JP2010264422A - Denitrification treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make water to be treated and a carrier flow in a denitrification tank so that microorganisms are not exfoliated from a carrier charged in the denitrification tank and the career is not destroyed and further to dispense with a screen for preventing the career from flowing out. <P>SOLUTION: In a denitrification treatment apparatus 10 equipped with the denitrification tank 12 where water to be treated flows in and a lot of careers 30 carrying denitrifying bacteria are charged to carrying out denitrification treatment of water to be treated, a cylindrical member 14, an agitation means 18 and a control means 20 are provided. The cylindrical member 14 is vertically provided in the water to be treated in the denitrification tank 12 and partitions the inside of the denitrification tank 12 to a tube outside where the careers 30 are charged and a tube inside which communicates with the tube outside. The agitation means 18 forms a fluidized bed 32 of the careers 30 in an ascending stream at the tube outside by producing a descending flow at the tube inside by rotation of an agitation blade 16 provided at the tube inside of the cylindrical member 14 and further producing an ascending flow at the tube outside caused by reversal of the descending flow at a tank bottom to produce a vertical circulation flow in the water to be treated in the denitrification tank. The control means 20 controls an expansion ratio of the fluidized bed 32 by changing flow speed of the ascending stream by adjusting the rotating speed of the agitation blade 16. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a denitrification treatment apparatus, and more particularly, to a denitrification treatment apparatus that performs a denitrification treatment by filling a carrier carrying denitrification bacteria in a denitrification tank into which treated water flows.

  Conventionally, a nitrification / denitrification apparatus is known as an apparatus for treating ammonia in wastewater (for example, Patent Document 1). This nitrification / denitrification device is used for the purpose of efficient removal of ammonia by filling a carrier in which a microorganism containing nitrifying bacteria (for example, activated sludge) is supported on a supporting material into the nitrifying tank, It is usual to increase the nitrification efficiency by increasing the concentration.

  Examples of the carrier include an adherent carrier that attaches bacteria to the surface of a support material such as sponge and foamed plastic, and an encapsulated carrier that comprehensively immobilizes bacteria in a gel.

  In the nitrification tank filled with the carrier, it is important to flow the water to be treated and the carrier in the nitrification tank in order to increase the nitrification efficiency, and a flow means is provided. Since the nitrification reaction in the nitrification tank is an aerobic reaction, an air aeration apparatus is usually used as a flow means.

  Further, a screen is provided at the treated water outlet of the nitrification tank to prevent the carrier from flowing out along with the treated water. In this case, as shown in Patent Document 2, a guide plate is installed on the front side of the screen, and the screen is washed with the water flow by guiding the water flow caused by the air lift of the air aeration apparatus between the guide plate and the screen. This prevents the carrier from clogging the screen.

  That is, in the case of a nitrification tank in which an air aeration apparatus can be used as the flow means, even if a screen is provided, the screen can be prevented from being clogged by the air of air aeration.

  By the way, in order to improve the efficiency of the denitrification reaction of the nitrification / denitrification apparatus, it is preferable to fill the denitrification tank with a carrier carrying microorganisms containing denitrifying bacteria (for example, activated sludge).

  However, since the denitrification reaction in the denitrification tank is an anaerobic reaction, there is a problem that the air aeration apparatus cannot be used to prevent the clogging of the water to be treated and the carrier and the screen. However, if nitrogen gas or carbon dioxide gas, which is a gas other than air, is aerated, nitrogen and carbon dioxide are dissolved in the treated water, and there is a problem and the running cost becomes enormous.

  Therefore, the conventional denitrification tank is usually provided with an underwater agitator in the denitrification tank as means for flowing the water to be treated and the carrier.

JP 2000-285881 A JP 09-117785 A

  However, when an underwater stirrer is provided in a denitrification tank filled with a carrier, in the case of an adherent carrier, the attached bacteria are peeled off when the carrier comes into contact with the stirrer, and there is a problem that the denitrification performance is lowered. . Thereby, there exists a fault that the effect of using an adhesion | attachment support | carrier for a denitrification process is not fully exhibited.

  On the other hand, in the case of the entrapping carrier, there is a problem that the gel as the supporting material is finely broken due to contact with the stirrer or a stirring shearing force and flows out of the screen. Thereby, there exists a fault that the effect which uses a comprehensive support | carrier for a denitrification process is not fully exhibited.

  Further, since the denitrification tank can use an air aeration apparatus to prevent clogging of the screen like the nitrification tank, there is a problem that the screen is easily clogged and must be frequently cleaned. For this reason, in order to fill the denitrification tank with a carrier and improve the efficiency of the denitrification process, a denitrification tank that does not require a screen is desired.

  The present invention has been made in view of such circumstances, and the water to be treated and the carrier in the denitrification tank so that the microorganisms are not detached from the carrier filled in the denitrification tank or the carrier is damaged. It is an object of the present invention to provide a denitrification apparatus that can be made to flow and that does not require a screen for preventing carrier outflow.

  According to a first aspect of the present invention, in order to achieve the above object, denitrification is performed by filling a large number of carriers carrying denitrifying bacteria in a denitrification tank into which the water to be treated flows, and performing denitrification treatment of the water to be treated. In the treatment apparatus, a cylindrical member that is provided vertically in the water to be treated of the denitrification tank and divides the inside of the denitrification tank into a cylinder outside that is filled with the carrier and a cylinder that communicates with the cylinder outside, A stirring blade is provided in the cylinder of the cylindrical member, and the rotation of the stirring blade generates a downward flow in the cylinder and generates an upward flow in which the downward flow is reversed at the bottom of the tank outside the cylinder. By generating a vertical circulation flow in the water to be treated in the denitrification tank, the stirring means for forming the fluidized bed of the carrier in the upward flow outside the cylinder, and the rotation speed of the stirring blades are adjusted. Control means for controlling the expansion rate of the fluidized bed by changing the flow velocity of the upward flow. Providing denitrification apparatus, characterized in that the.

  Here, “supporting denitrifying bacteria” includes not only denitrifying bacteria but also a case of supporting a group of microorganisms mainly containing denitrifying bacteria (for example, activated sludge). In the denitrification tank, suspended activated sludge may be present together with the carrier.

  According to the present invention, the inside of the denitrification tank is partitioned by the cylindrical member into the outside of the cylinder filled with a large number of carriers carrying denitrifying bacteria and the inside of the cylinder communicating with the outside of the cylinder, and the stirrer is provided in the cylinder. A stirring blade was provided. Then, by rotating the stirring blade, a downward flow is generated in the cylinder and an upward flow is generated outside the cylinder, and a fluidized bed in which a large number of carriers flow in the upward flow outside the cylinder filled with the carrier. It was made to form.

  As a result, a longitudinal circulation flow passing through the fluidized bed is formed in the water to be treated which has flowed into the denitrification tank, so that the contact efficiency between the carrier and the water to be treated is improved and the denitrification efficiency is improved. be able to.

  Furthermore, in the present invention, a control means for controlling the stirring means is provided, and the expansion rate of the fluidized bed is controlled by changing the flow rate of the upward flow by adjusting the rotation speed of the stirring blades. Thereby, the support | carrier of a fluid bed does not flow in into the cylinder of a cylindrical member, and does not contact a stirring blade, or flows out from a denitrification tank.

  Therefore, the water to be treated and the carrier can flow in the denitrification tank so that the microorganisms are not detached from the carrier filled in the denitrification tank or the carrier is damaged, and the screen for preventing the carrier from flowing out. It is possible to provide a denitrification processing apparatus that does not need to be provided.

  In the present invention, it is preferable that detection means for detecting an upper end of the fluidized bed is provided, and the control means adjusts the rotation speed of the stirring blade based on a detection result of the detection means.

  Thereby, it can prevent reliably that the support | carrier of a fluid bed flows in into the cylinder of a cylindrical member, contacts a stirring blade, or flows out from a denitrification tank.

  In the present invention, the control means is configured so that the expansion rate is in a range of 150 to 200% when the expansion rate of the fluidized bed in a state where rotation of the stirring blade is stopped is 100%. It is preferable to adjust the number of rotations of the blades.

  If the expansion rate of the fluidized bed is less than 150%, the gap between the carriers forming the fluidized bed is insufficient, so that the solid content in the water to be treated easily blocks the fluidized bed. When the expansion rate exceeds 200%, the carrier easily flows into the cylinder of the cylindrical member.

  In the present invention, it is preferable that a taper is formed at a corner of the bottom of the denitrification tank. As a result, the downward flow formed in the cylinder is smoothly reversed to the upward flow outside the cylinder, so that the water to be treated is not retained at the corner of the bottom of the denitrification tank.

  In the present invention, the carrier is preferably a generic carrier in which denitrifying bacteria are generically immobilized on a gel.

  According to the denitrification treatment apparatus of the present invention, the water to be treated and the carrier can be flowed in the denitrification tank so that the microorganisms are not detached from the carrier filled in the denitrification tank or the carrier is damaged. In addition, it is not necessary to provide a screen for preventing the carrier from flowing out.

Conceptual diagram of the denitrification apparatus of the present invention The conceptual diagram in the case of providing a plurality of units in the denitrification tank in the denitrification processing apparatus of the present invention Conceptual diagram of conventional denitrification equipment Explanatory drawing explaining the test result of the test A in the Example of this invention Explanatory drawing explaining the test result of the test B in the Example of this invention

  Hereinafter, preferred embodiments of a denitrification apparatus of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, the denitrification apparatus 10 of the present invention mainly includes a denitrification tank 12, a cylindrical member 14 provided vertically in the water to be treated in the denitrification tank 12, and a cylinder of the cylindrical member 14. A stirring means 18 having a stirring blade 16 disposed therein and a control means 20 for controlling the rotational speed of the stirring blade 16 are configured.

  An inflow pipe 22 is connected to the bottom of the denitrification tank 12, and a pump 24 is provided in the inflow pipe 22. As a result, water to be treated (for example, a nitrification liquid from a nitrification tank (not shown)) flows through the inflow pipe 22 and flows into the denitrification tank 12. Moreover, the treated water piping 26 is connected to the upper part of the denitrification tank 12, and the treated water denitrified in the denitrification tank 12 is discharged out of the tank. A taper 13 is preferably formed at the corner of the bottom of the denitrification tank.

  The upper end opening 14A of the cylindrical member 14 is formed below the surface of the water to be treated, and the lower end opening 14B is formed at a position spaced from the bottom of the denitrification tank 12. Thereby, the outside of the cylinder of the cylindrical member 14 and the inside of the cylinder communicate with each other, and the water to be treated can flow. It is preferable that the cylindrical member 14 is disposed at the center in the width direction of the denitrification tank 12. Further, a stirring blade 16 is provided in the upper part of the cylindrical member 14 in the cylinder, and a rotating shaft 17 that rotates the stirring blade 16 is connected to a motor 28 disposed above the denitrification tank 12. The motor 28 is supported by a support member (not shown).

  Further, the inside of the denitrification tank 12 and the outside of the cylindrical member 14 is filled with a large number of carriers 30, 30. The filling rate of the carrier 30 is preferably in the range of 10 to 20% by volume (V / V%) of the effective volume of the denitrification tank.

  And the motor 28 rotates the stirring blade 16 in the rotation direction in which the downflow of the water to be treated is generated in the cylinder of the cylindrical member 14. As a result, the downward flow generated in the cylinder is discharged from the lower end opening 14B of the cylindrical member 14 toward the bottom of the denitrification tank 12, collides with the bottom of the denitrification tank 12, and the flow is reversed. The reversed flow rises as an upward flow outside the cylinder in the denitrification tank 12 and is taken in again from the upper end opening 14 </ b> A of the cylindrical member 14. Thereby, in the denitrification tank 12, a vertical circulation flow is formed in which the water to be treated flows as a downward flow in the cylinder of the cylindrical member 14 and flows as an upward flow outside the cylinder. A fluidized bed 32 of the carrier 30 is formed during counterflow.

  As the carrier 30 that forms the fluidized bed 32, an attached carrier in which denitrifying bacteria are attached to the surface of the carrier material, or a comprehensive carrier in which denitrifying bacteria are included inside the gel can be used. Here, “supporting denitrifying bacteria” includes not only denitrifying bacteria but also a case of supporting a group of microorganisms mainly containing denitrifying bacteria (for example, activated sludge).

  Further, the specific gravity of the carrier 30 used is settled at the bottom of the denitrification tank 12 in a state where the stirring blades 16 are not rotated, that is, in a state where no upward flow is generated outside the cylindrical member 14, It is necessary to flow in the upward flow by generating an upward flow. Specifically, the specific gravity of the carrier 30 is preferably 1.01 or more and 1.10 or less in any case of the adhering carrier and the entrapping carrier. More preferably, it is the range of 1.02-1.05.

  The adherent carrier forms a biofilm by attaching and retaining denitrifying bacteria on the surface of the carrier material, and has a large surface area such as a spherical carrier, a cylindrical carrier, a string carrier, a gel carrier, and a nonwoven material. If a carrier material with many irregularities is used, a large amount of denitrifying bacteria can be retained.

  The inclusion carrier is one in which at least a denitrifying bacterium and a monomer or prepolymer as a carrier material are mixed, and this mixture is polymerized to retain the denitrifying bacterium inside the gel. As the monomer material, acrylamide, methylenebisacrylamide, triacryl formal and the like can be suitably used. As the prepolymer, polyethylene glycol diacrylate or polyethylene glycol methacrylate can be suitably used. The shape of the inclusion carrier is preferably spherical or rectangular. In this case, the radial length from the carrier surface to the center of the carrier is preferably 2.5 mm or less (diameter of 5 mm or less). In the inclusion carrier, a denitrification reaction in which nitrogen gas is generated occurs inside the carrier, but if the radius is within 2.5 mm, the generated nitrogen gas can be smoothly discharged outside the carrier without accumulating inside the carrier.

Further, in both cases of the adherent carrier and the entrapping carrier, it is preferable that 10 ⁴ denitrifying bacteria / mL or more of the carrier are supported.

  The control means 20 is provided with detection means 34 for detecting the upper end of the fluidized bed 32, and the detection means 34 is disposed at a position below the upper end opening 14 </ b> A of the cylindrical member 14. The arrangement position of the detection means 34 is preferably, for example, about 30 to 50 cm below the upper end opening of the tubular member 14. The detection data detected by the detection means 34 is sequentially input to the control means 20, and the control means 20 is connected to the motor 28 of the stirring means 18 via a signal cable. As the detection means 34, an interface meter can be preferably used.

  Then, the control means 20 controls the rotation speed of the stirring blade 16 based on the detection result of the detection means 34. Specifically, it is preferable to adjust the rotation speed of the stirring blade 16 so that the expansion rate is in the range of 150 to 200%. Here, the expansion rate of the fluidized bed 32 is generated by the rotation of the agitating blade 16 when the expansion rate of the fluidized bed 32 is 100% when the rotation of the stirring blade 16 is stopped and the carrier 30 is settled. The ratio by which the layer thickness of the fluidized bed 32 expands upward due to upward flow. For example, an expansion rate of 200% means that the fluid has expanded to twice the bed thickness of the fluidized bed 32 due to the upward flow.

  If the expansion rate of the fluidized bed 32 is less than 150%, the gap between the carriers 30 forming the fluidized bed 32 is insufficient, so that the solid content in the water to be treated easily blocks the fluidized bed 32. If the expansion rate exceeds 200%, the carrier 30 easily flows into the cylinder of the cylindrical member 14, and the carrier 30 is broken by the stirring blade 16. Therefore, it is preferable that the detection means 34 is disposed at the upper end position of the fluidized bed 32 when the expansion rate is 200%.

  Next, the operation of the denitrification apparatus 10 configured as described above will be described.

  A large number of carriers 30 are filled outside the cylindrical member 14 disposed in the water to be treated in the denitrification tank 12. In this state, the control means 20 first rotates the stirring blade 16 of the stirring means 18 at a low speed to generate a low-speed circulation flow that circulates between the inside and the outside of the cylindrical member 14 in the denitrification tank 12. Form. As a result, a fluidized bed 32 having an expansion rate slightly exceeding 100% is formed outside the cylindrical member 14.

  Next, the control means 20 gradually increases the rotational speed of the stirring blade 16. As a result, the fluidized bed 32 expands and the upper end of the fluidized bed 32 is detected by the detection unit 34, so that the control unit 20 maintains the rotation speed of the stirring blade 16. Thereby, the fluidized bed 32 having an expansion rate of 150 to 200% is formed. Accordingly, a longitudinal circulation flow passing through the fluidized bed 32 is formed in the water to be treated which has flowed into the denitrification tank 12, so that the contact efficiency between the carrier 30 and the water to be treated is improved, and the denitrification efficiency is improved. Can be improved. Furthermore, the carrier 30 of the fluidized bed 32 does not flow into the cylinder of the cylindrical member 14 and come into contact with the stirring blade 16 or flow out of the denitrification tank 12.

  As a result, the water to be treated and the carrier 30 can flow in the denitrification tank 12 so that the microorganisms are not detached from the carrier 30 filled in the denitrification tank 12 or the carrier 30 is damaged. There is no need to provide a screen for preventing carrier outflow.

  In the denitrification treatment apparatus 40 of FIG. 2, a plurality of circulation units 42 for water to be treated including the cylindrical member 14 and the stirring means 18 are arranged in parallel in the denitrification tank 12. The description of the cylindrical member 14 and the stirring means 18 is the same as in FIG. 1 and will be omitted, and the same members as those in FIG. Moreover, although the number of the circulation units 42 is demonstrated below by the example of 3 units | sets shown in FIG. 2, it is not limited to this.

  As shown in FIG. 2, the treated water inflow pipe 22 is connected to one end side of the denitrification tank 12, and the treated water pipe 26 is connected to the other end side. A first circulation unit 42A, a second circulation unit 42B, and a third circulation unit 42C are arranged from the inflow pipe 22 side to the treated water pipe 26 side.

  The motor 28 of the stirring means 18 in each circulation unit 42A, 42B, 42C is connected to the control means 20 via a signal cable, and the detection result is detected from the detection means 34 for detecting the upper end of the fluidized bed 32. Are sent sequentially.

  As a result, the water to be treated that flows in from the inflow pipe 22 is first denitrified in the first circulation unit 42A, then denitrified in the second circulation unit 42B, and finally in the third circulation unit 42C. After the denitrification treatment, it is discharged from the treated water pipe 26. That is, by configuring the denitrification apparatus 40 as shown in FIG. 2, not only the same effects as described with reference to FIG. 1 can be achieved, but also the denitrification process can be performed in multiple stages in one denitrification tank 12. In this case, the control means 20 can change the expansion rate of the fluidized bed 32 formed by the circulation units 42A, 42B, and 42C by changing the rotation speed of the stirring blades 16 of the circulation units 42A, 42B, and 42C. . For example, since the expansion rate of the fluidized bed 32 can be reduced stepwise from the inflow pipe 22 side to the treated water pipe 26 side, or vice versa, the flow rate can be increased stepwise. Flexible denitrification treatment can be performed.

  Next, examples of the present invention will be described.

[Test A]
Test A is a comparison test comparing the denitrification performance and the state of the carrier between the denitrification apparatus of the present invention (Example) and the conventional denitrification apparatus (Comparative Example).

  The apparatus shown in FIG. 1 was used as the denitrification apparatus 10 of the example.

  Moreover, the apparatus shown in FIG. 3 was used as the denitrification processing apparatus 50 of the comparative example. As shown in FIG. 3, the water to be treated flows into the lower portion of one end of the denitrification tank 52 from the inflow pipe 54 by the pump 56, and the treated water is discharged from the upper end of the other end of the denitrification tank 52 through the treated water pipe 58. . Moreover, the to-be-processed water which flowed into the denitrification tank 52 and the filled carrier 60 are made to flow by the rotation of the stirring blade 62A of the underwater stirrer 62 disposed at the bottom of the tank.

(Test method)
In both Examples and Comparative Examples, synthetic wastewater having a nitrate nitrogen concentration (NO ₃ -N) of 40 mg / L was used as the water to be treated, and continuous operation was performed for one month. As a BOD source for performing the denitrification reaction, methanol was added so that the ratio of BOD / N = 3 in both Examples and Comparative Examples.

In both the examples and the comparative examples, the conditions of the carriers 30 and 60 were tested under the same conditions. That is, the carrier filling rate was set to 15% by volume of the effective volume (1 m ³ ) of the denitrification tanks 12 and 52. The carrier 30 used was a comprehensive carrier and an adherent carrier (plastic carrier material), and each carrier 30 and 60 was tested. Both the inclusion carrier and the adhesion carrier were in the form of 3 mm square pellets, and the specific gravity of the carriers 30 and 60 was 1.02.

  And in the Example, the rotation speed of the stirring blade 16 was controlled by the control means 20 so that the expansion rate of the fluidized bed 32 would be 150%. On the other hand, in the comparative example, the rotation speed of the stirring blade 62A of the underwater stirrer 62 was made the same as in the example.

  Further, in both the examples and the comparative examples, a 1.5-mm-wide carrier outflow prevention screen 63 is provided at positions of the denitrification tanks 12 and 52 where the treated water flows into the treated water pipes 26 and 58.

(Test results)
The test results are shown in the table of FIG.

  As can be seen from the table of FIG. 4, the denitrification apparatus 50 of the comparative example using the entrapping carrier was broken when the carrier 60 contacted the stirring blade 62 </ b> A of the underwater stirrer 62. Thus, after one month of the test, the original 3 mm square carrier 60 was reduced to 20% of the total. Further, as a result of the carrier 60 being broken and becoming finer, it became easy to flow out of the screen 63 together with the treated water, and the denitrification performance was lowered as the test was continued.

  On the other hand, in the denitrification processing apparatus 10 of the embodiment using the entrapping carrier, the fluidized bed 32 of the carrier 30 is formed outside the cylindrical member 14 and flows into the cylinder or out of the screen. I never did. Thus, since the carrier 30 does not contact the stirring blade 16 in the cylinder, the carrier 30 was not broken and the screen was unnecessary. Therefore, high denitrification performance could be stably maintained throughout the test one month.

  Further, as can be seen from the table of FIG. 4, in the denitrification apparatus 50 of the comparative example using the adherent carrier, the carrier material is plastic and it was not destroyed by the underwater agitator 62. However, the adherent cells attached to the carrier material were peeled off. Thereby, since the peeled adherent cells flow out from the denitrification tank 52 together with the treated water, the denitrification performance decreased as the test was continued.

  On the other hand, in the denitrification processing apparatus 10 of the embodiment using the adhered carrier, the carrier 30 forms a fluidized bed 32 outside the cylinder member 14 and flows into the cylinder or out of the screen. I never did. Thereby, since the support | carrier 30 does not contact the stirring blade 16 in a pipe | tube, while an attached microbial cell does not peel, the screen was unnecessary. Therefore, high denitrification performance could be maintained throughout the test month.

[Test B]
Test B compares the denitrification rate between the case where the denitrification apparatus 10 of the present invention of FIG. 1 is applied to a covering carrier and the case where it is applied to an adherent carrier. The carrier filling rate was 20% by volume (V / V%). The test operation was performed continuously for about 50 days at a nitrogen volume load of 3 kg / m ³ · day after the vehicle was conditioned. Others are the same as those in Test A.

(Test results)
The test results are shown in the table of FIG.

  As can be seen from the table of FIG. 5, when the entrapped carrier is used, the nitrogen gas generated by the denitrification reaction is discharged from the carrier 30 without staying inside the carrier, and a high denitrification performance with a 95% denitrification rate. And stable operation.

  On the other hand, in the case of an adherent carrier, the nitrogen gas generated by the denitrification reaction adheres to the carrier surface and easily floats, and when the adherent cells increase and the biofilm becomes thicker, The biofilm is peeled off by rubbing against the inner wall of the denitrification tank 12. For this reason, the denitrification reaction became unstable compared to the entrapped carrier, and the denitrification rate decreased to nearly 80% after about 20 days and about 40 days after operation. As a result, the denitrification apparatus of the present invention improves the denitrification performance when the entrapping carrier is used as the carrier rather than the attached carrier.

  DESCRIPTION OF SYMBOLS 10, 40 ... Denitrification processing apparatus, 12 ... Denitrification tank, 14 ... Cylindrical member, 16 ... Stirring blade, 18 ... Stirring means, 20 ... Control means, 22 ... Inflow piping, 24 ... Pump, 26 ... Treated water piping, 28 ... Motor, 30 ... Carrier, 32 ... Fluidized bed, 34 ... Detection means, 42A, 42B, 42C ... Circulation unit

Claims (5)

In a denitrification treatment apparatus for performing denitrification treatment of the treated water by filling a large number of carriers carrying denitrifying bacteria in a denitrification tank into which the treated water flows.
A cylindrical member that is provided vertically in the water to be treated of the denitrification tank and divides the inside of the denitrification tank into an outside cylinder filled with the carrier and an inside cylinder communicating with the outside of the cylinder
A stirring blade is provided in the cylinder of the cylindrical member, and a downward flow is generated in the cylinder by rotation of the stirring blade, and an upward flow in which the downward flow is reversed at the bottom of the tank is generated outside the cylinder. A stirring means for forming a fluidized bed of the carrier in the upward flow outside the cylinder by generating a vertical circulation flow in the water to be treated in the denitrification tank;
And a control means for controlling the expansion rate of the fluidized bed by changing the flow rate of the upward flow by adjusting the rotational speed of the stirring blade. A detecting means for detecting an upper end of the fluidized bed;
2. The denitrification apparatus according to claim 1, wherein the control unit adjusts the number of rotations of the stirring blade based on a detection result of the detection unit.   The control means sets the rotation speed of the stirring blade so that the expansion rate is in a range of 150 to 200% when the expansion rate of the fluidized bed in a state where the rotation of the stirring blade is stopped is 100%. The denitrification apparatus according to claim 1 or 2, wherein the denitrification apparatus is adjusted.   The denitrification apparatus according to any one of claims 1 to 3, wherein a taper is formed at a corner of the bottom of the denitrification tank.   The denitrification apparatus according to any one of claims 1 to 4, wherein the carrier is a comprehensive carrier in which denitrifying bacteria are comprehensively fixed to a gel.

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