing bacteria and anammox bacteria attached to the carrier, or a mixture of ammonia-oxidizing bacteria-attached carriers with ammonia-oxidizing bacteria attached to the carrier and anammox bacteria-attached carriers with anammox bacteria attached to the carrier. The wastewater is then contacted with the wastewater treatment carrier 12 to perform denitrification of the wastewater. That is, by containing ammonia-oxidizing bacteria and anammox bacteria attached to the carrier in a single reaction tank 14, oxidation of ammonia in the wastewater to nitrite by the ammonia-oxidizing bacteria and denitrification of ammonia and nitrite by the anammox bacteria can be carried out in a single reaction tank.

[0053] In this embodiment, the dissolved oxygen concentration of the wastewater in the reaction tank 14 is controlled to be 0.5 mg / L or more and 4.0 mg / L or less. Also, the ammonia concentration of the wastewater in the reaction tank 14 or the treated water discharged from the reaction tank 14 is controlled to be 10 mg / L or more and 500 mg / L or less.

[0054] In the wastewater treatment method of this embodiment, since ammonia-oxidizing bacteria, which are aerobic bacteria, and anammox bacteria, which are anaerobic bacteria, exist in the reaction tank 14, it is important to control the dissolved oxygen concentration in the reaction tank in order to maintain the activity of both. By setting the dissolved oxygen concentration within the above range, the nitrification reaction can be promoted and the anammox bacteria can be prevented from being deactivated.

[0055] The dissolved oxygen concentration can be controlled by controlling the aeration volume of the air from the blower 22 that supplies air into the reaction tank 14.

[0056] Furthermore, by controlling the ammonia concentration, it is possible to suppress the growth of nitrite-oxidizing bacteria in the reaction tank 14. The activity of nitrite-oxidizing bacteria to oxidize nitrite to nitrate can be inhibited by setting the ammonia concentration to a predetermined concentration or higher. The ammonia concentration of the wastewater in the reaction tank 14 or the treated water discharged from the reaction tank 14 is controlled to between 10 mg / L and 500 mg / L, preferably between 30 mg / L and 400 mg / L, and more preferably between 50 mg / L and 300 mg / L.

[0057] The ammonia concentration can be controlled by controlling at least one of the aeration volume of the blower 22 that supplies air into the reaction tank 14 and the inflow rate of the raw water before treatment that is supplied into the reaction tank 14 by the valve 34.

[0058] Furthermore, the pH of the wastewater in the reaction tank 14 or the treated water discharged from the reaction tank 14 is preferably controlled to 6.5 or higher and 8.5 or lower, more preferably 7.0 or higher and 8.0 or lower, and even more preferably 7.5. Note that the pH does not need to be controlled to 7.5 exactly, as long as it can be adjusted to around 7.5, for example, within a range of 7.5 ±0.2.

[0059] Since anammox bacteria are inactivated at high alkalinity, it is preferable to control the pH. By keeping the pH at 8.5 or less, it is possible to prevent the anammox bacteria from being inactivated. On the other hand, since the activity of anammox bacteria decreases even at low pH, it is preferable to keep the pH at 6.5 or higher. Since the pH in the reaction tank tends to decrease due to the nitrification reaction, it is preferable to increase the pH by adding a chemical such as sodium hydroxide (NaOH). Furthermore, if the pH is high, it is preferable to lower the pH by adding a chemical such as hydrochloric acid (HCl).

[0060] Also, ammonia (ammonium ion) is neutral, NH4 + However, when the wastewater becomes alkaline, it is liberated to become NH3, which is toxic to nitrite-oxidizing bacteria. Therefore, it is preferable to control the concentration of NH3 so that the nitrite-oxidizing bacteria do not grow too much in the wastewater or treated water in the reaction tank. The concentration of NH3 can be adjusted by adjusting the ammonia concentration and pH. The concentration of NH3 can be calculated, for example, using the following FA formula:

[0061]

number

[0062] The FA concentration is preferably 1.0 mg / L or higher. By setting the FA concentration to 1.0 mg / L or higher, the growth of nitrite-oxidizing bacteria can be suppressed. When the nitrite-oxidizing bacteria increase, nitrite oxidized from ammonia by ammonia-oxidizing bacteria in the reaction tank is nitrified to nitrate. Therefore, the amount of nitrite, which is the raw material for the anammox reaction, decreases, and the amount of nitrate that is not denitrified increases, resulting in a decrease in the nitrogen treatment rate. In order to suppress the growth of nitrifying and oxidizing bacteria, it is preferable to control the FA concentration to 1.0 mg / L or higher.

[0063] In the wastewater treatment method of this embodiment, the nitrogen load in the reaction tank 14 is set to 0.5 kg-N / m 3 / day or more 3.0kg-N / m 3 / day or less. More preferably, it is 1.0 kg-N / m 3 / day or more 3.0kg-N / m 3 / day or less, more preferably 1.0 kg-N / m 3 / day or more 2.5kg-N / m 3 / day or less. When the nitrogen load increases, the aeration rate must be increased to oxidize the ammonia using ammonia-oxidizing bacteria. Increasing the aeration rate increases the oxygen concentration in the reaction tank 14, which may reduce the activity of the anammox bacteria. By controlling the dissolved oxygen concentration and ammonia concentration in the wastewater as described above, denitrification can be performed without reducing the nitrogen treatment rate, even under reaction conditions with a higher nitrogen load than before.

[0064] According to the wastewater treatment device 10 and wastewater treatment method of the first embodiment, the dissolved oxygen concentration of the wastewater and the ammonia concentration of the wastewater or treated water are set within predetermined ranges, thereby maintaining the activity of ammonia-oxidizing bacteria and anammox bacteria and enabling stable denitrification treatment.

[0065] Second Embodiment [Wastewater treatment equipment] Fig. 2 is a conceptual diagram of a wastewater treatment device 110 of the second embodiment. In Fig. 2, parts common to those of the wastewater treatment device 10 of the first embodiment shown in Fig. 1 are given the same reference numerals, and detailed description thereof will be omitted, with the description focusing on characteristic parts of the second embodiment.

[0066] The wastewater treatment device 110 of the second embodiment shown in Fig. 2 differs from the wastewater treatment device 10 of the first embodiment shown in Fig. 1 in that an ammonia concentration measuring means 142 for measuring the ammonia concentration in raw water is provided in the raw water supply pipe 16, and a nitrate concentration measuring means 144 for measuring the nitrate concentration of wastewater in the reaction tank 14 is provided in the reaction tank 14. Another difference is that the wastewater treatment device 110 is provided with a calculation unit 146 for calculating a control value D, which is the ratio of the generated nitric acid to the amount of ammonia treated, from the ammonia concentration in the raw water, the ammonia concentration, and the nitrate concentration in the wastewater, and the control means 28 has a function of controlling the control value D within a predetermined range.

[0067] As the ammonia concentration measuring means 142, a device similar to the ammonia concentration measuring means 26 provided in the reaction tank 14 can be used.

[0068] The nitric acid concentration measuring means 144 may be, but is not limited to, a nitric acid ion electrode, an automatic nitric acid analyzer, or the like.

[0069] The calculation unit 146 calculates a control value D, which is the ratio of the amount of nitric acid produced to the amount of ammonia treated, from the ammonia concentration of the raw water measured by the ammonia concentration measurement means 142, the ammonia concentration of the wastewater measured by the ammonia concentration measurement means 26, and the nitrate concentration of the wastewater measured by the nitrate concentration measurement means 144. Nitrate (NO3) is also produced from the anammox reaction, so by comparing the amount of NO3 produced with the amount of ammonia treated, it is possible to confirm that the nitrification reaction of nitrite to nitrate by nitrite-oxidizing bacteria is progressing.

[0070] The control value D, which is the ratio of the NO3 production rate to the ammonia treatment rate, can be calculated by dividing the NO3 production rate (C) by the ammonia treatment rate (AB), where A is the ammonia concentration in the raw water, B is the ammonia concentration in the wastewater from the reaction tank 14, and C is the nitrate concentration in the wastewater from the reaction tank 14, as follows: D = C / (AB). The control means 28 controls the blower 22 to adjust the aeration air volume or the valve 34 to adjust the inflow rate of the raw water supplied to the reaction tank 14 so that the control value D is between 0.05 and 0.25. It is more preferable that the control value D be between 0.08 and 0.20. By setting the control value D within the above range, it can be confirmed that the NO3 produced by the anammox reaction accounts for a large proportion of the NO3 produced in the reaction tank, suppressing the production of NO3 by nitrite-oxidizing bacteria and suppressing the activity of the nitrite-oxidizing bacteria. Furthermore, a low control value D indicates a low amount of NO3, indicating that the anammox reaction is not progressing.

[0071] 2, the ammonia concentration of the raw water is measured by an ammonia concentration measuring means 142 provided in the raw water supply pipe 16, but instead of the ammonia concentration measuring means 142, a total nitrogen concentration measuring means may be provided to measure the total nitrogen concentration of the raw water, and the total nitrogen concentration may be designated as A to determine the control value D. The total nitrogen concentration measuring means may be, but is not limited to, a total nitrogen automatic analyzer. Since most of the nitrogen components in the raw water are ammonia components, the total nitrogen concentration and the ammonia concentration will be close values, and therefore the control value D may be calculated using the total nitrogen concentration of the raw water.

[0072] Furthermore, the ammonia concentration of the wastewater may be the ammonia concentration of the treated water, and the nitric acid concentration of the wastewater may be the nitric acid concentration of the treated water.

[0073] [Wastewater treatment method] Next, a wastewater treatment method of a second embodiment will be described. The wastewater treatment method of the second embodiment can be performed, for example, using the wastewater treatment device 110 shown in FIG. 2. The wastewater treatment method of the second embodiment differs from the wastewater treatment method of the first embodiment in that a control value D, which is the ratio of generated nitric acid to the amount of ammonia treated, is controlled within a predetermined range. Detailed descriptions of the parts common to the wastewater treatment method of the first embodiment will be omitted, and the description will focus on the characteristic parts of the second embodiment.

[0074] In the wastewater treatment method of the second embodiment, as in the wastewater treatment method of the first embodiment, ammonia-oxidizing bacteria and anammox bacteria attached to a carrier are contained in one reaction tank 14, so that oxidation of ammonia in the wastewater to nitrite by the ammonia-oxidizing bacteria and denitrification of ammonia and nitrite by the anammox bacteria are carried out in the single reaction tank. The dissolved oxygen concentration of the wastewater in the reaction tank 14 is controlled to between 0.5 mg / L and 4.0 mg / L, and the ammonia concentration of the wastewater in the reaction tank 14 or the treated water discharged from the reaction tank 14 is controlled to between 10 mg / L and 500 mg / L.

[0075] Furthermore, in the wastewater treatment method of the second embodiment, a control value D is calculated, which is the ratio of the amount of nitric acid produced to the amount of ammonia treated, from the ammonia concentration or total nitrogen concentration in the raw water, the ammonia concentration in the wastewater or treated water, and the nitrate concentration in the wastewater or treated water. The control value D can be calculated by dividing the amount of NO3 produced (C) by the amount of ammonia treated (AB), where A is the ammonia concentration or total nitrogen concentration in the raw water, B is the ammonia concentration in the wastewater in the reaction tank 14 or the treated water discharged from the reaction tank 14, and C is the nitrate concentration in the wastewater in the reaction tank 14 or the treated water discharged from the reaction tank 14, as follows: D = C / (AB). The control value D is then controlled to be between 0.05 and 0.25. The control value D can be controlled by controlling at least one of the blower 22 to control the aeration airflow rate or the valve 34 to control the inflow rate of raw water supplied to the reaction tank 14. The control value D is more preferably between 0.08 and 0.20.

[0076] Nitrate (NO3) is also produced in the anammox reaction, so by comparing the amount of NO3 produced with the amount of ammonia treated, it is possible to confirm that the nitrification reaction from nitrite to nitrate by nitrite-oxidizing bacteria is progressing. By setting the control value D within the above range, it is possible to confirm that the NO3 produced by the anammox reaction accounts for a large portion of the amount of NO3 produced in the reaction tank, suppressing the production of NO3 by nitrite-oxidizing bacteria and suppressing the activity of nitrite-oxidizing bacteria. Furthermore, when the control value D is low, it is possible to confirm that the amount of NO3 is low and the anammox reaction is not progressing. If the nitrification of nitrite by nitrite-oxidizing bacteria progresses, the amount of nitrite, which is the raw material for the anammox reaction, decreases and remains as nitrate in the treated water, which is undesirable because it reduces the nitrogen treatment rate.

[0077] According to the wastewater treatment device 110 and wastewater treatment method of the second embodiment, the activity of ammonia-oxidizing bacteria and anammox bacteria can be maintained and stable denitrification treatment can be performed by setting the dissolved oxygen concentration of the wastewater and the ammonia concentration of the wastewater or treated water within a predetermined range. In addition, the amount of nitrate produced from nitrite by nitrite-oxidizing bacteria can be reduced, preventing a decrease in the nitrogen treatment rate. [Example]

[0078] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples and can be modified as appropriate without departing from the spirit of the present invention.

[0079] [Production of Anammox Bacteria Adhesion Carrier] Anammox bacteria-attached carriers for use as carriers for wastewater treatment were produced. Figure 3 shows an experimental apparatus 200 used to produce anammox bacteria-attached carriers. The reaction tank 202 had an effective volume of 1.44 L and was filled with carriers 204 at a carrier filling rate of 20%. The reaction tank 202 was adjusted to a water temperature of 30°C using a water jacket 206. The pH in the reaction tank 202 was measured using a pH sensor 218, and a pump (not shown) was controlled by a pH controller (not shown). The pH was adjusted to 7.6 using a 0.2 N hydrochloric acid solution. The reaction tank 202 was equipped with a raw water supply pipe 208 for supplying raw water, a discharge pipe 210 for discharging treated water, an acid solution supply pipe 212 for supplying 0.2 N hydrochloric acid, and a gas supply pipe 214 for supplying N2 gas. The reaction tank 202 also had an agitator 216 for agitating the treated water and carriers 204 in the reaction tank 202. A magnetic stirrer (As One, VPS-160S) and a stirring bar were used as the stirrer 216. The nitrogen load was 6.0 kg / m 3 The reactor conditions are shown in Table 1.

[0080] [Table 1]

[0081] {Test carrier} A polyvinyl alcohol (PVA) bead-shaped gel carrier was used as the carrier 204. The carrier 204 was filled into the reaction vessel 202 after anammox bacteria had been attached to it in advance by pre-acclimation.

[0082] {Test drainage} The composition of the synthetic wastewater used to manufacture the anammox bacteria adhesion carrier is shown in Table 2. Trace components 1 and 2 were weighed according to the compositions in Tables 3 and 4 and dissolved in tap water to prepare the solution. Trace components 1 and 2 were added at 1 mL per 1 L of synthetic wastewater.

[0083] [Table 2]

[0084] [Table 3]

[0085] [Table 4]

[0086] Using the above reactor and test wastewater, anammox bacteria were attached to PVA carriers to produce carriers with sufficient activity, which were then used in a one-tank system.

[0087] [Production of ammonia-oxidizing bacteria-attached carrier] Ammonia-oxidizing bacteria-attached carriers were produced for use as carriers for wastewater treatment. Figure 4 shows an experimental apparatus 300 used to produce the ammonia-oxidizing bacteria-attached carriers. The reaction tank 302 had an effective volume of 1.44 L and was filled with carriers 304 at a carrier filling rate of 10%. The reaction tank 302 was adjusted to a water temperature of 30°C using a water jacket 306. The pH in the reaction tank 302 was measured by a pH sensor 318, and a pump (not shown) was controlled by a pH controller (not shown) to adjust the pH to 7.6 using a 2.0 N sodium hydroxide (NaOH) solution. The reaction tank 302 was equipped with a raw water supply pipe 308 for supplying raw water, a discharge pipe 310 for discharging treated water, and an alkaline solution supply pipe 312 for supplying 2.0 N sodium hydroxide solution. The reactor 302 is also equipped with an air supply pipe 320 connected to a blower (not shown) to supply air to maintain an aerobic state inside the reactor 302, and an N2 gas supply pipe 314 to supply N2 gas used for stirring to maintain the fluidity of the carriers. The carriers may be stirred using a stirrer. The nitrogen load is 1.0 kg / m 3 The reactor conditions are shown in Table 5.

[0088] [Table 5]

[0089] {Test carrier} A polyvinyl alcohol (PVA) bead-shaped gel carrier was used as the carrier 304. At the start of operation of the device, activated sludge collected from a sewage treatment plant was added so that the SS concentration would be 2000 mg / L.

[0090] {Test drainage} The composition of the synthetic wastewater used to manufacture the ammonia-oxidizing bacteria attachment carrier is shown in Table 6. Trace components 1 and 2 were weighed according to the compositions in Tables 3 and 4 and dissolved in tap water to prepare the solution. Trace components 1 and 2 were added at 1 mL per 1 L of synthetic wastewater.

[0091] [Table 6]

[0092] Using the above reactor and test wastewater, ammonia-oxidizing bacteria were attached to a PVA carrier to produce ammonia-oxidizing bacteria-attached carriers with sufficient activity, which were then used in a one-tank system.

[0093] [Experimental Example 1: Start-up test] The experimental equipment used was an acrylic experimental device with an external water jacket, as shown in Figure 4. Aeration was performed using a blower to create an aerobic environment inside the reaction tank. At the same time, N2 gas or a stirrer was used to maintain the fluidity of the carrier.

[0094] The reactor conditions are shown in Table 7. The effective volume of the reactor was 1.44 L, and the carrier filling rate was 7.5% for anammox bacteria-attached carriers and 10% for ammonia-oxidizing bacteria-attached carriers. The pH was controlled at 7.6 using a pH controller. The temperature in the reactor was maintained at 30°C using a water jacket. The nitrogen load was 1.0 to 3.0 kg / m per reactor. 3 I set it to / day.

[0095] [Table 7]

[0096] The water quality data of Experimental Example 1 in the performance evaluation of the single-tank anammox reactor is shown in Figure 5. The nitrogen treatment rate is also shown in Figure 6. + " is the ammonia concentration in the raw water, "Eff.NO2 - " is the nitrite concentration of the treated water, "Eff.NH4 + " is the ammonia concentration of the treated water, "Eff.NO3 - " indicates the nitrate concentration of treated water. The same applies below.

[0097] The DO concentration at the start of the equipment was controlled to 0.5-2.0 mg / L by adjusting the aeration air volume. At the start of the equipment operation (day 0), the DO concentration was set to 0.6 mg / L, taking into consideration the oxygen inhibition of anammox bacteria. Furthermore, NO2- To prevent inhibition, the water in the tank was replaced with tap water and the raw water pump was stopped. After that, the supply of raw water was started from the first day. At this time, NO2 - Inflow NH4 + The HRT (hydraulic retention time) was set to 24 hours, and the nitrogen load was 1.0 kg / m 3 I set it to / day.

[0098] Until the 8th day, the NH4 + The aeration air volume was increased to about 50 mg / L, and the nitrification performance was improved. Then, on the 9th day, when the aeration air volume was 2.0 L / min, the NH4 + -N was 53 mg / L, and NH4 + -N showed low values, indicating high nitrogen treatment performance. + -N is 1000mg / Lm, nitrogen load is 1.0kg / m 3 / day NH4 + On the 17th day, which was the initial stage of the change, the NH4 + The treatment efficiency was stable until the 25th day, and the start-up was completed.

[0099] As shown in Figure 6, the nitrogen treatment rate during the start-up period was 86% at its maximum, and 76.8% on average. The nitrogen treatment rate was calculated based on the following: (1) Inflow ammonia nitrogen Inf.NH4 + and nitrite nitrogen Inf.NO2 - and nitrate nitrogen Inf.NO3 - From the sum of (2) Ammonia nitrogen in water Eff.NH4 + and nitrite nitrogen Eff.NO2 - and nitrate nitrogen Eff.NO3 - The sum of the above is subtracted, divided by (1), and expressed as a percentage. Specifically, this was calculated using the following formula:

[0100]

number

[0101] [Experimental Example 2: High nitrogen load test] The test in Experimental Example 1 was continued, and a high nitrogen load test was conducted by changing the nitrogen load. Figures 7 and 8 show the water quality data for Experimental Example 2 in the performance evaluation of the single-tank anammox reactor. Figure 9 shows the time-dependent changes in nitrogen load (NLR) and nitrogen treatment rate (NCR). As shown in Figure 8, the DO concentration was controlled at 1.5 to 2.0 mg / L by adjusting the aeration airflow until the 85th day.

[0102] From the 60th to 73rd day of operation, the nitrogen load was 1.0 kg / m 3 / day. The average Eff.NH4 + , Average Eff.NO3 - were 25 mg / L and 3.1 mg / L, respectively, demonstrating high treatment capacity.

[0103] However, from the 70th day, the NH4 + The activity of nitrite-oxidizing bacteria increases, and NO3 - Therefore, on the 73rd day, the nitrogen load was increased to 2.0 kg / m 3 / day, the NH4 + We decided to increase the amount of nitrite in the nitrite-oxidizing bacteria and suppress the activity of nitrite-oxidizing bacteria.

[0104] (Detection of oxidative activity of nitrite-oxidizing bacteria) No. 3 - As a result of the increase in NO3 - It was determined whether the increase in NO3 was due to the anammox reaction or an increase in the activity of nitrite-oxidizing bacteria. This was done by comparing the ammonia treatment amount ΔNH4, i.e., the value obtained by subtracting the NH4 in the treated water from the NH4 in the raw water (inflow), with the ratio of the produced NO3 (ΔNO3) (control value D).

[0105] Figure 10 shows the graph with ΔNO3 / ΔNH4 added. As shown in Figure 10, on the 67th day, ΔNO3 / ΔNH4 was 0.17, but because the ammonia in the treated water fell below 10 mg / L, it suddenly rose to ΔNO3 / ΔNH4 = 0.31 on the 71st day. Therefore, the amount of raw water inflow was increased to raise the ammonia concentration in the reaction tank. On the 73rd day, the ammonia concentration rose to 394 mg / L, and on the 74th day, it recovered to ΔNO3 / ΔNH4 = 0.17.

[0106] Figure 11 shows the changes in FA and ΔNO3 / ΔNH4. When FA was 1.0 mg / L or higher, ΔNO3 / ΔNH4 was 0.2 or less, but after the 70th day, when FA fell below 1.0 mg / L, the ΔNO3 / ΔNH4 value rose sharply. It can also be seen that after the 73rd day, when the FA concentration was increased, the ΔNO3 / ΔNH4 value fell sharply.

[0107] Therefore, since the FA concentration can be adjusted by adjusting the ammonia concentration and pH, it was confirmed that by operating the system to maintain FA at 1.0 mg / L or higher, the increase in the ΔNO3 / ΔNH4 value can be suppressed, and the activity of nitrite-oxidizing bacteria can be suppressed.

[0108] [Experimental Example 3: Ultra-high load test] The tests of Experimental Examples 1 and 2 were continued, and an ultra-high load test was conducted by changing the nitrogen load. Figure 12 shows the water quality data of Experimental Example 3 in the performance evaluation of the single-tank anammox reactor. Figure 13 shows the change in nitrogen treatment rate over time, and Figure 14 shows the change in nitrogen load (NLR) and nitrogen treatment rate (NCR) over time. Note that the data from 60th to 90th days after the start of operation is common to Experimental Example 2.

[0109] The DO concentration was 1.7 mg / L from the 60th to 67th day after the start of operation, and good treatment performance was obtained. After that, as the nitrogen load increased, the aeration volume was increased and the DO concentration in the reactor was maintained at 2 to 2.5 mg / L, and good treatment performance was obtained. However, after the 98th day, when the DO concentration exceeded 3.0 mg / L, the treatment rate increased, but the Eff.NO3 - increased and a decrease in nitrogen treatment rate was observed.

[0110] Nitrogen load 2.5kg / m 3 When I raised it to / day, the Eff. NO.3 was achieved from the beginning of the change. - This is because the aeration volume was too high. Therefore, by increasing the nitrogen load, the NH4 + The nitrogen load was 2.5 kg / m and the activity of nitrite-oxidizing bacteria was suppressed. 3 Average Eff.NH4 per day + , Average Eff.NO3 - were 76 mg / L and 7.8 mg / L, respectively.

[0111] Nitrogen load is 3.0 kg / m 3 / day, the aeration air volume was gradually increased to 14 L / min to increase nitrification activity, but no increase in nitrification performance was observed beyond a certain point. This can be attributed to the limit of oxygen supply to the microorganisms. Therefore, under these conditions, the average Eff.NH4 + , Average Eff.NO3 - were 176 mg / L and 8.4 mg / L, respectively. [Explanation of symbols]

[0112] 10...wastewater treatment device, 12...wastewater treatment carrier, 14...reaction tank, 16...raw water supply pipe, 18...treated water discharge pipe, 20...aeration plate, 22...blower, 24...dissolved oxygen concentration measuring means, 26...ammonia concentration measuring means, 28...control means, 30...agitator, 32...motor, 34...valve, 36...pH measuring means, 38...pH control means, 40...chemical tank, 110...wastewater treatment device, 142...ammonia concentration measuring means, 144...nitric acid concentration measuring means, 146...calculation unit, 2 00...experimental equipment, 202...reaction tank, 204...carrier, 206...water jacket, 208...raw water supply pipe, 210...discharge pipe, 212...acidic solution supply pipe, 214...gas supply pipe, 216...agitator, 218...sensor, 300...experimental equipment, 302...reaction tank, 304...carrier, 306...water jacket, 308...raw water supply pipe, 310...discharge pipe, 312...alkaline solution supply pipe, 314...N2 gas supply pipe, 318...pH sensor, 320...air supply pipe

Claims

1. A wastewater treatment method for denitrifying wastewater by contacting wastewater containing ammonia with the wastewater treatment carrier in a reaction tank containing a wastewater treatment carrier having ammonia-oxidizing bacteria and anammox bacteria attached thereto, or a wastewater treatment carrier having a mixture of ammonia-oxidizing bacteria-attached carriers having ammonia-oxidizing bacteria attached thereto and anammox bacteria-attached carriers having anammox bacteria attached thereto, The dissolved oxygen concentration of the wastewater in the reaction tank is controlled to be 0.5 mg / L or more and 4.0 mg / L or less, Controlling the ammonia concentration of the wastewater in the reaction tank or the treated water discharged from the reaction tank to 10 mg / L or more and 500 mg / L or less; When the ammonia concentration or total nitrogen concentration of the raw water before the treatment of the wastewater is A, the ammonia concentration of the wastewater from the reaction tank or the treated water discharged from the reaction tank is B, and the nitric acid concentration of the wastewater from the reaction tank or the treated water discharged from the reaction tank is C, the control value D, which is the ratio of the generated nitric acid to the amount of ammonia treated, is calculated by D = C / (A - B), The control value D is controlled to be equal to or greater than 0.05 and equal to or less than 0.

25. Wastewater treatment methods.

2. The control of the dissolved oxygen concentration is carried out by controlling the aeration volume of air supplied into the reaction tank. The wastewater treatment method according to claim 1.

3. The ammonia concentration is controlled by controlling at least one of the aeration volume of air supplied into the reaction tank and the inflow rate of the raw water before treatment of the wastewater. The wastewater treatment method according to claim 1 or 2.

4. Controlling the pH of the wastewater in the reaction tank or the treated water discharged from the reaction tank to 6.5 or more and 8.5 or less; The wastewater treatment method according to any one of claims 1 to 3.

5. The nitrogen load on the reactor is 0.5 kg-N / m ３ / day or more 3.0kg-N / m ３ / day or less, The wastewater treatment method according to any one of claims 1 to 4.

6. The carrier is polyvinyl alcohol. The wastewater treatment method according to any one of claims 1 to 5.

7. A reaction tank containing a wastewater treatment carrier in which ammonia oxidizing bacteria and anammox bacteria are attached to a carrier, or a wastewater treatment carrier in which ammonia oxidizing bacteria-attached carrier in which ammonia oxidizing bacteria are attached to a carrier and anammox bacteria-attached carrier in which anammox bacteria are attached to a carrier are mixed; a raw water supply pipe for supplying raw water before treatment to the reaction tank; a treated water discharge pipe for discharging treated water treated in the reaction tank; an air supply means for supplying air into the reaction vessel; a dissolved oxygen concentration measuring means for measuring the dissolved oxygen concentration of the wastewater in the reaction tank; an ammonia concentration measuring means for measuring the ammonia concentration of the wastewater in the reaction tank or the treated water; a control means for controlling the dissolved oxygen concentration measured by the dissolved oxygen concentration measuring means to be 0.5 mg / L or more and 4.0 mg / L or less, and for controlling the ammonia concentration measured by the ammonia concentration measuring means to be 10 mg / L or more and 500 mg / L or less, and further comprising: A calculation unit is provided that calculates a control value D, which is the ratio of the generated nitric acid to the amount of ammonia treated, by D = C / (A - B), where A is the ammonia concentration or total nitrogen concentration of the raw water, B is the ammonia concentration of the wastewater from the reaction tank or the treated water discharged from the reaction tank, and C is the nitric acid concentration of the wastewater from the reaction tank or the treated water discharged from the reaction tank, The control means controls the control value D to be equal to or greater than 0.05 and equal to or less than 0.

25. Wastewater treatment equipment.

8. The control means controls the dissolved oxygen concentration by controlling the aeration air volume of the air supply means. The wastewater treatment device according to claim 7.

9. The control means controls the ammonia concentration by controlling at least one of the aeration air volume by the air supply means and the inflow rate of the raw water. The wastewater treatment device according to claim 7 or 8.

10. a pH measuring means for measuring the pH of the wastewater in the reaction tank or the treated water; and a pH control means for controlling the pH measured by the pH measurement means to be 6.5 or more and 8.5 or less. The wastewater treatment device according to any one of claims 7 to 9.

11. The nitrogen load on the reactor is 0.5 kg-N / m ３ / day or more 3.0kg-N / m ３ / day or less, The wastewater treatment device according to any one of claims 7 to 10.

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