JPH1094795A - Treatment of waste water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove nitrogen in waste water by circulating a part of flow-out water from the downmost stream side reactor to the uppermost stream side reactor and making the upper most stream reactor into free from oxygen to keep a part of the generated NO2 -N in the oxygen free state in the prestage of the reactor thereby denitrificating the waste water by microorganism stuck to a carrier. SOLUTION: The reactor is divided into three stages and the flow-in waste 1 is charged to the 1st stage reactor 7 in the uppermost stream side, treated in the 2nd and 3rd stage reactor 8, 10, and discharged. A part of the discharged treated water 2 is circulated to the 1st stage reactor 7 through a circulating line 3. In such a case, a screen 4 for separating the carrier is provided between each state of the reactors and a microorganism-immobilizing carrier 5 is always kept in each reactor. In the 1st stage reactor 7, air is diffused by a coarse bubble generating device 6 and the carrier is stirred and fluidized. Since the diameter of the blown bubble is large, the oxygen is hardly dissolved into the reactor, and the reactor is kept in the oxygen free state sufficient to cause the denitrification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biological treatment method for wastewater.

[0002]

2. Description of the Related Art Influent water is introduced into a reaction tank containing a microorganism-immobilized carrier, and oxygen-containing gas is blown into the reaction tank from the bottom, whereby pollutants in the inflow water adhere to the carrier under aerobic conditions. A system has been put into practical use in which after being decomposed and removed by microorganisms, solid-liquid separation is performed by a solid-liquid separator such as a filtration pond to obtain treated water.

As a method for biologically removing nitrogen components from wastewater, a nitrification liquid circulation method has been used. In this method, a denitrification tank and a final sedimentation tank are provided, a part of the nitrification tank treated water and return sludge from the sedimentation tank are introduced into the denitrification tank, and NO ₃ -N or NO ₂ -N
(Hereinafter, NO ₃ -N and NO ₂ -N are collectively referred to as NO _X -N
Is reduced to nitrogen gas to remove nitrogen components from wastewater, and ammonia nitrogen (NH ₄ —N) and organic nitrogen are reduced to NO by the action of nitrifying bacteria under aerobic conditions in a nitrification tank.
Those oxidized to _X -N, some of nitrification tank treatment liquid circulated to the denitrification tank as described above, the remaining nitrification tank treatment liquid is introduced into the settling tank, the treated water is obtained as a supernatant Part of the settled sludge is returned to the denitrification tank as described above (returned sludge). Part of the returned sludge is extracted as excess sludge.

In this process, the remaining BOD component is used in the denitrification tank as a reducing agent for denitrification.
Although a part of the BOD component is also removed in the denitrification tank, most of the BOD component in the sewage is decomposed and removed under aerobic conditions in the aerobic tank.

[0005]

In order to biologically remove nitrogen-based pollutants from wastewater, ammonia nitrogen and organic nitrogen in wastewater are subjected to the action of nitrifying bacteria under aerobic conditions in the presence of oxygen. the nO was oxidized to _X -N, nO in oxygen-free conditions in the absence of oxygen by the action of denitrifying bacteria _X
Although it is necessary to perform atmospheric emission after changing -N to nitrogen gas, in the method of treating wastewater using a microorganism-immobilized carrier as shown in Patent Document 1, all the reaction tanks are under aerobic conditions. is it is oxidized to nO _X -N occurs because that, since the denitrification to nitrogen gas does not occur, the removal of nitrogen-based pollutants has a problem not achieved.

[0006] In the recirculation type nitrification and denitrification method using suspended sludge, there is a problem that the reaction tank becomes large because the concentration of microorganisms in the reaction tank cannot be increased. The present invention has been made in view of the above-described circumstances, and enables removal of nitrogen-based pollutants, and the quality of inflow water,
An object of the present invention is to provide a method for treating wastewater that can ensure a good quality of treated water with a stable high nitrogen removal rate according to the quality of treated water and the amount of treated water. Reference 1: A report on the evaluation of the modified nitrification-promoted circulation method "Pegasus" using a comprehensive immobilization carrier, edited by the Technology Development Department, Japan Sewerage Corporation, June 1993

[0007]

The wastewater treatment method of the present invention is a wastewater treatment method in which a microorganism-immobilized carrier is charged into a plurality of reaction tanks.
It is characterized by being circulated to the most upstream side reaction tank and making the most upstream side reaction tank oxygen-free.

[0008] Thus, removal part of the NO _X -N generated by nitrification under aerobic part of the reaction vessel subsequent stage, placed in anoxic conditions in the reaction vessel front, by microorganisms adhering to the reaction vessel preceding carrier Nitrogen is removed from wastewater due to nitrification.

The wastewater treatment apparatus is a wastewater treatment apparatus comprising a plurality of reaction tanks charged with a microorganism-immobilized carrier, wherein a part of the effluent of the most downstream reaction tank is circulated to the most upstream reaction tank. It is characterized by having an apparatus and an apparatus for making the uppermost-stream side reaction tank anoxic.

[0010] This apparatus is characterized in that it has at least one intermediate reaction tank which can be controlled under both anoxic conditions and aerobic conditions. In this way, the middle stage of the reaction tank can be controlled under both anoxic condition and aerobic condition according to the inflow water quality and the inflow water amount, so that the tank volumes of the aerobic portion and the anoxic portion are appropriately set. Therefore, it is possible to obtain an effect of stably ensuring good water quality even when the load fluctuates.

Further, since the microorganism-immobilized carrier is used, the concentration of microorganisms in the reaction tank can be increased. Furthermore, in the suspended sludge method, nitrifying bacteria, which were difficult to hold in the reaction tank, preferentially adhere to the aerobic layer carrier,
The nitrification treatment is stabilized, and the size of the entire processing apparatus can be reduced.

[0012] Further, the microorganism-immobilized carrier has a hollow shape, and the main component of the carrier is polypropylene.
A carrier having a specific gravity of 0.99 to 1.03 is used. Thus, when a hollow-shaped carrier is used, the hollow portion can also be used for immobilizing microorganisms, so that the effective microorganism concentration increases, and diffusion of oxygen in the hollow portion is restricted, so that the hollow portion is in an oxygen-free state. And a denitrification reaction is likely to occur, and the nitrogen removal rate is improved. Alternatively, the effect of reducing the size of the reaction tank can be obtained.

Further, the specific gravity of the carrier is from 0.99 to 1.0.
By setting to 3, the effect that the carrier is fluidized even with a small stirring intensity can be obtained. Furthermore, if the main component of the carrier is polypropylene, the strength of the carrier is large,
As a stirrer under oxygen-free conditions, there is an advantage that breakage of the carrier does not occur even if a mechanical underwater stirrer is used,
As a stirrer under anoxic conditions, a submersible stirrer or a pump for circulating the inside of the reaction tank can be used.

In order to operate the reactor under oxygen-free conditions, a coarse bubble generator is installed in the reactor. In the case of coarse bubbles, since the oxygen dissolving efficiency is low, it is effective to stir the inside of the reaction tank while keeping the reaction tank free of oxygen.

Further, a draft tube or a baffle plate is provided in a reaction tank operated under oxygen-free conditions, and the inside of the tank is divided into a part where liquid rises and a part where liquid descends. As a result, the bubbles rise with the upward flow of the liquid, and the bubbles have an upward slip speed with respect to the liquid flow velocity, so that the residence time of the bubbles in the liquid (gas-liquid contact time) is shortened. In addition, the amount of dissolved oxygen can be further reduced, and the stirring energy in the tank is increased, so that a better stirring state can be obtained.

Further, at least a part of the bottom of the most upstream reaction tank operated under anoxic condition has a concave shape. Thereby, the sludge settles and accumulates in the concave portion, and is again transferred to the upper portion of the intermediate tank by the air lift effect. Therefore, it is possible to obtain a good stirring state in the tank while preventing sludge from accumulating on the bottom portion.

Further, a diffuser for generating coarse bubbles in the uppermost stream reaction tank operated under oxygen-free conditions is operated intermittently. As a result, an operation in which the amount of dissolved oxygen in the intermediate tank is reduced becomes possible, and good nitrogen removal is achieved.

The upper space of the uppermost stream reaction tank operated under oxygen-free conditions has a closed structure, and a device for repeatedly blowing gas existing in the upper space of the tank into the tank is provided. With this configuration, the gas present in the upper space is repeatedly blown into the tank, whereby the oxygen concentration in the blown gas gradually decreases, and the amount of dissolved oxygen in the reaction tank operated under oxygen-free conditions is greatly reduced. It is possible to drive
Good nitrogen removal is achieved.

[0019]

FIG. 1 is an overall configuration diagram showing an example of an embodiment of the present invention. The reaction tank is divided into three stages. Inflow water 1 is introduced into the first-stage reaction tank 7 at the most upstream,
After undergoing treatment in the second-stage reaction tank 8 and the third-stage reaction tank 10, it is discharged from the reaction tank 10. Part of the treated water discharged from the reaction tank 10 is circulated to the first-stage reaction tank 7 through the circulation line 3. A microbe-immobilized carrier 5 is charged into each reaction tank.

The amount of the microorganism-immobilized carrier is about 1% to 40% based on the true volume of the carrier. The length of the main component is 2 to 8 mm mainly composed of polypropylene, and the outer shape is 2 to 8 mm.
When a hollow cylindrical carrier of about mm is used, the amount of the microorganism-immobilized carrier is 3% to 15% based on the true volume of the carrier.
% Is appropriate.

A screen 4 for separating carriers is provided between each stage of the reaction tank, and the microorganism-immobilized support 5 is always maintained in each reaction tank. In the first-stage reaction tank 7, air is diffused from the coarse bubble generation device 6, and the carrier is stirred and fluidized. Here, since the diameter of the bubble blown is large, the amount of dissolved oxygen in the reaction tank is small, and the reaction tank is maintained in an oxygen-free state sufficient for the denitrification reaction to occur.

The second-stage reaction tank 8 includes a coarse bubble generator 6
When the reaction tank 8 is operated under aerobic conditions, air is blown from the air diffusion apparatus 9, while when the reaction tank 8 is operated under oxygen-free conditions, coarse bubbles are formed. Air is blown from the generator 6.

The condition of the reaction tank 8 under aerobic conditions or oxygen-free conditions is determined in consideration of the quality of the inflow water, the quality of the treated water discharged from the reaction tank 7, the temperature of the water, and the like. If NO _X -N concentration of effluent water from 7 is small, specifically under aerobic conditions when depending on inflow water quality and request processing quality of 2 (g / m ³⁾ or less, in the case of more One of the guidelines is to operate in anoxic condition.

It is also possible to set the conditions of the reaction tank 8 using a measuring device for ammoniacal nitrogen ゃ NO _x -N, a D0 meter, an ORP meter and the like. In the third-stage reaction tank 10, air is blown from the air diffuser 9 to fluidize the carrier and supply oxygen to microorganisms attached to the carrier.

The configuration shown in FIG. 1 shows one embodiment of the present invention, and the present invention is not limited to the configuration shown in FIG. 1, but various processing modes utilizing the present invention. Can be considered.

In the present invention, as a method of operating the intermediate tank under aerobic conditions, an oxygen supply device is installed in the reaction tank. Examples of the oxygen supply method include a method using an aerator such as a jet aerator, a method in which a diffuser plate, a diffuser, and the like are installed in a reaction tank, and an oxygen-containing gas is blown into the reaction tank through these.

Next, as a method of stirring the inside of the reaction tank under oxygen-free conditions, a method of installing a submersible stirrer inside the reaction tank,
A method of installing a stirrer at the top of the reaction tank, a method of installing a pump for internal circulation of the reaction tank, and making the space above the reaction tank a closed structure,
There is a method of repeatedly blowing gas existing in the upper space of the reaction tank into the reaction tank.

Further, a diffuser 6 for generating bubbles having a large diameter can be provided in the reaction tank, and the inside of the reaction tank can be stirred by blowing air into the diffuser. In this method, although the dissolution of oxygen in the blown air poses a problem, the diameter of bubbles to be diffused should be increased by increasing the pore diameter of the bubble diffusion portion of the diffuser, or (and) the depth of the diffused water. It is also possible to reduce the amount of oxygen dissolved by reducing the depth of the reaction vessel and keep the inside of the reaction tank under conditions that cause a denitrification reaction.

In the method of blowing air from a diffuser having a large diameter, the amount of dissolved oxygen may be reduced by reducing the amount of blown air. In that case, the power for stirring inside the reaction tank is also reduced. There is a problem.

However, as shown in FIG. 2, by diffusing air from only one side or the center of the reaction tank, the reaction tank is divided into a part where the liquid rises and a part where the liquid descends. By generating a swirling flow in the reaction vessel, a sufficient stirring flow rate can be obtained inside the reaction vessel while reducing the amount of dissolved oxygen.

This is because, when a swirling flow is generated, the bubbles rise in the form accompanied by the rising flow of the liquid, and the bubbles themselves have a further upward slip speed with respect to the flow of the liquid. This is because the residence time in the liquid (gas-liquid contact time) is reduced and the oxygen dissolving efficiency is reduced, and the swirling flow method has a higher stirring power than the full air diffusion method.

Also, as shown in FIG. 3, a draft tube or a baffle plate 12 is installed inside the reaction tank, and air is blown into the reaction tank. A similar effect can be obtained by clear separation.

Further, as shown in FIGS. 4 and 5, a concave portion 13 is provided at the bottom of the reaction tank, and the settled sludge is collected in the concave portion. By transferring to the upper part of the tank, it is possible to stir the inside of the reaction tank without depositing sludge on the bottom part.

In installing a draft tube or a partition plate in the reaction tank, the inside of the reaction tank can be finely divided by installing a plurality of draft tubes or partition plates in the reaction tank.

Further, in the method of blowing air from a diffuser having a large diameter, intermittent aeration is also effective. This is because the amount of oxygen dissolved in the reaction tank can be further reduced by intermittent aeration, and sufficient stirring in the reaction tank is possible even in the intermittent aeration method.

The period of the intermittent aeration is determined by the anaerobic degree and the stirring state of the reaction tank, and the period can be determined from the empirical value.
Automatic control can also be performed using an oxidation-reduction potential (ORP) meter, a sludge concentration meter, a sludge interface meter, or the like.

It should be noted that as a matter common to all the above-described agitation methods using aeration, the amount of dissolved oxygen can be reduced by making the water depth of the aeration device shallow. In addition, as a matter common to all the above-described agitation methods using aeration, it is known that the biological denitrification reaction proceeds even if there is some dissolved oxygen on the liquid side. It is not necessary to make the inside of the reaction tank completely oxygen-free in order to advance the reaction. As a guide, the dissolved oxygen concentration (DO) in the reaction tank may be set to about 0.5 (g / m ³ ) or less.

When a hollow carrier is used as the carrier, there is a merit that the denitrification reaction is more likely to occur because the DO concentration is locally reduced in the hollow portion. Further, it is also possible to stir in an oxygen-free state by making the upper space of the intermediate tank a closed structure and repeatedly blowing gas present in the upper space into the reaction tank. In this case, even if oxygen gas is present at the top of the reaction tank at the beginning,
Oxygen gas is dissolved in the liquid side, and the oxygen concentration in the gas gradually decreases, so that anoxic conditions are ensured. In addition, the upper space may be supplemented with a volume of air corresponding to the dissolved amount. As described above, the denitrification reaction proceeds even if a small amount of DO is present, so that the airtightness of the upper space does not need to be perfect.

Further, the reactor does not need to have three stages,
Although two or four stages can be applied, the more stages, the more precise control can be performed, and a greater improvement in treated water quality can be achieved.

In the case of the second stage, the first stage is operated under the oxygen-free condition. However, when the number of stages is increased, each stage is operated under the oxygen-free condition in consideration of the inflow water quality and the treated water quality of each stage. Or aerobic conditions may be determined. In the case of multiple stages, by setting the middle reaction tank to anoxic condition or aerobic condition according to the treatment situation, a high nitrogen removal rate more stable against fluctuations in the amount and quality of inflow water is achieved. Is done.

The water depth of the reaction tank is generally about 5 m, but the present invention can be applied to an aeration tank having a water depth of about 10 m to 20 m, which is called a deep aeration method, and the same effect can be obtained.

As the carrier, any carrier having the ability to immobilize microorganisms can be used. The most suitable carrier for immobilizing microorganisms is hollow and the main component of the carrier is polypropylene. The carrier has a specific gravity of 0.99 to 1.03. When the specific gravity of the carrier is large, the amount of blown air necessary for fluidization becomes large, and the amount of dissolved oxygen in the reaction tank becomes large. There is a problem that the nitrogen reaction is suppressed, but if the specific gravity of the carrier is 0.99 to 1.03,
A sufficient flow of the carrier can be secured while maintaining the oxygen-free condition.

The method of installing an underwater stirrer inside the reaction tank or installing a pump for circulating the inside of the reaction tank is the simplest method of stirring the reaction tank under oxygen-free conditions, but it has a low strength. In the case of a microorganism-immobilized carrier, specifically, a carrier mainly composed of a gel of a water-soluble polymer such as polyethylene glycol, polypropylene glycol, polyvinyl alcohol, and polyacrylamide, the carrier is damaged. Can not be adopted.

On the other hand, in the case of a carrier containing polypropylene as a main component, the strength of the carrier is large, and a method of installing an underwater stirrer inside the reaction tank or a method of installing a pump for circulating the inside of the reaction tank is used. It has been confirmed that it can be adopted.

Further, when a hollow-shaped carrier is used, the microorganisms in the hollow portion are also used for the treatment, so that the effective microorganism concentration is increased. The part easily becomes anoxic and the denitrification reaction easily occurs, thereby improving the quality of treated water or reducing the size of the reaction tank.

As described above, according to the present method, the removal of nitrogen-based pollutants, which was impossible with the conventional method, is possible with a small-sized apparatus, and more stable against fluctuations in the amount and quality of inflow water. A high nitrogen removal rate is achieved.

[0047]

An embodiment of the present invention will be described below with reference to Table 1.

[0048]

[Table 1]

RUN1 in Table 1 indicates the treatment system (the present method A) to which the present method shown in FIG. 1 is applied and the conventional method, that is, the first, second and third stages of the reaction tank under aerobic conditions. Drive,
It shows the processing conditions and processing results when the circulation of the processing water is not performed.

As is clear from the treatment results, in the conventional method, only the nitrification reaction occurs and the denitrification reaction hardly occurs, so that a high concentration of NO _X -N remains in the treated water and the total nitrogen ( Although the (TN) concentration was 30 (g / m ³ ), in the present method A, since the treated water was circulated in the first stage of the reaction tank under anoxic condition, the total nitrogen (T -N) concentration is 9.
0 (g / m ³ ), which is significantly reduced as compared with the conventional method.

Furthermore, in the conventional circulating nitrification denitrification method using suspended sludge, the residence time of inflow water in the entire reaction tank required for good nitrogen removal is about 14 to 16 hours. In method A, good treatment was performed with a residence time of 6 hours. This is considered to be the effect of immobilizing a large amount of microorganisms on the microorganism-immobilized carrier.

Further, the DO of the oxygen-free tank is 0.1 (g / m
³ ) The following conditions were satisfied, and the reaction tank could be maintained in an oxygen-free condition enough for denitrification to occur sufficiently by coarse bubble aeration. Next, RUN2 in Table 1 shows a case where the second stage was subjected to aerobic conditions (this method A) and a case where the second stage was subjected to anoxic conditions (this method B) in the three-stage method. The method B
The TN concentration of the treated water was smaller in the case of.

As compared with RUN1, RUN2 has a smaller value of the BOD and TN concentration of the inflow water.
Nitrification had progressed 100% in the stage alone, and the denitrification rate was low due to the low BOD concentration of the influent. Therefore, in the case of the present method A in which the second stage is aerobic, 3
The stage is a useless tank that hardly participates in the reaction. Since the denitrification is performed only in the first stage, the denitrification becomes insufficient, and as a result, the concentration of NO _X -N remaining in the treated water becomes large. Had become.

On the other hand, in the present method B, nitrification of 100% proceeds in the third stage alone, and denitrification is performed in the two tanks of the first and second stages. TN of treated water
Is smaller than that of the method A.

As described above, based on the results of RUN2, the second-stage reaction tank can be switched to aerobic conditions and anoxic conditions in accordance with the inflow water quality, inflow water amount, required treatment water quality, water temperature, etc. It was shown that the quality of treated water can be improved by switching.

Next, RUN3 is a comparison between the present method B and the present method C, and the difference between the two is in the carrier used. That is, in the present method B, a hollow cylindrical carrier having a specific gravity of 1.01, an outer diameter of 4 mm, an inner diameter of 3 mm, and a length of 5 mm was used, whereas in the present method C, a polyethylene glycol, specific gravity of 1.04, A cubic carrier having a side of 3 mm was used.

The NO _X -N of the treated water is 7.2 in the present method B.
(G / m ³ ), whereas 9.8 (g
/ M ³ ) and T-N were 8.2 (g / m ³ ) in the present method B, whereas they were 11.8 (g / m ³ ) in the present method C, both of which were 60% or more. A nitrogen removal rate has been obtained.

However, made of polypropylene, specific gravity 1.0
1. In the case of the present method B using a hollow cylindrical carrier having an outer diameter of 4 mm, an inner diameter of 3 mm and a length of 5 mm, the treated water quality was better.
This is because the hollow portion of the hollow carrier is more likely to be anoxic and denitrification is more likely to occur, and the specific gravity of the cubic carrier made of polyethylene glycol, 1.04, 3 mm on a side has a large specific gravity and is difficult to fluidize. This is because the amount of air blown must be large, and the DO in the oxygen-free tank is high, so that denitrification is unlikely to occur.In this method, a carrier such as polyethylene glycol can be used. It has been confirmed that higher performance can be obtained by using a hollow cylindrical carrier made of aluminum.

In this experiment, the capacity of each tank was set to the value shown in Table 1. However, the capacity of the reaction tank in the actual facility was determined based on the quality of the inflow water, the required quality of the treated water, and the facility area. Is determined in consideration of

[0060]

As described above, according to the present invention, anoxic conditions are provided on the upstream side of the reaction tank into which the microorganism-immobilized carrier has been charged,
Further, since the treated water is configured to be circulated to the upstream side of the reaction tank, it is possible to remove nitrogen-based pollutants which cannot be achieved by the conventional method.

Further, an intermediate tank which can be set under any of the aerobic condition and the anaerobic condition is provided between the anoxic tank and the aerobic tank, and the operation of the intermediate tank is controlled according to the inflow water quality and the treated water quality. Since the conditions can be appropriately managed, the effect of stably ensuring good treated water quality can be obtained.

Further, the specific gravity of 0.99-1.
Since the microorganism-immobilized carrier of No. 03 is used, low energy consumption and low oxygen dissolution in an oxygen-free tank are achieved, thereby reducing processing energy and improving processing water quality.

In particular, when a hollow carrier is used,
Since the hollow interior is maintained in an oxygen-free condition, there is an effect that the denitrification rate is improved, the quality of treated water is improved, or the size of the treatment apparatus is reduced.

[Brief description of the drawings]

FIG. 1 is a schematic flow chart showing an example of an embodiment of the present invention.

FIG. 2 shows an example of a reaction tank structure in a coarse bubble blowing system.

FIG. 3 shows an example of a reaction tank structure in a coarse bubble blowing system.

FIG. 4 shows an example of a reaction tank structure in a coarse bubble blowing system.

FIG. 5 shows an example of a reaction tank structure in a coarse bubble blowing system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inflow water, 2 ... Treatment water, 3 ... Circulation line, 4 ... Carrier separation screen, 5 ... Carrier, 6 ... Large bubble generator, 7 ...
First-stage reaction tank, 8: Second-stage reaction tank, 9: Aeration device, 10
... third-stage reaction tank, 11 ... coarse bubble generator, 12 ... baffle plate or draft tube, 13 ... recess.

Claims (10)

[Claims] 1. A method for treating wastewater in which a microorganism-immobilized carrier is charged into a plurality of reaction vessels, wherein a part of the effluent of the most downstream reaction vessel is circulated to the most upstream reaction vessel, and A method for treating wastewater, wherein the tank is placed under anoxic conditions. 2. A wastewater treatment apparatus comprising a plurality of reaction tanks charged with a microorganism-immobilized carrier, wherein a device for circulating a part of the effluent of the most downstream reaction tank to the most upstream reaction tank; A wastewater treatment device, comprising: a device for setting a reaction tank in an oxygen-free condition. 3. The wastewater treatment apparatus according to claim 2, further comprising at least one intermediate reaction tank that can be controlled under both anoxic conditions and aerobic conditions. . 4. The wastewater treatment apparatus according to claim 2, wherein the microorganism-immobilized carrier charged has a hollow shape, the main component of the carrier is polypropylene, and the specific gravity of the carrier. Is from 0.99 to 1.03. 5. The wastewater treatment apparatus according to claim 2, wherein the apparatus for setting the uppermost stream side reaction tank in an oxygen-free condition is a mechanical stirrer or a pump for circulating the inside of the reaction tank. Wastewater treatment equipment. 6. The wastewater treatment apparatus according to claim 2, wherein the apparatus that sets the uppermost-stream side reaction tank in an oxygen-free condition is a coarse bubble generator. 7. The wastewater treatment apparatus according to claim 6, further comprising a draft tube, a baffle plate, and the like that divide the uppermost reaction tank into a liquid rising part and a liquid falling part. Wastewater treatment equipment. 8. The wastewater treatment apparatus according to claim 6, wherein at least a part of the bottom of the most upstream reaction tank has a concave shape. 9. An apparatus for treating wastewater according to claim 6, wherein the air is diffused intermittently to generate coarse bubbles in the most upstream reaction tank. Wastewater treatment method. 10. The wastewater treatment apparatus according to claim 2, further comprising a device for repeatedly blowing gas present in an upper space of the uppermost-stream side reaction tank into a liquid in the tank. Waste water treatment apparatus characterized by the above-mentioned.