JP2011062655A - Method of operating denitrification reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of operating a denitrification reactor which recovers the denitrification performance of the denitrification reactor, reducing nitrate nitrogen or nitrite nitrogen in wastewater to nitrogen using methanol as a hydrogen donor by denitrifying bacteria, in a short period of time when the activity of various germs are increased and the denitrification performance of the denitrification reactor is decreased. <P>SOLUTION: In the denitrification reactor which reduces nitrate nitrogen or nitrite nitrogen in wastewater to nitrogen using methanol as a hydrogen donor by denitrifying bacteria, when the activity of various germs are increased and the denitrification performance of the denitrification reactor is decreased, a part of methanol is substituted by acetic acid, and a mixture of the methanol and acetic acid is subjected to pH adjustment, and then supplied to the denitrification reactor as a hydrogen donor. As the acetic acid decreases the activity of the various germs, the activity of the denitrifying bacteria is increased to recover the denitrification performance in a short period of time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a denitrification reactor that denitrifies nitrogen-containing wastewater, and more particularly to a method for operating a denitrification reactor that recovers when the activity of various bacteria is increased and the denitrification performance of the denitrification reactor is reduced.

  Nitrogen contained in wastewater is a cause of eutrophication, and many techniques for removing nitrogen in wastewater have been developed. Biological nitrogen treatment methods that remove nitrogen in wastewater using microorganisms, which are one of these, have also been widely used in the past. Progressive feeding methods, AO (anaerobic-oxic) methods, A2O (anaerobic-anoxic) methods. Many processes have been proposed, including cyclic methods such as -Oxic) and UASB (Upflow Analytic Sliding Blanket) -DHS (Downflow Hanging Sponge Cube) method. The biological nitrogen treatment method uses a nitrification process in which ammonia nitrogen in wastewater is oxidized to nitrite nitrogen or nitrate nitrogen by nitrifying bacteria, which are aerobic bacteria, and denitrifying bacteria, which are anaerobic bacteria. A denitrification process that reduces nitrate and nitrite nitrogen to nitrogen has been developed, and treatment processes and reactors have been developed in accordance with the properties of waste water.

  Nitrogen-containing wastewater ranges from wastewater containing a large amount of organic matter, such as sewage, to wastewater discharged from factories and containing little organic matter. In general, when nitrogen-containing wastewater containing a relatively large amount of organic substances is treated by a biological nitrogen treatment method, a denitrification tank is often arranged upstream and a nitrification tank is arranged downstream. In the circulating UASB-DHS method, the denitrification reaction is performed in the preceding UASB reactor, the nitrification reaction is performed in the subsequent DHS reactor, and a part of the treated water in which the subsequent nitrification reaction has progressed is the UASB in the preceding denitrification tower. The organic substance in the treated water is used as a hydrogen donor for the denitrification reaction (see, for example, Patent Document 1). On the other hand, when nitrogen-containing wastewater containing almost no organic matter is treated by a biological nitrogen treatment method, a nitrification tank is generally disposed upstream and a denitrification tank is disposed downstream. In such a biological nitrification denitrification treatment apparatus, a method for adding an extract extracted from a plant to a denitrification tower or a nitrification tower in order to maintain high nitrification performance and denitrification performance has been proposed (for example, patents). Reference 2).

JP-A-11-285696 JP 2007-275748 A

  By the way, when nitrogen-containing wastewater containing almost no organic matter is treated with a biological nitrification denitrification device, the activity of denitrifying bacteria increases when the activity of various bacteria increases in the denitrification tower where methanol is used as a hydrogen donor and denitrification treatment is performed. Decrease or denitrifying bacteria are inactivated and denitrification performance is reduced. When denitrifying bacteria are inactivated, it is difficult to regenerate them. Conventionally, the sludge in the denitrifying tower was extracted and inserted with new activated sludge. It has been. The technique described in Patent Document 2 is for maintaining the denitrification tank at high performance, and does not regenerate the denitrification tank in which the activity of the denitrifying bacteria is reduced or the denitrifying bacteria are deactivated and the denitrifying performance is reduced. .

  In the denitrification method using denitrifying microorganisms using ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor, hydrazine and hydroxyamine are added to restore the activity when the activity of the denitrifying microorganism decreases. Although the method to make is disclosed in Japanese Patent Application Laid-Open No. 2003-33791, it is different from the denitrifying bacterium in which methanol is a hydrogen donor and nitrate and nitrite nitrogen is reduced to nitrogen, and the method is applied as it is. I can't. So far, when the activity of miscellaneous bacteria increases in the denitrification tower that performs denitrification treatment using methanol as a hydrogen donor, the denitrification activity decreases and the denitrification performance deteriorates, and this is recovered within a short period of time. No method has been developed.

  The object of the present invention is to improve the activity of various bacteria in a denitrification reactor in which methanol is a hydrogen donor and nitrate nitrogen or nitrite nitrogen in waste water is reduced to nitrogen by denitrifying bacteria. It is intended to provide a method of operating a denitrification reactor that recovers the denitrification performance within a short period of time when the temperature decreases.

  The present invention according to claim 1 is a denitrification reactor in which methanol is used as a hydrogen donor and nitrate nitrogen or nitrite nitrogen in waste water is reduced to nitrogen by denitrifying bacteria, so that the activity of various bacteria increases and the denitrifying reactor When the denitrification performance of the denitrifier is reduced, it is possible to reduce the activity of miscellaneous bacteria and inject an organic substance as an alternative hydrogen donor for the methanol to increase the activity of the denitrification bacteria and restore the denitrification performance of the denitrification reactor Is a method of operating a denitrification reactor.

  The present invention according to claim 2 is the operation method of the denitrification reactor according to claim 1, wherein the organic substance is acetic acid, the methanol injection amount is reduced, and acetic acid corresponding to the methanol reduction amount is reduced. The pH is adjusted and injected into the denitrification reactor.

  According to a third aspect of the present invention, in the method for operating a denitrification reactor according to the second aspect, the injection amount of the acetic acid is 0.75 or less in molar ratio to methanol.

  According to a fourth aspect of the present invention, in the method for operating a denitrification reactor according to any one of the first to third aspects, the denitrification reactor is a UASB reactor having granular sludge. And

  According to a fifth aspect of the present invention, in the method for operating a denitrification reactor according to any one of the first to fourth aspects, the waste water is low organic matter-containing waste water or inorganic waste water.

  The operation method of the denitrification reactor according to the present invention injects organic matter that can reduce the activity of germs when the activity of the germs increases and the denitrification performance of the denitrification reactor decreases, Can be reduced. Thereby, the activity of the denitrifying bacteria is enhanced, and the denitrification performance of the denitrification reactor can be recovered within a short period of time. In addition, since the injected organic substance serves as an alternative hydrogen donor for methanol, the performance of the denitrification reactor can be recovered without increasing the COD in the wastewater by replacing a part of the methanol with the organic substance.

  Further, according to the present invention, since the organic substance is acetic acid, the bactericidal action is high, the activity of various germs is reduced, and the denitrification performance of the denitrification reactor can be recovered within a short period of time. Acetic acid is preferred as a chemical that restores the performance of the denitrification reactor because it is readily available and inexpensive.

  According to the present invention, acetic acid is injected into the denitrification reactor together with methanol, and the injection amount is 0.75 or less in molar ratio to methanol, so that the concentration of acetic acid does not become extremely high. For this reason, it becomes possible to reduce the activity of various bacteria without reducing the activity of the denitrifying bacteria, and the performance of the denitrifying reactor can be recovered.

  Moreover, according to this invention, the operating method of the denitrification reactor which concerns on this invention can be used suitably, when the activity of the UASB reactor holding granule sludge falls.

  Also, according to the present invention, the denitrification reactor operating method according to the present invention is preferably used when the denitrification performance of a denitrification reactor targeting low organic matter-containing wastewater such as ammonia wastewater or inorganic wastewater is reduced. Can do.

It is a figure for demonstrating the operating method of the denitrification reactor of this invention, Comprising: It is a process flow figure of the typical biological nitrification denitrification apparatus 1. FIG. It is a figure which shows the experimental result of Example 1 of this invention.

  The denitrification reactor according to the present invention operates in a denitrification reactor in which methanol is used as a hydrogen donor and nitrate nitrogen or nitrite nitrogen in the waste water is reduced to nitrogen by denitrifying bacteria. When the denitrification performance of the nitrogen reactor is reduced, it is possible to reduce the activity of various bacteria and inject organic substances that serve as an alternative hydrogen donor for methanol, thereby increasing the activity of the denitrifying bacteria by reducing the activity of the various bacteria. This is a method for recovering the denitrification performance of the nitrogenation reactor within a short period of time.

  Hereinafter, a method for regenerating a denitrification reactor according to the present invention will be described by taking as an example a case where nitrogen-containing wastewater containing almost no organic matter is treated by the biological nitrification denitrification apparatus 1. FIG. 1 is a typical process flow diagram of a biological nitrification denitrification apparatus 1 for treating nitrogen-containing wastewater containing almost no organic matter.

  The nitrogen-containing wastewater in the wastewater storage tank (hereinafter sometimes simply referred to as wastewater) is sent to the mixing tank 5 through the wastewater supply line 3. The total nitrogen concentration in the waste water is measured by a sampling dropper 7 provided in the supply line 3. The waste water sent to the mixing tank 5 is mixed with the treated water sent from the treated water storage tank 23 so that the total nitrogen concentration in the waste water is 500 mg / L or less. Further, the main purpose is to supply carbon dioxide, which is an inorganic carbon source, from the nutrient salt supply device 9 to the mixing tank 5, and the nutrient salts shown in Table 1 are supplied. Further, hydrochloric acid, sulfuric acid, etc. from the pH adjuster supply device 11 PH adjuster is supplied.

The waste water adjusted in the mixing tank 5 is sent to the DHS nitrification tower 13. The DHS nitrification tower 13 is filled with a plurality of microorganism immobilization carriers (not shown), and air is supplied to the DHS nitrification tower 13 from below. The waste water is sprinkled from the upper part of the DHS nitrification tower 13, and when passing through the microorganism-immobilized carrier, it is oxidized with oxygen in the air by the action of nitrifying bacteria adhering to the microorganism-immobilized carrier, and the ammonia nitrogen in the waste water is It becomes nitrate nitrogen or nitrite nitrogen. The reaction formula of the nitrification reaction is represented by the following formula (1).
^{_{NH 4 + + 0.103CO 2 + 1.86O}} 2 → 0.0182C 2 H 5 NO 2 + 0.00245C 5 H 7 NO 2 + 0.979NO 3 - + 1.98H + + 0.938H 2 O ··· (1)

  The nitrified waste water is sent to the UASB denitrification tower 17 through the line 15. In the middle of the line 15, a methanol supply device 19 is connected to supply a predetermined amount of methanol, and the waste water is sent to the UASB denitrification tower 17 together with methanol. Methanol is provided as a hydrogen donor necessary for the denitrification reaction, and an amount corresponding to the total nitrogen amount at the inlet of the DHS nitrification tower 13 is supplied.

The UASB denitrification tower 17 holds granule sludge inside, and nitrate nitrogen or nitrite nitrogen in the waste water sent to the UASB denitrification tower 17 is methanol by the action of denitrifying bacteria in the granule sludge. Reacts with nitrogen gas and carbon dioxide gas. The denitrification reaction is represented by the formula (2). By these steps, ammonia nitrogen in the waste water is decomposed into nitrogen gas.
^{_{6NO 3 - + 5CH 3 OH →}} 3N 2 + 5CO 2 + 7H 2 O + 6OH - ··· (2)

  The treated water passes through the line 21 and is sent to the treated water storage tank 23. A sampling point 25 for measuring the total nitrogen concentration and the COD concentration in the treated water is provided in the middle of the line 21. After it is confirmed that the total nitrogen concentration and COD concentration in the treated water are both below the regulation value, the treated water in the treated water storage tank 23 is discharged to the river or the sea area through the treated water discharge line 27. A part of the treated water is returned to the mixing tank 5 through the circulation line 29.

  In the biological nitrification denitrification apparatus 1 shown in FIG. 1 above, while the denitrifying bacteria are functioning normally, the denitrification performance of the UASB denitrification tower 17 is sufficiently high, and the total nitrogen concentration in the treated water is regulated. It can be as follows. If the environment, operating conditions, drainage properties, etc. of the UASB denitrification tower 17 are stable, the denitrification performance of the UASB denitrification tower 17 is stable, but if the environment of the UASB denitrification tower 17 changes, For example, if a large amount of oxygen is contained in the wastewater sent to the UASB denitrification tower 17, the denitrification performance of the UASB denitrification tower 17 may be greatly reduced.

  Granule sludge in the UASB denitrification tower 17 contains not only denitrifying bacteria but also many types of bacteria such as methanogens and aerobic bacteria, so if the environment in the UASB denitrifying tower 17 changes, the denitrifying bacteria The activity of other bacteria (hereinafter referred to as miscellaneous bacteria) increases, the activity of denitrifying bacteria decreases, and the denitrifying performance decreases. Cases in which the activity of germs in the granular sludge is increased include cases where the pH in the wastewater has changed and the performance of the nitrification tower has been lowered.

In the UASB denitrification tower 17, it can be confirmed as follows that the activity of various bacteria is increased and the denitrification performance is lowered. Table 2 shows the relationship between the situation of the UASB denitrification tower 17, the COD concentration in the treated water, and the total nitrogen concentration when the DHS nitrification tower 13 is functioning normally.

  As shown in Table 2, when the DHS nitrification tower 13 is functioning normally, the COD concentration in the treated water is low and the total nitrogen concentration is high. This is the case where the nitrogen performance deteriorates and the case where the methanol injection amount is insufficient. When the activity of miscellaneous bacteria is high and the activity of denitrifying bacteria is low, the COD concentration in the treated water becomes low. Although methanol is not used for the denitrification reaction, the miscellaneous bacteria decompose the methanol, resulting in a low COD concentration. Therefore, when the methanol injection amount is normal, the COD concentration in the treated water is low, and the total nitrogen concentration is high, it is presumed that the activity of various bacteria increases and the denitrification performance decreases. A method for recovering the denitrification performance of the UASB denitrification tower 17 in such a case to normal will be described.

  In order to restore the denitrification performance of the UASB denitrification tower 17 to normal, it replaces with methanol injected as a hydrogen donor necessary for the denitrification reaction, and a part of the methanol is replaced with acetic acid. Inject into the UASB denitrification tower 17. Specifically, a mixed liquid of methanol and acetic acid is sent to the UASB denitrification tower 17 via the methanol supply device 19. Here, it is necessary to replace a part of the methanol with acetic acid and inject an amount of acetic acid corresponding to the amount of methanol decrease. Injecting acetic acid in the form of adding acetic acid is not preferable because the hydrogen donor becomes excessive.

Although acetic acid is known to cause the denitrification reaction represented by the formula (3), in this case, acetic acid not only functions as a hydrogen donor but also has a bactericidal action, so the UASB denitrification tower 17 It functions to reduce the activity of various germs.
^{_{8NO 3 - + 5CH 3 COOH →}} 4N 2 + 10CO 2 + 6H 2 O + 8OH - ··· (3)
When a mixed solution of methanol and acetic acid is injected into the UASB denitrification tower 17 via the methanol supply device 19, sodium hydroxide or the like is used so that the pH in the UASB denitrification tower 17 is normal. Adjust and inject pH. Needless to say, methanol and acetic acid may be injected by separate apparatuses.

  When the amount of acetic acid injected is small, the ability to reduce the activity of various bacteria is low. Conversely, when the amount of acetic acid injected is too large, not only the bacteria but also the activity of denitrifying bacteria is reduced. Is necessary. Specifically, it is preferable that the amount of acetic acid injected is 0.75 or less in terms of molar ratio with respect to methanol, and is injected while confirming the properties of the treated water. The injection amount of acetic acid at a molar ratio of 0.75 to methanol corresponds to 50% of the amount of hydrogen donor required for the denitrification reaction. Thereby, the denitrification performance of the UASB denitrification tower 17 can be recovered within a short period of time. Depending on the properties of the waste water and the properties of the granular sludge, organic substances other than acetic acid that can reduce the activity of various bacteria can be used. Examples of such organic substances include formic acid, ethanol, propanol and the like.

  The operation method of the denitrification reactor according to the present invention reduces the activity of bacteria, represented by acetic acid, when the activity of the bacteria increases in the denitrification tower and the denitrification performance decreases as shown in the above embodiment. It is possible to inject an organic substance that can be used as an alternative hydrogen donor for methanol to increase the activity of denitrifying bacteria and restore the denitrification performance of the denitrification reactor, so there is no need to replace granular sludge, etc. be able to. Such an operation method of the denitrification reactor can be widely applied to nitrogen-containing wastewater, and among them, it can be suitably used for wastewater or inorganic wastewater in which the amount of organic matter contained in the wastewater is small. Examples of such wastewater include wastewater discharged from a condensate demineralizer discharged from a coal-fired power plant, washing wastewater from an electric dust collector, desulfurization wastewater, or wastewater mixed with these. In the above embodiment, an example using the UASB denitrification tower is shown, but it goes without saying that the denitrification tower is not limited to these reactors.

  FIG. 2 is a diagram showing the measurement results of the denitrification rate with respect to the number of days elapsed when methanol and acetic acid are injected in the UASB denitrification tower with reduced denitrification performance. In FIG. 2, the denitrification rate is the removal rate of nitrate nitrogen and nitrite nitrogen in the waste water at the outlet of the UASB denitrification tower with respect to nitrate nitrogen and nitrite nitrogen in the waste water at the inlet of the UASB denitrification tower. On the negative day of the elapsed days, only methanol is injected, and on days after the elapsed day 0, a part of the methanol is replaced with acetic acid, and the molar ratio of methanol and acetic acid is 1: 0.75. The solution was injected with pH adjusted. As a result, the UASB denitrification tower, which had a denitrification performance of 50% or less, had a denitrification rate of nearly 90% in 6 days from the start of the mixture injection of methanol and acetic acid.

DESCRIPTION OF SYMBOLS 1 Biological nitrification denitrification apparatus 3 Waste water supply line 5 Mixing tank 7 Sampling point 9 Nutrient supply apparatus 11 pH adjuster supply apparatus 13 DHS nitrification tower 15 Line 17 UASB denitrification tower 19 Methanol supply apparatus 21 Line 23 Treated water storage tank 25 Sampling point 27 Treated water discharge line 29 Circulation line

Claims (5)

  In a denitrification reactor in which methanol is a hydrogen donor and nitrate nitrogen or nitrite nitrogen in the wastewater is reduced to nitrogen by denitrifying bacteria, when the activity of various bacteria increases and the denitrification performance of the denitrifying reactor decreases, The denitrification reactor operating method is characterized by injecting an organic substance that can reduce the activity of the methanol and serving as an alternative hydrogen donor for the methanol to increase the activity of the denitrification bacteria and restore the denitrification performance of the denitrification reactor .   2. The denitrification according to claim 1, wherein the organic substance is acetic acid, the injection amount of the methanol is decreased, and acetic acid corresponding to the methanol decrease amount is injected into the denitrification reactor by adjusting PH. Reactor operation method.   The method of operating a denitrification reactor according to claim 2, wherein the amount of acetic acid injected is 0.75 or less in molar ratio to methanol.   The method for operating a denitrification reactor according to any one of claims 1 to 3, wherein the denitrification reactor is a UASB reactor that holds granular sludge.   The method for operating a denitrification reactor according to any one of claims 1 to 4, wherein the waste water is waste water containing low organic matter or inorganic waste water.

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