KR100848331B1 - Denitrification Method Using A Bio-Electro-Chemical System - Google Patents

Abstract

The present invention provides a denitrification method using a bioelectrochemical system, wherein a space inside a housing containing a nitrate nitrogen component dissolved in water is separated into two spaces, namely, an anode part and a cathode part, by the cation selective separator 14. An insoluble anode electrode 12 is provided in the portion, and a carbon-based cathode electrode 16 having an anaerobic microbial film attached thereto is provided at the cathode portion, and a DC power supply portion between the anode electrode 12 and the cathode electrode 16. By using a bioelectrochemical system 10 configured to supply a direct current through 18, the cathode electrode 12 and the anode electrode 12 at the DC power supply 18 are maintained while maintaining the anaerobic environment. A constant direct current of 10 mA to 400 mA is supplied between the cathode electrodes 16. According to this, it is possible to remove not only nitrogen in low concentration drinking water but also high concentration of nitrogen contained in domestic sewage and various industrial wastewater.

Denitrification, Nitric Acid Nitrogen, Bioelectrochemistry, Microorganisms, Electrodes

Description

Denitrification Method Using A Bio-Electro-Chemical System

1 is a schematic cross-sectional view schematically showing the structure of a bioelectrochemical system used in the method of the present invention.

2 is a view showing the observation of the microbial membrane attached to the cathode electrode used in one embodiment of the method of the present invention using an electron microscope (SEM).

3 is a graph showing the reduction and redox potential (OPR) change of nitrate nitrogen in one embodiment of the method of the present invention.

Figure 4 is a graph showing the degree of reduction of nitrite nitrogen by an appropriate current in one embodiment of the method of the present invention.

5 is a graph showing the reduction of nitrate nitrogen and the change of nitrite nitrogen according to the initial concentration change of nitrate nitrogen in one embodiment of the method of the present invention.

<Brief description of the major symbols in the drawings>

10: bioelectrochemical system (bioreactor)

12 anode electrode 14 cation selective separator

16 cathode electrode 17 gas collector

18: DC power supply

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitrification method for removing nitrogen contained in wastewater and the like, and more particularly, to the anaerobic respiration of a microorganism using a cathode electrode or a reduced electrode as an electron donor and using nitrate nitrogen as a transcription receptor. The present invention relates to a method for removing nitrate nitrogen contained in waste water by performing a denitrification reaction.

In general, nitrogen is removed by using microorganisms in the water, which can be classified into heterotrophic denitrification and autotrophic denitrification. Currently, most rely on heterotrophic denitrification, which supplies the carbon source of microorganisms from outside. This method has low treatment efficiency, high energy cost during recirculation (100-400%), and requires organic carbon sources (methanol, acetic acid) as electron donors. In addition, there is a disadvantage in that the treatment cost increases because the untreated organic material must be removed in a subsequent process.

Therefore, in recent years, interest in autotrophic denitrification, which is relatively poorly studied, is increasing rather than heterotrophic denitrification having such disadvantages. Autotrophic denitrification does not require external carbon sources, enables low-cost processes, and generates less sludge produced by-products. Autotrophic denitrification can be divided into hydrogen soluble autohydrogentrophic denitrification using hydrogen (H ₂ ), and iron (sulfur). Hydrogen-soluble autotrophic denitrification has the disadvantages of low solubility and explosion risk of hydrogen, and sulfur-soluble autotrophic denitrification destroys alkalinity during denitrification. This process does not proceed anymore, and the treatment of wastewater has been limited because of the side disadvantages of high concentrations of nitrates that produce high levels of sulfate ions as by-products. One way to overcome this is to study the process of supplying alkalinity by mixing limestone with sulfur particles in foreign countries. However, there is still a problem of limiting alkalinity supply of limestone, increase of TDS, and increase of sulfate ion concentration in high nitrogen treatment. (Kim, 2002) has the disadvantage of being difficult to remove high concentrations of nitrate nitrogen.

Therefore, it would be advantageous to provide an economical denitrification method capable of effectively removing high concentration nitrogen of the conventional autotrophic denitrification method while eliminating the secondary pollution problem of the conventional heterotrophic method.

The present invention is to solve the problems of the conventional biological or electrochemical method described above, in particular by adopting a bioelectrochemical method in which the electrochemical method and the biological method is fused using conventional iron, hydrogen, sulfur proton (H ⁺ ) and electronic (e ^- and not a way to throw passes) to provide a biological denitrification method using the electrochemical system is configured to provide direct microorganisms that purpose.

In general, bioelectrochemical methods are currently widely used in the field of biofuel cells or microbial fuel cells. The microbial fuel cell transfers protons and electrons generated while decomposing organic substances using microorganisms in the anode part to the cathode part and consumes protons and electrons using oxygen (O ₂ ) at the anode part. That's the way. The microbial fuel cell is well known as a device for producing electricity by decomposing organic substances such as glucose and acetate.

However, the present invention is a different concept from the microbial fuel cell, by using electrons and protons at the cathode by using protons and electrons generated by the electrolysis of water at the anode. It is characterized by the ability to reduce acidic nitrogen.

This object is achieved by a denitrification method using a bioelectrochemical system provided according to the present invention.

The denitrification method provided in accordance with the present invention is a denitrification method using a bioelectrochemical system, wherein a space inside a housing containing nitrate nitrogen dissolved in water is separated into two spaces, namely, an anode part and a cathode part, by a cation selective separator. And installing an insoluble anode electrode in the anode portion, and installing a carbon-based cathode electrode on which the anaerobic microbial membrane is attached to the cathode portion, and supplying a direct current through a DC power supply portion between the anode electrode and the cathode electrode. By using a bioelectrochemical system, while maintaining the anaerobic environment in the cathode space, the DC power supply is characterized in that for supplying a constant direct current of 10 mA to 400 mA between the anode electrode and the cathode electrode .

In a preferred embodiment, the positive electrode is a thin plate-shaped electrode containing insoluble Ag / AgCl as a main component and surrounded by a 3.3 M KCl aqueous solution, and the negative electrode is a thin plate-type electrode containing graphite felt as a main component.

In a preferred embodiment, at least one surface of the thin plate-shaped negative electrode mainly composed of graphite felt is covered with an anaerobic microbial membrane formed by culturing microorganisms collected from anaerobic sludge derived from wastewater.

Hereinafter, with reference to the accompanying drawings a specific embodiment of the present invention will be described in detail.

1 is a schematic cross-sectional view schematically showing the structure of a bioelectrochemical system used in the method of the present invention, Figure 2 is an electron microscope (SEM) microbial membrane attached to the cathode electrode used in one embodiment of the method of the present invention Figure 3 is a view showing the appearance, Figure 3 is a graph showing the reduction and redox potential (OPR) change of nitrate nitrogen in one embodiment of the method of the present invention, Figure 4 is one of the method of the present invention Example is a graph showing the degree of reduction of nitrite nitrogen by the appropriate current, while Figure 5 is a reduction of nitrate nitrogen and the nitrite nitrogen in accordance with the initial concentration change of nitrate nitrogen in one embodiment of the method of the present invention This graph shows the change.

The present invention is characterized in that the microorganism performs a denitrification reaction through anaerobic respiration using a cathode electrode, that is, a reduced electrode as an electron donor and an nitrate nitrogen as an electron acceptor. In other words, the present invention relates to a new method of autotrophic denitrification by applying electrolysis to replace the existing heterotrophic denitrification to remove nitrogen in water. The present invention particularly, the positive electrode portion, by electrolysis of water protons (H ⁺⁾ and electron (e ^-) and generates, in the cathode portion of the proton (H ⁺⁾ and electron (e ^-) generated in the anode compartment accepts The bioelectrochemical method is characterized by the final denitrification of nitrate nitrogen (NO ₃ ^-- N) to N ₂ .

In the bioelectrochemical system 10 used in the present invention shown in FIG. 1, a space inside a housing containing nitrate nitrogen dissolved in water is divided into two spaces, namely, an anode part and a cathode part, by a cation selective separator 14. And a carbon-based negative electrode 16 having an anaerobic microbial film attached thereto, and the positive electrode 12 and the negative electrode 16 are disposed in the positive electrode portion. It is configured to supply a DC current through the DC power supply 18 in between.

In a preferred embodiment, the positive electrode 12 is a thin plate-shaped electrode mainly composed of insoluble Ag / AgCl and is in contact with a 3.3 M KCl aqueous solution, and the negative electrode 18 is a thin plate-shaped electrode mainly composed of graphite felt. Electrode.

In a preferred embodiment, at least one surface of the thin plate-type cathode electrode 16 mainly composed of the graphite felt is covered with an anaerobic microbial membrane formed by culturing microorganisms collected from anaerobic sludge derived from wastewater.

The anaerobic microbial membrane is obtained by culturing and attaching microorganisms collected from activated sludge from wastewater treatment. The properties and culture methods of such microbial membranes are well known in conventional biofuel cells and their application fields. Examples of biofuel cells and applications thereof are described in Patent Application No. 10-1996-0036468 “Biofuel Cell Using Metal Salt Reducing Bacteria”, Patent Application No. 10-1999-0027168 “Biofuel Using Activated Sludge for Wastewater and Wastewater Treatment Batteries, and Patent Application No. 10-1999-0027167 "Methods for Electrochemical Enrichment of Microorganisms and Biosensors for Organic Substances and BOD Analysis", and the like.

The anaerobic microorganisms used in the present invention use the final electron acceptor other than oxygen to consume organic matter in the absence of oxygen and electrons generated in this process. Since 1990, an anaerobic microorganism using metal salt as a transcription receptor is used. "Metal deducing bacteria" are known. Shewanella putrefaciens, for example, is a metal salt reducing bacterium that can transfer electrons to electron acceptors that exist directly outside the cell without electron transport media used in microbial fuel cells. The microorganisms used in the present invention are preferably microorganisms used in the field of medium-free microbial fuel cells (or biofuel cells), and are well known to those skilled in the art, Thickening on plate Culture methods are also well known.

According to the method, the bioelectrochemical system 10 can be used to purge nitrogen gas, for example using a mechanism such as the gas collector 17 so that the cathode space is maintained in an anaerobic environment. Under such anaerobic environment, the DC power supply unit 18 is characterized in that to supply a constant direct current of 10 mA to 400 mA between the anode electrode 12 and the cathode electrode 16.

Water is electrolyzed at the anode electrode 12 by the supplied current to generate electrons and cations. The generated electrons are moved to the cathode electrode 16 along the conducting wire connected between the electrodes, and the generated cations are passed through the cation selective separator 14 through the electrolyte solution between the two electrodes. To 16). The microorganisms in the microbial membrane attached to the cathode electrode 16 undergo anaerobic respiration, using electrons arriving at the cathode electrode 16 as electron donors, and using nitrate nitrogen in the electrolyte material as the electron acceptor. . In particular, these microorganisms directly use the electrons of the cathode electrode 16 without a separate medium.

<Example>

In the bioelectrochemical system 10 used in the denitrification method of the present invention, protons and electrons are transferred from the anode to the cathode and used as an electron donor, and nitrate nitrogen is used as the electron donor. As a reactor for reducing, it can be said to be a 'bioreactor' made by enriching microorganisms on the cathode electrode. The bioreactor 10 has an anode or anode electrode 12, a cathode or cathode electrode 16, a cation-selective membrane 14 and a power supply. It consists of 18.

The anode part used insoluble electrode to prevent oxidation, the cathode part used graphite felt electrode, and formed a biofilm by attaching microorganisms to the surface of the cathode part. In the anode section, water is electrolyzed to produce protons and electrons.

_{(+): 2H 2 O -} > O 2 + 4H + + 4e - ---- (1)

The cathode portion of these proton (H ⁺⁾ and electron (e ^-) by reduction of nitrate nitrogen to be received is converted to the final N _2.

^{_{(-): 2NO 3 - +}} 5H + + 5e - -> N 2 + 4H 2 O + 2OH - ---- (2)

In addition, the bioreactor 10 has a cation selective separator 14 installed between the anode portion 12 and the cathode portion 16 to selectively transfer only protons to the cathode portion 16. Electrons are transferred from the anode portion 12 to the cathode portion 16 along the lead.

1. Bioreactor Configuration and Experiment Medium

The total capacity of the bioreactor 10 used in the embodiment of the present invention is 2.5 liters and the actual reaction capacity, that is, the capacity of the negative electrode portion separated by the proton selective membrane is 1 liter. The area of the positive electrode and the negative electrode is 105 cm ^2, respectively.

Anaerobic sludge was taken from the Seoul Gravity Sewage Treatment Plant to form a microbial membrane in the negative electrode, and concentrated and cultured on the negative electrode for about 60 days. The DC power was supplied from the power supply to maintain the current at 200 mA. At this time, nitrate nitrogen was continuously injected at low concentration into the cathode portion.

The temperature of the bioreactor 10 was maintained at about 25-30 ℃. The medium used for the bioreactor 10 consists of 6.8 g / l K ₂ HPO ₄ , 8.7 g / l KH ₂ PO ₄ , 2.0 g / l NaHCO ₃ , and 1 ml of trace element solution. Trace element solution is MgSO ₄ 7H ₂ O 10.0 g / l, ZnSO ₄ 7H ₂ O 2.2 g / l, CaCl ₂ 2H ₂ O 7.3 g / l, MnCl ₂ 4H ₂ O 2.5 g / l, CoCl ₄ 6H is composed of _{2 O 0.5 g / l, FeSO} 4 · 7H 2 O 5.0 g / l, CuSO 4 · 5H 2 O 0.2 g / l.

2. cathode electrode Thickened Biofilm  Confirm

Referring to FIG. 2, the cathode electrode (B. control, graphite felt electrode surface of FIG. 2) before the addition of microorganisms and the cathode electrode after incubation by adding microorganisms to confirm the biofilm enriched in the cathode electrode ( A. enrichment culture of FIG. 2 coated with a microbial membrane) was taken and fixed in 1% glutaldehyde / formaldehyde, and the biofilm was confirmed using a scanning electron microscope (SEM) (Bond and Lovley [16]).

3. To denitrification  Change in redox potential

Ag / AgCl / (3.3M) KCl electrode was used to measure the redox potential by denitrification as shown in the graph shown in FIG. 3. As shown, the oxidation reduction potential (ORP) decreases from -89.67 mV to -260.67 mV when nitrate nitrogen 70 mg NO ₃ ^-- N / l is reduced using the bioreactor (10). Showed a tendency. It can be seen that the redox potential is changed due to the reduction of nitrate nitrogen. In addition, the pH value was found to increase the nitrate nitrogen by reduction.

4. Denitrification of Bioreactors Using Electrons

As shown in Figure 4, the degree of denitrification was checked while changing the value of the current in order to find the optimum optimum current of the microorganism having the electrical activity. The current was changed in 5 mA steps from 10 mA to 500 mA to determine the degree of denitrification to the current. When the current was increased to 200 mA, denitrification was about 98%, but when the current exceeded 200 mA, it tended to decrease. As can be seen, when the current flowed from 10 mA to 400 mA, more than 80% of the denitrification effect was seen. In the Bond and Lovley paper, the amount of hydrogen produced at a constant current of 100 mA was 1000 times shorter than the amount of nitrogen reduced at the same current. In this experiment, the amount of hydrogen produced at 200 mA and the reduction of nitrate nitrogen were also reduced. When the amount was calculated, the difference was more than 100 times. Therefore, this is not a denitrification by hydrogen, but a bioreaction by electrons generated by bioelectrochemical methods.

5. Reduction of high concentration nitrate nitrogen

As shown in Figure 5, to confirm the reduction of high concentration nitrate nitrogen by the bioreactor was confirmed the concentration of nitrate nitrogen at various concentrations. The concentration of nitrate nitrogen was varied from 20-492 mg NO ₃ ^-- N / l and the changes of nitrate nitrogen and nitrite nitrogen were observed at each concentration. As the initial concentration of nitrate increased, the reduction rate also increased. The nitrite nitrogen production concentration also increased, but it did not affect the reduction of nitrate nitrogen. While other autotrophic denitrification experiments have been conducted at almost low concentrations (50 mg NO ₃ ^-- N / l) (6, 20, 21, 22), in this experiment high concentrations of about 500 mg NO ₃ ^-- N / l Almost nitrate nitrogen was reduced even in the experiment. The maximum nitrate nitrogen reduction rate obtained using the Monad kinetic model was 0.17 mg NO ₃ ^-- N / cm ² (biofilm surface area) / day. This value was compared with the maximum reduction rate obtained from other autotrophic denitrification reactions previously studied using biofilm reactors. Kurt et al. For [20], the maximum rate of nitrate nitrogen reduction was 0.031 mg NO ₃ ^-- N / cm ² (biofilm surface area) / day, Liessens et al. 0.023 mg NO ₃ ⁻ -N / cm ² (biofilm surface area) / day for [25], 0.083 mg NO ₃ ⁻ -N / cm ² (biofilm surface area) / day for MacDonald [26]. For Sakakibara and Kuroda [9], 0.038 mg NO ₃ ^-- N / cm ² (biofilm surface area) / day and Gregory et al. [11] for 0.13 mg NO ₃ ⁻ -N / cm ² (biofilm surface area) / day. The reduction rate of the maximum nitrate nitrogen obtained in the experiments using the biofilm was much better than that of other studies.

The present invention has been described above with reference to specific embodiments, but the scope of the present invention is not limited to the described examples, and those skilled in the art, that is, those skilled in the art based on the disclosed contents Various modifications and changes are possible by applying common knowledge. Therefore, it is pointed out that the scope of the present invention should be interpreted not by the examples described, but by the appended claims.

As described above, according to the present invention, when using a bioreactor using a bioelectrochemical method, there is an advantage that can solve the secondary pollution problem raised in the heterotrophic denitrification method that has been studied a lot. In addition, although the existing autotrophic denitrification method was available only for low concentration denitrification, this bioreactor provides the effect of removing nitrogen in low concentration drinking water as well as high concentration nitrogen contained in domestic sewage and various industrial wastewater.

Claims (3)

delete As a denitrification method using the bioelectrochemical system 10, a space inside a housing containing nitrate nitrogen dissolved in water is separated into two spaces, that is, an anode portion and a cathode portion, by a cation selective separator 14, and the anode portion An insoluble anode electrode 12 is provided in the inside, and a carbon-based cathode electrode 16 to which an anaerobic microbial film is attached to the cathode portion is disposed between the anode electrode 12 and the cathode electrode 16. 18, the anode electrode 12 and the cathode at the DC power supply 18, while maintaining the anaerobic environment, using the bioelectrochemical system 10 configured to supply a direct current through It is characterized by supplying a constant direct current of 10 mA to 400 mA between the electrodes 16, The anode electrode 12 is a thin plate-shaped electrode made of insoluble Ag / AgCl and contained in a 3.3M KCl aqueous solution, and the cathode electrode 16 is characterized in that the thin plate-type electrode mainly composed of graphite felt, Denitrification using bioelectrochemical systems. 3. The bioelectrochemical method according to claim 2, wherein at least one surface of the thin plate-shaped cathode electrode 16 made of graphite felt is covered with an anaerobic microbial membrane formed by culturing microorganisms collected from anaerobic sludge derived from wastewater. Denitrification method using the system.

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