JPH091184A - Wastewater treatment method - Google Patents

Abstract

(57) [Abstract] [Purpose] Nitrification and denitrification of wastewater can be performed in the same treatment tank, and equipment can be made compact, and nitrogen components in the treated water can be reduced. [Structure] A treatment tank 1 in which a carrier 24 on which at least nitrifying bacteria are immobilized and an activated sludge 22 coexist in the treatment tank 12.
Air is aerated into the inside of the container 2, and the carrier 24 and the activated sludge 22 are brought into contact with waste water while flowing under aerobic conditions. Next, after the aeration is stopped, the inside of the treatment tank 12 is stirred while stirring the inside of the treatment tank 12 with the agitator 16 so that the carrier 24 sinks and the activated sludge 22 floats by utilizing the difference in specific gravity between the carrier 24 and the activated sludge 22. Degass the activated sludge so that it contacts the nitrification solution under anaerobic conditions. Then, the nitrification treatment and the oxidation / denitrification treatment are performed once or more in the same treatment tank 12 depending on the quality of the wastewater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method, and more particularly to a biological wastewater treatment method using immobilized microorganisms.

[0002]

2. Description of the Related Art In recent years, the examination of measures for preventing water pollution on a global environmental scale is being questioned, and in biological wastewater treatment, one of the development issues is to increase the efficiency of nitrogen removal from organic wastewater. , Various measures are being considered. Conventionally, a modified activated sludge circulation method has been adopted for biological nitrogen removal. This method consists of two tanks, an anaerobic denitrification tank and an aerobic nitrification tank. In the denitrification tank, organic substances in wastewater are decomposed and denitrified by denitrifying bacteria, and in the nitrification tank by nitrifying bacteria. Ammonia nitrogen in wastewater is nitrified to nitric acid. Then, the nitrification solution nitrified in the nitrification tank is circulated to the denitrification tank, so that the nitrogen component in the waste water is released to the atmosphere as nitrogen gas and removed. In this modified activated sludge circulation method, immobilization of nitrifying bacteria has been studied in order to improve nitrification efficiency, and a process of introducing the immobilized nitrifying bacteria into a nitrification tank has been studied. Furthermore, a process in which immobilized denitrifying bacteria are put into a denitrification tank is also under study.

[0003]

However, in the above-mentioned conventional wastewater treatment method, it is essential to circulate the liquid between the denitrification tank and the nitrification tank, and two tanks of the denitrification tank and the nitrification tank are required. At the same time, there is a drawback in that additional equipment such as a circulating water channel for circulating the liquid between the tanks is required, and the size of the apparatus becomes large.

Further, since a part of the nitrification solution nitrified in the nitrification tank is discharged to the treated water discharge channel provided in the nitrification tank, there is a drawback that nitrogen components are likely to remain in the treated water. The present invention has been made in view of such circumstances, and nitrification treatment and denitrification treatment of wastewater can be performed in the same treatment tank, and the equipment can be made compact, and nitrogen in the treated water can be achieved. It is an object of the present invention to provide a wastewater treatment method capable of reducing the components.

[0005]

In order to achieve the above object, the present invention has an activated sludge and at least nitrifying bacteria immobilized in a treatment tank into which an organic wastewater containing a nitrogen component flows and has a specific gravity of A carrier formed so as to be larger than the activated sludge coexists, aerates the inside of the treatment tank to form an aerobic state in the treatment tank, and causes the carrier and the activated sludge to flow and the waste water. After nitrification treatment to nitrify the ammonia nitrogen component in the wastewater by contacting, and after stopping the aeration, the inside of the treatment tank so that the carrier sediments and the activated sludge floats by utilizing the difference in specific gravity. The inside of the treatment tank is degassed while stirring, and the activated sludge is brought into contact with the nitrification-treated wastewater in an anaerobic state to oxidize organic matter in the wastewater and denitrify nitrate nitrogen components. The same as nitrification And carrying out one or more times in physical tank.

Further, in order to achieve the above object, the present invention provides:
A denitrifying bacterium carrier in which at least denitrifying bacteria are immobilized and at least nitrifying bacteria are immobilized in the treatment tank into which organic wastewater containing a nitrogen component flows, and a specific gravity is formed to be larger than the denitrifying bacterium carrier. Coexisting with a nitrifying bacterium carrier,
A nitrification treatment for nitrifying the ammonia nitrogen component in the wastewater by contacting the wastewater by flowing both the carriers together with forming an aerobic state in the treatment tank by aerating the treatment tank, After stopping the aeration, the nitrifying bacterium carrier is degassed while stirring in the treatment tank so that the nitrifying bacterium carrier precipitates and the denitrifying bacterium carrier floats by utilizing a difference in specific gravity, and a denitrifying bacterium carrier is obtained. Performing oxidation and denitrification treatment in which the nitrification-treated wastewater is contacted in an anaerobic state to oxidize organic matter in the wastewater and denitrify nitrate nitrogen components in the same treatment tank at least once. Is characterized by.

[0007]

According to the invention of claim 1, air is aerated in the treatment tank in a state where at least the carrier on which nitrifying bacteria are immobilized and the activated sludge coexist in the treatment tank, and the carrier and the activated sludge are aerobic. Efficiently contact wastewater while flowing under conditions.
As a result, the nitrifying bacteria contained in the carrier or activated sludge and working in an aerobic state nitrify the ammoniacal nitrogen component in the wastewater to convert it into a nitrate nitrogen component. In this nitrification treatment, a carrier on which nitrifying bacteria are immobilized mainly works.

[0008] Next, after stopping the aeration, the inside of the treatment tank is degassed while being stirred so that the carrier sediments and the activated sludge floats by utilizing the difference in specific gravity between the carrier and the activated sludge. Ensure sludge efficiently contacts nitrifying wastewater under anaerobic conditions. As a result, the denitrifying bacteria working in the anaerobic state in the activated sludge oxidize and decompose the organic matter in the wastewater and denitrify the nitrified nitrate nitrogen component. Since the carrier is settled in this oxidation / denitrification process,
It is possible to prevent breakage of the carrier due to stirring and clouding of the treated water due to breakage. Then, the above-mentioned nitrification treatment and oxidation / denitrification treatment are performed once or more in the same treatment tank depending on the quality of the wastewater. As a result, it is possible to efficiently perform nitrification treatment and oxidation / denitrification treatment in one treatment tank, and obtain treated water with good water quality.

According to the invention of claim 2, a denitrifying bacterium carrier on which at least denitrifying bacteria are immobilized, and a nitrifying bacterium carrier formed so that at least nitrifying bacteria are immobilized and the specific gravity is larger than that of the denitrifying bacterium carrier. Is coexisted in the treatment tank, and the same operation as in claim 1 is performed by utilizing the difference in specific gravity between the denitrifying bacterium carrier and the nitrifying bacterium carrier.

[0010]

The preferred embodiments of the wastewater treatment method according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a basic configuration diagram of a wastewater treatment device to which the wastewater treatment method according to the present invention is applied. As shown in FIG. 1, the wastewater treatment apparatus 10 includes a treatment tank 12 into which wastewater such as sewage mainly containing organic substances and ammonia nitrogen components flows, and a treatment tank 12.
Aeration device 1 that is installed at the bottom of the inside to aerate air into wastewater 1
4, a stirrer 16 for stirring the waste water in the treatment tank 12, a settling tank 18 for settling the activated sludge entrained in the treated water treated in the processing tank 12, and a treatment tank for the activated sludge settling in the settling tank 18. It is composed of a return line 20 for returning to 12. Compressed air is supplied to the aeration device 14 from a blower 15. Then, in this treatment tank 12, activated sludge 22
(Indicated by fine dots in the figure) and at least the immobilized microbial carrier 24 on which nitrifying bacteria are immobilized are introduced, and at the treated water outlet 26 of the treatment tank 12, the immobilized microbial carrier 24 is treated. The screen 28 is provided so as to be inclined inward so as not to flow out from the inside.

Immobilization of the immobilized microbial carrier 24 is carried out by acclimating the returned sludge of the sewage treatment plant, which is performing the standard activated sludge method, to increase the number of nitrifying bacteria and using it as the immobilizing seed bacteria. 2% by weight of sludge, 15% by weight of polyethylene glycol prepolymer, 0.5% by weight of N, N, N ', N'-tetramethylethylenediamine, and 0.25% by weight of potassium persulfate are mixed in water, It was performed by gelling. The obtained gel was cut into 3 mm square pellets for use.

Next, the wastewater treatment method of the present invention will be described using the wastewater treatment apparatus 10 constructed as described above. First,
With the immobilized microbial carrier 24 and the activated sludge 22 coexisting in the treatment tank 12, compressed air is aerated from the bottom of the treatment tank 12 into the waste water for a predetermined time by the aeration device 14. Due to this aeration, the immobilized microbial carrier 24 and the activated sludge 22 efficiently contact the wastewater while flowing under aerobic conditions as shown in FIG. As a result, the nitrifying bacteria contained in the immobilized microbial carrier 24 and the activated sludge 22 and operating in an aerobic state nitrify the ammonia nitrogen component (NH ₄ —N) in the wastewater to perform the nitrite nitrogen component (NO ₂ −). N) and further to nitrate nitrogen component (NO ₃ -N). The immobilized microbial carrier 24 mainly works in the nitrification process. That is, nitrifying bacteria that perform nitrification treatment have a slower growth rate than denitrifying bacteria and have a drawback that the nitrification reaction hardly progresses only with the activated sludge 22. However, the immobilized microbial carrier 24 immobilizing nitrifying bacteria is brought into contact with wastewater. As a result, the rate of nitrification reaction is accelerated, so that the efficiency of nitrification treatment can be improved.

Next, after the aeration is stopped, the agitator 16 is slowly set to a predetermined position so that the immobilized microbial carrier 24 settles and the activated sludge 22 floats by utilizing the difference in specific gravity between the immobilized microbial carrier 24 and the activated sludge 22. The inside of the processing tank 12 is deaerated by rotating for a time. By this agitation, the activated sludge efficiently comes into contact with wastewater that has been nitrified under the anaerobic condition (hereinafter referred to as nitrification liquid). As a result, the denitrifying bacteria in the activated sludge 22 that work in an anaerobic state oxidize and decompose the organic matter (BOD component) in the wastewater and denitrify the nitrified nitrate nitrogen component. That is, the nitrite nitrogen component and the nitrate nitrogen component produced by the nitrification treatment are denitrified using the BOD component as a hydrogen donor. Activated sludge mainly works in denitrification. The reason why the immobilized microbial carrier 24 is allowed to settle by this oxidation / denitrification treatment is to prevent the gel-like carrier 24 from being damaged by physical shearing during stirring, and the turbidity of the treated water to prevent clouding of the treated water. .

The above-mentioned nitrification treatment and oxidation / denitrification treatment are carried out once or plural times so that treated water of good quality can be obtained depending on the quality of waste water. As a result, the nitrification treatment and the oxidation / denitrification treatment can be efficiently performed in one treatment tank 12. Therefore, it is not necessary to provide two tanks, a nitrification tank and a denitrification tank, unlike the conventional wastewater treatment apparatus, and an additional equipment such as a circulating water channel for circulating the liquid between the tanks is not required.
The wastewater treatment device can be made compact. Also,
Depending on the quality of the wastewater, nitrification treatment and oxidation / denitrification treatment can be performed multiple times in the same treatment tank. The nitrogen component of can be reduced. Further, since the immobilized microbial carrier 24 is allowed to settle during the oxidization / denitrification treatment, it is possible to prevent damage to the immobilized microbial carrier 24 and clouding of the treated water which is considered to be caused by this damage.

An example of conducting a long-term continuous wastewater treatment experiment on synthetic wastewater and actual sewage wastewater by the wastewater treatment method of the present invention will be described below. (Example 1) As the apparatus, the wastewater treatment apparatus 10 having the above-mentioned basic configuration was used as it was, and continuous operation was performed for about 12 days. The quality of the wastewater is 40 mg / liter of ammonia nitrogen,
A synthetic wastewater having a composition of sodium acetate concentration of 410 mg / liter was used. In addition, 32 times of waste water is always stored in the treatment tank (4 liter capacity) both during aeration and when aeration is stopped.
The flow rate was liter / day. And the processing tank 12
In addition to activated sludge 22, 3 mm square immobilized microbial carrier 2
4 and the activated sludge 22 were aerated, and aerated for 20 minutes to bring the immobilized microbial carrier 24 and the activated sludge 22 into contact with the waste water in an aerobic state to perform nitrification treatment. At this time, the stirrer 16 is stopped. Next, after stopping the aeration, the stirrer was rotated for 40 minutes to settle the immobilized microbial carrier, the activated sludge was floated, and the activated sludge and the nitrification solution were brought into contact with each other to perform the oxidation / denitrification treatment.

3 and 4 are graphs showing the processing results. FIG. 3 shows changes in dissolved oxygen (DO) and redox potential (ORP) in wastewater during the aeration period and during the aeration stop period. Further, FIG. 4 shows changes in the quality of treated water during the continuous operation period. The water quality of the treated water is analyzed by collecting the supernatant water of the settling tank 18, and the total concentration of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the treated water is shown as TN (total nitrogen) as an analysis item. It was

As a result, the concentration of ammonia nitrogen is 40 m.
The water quality of the treated water obtained by treating the wastewater containing g / liter by the wastewater treatment method of the present invention has a TN of 5 during the operation period.
It remained stable below mg / liter. On the other hand, as comparative examples to Example 1 of the wastewater treatment method of the present invention, (1) a standard activated sludge method in which only aeration is performed using activated sludge, and (2) aeration with addition of the above-mentioned immobilized microbial carrier to activated sludge It was compared with two conventional methods of activated sludge method with carrier, which is only carried out.
The conditions such as the composition of waste water and the flow rate of waste water flowing into the treatment tank were the same as in Example 1, and only aeration was continuously performed.

The results of this comparison are shown in FIG. As is clear from FIG. 5, and the T-N of the treated water was 20 mg together.
/ L, and the nitrogen component is about 4 as compared with T-N of 5 mg / L or less in the treated water in the wastewater treatment method of the present invention.
It remained twice. From this, it was found that the treated water obtained by the wastewater treatment method of the present invention had good water quality.

As a conventional wastewater treatment method, there is a batch activated sludge method in addition to the above-mentioned method, but this method has a drawback that the treatment time is long. On the other hand, in the case of this method, it takes about 3 hours in the case of actual sewage wastewater. (Example 2) In Example 2, the aeration time and the aeration stop time are shown in Example 1.
Aeration of the aeration device 14, aeration stop, and agitator 16 based on the ammonia nitrogen concentration of the treated water
It controls the operation of. The composition of wastewater and the flow rate of wastewater flowing into the treatment tank are the same as in Example 1, and
Continuous operation was performed for a month.

FIG. 6 shows the construction of the wastewater treatment equipment used in Example 2, which has the same members as the basic construction of the equipment described in FIG.
The same reference numerals are given to the devices, and description thereof will be omitted. That is,
In Example 2, the supernatant water obtained by settling and separating the activated sludge 22 from the treated water sent to the settling tank 18 was taken into the analyzer 32 through the intake system passage 30, and the ammonia nitrogen concentration was measured and measured. The clear water returns to the settling tank 18 via the return line 34. The measured value of the ammonia nitrogen concentration of the treated water measured by the analyzer 32 is output to the controller 36, and the controller 36 operates the blower 15 and turns on / off the stirrer 16 based on the measured value to perform aeration and aeration. The stop and the operation of the stirrer 16 are controlled. For example, the controller 36
Operates the blower 15 when the ammonia nitrogen concentration of the treated water measured by the analyzer 32 is 1 mg / liter or more, stops the blower 15 when the ammonia nitrogen concentration is 0.8 mg / liter or less, and turns the stirrer 16 on. drive.

As a result, the concentration of ammonia nitrogen is 40 m.
The water quality of the treated water obtained by treating the wastewater contained in g / liter by the wastewater treatment method of the present invention is 1 to 3 mg during the operation period.
The value was stable and the result was even better than that of Example 1. (Example 3) In Example 3, an aerobic denitrification tank is provided in the latter stage of the wastewater treatment device 10 having the above-described basic configuration, and finishing treatment is performed in the aerobic denitrification tank. FIG. 7 shows the configuration of the wastewater treatment device used in Example 3, and the same members and devices as those of the wastewater treatment device 10 having the basic configuration described in FIG. The aerobic denitrification tank 38 is provided adjacent to the wastewater treatment device 10 having the basic configuration, and the aerobic denitrification tank 3 is provided.
The aerator 40 for aerobic denitrification tank is provided at the bottom of 8, and the aerator 40 for aerobic denitrification tank has a blower 42 for aerobic denitrification tank.
From which compressed air is supplied. Further, the processing tank 12 has 150
The aerobic denitrification tank 38 had a capacity of 250 liters.

Actual sewage wastewater is used as wastewater and continuously operated for two months. The quality of the wastewater during that time is such that the concentration of ammonia nitrogen is 32 to 40 mg / liter and T-N is 45 to 56 m.
The composition was g / liter and BOD 64-124 mg / liter. The waste water was always flowed into the treatment tank 12 at a flow rate of 1600 liters / day during aeration and while aeration was stopped. In addition to the activated sludge 22 in the treatment tank 12, 3 m
Add 15 liters of the m-square fixed microbial carrier 24, and
Aeration was carried out for 0 minutes, and the immobilized microbial carrier 24 and the activated sludge 22 were brought into contact with the wastewater in an aerobic state to perform nitrification treatment. At this time, the stirrer 16 is stopped. Next, after stopping the aeration, the stirrer 16 is rotated for 40 minutes to settle the immobilized microbial carrier 24 and the activated sludge 22 is suspended, and the activated sludge 22 and the nitrification solution are brought into contact with each other to perform the oxidation / denitrification treatment. It was The wastewater was treated in the treatment tank 12 and then further subjected to finishing treatment in the aerobic denitrification tank 38. In the aerobic denitrification tank 38, the liquid treated in the treatment tank 12 is aerated and the activated sludge 22
Aerobic denitrification proceeds by contact with The treated water treated in the aerobic denitrification tank 38 is sent to the settling tank 18 and the activated sludge 22 entrained in the treated water is settled and separated. The separated activated sludge 22 is returned to the treatment tank 12 as return sludge. The supernatant water of the precipitation tank 18 was used for the analysis of the treated water.

As a result, the quality of treated water during the operation period is
Ammonia nitrogen concentration is less than 1mg / l, T-N is 5m
It was stable at g / liter or less and BOD of 10 mg / liter or less, and extremely good water quality could be obtained. On the other hand, as a comparative example to Example 3 of the wastewater treatment method of the present invention, two types of conventional methods, that is, a modified nitrification-promoted activated sludge circulation method and an aerobic treatment method were compared.

FIG. 8 is a block diagram of an apparatus for carrying out the modified nitrification-promoting activated sludge circulation method. The same apparatus and members as those used in the wastewater treatment apparatus having the above-mentioned basic structure are designated by the same reference numerals. To do. As shown in FIG. 8, a 250-liter denitrification tank 4
4 and 150 liters of nitrification tank 46
An aerator 14 is provided at the bottom of the nitrification tank 4
In addition to the activated sludge 22, a fixed microbial carrier 24 having a size of 3 mm 3 (15 liters) was added to the sample 6, as in Example 3. On the other hand, the denitrification tank 44 is provided with a stirrer 16 to activate the activated sludge 2
2 has been thrown. Then, in the nitrification tank 46, the nitrification treatment is performed in an aerobic state by being aerated from the aeration device 14, and the nitrified nitrification liquid is circulated to the denitrification tank 44 through the circulation water channel 48 so that the circulation ratio becomes 3. It Denitrification tank 44
In the anaerobic state, oxidation of organic substances and denitrification of nitrification liquid are performed. The quality of the wastewater used in Comparative Example 1 was the same as that of the wastewater used in Example 3, and continuous operation was performed for 2 months.

As a result, the quality of the treated water during the continuous operation period in the modified nitrification-promoted activated sludge circulation method was such that the concentration of ammonia nitrogen was 1 mg / l or less, and the T-N ratio was 4 to 9 mg / l.
The BOD was 10 mg / l or less, which was slightly inferior to the result obtained in Example 3 of the present invention in terms of T-N. FIG. 9 is a configuration diagram of an apparatus for performing an aerobic treatment method, and the same apparatus and members as those used in the wastewater treatment apparatus having the above-described basic configuration will be described with the same reference numerals. As shown in FIG. 9, the apparatus for performing the aerobic treatment method is a first treatment tank 50 of 150 liters adjacent to each other.
And a second treatment tank 52 of 250 liters. In addition to the activated sludge 22, a fixed microbial carrier 24 of 3 mm square was added to the first treatment tank 50 in an amount of 15 liters as in Example 3.
Only the activated sludge 22 was put into the treatment tank 52. And
The first and second treatment tanks 50 and 52 are provided with aeration devices 14 and 14, respectively, and are constantly aerated. The water quality of the waste water used in the comparative example was the same as that of the waste water used in Example 3, and continuous operation was performed for 2 months.

As a result, the quality of treated water during the continuous operation period in the aerobic treatment method was such that the concentration of ammonia nitrogen was 2 mg.
/ L or less, 18-31 mg / L in TN,
The BOD was 10 mg / liter or less, which was clearly inferior to the result obtained in Example 3 of the present invention. In addition, in the present example, the combination of the immobilized microbial carrier and the activated sludge has been described, but at least the denitrifying bacterium carrier in which at least the denitrifying bacterium is immobilized, and at least the nitrifying bacterium is immobilized and the specific gravity is larger than that of the denitrifying bacterium carrier. The nitrifying bacterium carrier formed in the above step may coexist in the treatment tank. In this case, it is necessary to devise a method to prevent the denitrifying bacteria carrier from being damaged by stirring during the oxidation / denitrification process, but since activated sludge is not entrained in the treated water, a settling tank is no longer required, and it can be used in urban areas. Optimal when it is difficult to secure a large site area. The gel used for immobilizing the immobilized microbial carrier is not particularly limited, and various polymer substances such as polyacrylamide, polyethylene glycol, polyvinyl alcohol, agar, carrageenan, and alginic acid solution can be used.

[0027]

As described above, according to the wastewater treatment method of the present invention, it is possible to perform nitrification treatment and denitrification treatment of wastewater in the same treatment tank. Since it is not necessary to provide two tanks, a denitrification tank and a denitrification tank, and additional equipment such as a circulating water channel for circulating the liquid between the tanks is not required, the waste water treatment device can be made compact.

Further, the nitrification treatment and the oxidation / denitrification treatment can be carried out a plurality of times in the same treatment tank depending on the quality of the wastewater, so that a part of the nitrified wastewater can be mixed into the treated water as in the conventional case. Since it does not exist, the nitrogen component in the treated water can be reduced. Also, since the carrier is settled during the oxidation / denitrification process,
It is possible to prevent breakage of the carrier and clouding of the treated water which is considered to be caused by this breakage.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a wastewater treatment apparatus to which a wastewater treatment method according to the present invention is applied, showing a state during aeration.

FIG. 2 is a basic configuration diagram of a wastewater treatment apparatus to which the wastewater treatment method according to the present invention is applied, showing a state when aeration is stopped.

FIG. 3 is a data diagram of oxygen concentration and redox potential of wastewater in Example 1 of the present invention.

FIG. 4 is a data diagram showing the quality of treated water in Example 1 of the present invention.

FIG. 5 is a water quality comparison result diagram of treated water in Example 1 of the present invention and treated water in a comparative example.

FIG. 6 is a block diagram of an apparatus in Example 2 of the present invention.

FIG. 7 is a block diagram of an apparatus in Example 3 of the present invention.

FIG. 8 is a device configuration diagram of a modified nitrification-promoting activated sludge circulation method as a comparative example with respect to Example 3 of the present invention.

FIG. 9 is an apparatus configuration diagram of an aerobic treatment method as a comparative example with respect to Example 3 of the present invention.

[Explanation of symbols]

 10 ... Wastewater treatment device 12 ... Treatment tank 14 ... Aeration device 16 ... Stirrer 18 ... Sedimentation tank 20 ... Return system path 22 ... Activated sludge 24 ... Immobilized microbial carrier 26 ... Treated water outlet 28 ... Screen 32 ... Analytical device 36 ... Control Device 38 ... Aerobic denitrification tank

Claims (2)

[Claims] 1. An activated sludge and a carrier formed so that at least nitrifying bacteria are immobilized and the specific gravity is larger than that of the activated sludge, coexisting in a treatment tank into which an organic wastewater containing a nitrogen component flows. Then, aeration is performed in the treatment tank to form an aerobic state in the treatment tank, and at the same time, the carrier and the activated sludge are made to flow and brought into contact with the wastewater to nitrify the ammonia nitrogen component in the wastewater. Nitrification and, after stopping the aeration, the inside of the treatment tank while stirring the inside of the treatment tank so that the carrier sediments and the activated sludge floats by utilizing the difference in specific gravity between the carrier and the activated sludge. The same treatment tank is used to oxidize and denitrify nitrate nitrogen components of organic matter in wastewater by deaeration and contacting the activated sludge with the nitrification-treated wastewater in an anaerobic state. Row more than once Wastewater treatment wherein the. 2. A denitrifying bacterium carrier in which at least denitrifying bacteria are immobilized and at least nitrifying bacteria are immobilized and a specific gravity is larger than that of the denitrifying bacterium carrier in a treatment tank into which organic wastewater containing a nitrogen component flows. By coexisting with a nitrifying bacterium carrier formed so as to form an aerobic state in the treatment tank by aerating in the treatment tank and flowing both carriers into contact with the wastewater Nitrification treatment for nitrifying ammonia nitrogen component in the inside, and after stopping the aeration, the nitrifying bacterium carrier precipitates and the denitrifying bacterium carrier floats by utilizing the difference in specific gravity between the nitrifying bacterium carrier and the denitrifying bacterium carrier. As described above, the inside of the treatment tank is degassed while being stirred, and the denitrifying bacteria carrier and the nitrification-treated wastewater are brought into contact with each other in an anaerobic state to oxidize organic matter and nitrate nitrogen components in the wastewater. Denitrifying Wastewater treatment method, which comprises carrying out one or more times and oxidation and denitrification, the same treatment tank.