JP2005296743A - Method for removing nitrate nitrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing nitrate nitrogen, in which it is not necessary to separate the liquid to be treated into a section on the anode side and another section on the cathode side differently from the conventional nitrate nitrogen removing method and the nitrate nitrogen in the liquid is removed so that the properties of the treated liquid are not changed from those of the liquid before treated. <P>SOLUTION: This method for removing the nitrate nitrogen contained in the liquid is based on an electrochemical reduction and a reduction with hydrogen. The electrochemical reduction is advanced by arranging a pair of AC electrodes and at least one grounded electrode to be close to the AC electrodes in the liquid, heating the liquid to the predetermined temperature and impressing an AC voltage between the pair of the AC electrodes to electrolyze the liquid and the reduction with hydrogen is advanced by generating hydrogen from the pair of the AC electrodes and/or the grounded electrode and reacting the generated hydrogen with the nitrate nitrogen to remove the nitrate nitrogen. As a result, it is not necessary to separate the liquid to be treated into the section on the anode side and the section on the cathode side and the nitrate nitrogen in the liquid can be removed so that the properties of the treated liquid are not changed from those of the liquid before treated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for removing nitrate nitrogen contained in liquids such as drinking water, groundwater, and wastewater, and more specifically, electrochemical decomposition of nitrate nitrogen, and nitrate nitrogen and atomic hydrogen. And a method for decomposing and removing the nitrate nitrogen from the liquid.

Conventionally, this type of technology includes, for example, a storage unit that stores water to be treated and a first electrode pair provided in the storage unit, and the cathode of the first electrode pair includes an amphoteric metal. There is a water treatment device which is a first member made of an alloy containing.
JP 2003-31274 A

  In the known technique of Patent Document 1, a first electrode pair, that is, a cathode and an anode is disposed in a housing portion, and when direct current is passed through the water to be treated from the first electrode pair, The amphoteric metal that forms lysates and reacts with anions in the aqueous solution to form a flocculant and remove nitrate nitrogen.

  However, in the known technique of Patent Document 1, since direct current is supplied to the water to be treated and the inside of the housing is separated into the cathode and the anode, the water to be treated on the anode side cannot be used. Even if the water to be treated is neutral water, the treated water on the cathode side and the anode side in the treated water move to the cathode side and the anode side, respectively. On the other hand, there is a problem that the treated water on the anode side becomes acidic and the properties of the treated water change.

  In addition, since the water to be treated must be separated into the anode side and the cathode side as described above, as the water to be treated, for example, when the known technique of Patent Document 1 is used in a reservoir or a water purification plant. Can not be treated in a state where the treated water is stored in the water storage lake or water purification plant, etc., and the treated water must be accommodated in the accommodating portion in which the cathode and the anode are disposed. It will not be.

  Therefore, in the conventional method for removing nitrate nitrogen, it is not necessary to separate the liquid to be treated into the anode side and the cathode side, and the properties of the liquid after the treatment are not changed, so that the nitrate nitrogen in the liquid is not changed. There is a problem that must be solved by removing the.

  As a specific means for solving the problems of the conventional example described above, the method for removing nitrate nitrogen according to the present invention is a method for removing nitrate nitrogen contained in a liquid by electrochemical reduction and hydrogen reduction. A pair of AC electrodes and at least one ground electrode adjacent to the pair of AC electrodes are disposed in the liquid, the liquid is heated to a predetermined temperature, and AC is exchanged between the pair of AC electrodes. And applying electrochemical decomposition to electrochemical reduction, generating hydrogen from the pair of AC electrodes and / or the ground electrode, and removing the nitrate nitrogen by the reaction of the hydrogen with nitrate nitrogen. Main features.

  In the present invention, the pair of AC electrodes are titanium, zinc, aluminum alloy, iron, cobalt, nickel, tin, or magnesium alloy, and the ground electrode is titanium, palladium, silver, zinc, aluminum, copper, brass. Carbon, nickel, iron, cobalt, or stainless steel; the ground electrode periodically applies an alternating current from a ground potential or a positive potential; the liquid is heated by a heating means or a pair of alternating currents Performing with heat generated from the electrodes; the predetermined temperature is that the temperature of the liquid is approximately 30 ° C. or higher; the liquid degass the oxygen contained therein; decomposition of ammonia generated at the end of decomposition of nitrate nitrogen Therefore, it is necessary to set the ground electrode to a positive potential for several minutes to several hours.

  A method for removing nitrate nitrogen according to the present invention is a method for removing nitrate nitrogen contained in a liquid by electrochemical reduction and hydrogen reduction, wherein the liquid is paired with a pair of alternating current electrodes and the pair of alternating electrodes. And at least one ground electrode adjacent to the alternating current electrode, heating the liquid to a predetermined temperature, applying alternating current between the pair of alternating current electrodes and performing electrolysis to perform electrochemical reduction The liquid to be treated is separated into the anode side and the cathode side by generating hydrogen from the pair of AC electrodes and / or the ground electrode and removing the nitrate nitrogen by the reaction of the hydrogen with the nitrate nitrogen. Since the properties of the liquid after the treatment are not changed, for example, the liquid in the reservoir or the water purification plant is not moved into a special storage unit or the like. In liquids Removing the organic and the nitrate nitrogen exhibits an excellent effect that allow.

  A pair of alternating current electrodes and at least one ground electrode adjacent to the pair of alternating current electrodes are disposed in the liquid, and the liquid is heated to a temperature of about 30 ° C. or higher to degas oxygen from the liquid. AC is applied between the pair of AC electrodes, and the ground electrode is periodically applied with an AC potential from the ground potential or is changed to a positive potential to perform electrolysis by AC, and the pair of AC electrodes and / or the ground This is realized by generating hydrogen from the electrode to remove nitrate nitrogen.

Next, the present invention will be described in detail based on specific examples.
An electric circuit of Example 1 that can be used in the method for removing nitrate nitrogen according to the present invention is shown in FIG. In the liquid 2 to be processed accommodated in the processing tank 1, a pair of AC electrodes 3a and 3b and at least one ground electrode 4 adjacent to the pair of AC electrodes 3a and 3b are disposed. Yes. The treatment tank 1 is not necessarily a container-like treatment tank, and may be, for example, a facility in which a liquid 2 such as a water storage lake or a water purification plant is stored.

  In addition, as the liquid 2, for example, drinking water such as general tap water, water stored in a water storage lake or water purification plant, ground water, domestic household waste water, factory waste water, mineral water, or the like liquid is treated. It is what is used.

  As the pair of AC electrodes 3a and 3b, for example, a highly soluble metal such as titanium, zinc, aluminum alloy, iron, cobalt, nickel, tin, or magnesium alloy can be used. For example, metals having a high ionization tendency such as titanium, palladium, silver, zinc, aluminum, copper, brass, carbon, nickel, iron, cobalt, and stainless steel can be used.

  The pair of AC electrodes 3a and 3b are connected to the secondary side of the transformer 6 whose temporary side is connected to the AC cord 5, for example, and the AC voltage supplied from the AC cord 5 is predetermined by the transformer 6. Thus, the AC voltage can be applied between the pair of AC electrodes 3a and 3b.

  Further, the cathodes of the diodes 7a and 7b are connected to the respective wirings on the secondary side of the transformer 6, and the ground electrode 4 is connected to the anodes of the diodes 7a and 7b. Therefore, the ground electrode 4 is substantially at ground potential.

  A heating unit 8 is disposed at the bottom of the processing tank 1, and the heating unit 8 can heat the liquid 2 stored in the processing tank 1 to a predetermined temperature. The predetermined temperature of the liquid 2 is preferably about 30 ° C. or higher.

  The heating means 8 may be used as necessary, and may be omitted when the temperature of the liquid 2 is approximately 30 ° C. or higher in advance. The temperature of the liquid 2 may be about 30 ° C. or higher, and is preferably about 40 ° C. to about 65 ° C.

  Further, even when the temperature of the liquid 2 is approximately 30 ° C. or lower, an alternating current is applied to the pair of alternating current electrodes 3a and 3b, and generated from the pair of alternating current electrodes 3a and 3b when electrolysis is performed by the alternating current. Since the liquid 2 can be heated by heat, it is not always necessary to dispose the heating means 8 when the purpose is not to obtain a treatment effect in a short time.

  Thus, when the temperature of the liquid 2 is set to about 30 ° C. or higher, an alternating current is applied between the pair of alternating current electrodes 3a and 3b, and the liquid 2 is contained in the liquid 2 when the liquid electrolysis is performed. The oxygen that is released will be degassed.

  Then, by connecting the AC cord 5 to an AC power source (not shown), AC is applied between the pair of AC electrodes 3a, 3b, and the pair of AC electrodes 3a, 3b and / or the ground electrode 4 is applied. From this, hydrogen (hydrogen ions, atomic hydrogen) is generated.

  In this way, by applying an alternating current between the pair of alternating current electrodes 3a and 3b, the liquid 2 can be electrolyzed by the alternating current, and the liquid 2 can be electrochemically reduced. By generating hydrogen (hydrogen ions, atomic hydrogen) therein, the generated hydrogen reacts with nitrate nitrogen contained in the liquid 2 and is reduced. At this time, the following reaction occurs in the liquid 2 on the ground electrode 4 side.

  Further, the changeover switch 9 is connected between the diodes 7a and 7b and the ground electrode 4, and the anodes of the diodes 10a and 10b are connected to the respective wirings on the secondary side of the transformer 6, so that the diodes 10a and 10b are connected. The cathode side of the switch may be connected to the other terminal of the changeover switch 9 so that the changeover switch 9 can be used for switching.

  The changeover switch 9 is switched at the end of the decomposition of nitrate nitrogen of the liquid 2, and the ground electrode 4 is set to a positive potential for several minutes to several hours in order to decompose ammonia generated at the end of the decomposition of nitrate nitrogen. The ammonia in the liquid 2 is decomposed.

Reduction reaction of hydrogen ion (formula 1) (mainly electrochemical reduction)
2H ⁺ + 2e → 2H → H ₂

Reduction reaction of nitrate ion (formula 2) (mainly electrochemical reduction)
NO ⁻ ₃ + 2H ⁺ + 2e → NO ⁻ ₂ + H ₂ O

Reduction reaction of nitrite ion (Formula 3) (mainly electrochemical reduction)
2NO ⁻ ₂ + 8H ⁺ + 6e → N ₂ + 4H ₂ O
(Formula 4) (Mainly electrochemical reduction)
NO ^- ₂ + 4H ⁺ + 2e → NH ⁺ ₄ + 2H ₂ O

  Further, although not confirmed, the following reaction may be caused by hydrogen (hydrogen ions, atomic hydrogen) on the ground electrode 4 side in the liquid 2.

(Formula 5) (mainly chemical reduction)
^{_{NO - 3 + 2H → NO 2}} - + H 2 O
(Formula 6) (mainly chemical reduction)
2NO ⁻ ₂ + 6H + 2H ⁺ → N ₂ + 4H ₂ O
(Formula 7) (mainly chemical reduction)
NO ^- ₂ + 6H + 2H ⁺ → NH ⁺ ₄ + 2H ₂ O

  Further, unlike the conventional direct current electrolysis, in the alternating current electrolysis, a reaction represented by the following equation 8 occurs on the pair of alternating current electrodes 3a and 3b side in the liquid 2.

Ammonium ion oxidation reaction (Formula 8)
NH ⁺ ₄ + 4OH ⁻ → 1 / 2N ₂ + 4H ₂ O + 3e

Further, when chlorine ions (Cl ⁻ ) are contained in the liquid 2, the chlorine ions are oxidized by the pair of AC electrodes 3 a and 3 b to generate hypochlorite ions (ClO ⁻ ), or the chlorine ions There is oxidized occurs Cl _2, the Cl ₂ is hypochlorite ions by disproportionation. The ammonia ions are oxidized by hypochlorite ions to become N ₂ gas.

(Formula 9)
2NH ⁺ ₄ + 3ClO ⁻ → N ₂ + 2H ⁺ + 3Cl ⁻ + 3H ₂ O

  Therefore, it is not necessary to separate the treatment tank 1 into two parts and separate the treatment target liquid 2 into the anode side and the cathode side as in the prior art. Nitrate nitrogen is electrochemically electrolyzed by alternating current and generated from the pair of alternating current electrodes 3a, 3b and / or the ground electrode 4 even if it is not moved into a special housing or the like. Nitric acid contained in the liquid of the water storage lake or water treatment plant by the reaction of the generated hydrogen (hydrogen ions, atomic hydrogen) and nitrate nitrogen to reduce nitrate nitrogen. In this case, since the voltage applied to the pair of AC electrodes 3a and 3b is alternately repeated between plus and minus, the property of the liquid 2 after the treatment does not change. It is.

  The oxygen generated during the AC electrolysis is degassed from the liquid 2 by heating the liquid 2 to a predetermined temperature as described above, and the remaining oxygen is dissolved in the soluble oxygen. Since it reacts with a pair of alternating current electrodes 3a and 3b formed of a high metal, it will hardly exist as oxygen molecules in the liquid 2 and will hinder the reaction between hydrogen and nitrate nitrogen. There is no.

  In the electric circuit of the first embodiment, the AC cord 5 is connected to an AC power source as a method for supplying power to the electric circuit. However, the method for supplying power to the electric circuit is not limited thereto. For example, a DC power source (for example, a battery) may be used, and a circuit for converting the DC power source into AC may be formed so that AC can be applied to the pair of AC electrodes 3a and 3b.

  Therefore, by using, for example, a battery as a power source and using the method for removing nitrate nitrogen according to the present invention in a float-type device as described in Japanese Patent No. 3325081 related to the same applicant, The nitrate nitrogen can be easily removed from the liquid 2 simply by floating the float-like device on the liquid stored in the field.

Further, the ground electrode 4 is periodically connected to AC wiring supplied to the pair of AC electrodes 3a and 3b to periodically apply AC, or periodically connected to the positive side of the DC power source. By periodically changing the ground potential to a positive potential, the scale adsorbed on the ground electrode 4 can be removed and cleaned, so that the amount of hydrogen generated from the ground electrode 4 does not decrease. Thus, the amount of hydrogen generated can be stably maintained. In addition, oxygen is replenished in the liquid 2 and ammonia (NH ₄ ) can be decomposed.

  Next, the result of having performed the test which confirms that the nitrate nitrogen contained in a liquid is removed using the removal method of nitrate nitrogen which concerns on this invention is shown below. In these tests, a zinc plate was used as the pair of AC electrodes, and a brass plate was used as the ground electrode. In addition, as a liquid, tap water is mixed with nitric acid so that the nitric acid contained in the liquid is adjusted to about 200 ppm. Therefore, as nitrate nitrogen, particularly nitric acid is removed. -By confirming the decrease, removal and reduction of nitrate nitrogen are also confirmed.

(Test 1)
In Test 1, the temperature of the liquid was heated to about 31 ° C. This liquid was about pH 4. Table 1 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by Test 1.

(Test 2)
In Test 2, a liquid having a temperature of about 12 ° C. was used. This liquid was about pH 11.1. Table 2 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by Test 2.

(Test 3)
In Test 3, the liquid was boiled and then cooled and the temperature dropped to about 31 ° C. This liquid was about pH 11.2. Table 3 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by Test 3.

(Test 4)
In Test 4, the temperature of the liquid was heated to about 65 ° C. This liquid was about pH 11.0. Table 4 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by Test 4.

(Test 5)
In Test 5, the temperature of the liquid was about 31 ° C. This liquid was about pH 9.0. Table 5 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by Test 5.

(Test 6)
In this test 6, the temperature of the liquid was heated to about 39 ° C. This liquid was about pH 6. Table 6 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by this test 6.

(Test 7)
In this test 7, the temperature of the liquid was heated to about 37 ° C. This liquid was about pH 6. Table 7 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by Test 7.

(Test 8)
In Test 8, the temperature of the liquid was heated to about 32 ° C. This liquid was about pH 4. Table 8 shows the results of confirming removal / reduction of nitrate nitrogen (particularly nitric acid) by Test 8.

  As is apparent from Tables 1 to 8, by using the method for removing nitrate nitrogen according to the present invention, nitric acid (nitrate nitrogen) contained in the liquid can be removed and reduced. It can be understood that nitric acid (nitric nitrogen) contained in the liquid can be efficiently removed / reduced when the temperature of is about 30 ° C. or higher.

  Next, FIG. 2 shows an electric circuit of Example 2 that can be used in the method for removing nitrate nitrogen according to the present invention. In the second embodiment, the pair of AC electrodes 3a and 3b of the first embodiment is connected to a high-frequency switch composed of a transistor, the heating means is omitted, and other configurations are as follows. Since it is substantially the same as that of the first embodiment, the same reference numerals are given to the portions that are substantially the same as those of the first embodiment, and the description thereof is duplicated, so that the detailed description thereof is omitted.

  In the second embodiment, the heating means used in the first embodiment is omitted. Thus, even when the heating means is omitted, the liquid 2 is heated by the heat generated from the pair of AC electrodes 3a and 3b during AC electrolysis.

  In the second embodiment, the AC cord 5 is connected to the primary side of the transformer 6, and since the diode bridge circuit 11 is connected to the secondary side of the transformer 6, the AC cord 5 is supplied from the AC cord 5. The alternating current is rectified by the diode bridge circuit 11 and converted into substantially direct current.

  A high-frequency oscillator 12 is connected to the diode bridge circuit 11, and once converted into a substantially direct current via the diode bridge circuit 11, the high-frequency oscillator 12 converts the high-frequency oscillator 12.

  The high-frequency oscillator 12 is connected to a high-frequency switching command circuit 13 formed of a flip-flop circuit. The high-frequency switching command circuit 13 performs high-frequency switching, and the switched high-frequency alternating current is transmitted to the high-frequency switching command circuit 13. The signal is input to a high frequency switch composed of transistors 14a, 15a and 14b, 15b connected to the circuit 13, and is applied to the pair of AC electrodes 3a, 3b via the high frequency switch.

  As described above, as an electric circuit used in the method for removing nitrate nitrogen according to the present invention, not only the alternating current supplied from the AC cord 5 is directly used but also converted into a high-frequency alternating current. Also, the frequency of the alternating current may be changed in time.

  Next, FIG. 3 shows an electric circuit of Example 3 that can be used in the method for removing nitrate nitrogen according to the present invention. In the third embodiment, a deaeration device is provided in the first embodiment, and the other configurations are substantially the same as those in the first embodiment. Therefore, the third embodiment is substantially the same as the first embodiment. The same parts are denoted by the same reference numerals, and the description thereof is duplicated, so that the detailed description thereof is omitted.

  In the third embodiment, as the deaeration device 21 in the first embodiment, a semi-transparent film pipe (electrode cover) is disposed around each of the pair of AC electrodes 3a and 3b in the decompression chamber. . As the deaerator 21, for example, a nitrogen gas bubbling device or the like can be used in addition to the semi-transparent film pipe (electrode cover), and without using the deaerator 21, The liquid 2 may only be heated and degassed.

  As described above, by degassing oxygen in the liquid 2, the reaction between hydrogen generated from the pair of AC electrodes 3a, 3b and / or the ground electrode 4 and nitrate nitrogen is performed more smoothly. It becomes.

  Next, FIG. 4 shows an electric circuit of Example 4 that can be used in the method for removing nitrate nitrogen according to the present invention. In the fourth embodiment, the deaeration device is provided in the first embodiment, and the other configurations are substantially the same as those in the first embodiment. Therefore, the fourth embodiment is substantially the same as the first embodiment. The same parts are denoted by the same reference numerals, and the description thereof is duplicated, so that the detailed description thereof is omitted.

  In the fourth embodiment, a net-like pipe (electrode cover) made of a metal such as stainless steel or titanium is disposed around each of the pair of AC electrodes 3a and 3b as the deaeration device 31 in the first embodiment. The potential is the same as that of the ground electrode 4.

  As described above, since the deaeration device 31 is at the ground potential, oxygen generated from the pair of AC electrodes 3a and 3b is adsorbed by the deaeration device 31 formed of a net-like pipe. Is degassed, and the reaction between hydrogen generated from the pair of AC electrodes 3a, 3b and / or the ground electrode 4 and nitrate nitrogen is performed more smoothly.

  In addition, when metal ions are generated in the liquid 2 by the method for removing nitrate nitrogen according to the present invention, it is removed by using various flocculants or the like, or by using a removal filter. be able to.

It is an electric circuit which can be used for the removal method of nitrate nitrogen which concerns on Example 1 of this invention. It is an electric circuit which can be used for the removal method of nitrate nitrogen which concerns on Example 2 of this invention. It is an electric circuit which can be used for the removal method of nitrate nitrogen which concerns on Example 3 of this invention, and is the schematic which arrange | positioned the deaeration apparatus which consists of a semi-transparent film-like pipe to a pair of alternating current electrode. It is the electric circuit which can be used for the removal method of nitrate nitrogen which concerns on Example 4 of this invention, and is the schematic which arrange | positioned the deaeration apparatus which consists of a metal-made net-like pipe to a pair of alternating current electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processing tank 2 Liquid 3a, 3b A pair of AC electrode 4 Ground electrode 5 AC cord 6 Transformers 7a, 7b, 10a, 10b Diode 8 Heating means 9 Changeover switch 11 Diode bridge circuit 12 High frequency oscillator 13 High frequency change command circuit 14a, 15a , 14b, 15b Transistors 21, 31 Deaerator (electrode cover)

Claims (7)

A method of removing nitrate nitrogen contained in a liquid by electrochemical reduction and hydrogen reduction,
A pair of alternating electrodes in the liquid and at least one ground electrode disposed close to the pair of alternating electrodes;
Heating the liquid to a predetermined temperature;
While applying an alternating current between the pair of alternating electrodes to perform electrolysis and electrochemical reduction,
A method for removing nitrate nitrogen, wherein hydrogen is generated from the pair of AC electrodes and / or the ground electrode, and the hydrogen reacts with nitrate nitrogen to remove nitrate nitrogen. The pair of AC electrodes is titanium, zinc, aluminum alloy, iron, cobalt, nickel, tin, or magnesium alloy,
The method for removing nitrate nitrogen according to claim 1, wherein the ground electrode is titanium, palladium, silver, zinc, aluminum, copper, brass, carbon, nickel, iron, cobalt, or stainless steel. The ground electrode is
The method for removing nitrate nitrogen according to claim 1 or 2, wherein alternating current is applied periodically from a ground potential or is made a positive potential. The heating of the liquid is
The method for removing nitrate nitrogen according to claim 1, wherein the removal is performed by heat generated from a heating means or a pair of AC electrodes. The predetermined temperature is
The method for removing nitrate nitrogen according to claim 1, wherein the temperature of the liquid is approximately 30 ° C. or higher. The liquid is
The method for removing nitrate nitrogen according to claim 1, wherein the oxygen contained is degassed. The method for removing nitrate nitrogen according to claim 1, wherein the ground electrode is set to a positive potential for several minutes to several hours for the decomposition of ammonia generated at the end of the decomposition of nitrate nitrogen.

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