JPH0722660B2 - Electro-osmotic dehydrator - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electroosmotic dehydrator for dehydrating sludge for sludge generated in a treatment process at a sewage treatment plant or a night soil treatment plant.

[Conventional technology]

As an electroosmotic dehydrator for continuously dehydrating sludge by applying electroosmosis, the one having a structure shown in FIGS. 5 and 6 is known in JP-A-60-25597.

In the figure, 1 is a rotary drum equipped with an electrode 1a on the anode side, 2 is a press belt which also faces the rotary drum 1 and also serves as a cathode electrode, and 3 is on the peripheral surface of the press belt 2. A filter belt 4 such as a filter cloth laid on top of each other is a DC power source for applying a voltage between the electrode 1a on the anode side and the electrode 2 on the cathode side, and is composed of the rotary drum 1 and the press belt 2 described above. A sludge passage, which serves as a dehydration area, is formed in the facing surface area between them.

With such a configuration, when the press belt 2 is driven and the pre-dehydrated sludge 5 is supplied to the sludge passage in a state where a voltage is applied between the electrodes, the sludge 5 is rotated by the rotary drum 1 and the press belt 2.
It is sandwiched between and and conveyed by a belt, and in this process, in addition to mechanical squeezing force, it is subjected to electroosmotic action by the electric field between the counter electrodes. That is, the particles of the sludge 5 (negative in ζ-potential) are negative, the contained water is positively charged, the sludge water flows toward the press belt 2 on the cathode side, and is discharged to the electrode member there, and at the same time, the filter belt. It permeates through 3 and is separated and dehydrated from sludge 5. Further, the filtered water that has passed through the filter belt 3 is dropped below the drainage hole 2a (FIG. 6) formed in the press belt 2 and drained out of the system from here. On the other hand, the sludge 5 is dehydrated into a cake with a low water content, and the press belt 2
It is carried out along with and collected.

Since the ζ-potential of the particles of the sludge 5 is negative, the polarity of the electrode 1a (discharging water side) of the rotary drum 1 is positive and the polarity of the electrode of the press belt 2 (water collecting side) is negative. However, in particular, when the ζ-potential of the sludge particles is positive, on the contrary, the voltage is applied with the polarity of the rotating drum side electrode 1a being negative and the polarity of the press belt 2 side being positive.

[Problems to be Solved by the Invention]

By the way, general sludge generated in sewage treatment plants, human waste treatment plants, etc., contains a large amount of sulfate ions, chlorine ions, etc. in the contained water. For this reason, sludge-containing water is electrolyzed in the electroosmosis process, oxygen gas and chlorine gas on the anode side,
Further, hydrogen gas is generated on the cathode side. In this case, the gas generated on the surface of the cathode side electrode (press belt 2) passes through the filter belt together with the filtered water separated from the sludge and is removed from the system. On the other hand, the gas generated on the surface of the anode side electrode (rotary drum 1) has no escape, so that the gas G stays between the surface of the anode side electrode 1a and the sludge 5 as shown in FIG. Become. Moreover, since the generated gas is non-conductive, as a result, the electric resistance of the contact surface between the electrode 1a and the sludge 5 is increased.

On the other hand, the amount of water transferred by electroosmosis, that is, the dehydration capacity, is proportional to the magnitude of the electric current flowing through the sludge, so that the gas is trapped between the electrode and sludge as described above. In that case, the conductivity is obstructed, and it becomes difficult for an electric current to flow in the sludge, and if it is left as it is, the dehydration ability of the electroosmosis decreases. Therefore, in order to maintain a predetermined dehydration treatment capacity in the electroosmotic dehydrator, it is necessary to increase the voltage applied between the electrodes so as to compensate for the increase in electric resistance caused by the residual gas. Therefore, when the applied voltage is increased, the power consumption increases, resulting in an increase in the running cost of the electroosmotic dehydrator, and the dewatering efficiency represented by the ratio of the power consumption to the sludge dewatering amount decreases.

The present invention has been conceived in view of the above points, in which gas generated between the non-collecting side electrode not equipped with a filter member (filter belt) and the sludge by electrolysis in the electroosmosis process is considered. By eliminating it outside the system by simple means, avoiding an increase in contact electrical resistance due to gas retention,
It is an object of the present invention to provide an electroosmotic dehydrator capable of efficiently performing electroosmotic dehydration with a small amount of power consumption.

[Means for Solving the Problems]

In order to solve the above problems, according to the present invention, firstly,
As a means for solving the problem, for the electrode on the non-water collecting side, a gas vent passage is formed between the surface of the electrode and the sludge, and a string, a part of which contacts the surface of the electrode, is placed inside and outside the sludge passage. A plurality of them are laid down and dispersed, and the gas generated between the non-water collecting side electrode and the sludge in the electroosmosis process is discharged to the outside of the system through the gas vent passage.

As a second solution, a string having gas permeability is laid across the opposite electrodes so as to traverse the sludge passage, and gas generated between the non-water collecting side electrode and the sludge in the electroosmosis process. Is guided to the filtering member provided on the water collecting side electrode through the internal pores of the string, and is excluded from the system out of the filtering member.

[Action]

First, in the first means, the string is, for example, a synthetic rubber belt body having a convex cross-section, the narrow end surface of which is brought into contact with the electrode surface of the non-water collecting side electrode, and the inside and outside thereof are parallel to the sludge passage. Is laid. If the non-water collecting side electrode is a rotary drum type, the string is laid along the peripheral surface of the rotary drum. Here, when pre-dehydrated sludge (having lower fluidity than raw sludge) is supplied to the sludge passage between the opposing electrodes, the above-mentioned string bites into the sludge and forms a gas vent passage behind the wide end face of the string. Voids that communicate with the functioning atmosphere side are left to be molded. Therefore, the gas generated on the surface of the non-water collecting side electrode due to the electrolysis of the sludge water in the electroosmosis process is removed to the atmosphere side via the gas vent passage. As a result, the generated gas does not remain between the sludge and the electrode surface, and it is possible to prevent the contact electric resistance between the electrode and the sludge from increasing due to the residual gas.

On the other hand, in the second means, the string is a gas permeable belt body made of, for example, a sponge-like synthetic rubber having open-cell-shaped pores, and one end surface of the string contacts the electrode surface on the non-water collecting side. The other end surface is laid so as to come into contact with the filtering member laid on the counter electrode. Therefore, the gas generated on the surface of the non-collection side electrode due to the electrolysis of sludge water in the electroosmosis process diffuses through the internal pores of the gas-permeable string described above without staying in this portion, and Is removed to the atmosphere side through the filter member that is in contact with the other end face of the.

〔Example〕

Next, referring to FIGS. 1 and 2, and FIGS. 3 and 4, an embodiment of the first solving means and the second solving means will be described. In each drawing, the same members corresponding to those in FIGS. 5 and 6 are designated by the same reference numerals.

Embodiment 1 First, in FIGS. 1 and 2, 6 is a string which is an endless belt body, and a plurality of strings 6 are arranged along the width direction of the rotary drum 1 so as to surround the peripheral surface of the rotary drum 1. Distributed and laid at pitch intervals. Further, the string 6 has a convex cross-sectional shape, and as shown in FIG.
While being in contact with the surface of 1a, it is stretched over the rotating drum 1 and the pulley 7 as shown in FIG.

Here, when the sludge 5 pre-dehydrated in the previous stage is supplied to the sludge passage between the opposing electrodes, the string 6 comes into the sludge 5 as shown in FIG. In this case, since the sludge 5 has low fluidity due to pre-dehydration, the ratio of spreading in the lateral direction is small. Therefore, when the string 6 bites into the sludge 5 as described above, the maximum width range of the string 6 is reached. Thus, the sludge 5 is pushed away, and a void functioning as a gas vent passage surrounded by the surface of the electrode 1a and the sludge 5 is formed on the back side of the string 6 as indicated by reference numeral 6a. The gas vent passage 6a is formed along the string member 6 laid inside and outside the sludge passage, and is open to the atmosphere side at the entrance and exit points of the sludge passage.

Therefore, the gas generated on the surface of the electrode 1a due to the electrolysis of the sludge-containing water during the electroosmosis process of the sludge 5 moves to the degassing passage 6a which is open in the vicinity thereof, and is discharged to the atmosphere side through the passage. To be done. As a result, the rotating drum 1
The generated gas does not remain between the electrode surface and the sludge 5 and high conductivity is ensured by avoiding an increase in the contact electric resistance between the electrode 1a and the sludge 5 due to the residual gas. As a result, it is possible to maintain a high electro-osmotic dehydration capacity by continuously supplying a sufficient current to the sludge 5 without increasing the applied voltage more than necessary.

Next, the results of an actual machine test conducted to confirm the effect of the present invention will be described. In this test, raw sludge generated at a sewage treatment plant was pre-dewatered with a roll dehydrator to a water content of 81%, and the sample was treated at a treatment speed of 90 kg / m ² · hr (dewatering filtration area per 1 m ² The sludge sample was dehydrated by the electroosmosis dehydrator shown in Fig. 1 and Fig. 5 under the condition that it was dehydrated to a water content of 65% and converted into a cake, and the amount of electricity required for this dehydration treatment was compared. did.

According to this test result, the conventional electro-osmotic dehydrator (No. 5
In the figure), an applied voltage of 75 V was required to maintain stable electroosmotic dehydration, and the power consumption was 0.38 KWH / kg (dehydrated cake of sludge). On the other hand, in the electroosmotic dehydrator (Fig. 1) in which strings are installed at intervals of 70 mm around the rotating drum, stable electroosmotic dehydration can be maintained at an applied voltage of 60 V, and the power consumption is 0.3 KWH / It was kg (dehydrated cake of sludge).

In other words, it was confirmed that the applied voltage can be reduced by 15 V compared to the conventional one, and the power consumption required for the sludge dewatering treatment can be significantly reduced in accordance with the decrease in the applied voltage.
In addition, it was not observed by visual observation that the degassing passage of the string was blocked with sludge during the dehydration process.
Further, during the dehydration treatment, it was confirmed that the gas generated by the electrolysis together with the steam generated by the heat generation is blown out through the degassing passage of the string.

Second Embodiment: Next, a third embodiment of the second means of the present invention will be described.
It is shown in Fig. 4 and Fig. 4. In this embodiment, as the string 8, an endless belt body having a rectangular cross section made of an open-cell sponge made of synthetic rubber having a pore diameter of about 50 to 100 μm is adopted, and the space is arranged in the width direction of the rotary drum 1. A plurality of strings 8 arranged side by side include a rotary drum 1 and a pulley 7.
It is stretched over between and. In addition, the cross section of this string 8, especially the thickness dimension in the height direction, has a height of the sludge passage so that the outer end surface of the string 8 contacts the filter belt 3 superposed on the press belt 2 of the opposite electrode when loaded in the machine. It is set to be larger than h. The string 8 is attached at a pitch of about 70 mm.

Therefore, the gas generated on the surface of the electrode 1a due to the electrolysis of the sludge-containing water during the electroosmosis process of the sludge 5 moves to the porous string 8 arranged in the vicinity thereof and diffuses through the internal pores of the string 8. , Through the filter belt 3 from the end surface to the atmosphere side. As a result, the generated gas does not remain between the electrode surface of the rotating drum 1 and the sludge 5, and an increase in the contact electric resistance between the electrode 1a and the sludge 5 caused by the residual gas is avoided and high conductivity is achieved. You can secure the sex.

In addition, regarding this embodiment, the above-mentioned embodiment (Figs. 1 and 2
The result of the same test as the evaluation test described in
It has been confirmed that almost the same effects can be obtained in terms of applied voltage and power consumption.

〔The invention's effect〕

Since the electroosmotic dehydrator according to the present invention is configured as described above, it has the following effects.

That is, a string that provides a gas releasing function is laid in the sludge passage between the opposing electrodes, and the gas generated between the sludge and the non-water collecting side electrode is left in place by the electrolysis action in the electroosmotic dehydration process. It is possible to avoid the increase in the electrical resistance at the contact surface between the electrode and the sludge due to the residual gas, and to maintain a high electrical conductivity by eliminating it outside the system without any problem. Higher dewatering efficiency can be obtained by reducing the power consumption required for dewatering sludge.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 3 are different overall configuration diagrams of an embodiment of the present invention, and FIGS. 2 and 4 are enlarged sectional views of the sludge passage portion in FIG. 1 and FIG. 3, respectively. FIG. 5 is an overall configuration diagram of a conventional electroosmotic dehydrator, and FIG. 6 is an enlarged cross-sectional view of the sludge passage portion in FIG. In the figure, 1: rotating drum, 1a: electrode (non-water collecting side electrode), 2: press belt (water collecting side electrode), 3: filter belt (filtering member),
4: Power supply, 5: Sludge, 6: String, 6a: Gas vent passage, 8:
Gas permeable string.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshitaka Arai 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 within Fuji Electric Co., Ltd. (56) References Japanese Patent Publication Sho 63-45605 (JP, B2)

Claims (2)

[Claims] 1. A voltage is applied between the electrodes on the anode and cathode sides facing each other across the sludge passage, and the water contained in the sludge supplied to the sludge passage is collected on one electrode side by electroosmosis and then filtered. In an electroosmotic dehydrator designed to drain filtered water out of the system through a member, a gas vent passage is formed between the surface of the electrode and the sludge with respect to the electrode on the non-water collecting side A plurality of strings that are in contact with the surface of the electrode are distributed and laid inside and outside the sludge passage, and the gas generated between the non-water collecting side electrode and the sludge during the electroosmosis process is removed to the outside of the system through the gas vent passage. An electro-osmotic dehydrator characterized in that 2. A voltage is applied between the electrodes on the anode and cathode sides facing each other across the sludge passage, and the water contained in the sludge supplied to the sludge passage is collected on one electrode side by electroosmosis, and then the electrode is formed. In an electroosmotic dehydrator configured to drain filtered water out of the system through a filtering member provided on the surface, a string having gas permeability is laid across the opposite electrodes across the sludge passage, The gas generated between the non-collecting side electrode and the sludge in the permeation process is guided to the filtering member provided on the collecting side electrode through the internal pores of the Stirling, and is removed from the system out of this. An electro-osmotic dehydrator.