JP2002186972A - Method and device for electrochemically removing nitrate nitrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct electrochemical denitrification with high efficiency at low cost though denitrification of waste water is mainly conducted biologically. SOLUTION: The device is provided with an ion-permeable diaphragm and a cathode plate and an anode plate disposed parallel with the diaphragm inbetween in a treatment bath, wherein moldings made of a conductive material are packed between the diaphragm and the cathode plate, and treated water is made to flow among the moldings with DC voltage or pulse voltage applied between the cathode plate and the anode plate, thereby reducing nitrate nitrogen in the treated water into nitrogen gas, and the nitrate nitrogen in the treated water is thus removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of various types of wastewater, and more specifically, from domestic wastewater, food factories, chemical factories, petroleum plants, paper mills, semiconductor factories, and industrial waste storage sites. The present invention relates to a method and an apparatus for reducing and removing nitrate nitrogen contained in wastewater and the like.

[0002]

2. Description of the Related Art Among the so-called biological treatments, there is a biological denitrification method of converting nitrate nitrogen into nitrogen gas by anaerobic-aerobic treatment to remove nitrate nitrogen from so-called biological treatment. There is a limit to the concentration of nitric acid to be treated in order to utilize the assimilation action of reducing bacteria.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a processing method and apparatus which require a shorter processing time and a lower processing cost as compared with the biological denitrification method. Aim.

[0004]

According to a first aspect of the present invention, there is provided a treatment method comprising providing an ion-permeable diaphragm in a treatment tank, and installing a cathode and an anode electrode plate in parallel across the diaphragm. In, filling a molding molded with a material having conductivity between the cathode and the diaphragm, water to be treated is passed between the moldings, applying a DC voltage or a pulse voltage between the cathode and the anode, A method for electrochemically removing nitrate nitrogen, which reduces nitrate nitrogen contained in water to be treated and converts it into nitrogen gas or volatile nitrogen oxides to remove nitrate nitrogen contained in the water to be treated. It is. In this case, the diaphragm has a function of preventing the liquid on the cathode side from mixing the fluid with the anode and at the same time preventing a direct contact between the molded product and the anode. Specifically, a polyurethane film or a nonwoven fabric film having open cells can be used. Further, the diaphragm is preferably made of a material having no conductivity. In addition, the material of the electrode is the same as that in the Periodic Table of the Elements.
The elements and their oxides belonging to the genera A, 7A, 8A, 1B, and 2B, and mainly the elements and oxides generally called transition metals, Alloy, carbon, and a mixture of carbon and a metal or a metal oxide are also included, and all materials having conductivity can be used. The diaphragm and the anode do not directly contact each other to form a space, and the cathode and the molded product may or may not directly contact. The molding and the diaphragm may or may not directly contact.

The applied voltage is a DC voltage and a pulse voltage. In this case, the pulse voltage indicates a current having all waveforms other than the DC voltage. Further, the method of passing the water to be treated between the moldings may be either an upward flow or a downward flow.

According to a second aspect of the present invention, there is provided the treatment method according to the first aspect, wherein the molded article molded from the conductive material is formed of a metal, a metal oxide, or a mixture thereof. This is a method for electrochemically removing nitrate nitrogen, which is a flaky, spherical, or cylindrical molded product. The shape of the molded product used in the present invention is not particularly limited, and may be, for example, a flake shape, a spherical shape, a columnar shape, or the like. It can also increase ancestry and increase surface area. Kinds of metals are 3 genus A, 4 genus A, 5 genus A, 6 genus A, 7 genus A, 8 genus, 1 genus B, 2 genus B in the periodic table of elements.
And oxides thereof, which are mainly composed of elements generally called transition metals and oxides thereof, but also include alloys such as stainless steel.

According to a third aspect of the present invention, there is provided the treatment method according to the first aspect, wherein the molded article molded from the conductive material is formed of carbon and carbon and metal, or a metal oxide. This is a method for electrochemically removing nitrate nitrogen, which is a molded product molded using a mixture. There is no particular limitation on the shape of the molded product used in the present invention, for example, flaky,
Any of a spherical shape, a columnar shape and the like may be used, but fine holes may be formed on a solid surface to increase a contact area. As the material to be mixed with carbon, there are three genera A, four genera A, five genera A, six genera A, seven genera A, eight genera, one genera B, and two genera B in the periodic table of elements.
And oxides thereof, which are generally called transition metals and oxides thereof. Although carbon alone has electrical conductivity, it can be used alone, but it has been confirmed in our experiments that the incorporation of a transition metal increases the nitric acid reducing ability.

According to a fourth aspect of the present invention, there is provided a method as defined in the first aspect, wherein the water to be treated leached between the membrane and the anode is returned between the membrane and the cathode. This is the removal method. As a method of returning, a method using a circulating pump, a method using a submersible pump, a method using an air lift, a method of flowing out from the bottom between the anode and the diaphragm, and merging with the inflow line of the water to be treated can be considered, but any method may be used.

According to a fifth aspect of the present invention, there is provided the treatment apparatus according to the fourth aspect, wherein the water to be treated and the water to be returned are subjected to electrochemical removal of nitrate nitrogen. . More specifically, the water to be treated and the water to be returned are stored in a pH adjusting tank, and an acid such as hydrochloric acid, sulfuric acid, or acetic acid is added thereto, and the pH is adjusted. And a method of directly adding an acid with an injector can be considered.

According to a sixth aspect of the present invention, in the treatment apparatus, an ion-permeable diaphragm is provided in the treatment tank, and a cathode and an anode electrode plate are installed in parallel with the diaphragm interposed therebetween. This is an apparatus for electrochemically removing nitrate nitrogen, which is basically composed of a packed bed filled with a molded product formed of a conductive material.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method and an apparatus for electrochemically removing nitrate nitrogen according to an embodiment of the present invention will be described below.

First, an embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a schematic view of an apparatus for electrochemically removing nitrate nitrogen. An ion-permeable diaphragm 6 is provided in the processing tank 5, and an electrode plate of the cathode 1 and the anode 4 is installed in parallel with the diaphragm interposed therebetween, and is formed of a conductive material between the cathode 1 and the diaphragm 6. The molded article 7 is filled.

The water to be treated flows into the treatment tank 5 through the inflow pipe 2, passes through the molded product 7, and is discharged from the outflow pipe 8. If necessary, an air diffuser may be provided on the bottom surface of the molded product 7 to agitate the treated water by aeration or a circulation pump to enhance the contact efficiency between the molded product and the treated water. Further, the flow direction of the water to be treated is a downward flow in FIG. 1, but may be an upward flow.

The cathode 1 is placed in contact with a molded product, and the molded product receives a negative charge. The nitrate ions passing between the moldings are reduced by receiving a negative charge, and pass through nitrous acid.
Alternatively, it is directly converted to nitrogen gas or volatile nitrogen oxides.

On the other hand, on the anode side, nitrate ions passing through the diaphragm are concentrated, so that the cathode 1 and the diaphragm 6 are returned through the return pipe 3.
If it is returned during the period, nitric acid can be reduced efficiently. FIG. 1 shows a case where the return is performed by a submersible pump, but a method using a circulation pump or an air lift is also possible.
In addition, the position of water intake may be any of the bottom part, the surface part, and the middle part of the treatment tank, or a return pipe is installed on the bottom surface between the anode and the diaphragm of the treatment tank, and returned to the inflow pipe 2 via the circulation pump. Is also good.

The water to be treated and the water returned from the anode side can be treated without adjusting the pH. However, since the efficiency of nitric acid reduction is higher at a pH of 8 or less, the pH of the water to be treated and the water returned from the anode side are higher. After returning water is stored in a pH adjusting tank (not shown), the pH may be adjusted and flown into the processing tank 5.
Further, a static mixer (not shown) may be provided in a part of the inflow pipe 2 or the return pipe, and the acid may be directly injected from the injector.

[0018]

EXAMPLES The present invention will be further described below with reference to examples.
Table 1 shows the results of treating industrial wastewater containing nitrate ions with this device. In addition, coagulation sedimentation was performed at the same time, and the results were compared.

[0019] As a result of the experiment, 89.7% of raw water in 30 minutes treatment, 97.6% in 60 minutes treatment
% Removal rate, but little effect was seen in coagulation sedimentation.

On the other hand, in order to carry out the biological denitrification treatment of this wastewater, it is necessary to make the treated water anaerobic, which requires an anaerobic tank, and it is difficult to make the treated water having a low BOD an anaerobic state.

[0021]

As described above, when the present invention is utilized, it is possible to efficiently denitrify treated water which is difficult by the biological denitrification method. In addition, since the living thing does not participate in the treatment of the present invention, the treatment can be efficiently performed even in a wastewater containing a high concentration of nitrate ions or a treatment at a low temperature.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a processing apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 1: Cathode 2: Inflow pipe 3: Return pipe 4: Anode 5: Treatment tank 6: Diaphragm 7: Molded bed 8: Outflow pipe 9: Return pump 10: Molded article

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Zhang Court 1-35-1, Mizobata-cho, Sakado-shi, Saitama (72) Inventor Toshiki Yoshimura 642-113, Yoshida, Kawagoe-shi, Saitama F-term (reference) 4D061 DA08 DB18 DC14 EA04 EB01 EB07 EB13 EB17 EB19 EB22 EB27 EB28 EB29 EB31

Claims (6)

[Claims] 1. An apparatus in which an ion-permeable diaphragm is provided in a treatment tank, and a cathode and an anode electrode plate are provided in parallel with the diaphragm interposed therebetween, and is formed of a conductive material between the cathode and the diaphragm. The molded product is filled, treated water is passed between the molded products, a DC voltage or a pulse voltage is applied between the cathode and the anode, and nitrate nitrogen contained in the treated water is reduced to reduce nitrogen. A method for electrochemically removing nitrate nitrogen, which converts into gas or volatile nitrogen oxides and removes nitrate nitrogen contained in the water to be treated. 2. The removing method according to claim 1, wherein the molded article molded from a conductive material is a molded article molded from a metal, a metal oxide, or a mixture thereof. A method for electrochemical removal of nitrogen. 3. The removing method according to claim 1, wherein the molded article molded from a material having conductivity is a molded article molded using carbon and a mixture of carbon and metal, or a metal oxide. A method for electrochemical removal of nitrate nitrogen. 4. The method according to claim 1, wherein the water to be treated leached between the membrane and the anode is returned between the membrane and the cathode. 5. The method of electrochemically removing nitrate nitrogen according to claim 3, wherein the water to be treated and the water to be returned are adjusted to pH 8 or less. 6. An ion-permeable diaphragm is provided in the treatment tank, and a cathode and an anode electrode plate are installed in parallel with the diaphragm interposed therebetween.
An electrochemical device for removing nitrate nitrogen, which is basically composed of a packed bed filled with a molded product formed of a conductive material between a cathode and a diaphragm.