JP2015202481A - Electroosmotic dehydrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroosmotic dehydrator excellent in anticorrosion property on an anode surface.SOLUTION: A conveyor belt 1 made of a filter cloth is endlessly bridged between rollers 2, 3 and can endlessly rotate along the upper surface of a cathode 4. Anode units 21-25 are arranged in the conveying direction of the conveyer belt 1. The undersurfaces of the anode units 21-25 are composed of anode plates 30 formed with a ground layer for corrosion protection and noble metal coating on the surface of a titanium mother plate. The ground layer is made of niobium, tantalum, titanium, zirconium, tungsten and the like.

Description

  The present invention relates to an electroosmotic dehydrator for dehydrating water-containing substances such as wastewater biologically treated sludge and clean water sludge, and more particularly to an electroosmotic dewaterer that prevents corrosion of an anode.

  Electroosmotic dehydration is well known as a method for dehydrating hydrated materials such as sludge generated during biological treatment of wastewater (Patent Documents 1 and 2). 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 dehydration apparatus of Patent Document 1 supplies sludge on a conveyor belt that rotates endlessly, and sandwiches water-containing 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. This anode plate can be moved up and down by an air cylinder or the like. The conveyor moves the hydrated material by one span (anode unit installation interval) with the anode plate raised.

  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.

  Patent Documents 1 and 2 describe using a titanium base plate with a noble metal coating such as platinum or ruthenium oxide as an anode plate.

In such an electroosmotic dehydration method, halogen gas such as chlorine gas is generated on the surface of the anode (anode) by a reaction such as 2Cl ⁻ → Cl ₂ + 2e ⁻ . In addition, electrolytes such as sodium chloride, sodium sulfate, and sodium carbonate may be added to the water to be treated as a dehydration accelerator, and the addition of these increases the amount of strong acid generated at the anode.

  Chlorine gas and sulfuric acid are highly corrosive and corrode the anode and equipment details. In particular, chlorine gas dissolves in water vapor dew condensation water to form low pH dew condensation water, and also dissolves as chlorine gas.

  In order to prevent the generation of chlorine gas, reducing agents such as sodium bisulfite and sodium thiosulfate may be added to the sludge, but the reduction of chlorine gas generates sulfuric acid and hydrochloric acid, which corrodes the anode. It becomes easy.

  By applying a noble metal coating to the anode, the corrosion of the anode is suppressed. However, when acid is generated as described above, the acid penetrates between the noble metal coating and the titanium base plate, and crevice corrosion occurs between the cake and the cake. Such a phenomenon occurs, and the titanium base plate is corroded or the noble metal coating is peeled off to expose the titanium base plate.

  The exposed surface of the titanium base plate is oxidized to titanium oxide, increasing the current-carrying resistance of the anode. In addition, the exposed titanium has high adhesion of the sludge cake, and the corrosion of the anode easily proceeds.

JP2011-136292 JP-A-6-1554797

  An object of the present invention is to provide an electroosmotic dehydrator having excellent corrosion resistance on the anode surface.

  The electroosmotic dehydration apparatus of the present invention comprises: an anode and a cathode arranged opposite to each other; a current-carrying means for energizing between the anode and the cathode; a filter medium arranged between the anode and the cathode; A clamping means for clamping the hydrated material to be treated between the filter medium and one of the electrodes, and an anode plate having a titanium mother plate and a noble metal coating is provided on the anode. In the electroosmotic dewatering apparatus, an anticorrosion base layer is provided between the titanium base plate of the anode plate and the noble metal coating.

  As the underlayer, a metal made of one kind of niobium, tantalum, zirconium, titanium, and tungsten, or an alloy of two or more kinds can be used.

  The electroosmotic dehydration apparatus of the present invention may include a reducing agent adding means and a cleaning means for cleaning the anode surface.

  In the present invention, since the base layer for anticorrosion is provided between the titanium base plate constituting the anode plate and the noble metal coating, corrosion of the titanium base plate is prevented and peeling of the noble metal coating is also prevented. This prevents an increase in the energization resistance of the anode and also prevents the sludge cake from adhering to the anode.

(A) A figure is a schematic longitudinal cross-sectional view at the time of press dehydration 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 in the belt feeding process 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.

  Hereinafter, the first embodiment will be described with reference to FIGS. FIG. 2 shows the belt feeding process of the electroosmotic dehydrator of FIG.

  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 transport side of the water to be treated, 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 on the upper surface of the conveyor belt 1.

  Anode units 21 to 25 are installed above the conveying section of the conveyor belt 1. As shown in FIG. 1B, side wall plates 20 made of an electrically insulating material are erected on both sides of the conveying portion of the conveyor belt 1 so that the sludge on the conveyor belt 1 does not protrude sideways. ing. The anode units 21 to 25 are disposed between the side wall plates 20 and 20. The anode units 21 to 25 can be moved up and down by an air cylinder (not shown). 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.

  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 of the anode units 21 to 25 includes an anode plate 30 on the lower surface. A direct current voltage is applied from a direct current power supply device (not shown) between the anode plate 30 and the cathode 4 of each of the anode units 21 to 25, and a direct current is applied.

  The anode plate 30 has a titanium base plate, a noble metal coating that forms the outermost surface of the anode plate 30, and an anticorrosion foundation layer between them. A pure titanium plate or a titanium alloy plate is used as the titanium base plate.

  As the base layer for anticorrosion, one or more metals or alloys of niobium, tantalum, zirconium, titanium and tungsten can be used. For example, at least one selected from tantalum, niobium, zirconium and tungsten An alloy layer or the like formed by performing discharge scanning on the surface of a titanium base plate using an alloy of 50 to 96% by weight of a metal and 50 to 4% by weight of titanium as an electrode material is suitable. It is not limited.

  Prior to the formation of the base layer, it is preferable to roughen the titanium base plate by a kelen treatment such as sandblasting.

  An alloy composed of one or more metals selected from titanium, tantalum, niobium, zirconium and tungsten can be produced by a method known per se, for example, high frequency melting, plasma arc melting, powder sintering, etc. A powder sintering method is preferred. Thereafter, polishing, machining and cutting can be performed to obtain an alloy electrode rod.

  By using this electrode rod, the base layer can be formed by performing electric discharge machining by scanning the surface of the titanium base plate. The thickness of the underlayer is preferably 0.5 to 50 μm, particularly 1 μm or more.

  A noble metal-based coating (hereinafter referred to as a noble metal coating) made of a noble metal such as platinum or ruthenium oxide or its oxide is formed on the underlayer. In order to form this noble metal coating, a noble metal compound, for example, an alkoxide such as chloride or ethoxide is dissolved in a lower alcohol such as methanol, ethanol, propanol or isopropanol to obtain a solution. This solution is applied on the base layer, dried, and fired at 400 to 700 ° C. in an air atmosphere to form a noble metal coating. The platinum coating can also be formed by electric discharge machining or vapor deposition using a platinum electrode rod. The average thickness of the noble metal coating is preferably about 0.5 to 50 μm.

  In this embodiment, as a mechanism for adding a reducing agent to sludge, a reducing agent supply device 10 including a storage tank of a reducing agent aqueous solution and a chemical injection pump, and spray nozzles 11 and 12 are provided. The spray nozzle 11 is for adding a reducing agent to the sludge in the hopper 5. The reducing agent added into the hopper 5 is mixed with the sludge when the sludge passes through the hopper 5. Note that the hopper 5 may be provided with a stirrer to promote mixing. Alternatively, a mixer may be installed in front of the hopper 5, a reducing agent may be added to the mixer, and sludge and reducing agent may be added before introducing the sludge into the hopper 5.

  The spray nozzle 12 is for spraying the reducing agent aqueous solution on the surface of the sludge S in contact with the anode, that is, on the top surface of the sludge sent out from the hopper 5 onto the conveyor 1.

  As the reducing agent, sodium bisulfite, sodium thiosulfate and the like are preferable.

  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 sent out onto the conveyor belt 1, and between each anode unit 21 to 25 and the cathode 4. While direct current is applied, air is supplied to the air cylinder, and this sludge is pressed from above by the anode plate 30 of the anode units 21 to 25. The reducing agent is added into the hopper 5 from the spray nozzle 11 or the reducing agent is sprayed from the spray nozzle 12 onto the upper surface of the sludge on the conveyor 1.

  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.

  In this way, by energizing between the anode units 21 to 25 and the cathode plate 4 and pressing the sludge with the anode plate 30 of the anode units 21 to 25, the sludge is electroosmotic dehydrated. Then, the dehydrated filtrate passes through the conveyor belt 1, passes through the holes of the cathode plate 4, falls onto the tray 6, and flows out to the drain line 7.

  When each of the anode units 21 to 25 is energized as shown in FIG. 1 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 cylinder, and the anode units 21 to 25 are 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. Further, non-dehydrated sludge is introduced from the hopper 5 to the lower side of the anode unit 21.

  When the reducing agent is sprayed on the upper surface of the sludge S, the anode units 21 to 25 are raised as described above, and the conveyor belt 1 is moved by one pitch and moved from the spray nozzle 12 to the conveyor belt 1. It is preferable to spread on the upper surface of the sludge S.

  After the conveyor belt 1 is moved and moved by one pitch, the anode units 21 to 25 are pushed down and energized between the anode units 21 to 25 and the cathode 4 to perform electroosmotic dehydration treatment of sludge. Thereafter, the sludge is electroosmotic dehydrated by repeating this process.

By adding a reducing agent to the sludge S, generation of halogen gas such as chlorine gas is suppressed. However, the reducing agent reacts with chlorine gas to produce sulfuric acid and hydrochloric acid. For example, when sodium thiosulfite reacts with chlorine, sulfuric acid and hydrochloric acid are generated by the reaction of Na ₂ S ₂ O ₃ + 4Cl ₂ + 5H ₂ O → 2H ₂ SO ₄ + 2NaCl + 6HCl. In this embodiment, since the anticorrosion base layer is provided on the anode 30, corrosion of the titanium base plate is prevented even if sulfuric acid or hydrochloric acid is generated.

  In the above embodiment, the sludge is electroosmotic dehydrated by the anode units 21 to 25, the conveyor belt 1 and the cathode 4, but the present invention is also applicable to another type of electroosmotic dehydration apparatus. For example, as shown in FIG. 3, the present invention can also be applied to an electroosmotic dehydrator that sandwiches sludge S between an anode drum 61 and a conveyor belt 62 that also serves as a cathode. Moreover, although illustration is abbreviate | omitted, it can apply also to the electroosmosis dehydration device of the type which clamps a to-be-processed hydrated material between filter media.

  In the present invention, after the electroosmotic dehydrator is operated for a predetermined time, the surface of the anode plate is preferably washed with high-pressure water jet, a brush, a scraper or the like to remove the attached cake.

  In addition, although it does not corrode immediately under the influence of the attached dehydrated cake, it is preferable to wash before the attached dehydrated cake is fixed. Ease of fixing varies depending on the moisture content, viscosity, and adhesion of the dehydrated cake, and the frequency of cleaning cannot be determined uniformly, but the standard for cleaning is about once / day to once / month.

  In addition, in the case of the electroosmotic dehydrator of the type shown in FIG. 3 that sandwiches the dehydrated cake while rotating the electrode and energizes the electroosmotic dehydrator, the scraper cleaning is performed every time or intermittently when the electrode surface is at the upper part, It is preferable that the cleaning water W is sprayed by the nozzle 63 to perform water cleaning.

[Example 1]
The dewatered cake obtained by dewatering excess sludge generated by the aerobic biological treatment was dewatered by an electroosmotic dehydrator having the structure shown in FIGS. The number of anode units is 16, the area of one anode plate 30 is 3300 cm ² , the underlying layer alloy covering the titanium base plate is titanium / tantalum alloy (titanium 70 wt%) (thickness 10 μm), and the thickness of the platinum coating on the surface 10 μm.

  The dehydration operation was paused twice in the middle, but otherwise it was almost continuous.

Operating conditions: Energizing time 1000 hours (intermittent operation)
Energizing condition Maximum 760A / m ²
60V maximum
Periodic washing Washing with high-pressure water was performed once every 170 hours (one week).

  As a result, dehydration was performed as follows.

Moisture content of dehydrated cake before electroosmosis 82-84%
Moisture content of dehydrated cake after electroosmotic dehydration 60-65%
When the surface state of the anode after operation was observed, the platinum coating remained on the entire surface (100%).

[Example 2]
The operation was performed under the same conditions as in Example 1 except that periodic cleaning with high-pressure water was not performed. As a result, cake adhesion was observed on part of the end. The platinum coating on the anode plate surface remained on 95% of the surface.

[Comparative Example 1]
The operation was performed under the same conditions as in Example 2 except that the underlayer was not formed. As a result, the platinum coating on the surface of the anode plate remained only on 60% of the surface.

[Discussion]
As is clear from the above examples and comparative examples, according to the present invention, corrosion of the anode of the electroosmotic dehydrator can be prevented. Thereby, the durability of the anode can be greatly improved, and the replacement frequency can be reduced.

  In Comparative Example 1, the corrosion of the base material was confirmed at a portion to which the sludge was adhered, particularly at the end portion. In Examples 1 and 2, it was found that the base material was not corroded. Also, corrosion can be greatly reduced by regular cleaning.

DESCRIPTION OF SYMBOLS 1 Conveyor belt 2,3 Roller 4 Cathode 5 Hopper 10 Reducing agent supply machine 11,12 Spray nozzle 21-25 Anode unit 30 Anode plate 60 Anode drum 62 Conveyor belt

Claims (4)

Oppositely disposed anode and cathode;
Energizing means for energizing between the anode and the cathode;
A filter medium disposed between the anode and the cathode;
A clamping means for clamping the water to be treated between the filter media or between the filter media and one of the electrodes;
In an electroosmotic dehydration apparatus in which an anode plate having a titanium mother plate and a noble metal coating is provided on the anode,
An electroosmotic dehydration apparatus, wherein an anticorrosion base layer is provided between a titanium base plate of the anode plate and a noble metal coating.   2. The electroosmotic dehydration apparatus according to claim 1, wherein the anticorrosion underlayer is made of at least one metal or alloy selected from niobium, tantalum, zirconium, titanium, and tungsten.   3. The electroosmotic dehydration apparatus according to claim 1 or 2, further comprising cleaning means for cleaning the surface of the anode plate.   The electroosmotic dehydration apparatus according to any one of claims 1 to 3, further comprising addition means for adding a reducing agent to the water to be treated.

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