JP3697729B2 - Biological sludge ozone treatment equipment - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an ozone treatment apparatus for biological sludge for ozone oxidation of biological sludge.
[0002]
[Prior art]
For the purpose of reducing the volume of excess sludge and the like in activated sludge treatment, biological sludge such as excess sludge (hereinafter sometimes simply referred to as sludge) is reacted with ozone to undergo oxidative decomposition.
In the conventional sludge ozone treatment method, an apparatus is used in which a sludge-containing liquid is filled in a reaction tank, ozone-containing gas is blown into the sludge-containing liquid, gas-liquid contact is performed, and sludge is decomposed. In this conventional device, the gas-liquid contact area is small, so it is necessary to lengthen the residence time in order to sufficiently react sludge with ozone, and efficient treatment such as wasteful consumption of expensive ozone. There is a problem that is not performed. Although the gas-liquid contact area can be increased by mechanical stirring of the liquid to be processed and the processing efficiency can be improved, there is a problem that the processing cost increases in this case.
[0003]
By the way, if ozone treatment is performed by blowing ozone-containing gas into the sludge-containing liquid in the reaction tank, the sludge-containing liquid is foamed and the bubbles are easily taken out of the tank. For this reason, conventionally, defoaming is performed by adding an antifoaming agent, or a spray nozzle is provided in the upper part of the reaction tank, and industrial water or final treated water is sprayed from the nozzle to the liquid surface to eliminate foaming. Is preventing.
Thus, in the conventional sludge ozone treatment method, foaming is suppressed as much as possible to perform ozone treatment, and ozone treatment using foaming has not been performed so far.
[0004]
[Problems to be solved by the invention]
The objective of this invention is providing the ozone treatment apparatus of the biological sludge which can ozone-treat biological sludge efficiently at low cost.
[0005]
[Means for Solving the Problems]
The present invention includes a reaction tank that receives a biological sludge-containing liquid and performs ozone treatment;
A liquid-phase contact area in which ozone-containing gas is blown into the biological sludge-containing liquid in the reaction tank and brought into gas-liquid contact;
A foam contact area for forming a foam layer on the upper part of the liquid phase contact area by gas-liquid contact by blowing ozone-containing gas;
Aerated by introducing ozone treatment liquid from the reaction vessel, and the exhaust ozone gas discharged from the foam contact area released in the mixture, while maintaining the reaction vessel and liquid seal under pressure, the ozone A biological sludge ozone treatment apparatus comprising: an aeration tank that absorbs and removes the mixed liquid .
[0006]
The biological sludge ozone treatment apparatus of the present invention is preferably constructed as follows because the foam layer can be maintained and controlled.
(A) When the biological sludge concentration of the biological sludge-containing liquid is 2,000 to 20,000 mg / l, the foam layer can be easily maintained.
(B) When the height of the foam layer in the foam contact area of the reaction vessel is 1 m or more, the processing efficiency is increased.
(C) If a liquid spraying device for spraying the liquid is installed above the foam contact area of the reaction tank, the height of the foam layer can be easily controlled.
(D) When the biological sludge-containing liquid in the reaction tank is used as a part of the sprayed liquid of the liquid spraying apparatus and this is circulated and sprayed, it is easy to control the height of the foam layer and ozone can be used effectively.
[0007]
The biological sludge to be treated in the present invention is sludge containing biological sludge generated in aerobic treatment, anaerobic treatment, etc., and is preferably composed mainly of biological sludge like excess sludge. As such, it may contain some inorganic substances. The biological sludge concentration in the biological sludge-containing liquid is 2,000 to 20,000 mg / l, preferably 5,000 to 15,000 mg / l. When it exists in this range, the height of a foam layer can be hold | maintained at 1 m or more by selecting foaming conditions, such as the ozone flow volume, spray flow volume, and the presence or absence of a foam holding member.
[0008]
The reaction tank used for the ozone treatment in the present invention is a tank for reacting the sludge in the sludge-containing liquid with the ozone-containing gas to oxidize, and in the lower part, the ozone-containing gas is blown into the liquid-phase sludge-containing liquid. A liquid phase contact area for gas-liquid contact is formed, and a foam contact area for contacting the foamed foam and the ozone-containing gas is formed on the upper part. The height of the liquid phase contact area is 0.2 to 3 m, preferably 0.5 to 1.5 m. The height of the foam contact area is 1 m or more, preferably 1 to 10 m, more preferably 2 to 5 m from the liquid surface of the sludge-containing liquid in the liquid phase contact area.
[0009]
It is preferable to maintain the liquid phase contact area at a substantially constant height.For example, the reaction tank is provided with a tank liquid discharge port using a pressure-controlled valve, and the liquid level of the liquid in the tank is maintained at a constant height. Can be drunk. The foam contact area is preferably formed in the space above the liquid surface (liquid outlet in the tank) of the liquid phase contact area.
[0010]
The foam contact area can be filled with a foam holding member, which makes it difficult for bubbles to be retained due to the large inner diameter of the reaction tank, or when the sludge-containing liquid is difficult to foam due to low biological sludge concentration. Even in such a case, the foam can be efficiently held, and the ozone treatment efficiency can be increased. The foam holding member may be of any structure that can hold the foam, but preferably has a partition plate structure such as a honeycomb or lattice.
[0011]
As the ozone-containing gas, ozone-containing air, ozonized air, or the like can be used. The amount of ozone introduced is 1 to 10%, preferably 3 to 5%, based on the VSS weight of the biological sludge to be introduced. The flow rate of the ozone-containing gas is 1 to 30 m / hr, preferably 5 to 20 m / hr, as the gas linear velocity of the reaction tank.
[0012]
In the present invention, in order to maintain the inside of the reaction tank in a pressurized state, aeration is performed by introducing ozone treatment liquid from the reaction tank and aeration, and discharging exhaust ozone gas discharged from the foam contact area into the liquid mixture and liquid sealing A tank is provided.
[0013]
The aeration tank is preferably provided with an air diffuser that discharges exhaust ozone gas into the liquid in the tank. As a diffuser, in addition to a porous tube with a large number of small holes formed in a hollow pipe, a porous hollow tube made of a porous material, a flexible synthetic resin tube is provided with a large number of cuts and opened when gas is blown out. However, an air diffuser of the type that is closed when the gas is stopped to prevent backflow can be used. The liquid depth at which such a gas outlet such as an air diffuser is provided is 1 to 50 m, preferably 3 to 10 m.
[0014]
The pressure of the reaction tank maintained by the aeration tank is set to a gauge pressure of 0.1 to 5 kgf / cm ² , preferably 0.5 to ² kgf / cm ² . In order to maintain such a pressure, gauge pressure 0.1~5kgf / cm ² the ozone-containing gas, preferably supplied in 0.5~2kgf / cm ^2, the pressure in the path to take out the process liquid from the reaction vessel It is preferable to provide a valve and close the valve when the pressure is lower than the predetermined pressure, and open the valve when the predetermined pressure is exceeded, but keep the liquid level of the reaction tank constant, and the ozone-containing gas according to the pressure The supply amount and / or the discharge amount may be controlled.
[0015]
[Action]
In the biological sludge ozone treatment apparatus of the present invention, a liquid sludge containing liquid is introduced into a reaction tank to form a liquid phase contact area. 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 subjected to ozone treatment. At the same time, a foam layer is formed in the upper part of the liquid phase contact area by foaming, and in this foam layer, contact between biological sludge and ozone occurs, and a foam contact area is formed. As a result, the sludge is contacted with ozone in both the liquid phase contact area and the foam contact area, and the sludge is oxidized by ozone.
[0016]
When ozone gas moves to the liquid side in the reaction tank, the rate of mass transfer is proportional to the contact area and the concentration difference, but if the exhaust ozone gas released from the foam contact area is discharged into the atmosphere as it is, the inside of the reaction tank is almost large. Since it becomes equal to the atmospheric pressure, there is a limit to the concentration difference. On the other hand, by sealing the exhaust ozone gas in the aeration tank , the inside of the reaction tank is pressurized, the concentration increases, and the mass transfer speed increases. Thereby, ozone absorption efficiency becomes high and the oxidation effect of sludge becomes high.
[0017]
At the same time, the ozone in the exhaust ozone gas is absorbed and removed by the liquid and discharged in a harmless state. In particular, when an aeration tank is used as a liquid sealing device, if the liquid sealing is performed with a mixed solution containing an oxidizable substance, ozone absorption efficiency is high, and leakage of ozone into the exhaust gas is prevented. Even in this case, since the ozone absorption rate in the reaction tank is high, the amount of ozone remaining in the exhaust ozone gas is usually about 1 mg / l, and the influence on microorganisms in the activated sludge of the aeration tank is small. Further, when exhausted ozone gas is blown using an air diffuser in the aeration tank , it is released as fine bubbles, so that the ozone absorption efficiency is increased.
[0018]
A liquid spraying device is installed above the foam contact area in the reaction tank, and the liquid to be treated, industrial water, final treatment liquid, withdrawal liquid from the reaction tank, or a mixture of the withdrawal liquid and the liquid to be treated is used as a foam layer. It is possible to spray toward the surface, thereby suppressing excessive foaming and maintaining the foam contact area at a predetermined height. In this case, it is preferable to use a liquid to be treated, a drawing liquid or a mixed liquid of a drawing liquid and a liquid to be treated because the sludge concentration of the liquid in the tank does not decrease.
[0019]
Extracting and spreading sludge-containing liquid, including in the case of biological sludge, is not generally done because solids can easily block the nozzle, but in systems where biological sludge is treated with ozone, biological sludge is not The inventors have confirmed that the nozzles and the like are not clogged even when the liquid in the tank is sprayed because the adhesion is reduced as the size is reduced. In addition, since the liquid to be treated is diluted with the liquid mixture of the liquid in the tank and the liquid to be treated, clogging of the nozzle etc. hardly occurs, but if the liquid to be treated that is not ozone-treated is used alone, the nozzle is likely to clog. It is preferable not to use it for spraying.
[0020]
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 that fills the reaction tank with the liquid to be treated, resulting in a low-cost apparatus.
The ozone treatment apparatus of the present invention can be used when the excess sludge is treated with ozone to reduce the volume, or when the mixed liquid in the tank is extracted from a biological treatment tank, for example, an aerobic treatment tank, and is ozone-treated.
[0021]
In the reaction tank, sludge reacts with ozone to be oxidatively decomposed and converted into BOD components. The sludge-containing liquid (tank liquid) that has been subjected to ozone treatment increases in viscosity and becomes a liquid having a very high foaming property. For this reason, by making a sludge containing liquid and ozone containing gas contact, it foams easily and a foam layer is formed. In the present invention, since a foam layer is formed and brought into contact with the ozone-containing gas, the sludge present in the liquid in the tank becomes foam in a state of contact with ozone, and further contacts with ozone in the state of foam. It is disassembled and repeated. For this reason, compared with the case where it contacts only in a liquid phase contact area, the efficiency of ozone treatment becomes high. If contact is made only in the foam contact area, the ozone-containing gas can easily pass through the foam layer by channeling, but by blowing into the liquid phase contact area, the ozone-containing gas is made into fine bubbles to increase the contact efficiency and form the foam layer. can do.
[0022]
In this case, the ozone gas mass transfer speed is increased by sealing the exhaust ozone gas with a liquid sealing device and pressurizing the reaction tank, and in particular, the movement speed increases at a large contact area such as a foam contact area. Absorption efficiency increases.
Filling the foam contact area with a foam holding member makes it possible to hold the foam well even when the internal diameter of the reaction tank is large and it is difficult to hold the foam, or when the biological sludge-containing liquid is difficult to foam. Therefore, the ozone treatment can be performed by forming a foam layer having an appropriate height.
[0023]
【Example】
The invention will now be described by way of example in the drawings.
FIG. 1 is a system diagram showing an ozone treatment apparatus for biological sludge according to an embodiment. In FIG. 1, 1 is a reaction tank and 2 is an aeration tank, which is used as a liquid sealing device . 3 is a solid-liquid separation tank.
In the reaction tank 1, a sludge-containing liquid is accommodated in the lower part as a tank liquid 11, and a liquid phase contact area 12 is formed. The upper part of the liquid surface of the liquid phase contact area 12 is a foam contact area 13, and the foam liquid 14 is formed by foaming the liquid 11 in the tank.
[0024]
A circulation path 16 is connected to the reaction tank 1 so as to draw the liquid 11 in the tank from the lower liquid phase contact area 12 and circulate to the upper part of the foam contact area 13, and a circulation pump 17 is provided in the middle part thereof. A spray nozzle 18 is provided at the tip. In the middle of the circulation path 16, a sludge-containing liquid introduction path 21 having a liquid feed pump 20 is connected. An in-tank liquid discharge path 24 having a pressure indicator 22 and a pressure valve 23 is connected to the aeration tank 2 from the liquid phase contact area 12 at the bottom of the reaction tank 1.
At the bottom of the reaction tank 1, an air diffuser 26 that blows ozone-containing gas into the liquid phase contact area 12 is provided, and an ozone-containing gas introduction path 28 is connected from an ozone generator 27. An exhaust ozone gas passage 29 for exhausting exhaust ozone gas from the top of the reaction tank 1 is connected to an air diffuser 31 provided at the bottom of the aeration tank 2.
[0025]
The aeration tank 2 is used as a liquid sealing device. In addition to the air diffuser 31, the air diffuser 33 is provided in the mixed liquid 32 as the sealing liquid , and the air supply path 35 communicates from the blower 34. Yes. The liquid tank 36 and the return sludge path 37 communicate with the aeration tank 2, and the transfer path 38 communicates with the solid-liquid separation tank 3. A separation liquid take-out path 39 communicates with the upper part of the solid-liquid separation tank 3, a sludge take-out path 40 communicates with the bottom, and its tip branches into a sludge-containing liquid introduction path 21 and a return sludge path 37.
[0026]
In order to ozone-treat biological sludge-containing liquid using the apparatus of FIG. 1, the feed pump 20 is driven to supply the sludge-containing liquid from the sludge-containing liquid introduction path 21, and the circulation pump 17 is driven from the circulation path 16. The tank liquid 11 is drawn out and circulated. In this way, the sludge-containing liquid and the drawing liquid are mixed in the circulation path 16, and this mixed liquid is sprayed from the spray nozzle 18 toward the foam layer 14. This introduces the sludge-containing liquid into the reaction tank 1 and adjusts the height of the foam layer 14 so that the foam contact area 13 maintains a predetermined height.
[0027]
On the other hand, ozone-containing gas is introduced from the ozone generator 27 through the ozone-containing gas introduction path 28, diffused by the air diffuser 26, and blown into the liquid 11 in the tank. 11 and ozone-containing gas are brought into contact with each other to oxidize and decompose sludge and to foam, thereby forming a foam layer 14 in the foam contact area 13. The ozone-containing gas rising in the foam contact area 13 also comes into contact with the sludge in the foam layer 14 and decomposes the sludge. In this case, the ozone-containing gas blown into the liquid phase contact area 12 foams while reacting with the sludge, enters the foam layer 14 as it is, reacts with the sludge as it is, and the sludge-containing liquid that forms the foam layer 14 is ozone. With the separation of the contained gas, it becomes a droplet and returns to the liquid phase contact area 12, and this is repeated. The foam layer 14 has a large surface area, and since the inside of the reaction tank 1 is in a pressurized state, the gas-liquid contact efficiency is high. Therefore, the processing efficiency is higher than when foaming or no pressure is applied. Moreover, since the load of the foam layer 14 is small, the intensity | strength of the reaction tank 1 may be small.
[0028]
The ozone exhaust gas separated from the foam contact area 13 is raised as it is, introduced into the aeration tank 2 from the exhaust ozone gas passage 29, and discharged from the diffuser 31 into the mixed solution 32. As a result, the inside of the reaction tank 1 is maintained in a pressurized state, and the ozone absorption efficiency in the reaction tank 1 is increased, and the ozone contained in the exhaust ozone gas is absorbed by the mixed liquid 32, thereby detoxifying and dissipating into the atmosphere. .
[0029]
Part of the tank liquid that has been subjected to ozone treatment in the reaction tank 1 and oxidized to sludge is introduced into the aeration tank 2 from the tank liquid discharge passage 24 through the pressure valve 23. At this time, when the pressure indicator 22 reaches a predetermined pressure, the pressure valve 23 is opened and closed to keep the reaction tank 1 at a predetermined pressure.
[0030]
In the aeration tank 2, the ozone treatment liquid introduced from the tank liquid discharge passage 24, the treatment liquid introduced from the treatment liquid introduction passage 36, and the return sludge introduced from the return sludge passage 37 are mixed together, and the blower 34 is mixed. To the air supply path 35 and aeration is performed by aeration from the aeration device 33 to remove BOD. The mixed liquid 32 as the sealing liquid is introduced into the solid-liquid separation tank 3 from the transfer path 38 to perform solid-liquid separation, and the separated liquid is taken out from the separated liquid take-out path 39 as a processing liquid. Further, the separated sludge is taken out from the sludge take-out passage 40, a part thereof is returned as return sludge from the return sludge passage 37 to the aeration tank 2, and the remainder is introduced into the reaction tank 1 from the sludge-containing liquid introduction passage 21 to perform ozone treatment.
[0031]
When the sludge-containing liquid is introduced from the upper part of the reaction tank 1 and brought into contact with the ozone-containing gas in countercurrent, the contact efficiency is improved as compared with the case where the sludge-containing liquid is introduced from the lower part and brought into contact in parallel flow. be able to.
The sludge-containing liquid introduction path 21 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 12 without being connected to the circulation path 16.
[0032]
Test example 1
With the apparatus shown in FIG. 1, however, the inside diameter of the reaction tank 1 is set to 1 m, the height of the foam layer 14 is set to 3.5 m, and the depth of the liquid 11 in the tank is set to 1 m. Ozone treatment was performed by blowing the contained gas.
Activated sludge concentration in sludge-containing liquid: 10.000 g / m ³
Sludge-containing liquid flow rate: 1m ³ / h
Ozone concentration: 20 g / m ³
Ozone-containing gas flow rate: 25m ³ / h
Ozone gas supply pressure: 1.0 kgf / cm ² (gauge pressure)
[0033]
In the above treatment, the exhaust ozone gas was diffused from the diffuser 31 provided at the position of the liquid depth of 5 m below the aeration tank 2 to perform liquid sealing. Then the pressure valve 23 was operated so as to open at a gauge pressure of 0.6 kgf / cm ² closed, at 0.7 kgf / cm ^2. As a result, the ozone absorption rate in the reaction tank 1 was 96% by weight.
[0034]
Comparative Example 1 In Test Example 1, the aeration tank 2 was not used, the exhausted ozone gas was discharged into the atmosphere to perform ozone treatment, and the liquid in the tank was drawn out from the bottom of the reaction tank through an overflow pipe having a height of 2 m. . As a result, the absorption rate of ozone was 70% by weight. In order to obtain the same 96 wt% ozone absorption rate as in Test Example 1, it was necessary to reduce the flow rates of the liquid to be treated and the ozone-containing gas by half.
[0035]
【The invention's effect】
In the biological sludge ozone treatment device of the present invention, ozone-containing gas is blown into the liquid phase contact area in the reaction tank to cause foaming, a foam contact area is formed above the liquid phase contact area, and the exhaust ozone gas is liquidated in the aeration tank. Since it is sealed, the biological sludge-containing liquid can be efficiently contacted with the ozone-containing gas, and the ozone concentration efficiency in the reaction tank can be increased by keeping the reaction tank in a pressurized state and increasing the ozone concentration difference. At the same time, the amount of ozone remaining in the exhaust ozone gas can be reduced, and the ozone in the exhaust ozone gas in the aeration tank can be absorbed and removed into the liquid mixture with high ozone absorption efficiency, thereby making it harmless. It is possible to ozone-treat biological sludge efficiently at low cost.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an ozone treatment apparatus for biological sludge according to an embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Aeration tank 3 Solid-liquid separation tank 11 Liquid in tank 12 Liquid phase contact area 13 Foam contact area 14 Foam layer 16 Circulation path 17 Circulation pump 18 Spray nozzle 20 Feed liquid pump 21 Sludge containing liquid introduction path 22 Pressure indicator 23 Pressure valve 24 Tank liquid discharge passages 26, 31, 33 Air diffuser 27 Ozone generator 28 Ozone-containing gas introduction passage 29 Waste ozone gas passage 32 Mixed liquid 34 Blower 35 Air supply passage 36 Liquid to be treated introduction passage 37 Return sludge passage 38 Transfer path 39 Separation liquid extraction path 40 Sludge extraction path

Claims (1)

A reaction tank for receiving biological sludge containing liquid and performing ozone treatment;
A liquid-phase contact area in which ozone-containing gas is blown into the biological sludge-containing liquid in the reaction tank and brought into gas-liquid contact;
A foam contact area for forming a foam layer on the upper part of the liquid phase contact area by gas-liquid contact by blowing ozone-containing gas;
Aerated by introducing ozone treatment liquid from the reaction vessel, and the exhaust ozone gas discharged from the foam contact area released in the mixture, while maintaining the reaction vessel and liquid seal under pressure, the ozone A biological sludge ozone treatment apparatus, comprising: an aeration tank that absorbs and removes the mixed liquid .

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