JP2005177758A - Biological deodorization method of odorant gas containing ammonia and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological deodorization method and an apparatus therefor, wherein a deodorizing performance of an odorant gas containing NH<SB>3</SB>, of a high concentration with a large variation of concentration is easily stabilized with low cost and also a water quantity consumed and a water quantity discharged can be lowered. <P>SOLUTION: The biological deodorization method is composed of a circulation style of nitrification and denitrification method, wherein the odorant gas 1 containing NH<SB>3</SB>is contacted 7 with a circulation water 5 in a nitrification step 3 and NH<SB>3</SB>contained is absorbed to be biologically nitrification-treated by nitrifying bacteria, and also this nitrification liquid 5 is guided to a denitrification step 4 and the denitrification-treated liquid is again returned 9 as the circulation water 5 to the nitrification step . In this deodorization method, a pH buffer solution is used as the circulation water 5, wherein the pH buffer solution is a phosphate buffer solution or a carbonate buffer solution, and also the said pH buffer solution can be controlled by feeding a reagent such that a pH of the circulation water is in the range of 6.0 and 7.5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for biological deodorization of odor gas, and in particular, odor gas generated from composting facilities, sewage treatment facilities, human waste treatment facilities, waste treatment facilities, various factories, etc., containing ammonia, The present invention relates to a method and an apparatus for deodorizing.

In recent years, the demand for composting treatment such as garbage and sludge has been increasing, and the processing of gas containing high concentration of ammonia generated from composting facilities has become a problem.
Conventionally, deodorization of ammonia-containing gas has been generally performed by a wet cleaning method using a chemical solution such as water or acid as an absorbent. However, this method not only requires a large amount of water and chemicals, but also has a problem that a large amount of wastewater containing ammonia is discharged.
In addition, deodorizing methods using adsorbents such as activated carbon and zeolite may be applied, but these adsorbents have a small amount of adsorbed ammonia, so a large amount of adsorbent is required when the load of ammonia is high. In addition, the adsorbent replacement operation is complicated, and there is a problem that waste such as used adsorbent is generated.

Compared to these deodorization methods, the packed tower-type biological deodorization method which has recently gained attention in the treatment of sulfur-containing malodorous substance-containing gases has the advantages of easy maintenance and low running costs. However, when the ammonia-containing odor is treated by this method, there are two major problems. First, when ammonia is biologically nitrified, nitrate nitrogen accumulates in the circulating water used for watering. Since excessive accumulation of nitrate nitrogen affects the processing performance, it is difficult to maintain the deodorizing performance for a long time. In order to suppress the accumulation of nitrate nitrogen, a large amount of water is required to dilute it, and at the same time, a large amount of nitrate nitrogen-containing wastewater is discharged.
Therefore, it has been difficult to apply to facilities where the amount of water used and the amount of drainage are restricted, such as composting facilities.

To solve this problem, a method for converting ammonia in odor to nitrogen gas by combining a nitrification step and a denitrification step in the biological deodorization method for ammonia-containing odor gas has been proposed. In this method, accumulation of nitrogen components in the aqueous phase is suppressed, and the nitrification reaction and denitrification reaction proceed in a well-balanced manner,
Since the pH of the circulating water is maintained neutral, the water can be reused. Therefore,
According to this method, the problem of the amount of water used and the amount of drainage is solved.
The second problem is that, in general, the ammonia concentration in the ammonia-containing odor fluctuates significantly, and it is difficult to maintain stable performance with the biological deodorization method only by adopting the above method. That is to say. In particular, when the ammonia concentration rapidly rises, the nitrification reaction cannot catch up, and ammonia temporarily accumulates in the circulating water at a high concentration, so that the pH of the circulating water rises. As a result, the ability to absorb and remove ammonia from odors is reduced, and the biological nitrification denitrification reaction is inhibited.

Furthermore, when the pH rises, as shown in the following formula (1), most of the ammonia absorbed in the circulating water becomes free ammonia, and when this free ammonia becomes high, the biological nitrification reaction is remarkably increased. Inhibit. Because nitrifying bacteria have a slow growth rate,
As the free ammonia concentration increases, the ammonia removal performance decreases over a long period of time.
NH ₄ ⁺ + OH ⁻ → NH ₃ + H ₂ O (1)
In addition, such large fluctuations in ammonia load and circulating water pH also lead to an imbalance between the nitrification reaction and the denitrification reaction. As a result, nitrate nitrogen accumulates in the circulating water, the pH is excessively lowered, and the nitrification / denitrification reaction is inhibited, resulting in a decrease in ammonia removal performance.

As described above, in the treatment of ammonia-containing odor gas by the biological deodorization method, p
H stabilization is one of the most important factors for maintaining performance.
As a method for stabilizing the pH, there is a method of controlling the pH with an acid agent or an alkali agent. However, when this method is adopted in the circulation type nitrification denitrification treatment, the following problems occur.
(1) Where ammonia accumulates, an acid agent is added, whereas when nitric acid accumulates, an alkali agent needs to be added, so the amount of neutralizing agent added becomes enormous.
(2) When the nitrification / denitrogenation reaction is completed, the neutralizing agent added in the above (1) becomes a residue, which may have to be neutralized again. The amount of added becomes enormous.
(3) Even if the pH is maintained in the optimum range, the increase in the salt concentration caused by the added neutralizing agent inhibits the nitrification / denitrification reaction.

In addition, in order to solve the problems of these methods, a biological deodorization method of ammonia-containing exhaust gas using a porous inorganic carrier cured body containing calcium as a microorganism carrier and using circulating water as phosphoric acid-containing water has been proposed. ing. In this method, phosphoric acid fixes ammonia by the reaction between ammonia and phosphoric acid, so that it is possible to odorlessly odor even when the nitrification reaction of microorganisms at the time of starting the apparatus is insufficient.
Further, as shown in the following equation (2), calcium hydrogen phosphate is converted to apatite hydroxide by the action of ammonia, and phosphoric acid is released, so that it is neutralized by this phosphoric acid.
10CaHPO ₄ + 2H ₂ O → Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ +
4H ₃ PO ₄ (2)

On the other hand, when ammonia is biologically decomposed and removed, the reverse reaction may occur, and phosphoric acid may be fixed as calcium phosphate again. That is, there is a possibility that a release reaction of phosphoric acid into the aqueous phase and a recovery reaction into the solid phase occur depending on the ammonia concentration in the system. Therefore, it is possible to prevent the amount of chemicals used and the increase of the salt concentration of the aqueous phase.
However, when the ammonia concentration of the odor to be treated is high and the concentration fluctuation is large, it is difficult to stabilize the processing performance because the pH fluctuation cannot be suppressed following the ammonia concentration fluctuation for the following reason. .
(1) The reaction rate of the formula (2) is slow.
(2) When the pH of the circulating water is neutral and calcium and phosphoric acid coexist, the main form is considered to be calcium hydrogen phosphate, and this salt has extremely low solubility in water. The concentration of phosphoric acid or phosphate present in the liquid phase is very low.
JP-A-57-180421

The present invention solves the above-mentioned problems, can stabilize the deodorization performance of ammonia-containing odor gas having a high concentration and a large concentration variation by a low-cost and extremely simple method, and reduces the amount of water used and the amount of drainage. It is an object of the present invention to provide a biological deodorization method and apparatus that can be used.

In order to solve the above problems, in the present invention, ammonia containing odorous gas is brought into contact with circulating water in the nitrification step to absorb the ammonia contained therein, and biologically nitrified by nitrifying bacteria, and the nitrifying solution In the biological deodorization method of the circulation type nitrification / denitrogenation method, which leads to the denitrification process and returns the denitrification treatment liquid to the nitrification process again as circulating water,
A pH buffer solution is used for the circulating water.
In the deodorization method, the pH buffer solution may be a phosphate buffer solution or a carbonate buffer solution, and the pH buffer solution may supply a drug and have a circulating water pH of 6.0. The pH can be controlled to be in the range of ˜7.5.
Further, in the present invention, nitrification deodorization having a packed bed in which nitrifying bacteria that pass ammonia-containing odor gas are supported, a watering device for spraying circulating water in the packed bed, and a circulating water tank for storing the circulating water. In a biological deodorization apparatus having a tower, a denitrification tank for denitrifying nitrification liquid from the nitrification deodorization tower, and a path for circulating water to circulate between the denitrification tank and the nitrification deodorization tower, A pH buffer solution is used.

In the method of the present invention, the ammonia-containing odor gas is guided to the nitrification step, biologically nitrified by nitrifying bacteria, the nitrification solution is guided to the denitrification step, and the denitrification solution is returned to the nitrification step again. In the biological deodorization method of the circulatory nitrification and denitrification method, by using a pH buffer solution for the circulating water, even when the fluctuation of ammonia load is large and the amount of water used and the amount of drainage are limited, it is a low cost and simple method. , Circulating water pH
Can be maintained in a neutral range suitable for nitrifying bacteria and denitrifying bacteria, so that ammonia can be stably removed by biological deodorization.

The present invention focuses on the following points regarding the treatment of ammonia by the biological deodorization method of the circulatory nitrification and denitrification method, and is widely used industrially for the purpose of stabilizing the pH instead of simply using biologically treated water for the circulating water. The pH buffer solution is used.
(1) In the circulatory nitrification denitrification treatment, if the reaction is carried out without excess or deficiency, pH adjustment is essentially unnecessary. Therefore, when the ammonia concentration is high and the fluctuation is large, it is only necessary to prevent even a temporary pH fluctuation caused by the accumulation of ammonia or nitric acid.
(2) In the biological deodorization method, water is not an object to be treated, but a mere medium for proceeding with biological nitrification / denitrification reaction. Since no change occurs, it can be reused any number of times without draining outside the system.

Treatment of ammonia-containing odor gas by the biological deodorization method of circulatory nitrification and denitrification method
The process proceeds according to the following formulas (3) to (5).
NH ₃ + H ₂ O → NH ₄ ⁺ + OH ⁻ (3)
NH ₄ ⁺ + 2O ₂ → NO ₃ ⁻ + 2H ⁺ + H ₂ O (4)
2NO ₃ ⁻ + 5H ₂ → N ₂ + 2OH ⁻ + 4H ₂ O (5)
In the treatment, the accumulation of ammonia in the formula (3) and the denitrification reaction in the formula (5) increase the hydroxide ion concentration and increase the pH, whereas the nitrification reaction in the formula (4) The hydrogen ion concentration increases and the pH decreases. When the reactions of formulas (3) to (5) are completed and ammonia is converted to nitrogen gas, the pH increase and decrease are offset, and the pH becomes constant.

However, if the balance of these reactions is lost due to fluctuations in the ammonia load,
Variations in pH occur due to the accumulation of ammonia and nitric acid. Outside the appropriate pH range, not only the ability to absorb and remove ammonia from odors is lowered, but also biological nitrification denitrification reaction is inhibited, so once out of the appropriate pH range, the pH is adjusted thereafter. But the biological response does not recover immediately. Therefore, the ammonia removal performance decreases over a long period of time.
In the present invention, as described above, since the pH buffer solution is used in the circulating water of the biological deodorization apparatus for treating the ammonia-containing odor, even if ammonia or nitrate ions temporarily accumulate, the hydroxide ion concentration Since the pH buffering action that maintains the hydrogen ion concentration constant immediately works, the pH is kept constant. The pH buffering action when a phosphate buffer is used as the pH buffering solution is expressed by equations (6) and (7).
_{^{HPO 4 2- + H + → H}} 2 PO 4 - (6)
_{^{H 2 PO 4 - + OH -}} → HPO 4 2- + H 2 O (7)

Therefore, even if ammonia or nitrate ions temporarily accumulate, there is no inhibition of the nitrification and denitrification reaction due to pH fluctuations. Therefore, the temporarily accumulated ammonia and nitric acid will eventually be converted to nitrogen gas as processing continues. Converted. In addition, when an alkali agent or acid agent is used, the pH adjustment effect is transient, whereas when a pH buffer solution is used, the pH adjustment effect is that ammonia and nitrate ions are converted to nitrogen gas. By doing so, the pH buffering capacity is restored. As described above, in the biological deodorization method, water is not a treatment target, but is a medium for causing a microbial reaction to proceed.
Recycling can be done by reducing the amount discharged outside the system as much as possible. Therefore, not only can the amount of water used be reduced, the amount of drainage can be reduced or no drainage can be achieved,
The amount of a drug (hereinafter referred to as a pH buffering agent) to be added to make a buffer solution may be small. The main loss of the pH buffering agent in the case of the non-drainage system is only the part that is discharged as a mist accompanying the processing gas and the part that is consumed as a nutrient source for microorganisms.

The pH buffering agent may be appropriately supplied in an amount calculated for these losses, but the pH of the circulating water can be measured and the supply amount of the pH buffering agent can be controlled by the measured value. The method of pH control injection can be performed by directly injecting a concentrated solution of pH buffer. Further, since the pH buffer is generally composed of two components, an alkaline component and an acidic component, these components may be separately injected into the circulating water to control the pH. In addition, it is suitable to control the pH of circulating water in the range of 6.0-7.5.

Examples of the pH buffer solution used in the present invention include a phosphate buffer solution and a carbonate buffer solution.
Those that do not affect biological nitrification and denitrification are good. As a combination of pH buffering agents in this case, those in which the pH of the buffer solution itself is neutral are good. For example, potassium dihydrogen phosphate + dipotassium hydrogen phosphate, sodium dihydrogen phosphate + disodium hydrogen phosphate , Tripotassium phosphate + phosphate, trisodium phosphate + phosphate,
Tripotassium phosphate + sulfuric acid, trisodium phosphate + sulfuric acid, tripotassium phosphate + hydrochloric acid, trisodium phosphate + hydrochloric acid, potassium dihydrogen phosphate + sulfuric acid, sodium dihydrogen phosphate + sulfuric acid, potassium dihydrogen phosphate + Potassium hydroxide, sodium dihydrogen phosphate + sodium hydroxide, phosphoric acid + dipotassium hydrogen phosphate, phosphoric acid + disodium hydrogen phosphate, phosphoric acid + potassium dihydrogen phosphate, phosphoric acid + sodium dihydrogen phosphate, Combinations of potassium carbonate + sulfuric acid, potassium carbonate + hydrochloric acid, sodium carbonate + sulfuric acid, sodium carbonate + hydrochloric acid, potassium hydrogen carbonate + sulfuric acid, potassium hydrogen carbonate + hydrochloric acid, sodium hydrogen carbonate + sulfuric acid, sodium hydrogen carbonate + hydrochloric acid, etc. Use at a neutral mixing ratio. If the odor gas contains carbon dioxide at a high concentration, sodium hydrogen carbonate, potassium hydrogen carbonate, potassium carbonate, sodium carbonate,
An alkaline agent such as potassium hydroxide or sodium hydroxide may be added to absorb the carbon dioxide gas in the odor gas.

In the method of the present invention, the form of the nitrification step into which the odor gas is introduced may be a gas dispersion method using an aeration water tank or the like, but ammonia in the odor is very easily absorbed by water, so a packed tower, a spray tower, A liquid dispersion method such as a venturi scrubber or a cyclonic scrubber may be used.
Moreover, since it is necessary to maintain an oxygen-free state in a denitrification process, it is necessary to make a reaction phase into a submerged type, but the form may be any of an activated sludge system, a fluidized bed system, and a fixed bed system. Further, when the nitrification step is a liquid dispersion type, the circulating water tank may be used also as the denitrification tank. In order to increase the denitrification reaction rate, a hydrogen donor may be appropriately supplied to the denitrification step. From the viewpoint of reducing the amount of water used and the amount of wastewater,
It is preferable to use a decomposition product that does not remain in the circulating water. Examples of such a hydrogen donor include organic compounds such as methanol, ethanol, acetic acid, acetone and glucose, hydrogen gas, and the like.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of an apparatus used in the deodorization method of the present invention.
The nitrification / deodorization tower 3, which is a nitrification process, includes a packed bed 7 filled with a filler for supporting microorganisms, a sprinkling unit 6 for sprinkling water into the packed bed 7, a sprinkling pump 8 for sprinkling water, and circulation. A circulating water tank 5 for storing water is provided. The denitrification tank 4 in the denitrification process includes a packed bed 10 filled with a filler for supporting microorganisms and a treatment liquid circulation pump 9 that returns the denitrification treatment liquid to the nitrification process. Note that a hydrogen donor is supplied from the hydrogen donor reservoir 12 by the hydrogen donor supply pump 13 to the nitrification liquid supplied to the denitrification step.
Seed sludge such as activated sludge containing microorganisms is added to the circulating water tank 5, and the circulating water pump 8 circulates water from the sprinkling unit 6 to the packed bed 7, and the treated liquid circulating pump 9 applies seed sludge to the packed bed 10. Supply. At the same time, odor gas 1 containing ammonia is nitrified and deodorized tower 3
And deodorized to remove ammonia. In addition, even if ammonia and nitrate nitrogen accumulate in circulating water, so that pH can be maintained at 6.0-7.5,
A pH buffer is added to the circulating water.

FIG. 2 is a schematic configuration diagram showing another example of an apparatus used in the deodorization method of the present invention.
The nitrification / deodorization tower 3, which is a nitrification process, includes a packed bed 7 filled with a filler for supporting microorganisms, a sprinkling unit 6 for sprinkling water into the packed bed 7, a sprinkling pump 8 for sprinkling water, and circulation. A circulating water tank 5 for storing water is provided. The denitrification tank 4 in the denitrification step includes a packed bed 10 filled with a filler for supporting microorganisms, and a treatment liquid circulation pump 9 for returning the denitrification treatment liquid to the nitrification step. Note that a hydrogen donor is supplied from the hydrogen donor reservoir 12 by the hydrogen donor supply pump 13 to the nitrification liquid supplied to the denitrification step.
Seed sludge such as activated sludge containing microorganisms is added to the circulating water tank 5, and the circulating water pump 8 circulates water from the sprinkling unit 6 to the packed bed 7, and the treated liquid circulating pump 9 applies seed sludge to the packed bed 10. Supply. At the same time, the odor gas 1 containing ammonia is introduced into the nitrification deodorization tower 3 to perform deodorization for removing ammonia. In addition, the pH of circulating water is pH-controlled injection of the pH buffering agent 14 with the pH buffering agent supply pump 15 based on the signal 17 from the pH meter 16 installed in the circulating water tank.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
Example 1
An apparatus having the structure shown in FIG. 1 was used.
Ammonia-containing odorous gas generated from composting facilities was targeted. In addition, the ammonia concentration in odor gas fluctuates violently by being affected by composting conditions, composting process and the like.
The experimental conditions are as follows.

Ammonia concentration in odor gas: 5 to 500 ppm
Odor gas temperature: 30-40 ° C
Processed air volume: 40 m ³ / min
Superficial velocity of nitrification process: 200h ^-1
Sprinkling amount in the nitrification process (sprinkling amount per unit processing gas amount): 3 liters / m ³
Circulating water tank capacity for nitrification process: 10m ³
Replenishment water volume: 50 liters / day Nitrification / denitrogenation circulation water volume: 2 liters / minute Denitrification tank packed bed capacity: 10 m ³
Type of hydrogen donor: Methanol Type of circulating water: Phosphate buffer solution

Method of injecting chemicals to make circulating water into pH buffer solution: Fixed injection After charging 1m ³ of nitrification tank sludge with a concentration of about 1.2g / L into the circulating water tank, the odorous gas is sprinkled while continuously circulating the circulating water. Aerated continuously. Immediately after the start of aeration, the ammonia removal rate was 90% or more, and showed a stable removal rate thereafter. In addition, p per day
The amount of H buffer added was 0.68 kg of potassium dihydrogen phosphate and 0.88 kg of dipotassium hydrogen phosphate. Table 1 shows the ammonia removal performance from the start of operation to about 1 month.

Example 2
An experimental apparatus having the structure shown in FIG. 2 was used. The operating conditions are not to inject the pH buffering agent into the circulating water, but to adjust the pH of the circulating water to 6.0 to 7.5.
Example 1 is the same as Example 1 except that control injection is performed.
After adding 1 m ³ of nitrification tank sludge having a concentration of about 1.2 g / L to the circulating water tank, the odor gas was continuously vented while continuously circulating the circulating water. Immediately after the start of aeration, the ammonia removal rate was 90% or more, and showed a stable removal rate thereafter. In addition, p per day
The amount of H buffer added was 0.27 kg of potassium dihydrogen phosphate and 0.35 kg of dipotassium hydrogen phosphate. Table 1 shows the ammonia removal performance from the start of operation to about 1 month.

Comparative Example 1
An apparatus having the same structure as in Example 1 was used. The operating conditions are the same as in Example 1 except that no pH buffer was injected into the circulating water.
After adding 1 m ³ of nitrification tank sludge having a concentration of about 1.2 g / L to the circulating water tank, the odor gas was continuously vented while continuously circulating the circulating water. Immediately after the start of aeration, the ammonia removal rate was 90% or more, but the circulating water pH fluctuated due to fluctuations in the ammonia load, and the ammonia removal performance was unstable. Table 1 shows the ammonia removal performance from the start of operation to about 1 month.

Comparative Example 2
An apparatus having the same structure as in Example 2 was used. Operating conditions include control of circulating water pH, pH
Example 2 is the same as Example 2 except that a neutralizing agent such as sulfuric acid and an aqueous sodium hydroxide solution was injected instead of a buffering agent.
After adding 1 m ³ of nitrification tank sludge having a concentration of about 1.2 g / L to the circulating water tank, the odor gas was continuously vented while continuously circulating the circulating water. Immediately after the start of aeration, the ammonia removal rate was 90% or more, but the salt concentration in the circulating water gradually increased and the nitrification performance decreased. Furthermore, a scale is generated in the packed bed in the nitrification process, resulting in gas drift,
The ability to absorb and remove ammonia in odors also declined. Table 1 shows the ammonia removal performance from the start of operation to about 1 month.

Example 3
The same procedure as in Example 2 was performed except that sodium bicarbonate and sulfuric acid were used as the pH buffer solution.
Table 1 shows the ammonia removal performance from the start of operation to about 1 month.

The schematic block diagram which shows an example of the apparatus used for the deodorizing method of this invention. The schematic block diagram which shows the other example of the apparatus used for the deodorizing method of this invention.

Explanation of symbols

1: Odor gas, 2: Treatment gas, 3: Nitrification / deodorization tower, 4: Denitrification tank, 5: Circulating water tank, 6: Sprinkling part, 7: Packing bed, 8: Sprinkling pump, 9: Treating liquid circulation pump, 10: packed bed, 11: drainage, 12: hydrogen donor reservoir, 13: hydrogen donor supply pump, 1
4: pH buffer storage tank, 15: pH buffer supply pump, 16: pH meter, 17: Control signal

Claims (5)

  Ammonia-containing odorous gas is brought into contact with circulating water in the nitrification process to absorb the ammonia contained therein, and biologically nitrified by nitrifying bacteria, and the nitrification liquid is guided to the denitrification process. A deodorizing method characterized by using a pH buffer solution for circulating water in a biological deodorization method of circulating nitrification and denitrification, which is returned to the nitrification step as circulating water.   The deodorizing method according to claim 1, wherein the pH buffer solution is a phosphate buffer solution.   The deodorizing method according to claim 1, wherein the pH buffer solution is a carbonate buffer solution.   The deodorizing method according to claim 1, 2 or 3, wherein the pH buffer solution is supplied with a chemical to control the pH of the circulating water to be in the range of 6.0 to 7.5.   A nitrification deodorization tower having a packed bed carrying nitrifying bacteria that pass ammonia-containing odor gas inside, a sprinkling device for sprinkling circulating water in the packed bed, a circulating water tank for storing the circulating water, and the nitrification deodorization In a biological deodorization apparatus having a denitrification tank for denitrating nitrification liquid from a tower and a path for circulating water to circulate between the denitrification tank and the nitrification deodorization tower, a pH buffer solution is used for the circulating water. Deodorizing device characterized by.

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