WO2014119599A1 - Electroosmotic dewatering method and electroosmotic dewatering apparatus - Google Patents

Abstract

[Problem] To provide an electroosmotic dewatering method and an electroosmotic dewatering apparatus, each of which enables the dewatering of a water-containing material of interest without generating a halogen gas. [Solution] A conveyer belt (1) made from 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). A reducing agent such as sodium hydrogen sulfite and/or sodium thiosulfate is added to a water-containing material of interest.

Description

Electroosmotic dehydration method and apparatus

The present invention relates to an electroosmotic dehydration method and apparatus for dewatering water-containing materials such as biologically treated sludge and sewage sludge from wastewater, and in particular, the generation of halogen gas at the anode (anode) is prevented. The present invention relates to an electroosmotic dehydration method and apparatus.

Electro-osmotic dehydration is well known as a method for dehydrating hydrated materials such as sludge generated during biological treatment of wastewater (Patent Documents 1 to 6, 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 dehydration apparatus 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, a halogen gas such as chlorine gas is generated on the surface of the anode (anode) by a reaction such as 2Cl ⁻ → Cl ₂ + 2e ⁻ . Salt may be added to the water to be treated as a dehydration accelerator. By adding this salt, the amount of chlorine gas generated at the anode increases.

Chlorine gas is highly corrosive and corrodes 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.

As a measure to prevent corrosion by generated chlorine gas as much as possible, it is conceivable to ventilate the vicinity of the electroosmosis dehydrator, but if the amount of generated chlorine gas is large, exhaust gas treatment (chlorine gas removal treatment) is required.

Patent Document 6 describes that a hole or groove is provided in the anode-side electrode member in order to exclude gas generated on the anode side, but does not describe prevention of gas generation.

JP-A-1-189311 JP-A-6-154797 WO2007 / 143840 JP 7-73646 Japanese Patent No. 3576269 Shoko 63-45605

An object of the present invention is to provide an electroosmotic dehydration method and apparatus capable of preventing (including suppressing) the generation of halogen gas at the anode.

The electroosmotic dehydration method of the present invention 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 pressing and adding a reducing agent to the water to be treated. It is characterized by this.

As the reducing agent, sodium bisulfite and / or sodium thiosulfate is preferable.

In one aspect of the electroosmotic dehydration method of the present invention, a reducing agent is added to and mixed with the water to be treated. In this case, the halide ion concentration and the reducing substance concentration in the water to be treated are measured, the required reducing agent equivalent is calculated from the difference between the two, and the reducing agent in an amount 1 to 1.5 times the required reducing agent equivalent is added. It is preferable to add.

In another aspect of the electroosmotic dehydration method of the present invention, a reducing agent is sprayed on the surface of the hydrated material to be treated that is in contact with the anode. In this case, measure the halide ion concentration and the reducing substance concentration in the treated water-containing material, calculate the required reducing agent equivalent from the difference between the two, and spray the reducing agent in an amount 0.5 to 1 times the required reducing agent equivalent. It is preferable to do.

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 a treated water-containing material between electrodes, comprising a reducing agent adding means for adding a reducing agent to the treated water-containing material. is there.

In the present invention, the generation of halogen gas at the anode is prevented by adding a reducing agent to the water to be treated. When the reducing agent is sodium bisulfite, near the anode interface, NaHSO ₃ + Cl ₂ + H ₂ O → H ₂ SO ₄ + NaCl + HCl
Reaction proceeds, and generation of halogen gas such as chlorine gas is prevented. When the reducing agent is sodium thiosulfate,
Na ₂ S ₂ O ₃ + 4Cl ₂ + 5H ₂ O → 2NaCl + 2H ₂ SO ₄ + 6HCl
Reaction proceeds, and generation of halogen gas such as chlorine gas is prevented.

The reducing agent may be added to and mixed with the water to be treated, or may be dispersed on the surface of the water to be treated that contacts the anode. Thus, when the reducing agent is sprayed on the surface of the hydrated material to be treated that comes into contact with the anode, the amount of the reducing agent can be reduced even if the amount of the reducing agent is smaller than when the reducing agent is added to the hydrated material to be treated and mixed. Generation of gas can be prevented.

FIG. 1a is a schematic longitudinal sectional view at the time of press dehydration of the electroosmotic dehydrator according to the embodiment, and FIG. 1b is a sectional view taken along line Ib-Ib of FIG. 1a. 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. It is a longitudinal cross-sectional view of the experimental apparatus used in the Example. It is a graph which shows an experimental result.

Hereinafter, the first embodiment will be described with reference to FIGS. 1a and 1b and FIG. FIG. 2 shows the belt feeding process of the electroosmotic dehydrator of FIGS. 1a and 1b.

The 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 the transport side of the water to be treated, and the lower surface side is the 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 of the conveyor belt 1 in the transport direction.

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 conveyor unit of the conveyor belt 1 so that sludge on the conveyor belt 1 does not protrude sideways. The anode units 21 to 25 are disposed between the side wall plates 20 and 20.

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

Each anode unit 21 to 25 has an anode plate 30 on the lower surface. 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.

Between the anode plate 30 and the cathode 4 of each anode unit 21 to 25, a DC voltage is applied from a DC power supply device (not shown), and a DC current is applied.

As a mechanism for adding the reducing agent to the sludge, there are provided a reducing agent feeder 10 including a storage tank of a reducing agent aqueous solution and a chemical injection pump, and spray nozzles 11 and 12. 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. The hopper 5 may be provided with a stirrer to promote mixing. 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 from the hopper 5 onto the conveyor 1. A plurality of spray nozzles 12 may be arranged in the width direction of the conveyor 1, and one spray nozzle extending in the width direction of the conveyor 1 may be provided.

In this embodiment, both the spray nozzles 11 and 12 are provided, but only one of them may be provided. When both the spray nozzles 11 and 12 are installed, a switching valve may be provided so as to selectively supply the reducing agent to the spray nozzles 11 and 12.

Although not shown, a reducing agent spraying spray nozzle may be provided between the anode units in the middle of the conveying direction of the conveyor 1, for example, between the anode units 23 and 24.

As the reducing agent, sodium bisulfite and / or sodium thiosulfate is preferable, but the reducing agent is not limited to this, and ferrous chloride, hydrazine and the like can also be used. The reducing agent is preferably used as an aqueous solution, and the concentration 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 reducing agent is small, and the dehydration efficiency is improved. However, the reducing agent may be added as a powder.

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 the anode units 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 plates 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.

Although it is preferable to apply the same voltage to each of the anode units 21 to 25 from the viewpoint of facilitating operation management of the apparatus, the voltage is increased or decreased on the downstream side in the transport direction. May be. You may control electricity supply so that the electric current value of each anode unit may become the same.

The air having the same pressure may be supplied to the air cylinders of the anode units 21 to 25, or 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. The dehydrated filtrate passes through the conveyor belt 1, passes through the holes of the cathode plate 4, falls on the tray 6, and flows out to the drain line 7.

As shown in FIGS. 1a and 1b, each of the anode units 21 to 25 is energized, and when the sludge is pressed by the anode units 21 to 25, the conveyor belt 1 is stopped. After pressing and energizing the anode units 21 to 25 for a predetermined time, air is discharged from the air cylinder, and the anode units 21 to 25 are raised as shown in FIG. The conveyor belt 1 is moved by one pitch of the arrangement pitch of the anode units 21 to 25. As a result, 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. Undehydrated sludge is introduced from the hopper 5 to the lower side of the anode unit 21.

When spraying the reducing agent on the upper surface of the sludge S, the anode units 21 to 25 are lifted in this way, and while the conveyor belt 1 is fed and moved by one pitch, the spray nozzle 12 moves onto the conveyor belt 1. It is preferable to spread on the upper surface of the sludge S.

After the conveyor belt 1 is 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 prevented, and corrosion of equipment is prevented.

The amount of reducing agent added is preferably determined according to the halide ion (especially chloride ion) concentration and reducing substance concentration in the sludge. When adding a reducing agent to the hopper 5, it is preferable to determine a required addition amount as follows based on the chloride ion concentration and reducing substance concentration which are contained in sludge.

That is, first, the amount of chlorine gas generated is determined by the following equation (1).
Equivalent amount of chlorine gas generated = Equivalent amount of chloride ion in sludge-Equivalent amount of reducing substance in sludge (1)
What is necessary is just to add the reducing agent more than the equivalent which can reduce | restore the generation amount chlorine gas estimated by this (1) Formula.

The concentration of reducing substances in sludge can be confirmed by iodine consumption. Chloride ion concentration can be measured directly.

When sodium bisulfite is used as the reducing agent, an example of calculating the amount added is shown below.
Chloride ion concentration in sludge: 1000 mg-Cl / kg-sludge Reducing substance concentration in sludge: Iodine consumption as 1000 mg-I / kg Chlorine atomic weight is 35.5 and iodine atomic weight is 127 ,
Chlorine gas generation from 1 kg of sludge (mol / kg) = 1000 / 35.5-1000 / 127 = 20.3 mol / kg-sludge The reaction formula of sodium hydrogen sulfite and chlorine gas is NaHSO ₃ + Cl ₂ + H ₂ O → H ₂ SO ₄ + NaCl + HCl,
Since the molecular weight of sodium bisulfite is 104,
Necessary addition amount of sodium bisulfite (mg / kg) = {chloride ion concentration / chlorine atom amount−iodine consumption / iodine atom amount} × sodium hydrogen sulfite atomic weight = {1000 / 35.5-1000 / 127} × 104 = 2110 mg-NaHSO ₃ / kg-sludge Therefore, it is preferable to add 2110 mg / kg-sludge or more of sodium hydrogen sulfite.

Usually, it is preferable to add 1 to 1.5 times, particularly 1 to 1.2 times the reducing agent equivalent (2110 mg / kg-sludge in this case).

When the reducing agent is sprayed from the spray nozzle 12 onto the upper surface of the sludge S, most of the sprayed reducing agent stays in the vicinity of the upper surface of the sludge S on the conveyor 1. Is preferably about 0.5 to 1 times, particularly 0.5 to 0.6 times the reducing agent equivalent.

In 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 dehydrator. 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. 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), 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, experimental examples will be described.

[Experimental Example 1]
The chloride ion concentration is 500 mg / kg (14.1 mol / kg), and the iodine consumption is 1000, 1200, 1500, 2100 or 3000 mg / kg (7.9, 9.4, 11.8) as shown in Table 1. , 16.5 or 23.6 mol / kg), sodium bisulfite at 0, 200, 500, 800 or 1000 mg / kg (0, 1.9, 4.8, 7.7 or 9). .6 mol / kg) (no addition in the case of 0 mg / kg) and mixed, filled in the test apparatus 70 shown in FIG. It was measured. Sodium bisulfite was added as a 10 wt% aqueous solution. The same applies to Experimental Example 2 described later.

This test apparatus 70 includes a cylinder 71 having an inner diameter of 100 mm with the cylinder axis direction being the vertical direction, a bottom end 72 attached to the bottom of the cylinder 71, and a space between the bottom surface of the cylinder 71 and the top surface of the bottom end 72. A cathode 73 made of mesh sandwiched between the cylinders 71 and stretched along the bottom surface of the cylinder 71, a piston 74 in the cylinder 71, an anode 75 made of mesh attached to the lower surface of the piston 74, and an upper surface of the cylinder 71 And a top seal 76 provided on the surface. The sludge S is pressurized in a state where current is applied between the cathode 73 and the anode 75, and the chlorine gas concentration in the atmosphere in the space below the top seal 76 is detected by the Cl ₂ detector 77.

Table 1 shows the changes over time in the chlorine gas concentration when the sludge filling amount is 170 g, the applied voltage is 60 V, the maximum current value is 5.1 A, and the piston pressure is P = 0.2 kg / cm ² .

No. in Table 1. As shown in 1, 6 to 9, in the case of sludge A in which the chloride ion concentration (mol) in the sludge is higher than the iodine consumption (mol), the addition of sodium bisulfite reduces the chlorine gas generation amount. When the total amount of sodium bisulfite added (mol) and iodine consumption (mol) in the sludge exceeds the chloride ion concentration (mol) in the sludge, chlorine gas is not generated.

No. No sodium bisulfite added Even in the case of 1 to 5, as the difference between the chloride ion concentration (mol) and the iodine consumption concentration (mol) in the sludge becomes smaller, the chlorine gas generation amount decreases (No. 2, 3), When the iodine consumption concentration (mol) is higher than the chloride ion concentration (mol), chlorine gas is not generated (No. 4, 5).

From Experimental Example 1, it was confirmed that the addition of the reducing agent was effective in preventing the generation of chlorine gas at the anode.

[Experiment 2]
As shown in Table 2, sodium bisulfite is not added to sludge F with a chloride ion concentration of 1400 mg / kg (39.4 mol / kg) and iodine consumption of 200 mg / kg (1.6 mol / kg). Alternatively, 1500, 2000, or 3000 mg / kg (14.4, 19.2, or 28.8 mol / kg) was added and mixed, filled in the test apparatus of FIG. 4, and the amount of chlorine gas generated was measured in the same manner ( No. 10, 13-15).

Separately, this sludge F is filled in the apparatus shown in FIG. 4, and sodium bisulfite is sprayed on the upper surface thereof at a rate of 500 or 1500 mg / kg (4.8 or 14.4 mol / kg). Then, the amount of chlorine gas generated was measured (No. 11, 12). The results are shown in Table 3 and FIG. In addition, FIG. 5 shows No. 10 of no addition of sodium hydrogen sulfite, No. 12 of 1500 mg / kg application | coating, and No. 12 of 1500 mg / kg mixing among the data of Table 3. Only 13 is shown.

As shown in Table 3 and FIG. 5, the amount of chlorine gas generated decreases as the amount of sodium bisulfite added increases. Even in the case of the same addition amount, the amount of chlorine generated is smaller when sprayed than when sodium bisulfite is mixed, and the amount of chlorine gas generated when 3000 mg / kg sodium bisulfite is mixed and 1500 mg / kg is sprayed. Were found to be approximately equivalent.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2013-014522 filed on January 29, 2013, which is incorporated by reference in its entirety.

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 70 Test apparatus 71 Cylinder 73 Cathode 74 Piston 75 Anode

Claims (12)

1. In the electroosmotic dehydration method of sandwiching the water to be treated between the anode and the cathode and dehydrating by energizing both electrodes while pressing,
   An electroosmotic dehydration method comprising adding a reducing agent to a treated water-containing material.
2. 2. The electroosmotic dehydration method according to claim 1, wherein the reducing agent is sodium bisulfite and / or sodium thiosulfate.
3. 3. The electroosmotic dehydration method according to claim 1 or 2, wherein a reducing agent is added to the water to be treated and mixed.
4. 4. The halide ion concentration and the reducing substance concentration in the water to be treated are measured in claim 3, the required reducing agent equivalent is calculated from the difference between the two, and the amount of reduction is 1 to 1.5 times the required reducing agent equivalent. An electroosmotic dehydration method comprising adding an agent.
5. 3. The electroosmotic dehydration method according to claim 1 or 2, wherein the reducing agent is sprayed on the surface of the water to be treated which is in contact with the anode.
6. 6. In claim 5, the halide ion concentration and the reducing substance concentration in the water to be treated are measured, the required reducing agent equivalent is calculated from the difference therebetween, and the amount of reduction is 0.5 to 1 times the required reducing agent equivalent. An electroosmotic dehydration method characterized by spraying an agent.
7. 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 reducing agent adding means for adding a reducing agent to a water to be treated.
8. The electroosmotic dehydration apparatus according to claim 7, wherein the reducing agent is sodium bisulfite and / or sodium thiosulfate.
9. 9. The electroosmotic dehydration apparatus according to claim 7 or 8, wherein the reducing agent adding means adds and mixes the reducing agent to the water to be treated.
10. 10. The reducing agent addition means according to claim 9, wherein the reducing agent addition means measures a halide ion concentration and a reducing substance concentration in the water to be treated, calculates a necessary reducing agent equivalent from the difference between the two, and 1 to 1 of the necessary reducing agent equivalent. An electroosmotic dehydrator characterized by adding a reducing agent in an amount five times as large.
11. 9. The electroosmotic dehydration apparatus according to claim 7 or 8, wherein the reducing agent adding means sprays the reducing agent on a surface of the treated water-containing material that contacts the anode.
12. In Claim 11, the said reducing agent addition means measures the halide ion density | concentration in a to-be-processed hydrate, and a reducing substance density | concentration, calculates a required reducing agent equivalent from the difference of both, 0.5 of required reducing agent equivalent An electroosmotic dehydrator characterized by spraying a reducing agent in an amount of 1 times.

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