JP7708372B2 - Fluorine-containing water treatment device - Google Patents

Description

This invention relates to a treatment device that removes fluorine from fluorine-containing water.

In some areas, groundwater used for drinking water may contain high concentrations of fluoride derived from geological features, and treatment to remove fluoride is necessary to prevent the health hazards of fluorosis. Some treatment devices for removing fluoride from such fluoride-containing water are equipped with an electrolytic cell that electrolyzes the fluoride-containing water to obtain cathode water.

The fluorine-containing water treatment device in Patent Document 1 is equipped with an electrolytic cell that introduces fluorine-containing water and electrolyzes it, a porous clay plate diaphragm that separates the cell into a cathode chamber and an anode chamber, a sand filter that filters the cathode water produced in the cathode chamber of the electrolytic cell, and a pH adjustment tank that adjusts the pH of the cathode water filtered by the sand filter, and the electrolytic cell, sand filter, and pH adjustment tank are all connected to each other by connecting pipes. The cathode water is purified of fluorine and foreign matter, and the pH is adjusted, making it a product that can be used as drinking water.

In the method for producing electrolytic ionized water described in Patent Document 2, an electrolytic cell is provided for electrolyzing tap water. The electrolytic cell is provided with one anode and a pair of cathodes sandwiching the anode, and a diaphragm is provided between the cathode and anode to separate them into one anode chamber and two cathode chambers. Pipes for introducing tap water are connected to the one anode chamber and the two cathode chambers, respectively. After electrolysis in the electrolytic cell, electrolytic ionized water is extracted from the cathode chamber and used as the product.

Publication No. 2016-168529 Japanese Patent Application Publication No. 8-99088

In the case of Patent Document 1 of the background art mentioned above, an anode chamber and a cathode chamber are provided, and the principle is the coprecipitation removal of polyvalent metals and fluorine in the cathode chamber, so if the raw water does not contain polyvalent metals, it is not possible to obtain a drinking water product. In the case of Patent Document 2 of the background art mentioned above, one anode chamber and two cathode chambers are provided, so the efficiency of obtaining the product is high, but three pipes are required to flow tap water into each chamber, so a lot of equipment is required.

This invention was made in consideration of the problems in the background art described above, and aims to provide a fluorine-containing water treatment device that can reliably remove fluorine from fluorine-containing water, efficiently obtain a product in which fluorine has been removed from the fluorine-containing water, and generate little wastewater.

The present invention provides an electrolytic cell for electrolyzing fluorine-containing water, the electrolytic cell being provided with a water tank into which the fluorine-containing water flows, the water tank being divided into five thin compartments parallel to one direction by four diaphragms, one compartment located in the center of the water tank being an anode chamber in which an anode is provided, two compartments on both sides of the anode chamber being water injection chambers into which the fluorine-containing water is directly introduced, the two compartments on both sides of the water injection chamber being compartments along the back side of both sides of the water tank being cathode chambers in which a cathode is provided, the diaphragms being ceramic plates, the lower end of the diaphragm being separated from the bottom of the water tank by a gap of a predetermined length, the gap being, for example, 0.5 to 1 mm, and on one side of the water tank, two fluorine-containing water injection ports through which the fluorine-containing water is injected are each connected to the water injection chamber. a fluorine-containing water treatment device in which two cathode water outlets, from which cathode water from which fluorine has been removed by electrolysis flows out, are provided on a side surface opposite to the side surface on which the fluorine-containing water inlet is provided, and each of the two cathode water outlets is connected to the cathode chamber, and an anode water outlet, from which anode water containing fluorine flows out, is provided on the side surface on which the cathode water outlet is provided, and is connected to the anode chamber, and a height of the cathode water outlet from the bottom of the water tank is slightly lower than that of the anode water outlet, a pump is connected to the cathode water outlet, and a flow rate of the pump is smaller than an amount of the fluorine-containing water flowing in, the cathode water is drawn out from the cathode water outlet by the pump, and a difference between the amount of the fluorine-containing water and the amount of the cathode water drawn out by the pump is discharged as wastewater from the anode water outlet. The anode water outlet is located at a height of about 25 cm from the bottom of the water tank, for example, and is 5 cm higher than the cathode water outlet. The height of the fluorine-containing water inlet is arbitrary.

A pH adjustment tank is provided downstream of the electrolytic cell, and a pH adjustment tank is provided in the pH adjustment tank to receive the cathode water and anode water of the electrolytic cell. The pH adjustment tank is divided into two thin compartments parallel to one direction by a cation exchange membrane, one of which is a pH adjustment anode chamber having a pH adjustment anode, and the other is a pH adjustment cathode chamber having a pH adjustment cathode. On one side of the pH adjustment tank, there are two cathode water inlet ports through which the cathode water electrolyzed in the electrolytic cell is injected, each of which is connected to the pH adjustment anode chamber. On the side where the cathode water inlet is provided, an anode water inlet through which anode water electrolyzed in the electrolytic cell is injected is provided in communication with the pH-adjusting cathode chamber, and on the side opposite to the side where the cathode water inlet and the anode water inlet are provided, a treated water outlet through which treated water whose pH has been lowered by electrolysis flows out is provided in communication with the pH-adjusting anode chamber, and on the side where the treated water outlet is provided, a wastewater outlet through which wastewater containing fluorine flows out is provided in communication with the pH-adjusting cathode chamber.

The fluorine-containing water treatment device of the present invention can reliably remove fluorine from fluorine-containing water even if the raw water does not contain polyvalent metal ions, and can efficiently obtain a product in which fluorine has been removed from fluorine-containing water with little wastewater. The device has a simple structure, and two cathode chambers can be provided in one anode chamber in an electrolytic cell, and the yield can be increased because there is little anode water in the anode chamber that becomes wastewater. A pH adjustment chamber that adjusts the pH by electrolysis is provided in series downstream of the electrolytic cell, making it compact, highly efficient, and with high treatment capacity. In addition, a water injection chamber for introducing fluorine-containing water is provided between the cathode chamber and the anode chamber of the electrolytic cell, so that the cathode water and the anode water do not mix.

FIG. 2 is a plan view of the treatment apparatus for fluoride-containing water according to the embodiment. 1A is a plan view of an electrolytic cell of the fluorine-containing water treatment device of this embodiment, FIG. 1B is a vertical sectional view taken along line AA of FIG. 1A, and FIG. 1B is a vertical sectional view taken along line BB of FIG.

Embodiments of the present invention will now be described with reference to the drawings. Figs. 1 and 2 show one embodiment of the present invention, in which a fluorine-containing water treatment device 10 is provided with an electrolytic cell 12 that electrolyzes fluorine-containing water 11. The fluorine-containing water 11 may be any type of water, such as groundwater, river or swamp water, or rainwater.

The electrolytic cell 12 will now be described. As shown in FIG. 2, the electrolytic cell 12 includes a water tank 14 for holding fluorine-containing water 11. The water tank 14 is made of, for example, acrylic and has a rectangular bottom 14a that is long in one direction and sides 14b, 14c, 14d, and 14e that are continuous with the bottom 14a. The top is closed, and a vent is provided for releasing gas and connected to the atmosphere. The sides 14b and 14c are small rectangles that are continuous with the short sides of the bottom 14a, and the sides 14d and 14e are large rectangles that are continuous with the long sides of the bottom 14a. The size of the water tank 14 is, for example, 300 mm x 150 mm for the bottom 14a and 250 mm or more deep. The fluorine-containing water 11 flows in the electrolytic cell 12 along the longitudinal direction of the water tank 14, that is, parallel to the sides 14d and 14e, and is electrolyzed.

The water tank 14 is divided into five thin chambers parallel to the longitudinal direction by four diaphragms 20. One of the chambers located in the center of the water tank 14 is the anode chamber 26 in which the anode 16 is provided. The anode 16 is a platinum wire provided in the center of the water tank 14, and is erected at approximately right angles to the bottom 14a of the water tank 14. For example, five anodes 16 are provided, and are arranged at approximately equal intervals in the longitudinal direction of the water tank 14, i.e., parallel to the sides 14d and 14e.

The two outer compartments of the anode chamber 26 are water injection chambers 24 into which the fluorine-containing water 11 is directly poured, and are surrounded by a pair of diaphragms 20 without any electrodes. The two compartments on both sides of the water injection chamber 24 are the outermost compartments, i.e., the compartments along the back sides of the sides 14d and 14e, and are cathode chambers 22 in which the cathode 18 is provided. The cathode 18 is a rectangular stainless steel plate that is attached along the inner wall surfaces of a pair of sides 14d and 14e along the longitudinal direction of the water tank 14, and is large enough to cover almost all of the inner wall surfaces of the sides 14d and 14e. The width of the anode chamber 26 crossing the flow direction is, for example, 50 mm, the width of each cathode chamber 22 crossing the flow direction is, for example, about 25 mm, and the width of each water injection chamber 24 crossing the flow direction is 25 mm.

The diaphragm 20 is, for example, a porous ceramic plate. The ceramic plate used here has the characteristics of reliably preventing the mixing of the solutions in the electrolytic cell 12, allowing ions to pass through the electrolytic cell 12, and having low electrical resistance and low power consumption during use. In addition to the ceramic plate, nylon cloth or fiber filters having similar functions may be used. The diaphragm 20 is rectangular, has a length that reaches the sides 14b and 14c of the water tank 14 in one direction, is fixed to the sides 14b and 14c, and has a length that reaches a position slightly lower than the bottom 14a in the intersecting vertical direction, and the lower end 20a of the diaphragm 20 is separated from the bottom 14a of the water tank 14 with a gap 21 of a predetermined length. The gap 21 between the lower end 20a of the diaphragm 20 and the bottom 14a is, for example, 0.5 to 1 mm. Four diaphragms 20 are provided in the water tank 14, two of which are provided between the anode 16 and the cathode 18. The two diaphragms 20 provided between the anode 16 and the cathode 18 are positioned parallel to each other with a predetermined distance between them.

One side surface 14b of the water tank 14 is located upstream of the fluorine-containing water 11, and the side surface 14b is provided with a fluorine-containing water inlet 28 through which the fluorine-containing water 11 is injected, near the upper opening. Two fluorine-containing water inlets 28 are provided, one at a position facing the two water injection chambers 24 and connected to the water injection chambers 24. The side surface 14c opposite the side surface 14b is provided with a cathode water outlet 30 through which the cathode water from which fluorine has been removed by electrolysis flows out. Two cathode water outlets 30 are provided, one at a position facing the two cathode chambers 22 and connected to the cathode chambers 22. The cathode water outlet 30 is located at a height of about 20 cm from the bottom 14a of the water tank 14 and is close to the upper opening. In addition, between the pair of cathode water outlets 30 on the side surface 14c, an anode water outlet 32 through which the anode water containing fluorine flows out is provided, and is connected to the anode chamber 26. The anode water outlet 32 is located at a height of, for example, about 25 cm from the bottom 14a of the water tank 14, and is 5 cm higher than the cathode water outlet 30. The height of the fluorine-containing water inlet 28 may be close to the upper opening, and the dimensions are not limited.

A pump (not shown) is connected to the pair of cathode water outlets 30, and cathode water is drawn off at a constant flow rate. At this time, the flow rate of the fluorine-containing water 11, which is the water to be treated, is set to be greater than the flow rate of the cathode water drawn off by the pump. As a result, anode water in an amount that is in excess of the amount of the water to be treated that flows in compared to the amount of the cathode water drawn off is discharged as wastewater from the anode water outlet 32.

Downstream of the electrolytic cell 12, a pH adjustment cell 34 is provided to adjust the pH of the cathode water. In the electrolytic cell 12, the pH of the cathode water rises above 10 due to hydroxide ions generated at the cathode, so the pH adjustment cell 34 is installed and the pH is lowered to less than 10 through electrolysis to produce products such as drinking water. The electrolytic cell 12 and the pH adjustment cell 34 are connected in series.

The pH adjustment tank 34 is equipped with a pH adjustment tank 36 that is approximately the same size as the tank 14 of the electrolytic cell 12. The pH adjustment tank 36 is also made of, for example, acrylic and consists of a rectangular bottom 36a that is long in one direction and sides 36b, 36c, 36d, and 36e that are continuous with the bottom 36a. The top is closed, and a vent is provided to allow gas to escape and is connected to the atmosphere. The sides 36b and 36c are small rectangles that are continuous with the short side of the bottom 36a, and the sides 36d and 36e are large rectangles that are continuous with the long side of the bottom 36a. The cathodic water and anodic water electrolyzed in the electrolytic cell 12 flow into the pH adjustment tank 34 along the longitudinal direction of the pH adjustment tank 36, and are further electrolyzed to lower the pH of the cathodic water.

A pH-adjusting anode 38 is provided on the inner wall surface of one side 36d along the longitudinal direction of the pH-adjusting water tank 36, and a pH-adjusting cathode 40 is provided on the inner wall surface of the opposite side 36e. A cation exchange membrane 42 is provided in the center of the pH-adjusting water tank 36, which divides the water tank 36 into two thin chambers parallel to the longitudinal direction, with the side 36d side being the pH-adjusting anode chamber 44 having the pH-adjusting anode 38, and the side 36e side being the pH-adjusting cathode chamber 46 having the pH-adjusting cathode 40. The pH-adjusting anode 38 is made of platinum wire or platinum-plated titanium plate, and the pH-adjusting cathode 40 is made of stainless steel plate or the like. The cation exchange membrane 42 reliably prevents the solutions from mixing, allows only cations to pass through, has low electrical resistance, and consumes little power, so that the fluorine removed in the electrolytic cell 12 does not move from the pH adjustment cathode chamber 46 to the pH adjustment anode chamber 44.

One side surface 36b of the pH adjustment water tank 36 is located on the upstream side, and a cathode water inlet 48 is provided on the side surface 36b near the upper opening, into which the cathode water electrolyzed in the electrolytic cell 12 and flowing out of the cathode water outlet 30 is injected. Two cathode water inlets 48 are provided, arranged side by side in positions facing the pH adjustment anode chamber 44, and each is connected to the pH adjustment anode chamber 44. One anode water inlet 50 is provided on the side surface 36b near the upper opening, approximately the same as the cathode water inlet 48, into which the anode water electrolyzed in the electrolytic cell 12 is injected, and is connected to the pH adjustment cathode chamber 46.

On the side 36c opposite to the side 36b, a treated water outlet 52 is provided through which treated water with fluorine removed and a lowered pH flows out, and is provided at a position facing the pH adjustment anode chamber 44 and connected to the pH adjustment anode chamber 44. On the side 36c, a wastewater outlet 54 containing fluorine is provided at a position facing the pH adjustment cathode chamber 46 and connected to the pH adjustment cathode chamber 46. The treated water outlet 52 and the wastewater outlet 54 are provided at any position close to the upper opening. The total amount of water flowing out from the treated water outlet 52 and the wastewater outlet 54 is approximately equal to the amount of water injected from the pair of cathode water inlet 48 and anode water inlet 50. This makes the water level in the pH adjustment water tank 36 approximately constant. The treated water taken out from the treated water outlet 52 has a low fluorine content and a pH of 10 or less, making it a product that can be used as drinking water. If necessary, further filtration or other processing may be performed.

Next, an example of a treatment method using the fluorine-containing water treatment device 10 will be described. The flow rate of the fluorine-containing water 11 in the electrolytic cell 12 is, for example, 48 l/h, and when the yield is 85%, 7.2 l/h of wastewater is discharged. The voltage of the electrolytic cell 12 is about 110 V, and the current is 1 A x 2, totaling 2 A. The yield is 80 to 95%. The voltage of the pH adjustment cell 34 is about 130 V, and the current is 0.75 A. By using the fluorine-containing water treatment device 10 of this embodiment equipped with the electrolytic cell 12 and the pH adjustment cell 34, the fluorine concentration is reduced from 2.5 mg/l (fluorine-containing water 11) to 0.8 mg/l or less. The fluorine concentration standard value in the Food Sanitation Act is 2.0 mg/l, and if it is 0.8 mg/l or more, a label stating "Do not drink if under 7 years of age" is required.

As shown in FIG. 1, fluorine-containing water 11 is injected into the water injection chamber 24 from a pair of fluorine-containing water injection ports 28 of the electrolytic cell 12. The injected fluorine-containing water 11 also flows into the cathode chamber 22 and the water injection chamber 24 from the gap 21 between the lower end 20a of the diaphragm 20 and the bottom 14a of the water tank 14, and is filled up to the height of the anode water outlet 32, where electrolysis is performed. In the cathode chamber 22, fluorine is removed from the fluorine-containing water 11 to produce cathode water.

The cathode water from which fluorine has been removed in the cathode chamber 22 is extracted by a pump from each cathode water outlet 30 and injected into the pH adjustment tank 34 connected in series downstream of the electrolytic cell 12 through each cathode water inlet 48 into the pH adjusting anode chamber 44. The pH of the cathode water exceeds 10 due to hydroxide ions ^OH- generated at the cathode 18, but the pH is reduced to 10 or less due to hydrogen ions H ⁺ generated in the pH adjusting anode chamber 44 of the pH adjustment tank 34. The treated water in the pH adjusting anode chamber 44 with a reduced pH is extracted from the treated water outlet 52 and made into a product usable as drinking water.

According to the fluorine-containing water treatment device 10 of this embodiment, fluorine can be reliably removed from the fluorine-containing water 11, and drinking water can be produced from the fluorine-containing water 11. The efficiency of obtaining a product in which fluorine has been removed from the fluorine-containing water 11 is high, and the amount of wastewater is small. With a simple structure, two cathode chambers 22 can be provided for one anode chamber 26 in the electrolytic cell 12, and the amount of anode water in the anode chamber 26 that becomes wastewater is small, so that the amount of wastewater can be reduced and the yield can be increased. Since expensive platinum is used for the anode 16 in the anode chamber 26, there is a large cost advantage in halving the number of anode chambers 26 compared to the cathode chambers 22. When the fluorine-containing water 11 is poured into the electrolytic cell 12 through the fluorine-containing water inlet 28 that communicates with each water injection chamber 24, the fluorine-containing water 11 flows from the gap 21 between the lower end 20a of the diaphragm 20 and the bottom 14a of the water tank 14 to the cathode chamber 22 and the anode chamber 26, filling the water tank 14. Furthermore, the structure is simple with few pipes, and a water injection chamber 24 separated by a diaphragm 20 is provided between the cathode chamber 22 and the anode chamber 26, and fluorine-containing water 11 is injected into this chamber for electrolysis, so the cathode water and anode water do not mix, and the fluorine concentration of the cathode water can be kept low.

Furthermore, a pH adjustment tank 34 that adjusts the pH by electrolysis is provided in series downstream of the electrolytic tank 12, and is simple in structure, compact, has high processing capacity, and is efficient. The pH adjustment tank 34 can easily adjust the pH, and can reliably prevent fluorine from migrating from the pH adjustment cathode chamber 46. The product manufactured by the fluorine-containing water treatment device 10 has a low fluorine content, which prevents health damage caused by high fluorine concentration, and can be used safely as potable water. In addition, the pH is 10 or less, making it suitable for drinking water. If necessary, further filtration processing, etc. can be performed, and it can be used by connecting it to devices that perform various processes such as filtration processing and sterilization processing.

The fluorine-containing water treatment device of this invention is not limited to the above embodiment, but can be modified as appropriate. The size of the electrolytic cell's water tank, the gap between the diaphragm and the bottom of the water tank, the height of each inlet and each outlet, etc. can be freely changed. Materials for the water tank and electrodes other than those mentioned above can be used, and materials used in normal electrolytic treatment can be used.

10 Fluorine-containing water treatment device 11 Fluorine-containing water 12 Electrolytic cell 14 Water tank 14a Bottom 14b, 14c, 14d, 14e Side 16 Anode 18 Cathode 20 Diaphragm 21 Gap 22 Cathode chamber 24 Water injection chamber 26 Anode chamber 28 Fluorine-containing water inlet 30 Cathode water outlet 32 Anode water outlet 34 pH adjustment tank 36 pH adjustment water tank 38 pH adjustment anode 40 pH adjustment cathode 42 Cation exchange membrane 44 pH adjustment anode chamber 46 pH adjustment cathode chamber 48 Cathode water inlet 50 Anode water inlet 52 Treated water outlet 54 Wastewater outlet

Claims (3)

an electrolytic cell for electrolyzing fluorine-containing water is provided, the electrolytic cell is provided with a water tank into which the fluorine-containing water flows, the water tank is partitioned in one direction into five thin compartments by four diaphragms, one compartment located in the center of the water tank is an anode chamber in which an anode is provided, two compartments on both sides of the anode chamber are water injection chambers into which the fluorine-containing water is directly introduced, and the two compartments on both sides of the water injection chamber are cathode chambers which are compartments along the back sides of both sides of the water tank and in which a cathode is provided,
The lower end of the diaphragm is spaced apart from the bottom of the water tank by a predetermined length of gap,
one side of the water tank is provided with two fluorine-containing water inlets through which the fluorine-containing water is injected, each of which is in communication with the water injection chamber; a side opposite to the side with the fluorine-containing water inlets is provided with two cathode water outlets, each of which is in communication with the cathode chamber, from which cathode water from which fluorine has been removed by electrolysis flows out; and a side with the cathode water outlets is provided with an anode water outlet, which is in communication with the anode chamber and from which fluorine-containing anode water flows out;
a height of the cathode water outlet from the bottom of the water tank is lower than that of the anode water outlet; a pump is connected to the cathode water outlet, and a flow rate of the pump is smaller than an amount of the fluorine-containing water flowing in; the cathode water is extracted from the cathode water outlet by the pump, and a difference between an amount of the fluorine-containing water and an amount of the cathode water extracted by the pump is discharged as wastewater from the anode water outlet. a pH adjustment tank is provided downstream of the electrolytic cell, and a pH adjustment tank is provided in the pH adjustment tank in which cathode water and anode water of the electrolytic cell are placed, the pH adjustment tank is partitioned by a cation exchange membrane into two thin chambers parallel to one direction, one of which is a pH adjustment anode chamber having a pH adjustment anode and the other is a pH adjustment cathode chamber having a pH adjustment cathode,
2. The fluoride-containing water treatment device according to claim 1, wherein one side of the pH-adjusting water tank is provided with two cathode water inlets, through which cathode water electrolyzed in the electrolytic cell is injected, and the two cathode water inlets are each connected to the pH-adjusting anode chamber, and the side with the cathode water inlet provided with an anode water inlet, through which anode water electrolyzed in the electrolytic cell is injected, is provided with a treated water outlet connected to the pH-adjusting anode chamber, and the side opposite to the side with the cathode water inlet and the anode water inlet provided with a treated water outlet, through which treated water whose pH has been reduced by electrolysis flows out, is provided with a wastewater outlet connected to the pH-adjusting cathode chamber, and the side with the treated water outlet provided with a wastewater outlet through which wastewater containing fluoride flows out, is provided with a The fluorine-containing water treatment device according to claim 1 or 2, wherein the diaphragm is a ceramic plate and the gap is 0.5 to 1 mm.