JPH09155388A - Denitrification device using biocatalyst - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide a hydrogen denitrification device capable of improving the denitrification rate and stabilizing the denitrification activity. SOLUTION: This denitrification device is an electrochemical denitrification device using a biocatalyst, and comprises a cathode on which denitrification bacteria are immobilized,
It is characterized by having an anode separated from the cathode by a diaphragm capable of blocking the movement of oxygen gas.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to urban and sewage systems,
The present invention relates to a denitrification device that can purify industrial wastewater, domestic water discharged by living, etc., and particularly nitrogen-containing oxides (NOx: nitrate nitrogen oxides) that are contained in these waters and are regarded as causative substances of pollution. The present invention relates to a denitrification device capable of efficiently decomposing and removing, i.e., denitrifying by microorganisms.

[0002]

2. Description of the Related Art Kuroda et al. (Abstracts of the 48th Annual Scientific Lecture Meeting of the Japan Society of Civil Engineers, p1268, 1993) and JP-A-5-3
Japanese Patent No. 29497 proposes a method of supplying hydrogen, which is generated by electrolysis of water, to a microorganism as a reducing power to denitrify the microorganism. In this method, a carbon electrode is soaked in an activated sludge suspension containing denitrifying bacteria for about 1 month to form a microbial membrane on the electrode. The oxygen (O ₂ ) generated at the anode is converted into CO ₂ to prevent the system from becoming oxidative.

Japanese Laid-Open Patent Publication No. 6-500258 and R.
B. Mellor et al. (Nature, vol, 355,
P717-719, 1992), oxygens involved in denitrification are taken out from microorganisms or plants, immobilized on a carrier, and further pigment substances for efficiently carrying out electron transfer to these oxygen groups, for example, A method of immobilizing methyl viologen and the like at the same time and energizing it has been proposed.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the method proposed by Japanese Patent Laid-Open No. 7 and the like, oxygen generated at the anode does not become carbon dioxide completely even if a carbon electrode is used,
Many parts dissolve in the treated water as oxygen gas, and it is easy to form an environment that is detrimental to the system by oxidizing it. It is a method of denitrification by electricity using a microorganism without using the enzyme itself. However, the electron, that is, the reducing power is not efficiently transmitted to the denitrifying enzyme in the denitrifying bacteria, and the NOx removal rate is 2 mg / 1/2.
It is extremely small, less than an hour, and is not practical. In order to further increase the denitrification rate, it is necessary to increase the cell concentration. However, this method cannot specify the type of bacteria to be immobilized (including microorganisms other than denitrifying bacteria). Cannot adjust. Since the cell concentration cannot be adjusted, there is a problem that the denitrification rate is not stable due to the difference in the inflowing treated water.

Japanese Patent Publication No. 6-500258 discloses a method of isolating a reductase of a microorganism involved in denitrification, fixing it on an appropriate carrier or electrode, and performing denitrification treatment. However, in this method, when a reductase such as a denitrifying enzyme is separated from cells or the like, the stability is usually remarkably impaired, and the denitrifying activity rapidly disappears, or disappears within three months. Not suitable. This is the effect of oxygen in the solution. Once the denitrifying enzyme is inactivated, it is difficult to reactivate it. It is said that four types of enzymes are ultimately involved in reducing NOx to N ₂ , but isolating and purifying these enzymes with high purity requires very complicated operations and costs. And there are many practical problems. In fact, one of the four denitrifying enzymes could not be isolated, so only three enzymes were used in this method. In the actual waste water, the immobilized denitrifying enzyme is quickly covered with many microorganisms existing in the environment, and N to be treated
It is considered that the contact between Ox and the denitrifying enzyme is inhibited. This is also a cause of reducing the denitrification activity.

It is an object of the present invention to provide a denitrification device which solves the above problems and improves the denitrification rate and stabilizes the denitrification activity.

[0007]

The above-mentioned object is an electrochemical denitrification device using a biocatalyst, which comprises a cathode on which denitrification bacteria are immobilized and a cathode which is provided with a diaphragm capable of blocking the movement of oxygen gas. It is achieved by a denitrification device for decomposing and removing nitrogen-containing oxides from water containing nitrogen-containing oxides, which has an isolated anode.

Further, it is more preferably achieved by making the cathode hold an electron transfer substance in the denitrification apparatus.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION There is no limitation on the type of denitrifying bacterium immobilized on the cathode. For example, Rhodobacter sha may be used.
eroides f.s. denitrificans,
Pseudomonas denitrificans
(ATCC-13867), P. stutzeri
(ATCC-17588), P. aeruginos
a, Bacillus spp, Achromobac
ter spp, Thiobacillus deni
trificans, Thiophaera sp
p, and mixed bacteria thereof can be used. Among these, especially Rhodobacter sphaero
ides f.s. denitrificans has a denitrifying ability, and also has a remarkably high ability to reduce BOD in the aquatic environment in which it grows. Further, it is preferable because there is no risk of pathogenicity.

As a method for immobilizing the denitrifying bacteria on the cathode, the denitrifying bacteria may be once fixed on a carrier and attached to the electrode with this carrier, or the bacteria may be directly immobilized on the electrode.

Various known methods can be used to fix these denitrifying microorganisms to a carrier. For example, polyvinyl alcohol (PV
The PVA-freezing method using A) is preferred. At that time, PV
The A gel is not easily broken when the final concentration of PVA is 10 to 11%.

As a method for immobilizing the bond to the electrode, glutaraldehyde, N,
N-ethylene bismaleimide, bisdiazobenzidine,
There is a method of binding using a well-known substance such as N, N-polymethylenebisiodoacetamide and isocyanic acid derivative.

The amount of immobilized cells is 10 ⁵ per 1 cm ² of electrode.
About 10 to ¹² is suitable.

When the cells are immobilized on a carrier and attached to the electrode, the cells immobilized may be brought into close contact with the electrode or may be slightly spaced. For example, there is a method in which the PVA gel in which the above-mentioned denitrifying bacteria are entrapped and immobilized is shaped like a cap covering the electrode and the electrode is covered. At this time, the PVA gel may be fixed to the electrode with an appropriate supporter such as a net made of vinyl or tetron or a cellulose film so that the PVA gel does not separate from the electrode.

As the electron transfer material, known materials can be appropriately selected and used, but those which are not toxic to denitrifying bacteria are preferable. Examples of non-toxic substances are curcumin,
Safranin, neutral red, methyl red and the like can be mentioned.

The electron transfer substance is directly cross-linked as described in JP-A-6-500258, or is directly immobilized on the electrode surface with epoxy, cyanbromide, diisocyanate, carbodiimide, glutaraldehyde or the like via a spacer. Alternatively, it may be entrapped and immobilized together with the denitrifying bacteria. The immobilized amount of the electron transfer material is: bacterial weight: weight of the electron transfer material = 10: 1 to 1: 5
The degree is appropriate. It was confirmed that by immobilizing the electron transfer substance together with the denitrifying bacteria in the electrode or polymer gel, the reducing power is rapidly transferred to the denitrifying enzyme group in the bacterial cells, and the denitrifying activity can be significantly improved. did.

The materials of the cathode and the anode may be ordinary ones, for example, carbon electrodes may be used. The distance between the cathode and the anode is preferably about 5 to 40 mm in order to keep the voltage low.

In order to suppress the oxidation of the system due to the generated oxygen gas, a diaphragm is attached to the anode so that the reduction site can be spread from the cathode surface to the peripheral portion and the reaction rate can be increased. As the diaphragm, a dialysis membrane such as a cellulose film, tetron, fluorosulfonic acid membrane, nylon, cotton cloth, non-woven cloth and the like are used. Originally, the diaphragm is most preferably impermeable to liquids and oxygen molecules, but nylon or cotton cloth, which only has a function of not diffusing acid bubbles generated from the anode, is also effective. A film thickness of about 5 μm to 2000 μm is suitable, but a thickness of about 10 μm to 300 μm is preferable.

The distance between the diaphragm and the surface of the anode is 0.5 mm to 3 mm.
It is about 0 mm, preferably about 10 mm.

The energization condition is that the current density is 0.1 to 1
A range of about mA / cm ² and a voltage of about 1 to 10 V are preferable. The pH of the liquid to be treated is maintained at a pH at which the activity of the denitrifying bacteria is sufficiently exhibited, for example, pH 5 to 9, and for that purpose, an acid or an alkali is appropriately added. However, pH adjustment is
Limited only when the reaction is not stable and usually not needed.

In the device of the present invention, it is possible to bring the entire peripheral portion of the cathode into a reductive state by using the diaphragm. As a result, the reduction site was enlarged and the denitrification activity was improved.

A reductase such as a denitrifying enzyme is passed through air (oxygen).
Since it is easily deactivated and loses stability when directly contacted with, the denitrifying bacteria having a high denitrifying activity are directly immobilized on the electrode surface as bacterial cells or entrapped by PVA or the like. This stabilizes the activity of the denitrifying enzyme group and extends the enzyme life. Further, since the denitrifying bacteria grow on the electrode or in the entrapping immobilization carrier, new denitrifying enzyme can be replenished, and the denitrifying reaction can be performed for a long time as compared with the case where only the enzyme is immobilized. Further, the labor for isolation and purification of the denitrifying enzyme can be omitted, and the cost can be greatly reduced.

An electron transfer substance is simultaneously immobilized together with the denitrifying bacteria. As a result, the reducing power of nascent hydrogen (H) generated by electrolysis of water is quickly transmitted to the denitrifying enzyme of living bacteria, and the reduction rate of NOx to N ₂ , that is, the denitrification rate is remarkably improved. Measure

[0024]

【Example】

Example 1 The apparatus shown in FIG. 1 was used. This device is in the form of a closed box with a reaction vessel 1 having a volume of 1 liter and contains 20 × 20 × inside.
Five 0.5 cm carbon electrodes are suspended with an interelectrode distance of 0.5 cm. This electrode plate is composed of three cathodes 2 and two anodes 3 which are alternately arranged, and each is connected to a DC power supply 4. As shown in FIG. 2, the cathode 2 is coated with a gel 5 on which denitrifying bacteria and an electron transfer substance are fixed, and a frame 6 for protecting the gel 5 is attached to the outside thereof. On the other hand, the circumference of the anode 3 is surrounded by a diaphragm 7 made of a cellulose film (dialysis membrane) having a thickness of 200 μm that blocks the passage of oxygen gas.
(The distance between the electrode and the diaphragm is 1 mm. The bottom is open.) The reaction tank 1 has an inlet 8 for treated water, an outlet 9 for treated water,
A pump 1 for circulating the water to be treated is provided with a circulation line 10 and a gas outlet 11 for the water to be treated.
2 are provided. An ammeter 13 and a voltmeter 14 are attached to the DC power supply 4.

Pse cultivated according to a conventional method
udomonas denitrificans (AT
CC-13867) culture solution is centrifuged (8000 rp)
m, 15 minutes) to remove the supernatant, and the cells were suspended in 0.1-PIPES buffer. The cell: buffer ratio was set to about 1: 3. This suspension was mixed with a 14% PVA solution at a ratio of 1: 4, and was frozen and stored at -40 ° C for 24 hours while the carbon electrode was immersed in this solution. Then, it was thawed at 4 ° C or lower. Further, it was molded with a knife or the like so that the thickness of the gel covering the electrode surface was about 1 mm.

Water containing 50 ppm of NO ₃ --N as a liquid to be treated (KNO ₃ is dissolved in tap water to obtain 50 pp as N).
The above reaction tank was filled with water prepared so that the current density became m, and an electric current was applied so that the current densities shown in Table 1 were obtained. One hour later, NO ₃ −, NO ₂ −, NH ₄ —N in the reaction solution was measured, and from the NO ₃ —N concentration (50 ppm) before the reaction to (NO ₃ —N + NO ₂ —N + NH ₄ −) after the reaction was completed. The value obtained by subtracting the N) concentration was defined as the denitrification amount (ppm) per hour. Further, cover the electrode on the anode side with a cellulose film to prevent oxygen bubbles from spreading into the system, and also for 1 hour. Reacted. After each reaction, the denitrification amount of was measured.

The results obtained are shown in Table 1. Comparative Example 1 A denitrification reaction was carried out in the same manner as in Example 1 except that the anode was not provided with a diaphragm. Table 1 shows the obtained results.

[0028]

[Table 1]

Example 2 The apparatus shown in FIG. 1 was used.

Pseudomonas denitri
ficans (ATCC-13867) in PIPES buffer and 0.1 mM curcumin aqueous solution, 14%
The PVA solution was mixed at a ratio of 5: 1: 20, the carbon flat plate electrode was immersed in this solution, and it was frozen and stored at −40 ° C. for 24 hours. This was formed into a thin film having a thickness of 1 mm covering a carbon electrode serving as a cathode in the same manner as in Example 1.

Water containing 50 ppm of NO ₃ --N as the liquid to be treated (KNO ₃ is dissolved in tap water to obtain 50 pp as N).
(Water prepared so as to have m) This was flowed from one side of the reaction tank so as to pass between the electrodes with a residence time of 1 hour, and the electrodes were energized (current density: 0.3 mA / cm). Nitrogen content in the solution outflows of the _{(NO 3 -, NO 2,} NO 4 -N) were measured daily. The value obtained by subtracting _{(NO 3 -N + NO 2 -N} + NH 4 -N) concentration after the completion of the reaction from NO ₃ -N concentration before reaction (50 ppm) was de窒量per hour. 18 reaction
As shown in Table 2 for the results of continuous 0 days, the denitrification amount did not decrease so much and the high denitrification amount was maintained.

[0032]

[Table 2]

[0033]

By using the production of the present invention, the denitrification rate can be dramatically increased. The denitrification activity is stable and denitrification can be performed for a long time. This device can be significantly downsized. It can be installed in the final process of the existing sewage treatment plant to significantly improve the denitrification rate.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an apparatus used in an example of the present invention.

FIG. 2 is a side view of the cathode of the device.

FIG. 3 is a diagram showing a state of an apparatus in which a microorganism-immobilized gel is suspended and used.

[Explanation of symbols]

 1 Reaction Tank 2 Cathode 3 Anode 4 DC Power Supply 5 Inclusive Gel 6 Frame 7 Membrane 8 Treated Water × 0 9 Treated Water Outlet 10 Circulation Line 11 Gas Outlet 12 Pump 13 Ammeter 14 Voltmeter

Claims (2)

[Claims] 1. An electrochemical denitrification device using a biocatalyst, comprising a cathode on which denitrification bacteria are immobilized and an anode separated from the cathode by a diaphragm capable of blocking the movement of oxygen gas. A denitrification device which decomposes and removes nitrogen-containing oxides from water containing nitrogen-containing oxides. 2. The denitrification apparatus according to claim 1, wherein the cathode holds an electron transfer substance.