JP2007105673A - Treating method and treating apparatus of waste water containing nitrate nitrogen and electrolytic cell for treating waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treating method and a treating apparatus by which electric power consumption can be reduced and to provide an electrolytic cell therefor in waste water treatment in which nitrate nitrogen-containing waste water that is effective in waste water treatment of high concentration and a small scale is subjected to electrolytic treatment to produce ammonia and chlorine and then produced ammonia and chlorine are made to react with each other to carry out denitrification. <P>SOLUTION: In the nitrate nitrogen-containing waste water treatment, a chlorine ion source compound is added to the nitrate nitrogen-containing waste water and electrolytic treatment is carried out by using a non-diaphragm electrolytic cell and thereby hypochlorite ion formed at an anode and ammonium ion formed by electrolytic reduction of nitrate ion at a cathode are made to react to remove nitrogen portions in the waste water. In this waste water treatment, iron is used as the cathode of the electrolytic cell and thereby reduction reaction due to dissolution of the cathode material is utilized together with the electrolytic reduction reaction and produced ammonia and chlorine are made to react with each other to carry out denitrification due to reduction of the nitrate nitrogen components in the waste water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method and an apparatus for treating wastewater containing nitrate nitrogen, which is effective for high-concentration, small-scale wastewater treatment, and denitrifying wastewater containing nitrate nitrogen by electrolysis, and an electrolytic cell used therefor About.
More specifically, the present invention is effective for high-concentration, small-scale wastewater treatment. The wastewater containing nitrate nitrogen is electrolyzed to produce ammonia and chlorine, and the produced chlorine and ammonia are further reacted to remove it. TECHNICAL FIELD The present invention relates to a treatment method and apparatus that can efficiently reduce the amount of electricity used in wastewater treatment for nitriding, and an electrolyzer used therefor.

Wastewater containing nitrate nitrogen components is difficult to treat by the coagulation sedimentation method and other chemical additions, and is biologically treated exclusively by anaerobic bacteria.
Since the biological treatment method is performed by two steps, a nitrification step for converting ammonia nitrogen to nitrate nitrogen and a denitrification step for converting nitrate nitrogen to nitrogen gas, two different reaction tanks are required. However, since a very long processing time is required, there is a problem that the processing efficiency is extremely poor.

In addition, in this biological treatment method, a large-capacity anaerobic tank is required in order to retain denitrifying bacteria, and there is a problem that the equipment construction cost increases and the installation area of the apparatus increases.
Furthermore, the activity of the denitrifying bacteria is significantly affected by the ambient temperature environment, components contained in the water to be treated, and the like.
Therefore, especially in the winter when the temperature is low, the activity is reduced, and as a result, the denitrification action is lowered and the treatment efficiency becomes unstable.

In addition to this, in recent years, the development of effective and simple treatment methods has been increasing along with stricter wastewater treatment standards such as the total amount of nitrogen in wastewater being regulated.
In particular, there is a need for a treatment method that can meet the needs of high-concentration, small-scale wastewater treatment.
In recent years, a method for treating nitrate nitrogen-containing wastewater using electrolysis has been proposed as a method for dealing with it.
Japanese Patent No. 3530511 Electrochemistry, 70, No. 2 (2002), N HIRO, T KOIZUMI, T RAKUMA, D TAKAOKA, K TAKIZAWA

The method is disclosed in Non-Patent Document 1 or the like, which reduces nitrate ions (NO ₃ ⁻ ) at the cathode of the electrolytic cell to generate oxalate ions (NO ₂ ⁻ ), and then the NO ₂ ^−. Is further reduced to produce ammonia, while chlorine or active oxygen is produced at the anode, and the wastewater is denitrified by reacting the produced ammonia with chlorine or active oxygen to turn ammonia into nitrogen. This is also disclosed in Patent Document 1 as the prior art.

In the proposed method for treating wastewater containing nitrate nitrogen using electrolysis, in addition to the generation of chlorine or active oxygen on the anode side, the nitrite ions produced on the cathode side diffuse to the anode side, where A reverse reaction that oxidizes to generate nitrate ions also occurs as a side effect, causing a problem of reducing nitrogen removal efficiency.
Furthermore, on the cathode side, chlorine generated at the anode diffuses to the cathode side, and a reverse reaction that is reduced there to generate chlorine ions also occurs as a side effect, resulting in a problem of reducing nitrogen removal efficiency. Yes.

As described above, in this method for treating nitrate-nitrogen-containing wastewater, electric energy is also consumed in side reactions and is inefficient.
A technique for solving this problem has already been proposed in Patent Document 1, which uses an electrolytic cell partitioned into a cathode chamber and an anode chamber with an ion exchange membrane as a diaphragm, and drains containing nitrate nitrogen. After supplying ammonia to the cathode chamber and performing electrolysis to produce ammonia, the wastewater in which the ammonia is dissolved is moved to the anode chamber, and nitrogen is produced by reacting ammonia with hypochlorous acid or oxygen produced in the anode chamber. This is a method of denitrification.

By the way, in the denitrification method by electrolysis using the ion exchange membrane proposed in Patent Document 1, electrolysis and nitrogen formation reaction from ammonia are alternately performed, and the treatment of waste water containing nitrate nitrogen is performed. Are intermittent and discontinuous.
In this method, the diaphragm is present as described above, and a pump for transferring the processing liquid from the cathode chamber to the anode chamber is installed between the cathode chamber and the anode chamber.
As described above, in the case of denitrification by electrolysis using a diaphragm, it is inevitable that the structure of the apparatus and the processing operation become complicated, which is not satisfactory.

Therefore, the present inventor takes advantage of the drainage treatment by electrolysis described above, and takes advantage of the simple structure and simple operation of the method of denitrifying wastewater containing nitrate nitrogen using electrolysis with a diaphragm. At the same time, we sought to develop an efficient treatment method for wastewater containing nitrate nitrogen that can reduce waste of electrical energy as much as possible.
As a result, the present inventor, for example, when aluminum that is difficult to dissolve in a simple ammonia solution of around 1000 ppm of ammonia nitrogen is applied with a charge as a cathode in addition to that, specifically, ammonia in the presence of nitrate nitrogen The present inventors have found an unexpected phenomenon of forming a local battery and easily dissolving nitrate ions while reducing them under the electrolysis conditions in which N is generated.

In this case, the amount of electricity wasted due to the reverse reaction of generating nitrate ions or the reverse reaction of generating chloride ions by releasing electrons along with the dissolution and reducing the nitrate nitrogen component. It was also found that it can be compensated apparently.
Then, the present inventor has developed a new wastewater treatment technology including nitrate nitrogen that makes it possible to efficiently treat and denitrify nitrate nitrogen containing wastewater using the facts found. Successful and already filed a patent application (Japanese Patent Application No. 2005-247774).

The applied wastewater treatment technology is such that a chlorine ion source compound is added to wastewater containing nitrate nitrogen, and electrolytic treatment is performed using a diaphragm membrane electrolytic cell equipped with a conductor cathode and an anode for chlorine generation. In the treatment technology of wastewater containing nitrate nitrogen which reacts with hypochlorite ions generated at the anode and ammonium ions formed by electrolytic reduction of nitrate ions at the cathode to denitrify,
The cathode of the electrolytic cell is aluminum or an alloy containing it as a main component, and drains by reacting hypochlorite ions and ammonium ions, which are generated by using the electrolytic reduction reaction together with the reduction reaction by dissolving the cathode material. It is characterized by denitrifying by reducing the nitrate nitrogen component therein.

The above-mentioned wastewater treatment technology developed and patented by the present inventor can compensate for the amount of electricity wasted during electrolytic treatment by dissolving aluminum, and can efficiently treat nitrate nitrogen-containing wastewater. It is excellent.
However, on the other hand, aluminum hydroxide sludge is generated with the dissolution of aluminum, and the amount of generation increases as the amount of electricity compensated increases.
Furthermore, in order to discharge the wastewater after the wastewater treatment, it is necessary to avoid water pollution, and for that purpose, it is necessary to separate the aluminum hydroxide sludge by solid-liquid separation by filtration or the like. It has been found that the filterability is poor as it is, and additional means such as aging to improve the crystal structure are necessary to improve it.

Therefore, the present inventor is a metal other than aluminum and, like aluminum, dissolves while forming a local battery and easily reducing nitrate ions under electrolytic conditions in which ammonia is generated in the presence of nitrate nitrogen. As a result of diligent efforts to find a metal that can compensate for the amount of electricity wasted during the electrolytic treatment, it was found that iron has similar properties.
It was also found that iron was less dissolved than aluminum, and as a result, less sludge was generated.
It was also found that the generated sludge has better filterability than aluminum hydroxide sludge.

Therefore, the present invention makes use of the advantages of wastewater treatment by electrolysis in wastewater treatment technology containing nitrate nitrogen that is denitrified by reacting hypochlorite ions produced by electroless membrane electrolysis with ammonium ions. Therefore, it is an object of the present invention to provide an efficient device that can reduce waste of electric energy as much as possible.
It is also an object of the present invention to provide a treatment technique in which the amount of sludge generated during electrolysis is small and the generated sludge has good filterability.

The present invention provides a method and apparatus for treating wastewater containing nitrate nitrogen and the electrolytic cell for wastewater treatment for achieving the above object, and the former treatment method is a wastewater containing nitrate nitrogen. A hypochlorite ion produced at the anode by adding a chlorine ion source compound to the substrate and subjecting it to an electrolytic treatment using a non-diaphragm electrolytic cell equipped with a conductor cathode and an anode for generating chlorine, and a cathode In the method for treating wastewater containing nitrate nitrogen, which denitrifies by reacting ammonium ions formed by electrolytic reduction of nitrate ions in
The cathode of the electrolytic cell is iron, and the nitrate nitrogen component in the waste water is reduced by reacting hypochlorite ions and ammonium ions, which are produced by using the electrolytic reduction reaction together with the reduction reaction by dissolving iron. This is characterized by denitrification.

In addition, a treatment apparatus for wastewater containing nitrate nitrogen uses a non-diaphragm electrolyzer equipped with a conductor cathode and an anode for chlorine generation, adds a chlorine ion source compound, electrolyzes it, and produces it at the anode. A wastewater treatment apparatus containing nitrate nitrogen that reacts with hypochlorite ions and ammonium ions formed by electrolytic reduction of nitrate ions at the cathode to denitrify,
The cathode of the electrolytic cell is iron, and the nitrate nitrogen component in the waste water is reduced by reacting hypochlorite ions and ammonium ions, which are produced by using the electrolytic reduction reaction together with the reduction reaction by dissolving iron. This is characterized by denitrification.

And it is preferable to employ | adopt the following in the processing method and processing apparatus of these waste_water | drain.
(1) Use scrap pieces for the iron constituting the cathode
(2) A stainless steel porous plate or a titanium alloy porous plate is used as a current collector for contacting a scrap of iron constituting the cathode to supply a direct current.
(3) A structure in which an iron cathode piece exists between the anode for generating chlorine and the current collector for supplying direct current.
(4) As a cathode for generating chlorine, a ruthenium oxide layer, a composite oxide layer containing the same, or a composite oxide material layer of platinum and iridium with a platinum / iridium weight ratio of 3/7 is coated on the surface. Using a porous titanium plate
(5) The total amount of chlorine ions of the chlorine ion source compound added to the waste water is 0.5 to 1.5 in molar ratio with respect to the amount of nitrate nitrogen component in the waste water before the start of electrolysis.

Furthermore, the electrolytic cell for wastewater treatment according to the present invention is a rod-shaped cathode current collector, a resin porous cylindrical inner cage arranged at intervals around which a cathode piece made of iron can be filled, and narrow around it. A porous cylindrical anode arranged with a gap, a resin-made porous cylindrical basket further arranged with a narrow gap around the porous anode, and arranged at intervals around which the cathode pieces can be filled More preferably, the porous cylindrical cathode current collector is disposed, and further, a resinous porous cylindrical outer cage disposed with a narrow gap around the porous cylindrical cathode current collector is disposed. The apparatus adopts the structure of the electrolytic cell, and reacts hypochlorite ions and ammonium ions, which are produced by using both the electrolytic reduction reaction and the reduction reaction by dissolving the cathode material, thereby causing the nitrate nitrogen component in the waste water to react. More preferably, denitrification is carried out by reducing.

The method and apparatus for treating wastewater containing nitrate nitrogen according to the present invention treats wastewater containing nitrate nitrogen by electrolysis without using a diaphragm, as compared to the case of using a diaphragm. The device structure is simple and the processing operation is simple.
Furthermore, in the present invention, the nitrate nitrogen component can be reduced as the iron dissolves, so that the amount of electricity wasted by the reverse reaction that generates nitrate ions or the reverse reaction that generates chlorine ions is compensated apparently. In the present invention, nitrate nitrogen-containing wastewater can be efficiently treated and denitrified.

In the present invention, the amount of iron dissolved in the cathode is the same as that in the case of aluminum used in the above-described wastewater treatment technology containing nitrate nitrogen, which the inventor has developed and has already applied for a patent. In comparison, the amount of dissolution is small, and therefore the amount of sludge generated is also small.
Moreover, by-product sludge has better filterability than aluminum and can be easily separated without using additional means.
In the wastewater treatment method and treatment apparatus of the present invention, it is a matter of course that the high concentration and small scale wastewater treatment needs, which are the advantages of wastewater treatment by electrolysis, can be met.

In the following, the best mode for carrying out the present invention will be described in detail with reference to FIG. 1 and FIG. 2, but the present invention is not limited in any way by this embodiment, and claims Needless to say, it is specified by.
FIG. 1 shows an overall view of a preferred wastewater treatment apparatus of the present invention, and FIG. 2 shows a preferred non-diaphragm electrolytic cell used in a wastewater treatment apparatus.

In FIG. 1, nitrate nitrogen-containing waste water a is supplied to a circulating liquid tank 2 by a supply pipe 10 and then circulated and supplied to an electrolytic tank 1 by a circulating pump 5, where current is supplied by an anode 15 and a cathode. And constant current electrolysis.
During the electrolysis, the pH of the liquid to be treated rises due to the production of ammonium ions. Therefore, if necessary, sulfuric acid in the additive tank 3 is supplied to the circulating liquid tank 2 by the additive pump 6 to the drainage a. Add and adjust pH of waste water a.

In that case, in order to generate chlorine during electrolysis, a chlorine ion source compound such as sodium chloride is added to the circulating liquid tank from the liquid supply pipe 10 or the like.
The addition amount of the chlorine ion source compound is preferably 0.5 to 1.5 in terms of molar ratio with respect to the amount of nitrate nitrogen component in the waste water before the start of electrolysis.
It should be noted that nitrate nitrogen in the waste water there is not only nitrate nitrogen, but also nitric acid and ammonia which are intermediate products until nitric acid is reduced to nitrogen. In such a case, those nitrogen components are also included.

The electrolysis generates chlorine at the anode and ammonia is generated at the cathode. Nitrogen-containing waste water a is denitrified by generating nitrogen by reacting both.
The exhaust c such as nitrogen generated at this time is guided to the gas-liquid contact chamber 4 through the exhaust pipe 17 and is washed when ammonia, chlorine or the like, which is an intermediate product, is accompanied in the exhaust c. After being removed, it is discharged by the pump 7 into the atmosphere.
For the cleaning, a part of the nitrate nitrogen-containing waste water a supplied to the circulating liquid tank 2 is diverted and used.

FIG. 2 illustrates a diaphragmless electrolyzer 1 that is preferable for use in the wastewater treatment apparatus of the present invention as described above. The electrolyzer 1 is made of an insulating resin and has a cylindrical outer cage 21. In addition, a porous and cylindrical cathode current collector 14b is disposed, and a porous cylindrical inner cage 22 made of an insulating resin is disposed inside thereof.
Further, a porous cylindrical anode 15 is disposed inside thereof, a porous cylindrical inner cage 23 made of an insulating resin is disposed inside thereof, and a rod-shaped cathode current collector 14a is disposed at the center thereof. Be placed.

As for the shape of the electrolytic cell 1, a cylindrical shape as shown in FIG. 2 is preferable, but a rectangular tube shape may be used, and they can be sequentially arranged from the outer outer basket to the inner inner basket. It should be similar.
In addition, in the case of a rectangular tube shape, it is sufficient if it is a triangle or more that can form it.
In the electrolytic cell 1, there is a wide annular gap between the cathode current collector 14 b and the resin middle basket 22, and a cathode material piece is inserted into this gap.

In the present invention, iron is used for the cathode material, and various iron materials can be used for the iron without any particular limitation. Pure iron, carbon steel, and iron are the main components. Examples include alloy steel.
An iron piece cut to a size of about 25 × 25 mm to 150 × 150 mm is inserted into the gap to form a cathode piece.
Further, an annular gap similar to the above is also present between the cage 23 and the cathode current collector 14a, and an iron piece similar to the above is inserted into this gap to form a cathode.

The cathode current collector material used in the electrolytic cell is preferably made of stainless steel or titanium alloy, and its structure is preferably a porous material such as a net or a plate-like body having a number of punching holes. It is preferably cylindrical.
The anode material is made of titanium coated with a ruthenium oxide layer, a composite oxide layer containing the same, or a platinum and iridium composite oxide layer having a platinum / iridium weight ratio of 3/7. A porous plate-like body is good, and it is preferable that it forms a cylindrical shape.
The porous plate forming the anode is also preferably a porous plate such as a plate having a net or punching holes, and is preferably cylindrical.

The middle basket 22 and the inner basket 23 made of an insulating resin need to move freely in the drainage a in the electrolytic cell, and have a cylindrical porous body.
The outer cage 21 made of insulating resin may also be a porous cylinder, but in that case, it is necessary to further store it in a container that does not leak so that liquid does not leak from the outer cage. .
As for the three resin cages, an integrally molded one is preferable because it has a stable structure without moving between each other. However, the three cages are manufactured individually and have the positional relationship shown in FIG. In this case, it is preferable to adhere and fix.

The annular gap between the cathode current collector 14b and the resin-made middle basket 22 needs to have a width that can be filled with the iron piece, which is a cut cathode piece, depending on the size of the iron piece. Specifically, about 10 to 200 mm is preferable.
The annular gap between the cathode current collector 14a and the resin inner cage 23 is also filled with iron pieces in the same manner as described above, and therefore requires the same width.

As for the iron piece filled in the annular gap, an unused piece may be cut and used, but a scrap piece is sufficient, and its size is preferably about 25 to 100 mm.
As the scrap piece, specifically, a cut piece, a press punched piece, a cutting waste, or the like can be used. In the case of a cut piece or a press punched piece, further cutting is performed as necessary to obtain the above-mentioned size. become.
Note that the annular gap and the shape and size of the iron piece are preferably selected in consideration of the necessity of supplementation during electrolysis.

The inner cage 23 and the inner cage 22 are arranged adjacent to each other, and the interval between the inner cage 23 and the inner cage 22 may be any width as long as the cylindrical anode 15 can be arranged without contacting the inner and middle cages. Is preferably about 0.5 to 50 mm.
In particular, in this case, it is preferable to suppress the voltage increase due to the electrical resistance of the drainage as much as possible. For this reason, it is preferable that the width is as narrow as possible.
The outer basket 21 and the cathode current collector 14b are also disposed adjacent to each other, and there may be a gap that can be disposed without contact between the outer basket 21 and the cathode current collector 14b.

  The outer cage 21, the inner cage 22 and the inner cage 23 are all made of resin, and various materials can be used without limitation as long as the material is an insulating resin. Examples include PE, polypropylene (PP), polyvinyl chloride (PVC), and corrosion-resistant thermosetting resin molded products (FRP) such as bisphenol and epoxy containing glass fiber.

The treatment operation of nitrate nitrogen-containing wastewater using the wastewater treatment apparatus of the present invention having the electrolytic cell 1 shown in FIG. 2 will be described in detail below.
The nitrate nitrogen-containing waste water a is first supplied from the supply pipe 10 to the circulating liquid tank 2 and then supplied to the electrolytic tank 1 by the circulating pump 5 and electrically connected to the cathode current collectors 14a and 14b. Electrons are supplied at the cathode of the iron piece, and nitrate nitrogen (NO ₃ —N) is first reduced to nitrite nitrogen (NO ₂ —N) and further reduced to produce ammonia.
The reaction formula is as shown in the following formulas (1) and (2).
NO ₃ ⁻ + H ₂ O + 2e ⁻ → NO ₂ ⁻ + 2OH ⁻ Formula (1)
^{_{NO 2 - + 5H 2 O +}} 6e - → NH 3 + 7OH - Equation (2)
It is known that the concentration of oxalate ion and ammonium ion increases when the pH of the wastewater rises above 7.

On the other hand, in the anode 15, chlorine ions are oxidized to generate chlorine, and the chlorine and water react to generate hypochlorous acid.
The produced hypochlorous acid reacts with ammonia to produce nitrogen, whereby the nitrate nitrogen-containing waste water is denitrified and purified.
In addition, the exhaust c of nitrogen gas (N ₂ ) generated by the reaction of ammonia and chlorine in the electrolytic cell 1 is difficult to avoid accompanying with ammonia or chlorine. A part of the nitrate nitrogen-containing waste water circulated between the circulating liquid tank 2 and the electrolytic tank 1 is preferably supplied to the gas-liquid contact chamber 4 to wash the exhaust, and then discharged. .

Since there is no diaphragm in the electrolytic cell used in the present invention, unlike the electrolytic cell having the diaphragm, oxalate ions, ammonia and chlorine generated by electrolysis can freely move.
That is, oxalate ions and ammonia generated at the cathode can move to the anode side, and conversely, chlorine generated at the anode can move to the cathode, causing a reverse reaction at the moved electrode and wasting electrical energy. Will do.

The present invention apparently avoids this waste without the use of a diaphragm, which is due to the local battery being produced by melting of the cathode iron.
That is, at the cathode, a local battery is produced by the dissolution of iron, and a reduction reaction can be performed in excess of the amount of electricity supplied from the used external power source, so that nitrite nitrogen and ammonia can be produced. As a result, electric energy wasted due to the reverse reaction such as nitric acid generation that occurs is compensated.
Furthermore, also in the reverse reaction of generating chlorine ions from chlorine at the cathode, the waste of electric energy supplied from an external power source is compensated and reduced by using electricity generated by dissolving iron in the same manner. It will be.

In the present invention, as described above, the chlorine ion source compound is used for decomposing ammonia generated by electrolyzing wastewater containing nitrate nitrogen by chlorine generated by electrolysis and generating chlorine, The amount used is preferably such that the total amount of chloride ions is 0.5 to 1.5 in molar ratio with respect to the amount of nitrate nitrogen component in the waste water before the start of electrolysis.
The nitrate nitrogen in the waste water here is not limited to nitrate nitrogen. In addition, nitric acid and ammonia, which are intermediate products until nitric acid is reduced to nitrogen, coexist. In such a case, those nitrogen components are also included.
Since the pH of the wastewater during electrolysis gradually increases due to the generation of ammonia, it is preferable to measure the pH while adding sulfuric acid and maintain it around 7 in order to avoid the reverse reaction at the anode.

As described above, even if sulfuric acid is added and the pH is measured by a pH meter and controlled to around neutral 7, the local pH fluctuation in the vicinity of the electrode cannot be made zero.
Therefore, at pH 7, it may become 7 or less locally, so that the solubility of chlorine gas decreases, the loss of chlorine ions increases, and the release of harmful chlorine gas increases.
Therefore, in order to avoid the loss of chlorine ions, it is optimal to maintain the pH at 8-9. In this case, the solubility of iron is lowered and the current efficiency is lowered. It is preferable to maintain around 7.

In the present invention, sludge is generated by dissolving the cathode as in the invention for which the patent application has been filed. However, in cases where the subsequent process of wastewater treatment is adversely affected, the sludge is separated using a filtration device. It is effective to use various known means.
The sludge generated in the present invention is iron hydroxide or iron oxide sludge. The amount of generated sludge is smaller than that of aluminum hydroxide sludge generated when aluminum is used, the filterability is good, and it is easy to handle.
Furthermore, it has been found that this sludge is magnetic depending on the processing conditions, and in this respect, the separation property is excellent.

In the embodiment shown in FIG. 1 and FIG. 2, iron is used for the cathode and a cathode current collector is used for connecting the power source to the cathode. As described above, the alloy can be used.
In this case, the main component is 80% or more of iron, preferably 95% or more.
Examples of such iron alloys include Fe—Cu alloys, Fe—Mn alloys, Fe—Si alloys, and the like.

In the wastewater treatment electrolytic cell used in the wastewater treatment apparatus of the present invention, it is of course possible to connect the power source directly to the cathode without using the cathode current collector.
In that case, the cathode is not an aggregate of small cathode pieces, but a single iron plate or iron bar.
FIG. 3 shows an electrolyzer for wastewater treatment using a cylindrical iron plate as a cathode, and a power source can be directly connected to the cathode, and it is not necessary to use a cathode current collector.
In the electrolytic cell of FIG. 3, an iron plate is used for the cathode, and it will be consumed in a short period of time. Therefore, it should be used continuously for a long time by using a rod or a wire with a certain thickness instead of the plate. Can do.

In the following, a plurality of examples and comparative examples of the present invention will be shown, but the present invention is not limited by these examples, and it is needless to say that the present invention is specified by the claims. Absent.
First, Example 1 in which denitrification of wastewater containing nitrate nitrogen was performed using the wastewater treatment apparatus shown in FIG. 1 and the non-diaphragm electrolytic cell shown in FIG.
In the electrolytic cell 1, a scrap piece obtained by cutting a 1.6 mm thick carbon steel sheet for structural use into a size of about 30 × 50 mm at the cathode, and 1.5 mmt × opening 5 mmH with ruthenium oxide baked on the anode. A × 10 mmL titanium lath plate was used.

As the waste water containing nitrate nitrogen, one containing nitrate nitrogen as N and 1077 mg / L and chloride ion as 2180 mg / L (Molar ratio of Cl ⁻ / NO ₃ ⁻ = 0.88) was used.
The waste water a was received from the supply pipe 10 into the circulating liquid tank 2 and electrolyzed at a constant current of 380 A (batch electrolysis) while being circulated at 70 L / min by the circulation pump 5.
In addition, the salt of the chlorine ion source compound was also received from the supply pipe 10 into the circulating liquid tank 2 and the concentration was as described above.
The cathode of the carbon steel piece was accommodated in a cathode current collector 14b having a cylindrical shape with a wire diameter of 2 mm × 25 mesh SUS304 arranged in an outer cage 21 made of polyethylene.
Furthermore, it was also accommodated in an inner basket 23 made of polyethylene disposed inside the anode 15 made of a cylindrical titanium lath plate disposed in the central portion of the current collector.

During the electrolysis, the pH of the wastewater rises due to the production of ammonium ions, so 25% sulfuric acid contained in the additive tank 3 is added to the wastewater by the additive pump 6 to adjust the pH. The set value of the pH was 7, and was automatically adjusted by adding the sulfuric acid.
The exhaust c such as nitrogen (N ₂ ) generated by the reaction of ammonia and chlorine in the electrolytic cell 1 is difficult to avoid that ammonia or chlorine is accompanied by nitrogen. The contact chamber 4 is supplied with a part of the nitrate nitrogen-containing waste water circulated between the circulating liquid tank 2 and the electrolytic tank 1 used in the previous denitrification treatment, and then washed there. Release into the atmosphere.

Then, the electrolyte in the first embodiment, the waste water composition and the reaction formula (1) (2) nitrate ion reducing based on (NH ₃ generated) (reduction also calculated as current efficiency by cathodic dissolution of the) current efficiency with respect to time Sequential measurements were made according to the course.
The results are as follows.
The drainage composition 40 minutes after the start of electrolysis was ammonia nitrogen [NH ₃ —N (as N)] 0.8 mg / L, nitrite nitrogen [NO ₂ —N (as N)] 0 mg / L, nitrate Nitrogen [NO ₃ —N (as N)] was 637 mg / L, and the current efficiency for nitrate ion reduction (NH ₃ production) was 105%.

The drainage composition 80 minutes after the start of electrolysis was ammonia nitrogen (as N) 1.7 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 323 mg / L, nitric acid The current efficiency for ion reduction (NH ₃ production) was 90.4%.
The wastewater composition 120 minutes after the start of electrolysis is ammonia nitrogen (as N) 1.7 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 135.5 mg / L The current efficiency for nitrate ion reduction was 75.6%.
The drainage composition 160 minutes after the start of electrolysis was ammonia nitrogen (as N) 0.8 mg / liter, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 49.7 mg / L The current efficiency for nitrate ion reduction was 62.0%.

And when it measured about iron content in waste_water | drain, it was 127 mg / L.
In addition, the measurement is performed by dissolving sludge for waste water 160 minutes after the start of electrolysis.
Moreover, when it measured about the case where it electrolyzed by making aluminum into a cathode on the same conditions, content of aluminum was 2470 mg / L.

In this example, the same apparatus as in Example 1 was used, and electrolysis was performed in the same manner as in Example 1 except that the pH set value was set to 10. The drainage composition and nitrate ion reduction (NH ₃ production) were performed in the same manner as in this case. ) (Reduction by dissolution of the cathode is also converted into current efficiency) was sequentially measured over time.
The results are as follows.
The drainage composition 40 minutes after the start of electrolysis is ammonia nitrogen (as N) 17.5 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 657.2 mg / L The current efficiency for nitrate ion reduction (NH ₃ production) was 87.0%.

The drainage composition 80 minutes after the start of electrolysis was ammonia nitrogen (as N) 14.8 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 314 mg / L, nitric acid The current efficiency for ion reduction (NH ₃ production) was 85.9%.
The wastewater composition 120 minutes after the start of electrolysis is ammonia nitrogen (as N) 0.8 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 110.7 mg / L The current efficiency for nitrate ion reduction was 73.2%.

The drainage composition 160 minutes after the start of electrolysis was ammonia nitrogen (as N) 0.8 mg / liter, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 31.6 mg / L The current efficiency for nitrate ion reduction was 59.6%.
The exhaust c such as nitrogen (N ₂ ) generated by the reaction of ammonia and chlorine in the electrolytic cell 1 is difficult to avoid that ammonia or chlorine is accompanied by nitrogen. The contact chamber 4 is supplied with a part of the nitrate nitrogen-containing waste water circulated between the circulating liquid tank 2 and the electrolytic tank 1 used in the previous denitrification treatment, and then washed there. Release into the atmosphere.

[Comparative example]
In this comparative example, the waste water containing nitrate nitrogen is denitrified using the waste water treatment apparatus shown in FIG. 1 and the non-diaphragm electrolytic cell shown in FIG. 2 used in Example 1. Used a cathode current collector as a cathode without using a carbon steel piece as a cathode.
Other than that, the same waste water as Example 1 was used, and it electrolyzed on the same conditions, and processed the waste water.
The pH was adjusted in the same manner as in Example 1.

The drainage composition 40 minutes after the start of electrolysis is ammoniacal nitrogen (as N) 0.8 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 749.7 mg / L The current efficiency with respect to nitrate ion reduction (NH ₃ production) was 53.0%.
The drainage composition 80 minutes after the start of electrolysis was ammonia nitrogen (as N) 5 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 546.5 mg / L, nitric acid The current efficiency for ion reduction was 47.4%.

The drainage composition 100 minutes after the start of electrolysis was ammonia nitrogen (as N) 1 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 453.9 mg / L, nitric acid The current efficiency for ion reduction was 45.1%.
The wastewater composition 120 minutes after the start of electrolysis was ammonia nitrogen (as N) 0.8 mg / liter, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 365.8 mg / L The current efficiency for nitrate ion reduction was 43.4%.

In Example 3, drainage containing nitrate nitrogen was denitrified using the electrolytic cell shown in FIG. 3 having a structure in which a power source was directly connected to a carbon steel cathode without using a cathode current collector. An example is shown.
The electrolytic cell has a cylindrical shape, and a spacer 35 is disposed at the center thereof. A cylindrical inner cathode 31 is formed on the outer side, a cylindrical anode 32 is provided on the outer side, and a cylindrical outer cathode is provided on the outer side. 33 are arranged in order.

The spacer 35 was disposed in order to prevent the water to be treated from staying in the central portion of the electrolytic cell and to obtain a stable current efficiency by making the flow of the water to be treated that passes between the electrodes uniform.
The flow rate of the water to be treated passing through the electrolytic cell is preferably 0.05 m / sec or more, and in this example, it was set to 0.113 m / sec.
In addition, between the inner cathode 31 and the cylindrical anode 32, and between the cylindrical anode 32 and the outer cathode 33, a net-like short-circuit prevention cylinder 34 made of an insulating resin is disposed.

The specific structure of the electrolytic cell is further shown as follows.
The cathode used is a general industrial carbon steel lath plate with an outer diameter of 172 mm x 960 mmH and an outer cathode of 1.6 mmt with a mesh opening of 1.6 mmt and an aperture of 7 mmH x 14 mmL. A 7 mmH × 14 mmL general industrial carbon steel lath plate having a cylindrical shape with an outer diameter of φ200 mm × 940 mmH was used.
Further, a 1.5 mmt ruthenium oxide baked, 5 mmH × 10 mmL titanium lath plate with an outer diameter of 186 mm × 940 mmH was used as the anode.

Except that this electrolytic cell was replaced with the electrolytic cell shown in FIG. 1, a wastewater treatment apparatus similar to that shown in FIG. 1 was constructed.
Using this wastewater treatment apparatus, denitrification treatment of wastewater containing nitrate nitrogen was performed under the same conditions as in Example 1.
The results are as follows.
The drainage composition 40 minutes after the start of electrolysis is ammoniacal nitrogen (as N) 0.8 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 614.2 mg / L The current efficiency with respect to nitrate ion reduction (NH ₃ production) was 112.3%.

The drainage composition 80 minutes after the start of electrolysis is ammonia nitrogen (as N) 0 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 257.4 mg / L, nitric acid The current efficiency for ion reduction (NH ₃ production) was 99.8%.
The wastewater composition 120 minutes after the start of electrolysis was ammonia nitrogen (as N) 0 mg / L, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 92.6 mg / L, nitric acid The current efficiency for ion reduction was 77.5%.
The drainage composition 160 minutes after the start of electrolysis is ammonia nitrogen (as N) 0 mg / liter, nitrite nitrogen (as N) 0 mg / L, nitrate nitrogen (as N) 27.1 mg / L, The current efficiency for nitrate ion reduction was 63.6%.

The figure which shows one preferable specific example of the waste water treatment equipment of this invention. The figure which shows the preferable electrolytic vessel used for the waste water treatment equipment of this invention. The figure which shows the electrolytic cell of the form different from FIG. 2 used for the waste water treatment equipment of this invention.

Explanation of symbols

a Nitrate nitrogen-containing wastewater 1 Electrolysis tank 2 Liquid circulation tank 3 Additive tank 4 Gas-liquid contact chamber 10 Supply pipe 14 Cathode current collector 15 Anode 17 Exhaust pipe 21 Outer basket 22 Inside basket 23 Inside basket 23 Inside basket

Claims (13)

By adding a chlorine ion source compound to waste water containing nitrate nitrogen and subjecting it to electrolysis using a diaphragm electrolyzer equipped with a conductor cathode and an anode for chlorine generation, hypochlorite produced at the anode In a method for treating wastewater containing nitrate nitrogen, which reacts with chlorate ions and ammonium ions formed by electroreduction of nitrate ions at the cathode to denitrify,
The cathode of the electrolytic cell is iron, and the nitrate nitrogen component in the waste water is reduced by reacting hypochlorite ions and ammonium ions, which are produced by using the electrolytic reduction reaction together with the reduction reaction by dissolving iron. A method for treating wastewater containing nitrate nitrogen, characterized by denitrification. The processing method of the waste_water | drain containing nitrate nitrogen of the said Claim 1 which uses a scrap piece for the iron which comprises the cathode of the said electrolytic vessel. 2. A stainless steel porous plate or a titanium alloy porous plate is used as a current collector for contacting a scrap of iron constituting the cathode of the electrolytic cell to supply a direct current. Or the processing method of the waste_water | drain containing nitrate nitrogen of 2. The nitrate electrolysis cell according to claim 3, wherein the diaphragm electrolyzer has a structure in which a cathode of iron scrap pieces exists between an anode for generating chlorine and a current collector for supplying a direct current. A method for treating wastewater containing nitrogen. Titanium coated on the surface with a ruthenium oxide layer, a composite oxide layer containing the same, or a platinum and iridium composite oxide material layer having a platinum / iridium weight ratio of 3/7 as the anode for generating chlorine The processing method of the waste_water | drain containing nitrate nitrogen of any one of Claim 1 thru | or 4 using the porous plate-shaped body of this. The total amount of chlorine ions of the chlorine ion source compound added to the waste water is 0.5 to 1.5 in terms of molar ratio with respect to the amount of nitrate nitrogen component in the waste water before the start of electrolysis. A method for treating waste water containing nitrate nitrogen as described in 1. Electrolyze by adding a chlorine ion source compound using a diaphragm electrolyzer equipped with a conductor cathode and an anode for chlorine generation, and hypochlorite ions generated at the anode and nitrate ions electrolyze at the cathode A wastewater treatment device containing nitrate nitrogen that reacts with reduced ammonium ions to denitrify,
The cathode of the electrolytic cell is iron, and the nitrate nitrogen component in the waste water is reduced by reacting hypochlorite ions and ammonium ions, which are produced by using the electrolytic reduction reaction together with the reduction reaction by dissolving iron. Waste water treatment equipment containing nitrate nitrogen characterized by denitrification. The wastewater treatment apparatus containing nitrate nitrogen according to claim 7, wherein scrap pieces are used for iron constituting the cathode of the electrolytic cell. 9. A stainless steel porous plate or a titanium alloy porous plate is used as a current collector for making contact with iron scrap pieces constituting the cathode of the electrolytic cell to supply a direct current. An apparatus for treating wastewater containing nitrate nitrogen as described in 1. 10. The nitrate nitrogen according to claim 9, wherein the non-diaphragm electrolytic cell has a structure in which a cathode of scrap pieces exists between an anode for generating chlorine and a current collector for supplying a direct current. Including wastewater treatment equipment. As the chlorine generating anode, a ruthenium oxide layer on its surface, a composite oxide layer containing the same, or a titanium / platinum composite oxide material layer having a platinum / iridium weight ratio of 3/7 is coated. The apparatus for treating waste water containing nitrate nitrogen according to any one of claims 7 to 10, wherein a porous plate-like body is used. A rod-shaped cathode current collector, a resin-made porous cylindrical inner cage arranged at intervals around which a cathode piece can be filled, a porous cylindrical anode arranged with a narrow gap around the cage, A resin-made porous cylindrical inner cage further arranged with a narrow gap around the periphery, a porous cylindrical cathode current collector arranged with a space that can be filled with a cathode piece around it, and a narrower circumference Using an electrolytic cell with a resin porous outer cylindrical cage arranged with a gap, a chlorine ion source compound is added and electrolyzed, hypochlorite ions generated at the anode, and nitric acid at the cathode A wastewater treatment apparatus containing nitrate nitrogen that denitrifies by reacting ammonium ions formed by electrolytic reduction of ions,
Nitrate nitrogen component in waste water by reacting hypochlorite ions and ammonium ions produced by using iron pieces as the cathode pieces of the electrolytic cell and using the electrolytic reduction reaction together with the reduction reaction by dissolving the cathode material An apparatus for treating wastewater containing nitrate nitrogen, characterized in that denitrification is performed by reducing the amount of nitrogen. A rod-shaped cathode current collector, a resin-made porous cylindrical inner cage arranged at intervals around which a cathode piece made of iron can be filled, and a porous cylindrical shape arranged with a narrow gap around it An anode, a resin-made porous cylindrical inner cage further arranged with a narrow gap around the anode, a porous cylindrical cathode current collector arranged with an interval at which the cathode pieces can be filled around the anode, and Hypochlorous acid produced by combining a reduction reaction by dissolving a cathode material together with an electrolytic reduction reaction, characterized in that a resin-made porous cylindrical outer cage arranged with a narrow gap is arranged around it An electrolytic cell for wastewater treatment containing nitrate nitrogen that reacts ions and ammonium ions to reduce nitrate nitrogen in the wastewater to denitrify.

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