JPH0760300A - Treatment for concentrating and dehydrating sewage sludge and device therefor - Google Patents

Abstract

PURPOSE:To provide a device in which a flocculating agent is used efficiently and effectively and economical and the flocculating agent to be added is easily controlled and a machine for preconcentration is not provided and initially settled sludge and excess sludge are efficiently concentrated and dehydrated. CONSTITUTION:A device for concentrating and dehydrating sewage sludge is equipped with a rotating cylindrical body 2 rotated around a horizontal shaft and a screw conveyor 3 rotated in the rotating cylindrical body 2. A sludge supply pipe 6 is penetrated from the rear part to the front in the screw conveyor 3. The pipe 6 supplys initially settled sludge A along the center part of rotation in the rear end face of the screw conveyor 3. The discharge port 10 of the initially settled sludge A is opened in the front wall surface of the hollow drum part 3a of the screw conveyor 3. A feed pipe 12 for excess sludge is constituted of a double pipe from the vicinity of the rear end thereof and placed around the sludge supply pipe 6. The discharge port 16 of excess sludge B is opened in the wall surface of the middle part of the hollow drum part 3a of the screw conveyor 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for concentrating or dewatering sewage sludge generated mainly in a sewage treatment plant, and a concentrating and dewatering apparatus used for the method.

[0002]

2. Description of the Related Art In a sewage treatment plant, sewage first flows into a settling basin to precipitate sludge, and then the supernatant liquid is introduced into an aeration tank to be biologically decomposed by various bacteria, and this is finally treated. The excess sludge is settled by flowing into a settling basin, and the supernatant is discharged to a river or the sea for processing.
The sludge generated in such a sewage treatment process is roughly classified into a first settling sludge settling in the first settling basin and an excess sludge settling in the final settling basin. And the initial sludge has a relatively high concentration (solid matter ratio) and is excellent in dehydration, while
Excess sludge, also called activated sludge, has a low concentration and poor dewatering properties.

Therefore, conventionally, a method has been generally employed in which surplus sludge is pre-concentrated by a centrifugal concentrator and then mixed with primary sludge to be dehydrated. In addition, JP-A-3-
As described in Japanese Patent No. 114600, there is also proposed a method of mixing initial sludge with excess sludge, adding a coagulant to the sludge, pre-concentrating it using a rotary concentrator, and then performing centrifugal dehydration treatment. ing.

[0004]

However, each of the conventional methods described above has the following disadvantages.

There is a tendency to excessively add a coagulant in order to improve the dewaterability of sludge, and it is uneconomical that a considerable amount of the coagulant that is not used is discharged together with the filtrate after dehydration. That is, if priority is given to the improvement of dehydration property, it is desirable to add about 2% of the coagulant in terms of solid content.
On the other hand, from the viewpoint of collecting the filtrate, the solid content ratio is 0.2 to 0.
It is desirable to add a small amount of coagulant such as 4%. However, in the conventional method, improvement of dehydration property is emphasized, and the coagulant is wasted.

As the mixing ratio of the initial sludge and the excess sludge changes with time, the properties of the mixed sludge also change, and it is very difficult to control the addition rate of the coagulant and the like.

From the viewpoint of equipment, since it is necessary to install a centrifugal concentrator or a rotary concentrator for preconcentration in addition to the centrifugal dehydrator, the equipment cost becomes high, and because of the machine installation, Requires a large site.

The present invention solves the above-mentioned problems of the prior art by using a coagulant effectively without waste, and is economical.
A coagulant to be added can be easily managed, and a method capable of efficiently concentrating and dewatering the first settled sludge and the surplus sludge without providing a machine for preconcentration, and a concentration and dewatering device therefor are provided. Is intended.

[0009]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the method of concentration and dehydration treatment of the present invention is as follows: 1) Agglomeration of about 1 to 3% in terms of solid content in the first settling sludge settled in the first settling tank. 2) After mixing the agent, 2) this initial sludge is subjected to solid water separation by centrifugal dehydration to collect solids, and the filtrate is mixed with the excess sludge generated in the final settling pond and contained in the filtrate. The surplus sludge is concentrated by the coagulation action and centrifugal sedimentation action of the residual coagulant, and 3) solidified water is separated from the concentrated excess sludge by the centrifugal dehydration action to recover solid matter. The filtrate is reprocessed by flowing into the first settling tank or aeration tank together with the sewage.

In order to achieve the above-mentioned object, the concentrating and dehydrating apparatus of the present invention comprises: a) a screw decanter type sewage equipped with a rotary cylinder and a screw conveyor which rotates about the same axis in the rotary cylinder. In the sludge concentrating and dewatering device, b) along the center of rotation of the rear end surface of the screw conveyor, a sludge supply pipe for continuously supplying the first settled sludge, from the rear of the screw conveyor to the front of the screw conveyor. While penetrating over, c) the discharge port of the initial sludge is opened in communication with the supply port at the tip of the sludge supply pipe on the front wall surface of the hollow body of the screw conveyor, and d) of the sludge supply pipe. Around the periphery, a surplus sludge supply pipe is provided with a double pipe structure extending from near the rear end to slightly behind the front end supply port, and e) a surplus sludge discharge port,
An opening is provided in the middle wall surface of the hollow body of the screw conveyor so as to communicate with the supply port at the tip of the excess sludge supply pipe.

According to a third aspect of the present invention, it is preferable that the discharge port for the initial sludge is arranged in the dehydration section in the rotary cylinder and the discharge port for the excess sludge is arranged in the sedimentation separation section in the rotary body. .

[0012]

According to the method for concentration and dehydration treatment of the present invention having the above-mentioned constitution, centrifugal sludge dehydration is carried out in the state where the coagulant in an amount sufficient to improve dehydration property is added to the initial sludge,
The primary sludge is effectively dehydrated. As a result, the sludge cake is efficiently separated into the sludge and the solid matter (sludge cake) is recovered, while the sludge is mixed with the excess sludge.
As a result, the residual coagulant used after dewatering the initially settled sludge has a solid content ratio of about 0.2 to 0.4% and is mixed with the excess sludge to exhibit a coagulating action. In this way, the excess sludge is also effectively dehydrated, and the solid matter (excess sludge cake) is recovered together with the sludge cake. Then, the filtrate after dehydration treatment is re-treated by flowing into the first settling basin together with the sewage, but the amount of the flocculant contained in the filtrate in this state is very low, and there is almost no waste. Absent.

Further, according to the concentrating and dehydrating apparatus of the present invention having the above-mentioned structure, the first sludge is treated with the coagulant through the sludge supply pipe in a state where the rotary cylinder and the screw conveyor are rotated at predetermined speeds. By adding and continuously supplying to the front part in the screw conveyor, the initial sludge is centrifugally separated into a sludge cake and a filtrate under an extremely high gravity (for example, 3000 G). Then, the sludge cake is conveyed forward by the screw conveyor in the rotary cylinder, then discharged and collected from the rotary cylinder, and the filtrate is sent backward in the rotary cylinder. At the same time, by continuously supplying the excess sludge through the excess sludge supply pipe outside the sludge supply pipe, the excess sludge is centrifugally separated from the first settled sludge in the rotating cylinder while being subjected to the centrifugal force. It is mixed and stirred with the above-mentioned filtrate. The excess sludge is mixed with the residual coagulant in the filtrate and is subjected to the coagulation action and the action of centrifugal force, while being separated into the excess sludge cake and the filtrate.
The excess sludge cake is sent forward in the rotary cylinder by a screw conveyor and mixed with the first settled sludge. Therefore, the sludge cake and the filtrate are centrifuged under extremely high gravity due to the action of centrifugal force. The sludge cake is further forwarded in the rotary cylinder by the screw conveyor, discharged from the rotary cylinder and collected. On the other hand, the filtrate is discharged from the rear end of the rotary cylinder, and is first re-processed with the sewage again into the settling tank or the aeration tank.

Therefore, according to the apparatus of the present invention, both the first sludge and the surplus sludge can be centrifugally separated at the same time by one machine, a machine for preconcentration is not particularly required, and the flocculating agent and the surplus sludge are not necessary. It can be used effectively with sludge.

In the concentrating and dewatering device according to the third aspect of the present invention, since the initial sludge having excellent sedimentation and separation properties and a relatively high solid content ratio is directly discharged to the dewatering section in the rotary cylinder, it is effective due to the action of centrifugal force. Is dehydrated and discharged as sludge cake. On the other hand, excess sludge with low sludge concentration and poor dewatering property
Since it is discharged to the sedimentation separation section (also called the concentration zone) in the rotating cylinder, it is mixed there with the filtrate separated from the first settling sludge, and the residual coagulant in the filtrate efficiently aggregates it. It is concentrated by centrifugation. The excess sludge thus concentrated is
It is sent to the dewatering section in front by a screw conveyor and is dehydrated there. Therefore, the action of the centrifugal force received in the sedimentation / separation section on the excess sludge can be effectively utilized also in the dehydration section, which is advantageous from the viewpoint of kinetic energy.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sewage sludge concentration / dehydration apparatus according to the present invention will be described below with reference to the drawings, and a concentration / dehydration treatment method using the concentration / dehydration apparatus will be described.

As shown in FIG. 1, the concentrating and dehydrating apparatus 1 is a screw decanter type centrifugal separator, and in this embodiment, a rotary cylindrical body 2 in which a conical drum portion 2b is integrally combined with a front end of a cylindrical drum portion 2a. And a screw conveyor 3 rotatably mounted in the rotating cylinder body 2. The screw conveyor 3 is also formed in a cylindrical conical shape corresponding to the shape of the rotating cylinder body 2. The screw conveyor 3 has a hollow body 3a, and spiral blades 3b are integrally provided around the body 3a.

Rotating cylinder 2 and screw conveyor 3
Is rotatably supported around a horizontal axis along the central axis thereof, and is rotated at a predetermined speed by a driving device (not shown) via the speed reducer 4. In the figure, reference numeral 5a is a drive pulley on the screw conveyor side, and reference numeral 5b is a drive pulley on the rotary cylinder side.

A sludge supply pipe 6 having a front and rear opening from the rear to the front is inserted along the central axis of the body 3a of the screw conveyor 3, and the tip of the sludge supply pipe 6 is a partition wall 7.
Is provided to penetrate. Then, a conical partition wall 8 is fixedly provided in front of the partition wall 7 in the body portion 3a with a space therebetween, and a space between the partition walls 7 and 8 is formed in a supply chamber 9 for the initial sludge A. A large number of discharge ports 10 for the initial sludge A are bored at regular intervals in the circumferential direction at the portion of the body 3a where the supply chamber 9 is located. Further, the positions of these discharge ports 10 are immediately in front of the start position of the dehydration section (dehydration zone). Further, the sludge supply pipe 6 is provided with a coagulant E supply port 11 directed upward at the rear end thereof, and the sludge supply pipe 6 has a rear end opening 6a.
A pipe 25 for feeding the first sludge A is connected to the. Note that the first settling sludge A is sludge settling in the first settling basin 21 into which sewage first flows in the sewage treatment plant, and therefore one end of the feed pipe 25 is usually connected to the bottom of the first settling basin 21 and pumped First sludge A is sent by (not shown).

A surplus sludge supply pipe 12 is provided in a double pipe structure around the base end (rear end) of the sludge supply pipe 6 to the front part, and the tip of the surplus sludge supply pipe 12 is provided. The part penetrates the partition wall 13. And the body part 3a
A flat plate-shaped partition wall 14 is fixedly provided in front of the partition wall 13 inside the partition wall 13, and a space between the partition walls 13 and 14 is formed in a supply chamber 15 for the excess sludge B. A large number of discharge ports 16 for the excess sludge B are bored at regular intervals in the circumferential direction in the body portion 3a where the supply chamber 15 is located. The positions of the discharge ports 16 are behind the start position of the dehydration section (dehydration zone) and correspond to the sedimentation separation section (concentration zone). At the rear end of the excess sludge supply pipe 12, a supply port 12a for excess sludge B is provided upward. This supply port 12
A pipe 26 for feeding the excess sludge B is connected to a. The surplus sludge B is first settled when the supernatant liquid separated in the settling tank 21 flows into the aeration tank 22 and is biologically decomposed by various bacteria, and then when it flows into the final settling tank 23. Since it is sludge, one end of the supply pipe 26 is connected to the final settling tank 23, and the excess sludge B is supplied by a pump (not shown). Further, since the excess sludge B contains a large amount of bacteria (bacteria) capable of decomposing sludge, a part of the excess sludge B is fed from the pipe 26 for supplying the excess sludge B to the branch pipe 27 to form an aeration tank. Returned to 22.

A large number of outlets 17 for solid matter (sludge cake) C are provided at the tip end (front end) of the rotary cylinder 2 at circumferential intervals, and the outer peripheral surface of the rotary cylinder 2 is provided. Annular flanges 18, 18 are provided in front of and behind the outlets 17, respectively. Further, the periphery of the discharge port 17 has a flange 18
The entire body including 18 is covered with a cover body 19 having an open lower end, and the sludge cake C is discharged below the cover body 19.

On the other hand, the rear end of the rotary cylinder 2 is bent at a right angle toward the center of rotation to form an annular weir 2c for the final filtrate D. Then, the periphery of the rear end of the rotary cylinder 2 is
The filtrate D, which is covered with the cover body 20 having an open lower end and overflows the annular weir 2c, is discharged below the cover body 20.

Next, a dehydration treatment mode by the concentration / dehydration apparatus 1 of the present embodiment configured as described above will be described.

(1) In FIG. 1, the first settling sludge A is supplied through a sludge supply pipe 6 to a front supply chamber 9 in the screw conveyor 3.
Coagulant E injected from the supply port 11 at the rear end of the sludge supply pipe 6 is mixed with the initial sludge A during the supply. The amount of the flocculant E added is usually set to about 1 to 3% in terms of the solid matter ratio of the first settling sludge A, with an emphasis on improving the dewaterability of the sludge. In other words, both the initial sludge A and the surplus sludge B are supplied to the concentration / dehydration apparatus 1 to be subjected to centrifugal dehydration treatment, but if the addition rate of the coagulant E is set (determined) based on the initial sludge A, Good and very easy to manage. And
The first settling sludge A is agglomerated by the aggregating action of the aggregating agent E, and is efficiently dehydrated and separated by the action of centrifugal force due to the rotation of the rotary cylinder 2 and the screw conveyor 3,
The sludge cake C is discharged from the discharge port 10 to the dewatering section in the rotary cylindrical body 2, then is sent forward by the screw conveyor 3, passes through the discharge port 17 and is discharged below the cover body 19.

(2) Excess sludge B discharged from the discharge port 16 to the sedimentation separation section in the rotary cylinder 2 through the excess sludge supply pipe 12 is the filtrate separated from the initial sludge A flowing from the front. D'is mixed and stirred, and concentrated by the aggregating action of the aggregating agent remaining in the filtrate D'and the centrifugal sedimentation action of the rotating cylinder 2. Excess sludge B concentrated in this way
Is sent to the front dewatering section in the rotary cylinder 2 by the screw conveyor 3, and is dewatered and discharged with the dehydrated cake C of the first settled sludge A through the discharge port 17 to the lower side of the cover body 19. In this state, the centrifugal force of the surplus sludge B that has been separated by sedimentation has the effect of reducing the load on the dehydration unit. On the other hand, the filtrate D separated from the surplus sludge B is stored in the rear part of the rotary cylinder 2 in a state of being mixed with the filtrate D ′ separated from the first settling sludge A, and the annular weir 2c
The overflowed filtrate D is discharged below the cover body 20. In addition, the filtered filtrate D was first collected in the sedimentation tank 2
1 is returned to the inlet side (or the aeration tank 22) and treated together with the sewage. The filtrate D contains a part of the flocculant E added to the first settling sludge A from the supply port 11, but the excess sludge solids ratio is 0.2 to 0. Four
%, The residual concentration is finally reduced to 0, so that the coagulant E is not wasted.

Although one embodiment of the present invention has been described above, the present invention can be carried out as follows.

(A) The concentration and dehydration apparatus 1 of the present invention is used for the first settling sludge A.
Also, it can be used for pre-concentration of the excess sludge B, but in this case, the flocculating agent E is not added to the initial sludge A.

(B) For example, if the coagulant E is added to the first settled sludge A during the feeding through the feeding pipe 25, the coagulant E supply port 11 can be omitted.

[0029]

As is apparent from the above description,
The method and apparatus for concentrating and dehydrating sewage sludge of the present invention have the following excellent effects.

(1) According to the method of the present invention, the coagulant is effectively used without waste, it is economical and the control of the coagulant to be added is easy.

(2) According to the device of the present invention, it is possible to centrifuge both the first settled sludge and the surplus sludge at the same time with one machine, and the machine for preconcentration can be omitted, and the equipment cost and the installation space can be reduced. To be done. In addition, the coagulant can be effectively used for the first settling sludge and the surplus sludge.

(3) In the concentrating and dewatering device according to the third aspect, in addition to the effect of the device according to the second aspect of the present invention described above, the action of the centrifugal force exerted on the excess sludge in the sedimentation separation part is also exerted in the dewatering part. Since it is effectively used, there is an effect that it is advantageous from the viewpoint of kinetic energy.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view showing a block flow of a treatment process in a sewage treatment plant and an embodiment of a sewage sludge concentrating and dewatering device according to the present invention.

[Explanation of symbols]

 1 Concentration Dewatering Device 2 Rotating Cylindrical Body 3 Screw Conveyor 3a Hollow Body 3a 6 Sludge Supply Pipe 10/16 Discharge Port 12 Excess Sludge Supply Pipe A Initial Sludge B Excess Sludge C Dewatering Cake D Filtration E Flocculant

Claims (3)

[Claims] 1. A method for concentrating and dewatering sewage sludge produced in a sewage treatment plant, wherein sewage first flows into a settling basin, and the supernatant is treated and discharged through an aeration tank and a final settling basin. The first sludge that settles in the pond has a solid content of 1 to
After mixing about 3% of coagulant, this initial sludge is separated into solid water by centrifugal dehydration to collect solids, and the filtrate is mixed with the excess sludge generated in the final settling basin to obtain the filtrate. A sewage sludge characterized by concentrating the excess sludge by a flocculating action and a centrifugal sedimentation action by a residual flocculant contained in the concentrated sludge and separating the concentrated excess sludge by solid water separation by a centrifugal dehydration action to recover solid matter. Concentration and dehydration treatment method. 2. A screw decanter type sewage sludge concentrating and dewatering device comprising a rotating cylinder and a screw conveyor rotating about the same axis in the rotating cylinder, wherein a rotation center of a rear end surface of the screw conveyor. Along with, a sludge supply pipe for continuously supplying the initial sludge is pierced from the rear of the screw conveyor to the front part of the screw conveyor, and the discharge port of the initial sludge is connected to the hollow of the screw conveyor. The front wall of the body is opened to communicate with the supply port at the tip of the sludge supply pipe, and a surplus sludge supply pipe is doubled around the sludge supply pipe from near the rear end to slightly behind the tip supply port. In addition to having a pipe structure, the discharge port for excess sludge is provided on the intermediate wall surface of the hollow body of the screw conveyor at the supply port at the tip of the excess sludge supply pipe. Through was concentrated dehydrator of sewage sludge, characterized in that an opening. 3. The concentration of sewage sludge according to claim 2, wherein the discharge port of the initial sludge is arranged in a dehydration section in the rotary cylinder, and the discharge port of the excess sludge is arranged in a sedimentation separation section in the rotary body. Dehydrator.