JP2003033787A - Method for nitrifying drainage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for nitrifying drainage capable of nitrification treatment to efficiently convert ammoniacal nitrogen to nitrites without converting hardly any amount of it to nitrates. SOLUTION: An ammoniacal nitrogen-containing raw water is introduced into a first chamber 1 of a nitration tank 10 having four nitration chambers 1, 2, 3 and 4 and passes each of the chambers 1, 2, 3 and 4 in this order. The air-dispersion amount (aerated amount) from an air-dispersion tube is regulated by a controller 11 and an air-flow adjustment valve 12. The first chamber 1 is the highest in the aerated amount followed by the chambers 2, 3 and 4 in this order. A stirrer 13 is installed in the chambers 2, 3 and 4, respectively where the aerated amount is low. The effluent, nitrified liquid from the last chamber 4 of the nitrification tank 10 is isolated by a solid-liquid separator 15 from solid components, and the liquid thus separated is taken out as treated water. A part of the solid components, thus separated is taken out as excess dirt and mud, and the remaining components are returned to the first chamber 1.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for biologically nitrifying raw water containing ammoniacal nitrogen.

[0002]

In the process of biologically nitrifying and denitrifying raw water containing ammoniacal nitrogen, ammonia-oxidizing bacteria are retained in the form of activated sludge or biofilm. Ammonia is oxidized to nitrous acid and further to nitric acid. The inside of the nitrification tank is kept under conditions suitable for both nitrite and nitration. Nitric acid is reduced to nitrogen gas by denitrifying bacteria and removed.

In this nitrifying and denitrifying process, it is important to efficiently carry out the nitrite forming process. Heretofore, the following methods have been proposed as the nitrite conversion process. 1. A method utilizing the relatively high toxicity of nitrite nitrogen or nitrate nitrogen or ammonia nitrogen to nitrifying bacteria (An
thoniesen et al. 1976). This method has been put to practical use as a method for providing a region that reduces the activity of nitrifying bacteria (Suthersen and Ganczarczyk, 1986). 2.
A method that utilizes the difference in the growth rate of nitrite bacteria and nitrifying bacteria at high temperatures (SHARON process).

Although a method of lowering the dissolved oxygen (DO) concentration in the tank has been proposed in order to preferentially promote the nitrite reaction (Hanaki, 1990), when the DO is low, the reaction of the nitrite reaction occurs. This method is not practical because the speed itself is small.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for nitrifying raw water containing ammoniacal nitrogen, which can efficiently convert this nitrification form into a nitrite type.

[0006]

The method for nitrifying wastewater according to the present invention is a method of supplying raw water containing ammoniacal nitrogen to a nitrification tank and aerating in the presence of ammonia-oxidizing bacteria to perform nitrification treatment. The nitric acid is controlled to a nitrite type by providing a temporal concentration gradient or a local concentration gradient to the dissolved oxygen concentration of.

Providing a temporal concentration gradient to the dissolved oxygen concentration in the nitrification tank means changing the dissolved oxygen concentration in the nitrification tank with time in the same nitrification tank. For example,
This corresponds to a mode in which the dissolved oxygen concentration in the nitrification tank is increased or decreased over time.

In the present invention, raw water is introduced into a nitrification tank in which ammonia oxidizing bacteria are placed under a DO concentration gradient.

In one aspect of the present invention, the sludge flowing out of the nitrification tank is solid-liquid separated and returned to the nitrification tank. D
The sludge is kept under a high DO concentration for a predetermined time in order to provide a concentration gradient of O 2. By processing under this high DO concentration,
Ammoniacal nitrogen in raw water is mainly oxidized to nitrous acid with high efficiency. The time to keep sludge under high DO concentration is
It is preferably 50% or less of the total HRT.

After the treatment at the high DO concentration, the sludge is kept at the low DO concentration, which significantly reduces the oxidation rate of ammonia nitrogen. As a result, the inside of the tank has a low DO condition that inhibits the activity of the nitrifying bacterium, which has a high activity under the low DO as compared with the nitrite bacterium.

When sludge containing nitrites and nitrites is kept under low DO conditions and then returned to a high DO concentration, the nitrites are activated more than the nitrites. As a result, the nitrification form becomes a nitrite type. In this way, by giving a temporal concentration gradient to the DO in the nitrification tank, it is possible to efficiently nitrite the ammoniacal nitrogen without nitrifying it.

Providing a local concentration gradient for the DO concentration in the nitrification tank means forming regions having different dissolved oxygen concentrations in the nitrification tank. For example, this includes a mode in which the inside of the nitrification tank is divided into a plurality of (preferably 4 or more) small chambers and the DO concentration of each chamber is made different.

In the present invention, it is preferable to provide a concentration gradient so that the maximum value of the dissolved oxygen concentration in the nitrification tank is 6 mg / L and the minimum value thereof is 0 mg / L. Further, the time for which the dissolved oxygen concentration is 0 to 0.5 mg / L is preferably 25 to 50% of the raw water retention time in the nitrification tank.

The ammonia-oxidizing bacteria are preferably retained in the nitrification tank in the form of suspended sludge or a biofilm, but they may be retained after being self-granulated.

In one embodiment of the present invention, raw water is continuously passed through the nitrification tank.

In another embodiment of the present invention, raw water is batch-charged into a nitrification tank, aeration is carried out by providing a temporal concentration gradient to the DO concentration in the nitrification tank, aeration is stopped and solid-liquid separation is carried out, and supernatant water is obtained. Discharge.

[0017]

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

FIGS. 1 and 2 are flow charts showing an example of a nitrification method for waste water according to each embodiment. Figure 1,
In both cases, the DO concentration in the tank is graded by adjusting the amount of aerated air in the tank. In the present invention, it is preferable to use a multi-chamber nitrification tank having at least four nitrification chambers as shown in the figure.

In the method of FIG. 1, raw water containing ammoniacal nitrogen is introduced into a first chamber 1 of a nitrification tank 10 having four nitrification chambers 1, 2, 3, 4 and each of the chambers 1, 2, Pass 3 and 4 in sequence. Air diffusers are provided below the chambers 1 to 4, respectively, and the amount of air diffused from each diffuser (aeration air amount) is adjusted by the controller 11 and the air flow rate adjusting valve 12. The amount of aeration is highest in the 1st chamber 1, 2nd, 3rd, 4th
The order of the rooms is decreasing. An agitator 13 is provided in the second, third, and fourth chambers where the aeration amount is small.

The nitrification liquid flowing out from the final fourth chamber 4 of the nitrification tank 10 is solid-liquid separated by the solid-liquid separator 15, and the separated liquid is taken out as treated water. Part of the separated solid content is taken out as excess sludge, and the rest is returned to the first chamber 1.

As the solid-liquid separator 15, various types such as a sedimentation type and a membrane separation type can be used.

In the method of FIG. 2, the raw water is the nitrification tank 10.
Is introduced into the second chamber 2 and flows from the second chamber 2 to the third chamber 3 and the fourth chamber 4 in this order, and is taken out from the fourth chamber and sent to the solid-liquid separator 15 for solid-liquid separation. . As in the case of FIG. 1, the separated liquid is taken out as treated water. Part of the separated solid content is taken out as excess sludge, and the rest is returned to the first chamber 1.

The second chamber 2 has the largest aeration amount, and the third chamber 3,
The fourth chamber 4 and the first chamber 1 are decreasing in order.

The sludge returned from the solid-liquid separator 15 to the first chamber 1 is kept under a condition of lower DO than the fourth chamber 4.

In any of the methods shown in FIGS. 1 and 2, a long SR can be performed without discharging excess sludge from the solid-liquid separator 15.
It is possible to operate so as to treat the raw water under the condition of T, but it is also possible to set an operating condition in which the excess sludge is extracted from the solid-liquid separator 15 by controlling the nitrification rate.

1 and 2 use a solid-liquid separator 15 because it is a floating system in which activated sludge is in a floating state, but in the present invention, a biofilm method or the like using a carrier for fixing microorganisms is adopted. It is also possible to use granulated sludge obtained by self-granulating sludge. In these cases,
The solid-liquid separator 15 may be omitted.

In the case of the biofilm method using a carrier, the carrier has a specific gravity of 0.8 to 1.5 and an open cell pore diameter of 5 to 5000 μm.
m, preferably 10 to 1000 μm, porosity 10 to 90
%, Preferably 30 to 90%, specific surface area 500 to 100
It is preferable that the particle size is 00 m ² / m ³ and the particle size is 1 to 20 mm.

Preferred materials for the carrier are polypropylene, polyurethane, cellulose, polyester,
A plastic carrier or sponge made of polyvinyl alcohol, PVF, polyethylene glycol-based resin, acrylic resin, acrylamide-based resin, olefin-based resin, styrene-based resin, polysaccharide, polyether, or other organic polymer compound having an internal mesh structure. Carriers, fibrous carriers, non-woven fabrics, gel carriers, other porous inorganic polymer compounds,
Activated carbon etc. are mentioned.

The granular carrier may have any shape such as a sphere, a cube, an indeterminate shape, and a tubular shape.

[0030]

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

Example 1 Raw water was nitrified by the process shown in FIG. Figure 3
The process is similar to that of FIG. 1, but the inside of the first chamber 1 of the nitrification tank 10 is divided into two parts, a front part 1a and a rear part 1b. Raw water and returned sludge are introduced into the front part 1a
Water overflows from a into the rear part 1b. The front part 1a is not aerated and only the rear part 1b is aerated.

A nitrogen purging diffuser for purging DO with nitrogen gas is provided in the second, third and fourth chambers. The first chamber 1 is not purged with nitrogen.

The volume of each chamber 1, 2, 3, 4 is 2.5 L (liter). The volume of the front part 1a of the first chamber 1 is 0.5L
The capacity of the rear portion 1b is 2.0 L.

The DO concentration in each chamber was controlled by controlling the air and nitrogen gas flow rates. In addition, the pH in the first chamber 1
Sodium carbonate was added so that the ratio was about 7.6.

NH ₄ Cl 2000 mg / L, KH ₂ PO
₄ 10 mg / L of synthetic waste water was supplied to the first chamber 1. This supply amount is 20 L / day on average, but the ammonia nitrogen concentration in the first chamber 1 is 500 to 600 mg / L.
Was adjusted so that DO in each room for 3 months
When operated so that the concentration was as shown in Table 1, the concentrations of ammoniacal nitrogen, nitrite nitrogen and nitrate nitrogen in the treated water were as shown in Table 1.

Comparative Example 1 In Example 1, all the DO concentrations in the chambers 1 to 4 are shown in Table 1.
Example 1 except that the same concentration was used as shown in FIG.
When the same synthetic wastewater was treated for 3 months in the same manner as above, the water quality of the treated water was as shown in Table 1.

[0037]

[Table 1]

[0038]

As is clear from the above Examples and Comparative Examples, according to the present invention, nitrification treatment can be carried out so that ammoniacal nitrogen can be efficiently nitrided with almost no nitrification.

[Brief description of drawings]

FIG. 1 is a flowchart showing an embodiment of a wastewater nitrification method of the present invention.

FIG. 2 is a flowchart showing another embodiment of the wastewater nitrification method of the present invention.

FIG. 3 is a flowchart of an example.

[Explanation of symbols]

1st room 2 second room 3rd room 4th room 10 Nitrification tank 11 Controller 15 Solid-liquid separator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takaaki Tokutomi             Kurita, 3-4-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo             Industry Co., Ltd. F-term (reference) 4D040 BB22 BB42 BB65 BB91

Claims (6)

[Claims] 1. A method of supplying raw water containing ammoniacal nitrogen to a nitrification tank and aerating in the presence of ammonia-oxidizing bacteria to perform nitrification treatment, wherein the dissolved oxygen concentration in the nitrification tank has a temporal concentration gradient or a local concentration. A nitrification method for wastewater, characterized by controlling nitrification to a nitrite type by providing a gradient. 2. The nitrification method for wastewater according to claim 1, wherein a concentration gradient is provided such that the maximum dissolved oxygen concentration is 6 mg / L and the minimum dissolved oxygen concentration is 0 mg / L. 3. The dissolved oxygen concentration in the nitrification tank has a temporal concentration gradient or a so that the time for which the dissolved oxygen concentration is 0 to 0.5 mg / L is 25 to 50% of the raw water retention time in the nitrification tank. The nitrification method for wastewater according to claim 1 or 2, wherein a local concentration gradient is provided. 4. The method for nitrifying wastewater according to claim 1, wherein the ammonia-oxidizing bacteria are held in the nitrification tank in the form of suspended sludge or a biofilm. 5. The method for nitrifying wastewater according to claim 1, wherein raw water is continuously passed through the nitrification tank. 6. A process of batch-feeding raw water into a nitrification tank, performing aeration by providing a temporal concentration gradient to the dissolved oxygen concentration in the nitrification tank, stopping aeration and performing solid-liquid separation, and discharging the supernatant water. The nitrification method for wastewater according to any one of claims 1 to 4, which is repeated.