JP2012176387A - Electro-osmotic dewatering method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide electro-osmotic dewatering method and apparatus that can obtain the dehydration product of a given water content even if the properties of a water-containing object to be processed change.SOLUTION: A conveyor belt 1 consisting of a filter cloth is endlessly spanned between rollers 2 and 3, and is made to be able to turn endlessly. Anode units 21-23 are arranged to the conveyance direction of the conveyor belt 1, and a spray nozzle 12 is provided between the anode units 23 and 24 on the way. A dehydration aid is added from a nozzle 11 or the spray nozzle 12 to sludge according to the resistance value of the water-containing object to be processed. The sludge charge rate may be controlled according to the resistance value of the water-containing object.

Description

  The present invention relates to an electroosmotic dehydration method and apparatus for dehydrating hydrated materials such as biologically treated sludge and sewage sludge of wastewater, and in particular, depending on the resistance value of the hydrated material to be treated, The present invention relates to an electroosmotic dehydration method and apparatus for controlling the supply amount of water to be treated.

  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.

  In such an electroosmotic dehydration method, the dehydration amount is proportional to the energization amount, and therefore, when the electrical conductivity of the sludge is increased, the moisture content of the dewatered cake tends to decrease. Therefore, in order to increase the dehydration efficiency, it has been proposed to increase the electrical conductivity of the hydrated material as in the following (a) to (c).

  (A) The pH and electrical conductivity of the cake after dehydration are adjusted by collecting the dehydrated filtrate and adding it to the sludge before dehydration (Patent Document 1).

  (B) An electrolyte such as sodium chloride, sodium sulfate, or sodium carbonate is added to the sludge (Patent Document 4).

  (C) A conductive activator is added to the sludge (Patent Document 2. However, Patent Document 2 does not specifically describe what the conductive activator is).

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 dehydration method, when the property of the water-containing material to be treated changes, the water content of the dehydrated material changes. An object of the present invention is to provide an electroosmotic dehydration method and apparatus capable of obtaining a dehydrated product having a predetermined moisture content even if the properties of the treated water-containing product are changed.

  By the way, in the electroosmotic dehydration method, most of the cations that are the driving force for dehydration are discharged together with the filtrate in the first half of dehydration. For this reason, when an electrolyte is added to the water to be treated in advance, in the latter half of the dehydration, the electrical conductivity of the sludge decreases due to the lack of cations, and the ultimate moisture content of the dehydrated cake is unlikely to decrease. When a large amount of electrolyte is added to the water to be treated to retain cations until the latter half of the dehydration, the moisture content of the dehydrated cake decreases, but an excessive amount of current flows in the initial stage of dehydration, resulting in an increase in energy consumption.

  In the case of recycling the filtrate of Patent Document 1, a filtrate having a high electrical conductivity is generated in the first half of the dehydration, but the filtrate in the latter half of the dehydration has a low electrical conductivity. In Patent Document 1, since all the filtrate generated by dehydration is recovered and reused, the filtrate with low electrical conductivity is reused. For this reason, the amount of added filtrate increases, and sludge having a high water content is electroosmotic dehydrated, so that the ultimate water content is unlikely to decrease.

  In one aspect, the present invention provides an electroosmotic dehydration method and apparatus in which an electrolyte is added to a treated water-containing material to increase the electrical conductivity of sludge and to reduce the water content of the dehydrated product. It is an object of the present invention to provide an electroosmotic dehydration method and apparatus capable of efficiently further reducing the rate.

  The electroosmotic dehydration method according to claim 1 is an electroosmotic dehydration method in which a treated water-containing material is sandwiched between an anode and a cathode, and is dehydrated by energizing both electrodes while being compressed. In the electroosmotic dehydration method to be added to a product, the addition amount of the dehydration aid is controlled according to the resistance value of the water to be treated.

  The electroosmotic dehydration method of claim 2 is characterized in that, in claim 1, a dehydrating aid is added to the water to be treated during dehydration.

  The electroosmotic dehydration method according to claim 3 is characterized in that, in claim 1 or 2, the resistance value is a value obtained by dividing an applied voltage between the anode and the cathode by a current value between both electrodes. It is.

  The electroosmotic dehydration apparatus according to claim 4 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 between the filter medium and one of them. In the electroosmosis dehydration apparatus having a clamping means for clamping the treated water-containing material between the electrodes, a dehydration agent is added to the treated water-containing material according to the resistance value of the treated water-containing material An auxiliary agent adding means is provided.

  The electroosmotic dehydration apparatus according to claim 5 is characterized in that, in claim 4, the dehydrating auxiliary agent adding means adds the dehydrating auxiliary agent to the treated water-containing material during dehydration.

  The electroosmotic dehydration method according to claim 6 is an electroosmotic dehydration method in which a treated water-containing material is sandwiched between an anode and a cathode and is dehydrated by energizing both electrodes while being compressed, depending on the resistance value of the treated water-containing material. Thus, the supply amount of the hydrated material to be treated is controlled.

  The electroosmotic dehydration method according to claim 7 is characterized in that, in claim 6, the resistance value is a value obtained by dividing an applied voltage between the anode and the cathode by a current value between both electrodes. .

  The electroosmotic dehydration apparatus according to claim 8 is an electrode disposed oppositely, 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. In the electroosmotic dehydration apparatus having a clamping means for clamping the treated water-containing material between the electrodes, the treated material for controlling the supply amount of the treated water-containing material according to the resistance value of the treated water-containing material A hydrate content supply control means is provided.

  In the present invention (first invention), since a dehydration aid is added to the water to be treated according to the resistance value of the water to be treated, even if the properties of the water to be treated change, an appropriate amount of dewatering aid Thus, a dehydrated product having a predetermined moisture content can be obtained.

  In one embodiment of the present invention, since the dehydration aid is added to the water to be treated during the dehydration step, the dehydration efficiency in the latter half of the dehydration step is improved. As described above, in the first half of the dehydration process, a large amount of electrolyte is present in the water to be treated, so that the dehydration efficiency is high. In one embodiment of the present invention, even in the latter half when the electrolyte decreases, the dehydration efficiency is increased by the addition of the dehydration aid, so that a dehydrate with a low water content can be obtained.

  In the present invention (second invention), by controlling the supply amount of the water to be treated in accordance with the resistance value of the water to be treated, dehydration with a predetermined moisture content can be achieved even if the properties of the water to be treated are changed. A processed product can be obtained.

(A) A figure is a schematic longitudinal cross-sectional view at the time of press dehydration of the electroosmotic dehydration apparatus which concerns on embodiment, (b) A figure and (c) figure are the BB line and CC line of (a) figure FIG. (A) The figure is a schematic longitudinal cross-sectional view in the belt feeding process of the electroosmotic dehydration apparatus which concerns on embodiment, (b) A figure is the BB sectional drawing of (a) figure. It is a schematic longitudinal cross-sectional view of the electroosmosis dehydration apparatus which concerns on another embodiment. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result.

  Hereinafter, embodiments will be described with reference to the drawings. 1 (a) and 2 (a) are longitudinal sectional views along the longitudinal direction (belt rotation direction) of the electroosmotic dehydrator according to the embodiment, and FIG. 1 (b) and FIG. 1 (c). FIG. 2 is a sectional view taken along line BB and CC in FIG. 1 (a), and FIG. 2 (b) is a sectional view taken along line BB in FIG. 1 (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 sludge 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 on the upper surface of the conveyor belt 1.

  Of the side wall surface of the hopper 5, the sludge outflow side is a gate wall 5a movable in the vertical direction. The sludge is supplied onto the conveyor belt 1 through the lower side of the gate wall 5a. When the gate wall 5a is raised by the driving device 6, the sludge supply amount increases, and when it is lowered, the sludge supply amount decreases.

  In this embodiment, a resistance value detecting means 7 for detecting the resistance value of sludge and a controller 8 to which the detected value of the resistance value detecting means 7 is inputted are provided. 8 to be controlled.

  Anode units 21, 22, and 23 are installed above the conveyor unit of the conveyor belt 1. As shown in FIGS. 1 (b) and 1 (c), side wall plates 20 made of an electrically insulating material are erected on both sides of the conveying portion of the conveyor belt 1, and sludge on the conveyor belt 1 is lateral. It is configured not to protrude. The anode units 21 to 23 are disposed between the side wall plates 20 and 20.

  In this embodiment, three 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 to 23 includes an anode plate 30 on the lower surface. The anode units 21 to 23 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.

  A DC voltage is applied from a DC power supply (not shown) between the anode plate 30 and the cathode 4 of each anode unit 21 to 23, and a DC current is applied.

  A nozzle 11 is provided in the hopper 5 so as to add a dehydrating aid. The spray nozzle 12 is disposed between the anode unit 21 and the anode unit 22. In this embodiment, two spray nozzles 12 are provided in the width direction of the conveyor belt 1, but one or three spray nozzles may be provided. Moreover, you may install the spray nozzle which has a slit-like spraying hole long in a conveyor belt width direction.

  A dehydration aid is supplied to the nozzles 11 and 12 via a chemical injection pump 10 from a tank (not shown) containing a dehydration aid made of a solution. In FIG. 1, the dehydration aid is configured to be supplied from the pump 10 to both the nozzles 11 and 12, but only one nozzle may be provided. Further, a switching valve may be provided so that the dehydrating aid is selectively supplied to the nozzles 11 and 12.

  In this embodiment, the resistance value detecting means 7 detects the resistance value R of sludge between the anode units 21, 22, 23 and the cathode 4, and specifically, the anode units 21-23, It is a value (R = V / I) obtained by dividing the applied voltage V between the cathode 4 and the energization current value I between them.

  As the dehydration aid, an electrolyte solution is suitable. Examples of such an electrolyte solution include, but are not limited to, a salt solution such as sodium chloride, sodium sulfate, sodium carbonate, sodium bicarbonate, and potassium chloride, and an acid solution such as hydrochloric acid, sulfuric acid, and nitric acid. .

  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 23 and the cathode 4. While supplying a direct current, 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 23.

  Applying the same voltage to each of the anode units 21 to 23 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.

  Air of the same pressure may be supplied to the air cylinders of the anode units 21 to 23, and the supply air pressure may be increased or decreased as the anode unit on the downstream side.

  In this way, the current is passed between the anode units 21 to 23 and the cathode plate 4, and the sludge is electroosmotic dehydrated by pressing the sludge with the anode plate 30 of the anode units 21 to 23. Then, the dehydrated filtrate passes through the conveyor belt 1 and passes through the holes of the cathode plate 4 and falls.

  As shown in FIG. 1, when the anode units 21 to 23 are energized and the sludge is pressed by the anode units 21 to 23, the conveyor belt 1 is stopped. After pressing and energizing the anode units 21 to 23 for a predetermined time, air is discharged from the air cylinder, and the anode units 21 to 23 are raised as shown in FIG. Then, the conveyor belt 1 is moved by one pitch of the arrangement pitch of the anode units 21 to 23. Thereby, the sludge located on the lower side of the anode unit 23 is sent out as dehydrated sludge, and the sludge located on the lower side of each of the anode units 21 to 22 is downstream of the anode unit 22 to the downstream side. 23 move down. Further, non-dehydrated sludge is introduced from the hopper 5 to the lower side of the anode unit 21.

  In this embodiment, while the conveyor belt 1 is fed and moved by one pitch, the dehydrating aid is added from the nozzle 11 to the sludge in the hopper 5 and the dehydrating aid is sprayed from the spray nozzle 12 to convey the conveyor. Add to sludge S on belt 1.

  After the conveyor belt 1 is moved by one pitch, spraying of the dehydrated filtrate from the spray nozzle 12 is stopped, and then each anode unit 21 to 23 is pushed down and between each anode unit 21 to 23 and the cathode 4. Energize and perform electroosmotic dehydration of sludge. Thereafter, the sludge is electroosmotic dehydrated by repeating this process.

  By adding a dehydrating aid to the sludge S, the electrical conductivity of the treated sludge is increased and the dewaterability of the sludge is improved. In addition, by adding the dehydration aid from the spray nozzle 12 to the sludge S to be treated, the electrical conductivity of the sludge to be treated in the latter half of the dehydration process is increased, and the gap between the anode units 22 and 23 and the cathode plate 4 is increased. The electrical conductivity of the sludge increases and the dewaterability improves.

  In this embodiment, since the addition amount of the dewatering aid is controlled based on the resistance value of the sludge to be treated, the water content of the obtained dewatered sludge can be adjusted as is apparent from the examples described later. .

  In this embodiment, the spray nozzle 12 is disposed between the anode units 21 and 22. In the vicinity of the spray nozzle 12, the sludge is dehydrated to some extent and has a low moisture content. Therefore, even if the sludge is pressed by the anode unit after the dehydrated filtrate is sprayed from the spray nozzle 12, it is between the anode units 21 and 22. Sludge does not leak from the space.

  In the electroosmotic dehydration apparatus of the above embodiment, the spray nozzle 12 is disposed between the anode units 21 and 22. However, as shown in FIG. Alternatively, the dehydrated filtrate may be sprayed and added to the sludge S on the conveyor belt 1.

  If it does in this way, the clearance gap between anode units 21 and 22 can be made small, and it can prevent that sludge leaks out between this anode units 21 and 22 at the time of sludge press.

  In the present invention, a spray nozzle may be disposed between the anode units 22 and 23.

  In the above embodiment, the sludge resistance value is obtained from the applied voltage and the energizing current between the anode units 21 to 23 and the cathode 4, but the resistance value sensor is installed in the sludge storage tank, sludge transfer pipe, hopper 5, etc. May be.

  In the above embodiment, the addition amount of the dewatering aid is controlled according to the sludge resistance value, but the sludge supply amount may be controlled according to the sludge resistance value. In order to control the sludge supply amount, it is preferable to move the gate wall 5a up and down, but the sludge supply amount may be controlled by changing the transfer speed of the conveyor belt 1.

  In the above embodiment, the sludge is electroosmotic dehydrated by the anode units 21 to 23, the conveyor belt 1 and the cathode 4, but the present invention is also applicable to other types of electroosmotic dehydration apparatuses. For example, the present invention can also be applied to an electroosmotic dehydrator that sandwiches sludge S between an anode drum and a conveyor belt that also serves as a cathode. Further, the present invention can also be applied to an electroosmotic dehydration apparatus of a type in which a workpiece 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.

  Hereinafter, examples and comparative examples will be described.

  Using the electroosmosis dehydrator shown in FIG. 1, sewage sludge with a water content of 82% was electroosmotic dehydrated. Moreover, the resistance value of the sludge was calculated | required from the voltage and electric current between the anode units 21-23 and the cathode 4. FIG. The operating conditions are as follows.

Number of anode units arranged in the conveyor belt conveyance direction: 3 Position of spray nozzle 12: Between first and second anode units Sludge supply speed: 360 kg / hr
Applied voltage to anode unit: 60V

<Comparative Example 1>
The sludge was subjected to electroosmotic dehydration treatment under the above conditions without adding a dehydration aid. As a result, the moisture content of the dewatered sludge was 69.0%, and the resistance value of the sludge was 0.75Ω.

<Example 1>
In the comparative example 1, an aqueous sodium bicarbonate solution having a concentration of 8 wt% was added only when the conveyor belt 1 was moved from the spray nozzle 12 between the first and second anode units. The amount added was 1 wt%, 2 wt% or 3 wt% with respect to the raw sludge. The results (resistance value and moisture content) are shown in Table 1, FIG. 4 and FIG. FIG. 6 shows the relationship between the resistance value based on FIGS. 4 and 5 and the water content.

  As shown in FIGS. 4 and 5, when the addition amount of the dehydrating aid is increased, the moisture content is lowered and the resistance value is lowered. As shown in FIG. 6, there is a linear relationship between the resistance value and the moisture content. By selecting the resistance value at which the target moisture content is obtained from FIG. 6 and controlling the addition amount of the dehydrating aid so as to be the resistance value, the dehydrated sludge having the target moisture content can be obtained.

<Example 2>
The same sludge as in Example 1 was supplied at 250, 280, 300, or 340 kg / hr to the electroosmotic dehydrator of Example 1, and the resistance value and the sludge moisture content after the dehydration treatment were measured. The results are shown in Table 2 and FIGS. 7 and 8. FIG. 9 shows the relationship between the resistance value and the moisture content based on FIGS.

  As shown in FIGS. 7 and 8, when the sludge supply amount is increased, the moisture content increases and the resistance value increases. As shown in FIG. 9, there is a linear relationship between the resistance value and the moisture content. By selecting a resistance value to be the target moisture content from FIG. 9 and controlling the sludge supply amount so as to be the resistance value, dehydrated sludge having the target moisture content can be obtained.

DESCRIPTION OF SYMBOLS 1 Conveyor belt 2, 3 Roller 4 Cathode 5 Hopper 7 Resistance value detection means 8 Controller 12, 13 Spray nozzle 21-23 Anode unit 30 Anode plate

Claims (8)

An electro-osmotic dehydration method in which water to be treated is sandwiched between an anode and a cathode and dehydrated by energizing both electrodes while being compressed,
In the electroosmotic dehydration method in which a dehydration aid is added to the water to be treated,
An electroosmotic dehydration method characterized in that the amount of dehydration aid added is controlled according to the resistance value of the water to be treated.   2. The electroosmotic dehydration method according to claim 1, wherein the dehydration aid is added to the water to be treated during dehydration.   3. The electroosmotic dehydration method according to claim 1, wherein the resistance value is a value obtained by dividing an applied voltage between the anode and the cathode by a current value between both electrodes. Oppositely arranged electrodes;
Energizing means for energizing between the opposing electrodes;
A filter medium disposed between the opposing electrodes;
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 dehydrator having
An electroosmotic dehydration apparatus comprising a dehydrating auxiliary agent adding means for adding a dehydrating auxiliary agent to a water to be treated according to a resistance value of the water to be treated.   5. The electroosmotic dehydration apparatus according to claim 4, wherein the dehydrating auxiliary agent adding means adds the dehydrating auxiliary agent to the water to be treated during dehydration. 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 characterized by controlling a supply amount of a water to be treated according to a resistance value of the water to be treated.   7. The electroosmotic dehydration method according to claim 6, wherein the resistance value is a value obtained by dividing an applied voltage between the anode and the cathode by a current value between both electrodes. Oppositely arranged electrodes;
Energizing means for energizing between the opposing electrodes;
A filter medium disposed between the opposing electrodes;
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 dehydrator having
An electroosmotic dehydration apparatus comprising a treated water supply amount control means for controlling a supply amount of a treated water content according to a resistance value of the treated water content.

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