JP2001145896A - Apparatus for treating nitrogen-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus not requiring a reaeration process and a sedimentation process in the treatment of nitrogen-containing waste water using a nitrifying process and a denitrifying process, an organism fixing electrode for treating a nitrogen compound comprising a new conductive electrode material and a microbiological and electrobiochemical denitrifying treatment apparatus capable of keeping the concentration of organisms in a reaction tank more uniform. SOLUTION: An apparatus for treating nitrogen-containing waste water includes a nitrifying tank 1 for changing a nitrogen compound in waste water to nitric acid under aeration and a denitrifying tank 2 receiving waste water from the nitrifying tank 1 and having a cathode 6, an anode 7 and a housing, characterized by that either one of the cathode and the anode or both of them comprise an organism fixing electrode and changing nitric acid to nitrogen gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrochemical reaction of nitrogen compounds contained in industrial effluents such as power plant effluents and other effluents, particularly nitrite nitrogen and nitrate nitrogen such as ammonia and nitrite. TECHNICAL FIELD The present invention relates to a wastewater treatment apparatus for biologically treating while utilizing water, and a biological fixed electrode used in the wastewater treatment apparatus.

[0002]

2. Description of the Related Art At present, as a technique for treating nitrogen in wastewater present as ammonia or nitrite, nitrifying bacteria (nitrifying bacteria,
The nitrogen compound is converted to nitric acid by the action of nitrifying bacteria, and the nitrate nitrogen generated in the nitrification tank is released into the atmosphere as nitrogen gas by the action of the denitrifying bacteria to treat the nitrogen in the water to be treated. That is being done. At this time, methanol is added in the denitrification tank, but the surplus that has not been used needs to be treated in the oxidation tank (re-aeration tank). Further, a sedimentation tank for separating activated sludge containing nitrifying bacteria, denitrifying bacteria, and oxidizing bacteria from the water to be treated is required.

[0003] Nitrifying bacteria are nitrites that oxidize ammonia under aerobic conditions to produce nitrite, and so-called nitrite bacteria that similarly oxidize nitrite to nitrate under aerobic conditions. Is a generic term for Nitrifying bacteria are autotrophic bacteria that grow by performing carbon fixation using the energy obtained from the above reaction, and generally do not require organic matter for growth. Known examples of nitrifying bacteria include the genus Nitrosomonas and the genus Nitrobacter. Also, denitrifying bacteria are a general term for a wide variety of microorganisms that perform reactions to reduce nitric acid or nitrous acid under anaerobic conditions, and these denitrifying bacteria require organic substances for growth. Heterotrophic microorganisms or autotrophic microorganisms that do not require organic matter. Known examples of denitrifying bacteria include activated sludge from a sewage treatment plant.

[0004] Therefore, two tanks necessary for actually performing the nitrogen treatment of the water to be treated are a nitrification tank and a denitrification tank. However, in order for denitrification bacteria to work in a denitrification tank, addition of methanol is essential, and even if the nitrogen load fluctuates, in order to stably perform the treatment, methanol must always be added in excess. Therefore, excess methanol is generated, and this methanol becomes a COD source, and requires treatment. That is, a tank (re-aeration tank or sedimentation tank) that is substantially unrelated to the treatment of nitrogen in the wastewater is attached.

On the other hand, Kuroda et al., Abstracts of the 48th Annual Meeting of the Japan Society of Civil Engineers, p. 1268, 1993, and
JP-A-329497 proposes a method of denitrifying by supplying hydrogen generated by electrolysis of water to a microorganism as a reducing power. In this method, a carbon electrode is immersed in an activated sludge suspension containing denitrifying bacteria for about one month to form a microbial membrane on the electrode, and a nitrate nitrogen treatment is carried out by applying an electric current to the microbial membrane. The electrodes described in these documents have a biocatalyst fixed to a rod-shaped or plate-shaped conductive solid surface such as carbon or metal. Moreover,
JP-A-8-19788 discloses that a granular biocatalyst-fixed conductive material is housed in a porous container and used as an electrode.

[0006] The plate or rod-shaped electrode has the following problems. In other words, when the biocatalyst is immersed in flowing water to be treated for actual treatment, the biocatalyst may peel off due to the shearing force of the fluid. In addition, the amount of the biocatalyst that can be immobilized is suppressed due to the restriction due to the diffusion phenomenon of the substrate in the immobilization tank. Furthermore, if the electrode in the tank is enlarged to increase the amount of wastewater to be treated in the water treatment tank, the effective volume in the treatment tank decreases, and the reaction rate per unit volume of the reactor decreases. Efficiency decreases.

Japanese Patent Application Laid-Open No. 8-224598 discloses an ion exchange membrane between an anode and a cathode of a denitrification tank, in which hydrogen is generated at the cathode, and the hydrogen is used for hydrogen-assisted denitrification. An apparatus that attempts to denitrify by bacteria is disclosed. However, there is a tendency that the denitrifying bacteria float up together with the generated hydrogen gas and the processing does not proceed, and this becomes a more serious problem as the current is increased to increase the processing capacity. Also, as a result of the provision of the ion exchange membrane,
There is a problem that the pH on the cathode side increases and the rate of denitrification by microorganisms decreases (see JP-A-9-75996).

In the denitrification tank of the fixed bed method currently used for wastewater treatment, the flow of the water to be treated is either an upward flow or a downward flow, and is always in one direction. According to this method, the concentration of organisms increases on the inlet side of the wastewater with a high load, and decreases on the outlet side where the load decreases. In this way, when the concentration of organisms in the tank is uneven, the entire tank cannot be used effectively, and the efficiency is reduced.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, the present invention provides a method and an apparatus which do not require a re-aeration step and a precipitation step in a nitrogen compound treatment using a nitrification step and a denitrification step. The purpose is to provide. Another object of the present invention is to provide a biologically immobilized electrode for treating a nitrogen compound, comprising a novel conductive electrode material. Further, another object of the present invention is to provide a microbiological electrobiochemical denitrification treatment apparatus capable of keeping the concentration of organisms in a reaction tank more uniform.

[0010]

SUMMARY OF THE INVENTION The present invention provides a nitrification tank for converting nitrogen compounds in wastewater into nitric acid by the action of nitrifying bacteria while receiving a wastewater from the nitrification tank. A nitrogen-containing wastewater, wherein at least the cathode is a biological fixed electrode in which denitrifying bacteria are fixed, and a denitrification tank for converting nitric acid to nitrogen gas by the action of an electric current flowing between the anode and the cathode and the denitrifying bacteria. Of the present invention. Furthermore, the present invention provides a nitrification step in which nitrogen compounds present in wastewater are converted into nitric acid by the action of nitrifying bacteria while aerating, And a denitrification step of converting nitric acid to nitrogen gas by the action of nitrogen. As the biological fixed electrode, a conductor in the form of a pellet, a particle, a cloth, or the like can be used as a material, and denitrifying bacteria adhere to the surface of the conductor.

That is, the nitrification tank of the nitrogen-containing wastewater treatment apparatus of the present invention comprises air supply means for aeration and resin pellets acting as a carrier for holding nitrifying bacteria, and the denitrification tank comprises a cathode, an anode and An organic matter supply means for supplying methanol or the like as necessary, and a power supply for supplying power between the cathode and the anode, wherein one or both of the cathode and the anode are biologically fixed electrodes on which denitrifying bacteria are fixed. There is something. The present invention employs an electrochemical denitrification process in which an electric current is applied by using a biological fixed electrode instead of a conventional denitrification process, so that a smaller amount of an organic substance such as methanol alone or an organic substance is added. Thus, sufficient denitrification is performed without the need for re-aeration and sedimentation steps, which were conventionally required.

The present invention also provides a biological fixed electrode for a denitrification tank, comprising a current collector, a conductive fabric, and a conductive fiber for fixing the current collector and the conductive fabric. I do.
The present invention also provides a biological fixed electrode for a denitrification tank, comprising a current collector and a conductive fabric bonded to the current collector. The present invention further provides a biological fixation for a denitrification tank, comprising a current collector, a three-dimensional fabric made of conductive fibers, and a conductive fiber for fixing the current collector and the three-dimensional fabric. Provide electrodes. The present invention further provides a biological fixed electrode for a denitrification tank, comprising a current collector and a three-dimensional woven fabric made of conductive fibers fixed to the current collector.

The biological fixed electrode used in the denitrification tank for the treatment of wastewater containing nitrogen compounds can be used as either an anode or a cathode, and has a large effective surface area as an electrode without increasing the volume of the electrode so much. Is what you can do. Since the electrodes are compact, the processing speed can be increased without significantly reducing the effective volume of the reaction vessel. The conductive fabric includes carbon cloth, and the conductive fiber includes carbon fiber.
In addition to the conductive fibers for fixing, these woven fabrics and fibers may be other than carbon. However, carbon fibers and carbon cloths are preferable in consideration of the affinity with microorganisms.

On the fiber surface of such an electrode, denitrifying bacteria capable of treating nitrate nitrogen are fixed.
And, as described above, the denitrification tank using this electrode
It is also used in combination with the above-mentioned nitrification tank, and can reduce the amount of organic substances added from the outside as compared with the case where no voltage is applied to the electrodes. This denitrification tank also minimizes power waste.

In order to cope with the problem that the oxygen generated at the anode inhibits the denitrification action at the cathode, a diaphragm is provided between the anode and the cathode (Japanese Patent Laid-Open No. 8-2).
By using a woven fabric for the electrode in this way, it is possible to prevent oxygen and other electrochemical reaction products from migrating to the opposite electrode and inhibiting the desired reaction. In some cases, a diaphragm is not required.

Further, the present invention has a cathode, an anode and a diaphragm, and microorganisms are fixed on at least the cathode.
Provided is a denitrification tank having means for reversing the flow of water to be treated. By inverting the flow of the water to be treated from time to time, the distribution of the denitrifying bacteria fixed to the cathode or anode can be made more uniform, and the operation efficiency of the denitrification tank can be improved.

The present invention further comprises a cathode, an anode, and a diaphragm, wherein at least the cathode has microorganisms fixed thereon, and the cathode and / or anode on which the microorganisms are fixed are used for back washing. Provided is a denitrification tank having an air blowing means. By blowing air with air blowing means, the microorganisms fixed on the cathode and / or the anode are once peeled off from these electrodes,
The peeled microorganisms can be more uniformly distributed on the electrode.

The present invention also provides a denitrification tank having a cathode, an anode, and a diaphragm, wherein microorganisms are fixed on at least the cathode, and a plurality of organic substance supply ports are provided. The organic matter here is, for example, methanol required by denitrifying bacteria, and by supplying it to the denitrification tank from a plurality of locations, the distribution of microorganisms on the electrode can be made more uniform.

The form of the electrodes in these denitrification tanks is not particularly limited, and may be a flat plate or a rod.
A pellet, granular, fibrous, or woven conductor having a large surface area is preferred.

[0020]

FIG. 1 shows an embodiment of an apparatus and a method for treating nitrogen in waste water according to the present invention. This nitrogen treatment device
It comprises a nitrification tank 1 and a denitrification tank 2. Nitrite nitrogen compounds such as ammonia and nitrite are contained in the wastewater.
In the nitrification tank 1, an air nozzle 3 at the bottom is provided.
The air for aeration is blown in from. Then, a large number of pellets 4 made of a synthetic polymer compound such as polyethylene or polypropylene, or a natural polymer such as agar, calcium alginate, or cellulose follow the flow of bubbles 5 in the water being treated. Circulating. Nitrifying bacteria, such as Nitrosomonas, Nitrosococcus, and Nitrobacter, which oxidize nitrite, adhere to the surface of the pellet 4, and convert nitrite nitrogen into nitrate. It works to oxidize to nitrogen.

The waste water from the nitrification tank 1 is supplied to a denitrification tank 2 together with methanol. The denitrification tank 2 includes a cathode 6, an anode 7, a membrane 8, and carbon pellets 9 filled between the membrane 8 and the cathode 6. The cathode and anode are
Here, a carbon material is used, but other metals plated with platinum or the like can also be used. This film may be made of any material, such as cloth, a resin film having many holes, or a resin net. Below the cathode 6 and the anode 7, there is an insulator net 10 connecting the two electrodes, and holds the pellet 9. Carbon pellets 9
Here, a cylindrical shape having a diameter of about 5 mm and a length of about 6 mm is used, but the size is not particularly limited, and the shape is also prismatic, spherical, irregular shaped particles, and the like. Various things can be used. In addition to the pellets, a woven cloth or the like can be used. Here, pellets made of carbon are used, but other conductors can also be used. In this way, instead of using only a rod-shaped or plate-shaped electrode, by using a pellet or the like, the area to which microorganisms adhere is increased, and the current per unit area can be reduced. An electric current can be passed through the denitrification tank, and the efficiency of the treatment can be improved. Cathode 6 and anode 7
The galvanostat 11 is connected, and is adjusted so that a voltage of about several volts is applied and a current of about 100 mA flows.

In the denitrification tank 2, the surface of the carbon pellet 9 is provided on the surface of the carbon pellet 9 with a micro-genus represented by Pseudomonas denitrificans (genus Pseudomonas denitrificans) and Micrococcus denitrificans (micrococcus denitrificans). Denitrifying bacteria such as the genus Coccus and other Thiobacillus denitrificans and Bacillus subtilis attach to oxidize nitrate ions contained in wastewater to nitrogen gas.

As shown in FIG. 2, in the denitrification tank 2 ', if not only the cathode 6 but also the anode 7 is made of carbon pellets 15 or a woven cloth held by the membrane 14, the electrodes are oxidized. Consumption can be reduced, and the applied voltage can be reduced while keeping the flowing current constant, so that power consumption can be reduced.

Referring to FIG. 3, a second embodiment of the biological fixed electrode according to the present invention will be described. In this embodiment, the electrode includes a current collector 30, a conductive fabric 31 such as carbon cloth, and a fixing conductive fiber 32 for integrating the current collector 30 and the conductive fabric 31. Current collector 30
May be made of a conductor, and its material is not particularly limited, but materials such as carbon, stainless steel, and steel material plated with a noble metal may be used. Its shape is
A frame or lattice shape is advantageous for fixing the conductive fabric 31, but other shapes such as a flat plate shape can be adopted. As the conductive fiber 32 for fixing, a noble metal wire,
Carbon fiber or the like can be used.

The current collector 30 is connected to an external power supply, and a current flows from the current collector 30 to the conductive fibers 32 and the conductive fabric 31. At this time, denitrifying bacteria capable of treating nitrate nitrogen are fixed on the surfaces of the current collector 30 and the conductive fabric 32, and the nitrate nitrogen in the water to be treated can be treated efficiently. By using a conductive cloth such as carbon cloth, the effective electrode area can be increased, the amount of microorganisms supported can be increased, and the entire denitrification tank can be made compact.

Referring to FIG. 4, a third embodiment of the biological fixed electrode according to the present invention will be described. In this embodiment, the electrode is composed of a current collector 33, a three-dimensional woven fabric 34 made of conductive fibers such as carbon fiber, and a fixing conductive material for integrating the current collector 33 and the three-dimensional woven fabric 34. And fibers 35. Since microorganisms can be fixed on the surface or inside of the three-dimensional fabric 34, the effective electrode area and the amount of fixed microorganisms can be increased. Also,
A three-dimensional woven fabric made of conductive fibers can be freely prepared according to the size and thickness of the device, such as its shape.
Compared with the conductive woven fabric of Example 2, the amount of adhered microorganisms can be further increased.

The current collector 33 made of a conductor is connected to an external power supply, and current flows from the current collector 33 to the three-dimensional fabric 34 through conductive fibers 35 for fixing. The material and the like of each member are the same as in the case of the second embodiment.

Next, a fourth embodiment of the biological fixed electrode according to the present invention will be described with reference to FIG. In this embodiment, the electrode comprises a current collector 36 and a three-dimensional fabric 37 made of a conductive fiber such as carbon fiber. In the illustrated example, the three-dimensional fabric 37 is joined to both sides of the current collector 36, but the three-dimensional fabric 37 is attached to only one side.
Can be joined. Current collector 36 and three-dimensional fabric 37
Can be joined using a conductive adhesive or the like. Here, the shape of the current collector is not particularly limited, but may be a plate shape, a grid shape, a frame shape, or the like. Further, the current collector 36 may be in the form of a basket, and the three-dimensional fabric 37 may be placed therein.

Next, a fifth embodiment of the biological fixed electrode according to the present invention will be described with reference to FIG. In this embodiment, the electrode comprises a current collector 38 and a conductive fabric 39 such as carbon cloth. The current collector 38 has a flat plate shape in FIG. 4, but may have another shape. Conductive fabrics are not limited to woven fabrics, and nonwoven fabrics can be substituted.However, woven fabrics are generally superior in terms of fiber density, etc., and oxygen and ions generated at each electrode are mixed. It is preferable to use a woven fabric so that they do not match. As in the fourth embodiment, the current collector 38 may be formed in a cage shape and a conductive fabric may be placed in the cage. Current collector 38 and fabric 3
9 can be joined using a conductive adhesive or the like.

Next, an embodiment of the denitrification tank according to the present invention will be described with reference to FIG. The denitrification tank 50 includes an anode section 51,
It comprises a diaphragm part 52, a cathode part 53, and a housing 54.

The anode part 51 includes a casing 55 made of transparent vinyl chloride or the like, a current collector 56 made of, for example, carbon steel and plated with platinum,
And a conductive microorganism carrier 26 made of carbon pellets or the like having an appropriate size, which is accommodated in the frame of the current collector. In this embodiment, the current collector 56 is provided with an air blowing pipe 28 for blowing air for backwashing. As the microorganism carrier 56, carbon particles or carbon pellets having a particle size or diameter of about 1 mm to several mm can be used. The carrier 26 may be made of another conductive material, but carbon is most preferable in consideration of affinity with living things and cost.

The diaphragm part 52 is composed of lattice-like diaphragm holding members 61 and 62 made of plastic or the like, and a diaphragm 60 interposed therebetween. The diaphragm 60 is for preventing oxygen generated at the anode from reaching the cathode. Therefore, an ion exchange membrane is suitable as the diaphragm, but a ceramic membrane, a microfiltration membrane, or the like may be used. In this embodiment, it is a polypropylene film. Furthermore, in order to prevent nitrate ions from moving to the anode and reducing the denitrification effect,
Cation exchange membranes are preferred. However, as described above, the isolation film 60 is not essential, and may not be necessary depending on the conditions.

The cathode portion 53 is made of a casing 67 made of transparent vinyl chloride or the like, similarly to the anode portion 51.
And a current collector 34 made of, for example, carbon steel and plated with platinum, and a conductive microorganism carrier 65 made of carbon pellets or the like having an appropriate size and housed in a frame of the current collector 64. . In this embodiment, the current collector 34
And an air blowing pipe 66 for blowing air for back washing.
Is provided. As the microorganism carrier 35, carbon particles or carbon pellets having a particle diameter or diameter of about 1 mm to several mm can be used. This carrier 6
5 may be another conductive material, but carbon is most desirable in the same manner as in the case of the anode part 51 in consideration of affinity with living things and cost.

The anode part 51, the diaphragm part 52, and the cathode part 53 are housed in a housing 54 to form a denitrification tank 50. Although not shown, the denitrification tank 50 is further provided with a methanol supply means so that microorganisms can supply necessary organic substances. The denitrification tank 50 is provided with piping for supplying and discharging the water to be treated as shown in the figure. The piping system, there are four solenoid valves _{V 1, V 2, V 3} , V 4, of which, in the illustrated state, V ₁ and V4 are open, V ₂ and V ₃ are closed ing. Therefore, the supplied raw water (water to be treated) enters the denitrification tank 50 from above, flows downward, and is discharged from the lower part of the denitrification tank 50. If this operation is continued for a while, more microorganisms will be attached to the upper ones of the anode and cathode carriers, and the actual denitrification reaction will occur only in that part, and the effective use of the entire denitrification tank will be improved. Unexpectedly, the efficiency of denitrification decreases. Therefore, after a certain time, it closes the electromagnetic valve V ₁ and V _4, opening the V ₂ and V _3. Then, the raw water flows in from the lower part of the denitrification tank 50, flows upward, and is discharged from the upper part of the denitrification tank 50. When such switching is repeated, the microorganisms are more uniformly distributed in each of the anode and the cathode, and the efficiency of the denitrification treatment is improved.

When air is blown from the air blowing pipes 58 and 66, the microorganisms adhering to the carrier are separated by the air rising from the bottom to the top and circulated in the denitrification tank 50, and the anode part 51 and the cathode are separated. Reattach to the carrier in the part 53. Thereby, the microorganisms are more uniformly distributed, and the operation efficiency of the denitrification device is improved.

[0036]

As described above, according to the present invention, sufficient denitrification can be performed using only a small amount of an organic substance such as methanol or without adding an organic substance. Also,
By using a conductive fabric, particularly preferably a three-dimensional fabric, as the material of the electrode, the amount of microorganisms attached can be increased. Furthermore, by blowing air,
Alternatively, by inverting the flow path of the wastewater, once the microorganisms adhering to the electrode and the carrier are peeled off,
It can be re-deposited more uniformly.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a nitrogen-containing wastewater treatment device of the present invention.

FIG. 2 is a schematic diagram showing another example of a denitrification tank that can be used in the nitrogen-containing wastewater treatment device of the present invention.

FIG. 3 is a schematic perspective view showing Example 2 of the biological fixed electrode according to the present invention.

FIG. 4 is a schematic perspective view showing Embodiment 3 of the biological fixed electrode according to the present invention.

FIG. 5 is a schematic perspective view showing Example 4 of the biological fixed electrode according to the present invention.

FIG. 6 is a schematic perspective view showing Example 5 of the biological fixed electrode according to the present invention.

FIG. 7 is an exploded and assembled view showing an embodiment according to the denitrification tank of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nitrification tank 2 Denitrification tank 3 Air nozzle 4 Pellets 5 Bubbles 6 Cathode 7 Anode 8 Membrane 9 Carbon pellet 10 Net 11 Galvanostat 14 Film 15 Carbon pellet 30, 33, 35, 38 Current collector 31, 39 Conductive textile 32, 35 conductive fiber 34,37 three-dimensional fabric 50 denitrification tank 51 anode part 52 diaphragm part 53 cathode part 54 housing 55,67 casing 56,64 current collector 57,65 carrier 58,66 air blowing tube 60 diaphragm 61,62 diaphragm Holding material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiro Hamasaki 2-1-1 Shinama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Ikumasa Ogi 2-1-1, Araimachi, Takarai City, Hyogo Prefecture No. 1 Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Takayuki Kurimura 2-1-1, Shinhama, Araimachi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. F-term (reference) 4D003 AA14 AB02 CA07 EA14 EA21 EA30 FA06 4D040 AA34 AA61 DD03 DD14 DD31 4D061 DA08 DB19 DC14 EA02 EB04 EB12 EB13 EB17 EB19 EB28 EB29 EB30 EB33 EB35 EB39 ED20 FA15 GC12 GC14

Claims (12)

[Claims] 1. A nitrification tank for converting nitrogen compounds in wastewater into nitric acid while aeration is performed, and a wastewater from the nitrification tank is received, and a cathode and an anode are provided. At least the cathode fixes denitrifying bacteria. A nitrogen-containing wastewater treatment device, comprising: a biological fixed electrode; and a denitrification tank for converting nitric acid to nitrogen gas by the action of a current flowing between the cathode and the anode and a denitrifying bacterium. 2. The nitrogen according to claim 1, wherein the cathode and / or the anode are electrodes formed by arranging conductors each having a shape selected from pellets, particles, and cloth adjacent to each other. Contained wastewater treatment equipment. 3. A nitrification step of converting nitrogen compounds present in wastewater into nitric acid by the action of nitrifying bacteria while aerating,
A denitrification step of changing nitric acid to nitrogen gas by the action of a denitrifying bacterium while passing an electric current in a denitrification tank having a biologically fixed electrode on which the denitrifying bacterium is fixed. 4. A biological fixed electrode for a denitrification tank, comprising: a current collector; a conductive fabric; and a conductive fiber for fixing that integrates the current collector and the conductive fabric. 5. A biological fixed electrode for a denitrification tank, comprising: a current collector; and a conductive fabric bonded to the current collector. 6. A biological fixed electrode for a denitrification tank, comprising a current collector, a three-dimensional woven fabric made of conductive fibers, and a conductive fiber for fixing the current collector and the three-dimensional woven fabric. . 7. A biological fixed electrode for a denitrification tank, comprising a current collector and a three-dimensional woven fabric made of conductive fibers fixed to the current collector. 8. An apparatus for treating nitrogen in wastewater, comprising the biological fixed electrode according to claim 4. Description: 9. A denitrification tank having a cathode, an anode, and a diaphragm, wherein microorganisms are fixed to at least the cathode among the cathode and the anode, and a means for reversing the flow of the water to be treated. 10. A cathode, an anode, and a diaphragm, wherein microorganisms are fixed to at least the cathode of the cathode and the anode, and the cathode and / or the anode on which the microorganisms are fixed are reversed. A denitrification tank having an air blowing means for washing. 11. A denitrification tank having a cathode, an anode, and a diaphragm, wherein microorganisms are fixed to at least the cathode among the cathode and the anode, and a plurality of organic substance supply ports are provided. 12. The denitrification tank according to claim 9, wherein the anode and / or the cathode are formed of a pellet, granular, fibrous or woven conductor.