JP2002248477A - Electrochemical water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical water treatment method cable of sterilizing with high efficiency microorganisms existing in every kind of water such as drinking water, industrial water or the like by performing the treatment stably over a long period. SOLUTION: In the water treatment method for supplying a current to an electrolytic cell wherein a porous carbon electrode is mounted between power supply terminal electrodes to polarize the porous carbon electrode and supplying water to be treated containing microorganisms to the electrolytic cell to sterilize microorganisms electrochemically, the porous carbon electrode is periodically taken out of the electrolytic cell to be subjected to heat treatment and subsequently washed with water to remove the residue bonded to the porous carbon electrode. The heat treatment is preferably performed in air for one hr or more at 180-400 deg.C or performed in an inert atmosphere for one hr or more at 180-1,200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water for electrochemically sterilizing various kinds of treated water containing microorganisms such as drinking water, various treated water in the food field, bath water and the like, or industrial water. Regarding the processing method.

[0002]

2. Description of the Related Art Drinking water such as tap water and well water and domestic water,
Fungi, protozoa, algae,
There are microorganisms such as bacteria, and these microorganisms remarkably proliferate depending on environmental conditions such as temperature, so that water quality is impaired, and there is also a case where trouble occurs in equipment.
Therefore, various methods have been conventionally developed for sterilizing microorganisms in water, and methods of adding agents such as chlorine and hydrogen peroxide have been widely used. However, the sterilization treatment with chlorine causes a new problem due to residual chlorine, and the method of adding hydrogen peroxide or ozone, in which the residue does not cause a problem, is costly and thus is not preferable as a means for sterilizing a large amount of water. . In addition, there are sterilization methods such as irradiation with ultraviolet light and boiling by heating, but the cost is high due to poor efficiency, and it is not suitable as a means for efficiently sterilizing a large amount of water.

[0003] In recent years, a method for sterilizing microorganisms by electrochemical oxidation has been developed as a means for efficiently and efficiently sterilizing large amounts of water at low cost. In this method, a porous carbon electrode sandwiched between mesh metal electrodes via an insulating material is laminated in multiple stages, and a DC voltage or an AC voltage of 10 Hz or less is applied to the upper and lower mesh metal electrodes to form a porous carbon electrode. When the treated water containing the microorganisms is supplied, the treated water containing the microorganisms undergoes an electrochemical reaction at the polarized anode portion in the process of flowing through the fine pores of the porous carbon electrode, that is, the microorganisms and the anode portion. The transfer of electrons between them causes the microorganisms to die. Therefore, sterilization of microorganisms continues as long as electricity is supplied,
Furthermore, since only a very small current flows in the electrochemical reaction for killing the microorganism, the electrolysis reaction accompanied by gas generation does not substantially occur in the polarized anode and cathode parts, so that the operation is economically advantageous. Is also possible, and the oxidative wear of the carbon electrode is also suppressed.

However, when the sterilization treatment of microorganisms is interrupted for a relatively long time, the growth of microorganisms proceeds, and a part of the open pores of the porous carbon electrode, which is a flow hole of the water to be treated, is reduced. Becomes blocked by the propagated microorganisms. On the other hand, when the operation is continued for a long time and the water treatment is performed, dead microorganisms and various organic substances contained in the water to be treated accumulate and accumulate on the surface of the porous carbon electrode and the open pores. . As a result, it becomes difficult for the water to be treated to smoothly flow through the open pores of the porous carbon electrode, and there is a problem that the water treatment efficiency and the water treatment efficiency decrease.

[0005]

SUMMARY OF THE INVENTION In order to solve these problems, one of the applicants of the present invention has proposed a method of electrochemically sterilizing microorganisms in a water treatment method.
A water treatment method characterized by washing with a hydrogen peroxide solution having a concentration of 0% or less or an aqueous solution of sodium hypochlorite having a concentration of 12% or less as a cleaning solution has been developed and proposed (JP-A-9-2254).
No. 67). According to this method, microorganisms and organic substances are chemically oxidized and decomposed, so that the microorganisms and organic substances that accumulate on the open pores of the porous carbon electrode and block are effectively sterilized,
Decomposes and can always maintain sterilization performance.

Further, the present inventors have conducted research from a different point of view in order to solve the above-mentioned problems, and as a result, the open pores of the porous carbon electrode have been subjected to a heat treatment which is a simpler method than the chemical oxidative decomposition treatment. It was confirmed that microorganisms, dead bodies, various organic substances, and the like that accumulate on the portions and block the pores can be decomposed and removed. In other words, the present invention has been developed based on this finding, and its purpose is to accumulate in the open pores of the porous carbon electrode serving as the flow path of the water to be treated, and to remove microorganisms and the like that block the flow path. It is an object of the present invention to provide an electrochemical water treatment method capable of removing the dead body, various organic substances, and the like and efficiently sterilizing microorganisms present in the water to be treated.

[0007]

According to the present invention, there is provided an electrochemical water treatment method comprising the steps of: supplying electricity to an electrolytic cell provided with a porous carbon electrode between power supply terminal electrodes; In a water treatment method in which the carbon electrode is polarized and the microorganisms are killed electrochemically by supplying treated water containing microorganisms to the electrolytic cell, the porous carbon electrode is periodically taken out of the electrolytic cell and heat-treated, Then, the structure is characterized by removing the residue attached to the porous carbon electrode by washing with water.

[0008] The heat treatment is specifically performed in air at 180 ° C.
At a temperature of ~ 400 ° C or in an inert atmosphere 180-1
The heat treatment is preferably performed at a temperature of 200 ° C. for one hour or more.

[0009]

FIG. 1 is a schematic vertical sectional view illustrating a water treatment apparatus (electrolysis tank) 9 for sterilizing microorganisms electrochemically. In FIG. 1, a cylindrical electrolytic cell case 1 is made of an electrically insulating material such as a synthetic resin, and upper and lower ends inside the electrolytic cell case 1 have an upper electrode 2 (anode) serving as a power supply terminal electrode and a lower electrode. An electrode 3 (cathode) is provided. A ring-shaped spacer 5 is provided between the upper electrode 2 and the lower electrode 3 so that the porous carbon electrode 4 maintains electrical insulation.
(Five in the illustrated example) are laminated through the electrode, and a titanium mesh electrode 6 coated with platinum or the like having a lower oxygen overvoltage than the carbon electrode is formed on the upper and lower surfaces of the porous carbon electrode 4.
Is attached.

When a DC voltage is applied to the upper and lower electrodes for power supply and energized, the lower surface of the porous carbon electrode 4 is polarized positively and the upper surface is polarized negatively. When water to be treated containing microorganisms is supplied from the lower inlet 7 of the water to be treated to the electrolytic cell in this state, the water to be treated flows through many fine open pores of the porous carbon electrode 4 and flows out of the upper outlet 8. Is done. Then, in the water to be treated, electrons are transferred between the microorganisms and the electrodes by an electrochemical reaction at the anode portion polarized in the process of flowing through the fine open pores, and the microorganisms are killed by the oxidation-reduction reaction. In this manner, various kinds of water to be treated containing microorganisms can be electrochemically sterilized.

Regarding the porous carbon material used for the porous carbon electrode, if it has a porous structure having a small water flow resistance and a large contact area with the water to be treated, regardless of the production method, for example, coke of which particle size is adjusted, Particles are kneaded with a pitch binder, molded, and calcined and carbonized.A particle-bonded porous carbon material, and a sheet obtained by forming carbon fibers and organic fibers for carbon fiber production together with pulp into an organic material such as a thermosetting resin. For example, a porous carbon material obtained by integrating with a polymer carbide can be used.

In the porous carbon material, the water to be treated flows smoothly,
In addition, it is necessary that an electrochemical reaction occurs efficiently when flowing through the pores to kill microorganisms, and the pores preferably have an average pore diameter of 25 to 500 µm. If the average pore diameter is larger than 500 μm, the microorganisms in the water to be treated will pass through without contacting the electrode part sufficiently, resulting in reduced sterilization efficiency. If it is smaller than 25 μm, water flow resistance will increase and clogging will occur. This is because easy and smooth driving is hindered. The porosity is 2
It is 0 to 80%, more preferably 30 to 60%.

When electricity is supplied to the electrolytic cell to polarize the porous carbon electrode and pass through the water to be treated to electrochemically kill microorganisms in the water to be treated, the dead bodies of the microorganisms are electrolyzed together with the flow of the water to be treated. Although the water is discharged from the tank, if the water treatment is continued for a long period of time, a part of the dead body of the microorganisms is deposited on the open pores of the porous carbon electrode and gradually closes the open pores. Further, various organic substances contained in the water to be treated also accumulate. On the other hand, when the operation of the water treatment apparatus is interrupted for a long period of time, rapid growth of microorganisms occurs due to the temperature environment and the like, and the microorganisms accumulate in the open pores of the porous carbon electrode and close the open pores.

In this way, when a part of the open pores of the porous carbon electrode, which is the flow passage of the water to be treated, is blocked, the smooth flow of the water to be treated is hindered, and the sterilization efficiency is remarkable. This will lead to a decrease. Therefore, in order to stably perform water treatment with high sterilization efficiency, it is important to remove microorganisms, their dead bodies, various organic substances, and the like before large amounts are accumulated in the open pores.

Therefore, in the present invention, the porous carbon electrode is periodically taken out of the electrolytic cell and subjected to heat treatment to decompose and remove microorganisms and their dead bodies, various organic substances, etc., deposited on the open pores. . As the heat treatment conditions, it is preferable to perform the treatment at a temperature of 180 to 400 ° C. in air or at a temperature of 180 to 1200 ° C. in an inert atmosphere for an appropriate time, for example, 1 hour or more.

If the heat treatment temperature in the air is lower than 180 ° C., combustion and decomposition and removal do not proceed sufficiently. If the temperature exceeds 400 ° C., the surface of the porous carbon electrode is oxidized, and the sterilizing effect is reduced and the durability is reduced. Lower. If the heat treatment temperature in an inert atmosphere is lower than 180 ° C., the thermal decomposition removal of the deposit does not sufficiently proceed, but even if the heat treatment is performed at a temperature higher than 1200 ° C., the improvement of the decomposition removal effect is not so much recognized. .

By performing the heat treatment as described above, microorganisms, their dead bodies, organic substances, and the like deposited on the open pores of the porous carbon electrode are removed by oxidation, dehydration, volatilization, decomposition, and the like. Remains in the open pores. These residues can be removed by passing water through the porous carbon electrode and flowing water through the open pores.

The heat treatment of the porous carbon electrode is performed, for example, by periodically taking out the porous carbon electrode from the electrolytic cell when a predetermined water treatment time, water treatment amount, or the like is reached, and performing heat treatment. Changes in operating conditions during water treatment, for example, the degree of decrease in the flow rate of water to be supplied under a constant water pressure, the degree of increase in pressure loss for securing a predetermined flow rate, or the degree of decrease in sterilization efficiency It is desirable to set the point of time for performing the heat treatment periodically using the index as an index. In this way, the porous carbon electrode that has been periodically heat-treated can be mounted again in the electrolytic cell, and the water flow rate, the sterilization efficiency, etc. can be restored to the original state, and the water treatment efficiency and water treatment efficiency can be raised to a high level. The retained electrochemical water treatment becomes possible.

[0019]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

Examples 1 to 8 A carbon fiber impregnated with a thermosetting resin was laminated, fired and carbonized to form a disk-shaped porous carbon electrode having a diameter of 74.5 mm and a thickness of 9 mm (average open pore diameter of 50 μm, A porosity of 58%) was prepared, and a platinum-plated expanded titanium metal mesh having a diameter of 74.5 mm and a thickness of 1 mm was applied to the upper and lower surfaces thereof, and was transparent through a 1 mm-thick EPDM ring-shaped spacer. 75mm inside diameter, height 100 made of perfect rigid polyvinyl chloride
It was installed in a cylindrical electrolytic cell case of mm. The porous carbon electrodes were laminated in eight stages, and metal electrodes made of platinum-plated expanded titanium were arranged on both upper and lower ends as power supply terminal electrodes. Thus, the electrolytic cell as the electrochemical water treatment apparatus shown in FIG. 1 was assembled.

A constant voltage of 35 V is applied from a DC power source to the terminal electrode of this electrolytic cell to polarize the porous carbon electrode, and the test water to be treated containing about 10,000 cells / milliliter of general bacteria (COD 5 mg oxygen / l) 100 liters for 1.
3 kg / at a pressure of cm ² is supplied from the lower inlet of the electrolytic cell by flowing the open pores of the porous carbon electrode, the treatment water flowing out from the upper outlet was circulated by supplying the lower inlet again electrolyzer.
The flow rate was 3.0 liter / min, and the current was 50 mA.

The water flow rate and the 1-pass sterilization rate after continuous water treatment for 30 days by this circulation system and the 1-pass sterilization rate [{1- (number of viable bacteria on the exit side / number of viable bacteria on the entrance side)] × 100 (%)] It was measured. Next, the porous carbon electrode was removed from the electrolytic cell, the conditions were changed, and heat treatment and water washing were performed under different conditions. Then, the cell was mounted on the electrolytic cell again, and water treatment was restarted. .

The heat-treated porous carbon electrode was processed to a thickness of 9 mm, a width of 10 mm, and a length of 70 mm, and a 0.0012 mol / l aqueous solution of sodium sulfate (water temperature of 30).
℃), set the anode potential to 1.2 V / RHE and conduct a constant potential corrosion test, and the current value (corrosion current) after the corrosion test for 24 hours
Was measured.

Comparative Example 1 After water treatment for 30 days continuously by the same circulation method as in the example, the water flow rate and the 1-pass sterilization rate [｛1- (the number of viable bacteria on the exit side /
The number of viable bacteria on the inlet side)｝ × 100 (%)], and then
The porous carbon electrode was removed from the electrolytic cell, and only water washing was performed without performing heat treatment. The cell was again mounted in the electrolytic cell to restart water treatment, and the amount of water passed immediately after the restart and the 1-pass sterilization rate were measured. Further, the corrosion current was measured by the same method as in the example.

COMPARATIVE EXAMPLE 2 After water treatment for 30 days continuously by the same circulation method as in the example, the water flow rate and the 1-pass sterilization rate [# 1- (the number of viable bacteria on the exit side /
The number of viable bacteria on the inlet side)｝ × 100 (%)], and then
Remove the porous carbon electrode from the electrolytic cell, and the concentration is 10% by weight.
Was immersed in 5 liters of an aqueous solution of sodium hypochlorite (temperature: 20 ° C.) for 24 hours and then washed with water. The porous carbon electrode was mounted on the electrolytic cell again, and the water treatment was restarted. The water flow rate and the 1-pass sterilization rate immediately after the restart were measured, and the corrosion current was measured by the same method as in the example.

Table 1 shows the heat treatment conditions of the porous carbon electrode after continuous water treatment for a predetermined period of time, changes in the water flow rate and the 1-pass sterilization rate before and after the heat treatment, the corrosion current value, and the like. Indicated.

[0027]

[Table 1] (Note) * 1 Immersion treatment in sodium hypochlorite aqueous solution instead of heat treatment

From the results shown in Table 1, after the water treatment was continuously performed for 30 days, the porous carbon electrode was taken out of the electrolytic cell, heat-treated, and washed with water to remove the residue attached to the porous carbon electrode. In the embodiment in which the water treatment was resumed by re-attaching to the electrolytic cell, the water flow rate and the sterilization rate both increased, and the water treatment performance was recovered to be equal to or more than that of Comparative Example 2 immersed in the sodium hypochlorite aqueous solution. You can see that
In particular, when the heat treatment is performed in air at a temperature of 180 to 400 ° C. or in an inert atmosphere at a temperature of 180 to 1200 ° C. for 1 hour or more, it is recognized that the water treatment performance is remarkably recovered. In addition, even when these heat treatments are performed, the corrosion current is low, and no decrease in the durability of the porous carbon electrode due to the heat treatment is observed. On the other hand, in Comparative Example 1 in which the heat treatment was not performed, the water flow rate and the sterilization rate were hardly changed, and it was found that the water treatment performance was not recovered or improved.

[0029]

As described above, according to the electrochemical water treatment method of the present invention, during the water treatment, the porous carbon electrode is periodically taken out of the electrolytic cell and subjected to heat treatment and water washing. Thereby, microorganisms and their dead bodies, various organic substances, and the like deposited on the open pores of the porous carbon electrode, which is the flow path of the water to be treated, can be effectively decomposed and removed. Therefore, it is possible to prevent a decrease in water treatment performance such as a flow rate and a sterilization efficiency, and to stably electrochemically sterilize water to be treated containing microorganisms with high efficiency and efficiency for a long period of time. It is extremely useful as a water treatment method for electrochemically sterilizing microorganisms present in water, such as various treated waters in the field of water and food, and industrial water.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view illustrating a water treatment apparatus (electrolysis tank) for electrochemically sterilizing microorganisms.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyzer case 2 Upper electrode 3 Lower electrode 4 Porous carbon electrode 5 Ring-shaped spacer 6 Mesh electrode 7 Lower inlet of treated water 8 Upper outlet of treated water 9 Electrolyzer

Claims (2)

[Claims] An electrolytic cell having a porous carbon electrode mounted between terminal terminals for power supply is polarized to polarize the porous carbon electrode, and water to be treated containing microorganisms is supplied to the electrolytic cell to perform electrochemical treatment. In a water treatment method that kills microorganisms,
An electrochemical water treatment method comprising periodically removing a porous carbon electrode from an electrolytic cell and heat-treating the same, and then removing the residue attached to the porous carbon electrode by washing with water. 2. The heat treatment is carried out at a temperature of 180 to 400 ° C. in air or at a temperature of 180 to 1200 ° C. in an inert atmosphere.
The electrochemical water treatment method according to claim 1, wherein the treatment is carried out for at least one hour.