JP4453397B2 - Biological nitrogen removal method - Google Patents

Description

  In the present invention, raw water containing ammonia nitrogen is brought into contact with ammonia oxidizing bacteria under aerobic conditions to nitrify at least a part of the ammonia nitrogen in the raw water to nitrite nitrogen, The present invention relates to a biological nitrogen removal method in which biological denitrification is performed by the action of a denitrifying bacterium using nitrogen as an electron donor and nitrite nitrogen as an electron acceptor.

  Ammonia nitrogen contained in the effluent is one of the causative substances of eutrophication in rivers, lakes and oceans, and it is necessary to remove it efficiently in the effluent treatment process. In general, ammonia nitrogen in wastewater is oxidized by ammonia oxidizing bacteria to nitrite nitrogen, and nitrifying nitrogen is oxidized to nitrate nitrogen by nitrite oxidizing bacteria. Nitrite nitrogen and nitrate nitrogen are denitrified bacteria, which are heterotrophic bacteria, and are converted into nitrogen gas through a two-stage biological reaction with a denitrification process that decomposes organic matter into nitrogen gas using an electron donor. Disassembled.

  However, such a conventional nitrification denitrification method requires a large amount of organic matter such as methanol as an electron donor in the denitrification step, and also requires a large amount of oxygen in the nitrification step, so that the running cost is high. is there.

On the other hand, in recent years, nitrite nitrogen and ammonia nitrogen are reacted using autotrophic bacteria (autotrophic bacteria) using ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. A method of denitrifying by letting go was proposed. If this method is used, it is not necessary to add an organic substance, so that the cost can be reduced as compared with a method using heterotrophic denitrifying bacteria. Moreover, since the yield of autotrophic bacteria is low and the amount of sludge generated is significantly less than that of heterotrophic bacteria, the amount of surplus sludge generated can be suppressed. Furthermore, there is also a feature that there is no generation of N ₂ O observed by the conventional nitrification denitrification method, and the burden on the environment can be reduced.

  The biological denitrification process using this autotrophic denitrifying bacterium (hereinafter sometimes referred to as “ANAMOX bacteria”) is a reaction of nitrite nitrogen and ammonia nitrogen in the following reaction to form nitrogen gas. It is thought to be broken down.

  Since nitric acid is produced in addition to nitrogen as a reaction product of the reaction formula (1), a nitrogen removal process is performed by performing a biological denitrification process in the presence of an organic substance such as methanol after the ANAMOX process. The removal rate can be increased, and treated water with good water quality can be obtained.

When the denitrification treatment is performed using the ANAMMOX bacteria, the water to be treated (raw water) flowing into the ANAMMOX reaction tank holding the ANAMOX bacteria needs to contain nitrite nitrogen and ammonia nitrogen. For this reason, conventionally, for example, wastewater containing ammonia nitrogen is nitrified in advance, and a portion of ammonia nitrogen in the waste water is oxidized into nitrite nitrogen by ammonia oxidizing bacteria as raw water. . As is clear from the above reaction formula, this raw water reacts with nitrite nitrogen and ammonia nitrogen at a molar ratio of 1: 1.32, so that the molar concentration b of ammonia nitrogen (NH ₄ -N) and It is preferable that the ratio a / b with respect to the molar concentration a of nitrate nitrogen (NO ₂ —N) is about 1.3.

  However, it is difficult to react with wastewater with varying concentration and flow rate by flowing it into the ANAMOX process so that the molar ratio a / b of nitrite nitrogen to ammonia nitrogen is always about 1.3, Therefore, nitrite nitrogen or ammonia nitrogen often remains in the treated water of the ANAMOX process.

  In addition, it is known that ANAMMOX bacteria are inhibited by various factors such as organic matter, oxygen, and pH. In the case where the activity of the AMAMOX bacteria is reduced due to inhibition by these factors, ammonia nitrogen and nitrite nitrogen remain in the treated water of the ANAMMOX process.

  Since the nitrite nitrogen remaining in the treated water of the ANAMOX process is removed in the denitrification process that is provided in the latter stage of the ANAMOX process for removing nitric acid and biologically denitrifies in the presence of an organic substance such as methanol. Nitrite nitrogen remaining in the process water does not deteriorate the overall nitrogen removal rate of the process.

  However, ammonia nitrogen remaining in the treated water of the ANAMOX process cannot be removed in the subsequent denitrification process, which causes a reduction in the nitrogen removal rate of the entire process.

  In order to solve such problems, the raw water containing ammonia nitrogen is brought into contact with ammonia oxidizing bacteria under aerobic conditions to nitrify at least a part of the ammonia nitrogen in the raw water to nitrite nitrogen. A nitrification step, and a nitrification step in which the nitrification step is performed, and a denitrification step of biological denitrification by the action of a denitrifying bacterium using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor, In the method of removing biological nitrogen, when ammonia is detected in the denitrification treatment liquid from the denitrification process, nitrite and nitrite are used against the nitrification liquid sent from the nitritation process to the denitrification process. Alternatively, adding nitrite-containing nitrogen-containing waste water is described in JP-A No. 2003-53387, particularly in paragraphs 0037 to 0039 thereof.

  According to the method of the same publication, by maintaining the denitrification process at the ammoniacal nitrogen rate-limiting condition, ammonia nitrogen is not left in the treated water of the denitrification process, and a high nitrogen removal rate can be stably obtained. Can do.

In the same publication, ammonia ion concentration is measured by a colorimetric method using a reagent, an ion chromatograph method for measuring conductivity, an ion electrode method, and the like. It is described that the use of an electrode is preferable from the viewpoints of equipment cost and quickness and reliability of measurement. The principle of the ion electrode is basically similar to that of the pH electrode, and uses a diaphragm that selectively passes the component to be measured, and detects the liquid concentration of the target component from the difference in ion concentration in the electrode. . A concentration signal is output as an electrical signal from the ion electrode, and the ammonia nitrogen concentration is monitored and controlled based on this signal.
JP 2003-53387 A

  In the above Japanese Patent Application Laid-Open No. 2003-53387, even if a large amount of nitrite nitrogen remains in the denitrification treated water from the denitrification process, it is not detected and flows out as treated water as it is. Residual nitrogen concentration increases. Moreover, the ANAMMOX reaction is inhibited by the high concentration of nitrous acid remaining in the tank.

  Furthermore, according to the method of the same publication, the ammonia nitrogen concentration of the treated water is detected and fed back to control, so that there is a time delay in the control depending on the size of the reaction tank and the residence time of water. In some cases, good treated water quality cannot be maintained.

  An object of the present invention is to solve such problems and to provide a biological nitrogen removal method in which the nitrogen concentration in the treated water is stably lowered.

Biological nitrogen removal process of the present invention, the raw water containing ammonia nitrogen is contacted with ammonia-oxidizing bacteria in aerobic conditions, nitrous for nitrification at least a portion of the ammoniacal nitrogen in the raw water to nitrite nitrogen A nitrification step, and a nitrification step in which the nitrification step is performed, and a denitrification step of biological denitrification by the action of a denitrifying bacterium using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor, In this biological nitrogen removal method, the denitrification step includes a first denitrification step and a second denitrification step of further denitrifying the primary denitrification solution from the first denitrification step. The molar concentration (a) of nitrite nitrogen in the primary denitrification treatment liquid and ammonia by adding nitrite nitrogen or ammonia nitrogen to the primary denitrification treatment liquid The ratio a / b with respect to the molar concentration (b) of crystalline nitrogen is 1 to 1.5 It is an butterfly.

In the present invention, the raw water is subjected to a nitritation treatment to obtain a nitrification liquid in which the component ratio of ammonia nitrogen and nitrite nitrogen is adjusted to some extent. This nitrification solution is subjected to ANAMOX treatment in two stages. In the present invention, the concentration of ammonia nitrogen and nitrite nitrogen in the ANAMOX treated water is measured, and ammonia nitrogen or nitrite nitrogen is added to the ANAMMOX treated water based on the measured value. The ANAMMOX treatment is performed while maintaining the molar ratio a / b of nitrite nitrogen and ammonia nitrogen at an optimum ratio of 1 to 1.5 (preferably 1.3). Thereby, the concentration of ammonia nitrogen and nitrite nitrogen remaining in the ANAMOX treated water can be reduced, and a high nitrogen removal rate can be stably obtained.

  Embodiments of the biological nitrogen removal method of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram of a biological denitrification apparatus for explaining an embodiment of a biological nitrogen removal method according to a reference example .

  In FIG. 1, raw water is first introduced into a nitritation tank 1 and aerated, and a part of ammonia nitrogen in the raw water is partially oxidized to nitrite nitrogen by ammonia oxidizing bacteria (nitrification step).

  The effluent (nitrification liquid) of the nitritation tank 1 is introduced into the ANAMOX reaction tank 2, and ammonia nitrogen and nitrite nitrogen are removed by the ANAMMOX reaction by the ANAMOX bacteria under stirring (denitrification process).

  Although not shown, the effluent of the ANAMOX reaction tank 2 is then introduced into the denitrification tank, and organic substances such as methanol are added. Under stirring, the nitric acid produced in the ANAMOX reaction is degassed by the denitrifying bacteria under anaerobic conditions. Is broken down into Further, when nitrite nitrogen remains in the effluent of the ANAMOX reaction tank 2, this nitrite nitrogen is also decomposed into nitrogen gas.

  In the present invention, the raw water to be treated is water containing ammonia nitrogen, and may contain organic matter and organic nitrogen. However, they are preliminarily converted to ammonia nitrogen before denitrification treatment. It is preferable to decompose. The raw water may contain an inorganic substance.

  In general, wastewater containing ammonia nitrogen, organic nitrogen and organic matter such as sewage, human waste, anaerobic digestion and desorption liquid is often treated. In this case, these are treated aerobically or anaerobically. Thus, it is preferable that the organic matter is decomposed and the organic nitrogen is decomposed into ammonia nitrogen, and then introduced into the nitritation tank 1.

  As described above, in the ANAMMOX reaction, nitrite nitrogen and ammonia nitrogen react at a molar ratio of 1: 1.3. Therefore, the influent water in the ANAMOX reaction tank 2 is a molar ratio of nitrite nitrogen and ammonia nitrogen. It is preferable to contain nitrite nitrogen and ammonia nitrogen in such a ratio that a / b is 1 to 1.5, preferably 1.1 to 1.4, and particularly preferably 1.3. For this reason, the nitrite nitrogen concentration a and the ammonia nitrogen concentration b in the nitrification liquid flowing out from the nitrification tank are measured by the measuring device 3, and based on this measured value, the concentration control device 4 uses the chemical injection valve 12. Alternatively, 22 is controlled and an aqueous nitrite solution or an aqueous ammonium salt solution is added to the nitrification solution. The nitrite is sodium nitrite in this embodiment, but may be other nitrites or nitrites. However, nitrite, particularly inexpensive sodium nitrite, is preferred because it is easy to handle and can accurately control the nitrite concentration.

  As the ammonium salt, ammonium sulfate is suitable, but other ammonium salts may be used. Further, instead of the aqueous solution of ammonium salt, a part of ammonia nitrogen-containing water, for example raw water, may be added to the nitrification solution. However, in order to accurately control the nitrite nitrogen concentration, an ammonium salt, particularly an inexpensive ammonium sulfate is preferable.

  In addition, each aqueous solution of nitrite and ammonium is converted into a nitrification solution from the nitrification tank 1 through a chemical injection unit including tanks 10 and 20, chemical injection pumps 11 and 21, and the chemical injection valves 12 and 22, respectively. Added.

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

  In this embodiment, the nitrification liquid from the nitritation tank 1 is introduced into the first ANAMOX reaction tank 2a and denitrified by the ANAMOX bacteria to become primary denitrified water. This primary denitrification treated water is introduced into the second ANAMOX reaction layer 2b and further denitrified by the ANAMOX bacteria to obtain secondary denitrification treated water.

The nitrite nitrogen concentration and the ammonia nitrogen concentration in the primary denitrification treated water flowing out from the first ANAMMOX tank are measured by the concentration measuring device 3, and based on this measurement result, the a / b ratio of the primary denitrification treated water is determined. A nitrite or ammonium salt is added so as to be 1 to 1.5, preferably 1.1 to 1.4, particularly preferably 1.3. The structure of the chemical injection unit for performing this addition is the same as that of FIG. 1, and the same code | symbol has shown the identical part.
1 and 2, ammonia nitrogen can be substantially prevented from remaining in the treated water in the ANAMOX reactors 2 and 2b.

The pH, DO concentration, and temperature of the nitritation tank 1 are
pH: 6.0-8.5, especially 6.5-7.5
DO concentration: 0.05-5 mg / L, especially 0.1-1.5 mg / L
Temperature: 10-40 ° C, especially 25-35 ° C
Is preferred.

In the ANAMOX reactors 2, 2a, 2b,
pH: 6-9, especially 6.5-8.0
DO concentration: 0 to 2.5 mg / L, especially 0 to 0.2 mg / L
Temperature: 10-40 ° C, especially 20-35 ° C
BOD concentration: 0-50 mg / L, especially 0-20 mg / L
Nitrogen load: 0.1 to 10 kg-N / m ³ · day, especially 0.2 to 5 kg-
N / m ³ · day
Is preferred.

  In addition, there is no restriction | limiting in particular in the type | mold of the reaction tank of nitritation tank 1 or ANAMMOX reaction tank 2, 2a, 2b, In addition to sludge suspension system, fixed bed, fluidized bed, granule method, carrier addition method, etc. It may be based on a biofilm method. Moreover, you may provide solid-liquid separation apparatuses, such as a precipitation tank and a membrane separator, in the back | latter stage of each of a nitritation tank and an ANAMOX reaction tank. The nitritation tank may be an airlift aeration tank. The NAAMMOX reactor may be a gas lift type reactor using nitrogen gas instead of air, and is a USB (Upflow Sludge Bed) reactor that forms a granular sludge bed of ANAMMOX bacteria. There may be.

  Hereinafter, the present invention will be described more specifically with reference to comparative examples and examples.

Comparative Example 1
The dehydrated filtrate after the anaerobic digestion treatment of sewage sludge containing ammonia was treated as water to be treated, and the ANAMMOX reactor having a volume of 3.0 L shown in FIG. The raw water was passed through under the condition of day. The operating conditions were pH 7.3 and the temperature inside the ANAMOX tank was adjusted to 30 ° C.

The addition of nitrite and ammonia salt was not carried out, and the changes over time in the water to be treated and the treated water when operated for 20 days under the above conditions were examined, and the results are shown in FIG .

Real Example 1
In FIG. 2 where the ANAMOX reaction tank is divided into two stages in series, the measurement device 3 measures the ammonia nitrogen concentration and nitrite nitrogen concentration of the primary denitrification treated water from the first stage ANAMMOX reaction tank 2a. Is detected, sodium nitrite is detected, ammonium nitrate is detected when nitrous acid is detected, and the concentration ratio of NO ₂ —N / NH ₄ —N is 1.3 so that the optimum ratio is 1.3. It added to the primary denitrification process water, and processed with the 2nd step | paragraph ANAMOX reaction tank 2b. The operating conditions of flow rate, pH, and temperature were the same as in the comparative example. FIG. 3 shows the daily changes in the ammonium nitrogen concentration and nitrite nitrogen concentration of the secondary denitrification water flowing out from the second-stage reaction tank 2b.

The following is clear from FIG. In Comparative Example 1 in which the concentration control of the ANAMOX treated water was not performed, an average of 50 mg N / L nitrogen remained in the treated water. In contrast, Anammox total nitrogen concentration in the treated water in Example 1 were carried out control based on the water to be treated is less than 2 mgN / L, it was possible to obtain a low residual nitrogen concentration better treated water.

It is a systematic diagram of the biological denitrification apparatus explaining embodiment of the biological nitrogen removal method which concerns on a reference example . It is a systematic diagram of the biological denitrification apparatus explaining embodiment of the biological nitrogen removal method of this invention. It is a graph showing the passage of days changes in total nitrogen concentration in the treated water in Comparative Example 1 and the raw water in Example 1.

1 Nitrite tank 2, 2a, 2b ANAMMOX reactor

Claims (2)

A nitritation step of contacting raw water containing ammonia nitrogen with ammonia oxidizing bacteria under aerobic conditions to nitrify at least a portion of the ammonia nitrogen in the raw water to nitrite nitrogen;
A denitrification step in which the nitrification solution in the nitrification step is biodenitrified by the action of a denitrifying bacterium using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor;
In a biological nitrogen removal method having
The denitrification step includes a first denitrification step and a second denitrification step of further denitrifying the primary denitrification treatment liquid from the first denitrification step,
By adding nitrite nitrogen or ammonia nitrogen to the primary denitrification solution, the molar concentration (a) of nitrite nitrogen and the molar concentration of ammonia nitrogen (b And a ratio of a / b to 1 to 1.5. Oite to claim 1, nitrite is added as a nitrite nitrogen, biological nitrogen removal method is characterized by adding an ammonium salt as ammonium nitrogen.

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