JPH0685845B2 - Electro-osmotic dehydrator - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electroosmotic dehydrator for dehydrating surplus sludge and the like generated in large amounts in a treatment process such as a sewage treatment plant and a night soil treatment plant.

[Conventional technology]

Excess sludge generated in large amounts at the various treatment plants mentioned above is usually burned or composted after the dehydration process and disposed of, so that it is compared with conventional mechanical press dehydrators as dehydrators. An electroosmotic dehydrator that can obtain a high dehydration rate has been widely used.

Here, taking the belt press type electroosmotic dehydrator as an example, the configuration of a conventional electroosmotic dehydrator for dehydrating the excess sludge will be described with reference to FIG. In the figure, 1 is a sludge supply hopper, 2 is a filter belt which also serves as a cathode side electrode stretched between a pair of rollers 4 along a lower side of a sludge passage 3 leading to the hopper 1, and 5 is a filter belt 2. A drive motor, 6 is a press belt stretched between rollers 7 so as to face the filter belt 2 across the sludge passage 3, and a press belt 8 also serves as the above-mentioned anode and cathode side electrodes. , 2
A DC power source for applying a voltage to the filter belt 9 is a filtrate receiving tray arranged below the filter belt 2. Each of the above belts 2,6
For this purpose, a caterpillar belt having drainage and degassing grooves made of a metal having a high corrosion resistance or a conductive material such as carbon, or a net belt made of a mesh of conductive wires is used.

The dehydrating action of such an electroosmotic dehydrator is well known, and a voltage is applied between the belts 2 and 6 from a DC power source 8 and the filter belt 2 is driven by the drive motor 5 to drive the filter passage 2 from the hopper 1 to the sludge passage 3 By supplying the sludge 10 such as sludge, which is a substance to be dehydrated, to the filter belt 2 while the sludge 10 is conveyed along the passage 3 from the inlet side to the outlet side.
It is sandwiched between the press belt 6 and the press belt 6 to receive a squeezing force, and an electroosmotic action based on an electric field formed between the counter electrodes is applied. As a result, the water contained in the sludge 10 (the ζ potential (extra-kinetic potential) of the excess sludge) is positively charged and flows toward the cathode side, permeates the filter belt 2 and drops on the drainage pan 9 It is later discharged to the outside of the system. On the other hand, the dehydrated sludge 10 is conveyed by a belt as it is, and is recovered as an dehydrated cake 11 from the exit of the passage 3 and then incinerated or composted for disposal.

[Problems to be Solved by the Invention]

By the way, with the above-mentioned conventional electroosmotic dehydrator,
In addition to the large power consumption required for electroosmotic dehydration, when the sludge containing suspended particles of various components such as surplus sludge generated at the sewage treatment plant is dehydrated, the pH of the dehydrated cake is Compared with raw sludge, it changes significantly and causes problems in the subsequent disposal of dehydrated cake.

This point will be described next with reference to FIG. 4 by taking an example of surplus sludge generated in a sewage treatment plant. FIG. 4 shows a cross section in the middle of the sludge passage in FIG. 3. Sludge 10 as excess sludge is sandwiched between the anode side press belt 6 and the cathode side filter belt 2, and the belt is conveyed in this state. While being subjected to electroosmotic dehydration. Here, the normal excess sludge ζ potential generated in a sewage treatment plant or the like is negative, and the water contained in the sludge flows toward the filter belt 2 on the cathode side, passes through the filter belt 2 and is discharged to the outside of the system. . Since the water contained in the excess sludge flows unilaterally toward the filter belt 2 as described above, as the electroosmotic dehydration progresses, the water content of the sludge portion showing 10a particularly on the side in contact with the press belt 6 on the anode side. Is greatly reduced and becomes dry. By the way, the reason why the sludge 10 has conductivity is that the ions dissolved in the water contained in the sludge move by the action of the electric field. Therefore, as described above, the sludge 10a on the side in contact with the press belt 6 becomes dry. Then, the resistance of the slurry increases and the conductivity decreases, and it becomes difficult for the current to flow in the slurry sandwiched between the electrodes. For this reason, passing a current necessary for electroosmotic dehydration requires increasing the applied voltage between the electrodes toward the outlet side of the slurry passage, resulting in an increase in power consumption.

The surplus sludge contains ions such as Na ⁺ , Ca ²⁺ , K ⁺ , SO ₄ ²⁻ , Cl ⁻ , NO ₃ ⁻ . These ions flow according to the direction of the electric field, and cations such as Na ⁺ , Ca ²⁺ , and K ⁺ move toward the filter belt 2 on the cathode side together with the contained water and are discharged out of the system. , SO ₄ ²⁻ , Cl ⁻ , NO ₃ ^{− and the} like move toward the press belt 6 on the anode side. However, since all the water contained in the sludge moves to the cathode side, most of the anions are not discharged and remain in the sludge. As a result, the filtrate discharged to the outside of the system through the filter belt 2 contains a large amount of the above-mentioned cations and the pH is biased toward alkaline, whereas the dehydrated cake of dehydration treatment contains a large amount of the above-mentioned anions and is acidic. Will be biased toward.

On the other hand, when dewatering cake of surplus sludge is incinerated in an incinerator or is disposed of after composting, it is preferable that the pH of the dehydrated cake is as close to neutral as possible, and if the pH of the dehydrated cake is acidic, it is incinerated. In order to shorten the life of the furnace and to compost it, another neutralization treatment is required for the dehydrated cake in order to suppress the bias toward acidity in consideration of the influence on soil.

This invention has been conceived in view of the above points, and its purpose is to reduce the power consumption required for electroosmotic dehydration of surplus sludge and the pH of the dehydrated cake after dehydration treatment An object of the present invention is to provide an electro-osmotic dehydrator capable of suppressing a large change as compared with.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, according to the present invention, a pair of electrodes are arranged so as to face each other with a sludge passage interposed therebetween, and electricity is applied for electroosmotic dehydration of the sludge supplied to the passage with a voltage applied between the electrodes. In the osmosis commodity dehydrator, when the ζ potential of the suspended particles is negative from the electrode side of the polarity opposite to the ζ potential polarity of the suspended particles contained in the sludge toward the sludge part in contact with the electrode, an alkaline liquid is used. , Ζ potential is positive, a liquid supply means for externally supplying an acidic liquid is provided.

[Action]

In the above, the liquid supply means is a separately prepared acidic or alkaline liquid corresponding to the polarity of the ζ potential of the suspended particles of the sludge to be dehydrated from the electrode side opposite to the polarity of the ζ potential. Removed from the shower nozzle toward the sludge part that is in contact with, or the filtrate discharged through the electrode side having the same polarity as the ζ potential polarity of the suspended particles, and the opposite polarity facing the electrode through the liquid feed line and shower nozzle. It is designed to be removed from the electrode side toward the slurry.

As a result, when the polarity of the ζ potential of the suspended particles of the slurry is negative, the alkaline liquid, and when the ζ potential is positive, the acidic liquid from the electrode side of the opposite polarity facing the electrode on the filtrate discharge side It is supplied toward the slurry that contacts the electrode.
Therefore, it is possible to prevent the sludge from drying as the electroosmotic dehydration progresses and maintain the conductivity necessary for electroosmotic dehydration throughout the sludge passage, and at the same time, to remove the ionicity of the sludge that is discharged together with the filtered water by the dehydration process. By adding the ingredients to the slurry, the pH of the dehydrated cake can be prevented from being extremely acidic or alkaline.

〔Example〕

FIG. 1 and FIG. 2 show different embodiments of the present invention in which an electro-osmotic dehydration treatment is carried out using surplus sludge (negative ζ potential) generated from a sewage treatment plant as a substance to be dehydrated. Corresponding identical members are designated by the same reference numerals.

First, in the embodiment shown in FIG. 1, the basic structure of electroosmotic dehydration is the same as that shown in FIG. 3, but in particular, according to the present invention, the alkaline liquid is directed from the press belt 6 side also serving as the anode electrode toward the slurry 10 in contact with the press belt. A liquid supply means for removing and supplying is newly provided. This liquid supply means includes a tank 13 storing an alkaline supply liquid 12 and a pump 14 from the tank 13.
And a shower nozzle 16 connected to the liquid feed line 15 and arranged in parallel from the press belt 6 side toward the sludge passage 3.

With such a configuration, in the process of performing electroosmotic dehydration treatment of excess sludge having a negative ζ potential supplied from the hopper 1 to the sludge passage 3, the alkaline liquid 12 passes through the liquid feed line 15 and the shower nozzle 16 from the anode press belt 6 side. Remove it toward slurry 10. As a result, especially on the side in contact with the press belt 6,
The supply liquid 12 is impregnated in 10 and the wet state is maintained.
Therefore, it is possible to prevent the slurry from being dried, maintain the conductivity required for electroosmosis, and prevent an increase in power consumption. At the same time, the alkaline solution is replenished so as to compensate for the cationic component discharged through the filter belt 2 on the cathode side together with the filtered water, so that the pH of the sludge is neutralized and becomes extremely acidic. The pH of the dehydrated cake after dehydration can be returned to about the same level as the original sludge.

Next, the results of experiments conducted using the apparatus according to the embodiment shown in FIG. 1 will be described. As the experimental conditions, excess sludge from the sewage treatment plant (negative ζ potential) was pre-dewatered with a normal belt press to a water content of 88%.
Using an aqueous solution of OH (0.5% by weight), the test sample has a water content of 70%
Was subjected to electroosmotic dehydration treatment. According to the results of this experiment, the power consumption required for dehydration treatment per ton of dehydrated cake is
The pH of the dehydrated cake was 250 KWH and 6.2. In contrast,
According to the experimental results of dehydrating the same sample to a water content of 70% by the conventional method without supplying alkaline liquid, the power consumption per ton of dehydrated cake is 80 KWH and the pH of the dehydrated cake is
It was 3.1, and it was confirmed that the method of the present invention can significantly reduce the power consumption and, at the same time, prevent the pH of the dehydrated cake from being biased to be acidic.

Next, another embodiment of the present invention is shown in FIG. In this embodiment, the filtrate discharged through the filter belt 2 is utilized as the supply liquid supplied from the press belt 6 side toward the sludge 10, and the liquid supply means of the liquid is the filter belt 2.
A liquid delivery line 15 is installed between a tank 12 that stores the filtrate that has passed through and is discharged, and a shower nozzle 16 that is drawn out from the tank 12 and arranged in parallel on the press belt 6 side.

With such a structure, voltage is applied with the press belt 6 as an anode and the filter belt 2 as a cathode to apply excess sludge (negative ζ potential).
In the case of electroosmotic dehydration, the filtrate discharged through the filter belt 2 becomes an alkaline liquid containing a large amount of cation components in addition to the water contained in the sludge. Therefore, by removing the filtrate collected in the tank 12 from the press belt 6 side of the anode toward the slurry 10 through the liquid sending line 15 and the shower nozzle 16, the same effect as described in the embodiment of FIG. 1 can be obtained. You can

When the ζ potential of the sludge 10 is negative like surplus sludge in a sewage treatment plant, the press belt 6 is used as an anode and the filter belt 2 is used as a cathode to apply a voltage to perform electroosmotic dehydration as described above to obtain filtrate. Is discharged through the lower filter belt 2, and when the sludge 10 has a positive ζ potential like aluminum hydroxide sludge, conversely to the above, the filter belt 2 is used as the anode and the press belt 6 is By applying a voltage as the cathode, the filtrate also passes through the lower filter belt 2 and is discharged. Therefore, by using the liquid supply means shown in the embodiment of FIG.
This is convenient because it can cope with both sludges having positive and negative ζ potentials simply by switching the electrode polarities of the filter belt 2 and the press belt 6.

Next, the experimental results of electroosmotic dehydration using the apparatus according to the embodiment of FIG. 2 and using aluminum hydroxide sludge as a sample to be dehydrated will be described. Since the aluminum hydroxide sludge has a positive ζ potential, a voltage was applied using the filter belt 2 as an anode and the press belt 6 as a cathode as described above. Here, when aluminum hydroxide sludge with a water content of 85% was dehydrated to a water content of 70%, the pH of the filtrate discharged from the filter belt 2 side was 2.5, the power consumption cost per ton of dehydrated cake was 450 KWH, The pH was 8.0. On the other hand, in the conventional method in which the filtrate is not returned to the sludge, the power consumption is 640 KWH per ton of dehydrated cake, and the pH of the dehydrated cake is 10.5. It was confirmed that extreme bias in pH of the dehydrated cake could be prevented along with the conversion.

〔The invention's effect〕

As described above, according to the present invention, an electroosmotic commodity dehydrator in which a pair of electrodes are arranged to face each other across a sludge passage and the sludge supplied to the passage is electroosmotically dehydrated while a voltage is applied between the electrodes. Of suspended particles contained in sludge at
An alkaline liquid is supplied from the electrode side having a polarity opposite to the potential polarity toward the sludge portion in contact with the electrode when the ζ potential of the suspended particles is negative, and an acidic liquid is supplied from the outside when the ζ potential is positive. Is provided with a liquid supply means for supplying the liquid satisfying the above conditions toward the slurry from the electrode side having the opposite polarity to the filtrate discharge side electrode during the electroosmotic dehydration. It prevents the drying of the sludge and keeps the conductivity of the sludge to reduce the power consumption, and at the same time compensates for the ionic components discharged from the sludge with the filtrate, resulting in an extremely acidic pH of the dehydrated cake. It is possible to obtain effects such as preventing the alkaline bias and solving the problem of incinerating and composting the dehydrated cake for disposal.

[Brief description of drawings]

1 and 2 are configuration diagrams of different embodiments of the present invention, and FIG. 3 is a configuration diagram of a conventional electroosmotic dehydrator,
FIG. 4 is a sectional view of the sludge passage of FIG. In each figure, 2: filter belt that also serves as electrode, 3: sludge passage, 6: press belt that also serves as electrode, 8: DC power supply, 9: filtrate tray, 10:
Sludge, 11: dehydrated cake, 12: supply liquid, 13: tank, 15: liquid transfer line, 16: shower nozzle.

Claims (2)

[Claims] 1. An electro-osmotic dehydrator in which a pair of electrodes are disposed opposite to each other with a sludge passage interposed therebetween and the sludge supplied to the passage is electro-osmotically dehydrated while a voltage is applied between the electrodes. When the ζ potential of the suspended particles is negative from the electrode side of the polarity opposite to the ζ potential of the suspended particles toward the sludge portion in contact with the electrode, the alkaline liquid is used, and when the ζ potential is positive, Is an electroosmotic dehydrator characterized by comprising a liquid supply means for supplying an acidic liquid from the outside. 2. The electroosmotic dehydrator according to claim 1, wherein the liquid supply means discharges the filtrate discharged through the electrode side having the same polarity as the ζ potential polarity of the suspended particles, in a liquid feed line,
An electro-osmotic dehydrator, characterized in that it is removed and supplied toward the sludge from the electrode side of the opposite polarity facing the electrode through a shower nozzle.