JP2003024987A - Nitrification method for ammonia nitrogen-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrification method capable of stably performing nitrous acid type nitrification and enabling high load operation, in a method for nitrifying ammonia nitrogen-containing water by introducing ammonia nitrogen- containing water into a nitrification tank aerating the ammonia nitrogen- containing water in the presence of ammonia oxidizing bacteria to nitrify the same. SOLUTION: In the nitrification method for ammonia nitrogen-containing water, a biological film of ammonia oxidizing bacteria is formed to the inside of a nitrification tank 1 and the aeration quantity of air is regulated to perform operation in low DO(dissolved oxygen) concentration.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method of aerating ammoniacal nitrogen-containing water in the presence of ammonia-oxidizing bacteria to nitrify, and particularly to forming a biofilm of ammonia-oxidizing bacteria in a nitrification tank and aerating the same. The present invention relates to a nitrification method for ammonia-containing nitrogen-containing water, which controls the air volume to perform stable and efficient nitrite-type nitrification.

[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.

In such nitrification and denitrification treatment, the aeration power required to oxidize ammoniacal nitrogen occupies most of the operating cost.

As a method of reducing the cost for aeration, a method of producing nitrite nitrogen without producing nitrate nitrogen and denitrifying the nitrite nitrogen is conceivable. It was difficult to carry out nitrite-type nitrification that stably produces nitrite nitrogen.

In recent years, a method by inhibiting ammonia nitrogen in the reaction vessel (JP-A-2000-61494) and a method of controlling the dissolved oxygen (DO) concentration (JP-A-4-12249).
8), a method utilizing the difference in the growth rate of microorganisms (EP08
It has been studied to realize nitrite type nitrification by 26639A1). Each of these attempts to accumulate a high concentration of nitrite in the reaction tank by inhibiting the activity of nitrite-oxidizing bacteria and creating a condition in which only ammonia-oxidizing bacteria can act.

[0006]

Among the above-mentioned conventional methods, in the method utilizing inhibition by ammoniacal nitrogen, the ammoniacal nitrogen remains at a high concentration in the treated water. It is necessary to oxidize and treat it up to the point where the advantage of producing nitrous acid is lost.

Further, the DO control has a problem that the treatment activity per sludge is lowered because the concentration of oxygen as a substrate is lowered, and a high load cannot be taken. Even with the method utilizing the difference in growth rate, there is a problem that the sludge concentration cannot be increased due to the chemostat culture and a high load cannot be taken.

The present invention solves the above-mentioned conventional problems and stabilizes nitrite type nitrification in a method of introducing nitric acid by introducing water containing ammoniacal nitrogen into a nitrification tank that aerates in the presence of ammonia-oxidizing bacteria. It is an object of the present invention to provide a method for nitrifying water containing ammoniacal nitrogen, which can be performed at high load and can be operated under high load.

[0009]

The method for nitrifying ammoniacal nitrogen-containing water of the present invention is a method of introducing nitrification by introducing the ammoniacal nitrogen-containing water into a nitrification tank that aerates and nitrifies in the presence of ammonia-oxidizing bacteria. Therefore, in the nitrification method in which the amount of aeration air in the nitrification tank is adjusted to control nitrification to a nitrite type, the ammonia-oxidizing bacteria are retained in the nitrification tank in the form of a biofilm.

As described above, when trying to maintain the nitrite type nitrification by controlling the DO concentration in the nitrification tank, the concentration of oxygen as a substrate is lowered, so that the treatment activity per sludge becomes low, and the same. There was a problem that the load was lower under the condition of sludge concentration than when there was sufficient oxygen.

As a result of studying this problem, the inventors of the present invention ensured a sufficient amount of sludge in the nitrification tank to supplement the treatment activity per sludge when the DO concentration was controlled to be low. If possible, it was considered that the same level of processing activity could be obtained per volume of nitrification tank as when the DO concentration was high. Then, as a method of holding sludge in a nitrification tank at a high concentration, focusing on a method of forming a biofilm, a method of performing highly efficient treatment even under a low DO concentration condition was found, and the present invention was completed.

The mechanism of action of nitrite type nitrification by a biofilm at a low DO concentration in the present invention is as follows.

Microorganisms used for biological treatment originally have the ability to form flocs, granules, and biofilms, and are widely used in ordinary wastewater treatment. In a normal aeration tank, the shearing force due to aeration is so strong that microorganisms can only form very small flocs of a few hundred microns. Flock has an advantage that there is no diffusion resistance of the substrate inside, but the density of microorganisms is not so high and the sedimentation speed is about 10 m / day, so that high load operation is difficult.

On the other hand, a biofilm method has been put into practical use as a biological treatment method that does not use flocs, and in this case, the restriction on the sedimentation rate of sludge is greatly relaxed. That is,
In the case of a fixed bed, it is not necessary to consider the sedimentation speed, and a biofilm such as granule has a high density and good sedimentation property, and the sedimentation speed is very high at 10 m / hr or more. Since the concentration of microorganisms is extremely high inside the biofilm, a large amount of wastewater can be treated with a high load in a small-capacity nitrification tank if the surface area can be secured.

Further, in the biofilm, the substrate is consumed from the surface portion, but due to the high density of microorganisms, the substrate is reached before reaching deep inside the granule. This property works very effectively in limiting DO given to microorganisms, and oxygen is always depleted inside the biofilm. Especially, the DO concentration in the nitrification tank is 1.5m
Below g / L, preferably below 0.5 mg / L, activity is limited to the vicinity of the surface of the biofilm.

Under this condition, only ammonia-oxidizing bacteria can be activated and nitrite is accumulated in the nitrification tank. Also, the space where the microorganisms can grow is only the surface of the biofilm, and competition between the microorganisms will occur even when going through this space. However, under conditions of low DO concentration, only fast-growing ammonia-oxidizing bacteria can grow preferentially. become.
As a result, nitrite type nitrification under high load becomes possible.

In the method for nitrifying water containing ammoniacal nitrogen according to the present invention, D in the nitrification tank is adjusted by adjusting the amount of aeration air.
It is preferable to control the O concentration to be a low DO concentration of 1.5 mg / L or less.

As for the form of the biofilm of the ammonia-oxidizing bacterium, even if the biofilm is formed on the surface of the carrier,
It may be a granule forming a biofilm by self-granulation.

The nitrification tank used in the present invention preferably has an air blowing section, an ascending section and a descending section,
In particular, an air lift type aeration tank which has an inner cylinder opened vertically and aerates from below the inner cylinder is preferable, and such an air lift type aeration tank enables high load operation with a compact device. .

[0020]

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

FIG. 1 is a diagram showing a schematic structure of an air-lift type aeration tank suitable for carrying out the present invention. In this air-lift type aeration tank 1, an inner cylinder 2 whose upper and lower sides are opened is arranged coaxially. The inner cylinder 2 has an air diffuser 3 in the lower part, and an air lift due to aeration is generated in the inner cylinder 2. A gas-liquid separator 4 is provided on the upper part of the inner cylinder 2. The inner cylinder 2 holds a biofilm sludge of ammonia-oxidizing bacteria.

Raw water (water containing ammoniacal nitrogen) is introduced into the aeration tank 1 from the lower part of the aeration tank 1 and flows in the inner cylinder 2 in an upward flow by an air lift due to aeration from the air diffusing section 3, and in the meantime. Nitrification is performed by contact with sludge.

The ascending flow in the inner cylinder 2 is gas-liquid separated in the gas-liquid separation section 4, and then partly discharged as treated water through the sedimentation separation section 5, while the remaining part is formed between the inner cylinder 2 and the aeration tank 1. The part between them is lowered, and is circulated together with the raw water introduced from the lower part of the aeration tank 1.

In the present invention, in order to carry out stable nitrite type nitrification, the DO concentration in the aeration tank 1 is 1.5 mg /
L or less, preferably 1 mg / L or less, particularly preferably 0
The amount of aeration air from the air diffuser 3 is adjusted so that the low DO concentration is about 0.5 mg / L. The amount of aeration air can be adjusted by, for example, providing a DO meter in the aeration tank 1 and controlling the amount of air of a blower that supplies air to the air diffuser 3 based on the measurement result of the DO meter. .

If the DO concentration in the aeration tank 1 exceeds 1.5 mg / L, the DO becomes excessive and the nitrification reaction becomes a nitric acid type to generate nitrate nitrogen, which is not preferable.

In the aeration tank 1 of FIG. 1, prior to starting the passage of raw water, sludge containing nitrifying bacteria as seed sludge is introduced into the inner cylinder 2 to pass raw water containing ammoniacal nitrogen. Then, aeration is performed so that the DO concentration becomes the above-mentioned and water is continuously supplied to form granules of biofilm by self-granulation of ammonia-oxidizing bacteria. In this case, a carrier may be filled in advance in the aeration tank and a biofilm may be formed on the surface of the carrier. The rising velocity of the sedimentation / separation unit 5 is appropriately determined according to the balance between sludge growth and separation, the outflow amount to the outside of the system, and the sedimentation velocity of the granule itself. Since the sludge settling speed in the method is very high at 10 m / hr or more, the LV of the settling separation section 5 is 10 m / hr after sufficient biofilm formation.
Above, it can be preferably set to 10 to 50 m / hr.

The air lift type aeration tank shown in FIG.
This is an example of a nitrification tank suitable for carrying out the present invention, and the present invention is not limited to the embodiment using the illustrated aeration tank.

Any nitrification tank can be used as long as it can maintain a biofilm, and any of a fixed bed, a fluidized bed, a granule method and a carrier addition method can be adopted.

[0029]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 Using the air-lift type aeration tank (volume 3 L) shown in FIG. 1, 20 synthetic waste water having an ammoniacal nitrogen concentration of about 420 mg / L was used.
Water was passed under the condition of L / day for treatment.

Prior to the start of water flow, 3 L of 8000 mg / L of sewage sludge that had been subjected to nitrification and denitrification was put into an air lift type aeration tank. Further, the aeration air volume was adjusted so that the DO concentration of the liquid in the tank was 1 mg / L or less (0.8 to 1.0 mg / L).

The rising velocity LV in the sedimentation / separation section 5 is 1
It was 0 m / hr.

As a result, about 6 months after the start of water flow, granules having a diameter of about 0.3 mm were formed, and the amount thereof was gradually increased.

Quality of treated water (NH ₄ —N concentration, NO ₂ —
The N concentration and NO ₃ —N concentration) are as shown in FIG. 2, and stable nitrite type nitrification was performed, and ammoniacal nitrogen was efficiently oxidized to nitrite nitrogen.

[0035]

As described in detail above, according to the method for nitrifying ammoniacal nitrogen-containing water of the present invention, the amount of aeration air in the nitrification tank in which the biofilm is formed is adjusted to operate at a low DO concentration. As a result, the nitrite type nitrification that is stable for a long period of time can be performed under high load operation with a compact device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an air lift type aeration tank suitable for carrying out the nitrification method of ammoniacal nitrogen-containing water of the present invention.

FIG. 2 is a graph showing changes over time in the quality of treated water in Example 1.

[Explanation of symbols]

1 aeration tank 2 inner cylinder 3 Air diffuser 4 Gas-liquid separation unit 5 Sedimentation and separation section

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Rei Imajo             Kurita, 3-4-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo             Industry Co., Ltd. F-term (reference) 4D003 AA01 AA12 AB02 BA02 CA05                       DA07 DA11 DA15 EA01 FA01                       FA05                 4D040 BB07 BB42 BB91

Claims (5)

[Claims] 1. A method for introducing nitric acid by introducing water containing ammoniacal nitrogen into a nitrification tank that aerates and nitrifies in the presence of ammonia-oxidizing bacteria, wherein nitrification is performed by adjusting the amount of aeration air in the nitrification tank. In the nitrification method of controlling the type, the ammonia-oxidizing bacteria are retained in the nitrification tank in the form of a biofilm, and the nitrification method of ammoniacal nitrogen-containing water is characterized. 2. The dissolved oxygen concentration in the nitrification tank is 1.5 mg.
The method for nitrifying ammoniacal nitrogen-containing water according to claim 1, wherein the amount of aeration air is adjusted to be not more than / L. 3. The ammonia-oxidizing bacterium has a biofilm formed on the surface of a carrier.
Or the method for nitrifying water containing ammoniacal nitrogen according to 2. 4. The method for nitrifying ammoniacal nitrogen-containing water according to claim 1 or 2, wherein the ammonia-oxidizing bacterium forms a biofilm by self-granulation. 5. The ammoniacal nitrogen-containing water according to claim 1, wherein the nitrification tank has an air blowing section, an ascending section, and a descending section in the tank. Nitrification method.