KR200267140Y1 - equipment for advanced wastewater-treatment - Google Patents

Abstract

This design is an advanced sewage treatment method that additionally removes nitrogen and phosphorus biologically by changing the flow path and adding some device for improving microbial activity in the existing sewage and wastewater treatment process. It is a structure that can maximize the use of existing facilities.

The advanced sewage treatment apparatus generates nitrate by nitrification from a bioreactor 1 in which sewage or wastewater from which grit has been removed from the sedimentation basin is introduced into the raw water, and from raw water treated in the bioreactor 1. The first aeration tank (2), and the after-denitrification tank (3) for denitrifying the nitrate introduced from the first aeration tank with nitrogen gas by endogenous breathing of denitrification microorganisms, external carbon source, organic matter of raw water, etc. The second aeration tank 4 for degassing the nitrogen gas produced in the tank 3 to improve the sludge settling property of the subsequent final sedimentation basin 50 and to oxidize untreated organic matter, ammonia nitrogen, and other contaminants. And a final sedimentation basin 50 for separating and discharging the supernatant and sludge purified by solid-liquid separation, and similar A ² / O (Anaerobic / Aonxic / O) capable of simultaneously removing organic substances and nutrients. xic) part of the sludge precipitated and discharged in the final sedimentation basin (50) is returned to the bioreactor (1) to maintain post-denitrification and total denitrification at the same time to maintain the microbial residence time (SRT), In the advanced sewage treatment apparatus for returning the aeration tank effluent from the aeration tank 2 to the bioreactor 1 and denitrifying the inflowing water from the bioreactor 1, the bioreactor 1 is a cross passage 10b, Except 20b), a plurality of separation chambers 11, 12, 13, 14, 15, 16, and 17 separated by a plurality of separation walls 10a are used as the first tank 10 having a long residence time. The first aeration tank (2), the post-denitrification tank (3) and the second aeration tank (4) are divided into upper and lower separation chambers (21, 22) by the separating walls (20c, 20d), the lower left It consists of a second tank 20 separated into the separation chamber 30 and the lower right separation chamber 40, the raw water, such as sewage flow into the left, lower portion of the first tank 10 The first tank 10 and the second tank 20 are connected to the passage P2 at an upper portion thereof, and the upper upper and lower separation chambers 21 and 22 have passages P7 at the lower right side and the lower right side thereof. By the passage (P3) is characterized in that connected to the right middle portion or lower portion of the first tank 10, the lower left separation chamber (30).

Description

Advanced sewage treatment unit {equipment for advanced wastewater-treatment}

The present invention relates to an advanced sewage treatment apparatus, and in particular, to effectively improve or improve the existing municipal sewage treatment facility for applying the basic concept of improving the existing organic matter and suspended solids treatment method. The present invention relates to a sewage treatment system having a structure capable of maximizing the removal efficiency and maximizing the use of an existing facility without using site expansion by using two tanks.

Rivers and reservoirs where eutrophication is progressing rapidly breed algae such as green algae and red tide, causing various water quality problems.

Therefore, in order to prevent eutrophication, nutrient components in the sewage and wastewater have to be removed before they enter the body of the river.

Methods for treating nitrogen and phosphorus in sewage and wastewater include physicochemical treatment and biological treatment.

The physicochemical treatment method involves injecting air while increasing the hydrogen ion concentration (pH) of the wastewater, forming nitrogen in ammonia, and degassing it by selective adsorption using ion exchange material and using flocculant such as slaked lime. To precipitate the phosphorus.

Biological treatment methods include the use of microorganisms in the Bardenpho process, A / O, A ₂ O and SBR (Sequencing Batch Reactor), and in the case of nitrogen, nitrification is carried out by aerobic microorganisms under aerobic conditions. Denitrification process ie

It is removed by nitrogen gas by quasi-anaerobic microorganisms. In the case of phosphorus, phosphorus is removed from the sewage by contacting the influent sewage with microorganisms under anaerobic conditions to release phosphorus and then ingesting excessive phosphorus by the microorganisms under aerobic conditions.

In addition, the simultaneous removal of nitrogen and phosphorus using the electrolytic method disclosed in Patent Publication No. 1999-454 (published date: January 15, 1999, Patent Application No. 1997-23366), electrochemical method and physicochemical method The present invention relates to a device capable of simultaneously removing nitrogen and phosphorus by using an electrolytic method for removing organic matter from wastewater. Particularly, electrolytic coagulation reactions using iron electrodes with nitrogen and phosphorus, which are the main causes of water pollution due to eutrophication, Air contact oxidation removes nitrogen and phosphorus simultaneously in a single reactor.

As described above, methods for purifying wastewater include physicochemical methods and biological treatment methods, thereby preventing contamination of the water caused by eutrophication.

However, the physicochemical treatment method has a problem in that a high processing cost is required and a high technology in operation is required.

In addition, in the biological treatment method, the organic matter in the wastewater is decomposed mostly in the aerobic state in the nitrogen treatment process, and in the subsequent quasi-anaerobic denitrification process, the organic material does not exist and the nitrogen nitrate is denitrated by the endogenous breathing of microorganisms, which is very slow. However, there was a problem that the nitrogen removal efficiency was low and the facility itself had to be enlarged.

This is the conventional sewage and wastewater method, which is mainly used for the removal of organic substances, and the nitrogen and causal factors, which are factors of eutrophication, were not suitable for the characteristics of Korean sewage with low concentrations of organic substances and relatively high nitrogen concentrations. The same nutrient removal had limitations.

For example, the nitrogen removal rate was 10-40% and the phosphorus removal rate was about 5-20% according to the conventional treatment method, and the Bardenpho process, A / O, and A ₂ O processes were used. In order to increase the efficiency of wastewater treatment, the internal circulation must be maintained at about four times the amount of wastewater inflow. Therefore, the operation is complicated and excessive facilities are required. The continuous batch reactor serves as the primary sedimentation basin and the aeration basin secondary sedimentation basin. Because of this, there was a problem that it is difficult to treat a large amount of wastewater generated continuously.

The present invention is to solve the above-mentioned problems, it is possible to optimally adopt a method of simultaneously treating the organic matter, nitrogen, phosphorus in the sewage and wastewater in accordance with the sewage characteristics of Korea, low concentration of organic substances and relatively high nitrogen concentration. Furthermore, by effectively improving or improving existing municipal sewage treatment facilities, it is possible to significantly improve the removal efficiency of nitrogen and phosphorus as well as organic matters, and maximize the use of existing facilities without site expansion by using two tanks. The purpose is to provide an advanced sewage treatment apparatus of a structure.

1 is a block diagram showing the configuration according to an embodiment of the advanced sewage treatment method associated with the present invention,

2 is a block diagram showing a configuration according to another embodiment of the advanced sewage treatment method associated with the present invention,

3 is a schematic configuration diagram of an advanced sewage treatment apparatus according to the present invention,

4 is a schematic configuration diagram according to an embodiment of the advanced sewage treatment apparatus of the present invention.

<Description of the symbols for the main parts of the drawings>

1: bioreactor 2: first aeration tank

3: after-denitrification tank 4: second aeration tank

10: first tank 10a, 20a, 20c, 20d: partition wall

10b, 20b: passage 11, 12, 13, 14, 15, 16, 17: separation chamber

20: second tank 21, 22: upper and lower separation chamber

30: lower left separation chamber 40: lower right separation chamber

50: final settlement 60: external carbon source injection device

L1, L2, L3, L4, L5, L6, L7: Line

P2, P3, P4, P5, P6, P7: Pathway

Advanced sewage treatment apparatus according to an embodiment of the present invention for this purpose, the nitrate by the nitrification process from the bioreactor in which the sewage or waste water from which the grit is removed from the settling basin into the raw water, and the raw water treated in the bioreactor A first aeration tank for generating a gas, and a post-denitrification tank for degassing the nitrate introduced from the first aeration tank with nitrogen gas by endogenous breathing of denitrification microorganisms, external carbon source, organic matter of raw water, etc. Degassing nitrogen gas to improve the sludge sedimentation of the final sedimentation basin and at the same time separates the second aeration tank for oxidizing untreated organic matter, ammonia nitrogen and other contaminants, and supernatant and sludge purified by solid-liquid separation And similar A ² / to remove both organic and nutrients simultaneously. Part of the sludge precipitated and discharged in the final sedimentation basin to O (Anaerobic / Aonxic / Oxic) system is carried out to the bioreactor and maintained during the microbial residence time (SRT), so that the denitrification and the total denitrification can be carried out simultaneously. An advanced sewage treatment apparatus for returning aeration tank effluent from an aeration tank to a bioreactor for total denitrification of the inflowing water in the bioreactor: The bioreactor is divided into a plurality of separation chambers separated by a plurality of separation walls except for cross passages. The first aeration tank, the post-denitrification tank, and the second aeration tank are separated into upper and lower separation chambers, lower left separation chambers, and lower right separation chambers separated by upper and lower sides by separating walls. Consists of a second tank, the raw water, such as sewage flows into the left and the bottom of the first tank, the first tank and the second tank is connected to the passage from the top, The vertical separation chamber, characterized in that the connection chamber right middle portion or the lower portion and the lower left side of the first separation tank by the passage and the passage in the lower right and lower right.

By contacting the inlet water with the sludge in the nutrient-poor state to release the phosphorus by using the organic matter in the inlet water under anaerobic conditions, the location to return the nitrified aeration tank effluent in order to maximize the denitrification efficiency and denitrification efficiency according to the raw water quality It is preferable that the passage is separated and connected from the upper upper and lower separation chambers, which are the first aeration tank, to the first half (lower portion) and the middle half (middle portion) of the second aeration tank so as to control the first half and the middle half of the first tank.

The first tank and the lower left separation chamber are connected to a passage to separate the inflow water to bypass some of the organic materials as an electron donor to the post-denitrification tank lower left separation chamber, in which case, nutrients are removed. In consideration of the lack of organic matter, an external carbon source injection device is added to inject carbon with the inflow of incoming water into the lower left separation chamber of the post-denitrification tank to maximize the post-denitrification effect and minimize the internal circulation ratio for pre-denitrification. Also included is a preferred structure.

The present invention is described in detail with the accompanying exemplary drawings as follows.

1 to 3 are for the description of the invention as a premise of the present invention, Figure 4 is a plan view showing a structure according to an embodiment of the present invention.

1 and 3, in the block diagram showing the configuration according to an embodiment of the advanced sewage treatment method and apparatus associated with the present invention, the advanced sewage treatment method, as conventional, grit in the settlement The removed sewage or wastewater may be introduced into the raw water so that the similar A ² / O (Anaerobic / Aonxic / Oxic) system capable of simultaneously removing organic substances and nutrients can be carried out at the same time as the post-denitrification step and the total denitrification step. The bioreaction step of returning a part of the sludge precipitated and discharged in the precipitation step to maintain during the microbial residence time (SRT), and return the aeration tank effluent from the first aeration step to the bioreactor (1) to denitrate from the influent source water And a first aeration step of producing nitrate by nitrification at least in the first aeration tank and a nitrate introduced from the first aeration step in the denitrification tank 3 of the denitrification microorganism. Sludge sedimentation of the final sedimentation basin 50 after the denitrification step of degassing with nitrogen gas by endogenous breathing, external carbon source, organic matter of raw water, etc. At the same time, the second aeration step of oxidizing untreated organic matter, ammonia nitrogen and other contaminants, and after the second aeration step, the supernatant and sludge purified by solid-liquid separation in the final settling basin 50 Characterized in that it comprises a sedimentation step to separate, discharge.

As shown in Figure 2 and 3, the configuration according to another embodiment of the advanced sewage treatment method of the present invention, by contacting the influent source with the sludge in the nutrient nutrient state using phosphorus organic matter in the influent source water under anaerobic conditions By discharging, the position for conveying the nitrified aeration tank effluent to maximize the denitrification efficiency along with the denitrification efficiency according to the raw water quality is adjusted to the first half and the middle half of the bioreactor 1 by separating the line L7.

In addition, the step of separating the inflow water to bypass the denitrification tank (3) so that some organic material is used as an electron donor, and in this case, the post-denitrification effect in view of the lack of organic matter to remove nutrients Injecting carbon from the external carbon source injection device 60 together with some inflow water flowing into the after-denitrification tank 3 to minimize the internal circulation ratio for the total denitrification at the same time. That is, the internal circulation rate is reduced to 1 to 2 times the amount of inflow, and bypasses a portion of the external carbon source or raw water to enter the post-denitrification tank 3 to prevent the denitrification rate decrease due to the lack of the organic carbon source during the rainy season.

In Figure 3, the configuration according to an embodiment of the advanced sewage treatment apparatus, the post-denitrification and total denitrification is performed in a similar A ² / O (Anaerobic / Aonxic / Oxic) system that can remove organic substances and nutrients at the same time Part of the sludge precipitated and discharged in the final sedimentation basin 50 is returned to the raw water by flowing the sewage or waste water from which the grit is removed from the settling basin so as to be retained for the microbial residence time (SRT). The aeration tank effluent is conveyed from the aeration tank 2, and is characterized by including a bioreactor 1 for causing total denitrification from the inflow source water upstream of the first aeration tank 2. Further, downstream of the first aeration tank 2 for producing nitrate by nitrification process, and the nitrate introduced from the first aeration tank is degassed with nitrogen gas by endogenous breathing of denitrifying microorganisms, external carbon source, organic matter of raw water and the like. The denitrification tank 3 and the nitrogen gas produced in the post-denitrification tank 3 are degassed to improve the sludge settling properties of the final sedimentation basin 50, and untreated organic matter, ammonia nitrogen, and the like. And a second aeration tank 4 for oxidizing contaminants therein and a final sedimentation basin 50 for separating and discharging the supernatant and sludge purified by solid-liquid separation.

The bioreactor (1) and the first aeration tank (2), the first aeration tank (2) and the post-denitrification tank (3), the second aeration tank (4) and the final sedimentation basin (50) are lines (L2, L3, L4). Waste sludge is discharged from the final settling tank 50 through line L5.

4, the configuration according to the embodiment of the advanced sewage treatment apparatus of the present invention includes a first tank 10, a second tank 20, and a final sedimentation basin 50, and a final sedimentation basin 50 and a second Tank 20 is connected by a line (L4), the final settling tank 50 and the first tank 10 is connected by a line (L5).

In FIG. 3, the bioreactor 1 includes a plurality of separation chambers 11 in which the first tank 10 is separated into a plurality of separation walls 10a except for passages 10b and 20b intersected with each other in FIG. 4. 12, 13, 14, 15, 16, 17).

The first aeration tank 2, the post-denitrification tank 3 and the second aeration tank 4 in FIG. 3 are divided into upper and lower separation chambers 21 and 22, lower and upper and lower sides separated by the separation walls 20c and 20d. The second tank 20 is separated into a left separation chamber 30 and a lower right separation chamber 40.

In addition, raw water such as sewage flows into the left and lower portions of the first tank 10, and the first tank 10 and the second tank 20 are connected to a passage P2 at an upper portion thereof, and an upper upper and lower separation chambers. (21, 22) is connected to the right middle part or the lower part of the first tank (10) and the lower left separation chamber (30) by the passage (P7) and the passage (P3) at the lower right side and the lower right side thereof. .

Here, the concept of up, down, left, and right refers to the thing on the drawing of FIG.

In addition, by contacting the inlet water with the sludge in poor nutrition state to release the phosphorus using the organic matter in the inlet water under anaerobic conditions to return the nitrified aeration tank effluent to maximize the denitrification efficiency and denitrification efficiency according to the raw water quality From the upper and lower separation chambers 21 and 22, which are the first aeration tank 2, to the front and middle portions of the first tank 10, which is the bioreactor 1, the first half of the second tank 20 (lower portion, That is, the passage P7 is separated and connected to the separation chamber 12 and the middle portion (the middle portion, that is, the separation chamber 14).

In addition, the upper upper and lower separation chambers 21 and 22 are separated by the separation wall 20a, connected to the passage P8 and the passage 20b, and are inclined to the upper lower separation chamber 22 in the form of an inclined plate. It is possible to settle and separate according to the concentration difference of the microorganisms by the separator 20e to be controlled, and to control and separate the accumulated microorganisms accumulated on the inclined plate.

In addition, in FIG. 4, the first tank 10 and the lower portion are separated to separate the inflow source water to use the organic material as the electron donor and bypass the lower left separation chamber 30 which is the post-denitrification tank 3. Left separation chamber 30 is connected to the passage (P6), in this case, in consideration of the lack of organic matter for removing nutrients, after denitrification to maximize the post-denitrification effect and minimize the internal circulation ratio for pre-denitrification It further includes an external carbon source injection device 60 for injecting carbon with the inflow of the inflow source water to the lower left separation chamber 30 that is the tank (3).

The present invention as described above, the sludge is continuously conveyed from the final sedimentation basin 50, the conveying sludge is introduced into the first half of the first tank 10, the bioreactor 1 and completely denitrate the nitrate present in the sludge. The sewage and sewage raw water, which has been removed from the settling ground and removed the grit, is brought into contact with the nutrient sludge so that phosphorus can be released by using the organic matter in the influent water under anaerobic conditions. In the middle portion of the first tank 10, which is the bioreactor 1, the nitrate produced by nitrification in the upper upper and lower separation chambers 21, 22 of the second tank 20, which is the first aeration tank 2, is passaged (P7). ) And organic nitrogen, phosphorus and phosphorus are removed at the same time by denitrification and dephosphorization under anoxic conditions, and dissolved ammonia nitrogen is the second tank 20 as the first aeration tank 2 through the passage P2. Inflow into the upper and lower separation chamber (21, 22) of the). The upper upper and lower separation chambers 21 and 22 of the second tank 20, which is the first aeration tank 2, are operated under aerobic conditions, nitrified by nitrifying microorganisms, and excessive intake of released phosphorus. One to three times the amount of nitrate produced by the nitrification reaction is transferred to the middle portion of the first tank 10, which is the bioreactor 1, and the rest is the post-denitrification tank 3 through the passage P3. It flows into the lower left separation chamber 30 of the second tank 20. Some of the nitrates introduced into the lower left separation chamber 30, which is the post-denitrification tank 3, are degassed with nitrogen gas by endogenous breathing of denitrification microorganisms, external carbon sources, or organic matters of raw water, and the second lower aeration tank 4 which follows. It flows into the right separation chamber 40. In the lower right separation chamber 40, which is the second aeration tank 4, degassing the nitrogen gas generated above to improve the sludge settling property of the final settler 50, and at the same time, untreated organic matter and ammonia nitrogen. It serves to oxidize pollutants, such as. The final settler 50 serves to separate the sludge and the purified supernatant by solid-liquid separation, and the purified supernatant is finally discharged. The precipitated sludge is partially returned to maintain the microbial residence time (SRT), and some are discarded to remove phosphorus by treating it with excess sludge. The return sludge consists of a step of continuously flowing the first tank 10, particularly the separation chamber 11, which is the bioreactor 1, to maintain the activated sludge concentration MLSS.

Here, generally, in the nutrient removal process, the nitrate internal circulation passage P7 generated in the upper upper and lower separation chambers 21 and 22 of the second tank 20, which is the first aeration tank 2, is used to remove the substance to be removed from the raw water. According to the change, it is preferable to be separated so as to be introduced into the first half and the middle of the first tank 10, which is a total denitrification tank 1, and the entire first tank 10, which is the bioreactor 1, is anoxic for denitrification. It is also possible to switch between the operating modes according to the characteristics of the sewage by allowing both anaerobic and anaerobic conditions to be carried out simultaneously for conditions and phosphorus release.

Due to the characteristics of the sewage in Korea, where the concentration of organic substances is low and the nitrogen concentration is relatively high, the removal of nutrients such as nitrogen and phosphorus is limited. The present invention bypasses part of the inflow and wastewater through the passage P6 to the lower left separation chamber 30, which is the post-denitrification tank 3, in the lower left separation chamber 30, which is the post-denitrification tank 3. Can be increased.

In this case, nitrates not raised by the total denitrification reaction are completely removed by the post-denitrification reaction to maximize nitrogen removal efficiency, reduce internal circulation rate, minimize power consumption, and bioreactor (1) and post-denitrification tank (3). By introducing only the advantages of maximizing nutrient processing efficiency and economical advantage of using the limited organic material to the maximum. On the other hand, due to the characteristics of the domestic climate where rainfall due to rainy seasons and typhoons are concentrated in summer, it is possible to supply external carbon sources, such as methanol, which is commonly used when it is difficult to remove biological nutrients due to the dilution effect. By using the carbon source injection device 60, the denitrification rate in the lower left separation chamber 30, which is the post-denitrification tank 3, is improved to improve the nitrogen removal efficiency.

As described above, according to the present invention, the first tank 10 and the second tank 20 to maximize the effect of simultaneously removing the ammonia nitrogen which is a problem in domestic sewage and wastewater as well as organic materials and phosphorus. ) And the final sedimentation basin (50) can be easily configured, and it is possible to flexibly cope with the growth of sewage and wastewater and climatic specificity by switching the operation mode, and also to reduce power consumption by internal circulation. In addition, the use of limited organic materials can be utilized to improve the removal of nutrients, thereby reducing operating costs. In particular, based on the biological sewage and wastewater treatment facilities consisting of the conventional primary sedimentation cell, aeration tank, and final sedimentation cell, the primary sedimentation basin is converted into a bioreactor for dephosphorization and denitrification, and thus the present invention is upgraded to an advanced treatment facility. It is also possible to maximize the use of existing facilities without site expansion.

Claims (3)

A bioreactor (1) into which sewage or wastewater from which grit is removed from the settling basin is introduced into the raw water, and a first aeration tank (2) for producing nitrate from nitrification from raw water treated in the bioreactor (1) And a post-denitrification tank (3) for denitrifying the nitrate introduced from the first aeration tank with nitrogen gas by endogenous breathing of denitrification microorganisms, external carbon source, organic matter of raw water and the like, and the post-denitrification tank (3). The second aeration tank 4 for deoxidizing contaminants such as untreated organic matter, ammonia nitrogen, and purifying the sludge settling property of the final sedimentation basin 50 by degassing nitrogen gas, and purifying by solid-liquid separation the supernatant and remove the sludge, comprising: a final sedimentation basin (50) for discharging, denitrification and copper and then with an organic material similar to remove the nutrients at the same time ^{a 2 / O (Anaerobic / Aonxic} / Oxic) system Part of the sludge precipitated and discharged in the final sedimentation basin 50 to be carried out in the final settling tank 50 is returned to the bioreactor 1 and maintained for the microbial residence time (SRT), the aeration tank effluent from the first aeration tank (2) In the advanced sewage treatment apparatus for returning to the bioreactor (1) to denitrify the incoming water from the bioreactor (1): The bioreactor 1 is composed of a plurality of separation chambers 11, 12, 13, 14, 15, 16, and 17 separated by a plurality of separation walls 10a, except for passages 10b and 20b that are staggered from each other. And a first tank 10 having a long residence time, and the first aeration tank 2, the post-denitrification tank 3, and the second aeration tank 4 are separated up, down, left, and right by separating walls 20c and 20d. It consists of the upper and lower separation chamber 21, 22, the lower left separation chamber 30 and the second tank 20 is separated into the lower right separation chamber 40, the left and the bottom of the first tank (10) Raw water such as sewage flows in, and the first tank 10 and the second tank 20 are connected to the passage P2 from the upper side, and the upper upper and lower separation chambers 21 and 22 are the lower right side and the lower right side. Elevated sewage treatment apparatus, characterized in that connected by the passage (P7) and the passage (P3) to the right middle portion or lower portion of the first tank (10), the lower left separation chamber (30). The aeration tank effluent nitrified for maximizing denitrification efficiency and denitrification efficiency according to raw water quality by contacting the inflow source with sludge in poor nutrition and releasing phosphorus using organic matter in the inflow source under anaerobic conditions. The first half of the second tank 20 from the upper and lower separation chambers 21 and 22, which are the first aeration tanks 2, to adjust the position of conveying the first half and the middle of the first tank 10, which is the bioreactor 1, to be adjusted. The passage P7 is separated and connected to the lower portion and the middle portion (the middle portion); The upper upper and lower separation chambers 21 and 22 are separated by the separation wall 20a, connected to the passage P8 and the passage 20b, and the angle is adjusted in the form of an inclined plate to the upper lower separation chamber 22. By providing a separator (20e) to be settled, separated according to the concentration difference of the microorganism, it is possible to control and separate the accumulated microorganisms accumulated on the inclined plate, the advanced sewage treatment apparatus, characterized in that. The method of claim 1, wherein the first tank (10) to bypass the inlet water to the lower left separation chamber 30, which is a post-denitrification tank (3) in order to use some organic material as an electron donor Lower left separation chamber 30 is connected to the passage (P6), in this case, in consideration of the lack of organic matter for removing nutrients after maximizing post-denitrification effect while minimizing the internal circulation ratio for pre-denitrification Advanced sewage treatment apparatus, characterized in that it further comprises an external carbon source injection device (60) for injecting carbon into the lower left separation chamber (30), which is a denitrification tank (3).