JPH08132099A - Device for ozonating biological sludge - Google Patents

Abstract

PURPOSE: To provide a device for ozonating biological sludge capable of efficiently ozonating biological sludge and converting the sludge to BOD by micronizing the bubble into microbubbles having a uniform diameter and enhancing the ozone absorptivity. CONSTITUTION: An ozone-contg. gas 20 is blown into the liq.-phase contact region 3 of a reaction tank 1 to decompose the sludge by oxidation and to foam the liq., and hence the bubble contact region 4 is formed above the liq.- phase contact region 3. An agitator 8 is provided in the liq.-phase contact region 3 and/or bubble contact region 4 to micronize the bubble into the microbubbles having a uniform diameter, and gas-liq. contact is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological sludge ozone treatment apparatus for ozone-oxidizing biological sludge.

[0002]

2. Description of the Related Art For the purpose of reducing the volume of surplus sludge and the like in activated sludge treatment, biological sludge such as surplus sludge (hereinafter sometimes simply referred to as sludge) is reacted with ozone for oxidative decomposition. ing. In the conventional ozone treatment method for sludge, a device is used in which the reaction tank is filled with a sludge-containing liquid, and ozone-containing gas is blown into the sludge-containing liquid to bring them into gas-liquid contact to decompose the sludge. In conventional devices, the gas-liquid contact area is small, so it is necessary to lengthen the residence time in order to sufficiently react sludge with ozone.
In addition, there is a problem that efficient processing cannot be performed, such as wasteful consumption of expensive ozone. Although it is possible to increase the gas-liquid contact area and improve the processing efficiency by mechanically stirring the liquid to be processed, in this case, there is a problem that the processing cost becomes high.

By the way, when ozone-containing gas is blown into the sludge-containing liquid in the reaction tank for ozone treatment, the sludge-containing liquid is foamed, and the foam is likely to be taken out of the tank. For this reason, conventionally, defoaming was performed by adding an antifoaming agent, or a spray nozzle was installed in the upper part of the reaction tank, and industrial water or final treated water was sprayed on the liquid surface from this nozzle to defoam, resulting in foaming failure. Is being prevented. As described above, in the conventional sludge ozone treatment method, the ozone treatment is performed while suppressing the foaming as much as possible, and the ozone treatment utilizing the foaming has not been performed so far.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ozone treatment apparatus for biological sludge, which is capable of efficiently ozone treating biological sludge at low cost.

[0005]

The present invention is directed to a reaction tank for receiving a biological sludge-containing liquid for ozone treatment, and a liquid for blowing ozone-containing gas into the gas-liquid contact in the biological sludge-containing liquid in the reaction tank. A phase contact area, a foam contact area for forming a foam layer on the liquid phase contact area by blowing ozone-containing gas to form gas-liquid contact, and a liquid phase contact area and / or a foam contact area And an agitating device for the biological sludge.

The ozone treatment apparatus for biological sludge of the present invention is preferably constructed as follows because the foam layer can be maintained and controlled. (A) The biological sludge concentration of the biological sludge-containing liquid is 2,000 to 2
If it is set to 20,000 mg / l, it is easy to maintain the foam layer. (B) When the height of the foam layer in the foam contact area of the reaction tank is 1 m or more, the treatment efficiency becomes high. (C) If a liquid spraying device for spraying the liquid is installed above the foam contact area of the reaction tank, it is easy to control the height of the foam layer. (D) When the biological sludge-containing liquid in the reaction tank is used as a part of the spray liquid of the liquid spraying device and the liquid is circulated and sprayed, the height of the foam layer can be easily controlled and ozone can be effectively used.

The biological sludge to be treated in the present invention is a sludge containing biological sludge produced in aerobic treatment, anaerobic treatment and the like, and it is preferable to mainly use biological sludge like surplus sludge, It may be one that contains a small amount of inorganic substances such as coagulated sludge. The biological sludge concentration in the biological sludge-containing liquid is 2,000 to 20,000 mg / l, preferably 5,0.
It is preferably from 0 to 15,000 mg / l. In this range, the height of the foam layer can be maintained at 1 m or more by selecting the foaming conditions such as the ozone flow rate, the spray flow rate, the presence or absence of the foam holding member.

The reaction tank used for the ozone treatment in the present invention is a tank for reacting sludge in the sludge-containing liquid with the ozone-containing gas for oxidation treatment. A liquid-phase contact region for blowing gas into liquid is formed, and a foam contact region for contacting the foamed foam and the ozone-containing gas is formed on the liquid-phase contact region. The height of the liquid phase contact area is 0.2 to 3 m, preferably 0.5 to 1.5 m
And The height of the foam contact area is 1 m or more, preferably 1 to 10 m, and more preferably 2 to 5 m from the liquid surface of the sludge-containing liquid in the liquid phase contact area.

It is preferable to maintain the liquid phase contact area at a substantially constant height. For example, an overflow type in-tank liquid outlet is provided in the lower or middle part of the reaction tank so that the liquid level in the tank is constant. Can be kept at. It is preferable that the foam contact area is formed in a space above the liquid surface in the liquid phase contact area (liquid outlet in the tank).

A stirrer is provided in the liquid phase contact area and / or the foam contact area to subdivide air bubbles to enhance the contact efficiency between sludge and ozone. The stirrer is rod-shaped in the radial direction from the rotating shaft,
Examples thereof include plate-shaped and other-shaped paddles, blades and the like provided, or those having protrusions on the paddles and blades. The above paddles, blades and the like may be provided only in the liquid phase contact area or only in the foam contact area, but it is preferable to provide them in both.

The stirrer provided in the liquid-phase contact region subdivides the bubbles generated in the liquid phase, and the stirrer provided in the foam-contact region prevents the bubbles from gathering in the foam-contact region and increases in diameter, and Is configured to subdivide. For example, the number of paddles, blades, etc. protruding from the rotation axis in two directions, four directions, etc. can be arbitrarily determined according to the diameter of the reaction tank. The distance between the paddles and blades in the direction of the rotation axis varies depending on the size of the reaction tank and the like, but is preferably about 20 to 80 cm. The rotation speed of the stirrer varies depending on the size of the reaction tank, the structure of the stirrer, etc., but is generally 100 to 1
The rotation speed is preferably 000 rpm and the peripheral speed is about 0.02 to 0.2 m / sec.

As the ozone-containing gas, ozone-containing air,
Ozonized air can be used. The amount of ozone introduced is preferably 1 to 10%, and more preferably 3 to 5%, with respect to the VSS weight of the biological sludge to be introduced. The flow rate of the ozone-containing gas is 5 to 50 m / in terms of the linear gas velocity in the reaction tank.
It is desirable that the rate is hr, preferably 10 to 30 m / hr.

[0013]

In the ozone treatment apparatus for biological sludge of the present invention, the liquid containing sludge is introduced into the reaction tank to form the liquid phase contact area. Then, when the ozone-containing gas is blown into the liquid-phase contact area and brought into contact with the biological sludge-containing liquid, the sludge is treated with ozone. At the same time, foaming causes a foam layer to be formed in the upper part of the liquid phase contact area, and contact between the biological sludge and ozone occurs in this foam layer to form a foam contact area. As a result, sludge and ozone are brought into contact with each other in both the liquid phase contact area and the foam contact area.

Even when the liquid phase contact area and the foam contact area are formed in the reaction tank, when the diameter of the reaction tank becomes large, gas drift occurs in the foam contact area and the bubble diameter tends to become non-uniform, resulting in a large diameter. The foam rises quickly and the contact efficiency with ozone decreases,
By providing the stirrer, the foam is subdivided to make the bubble diameter uniform, and the paddles, blades, etc. of the stirrer function as a gas-liquid contact medium, so that the contact efficiency is increased.

A liquid spraying device is provided above the foam contact area in the reaction tank to store the industrial water to be treated, the final treatment liquid, the drawing liquid from the reaction tank, or the mixed liquid of the drawing liquid and the treatment liquid. It can be sprayed towards the foam layer, which can prevent excessive foaming and maintain the foam contact area at a predetermined height. In this case, it is preferable to use the liquid to be treated or a liquid mixture of the liquid to be treated and the liquid to be treated since the sludge concentration of the liquid in the tank does not decrease.

[0016] Including the case of biological sludge, it is not generally practiced to draw out and spray the sludge-containing liquid because solid matter easily clogs the nozzle, but in a system for treating biological sludge with ozone, It has been confirmed by the present inventor that the clogging of the nozzle and the like does not occur even when the liquid in the tank is sprayed, because the biological sludge is miniaturized and the adhesiveness is reduced. Also, since the liquid to be treated is diluted even with a mixed liquid of the liquid in the bath and the liquid to be treated, the nozzles and the like are hardly clogged, but if the liquid to be treated not subjected to ozone treatment is used alone, the nozzles are easily clogged. It is preferable not to use it for spraying.

Since the foam contact area of the ozone treatment apparatus of the present invention is only filled with foam, the strength of the reaction tank may be smaller than that of the apparatus which fills the reaction tank with the liquid to be treated, which makes the apparatus less expensive. Become. INDUSTRIAL APPLICABILITY The ozone treatment apparatus of the present invention can be used when ozone treatment is performed on excess sludge to reduce its volume, or when a mixed solution in the tank is drawn out from a biological treatment tank, for example, an aerobic treatment tank, for ozone treatment.

In the reaction tank, sludge reacts with ozone to be oxidatively decomposed and converted into BOD components. The sludge-containing liquid (in-tank liquid) that has been subjected to the ozone treatment has an increased viscosity and becomes a liquid having a very high foaming property. Therefore, when the sludge-containing liquid and the ozone-containing gas are brought into contact with each other, they easily foam to form a foam layer. In the present invention, since the foam layer is formed so as to be brought into contact with the ozone-containing gas, the sludge present in the liquid in the tank becomes a foam in a state of being in contact with ozone, and further in contact with ozone in a state of foam. It is disassembled and repeated. Therefore, the efficiency of ozone treatment is higher than that in the case of contacting only in the liquid phase contact area. Also, if the ozone-containing gas is contacted only in the foam contact area, it is easy for the ozone-containing gas to pass through the foam layer by channeling, but by blowing it into the liquid-phase contact area, the ozone-containing gas is made into fine bubbles to improve the contact efficiency and form the foam layer. can do.

[0019]

The present invention will now be described with reference to the embodiments of the drawings.
FIG. 1 is a system diagram showing an ozone treatment apparatus for biological sludge according to an embodiment. In FIG. 1, reference numeral 1 is a reaction tank, in which a liquid (biological sludge-containing liquid) 2 in the tank is accommodated in a lower portion to form a liquid phase contact area 3. The upper part of the liquid surface of the liquid phase contact area 3 is a foam contact area 4, and the in-tank liquid 2 is foamed to form a foam layer 5.

The liquid phase contact area 3 and the foam contact area 4 in the reaction tank 1 are provided with a stirrer 8 in which a paddle 7 projects radially from a rotary shaft 6 and can be rotated by a motor 9.

A circulation path 11 is connected to the reaction tank 1 so as to draw the in-tank liquid 2 from the lower liquid phase contact area 3 and circulate it above the foam contact area 4, and a circulation pump 12 is provided in the middle thereof. A spray nozzle 13 is provided at the tip. In the middle of the circulation path 11, a liquid to be treated 15 having a liquid supply pump 14 is connected. In the liquid phase contact area 3 below the reaction tank 1, a drainage path 17 having a siphon breaker 16 is provided.
Is connected. An air diffuser 18 for injecting an ozone-containing gas into the liquid phase contact area 3 is provided at the bottom of the reaction tank 1, an ozone-containing gas introduction path 20 is connected from an ozone generator 19, and exhaust ozone gas is provided at the top. Exhaust ozone gas path 2 to be discharged
1 is connected.

For ozone treatment of the liquid to be treated by the apparatus of FIG. 1, the liquid supply pump 14 is driven to supply the liquid to be treated from the liquid passage 15 to be treated, and the circulation pump 12 is driven to circulate the liquid. The in-tank liquid 2 is extracted from the tank and circulated. In this way, the liquid to be treated and the drawing liquid are mixed in the circulation path 11, and the mixed liquid is sprayed from the spray nozzle 13 toward the foam layer 5. Thereby, the liquid to be treated is introduced into the reaction tank 1, and the height of the foam layer 5 is adjusted so that the foam contact area 4 maintains a predetermined height.

On the other hand, the ozone-containing gas is introduced from the ozone generator 19 through the ozone-containing gas introduction path 20, diffused by the diffuser 18 and blown into the liquid 2 in the tank, whereby the liquid-phase contact area 3 is obtained. The in-tank liquid 2 and the ozone-containing gas are brought into contact with each other to oxidize and decompose the sludge and foam it to form a foam layer 5 in the foam contact region 4. The ozone-containing gas rising in the foam contact area 4 also contacts the sludge in the foam layer 5 and decomposes the sludge.
In this case, the ozone-containing gas blown into the liquid-phase contact area 3 foams in a state of reacting with the sludge, enters the foam layer 5 as it is, and further reacts with the sludge, and the sludge-containing liquid forming the foam layer 5 is ozone. With the release of the contained gas, it returns to the liquid-phase contact region 3 as droplets, and this is repeated. Since the foam layer 5 has a large surface area, the gas-liquid contact efficiency is high, and therefore, the treatment efficiency is higher than that in the case where no foam is formed. Further, since the load on the foam layer 5 is small, the strength of the reaction tank 1 may be small.

During this time, when the agitator 8 is rotated by the motor 9, the paddle 7 rotates in the liquid phase contact area 3 and the foam contact area 4 to shear and subdivide the foam. As a result, the foam generated in the liquid phase contact area 3 and the foam rising in the foam contact area 4 are subdivided, the bubble diameter becomes uniform, and the gas-liquid contact efficiency increases. At the same time, the stirring device 8 itself also functions as a gas-liquid contact medium, and the gas-liquid contact efficiency is increased.

The ozone exhaust gas separated from the foam contact area 4 is raised as it is and discharged from the exhaust ozone gas passage 21.
A part of the in-tank liquid 2 is discharged from the drainage path 17 as an ozone treatment liquid. At this time, since the siphon breaker 16 is open to the atmosphere, the in-tank liquid 2 is discharged in an overflow manner, and the liquid level in the liquid phase contact area 3 is kept constant.

When the liquid to be treated containing sludge is introduced from the upper part of the reaction tank 1 and brought into contact with the ozone-containing gas in a countercurrent, the contact efficiency is improved as compared with the case where the liquid to be treated is introduced from the lower part and brought into parallel flow contact. Ozone treatment can be performed more efficiently. The liquid passage 15 to be treated may be directly connected to the reaction tank 1 in the range from the upper part of the reaction tank 1 to the upper part of the liquid phase contact area 3 without being connected to the circulation path 11.

Test Example 1 Using the apparatus of FIG. 1, except that the inner diameter of the reaction tank 1 was set to 1 m, the height of the foam layer 5 was set to 3.5 m, and the depth of the liquid 2 in the tank was set to 1 m, and the paddle of the stirring device 8 was set. 8 were provided in the vertical direction at intervals of 0.5 m, and ozone-containing gas was blown into the activated sludge-containing liquid under the following conditions for ozone treatment. As a result, the absorption rate of ozone was 96% by weight. Activated sludge concentration in the liquid to be treated: 10,000 g / m ³ Flow rate of the liquid to be treated: 1 m ³ / h Ozone concentration: 20 g / m ³ Flow rate of ozone-containing gas: 25 m ³ / h

Comparative Example 1 In Test Example 1, ozone treatment was performed without operating the stirrer 8. As a result, the absorption rate of ozone was 65% by weight. In order to obtain the same ozone absorption rate of 96% by weight as in Test Example 1, the flow rates of the liquid to be treated and the ozone-containing gas were set to 1
It had to be reduced to / 2.

[0029]

EFFECT OF THE INVENTION In the biological sludge ozone treatment apparatus of the present invention, the ozone-containing gas is blown into the liquid-phase contact area in the reaction vessel to cause foaming, and a foam contact area is formed above the liquid-phase contact area. Since the stirrer is provided in the phase contact area and / or the foam contact area, the foam can be subdivided to make the foam diameter uniform, and the biological sludge-containing liquid can be efficiently contacted with the ozone-containing gas. It is possible to efficiently treat the biological sludge with ozone.

[Brief description of drawings]

FIG. 1 is a system diagram showing an ozone treatment apparatus for biological sludge according to an embodiment.

[Explanation of symbols]

 1 Reaction tank 2 Liquid in tank 3 Liquid contact area 4 Foam contact area 5 Foam layer 6 Rotating shaft 7 Paddle 8 Stirrer 9 Motor 11 Circulation path 12 Circulation pump 13 Spray nozzle 14 Liquid feed pump 15 Treated liquid path 16 Siphon breaker 17 Drainage Channel 18 Diffuser 19 Ozone Generator 20 Ozone-Containing Gas Introduction Channel 21 Exhaust Ozone Gas Channel

Claims (1)

[Claims] 1. A reaction tank for receiving a biological sludge-containing liquid for ozone treatment, a liquid-phase contact area for injecting an ozone-containing gas into the liquid-liquid contact in the biological sludge-containing liquid in the reaction tank, and an ozone-containing gas And a stirrer provided in the liquid phase contact area and / or the foam contact area. An apparatus for treating biological sludge using ozone.