JP2003024988A - Biological denitrification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stable and efficient denitrification treatment forming dense granular sludge having high strength and good sedimentation properties in a method for performing the biological denitrification of raw water containing ammonia nitrogen and nitrous nitrogen by passing the raw water through a reaction tank, which holds granular sludge containing autotrophic denitrifying microorganisms using ammonia nitrogen as an electron doner and nitrous nitrogen as an electron acceptor, as an ascending flow. SOLUTION: The raw water is passed through the reaction tank 1 while adding an organic flocculant to the reaction tank 1 to be biologically denitrified. The granular sludge in the reaction tank 1 is dawn out to be crushed before returned to the reaction tank 1.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an autotrophic denitrifying microorganism in which raw water containing ammoniacal nitrogen and nitrite nitrogen is used as an electron donor for ammoniacal nitrogen and an electron acceptor for nitrite nitrogen. The present invention relates to a method for biological denitrification by passing an upward flow into a reaction tank that holds granule sludge containing water, and in particular, in this method, a granular sludge that is dense, has high strength, and has good sedimentation properties is formed and stabilized. And a method for performing efficient denitrification treatment.

[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. Biotecnol., 50, p.589-596 (1998), it is considered that ammonia nitrogen and nitrite nitrogen react with each other in the following reaction to decompose into nitrogen gas. .

[0006]

[Chemical 1]

However, in the above-mentioned biological denitrification method, since the yield of the ANAMMOX microorganisms involved in the reaction is low, the growth rate is slow and it is difficult to maintain a high concentration in the reaction tank, and therefore the treatment efficiency is high. There was a problem that could not be raised.

By the way, in the conventional nitrifying denitrification method utilizing denitrifying bacteria, which are heterotrophic bacteria, raw water is allowed to flow upward from the lower part of the reaction tank without using an adherent carrier for the bacteria.
USB that performs high load treatment by blocking or granulating sludge to form a sludge bed (sludge blanket) of granule sludge with a particle size of 1 to several mm and holding high concentration of microorganisms in the reaction tank ( Upflow Sludge Bed; Upstream Sludge Bed is used for treatment.

[0009]

SUMMARY OF THE INVENTION Therefore, ANAMMO
Regarding X microorganisms, it is possible to perform biodenitrification treatment with a high load by the USB method using granulated sludge granulated in an upflow reactor or SBR (batch reactor).
The ANAMMOX microorganism is autotrophic, and therefore has a low growth rate and a small amount of mucilage (extracellular polymer), and the strength of granule sludge formed due to this is weak and sludge caused by gas generation. Granule sludge is likely to collapse due to agitation in the floor or disturbance due to rising flow of raw water. Therefore, there is a drawback that the granule sludge cannot be stably held in the reaction tank.

In order to increase the strength of the granule sludge of the ANAMMOX microorganism, a small amount of a BOD source may be added to allow other heterotrophic microorganisms to adhere to the granule sludge to grow, but this method is used.
It is not a preferable method because it may deteriorate the growth environment of the microorganism and cause a decrease in the activity of the ANAMMOX microorganism.

Further, in the biological denitrification process using the granule sludge, as the particle size of the granule sludge increases, the granule sludge in which the microorganisms inside are deactivated and cavities are generated is a gas generated by the reaction. Therefore, there is also a problem in that, in a remarkable case, it flows out from the reaction tank.

The present invention solves the above-mentioned conventional problems, and in carrying out biological denitrification treatment while holding granule sludge of ANAMMOX microorganisms in a reaction tank, it is dense and high in strength.
An object of the present invention is to provide a biological denitrification method capable of forming a granular sludge having a good sedimentation property and performing stable and efficient treatment.

[0013]

The method for biological denitrification of the present invention uses raw water containing ammoniacal nitrogen and nitrite nitrogen as an electron donor for ammoniacal nitrogen and as an electron acceptor for nitrite nitrogen. In the method for biological denitrification by passing the granulated sludge containing autotrophic denitrifying microorganisms in an upward flow into a reaction tank, raw water is added to the reaction tank while adding an organic flocculant to the reaction tank. It is characterized by passing liquid.

As described above, the ANOMMOX microorganism, which is an autotrophic denitrifying microorganism, has a low growth rate and produces a small amount of mucilage. By adding an agent (hereinafter referred to as "polymer"), the adhesion action between microorganisms is strengthened and a strong microbial membrane is formed, which makes it possible to form a strong and dense granule sludge. .

As the polymer to be added, a cationic water-soluble polymer having low air bubble adhesion is preferable from the viewpoint of the settling property of granule sludge.

The granule sludge formed by adding such a polymer is strong and dense and therefore has excellent settling property. However, as described above, the increase in particle size of the granule sludge causes loss of internal microorganisms. To create a cavity,
This causes a problem that the specific gravity of the granule sludge becomes small and the granule sludge floats up.

Therefore, in the present invention, it is preferable that the granule sludge is drawn out from the reaction tank, crushed and then returned to the reaction tank. The crushed pieces of granule sludge returned to the reaction tank become the core of the granule sludge, and again form a strong granule sludge. Even in this case,
If the strength of the granule sludge is weak, the granule sludge will not be crushed into pieces by crushing to form the core of the granule sludge, and it easily flows out together with the treated water. Granule sludge with moderate elasticity is formed, so even if it is crushed it will not be shattered into pieces, and it will be possible to obtain a crushed product that can be stably held in the reaction tank as the core of granule sludge. You can

[0018]

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

FIG. 1 is a system diagram showing an example of a USB reaction tank suitable for carrying out the biological denitrification method of the present invention.

This USB reaction tank 1 has an ANAMM inside.
A granular sludge bed 2 of OX microorganisms is formed, and a raw water inflow pipe 3 is connected to the bottom. A gas-liquid solid separation device 4 is provided above the reaction tank 1.
From this, a discharge pipe 5 of treated water and a circulation pipe 6 for returning a part of the treated water to the raw water inflow pipe 2 as circulating water are drawn out. In addition, the raw water inflow pipe 3 is provided with a polymer injection pipe 7
Are connected.

The raw water together with the circulating water from the pipe 6 is the pipe 3
The polymer is added from the pipe 7 while being introduced from the bottom to the USB reaction tank 1. The raw water introduced into the USB reaction tank 1 is biologically denitrified by the ANAMMOX microorganisms while rising in the upward flow of the granule sludge bed 2 of the ANAMMOX microorganisms, and the treated water is discharged from the system through the pipe 5. . Further, a part of the treated water is circulated from the pipe 6 to the raw water introduction pipe 3.

The polymer to be added is an anionic polymer,
Cationic or nonionic synthetic or natural polymer can be used, but preferably has a molecular weight of 10 ³
A polymer having a relatively low molecular weight of about 10 to 10 ⁶ is preferable, and in particular, a homopolymer of a cationic monomer such as dimethylaminoethyl acrylate or dimethylaminoethyl methacrylate having a cation site with low air bubble adhesion, and a cationic monomer thereof and acrylamide. Preferred are cationic water-soluble polymers such as copolymers with methacrylamide, polyvinylamidine, and chitosan.

If the amount of the polymer added is small, the effect of improving the strength of the granule sludge by the addition cannot be sufficiently obtained, and if it is too large, the granule sludge adheres to each other to form agglomerates, which makes it easy to capture gas. , Because the floatability is enhanced,
It is preferable to add it at a concentration of about 0.1 to 5 mg / L with respect to the amount of water flowing into the USB reaction tank 1 (total amount of raw water and circulating water).

The polymer may be added continuously or intermittently. In the case of intermittent addition, the frequency of addition is preferably about once every 10 to 100 minutes.

Further, in the present invention, preferably, the granular sludge is pulled out from the reaction tank, crushed and returned to the reaction tank to prevent the floating of the granular sludge. As the crushing means, any device capable of mechanically crushing the granulated sludge may be used, and a cutter pump with a rotary blade, a homogenizer, a grinder pump or the like can be used.

The withdrawal of granule sludge for crushing may be carried out continuously or intermittently. Further, the amount of withdrawal and the degree of crushing may be any as long as they can prevent the floating of the granule sludge, and are appropriately determined depending on the treatment conditions, raw water condition, specifications of the reaction tank, and the like. It is also effective to capture and crush the floating granules near the water surface.

Generally, the particle size of the granule sludge constituting the granule sludge bed in the reaction tank is 0.25 to 2.
It is preferable to extract and smash the granulated sludge as necessary so that it becomes 0 mm.

The granule sludge crushing means may be provided in the reaction tank to directly crush the sludge in the granule sludge bed, but the sludge may be pulled out from the reaction tank and crushed and then returned. .

In the biological denitrification method of the present invention, the raw water to be treated is water containing ammoniacal nitrogen and nitrite nitrogen, and may contain organic matter and organic nitrogen. Prior to the denitrification treatment, it is preferable to decompose it to the extent that it becomes ammoniacal nitrogen, and if the dissolved oxygen concentration is high, it is preferable to remove the dissolved oxygen as necessary. Raw water may contain an inorganic substance. Further, 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 can be subjected to aerobic treatment in the presence of ammonia-oxidizing microorganisms, and a part of the ammoniacal nitrogen, preferably one-half of which can be partially oxidized to nitrous acid, can be used as raw water. . Furthermore, a part of the wastewater containing ammoniacal nitrogen is subjected to aerobic treatment in the presence of ammonia-oxidizing microorganisms to oxidize the ammoniacal nitrogen to nitrous acid,
The raw water may be a mixture with the rest of the wastewater containing ammoniacal nitrogen.

In general, wastewater containing ammonia nitrogen, organic nitrogen and organic matter such as sewage, night soil, anaerobic nitrifying and desorbing 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 ammoniacal nitrogen in a molar ratio. 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 the biological denitrification of the raw water include, for example, the temperature of the liquid in the reaction vessel is 10 to 40 ° C., especially 20 to 35 ° C., and the pH.
5-9, especially 6-8, dissolved oxygen concentration 0-2.5 mg
/ L, especially 0-0.2 mg / L, BOD concentration 0-50
mg / L, especially 0-20 mg / L, nitrogen load 0.1-
10 kg-N / m ³ · day, especially 1 to 5 kg-N / m
^It is preferably in the range of ³ · day.

In the case of forming granule sludge, since it takes a long time to form the granules only by 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 the microbial granules used as nuclei include anaerobic microorganisms such as methane bacteria granules and heterotrophic denitrifying bacteria 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 biological denitrification method of the present invention is, specifically, a UASB system or an EGSB system as seen in anaerobic treatment, in which granule sludge of ANAMMOX microorganisms in a reaction vessel is developed in an upward flow of raw water. It is preferable to form the granule sludge bed by using the above method because the contact efficiency between the raw water and the granule sludge can be increased. It should be noted that part of the treated water is returned to the raw water introduction side of the reaction tank as circulating water.

In this case, in the case of the UASB system, the circulating water amount is 0.5 to 10 times the raw water amount, and the upward flow velocity in the reaction tank (the total flow velocity of the raw water and the circulating water) is 0.5 to 2 m / hr
Is preferred. In the case of the EGSB method, the circulating water amount is 0.5 to 20 times the raw water amount, the upward flow velocity in the reaction tank (the total flow velocity of the raw water and the circulating water) is 2 to 15 m / hr, and the granulated sludge bed is used. Deploy and let through.

In the present invention, when the raw water is passed through the reaction tank holding the granule sludge of the ANAMMOX microorganism in the upward flow to perform the biological denitrification treatment, the raw water is added to the reaction tank while the polymer is added to the reaction tank. To pass through
The polymer can be injected from an injection pipe different from the raw water, but in order to uniformly add it to the reaction tank together with the raw water, it is preferable to inject the polymer into the introduction pipe of the raw water as shown in FIG. .

In the USB reaction tank 1 of FIG. 1, the polymer injection pipe may be provided in the circulating water circulating pipe 6, and the raw water introducing pipe 3 upstream of the connecting position of the circulating pipe 6 may be provided. It may be provided.

[0041]

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

Example 1 In the USB reaction tank shown in FIG. 1, ammonia and nitrous acid were added to treated sewage water to obtain NH ₄ —N concentration of 300 mg / L, N.
O ₂ -N was adjusted to a concentration 300 mg / L, 7.0 to a pH
The synthetic wastewater adjusted to 7.5 was used as raw water, and a cationic water-soluble polymer was added while passing through.

The USB reaction tank has an inner diameter of 10 cm and a height of about 12
It is a 0 cm PVC column (capacity: about 7.5 L), and inside is about 4 L of granulated sludge conditioned from denitrification sludge having an average particle size of 1.2 mm and a sludge concentration of 30,000 mg / L (ANAMMOX microorganism). (About 120 g-VSS). The reaction tank was installed in a thermostatic chamber controlled at 30 ° C.

Raw water is 2.5 L / hr (60 L / day)
The water was passed through the reaction tank with a pump.

Of the treated water, about 6.0 L / hr (about 100 L
(mL / min: 2.4 times the circulation amount of raw water) was circulated as circulating water to the bottom of the reaction tank by a pump. The upward flow velocity in the reaction tank was 1.1 m / hr.

The nitrogen load in the reaction tank at this time is N
2.4 kg-N / m ³ / day, N as H ₄ -N load
4.8 kg-N / m as the total load including O ₂ -N
It was ³ / day.

As the cationic water-soluble polymer, a 1000 ppm aqueous solution of a polyacrylamide cationic polymer having a molecular weight of about 500,000 was used and added to the raw water so that the polymer concentration would be 5 mg / L. This added amount corresponds to about 1.5 mg / L with respect to the total of the raw water and the circulating water.

The amount of polymer added was 300 as the amount of aqueous solution.
Since it is a small amount of mL / day, it is not 1
Intermittent addition (12.5 mL / hr) by operating the chemical injection pump with a timer at a frequency of 24 times a day (once per hour)
did.

Immediately after the passage of the liquid, 1 month (30 days) and 2 months (60 days), the strength of the granule sludge in the reaction tank was evaluated by the following method, and the results are shown in Table 1. . [Evaluation method] Granule sludge was collected from the reaction tank and 1
An L graduated cylinder was filled with a static volume of 100 mL.
Add pure water to the level of 500 mL and add nitrogen gas to 30 m
L / min was fed into the graduated cylinder through a ceramic diffuser to stir the inside of the graduated cylinder, and the existence form of sludge after 24 hours was evaluated. Grading is 0.25
It was carried out by examining the proportion of the sludge dispersed in fine sludge having a size of not more than mm, in the whole sludge. The smaller this value, the higher the strength of the granule sludge.

Further, the water quality of the treated water, the nitrogen removal rate, the total amount of sludge in the reaction tank, and the average particle size of the granule sludge were examined 2 months after the start of the passage, and the results are shown in Table 2.

Comparative Example 1 The same treatment as in Example 1 was carried out except that the polymer was not added, and the strength of the granule sludge was examined in the same manner. The results are shown in Table 1.

Further, the water quality of the treated water, the nitrogen removal rate, the total amount of sludge in the reaction tank and the average particle size of the granule sludge were examined 2 months after the start of the passage, and the results are shown in Table 2.

[0053]

[Table 1]

From Table 1, it can be seen that the strength of the granulated sludge is remarkably increased by adding the polymer.

As is clear from Table 2 below, the nitrogen removal rate in both Example 1 and Comparative Example 1 was 90%.
Although the treatment performance was the same as above, in Comparative Example 1, suspended sludge was conspicuous in the treated water. In addition, from the start of liquid passing 2
The total amount of sludge in the reaction tank after 4 months was about 4,40 in Example 1.
Although it was 0 mL, it was 3,900 mL in Comparative Example 1, and when the polymer was added, sludge growth was also good.

Example 2 In Example 1, about 100 mL (about 3 g-VSS) of granule sludge was drawn from the sludge bed once every 10 days, and 3.0 g at 2000 rpm using a household mixer.
The treatment was performed in the same manner except that the material was crushed for sec and then returned to the reaction tank.

By this crushing, the particle size range extracted from the reaction tank was 0.3 to 3.0 mm, and the average particle size was 1.6 mm.
Granule sludge with a particle size range of 0.1 to 2.2 m
m, and the average particle size was about 0.8 mm.

The quality of the treated water, the nitrogen removal rate, the total amount of sludge in the reaction tank, and the average particle size of the granule sludge were examined 2 months after the start of the passage, and the results are shown in Table 2.

[0059]

[Table 2]

From Table 2, by adding the polymer and extracting the granulated sludge from the reaction tank and crushing it, the granulated sludge is returned to the reaction tank to prevent floating upflow due to enlargement of the granulated sludge and to react the granulated sludge. It can be seen that it can be stably maintained in the tank and a higher denitrification effect can be obtained.

[0061]

As described in detail above, according to the method for biodenitrification of the present invention, a method for biodenitrification by passing raw water through an upward flow into a reaction tank holding granulated sludge of ANAMMOX microorganisms. In addition, by adding the polymer, it is possible to perform a stable and efficient denitrification treatment by forming a granular sludge having a high density and a high strength and a good sedimentation property.

In particular, according to the method of claim 2, the use of a cationic water-soluble polymer as the polymer makes it possible to form granule sludge having a better sedimentation property.

According to the method of claim 3, the granular sludge in the reaction tank is extracted, crushed, and then returned to the reaction tank to prevent the swelling and outflow of the enlarged granule sludge and stabilize the treatment. Can be realized.

[Brief description of drawings]

FIG. 1 is a UASB suitable for carrying out the biological denitrification method of the present invention.
It is a systematic diagram which shows an example of a reaction tank.

[Explanation of symbols]

1 USB reaction tank 4 Gas-liquid solid separation device

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 3/06 C02F 3/06 3/10 3/10 A C12N 1/00 C12N 1/00 R (72) Inventor Tokutomi Takaaki 3-4-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd. F-term (reference) 4B065 AA01X AA99X BB40 BC25 CA56 4D003 AA01 EA01 EA14 EA22 EA23 EA24 EA25 EA30 FA04 FA06 FA10 4D015 BA19 BB05 CA01 DB16 CA03 DB03 DB03 DB03 DB23 FA26 4D040 DD03 DD14

Claims (3)

[Claims] 1. Granule sludge containing autotrophic denitrifying microorganisms containing raw water containing ammoniacal nitrogen and nitrite nitrogen as an electron donor with ammoniacal nitrogen and electron acceptor with nitrite nitrogen. A method for biological denitrification by passing an upward flow through a holding reaction tank, wherein raw water is passed through the reaction tank while adding an organic coagulant to the reaction tank. 2. The biological denitrification method according to claim 1, wherein the organic flocculant is a cationic water-soluble organic flocculant. 3. The biodenitrification method according to claim 1, wherein the granular sludge in the reaction tank is extracted from the reaction tank, crushed and then returned to the reaction tank.