JP3125628B2 - Wastewater treatment method - Google Patents

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, there has been a need to consider measures for preventing water pollution on a global environmental scale. 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, a denitrification tank in an anaerobic state and a nitrification tank in an aerobic state. In the denitrification tank, organic matter in wastewater is decomposed and denitrified by denitrification bacteria. Ammonia nitrogen in the wastewater is nitrified to nitric acid. Then, the nitrification solution that has been nitrified in the nitrification tank is circulated to the denitrification tank, whereby nitrogen components in the wastewater are released to the atmosphere as nitrogen gas and removed. In this activated sludge circulation modification, immobilization of nitrifying bacteria is being studied in order to increase the nitrification efficiency, and a process in which the immobilized nitrifying bacteria is put into a nitrification tank is being studied. Further, a process in which immobilized denitrifying bacteria are put into a denitrification tank is also being studied.

[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, ancillary equipment such as a circulating water channel for circulating the liquid between the tanks is required, and there is a disadvantage that the apparatus becomes large.

[0004] Further, since a part of the nitrification solution which has been nitrified in the nitrification tank is discharged to a discharge channel of treated water provided in the nitrification tank, there is a disadvantage that nitrogen components easily 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, equipment can be downsized, and nitrogen in treated water can be reduced. An object of the present invention is to provide a wastewater treatment method capable of reducing components.

[0005]

According to the present invention, in order to achieve the above object, activated sludge and at least nitrifying bacteria are immobilized and specific gravity is fixed in a treatment tank into which organic wastewater containing a nitrogen component flows. A carrier formed to be larger than the activated sludge , wherein the carrier is a gelled polymer substance.
And coexist, forming an aerobic state in the treatment tank by aerating the treatment tank and flowing the activated sludge with the carrier and contacting the wastewater by contacting the wastewater with the ammonia nitrogen component of the wastewater. After the nitrification treatment for performing nitrification and stopping the aeration, the treatment is performed while stirring the inside of the treatment tank so that the carrier is settled and the activated sludge floats using the specific gravity difference between the carrier and the activated sludge. Degassing the inside of the tank, and oxidizing and denitrifying the organic matter in the wastewater and denitrifying the nitrate nitrogen component by bringing the activated sludge into contact with the nitrified wastewater in an anaerobic state. There line more than once in the same treatment tank, stop the agitator during the nitrification process, the de
During the nitriding treatment, the mixture is stirred using a stirrer .

[0006] In order to achieve the above object, the present invention provides:
In a treatment tank into which an organic wastewater containing a nitrogen component flows, a denitrifying bacterium carrier on which at least denitrifying bacteria are immobilized, and at least nitrifying bacteria are immobilized and formed such that the specific gravity is larger than that of the denitrifying bacterium carrier. With the nitrifying bacteria carrier,
A nitrification treatment for aerating the treatment tank to form an aerobic state in the treatment tank and for nitrifying ammonia-nitrogen components in the wastewater by contacting the wastewater by flowing both the carriers. After stopping the aeration, denitrifying the inside of the treatment tank while stirring the inside of the treatment tank so that the nitrifying bacteria carrier settles and the denitrifying bacteria carrier floats using the specific gravity difference, and the denitrifying bacteria carrier and The oxidation and denitrification treatment of oxidizing organic substances in the wastewater and denitrifying nitrate nitrogen components by contacting the nitrified wastewater in an anaerobic state is performed at least once in the same treatment tank. It is characterized by.

[0007]

According to the first aspect of the present invention, air is aerated in the treatment tank in a state in which at least the carrier having the nitrifying bacteria immobilized therein and the activated sludge coexist in the treatment tank, and the carrier and the activated sludge are aerobic. It is in efficient contact with wastewater while flowing under conditions.
Thereby, the nitrifying bacteria contained in the carrier or the activated sludge and working in the aerobic state convert the ammonia nitrogen component in the wastewater into nitrate nitrogen component by nitrifying. In the nitrification treatment, a carrier on which nitrifying bacteria are immobilized mainly works.

Next, after stopping the aeration, the inside of the treatment tank is degassed 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. Ensure that the sludge comes into efficient contact with the nitrified wastewater under anaerobic conditions. Thereby, the denitrifying bacteria working in the anaerobic state in the activated sludge oxidize and decompose the organic matter in the wastewater, and also denitrify the nitrified nitrate nitrogen component. Since the carrier is settled in this oxidation and denitrification treatment,
Damage to the carrier due to agitation and turbidity of the treated water due to the damage can be prevented. Then, the nitrification treatment and the oxidation / denitrification treatment are performed once or more in the same treatment tank according to the quality of the wastewater. Thereby, the nitrification treatment and the oxidation / denitrification treatment can be efficiently performed in one treatment tank, and the treated water having good water quality can be obtained.

The invention of claim 2 provides a denitrifying bacteria carrier on which at least denitrifying bacteria are immobilized, and a nitrifying bacteria carrier on which at least nitrifying bacteria are immobilized and whose specific gravity is larger than that of the denitrifying bacteria carrier. Are coexisted in a treatment tank, and the same operation as in claim 1 is performed using the difference in specific gravity between the denitrifying bacteria carrier and the nitrifying bacteria carrier.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a wastewater treatment method according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a basic configuration diagram of a wastewater treatment apparatus to which the wastewater treatment method according to the present invention is applied. As shown in FIG. 1, a wastewater treatment apparatus 10 includes a treatment tank 12 into which wastewater such as sewage mainly containing an organic substance and an ammonia nitrogen component flows, and a treatment tank 12.
Aeration device 1 that is located at the bottom of the inside to aerate air into wastewater
4, a stirrer 16 for stirring wastewater in the treatment tank 12, a sedimentation tank 18 for settling activated sludge entrained in the treated water treated in the treatment tank 12, and an activated sludge settled in the sedimentation tank 18. And a return path 20 for returning the signal to the return path 12. Compressed air is supplied to the aeration device 14 from a blower 15. The activated sludge 22 is provided in the treatment tank 12.
(Shown by fine dots in the figure) and an immobilized microorganism carrier 24 on which at least nitrifying bacteria are immobilized, and the immobilized microorganism carrier 24 is placed in the treated water outlet 26 of the treatment tank 12. The screen 28 is provided to be inclined inward so as not to flow out of the screen.

The immobilized microorganism carrier 24 is immobilized by accumulating the returned sludge of a sewage treatment plant that uses the standard activated sludge method to increase the number of nitrifying bacteria as a seed for immobilization. 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, Performed by gelling. The obtained gel was cut into pellets of 3 mm square and used.

Next, the wastewater treatment method of the present invention using the wastewater treatment apparatus 10 configured as described above will be described. First,
In a state where the immobilized microorganism carrier 24 and the activated sludge 22 coexist in the treatment tank 12, compressed air is aerated from the bottom of the treatment tank 12 into the wastewater for a predetermined time by the aeration device 14. By this aeration, the immobilized microorganism carrier 24 and the activated sludge 22 come into efficient contact with the wastewater while flowing under an aerobic condition as shown in FIG. As a result, the nitrifying bacteria contained in the immobilized microorganism carrier 24 and the activated sludge 22 and operating in the aerobic state nitrify the ammonia nitrogen component (NH ₄ —N) in the wastewater to perform the nitrite nitrogen component (NO ₂ −). It changed to N), varying further nitrate nitrogen components (NO ₃ -N). In the nitrification treatment, the immobilized microorganism carrier 24 mainly works. That is, the nitrifying bacterium that performs the nitrification treatment has a disadvantage that the growth rate is slower than that of the denitrifying bacterium and the nitrification reaction hardly proceeds with only the activated sludge 22, but the immobilized microorganism carrier 24 on which the nitrifying bacterium is immobilized is brought into contact with wastewater. As a result, the nitrification reaction rate is accelerated, so that the efficiency of the nitrification treatment can be increased.

Next, after the aeration is stopped, the stirrer 16 is slowly moved to a predetermined position so that the immobilized microorganism carrier 24 is settled and the activated sludge 22 floats by utilizing the specific gravity difference between the immobilized microorganism carrier 24 and the activated sludge 22. The inside of the processing tank 12 is degassed by rotating for a time. By this agitation, the activated sludge comes into efficient contact with wastewater that has been nitrified under anaerobic conditions (hereinafter, referred to as nitrification liquid). As a result, the denitrifying bacteria in the anaerobic state in the activated sludge 22 oxidatively decompose the organic matter (BOD component) in the wastewater and denitrify the nitrified nitrate nitrogen component. That is, denitrification is performed on the nitrite nitrogen component and the nitrate nitrogen component generated by the nitrification treatment using the BOD component as a hydrogen donor. Activated sludge mainly works in the denitrification treatment. The reason for the sedimentation of the immobilized microorganism carrier 24 by this oxidation / denitrification treatment is to prevent the gel carrier 24 from being damaged by physical shearing during stirring, or to prevent the treatment water from becoming cloudy due to the breakage of the carrier 24. .

The above-mentioned nitrification treatment and oxidation / denitrification treatment are carried out once or a plurality of times so as to obtain treated water of good quality according to the quality of wastewater. Thereby, the nitrification treatment and the oxidation / denitrification treatment can be efficiently performed in one treatment tank 12. Therefore, unlike the conventional wastewater treatment apparatus, there is no need to provide two tanks, a nitrification tank and a denitrification tank, and there is no need for ancillary equipment such as a circulation channel for circulating the liquid between the tanks.
The wastewater treatment device can be made compact. Also,
Nitrification treatment and oxidation / denitrification treatment can be performed multiple times in the same treatment tank depending on the quality of the wastewater, and a portion of the nitrified wastewater does not mix into the treated water as in the past. Nitrogen component can be reduced. In addition, since the immobilized microorganism carrier 24 is settled during the oxidizing and denitrifying treatment, it is possible to prevent the immobilized microorganism carrier 24 from being damaged, and to prevent the treated water from being clouded due to the damage.

The following is an example of conducting a long-term continuous wastewater treatment experiment on synthetic wastewater and actual sewage wastewater using the wastewater treatment method of the present invention. (Example 1) The apparatus used the wastewater treatment apparatus 10 having the above-mentioned basic configuration as it was, and was operated continuously for about 12 days. As wastewater quality, synthetic wastewater having a composition having an ammonia nitrogen concentration of 40 mg / liter and a sodium acetate concentration of 410 mg / liter was used. In addition, the aeration tank (4 liter capacity) always contains 32 liters of wastewater at the time of aeration and when the aeration is stopped.
Flowed in daily flow. Then, in addition to the activated sludge 22, the immobilized microorganism carrier 24 having a square shape of 3 mm is charged into the treatment tank 12, and aerated for 20 minutes, and the immobilized microorganism carrier 24 is aerobic.
Activated sludge 22 and wastewater were brought into contact with each other to perform nitrification treatment.
At this time, the stirrer 16 is stopped. Next, after the aeration was stopped, the stirrer was rotated for 40 minutes to settle the immobilized microorganism carrier, suspend the activated sludge, and perform oxidation and denitrification treatment by bringing the activated sludge into contact with the nitrification solution.

FIGS. 3 and 4 are graphs showing the processing results. FIG. 3 shows changes in dissolved oxygen (DO) and oxidation-reduction potential (ORP) in wastewater during the aeration period and during the aeration stop period. FIG. 4 shows a change in the quality of the treated water during the continuous operation period. The water quality analysis of the treated water is performed by collecting the supernatant water of the sedimentation tank 18, and the analysis items indicate the total concentration of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen as TN (total nitrogen) in the treated water. Was.

As a result, the ammonia nitrogen concentration is 40 m
g / liter of wastewater treated by the wastewater treatment method of the present invention has a T-N of 5 during the operation period.
It was stable at less than mg / liter. On the other hand, as a comparative example with respect 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 by adding the immobilized microorganism carrier to activated sludge. This was compared with two types of conventional activated sludge methods using a carrier, in which only the activated sludge method was used.
The conditions such as the composition of the wastewater and the flow rate of the wastewater flowing into the treatment tank were the same as in Example 1, and only aeration was performed continuously.

FIG. 5 shows the result of this comparison. As is clear from FIG. 5, and together, the TN of the treated water was 20 mg.
Per liter, and the nitrogen component is about 4 compared to 5 mg / liter or less of T-N of treated water in the wastewater treatment method of the present invention.
It was twice surviving. 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 disadvantage 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) Example 2 shows the aeration time and the aeration stop time as Example 1.
The aeration of the aeration device 14, the stop of the aeration and the agitator 16 based on the ammonia nitrogen concentration of the treated water without setting
Is controlled. The composition of the wastewater and the flow rate of the wastewater flowing into the treatment tank were 2 in the same manner as in Example 1.
It has been running continuously for months.

FIG. 6 shows the structure of the wastewater treatment apparatus used in the second embodiment. The same members as those in the basic structure of the apparatus described in FIG.
The same reference numerals are given to the devices, and the description is 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 sedimentation tank 18 was taken into the analyzer 32 via the water intake system 30 and the ammonia nitrogen concentration was measured. The clear water returns to the settling tank 18 via the return line 34. The measured value of the concentration of ammonia nitrogen in the treated water measured by the analyzer 32 is output to the controller 36. The controller 36 turns on and off the operation of the blower 15 and the agitator 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 control device 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 switches the stirrer 16 drive.

As a result, the ammonia nitrogen concentration was 40 m
g / liter of wastewater treated by the wastewater treatment method of the present invention has a water quality of 1 to 3 mg during the operation period.
Per liter / liter, and a better result than the result of Example 1 was obtained. (Example 3) In Example 3, an aerobic denitrification tank was provided downstream of the wastewater treatment apparatus 10 having the above-described basic configuration, and the finishing treatment was performed in the aerobic denitrification tank. FIG. 7 shows the configuration of the wastewater treatment apparatus used in Example 3, and the same members and devices as those of the wastewater treatment apparatus 10 having the basic configuration described with reference to FIG. The aerobic denitrification tank 38 is provided adjacent to the wastewater treatment apparatus 10 having the basic configuration, and is provided with the aerobic denitrification tank 3.
An aerobic denitrification tank aerating device 40 is provided at the bottom of 8, and the aerobic denitrification tank aerating device 40 has an aerobic denitrification tank blower 42.
Supplies compressed air. The processing tank 12 has a capacity of 150
A liter capacity was used, and the aerobic denitrification tank 38 used was a 250 liter capacity.

The continuous operation is performed for two months using actual sewage wastewater as the wastewater. During the operation, the wastewater has an ammonia nitrogen concentration of 32 to 40 mg / liter and a T-N of 45 to 56 m.
g / liter and a BOD of 64 to 124 mg / liter. Wastewater was constantly introduced into the treatment tank 12 at a flow rate of 1600 liters / day both when aeration was performed and when aeration was stopped. And, in addition to the activated sludge 22, 3 m
15 liters of the m-size immobilized microorganism carrier 24 was added, and 2
Nitrogenation treatment was performed by contacting the immobilized microorganism carrier 24 or the activated sludge 22 with the wastewater in an aerobic state by aeration for 0 minutes. 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 microorganism carrier 24 and suspend the activated sludge 22, and perform the oxidation and denitrification treatment by bringing the activated sludge 22 into contact with the nitrification liquid. Was. After the wastewater was treated in the treatment tank 12, the wastewater was further subjected to a 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 where the activated sludge 22 accompanying the treated water is settled and separated. The separated activated sludge 22 is returned to the treatment tank 12 as returned sludge. Further, the analysis of the treated water used the supernatant water of the sedimentation tank 18.

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

FIG. 8 is a block diagram of an apparatus for performing a modified nitrification-promoting activated sludge circulation method. The same apparatus and members as those used in the wastewater treatment apparatus having the above-described basic structure are denoted by the same reference numerals. I do. As shown in FIG. 8, a 250-liter denitrification tank 4
4 and a nitrification tank 46 of 150 liters.
6 is provided with an aeration device 14 at the bottom thereof and a nitrification tank 4.
In 6, in addition to the activated sludge 22, 15 liters of a 3 mm-square immobilized microorganism carrier 24 are charged as in Example 3. On the other hand, the denitrification tank 44 is provided with the stirrer 16 and the activated sludge 2
2 has been thrown. Then, in the nitrification tank 46, nitrification is performed in an aerobic state by aeration from the aeration device 14, and the nitrified nitrate is circulated to the denitrification tank 44 through the circulation channel 48 so that the circulation ratio becomes 3. You. Denitrification tank 44
In the anaerobic state, oxidation of organic matter and denitrification of nitrification liquid are performed. The quality of the wastewater used in Comparative Example 3 was the same as the wastewater used in Example 3, and the continuous operation was performed for two months.

As a result, the quality of the treated water during the continuous operation period in the modified nitrification-promoting activated sludge circulation method has an ammonia nitrogen concentration of 1 mg / l or less, a TN of 4 to 9 mg / l,
The BOD was 10 mg / l or less, and the TN was slightly inferior to the result obtained in Example 3 of the present invention. FIG. 9 is a configuration diagram of an apparatus for performing an aerobic treatment method. The same apparatus and members as those used in the wastewater treatment apparatus having the above-described basic configuration are denoted by the same reference numerals. As shown in FIG. 9, the apparatus for performing the aerobic treatment method includes a 150-liter first treatment tank 50 adjacent to the first treatment tank.
And a second treatment tank 52 of 250 liters. In the first treatment tank 50, in addition to the activated sludge 22, 15 liters of the immobilized microorganism carrier 24 of 3 mm square as in Example 3 were introduced.
Only the activated sludge 22 was put into the treatment tank 52. And
The first and second processing tanks 50 and 52 were provided with aeration devices 14 and 14, respectively, and were constantly aerated. The quality of the wastewater used in Comparative Example 2 was the same as that of the wastewater used in Example 3, and the continuous operation was performed for two months.

As a result, the quality of the treated water during the continuous operation period in the aerobic treatment method is such that the ammonia nitrogen concentration is 2 mg.
/ Liter or less, 18 to 31 mg / liter in TN,
The BOD was 10 mg / liter or less, which was clearly inferior to the results obtained in Example 3 of the present invention. In this example, the combination of the immobilized microorganism carrier and the activated sludge was described, but at least the denitrifying bacteria carrier on which the denitrifying bacteria were immobilized, and at least the specific gravity of the denitrifying bacteria carrier were increased while the nitrifying bacteria were immobilized. The nitrifying bacteria carrier formed in the above step may coexist in the treatment tank. In this case, it is necessary to take measures to prevent the denitrifying bacteria carrier from being damaged by agitation during the oxidation and denitrification treatments.However, since activated sludge is not entrained in the treated water, a sedimentation tank is not required, as in urban areas. This is ideal when it is difficult to secure a large site area. The gel used for immobilizing the immobilized microorganism carrier is not particularly limited, and various polymer substances, for example, polyacrylamide, polyethylene glycol, polyvinyl alcohol, agar, carrageenan, alginic acid solution and the like can be used.

[0027]

As described above, according to the wastewater treatment method of the present invention, the nitrification treatment and the denitrification treatment of wastewater can be performed in the same treatment tank. It is not necessary to provide two tanks, i.e., a denitrification tank, and no additional equipment such as a circulating water channel for circulating the liquid between the tanks, so that the wastewater treatment apparatus can be made compact.

Further, the nitrification treatment and the oxidation / denitrification treatment can be performed a plurality of times in the same treatment tank depending on the quality of the wastewater, and a part of the nitrified wastewater can be mixed into the treated water as in the prior art. Since it is not available, the nitrogen component in the treated water can be reduced. Also, since the carrier is settled during the oxidation and denitrification treatment,
Damage to the carrier and turbidity of the treated water, which may be caused by the damage, can be prevented.

[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 oxidation-reduction 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 diagram showing water quality comparison results of treated water in Example 1 of the present invention and treated water in a comparative example.

FIG. 6 is a configuration diagram of an apparatus according to a second embodiment of the present invention.

FIG. 7 is a configuration diagram of an apparatus according to a third embodiment of the present invention.

FIG. 8 is an apparatus configuration diagram of a modified nitrification promotion type 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]

 DESCRIPTION OF SYMBOLS 10 ... Waste water treatment apparatus 12 ... Treatment tank 14 ... Aeration apparatus 16 ... Agitator 18 ... Settling tank 20 ... Return system 22 ... Activated sludge 24 ... Immobilized microorganism carrier 26 ... Treatment water outlet 28 ... Screen 32 ... Analyzer 36 ... Control Device 38 ... Aerobic denitrification tank

(56) References JP-A-62-33593 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 3/34 101 C02F 3/08 C02F 3/30

Claims (2)

(57) [Claims] To 1. A within treatment tank organic wastewater flows containing nitrogen components, and activated sludge, a carrier density is formed to be larger than the activated sludge with at least nitrifying bacteria are immobilized The carrier gelled the polymeric material
A carrier and coexistence, the aeration in the treatment tank to form an aerobic state in the treatment tank, and the carrier and the activated sludge are fluidized and contacted with the wastewater to form an ammonia nitrogen component in the wastewater. After the nitrification treatment for performing nitrification, after the aeration is stopped, the carrier is settled by using a specific gravity difference between the carrier and the activated sludge, and the inside of the treatment tank is stirred while the activated sludge is floating. Deaeration of the inside of the treatment tank, oxidation and denitrification treatment of oxidizing organic matter in the wastewater and denitrifying nitrate nitrogen components by contacting the activated sludge with the nitrified wastewater in an anaerobic state, gastric row more than once in the same treatment tank, wherein during nitrification process stops stirrer, when the denitrified
A method for treating wastewater, wherein the method comprises stirring using a stirrer . 2. A denitrifying bacterium carrier on which at least denitrifying bacteria are immobilized, and a denitrifying bacterium on which at least nitrifying bacteria are immobilized, and a specific gravity larger than that of the denitrifying bacterium carrier, in a treatment tank into which organic wastewater containing a nitrogen component flows. A nitrifying bacteria carrier formed so as to form an aerobic state in the treatment tank by aerating the treatment tank and causing both the carriers to flow and contact the wastewater to produce wastewater. Nitrification treatment for nitrification of the ammonia nitrogen component in, after stopping the aeration, the nitrifying bacteria carrier settles using the specific gravity difference between the nitrifying bacteria carrier and the denitrifying bacteria carrier, and the denitrifying bacteria carrier floats The inside of the treatment tank is degassed while stirring the inside of the treatment tank so that the denitrifying bacteria carrier and the nitrified wastewater are brought into contact with each other in an anaerobic state, thereby oxidizing organic substances in the wastewater and nitrate nitrogen components. Denitrification of Wastewater treatment method, which comprises carrying out one or more times and oxidation and denitrification, the same treatment tank.