JP3270652B2 - Wastewater nitrogen removal method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an organic pollutant and a reducing nitrogen compound, such as municipal sewage, organic industrial wastewater, sludge treated water, and municipal sewage into which a large amount of organic industrial wastewater flows. The present invention relates to a method for removing nitrogen from wastewater containing waste nitrogen and ammonia compounds stably and efficiently.

[0002]

2. Description of the Related Art Technologies for removing nitrogen from wastewater include:
Although physical and chemical treatment methods have been studied,
Biological methods are cost-effective and most prevalent. Biological nitrogen removal is basically based on ammoniacal nitrogen (NH ₄ −) by nitrifying bacteria under aerobic conditions.
N) Oxidation of N) to produce nitrate nitrogen (NO ₃ -N) (nitrification reaction, see formula (1) below) and reduction of NO ₃ -N by facultative anaerobic bacteria under anaerobic conditions It is carried out in combination with nitrogen gas generation (denitrification reaction, see the following formula (2)). The denitrification reaction is a respiration under the condition that dissolved oxygen (DO) of facultative anaerobic bacteria does not exist. Organic matter and methanol in sewage are carbon sources (hydrogen donor).
Is necessary. _{NH 4 -N → NO 2 -N →} NO 3 -N ( _{nitrification) ......... (1) NO 3 -N} → NO 2 -N → N 2 ( denitrification) ......... (2)

[0003] Various biological nitrogen removal processes have been proposed for the purpose of reducing equipment area, reducing organic carbon sources as hydrogen donors, reducing alkali agents as neutralizing agents, and the like. It can be broadly classified into a series system, a circulation system, and a combination thereof.

[0004] In the serial system, nitrification is first performed, and then denitrification is performed. The hydrogen donor required for denitrification is added from the outside, and the endogenous respiration of activated sludge without addition is performed. May be used.

On the other hand, as a circulation system, as shown in FIG. 3, a nitrification liquid circulation system in which denitrification is performed first and then nitrification is performed has been widely studied (modified activated sludge circulation method). This method has an advantage that the alkalinity consumed by nitrification can be recovered to some extent by denitrification by circulation of the nitrification liquid. However, in the activated sludge circulation modified method, since a part of the nitrification liquid which is not circulated and returned flows out without passing through the denitrification tank, the total nitrogen removal rate (TN removal rate) is limited.

[0006] Furthermore, nitrifying bacteria have a slower growth rate than ordinary activated sludge, and there is a problem that it is difficult to maintain a high concentration in a reactor. Therefore, various methods have been proposed in which various carriers are added to a reactor, nitrifying bacteria are adhered to the carrier, the nitrifying bacteria are maintained at a high concentration in the reactor, and efficiency is improved.

[0007] For example, Japanese Patent Application Laid-Open No. 54-24774 discloses that a reactor containing activated sludge is divided into four anaerobic tanks, one aerobic tank, two anaerobic tanks and two aerobic tanks. Odor and anaerobic are measured by oxidation-reduction potential (ORP: Oxygen).
Reducing the BOD, nitrogen compounds, and phosphorus compounds in municipal sewage by adding blast furnace granulated slag and carbon fine powder to the reactor as a carrier for immobilizing microorganisms while controlling using Reduction Potential as an index. A method is described.

[0008]

In the conventional biological nitrogen removal process for municipal sewage and the like, municipal sewage rarely contains components that inhibit nitrification and denitrification reactions. NH ₄ since -N is about 20-50 mg / l, the NH ₄ -N in sewage can biologically relatively easily oxidized to NO ₃ -N, also generated NO ₃ -N
Can be denitrified to nitrogen gas.

[0009] However, wastewater is used as BW, such as various industrial wastewaters such as leather industry, textile industry, and chemical industry, and sludge treated water.
OD (Biological Oxygen Dema
nd) and COD (Chemical Oxygen D)
(e.g., organic compounds) such as aromatic organic substances that inhibit the nitrification reaction and the denitrification reaction, and that NH ₄ —N is 5%.
When it is contained in an amount of 0 mg / l or more, it is very difficult to remove nitrogen by a conventional method.

Hereinafter, the nitrification reaction and the denitrification reaction are divided into
The problems of the conventional biological nitrogen removal process will be described.
First, regarding the nitrification reaction, when NH ₄ —N is contained in wastewater at a higher concentration than in city sewage, the reaction from NH ₄ —N to NO ₃ —N is completed in the reactor. Instead, nitrite nitrogen (NO ₂ -N) tends to accumulate. Nitrifying bacteria are a group of bacteria that oxidize NH ₄ —N to NO ₂ —N (Nitrozomonas: Nitrosomona).
s) and bacteria that oxidize NO ₂ -N to NO ₃ -N (Nitrobactor, etc.). Nitrozomonas have a higher growth rate than Nitrobactor, and are targeted at urban sewage. In Case of,
Does not NO ₂ -N is accumulated. However, when dissolved oxygen (DO) is deficient or an inhibitory substance is present in the wastewater, the growth rate of Nitrobacter is extremely reduced because Nitrobacter is more susceptible to inhibition than Nitrozomonas. In such a case, NO ₂ -N
Is easy to accumulate. NO ₂ − accumulated in large quantities in the reactor
N has a danger of inhibiting the function of microorganisms that degrade organic substances and nitrifying bacteria themselves. Furthermore, when NO ₂ -N accumulates in the treated water, 1 mg of the NO ₂ -N is measured as 1.14 mg as the COD, and there is a concern that the COD in the treated water may increase.

In order to prevent such a nitrification reaction for producing NO ₂ -N and to promote a nitrification reaction for producing NO ₃ -N, it is necessary to reduce the NH ₄ -N load on the reactor and the organic matter load. , Aerobic control of reactor, microorganism retention time (SRT: Sludge Retention Time)
e) increase, reactor residence time (HRT: Hydr)
It seems necessary to take measures such as an increase in audio retention time. However, a process using suspended nitrifying bacteria, such as the conventional activated sludge circulation method,
It is quite difficult to efficiently prevent the nitrification reaction that produces NO ₂ -N by such a method. This is SR
This is because an increase in T or HRT results in an increase in the size of the equipment.

This is described, for example, in "Wat. Res.,
1990, Vol. 3, pp. 303-312 "
Has been pointed out. An artificial wastewater containing 80 mg / l of NH ₄ —N, maintaining dissolved oxygen (DO) at 0.5 mg / l,
NO if the HRT of the reactor was processed on condition of 4 days
_The authors reported that 60 mg / l of _2- N was accumulated, and concluded that the oxidation reaction to produce NO ₂ -N would proceed even at low DO. Furthermore, an experiment was conducted in which the COD of the influent was varied, and it was reported that the organic matter load affected the generation and accumulation of NO ₂ -N.

As described above, a conventional floating activated sludge, such as a modified activated sludge circulation method, is used for wastewater having a high concentration of organic substances and hardly decomposable substances and a high concentration of NH ₄ -N. When a nitrification reaction is to be advanced by a biological nitrogen removal process, NO ₂ —N tends to accumulate, and many problems remain regarding the control of the nitrification reaction.

Further, plastic, granulated blast furnace slag,
This is a method of adding a carrier for binding and immobilization such as fine carbon powder and a carrier for inclusive immobilization such as polyacrylamide to a reactor for nitrification such as a modified activated sludge circulation method in order to efficiently perform the nitrification reaction. There is an advantage that the nitrifying bacteria attached to the immobilized carrier can be maintained at a high concentration in the reactor.
However, when the concentration of the organic matter or the inhibitory component in the wastewater is high, the function of the nitrifying bacteria itself tends to decrease, and it is quite difficult to significantly reduce the HRT of the reactor.

Next, regarding the denitrification reaction, when organic matter or municipal sewage or methanol is used as a carbon source, the reaction proceeds from NO ₃ -N to N ₂ as shown in the above formula (2) in the reactor. reaction is complete, nO ₂ -N it will not be accumulated. However, in the case of the denitrification reaction, the same phenomenon as that described in the nitrification reaction may occur. That is, it is considered that the denitrifying bacteria are roughly classified into a group of bacteria that reduce NO ₃ -N to NO ₂ -N and a group of bacteria that reduce NO ₂ -N to N ₂ . Although there is no clear classification like nitrifying bacteria, the function of bacteria that reduce NO ₂ -N to N ₂ is reduced by inhibition of organic substances, and NO ₂ -N accumulates in the denitrification reactor The phenomenon is often observed. Further, when NO ₂ -N accumulates in the treated water, 1 mg of NO ₂ -N is measured as 1.14 mg as COD,
There is a concern that COD in the treated water may increase.

[0016] Further, the problem of the method of the combination of nitrification and denitrification will be described. First, the in-line method, in which nitrification is performed first and then denitrification is performed, has a high concentration of organic substances and persistent substances,
Furthermore, when the target is wastewater containing NH ₄ —N of 50 mg / l or more, the nitrification reaction tends to be a NO ₂ —N accumulation type and is unstable. Furthermore, it is necessary to add a hydrogen donor such as methanol necessary for denitrification from the outside to the whole, which increases the processing cost. The method of utilizing endogenous respiration of activated sludge without adding methanol is extremely slow in processing speed and is not practical.

Next, a nitrification liquor circulation method (modified activated sludge circulation method) in which denitrification is performed first and then nitrification is performed. In this method, an organic substance requiring a denitrification reaction is circulated by circulating the nitrification liquid. Since organic matter in wastewater can be used, there is an advantage that addition of carbon such as methanol can be reduced. However, the activated sludge circulation method has a limit on the nitrogen reduction rate in principle,
A part of the nitrification liquid that is not circulated flows out. For this reason, when NO ₂ —N is generated and accumulated in the nitrification process, it flows out into the treated water as it is, causing an increase in COD. Further, since the organic matter in the wastewater is used for denitrification, NO ₂ -N may accumulate in the anaerobic tank. In addition, DO contained in the circulating nitrification liquid sometimes acts as an inhibitory component of the denitrification reaction.

Finally, regarding the control method of the aerobic tank, DO is generally used as a management index in many cases. However, DO has little inhibitory component in wastewater, and it is hard to be an effective index in a situation where the activity of microorganisms tends to decrease. There are many reports on the correlation between the nitrification reaction and DO, such that the nitrification reaction proceeds as the DO becomes higher. However, although DO is necessary for the nitrification reaction, nitrification does not necessarily proceed because DO is high. That is, for example, when nitrifying bacteria are inhibited, DO increases because oxygen consumption by microorganisms decreases. Therefore, from the viewpoint of measuring the progress of the nitrification reaction, the D
Performing O control cannot be evaluated. However, DO is important from the viewpoint of maintaining the growth rate of nitrifying bacteria, and needs to be maintained at 2 mg / l or more.

The present invention eliminates the problems when a treatment method such as a conventional activated sludge circulation method is applied to wastewater containing organic matter and high concentration of nitrogen as described above,
An object of the present invention is to establish a method for stably and efficiently removing nitrogen compounds in wastewater.

[0020]

According to the present invention, there is provided a method for controlling the concentration of an organic substance.
In the treatment of organic wastewater containing 50 mg / l or more of reducing nitrogen compounds at a high rate, after performing denitrification treatment in an anaerobic tank, oxidizing organic substances in an aerobic tank, and then aerobic fixed bed reactor Nitrification treatment, and then
This is a method for removing nitrogen from wastewater, which comprises circulating nitrification-treated water of an aerobic fixed-bed reactor to an anaerobic tank at a preceding stage.

In the above-mentioned treatment method, the circulation amount of nitrification treatment water in the aerobic fixed-bed reactor is adjusted to the final target so that the oxidation-reduction potential (based on Ag / AgCl) of the anaerobic tank is maintained at -100 mV or less. In the range of the nitrogen removal rate, circulate the wastewater to a maximum of 300%, and if the oxidation-reduction potential does not decrease to -100 mV or less even if the circulation is reduced, supply a hydrogen donor such as methanol to the anaerobic tank. It is efficient that the oxidation-reduction potential of the anaerobic tank is adjusted to -100 mV or less by adding methane.

Further, the oxidation-reduction potential (Ag /
AgCl (based on AgCl) is -50 to +50 mV, and the redox potential (based on Ag / AgCl) of the aerobic fixed bed reactor is +1.
It is also effective to control the amount of air and / or oxygen-enriched air and / or oxygen blown into the aerobic tank and the aerobic fixed bed reactor so as to be maintained at 00 to +200 mV.

[0023]

Hereinafter, the present invention will be described in detail. FIG. 1 shows a processing flow of the present invention. The term “anaerobic / aerobic activated sludge method” includes the denitrification in the anaerobic tank, the organic matter oxidation in the aerobic tank, and the return of the precipitated sludge to the anaerobic tank in the present invention.

The aerobic tank in the conventional activated sludge circulation modification method removes organic substances and promotes the nitrification reaction. However, the aerobic tank in the anaerobic / aerobic activated sludge method according to the present invention uses organic substances contained in wastewater. Is only removed.

There is a close relationship between the ORP of the aerobic tank in the anaerobic / aerobic activated sludge process and the organic matter removal performance of wastewater. By maintaining the ORP of the aerobic tank at -50 to +50 mV (based on Ag / AgCl), the decomposition of organic substances in the wastewater can be sufficiently promoted. If the ORP of the aerobic tank is kept at +50 mV or more, the performance of removing organic substances is further improved, but the accumulation of NO ₂ -N in the treated water tends to occur, which is not preferable. When the concentration of organic matter in the wastewater is high, it may be difficult to maintain the ORP of the aerobic tank at -50 to +50 mV by aeration with air. In such a case, if too much air is used, the activated sludge in the aerobic tank will be destroyed and fragmented, and will not settle sufficiently in the sludge sedimentation tank, but will flow out into the treated water and cause deterioration in the treated water quality. There is. In such a case, a method of supplying oxygen-enriched air and / or oxygen to perform aeration is desirable. Further, by maintaining the ORP of the aerobic tank at -50 to +50 mV, preferably 0 mV, accumulation of NO ₂ -N can be prevented. NO ₂
Since -N has an inhibitory effect on bacteria that degrade organic substances, it is desirable to prevent accumulation.

The aerobic fixed-bed reactor according to the present invention comprises a nitrogen compound, mainly organic nitrogen, N
NO ₄ is reduced by nitrification reaction of a reducing nitrogen compound such as H ₄ —N.
Biologically oxidizes efficiently to _3- N. Disgust
Organic matter in the wastewater has been sufficiently removed by the aerobic activated sludge method. For this reason, the inhibitory effect of the organic substance on the nitrification reaction is reduced, and the nitrification reaction for generating NO ₃ —N can be efficiently advanced.

Furthermore, nitrifying bacteria such as Nitrobacter, which has a slow growth rate, are immobilized at a high concentration on a carrier such as saddle-type ceramics, silica-alumina-based ceramics, and plastics mainly made of granulated blast furnace slag. The nitrification reaction that produces NO ₃ —N can be efficiently advanced. In particular, saddle-type ceramics mainly made of granulated blast furnace slag are porous and have a large surface area, and nitrifying bacteria are easily immobilized. Further, because of the saddle shape, the gas-liquid mixing performance in the fixed bed reactor is excellent, and it is most desirable as an immobilized carrier for the fixed bed reactor.

Furthermore, the OR of the aerobic fixed bed reactor
By maintaining P at +100 mV (based on Ag / AgCl), reducing nitrogen compounds such as NH ₄ —N
By the nitrification reaction, it can be efficiently oxidized to NO ₃ -N. In the case where the concentration of reducing nitrogen compounds in wastewater is high, the ORP of the reactor is increased by +100 by air aeration.
In some cases, it may be difficult to maintain the voltage at mV or more, and in such a case, it is preferable to supply the oxidation-enriched air and / or oxygen to perform aeration. Furthermore, nitrifying bacteria are susceptible to water temperature, and when the water temperature decreases, the processing capacity tends to decrease.
The aerobic fixed-bed reactor of the present invention has a water temperature of 5 to 10
It has a processing capacity of 10 mgN / l · h or more even under conditions such as ° C.

The treated water obtained by nitrifying the fixed bed reactor is returned to the anaerobic tank. The anaerobic tank biologically and efficiently reduces NO ₃ —N contained in the fixed-bed reactor treated water to nitrogen gas. The anaerobic tank may be filled as a carrier with a saddle type ceramic made mainly of granulated blast furnace slag, a ceramic or a plastic made mainly of silica-alumina clay, or the like. By immobilizing a denitrifying bacterium with a slow growth rate at a high concentration on a microorganism-immobilized carrier, the denitrification reaction can be efficiently advanced. However,
When a carrier is added to the anaerobic tank, clogging is likely to occur due to the growth of denitrifying bacteria, so a backwashing operation is required.

Further, in order to keep the activity of the denitrifying bacteria in the anaerobic tank good, the ORP of the anaerobic tank should be -100 to-
By maintaining at 150 mV (based on Ag / AgCl), NO ₃ —N can be biologically and efficiently reduced to nitrogen gas by a denitrification reaction. ORP tends to decrease due to wastewater, organic substances, and reducing nitrogen compounds such as NH ₄ —N, and conversely tends to increase due to NO ₃ —N and DO. ORP management of the anaerobic tank is performed by the following method.

Generally, the circulation amount of the treated water in the aerobic fixed-bed type reactor is varied according to the target value of the nitrogen concentration of the treated water. For example, when the circulation ratio is 2, the theoretical nitrogen removal rate is 66%, but when the circulation ratio is increased to 3, the theoretical nitrogen removal rate becomes 75%. Theoretical nitrogen removal rate = {R / (1 + R)} × 100 R: Circulation ratio (Circulation amount / Wastewater amount) In theory, increasing the circulation ratio increases the theoretical nitrogen removal rate, but actually, the anaerobic tank ORP in the anaerobic tank is likely to increase due to a large amount of NO ₃ -N or DO flowing into the anaerobic tank.
When the ORP of the anaerobic tank is -100 mV or more, the treatment performance tends to deteriorate because inhibition of denitrifying bacteria occurs. Conversely, if the ORP in the anaerobic tank is too low, the function of the denitrifying bacteria may be hindered by the generation of methane gas, hydrogen sulfide gas, and the like.

Therefore, using the ORP of the anaerobic tank as an index,
It is effective to change the circulation ratio by changing the flow rate of the circulation pump. For example, when the nitrogen removal rate of the treatment target is 65% or more, the circulation ratio =
If the ORP of the anaerobic tank is increased or decreased by operating at 2.5, the following operation is measured. -ORP of the anaerobic tank: -200 mV or less → Increase the circulation ratio to a maximum of 3.-ORP of the anaerobic tank: -100 mV to -200 mV-Operation at a circulation ratio = 2.5-ORP of the anaerobic tank: -100 mV or more-The circulation ratio Reduced to a minimum of 2-ORP in anaerobic tank: -50 mV or more → Circulation ratio = minimum 2 and addition of methanol, isopropyl alcohol, etc.

Further, all or a part of the treated water of the aerobic fixed-bed type reactor circulating in the anaerobic tank of the anaerobic / aerobic activated sludge treatment method is injected into the return sludge line of the anaerobic / aerobic activated sludge treatment method. As a result, the DO of the treated water in the fixed-bed reactor can be reduced in advance, and the ORP in the anaerobic tank can be prevented from rising.

Further, even if the circulating ratio of the ORP in the anaerobic tank is increased to a maximum of 3, the ORP may be reduced to -200 mV or less. When the ORP is abnormal as described above, the function of the denitrifying bacteria may be hindered by the generation of methane gas, hydrogen sulfide gas, and the like, as described above. In order to prepare for such a case, it is also desirable to install a device for supplying air to the anaerobic tank by ORP control.

[0035]

EXAMPLE An on-site experiment using actual sewage was conducted in an urban sewage treatment plant into which a large amount of organic industrial wastewater flows. FIG.
Shows an outline of the method. The actual sewage has an average BOD of 5
00 mg / l, COD was 500 mg / l on average, and ammonia nitrogen was 150 mg / l on average, and the sewage was higher in organic matter concentration and ammonia nitrogen concentration than municipal sewage.
The water temperature of the reactor 3 in winter varied in the range of 5 to 12 ° C.

The reactor 3 was treated by passing actual sewage water so that the HRT was 6 hours in the anaerobic tank 4 and 12 hours in the aerobic tank 5. The ORP of the anaerobic tank 4 was set as shown in Table 1, and was controlled by using the ORP controller 7 by changing the circulation ratio and adding methanol (adding from the methanol tank 12 to the anaerobic tank 4 by the methanol addition pump 11).

[0037]

[Table 1]

The ORP of the aerobic tank 5 was controlled to +0 mV by supplying air from the blower 10 by the ORP controller 9 using air. The aerobic fixed-bed reactor 17 filled with saddle-type ceramics mainly made of granulated blast furnace slag as a carrier for immobilizing microorganisms was first charged with activated sludge collected from an actual sewage treatment plant into the reactor for one day. Activated sludge was fixed to ceramics by circulating. After that, the HRT of the reactor became 8
An anaerobic / aerobic activated sludge process was passed through the reactor treated water so that the treatment time was reached. The ORP of the aerobic fixed-bed reactor 17 was controlled at +150 mV by oxygen-enriched air sent from the oxygen-enriched air production device 25 through the blower 26 via the ORP control device 24.
Further, the pH of the aerobic fixed-bed reactor 17 tends to decrease with the progress of nitrification. Therefore, NaOH is charged from the NaOH tank 20 by the pH control device 22, and pH =
Controlled at 7. Further, the entire amount of nitrification treatment water of the aerobic fixed-bed reactor 17 circulating in the anaerobic tank 4 of the anaerobic / aerobic activated sludge treatment method is returned to the sludge line of the anaerobic / aerobic activated sludge treatment method using the circulation pump 18. Was injected.

Table 2 shows the experimental results of the low water temperature period in winter from January to March. From the results in Table 2, the final treated water in this method was BO
D: 20 mg / l or less, COD: 50 mg / l or less, TN
Was 50 mg / l or less, and good results were obtained. From this experimental result, it was clarified that the present method can efficiently remove organic substances and nitrogen compounds in sewage even in a low water temperature period in winter with a total treatment time of about 20 to 24 hours.

[0040]

[Table 2]

[0041]

As described above, the present invention has the following advantages in treating wastewater containing a high concentration of reducing nitrogen compounds such as ammoniacal compounds. That is, in the case of such a wastewater treatment, in a single anaerobic / aerobic activated sludge method, nitrification and denitrification are inhibited by the wastewater component. For this reason, NO ₂ —N serving as a COD source easily accumulates in the treated water, and this control is the most problematic. In this method, the two-stage treatment of the organic compound removal process and the nitrogen compound oxidation process by the aerobic fixed-bed reactor and the ORP control are performed, so that the influence of the inhibitory component is smaller than that of the single biological treatment process. As a result, reducing nitrogen compounds such as ammonia nitrogen in wastewater can be efficiently removed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of a method for removing nitrogen from wastewater in the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a flow of wastewater treatment by a conventional activated sludge circulation modified method.

[Explanation of symbols]

 Reference Signs List 1 wastewater tank 2 wastewater pump 3 anaerobic / aerobic activated sludge reactor 4 anaerobic tank 5 aerobic tank 6 ORP sensor 7 ORP controller 8 ORP sensor 9 ORP controller 10 blower 11 methanol addition pump 12 methanol tank 13 sludge sedimentation tank 14 return Sludge pump 15 Treatment water tank 16 Transfer pump 17 Aerobic fixed-bed reactor 18 Nitrification liquid circulation pump 19 NaOH pump 20 NaOH tank 21 pH sensor 22 pH control device 23 ORP sensor 24 ORP control device 25 Oxygen-enriched air production device 26 Blower 27 Treated water tank 28 Final treated water

Continuation of the front page (56) References JP-A-2-139909 (JP, A) JP-A-60-54792 (JP, A) JP-A-64-51197 (JP, A) JP-A-6-31297 (JP) JP-A-6-496 (JP, A) JP-A-7-100485 (JP, A) JP-A-7-39899 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C02F 3/34 101 C02F 3/30

Claims (5)

(57) [Claims] In the treatment of an organic wastewater having a high organic matter concentration and further containing a reducing nitrogen compound in an amount of 50 mg / l or more , after performing a denitrification treatment in an anaerobic tank, an oxidation treatment of the organic matter is performed in an aerobic tank, Thereafter, nitrification treatment is performed by an aerobic fixed-bed reactor, and then nitrification treatment water of the aerobic fixed-bed reactor is circulated to an anaerobic tank in a preceding stage. 2. An oxidation-reduction potential (Ag / AgCl) in an anaerobic tank.
Criterion) is maintained at -100 to -200 mV,
In the aerobic fixed-bed type reactor, the circulating amount of nitrification treatment water should be up to 30 times the amount of wastewater within the range of the final target nitrogen removal rate.
If the oxidation-reduction potential of the anaerobic tank does not decrease to -100 mV or less even if the circulation amount is adjusted to 0% and the circulation amount is reduced, a hydrogen donor such as methanol is added to the anaerobic tank to oxidize the anaerobic tank. 2. The method for removing nitrogen from wastewater according to claim 1, wherein the potential is -100 mV or less. 3. The oxidation-reduction potential of an aerobic tank (Ag / AgCl
(Reference) is -50 to +50 mV, and the oxidation-reduction potential (based on Ag / AgCl) of the aerobic fixed bed reactor is +100 to ++
3. The method according to claim 1, wherein the amount of air and / or oxygen-enriched air and / or oxygen blown into the aerobic tank and the aerobic fixed-bed reactor is controlled so as to be maintained at 200 mV. Wastewater nitrogen removal method. 4. The nitrogen of the wastewater according to claim 1, 2, or 3, wherein the whole or a part of the nitrification-treated water of the aerobic fixed-bed reactor circulating in the anaerobic tank is injected into a return sludge line. Removal method. 5. The nitrogen of the wastewater according to claim 1, 2, 3 or 4, wherein the fixed bed type reactor uses a saddle type ceramic mainly composed of granulated blast furnace slag as a carrier for immobilizing microorganisms. Removal method.