JPH08155491A - Biological denitrification apparatus - Google Patents

Abstract

PURPOSE: To prevent sludge in a denitrification tank from floating and to enable stable and efficient denitrification by removing sludge which floated from the denitrification tank in which dirty water is passed through a sludge bed added with elemental sulfur in a upward current, adding a surface active agent to the sludge in a reaction vessel, mixing them, and returning liquid in the reaction vessel to the denitrification tank. CONSTITUTION: In a denitrification apparatus, raw water is introduced from a raw water inflow pipe 2 to the bottom part of a denitrification tank 1 in which a fluidized bed 1A added with elementary sulfur as an electron donor is formed to be denitrified in an upward current. The treated water is removed from the upper part of the tank through a treated water take off pipe 3. In this process, an extraction pipe 4 for floating sludge is placed near the upper part of the fluidized bed 1A, sludge extracted from the pipe 4, after being added with a surfactant in a surfactant storage tank 6 by a pipe 5, is modified in a reaction vessel 7, and the modified sludge is refluxed to the bottom part of the denitrification tank 1 through a pipe 8. In this way, the sludge is prevented from floating and flowing out so that the amount of sludge held in the denitrification tank 1 is kept high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for biologically denitrifying sewage (raw water) containing nitrate nitrogen and / or nitrite nitrogen, and more particularly to adding elemental sulfur as an electron donor. The present invention relates to a biological denitrification device for maintaining a high retained sludge amount in a device for performing denitrification treatment by passing raw water through an upstream sludge bed.

[0002]

2. Description of the Related Art Conventionally, biological nitrification denitrification has been performed as a method for treating human waste, municipal wastewater, and other nitrogen-containing organic wastewater. This biological nitrification / denitrification treatment is a nitrification step of biologically nitrifying nitrogen components in raw water into nitrate ions or nitrite ions, and biologically converting nitrate ions or nitrite ions into nitrogen (N ₂ ). And a denitrification step of reducing. Conventionally, as a biological denitrification apparatus, a sludge bed is generally formed in a denitrification tank, raw water is upwardly circulated, and treated water is taken out from the upper part of the tank.

By the way, in the biological denitrification process,
As electron donors necessary for the denitrification reaction, organic substances such as methanol, ethanol and acetic acid are added to grow the denitrifying bacteria.

[0004] However, since the organic matter has such problems that it is necessary to control so that the amount of addition is appropriate and that the amount of excess sludge generated is large, elemental sulfur is used as an electron donor instead of the organic matter. Is proposed (Japanese Patent Publication No. 53-9469).

[0005]

In the above-mentioned upflow type denitrification device, when elemental sulfur is added as an electron donor,
Denitrifying bacteria adhere to the added elemental sulfur and proliferate to form sludge, but in this case, the sludge easily floats in the upward flow of raw water and easily flows out together with the treated water. Therefore, there is a problem that the sludge holding amount in the denitrification tank cannot be maintained high.

The present invention solves the above-mentioned conventional problems and prevents the sludge from floating in an upflow type denitrification device in which elemental sulfur is added as an electron donor, thereby increasing the sludge retention amount in the denitrification tank. An object of the present invention is to provide a biological denitrification device that can be maintained at a high level.

[0007]

The biological denitrification device of the present invention passes sewage containing nitrate nitrogen and / or nitrite nitrogen upflow through a sludge bed containing elemental sulfur. A denitrification tank, a means for taking out sludge floating from the denitrification tank, a reaction tank for adding and mixing a surfactant to the taken out sludge, and a means for returning the liquid in the reaction tank to the denitrification tank. .

[0008]

[Function] In the upward flow type denitrification device for adding elemental sulfur, the mechanism of floating sludge is that the nitrogen gas generated by denitrification adheres to highly hydrophobic elemental sulfur and It is considered that the sludge containing is easily floated.

In the present invention, the floating sludge is taken out from the denitrification tank, mixed with the surfactant and returned to the denitrification tank, and the elemental sulfur is generated by the denitrification reaction due to the wetting action of the surfactant. Nitrogen gas is less likely to adhere and sludge is prevented from floating.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the biological denitrification apparatus of the present invention.

In this denitrification apparatus, raw water is introduced from a raw water inflow pipe 2 to the bottom of the denitrification tank 1 in which a fluidized bed 1A is formed in the tank, and the denitrification treatment is performed in an upward flow to obtain treated water. Is taken out from the upper part of the tank through the treated water taking-out pipe 3, and the fluidized bed 1
At a position near the upper part of A, a floating sludge extraction pipe 4 is provided. The sludge drawn from this drawing pipe 4
After the surfactant in the surfactant storage tank 6 is added from the pipe 5, it is sufficiently mixed with the surfactant in the reaction tank 7.
The sludge modified with the surfactant in the reaction tank 7 is returned to the bottom of the denitrification tank 1 together with the raw water via the pipe 8.

In this way, by mixing the surface-active agent with the floating sludge and returning it to the denitrification tank again, it is possible to prevent the sludge from floating and flowing out, and to maintain a high sludge retention amount in the denitrification tank. it can.

The surfactant to be added here is not particularly limited, but nonionic surfactants such as polyoxyethylene sorbitan monooleate are preferable, and the addition amount thereof is 10 mg / l or more relative to the sludge volume. , Especially 20
It is preferably set to 200 mg / l.

In the present invention, as the elemental sulfur added as an electron donor, sulfur powder having a particle size of about 10 to 100 μm is preferably used. Sulfur powder is added to the denitrification tank together with the seed sludge in advance, but it is consumed as the denitrification progresses, so it is replenished to the denitrification tank as needed.
In the usual case, it is preferable to add the sulfur powder in a ratio of about 2 to 3 times (weight ratio) with respect to the total amount of nitrogen to be removed.

The present invention will be described in more detail with reference to specific examples and comparative examples.

Example 1 Raw water was treated by the denitrification apparatus shown in FIG.

In the denitrification tank (6 liters), 3000 mg / l of activated sludge from the sewage treatment plant was added as seed sludge, and 200 g of sulfur powder (particle size 10 to 100 μm) was added to continue denitrification treatment for 1 month. did. The flow rate of raw water is 20m
1 / min, 300 ml of floating sludge during denitrification
The mixture was taken out at a rate of / day, and the nonionic surfactant (polyoxyethylene sorbitan monooleate) was added at a rate of 100 mg / l in the reaction tank and mixed, and then returned to the denitrification tank.

Table 1 shows the amount of sludge in the denitrification tank at the start of denitrification treatment and the amount of sludge in the denitrification tank after one month. Table 1 shows the raw water quality and the average quality of treated water for one month.

Comparative Example 1 In Example 1, the sludge was not circulated, that is, the sludge was not taken out and the surfactant was added and returned, and the other conditions were the same.

Table 1 shows the amount of sludge in the denitrification tank at the start of denitrification treatment and the amount of sludge in the denitrification tank after 1 month. Table 1 shows the raw water quality and the average quality of treated water for one month.

[0022]

[Table 1]

From Table 1, it is clear that according to the biological denitrification apparatus of the present invention, floating of sludge can be prevented, and the sludge retention amount in the denitrification tank can be maintained high to obtain high quality treated water. Is.

[0024]

As described in detail above, according to the biological denitrification apparatus of the present invention, it is possible to effectively prevent the sludge from floating in the denitrification tank and maintain a high sludge retention amount in the denitrification tank. Therefore, stable and efficient denitrification can be performed.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a biological denitrification device of the present invention.

[Explanation of symbols]

 1 Denitrification tank 6 Surfactant storage tank 7 Reaction tank

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuro Fukase 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd.

Claims (1)

[Claims] 1. A denitrification tank for passing sewage containing nitrate nitrogen and / or nitrite nitrogen in an upward flow to a sludge bed to which elemental sulfur has been added, and means for removing the sludge floating from the denitrification tank. A biological denitrification apparatus comprising: a reaction tank for adding and mixing a surfactant to the taken out sludge; and means for returning the liquid in the reaction tank to the denitrification tank.