JP2002035780A - Method and apparatus for improving sludge settling property and sludge treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for improving sludge sedimentation by a simple method, i.e., by pressurizing sludge with air without adding a flocculant and to provide an apparatus therefor. SOLUTION: A treatment method for organic wastewater and an apparatus therefor are provided whereby the solid-liquid separation of sludge can be efficiently carried out. Air pressurized to a pressure higher than a normal pressure with a pressurizing apparatus is supplied to sludge to a supersaturated state. Then, the supersaturated sludge is subjected to pressure reduction to normal or negative pressure with a pressure reduction apparatus, thus improving the sedimentation of the sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for improving sedimentation of a sludge, and a sludge treatment apparatus, and more particularly to a sludge capable of efficiently separating solid-liquid sludge in biological wastewater treatment. The present invention relates to a method and apparatus for improving sedimentation, and a sludge treatment apparatus.

[0002]

2. Description of the Related Art The activated sludge method can decompose BOD (biochemical oxygen demand) components in wastewater into carbon dioxide gas, and the treatment cost is relatively low. Numerous processing facilities using are operating. The activated sludge method includes, as shown in FIG. 10, a reaction tank 51 in which aerobic microorganisms inhabit (hereinafter, referred to as an aeration tank 51).
It comprises a sedimentation tank 53 for solid-liquid separation of microbial sludge and treated water, and a sludge return system 55 such as a sludge return pump for returning precipitated sludge to the aeration tank 51. Aeration tank 5
Numeral 1 receives raw water and receives air from the blower 57 to generate aerated bubbles Va. The sedimentation basin 53 receives the sludge to be treated, performs solid-liquid separation into microbial sludge and treated water, stores sedimented sludge, and discharges treated water. The sludge return system 55 returns the settled sludge Qa in the sedimentation basin 53 to raw water by the sludge return pump 59.

[0003] However, when a lot of proteins and lipids are contained, such as wastewater from food factories, filamentous bacteria are generated in the aeration tank 51, and there is a serious problem that the bulking phenomenon is likely to occur. The bulking is a phenomenon in which filamentous bacteria such as actinomycetes grow preferentially in activated sludge, and the sludge settling property in a sedimentation basin is deteriorated. If such filamentous bacteria proliferate, solid-liquid separation becomes difficult, and a trouble occurs in which sludge flows out together with the treated water from the sedimentation basin 53.

[0004] Therefore, as a method of solid-liquid separation of bulked sludge, as shown in FIG. 11, a flocculant reaction tank 63 including a stirrer 61 or the like between aeration tank 51 and settling tank 53 is provided. A method of disposing the polymer coagulant to the sludge by the coagulant injection pump 65 to increase the specific gravity and forcibly settle and separate the sludge is often used.

[0005]

However, FIG.
As described above, the addition of a polymer flocculant requires special equipment and a problem that a stirrer is required to disperse the flocculant. In the activated sludge method, as described above, the sludge separated in the sedimentation basin for keeping the sludge concentration in the aeration tank constant is returned to the aeration tank. However, when a coagulant is added, the sludge is coagulated and has different properties, and it is difficult to return the sludge. For this reason, it was difficult to maintain the sludge concentration in the aeration tank, and there was a major problem that the quality of treated water deteriorated.

The present invention focuses on the above problems, and relates to a method and an apparatus for improving sludge sedimentation property. In particular, the present invention relates to a method for pressurizing sludge with air or other gas without adding a flocculant. It is an object of the present invention to provide a method and apparatus for improving sedimentation of sludge, which can improve the sedimentation.

[0007]

Means for Solving the Problems In order to achieve the above object, a method for improving the sedimentation of sludge according to the present invention is disclosed. Is separated by flotation and the remaining sludge is supplied to a sedimentation treatment system to perform solid-liquid separation. That is, after the pressurized air higher than the normal pressure is supplied to the sludge to make it supersaturated, the pressurized sludge is reduced to the normal pressure or the negative pressure to improve the sludge settling property. In this case, the sludge is preferably pressurized in the range of 0.03 to 0.5 MPa.

[0008] A sludge settling improving apparatus according to the present invention comprises gas dissolving means for supersaturating and dissolving gas in sludge, pressure reducing means disposed on the outlet side of the gas dissolving means for decompressing gas supersaturated sludge, and depressurized sludge. And a flotation means for removing air-bubble bacteria from the air.

The sludge treatment apparatus according to the present invention includes a dissolving tank for supplying sludge supplied from an aeration tank under pressure and supplying gas under pressure to form sludge in which gas is supersaturated and dissolved. Is provided with a deaeration tank having a flotation separation means for separating the bacteria that float by decompressing the gas supersaturated dissolved sludge, and supplying the sludge discharged from the deaeration tank to a sedimentation basin for solid-liquid separation. Was formed.

[0010] Further, a dissolving tank for supplying sludge separated by the sedimentation basin under pressure and supplying gas under pressure to form sludge in which the gas is supersaturated and dissolved is provided. A deaeration tank having a flotation means for separating the bacterial groups that float by decompressing the supersaturated dissolved sludge is provided, and after supplying the sludge discharged from the deaeration tank to the aeration tank, the sludge is re-supplied to the sedimentation tank. It is also possible to configure so as to perform solid-liquid separation.

That is, according to the present invention, air and other gases are pressurized by a pressurizing device at a pressure higher than normal pressure and supplied to the sludge to be supersaturated, and the supersaturated sludge is reduced to normal pressure or negative pressure by a pressure reducing device. The pressure is reduced to improve the sludge settling property.

[0012] According to the above configuration, the gas such as air is dissolved in the sludge in a supersaturated state, and then the pressure is rapidly changed to a normal pressure or a negative pressure state. A gas such as natural air floats as fine bubbles. At this time, the filamentous bacterial group that causes bulking has a specific filamentous shape, so that fine bubbles are easily attached or included and easily float with the bubbles. On the other hand, microbial bacteria such as bacilli mainly involved in wastewater treatment are hardly affected by microbubbles and hardly float. For this reason, filamentous bacteria which cause bulking are preferentially floated and separated. In addition, since the specific filamentous structure of filamentous bacteria is destroyed by the rapid pressure change of pressurization and decompression, the sludge properties are changed. It is presumed that the effects are synergistic and the sludge settling property is improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sludge settling property improving method and a sludge treatment facility provided with the apparatus according to the present invention will be described in detail with reference to the accompanying drawings. The same parts as those in the conventional example are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 is an overall configuration diagram of a first sludge settling property improving device 1 of a first embodiment. In FIG. 1, in a first sludge sedimentation improving apparatus 1, sludge to be treated (hereinafter, referred to as sludge) stored in an aeration tank 51 is sent to a pressurized air dissolving tank 5 by a pressure pump 3. Compressed air pressurized by the air compressor 7 is sent to the pressurized air dissolving tank 5. In the pressurized air dissolving tank 5, the sludge to be treated supersaturates and dissolves the pressurized compressed air from the air compressor 7.

A pressure gauge 9 is attached to the pressurized air dissolving tank 5 and can be adjusted to a predetermined pressure by adjusting the pressure with a pressurizing valve 11 attached to the pressurized air dissolving tank 5 according to the operating conditions. it can. Further, the air pressure from the air compressor 7 may be controlled to a predetermined pressure. At this time, the air pressure from the air compressor 7 is 0.03
To 0.5 MPa. The sludge whose pressure is adjusted by the pressurizing valve 11 is sent from the pressurized air dissolving tank 5 to the deaeration tank 13 via the pressurizing valve 11. In the degassing tank 13, the sludge obtained by supersaturating and dissolving the compressed air is rapidly reduced in pressure, so that fine bubbles Wa are generated. At this time, large-sized bacteria, such as filamentous bacteria, easily attach air bubbles and float on the water surface, so that the sludge properties change and sedimentation and separation are facilitated. The sludge that has been favorably settled and separated in the degassing tank 13 and solid-liquid separated is separated as treated sludge by the straightening plate 15 and then discharged from the degassing tank 13 as treated sludge. In the above description, the air pressure is used, but another gas may be used. Hereinafter, similarly, the term "air" is used, but another gas can be used similarly.

FIG. 2 is an overall configuration diagram of a second sludge settling property improving apparatus 1A of a second embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In FIG. 2, a second sludge settling property improving device 1A is obtained by partially changing the first sludge settling property improving device 1. In the first sludge settling property improving device 1, the tank 13a of the deaeration tank 13 is open to the atmosphere. However, in the second sludge settling property improving device 1A, a sealed tank 13b is used as the tank, and the pressure reducing device 2 is used.
1 is attached. With the provision of the pressure reducer 21, in the second sludge sedimentation improving apparatus 1A of the second embodiment, the degassing layer 13 can be brought into a negative pressure (negative pressure) state. Thereby, the generation efficiency of fine bubbles in the degassing tank 13 can be improved.

FIG. 3 is an overall configuration diagram of a third sludge settling property improving apparatus 1B of a third embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In FIG. 3, a third sludge settling property improving device 1 </ b> B is obtained by partially changing the first sludge settling property improving device 1. In the first sludge settling property improving device 1, the sludge supplied using the pressurized air dissolving tank 5 is supersaturated and dissolved by pressurized compressed air. On the other hand, in the third sludge sedimentation improving apparatus 1B, the discharge pipe 25 for air from the air compressor 7 is connected to the discharge pipe 23 for sludge of the pressurizing pump 3 for supplying sludge, and the discharge pipe for sludge is connected. The compressed air pressurized into the sludge in 23 is supersaturated and dissolved. The pressurized compressed air at this time is controlled in the same manner as in the first embodiment. In the third embodiment, the tank 13a of the first embodiment is used. However, the sealed tank 13b of the second sludge sedimentation improvement device 1A may be used. Any of the sealed tanks 13b may be used.

FIG. 4 is an overall configuration diagram of a fourth sludge settling property improving apparatus 1C of a fourth embodiment. FIG. 5 is a schematic side sectional view of an ejector used in the fourth sludge settling property improving device 1C. The same parts as those in the first embodiment and the third embodiment are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 4, a fourth sludge settling property improving device 1C is obtained by partially changing the third sludge settling property improving device 1B. In the third sludge sedimentation improving apparatus 1B, the sludge is pressurized using the air compressor 7 and supersaturated and dissolved with compressed air. On the other hand, in the fourth sludge settling property improving apparatus 1C, the ejector 25 is inserted into the sludge discharge pipe 23 of the pressurizing pump 3 for supplying the sludge, and the air sucked by the ejector 25 is supplied to the sludge, and the sludge is supplied. The compressed air pressurized to the sludge in the discharge pipe 23 is supersaturated and dissolved. The pressurized compressed air at this time is controlled in the same manner as in the first embodiment.

In FIG. 5, an ejector 25 has a chamber 27 connected to a sludge discharge pipe 23. A nozzle 29 having a diameter gradually reduced along the flow is provided inside the chamber 27. The outer chamber 27 in which the nozzle 29 is provided is provided with an air inlet 31 that is connected to the atmosphere. The ejector 25 is a jet pump, and is capable of sucking air by itself.
The sludge that has entered the pressurized state by the pressurizing pump 3 passes through the nozzle 29. At this time, the pressure inside the chamber 27 decreases due to the high flow velocity ejected from the nozzle 29, and the air is self-supplied. At the nozzle discharge part Nd, air and sludge are mixed and can be efficiently dissolved. For this reason, the same effect as the above-described method can be obtained.

Next, the effect of improving the sedimentation property was confirmed using the above-described embodiment of the sludge sedimentation improvement apparatus 1 of the present invention. In order to confirm the effect of improving sedimentation, the pressurization pressure and sludge sedimentation were examined in batch experiments as a basic study. Bulk sludge is introduced into the pressurized air dissolving tank 5 and air is
After dissolving for minutes, the pressure was reduced to normal pressure. The sludge settling property was determined by measuring the percentage of settled sludge after the sample was allowed to stand for 30 minutes. The sludge used was bulky sludge. The initial settling sludge ratio was 99%, and the sludge hardly settled. Pressurization of pressurized air dissolution tank 5 is 0.01 to 0.7MP
Performed under the condition of a. FIG. 6 shows the result. The sedimentation property was significantly improved in the pressurized condition in the range of 0.03 to 0.5 MPa. In addition, even under a slightly pressurized state of 0.03 MPa, about 6
It could be concentrated to 0%.

Next, a continuous experiment was conducted on the method using the ejector 25 in which the effect of improving the sedimentation property was confirmed.
FIG. 7 is an overall schematic diagram of an activated sludge treatment apparatus 30 that has been subjected to the continuous experiment. The activated sludge treatment apparatus 30 has the above-described ejector 25 added to FIG. 7, the activated sludge treatment apparatus 30 of the present invention connects an aeration tank 51 and a sedimentation basin 53 with a sludge discharge pipe 23, and sequentially connects the pressurized pump 3 and the ejector 25 to the sludge discharge pipe 23. , A pressure valve 11, and a pressure gauge 9 are provided. In FIG. 7, a first valve 35 is provided on the sludge discharge pipe 23 and between the aeration tank 51 and the pressurizing pump 3 for performing a comparative test. A test pipe 37 branched from the sludge discharge pipe 23
And the second valve 3 is connected to the test pipe 37.
9 are arranged. The test pipe 37 is connected to the aeration tank 5
It branches at the position Sa of the sludge discharge pipe 23 between the first valve 35 and the first valve 35 and is connected at the position Sb of the sludge discharge pipe 23 between the ejector 25 and the pressure valve 11.

In the activated sludge treatment apparatus 30, the activated sludge used in this experiment was previously in a bulking state. The sludge concentration in the aeration tank 51 was 800 mg / L. The amount of air suction from the ejector 25 was 3% of the amount of treated sludge, and the pressure of the sludge was 0.2 MPa. The treated sludge was sent to the sedimentation basin 53 and deaerated in the sedimentation basin 53 to separate the floating sludge.

First, in the comparative test, the second valve 39 is closed without closing the first valve 35 and passing the ejector 25 through.
Was opened, and an operation in which the conventional test pipe 37 was flowed was performed. In this case, since the sludge separation in the sedimentation basin 53 was not performed well, the sludge was mixed into the treated water, and the solid concentration of the treated water was as high as 540 mg / L. Next, the second valve 39
, And the operation was performed with the activated sludge treatment apparatus 30 of the present invention in which the first valve 35 was opened and the ejector 25 was passed. As a result, the sludge settling property is greatly improved, and the solid concentration of the treated water is increased from the conventional 540 mg / L to the 20% of the present invention.
mg / L, which was very good. As described above, in the present invention, as the activated sludge treatment device 30, the aeration tank 51 and the sedimentation basin 53 are connected by the sludge discharge pipe 23, and the ejector 25 of the present invention is connected to the sludge discharge pipe 23.
By using, the sedimentation of sludge is greatly improved. The ejector 2 is located between the aeration tank 51 and the sedimentation tank 53.
5, the sludge settling property improving apparatus 1 of the above embodiment can be used to improve the sludge settling property.

FIG. 8 is an overall schematic view of a first activated sludge treatment apparatus 30A according to another embodiment. In the first activated sludge treatment apparatus 30A, instead of the ejector 25 shown in FIG.
A pressurized air melting tank 5 and a degassing tank 13 are used. Further, a branch pipe 41 branched from the sludge discharge pipe 23 is provided, and a second valve 39 is provided in the branch pipe 41, and the branch pipe 41 is connected to the sedimentation tank 53.

With the above configuration, the first activated sludge treatment device 3
At 0A, the first valve 35 is opened and the second valve 39 is closed to use the sludge settling property improving device 1 of the present invention.
9 is opened so that a conventional activated sludge treatment apparatus can be used. Thereby, the sludge settling property of the conventional activated sludge treatment device can be easily improved by adding the sludge settling property improving device 1 of the present invention to the conventional activated sludge treatment device. Further, the first valve 35 is opened and the second valve 39 is also opened, so that the sludge settling property improving device 1 of the present invention can be used. Thereby, for example, raw water can be reduced to 10
0 tons / day, sludge with improved liquid quality is returned from the sludge return system 55 to 100 tons / day, and the aeration tank 51 can be supplied and treated with a total of 200 tons / day of raw water and sludge.

FIG. 9 is an overall schematic view of a second activated sludge treatment apparatus 30B according to another embodiment. In the activated sludge treatment device 30 and the first activated sludge treatment device 30A described above, the sludge settling property improving device 1 is disposed between the aeration tank 51 and the sedimentation basin 53, but in the second activated sludge treatment device 30B. The sludge settling property improving device 1 is provided in the sludge return system 55. As shown in FIG. 9, the pressurizing pump 3, the pressurized air dissolving tank 5, the pressurizing valve 11, and the deaeration tank 13 are sequentially connected to the sludge return pump 59, and the sludge is removed from the aeration tank 51. To return to. Thus, by circulating the sludge between the aeration tank 51 and the sedimentation basin 53, the liquid quality is gradually improved and the sediment is easily settled. In addition, by adding the sludge settling property improving device 1 to the sludge return system 55 and adding the sludge settling property improving device 1 of the present invention to the conventional activated sludge treatment device in the same manner as described above, It is possible to easily improve the sludge settling property of the device.

As described above, according to the present invention, after gas is supersaturated and dissolved in sludge, the sludge is subjected to decompression treatment to float and separate the bacteria entrained by air bubbles, and the residual sludge can be supplied to the precipitation treatment system. . That is, air is pressurized by a pressurizing device higher than normal pressure and supplied to the sludge to be supersaturated, and the supersaturated sludge is depressurized to a normal pressure or a negative pressure by a decompression device to improve sludge sedimentation. Therefore, it is possible to improve the sludge sedimentation by a simple method of pressurizing the sludge with air and another gas without adding a flocculant.

[0028]

As described above, according to the sludge sedimentation improving apparatus of the present invention, after pressurized air higher than normal pressure is supplied to the sludge to make it supersaturated, the pressurized sludge is Is reduced to normal pressure or negative pressure to improve the sedimentation of sludge, so that the filamentous bacteria that are the cause of bulking can be separated, and the bacterial form can be changed to change the sludge properties and improve the sedimentation. It is possible to improve.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a first sludge settling property improving device of a first embodiment according to the present invention.

FIG. 2 is an overall configuration diagram of a second sludge settling property improving device of a second embodiment according to the present invention.

FIG. 3 is an overall configuration diagram of a third sludge settling property improving device of a third embodiment according to the present invention.

FIG. 4 is an overall configuration diagram of a fourth sludge settling property improving device of a fourth embodiment according to the present invention.

FIG. 5 is a schematic view of an ejector according to the embodiment of the present invention.

FIG. 6 is a view showing the results of a batch experiment.

FIG. 7 is an overall schematic diagram showing an experimental apparatus using the activated sludge treatment apparatus of the present invention.

FIG. 8 is an overall schematic diagram of a first activated sludge treatment apparatus of the present invention.

FIG. 9 is an overall schematic diagram of a second activated sludge treatment device of the present invention.

FIG. 10 is a schematic diagram showing a conventional activated sludge treatment system.

FIG. 11 is a schematic diagram of a conventional activated sludge treatment system using both a coagulant reaction tank and a sedimentation tank.

[Explanation of symbols]

1, 1A, 1B, 1C ... sludge settling property improving device, 3 ...
Pressurizing pump, 5 ... Pressurized air dissolving tank, 7 ... Air compressor, 9 ... Pressure gauge, 11 ... Pressurizing valve, 13 ... Degassing tank, 21 ... Depressurizer, 25 ... Ejector , 30,30
A, 30B: activated sludge treatment apparatus, 51: reaction tank 51
(Aeration tank 51), 53 ... sedimentation basin, 55 ... sludge return system, 57 ... blower,

Claims (5)

[Claims] 1. A sludge settling method characterized in that, after a gas is supersaturated and dissolved in sludge, the sludge is subjected to a reduced pressure treatment to separate air-bubble bacterial groups by flotation and to supply residual sludge to a sedimentation treatment system. How to improve. 2. The method for improving sedimentation of sludge according to claim 1, wherein the sludge is pressurized in the range of 0.03 to 0.5 MPa to supersaturate and dissolve the gas in the sludge. 3. A gas dissolving means for supersaturating and dissolving a gas in sludge, a decompression means disposed on an outlet side of the gas dissolving means for decompressing the gas supersaturated sludge, and a flotation for removing bubble-entrained bacteria from the decompressed sludge. A sludge settling property improving device comprising: a separation unit. 4. A dissolution tank for supplying sludge supplied from an aeration tank under pressure and supplying gas under pressure to form sludge in which gas is supersaturated and dissolved, and a gas supersaturation is provided at an outlet side of the dissolution tank. A degassing tank having a flotation separation means for separating bacteria that float by decompressing the dissolved sludge is provided, and sludge discharged from the degassing tank is supplied to a sedimentation tank to perform solid-liquid separation. Sludge treatment equipment. 5. A dissolving tank for supplying sludge separated in a sedimentation tank under pressure and supplying gas under pressure to form sludge in which gas is supersaturated and dissolved, and a gas outlet is provided on the discharge side of the dissolving tank. A deaeration tank having a flotation means for separating the bacterial groups that float by decompressing the supersaturated dissolved sludge is provided, and after supplying the sludge discharged from the deaeration tank to the aeration tank, the sludge is re-supplied to the sedimentation tank. A sludge treatment device characterized by performing solid-liquid separation.