JPH03224684A - Electrochemical treatment of liquid to be treated - Google Patents

Abstract

PURPOSE:To efficiently make treatment, such as sterilization, of potable water, etc., at a low cost by supplying water to be treated to a three-dimensional electrode type electrolytic cell and bringing the water into contact with three dimensional electrodes consisting of a carbon material, thereby making the electrochemical treatment of the water CONSTITUTION:A meshed anode 3 for power supply consisting of the carbon material and a cathode 4 for power supply consisting of a metallic material are disposed near the top and bottom ends in the electrolytic cell body 2. The rear surfaces of respective fixed beds 5 are polarized positive and te front surfaces negative and a potential is generated in and between the fixed beds 5 when the electrodes are energized while the liquid to be treated, such as potable water, is supplied from below like arrows. The liquid to be treated passing the inside of the electrolytic 2 is polarized by this potential and comes into contact with the fixed beds 5, by which the reforming treatments, such as sterilizing of the fungi and bacteria in the liquid to be treated and deposition and removal of the calcium and magnesium, are executed. The water is taken out of the upper part of the electrolytic cell body 2 and is supplied to a water cleaning plant.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an electrochemical treatment method for sterilizing and improving the performance of liquids to be treated, particularly drinking water ingested into the body, and more particularly, This method uses a three-dimensional electrode electrolytic cell to electrochemically treat drinking water supplied for home and commercial use, thereby sterilizing and reforming the drinking water to improve its performance. Regarding the method.

(Prior Art) Drinking water is water stored in a water source such as a reservoir, sterilized at a water purification plant, and then supplied to each home, restaurant, etc. through the water supply system. The above-mentioned sterilization of drinking water is generally carried out by treatment with chlorine gas, but although chlorine treatment sterilizes drinking water relatively well, foreign substances may be mixed into the treated drinking water due to the influence of residual chlorine. The disadvantage is that the mellowness of natural water is lost due to the unpleasant feeling that occurs in water.

Drinking water is directly related to human health, and it is essential to sterilize the bacteria contained in it and prevent the growth of mold, that is, kill and remove microorganisms. It's mainstream.

However, water sterilization in urban areas has the disadvantage of producing organic halides because the raw water, such as river water or lake water, is contaminated with various organic substances and more chlorine is added than is necessary to kill microorganisms. There is. In order to overcome the drawbacks of the chlorine method, sterilization methods other than chlorine have been proposed.

For example, methods have been proposed in which the drinking water is reformed by ozone addition treatment or activated carbon adsorption treatment, but when the drinking water to be treated is water from a water purification plant, for example, the amount of treatment is limited. Furthermore, even if water is treated at a water purification plant, there is a problem that microorganisms will reproduce again before reaching the faucet at the end of the water pipe, and there is currently no method superior to chlorine addition treatment.

However, as mentioned above, there is a need for a method for treating drinking water that is not harmful to the human body and can replace chlorine treatment, which tends to produce organic chlorine compounds that are harmful to the human body.

Furthermore, in addition to drinking water, there are various types of domestic water that are indirectly ingested into the body, such as treated water for food products, and methods other than chlorination are desired for these domestic waters as well.

(Problems to be Solved by the Invention) As described above, the conventional reforming treatment methods for drinking water, etc. are mainly based on the chlorine method and the electrolytic method. In addition, the latter method has the drawback that the processing cost is high and the modification effect is not as high as the cost increases.

(Objective of the Invention) An object of the present invention is to provide a method for effectively modifying drinking water, such as sterilization, at low cost, without making the taste of the drinking water bad.

(Means for Solving the Problems) The present invention supplies a liquid to be treated to a three-dimensional electrode type electrolytic cell having a three-dimensional electrode made of a carbon-based material, and brings the liquid to be treated into contact with the three-dimensional electrode. This is a method for electrochemically treating a liquid to be treated. In the present invention, since a substantial electrochemical reaction may not occur on the surface of the electrode etc., the tank used in the present invention should be called an electrochemical treatment tank, but will be called an electrolytic tank according to the general name.

The present invention will be explained in detail below.

The present invention involves supplying a liquid to be treated, such as drinking water, to a three-dimensional electrode type electrolytic cell having a three-dimensional electrode made of a carbon-based material, and applying a DC voltage or a low-frequency alternating current voltage to the electrolytic cell. This method is characterized in that the liquid to be treated is sterilized with or without gas generation. The liquid to be treated by the method of the present invention is mainly intended for drinking water ingested by the human body and food processing water, and drinking water is tap water that flows through the water supply and is poured out from taps in homes, restaurants, etc. In addition, it includes untreated water stored in water purification plants, and food-treated water includes washing water for fresh foods and water contained in water-containing foods such as tofu.

The reason why the liquid to be treated is sterilized or its performance is improved by the voltage application is not necessarily clear, but it can be inferred as follows.

BACKGROUND ART Drinking water and food-processed water, especially water stored in water treatment plants, have a moderate temperature and are in an environment where mold, bacteria, and the like can easily grow.

When a voltage is applied to the liquid to be treated according to the present invention, mold and bacteria in the liquid to be treated are moved by liquid flow to the anode of a three-dimensional electrode type electrolytic cell, or to a three-dimensional electrode such as a dielectric or particles as described below. It is thought that when it comes into contact with these substances, it undergoes a strong oxidation-reduction reaction on their surfaces, weakening its activity or killing itself. The sterilizing effect in this case depends only on the potential of the three-dimensional electrode and does not depend on the amount of current flowing. Therefore, even if water treatment is performed by applying a high potential that generates oxygen or hydrogen and passing an electric current as in the conventional method, a sterilizing effect proportional to the electric potential will only occur; No substantial increase in treatment effects can be expected. In the method of the present invention, the electrolytic treatment may be performed while substantially generating gas, and in this case, it can be confirmed by the gas generation that the electrolytic treatment is actually being performed. When processing is performed while applying a voltage that does not cause substantial gas generation, the amount of current flowing is almost zero, and the amount of electricity consumed is also zero, so conventional chlorine addition can be done while maintaining electricity costs almost zero. It is possible to reform the liquid to be treated, such as drinking water, with almost the same efficiency as the electrolysis method or electrolysis method, which requires high power consumption.

Tap water contains calcium ions and magnesium ions, and these ions contribute to the bad taste of drinking water, but when the drinking water is electrochemically treated, these ions can be removed using three-dimensional electrodes. Calcium hydroxide and magnesium hydroxide are deposited on the cathode of the electrolytic cell and removed from drinking water, improving the taste of the drinking water.

In addition, in drinking water and food processing water, trace amounts of ions and dissolved substances, including the above-mentioned calcium, exist as clusters with hydration water around them, but this hydration water causes the drinking water to lose its mellowness. This is a contributing factor. According to the present invention, when a voltage that does not cause a substantial electrolytic reaction is applied to the drinking water containing the hydration water, the ions in the drinking water migrate or move at high speed in the liquid according to the potential gradient. Clusters cannot move and large clusters are destroyed, or the aforementioned ions with residual hydration water are destroyed by a three-dimensional electrode, etc., and the number of hydration water is greatly reduced, resulting in a reforming effect on drinking water, etc. This is thought to occur.

The electrolytic cell used in the method of the present invention is preferably a three-dimensional electrode electrolytic cell, particularly a bipolar fixed bed three-dimensional electrode electrolytic cell. In the treatment of a liquid to be treated according to the present invention, the treatment efficiency increases as the number of opportunities for the liquid to be treated to come into contact with electrodes, dielectrics, particles, etc. to be described later increases. Therefore, when using a three-dimensional electrode electrolytic cell with a large surface area of electrodes, etc., and a bipolar fixed-bed three-dimensional electrode electrolytic cell with a particularly large surface area of electrodes among the three-dimensional electrode electrolytic cells, conventional electrolytic treatment of drinking water, etc. The treatment efficiency can be increased compared to other electrolyzers used in the industry, and the equipment size required to achieve the same treatment efficiency can be smaller than that of other electrolyzers. It's advantageous.

The three-dimensional electrode in the three-dimensional electrode electrolytic cell of the present invention is made of a porous material through which the liquid to be treated can pass, such as granular, spherical,
Carbon-based materials such as activated carbon, graphite, carbon fiber, etc. in the shape of felt, woven fabric, porous block, solid body with many through holes, etc., or carbon-based materials such as copper, nickel, iron, and precious metals therein. The three-dimensional electrode is placed in a direct current or low frequency alternating current electric field, and has a flat or expanded mesh or bar shape installed at both ends. A voltage is applied between an anode and a cathode for power supply made of a porous plate such as a Foratisod plate to polarize the dielectric, and positive and negative charges are formed at one end and the other end of the dielectric, respectively, and the dielectric is polarized. . In addition, separate from the power supply anode and cathode, three-dimensional materials that function as an anode or a cathode are installed alternately so as not to short-circuit and are electrically connected to a multi-electrode fixed bed electrolytic cell. It can be done. In addition, when the aforementioned solid body having a large number of through holes is used as a three-dimensional electrode, the aperture ratio should be set to 10% or more and 95% or less, preferably 20% so as not to obstruct the movement of the flowing liquid to be treated.
It is preferable that the through-holes have a diameter of 80% or less, and the diameter of the through-holes is so fine that the liquid to be treated can pass therethrough. The carbon-based material has no toxicity and does not form ions or their hydroxides, so it is preferable for treating liquids to be treated that are ingested into the body, such as drinking water. Furthermore, since the surface area is large, the opportunity for bacteria to come into contact with it is greatly increased, and the sterilization efficiency is greatly increased. Furthermore, carbon-based materials are inexpensive, and unlike other metal bridges, they do not corrode even when electrolysis is stopped, so they are advantageous both economically and in terms of operability.

When it is intended to lower the voltage by bringing the anode and cathode close to each other between the dielectric material or the power supply anode and cathode, use an electrically insulating spacer such as a mesh spacer made of an organic polymer material to prevent short circuits. Preferably, it is inserted.

If there is a relatively large gap in the electrolytic cell through which the liquid to be treated flows, through which the liquid to be treated can flow without coming into contact with the dielectric, the anode, or the cathode, the processing efficiency of the liquid to be treated will decrease. It is desirable that the dielectric material etc. be arranged so that the flow of the liquid to be treated in the electrolytic cell will not be short-circuited.

An electrolytic cell or a three-dimensional electrode electrolytic cell with such a configuration can be placed in the line of stored water at a water purification plant, close to the water faucet of a home or restaurant, or used for other liquids to be treated such as food-processed water. They are installed at appropriate locations, and all or a portion of these liquids to be treated are introduced into the electrolytic cell to perform treatments such as sterilization of the liquids in the electrolytic cell.

Note that if the liquid to be treated is supplied to the electrolytic cell in a laminar flow, it may pass through the electrolytic cell without making sufficient contact with the surface of the dielectric, etc., so the liquid to be processed passing through the electrolytic cell may be
It is preferable that the turbulent flow has a Reynolds number of 0 or more and is caused to pass through the electrolytic cell or the like while sufficiently moving in the lateral direction.

In addition, in the electrolytic cell of the present invention, a leakage current occurs in the electrolytic cell, and the leakage current flows from the electrolytic cell through the liquid to be treated into other metal members, such as water pipes, and causes electrochemical problems such as elution into the member. May cause corrosion. Therefore, a member with higher conductivity than the liquid to be treated is installed in the electrode part where the power feeding anode and cathode do not face each other in the electrolytic cell and/or in the inlet/outlet piping of the electrolytic cell so that one end thereof can be grounded. The leakage current can be cut off.

Next, a preferred example of an electrolytic cell that can be used in the present invention will be described based on the accompanying drawings, but the electrolytic cell that can be used in the method of the present invention is not limited to this electrolytic cell.

FIG. 1 is a schematic vertical sectional view showing an example of a bipolar fixed bed electrolytic cell that can be used as the electrolytic cell of the present invention, and FIG.
FIG. 3 is a schematic diagram showing the electrolytic cell shown in FIG. 1 installed in a water supply line of a water purification plant. FIG. 3 is a schematic diagram showing the electrolytic cell shown in FIG. 1 installed in a faucet of a domestic water pipe.

A mesoche-shaped power feeding anode 3 and a power feeding cathode 4 are provided near the upper and lower ends of a cylindrical electrolytic cell body 2 having flanges 1 on the upper and lower sides, respectively. Electrolytic cell body 2
is preferably made of an electrically insulating material that can withstand long-term use or repeated use, and is particularly made of synthetic resins such as polyepichlorohydrin, polyvinyl methacrylate, polyethylene, polypropylene, polyvinyl chloride, polyethylene chloride, and phenol. Formaldehyde resin and the like can be preferably used. The power feeding anode 3 that provides a positive DC voltage is made of, for example, a carbon material (such as activated carbon, charcoal, coke,
coal, etc.), graphite materials (e.g. carbon fiber, carbon cloth, graphite, etc.), carbon composite materials (e.g. carbon mixed with metal powder and sintered), activated carbon fiber nonwoven fabrics (e.g. KE-1000 felt, Toyobo Co., Ltd.), or materials that support platinum, platinum, palladium or nickel, as well as dimensionally stable electrical bridges (platinum group oxide coated titanium materials), platinum coated titanium materials, nickel materials, stainless steel materials, iron materials, etc. formed from. The power supply cathode 4 which faces the power supply anode 3 and applies a negative DC voltage is made of, for example, platinum, stainless steel, titanium, nickel, Hastelloy, graphite, carbon material, mild steel, or a metal material coated with a platinum group metal. ing.

A plurality of fixed beds 5, three in the illustrated example, are stacked between the two power supply electrodes 3.4, and between the fixed beds 5 and between the fixed bed 5 and the two power supply bridges 3.4. Four porous diaphragms or spacers 6 are sandwiched between them. Each fixed bed 5
is placed in close contact with the inner wall of the electrolytic cell main body 2 and does not pass through the inside of the fixed bed 5, so that the leakage flow of drinking water flowing between the fixed bed 5 and the side wall of the electrolytic cell main body 2 is minimized. .

When a diaphragm is used, a woven fabric, an unglazed plate, a particle sintered plastic, a perforated plate, an ion-exchange IPJ, etc. are used as the diaphragm, and a woven fabric, perforated plate, net, etc. made of an electrically insulating material are used as the spacer. A rod-shaped material is used. 7 and 8
are lids installed at the upper and lower openings of the electrolytic cell body 2, respectively, and in which a drinking water outlet 9 and a drinking water supply opening 10 are formed.

The drinking water supply port 10 of the lower lid body 9 is divided by a pair of flanges 11 provided in the middle, and both flanges 1
Between 1 and 1 is an earth terminal 1 whose outer circumference is approximately equal to that of the flange 11 and whose other end is grounded at the bottom.
A mesh body 13 made of a material having a higher conductivity than the drinking water to which 2 is connected, such as stainless steel, is sandwiched. The mesh body 13 may be coated with a catalyst such as platinum, so that the mesh body 13 contacts the drinking water flowing through the drinking water supply port 10 and exchanges leakage current and electrons through an electrochemical reaction. Leakage current flowing in drinking water is radiated from the mesh body 13 to the ground through the earth terminal 12. Since it is undesirable for the mesh body 13 to impede the flow of the drinking water and increase the pressure loss, it is formed into a porous plate shape, a net shape, a comb shape, or the like.

The electrolytic cell 2 having such a configuration is installed close to a water purification pond 21 of a water purification plant, as shown in FIG.
Drinking water stored in the electrolytic cell 1 is pumped up using a pump 22 and supplied to the electrolytic cell 2. As shown in FIG. 3, the electrolytic cell 2 is connected to the tip of a water pipe faucet 24 via a connecting pipe 25, and the tap water from the faucet 24 is subjected to reforming treatment such as sterilization in the electrolytic cell 2. After this treatment, water can be supplied as household water or commercial water to restaurants and other establishments.

When the liquid to be treated, such as drinking water, is supplied to the electrolytic cell 2 from below as indicated by the arrow in FIG. A potential is generated within the fixed bed 5 and between the fixed beds 5, and the liquid to be treated flowing through the electrolytic cell contacts the fixed bed 5, which is polarized positively or negatively by this potential, and the liquid in the liquid to be treated is polarized positively or negatively. After being subjected to modification treatments such as sterilization of mold and bacteria, removal of precipitated calcium and magnesium ions, and improvement of taste, the water is taken out from above the electrolytic cell 2 and sent from the water treatment plant through a line 23 as shown in Figure 2. It is supplied to homes, restaurants, etc. through the water supply system, or as domestic water, etc., as shown in Figure 3.

FIG. 4 shows another example of a bipolar fixed bed electrolytic cell that can be used in the present invention.

A mesoche-shaped power feeding anode 33 and a power feeding cathode 34 are provided near the top and bottom ends of the cylindrical electrolytic cell body 32 having flanges 31 on the top and bottom, respectively. The electrolytic cell body 32 is preferably made of an electrically insulating material, particularly a synthetic resin, which can withstand long-term use or repeated use.

Between the two power supply electrodes 33 and 34, there are a large number of fixed bed forming particles 35 made of a conductive material such as a carbon material, and a smaller number of insulating particles 36 made of synthetic resin, for example, than the fixed bed forming particles 35. are almost evenly mixed. The insulating particles 36 have a function of preventing the power feeding anode 33 and the power feeding cathode 34 from being completely short-circuited.

When electricity is supplied to the electrolytic cell having such a structure while supplying the liquid to be treated from below as shown by the arrow, each fixed bed forming particle 35 becomes negative on the power feeding anode 33 side and negative on the power feeding cathode 34 side. It functions as a three-dimensional electrode with positive polarization and a large surface area, and in the same way as the electrolytic cell shown in Figure 1, it sterilizes mold and bacteria in the liquid to be treated, removes calcium and magnesium, and improves the taste of the liquid to be treated. The electrolytic cell is taken out from above the electrolytic cell after being subjected to a reforming process such as the following.

(Example) Next, an example of drinking water reforming treatment by the method of the present invention will be described, but the present invention is not limited to this example.

The electrolytic cell shown in Fig. 1, which is made of transparent hard polyvinyl chloride resin and has a flanged cylindrical shape with a height of 400 mm and an inner diameter of 100 mm, was installed together with a pump in a tank of river water drawn from a river. Inside the electrolytic cell there is a diameter 10mm made of carbon fiber.
25 fixed beds with a thickness of 101 m are sandwiched between 26 polyethylene resin diaphragms with a diameter of 1001 mm and a thickness of 1.2 mm with an open area ratio of 80%, and platinum is applied to the surface of the diaphragms at both the upper and lower ends. Made of plated titanium, diameter 9811, thickness 1. Onm mesoche-like power feeding anode and power feeding cathode were placed in contact with each other. The upper and lower openings of the electrolytic cell are closed by lids, and a pair of flanges are formed at the drinking water supply port of the lower lid, the other end of which is grounded between the flanges, and the surface of which is platinized stainless steel. A Mesos body made of aluminum was sandwiched between the two.

The river water was treated by supplying unchlorinated river water to the electrolytic cell at a rate of 51/min, and applying the electrolysis voltage shown in Table 1 between the power supply electrodes. Table 1 summarizes the presence or absence of generated gas as determined by visual observation during the treatment operation, the calcium and magnesium ion concentrations of the river water before and after passing through the electrolytic cell, the number of bacteria, and the amount of power consumed.

Table 1 From Table 1, it can be seen that when river water is treated with an electrolytic cell, the concentration of calcium and magnesium ions and the number of bacteria are significantly reduced.

After 30 days, the electricity was turned off, the electrolytic cell was disassembled, and the insides of the river water supply port and treated liquid outlet of the electrolytic cell were visually observed, but no changes were observed.

Example 1 except that the electrode material forming the main fixed bed was changed
The liquid to be treated was electrochemically treated using the same electrolytic cell.

As the liquid to be treated, test water (bacteria count: 338 bacteria/m1) made by storing tap water in a water tank for 30 days was used, and the test water was subjected to 5.
The liquid to be treated was supplied to a three-dimensional electrode type electrolytic cell constructed using the substances shown in Table 2 at a flow rate of 31/min, and the sterilization rate [(number of bacteria at the inlet) - (Number of bacteria at outlet)/Number of bacteria at inlet] and electrolytic voltage were measured. The results are summarized in Table 2.

Table 2 It can be seen from Table 2 that when the electrode constituent material is a carbon-based material, the sterilization rate is close to 100%, whereas when it is a metal material, the sterilization rate is significantly reduced.

Using the electrolytic cell of Example 2 in which the electrode constituent material was graphite, we investigated the effect on the sterilization rate when the aperture ratio of graphite was changed and the pressure difference between the inlet and outlet of the electrolytic cell, that is, the pressure loss. It was measured. The results are summarized in Table 3.

Table 3 It can be seen from Table 3 that a satisfactory sterilization rate could be obtained within the range of the open area ratio of 10 to 95%.

(Effects of the Invention) The method of the present invention supplies a liquid to be treated such as drinking water to a three-dimensional electrode type electrolytic cell having a three-dimensional electrode made of a carbon-based material, and brings the liquid to be treated into contact with the three-dimensional electrode. This is a method for electrochemically treating a liquid to be treated (claim 1).

When a liquid to be treated such as drinking water is treated according to the present invention, it is possible to produce a killing effect almost comparable to the chlorine method in which chlorine remains in drinking water, etc., and at the same time, it is possible to remove calcium and magnesium. , it can also contribute to improving the taste required for drinking water. Furthermore, unlike conventional electrolytic methods that involve gas generation, it is economical because power consumption can be reduced to almost zero, and the effects of the treatment are almost the same as those of conventional electrolytic methods.

The method of the present invention uses a three-dimensional electrode electrolyzer having a three-dimensional electrode made of a carbon-based material with a large surface area. The carbon-based material is completely non-toxic and does not form ions or their hydroxides, so it is suitable for treating liquids that are ingested into the body, such as drinking water (claim 2). The opportunity for contact between the two is greatly increased, greatly increasing sterilization efficiency. Furthermore, carbon-based materials are inexpensive, and unlike other metal electrolytes, they do not corrode even when electrolysis is stopped.
It is advantageous both economically and from the viewpoint of the authorship.

This carbon-based material is usually used as a felt-like or fibrous three-dimensional electrode, and the porosity of the three-dimensional electrode is 10 to 95.
(Claim 3), and within this range, the sterilization rate is approximately 100%, although it depends on other conditions.

Further, in the electrolytic cell of the present invention, a leakage current may occur in the electrolytic cell, and the leakage current may flow into other metal members such as water pipes, causing electrochemical corrosion such as elution in the members. In order to prevent this, a member having higher conductivity than the liquid to be treated is installed at an appropriate location where the power supply cathode does not face each other so that one end of the member can be grounded (Claim 4). It can be dissipated.

In addition, if the liquid to be treated flowing in the electrolytic cell is a laminar flow, the liquid to be treated may pass through the three-dimensional electrode electrolytic cell without making sufficient contact with the electrodes etc. that process the liquid. Preferably, the liquid to be treated is a turbulent flow having a Reynolds number of 500 or more (claim 5) so that the liquid to be treated moves in the lateral direction and sufficiently contacts the electrodes and the like.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing an example of a fixed bed type three-dimensional electrode electrolytic cell that can be used as the electrolytic cell of the present invention, and FIGS. 2 and 3 show the installation status of the electrolytic cell shown in FIG. 1. A schematic diagram showing the
FIG. 4 is a longitudinal sectional view showing an example of another bipolar fixed bed electrolytic cell. 1.31...Flange 2.32...Electrolytic cell body 3.3
3... Anode for power supply 4.34... Cathode for power supply 5... Fixed bed 6... Spacer 7.8... Lid body 9...
・Drinking water outlet 10...Drinking water supply port 11...Flange 12...Earth terminal 13, 22, 24, 35...Mesh body 21...Water purification pond...Pump 23...Line ... Faucet 25 ... Connecting pipe/fixed bed forming particles 36 ... Insulating particles Figure 1

Claims (5)

[Claims] (1) The liquid to be treated is supplied to a three-dimensional electrode type electrolytic cell having a three-dimensional electrode made of a carbon-based material, and the liquid to be treated is brought into contact with the three-dimensional electrode to be electrochemically treated. Electrochemical treatment method. (2) The method according to claim 1, wherein the liquid to be treated is drinking water. (3) The aperture ratio of the three-dimensional electrode made of carbon-based material is 10%
The method according to claim 1 or 2, wherein the ratio is 95% or less. (4) A member with higher conductivity than the liquid to be treated can be grounded at one end on the back of the power supply electrode where the power supply anodes and cathodes in the three-dimensional electrode type electrolytic cell do not face each other and/or inside the inlet/outlet piping of the electrolytic cell. The method according to any one of claims 1 to 3, wherein the method is performed by installing the method in a. (5) The Reynolds number of the liquid to be treated flowing in the electrolytic cell is 50.
The method according to any one of claims 1 to 4, wherein the number is 0 or more.