JP5391011B2 - Nitrogen-containing wastewater treatment method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a nitrogen-containing wastewater treatment method using a biological nitrification denitrification treatment apparatus, and in particular, nitrogen using a biological nitrification denitrification treatment apparatus that performs denitrification treatment by adding a hydrogen donor after nitrification treatment. It relates to a wastewater treatment method.

  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 or nitrate nitrogen by nitrifying bacteria, which are aerobic bacteria, and denitrifying bacteria, which are anaerobic bacteria. It consists of a denitrification process in which nitrate and nitrite nitrogen are reduced to nitrogen, and various types of reactors have been developed.

  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 disposed upstream and a nitrification tank is disposed 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 treatment method, a new supply method of inorganic carbonic acid necessary for the nitrification reaction has also been proposed. (For example, refer to Patent Document 2).

JP-A-11-285696 JP 2006-320844 A

  When nitrogen-containing wastewater containing almost no organic matter is treated by the biological nitrogen treatment method, as described above, ammonia nitrogen in the wastewater is changed to nitrite or nitrate nitrogen by nitrifying bacteria, and anaerobic bacteria are used. It is common to reduce to nitrogen using some denitrifying bacteria. At this time, a hydrogen donor is required for the denitrification reaction, and this hydrogen donor is performed by injecting methanol or the like. In the wastewater treatment apparatus using such a biological nitrogen treatment method, when the methanol in the denitrification tank becomes excessive, the COD concentration in the denitrification tank increases. Originally, the denitrification tank that targets wastewater with low COD concentration has a low digestion capacity, and it takes a long time to reduce the COD concentration in the denitrification tank. For this reason, if the COD concentration in the denitrification tank increases, the COD concentration in the treated water also increases, and as a result, the treated water cannot be discharged. Conventionally, when such a situation occurs, the drainage of the denitrification tank and the treated water of the treated water storage tank are collected and treated separately, but it requires a lot of time and labor, and without collecting the drainage and treated water. Development of a processing method capable of processing in a short time has been awaited.

  An object of the present invention is to provide a nitrogen-containing wastewater treatment method using a biological nitrification denitrification treatment apparatus that performs a denitrification treatment by adding a hydrogen donor after nitrification treatment, and the COD concentration in the denitrification tank exceeds the set value. Is to provide a nitrogen-containing wastewater treatment method for reducing COD in a short time.

The present invention according to claim 1 is a biological nitrification denitrification method in which ammonia body nitrogen in waste water is nitrified with nitrifying bacteria in a nitrification tank, then a hydrogen donor is added and denitrification treatment is performed in a denitrification tank to remove nitrogen. using nitrogen device, wherein the method of treating a nitrogen-containing waste water while returning a portion of the treated water treated with denitrification tank to the nitrification tank, the nitrogen-containing waste water is a low organic matter containing wastewater or inorganic waste water, the denitrification tank When the COD concentration of water exceeds the set value , the return of the treated water to the nitrification tank is stopped to prevent a decrease in the activity of nitrifying bacteria, and nitrate is injected into the denitrification tank to decompose the COD component. It is a contained wastewater treatment method.

According to a second aspect of the present invention, in the nitrogen-containing wastewater treatment method according to the first aspect, the biological nitrification denitrification apparatus has a treated water storage tank on the downstream side of the denitrification tank, When the COD concentration exceeds a set value, nitrate is injected into the circulating water, the denitrification tank, or the treated water storage tank while circulating the wastewater between the denitrification tank and the treated water storage tank, and the COD components are decomposed. It is characterized by.

  The present invention according to claim 3 is the nitrogen-containing wastewater treatment method according to claim 1 or 2, wherein the nitrogen-containing wastewater is nitrogen-containing wastewater discharged from a coal-fired power plant.

  The present invention according to claim 4 is the nitrogen-containing wastewater treatment method according to any one of claims 1 to 3, wherein the hydrogen donor is methanol or acetic acid, and methanol or acetic acid in the denitrification tank is excessive. The COD concentration in the denitrification tank exceeds the set value.

  The present invention described in claim 5 is the nitrogen-containing wastewater treatment method according to any one of claims 1 to 4, wherein the nitrate has a nitrate ion concentration in the denitrification tank of less than 5,000 mg / L. It is characterized by injecting as follows.

  The present invention according to claim 6 is the nitrogen-containing wastewater treatment method according to any one of claims 1 to 5, wherein the nitrate is any one or more of potassium nitrate, sodium nitrate, calcium nitrate, and magnesium nitrate. It is characterized by being.

The nitrogen-containing wastewater treatment method according to the present invention stops the return of treated water to the nitrification tank and injects nitrate into the denitrification tank when the COD concentration in the denitrification tank exceeds the set value when the circulation method is adopted. To do. As a result, a denitrification reaction is caused by the COD component and nitrate ions, and the COD component is decomposed. Therefore, even when the denitrification tank is contaminated with high-concentration COD, the COD in the denitrification tank is reduced in a short time. be able to. Although the reaction rate of the digestion reaction in the denitrification tank is slow, the denitrification reaction has a fast reaction rate, so that the COD component can be decomposed in a short time. Also, it is not necessary to take out the waste water and treat it separately. In addition, the return of the treated water to the nitrification tank is stopped, and nitrate is injected into the denitrification tank to decompose the COD components, so it is possible to prevent nitrifying bacteria from being reduced in activity due to high-concentration COD drainage, and the COD in the denitrification tank Immediately after the concentration has dropped, normal operation can be resumed. Such a nitrogen-containing wastewater treatment method can be suitably applied to low organic matter-containing wastewater or inorganic wastewater, and can be suitably used for nitrogen-containing wastewater discharged from a coal-fired power plant.

Further, according to the present invention, when the treated water storage tank is provided on the downstream side of the denitrification tank, when the COD concentration in the denitrification tank exceeds the set value, the circulating water is circulated while circulating the wastewater between the denitrification tank and the treated water storage tank. Since nitrate is injected into the denitrification tank or the treated water storage tank, the water in the denitrification tank and the treated water storage tank can be treated at a time, which is preferable. In addition, when the denitrification tank is a UASB denitrification tank that holds granules, the drainage is circulated between the denitrification tank and the treated water storage tank, thereby fluidizing the granules in the UASB denitrification tank and the COD components and nitrate ions. Mixability can be improved, denitrification reaction can be promoted, and COD components can be decomposed in a short time.

  Moreover, the nitrogen-containing wastewater treatment method according to the present invention can be suitably applied when the hydrogen donor methanol or acetic acid is excessive in the denitrification tank and the COD concentration in the denitrification tank exceeds the set value. .

  Further, according to the present invention, nitrate is injected so that the nitrate ion concentration in the denitrification tank is less than 5,000 mg / L, so that the activity of the denitrifying bacteria can be kept high. Moreover, since nitrate is any one or more of potassium nitrate, sodium nitrate, calcium nitrate, and magnesium nitrate, it is almost neutral when dissolved in water, and a pH adjuster is unnecessary or a small amount is sufficient.

It is a figure for demonstrating the nitrogen-containing waste water treatment method of this invention, Comprising: It is a process flow figure of the typical biological nitrification denitrification apparatus 1. FIG. It is a figure for demonstrating the nitrogen-containing wastewater treatment method of this invention, Comprising: It is a process flow figure which shows the example which applied the nitrogen-containing wastewater treatment method of this invention to the typical biological nitrification denitrification apparatus 1. .

  The nitrogen-containing wastewater treatment method according to the present invention is a biological nitrification / denitrification device in which ammonia body nitrogen in wastewater is nitrified in a nitrification tank, and then a hydrogen donor is added and denitrification treatment is performed in a denitrification tank to remove nitrogen. When the COD concentration in the denitrification tank exceeds the set value in the nitrogen-containing wastewater treatment method using nitrile, an amount of nitrate necessary for decomposing the COD component is injected into the denitrification tank, and the COD component and nitrate ions are desorbed. In this method, a nitrogen reaction is caused to decompose the COD component, and the COD in the denitrification tank is reduced within a short time. The set value of the COD concentration in the denitrification tank may be set arbitrarily. For example, a regulated value that can be discharged into a river or the like may be adopted as the set value.

  Hereinafter, the nitrogen-containing wastewater treatment method 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. Here, the set value of the COD concentration in the denitrification tank is set to 30 mg / L that can be discharged into a river or the like. 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 support, it is oxidized by oxygen in the air by the action of nitrifying bacteria adhering to the microorganism-immobilized support. It becomes nitrate nitrogen or nitrite nitrogen. The reaction formula of the nitrification reaction is shown 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 acetic acid may be used instead of methanol.

The UASB denitrification tower 17 holds granules therein, and nitrate nitrogen or nitrite nitrogen in the wastewater sent to the UASB denitrification tower 17 is separated from methanol by the action of denitrifying bacteria in the granules. Reacts and decomposes into nitrogen gas and carbon dioxide gas. The denitrification reaction is represented by the formula (2). Through 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 confirming that the total nitrogen concentration and COD concentration in the treated water are both below the regulated value of 30 mg / L, the treated water in the treated water storage tank 23 is discharged to the river or sea 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, normally, methanol is supplied in an amount corresponding to the total nitrogen amount at the inlet of the DHS nitrification tower 13, and the biological nitrification denitrification apparatus 1 is normal. In some cases, there is no excess methanol in the UASB denitrification tower 17, and the COD concentration in the UASB denitrification tower 17 does not exceed the regulation value. However, if the methanol in the UASB denitrification tower 17 becomes excessive, the COD concentration in the treated water exceeds the regulation value and cannot be discharged. As a case where methanol becomes excessive, when the total nitrogen concentration in the raw water changes greatly, a failure of the methanol supply device 19 or an erroneous operation can be considered. Considering the residence time of the DHS nitrification tower 13, methanol is supplied in an amount corresponding to the total nitrogen quantity at the inlet of the DHS nitrification tower 13 several hours ago, so the total nitrogen quantity at the inlet of the DHS nitrification tower 13 is large. If changed, the methanol becomes excessive in the UASB denitrification tower 17.

  Hereinafter, the treatment method when the COD in the UASB denitrification tower 17 exceeds the regulation value in the biological nitrification denitrification apparatus 1 shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a process flow diagram in which the present invention is applied to the biological nitrification denitrification apparatus 1 shown in FIG. The same components as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

  When the COD of the treated water exceeds the regulation value, the treated water discharge line 27 is first closed to stop the treated water from being discharged to the outside. At the same time, the circulation line 29 is closed and the treated water sent to the mixing tank 5 is stopped. Instead, tap water or the like is led from another system and supplied to the mixing tank 5. When treated water with high COD is returned to the mixing tank 5, wastewater with high COD is sent to the DHS nitrification tower 13, and the activity of nitrifying bacteria is reduced. When a high COD component is added to a nitrifying bacterium that has grown in a state where the COD is very low, bacteria other than the nitrifying bacterium grow and the activity of the DHS nitrifying tower 13 decreases.

  The waste water in the UASB denitrification tower 17 and the treated water in the treated water storage tank 23 lower the COD in the following manner. In order to circulate water between the UASB denitrification tower 17 and the treated water storage tank 23, a return line 31 for returning water from the treated water storage tank 23 to the UASB denitrification tower 17 is provided. Further, a nitrate supply device 33 for supplying nitrate is connected to the return line 31. While circulating water between the UASB denitrification tower 17 and the treated water storage tank 23, a predetermined amount of nitrate is supplied from the nitrate supply device 33 to decompose methanol which is a COD component. The nitrate does not necessarily need to be supplied to the return line 31, and basically only needs to be supplied to the UASB denitrification tower 17 in which denitrification occurs, and may be supplied to the UASB denitrification tower 17 or the treated water storage tank 23. Good.

  Originally, methanol disappears due to a denitrification reaction with nitrate nitrogen and nitrite nitrogen contained in waste water sent from the DHS nitrification tower 13. However, in the state where the methanol contained in the waste water in the UASB denitrification tower 17 is excessive, there is no nitrate nitrogen and nitrite nitrogen necessary for causing the denitrification reaction. Does not disappear. Therefore, an amount of nitrate corresponding to methanol contained in the water circulating between the UASB denitrification tower 17 and the treated water storage tank 23 is added, and methanol and nitrate ions cause a denitrification reaction to decompose the methanol.

  While circulating water between the UASB denitrification tower 17 and the treated water storage tank 23, a predetermined amount of nitrate is supplied from the nitrate supply device 33 to decompose methanol, which is a COD component, with the UASB denitrification tower 17. The main purpose is to simultaneously treat the water in the treated water storage tank 23 and to improve the fluidization of granules in the UASB denitrification tower 17 and the mixing of methanol and nitrate ions to promote the denitrification reaction.

  Although nitrate may be supplied as a solid, a method of dissolving it in water and supplying it as an aqueous solution is easy in terms of quantitative supply and controllability. The amount of nitrate added is an amount necessary for denitrifying reaction with methanol to eliminate methanol. At this time, the nitrate is supplied in a controlled manner so that the nitrate concentration in the water circulating through the UASB denitrification tower 17 and the treated water storage tank 23 does not exceed 5000 mg / L. If the supply amount of nitrate is large and the nitrate ion concentration in water exceeds 5,000 mg / L, the activity of denitrifying bacteria is lowered, which is not preferable.

  The nitrate to be supplied is not particularly limited as long as it is dissolved in water to generate nitrate ions, and is preferably one that exhibits almost neutrality when dissolved in water. By using a nitrate which is almost neutral when dissolved in water, it is economical because the use of a pH adjuster is unnecessary or the amount used is small. Examples of such nitrates include potassium nitrate, sodium nitrate, calcium nitrate, and magnesium nitrate. These can be used alone or in combination of two or more.

  The methanol in the UASB denitrification tower 17 can be decomposed by the digestion action of the denitrification bacteria in the UASB denitrification tower 17 without supplying nitrate, but the digestion rate of the denitrification bacteria is very slow. About one week is required. In contrast, since the denitrification rate of the denitrifying bacteria is fast, the COD returns to a normal value within a few hours. After confirming that the total nitrogen concentration and COD concentration in the treated water are below the regulation values, the return line 31 and the nitrate supply device 33 are removed, and the treated water discharge line 27 and the circulation line 29 are opened for normal operation. Return. As described above, if the nitrogen-containing wastewater treatment method of the present invention is used, the wastewater in the UASB denitrification tower 17 or the treated water in the treated water storage tank is drawn out, and there is no need for separate treatment. The biological nitrification denitrification apparatus 1 can be returned to normal.

  Next, another case where the COD of treated water exceeds the regulation value will be described. Even when the activity of nitrifying bacteria in the DHS nitrification tower 13 is lowered, there is a risk that the COD in the UASB denitrification tower 17 exceeds the regulation value and becomes high. When the activity of nitrifying bacteria in the DHS nitrification tower 13 decreases, the nitrification ratio of ammonia nitrogen in the DHS nitrification tower 13 decreases, and the production of nitrate ions decreases. Therefore, nitrate nitrogen and nitrite nitrogen in the waste water sent to the UASB denitrification tower 17 are also lowered. On the other hand, since methanol is supplied in an amount corresponding to the total amount of nitrogen at the inlet of the DHS denitrification tower 13, when the concentration of nitrate nitrogen and nitrite nitrogen decreases, the amount of methanol in the UASB denitrification tower 17 decreases. Become excessive. In this case, since ammonia body nitrogen is contained in the treated water, not only the COD but also the total nitrogen concentration is high in the treated water.

  In this case as well, after the treated water discharge line 27 and the circulation line 29 are closed, the treated water storage tank 23 is used to circulate water between the UASB denitrification tower 17 and the treated water storage tank 23. A return line 31 for returning treated water to the UASB denitrification tower 17 is provided, and a nitrate supply device 33 for supplying nitrate is attached to the return line 31, and water is supplied between the UASB denitrification tower 17 and the treated water storage tank 23. While circulating the water, nitrate is supplied to decompose the COD component methanol. During this time, the DHS nitrification tower 13 is sounded and recovered, whereby the ammonia nitrogen is nitrified and can be returned to the steady operation.

  As shown in the above embodiment, the nitrogen-containing wastewater treatment method of the present invention can easily reduce the COD when the COD concentration in the denitrification tank exceeds a set value. Such a nitrogen-containing wastewater treatment method can be suitably used for wastewater or inorganic wastewater with a small amount of organic matter contained in the wastewater. 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, the DHS nitrification tower is used as the nitrification tower and the UASB denitrification tower is used as the denitrification tower, but it goes without saying that the nitrification tower and the denitrification tower are not limited to these reactors.

DESCRIPTION OF SYMBOLS 1 Biological nitrification denitrification apparatus 3 Drain 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 31 Return line 33 Nitrate feeder

Claims (6)

After nitrification treatment by nitrification bacteria ammonia body nitrogen in waste water in a nitrification tank, using a biological nitrification and denitrification device for removing the added denitrification and nitrogen denitrification tank hydrogen donor, treated with the denitrification tank a method of treating a nitrogen-containing waste water while returning a portion of the treated water in the nitrification tank,
The nitrogen-containing wastewater is low organic matter-containing wastewater or inorganic wastewater,
When the COD concentration in the denitrification tank exceeds the set value , the return of treated water to the nitrification tank is stopped to prevent the activity of nitrifying bacteria from decreasing, and nitrate is injected into the denitrification tank to decompose the COD components. Nitrogen-containing wastewater treatment method. The biological nitrification denitrification apparatus has a treated water storage tank on the downstream side of the denitrification tank,
When COD concentration in the denitrification tank exceeds a set value, the circulating water in while circulating wastewater in the denitrification tank and the treated water storage tank, nitrate is injected into said denitrification tank or the treated water storage tank, COD The nitrogen-containing wastewater treatment method according to claim 1, wherein components are decomposed.   The nitrogen-containing wastewater treatment method according to claim 1 or 2, wherein the nitrogen-containing wastewater is nitrogen-containing wastewater discharged from a coal-fired power plant.   The said hydrogen donor is methanol or acetic acid, methanol or acetic acid in a denitrification tank becomes excess, and the COD density | concentration in a denitrification tank exceeded the preset value, The any one of Claim 1 to 3 characterized by the above-mentioned. Nitrogen-containing wastewater treatment method.   The nitrogen-containing wastewater treatment method according to any one of claims 1 to 4, wherein the nitrate is injected so that a nitrate ion concentration in the denitrification tank is less than 5,000 mg / L.   The nitrogen-containing wastewater treatment method according to any one of claims 1 to 5, wherein the nitrate is at least one of potassium nitrate, sodium nitrate, calcium nitrate, and magnesium nitrate.

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