JP2012179572A - Electro-osmotic dewatering method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electro-osmotic dewatering method and an apparatus, in which the electroconductivity of sludge is raised by adding electrolyte to water-containing substance to be treated and the water content of dewatered substance is lowered, the water-containing substance to be treated can be dewatered at low cost without generating corrodible gas.SOLUTION: A conveyer belt 1 comprising a filtering cloth is endlessly stretched between rollers 2, 3 and can endlessly rotate. Anode units 21 to 23 are arranged in the conveying direction of the conveyer belt 1. Sodium hydrogen carbonate is added to the water-containing substance to be treated as dewatering auxiliary agent.

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, Patent Document 4 describes that an electrolyte such as sodium chloride, sodium sulfate, or sodium carbonate is added to sludge in order to increase the dehydration efficiency.

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

  Since salt as a dehydrating aid contains chlorine, corrosive chlorine gas may be generated by electroosmotic dehydration. Sodium sulfate may also generate corrosive sulfurous acid gas. Sodium carbonate has a high cost and the dehydration cost of the water to be treated is high.

  The present invention relates to an electroosmotic dehydration method and apparatus in which an electrolyte is added to a water to be treated 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 dehydrating a water to be treated at a cost.

  The electroosmotic dehydration method of the present invention is an electroosmotic dehydration method in which a water to be treated 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 sodium hydrogen carbonate, sodium bicarbonate is added as a dehydration aid.

  The electroosmotic dehydration apparatus of the present invention 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 mediums or one of the filter medium and the filter medium. An electroosmotic dehydration apparatus having a clamping means for clamping the water to be treated between the electrodes, and a dehydrating auxiliary agent adding means for adding sodium bicarbonate to the water to be treated as a dehydrating aid. It is characterized by this.

  In the present invention, sodium hydrogen carbonate is added as a dehydration aid to the water to be treated. Unlike sodium chloride and sodium sulfate, sodium hydrogen carbonate does not generate corrosive gases such as chlorine gas and sulfurous acid gas in the electroosmotic dehydration process. Also, sodium bicarbonate is less expensive than sodium carbonate. Since sodium hydrogen carbonate is alkaline, it also has an action of removing scales attached to the anode of the electroosmotic dehydrator. Since sodium bicarbonate has a small solubility change in the normal temperature range, even if it is used as a saturated solution, fluctuations in the amount added due to temperature change are prevented.

  In addition, as can be seen from the examples described later, it is recognized that when sodium hydrogen carbonate is used, the power consumption is lower than when sodium sulfate is used.

(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.

  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.

  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.

  As the dehydrating aid, sodium hydrogen carbonate is used, and particularly an aqueous solution of sodium hydrogen carbonate is used. The concentration of the sodium hydrogen carbonate aqueous solution is preferably a saturated concentration or a concentration close thereto (for example, 90% or more of the saturation solubility). When a high-concentration aqueous solution is used in this way, the amount of water added to the water to be treated with the addition of the dehydration aid is small, and the dehydration efficiency is improved.

  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. If necessary, a dehydrating aid is added from the nozzle 11 into the hopper 5.

  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.

  When adding the dewatering aid to the sludge in the middle of dewatering, the anode units 21 to 23 are lifted in this way, and the dewatering aid is supplied from the spray nozzle 12 while the conveyor belt 1 is fed and moved by one pitch. Spray and add to the sludge S on the conveyor 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.

  It is preferable to experimentally determine the addition amount of the dewatering aid according to the properties of the sludge, the moisture content of the dewatered sludge, and the like. In the case of normal biological treatment sludge, it is preferable to add sodium hydrogen carbonate as a solid content of sodium hydrogen carbonate to the raw sludge in an amount of 0.1 to 1 wt%.

  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 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 electroosmotic dewatering apparatus shown in FIG. 1, sewage sludge with a water content of 84.5% was electroosmotic dehydrated. In the examples, a dehydrating aid was added to the hopper 5. The operating conditions are as follows.

Number of anode units in the conveyor belt conveyance direction: 3 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 water content of the dewatered sludge was 81.4%, and the power consumption (the power consumption required to obtain 1 ton of desorption liquid) was 435 kwh / ton-desorption liquid.

<Example 1>
In the comparative example 1, a sodium bicarbonate aqueous solution having a concentration of 9.3 wt% was added to the hopper 5. The addition amount was 3 wt% as a sodium hydrogen carbonate aqueous solution with respect to the raw sludge. The results are shown in Table 1.

<Comparative example 2>
Sodium sulfate decahydrate was used as a dehydration aid in the form of a 10 wt% aqueous solution. The amount added was 6 wt% as the aqueous solution with respect to the raw sludge (the amount of sodium was the same as in Example 1). The results are shown in Table 1.

  As is apparent from Table 1, Example 1 and Comparative Example 2 to which a dehydration aid was added both had lower water content and power consumption of dehydrated sludge than Comparative Example 1 to which no dehydration aid was added, In Example 1, the moisture content and power consumption are further lower than in Comparative Example 2.

DESCRIPTION OF SYMBOLS 1 Conveyor belt 2, 3 Roller 4 Cathode 5 Hopper 12, 13 Spray nozzle 21-23 Anode unit 30 Anode plate

Claims (2)

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 comprising adding sodium hydrogen carbonate as the dehydration aid. 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 dehydration aid addition means for adding sodium hydrogen carbonate as a dehydration aid to a water to be treated.

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