JP6920056B2 - Sludge dewatering system and sludge dewatering method - Google Patents

Description

The present invention relates to a sludge dewatering system and a sludge dewatering method, and relates to a technique that contributes to an improvement in a solid matter recovery rate.

Conventionally, organic sludge is generated in the process of organic wastewater treatment such as public sewage, human waste, septic tank sludge, factory wastewater, etc., and there is a screw press dehydrator as one of the dehydrating devices for dehydrating this organic sludge. The screw press dehydrator has the advantage of lower power than the belt press dehydrator and the centrifugal dehydrator. However, the screw press dehydrator has a higher load of returned water to the water treatment process than the belt press dehydrator and the centrifugal dehydrator. This is because the opening (hole) of the metal screen provided in the screw press dehydrator is larger than the opening of the filter cloth provided in the belt press dehydrator, so that a large amount of solid content leaks into the drainage.

A sludge dewatering system using this screw press dewatering machine is described in, for example, Patent Document 1. In the solid-liquid separator, the internal space of the tubular body is divided into a first zone on the upstream side and a second zone on the downstream side along the sludge movement direction, and is located in the first zone. A first saucer that receives the water separated from the sludge and a second saucer that receives the water separated from the sludge in the second zone are provided, and the filtrate of the first saucer passes through the sludge tank. It was sent to the flocking device and the flocked sludge was returned to the solid-liquid separator.

Further, in Patent Document 2, the dehydration separation liquid from the dehydrator is treated together with the raw sludge, and after adding a polymer to the dehydration separation liquid and the raw sludge and performing the coagulation treatment under stirring in the first coagulation tank, the first 1 Coagulated sludge is introduced into a concentrator and concentrated. The concentrated sludge of the concentrator was subjected to a coagulation treatment under stirring in a second coagulation tank after adding a polymer, and then the second coagulation sludge in the second coagulation tank was dehydrated by a dehydrator.

Further, in Patent Document 3, after adding a polymer flocculant to organic sludge in the mixing step and mixing it, the coagulated sludge produced in the mixing step is concentrated in the concentration step to obtain a separation liquid and concentrated sludge. There is. Then, the concentrated sludge obtained in the concentration step is dehydrated by a screw press dehydrator in the dehydration step to obtain a dehydrated cake and a dehydration separation liquid, and the dehydration separation liquid obtained in the dehydration step is solid-liquid separated. The obtained sludge side was returned to the mixing step and / or the concentrating step.

Japanese Patent Application Laid-Open No. 09-220598 JP 2006-35166 Patent 4966258

In the screw press dehydrator, the SS concentration (suspended solids concentration) of the dehydrated filtrate is higher than the SS concentration of the dehydrated filtrate of other dehydrators, so the load for processing the dehydrated filtrate to make clear treated water is heavy. There is a big challenge.

Further, in Patent Document 1, since the fine flocs (condensation) contained in the filtrate flowing from the first saucer are mixed with the raw sludge in the sludge tank, the charge neutralization of the microflocs is disrupted. Therefore, in addition to the amount of coagulant required for agglomerating the solid content (suspended solids) in the raw sludge, the solid content (suspended solids) in the filtrate flowing in from the first saucer is reaggregated. Therefore, it is necessary to add the necessary amount of the coagulant together, and there is a problem that the total amount of the coagulant consumed increases.

Patent Document 2 requires two coagulation tanks, a first coagulation tank and a second coagulation tank, which causes a problem that the apparatus configuration becomes complicated and the total amount of coagulant consumed increases.

In Patent Document 3, the dehydration separation liquid obtained in the dehydration step is solid-liquid separated, and the obtained sludge is returned to the mixing step and / or the concentration step, so that the apparatus configuration becomes complicated and the dehydration separation liquid is complicated. The cost of installing a device for solid-liquid separation is added to the initial cost, and labor and cost for maintenance and repair are required.

The present invention solves the above problems, and provides a sludge dewatering system and a sludge dewatering method capable of increasing the recovery rate of solid content in a simple configuration without increasing the total consumption of the coagulant to be added. The purpose is.

In order to solve the above problems, in the sludge dehydration system of the present invention, the sludge supply system adds a polymer flocculant to the sludge to be dehydrated and stirs it, and sludge that supplies the sludge to be dehydrated to the flocculation device. A dehydrator that has a pump and dehydrates aggregated sludge containing aggregated sludge formed by an aggregater corresponds to the front concentration zone, the rear dehydration zone, and the front filtrate receiving part and the dehydration zone corresponding to the concentration zone. The direct return system, which has a rear filtrate receiving portion and directly returns the dehydrated filtrate flowing from the dehydration zone to the rear filtrate receiving portion, is located on the downstream side of the sludge pump and upstream of the sludge pump. It is characterized in that the dehydration filtrate is supplied to the sludge supply system on the side.

In the sludge dewatering system of the present invention, the filtration surface of the dehydrator is characterized in that the filtration surface of the concentration zone occupies 1/6 to 1/3 of the total length of the filtration surface, and the dewatering zone occupies the rest.

In the sludge dewatering system of the present invention, the dewatering machine is a screw press dewatering machine.

In the sludge dewatering system of the present invention, the screw press dewatering machine is characterized by having a filtration surface made of wedge wire on the front side of the screen and a filtration surface made of punching metal on the rear side.

In the sludge dehydration method of the present invention, sludge to be dehydrated is supplied to a coagulation device by a sludge pump of a sludge supply system, a polymer flocculant is added to the sludge to be dehydrated in the coagulation device and stirred, and agglomeration formed by the coagulation device is performed. Aggregated sludge containing flocs is dehydrated by a dehydrator having a front concentration zone and a rear dehydration zone, and the dehydrated filtrate flowing from the rear dehydration zone of the dehydrator to the rear filtrate corresponding to the dehydration zone is aggregated. The direct return system, which is directly returned to the apparatus, supplies the sludge filtrate to the sludge supply system on the downstream side of the sludge pump and on the upstream side of the aggregator .

In the sludge dewatering method of the present invention, the amount of the polymer coagulant added to the coagulator is characterized in that the amount required for the coagulation treatment is calculated only for the sludge to be dewatered flowing from the sludge supply system.

As described above, according to the present invention, the dehydrated filtrate discharged from the dehydration zone of the screw press dehydrator is directly returned to the coagulator by the direct return system, so that the minute flocs contained in the dehydrated filtrate are broken. Is returned to the coagulator.

Therefore, the total consumption of the coagulant required by the coagulator is necessary for the coagulation of the sludge to be dehydrated newly supplied from outside the system without increasing the consumption of the coagulant due to the return of the dehydrated filtrate. The amount can be suppressed, and the recovery rate of solid content can be increased without increasing the chemical injection rate of the flocculant.

Schematic diagram showing the sludge dewatering apparatus according to the embodiment of the present invention. Chart showing the results of distribution measurement of filtrate discharge under condition 1 in the sludge dehydrator Chart showing the results of distribution measurement of filtrate discharge under condition 2 in the sludge dehydrator

Hereinafter, the sludge dewatering apparatus according to the embodiment of the present invention will be described with reference to the drawings. In FIG. 1, various types of screw press dehydrators 10 can be used regardless of whether they are 1-axis type or 2-axis type. In this embodiment, a 2-axis screw press dehydrator is used, but 1-axis type is used. The same effect can be achieved with a mold screw press.

The screw press dehydrator 10 has a front concentration zone 12 and a rear dehydration zone 13 inside the outer body screen 11, and a biaxial screw 14 arranged along the axial direction of the outer body screen 11 is provided. I have. In the outer body screen 11, the concentration zone 12 is made of wedge wire and the dehydration zone 13 is made of punching metal.

The screw press dehydrator 10 has a back pressure presser 16 at the dehydrated cake discharge port 15 at the end of the dehydration zone 13, and has a pressing device 17 that presses the back pressure presser 16 toward the dehydrated cake discharge port 15. .. The back pressure applied to the back pressure presser 16 is adjusted by operating the pressing device 17, and the water content of the dehydrated cake is adjusted by adjusting the back pressure.

The screw press dehydrator 10 includes a front filtrate receiving portion 18 corresponding to the concentration zone 12 and a rear filtrate receiving portion 19 corresponding to the dehydration zone 13 on the outside of the outer body screen 11. The ratio of the regions of the concentration zone 12 and the dehydration zone 13 does not have to be 1: 1 and can be set to any ratio, and the front filtrate receiving portion 18 depends on the ratio of the regions of the concentration zone 12 and the dehydration zone 13. And the ratio of the rear filtrate receiving portion 19 is also changed.

In the present embodiment, the outer body screen 11 has a filtration surface made of wedge wire on the front side and a filtration surface made of punching metal on the rear side. As for the ratio of the regions of the concentration zone 12 and the dehydration zone 13 to the outer body screen 11, the concentration zone 12 occupies 1/6 to 1/3 of the total length of the screen, and the dehydration zone 13 occupies the rest. The boundary between the concentration zone 12 and the dehydration zone 13 does not necessarily coincide with the boundary between the filtration surface made of wedge wire and the filtration surface made of punching metal.

In the screw press dewatering machine 10, the sludge supply system 20 is connected to the concentration zone 12, the clear drainage system 30 is connected to the front filtrate receiving portion 18, and the direct return system 40 is connected to the rear filtrate receiving portion 19. The cake discharge system 50 is connected to the dehydrated cake discharge port 15.

The sludge supply system 20 includes a coagulation device 23 that adds a polymer flocculant 22 to the sludge 21 to be dehydrated and agitates it, and a sludge pump 24 that supplies the sludge 21 to be dewatered to the coagulation device 23. The sludge pump 24 press-fits the sludge to be dehydrated 21 into the aggregating device 23, and extrudes the agglomerated sludge containing the agglomerating flocs of the aggregating device 23 into the screw press chiller 10 at a predetermined pressure.

The flocculant supply system 25 is connected to the flocculant 23, and the flocculant supply system 25 has a flocculant pump 26 that supplies the polymer flocculant 22 to the flocculant 23. The polymer flocculant is preferably cationic or cationic / anionic, but the present invention is not limited to this, and an inorganic flocculant may be added, or a fibrous dehydration aid may be added.

The clarified drainage system 30 returns the clarified wastewater discharged from the front filtrate receiving portion 18 to a water treatment facility outside the system.

The direct return system 40 directly returns the dehydrated filtrate discharged from the dehydration zone 12 of the screw press dehydrator 10 to the coagulator 23, which has a return pump 41 and is upstream of the coagulator 23. Is connected to the sludge supply system 20. In addition to the return pump 41, the direct connection return system 40 can be provided with piping equipment such as a valve.

The dehydrated filtrate is a high-concentration wastewater with a high concentration of suspended solids containing fine flocs. The cake discharge system 50 discharges the dehydrated cake from which the dehydrated cake discharge port 15 is pushed out.

The operation of the above configuration will be described below. The aggregating device 23 agitates the sludge to be dehydrated 21 supplied by the sludge pump 24 and the aggregating agent supplied by the aggregating agent pump 26 to form an aggregating floc. As for the amount of the coagulant to be supplied to the coagulation device 23, the amount required for the coagulation treatment is calculated only for the sludge 21 to be dehydrated flowing from the sludge supply system 20. The agglomerated sludge containing the agglomerated flocs of the aggregating device 23 is press-fitted into the screw press dehydrator 10 under the supply pressure of the sludge pump 24.

In the screw press dewatering machine 10, coagulated sludge is conveyed toward the dewatered cake discharge port 15 by the twin-screw screw 14, and the dewatered cake is discharged to the outside of the machine from the dewatered cake discharge port 15. The clear wastewater desorbed in the concentration zone 12 flows out to the front filtrate receiving portion 18 and then is returned to the water treatment facility through the clear drainage system 30. The dehydrated filtrate that has flowed out from the dehydration zone 13 to the rear filtrate receiving portion 19 is returned to the sludge supply system 20 on the upstream side of the aggregating device 23 through the direct return return system 40 by the return pump 41, and is aggregated from the rear filtrate receiving portion 19. It flows directly into the device 23.

In this way, the dehydrated filtrate discharged from the dehydration zone 13 of the screw press dehydrator 10 is directly returned to the coagulator 23 by the direct return system 40, so that the minute flocs contained in the dehydrated filtrate neutralize the charges. It is kept and returned to the aggregator without breaking the flocs.

Therefore, the total consumption of the coagulant required by the coagulator 23 does not accompany an increase in the consumption of the coagulant due to the return of the dehydrated filtrate, and the coagulation of the sludge to be dehydrated newly supplied from outside the system. It can be suppressed to the required amount. Therefore, the recovery rate of the solid content can be increased without increasing the chemical injection rate of the flocculant. Moreover, the above-mentioned effect can be realized in a simple device configuration in which the dehydrated filtrate discharged from the dehydration zone 13 of the screw press dehydrator 10 is directly returned to the coagulator 23 by the direct return system 40.

That is, it is sufficient to divide the concentration zone 12 and the dehydration zone 13 into an appropriate ratio, and return only the dehydration filtrate containing a large amount of solid content discharged from the dehydration zone 12 to the coagulation device 23. No need to go through. If the concentration zone 12 and the dehydration zone 13 are divided into appropriate ratios, the configuration of solid-liquid separation and return of sludge as described in Patent Document 3 is unnecessary.

The results of the distribution measurement of the filtrate discharge amount in the present embodiment are shown in FIGS. 2 and 3. FIG. 2 shows the result under condition 1, and FIG. 3 shows the result under condition 2.

Here, if Category 1 is the concentration zone 12 and Category 2 and 3 are the dehydration zones 13, 80 to 88% of the filtrate volume, that is, the filtrate volume 1.5 m ³ / h in FIG. 2, and the filtrate volume in FIG. A clean dehydrated filtrate of 1.6 m ³ / h is discharged to the outside of the system, and a dehydrated filtrate having a high SS concentration of 12 to 20% is returned to the aggregating apparatus 23. If the categories 1 and 2 are set to the concentration zone 12 and the category 3 is set to the dehydration zone 13, the SS concentration of the dehydrated filtrate returned to the coagulator 23 becomes even higher and becomes a trace amount.

Further, as the recovery rate increases, the solid content separated from the sludge to be dehydrated increases, and as a result, the clarity of the clarified water returned to the water treatment step increases, and the return water load can be reduced.

Further, conventionally, in the screw press dehydrator 10, when the operating pressure, that is, the back pressure at the dehydrated cake discharge port 15 is increased, the water content of the dehydrated cake decreases, but as the back pressure increases, the screw press dehydrator 10 leaks. The amount of solid content (SS) leaked increases and the recovery rate decreases.

However, in the present embodiment, the solid content (SS) leaking from the screw press dewatering machine 10 is returned to the screw press dewatering machine 10 without increasing the coagulant, and the recovery rate is increased without increasing the chemical injection rate. Therefore, it is possible to operate the screw press dehydrator 10 under a high back pressure while maintaining a high recovery rate, and as a result, the water content of the dehydrated cake can be reduced.

10 Screw press dehydrator 11 Outer body screen 12 Concentration zone 13 Dewatering zone 14 2-axis screw 15 Dewatering cake discharge port 16 Back pressure presser 17 Pressing device 18 Front filtrate receiving part 19 Rear filtrate receiving part 20 Sludge supply system 21 Sludge supply system 21 Dewatering Target sludge 22 Polymer coagulant 23 Coagulant device 24 Sludge pump 25 Coagulant supply system 26 Coagulant pump 30 Clarified drainage system 40 Direct connection return system 41 Return pump 50 Cake discharge system

Claims (7)

The sludge supply system has a coagulation device that adds a polymer flocculant to the sludge to be dehydrated and agitates it, and a sludge pump that supplies the sludge to be dehydrated to the coagulation device.
A dehydrator that dehydrates agglomerated sludge containing agglomerated flocs formed by a coagulator is a front filtrate receiver corresponding to the front concentration zone, a rear dehydration zone and a concentration zone, and a rear filtrate receiver corresponding to the dehydration zone. Has a part,
The direct return system that directly returns the dehydrated filtrate that has flowed out from the dehydration zone to the rear filtrate receiving portion to the aggregator is the dehydrated filtrate to the sludge supply system on the downstream side of the sludge pump and upstream of the aggregator.
A sludge dewatering system characterized by supplying. The sludge dehydration system according to claim 1, wherein the filtration surface of the dehydrator occupies 1/6 to 1/3 of the total length of the filtration surface in the concentration zone, and the dehydration zone occupies the rest. The sludge dewatering system according to claim 1 or 2, wherein the dewatering machine is a screw press dewatering machine. The sludge dehydration system according to claim 3 , wherein the screw press dehydrator has a filtration surface made of wedge wire on the front side of the screen and a filtration surface made of punching metal on the rear side. The sludge dewatering system according to claim 3 or 4 , wherein the screw press dewatering machine is a biaxial type. The sludge to be dehydrated is supplied to the coagulation device by a sludge supply system sludge pump, a polymer coagulant is added to the sludge to be dehydrated in the coagulation device and stirred, and the coagulated sludge containing the coagulation floc formed by the coagulation device is fronted. A direct connection that dehydrates with a dehydrator having a concentration zone and a rear dehydration zone, and directly returns the dehydrated filtrate that has flowed out from the dehydration zone at the rear of the dehydrator to the rear filter fluid receiving portion corresponding to the dehydration zone. A sludge dehydration method, wherein the return system supplies the sludge filtrate to the sludge supply system on the downstream side of the sludge pump and on the upstream side of the aggregator. The sludge dewatering method according to claim 6, wherein the amount of the polymer coagulant added to the coagulator is calculated as the amount required for the coagulation treatment only for the sludge to be dewatered flowing from the sludge supply system. ..

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