JP2929528B2 - Sludge concentration method and apparatus - Google Patents

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 concentrating sludge such as sewage sludge by depressurizing and floating at a high speed, and more particularly, to an improvement in a method for floating and concentrating sludge in a closed tank and a method for concentrating sludge by gravity. Things.

[0002]

2. Description of the Related Art Conventionally, as described in Japanese Patent Publication No. 7-108399, anaerobic sludge is filled in a container and left standing to be in an anaerobic state, and generated gas such as CO ₂ and CH _4. Dissolves in sludge and promotes solid-liquid separation,
Then, the gas accumulated in the upper part of the container is degassed by supplying and filling sludge, and the gaseous phase part in the upper part of the container is eliminated, so that the sludge is almost filled and the outside air is not sucked in. A method of concentrating anaerobic sludge in the sludge discharge process is known in which the pressure inside the container is reduced by drawing the sludge from the lower part, the gas dissolved in the sludge is foamed under reduced pressure, and the sludge is separated by flotation. Have been.

[0003]

Problems to be Solved by the Invention
In the method for concentrating anaerobic sludge described in No. 8399, after the inside of the container is almost filled with sludge and the outside air is not sucked,
Since the pressure inside the container is reduced by pulling out the sludge from the bottom of the container by the sludge pump, that is, the speed at which the pressure inside the container is reduced in the process of discharging the sludge becomes slower.
There is a problem that the average diameter of the gas to be degassed during the depressurization step is large, the rate at which the foaming gas is desorbed from the sludge is high, and the floating and condensing rate of the sludge is low. In the conventional method, if the sludge speed can be increased and the decompression speed can be increased, many fine bubbles are generated, the sludge entrainment rate is high, and the flotation concentration speed can be increased, but the sludge pump (sludge pump) The capacity of this is large, which is uneconomical. As described above, the conventional vacuum deconcentration method in the sludge discharging process has a problem that the bubble diameter is large and the entrainment flotation separation efficiency of the sludge is low.

[0004] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to supply a desorbed liquid (filtrate) to the top of a tank, seal the tank, and then to the bottom of the tank. After forming a decompressed state close to vacuum by draining, sludge is rapidly supplied into the decompression tank from the mud supply port, so that the dissolved gas in the sludge is foamed as fine bubbles, and the sludge is rapidly formed. An object of the present invention is to provide a method and an apparatus for concentrating sludge to be floated and separated. Another object of the present invention is to apply the above-mentioned method and apparatus to concentrated sludge from a gravity concentration tank, and return the desorbed liquid to the inlet of the gravity concentration tank to thereby improve the gravity-concentrated sludge. An object of the present invention is to provide a concentration method and an apparatus. Still another object of the present invention is to apply the above method and apparatus to sludge in a concentrated sludge storage tank, install a sludge supply pump in the middle part of the storage tank, and provide a sludge concentration meter on the discharge side of the pump. Provided is a method and apparatus for efficiently concentrating stored sludge by sending the sludge to the above-mentioned storage tank or another storage tank when the sludge concentration is high, and returning to the upstream process when the sludge concentration is low. Is to do.

[0005]

In order to achieve the above object, a method for concentrating sludge according to the present invention has a supply port for supplying sludge or liquid at an upper portion, and a discharge port connected to a pump at a lower portion. Using a sealable sludge decompression flotation thickening tank with an outlet,
After the tank is filled with the liquid, the inside of the tank is evacuated by forcibly discharging the liquid with a pump, and then the sludge is introduced into the tank to foam the gas dissolved in the sludge, and the foaming gas is generated. The sludge is floated and separated. In order to achieve the above object, the method for concentrating sludge of the present invention has a supply port for supplying raw sludge or a filtrate (desorbed liquid) at an upper portion, and a lower portion connected to a sludge extraction pump. The following steps (1) to (6) are performed using a sealable sludge depressurized flotation / concentration tank having a discharge port to perform: (1) Supplying the filtrate to the top of the tank and exhausting the inside of the tank・ Exhaust process,
(2) A drainage / decompression step in which the filtrate in the tank is discharged to the bottom of the tank by a sludge extraction pump to reduce the pressure in the tank, (3)
A sludge supply / foaming step in which raw sludge is supplied to approximately the middle part of the tank to foam under reduced pressure; (4) a stationary / separation step in which the sludge in the tank is allowed to stand and the sludge is floated and separated; (5) a tank in the tank A drainage / dehydration step of discharging the lower desorbed liquid stored in the lower part by a sludge extraction pump, and (6) a drainage / concentration step of discharging the floating separated sludge in the tank by a sludge extraction pump, are sequentially repeated. (See FIGS. 1 to 8). The present invention can be applied to any sludge that dissolves a gas that can be degassed under reduced pressure.

Further, the method for concentrating sludge of the present invention is a method for gravity-concentrating sludge and separating it into a desorbed liquid and a concentrated sludge, wherein the gravity-concentrated sludge is treated as raw sludge by the above method. (See FIG. 9). Further, in the method for concentrating sludge of the present invention, the method for condensing sludge, storing the concentrated sludge and separating it into settled sludge, floating scum, and middle-layer desorbed liquid, wherein the sludge is formed between the settled sludge and floating scum The middle-layer desorbed liquid is sucked by a sludge suction pump, and the middle-layer desorbed liquid is treated as raw sludge by the above method (see FIG. 10).

The sludge concentration apparatus of the present invention comprises a sealable sludge depressurized flotation / concentration tank having a supply port at an upper portion and a discharge port at a lower portion, and a filtrate tank connected to the supply port via a valve. And a raw sludge tank, a sludge drawing pump connected to the discharge port, and a filtrate conduit having a valve connecting the sludge drawing pump and the filtrate tank, to constitute a sludge decompression flotation / concentration apparatus. (See FIGS. 1 to 8). In this apparatus, it is preferable to connect a thickened sludge tank via a thickened sludge conduit having a valve to the sludge extraction pump. Further, it is preferable to connect a gas discharge conduit having a valve to the sludge depressurized flotation / concentration tank. However, this gas discharge conduit is not always necessary and can be omitted.

In the sludge concentration apparatus of the present invention, in the gravity concentration tank for gravity-concentrating the sludge to separate it into a desorbed liquid and a concentrated sludge, the sludge decompression pipe is connected to the concentrated sludge discharge pipe from the gravity concentration tank. It is characterized in that a flotation concentrator is connected (see FIG. 9). Furthermore, the sludge concentration apparatus of the present invention is a concentrated sludge storage tank that stores concentrated sludge obtained by condensing sludge and separates the sludge into settling sludge, floating scum, and middle desorbed liquid. A sludge suction pump is arranged, and the above-mentioned sludge decompression flotation / concentration device is connected to a discharge pipe of the sludge suction pump (see FIG. 10). In this apparatus, a discharge pipe equipped with a sludge concentration meter is connected to the discharge port of the sludge decompression flotation / concentration apparatus, and a high-concentration sludge conduit equipped with a control valve and a low-concentration sludge conduit equipped with a control valve are provided downstream of the sludge concentration meter. Concentrated sludge conduits are connected in parallel to open and close these control valves according to the value of the sludge densitometer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 8 show an apparatus for carrying out a method for concentrating sludge according to the present invention, and show steps of a concentration operation by intermittent operation of a sludge extraction pump. FIG. 1 shows step (0), that is, before starting. Reference numeral 10 denotes a sealable sludge depressurized flotation / concentration tank which has a supply port 12 for supplying raw sludge or filtrate (or desorbed liquid) at an upper portion, and a discharge port 14 connected to a sludge extraction pump 16 at a lower portion. ing. A filtrate tank 18 and a raw sludge tank 20 are connected to the supply port 12 via valves A and B, respectively, and a sludge extraction pump 16 is connected to the discharge port 14. The sludge extraction pump 16 and the filtrate tank 18 are connected via a filtrate conduit 22 having a valve C. The sludge decompression flotation concentrator 24 is constituted by these devices and pipes (portions indicated by alternate long and short dash lines). Although FIG. 1 shows the case where the supply port 12 is also used, the filtrate supply port and the raw sludge supply port may be provided separately. Further, a concentrated sludge tank 28 is connected to the sludge withdrawing pump 16 via a concentrated sludge conduit 26 having a valve D, and a gas discharge conduit 30 having a valve E is connected to the sludge depressurized flotation / concentration tank 10. 30 is connected to the raw sludge tank 20, for example. In addition, sludge decompression flotation concentration tank 1
At 0, a level meter 32 and a pressure switch 34 are provided.

As shown in FIG. 1, before starting, valves A, B,
C, D, and E are all closed (the black valves indicate closed), and the sludge extraction pump 16 is stopped (the black pump indicates a stopped state). FIG. 2 shows the liquid supply / evacuation step of step (1). That is, the valves A and E are opened (open valves indicate open), the filtrate is supplied into the tank 10, and the gas in the tank 10 is supplied to the gas discharge conduit 3.
Release at 0. The gas discharge conduit 30 is not always necessary, and the gas can be exhausted via the valve A. When the filtrate is supplied into the tank 10, the "level L (low)" of the level meter 32 is canceled. The pressure in the tank 10 is about 1.0 kg / cm ² A.

FIG. 3 shows the drainage / decompression step of step (2). That is, when the pressure switch 34 detects a high pressure, for example, 1.1 kg / cm ² A, the valves A and E are closed and the valve C is opened. At the same time, the sludge extraction pump 16 is driven to drain the liquid (filtrate) in the tank 10 and returned to the filtrate tank 18 by the filtrate conduit 22. At this time, the pressure in the tank 10 is rapidly reduced, for example, to 0.1 kg / cm ² A. It should be noted that the white pump indicates a driving state.

FIG. 4 shows the mud supply / foaming step (3). That is, when the level meter 32 detects L (low), the valve B is opened and the sludge is rapidly supplied from the raw sludge tank 20 into the tank 10. At the same time, the sludge extraction pump 16 is stopped and the valve C
Is closed. A mud feed timer is connected to valve B,
Activate the mud timer and after a certain time, for example, 30
Seconds later, valve B is closed. When the raw sludge is rapidly supplied into the tank 10 under reduced pressure, the dissolved gas in the sludge rapidly foams as fine bubbles, and the sludge floats and separates at a high speed.

FIG. 5 shows the stationary / separating step of step (4). That is, the stationary timer connected to the valves A, B, C, D, and E is operated, and the state in which the valve B is closed from the state shown in FIG. 4 is left for a fixed time, for example, two hours.
During this time, the concentrated sludge and the desorbed liquid are separated in the tank 10.

FIG. 6 shows the drainage / dehydration step of step (5). That is, when the time set by the stationary timer elapses, the valve C is opened, and at the same time, the sludge extraction pump 16 is driven to send the desorbed liquid in the tank 10 to the filtrate tank 18.

FIG. 7 shows the sludge discharging / concentrating step (6). That is, the drainage timer connected to the valves C and D is operated for a fixed time, for example, 30 seconds, and after this time, the valve D is opened, the valve C is closed, and the tank 10 is closed.
The concentrated sludge inside is sent to the concentrated sludge tank 28. When the level meter 32 detects L (low), the sludge extraction pump 16 is stopped,
Close valve D.

FIG. 8 shows the liquid supply / evacuation step (7). That is, the valve A is opened to supply the filtrate in the filtrate tank 18 into the tank 10. Pressure switch 34 is H
When (high) is detected, the valve E is opened, and when the pressure switch detects a higher pressure, the valves E and A are closed. The pressure switch can be replaced by H (high) of the level gauge. Step (7) in FIG. 8 is the same state as step (1) in FIG. 1, and then proceeds to the drain / decompression step in step (2), and steps (3) to (7) are sequentially repeated.
By repeating the above steps (1) to (7) sequentially, the raw sludge is efficiently concentrated.

FIG. 9 shows a case where the above steps (1) to (7) are applied to sludge from a gravity concentration tank. 40
Is a gravity concentration tank which concentrates sludge by gravity and separates it into desorbed liquid and concentrated sludge. A sludge depressurized flotation concentrator 24 (the portion surrounded by a dashed line in FIG. 1) is connected to a condensed sludge extraction pipe 42 from the gravity concentrating tank 40, and the condensed sludge is supplied to this device 24, and step (1) is performed. ) ~
The operation of (7) is sequentially and repeatedly performed, and the desorbed liquid is returned to the gravity concentration tank 40, and the concentrated sludge is temporarily stored in the concentrated sludge tank 44, and then supplied to the dehydrator 46, where the sludge cake and the filtrate are supplied. And separated. 48 is a sludge hopper and 50 is a filtrate tank. The method and apparatus shown in FIG. 9 have the advantage that the concentrated sludge from the gravity concentration tank 40 can be further efficiently and quickly concentrated.

FIG. 10 shows a case in which the above steps (1) to (7) are applied to the sludge in the concentrated sludge storage tank to be a pretreatment for dehydration. Sludge (for example, sludge from the final sedimentation basin) is supplied to the sludge concentration tank 52 and separated into concentrated sludge and a desorbed liquid. The concentrated sludge is introduced into the concentrated sludge storage tank 54, and is separated into the settled sludge 56, the floating scum 58, and the middle-layer desorbed liquid 60 as time passes. This middle layer desorption liquid 6
A sludge suction pump 62 is suspended in the air in the sludge suction pump 62 and a discharge pipe 64 of the sludge suction pump 62 is connected to the sludge depressurized flotation / concentration apparatus 2.
4 (the configuration of a portion surrounded by a dashed line in FIG. 1) is connected, the middle-layer desorbing liquid is supplied to the device 24, and the operations of steps (1) to (7) are sequentially and repeatedly performed.

A discharge pipe 70 provided with a sludge concentration meter 68 is connected to a discharge port 66 of the sludge decompression flotation concentrator 24,
Downstream of this sludge concentration meter 68, a high concentration sludge conduit 74 having a control valve 72 and a low concentration sludge conduit 78 having a control valve 76 are connected in parallel.
The control valves 72 and 76 can be opened and closed. Reference numeral 80 denotes a sludge concentration detector. When the sludge concentration is high, for example, when it is higher than 0.5%, the treated sludge is sent to the pre-dewatering sludge storage tank 82 or the concentrated sludge storage tank 54, and when the sludge concentration is low, for example, when it is less than 0.5%, The treated sludge is transferred to an upstream process, for example, a sludge concentration tank 52 or a desorption liquid tank 84.
Return to The desorbed liquid in the sludge concentration tank 52 is sent to a desorbed liquid tank 84, and the desorbed liquid in the desorbed liquid tank 84 is sent to, for example, a water treatment device. Note that the sludge concentration tank 52 can be omitted.

[0020]

As described above, the present invention has the following effects. (1) The desorbed liquid or filtrate (desorbed liquid) is supplied to the top of the tank to make the tank hermetically closed, and then drained to the bottom of the tank to form a reduced pressure state close to vacuum. By rapidly supplying sludge into the tank from the mud supply port, the dissolved gas in the sludge is foamed as fine bubbles, and the sludge is floated and separated at high speed, and the sludge is efficiently separated into concentrated sludge and desorbed liquid. can do. (2) Since the depressurization in the tank is performed by draining the filtrate (desorbed liquid), the viscosity is lower than in the case of discharging sludge, the discharge speed is faster, and the concentration time is shortened. And the load on the drawing pump can be reduced. (3) When the present invention is applied to the sludge from the gravity thickening tank, the desorbed liquid from the sludge depressurized flotation thickening tank is returned to the gravity thickening tank to remove the degassed SS (suspended solids). The clarity of the syneresis is increased, and the SS recovery rate can be improved as a system. In addition, in the past, it was necessary to increase the capacity of pipes and sludge extraction pumps in order to prevent clogging of the concentrated sludge line, but since a sludge decompression flotation concentrator is arranged instead of the gravity concentrated sludge extraction pump, A conventional large-capacity sludge extraction pump (conventionally intermittent extraction) can be omitted. (4) When applying the present invention to a thickened sludge tank, a sludge suction pump is placed suspended in the existing thickened sludge storage tank,
By supplying the sludge from the middle layer to the sludge depressurized flotation concentrator of the present invention, the desorbed liquid formed in the middle layer can be discharged out of the system, and therefore, the amount of dewatered sludge can be reduced. Further, a stirrer for stirring and mixing the inside of the concentrated sludge storage tank can be eliminated. Furthermore, when the sludge concentration meter switches the decompression treated sludge to the sludge thickening tank side or the sludge storage tank side before dehydration, it is possible to improve the sludge concentration (improve the dewatering property), to eliminate the need for a stirrer, and to reduce the pressure. The SS concentration of the desorbed liquid can be reduced in the sludge concentration tank by the gas effect.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus for performing a sludge concentration method of the present invention, showing a state of step (0) (before starting).

FIG. 2 is a schematic configuration diagram showing a liquid supply / evacuation step of step (1).

FIG. 3 is a schematic configuration diagram showing a drainage / decompression step in step (2).

FIG. 4 is a schematic configuration diagram showing a mud supply / foaming step of step (3).

FIG. 5 is a schematic configuration diagram showing a stationary / separation step of step (4).

FIG. 6 is a schematic configuration diagram showing a drainage / dehydration step of step (5).

FIG. 7 is a schematic configuration diagram showing a sludge discharging / concentrating step in step (6).

FIG. 8 is a schematic configuration diagram showing a liquid supply / evacuation step of step (7).

FIG. 9 is a flow sheet showing an example when the present invention is applied to sludge from a gravity concentration tank.

FIG. 10 is a flow sheet showing an example in which the present invention is applied to a middle-layer desorbed liquid in a concentrated sludge storage tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Sludge decompression flotation thickening tank 12 Supply port 14 Outlet 16 Sludge extraction pump 18 Filtration tank 20 Raw sludge tank 22 Filtration conduit 24 Sludge decompression flotation concentrator 26 Concentrated sludge conduit 28 Concentrated sludge tank 30 Gas discharge conduit 32 Level meter 34 Pressure switch 40 Gravity thickening tank 44 Thickened sludge tank 52 Sludge thickening tank 54 Thickened sludge storage tank 56 Sedimented sludge 58 Floating scum 60 Middle desorbed liquid 62 Sludge suction pump 68 Sludge concentration meter 72 Control valve 74 High concentration sludge conduit 76 Control valve 78 Low concentration sludge conduit 82 Sludge storage tank before dehydration 84 Desorption liquid tank

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Makoto Terunuma 12-12-607, Keihei, Hiratsuka-shi, Kanagawa (56) References JP-B 7-108399 (JP, B2) (58) Fields surveyed (Int) .Cl. ⁶ , DB name) C02F 11/00-11/20

Claims (10)

(57) [Claims] 1. A sealable sludge depressurized flotation tank having a supply port for supplying sludge or a liquid at an upper portion and a discharge port connected to a pump at a lower portion, and after filling the tank with a liquid, By forcibly draining the liquid with a pump, the inside of the tank is evacuated, and then sludge is introduced into this tank to foam the gas dissolved in the sludge, and the sludge is floated and separated by the foaming gas. Characteristic sludge concentration method. 2. Use of a sealable sludge depressurized flotation / concentration tank having a supply port for supplying raw sludge or filtrate at an upper portion thereof and a discharge port connected to a sludge withdrawal pump at a lower portion. ) To (6), that is, (1) a supply / exhaust step of supplying the filtrate to the top of the tank and exhausting the inside of the tank, and (2) a bottom of the tank using a sludge drawing pump to remove the filtrate in the tank. Draining and depressurizing process to reduce the pressure inside the tank by discharging to the tank, (3) supplying sludge to almost the middle part of the tank and supplying the sludge under reduced pressure and foaming, and (4) allowing the sludge in the tank to stand still (5) Drainage / dewatering step of discharging the lower desorbed liquid stored in the lower part of the tank with a sludge drawing pump, (6) Floating separated sludge in the tank Characterized by sequentially repeating the sludge / concentration process of discharging sludge by a sludge extraction pump. Contraction method. 3. A method for concentrating sludge by gravity concentration to separate a desorbed liquid and a concentrated sludge, wherein the gravity-concentrated sludge is treated as raw sludge by the method according to claim 2. 4. A method of concentrating sludge, storing the concentrated sludge, and separating the sludge into settled sludge, floating scum, and middle desorbing liquid, comprising: 3. A method for concentrating sludge, wherein the sludge is sucked by a sludge suction pump, and the middle layer desorbed liquid is treated as raw sludge by the method according to claim 2 . 5. A sealable sludge depressurized flotation / concentration tank having a supply port at an upper portion and a discharge port at a lower portion, a filtrate tank and a raw sludge tank connected to the supply port via valves, respectively. A sludge withdrawing pump connected to the discharge port; a filtrate conduit having a valve connecting the sludge withdrawing pump to the filtrate tank; Concentrator. 6. The sludge thickening apparatus according to claim 5 , wherein the thick sludge tank is connected to the sludge withdrawing pump via a thick sludge conduit having a valve. 7. A sludge concentrating apparatus of claim 5 or 6, wherein connecting the gas discharge conduit having a valve in the sludge vacuum floating concentration tank. 8. In a gravity concentration tank for gravity-concentrating sludge and separating it into a desorbed liquid and a concentrated sludge, the sludge depressurized flotation concentrator according to claim 5 is connected to a concentrated sludge discharge pipe from the gravity concentration tank. An apparatus for concentrating sludge, characterized in that: 9. A concentrated sludge storage tank for storing concentrated sludge obtained by condensing sludge and separating the sludge into settled sludge, floating scum, and middle-layer desorbed liquid, wherein a sludge suction pump is arranged in the middle-layer desorbed liquid. An apparatus for concentrating sludge, wherein the sludge decompression flotation apparatus according to claim 5 is connected to a discharge pipe of the sludge suction pump. 10. A discharge pipe equipped with a sludge densitometer is connected to an outlet of the sludge decompression flotation / concentrator, and a high concentration sludge conduit equipped with a control valve and a control valve are provided downstream of the sludge densitometer. Claims wherein low-concentration sludge conduits are connected in parallel, and these control valves are opened and closed according to the value of the sludge concentration meter.
9. The sludge concentrator according to claim 9 .