JP2017121609A - Microbe electrolysis cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microbe electrolysis cell of high ability of decomposing organic matters, capable of removing nitrogen.SOLUTION: A microbe electrolysis cell includes a vessel, a liquid in the vessel that contains organic matters and electron-donating microbes, an anode and a cathode that are arranged so as to come into contact with the liquid, a voltage impression unit for applying voltage to between the anode and the cathode so that the anode voltage is lower than the cathode voltage, and an aerator for injecting an oxygen-containing gas into the liquid. Preferably, the aerator injects the gas into the liquid intermittently. Preferably, the amount or the time of gas injection by the aerator is adjusted according to a current between the anode and the cathode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a microbial electrolysis cell.

  For livestock farmers, the treatment of wastewater from barns is a heavy burden because it requires a great deal of cost and labor. In addition, in order to prevent environmental impacts, the development of new wastewater treatment technology that responds to the recycling of livestock biomass and stricter wastewater treatment standards is required. The development of new technologies that enable the appropriate treatment of organic wastewater and the recovery of resources from organic wastewater is required not only in the field of livestock production but also in a wide range of fields such as food processing, brewing, and sewage treatment in urban areas. Yes.

  In recent years, a new technique called a microbial electrolysis cell (MEC) has attracted attention (for example, see Non-Patent Document 1). In the microbial electrolysis cell, the microorganisms have a role of decomposing an organic substance by an oxidation-reduction reaction under anaerobic conditions and passing electrons generated at that time to the anode (negative electrode). The anode (negative electrode) and the cathode (positive electrode) are connected to a voltage application unit (power source, potentiostat, etc.), and the voltage application unit applies a voltage between the anode and the cathode. Thus, in the microbial electrolysis cell, it is necessary to input a little energy from the outside. The electrons collected at the anode move to the cathode and react with hydrogen ions in the liquid at the cathode surface. Thereby, hydrogen gas is generated on the cathode surface. By recovering this hydrogen, energy can be recovered. Since the amount of energy obtained as hydrogen is larger than the amount of energy input as voltage application, the entire microbial electrolysis cell has recovered energy from waste water.

  Microbial electrolysis cells can treat various types of organic wastewater. Since the organic matter in the wastewater is decomposed by this treatment, the microbial electrolysis cell also has a function of purifying the wastewater (removing the organic matter). Thus, the microbial electrolysis cell is expected as a future new technology because it can simultaneously purify wastewater and recover energy from wastewater.

  As described above, the microbial electrolysis cell utilizes the use of the anode as the final electron acceptor when the electron donating microorganism decomposes organic substances under anaerobic conditions. Thus, since the microbial electrolysis cell utilizes anaerobic treatment by electron donating microorganisms, it is considered essential that the inside of the microbial electrolysis cell container be maintained in an anaerobic state.

Douglas Call, and Bruce E. Logan, "Hydrogen Production in a Single Chamber Microbial Electrolysis Cell Lacking a Membrane", Environ. Sci. Technol., Vol. 42, pp. 3401-3406.

  Microbial electrolysis cells are expected not only to recover energy but also to perform purification treatment by decomposing organic substances in wastewater. However, the conventional microbial electrolysis cell has a lower ability to decompose organic matter than the activated sludge method. For this reason, development of a microbial electrolysis cell having a high ability to decompose organic substances is expected. Furthermore, removal of nitrogen in wastewater is also important for purification of wastewater, but conventional microbial electrolysis cells cannot be removed because they are operated in an anaerobic state.

  This invention is made | formed in view of this point, and it aims at providing the microorganisms electrolysis cell which has high decomposition | disassembly capability of organic substance, and can also remove nitrogen.

  The present inventors have surprisingly found that even if aeration is performed in a microbial electrolysis cell, generation of electric current and accompanying hydrogen generation can be continued. Furthermore, the present inventors have found that the ability of decomposing organic substances is remarkably increased by performing aeration in a microbial electrolysis cell, and nitrogen removal is also performed. The inventors further studied these findings and completed the present invention.

  That is, the present invention relates to the following microbial electrolysis cell.

[1] A container, a liquid containing an organic substance and an electron-donating microorganism contained in the container, an anode and a cathode disposed so as to be in contact with the liquid, and a potential of the anode higher than a potential of the cathode A microbial electrolysis cell, comprising: a voltage applying unit that applies a voltage between the anode and the cathode, and an aeration device that sends a gas containing oxygen to the liquid so as to be low.
[2] The microbial electrolysis cell according to [1], wherein the aeration apparatus intermittently feeds the gas into the liquid.
[3] The aeration apparatus intermittently sends the gas to the liquid, whereby an aerobic state and an anaerobic state are repeated in the liquid, and nitrogen in the liquid is removed. Microbial electrolysis cell.
[4] The microbial electrolysis cell according to any one of [1] to [3], wherein the gas is air.
[5] Any one of [1] to [4], wherein the aeration apparatus adjusts at least one of an amount of feeding the gas and a time for feeding the gas according to a current flowing between the anode and the cathode. The microbial electrolysis cell according to one item.
[6] The microbial electrolysis cell according to any one of [1] to [5], further including a hydrogen recovery unit that recovers hydrogen generated from the cathode.

  ADVANTAGE OF THE INVENTION According to this invention, the microbial electrolysis cell which has high decomposition | disassembly capability of organic substance and can also remove nitrogen can be provided.

  Moreover, according to the microbial electrolysis cell which concerns on this invention, decomposition | disassembly of organic substance and nitrogen removal can be performed with an aeration amount smaller than the activated sludge method. In the activated sludge method, a large amount of electric power is consumed for aeration. When organic matter is decomposed by the activated sludge method, when the amount of organic matter in the wastewater is sufficiently reduced, aeration should be stopped to reduce power consumption. However, normally, in the activated sludge method, since there is no sensor for detecting the organic matter concentration in the wastewater, excessive aeration is performed and electric power is wasted. On the other hand, in the microbial electrolysis cell according to the present invention, the amount of gas to be fed or the time to feed the gas can be adjusted according to the current flowing between the anode and the cathode, so that power consumption for aeration is required. Can be minimized.

FIG. 1 is a schematic cross-sectional view showing the configuration of the microbial electrolysis cell according to Embodiment 1. FIG. FIG. 2 is a schematic cross-sectional view showing the configuration of the microbial electrolysis cell according to the second embodiment. FIG. 3 is a graph showing the change with time of the current flowing between the anode and the cathode in the microbial electrolysis cell produced in the example. FIG. 4 is a graph showing changes over time in the total amount of hydrogen generated in the microbial electrolysis cell produced in the example. FIG. 5 is a graph showing a change with time of the oxidation-reduction potential (ORP) of the artificial wastewater in the microbial electrolysis cell. FIG. 6 is a graph showing measurement results of chemical oxygen demand (COD) of artificial wastewater in a microbial electrolysis cell. FIG. 7 is a graph showing the measurement results of the nitrogen concentration of artificial wastewater in the microbial electrolysis cell before and after operation. FIG. 8 is a graph showing the relationship between the current flowing between the anode and the cathode in the microbial electrolysis cell and the chemical oxygen demand (COD) of artificial wastewater.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
In the present embodiment, a microbial electrolysis cell having a power source as a voltage application unit will be described.

(Configuration of microbial electrolysis cell)
FIG. 1 is a schematic cross-sectional view showing a configuration of a microbial electrolysis cell 100 according to Embodiment 1. As shown in FIG. As shown in FIG. 1, the microbial electrolysis cell 100 includes a container 110, a liquid 120, an anode (negative electrode) 130, a cathode (positive electrode) 140, a power source 150, an aeration device 160, a hydrogen recovery unit 170, and a hydrogen storage unit 180. . The liquid 120 includes an organic substance and an electron donating microorganism 122. The aeration apparatus 160 includes a pump 162, an air diffuser 164, and a control unit 166. The anode 130 and the cathode 140 are electrically connected to the power source 150.

  The container 110 constitutes the main body of the microbial electrolysis cell 100 and accommodates the liquid 120. The material, shape, and size of the container 110 are not particularly limited, and can be set as appropriate according to the application. In the microbial electrolysis cell 100 according to the present embodiment, unlike the conventional microbial electrolysis cell, the container 110 may be opened to the outside because it is not always anaerobic.

The liquid 120 is accommodated in the container 110 and contains an organic substance serving as an energy source and an electron donating microorganism 122. Usually, the liquid 120 is an aqueous solution containing one or more electrolytes. The type of electrolyte is not particularly limited as long as it is a substance that can be ionized in water. Examples of the electrolyte include NaH ₂ PO ₄ / Na ₂ HPO ₄ , KH ₂ PO ₄ / K ₂ HPO ₄ , NaCO ₃ / NaHCO ₃ , NaCl, KCl, NH ₄ Cl and the like. The liquid 120 may further contain an electron-transmitting intermediary material such as an electron mediator or conductive fine particles as necessary.

  Among the electron donating microorganisms 122 in the liquid 120, at least some of the electron donating microorganisms 122 are supported on the anode 130. That is, the anode 130 also functions as a carrier that holds the electron-donating microorganism 122 at a high density. There may be one kind of electron-donating microorganism 122, or two or more kinds. When using organic wastewater or sludge, the electron-donating microorganisms that inhabit them can be used as they are without adding electron-donating microorganisms from the outside. For example, Pseudomonas and Geobacter inhabit every part of the natural environment such as soil, fresh water, and seawater, so if organic wastewater or sludge is used, they can be used without being added from the outside. Since the anode 130 can also hold microorganisms other than the electron donating microorganism 122, it can also function as a microorganism carrier that enhances the wastewater purification action.

  The kind of the organic substance serving as the energy source is not particularly limited as long as the electron donating microorganism 122 can be metabolized. Organic materials that can be used as energy sources include not only useful resources such as alcohol, monosaccharides, polysaccharides, proteins, and volatile fatty acids, but also unused resources such as agricultural and industrial waste, organic wastewater, human waste, sludge, and food residues (organic Waste) can also be used. An organic substance serving as an energy source is added as necessary to maintain and grow the electron-donating microorganism 122 and to continuously operate the microbial electrolysis cell 100.

  The anode 130 is disposed so as to contact the liquid 120. In the present embodiment, the anode 130 is immersed in the liquid 120. The material and shape of the anode 130 are not particularly limited, and can be appropriately selected according to the adhesion of the electron donating microorganism 122, the degree of electron transfer from the electron donating microorganism 122, and the like. Examples of the material of the anode 130 include carbon, metal, metal oxide, and the like. Examples of the shape of the anode 130 include a planar shape such as a cloth, and a three-dimensional shape such as a brush shape, a rod shape, and a granular shape. Examples of the anode 130 include carbon paper, graphite plate, carbon cloth, carbon mesh, graphite felt, graphite particles, activated graphite particles, carbon felt, reticulated vitrified carbon, carbon brush, stainless steel mesh, and the like.

  The cathode 140 is disposed so as to contact the liquid 120. In the present embodiment, the cathode 140 is immersed in the liquid 120. The material of the cathode 140 is not particularly limited as long as it has conductivity and is chemically stable. Further, the shape of the cathode 140 is not particularly limited, and can be appropriately selected according to the ease of recovery of hydrogen gas. Examples of the material of the cathode 140 include carbon, metal, metal oxide, and the like. Examples of the cathode 140 include carbon cloth, carbon felt, stainless steel mesh, platinum mesh, and the like. Further, a hydrogen ion reduction catalyst such as platinum may be supported on these surfaces.

  The power source 150 is electrically connected to the anode 130 and the cathode 140, and applies a voltage between the anode 130 and the cathode 140 so that the potential of the anode 130 is lower than the potential of the cathode 140. When a liquid 120 containing acetic acid and having a pH of 7 and 25 ° C. is used, the electrode potential of the anode 130 is −0.300 V (vs. NHE) (NHE: normal hydrogen electrode). The electrode potential of the cathode 140 for passing electrons is −0.414 V (vs. NHE). Therefore, theoretically, by applying a voltage of 0.114 V or more between the anode 130 and the cathode 140, electrons are finally transferred from the anode 130 to the cathode 140 through an external circuit, and the surface of the cathode 140 is Will generate hydrogen. Actually, it is preferable to apply a voltage of 0.13 V or more between the anode 130 and the cathode 140 in consideration of an overvoltage and a reaction rate, and a voltage of 0.4 to 5.0 V is preferably applied to the anode 130 and the cathode. It is more preferable to apply between 140 and 140. When operating with an emphasis on the production of hydrogen, it is preferable to apply a small voltage of about 0.4 to 0.8 V with little input energy. When operating with an emphasis on decomposition of organic matter and detection of concentration of organic matter rather than production of hydrogen, it is preferable to apply a voltage of 1.0 V or more.

  The aeration apparatus 160 includes a pump 162, an air diffuser 164, and a control unit 166. The aeration apparatus 160 sends a gas containing oxygen into the liquid 120. In the present embodiment, the aeration apparatus 160 sends air 168 into the liquid 120. The aeration apparatus 160 may be driven by electric power supplied from the power source 150 or may be driven by another power source (not shown).

  The aeration apparatus 160 may continuously send the air 168 into the liquid 120, but from the viewpoint of easily adjusting the balance between the hydrogen generation ability, the organic matter decomposition ability, and the nitrogen removal ability, the air 168 is intermittently supplied to the liquid 120. It is preferable to send to When the aeration apparatus 160 intermittently sends the air 168 to the liquid 120, the time of the aeration state and the time of the non-aeration state are the hydrogen generation capability of the microbial electrolysis cell 100, the decomposition capability of organic matter, and the concentration of the organic matter contained in the liquid 120. It adjusts suitably according to etc. For example, when the concentration of the organic matter contained in the liquid 120 is high, the aeration time per time is about 1 to 12 hours, and the non-aeration time per time is about 1 to 6 hours. When the organic matter is sufficiently decomposed and the liquid 120 is purified, the current flowing between the anode 130 and the cathode 140 decreases. That is, the concentration of the organic substance in the liquid 120 can be detected by the current flowing between the anode 130 and the cathode 140 (see FIG. 8). Therefore, the aeration apparatus 160 may adjust the amount of air 168 to be fed or the time to send the air 168 in accordance with the current flowing between the anode 130 and the cathode 140. For example, in the case of a current corresponding to when the biochemical oxygen demand (BOD) of the liquid 120 exceeds 500 mg / L, the aeration time per time is about 10 hours, and the non-aeration time per time is 30 minutes. About 2 hours may be used. In the case of a current corresponding to a BOD of 100 to 500 mg / L, the aeration time per time may be about 2 to 5 hours, and the non-aeration time per time may be about 1 to 2 hours. In the case of a current corresponding to a BOD of 50 to 100 mg / L, the aeration time per time may be about 2 hours, and the non-aeration time per time may be about 1 to 2 hours. In the case of a current corresponding to when the BOD is less than 50 mg / L, the aeration time per one time should be about 2 hours, and the non-aeration time per time should be about 2 to 10 hours, or aeration It is not necessary to perform. When the BOD is low but the nitrogen concentration is high, the nitrification reaction may be promoted by aeration. In this case, after the nitrification reaction, nitrogen can be removed by introducing a small amount of raw organic waste water into the container 110 as an electron donor to cause a denitrification reaction.

  The pump 162 feeds air taken from outside under the control of the control unit 166 to the diffuser pipe 164. The type of the pump 162 is not particularly limited, and can be appropriately selected according to the required air discharge amount.

  The air diffuser 164 discharges the air sent from the pump 162 into the liquid 120. When it is desired to increase the efficiency of dissolving oxygen in the liquid 120, the air diffuser 164 releases fine bubbles. The shape and configuration of the air diffuser 164 are not particularly limited as long as the above object can be achieved. Examples of the air diffuser 164 include a tube attached with a mesh, a membrane tube, and the like.

  The control unit 166 controls the operation of the pump 162 so that aeration is performed under preset conditions. For example, when aeration is intermittently performed, the control unit 166 controls the pump 162 so as to operate only for a predetermined time. Further, as described above, the control unit 166 may control the pump 162 in accordance with the current flowing between the anode 130 and the cathode 140. Aeration by the aeration apparatus 160 is performed to promote the decomposition of the organic matter in the liquid 120. Therefore, when the concentration of the organic matter in the liquid 120 is reduced, it is not necessary to aerate, and from the viewpoint of improving the hydrogen generation capability. In some cases, it is preferable to avoid aeration in order to achieve an anaerobic state. In such a case, the control unit 166 may stop the operation of the pump 162 when detecting a decrease in current. In this way, power consumption by the pump 162 can be suppressed.

  The hydrogen recovery unit 170 recovers the hydrogen gas 172 generated on the surface of the cathode 140. The configuration of the hydrogen recovery unit 170 is not particularly limited as long as the above object can be achieved. In the present embodiment, the hydrogen recovery unit 170 is a funnel-shaped member disposed on the cathode 140 in the liquid 120. The hydrogen recovery unit 170 sends the recovered hydrogen gas to the hydrogen storage unit 180.

  The hydrogen storage unit 180 stores the hydrogen gas 172 recovered by the hydrogen recovery unit 170. The configuration of the hydrogen storage unit 180 is not particularly limited as long as the above object can be achieved. Examples of the hydrogen storage unit 180 include a gas holder.

  In addition, the microbial electrolysis cell 100 further includes instruments such as a thermometer that measures the temperature of the liquid 120, a pH meter that measures the pH of the liquid 120, and an ion sensor that measures the concentration of ammonium ions and nitrate ions in the liquid 120. It may be. In this case, the control unit 166 controls the temperature of the liquid 120 (correlated with the activity of the electron donating microorganism 122), the pH of the liquid 120 (correlates with the ammonia concentration in the liquid 120), the oxidation-reduction potential (ORP) of the liquid 120 (ORP) ( The organic substance contained in the liquid 120 based on information such as whether the liquid 120 is anaerobic or aerobic) and the dissolved oxygen concentration of the liquid 120 (correlates with whether the liquid 120 is anaerobic or aerobic). It becomes possible to detect the density | concentration of a more highly sensitively, and it becomes possible to set aeration conditions more appropriately.

(Operation of microbial electrolysis cell)
Next, the operation of the microbial electrolysis cell 100 according to the present embodiment will be described.

  When a slight voltage (for example, 0.8 V) is applied between the anode 130 and the cathode 140 to operate the microbial electrolysis cell 100, the organic matter (for example, acetic acid) is converted into carbon dioxide by the electron donating microorganism 122 in the container 110. When decomposed, hydrogen ions and electrons are generated. Hydrogen ions generated by the decomposition of the organic matter move to the surface of the cathode 140. On the other hand, the electrons generated by the decomposition of the organic matter are collected by the anode 130 and move to the cathode 140 via an external circuit. In such a situation, hydrogen gas 172 is generated on the surface of the cathode 140 by the reaction between hydrogen ions and electrons. Therefore, by supplying an organic substance into the container 110, the above cycle can be maintained and the hydrogen gas 172 can be continuously generated.

  The microbial electrolysis cell 100 according to the present embodiment is mainly characterized by aeration during operation. Since the generation of hydrogen gas by the above mechanism uses anaerobic treatment, the conventional microbial electrolysis cell is designed to be in an anaerobic state (a state in which almost no dissolved oxygen is present) in the liquid. On the other hand, in the microbial electrolysis cell 100 according to the present embodiment, the dissolved oxygen concentration in the liquid 120 is increased to some extent by aeration continuously or intermittently, preferably intermittently, in order to improve the decomposition ability of organic matter. . By aeration in this way, in addition to the generation of hydrogen gas and the decomposition of organic substances by anaerobic treatment, the decomposition of organic substances by aerobic treatment can also be performed. As a result, organic substances can be decomposed more efficiently than the conventional activated sludge method using a microbial electrolysis cell or intermittent aeration (intermittent aeration activated sludge method). In addition, as shown in the Examples below, according to the experiments by the present inventors, it is known that the generation of hydrogen gas can be continued without killing the electron-donating microorganism 122 even if intermittent aeration is performed ( (See FIG. 4).

  In addition, since the microbial electrolysis cell 100 according to the present embodiment also uses aerobic treatment, it is possible to remove nitrogen, which was impossible with a conventional microbial electrolysis cell using only anaerobic treatment (see FIG. 7). ). For example, when the aeration apparatus 160 intermittently sends air 168 to the liquid 120, the aerobic state and the anaerobic state are repeated in the liquid 120. In an aerobic state, ammonia contained in the liquid 120 is oxidized to nitric acid. In an anaerobic state, the reaction from nitric acid to gaseous nitrogen is promoted using electrons supplied from organic matter, and denitrification occurs. Therefore, the microbial electrolysis cell 100 according to the present embodiment can also be used as a deodorization device by aeration using air containing bad odors from barns or compost. When aeration is performed using air containing malodor, malodorous components such as ammonia move to the liquid 120 and are converted to odorless nitrogen gas and deodorized by a cycle of aerobic treatment and anaerobic treatment.

(effect)
As described above, in the microbial electrolysis cell 100 according to the present embodiment, the aerobic treatment and the aerobic treatment are utilized by aeration to improve the decomposition ability of organic matter and nitrogen while maintaining the hydrogen generation ability. Realization of removal. That is, the microbial electrolysis cell 100 according to the present embodiment has a purification performance higher than that of the conventional microbial electrolysis cell in addition to the hydrogen generation capability.

  In addition, as described above, the microbial electrolysis cell 100 according to the present embodiment can detect the organic matter concentration in the liquid 120 in real time from the current flowing between the anode and the cathode. It is also possible to adjust the aeration time according to the above. For example, when the organic substance concentration in the liquid 120 is low, the aeration time is shortened to prevent unnecessary aeration, and the power consumed by the aeration is suppressed. By controlling in this way, the microbial electrolysis cell 100 functions as an energy-saving wastewater purification device. The function of the microbial electrolysis cell 100 as a sensor for detecting the organic substance concentration can also be used for water quality monitoring of the liquid 120, and is controlled to discharge the liquid 120 to the outside only when the organic substance is sufficiently removed. Can also be used. Further, in the microbial electrolysis cell 100 according to the present embodiment, since the anode 130 carries the electron-donating microorganism 122 at a high concentration, the organic substance is more efficiently obtained than the intermittent aeration activated sludge method without a member that carries the microorganism. It can also be disassembled. Moreover, since the microbial electrolysis cell 100 which concerns on this Embodiment utilizes not only an aerobic process but an anaerobic process, it can also reduce the generation amount of an excess sludge rather than the activated sludge method which does not use an anaerobic process. Moreover, the microbial electrolysis cell 100 which concerns on this Embodiment can also perform nitrogen removal and a deodorizing process (refer FIG. 7).

  As a method for estimating the organic substance concentration in the liquid, there are a method of estimating from a measured value of dissolved oxygen (DO) or redox potential (ORP), a method of estimating based on an optical ultraviolet-visible light difference value, and the like. Known (Hiroaki Tanaka, “Water quality measurement equipment in sewers”, Measurement and Control, Vol. 33, No. 8, pp. 639-644; Tanaka H., “Instruments of Water Quality Measurement in Sewerage System”, Journal of The Society of Instrument and Control Engineers, Vol. 33, No. 8, pp. 639-644). Wastewater such as livestock wastewater and municipal sewage contains many insoluble suspended solids and microorganisms, and such wastewater is often colored. When estimating the organic substance concentration by measuring the dissolved oxygen (DO) or oxidation-reduction potential (ORP) of such wastewater, solids adhere to the tip of the probe and clog the membrane. It is extremely difficult to estimate the organic matter concentration. Even in the estimation of the organic substance concentration by optical measurement, since the light transmission is hindered by insoluble suspended solids or coloring, it is extremely difficult to accurately estimate the organic substance concentration. Therefore, it is possible to stabilize the organic matter concentration such as chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in wastewater containing insoluble suspended solids such as livestock wastewater and colored wastewater for a long time. There is currently no practical method for measuring. On the other hand, since the microbial electrolysis cell 100 according to the present embodiment does not use a selective permeable membrane or an optical method, there is no problem of clogging, and it is not affected by any suspended matter or coloring in the wastewater. The organic matter concentration can be estimated. Therefore, the microbial electrolysis cell 100 according to the present embodiment can accurately estimate the organic substance concentration in various wastewaters such as livestock wastewater and municipal sewage without performing maintenance such as cleaning for a long period of time.

  In addition, the microbial electrolysis cell 100 according to the present embodiment is provided with an aeration apparatus 160 that sends air 168 into the liquid 120, a hydrogen recovery unit 170 that recovers hydrogen gas from the liquid 120, and a hydrogen storage unit 180. The anode 130 and the cathode 140 can be easily installed simply by contacting the liquid 120. Therefore, it is easy to introduce the microbial electrolysis cell 100 according to the present embodiment into an existing facility.

[Embodiment 2]
In the present embodiment, a microbial electrolysis cell having a potentiostat as a voltage application unit will be described.

(Configuration of microbial electrolysis cell)
FIG. 2 is a schematic cross-sectional view showing the configuration of the microbial electrolysis cell 200 according to Embodiment 2. As shown in FIG. As shown in FIG. 2, the microbial electrolysis cell 200 includes a container 110, a liquid 120, an anode (negative electrode, working electrode) 130, a cathode (positive electrode, counter electrode) 140, a reference electrode 240, a potentiostat 250, an aeration device 160, hydrogen. It has a recovery unit 170 and a hydrogen storage unit 180. The anode 130, the cathode 140, and the reference electrode 240 are electrically connected to the potentiostat 250.

  The microbial electrolysis cell 200 according to Embodiment 2 is different from the microbial electrolysis cell 100 according to Embodiment 1 in that it has a potentiostat 250 as a voltage application unit. Therefore, the same components as those in the microbial electrolysis cell 100 according to Embodiment 1 are denoted by the same reference numerals, and description thereof is omitted.

  The potentiostat 250 is electrically connected to the anode 130, the cathode 140, and the reference electrode 240, and the electrode potential of the anode (working electrode) 130 is −0.4 V (vs. Ag / AgCl) (Ag / AgCl: silver). -Silver chloride electrode) or more, preferably -0.2 to 2.0 V (vs. Ag / AgCl). The reference electrode 240 is used as a reference for controlling the electrode potential, and the electrode potential of the anode (working electrode) 130 is kept constant by passing electrons through the cathode (counter electrode) 140. As a result, the potentiostat 250 applies a voltage between the anode (working electrode) 130 and the cathode (counter electrode) 140, and electrons generated by the decomposition of the organic matter are transferred from the anode (working electrode) 130 to the potentiostat 250. And finally flows to the cathode 140, and hydrogen is generated on the surface of the cathode 140. Thus, the electrode potential of the anode (working electrode) 130 is always lower than the electrode potential of the cathode 140 by a predetermined potential difference.

  The reference electrode 240 is disposed so as to contact the liquid 120. In the present embodiment, reference electrode 240 is immersed in liquid 120. The type of the reference electrode 240 is not particularly limited and can be selected as appropriate. Examples of the reference electrode 240 include a silver-silver chloride electrode, a standard hydrogen electrode, and a calomel electrode.

(Operation of microbial electrolysis cell)
Next, the operation of the microbial electrolysis cell 200 according to the present embodiment will be described.

  With the potentiostat 250, the anode 130 and the cathode are used by using the reference electrode 240 as a reference so that the electrode potential of the anode (working electrode) 130 is always a predetermined value (for example, −0.2 V (vs. Ag / AgCl)). When the microbial electrolysis cell 200 is operated by applying a voltage to 140, hydrogen ions and electrons are generated in the container 110 when an organic substance (for example, acetic acid) is decomposed into carbon dioxide by the electron donating microorganism 122. Is done. Hydrogen ions generated by the decomposition of the organic matter move to the surface of the cathode 140. On the other hand, the electrons generated by the decomposition of the organic matter are collected by the anode 130 and move to the cathode 140 via an external circuit. In such a situation, hydrogen gas 172 is generated on the surface of the cathode 140 by the reaction between hydrogen ions and electrons. Therefore, by supplying an organic substance into the container 110, the above cycle can be maintained and the hydrogen gas 172 can be continuously generated.

(effect)
The microbial electrolysis cell 200 according to the present embodiment has the same effects as the microbial electrolysis cell 100 according to the first embodiment. In addition, the microbial electrolysis cell 100 according to the first embodiment has an advantage that a reference electrode is unnecessary and the power supply device is less expensive than a potentiostat, but the microbial electrolysis cell 100 according to the first embodiment has an anode 130. Electrode potential fluctuates with operation. On the other hand, in the microbial electrolysis cell 200 according to the present embodiment, the electrode potential of the anode 130 is always kept constant by the potentiostat. Therefore, in the microbial electrolysis cell 200 according to the present embodiment, it is possible to always maintain the optimum electrode potential for the reaction in which electrons generated by the decomposition of the organic matter by the electron donating microorganism 122 are transmitted to the anode 130. Even if pH, organic substance concentration, electric conductivity, etc. fluctuate, it can be operated stably.

  In each of the above embodiments, the hydrogen gas 172 generated on the surface of the cathode 140 is recovered. However, the hydrogen gas 172 does not have to be recovered if the purpose is not hydrogen production. In this case, it is not necessary to provide the hydrogen recovery unit 170 and the hydrogen storage unit 180.

  In the above embodiments, the current flowing between the anode 130 and the cathode 140 is measured by the ammeter included in the power supply 150 or the potentiostat 250. However, an ammeter is provided separately from the power supply 150 or the potentiostat 250. May be. In this case, the control unit 166 is connected to an ammeter provided outside.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

  In this example, a microbial electrolysis cell (see FIG. 2) according to the second embodiment was produced and its characteristics were evaluated. In this example, aeration was intermittently performed.

1. Production of Microbial Electrolysis Cell A rectangular container made of acrylic resin having a capacity of 10 L was prepared as a container. An air diffuser connected to a pump (air discharge amount: 1.7 to 2.0 L / min) was disposed at the bottom of the container. Artificial wastewater was prepared by mixing a medium having the composition shown in the following table and activated sludge as a source of electron-donating microorganisms at a ratio of 5: 1. 10 L of the obtained artificial waste water was introduced into the container.

  A carbon brush as an anode (working electrode, negative electrode), a platinum electrode as a cathode (counter electrode, positive electrode), and a silver-silver chloride electrode as a reference electrode were immersed in the artificial wastewater in the container. These electrodes are connected to a potentiostat. In addition, a funnel-shaped hydrogen recovery unit was installed above the cathode (platinum electrode) to recover hydrogen gas and to measure the amount of hydrogen gas.

2. Evaluation of microbial electrolysis cell The microbial electrolysis cell produced by applying a voltage to the anode and the cathode so that the electrode potential of the anode is -0.2 V with respect to the potential of the silver-silver chloride electrode (reference electrode) at room temperature. Was put into operation. At this time, aeration was intermittently performed in a cycle of aeration for 1 hour and non-aeration for 5 hours. The current flowing between the anode and the cathode and the amount of hydrogen generated were measured every minute after the microbial electrolysis cell was operated. In addition, the redox potential (ORP) of artificial wastewater was also measured every 10 minutes. In addition, the chemical oxygen demand (COD) of artificial wastewater was measured every few hours. Moreover, the total nitrogen (TN) concentration of the artificial wastewater was measured before the operation and 18.5 hours after the operation. Also, in an experiment to demonstrate the correlation between the COD of artificial wastewater and the amount of current generated, when artificial wastewater with various COD concentrations was put into a container and aeration was stopped once a day, 1 hour passed. The current and COD flowing between the anode and cathode were measured.

  FIG. 3 is a graph showing the change over time of the current flowing between the anode and the cathode in the microbial electrolysis cell, and FIG. 4 is a graph showing the change over time of the total amount of hydrogen generated in the microbial electrolysis cell. From these graphs, it can be seen that even when intermittent aeration is performed, the microbial electrolysis cell operates normally and hydrogen gas generation can be continued. Moreover, it turns out that the reduction | decrease of the electric current and hydrogen generation amount by the density | concentration of organic substance reducing with progress of time arises.

  FIG. 5 is a graph showing a change with time of the oxidation-reduction potential (ORP) of the artificial wastewater in the microbial electrolysis cell. From this graph, it can be seen that the oxidation-reduction potential has increased to a positive value due to aeration and is in an aerobic state.

  FIG. 6 is a graph showing measurement results of chemical oxygen demand (COD) of artificial wastewater in a microbial electrolysis cell. From this graph, it can be seen that the microbial electrolysis cell according to the present invention can decompose organic substances until the COD becomes a low value of 100 mg / L. This is because various microorganisms including electron donating microorganisms adhere to the anode at a high density, so that the microorganisms are kept at a high concentration in the container, and further, organic matter and electron donating microorganisms in the artificial wastewater are aerated by aeration. It is thought that it was possible to contact efficiently. Although the results are not shown here, the biochemical oxygen demand (BOD) also decreased in the same manner.

  FIG. 7 is a graph showing the measurement results of the nitrogen concentration of artificial wastewater in the microbial electrolysis cell before and after operation. From this graph, it can be seen that the microbial electrolysis cell according to the present invention can remove nitrogen in the mixed solution in the same manner as the intermittent aeration activated sludge tank. In addition, although a result is not shown here, nitrogen cannot be removed in the microbial electrolysis cell operated without performing the aeration process. This is considered to be because a microbial electrolysis cell operated without performing aeration treatment is always in an anaerobic state, and does not cause an ammonia oxidation reaction (nitrification) that occurs in an aerobic state and does not cause a denitrification reaction. . This shows that the removal of nitrogen is promoted by performing (intermittent) aeration in the microbial electrolysis cell.

  FIG. 8 is a graph showing the results of experiments conducted to demonstrate the correlation between chemical oxygen demand (COD) of artificial wastewater and current. This graph shows the relationship between the current flowing between the anode and cathode of the microbial electrolysis cell one hour after stopping aeration and the COD of the artificial wastewater at that time. A dotted line is a straight line indicating a linear approximation formula (y = 14722x + 63.13). From this graph, it can be seen that there is a high correlation between current and COD, and COD can be detected from the current. Although no results are shown here, there was a high correlation between current and COD even during aeration. Biochemical oxygen demand (BOD) is also highly correlated with current.

  In this embodiment, a potentiostat is used as the voltage application unit, but the same applies when a voltage of 0.8 V is applied between the anode and the cathode using a power source as the voltage application unit (see FIG. 1). The result was obtained.

  Since the microbial electrolysis cell according to the present invention has a high ability to decompose organic substances while maintaining the ability to generate hydrogen gas, it is useful in, for example, wastewater treatment in livestock barns or sewage purification treatment in urban areas.

100, 200 Microbial electrolysis cell 110 Container 120 Liquid 122 Electron donating microorganism 130 Anode 140 Cathode 150 Power supply 160 Aeration device 162 Pump 164 Air diffuser 166 Control unit 168 Air 170 Hydrogen recovery unit 172 Hydrogen gas 180 Hydrogen storage unit 240 Reference electrode 250 Potentiostat

Claims (6)

A container,
A liquid containing organic matter and electron-donating microorganisms contained in the container;
An anode and a cathode arranged to contact the liquid;
A voltage applying unit that applies a voltage between the anode and the cathode such that the potential of the anode is lower than the potential of the cathode;
An aeration apparatus for sending a gas containing oxygen to the liquid;
A microbial electrolysis cell.   The microbial electrolysis cell according to claim 1, wherein the aeration apparatus intermittently sends the gas into the liquid.   The microbial electrolysis cell according to claim 2, wherein the aeration apparatus intermittently feeds the gas into the liquid, whereby an aerobic state and an anaerobic state are repeated in the liquid, and nitrogen in the liquid is removed. .   The microbial electrolysis cell according to any one of claims 1 to 3, wherein the gas is air.   5. The aeration apparatus according to claim 1, wherein at least one of an amount of feeding the gas and a time of feeding the gas is adjusted according to a current flowing between the anode and the cathode. Microbial electrolysis cell.   The microbial electrolysis cell according to any one of claims 1 to 5, further comprising a hydrogen recovery unit that recovers hydrogen generated from the cathode.

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