JP2004141865A - Ozone treatment method of surplus sludge, treatment apparatus for surplus sludge, and sludge-ozone mixer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ozone treatment method of surplus sludge for increasing volume reduction rate by sufficiently reacting ozone with sludge when reducing volume of surplus sludge using ozone. <P>SOLUTION: In the surplus sludge treatment method for reducing the volume of the surplus sludge by bringing ozone into contact therewith, the surplus sludge is subjected to an aerobic treatment before ozone contact, a gaseous mixture of ozone and air is fed to the sludge to form a gas-liquid mixture, which is then forcibly fed to an ozone reactor 3 from the lower part thereof. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention provides an ozone treatment method and a treatment apparatus for treating excess sludge generated by treating organic wastewater such as sewage and industrial wastewater by using ozone to reduce the volume thereof, and bringing the excess sludge into contact with ozone. It relates to a sludge-ozone mixer.

Conventionally, when organic wastewater such as sewage and industrial wastewater is biologically treated, good treated water is obtained, but on the other hand, microorganisms proliferate and a large amount of excess sludge is generated. This excess sludge is partially composted and used effectively, but most of it is treated by dehydration incineration, landfill disposal, and the like. However, there are problems such as fear of harmful substances generated during incineration and shortage of disposal sites.

In view of the above, various techniques have been studied for contacting excess sludge with ozone to reduce its volume and to reduce the amount of generated sludge. For example, it is also possible to install a submerged pump in the ozone reaction tank 3, turn the pump while injecting ozone into the pump, and circulate the sludge in the tank, thereby bringing the sludge into contact with the ozone. However, if a pump is provided in the ozone reaction tank 3 as described above, the sludge in the reaction tank will be heated by the heat of the driving unit, and this will hinder biological treatment of the sludge after volume reduction. There is a possibility that the contact between the ozone and the sludge is insufficient in such a method, so that high volume reduction of the sludge cannot be expected.

On the other hand, as described in JP-A-2000-202485, ozone obtained from an ozone generator is injected into excess sludge by an ejector, the excess sludge is brought into contact with ozone to reduce the volume, and this is returned to an aeration tank. Biodegradation methods are known. According to this method, the above-mentioned problem is solved because the liquid temperature of the sludge does not rise, but the contact between the ozone and the sludge is still insufficient, so that the volume reduction rate cannot be increased. Further, in the apparatus described in the above publication for returning sludge reduced in volume by ozone to an existing aeration tank, since the existing aeration tank alone cannot completely process the sludge, it is necessary to increase the number of tanks and increase the amount of aeration. And other measures must be taken.

JP 2000-202485 A

The present invention has been made in view of the above points, and when reducing the volume of excess sludge using ozone, the excess volume that can sufficiently react ozone and sludge to increase the volume reduction rate can be increased. A first object is to provide a method for treating sludge with ozone. A second object of the present invention is to provide an apparatus for treating excess sludge which can independently decompose excess sludge without imposing a load on existing facilities. A third object of the present invention is to provide a sludge-ozone mixer suitable for bringing ozone into contact with sludge.

As a first means for solving the above-mentioned problems, the present invention relates to a method for treating excess sludge in which excess sludge is brought into contact with ozone to reduce the volume thereof. To provide an ozone treatment method characterized in that

Before the contact with the ozone, the excess sludge is aerobicized, so that the anaerobic sludge contained in the excess sludge is reformed to be aerobic. Volume reduction is promoted. In addition, the volume of excess sludge can be reduced by the self-digestion action of the sludge itself, and the volume reduction efficiency of excess sludge can be increased by both actions.

Further, as another means, the present invention relates to a method for treating excess sludge, in which ozone is brought into contact with excess sludge and introduced into the ozone reaction tank 3 to reduce the volume. An ozone treatment method is provided in which, after injecting a mixed gas mixture, the mixed gas is made into a gas-liquid mixed state, and the mixed gas is injected into the ozone reaction tank 3 from below the ozone reaction tank 3.

By injecting the mixed gas in which ozone and air are mixed in this manner, the mixed gas containing ozone in the sludge becomes a gas-liquid mixed state in which the mixed gas is dispersed as innumerable bubbles. And the reactivity of the two are increased. Furthermore, by injecting sludge in a gas-liquid mixed state into the tank from the lower part of the ozone reaction tank 3, they are discharged into the tank as if it were a jet jet, and the sludge in the tank is stirred and mixed. You. Therefore, the ozone and the sludge sufficiently react to increase the volume reduction rate.
Here, the reason for using a mixed gas in which air is mixed is that an excess gas is required to achieve a gas-liquid mixed state, so that using only ozone gas increases costs.

Further, it is preferable to inject ozone before injecting the mixed gas. By injecting ozone gas before injecting the mixed gas in this way, the initially injected high-concentration ozone is bubbled and stirred by the excess mixed gas injected later, thereby increasing the reactivity of sludge and ozone. . Further, in the case of such a multi-stage injection method, since a small amount of high-concentration ozone is initially injected, expensive ozone can be effectively used. In addition, as ozone of the mixed gas, it is preferable to use waste ozone collected after the ozone reaction tank 3.

Further, as a second means, the present invention provides a pretreatment tank 2 into which excess sludge discharged from a biological treatment facility for organic wastewater is introduced, and an ozone reaction for ozone-treating the sludge discharged from the pretreatment tank 2. A tank 3, a deozonization tank 5 for removing ozone from the sludge reduced in volume in the ozone reaction tank 3, and a biological material for biologically decomposing the sludge deozonized in the deozonization tank 5 to obtain treated water A treatment tank 6, wherein the pretreatment tank 2 is provided with an aerobic conversion means for aerobically reforming the excess sludge to be introduced. I do.

Since this apparatus includes the pretreatment tank 2 provided with the aerobicization means, the volume reduction of sludge is promoted. Furthermore, since it is provided with the ozone reaction tank 3, the deozone tank 5, the biological treatment tank 6, and the solid-liquid separation tank 7, for example, it is possible to return excess sludge discharged from the existing biological treatment facility to the biological treatment facility. And can be processed alone.
Furthermore, it is preferable to use a liquid dispersion type diffuser as the ozone removing means in the deozone tank 5, since ozone can be efficiently removed and collected without increasing the size of the deozone tank 5.

Further, as a third means, the present invention relates to a sludge-ozone mixer used when bringing ozone into contact with surplus sludge, comprising: a pressure feed passage 31 through which pressurized sludge can pass; Sludge-ozone, wherein injection parts 32 and 33 for injecting a mixed gas of air and air are provided. Provide a mixer.

As described above, according to the method for treating excess sludge according to the present invention, before contacting with ozone, the anaerobic sludge contained in the excess sludge is reformed to be aerobic, so that the subsequent reaction with ozone The capacity can be enhanced and the volume reduction can be promoted. Further, according to the method for treating excess sludge with ozone according to the present invention, the excess sludge and the ozone can be sufficiently contacted and reacted without increasing the temperature of the sludge when the excess sludge is brought into contact with the ozone. Therefore, it is possible to increase the volume reduction rate of sludge, and it is possible to extremely suppress the discharge of excess sludge by biologically treating the sludge.
Further, according to the apparatus for treating excess sludge according to the present invention, excess sludge can be efficiently reduced in volume, decomposed into treated water that can be discharged out of the system, and equipment costs can be reduced. be able to.
Furthermore, according to the sludge-ozone mixer according to the present invention, ozone can be caused to react by sufficiently contacting the sludge with ozone.

Hereinafter, an embodiment of the present invention will be described together with an ozone treatment method while describing an apparatus for treating excess sludge.
FIG. 1 is a schematic diagram showing both an ozone treatment method and a treatment apparatus for excess sludge, where P indicates a pump and B indicates a blower.
In FIG. 1, reference numeral 1 denotes a pretreatment tank 2 for aerobicizing excess sludge, an ozone reaction tank 3 for reacting ozone with the aerobicized excess sludge, and an ozone reaction tank. A deozone tank 5 for degassing and recovering ozone from the sludge reduced in volume in 3 (hereinafter sometimes referred to as “solubilized sludge”), and a biological treatment tank 6 for biologically decomposing the deozonized solubilized sludge. And a solid-liquid separation tank 7 for separating treated water from the solubilized sludge subjected to biological treatment and discharging the treated water to the outside of the system. This apparatus 1 can reduce the volume of excess sludge generated from a separate wastewater treatment facility, and treat the sludge without returning it to the wastewater treatment facility before it can be discharged to the outside independently (excess sludge). Functions as a self-contained processing device).

Specifically, wastewater is biologically treated in another wastewater treatment facility, and excess sludge extracted from a sedimentation tank (not shown) of the facility is introduced into the pretreatment tank 2. The excess sludge of this separate facility may be excess sludge generated by aerobic digestion of wastewater or excess sludge generated by anaerobic digestion, and the present invention provides any of aerobic sludge and anaerobic sludge. But the volume can be reduced.
The pretreatment tank 2 is provided with an aeration device 10 (blower) for blowing air as a means for making the sludge aerobic. The excess sludge is reformed to be aerobic in the pretreatment tank 2 by the aeration device 10, whereby the volume of the sludge can be reduced by self-digestion, and the reactivity with ozone is increased in the ozone reaction tank 3 in the subsequent stage. be able to. Further, by aerobicizing, when the solubilized sludge is decomposed in the biological treatment tank 6 and then solid-liquid separated by membrane filtration, clogging of the membrane surface can be reduced. It is more effective if oxygen gas is blown in instead of air.

Next, the sludge that has been subjected to the aerobic treatment is introduced into the ozone reaction tank 3 after passing through the fine mesh screen 8 in order to remove impurities such as hair. The excess sludge introduced into the ozone reaction tank 3 is pumped into a sludge-ozone mixer 30 via a pumping pump 11, where ozone obtained from an ozone generator 12 is first injected, and then ozone and air After the mixed gas of the above is excessively injected, the mixed gas is press-fitted into the tank 3 from below the ozone reaction tank 3 in a gas-liquid mixed state. Accordingly, the sludge in the ozone reaction tank 3 is drawn out, made into a gas-liquid mixture state containing ozone by the mixer 30, and circulated again to the ozone reaction tank 3.
In order to make the excess sludge and ozone more easily react with each other, the pH is set higher, or a radical generating substance such as a hydrogen peroxide solution is added to the extracted excess sludge before contacting with the ozone. Is preferred. In the figure, reference numeral 14 denotes the addition device.

The sludge-ozone mixer 30 is not particularly limited, but it is preferable to use a static mixer such as an ejector mixer or a static mixer because it does not generate heat by itself. Among them, it is more preferable to use an ejector mixer because the sludge is hardly clogged and the sludge can be sufficiently brought into contact with ozone. When a static mixer is used, the mixer may be installed in the ozone reaction tank 3, but is provided outside the ozone reaction tank 3 in this example for easy maintenance.

As a preferred sludge-ozone mixer 30 of the present invention, for example, as shown in FIG. 2, at least two injection portions 32 and 33 are provided in the longitudinal direction (pumping direction) of a pumping path 31 through which sludge is pumped. Mixers provided side by side at predetermined intervals are exemplified. More specifically, the mixer 30 has a nozzle-shaped inner tube having a narrow discharge port 35a formed in the front inside a nozzle-shaped outer pipe 34 having a narrow discharge port 34a formed in the front. 35 is fitted. In the outer tube 34, a first injection portion 32 for injecting ozone gas into a dead end portion 36 formed between the inner tube 35 and the outer tube 34 is formed. A second injection part 33 for injecting a mixed gas of ozone and air is formed in front of the discharge port 35a of the pipe 35.

The excess sludge is sent from the rear opening 37 of the mixer 30 into the pumping passage via the pumping pump 11, and the sludge is discharged into the mixing chamber 38 at a high flow rate from the discharge port 35 a of the inner pipe 35. Is done. In the mixing chamber 38, the high-concentration ozone injected from the first injection unit 32 comes into contact with sludge, and further, the mixed gas (of ozone and air) injected from the second injection unit 33 in front thereof is The ozone and the sludge are further stirred and mixed. Then, the sludge in a gas-liquid mixed state in which countless bubbles are present is vigorously discharged from the discharge port 34 a of the outer cylinder 34 to the ozone reaction tank 3, and the sludge and ozone are further stirred and mixed in the tank 3. In addition, stirring and mixing can be expected even when the bubbles rise in the ozone reaction tank 3.
The opening area ratio of the rear opening 37 of the inner pipe 35, the discharge port 35a of the inner pipe 35, and the discharge port 34a of the outer pipe 34 may be formed in a range of approximately 3: 1: 1 to 15: 1: 2. The amount of ozone gas injected from the first injection unit 32 is about 0.05 kg to 0.5 kg per 1 kg of sludge, and the amount of mixed gas injected from the second injection unit 33 is 2 m ³ to 1 kg SS of sludge. About 20 m ³ may be injected. The concentration of ozone gas injected from the first injection section 32 is about 1% by weight or more, preferably 5% by weight or more. On the other hand, the upper limit is not particularly limited, and the higher the concentration, the more preferable. Taking into account the capacity and production cost, it is preferably about 15% by weight or less. Further, the ozone concentration of the mixed gas injected from the second injection unit 33 varies depending on the injection amount from the first injection unit 32, the recovery rate, and the like, but is preferably about 0.02 to 2% by weight.

Next, the sludge reduced in volume in the ozone reaction tank 3 is introduced into the deozone tank 5, where ozone is removed and collected. The mixed gas of ozone and air collected in the deozone tank 5 is collected in the collecting pipe together with the mixed gas collected by the waste ozone collector 16 from the upper part of the ozone reaction tank 3, and is mixed with the sludge-ozone mixer 30. And is reused for the volume reduction process.
The ozone removing means of the deozone tank 5 is not particularly limited. For example, a gas dispersion method using a submerged stirring pump or the like can be adopted. It is preferable to use a liquid dispersion type disperser that removes ozone while dispersing the solubilized sludge in the air because the size can be reduced.
A part of the collected ozone is sent to a waste ozonizer 13 for removing ozone by an ozonizing agent or the like, and is rendered harmless. Further, in the apparatus 1 of the present invention, in order to prevent ozone from leaking out of the system, ozone leakage prevention means such as applying a negative pressure to the inside of the apparatus through which ozone flows is taken.
As such a liquid dispersion type diffuser, for example, as shown in FIG. 3, a dispersion tower in which a liquid reservoir 44 is provided on the upper part of a lower opening type cylindrical body 43 provided with an air intake 41 in a part thereof 40 and the like.
The principle of the stripping tower 40 is that the solubilized sludge introduced through the circulation pump 17 overflows from the liquid reservoir 44 and flows down along the inner peripheral surface of the cylindrical body 43 (indicated by a two-dot chain line in the figure). The ozone is removed by extracting the air inside the cylinder 43 with the blower 18. A part of the ozone collected by the blower 18 is detoxified by the waste ozonizer 13, and the remaining mixed gas of ozone and air is guided to the mixer 30 for reuse.

Then, the deozonized solubilized sludge is sent to the biological treatment tank 6 and biologically decomposed. The treatment in the biological treatment tank 6 includes an activated sludge method in which activated sludge, which is an aerobic microorganism, is suspended in the tank and aeration is performed, or a fixed bed of a biological carrier is provided in the tank, and a fixed-bed contact method in which aeration is performed. Various methods such as a treatment method and a fluidized bed type contact treatment method in which a biological carrier having organisms attached to a carrier having a large specific surface area are suspended and aerated can be adopted, but from the point that high load treatment can be performed. It is preferable to employ a fluidized bed contact treatment method. When the fluidized bed type is adopted, it is preferable to provide a movement preventing net 21 so that the carrier does not move to the solid-liquid separation tank 7 carelessly.
A part of the sludge generated in the biological treatment tank 6 is withdrawn by the return pump 19, sent to the ozone reaction tank 3, and subjected to the volume reduction process again.

(4) Finally, the sludge water treated in the biological treatment tank 6 is subjected to solid-liquid separation in the solid-liquid separation tank 7, and only the treated water is discharged out of the system. Although the solid-liquid separation means is not particularly limited, it is preferable to use an immersion-type porous flat membrane 20 (for example, Kubota's submerged membrane [registered trademark]) because of easy cleaning, A washing tank may be provided so that washing can be performed with a washing agent such as sodium hypochlorite. In addition, this treated water may be discharged as it is, or may be returned to the inflow side of another wastewater treatment facility that is a source of the excess sludge introduced into the present apparatus 1.

Although the embodiments of the present invention have been described above, the above-described embodiments are merely examples, and various design changes can be made. For example, three or more gas injection sections of the sludge-ozone mixer may be provided. In the above embodiment, the screen is provided in front of the ozone reaction tank. However, a screen may be provided in front of the pretreatment tank, or a screen may be provided on both sides to remove foreign substances contained in excess sludge. You may make it. In the above embodiment, the sludge is introduced from the sludge-ozone mixer to the lower part of the ozone reaction tank, but the lower part means not only the bottom part but also the side part of the ozone reaction tank. Further, in the above embodiment, the apparatus and the method for independently processing the excess sludge of the facility without returning it to the facility are illustrated. However, not only the self-contained processing apparatus, but also the ozone treatment of the present invention. The method may be applied to volume reduction treatment of known biological treatment facilities.

The following test was conducted to confirm the effect of the aerobic treatment in the pretreatment tank.
Example 1
The excess sludge (concentration 6000 mg / L) resulting from the activated sludge treatment of rural waste water treatment facility to prepare 500 kg, which cylindrical transparent vessel (bottom × height: about 0.28 m ² × 2.2 m) placed in a Then, air was blown from the bottom of the container at a gas amount of about 4 m ³ / hour for 40 minutes, and the volume reduction rate was determined to be 33.0%.
Next, ozone (ozone concentration: 1.1% by weight) obtained by the ozone generator was blown from the bottom of the container at a gas amount of 1 m ³ / hour for 40 minutes, and finally, the overall volume reduction rate was determined. Upon examination, it was 69.5%.
Volume reduction rate = (height of settled sludge before treatment−height of settled sludge after treatment) / height of settled sludge before treatment.
Comparative Example A transparent container filled with excess sludge was prepared in the same manner as in the above example. Ozone (ozone concentration: 1.1% by weight) obtained by an ozone generator was blown from the bottom of the container (without blowing air) at a gas amount of 1 m ³ / hour for 40 minutes, and then the volume was reduced. When the conversion was examined, it was 54.9%.
By performing the aerobic treatment before performing the ozone treatment, a remarkable difference was observed in the sludge volume reduction.

Example 2
Furthermore, a demonstration machine of this device was manufactured and the effect of volume reduction was confirmed.
Shows in outline ... Figure 1 of the apparatus, the pretreatment tank: 4.8 m ^3, an ozone reaction tank: 2.2 m ^3, the biological treatment tank 1.8 m ^3, the solid-liquid separation layer: Using those 1.8 m ³ did. The air-ozone mixer used had the structure shown in FIG.
Excess sludge: Surplus sludge (concentration: 15000 to 20000 mg / L) generated by activated sludge treatment in an agricultural settlement wastewater treatment facility (750 persons) was used.
Test period: about 50 days.
First, 4.8 m ^{3 of the} surplus sludge was charged into the pretreatment tank of this apparatus. As the volume reduction treatment proceeds, the excess sludge in the pretreatment tank is reduced every day. Therefore, surplus sludge was additionally supplied at intervals of about 7 to 8 days so as to fill the pretreatment tank. In this pretreatment tank, the excess sludge was blown with air at a rate of about 12 m ³ / hour throughout the day (without stopping during the test period). The sludge fluidized by the aerobic treatment in this pretreatment tank was led to an ozone reaction tank and reacted with ozone. In the ozone reaction tank, using an ozone mixer, the sludge is brought into contact with ozone gas (ozone concentration of about 7.4% by weight) at a gas amount of 0.24 m ³ / hour and a gas-liquid ratio of 5%. A process of bringing a gas (ozone concentration of about 0.035% by weight) into contact with a mixed gas amount of 3 m ³ / hour at a gas-liquid ratio of 62.5% and returning it vigorously from the lower part of the ozone reaction tank is repeatedly performed throughout the day. Was. Finally, the solubilized sludge reduced in volume in the ozone reaction tank was guided to a biological treatment tank of a fluidized bed type, and after biological treatment, treated water was discharged out of the system through a solid-liquid separation tank. Emissions per day treated water was approximately 0.5 m ³ before and after. The total amount of treated water obtained during the test period, with 23.2M ^3, sludge in the biological treatment tank immediately after the test period is 6.3 m ^3, volume reduction ratio from this 79% Met.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the ozone processing method of the excess sludge of this invention, and the processing apparatus of an excess sludge. In the figure, the alternate long and short dash line indicates the gas flow. FIG. 2 is a reference sectional view showing the mixer of the present invention. FIG. 3 is a reference sectional view showing a liquid dispersion type diffuser of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Treatment apparatus of excess sludge, 2 ... Pretreatment tank, 3 ... Ozone reaction tank, 5 ... De-ozone tank, 6 ... Biological treatment tank, 7 ... Solid-liquid separation tank, 30 ... Sludge-ozone mixer, 31 ... Pressure feeding Road, 32, 33 ... injection part, 40 ... stripping tower

Claims (7)

(4) A method for treating excess sludge, which comprises contacting ozone with excess sludge to reduce the volume thereof, wherein the excess sludge is aerobicized before the contact with ozone. In a method for treating excess sludge, in which ozone is brought into contact with excess sludge and introduced into an ozone reaction tank (3) to reduce the volume, after injecting a mixed gas of ozone and air into the excess sludge, An ozone treatment method for surplus sludge, comprising press-fitting the ozone reaction tank 3 from below the ozone reaction tank 3 in a gas-liquid mixed state. In the method for treating excess sludge, in which ozone is brought into contact with the excess sludge and introduced into the ozone reaction tank (3) to reduce the volume, ozone is injected into the excess sludge, and ozone and air are further mixed. An ozone treatment method for surplus sludge, which comprises injecting a mixed gas into the ozone reaction tank (3) from a lower part of the ozone reaction tank (3) in a gas-liquid mixed state. The ozone treatment method for surplus sludge according to claim 2 or 3, wherein the ozone of the mixed gas is waste ozone collected after the ozone reactor (3). A pretreatment tank (2) into which excess sludge discharged from the biological treatment facility for organic wastewater is introduced, an ozone reaction tank (3) for treating the sludge in the pretreatment tank (2) with ozone, and the ozone reaction tank A deozone tank (5) for removing ozone from the sludge reduced in volume in (3), and a biological treatment tank for obtaining treated water by biologically decomposing the sludge deozoned in the deozone tank (5). (6), wherein the pretreatment tank (2) is provided with an aerobicizing means for aerobicly reforming the excess sludge to be introduced, the apparatus being configured to treat excess sludge. . The apparatus for treating excess sludge according to claim 5, wherein the ozone removing means in the de-ozone tank (5) is a liquid dispersion type diffuser (40). A sludge-ozone mixer used when bringing excess sludge into contact with ozone, a pressure feed path (31) through which sludge passes, and an injection section (32, 33) into which ozone or a mixed gas of ozone and air is injected. ), Wherein the injecting section (32, 33) is arranged in parallel at least two places in the longitudinal direction of the pressure feed path (31).

Images