JPH0773646B2 - Batch electroosmosis dehydration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention uses an electrode made of a carbon material containing carbon fibers to squeeze a substance to be dehydrated such as sewage sludge while performing direct current energization for dehydration. A batch electroosmosis dehydration method.

(Prior Art) FIGS. 4 (a), (b) and (c) show an outline of a basic configuration and an operating process of a filter press type electroosmotic dehydrator. In FIG. 4 (a), the filter cloth (b) (b) and the compressed film (c) are sandwiched between a pair of filter plates (a) (a) of the filter press and tightened.
Sludge is press-fitted between the filter cloths from the stock solution inlet (d) by a stock solution pump, and the dehydrated liquid that has permeated the filter cloth is discharged from the filtrate outlet (e) to the outside of the machine. In FIG. 4 (b), the squeeze film is squeezed out by introducing squeeze pressure behind the squeeze film to expand and further solidify it. In the latter stage of squeeze dehydration, the electrode (f)
A direct current is applied during (f) to further promote dehydration by the electroosmotic effect. In Fig. 4 (c), the filter plate is opened, the filter cloth is pulled down, and the dehydrated cake (g) is taken out of the machine.

When a direct current is passed through the sludge during the process of compressing and dehydrating sludge containing a large amount of hardly dehydratable organic matter such as sewage sludge, the water in the sludge that cannot be dehydrated simply by pressing is also attracted to the cathode side by the electroosmotic action. It moves to the outside and dehydration is promoted,
The water content of the dehydrated cake can be remarkably reduced as compared with dehydration by only pressing pressure. For example, if sewage sludge pre-concentrated by flocculation and draining is supplied to a filter press and subjected to a dehydration treatment for about 20 minutes at a pressing pressure of 3 kg / cm ² ,
The water content of the dehydrated cake is 80-85%, and pressure above this
Even if it takes a long time, there is not much effect in reducing the water content of the dehydrated cake. On the other hand, if a DC voltage of about 40 V is applied during energization for about 15 minutes, the water content of the dehydrated cake will decrease to about 50% and the volume of the dehydrated cake will decrease to less than 1/2. To do.

As an electrode for electroosmotic dehydration, a metal plate, a carbon sintered plate, etc. have been conventionally used, but mechanical strength, conductivity,
It has advantages and disadvantages with respect to requirements such as life and price.

For example, a metal plate electrode made of stainless steel, nickel steel, or the like has strength, but is ionized by direct current application and is eluted and consumed to have a short life. Especially, dissolution of chromium causes a secondary pollution problem.
A metal electrode in which a titanium alloy is coated with platinum has a small amount of current consumption and good current-carrying performance, but is very expensive and cannot be used because platinum is peeled due to the opposite polarity.

Although the electrode of the carbon sintered plate is less corroded, the pendant coke part is selectively corroded by the oxygen consumption at the nascent stage, and the carbonaceous matter is often physically removed. It has low mechanical strength and is easily damaged by squeezing pressure. JP-A-60-147208 is a mixture of conductive fibers and a synthetic resin which is pressure-molded to improve the strength. In order to flow, the applied voltage must be increased, the utility cost is high, and using a high voltage in an environment handling water is at risk of electric shock.

(Problems to be Solved by the Invention) An electrode made of a carbonaceous material in which carbon fibers are bound to each other by carbon, which was developed as an electrode for electroosmotic dehydration, is a sufficient machine capable of withstanding the squeezing pressure of electroosmotic dehydration. Since the electroosmotic dehydration method has high mechanical strength and excellent electrical conductivity, the voltage drop inside the electrode during direct current application is small, and thus an economically viable electroosmotic dehydration method can be provided.

However, when an electroosmotic dehydration test was carried out using this electrode, a peculiar forbidden phenomenon that did not occur in the carbon sintered plate electrode containing no carbon fiber of the prior art appeared. That is, when a conventional carbon sintered plate was used for both negative and positive electrodes and a direct current was applied, this electrode plate was simply consumed, but an electrode plate made of the carbon material containing the above carbon fiber was used for a long time. When energized, a phenomenon occurs in which it becomes difficult for current to flow rapidly at some point.

The present invention aims to provide a solution to this problem.

(Means for Solving the Problem) This state was clarified in order to elucidate the phenomenon in which direct current conduction is almost impossible as described above by using an electrode made of a carbon material containing a carbon fiber for electroosmotic dehydration. The surface of the electrode at this time was measured by the ESCA method (Electron Spectroscopy for Chemical Ana
Surface analysis by lysis (X-ray photoelectron spectroscopy) revealed that a large amount of oxygen atoms were bonded to the carbonaceous surface of the electrode used as the anode. From this, it is presumed that the oxide insulating layer is formed on the carbonaceous surface.

As a result of earnestly studying a method and means for solving this problem and enabling effective application of an electrode made of a carbon material containing the above-mentioned carbon fiber having excellent other various properties to the electroosmotic dehydration, The batch electroosmotic dehydration method of the present invention has been reached.

That is, the batch-type electroosmotic dehydration method of the present invention uses an electrode and a cathode made of a carbon material containing a carbon fiber as an anode and a cathode, sandwiching a material to be dehydrated between both electrodes, and applying direct current between both electrodes while squeezing. In the batch-type electroosmotic dehydration method of electroosmotic dehydration, keep the continuous energization amount to 700 coulomb / cm ^{2 or} less until both electrodes have opposite polarities, and make the opposite polarities every 1 to 5 times to continuously apply direct current. It is characterized by energizing.

In the electroosmotic dehydration, the current direction may be temporarily reversed at the final stage of dehydration for the purpose of improving the dehydration property or preventing contamination of the electrode surface, but the present invention is different from this in that the two electrodes are opposite. With the polarity maintained, DC current is continuously applied until the next polarity change.

In this respect, in the method of the present invention, the continuous energization amount until the two electrodes have opposite polarities is 700 coulomb / cm ² per unit area of electrode.
It is preferably within the above range, and the lower limit is not particularly strict, but it is preferable in practice to set the energization amount close to the energization amount. More preferably, the polarity is opposite to that of less than 500 coulomb / cm ² and the amount of electric current is not far from the coulomb.

When performing batchwise electroosmotic dehydration by the method of the present invention, it is preferable that the polarities are reversed every 1 to 20 operations, although it depends on the amount of current applied for each operation. More preferably 1
The polarity is changed every 5 to 5 times. The current density per unit area of the electrode for effectively causing electroosmotic dehydration is preferably maintained at about 0.01 to 0.1 A / cm ² .

Further, in order to improve the conductivity of the material to be dehydrated, salt, sodium sulfate, calcium sulfate, and
An electrolyte substance such as sodium carbonate or calcium carbonate may be added.

In the method of the present invention, an electrode made of a carbon material containing carbon fibers used as an anode and a cathode is a carbonaceous material.
Carbon that is 10 to 50% by weight or has a fiber length of 2 to 20 mm, and is substantially two-dimensionally dispersed in a random direction and laminated, and the carbon fibers are bound to each other by carbon. Quality electrodes are preferred.

Such an electrode uses, for example, a carbon short fiber of a polyacrylonitrile-based single yarn diameter of 4 to 15 μm and a fiber length of 2 to 20 mm,
A paper-making binder such as polyvinyl alcohol is mixed with a paper-making medium diluted with water and stirred to form a sheet or a sheet,
It is dried to remove the solvent and used as an intermediate base material, which is impregnated with a solution of a carbonizable resin such as phenol resin, which is then hot-press molded to cure the resin and then 1000 to 3000 ° C in an inert gas atmosphere. It is obtained by carbonizing the impregnated resin by heating to.

(Operation) According to the method of the present invention, an electrode made of a carbon material containing a carbon fiber is used as an anode and a cathode for electroosmotic dehydration, and the electrode has excellent mechanical strength, conductivity, and wear resistance. In addition, the electroosmotic dehydration action can be continuously exerted without causing the phenomenon of obstructing the DC energization due to the continuation of DC energization of the same polarity.

(Example) A polyacrylonitrile-based carbon fiber, Torayca T-3000, manufactured by Toray Industries, Inc. was cut to a length of 12 mm and dispersed in an aqueous solution of polyvinyl alcohol to make a paper. Next, the papermaking paper was impregnated with a phenol resin and dried, and then the resin was cured by hot pressing. Then, the phenol resin was carbonized by heating and baking at 1600 ° C. in a nitrogen atmosphere to obtain an electrode having a thickness of about 1 mm, an apparent density of 1.05 g / cm ² , and a porosity of about 40%.

The compressive fracture strength of the obtained electrode is 100 kg / cm ² or more, and the electric resistance value in the thickness direction is 0.015 Ωcm.

This electrode was used as an anode (1) and cathode (2) As shown in FIG. 1, the Na ₂ SO ₄ 1.5 g / aqueous solution (3) DC in power supply (4)
When energized at a current density of 0.02 A / cm ² , the voltage is about 11 hours after energization as shown in the chart in which the horizontal axis of Fig. 2 shows the time and the vertical axis shows the voltage (V) of the voltmeter (5). It suddenly rose and was cut off. The accumulated amount of electricity is 0.02 × 11 × 3600 = 792 coulomb / c
It became less than m ² . In the present invention, when the polarity was switched to the opposite polarity at 700 coulomb / cm ² or less in the previous stage, it was possible to continue energizing, avoiding a non-conducting state, and enabling continuous execution of electroosmotic dehydration.

Similarly, when a current density of 0.04 A / cm ^{2 was} passed in an aqueous solution of NaCl 1.4 g /, the horizontal axis of FIG. 3 represents time, and the vertical axis represents voltage (V). The electricity has passed. On the contrary, a voltage drop was observed in the first period of energization, but the voltage surged in about 7 hours after energization. The energizing amount until then is 0.
It was 04 x 7 x 3600 = 1008 coulombs / cm ² . In the present invention, if the opposite polarity is switched at a previous stage, for example, 700 coulomb / cm ² or less, energization can be continued and a non-conducting state can be avoided.
It became possible to continue the electroosmotic dehydration.

Similarly, when a current density of 0.04 A / cm ² was applied with an aqueous solution of Na ₂ SO ₄ 2 g /, after about 6 hours of energization, a non-conducting state as shown at time point (E) in Fig. 3 was reached. The quantity is 0.04 × 6 × 3600 = 864 coulomb / cm ² . In the present invention, before that, for example, at 700 coulombs / cm ² or less, the polarity can be switched to the opposite polarity to continue energization, a non-conducting state can be avoided, and electroosmotic dehydration can be continuously performed.

(Effects of the Invention) As described above, according to the batchwise electroosmotic dehydration method of the present invention, an electrode made of a carbon material in which carbon fibers are bound to each other by carbon provides excellent properties in strength and conductivity. This electrode can be used to advantage, and the amount of electricity required to make both electrodes opposite polarity using both electrodes is 700 coulomb / cm ² and both electrodes are opposite polarity every 1 to 5 times. By continuously energizing with direct current, a disconnected state can be avoided, and electroosmotic dehydration can be continuously performed.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an apparatus used for an energization test according to the present invention, and FIG. 2 is an example of the energization test according to the present invention, in which the abscissa represents time of energization until a non-conducting state is shown, and the ordinate represents the time. FIG. 3 is a diagram showing a voltage, FIG. 3 is a diagram similar to FIG. 2 of another example of the current-carrying test according to the present invention, and FIG. 4 (a) is a basic of the filter press type electroosmotic dehydrator used in the present invention. FIG. 4 (b) is a vertical cross-sectional view showing the configuration, FIG. 4 (b) is a vertical cross-sectional side view when squeezing and direct current application, and FIG. 4 (c) is a vertical cross-sectional side view when the dehydrated cake is taken out. (1) …… Anode, (2) …… Cathode, (3) …… Aqueous solution, (4) …… DC power supply, (5) …… Voltmeter, (E) …… Time point, (a) …… Filtration Plate, (b) ... filter cloth, (c) ... pressed membrane, (d) ... stock solution inlet,
(e) …… filtrate outlet, (f) …… electrode, (g) …… dehydrated cake.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Teruyuki Miwa Inventor 1-11-1 Sonoyama, Otsu City, Shiga Prefecture Toray Co., Ltd. Shiga Plant (72) Inventor Tamotsu Takizawa 1-1-1, Sonoyama, Shiga Prefecture No. Toray Co., Ltd. Shiga Business Office (56) References JP-A-52-7876 (JP, A)

Claims (1)

[Claims] 1. An electrode made of a carbon material containing carbon fibers is used as an anode and a cathode, and an article to be dehydrated is sandwiched between both electrodes,
In the batch-type electroosmotic dehydration method in which direct current is applied between both electrodes while squeezing, the continuous energization amount until both electrodes have opposite polarities is set to 700 coulomb / cm ² and every 1 to 5 times. A batch-type electroosmotic dehydration method characterized in that both electrodes have opposite polarities and a direct current is continuously applied.