KR20110065324A - Bioelectrochemical method for anaerobic oxidation of ammonia and nitrogen removal - Google Patents

Abstract

PURPOSE: A method for eliminating bioelectrochemisty anaerobic nitrogen oxidation and nitrogen is provided to process subsurface water including nitrogen and to require no oxygenation required for the nitrification. CONSTITUTION: The method for eliminating bioelectrochemisty anaerobic nitrogen oxidation and nitrogen includes the steps of: spatially separating the cathode(1) and the anode(2) for eliminating the nitrogen from processing water in which the nitrogen is included; installing the cathode in the underwater of the negative pole reaction unit(5) for the microbial fuel battery; installing anode in the middle or the water surface; anaerobic nitrifying bacteria attaching and growing in the surface of the negative pole reaction unit for the microbial fuel battery. In the surface of anode, the autotrophic denitrification bacteria is attached and grows. The reducing catalyst is attached. The cathode and anode are connected to the conducting(3) with the outside direct current electricity source(4).

Description

Bioelectrochemical method for anaerobic oxidation of ammonia and nitrogen removal

The present invention relates to a method for removing nitrogen in water using a bioelectrochemical method, by using a nitrogen reducing bacterium such as anaerobic nitrogen oxidizing bacteria and autotrophic denitrification bacteria using an anode, ie, an anode as an electron acceptor, and an anode. That is, the reduction electrode is used as an electron donor to remove various types of nitrogen such as organic nitrogen, ammonia nitrogen, nitrite nitrogen and nitrate nitrogen contained in groundwater, river water, and wastewater by using a bioelectrochemical method. It is about a method.

Usually, the method of biologically removing nitrogen present in water is nitrification-denitrification. Oxidized nitrates were oxidized to nitrous and nitrate nitrogen as shown in Equation 1 below by using nitrifying bacteria in nitrosomonas and nitrobacter, which are independent nutrients under aerobic conditions. Say the reaction to make.

Denitrification refers to a method of removing nitrous nitrogen and nitrate nitrogen by nitrogen gas under anoxic conditions as shown in Equation 2 below using heterotrophic denitrification bacteria.

The nitrification process usually requires alkali and oxygen in the ratio of 7.1g as CaCO ₃ / g NH ₄ ⁺ -N and 4.6g O ₂ / g NH ₄ ⁺ -N, and the denitrification process depends on the composition ratio of dissolved oxygen and nitrite. Although different, they theoretically require an organic carbon source at the rate of 6.2g COD / g NO ₃ -N as an electron donor.

In order to examine the efficiency of nitrification-denitrification, the oxidation number of nitrogen in the process of ammonia nitrogen being oxidized to nitrate nitrogen and converted to the final nitrogen gas by the reduction process is as follows.

The oxidation number of ammonia nitrogen is -3, and in the nitrification process, 8 electrons are lost and oxidized to nitrite nitrogen, and 2 electrons are lost and finally oxidized to nitrate nitrogen. However, in order to convert nitrate nitrogen to nitrogen gas and remove it from water, a reduction process of receiving seven electrons is required. Therefore, the nitrogen removal method using the nitrification-denitrification method is inefficient and costly because it needs to remove a total of 10 electrons to oxidize ammonia to nitrate nitrogen and then supply 7 electrons to reduce nitrate nitrogen to nitrogen gas. This is how it takes a lot.

Recently, as a more economical nitrogen removal method, a uniaxial nitrogen removal method which oxidizes ammonia nitrogen to nitrite nitrogen in aerobic state and then denitrifies using an external carbon source has been studied. In this case, about 25% of oxygen required for nitrification is denitrated. It is known to save about 40% of the required carbon source (Jianlong et al., 2004). However, this technique has a disadvantage that nitrite is rapidly oxidized to nitrate, so that nitrite accumulation is carried out only under special environmental conditions.

The anaerobic AMMonia OXidation (ANAMMOX) process, which removes nitrogen from anaerobic conditions, uses oxygen and alkalinity required for nitrification because nitrite nitrogen is used as an electron acceptor as an electron donor, as shown in Equation 3 below. It is being studied as a technology that can save and save the organic carbon source required for denitrification (Molinuevo et al., 2009).

However, the Anamox process has a disadvantage in that it is difficult to apply to sewage water having a C / N ratio of 1.0 or more, and takes a few months to predominate the Anamox microorganisms during the initial operation.

Recently, research results on independent nutrient denitrification technology using sulfur as an electron donor as an economic nitrogen removal technology than the heterotrophic denitrification method have been reported. In particular, recently, bioelectrochemical methods for denitrifying the current supplied to the electrode by using the electrode as an electron donor instead of the organic carbon source for the denitrification of nitrite nitrogen or nitrate nitrogen have been studied. 10-0848331; Ghafari et al. 20080].

However, as described in the present invention, a technique for economically removing all of organic nitrogen, ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen which may exist economically in water using bioelectrochemical methods has been reported. There is no bar.

In the present invention, the negative electrode to which the anaerobic nitrifying bacteria adhere and grow on the surface is used as an electron acceptor, and the aerobic positive electrode or the oxygen-free positive electrode to which the autotrophic denitrifying bacteria are attached and grows as an electron donor, and maintains a voltage of 1200 mV or less between the negative electrode and the positive electrode. By using an external direct current power supply device, the organic nitrogen and ammonia nitrogen present in the negative electrode installed water are oxidized in the anaerobic state to be converted into oxidized form nitrogen such as nitrogen gas, nitrite nitrogen and nitric acid, and the oxidized form. It is an object of the present invention to provide a method for removing nitrogen from water by reducing nitrogen from anode to nitrogen gas.

The present invention also provides a method for bioelectrochemical removal of various types of nitrogen, such as organic nitrogen, ammonia nitrogen, nitrite nitrogen and nitrate nitrogen, which are contained in low or high concentrations in groundwater, river water, and wastewater. There is a purpose.

As an example for achieving the above object, the present invention is a method for bioelectrochemical removal of nitrogen in water, the cathode (1) and the anode (2) for removing nitrogen from the treated water containing nitrogen spatially The negative electrode 1 is installed in the water of the negative electrode reaction tank 5 for microbial fuel cells in which anaerobic nitrification bacteria adhere to the surface, and the positive electrode 2 is attached to the surface of the autotrophic denitrification bacteria. Reduction catalyst is attached to the water or the surface is installed and configured, the negative electrode (1) and the positive electrode (2) is connected to the external DC power source (4) by the wire (3), the negative electrode (1) and the positive electrode (2) And a method of bioelectrochemically removing nitrogen in water using a bioelectrochemical system configured to form a potential difference of 0 mV or more and 1,200 mV or less therebetween.

Hereinafter, a method of bioelectrochemically removing nitrogen in water of the present invention will be described in detail.

The present invention utilizes a bioelectrochemical system consisting of a cathode (1) and an anode (2) connected to each other by a conductor (3) in the form of organic nitrogen, ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in water. The present invention relates to a method for removing nitrogen present.

In this case, in the bioelectrochemical system of the present invention, the cathode 1 and the anode 2 for removing nitrogen from the treated water containing nitrogen are spatially separated, and the cathode 1 is attached to the surface of anaerobic nitrification bacteria. It is installed in the water of the negative electrode reaction tank (5) for growing microbial fuel cells, and the positive electrode (2) is an independent nutrient denitrification is attached to the surface growth or a reducing catalyst is attached to the water or on the water surface is configured.

The negative electrode 1 and the positive electrode 2 are connected to each other by a conductive wire 3 to form a circuit, and the conductive wire 3 is connected to an external DC power supply 4 to the negative electrode 1 and the positive electrode 2. Potential difference can be formed.

In order to spatially separate the cathode 1 and the anode 2, a separator 7 or a water layer may be provided between the cathode 1 and the anode 2, and a cationic selective separator may be used as the separator.

The negative electrode 1 is a porous material having a large specific surface area and may be made of a carbon material negative electrode material commonly used in microbial fuel cells. Preferably, the conductive material is made of graphite, activated carbon, carbon nanotubes, or these materials. Porous felt made of wood can be used. The negative electrode (1) forms a biofilm on which an autotrophic anaerobic nitrifier is attached and grown on the surface of the carbon material of the negative electrode material, and is installed in the water containing the reduced form nitrogen to maintain the anaerobic state. .

The positive electrode 2 may be made of a positive electrode material commonly used in microbial fuel cells, and preferably, a porous mat made of graphite, activated carbon, and carbon nanotubes having high conductivity and specific surface area. A catalyst such as platinum or transition metal may be attached to the surface of the anode in order to promote the reduction reaction proceeding at the anode 2, and autotrophic denitrification bacteria may be present on the surface of the anode in the form of a biofilm.

According to the present invention, the anode 2 can be kept in an oxygen free state or in an aerobic state. This will be controlled differently according to the type of nitrogen present in the water of the nitrogen-containing treated water, the present invention is able to remove various types of nitrogen present in the water with high efficiency at low energy costs .

That is, when oxidized nitrogen or nitrate nitrogen, which is an oxidized form of nitrogen, is present in the water to be treated, the anode 2 is installed to be immersed in anoxic water, but no oxidized form of nitrogen exists in the water. In the case where the product is an oxidized form of nitrogen, the anode 2 spatially separated from the cathode 1 may be installed in contact with oxygen.

That is, when the treated water contains oxidized nitrogen including organic nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and the like, the positive electrode 2 is installed to be submerged in water, and is formed in an oxygen free state so that Nitrogen and ammonia nitrogen are anaerobic nitrified with nitrogen gas, nitrite and nitrate, and nitrite nitrogen and nitrate nitrogen are denitrated on the anode surface to remove nitrogen in water.

In addition, when the treated water contains organic nitrogen or ammonia nitrogen and does not contain oxidized nitrogen, the anode 2 is installed on the surface of the treated water to expose one surface in the air or in the presence of dissolved oxygen. The reduction reaction of the electrons generated by the oxidation of organic nitrogen or ammonia nitrogen at the cathode is carried out to remove nitrogen from the water.

According to the present invention, the treated water containing nitrogen flows into the cathode reaction tank 5 carrying the anode 1, and the organic nitrogen and the ammonia nitrogen are the anode (1) by autotrophic nitrifying bacteria present in the biofilm on the cathode surface. ) Is anaerobic oxidized using an electron acceptor and converted into nitrogen gas, nitrite nitrogen and nitrate nitrogen as shown in Equations 4 to 6 below.

In Equation 4, E ₀ = -0.28V.

In Equation 5, E ₀ = -0.89V.

In Equation 6, E ₀ = -0.88V.

The standard oxidation potentials of the anaerobic oxidation of ammonia nitrogen to nitrogen gas, nitrite nitrogen and nitrate nitrogen at 0 ° C and 1 atm are standardized at -0.28 V, -0.89 V and -0.88 V, respectively, as in stoichiometry. The amount of change in free energy, the sign of which is opposite to the potential, is all positive, so that spontaneous reactions are not possible thermodynamically (Snoeyink et al., 1980).

However, in the anaerobic nitrification reactions described above, when the anode 1 is provided as an electron acceptor and the pH is maintained at neutral or higher, as in the bioelectrochemical system according to the present invention, the oxidation potential is changed to a negative value. A thermodynamic spontaneous reaction takes place. Therefore, maintaining the pH of the treated water in the range of 6.8 to 8.5 is preferable for the maintenance of the spontaneous reaction described above.

In addition, in the bioelectrochemical system according to the present invention, when the potential difference between the negative electrode 1 and the positive electrode 2 is artificially added to 1.2 V or less using an external DC power supply 4, anaerobic nitrification at the negative electrode 1 The reaction may be accelerated.

When the anode 2 is operated aerobic, water is generated by protons and electrons consuming oxygen as shown in Equation 7 below, and at the point where the anode reaction proceeds, as shown in Equation 8 below, As the value rises, ammonium ions are converted to ammonia, and physicochemical reaction of ammonia occurs.

When the anode (2) is operated in an oxygen-free condition without molecular oxygen, using a nitrite nitrogen and nitrate nitrogen generated from the cathode (1) as an electron acceptor as a reduction catalyst or autotrophic denitrification as shown in the following equation (9) Denitrification by bacteria proceeds. In this case, the denitrification mechanism by autotrophic denitrification bacteria is the same as reported in the previous study, and the nitrogen in the oxidized state is converted to nitrogen gas and removed (Korea Patent No. 10-0848331).

In Equation 9, E ₀ = 1.24V.

In particular, the denitrification reaction proceeding at the anode 2 increases in proportion to the voltage when the potential difference between the cathode 1 and the anode 2 is 1.2 V or less, but at 1.2 V or more, the denitrification is caused by oxygen generated by the electrolysis of water. The reaction can be disturbed and it is uneconomical because of the high power cost.

As described above, the treatment of nitrogen-containing wastewater or groundwater using the bioelectrochemical anaerobic nitrogen oxidation and nitrogen removal method according to the present invention does not require oxygen supply for nitrification, and transfer of organic carbon source required for denitrification. It is possible to reduce the economical nitrogen removal.

1 is a conceptual diagram of a bioelectrochemical system for explaining the anaerobic nitrogen oxidation and nitrogen removal method according to the present invention.
FIG. 2 is a graph illustrating results of observing current with time in a circuit between a cathode and an anode when the potential difference is 0 mV according to Example 1. FIG.

Hereinafter, the configuration, operation, and performance of the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited by these Examples.

Example  1: driving the anode aerobic

Batch bioelectrochemical consisting of a 1L anode reactor and a separator (Nafion 117) with a graphite felt anode of the same size as a 1L cathode reactor with a graphite felt anode having a surface area of 45 cm 2 (1 cm × 5 cm × 9 cm). The system was used to verify the effectiveness of the present invention.

First, supply enough alkalinity to domestic sewage to inject nitrifier into the cathodic reaction tank, inject about 225 mg / L of ammonia nitrogen, inject activated sludge, and aeration for 1 week to cultivate autotrophic nitrifier to prepare seed germ. It was.

As a negative electrode solution, a medium was prepared by a conventional method using KH ₂ PO ₄ , Na ₂ HPO ₄ , CaCl ₂ 2H ₂ O, MgCl ₂ , Fe-EDTA, FeCl ₂ 6H ₂ O, and the like (NH ₄ ) ₂ SO _The initial ammonia nitrogen concentration and alkalinity were adjusted to 200 mg NH ₄ -N / L and 1,000 mg / L as CaCO ₃ , respectively, using ₄ and NaHCO ₃ . In addition, a positive electrode solution was prepared using about 30 g / L of NaCl.

The seedlings and the cathode solution were injected into the cathode reaction tank to make 900mL, and the anode reaction vessel was prepared by injecting 900mL of the anode solution. The anode and the cathode of the prepared bioelectrochemical system were connected by wires to form a circuit. By connecting an external power source in the middle of the circuit, the potential difference between the positive and negative electrodes was 0, 300, 900 and 1,200mV while incubating in a 25 ℃ water bath.

At this time, the behavior of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen contained in the solution of the cathode and anode reaction tanks was observed over time. 1 is shown. FIG. 2 is a result of observing the current with time in the circuit between the cathode and the anode when the potential difference is 0 mV. The results demonstrate the anaerobic oxidation of ammonia nitrogen at the cathode and the electron reduction reaction at the anode. As shown in FIG. 2, electrons and protons are generated by the anaerobic oxidation of ammonia nitrogen at the cathode, and the electrons are moved to the anode through the circuit with the cathode and from the cathode reactor through the separator at the anode. It can be seen that the reaction is terminated by the reaction of oxygen present to produce water.

Item 0 mV 300 mV 900 mV 1200 mV Nitrite and Nitrate (mg / L) 94.2 98.3 97.3 90.7 Nitrogen Gas and Ammonia Degassing
(mg / L) 15.5 47.5 42.1 39.3 Residual ammonia nitrogen
(mg / L) 90.3 54.2 60.6 70.0 Total Ammonia Nitrogen Removal Rate
(%) 54.9 72.9 69.7 65.0

As shown in Table 2, the concentrations of nitrous nitrogen and nitrate nitrogen produced by anaerobic nitrification in the whole bioelectrochemical system after 12 days of system operation were 90.7 to 98.3 mg / L. In addition, the nitrogen removed in the bioelectrochemical system was 15.5 to 47.5 mg / L, which is the sum of the anaerobic oxidation of ammonia nitrogen with nitrogen gas and the denitrification of ammonia nitrogen at the anode. The total ammonia nitrogen removal rate was 54.9 to 72.9% depending on the voltage between the anode and the cathode.

Example  2: When driving the anode anaerobic

After the anaerobic digestion sludge was planted in the anode reactor, the reactor was operated in anoxic state, but the reactor, the electrode material, and the operating method of the bioelectrochemical system were operated under the same conditions as in Example 1.

Anaerobic nitrification and nitrogen removal efficiencies on day 10 of the anaerobic bipolar bioelectrochemical system with different potentials are shown in Table 2 below.

Item 0 mV 300 mV 900 mV 1200 mV Nitrite and Nitrate
(mg / L) 2.3 29.5 34.2 30.1 Nitrogen gas
(mg / L) 3.7 56.5 95.0 98.3 Residual ammonia nitrogen
(mg / L) 194.0 114.0 70.8 71.6 Total Ammonia Nitrogen Removal Efficiency
(%) 3.0 43.0 64.6 64.2

As shown in Table 2, when the potential difference was operated at 0 mV, the concentration of nitrate and nitrite in the system was low, and the amount of nitrogen removed by nitrogen gas was also small.

However, in the system operating the potential difference at 300, 900 and 1,200 mV, the concentrations of nitrous acid and nitrate nitrogen increased with the potential difference. In addition, the nitrogen removed by the nitrogen gas was 56.5 to 98.3 m / L when the potential difference is 300 to 1,200 mV. As the potential difference between the positive electrode and the negative electrode increased to 1,200 mV, the cathode efficiency as the electron acceptor and the anode efficiency as the electron donor increased, so that the total ammonia nitrogen removal efficiency gradually increased with the magnitude of the potential difference.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

DESCRIPTION OF SYMBOLS 1 cathode 2 anode 3 conductor 4 external DC power supply
5: cathode reactor 6: anode reactor 7: separator

Claims (4)

As a method of bioelectrochemical removal of nitrogen in water,
The cathode (1) and the anode (2) for removing nitrogen from the treated water containing nitrogen are spatially separated,
The negative electrode 1 is installed in the water of the negative electrode reaction tank 5 for microbial fuel cells in which anaerobic nitrification bacteria adhere to and grow on the surface.
The positive electrode (2) is composed of the autotrophic denitrification bacteria attached to the surface or attached to the reduction catalyst is installed in the water or on the water surface,
The negative electrode 1 and the positive electrode 2 are connected to an external direct current power source 4 by a conductive wire 3 so that a potential difference of 0 mV or more and 1,200 mV or less is formed between the negative electrode 1 and the positive electrode 2. A method for bioelectrochemical removal of nitrogen in water, characterized by using an electrochemical system.
The method according to claim 1,
And the anode (2) is bioelectrochemically oxidized and removed when the treated water contains organic nitrogen, ammonia nitrogen, nitrite nitrogen and nitrate nitrogen.
The method according to claim 1,
When the treated water contains organic nitrogen or ammonia nitrogen and the final product is nitrogen in an oxidized form, the anode 2 is exposed to molecular oxygen to remove and oxidize nitrogen in water bioelectrochemically. How to.
The method according to claim 1,
The treated water is bio-chemically oxidized to remove nitrogen in the water, characterized in that the pH is adjusted to the range of 6.8 to 8.5.

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