JP2008296164A - Nitrogen removal method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly efficiently remove nitric acid secondarily generated by anaerobic ammonia oxidation reaction by adding a small amount of an organic matter. <P>SOLUTION: A method for removing nitrogen in ammonia-containing wastewater comprises the nitrous acid type nitrification process of nitrifying a part of ammonia contained in the wastewater to nitrous acid by nitrifying bacteria, the first denitrification process of removing the ammonia and nitrous acid contained in the wastewater discharged from the nitrous acid type nitrification process by anaerobic ammonia-oxidizing bacteria, and a second nitrification process of removing residual ammonia contained in the waste water, discharged from the first denitrification process and the nitrous acid generated in the first denitrification process, by anaerobic ammonia-oxidizing bacteria and heterotrophic denitrifying bacteria. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nitrogen removal method and apparatus, and more particularly to a technique for treating ammonia-containing wastewater by an anaerobic ammonia oxidation reaction.

  The nitrogen component contained in sewage and industrial wastewater is desired to be removed because it causes eutrophication of lakes and marshes and lowers dissolved oxygen in rivers. Such nitrogen components mainly include ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, organic nitrogen, and the like.

  Conventionally, if the nitrogen component contained in sewage and industrial wastewater is low concentration, the method of removing by ion exchange method or the method of oxidizing and removing by chlorine or ozone has been adopted, but if the nitrogen component is medium or high concentration For example, the following biological treatment methods are adopted.

  As biological treatment, nitrification / denitrification treatment by aerobic nitrification and anaerobic denitrification is performed. In aerobic nitrification, ammonia nitrogen and nitrite nitrogen are oxidized by ammonia oxidizing bacteria (Nitrosomonas, Nitrosococcus, Nitrosospira, Nitrosolobus, etc.) and nitrite oxidizing bacteria (Nitrobactor, Nitrospina, Nitrococcus, Nitrospira, etc.). On the other hand, in anaerobic denitrification, denitrification by heterotrophic bacteria (Pseudomonas denitrificans etc.) is performed.

A nitrification tank for performing aerobic nitrification is operated at a load of 0.2 to 0.3 kg-N / m ³ / day, and a denitrification tank for anaerobic denitrification is 0.2 to 0.4 kg-N / m ³ / day. Operated with day load. Moreover, in order to process the total nitrogen concentration of 30 to 40 mg / L in sewage, a residence time of 6 to 8 hours is required in the nitrification tank and 5 to 8 hours in the denitrification tank, both of which are large-scale treatment tanks. It was necessary.

  Moreover, when denitrifying industrial wastewater containing only inorganic substances, it is necessary to add organic substances, and methanol of about 3 to 4 times the nitrogen concentration in the wastewater has been added. For this reason, there is a problem that not only the initial cost but also a great running cost is required.

  On the other hand, for example, Patent Document 1 proposes a nitrogen removal method by an anaerobic ammonia oxidation method. This anaerobic ammonia oxidation method is a method in which ammonia is used as a hydrogen donor, nitrite is used as a hydrogen acceptor, and ammonia and nitrous acid are simultaneously denitrified by an anaerobic ammonia oxidizing bacterium according to the following formula 1.

1.00 NH ₄ +1.32 NO ₂ +0.066 HCO ₃ + 0.13H ⁺
→ 1.02N ₂ + 0.26NO ₃ + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O
... (Formula 1)
In this method, since ammonia is used as a hydrogen donor, there is an advantage that the amount of organic matter (methanol or the like) added can be significantly reduced and the amount of sludge generated can be reduced.

Patent Document 2 proposes a method for controlling the composition ratio of ammonia and nitrous acid before performing the anaerobic ammonia oxidation reaction.
JP 2001-37467 A JP 2005-246136 A

  However, as shown in the above formula 1, the anaerobic ammonia oxidation reaction cannot completely remove the nitrogen component in the wastewater. That is, since nitric acid is produced as a secondary product by the anaerobic ammonia oxidation reaction, it is necessary to remove this nitric acid.

  As suggested in Patent Document 2, as a method for removing this nitric acid, a method of adding an organic substance and denitrifying with heterotrophic denitrifying bacteria is common. However, this conventional denitrification method requires about three times as much organic matter as the nitrogen concentration in the wastewater, so that not only a large amount of organic matter must be added, but also a large amount of sludge is generated. was there.

  In addition, since anaerobic ammonia oxidizing bacteria are easily damaged by nitrous acid, the ratio of ammonia to nitrous acid is less than the ideal reaction ratio shown in Equation 1 above so that nitrite is not accumulated in the treatment tank. Also, ammonia is excessive. For this reason, unreacted ammonia remains in the wastewater flowing out from the treatment tank, and it is necessary to remove this residual ammonia.

  As described above, it is desired to remove nitric acid that is secondaryly generated in the anaerobic ammonia oxidation reaction and residual ammonia with a small amount of organic substance addition and with high efficiency.

  The present invention has been made in view of such circumstances, and a nitrogen removal method for removing nitric acid and residual ammonia, which are secondaryly generated in an anaerobic ammonia oxidation reaction, with a small amount of organic substance addition and with high efficiency, and An object is to provide an apparatus.

  In order to achieve the above object, claim 1 of the present invention is a method for removing nitrogen from ammonia-containing wastewater, wherein a part of ammonia contained in the wastewater is nitrified to nitrite by nitrifying bacteria, and is a nitrite type nitrification step. A first denitrification step for removing ammonia and nitrous acid contained in the wastewater flowing out from the nitrite type nitrification step by anaerobic ammonia oxidizing bacteria; and a wastewater flowing out from the first denitrification step A second denitrification step for removing residual ammonia contained therein and nitric acid produced in the first denitrification step by anaerobic ammonia oxidizing bacteria and heterotrophic denitrifying bacteria. A featured nitrogen removal method is provided.

  According to claim 1, in the second denitrification step, the ammonia remaining after the first denitrification step and the nitric acid that is secondarily generated in the anaerobic ammonia oxidation reaction of the first denitrification step are Degradation and removal by anaerobic ammonia oxidizing bacteria and heterotrophic denitrifying bacteria (with organic matter as hydrogen donor).

  Thus, the residual ammonia and nitric acid contained in the waste water flowing out from the first denitrification step are not removed only by heterotrophic denitrification bacteria, but anaerobic ammonia oxidizing bacteria and heterotrophic denitrification are removed. Remove in combination with bacteria. For this reason, it is not necessary to add a large amount of organic substances, and ammonia and nitric acid contained in the waste water after the anaerobic ammonia oxidation reaction can be decomposed and removed with a small amount of organic substances and efficiently.

  In the second denitrification step, the ammonia removal step by the anaerobic ammonia oxidizing bacteria and the nitric acid removal step by the denitrification bacteria may be performed simultaneously or separately.

  A second aspect of the present invention is the first aspect, wherein the second denitrification step includes a step of reducing the nitric acid to nitrous acid by using the heterotrophic denitrifying bacterium as an organic substance as a hydrogen donor, and the sub-nitrogen generated in the step. A step of removing nitric acid and ammonia in the wastewater by the anaerobic ammonia oxidizing bacteria.

  According to claim 2, in the nitrate reduction reaction by heterotrophic denitrifying bacteria, it is only necessary to reduce nitric acid to nitrous acid, and nitrous acid and ammonia are decomposed and removed by anaerobic ammonia oxidizing bacteria. For this reason, the amount of organic matter added can be greatly reduced as compared with the case of reducing to nitrogen gas only by denitrifying bacteria.

  A third aspect of the present invention is characterized in that, in the first or second aspect, the composition ratio of the waste water flowing into the second denitrification step is 1: 1 ammonia: nitric acid.

According to claim 3, ammonia and nitric acid in wastewater can be decomposed and removed with high efficiency by anaerobic ammonia oxidizing bacteria and denitrifying bacteria. This is because nitric acid is reduced from nitric acid to approximately the same mole of nitrous acid by denitrifying bacteria (NO ₃ → NO ₂ ), and this nitrous acid (NO ₂ ) is anaerobic together with approximately the same mole of ammonia (NH ₄ ). This is because it is decomposed and removed by the reaction of the above formula (1) by the oxidative ammonia oxidizing bacteria.

  A fourth aspect of the present invention is the method according to the third aspect, wherein the composition ratio is formed by mixing waste water flowing out of the first denitrification step with waste water before performing the nitrite type nitrification step. .

  According to claim 4, the composition ratio of nitric acid and ammonia of the wastewater flowing into the second denitrification tank can be adjusted to an appropriate range.

  A fifth aspect of the present invention is characterized in that, in the third aspect, in the nitrite type nitrification step, the nitrification rate is 57% or less.

  According to claim 5, by reducing the nitrification rate to 57% or less, the ammonia concentration contained in the waste water after the nitrification step is increased, and at the same time, the nitric acid concentration generated in the first denitrification step is decreased, The composition ratio of ammonia and nitric acid in the wastewater flowing into the denitrification process 2 can be adjusted to an appropriate range.

  A sixth aspect of the present invention provides the method according to any one of the first to fifth aspects, wherein, in the second denitrification step, the C / N ratio of the added organic substance concentration C in the wastewater to the total nitrogen concentration N in the wastewater is 0.8. -1.3.

  In the second denitrification step, if the amount of organic matter added is too small, the activity of the denitrifying bacteria decreases, and if the amount of organic matter added is too large, the activity of the anaerobic ammonia-oxidizing bacteria decreases. According to the sixth aspect, since the concentration of the added organic substance in the wastewater satisfies the above range, the activity of the anaerobic ammonia oxidizing bacteria and the denitrifying bacteria can be maintained in a well-balanced manner, and the ammonia and nitric acid in the wastewater are decomposed. Can be removed.

  The added organic substance concentration C refers to the organic substance concentration (in the wastewater) added in the second denitrification step without including the organic substance concentration contained in the wastewater in advance. The C / N ratio is more preferably 0.9 to 1.2.

  Claim 7 of the present invention is a nitrogen removal apparatus for removing nitrogen components contained in ammonia-containing wastewater to achieve the above object, wherein a part of the ammonia contained in the wastewater is nitrified to nitrite by nitrifying bacteria. A nitrite-type nitrification tank that is disposed on the downstream side of the nitrite-type nitrification tank, and removes ammonia and nitrous acid contained in waste water flowing out of the nitrification tank by anaerobic ammonia-oxidizing bacteria. The denitrification tank of the first denitrification tank is provided downstream of the first denitrification tank and the residual ammonia contained in the waste water flowing out of the first denitrification tank and the nitric acid generated in the first denitrification tank are converted into anaerobic ammonia. There is provided a nitrogen removal apparatus comprising a second denitrification tank for removal by oxidizing bacteria and heterotrophic denitrifying bacteria.

  According to claim 7, the ammonia and nitric acid in the wastewater flowing out from the first denitrification tank are not removed only by heterotrophic denitrification bacteria, but in the second denitrification tank, anaerobic ammonia oxidizing bacteria And denitrifying bacteria. Therefore, ammonia and nitric acid contained in the waste water after the anaerobic ammonia oxidation reaction can be removed with a small amount of organic substance addition and high efficiency without adding a large amount of organic substance.

  An eighth aspect of the present invention is the method according to the seventh aspect, wherein the second denitrification tank is provided on the downstream side of the first treatment tank in which the anaerobic ammonia oxidizing bacteria are retained, and the first treatment tank. A second treatment tank in which bacteria are retained, and communicates the downstream side of the second treatment tank and the upstream side of the first treatment tank, and waste water flowing out from the second treatment tank. And a circulation channel for flowing at least a part into the first treatment tank.

  According to the eighth aspect, since the second denitrification tank is divided into two treatment tanks and another treatment is performed, competition between the anaerobic ammonia oxidizing bacteria and the heterotrophic denitrifying bacteria does not occur. Moreover, since at least a part of the waste water flowing out from the second treatment tank in which the heterotrophic denitrifying bacteria are retained flows into the first treatment tank in which the anaerobic ammonia oxidizing bacteria are retained, the second Nitrous acid produced in the treatment tank can be decomposed and removed by anaerobic ammonia oxidizing bacteria in the first treatment tank.

  A ninth aspect of the present invention is characterized in that, in the seventh aspect, the second denitrification tank holds the anaerobic ammonia oxidizing bacteria and the denitrifying bacteria in one treatment tank.

  According to the ninth aspect, since the anaerobic ammonia oxidizing bacteria and the denitrifying bacteria coexist in one processing tank, the processing tank can be made compact.

  A tenth aspect of the present invention provides the second denitrification tank according to any one of the seventh to ninth aspects, based on a measurement result of the nitric acid concentration measuring means for measuring the nitric acid concentration in the wastewater and the nitric acid concentration measuring means. And a composition ratio control means for controlling the composition ratio of ammonia and nitric acid in the inflowing wastewater.

  According to claim 10, the composition ratio of nitric acid and ammonia in the wastewater flowing into the second denitrification tank can be adjusted.

  An eleventh aspect of the present invention is the method according to any one of the seventh to tenth aspects, wherein a bypass flow path that branches off from a flow path in front of the nitrite type nitrification tank and communicates with a flow path in front of the second denitrification tank is provided. It is characterized by having.

  According to the eleventh aspect, the composition ratio of nitric acid and ammonia in the wastewater flowing into the second denitrification tank can be adjusted to an appropriate range.

  A twelfth aspect according to any one of the seventh to eleventh aspects is characterized in that the second denitrification tank is provided with an organic substance adding means.

  According to the twelfth aspect, the denitrifying bacterium in the second denitrification tank can decompose and remove nitric acid (and nitrous acid) using the organic substance as a hydrogen donor. In addition, when comprising separately a 2nd denitrification tank with the 1st processing tank provided with the anaerobic ammonia oxidizing bacteria, and the 2nd processing tank provided with the denitrifying bacteria, the 2nd processing tank It is assumed that an organic substance adding means is provided.

  A thirteenth aspect is based on any one of the seventh to twelfth aspects, based on the second denitrification tank, a nitrogen concentration measuring means for measuring the total nitrogen concentration in the wastewater, and a measurement result of the nitrogen concentration measuring means. And an addition amount control means for controlling the addition amount of the organic substance to the second denitrification tank to be within a predetermined range.

  According to the thirteenth aspect, the addition amount of the organic substance can be adjusted so that the denitrifying bacteria in the second denitrification tank can decompose and remove nitric acid with high efficiency using the organic substance as a hydrogen donor.

  According to the present invention, nitric acid generated by an anaerobic ammonia oxidation reaction and residual ammonia can be removed with a small amount of organic substance added and with high efficiency.

  Hereinafter, preferred embodiments of a nitrogen removal method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view for explaining the outline of a nitrogen removing apparatus 10 according to the present invention.

  As shown in FIG. 1, the nitrogen removal apparatus 10 mainly includes a nitrite type nitrification tank 12 that nitrifies a part of ammonia contained in ammonia-containing wastewater (hereinafter also simply referred to as “wastewater”) into nitrite. The first denitrification tank 14 that removes ammonia and nitrous acid in the wastewater flowing out from the nitrification tank 12 by anaerobic ammonia oxidizing bacteria, and the nitric acid in the wastewater produced as a secondary in the first denitrification tank 14 And a second denitrification tank 16 for removing residual ammonia.

  The nitrite type nitrification tank 12 (hereinafter also simply referred to as “nitrification tank 12”) communicates with an inflow passage 18 into which ammonia-containing wastewater flows. The nitrification tank 12 holds nitrifying bacteria that nitrify ammonia into nitrous acid, and is maintained in an aerobic atmosphere. In the nitrification tank 12, nitrite type nitrification is performed in which about half of the ammonia is nitrified to nitrite. Nitrite-type nitrification can be performed, for example, by controlling the DO (dissolved oxygen) concentration in the wastewater to be low.

The nitrification tank 12 is preferably operated at a volume load of 0.8 to 3.5 kg-N / m ³ / d, a water temperature of 20 to 37 ° C., and a DO concentration of 0.5 or less.

  A first denitrification tank 14 is provided on the downstream side of the nitrification tank 12 via a flow path 20. The first denitrification tank 14 holds anaerobic ammonia oxidizing bacteria that remove ammonia and nitrous acid by an anaerobic ammonia oxidation reaction, and is maintained in an anaerobic atmosphere. In the first denitrification tank 14, as shown in the following formula 1, nitrous acid and ammonia in the wastewater are removed by an anaerobic ammonia oxidation reaction, and at the same time, a small amount of nitric acid is generated as a secondary.

1.00 NH ₄ +1.32 NO ₂ +0.066 HCO ₃ + 0.13H ⁺
→ 1.02N ₂ + 0.26NO ₃ + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O
... (Formula 1)
Also, since nitrous acid has an adverse effect on anaerobic ammonia oxidizing bacteria, the amount of ammonia is adjusted to be slightly excessive so that nitrous acid is surely consumed by the reaction. For this reason, the waste water flowing out from the first denitrification tank 14 contains not only the by-produced nitric acid but also residual ammonia.

The first denitrification tank 14 is preferably operated at a volume load of 2 to 10 kg-N / m ³ / d, a water temperature of 20 to 37 ° C., and a DO concentration of 0.5 or less.

  A second denitrification tank 16 is provided on the downstream side of the first denitrification tank 14 via a flow path 22. The flow path 22 communicates with the inflow flow path 18 via the bypass flow path 24. A nitric acid concentration meter 26 that measures the concentration of nitric acid in the wastewater on the flow path 22 and the opening degree of the valve 28 provided in the bypass flow path 24 are adjusted based on the measurement result of the nitric acid concentration meter 26. Control means 30 is provided. Thereby, the composition ratio of ammonia and nitric acid in the wastewater flowing into the second denitrification tank 16 can be adjusted.

  The second denitrification tank 16 holds anaerobic ammonia-oxidizing bacteria and heterotrophic denitrifying bacteria (hereinafter simply referred to as denitrifying bacteria), and an organic substance required by the denitrifying bacteria is added to the downstream side. An organic substance supply tank (see FIG. 2) is provided. In the second denitrification tank 16, the residual ammonia and nitric acid in the wastewater are removed by anaerobic ammonia oxidizing bacteria and heterotrophic denitrifying bacteria (using organic matter as a hydrogen donor), and then the outflow channel 32. Discharged from.

  FIG. 2 is a schematic cross-sectional view illustrating an example of the configuration of the second denitrification tank 16.

  As shown in FIG. 2, the second denitrification tank 16 is partitioned into two processing chambers 36 </ b> A and 36 </ b> B by a partition plate 34.

  The processing chamber 36A preferentially holds anaerobic ammonia oxidizing bacteria, and the processing chamber 36B preferentially holds heterotrophic denitrifying bacteria. The processing chamber 36B is provided with an organic substance supply tank 38 for adding an organic substance such as methanol as a hydrogen donor to the denitrifying bacteria, and a supply pipe 38A extends from the organic substance supply tank 38 to the processing chamber 36B. Has been. The supply pipe 38A is provided with a valve 40 that can adjust the amount of organic matter added. The valve 40 is configured so that the amount of organic substance added can be controlled by the C / N ratio control means 42 based on the measurement result of the nitric acid concentration meter 26.

  The downstream side of the second denitrification tank 16 communicates with an outflow channel 32 through which the treated wastewater flows out. Further, a circulation channel 44 and a liquid feed pump 46 that communicate the outflow channel 32 and the channel 22 are provided, and the waste water discharged from the processing chamber 36B can be circulated to the processing chamber 36A. . As a result, when the wastewater flows into the second denitrification tank 16, the anaerobic ammonia-oxidizing bacteria in the wastewater is first captured in the treatment chamber 36A, and in the treatment chamber 36B, nitric acid in the wastewater is subordinated with the organic substance as a hydrogen donor. It is degraded to nitrous acid (or nitrogen) by nutrient denitrifying bacteria. The waste water containing nitrous acid is circulated again to the treatment chamber 36A via the circulation channel 44, so that nitrous acid in the waste water flowing from the circulation channel 44 and ammonia in the waste water flowing from the channel 22 Is decomposed and removed by anaerobic ammonia oxidizing bacteria.

  Thus, by providing the processing chamber 36A that performs the anaerobic ammonia oxidation reaction on the upstream side of the processing chamber 36B that performs the heterotrophic denitrification reaction, in the processing chamber 36A, the wastewater flowing out from the first denitrification tank 14 is obtained. The anaerobic ammonia oxidizing bacteria can be easily captured, and the anaerobic ammonia oxidizing bacteria can be efficiently propagated. Therefore, the operation of the second denitrification tank 16 can be quickly started up and the operation can be continued stably.

It is preferable that the second denitrification tank 16 is operated in a volume load of 0.2 to 2.0 kg-N / m ³ / d, a water temperature of 20 to 37 ° C., and a DO concentration of 0.5 or less.

  In order to efficiently perform the decomposition reaction of ammonia and nitric acid by the anaerobic ammonia oxidizing bacteria and denitrifying bacteria in the second denitrifying tank 16, (1) ammonia in wastewater flowing into the second denitrifying tank 16 and It is preferable that the composition ratio of nitric acid and (2) the amount of organic substance added to the second denitrification tank 16 (concentration of added organic substance in the wastewater in the second denitrification tank 16) be within an appropriate range.

The composition ratio (molar ratio) of ammonia and nitric acid in the wastewater flowing into the second denitrification tank 16 is adjusted so that ammonia: nitric acid is 1: 1. This is because nitric acid is reduced to approximately the same mole of nitrous acid by denitrifying bacteria (NO ₃ → NO ₂ ), and this nitrous acid (NO ₂ ) is anaerobic ammonia together with approximately the same mole of ammonia (NH ₄ ). This is because it is decomposed and removed by the reaction of the above formula (1) by oxidizing bacteria.

  The composition ratio of ammonia: nitric acid is, for example, the concentration of nitric acid in the wastewater is measured by the nitric acid concentration meter 26, and the flow rate of the ammonia-containing wastewater that the composition ratio control means 30 flows from the bypass passage 24 based on the measurement result. Is adjusted by a valve 28.

  In the 2nd denitrification tank 16, it is preferable to add an organic substance so that C / N ratio with respect to the total nitrogen amount density | concentration N of the addition organic substance density | concentration C in wastewater may be 0.8-1.3. That is, heterotrophic denitrifying bacteria require organic substances in the denitrification reaction, but if these organic substances are too little, they cannot exhibit sufficient activity, and if they are too much, anaerobic ammonia oxidation in wastewater. There is a risk of significantly reducing the activity of bacteria. For this reason, in order to improve the activity of both, the concentration of the added organic substance in the wastewater in the treatment chamber 36B is set to the above range.

  In the present invention, the added organic substance concentration C of C / N ratio means the organic substance concentration (contained in the wastewater) as a result of addition in the second denitrification step, and the organic substance concentration originally contained in the wastewater is Not included. That is, although the organic matter is contained in the waste water after anaerobic ammonia oxidation reaction, since these organic matter is hardly decomposable, it does not have the property as the organic matter required in the present invention. For this reason, it is important to define and operate the C / N ratio for the added organic matter concentration in the wastewater in the second denitrification tank 16 instead of the C / N ratio in consideration of the organic substances contained in the wastewater in advance. is there.

  As a method for adjusting the C / N ratio, for example, the total nitrogen concentration N in the wastewater before flowing into the second denitrification tank 16 is measured by the nitric acid concentration meter 26 or other nitrogen concentration meter (not shown), and the result Based on the above, the C / N ratio control means 42 controls the opening degree of the valve 40 to adjust the concentration of added organic matter in the wastewater. Examples of organic substances that can be used include molasses, acetic acid, propionic acid, and the like. In addition, since methanol reduces anaerobic ammonia oxidation activity, it is not preferable to use it as an organic substance.

  The method for retaining nitrifying bacteria, anaerobic ammonia-oxidizing bacteria, or denitrifying bacteria in each tank is not particularly limited. For example, a entrapping immobilization carrier in which microorganisms are entrapped and immobilized in a carrier material, and a microorganism in a carrier material. Adhesive immobilization carriers with adhering and fixing, granules utilizing self-granulation of microorganisms, and the like can be used.

  The material of the carrier in the entrapping immobilization carrier is not particularly limited, and examples thereof include polyvinyl alcohol, alginic acid, polyethylene glycol-based gel, and plastic carriers such as cellulose, polyester, polypropylene, and vinyl chloride. As the shape of the carrier, it is preferable to use a shape obtained by shaping a spherical body, a cylindrical body, a porous body, a cube, a sponge body, a honeycomb body or the like.

  The material of the fixed bed in the adhesion-immobilized carrier is not particularly limited, and examples thereof include plastic materials such as polyethylene, polyester, polypropylene, and vinyl chloride, and activated carbon fibers. The shape of the fixed floor is not particularly limited, and examples thereof include a fiber shape, a chrysanthemum shape, and a honeycomb shape.

  As described above, according to the present embodiment, nitric acid or secondary ammonia generated by the anaerobic ammonia oxidation reaction in the first denitrification tank 14 can be added without adding a large amount of organic matter in the second denitrification tank 16. It can be decomposed and removed with high efficiency.

  As mentioned above, although preferable embodiment of the nitrogen removal method and apparatus which concerns on this invention was described, this invention is not limited to the said embodiment, Various aspects can be taken.

  For example, in the above-described embodiment, the method of measuring the nitric acid concentration in the previous stage of the second denitrification tank 16 is used. However, for example, a method as shown in FIG.

  FIG. 3 is a schematic cross-sectional view illustrating a modification of the method for measuring the nitric acid concentration in wastewater. As shown in FIG. 3, ammonia concentration meters 48A and 48B for measuring the ammonia concentration in the wastewater are installed at the front and rear stages of the nitrification tank 12, respectively, and the decrease in ammonia concentration in the nitrification tank 12 (the amount of nitrous acid produced) Measure. That is, assuming that the ammonia concentration in the wastewater before nitrification is a and the ammonia concentration in the wastewater after nitrification is b, if the value of (ab) / a is 1.32 or less, the amount of nitrous acid produced is F × (ab). Here, the value of F varies depending on the type of wastewater, and the value of F is preferably 0.25 to 0.1, and more preferably 0.18 to 0.22.

  In each of the above embodiments, as a method of adjusting the composition ratio of ammonia and nitric acid in the wastewater, the wastewater flowing into the second denitrification tank 16 is subjected to nitrite type nitrification via the bypass channel 24. Although the example which mixes an ammonia containing wastewater was shown, the following methods are also employable, for example.

  That is, by reducing the nitrification rate in the nitrite-type nitrification tank 12 without using the bypass flow path 24 in FIG. 1, unreacted ammonia is increased and nitrite produced is reduced. When the amount of nitrous acid decreases, the amount of nitric acid generated by the anaerobic ammonia oxidation reaction in the first denitrification tank 14 also decreases. The nitrification rate is preferably 57% or less.

  Moreover, in the said embodiment, although the example which isolate | separates and fills anaerobic ammonia oxidation bacteria and denitrification bacteria in process chamber 36A, 36B was shown, it is not limited to this, For example, as shown in FIG. Two types of carriers in which the above two microorganism groups are entrapped and immobilized may be mixed in one second denitrification tank 16 ', or one of the above two microorganism groups may be mixed in one second denitrification tank 16'. It is also possible to immobilize and immobilize simultaneously in the carrier. Further, the immobilization method is not limited to the entrapping immobilization carrier, and an adhesion immobilization carrier in which microorganisms are adhered to the carrier material can be used.

  At this time, it is preferable to add the organic substance to the downstream side of the second denitrification tank 16, as shown in FIG. This is because normal denitrifying bacteria grow faster than anaerobic ammonia oxidizing bacteria, and when an organic substance is added upstream, adhesion and growth of anaerobic ammonia oxidizing bacteria are inhibited.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Example 1]
(Composition of waste water)
A wastewater treatment test was conducted using the synthetic wastewater shown in Table 1.

The nitrite type nitrification tank 12 was filled with a entrapping immobilization support on which nitrifying bacteria were immobilized. The volume load was 0.8 to 3.5 kg-N / m ³ / d, the water temperature was 30 ° C., and the DO was operated at 0.5 to 4.0.

The first denitrification tank 14 was filled with a entrapping immobilization support on which anaerobic ammonia-oxidizing bacteria were immobilized. The volume load was 2 to 10 kg-N / m ³ / d, the water temperature was 30 ° C., and the DO concentration was 0.5 or less.

  And when the nitrite type nitrification was performed for the waste water of Table 1 in the nitrification tank 12, ammonia nitrogen in the waste water was 420 mg / L and nitrite nitrogen was 560 mg / L.

  When this wastewater was subjected to anaerobic ammonia oxidation treatment in the first denitrification tank 14, ammonia nitrogen and nitrite nitrogen in the wastewater were both reduced to 5 mg / L or less, but 105 mg / L nitrate nitrogen was present. It was included (this wastewater is called “Wastewater A”).

  Next, the 2nd denitrification tank 16 used the thing of FIG. The treatment chamber 36A is filled with anaerobic ammonia-oxidizing bacteria adhered to a non-woven fabric, and the treatment chamber 36B is acclimated after heterotrophic denitrifying bacteria are adhered to a reticulated plastic filler. Was filled.

As the denitrifying bacteria, first, sludge collected from a sewage treatment plant is added to a treatment tank so as to be 5000 mg / L, and sodium acetate and sodium nitrate (80 mg / L as nitrogen concentration) are continuously supplied. A well-known one was used. It was confirmed that the denitrifying bacteria after acclimation showed a capacity of 0.3 kg-N / m ³ / d as a denitrification rate per volume.

The flow rate of the liquid feed pump 46 was set to about 4 times the flow rate of waste water before nitrite type nitrification was performed. The water temperature was 30 ° C., and sodium acetate was used as the organic substance to be added. The volume load of nitrite nitrogen to the second denitrification tank 16 was 0.3 kg-N / m ³ / d.

  And the waste water A containing nitric acid produced | generated in the 1st denitrification tank 14 and the ammonia containing waste water before performing nitrite type nitrification are mixed through the bypass flow path 24, and the composition ratio of ammonia and nitric acid is 1: 1. The waste water which becomes was denitrified in the second denitrification tank 16. As a result, the concentration of the added organic matter in the wastewater is less than that of nitrate nitrogen. It was about 0 times.

[Comparative Example 1]
As a conventional denitrification tank, 30% of a net-like plastic filler was filled, and denitrifying bacteria were attached thereto for acclimatization. This denitrifying bacterium is acclimatized by first adding sludge collected from a sewage treatment plant to a denitrifying tank so as to be 5000 mg / L and continuously supplying sodium acetate and sodium nitrate (80 mg / L as nitrogen concentration). did. After the acclimatization, it was confirmed that a denitrification rate per volume of 0.3 kg-N / m ³ / d was exhibited.

The waste water A was introduced into the denitrification tank, the volume load was 0.3 kg-N / m ³ / d, and the water temperature was 25 ° C. Sodium acetate was used as the organic substance.

  As a result, although nitrate nitrogen could be reduced to 5 mg / L or less, the concentration of added organic substances in the wastewater was about 2.8 times the total nitrogen concentration in the wastewater.

  From the above results, it was found that in Example 1 to which the present invention was applied, denitrification was possible at an added organic substance concentration of about half or less of the conventional Comparative Example 1.

[Example 2]
In the 2nd denitrification tank 16, the relationship between C / N ratio with respect to the total nitrogen concentration N of the addition organic substance density | concentration C in wastewater, and the denitrification performance was examined. The result is shown in FIG.

  As shown in FIG. 5, it has been clarified that the added amount of the organic substance has an appropriate ratio with respect to the amount of nitric acid in the wastewater. Further, it was found that the C / N ratio of the added organic substance concentration C to the nitrate nitrogen concentration N is preferably 0.8 to 1.3, and more preferably 0.9 to 1.2. If the concentration of the added organic substance in the wastewater is too low, it is considered that the reaction is not sufficiently performed and the efficiency is lowered. On the other hand, if the concentration of the added organic substance in the wastewater is too high, it is considered that it has an adverse effect on the anaerobic ammonia-oxidizing bacteria and has reduced the denitrification performance.

[Example 3]
The wastewater composition (composition ratio of ammonia and nitric acid) flowing into the second denitrification tank 16 was adjusted by reducing the nitrification rate in the nitrification tank 12. The composition of the wastewater after nitrifying nitrite was 486 mg / L for ammonia nitrogen and 515 mg / L for nitrite nitrogen (this wastewater is called wastewater A ′). When this wastewater A ′ was subjected to anaerobic ammonia oxidation treatment in the first denitrification tank 14, 92 mg / L of nitric acid was produced, and at the same time, 90 mg / L of ammoniacal nitrogen remained.

  Using this waste water, the denitrification treatment was performed in the second denitrification tank 16 shown in FIG. 2 in the same manner as in Example 1. As a result, ammonia nitrogen and nitrate nitrogen in the waste water after denitrification were both 5 mg / L. It was reduced to the following. Further, the concentration of the added organic substance in the wastewater at this time was 0.94 with respect to the nitrate nitrogen concentration, which was much smaller than that in the case of Example 1.

  From the above results, by reducing the nitrification rate in the nitrification tank 12, the amount of organic matter added can be reduced, and about 10% of ammonia nitrogen in the wastewater before nitrite type nitrification is further reduced. It was found that it could be removed by the second denitrification tank 16.

[Examples 4 and 5]
The addition position of the organic substance in the second denitrification tank 16 was examined.

  As shown in FIG. 4, when anaerobic ammonia oxidizing bacteria and denitrifying bacteria are mixed in one second denitrification tank 16 ′, an organic substance is added on the upstream side of the second denitrification tank 16 ′. In Example 4, as shown in FIG. 2, anaerobic ammonia-oxidizing bacteria are introduced into the treatment chamber 36A of the second denitrification tank 16, and the denitrification bacteria are introduced into the treatment chamber 36B of the second denitrification tank 16, and the organic matter enters the treatment chamber 36B. Was added as Example 5. Other operating conditions were the same as in Example 1.

  And as a result of comparing about the starting period of the denitrification activity in the 2nd denitrification tank 16, in Example 5 comprised like FIG. 2, it took one month for denitrification activity to stabilize. On the other hand, in Example 4 configured as shown in FIG. 4, it took 3 months for the denitrification activity to stabilize.

  From the above, by adding organic matter to the processing chamber 36B (downstream of the second denitrification tank 16) in which denitrifying bacteria are preferentially retained, it is possible to suppress adverse effects on anaerobic ammonia oxidizing bacteria, It was found that the activity of bacteria can be improved.

[Example 6]
Instead of the synthetic wastewater used in each of the above Examples 1 to 5, a wastewater treatment test was performed using a filtrate (hereinafter referred to as wastewater) obtained by dewatering wastewater after sludge digestion treatment collected from a sewage treatment plant. The main composition of this wastewater was NH ₄ —N: 1050 mg / L, COD: 320 mg / L, BOD: 80 mg / L, TOC: 300 mg / L. Other operating conditions were the same as in Example 1.

  When this waste water was subjected to nitrite type nitrification in the nitrification tank 12, the waste water after the nitrification treatment contained 504 mg / L of ammonia nitrogen and 520 mg / L of nitrite nitrogen.

  Subsequently, when this waste water was subjected to anaerobic ammonia oxidation treatment in the first denitrification tank 14, 80 mg / L of nitrate nitrogen was produced and 96 mg / L of ammonia nitrogen remained.

  Next, when the waste water treated in the first denitrification tank 14 was further treated in the second denitrification tank 16, the nitric acid could be reduced to 5 mg / L or less.

  At this time, the added organic substance concentration C in the wastewater in the second denitrification tank 16 was 0.9 (C / N ratio) with respect to the nitrate nitrogen concentration N. When this C / N ratio is expressed as an organic substance concentration C ′ in consideration of organic substances originally contained in the wastewater as in the past, the organic substance concentration C ′ and nitrate nitrogen in the wastewater after adding the organic substances to the wastewater The C ′ / N ratio with respect to the concentration is 4.65. This value does not make sense in the present invention, but this is clear from the following.

  In the second denitrification tank 16, when only the organic matter originally contained in the wastewater was treated without newly adding the organic matter (at this time, the C ′ / N ratio of the wastewater was 3 or more), the nitric acid could hardly be removed. . This suggests that organic substances originally contained in the wastewater cannot be used in the second denitrification tank 16. Therefore, it was found that the C ′ / N ratio in which the organic matter originally contained in the wastewater is added is not an index in the present invention, and it is necessary to newly add the organic matter.

It is a cross-sectional schematic diagram explaining an example of the nitrogen removal apparatus which concerns on this invention. It is a cross-sectional schematic diagram which shows an example of a structure of the 2nd denitrification tank in FIG. It is a cross-sectional schematic diagram which shows the modification of the measuring method of nitrogen concentration. It is a cross-sectional schematic diagram which shows the modification of a structure of a 2nd denitrification tank. It is a graph which shows the result in a present Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Nitrogen removal apparatus, 12 ... Nitrification tank, 14 ... 1st denitrification tank, 16, 16 '... 2nd denitrification tank, 24 ... Bypass flow path, 26 ... Nitric acid concentration meter, 28 ... Valve, 30 ... Composition ratio control means 36A, 36B ... processing chamber, 38 ... organic substance supply tank, 38A ... supply pipe, 40 ... valve, 42 ... C / N ratio control means, 44 ... circulation channel, 48A, 48B ... ammonia concentration meter

Claims (13)

A method for removing nitrogen in ammonia-containing wastewater,
A nitrite type nitrification step of nitrifying a part of ammonia contained in the wastewater to nitrite by nitrifying bacteria;
A first denitrification step of removing ammonia and nitrous acid contained in waste water flowing out of the nitrite type nitrification step by anaerobic ammonia oxidizing bacteria;
A second method for removing residual ammonia contained in the waste water flowing out from the first denitrification step and nitric acid produced in the first denitrification step by anaerobic ammonia oxidizing bacteria and heterotrophic denitrifying bacteria. Denitrification process of
A method for removing nitrogen, comprising: The second denitrification step includes
Reducing the nitric acid to nitrous acid using the heterotrophic denitrifying bacterium as an organic substance as a hydrogen donor;
Removing the nitrous acid produced in the step and ammonia in the wastewater by the anaerobic ammonia oxidizing bacteria;
The nitrogen removal method according to claim 1, comprising:   The nitrogen removal method according to claim 1 or 2, wherein the composition ratio of the wastewater flowing into the second denitrification step is 1: 1 ammonia: nitric acid.   The nitrogen removal method according to claim 3, wherein the composition ratio is formed by mixing waste water flowing out from the first denitrification step with waste water before performing the nitrite type nitrification step. .   The nitrogen removal method according to claim 3, wherein the nitrification rate is set to 57% or less in the nitrite type nitrification step.   The C / N ratio of the added organic substance concentration C in the wastewater to the total nitrogen concentration N in the wastewater is set to 0.8 to 1.3 in the second denitrification step. The method for removing nitrogen according to any one of the above. A nitrogen removal device for removing nitrogen components contained in ammonia-containing wastewater,
A nitrite type nitrification tank that nitrifies a part of ammonia contained in the wastewater into nitrite by nitrifying bacteria;
A first denitrification tank which is provided downstream of the nitrite type nitrification tank and removes ammonia and nitrous acid contained in waste water flowing out of the nitrification tank by anaerobic ammonia oxidizing bacteria;
Anaerobic ammonia-oxidizing bacteria and heterotrophic acid are provided on the downstream side of the first denitrification tank, and residual ammonia contained in the waste water flowing out of the first denitrification tank and nitric acid generated in the first denitrification tank are A second denitrification tank to be removed by a natural denitrifying bacterium,
A nitrogen removing apparatus comprising: The second denitrification tank is
A first treatment tank in which the anaerobic ammonia oxidizing bacteria are retained;
A second treatment tank provided downstream of the first treatment tank and holding the denitrifying bacteria,
The downstream side of the second treatment tank communicates with the upstream side of the first treatment tank, and at least a part of the waste water flowing out of the second treatment tank flows into the first treatment tank. A circulation channel;
The nitrogen removing apparatus according to claim 7, further comprising:   The nitrogen removal apparatus according to claim 7, wherein the second denitrification tank holds the anaerobic ammonia-oxidizing bacteria and the denitrifying bacteria in one treatment tank. A nitric acid concentration measuring means for measuring the nitric acid concentration in the waste water;
Composition ratio control means for controlling the composition ratio of ammonia and nitric acid in the wastewater flowing into the second denitrification tank based on the measurement result in the nitric acid concentration measurement means;
The nitrogen removing apparatus according to any one of claims 7 to 9, further comprising:   11. The apparatus according to claim 7, further comprising a bypass flow path that branches from a flow path upstream of the nitrite type nitrification tank and communicates with a flow path upstream of the second denitrification tank. The nitrogen removing apparatus according to item.   The nitrogen removing apparatus according to any one of claims 7 to 11, wherein the second denitrification tank is provided with an organic substance adding means. In the second denitrification tank, nitrogen concentration measuring means for measuring the total nitrogen concentration in the waste water,
Based on the measurement result of the nitrogen concentration measuring means, an addition amount control means for controlling the addition amount of the organic substance to the second denitrification tank to be within a predetermined range;
The nitrogen removing apparatus according to any one of claims 7 to 12, comprising:

Images