JP2011212525A - Electro-osmotic dewatering method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electro-osmotic dewatering method and apparatus which can efficiently reduce the water content of a dewatered product.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. Electricity is applied between the anode units 21-25 and a cathode plate 4 and sludge is pressed by anode plates 33 of the anode units 21-25, thereby performing the electro-osmotic dewatering of the sludge. An agitating means, such as an agitating blade 8, is provided which agitates the sludge to be subjected to the electro-osmotic dewatering treatment.

Description

  The present invention relates to an electroosmotic dehydration method and apparatus for dehydrating hydrated materials such as biologically treated sludge and wastewater sludge, and in particular, electroosmotic dehydration after stirring the hydrated material. The present invention relates to a dehydration method and 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 dewatering device of Patent Document 3 supplies sludge onto a conveyor belt that rotates endlessly, and sandwiches a 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

  When performing the electroosmotic dewatering treatment as in the above-mentioned patent document, there are many voids in the primary dewatered sludge to be treated sludge. Since current does not flow through the voids during the electroosmotic dehydration process, even if the sludge containing a large amount of voids is electroosmotic dehydrated, the water content of the dewatered sludge is unlikely to decrease.

  Moreover, the surface of the primary dewatered sludge may be slightly dry. The dried portion has a high electric resistance, and it is difficult for current to flow during the electroosmotic dehydration process, resulting in a decrease in electroosmotic dehydration efficiency.

  An object of this invention is to provide the electroosmosis dehydration method and apparatus which can reduce the moisture content of a dehydrate efficiently.

  The electroosmotic dehydration method according to claim 1 is the electroosmotic dehydration method in which the water to be treated is sandwiched between the anode and the cathode and dehydrated by energizing both electrodes while being compressed. It is characterized by electroosmotic dehydration.

  The electroosmotic dehydration method according to claim 2 is characterized in that, in claim 1, the hydrated material to be treated is subjected to primary dehydration treatment, the hydrated product after the primary dehydration treatment is stirred, and then electroosmotic dehydration is performed. .

The electroosmotic dehydration method of claim 3 is characterized in that, in claim 2, stirring is performed so that the electric resistance is 80% or less of the hydrated material after the primary dehydration treatment. Here, the electrical resistance is measured by compressing the same weight of the hydrated material before and after stirring at a predetermined pressure of 0.1 to 1.0 kgf / cm ² .

  The electroosmotic dehydration method according to claim 4 is characterized in that, in any one of claims 1 to 3, the stirring means is a stirring blade, a mono pump, a screw or a kneader.

  The electroosmotic dehydration apparatus according to claim 5 is 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 mediums or one of the filter mediums. An electroosmotic dehydration apparatus having a clamping means for clamping the treated water-containing material between the electrode and the electrode further comprises a stirring means for stirring the treated water-containing material.

  In the present invention, the hydrated material to be treated is agitated and then subjected to electroosmotic dehydration. Preferably, the water to be treated is agglomerated and then subjected to primary dehydration, and the primary dewatered sludge (cake) is stirred before electroosmotic dehydration. When the primary dewatered cake is stirred, the sheet-shaped or block-shaped primary dehydrated cake is crushed so that it can be easily adjusted to a uniform thickness, and the electroosmotic dewatering effect is enhanced. Moreover, the sludge particles in the primary dewatered cake form an aggregate called a ped and are present non-uniformly. Agitation breaks the bond between the pedt and the pedd, and also crushes the pedd itself to disperse the sludge particles, so that the primary dehydrated cake has a reduced shear strength and is soft.

Normally, a low pressure of about 1 kgf / cm ² or less is applied to the primary dehydrated cake during electroosmotic dehydration, but the primary dehydrated cake is softened by stirring, so it is compressed even at a low applied pressure, voids disappear, and the apparent density increases. . As the apparent density increases, the amount of primary dewatered cake that can be electroosmotic dehydrated per unit electrode area increases.

  By stirring the primary dehydrated cake, the moisture concentration of the primary dehydrated cake that was non-uniform on the surface and inside becomes uniform. The water concentration in the primary dewatered cake becomes uniform, and the water in the primary dewatered cake is connected by capillary water due to the dispersion of sludge particles. This lowers the electrical resistance of the primary dewatered cake and increases the electroosmotic dewatering effect.

It is a flowchart explaining the electroosmosis dehydration method which concerns on embodiment. (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. It is a schematic longitudinal cross-sectional view of the electroosmosis dehydration apparatus used for experiment.

  In the present invention, electroosmotic dehydration is performed after the water to be treated is stirred. Preferably, the hydrated material to be treated is subjected to primary dehydration, and the electrolyzed dehydration treatment is performed after the primary dehydrated product is stirred. FIG. 1 is a flow diagram showing this preferred form.

  As shown in FIG. 1, after adding a flocculant to the water to be treated, it is supplied to a primary dehydrator for primary dehydration. The primary dehydrated cake from the primary dehydrator is supplied to the stirrer and stirred, and then supplied to the electroosmotic dehydrator to conduct electroosmotic dehydration to obtain a secondary dehydrated cake. A dehydration accelerator may be added to a stirrer or an electroosmotic dehydrator. When the dehydration accelerator is added during or before stirring, the dehydration accelerator is uniformly dispersed in the sludge by stirring.

  In the present invention, there is no particular limitation on the hydrated material to be treated for electroosmotic dehydration treatment, but concentrated sludge (moisture content of 95 to 99% by weight (hereinafter, unit of moisture content) generated during the treatment of various industrial wastewaters. Is described as “%”).

The flocculant used for the flocculation treatment of the water to be treated is not particularly limited, and those having an excellent flocculation effect are used depending on the sludge properties, etc., but generally aluminum chloride (AlCl ₃ ), polychlorinated Aluminum, sulfuric acid band (Al ₂ (SO ₄ ) ₃ ), aluminum hydroxide (Al (OH) ₃ ) or aluminum oxide (Al ₂ O ₃ ) dissolved in hydrochloric acid (HCl) or sulfuric acid (H ₂ SO ₄ ) Aluminum-based flocculants such as aluminum salts, ferric chloride (FeCl ₃ ), ferric sulfate (Fe ₂ (SO ₄ ) ₃ ), iron salts such as ferrous sulfate (FeSO ₄ ), etc. 1 type or 2 types or more of various inorganic type flocculants, such as an iron type flocculant of these, and a silica type flocculant, can be used. Preferably, polyferric sulfate is used.

  An inorganic flocculant and a polymer flocculant may be used in combination. As the polymer flocculant to be used in combination, various polymer flocculants such as an anionic polymer flocculant, a cationic polymer flocculant, a nonionic polymer flocculant, and an amphoteric polymer flocculant can be used. It is preferable to use an amphoteric polymer flocculant (amphoteric polymer). As the amphoteric polymer flocculant, a monomer having an amino group or an ammonium base, a copolymer of (meth) acrylamide and (meth) acrylic acid or a salt thereof is preferable, and as a monomer having an amino group or an ammonium base, for example, (Meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloyloxy-2-hydroxypropyltrimethylammonium chloride and other (meth) acryloyloxyalkyl quaternary ammonium salts, (meth) (Meth) acryloyloxyalkyl tertiary amine salts such as acryloyloxyethyldimethylamine sulfate or hydrochloride, (meth) acryloyloxypropyldimethylamine hydrochloride, (meth) acryloyl (Meth) acryloylaminoalkyl quaternary ammonium salts such as nopropyltrimethylammonium chloride and (meth) acryloylaminopropyltrimethylammonium methyl sulfate can be mentioned (here, “(meth) acryl” means “acrylic and / or Or “methacryl”, and the same applies to “(meth) acryloyl”. These monomers can be used individually by 1 type, or can also be used in combination of 2 or more type. Among these, (meth) acryloyloxyalkyl quaternary ammonium salts are excellent in the dehydration effect and can be preferably used, and acryloyloxyethyltrimethylammonium chloride and methacryloyloxyethyltrimethylammonium chloride can be particularly preferably used. .

  Examples of (meth) acrylic acid or a salt thereof include (meth) acrylic acid, sodium (meth) acrylate, ammonium (meth) acrylate, calcium (meth) acrylate, and the like. Among these, acrylic acid and sodium acrylate can be particularly preferably used.

  The amphoteric polymer flocculant can be copolymerized with another comonomer. Examples of other comonomers include vinyl pyrrolidone, maleic acid, and methyl acrylate. The copolymerization amount of these comonomers is usually preferably 20 mol% or less, and more preferably 10 mol% or less.

  These polymer flocculants may be used individually by 1 type, and may use 2 or more types together.

  The amount of these flocculants added is appropriately determined so that dehydrated sludge having a desired water content can be obtained. When a polymer flocculant having a weak shearing force is used as the flocculant used for primary dehydration, the flocculant polymer is easily cut during stirring, and water is likely to be detached from sludge during electroosmotic dehydration.

  Examples of the primary dehydrator include a mechanical dehydrator such as a multiple disk dehydrator, a centrifugal dehydrator, a belt press, a screw press, and a filter press.

  The water content range of the primary dehydrated cake may be a water content of 80% or less for a primary dehydrated cake with an organic matter ratio of 0.8 or more, and a water content of 70% or less for a primary dehydrated cake with an organic matter ratio of 0.5 or less. preferable.

  As the stirrer, various types such as a rotary blade type and a rotary screw type can be used.

  In the present invention, it is desirable to stir so that the electrical resistance of the primary dehydrated cake after stirring is 90% or less compared to that before stirring, and it is particularly desirable to stir so as to be 80% or less.

  As dehydration accelerators, in addition to electrolytes, concentrated salts discharged from wastewater treatment facilities, especially high-conductivity filtrates discharged from the front stage of electroosmosis dehydration facilities, and dispersants that increase the zeta potential of sludge particles May be used. It is particularly desirable that the dehydration accelerator is added during a stirrer, a stirrer in an electroosmotic dehydration facility, or during electroosmotic dehydration.

In the present invention, the electroosmosis dehydration apparatus is not particularly limited, and the various electroosmosis dehydration apparatuses described above can be used. The electroosmotic dehydration treatment conditions are not particularly limited, but for example, the following conditions can be employed.
Applied pressure: 0.1 to 200 kPa
Applied voltage amount: 20-100V
Dehydration time: 5-60 minutes

  FIGS. 2 (a) and 3 are longitudinal sectional views along the longitudinal direction (belt rotating direction) of an electroosmotic dehydrator suitable for use in the present invention, and FIG. 2 (b) is a second view. It is sectional drawing which follows the BB line of a figure (a). FIG. 2 shows the state of the dehydration step, and FIG. 3 shows the state of the belt feeding step of this electroosmotic 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 made of a primary dewatered cake in this embodiment) to the upstream portion in the transport direction of the upper surface (transport section) of the conveyor belt 1. In this hopper 5, the stirring blade 8 rotated by the motor M is installed.

  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. 2 (b), side wall plates 20 are erected on both sides of the conveyor section of the conveyor belt 1, and sludge on the conveyor belt 1 is configured not to protrude laterally. 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).

  In this embodiment, an open screw conveyor 40 is installed in order to promote the evaporation of moisture from the dewatered sludge using the heat held by 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 sludge dewatering treatment by the electroosmosis dewatering device configured as described above, the sludge S supplied into the hopper 5 is stirred by the stirring blade 8 and then sent out onto the conveyor belt 1, and each anode unit 21- A direct current is applied to the air current 25, air is supplied to the air cylinders of the anode units 21 to 25, and the sludge is pressed by the anode plates 33 of the anode units 21 to 25 from above.

  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.

  When the anode units 21 to 25 are energized as shown in FIG. 2 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 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. 4, 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. Also in these cases, the water to be treated, preferably the primary dewatered sludge is stirred by the stirring means and then supplied to the electroosmotic dehydrator.

  Hereinafter, examples and comparative examples will be described.

  The stirred primary dewatered cake was subjected to electroosmosis dehydration using a column type electroosmosis dehydration tester shown in FIG. In this electroosmosis dehydration tester, a primary dewatering cake is accommodated in a vertical column 60 having a diameter of 100 mm, and a piston 61 is lowered by an air cylinder 62. A cathode 63 made of a perforated plate is provided at the lower end of the column 60. An anode 64 is provided on the lower surface of the piston. An electric current was passed between the anode and the cathode, and the electrical resistance of the primary dewatered cake before and after stirring was measured. Further, the filtrate was received in a beaker and weighed with an electronic balance. Test conditions are shown below.

<Primary dehydrated cake>
A primary dewatered cake mainly composed of organic sludge dehydrated to 80.6% water content by a belt press dehydrator was used. It is a block-like lump with a thickness of about 5 mm.

<Stirring conditions>
Example 1: The primary dewatered cake is stirred with a medicine basket.
Comparative Example 1: No stirring (still in block form).
Comparative Example 2: The primary dehydrated cake is crushed and passed through a 2 mm sieve.

<Electroosmotic dehydration conditions>
Primary dehydrated cake amount: 170g
Dehydration time: 10 min
Applied voltage: 60V
Pressure: 0.32 kgf / cm ²

<Electrical resistance measurement conditions>
170 g of the primary dehydrated cake was placed in the column, and a pressure of 0.32 kgf / cm ^{2 was} applied. The electrical resistance of the primary dewatered cake between the anode and cathode was measured with a digital meter.

<Test results>
Table 1 shows the results of the electroosmotic dehydration treatment of sludge under the above conditions. The electrical resistance in Table 1 is a value immediately after stirring under the above stirring conditions, storing in a column and applying the above pressure.

  As shown in Table 1, the examples were able to significantly reduce the ultimate moisture content as compared with the comparative examples. Even in Comparative Example 2 in which the primary dehydrated cake was crushed, the water content can be reduced by 2% compared to Comparative Example 1. However, Example 1 was able to reduce the moisture content by 6% compared to Example 1. The electrical resistance ratio was 0.73 in Example 1 (73% before stirring), and the electrical resistance was reduced compared to Comparative Example 2.

  From the above Examples and Comparative Examples, it was confirmed that the water content of electroosmotic 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

Claims (5)

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, wherein the hydrated material to be treated is stirred and then electroosmotic dehydrated.   2. The electroosmotic dehydration method according to claim 1, wherein the hydrated material to be treated is subjected to primary dehydration treatment, the hydrated product after the primary dehydration treatment is stirred, and then electroosmotic dehydration is performed.   3. The electroosmotic dehydration method according to claim 2, wherein the agitation is performed so that the electric resistance is 80% or less of the hydrated product after the primary dehydration treatment.   The electroosmotic dehydration method according to any one of claims 1 to 3, wherein the stirring means is a stirring blade, a mono pump, a screw, or a kneader. 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 stirring means for stirring the water to be treated.

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