JP2011072862A - Electroosmotic dewatering method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroosmotic dewatering method and apparatus which can efficiently reduce the water content of a dewatered product. <P>SOLUTION: A conveyor belt 1 made of filter cloth is stretched endlessly between rollers 2, 3, so that it can rotate endlessly. Anode units 21-25 are arranged in the transfer direction of the conveyor belt 1. Dewatered sludge subjected to electroosmotic dewatering treatment is introduced to a screw conveyor 40 where the upper surface of a casing 41 opens to the atmosphere. The dewatered sludge is stirred and steam is released to the atmosphere, whereby the water content of the sludge is reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an electroosmotic dehydration method and apparatus for dehydrating water-containing materials such as biologically treated sludge and sewage sludge from wastewater, and in particular, electroosmotic dewatering that promotes the diffusion of water vapor from the dehydrated material. The present invention relates to a method and an apparatus.

  Electroosmotic dehydration is well known as a method for dehydrating hydrated materials such as sludge generated during biological treatment of wastewater (Patent Documents 1 to 5, Non-Patent Document 1). In this electroosmosis dehydration treatment, the water to be treated is energized to attract the negatively charged sludge to the anode side, while dewatering by applying pressure while moving the sludge pore water to the cathode side for separation. Therefore, compared with the case of mechanical dehydration processing, dewatering efficiency is high, and it is possible to further reduce the moisture content of sludge.

  The electroosmotic dewatering device of Patent Document 1 is configured to electrolyze and dewater sludge between an endless rotating lower filter belt (cathode) and an endless rotating upper press belt (anode). .

  The electroosmotic dewatering device of Patent Document 2 is configured such that an electrode drum as an anode is disposed separately from the upper press belt, and the upper and lower belts are clamped by this electrode drum.

  The electroosmotic dehydration apparatus of Patent Document 3 supplies sludge onto a conveyor belt that rotates endlessly, and sandwiches the hydrated material between a cathode plate below the conveyor belt and an anode unit above the conveyor belt. The electroosmosis dehydration is performed by passing an electric current. A plurality of anode units are arranged in the conveyor moving direction. A horizontal anode plate is installed on the bottom surface of each anode unit. The anode plate can be pushed down by an air cylinder and can be pulled up by a spring. The conveyor moves the hydrated material by one span (anode unit installation interval) with the anode plate raised.

  In the electroosmotic dehydrator of Patent Documents 4 and 5, a two-leaf filter cloth is disposed between a pair of left and right filter plates having both poles. Sludge is supplied between the filter cloths, sandwiched between the filter cloths, and energized between the electrodes, whereby the sludge is subjected to electroosmotic dehydration. After the treatment, the filter plate is separated, and then the filter cloths are separated from each other to remove the dehydrated product.

JP-A-1-189311 JP-A-6-1554797 WO2007 / 143840 JP 7-73646 Japanese Patent No. 3576269

Water Treatment Management Handbook (September 30, 1998, Maruzen) 339-341

  In the electroosmosis dewatering section, Joule heat is generated because electric current is applied to sludge having electrical resistance. Accordingly, the sludge is heated while being dehydrated, and after dehydration, a dehydrated cake having a high temperature of about 60 to 100 ° C. is formed.

  At this time, since the dehydrated product (dehydrated cake) is at a high temperature, a part of the water inside the dehydrated product is changed to water vapor.

  Usually, the dehydrated cake is in the form of a sheet or a lump. When the heated dehydrated cake is transferred to the cake hopper in this shape, water vapor condenses into water as the dehydrated cake cools, and remains inside the dehydrated cake.

  An object of the present invention is to provide an electroosmotic dehydration method and apparatus that can promote the diffusion of water vapor from a dehydrated product dehydrated in an electroosmotic dehydration unit, and can further reduce the water content of the dehydrated product efficiently. .

  The electroosmotic dehydration method of the present invention (Claim 1) is a dehydration method in which the dehydrated dehydration method is performed in such a manner that the water to be treated is sandwiched between an anode and a cathode, and dehydration is performed by energizing both electrodes while pressing. The specific surface area increasing process for increasing the specific surface area of the product is performed.

  The electroosmotic dehydration method according to claim 2 is characterized in that, in claim 1, the specific surface area increasing process is a stirring process or a fragmenting process of the dehydrated product.

  The electroosmotic dehydration method according to claim 3 is characterized in that, in claim 1, the specific surface area increasing treatment is performed before the dehydrated product is allowed to cool.

  An electroosmotic dehydration apparatus according to the present invention (Claim 4) includes an electrode disposed opposite to each other, an energizing means for energizing between the opposed electrodes, a filter medium disposed between the opposed electrodes, and between the filter media. Alternatively, in an electroosmotic dehydration apparatus having a clamping means for clamping the water to be treated between the filter medium and one electrode, specific surface area increasing means for increasing the specific surface area of the electroosmotic dehydrated dehydrated product is provided. It is characterized by having.

  An electroosmotic dehydration apparatus according to a fifth aspect of the invention is characterized in that, in the fourth aspect, the specific surface area increasing means is a screw conveyor whose upper part of the casing is open to the atmosphere.

  An electroosmotic dehydration apparatus according to a sixth aspect of the invention is characterized in that, in the fourth aspect, the specific surface area increasing means is a dividing means for dividing the dehydrated product.

  In the present invention, the dehydrated product dehydrated in the electroosmotic dehydration unit is subjected to a specific surface area increasing process to promote the diffusion of water vapor from the dehydrated product. Thereby, the moisture content of a dehydration thing can be reduced.

(A) A figure is a schematic longitudinal cross-sectional view of the electroosmosis dehydration apparatus which concerns on embodiment, (b) A figure is sectional drawing which follows the BB line of (a) figure. It is a schematic longitudinal cross-sectional view at the time of conveyor belt conveyance of the electroosmosis dehydration apparatus which concerns on embodiment. It is a schematic longitudinal cross-sectional view of the electroosmosis dehydration apparatus which concerns on another embodiment. (A) A figure is a schematic longitudinal cross-sectional view of the electroosmosis dehydration apparatus which concerns on different embodiment, (b) A figure is sectional drawing which follows the BB line of (a) figure. It is a schematic longitudinal cross-sectional view of the electroosmosis dehydration apparatus used for another embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. 1 (a) and 2 are longitudinal sectional views along the longitudinal direction (belt rotation direction) of the electroosmotic dehydration apparatus according to the first embodiment, and FIG. 1 (b) is the first view. It is sectional drawing which follows the BB line of a figure (a). FIG. 1 shows the state of the dehydration process, and FIG. 2 shows the state of the belt feeding process of the electroosmosis dehydrator.

  A conveyor belt 1 made of filter cloth is stretched between the rollers 2 and 3 in an endless manner, and can be rotated endlessly.

  The upper surface side of the conveyor belt 1 is a conveyance side, and the lower surface side is a return side. A plate-like cathode 4 is disposed on the lower surface of the conveyor belt 1 on the conveyance side. The cathode 4 is a plate-like member made of a conductive material such as metal and has a large number of holes penetrating in the vertical direction. The cathode 4 extends from the immediate vicinity of the roller 2 to the immediate vicinity of the roller 3.

  A hopper 5 is provided so as to supply water to be treated (sludge S in this embodiment) to the upstream portion in the transport direction of the upper surface (conveyance unit) of the conveyor belt 1.

  A tray 6 is provided under the cathode 4 to receive the filtrate falling through the hole of the cathode 4.

  The filtrate collected in the tray 6 is sent to the water treatment facility via the pipe 7. A part of the filtrate may be returned to the hopper 5 and added to the sludge.

  Anode units 21, 22, 23, 24, and 25 are installed above the conveyor unit of the conveyor belt 1. As shown in FIG. 1 (b), side wall plates 20 are erected on both sides of the conveyor unit of the conveyor belt 1 so that sludge on the conveyor belt 1 does not protrude sideways. The anode units 21 to 25 are disposed between the side wall plates 20 and 20.

  In this embodiment, five anode units are arranged in the conveyor belt conveying direction, but the present invention is not limited to this. Usually, about 2 to 5 anode units may be arranged in the conveyor belt conveyance direction.

  Each anode unit 21-25 has the anode plate 33 fixed to the lower surface, and an air cylinder (not shown). The upper end of the air cylinder is fixed to the main body of the electroosmosis dehydrator, and when air is supplied into the air cylinder, the anode plate 33 moves downward. When air is discharged from the air cylinder, the anode plate 33 is lifted and raised.

  The upper end of the air cylinder is attached to a beam (not shown) which is the main body of the electroosmotic dehydrator. This beam is fixedly installed above the conveyor belt 1.

  A direct current is applied to the anode plate 33 of each of the anode units 21 to 25 from a direct current power supply device (not shown).

  A screw conveyor 40 is installed to convey the dewatered sludge sent out from the conveyor belt 1. The screw conveyor 40 includes a hopper 41, a casing 42, a screw 43 disposed in the casing 42, a motor 44 that drives the screw 43, and the like. The casing 42 has a substantially U-shaped longitudinal section in the direction orthogonal to the screw axis, and the upper part is open to the atmosphere. The screw conveyor 40 is preferably a multi-axis screw conveyor having two or more axes, but is not limited thereto.

  In order to perform the sludge dewatering process by the electroosmotic dewatering device configured as described above, the sludge S supplied into the hopper 5 is fed onto the conveyor belt 1 and a direct current is applied to each of the anode units 21 to 25. Then, air is supplied to the air cylinders of the anode units 21 to 25, and the sludge is pressed from above by the anode plates 33 of the anode units 21 to 25.

  The voltage is applied so that the anode units 21 to 25 are positive and the cathode plate 4 is negative. Applying the same voltage to each of the anode units 21 to 25 is preferable from the viewpoint of facilitating operation management of the apparatus. However, the voltage may be increased or decreased on the downstream side in the transport direction. May be. Further, energization control may be performed so that the current values of the anode units are the same.

  The air of the same pressure may be supplied to the air cylinders of the anode units 21 to 25, and the supply air pressure may be increased or decreased as the anode unit on the downstream side.

  As described above, the current is passed between the anode units 21 to 25 and the cathode plate 4 and the sludge is pressed by the anode plate 33 of the anode units 21 to 25, whereby the sludge is electroosmotic dehydrated. Then, the dehydrated filtrate passes through the conveyor belt 1, passes through the holes of the cathode plate 4, and falls on the tray 6. The filtrate dropped on the tray 6 is sent to a water treatment facility for processing. When the filtrate having a high electrical conductivity from the tray 6 is supplied into the hopper 5, the electrical conductivity of the sludge to be treated is increased, and the anode units 21 to 25 and the cathode plate 4 are separated from each other. The electrical conductivity of the sludge increases and the dewaterability improves. Thereby, the moisture content of the dewatered sludge obtained becomes low.

  As shown in FIG. 1, when the anode units 21 to 25 are energized and the sludge is pressed by the anode units 21 to 25, the conveyor belt 1 is stopped. After pressing and energizing for a predetermined time by the anode units 21 to 25, air is discharged from the air cylinders of the anode units 21 to 25, and the anode plate 33 is raised as shown in FIG. And the conveyor belt 1 is moved only 1 pitch of the arrangement pitch of the anode units 21-25. Thereby, the sludge located on the lower side of the anode unit 25 is sent out as dehydrated sludge, and the sludge located on the lower side of each of the anode units 21 to 24 is each one stage downstream of the anode units 22 to Move to the bottom of 25. The dewatered sludge on the end side of the conveying surface of the conveyor belt 1 falls so as to fall off the conveyor belt 1 at a position past the roller 3 and is introduced into the hopper 41 of the screw conveyor 40. Further, non-dehydrated sludge is introduced from the hopper 5 to the lower side of the anode unit 21. Next, the anode plate 33 of each anode unit 21 to 25 is pushed down and energized between each anode unit 21 to 25 and the cathode 4 to perform electroosmotic dehydration treatment of sludge. Thereafter, the sludge is electroosmotic dehydrated by repeating this process.

  The dewatered sludge that has fallen into the hopper 41 of the screw conveyor 40 moves in the casing 42 while being stirred by the screw 43. During this time, the dewatered sludge is loosened, the specific surface area is increased, and water vapor in the dewatered sludge is released into the atmosphere. Since the upper surface of the casing 42 of the screw conveyor 40 is open, the water vapor is quickly dissipated into the atmosphere. Thereby, the moisture content of the dewatered sludge sent out from the screw conveyor 40 becomes lower than when it is introduced into the hopper 41.

  In the present invention, it is preferable to perform a specific surface area increasing treatment on the dehydrated product before cooling at 60 ° C. or higher, particularly 80 ° C. or higher.

  In the present invention, the specific surface area of the dehydrated product is preferably increased to 5 times or more, particularly 10 times or more by the specific surface area increasing treatment.

[Another embodiment]
In the above embodiment, dehydrating sludge subjected to electroosmotic dehydration treatment is stirred and loosened by a screw conveyor to increase the specific surface area of the dehydrated sludge and promote the diffusion of water vapor, as shown in FIG. The specific surface area of the dewatered sludge may be increased by pressing the knife unit 50 on the conveyor belt 1 against the dewatered sludge subjected to the electroosmotic dewatering treatment and dividing the dewatered sludge. The knife unit 50 includes a large number of downward blades (knives) 51 and is moved up and down by a cylinder device 52. It is preferable that the dehydrated sludge is completely divided (cleaved) with the knife 51. However, the knife 51 may be pushed into the dehydrated sludge to such an extent that a groove is formed without being completely divided.

  Although the knife 51 extends in the width direction of the conveyor belt 1 in this embodiment, it may extend in the longitudinal direction of the conveyor belt 1 or may be provided in a cross beam shape. Further, the specific surface area may be increased by piercing the dehydrated sludge with a needle (needle) instead of the knife 51 and opening a needle hole.

  In FIG. 4, the knife plate 55 is disposed adjacent to the anode unit 25 so as to divide the dewatered sludge subjected to the electroosmotic dehydration process into strips.

  The knife plate 55 has the plate surface as the conveying direction of the conveyor belt 1. A plurality of knife plates 55 are provided at intervals in the width direction of the conveyor belt 1. The knife plate 55 is attached to the lower surface of the holder 56, and the lower end of each is in contact with the upper surface of the conveyor belt 1 or slightly higher than that.

  When the dewatered sludge is conveyed by the conveyor belt 1, the dewatered sludge is divided into strips by the knife plate 55, the specific surface area is increased, and the diffusion of water vapor is promoted.

  Although not shown, dehydrated sludge from the conveyor belt 1 may be crushed by a crusher to increase the specific surface area and promote the diffusion of water vapor.

  In the electroosmotic dehydration apparatus of the above embodiment, the sludge is electroosmotically dehydrated by the anode units 21 to 25, the conveyor belt 1 and the cathode 4, but the present invention can also be applied to another type of electroosmotic dehydration apparatus. It is. For example, as shown in FIG. 5, the present invention can also be applied to an electroosmotic dehydrator 60 that sandwiches sludge S between an anode drum 61 and a conveyor belt 62 that also serves as a cathode. Although not shown in the drawings, the present invention can also be applied to an electroosmotic dehydration apparatus of a type in which an object to be processed is sandwiched between filter media. For example, as described in Patent Document 4 (Japanese Patent Publication No. 7-73646), Patent Document 5 (Patent No. 3576269), Non-Patent Document 1 (Water Treatment Management Handbook P.340, Tables 8 and 6), a pair of filter plates The present invention can also be applied to a pressure-squeezing type electroosmotic dehydration apparatus that sandwiches sludge through a pressing membrane and an electrode. In these cases as well, the dehydrated material is processed to increase the specific surface area with a screw conveyor or the like, thereby promoting the diffusion of water vapor from the dewatered sludge.

  Hereinafter, examples and comparative examples will be described.

<Comparative Example 1>
The electroosmotic dehydration apparatus shown in FIGS. 1 and 2 (however, the screw conveyor 40 is omitted) was subjected to electroosmotic dehydration treatment of sewage sludge with a moisture content of 82%. The operating conditions are as follows.

Number of anode units in the conveyor belt conveyance direction: 5 Sludge supply speed: 12 L / hr
Applied voltage to anode unit: 60V
Thickness of dewatered sludge (dehydrated cake) at the conveyor belt end position: 10 mm
Temperature of dewatered sludge (dehydrated cake) at the conveyor belt end position: 90 ° C

  The sludge was subjected to electroosmotic dehydration treatment under the above conditions, and the moisture content of the 90 ° C. dehydrated cake immediately after discharge was measured and found to be 69%.

<Example 1>
In the above Comparative Example 1, the dehydrated cake was crushed immediately after dehydration, passed through a sieve having an opening of 5 mm, naturally cooled at room temperature, and the water content was measured and found to be 66%.

<Example 2>
In Comparative Example 1, after the sheet-like dehydrated cake was naturally cooled at room temperature, it was crushed and the moisture content was measured through a sieve having an opening of 5 mm. As a result, it was 68%.

  From the above Examples and Comparative Examples, it was confirmed that the water content of the dewatered sludge was reduced according to the present invention.

DESCRIPTION OF SYMBOLS 1 Conveyor belt 2, 3 Roller 4 Cathode 5 Hopper 6 Tray 8 Storage tank 9 Pump 21-25 Anode unit 33 Anode plate 40 Screw conveyor 43 Screw 50 Knife unit 51 Knife 55 Knife plate

Claims (6)

In the electroosmotic dehydration method of sandwiching the water to be treated between the anode and the cathode and dehydrating by energizing both electrodes while pressing,
An electroosmotic dehydration method comprising performing a specific surface area increasing process for increasing a specific surface area of a dehydrated dehydrated product.   2. The electroosmotic dehydration method according to claim 1, wherein the specific surface area increasing process is a dehydration stirring process or a fragmenting process.   3. The electroosmotic dehydration method according to claim 1, wherein the specific surface area increasing treatment is performed before the dehydrated product is allowed to cool. Oppositely arranged electrodes;
Energizing means for energizing between the opposing electrodes;
A filter medium disposed between the opposing electrodes;
In an electroosmotic dehydration apparatus having a clamping means for clamping the water-containing material to be treated between the filtering media or between the filtering media and one electrode,
An electroosmotic dehydration apparatus comprising specific surface area increasing means for increasing a specific surface area of a dehydrated product subjected to electroosmosis dehydration.   5. The electroosmotic dehydration apparatus according to claim 4, wherein the specific surface area increasing means is a screw conveyor whose upper part of the casing is open to the atmosphere.   5. The electroosmotic dehydration apparatus according to claim 4, wherein the specific surface area increasing means is a dividing means for dividing the dehydrated product.

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