JP2003033785A - Method and device for denitrification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily regulate to a favorable pH range without using an acid for adjusting a pH level and without strictly performing addition nor controlling of an ammoniacal nitrogen-containing raw water in the presence of nitrite nitrogen by the action of denitrifying microorganisms with ammoniacal nitrogen acting as an electron donor and nitrite nitrogen as an electron acceptor and perform efficient denitrification treatment by efficiently stirring the granules within the denitrification tank and making them flow. SOLUTION: Denitrification is performed by controlling the pH level within a denitrification tank 1 to which carbon dioxide is supplied. Biogas generated as a result of anaerobic living-organism treatment of organic wastes is used as a source of carbon dioxide. By circulating the carbon dioxide or denitrified waste gas the granules within the denitrification tank 1 are stirred and made to flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses raw water containing ammoniacal nitrogen as a source of denitrifying microorganisms using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. The present invention relates to a denitrification method and a denitrification apparatus, and more particularly to a denitrification method and a denitrification apparatus for easily and inexpensively adjusting pH in a denitrification tank in this method.

[0002]

2. Description of the Related Art Ammoniacal nitrogen contained in drainage is one of the causative substances of eutrophication in rivers, lakes and oceans, and it is necessary to remove it efficiently in the drainage treatment process. Generally, ammoniacal nitrogen in wastewater is a nitrification process in which ammoniacal nitrogen is oxidized to nitrite nitrogen by ammonia-oxidizing bacteria, and this nitrite nitrogen is further oxidized to nitrate nitrogen by nitrite-oxidizing bacteria. Nitrogen gas and nitrogen gas are transformed into nitrogen gas by a denitrification process in which organic substances are used as electron donors to decompose them into nitrogen gas by denitrifying bacteria, which are heterotrophic bacteria. Be disassembled.

However, in such a conventional nitrification denitrification method, a large amount of an organic substance such as methanol is required as an electron donor in the denitrification step, and a large amount of oxygen is required in the nitrification step, so that the running cost is high. There is a drawback that.

On the other hand, in recent years, ammoniacal nitrogen and nitrite nitrogen have been utilized by utilizing an autotrophic microorganism (autotrophic bacterium) having ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. A method of denitrifying by reacting with was proposed. This method does not require addition of organic matter, and thus can reduce the cost as compared with the method using heterotrophic denitrifying bacteria. In addition, the yield of autotrophic microorganisms is low, and the amount of sludge generated is significantly smaller than that of heterotrophic microorganisms, so that the amount of excess sludge generated can be suppressed. Furthermore, N observed by the conventional nitrification denitrification method
_It also has the feature that it does not generate ₂ O and can reduce the load on the environment.

This autotrophic denitrifying microorganism (hereinafter referred to as "ANA
Sometimes referred to as "MMOX microorganism". ) Is used in Strous, M, et al., Appl. Microbio
l. Biotechnol., 50, p.589-596 (1998), it is believed that ammoniacal nitrogen and nitrite nitrogen react with each other in the following reaction to decompose into nitrogen gas. .

[0006]

[Chemical 1]

Since hydrogen ions are consumed in this reaction, the pH of the denitrification treatment liquid increases. On the other hand, in order to allow the denitrification reaction to proceed smoothly, there is an optimum pH range, and it is usually necessary to control the pH to be in the range of 6 to 9, preferably pH 6.5 to 7.5. When the pH is not controlled, the pH finally rises to 9.0 or higher, and the denitrification activity remarkably decreases. Inorganic acids such as sulfuric acid and hydrochloric acid are usually used for this pH adjustment. However, these acids (1) need to be purchased as chemicals, which contributes to an increase in operating costs. (2) Since the alkalinity of the liquid inside the denitrification tank is low, strict chemical injection control must be performed. However, there is a drawback that the pH may drop too much. In particular, when the pH is too low, the ANAMMOX microorganism is inactivated and denitrification cannot be performed.

By the way, as an industrially advantageous process capable of recovering methane gas as a valuable resource, anaerobic biological treatment of organic waste is widely performed.

In the anaerobic biological treatment, organic substances are decomposed into methane gas and carbon dioxide gas, and in many cases, a trace amount of hydrogen sulfide gas is also generated. Normally, biogas containing methane gas, carbon dioxide gas, and a trace amount of hydrogen sulfide gas generated by anaerobic biological treatment, after removing hydrogen sulfide gas with a desulfurization device, recovers and reuses methane gas as energy in a boiler or the like. However, heretofore, there have been few examples of effectively utilizing carbon dioxide gas.

[0010] The ANAMMOX microorganism has a problem that it is difficult to maintain a high concentration in the reaction tank because of its low yield and a slow growth rate, which makes it impossible to enhance the treatment efficiency.

On the other hand, in the conventional nitrifying denitrification method utilizing denitrifying bacteria, which are heterotrophic bacteria, raw water is made to flow upward from the lower part of the reaction tank, and sludge is blocked without using a carrier to which the bacteria adhere. Alternatively, a granular sludge bed (sludge blanket) of granule sludge having a particle size of 1 to several mm is formed by granulation, and a high-concentration microorganism is retained in the reaction tank to perform high load treatment USB (Upflow Sludge Bed; Upflow sludge bed) is used for treatment.

Therefore, it is conceivable that the ANAMMOX microorganisms are also subjected to biodenitrification treatment under a high load by the USB method by using the granulated sludge granulated in the upflow reaction tank or the SBR (batch type reaction tank). .

[0013] When the treatment is carried out by the USB method, the granulated sludge that has been granulated tends to settle, so that there is an advantage that the sludge and the treatment liquid can be efficiently separated. In order to make efficient contact with the sludge and to granulate and maintain the granule sludge to have an appropriate particle size, it is necessary to sufficiently stir the granule sludge in the reaction tank and to develop and fluidize it. For this,
A part of the treated water is circulated to the bottom of the reaction tank as circulating water to increase the upward flow velocity in the tank, and in the case of aerobic treatment with activated sludge, the granulated sludge is agitated by air aeration. , Is flowing. However, ANAM
Since MOX microorganisms are inhibited by oxygen, air aeration cannot be applied as in the case of activated sludge.

[0014]

SUMMARY OF THE INVENTION Therefore, the present invention is not limited to pH.
An object of the present invention is to provide a denitrification method and a denitrification device capable of easily adjusting the inside of the ANAMMOX denitrification tank to a suitable pH range without using an acid for adjustment and without performing strict addition control. And

It is another object of the present invention to provide a denitrification method and a denitrification apparatus which can efficiently stir and flow the granules in the denitrification tank to perform an efficient denitrification process.

[0016]

According to the denitrification method of the present invention (Claim 1), raw water containing ammoniacal nitrogen is introduced into a denitrification tank, and the ammoniacal nitrogen in the denitrification tank is used as an electron donor. In the method of denitrifying in the presence of nitrite nitrogen by the action of a denitrifying microorganism having nitrite nitrogen as an electron acceptor, by supplying carbon dioxide gas to the denitrification tank, the pH in the denitrification tank is increased. It is characterized by performing denitrification by controlling.

Since carbon dioxide has a pH buffering ability as described below, by using carbon dioxide as an acid for pH adjustment, it is possible to prevent the pH from falling too low and to easily adjust it to a suitable pH range. You can

[0018]

[Chemical 2]

As the carbon dioxide gas, carbon dioxide gas in the biogas generated in the anaerobic biological treatment of organic waste can be effectively used, whereby the acid as a chemical is unnecessary and the treatment cost is reduced. can do.

Moreover, since hydrogen sulfide contained in biogas can be absorbed in the denitrification tank, the desulfurizing agent used in the desulfurizer can be saved.

In the present invention, it is preferable to adjust the inside of the denitrification tank to pH 6-9.

In the denitrification method of claim 4, the denitrification tank has a biofilm formed on the surface of carrier particles by the denitrification microorganisms, or the denitrification microorganisms are granulated by self-granulation. The carrier particles or the granules in which the denitrifying microorganisms have formed a biofilm on the surface by circulating and supplying a part of the denitrification exhaust gas generated in the denitrification treatment to the bottom of the denitrification tank. This method is characterized by stirring and flowing the granules.With this method, the denitrification exhaust gas is used to effectively stir the carrier particles or granules with the biofilm formed on the surface in the denitrification tank. It can be flowed and expanded.

In the denitrification method of claim 5, the denitrification tank has a biofilm formed on the surface of carrier particles by the denitrification microorganisms, or the denitrification microorganisms are granulated by self-granulation. The carbon dioxide gas is supplied to the bottom of the denitrification tank in excess of the equivalent amount necessary for pH adjustment, so that the denitrifying microorganisms have carrier particles having a biofilm formed on the surface or the granules. It is characterized by stirring and fluidizing the resin, and according to this method,
By using carbon dioxide gas such as biogas, the carrier particles or granules having the biofilm formed on the surface in the denitrification tank can be effectively stirred to flow and spread.

In this case, the LV (vacuum linear velocity) of the gas introduced into the denitrification tank is preferably 0.1 to 10 m / min.

The denitrification apparatus of the present invention uses raw water containing ammoniacal nitrogen as the electron donor with ammoniacal nitrogen,
A denitrification device that denitrifies in the presence of nitrite nitrogen by the action of a denitrification microorganism that uses nitrite nitrogen as an electron acceptor, wherein the denitrification microorganism forms a biofilm on the surface of carrier particles. Or a denitrification tank containing the denitrification microorganisms granulated by self-granulation, and a pH in the denitrification tank
PH measuring means for measuring, carbon dioxide gas supplying means for supplying carbon dioxide gas to the denitrification tank, means for controlling the carbon dioxide gas supply amount of the carbon dioxide gas supplying means based on the measured value of the pH measuring means, It is characterized by comprising means for discharging the denitrification gas generated by the denitrification treatment in the denitrification tank from the denitrification tank, and means for circulating a part of the discharged denitrification exhaust gas to the bottom of the denitrification tank. It is a thing.

With this denitrification device, the pH of the denitrification tank is adjusted with carbon dioxide gas such as biogas, and the denitrification exhaust gas is used to form carrier particles or granules having a biofilm formed on the surface of the denitrification tank. Can be effectively stirred to flow and spread.

In the following, the denitrifying microorganisms according to the present invention in which a biofilm is formed on the surface of carrier particles and those which are granulated by self-granulation may be collectively referred to as "granule". .

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the denitrification method and denitrification apparatus of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of the denitrification apparatus of the present invention.

The denitrification apparatus of FIG. 1 (a) is used as a denitrification tank.
A USB reaction tank 1 in which a granulated sludge bed of ANAMMOX microorganisms is formed is provided inside, and a raw water inflow pipe 2 is connected to the bottom of the reaction tank 1. A gas-liquid solid separation device 3 is provided above the reaction tank 1.
From this, a discharge pipe 4 for treated water and a circulation pipe 5 for returning a part of the treated water to the raw water inflow pipe 2 as circulating water are drawn out.

A gas exhaust pipe 6 for denitrifying exhaust gas is provided at the top of the reaction tank 1, and a blower B ₁ is branched to this gas exhaust pipe 6 to circulate a part of the denitrifying exhaust gas to the bottom of the reaction tank _1. A gas circulation pipe 7 is provided. Further, a CO ₂ gas (or biogas may be used) supply pipe 8 including a blower B ₂ for supplying carbon dioxide (CO ₂ ) for pH adjustment to the bottom of the reaction tank 1 is provided.

In the reaction tank 1, p for measuring the pH of the liquid in the tank is used.
An H meter 9 is provided, and the operation of the blower B ₂ of the CO ₂ gas supply pipe 8 is controlled based on the measurement result of the pH meter 9, and the CO ₂ gas supply amount is adjusted.

In this denitrification device, raw water is introduced from the pipe 2 to the bottom of the USB reaction tank 1 together with the circulating water from the pipe 5. The raw water introduced into the USB reaction tank 1 is ANA
While the granule sludge bed of MMOX microorganisms is rising in the upward flow, biodenitrification treatment is performed by the ANAMMOX microorganisms, and the treated water is discharged from the system through the pipe 4. A part of the treated water is circulated from the pipe 5 to the raw water introduction pipe 2.

In the denitrification apparatus of FIG. 1 (a), CO ₂ gas is introduced from the bottom of the reaction tank 1 through the pipe 8 by the blower B ₂ which is interlocked with the pH meter 9, whereby the liquid inside the tank of the reaction tank 1 is introduced. Is adjusted to a predetermined pH.

In order to effectively promote the denitrification reaction by the ANAMMOX microorganism, the pH in the reaction tank 1 is 6-9.
In particular, it is preferable to control to 6.5 to 7.5.

Further, this CO ₂ gas, the reaction tank 1 upward flow of CO ₂ gas is formed, granules in the bath is stirred, is fluidized by the upward flow, good granulation sludge formed In addition, the efficiency of contact between the sludge and the raw water is improved, and efficient denitrification treatment can be performed.

It is common to promote such sludge granulation.
In order to efficiently contact the sludge with the raw water, the reaction tank
LV (gas superficial velocity) 0.1 to 10 m / min gas in 1
It is desirable to form an upflow of Therefore, the reaction tank 1
CO into_TwoThe introduction of gas is such an upward flow of gas
It is desirable to do so as to form, but for pH adjustment
CO_TwoGas alone may not be sufficient to form an upward flow of gas
If not, secure the gas flow velocity by the following method.
Is desirable. (1) A part of the denitrification exhaust gas is blower B₁Pipe 7
It is then circulated to the bottom of the reaction tank 1 and introduced with this circulating gas.
CO_TwoA predetermined gas flow rate is obtained with the gas. In addition, this
In this case, undissolved CO is contained in the denitrification exhaust gas._TwoGas included
And this CO _TwoGas also contributes to pH adjustment by circulation
The Rukoto. (2) CO_TwoUse a gas that does not contain oxygen such as nitrogen gas.
It is diluted with soot and introduced into the reaction tank 1. This will adjust the pH
The amount of gas required for adjustment is increased, and a predetermined gas flow rate is obtained.
Will be able to. (3) CO_TwoAs an air diffuser that diffuses gas into the reaction tank 1.
A device that discharges large bubbles is used. This gives C
O_TwoThe gas is diffused in the reaction tank 1 as coarse bubbles and
The efficiency of dissolution of carbon dioxide into the water decreases. Therefore, the pH adjustment
Equivalent CO required for adjustment_TwoCO in a gas amount larger than the gas amount
_TwoEven if gas is supplied, the pH can be adjusted and the specified gas
The flow velocity can be obtained.

The above items (1) to (3) may be employed in combination of two or more.

CO_TwoGas has a pH buffering capacity,
Since it does not fluctuate significantly, pH adjustment in the reaction tank 1
CO used for adjustment_TwoWith the amount of gas, it is formed in the reaction tank 1.
Gas flow velocity is rarely too high, but gas flow velocity is high
If too much, CO_TwoDiffuse gas
Use a diffuser tube that discharges fine pores and use CO _Two
It is only necessary to increase the gas dissolution efficiency. Also, acid as a chemical
You may use together.

The denitrification apparatus shown in FIG. 1 (b) is an inner tube (draft tube) 1 which is opened vertically inside as a denitrification tank.
2 is an air lift type reaction tank having a double tube structure arranged coaxially (however, ascending flow similar to an air lift is formed not by air but by biogas or denitrifying exhaust gas) 11. Having an air diffuser 13 at the bottom of the inner cylinder 12,
The inner cylinder 12 is configured to generate an upward flow due to aeration. The inner cylinder 12 holds granule sludge of ANAMMOX microorganisms.

In this denitrification device, the biogas from the anaerobic digester 20 is introduced as CO ₂ gas. The other configurations of the denitrification device of FIG. 1B are the same as those of the denitrification device of FIG. 1A, and members having the same functions are designated by the same reference numerals and the description thereof will be omitted.

In this denitrification apparatus, raw water is introduced from the pipe 2 to the bottom of the reaction tank 11, and the biogas from the air diffuser 13 and an ascending flow of the denitrification exhaust gas circulated as needed due to aeration. It flows in the cylinder 2 in an upward flow, and in the meanwhile, it contacts the granules for denitrification.

A part of the ascending flow in the inner cylinder 12 is discharged from the pipe 4 as treated water, and the remaining part descends in the descending part formed between the inner cylinder 12 and the inner wall of the reaction tank 11, and the reaction tank 11 It is circulated together with the raw water introduced from the bottom of the.

Also in this reaction tank 1, the pH inside the tank is preferably 6 to 6 by the blower B ₂ which works in conjunction with the pH meter 9.
The amount of biogas supplied is adjusted so as to be 9, and more preferably 6.5 to 7.5.

When it is not possible to secure a sufficient LV in the tank with only the upward flow of biogas, the above-mentioned methods (1) to (3), such as circulating a part of the denitrification exhaust gas, are used. ,
The gas flow rate is adjusted so that the LV is 0.1 to 10 m / min.

In the present invention, the raw water to be treated is
Water containing ammoniacal nitrogen and nitrite nitrogen, which may contain organic matter and organic nitrogen, but these must be decomposed in advance to the extent of becoming ammoniacal nitrogen before denitrification treatment. Preferably, when the dissolved oxygen concentration is high, it is preferable to remove the dissolved oxygen as needed. Raw water may contain an inorganic substance. Also,
The raw water may be a mixture of a liquid containing ammoniacal nitrogen and a liquid containing nitrite nitrogen. For example, wastewater containing ammoniacal nitrogen may be subjected to aerobic treatment in the presence of ammonia-oxidizing microorganisms, and a part of the ammoniacal nitrogen, preferably about 1/2 of that partially oxidized to nitrous acid, may be used as raw water. it can. Furthermore, part of the wastewater containing ammoniacal nitrogen is subjected to aerobic treatment in the presence of ammonia-oxidizing microorganisms, the ammoniacal nitrogen is oxidized to nitrous acid, and the mixture with the rest of the wastewater containing ammoniacal nitrogen is used as raw water. Also good.

In general, wastewater containing ammonia nitrogen, organic nitrogen and organic matter such as sewage, night soil, anaerobic digestion and desorption liquid, etc. is often treated, but in this case, these are aerobic or It is preferable to use anaerobic treatment to decompose organic substances, decompose organic nitrogen into ammonia nitrogen, and further perform partial nitrite oxidation or partial nitrite oxidation as raw water.

The ratio of the ammoniacal nitrogen to the nitrite nitrogen in the raw water is preferably 0.5 to 2 and more preferably 1 to 1.5 with respect to 1 mole of the ammoniacal nitrogen. The concentrations of ammoniacal nitrogen and nitrite nitrogen in the raw water are preferably 5 to 1000 mg / L and 5 to 200 mg / L, respectively, but not limited to this if the treated water is circulated and diluted.

The conditions for biological denitrification of the raw water include, for example, the temperature of the liquid in the reaction vessel of 10 to 40 ° C., particularly 20 to 35 ° C., and the dissolved oxygen concentration of 0 to 2.5 mg / L, especially 0 to 0.2 mg / L.
L, BOD concentration 0 to 50 mg / L, especially 0 to 20 mg
/ L, nitrogen load is 0.1-10kg-N / m ³ · da
It is preferable to set y, particularly 1 to 5 kg-N / m ³ · day.

In the case of forming granule sludge, since it takes a long time to form the granules only with the microorganisms, it is desirable to add a substance serving as a nucleus and form a biofilm of the ANAMMOX microorganism around the nucleus. In this case, examples of the core include microbial granules and abiotic carriers.

Examples of microbial granules used as nuclei include anaerobic microbes such as methane bacterium granules and heterotrophic denitrifying bacterium granules. The methane granules are UASB (Upflow Anaerobic S
ludge Blanket; Upflow anaerobic sludge bed method or EG
What is used in the methane fermentation tank in which methane fermentation is performed by the SB (Expanded Granule Sludge Bed) method can be applied. Further, as the heterotrophic denitrification granule, one used in a normal USB type denitrification tank can be applied. These granules can be used as they are or as a crushed product. The autotrophic denitrifying microorganisms are likely to attach to such microbial granules, shortening the time required for granule formation. It is also more economical than using abiotic materials as the core.

As the abiotic material used as the core, for example, activated carbon, zeolite, silica sand, diatomaceous earth, calcined ceramics, ion exchange resin, etc., preferably activated carbon, zeolite, etc., having a particle size of 50 to 200 μm,
It is preferably 50 to 100 μm, and the average specific gravity is 1.01 to 1.01.
2.5, preferably 1.1 to 2.0 carriers can be mentioned.

ANAMMOX formed in this way
The microbial granule sludge has an average particle size of 0.25 to 3
mm, preferably 0.25 to 2 mm, more preferably about 0.25 to 1.5 mm and having an average specific gravity of 1.01 to 2.
It is desirable that it is 5, preferably 1.1 to 2.0.
Since the smaller the particle size of the granule, the larger the specific surface area, it is preferable from the viewpoint of maintaining a high sludge concentration and efficiently performing the denitrification treatment.

The denitrification apparatus shown in FIGS. 1 (a) and 1 (b) is an example of the embodiment of the present invention, and is not limited to the illustrated one as long as it does not exceed the gist of the present invention. Absent.
The type of denitrification tank is not limited to the USB reaction tank shown in FIG. 1 (a) or the air lift type reaction tank shown in FIG. 1 (b), and other types such as fluidized bed type, floating sludge type, fixed bed type, etc. Various denitrification tanks can be used. In the case of a floating sludge type denitrification tank, a solid-liquid separation means such as a settling tank for solid-liquid separating the denitrification tank effluent is provided.

[0055]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1 Water containing 4.3 mmol (about 62 mg-N / L) of ammonia and 5.7 mmol of nitrous acid was used as raw water.
A denitrification treatment was performed by the denitrification device shown in (a).

The reaction tank has an inner diameter of 20 cm and a height of 400 cm.
The capacity was 126 L, and 1500 g-VSS of granule sludge of ANAMMOX microorganism was put therein.

Raw water was passed through the reaction tank by a pump at a flow rate of 126 L / hr to obtain 3000 L / day of treated water,
The rest of the treated water was circulated to the raw water supply side.

The denitrification exhaust gas containing undissolved carbon dioxide was not circulated, but the entire amount was discharged. Also, in the reaction tank,
Carbon dioxide gas was blown in such that the pH in the tank became 6.8 to 7.2. The carbon dioxide gas is blown into the reaction tank so that LV
An upflow of gas of 0.2 m / min was formed.

As a result, during continuous operation for 2 months, the pH in the reaction tank was limited to the range of 6.8 to 7.2, and good treated water with an ammonia concentration of 5 mg-N / L was stably obtained. I was able to.

Comparative Example 1 When a continuous operation was carried out in the same manner as in Example 1 except that dilute sulfuric acid was used instead of carbon dioxide gas, the same treatment performance as in Example 1 was obtained for one and a half months from the start of the operation. Although it could be obtained, immediately after that, an accident occurred in which dilute sulfuric acid was excessively added, and the pH in the reaction tank dropped to 4. After that, the pH was neutralized and the passage of raw water was restarted, but ammonia could not be removed.

Example 2 The inner cylinder (draft tube) was removed from the denitrification apparatus shown in FIG. 1 (b), and 4.3 mmol (about 60 mg-N /
The denitrification treatment was performed using water containing L) of ammonia and 5.7 mmol of nitrous acid as raw water.

The reaction tank has an inner diameter of 20 cm and a height of 400 cm.
The capacity was 126 L, and 1500 g-VSS of granule sludge of ANAMMOX microorganism was put therein.

The raw water was passed through the reaction tank with a pump at a flow rate of 126 L / hr to obtain 3000 L / day of treated water.

As the carbon dioxide gas source, biogas (60% methane gas, 3% methane gas collected from an anaerobic digester of sewage sludge) was used.
(9.8% carbon dioxide gas, 0.2% hydrogen sulfide gas) was supplied. For aeration of biogas, a diffuser plate that generates fine bubbles having a particle size of 4 to 5 mm was used. The denitrification exhaust gas was not circulated.

In order to control the pH in the reaction tank between 6.8 and 7.2, it was necessary to inject biogas intermittently. However, when the flow rate of biogas was linked to the output of the pH meter so that the needle valve could control it, continuous aeration of biogas (flow rate continuously changes according to the output of the pH meter) was possible. . Therefore,
When the diffuser plate was replaced with a perforated tube forming coarse bubbles of about 6 to 8 mm, the dissolution efficiency of carbon dioxide gas decreased. As a result, although the flow rate of biogas was about 6 to 10 L / min, which was higher than before, continuous aeration was possible without significantly changing the flow rate itself. At this time, an upward flow of gas of 0.2 to 0.3 m / min was formed in the reaction tank.

After the operation for about 6 months, the formation of fine self-granulated sludge was observed in the reaction tank, and the particle size gradually increased. After about one year, the grain size growth stopped at 1-2 mm.

The ammonia concentration of the treated water is 5 mg-N / L
Thus, good treated water was obtained. In addition, hydrogen sulfide was hardly detected in the exhaust gas.

Example 3 4.3 mmol (about 60 mg-N / L) was obtained by the denitrification apparatus of FIG. 1 (b) in which a draft tube was placed in the reaction tank.
The denitrification treatment was performed by using the water containing ammonia and 5.7 mmol of nitrous acid as raw water.

The reaction vessel has an inner diameter of 20 cm and a height of 400 cm.
ANAM with a capacity of 126 L and not granulated inside
Granule sludge of MOX microorganism was added at 500 g-VSS.

The raw water was passed through the reaction tank by a pump at a flow rate of 126 L / hr to obtain 3000 L / day of treated water.

As the carbon dioxide gas source, biogas (60% methane gas, 3%, sewage sludge anaerobic digester) was used.
(9.8% carbon dioxide gas, 0.2% hydrogen sulfide gas) was supplied. For aeration of biogas, a perforated tube that generates coarse bubbles of about 4 to 5 mm was used. The denitrification exhaust gas was circulated.

As a result, the flow rate of biogas is 6 to 10 L.
Per minute, and a gas flow rate of 1 to 10 m / min was formed in the reaction tank. After 2 months from the start of operation, the particle size was 0.
Good granulated sludge granulated to 5 to 1.5 mm is formed,
Good treated water having an ammonia concentration of 10 mg / L or less was obtained. Almost no hydrogen sulfide was detected in the exhaust gas.

[0074]

As described above in detail, according to the denitrification method and denitrification apparatus of the present invention, the inside of the denitrification tank can be easily adjusted by adjusting the pH using carbon dioxide gas having a pH buffering ability. The pH range can be adjusted. Further, by effectively utilizing the biogas generated in the anaerobic biological treatment of the organic waste as the carbon dioxide gas, the acid as a chemical is not required and the treatment cost can be reduced.

Further, according to the present invention, the circulating gas of the carbon dioxide gas or the denitrifying exhaust gas effectively stirs and causes the granules in the denitrifying tank to flow and develop, thereby promoting granulation of the granules. Therefore, efficient denitrification treatment can be performed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a denitrification device of the present invention.

[Explanation of symbols]

1 USB reaction tank 3 Gas-liquid separation device 9 pH meter 11 Reaction tank 12 inner cylinder 13 Air diffuser 20 Anaerobic digester

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 3/10 C02F 3/10 A 3/28 3/28 Z (72) Inventor Rei Imagi Nishi Nishishinjuku, Shinjuku-ku, Tokyo 3rd-4th Kurita Industry Co., Ltd. F-term (reference) 4D003 AA14 BA02 CA02 CA08 DA07 DA11 DA15 DA29 EA01 EA23 EA24 EA25 EA30 FA02 FA05 FA10 4D040 AA04 AA12 AA34 AA54 AA58 AA61 AA62 BB04 BB07BB56 BB13 BB07BB56 BB13 BB07BB56 BB13 BB07BB56 BB13 BB07BB56 BB13BB42

Claims (7)

[Claims] 1. Raw water containing ammoniacal nitrogen is introduced into a denitrification tank, and by the action of a denitrifying microorganism in the denitrification tank, the ammoniacal nitrogen serves as an electron donor and the nitrite nitrogen serves as an electron acceptor. A method for denitrifying in the presence of nitrite nitrogen, comprising supplying carbon dioxide gas to the denitrification tank to control the pH in the denitrification tank to perform denitrification. 2. The carbon dioxide gas supplied to the denitrification tank is at least partly biogas containing carbon dioxide gas generated by anaerobic biological treatment of organic waste. Denitrification method. 3. The denitrification method according to claim 1, wherein the pH in the denitrification tank is controlled to 6 to 9. 4. The denitrification tank contains therein the denitrification microorganisms having a biofilm formed on the surface of carrier particles, or the denitrification microorganisms granulated by self-granulation. By circulating and supplying a part of the denitrification exhaust gas generated by the denitrification treatment to the bottom of the denitrification tank, the denitrification microorganisms can stir and flow the carrier particles having the biofilm formed on the surface or the granules. The denitrification method according to any one of claims 1 to 3, which is characterized. 5. The denitrification tank contains therein the denitrification microorganisms having a biofilm formed on the surface of carrier particles, or the denitrification microorganisms granulated by self-granulation. By supplying carbon dioxide gas to the bottom of the denitrification tank in excess of the equivalent amount necessary for pH adjustment, the denitrification microorganisms can stir the carrier particles having the biofilm formed on the surface or the granules to flow. Claim 1 to 3 characterized by the above-mentioned.
The denitrification method according to any one of 1. 6. The denitrification method according to claim 4, wherein the LV of the gas introduced into the denitrification tank is 0.1 to 10 m / min. 7. Denitrifying raw water containing ammoniacal nitrogen in the presence of nitrite nitrogen by the action of a denitrifying microorganism using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. A denitrification tank for holding a denitrification microorganism in which a biofilm is formed on the surface of carrier particles or a denitrification microorganism granulated by self-granulation, PH measuring means for measuring the pH inside, carbon dioxide gas supplying means for supplying carbon dioxide gas to the denitrification tank, and means for controlling the carbon dioxide gas supply amount of the carbon dioxide gas supplying means based on the measured value of the pH measuring means And a means for discharging the denitrification gas generated by the denitrification treatment in the denitrification tank from the denitrification tank, and a means for circulating a part of the discharged denitrification exhaust gas to the bottom of the denitrification tank. Characteristic denitrification equipment.