JP2016031778A - Microbial fuel battery system - Google Patents

Abstract

Disclosed is a microbial fuel cell system capable of stably generating power with good electric power while maintaining a redox potential of wastewater at a low potential.
An anaerobic tank 10 for performing anaerobic treatment of waste water containing organic substances, and an anaerobic tank 10 installed at the rear stage of the anaerobic tank 10 oxidatively decomposes an anode 22, a cathode 24, and a substrate contained in the waste water into the anode. A microbial fuel cell system 1, comprising a microbial fuel cell tank 20 that holds microorganisms that donate water. The waste water containing organic substances is transferred to the microbial fuel cell tank 20 after being subjected to anaerobic treatment for reducing the oxidation-reduction potential in the anaerobic tank 10.
[Selection] Figure 1

Description

  The present invention relates to a microbial fuel cell system.

  In recent years, development of microbial fuel cells that generate electricity using oxidation-reduction reactions by microorganisms has been promoted. A microbial fuel cell is a device that collects electrons generated in the process of microorganisms oxidizing and decomposing a substrate such as an organic substance or an inorganic substance using an electrode as a final electron acceptor. By incorporating the microbial fuel cell into the wastewater treatment system, it is possible to construct a microbial fuel cell system that integrates biological treatment of wastewater and power generation using wastewater, and microorganisms are acquired in the biological treatment of wastewater. A part of the generated energy can be taken off by shutting off the electron transmission system and recovered as electric energy. Therefore, the microbial fuel cell system is expected as a technology that realizes wastewater treatment with excellent energy saving and reduced generation of excess sludge.

  For the practical application of the microbial fuel cell system, further improvement of the generated power is required. In order to improve the power generated by microorganisms, it is important how to maintain the concentration of the substrate in which the microorganisms involved in power generation are oxidatively decomposed and the amount of cells of the microorganisms involved in power generation. In view of this, a technique has been proposed that prevents the microorganisms from flowing out of the microbial fuel cell and increases the concentration of the microorganisms involved in power generation, thereby improving the recovery efficiency of electric energy.

  For example, Patent Document 1 discloses an inflow process in which a liquid containing an organic substance is introduced into a fuel cell (microbial fuel cell) in which an anaerobic microorganism that functions as a catalyst is supported on an electrode; In a microbial fuel cell system comprising a power generation step of generating electricity while biologically treating a liquid containing a sexual substance and a separation step of solid-liquid separation of the liquid treated by the microbial fuel cell, the microbial fuel cell system is extracted by the separation step A technique for returning a liquid containing a solid component (excess sludge) to the microbial fuel cell is disclosed.

JP 2013-143363 A

  According to Patent Document 1, by returning the liquid containing the solid component (excess sludge) separated in the separation step to the microbial fuel cell, the concentration of microorganisms can be increased and the energy recovery efficiency can be increased. It is said that. However, in order to stably maintain the power generation in the microbial fuel cell system with the expected power, not only the entry and exit of such excess sludge but also the optimization of electron transfer by microorganisms (power generation microorganisms) involved in power generation desired.

  The oxidation-reduction potential suitable for the electron transfer system of the power generation microorganism is generally in a low potential range lower than the potential of about −100 mV to −200 mV. However, wastewater such as sewage used for supplying an electron donor to power generation microorganisms in a microbial fuel cell system has many opportunities to come into contact with air before being supplied, and the dissolved oxygen concentration becomes relatively high. Tend. In addition, since the organic matter concentration is relatively low, the consumption of dissolved oxygen accompanying decomposition of the organic matter remains low even in the presence of microorganisms, and the dissolved oxygen concentration is easily maintained at a high level. Therefore, in the microbial fuel cell system, the redox potential of the wastewater introduced for biological treatment is unlikely to be a low potential suitable for the electron transfer system of the power generation microorganism, and stable power generation with good power is possible. It is difficult to do this.

  Therefore, an object of the present invention is to provide a microbial fuel cell system capable of stably generating power with good electric power while maintaining the redox potential of wastewater at a low potential.

  In order to solve the above problems, a microbial fuel cell system according to the present invention includes an anaerobic tank that performs anaerobic treatment of wastewater containing organic matter, an anaerobic tank, and an anode, a cathode, and the wastewater. And a microbial fuel cell tank that holds microorganisms that oxidize and decompose the contained substrate to donate electrons to the anode.

  According to the present invention, the oxidation-reduction potential of wastewater can be lowered in advance by anaerobic treatment, so that the microorganism capable of stably generating power with good power while maintaining the oxidation-reduction potential of wastewater at a low potential A fuel cell system can be provided.

It is a figure which shows an example of a structure of the microbial fuel cell system which concerns on one Embodiment of this invention. It is a figure which shows an example of a structure of the microbial fuel cell system which concerns on the modification 1. It is a figure which shows an example of a structure of the microbial fuel cell system which concerns on the modification 2. It is a figure which shows an example of a structure of the microbial fuel cell system which concerns on the modification 3. It is a figure which shows an example of a structure of the microbial fuel cell system which concerns on an Example. It is a figure which shows the time-dependent change of the oxidation reduction potential of wastewater in the microbial fuel cell system which concerns on an Example, and the microbial fuel cell system which concerns on a comparative example. It is a figure which shows the time-dependent change of the power density of the electric power generation by the microbial fuel cell system which concerns on an Example, and the microbial fuel cell system which concerns on a comparative example.

  A microbial fuel cell system according to an embodiment of the present invention will be described below. In addition, the same code | symbol is attached | subjected to the common part in each figure, and description about the overlapping part is abbreviate | omitted.

  FIG. 1 is a diagram showing an example of the configuration of a microbial fuel cell system according to an embodiment of the present invention.

  As shown in FIG. 1, the microbial fuel cell system 1 according to this embodiment includes an anaerobic tank 10 and a microbial fuel cell tank 20. The microbial fuel cell system 1 is an apparatus that integrates biological treatment of wastewater and power recovery using wastewater to supply an electron donor by incorporating the microbial fuel cell into the wastewater treatment system. . In the microbial fuel cell system 1, the anaerobic tank 10 and the microbial fuel cell tank 20 are provided in this order, and raw water (waste water) treated in the anaerobic tank 10 is transferred to the microbial fuel cell tank 20 at the subsequent stage. After being treated, it is drained as treated water.

  In the microbial fuel cell tank 20, biological treatment of wastewater and power recovery (recovery of electric energy) using the wastewater and power generation microorganisms are performed. In the microbial fuel cell system 1, the anaerobic tank 10 is provided in the preceding stage of the microbial fuel cell tank 20, and the oxidization-reduction potential of the wastewater is reduced in advance by anaerobic treatment in the anaerobic tank 10. Stable power recovery is realized in the fuel cell tank 20.

  In the microbial fuel cell system 1, waste water containing organic substances is introduced as raw water. The wastewater is, for example, sewage such as domestic wastewater, factory wastewater, business site wastewater, rainwater collected from a side ditch through a rainwater pipe, or sewage such as mixed wastewater in a state where they are combined. Such waste water is introduced into the anaerobic tank 10 after removal of suspended solids, sedimentary solids, and the like via a first sedimentation tank (not shown).

As sewage to be introduced as raw water, the water quality index value for dissolved state is 0 mg / L to 500 mg / L for COD _Cr (oxygen consumption by potassium dichromate), COD _Mn (depending on potassium permanganate at 100 ° C. Oxygen consumption) 0 mg / L to 500 mg / L, BOD (Biochemical Oxygen Consumption) 0 mg / L to 500 mg / L, TOC (Organic Carbon) 0 mg / L to 100 mg / L, TN ( A waste water in the range of 0 mg / L to 100 mg / L is assumed for the total nitrogen concentration). Water quality index values for the dissolved state are preferably 10 mg / L to 100 mg / L for COD _Cr , 10 mg / L to 100 mg / L for COD _Mn , 10 mg / L to 100 mg / L for BOD, 5 mg / L to TOC 50 mg / L, TN ranges from 5 mg / L to 50 mg / L. In the microbial fuel cell system 1, it is possible to realize stable power recovery even when wastewater having a relatively low substrate concentration is used.

  It is assumed that DO (dissolved oxygen concentration) of sewage introduced as raw water is in the range of 0 mg / L to 7 mg / L, and preferably in the range of 0 mg / L to 4 mg / L. Note that the oxidation-reduction potential of the wastewater is usually 0 mV or more even when DO is about 0 mg / L. The microbial fuel cell system 1 can suitably treat wastewater in a non-aerated state in which DO of sewage introduced as raw water is 7 mg / L or less. When the sewage DO is about 4 mg / L or less, the redox potential is easily lowered to a desired low potential value in anaerobic treatment, which is advantageous from the viewpoint of the efficiency of power recovery.

  The anaerobic tank 10 is a treatment tank that performs anaerobic treatment of wastewater containing organic matter, and works to reduce the oxidation-reduction potential of wastewater introduced into the microbial fuel cell tank 20 in advance. The anaerobic tank 10 holds sludge containing anaerobic microorganisms, and the atmosphere of the treatment tank is maintained under a low free oxygen condition or a non-free oxygen condition. Further, the anaerobic tank 10 is provided with a stirring means 12 for stirring the wastewater to be anaerobically treated. The stirrer 12 stirs the wastewater to be anaerobically treated so that the sludge and wastewater are homogenized and the sludge sedimentation is suppressed. Further, as shown in FIG. 1, a redox potentiometer 14 for measuring the redox potential of wastewater can be installed in the anaerobic tank 10. The oxidation-reduction potential meter 14 can be managed so that the oxidation-reduction potential of the wastewater subjected to anaerobic treatment becomes a low potential.

  The sludge retained in the anaerobic tank 10 is preferably immobilized using an immobilization carrier or a fixed bed carrier. By immobilizing the sludge, the inflow of sludge from the anaerobic tank 10 to the microbial fuel cell tank 20 can be suppressed. The immobilization carrier is preferably a floating carrier on which anaerobic microorganisms are supported, and the fixed bed carrier preferably has a shape in which a top plate such as a support member constituting the immobilization carrier is exposed on the water surface of waste water. Decreasing the contact surface between the waste water and the gas phase held in the anaerobic tank 10 by floating a large number of immobilization carriers as floating carriers so as to cover the water surface or exposing the fixed bed carriers on the water surface. Can do. Therefore, even when the sealed anaerobic tank 10 is temporarily opened with water sampling or the like, it is possible to suppress the oxidation-reduction potential of the wastewater from becoming high due to oxygen in the outside air. Alternatively, even if the anaerobic tank 10 has a simple structure, it is possible to reduce the dissolution of oxygen in the outside air into the wastewater, and to reduce the cost of the structure of the anaerobic tank 10 while increasing the redox potential of the wastewater. It becomes possible to suppress.

As the floating carrier held in the anaerobic tank 10, a carrier made of resin, gel, or the like having an appropriate shape such as a cylindrical shape, a sponge shape, a rectangular parallelepiped, or a sphere can be used. As a material for the floating carrier, an appropriate material such as polypropylene, polyethylene, urethane foam, acrylic resin, polyethylene glycol, alginic acid, or cellulose can be used. The density of the floating carrier is 1.0 g / cm ³ or less, preferably 0.8 g / cm ³ or more and 1.0 g / cm ³ or less, more preferably 0.9 g / cm ³ or more and 0.95 g / cm ³ or less. . The size of the floating carrier is such that the maximum diameter is less than 10 cm, preferably 1 cm or more and less than 10 cm, more preferably 1 cm or more and 5 cm or less. As the floating carrier, a polypropylene cylindrical carrier having a density of 0.9 g / cm ^{3 to} 0.95 g / cm ³ and a maximum diameter of 1 cm to 5 cm is particularly suitable. . Such a floating carrier is advantageous in that the adhesion rate of microorganisms is high, and the ratio of covering the contact surface between the waste water and the gas phase becomes high when a large number of floating carriers are suspended on the water surface.

  In the anaerobic tank 10, wastewater introduced as raw water is anaerobically treated with anaerobic microorganisms under low free oxygen conditions or non-free oxygen conditions to decompose organic matter contained in the wastewater. By performing anaerobic treatment, dissolved oxygen is consumed by anaerobic microorganisms in the absence of external oxygen supply, and reductants are generated by decomposition treatment of organic matter, etc., reducing the redox potential of wastewater Will do. In order to reduce the oxidation-reduction potential of the wastewater to a desired low potential, the residence time of the wastewater in the anaerobic tank 10, the amount of sludge, the amount of inflow of wastewater, etc. may be adjusted as appropriate. Then, the redox potential of the waste water is measured by the redox potential meter 14, and the management is performed so that the outlet value of the redox potential is maintained in the low potential range indicating the reduced state.

  The redox potential of the wastewater in the anaerobic tank 10 is preferably in the range of −200 mV or less, more preferably −300 mV or less, and even more preferably −400 mV or less. This is because when the oxidation-reduction potential of the wastewater is a low potential of about −200 mV or less, power can be recovered significantly in the microbial fuel cell tank 20. Further, when the oxidation-reduction potential is lowered in this manner in the anaerobic tank 10, the wastewater is retained in the microbial fuel cell tank 20 even after flowing out of the anaerobic tank 10 and into the microbial fuel cell tank 20. Since the oxidation-reduction potential is likely to be lowered by the anaerobic treatment with sludge, the power recovery can be performed more suitably. The oxidation-reduction potential can be reduced to about −500 mV by ordinary anaerobic treatment. However, the lower the potential, the more the generated power increases and the power generation stability tends to improve. Treatment may be performed with a residence time such that substantially reaches equilibrium and the oxidation-reduction potential reaches a constant level. The waste water that has been treated in the anaerobic tank 10 is then transferred to the microbial fuel cell tank 20 via a pipe or the like that prevents air from entering.

  The microbial fuel cell tank 20 is a treatment tank in which a substrate contained in waste water is oxidized and decomposed into power-generating microorganisms, and electrons generated during the oxidative decomposition process are collected to collect power. The microbial fuel cell tank 20 is installed at the rear stage of the anaerobic tank 10 and holds an anode 22, a cathode 24, and power generation microorganisms (not shown).

  The anode 22 is an electrode that collects electrons generated in the process of the power generation microorganisms oxidizing and decomposing the substrate, and is held in a state of being immersed in waste water introduced into the microbial fuel cell tank 20. The anode 22 can be formed of a carbon material or a metal material formed into a flat plate shape, a film shape, or a cylindrical shape. Examples of the carbon material include carbon cloth, carbon felt, and carbon paper. Examples of the metal material include stainless steel and platinum.

  The cathode 24 is an electrode serving as a counter electrode of the anode 22 and is in the form of an air cathode in which one main surface is in contact with waste water while the other main surface is in contact with air. As shown in FIG. 1, the air cathode can be formed by forming a window portion on the side surface of the box body 26 whose upper surface is opened and closing the window portion with a breathable cathode 24 in a watertight manner. The box 26 (air cathode) provided with the cathode 24 may be held in a state of being semi-immersed in the waste water introduced into the microbial fuel cell tank 20 so that the upper opening is opened to the outside air. The breathable cathode 24 can be formed of a fibrous carbon material formed into a flat plate shape, a membrane shape, or a cylindrical shape. Examples of the carbon material include carbon cloth, carbon felt, carbon paper and the like, and those having a water repellency on the material surface and carrying a catalyst such as platinum are preferable.

  As shown in FIG. 1, the anode 22 and the cathode 24 are respectively connected to an external load R via a conducting wire to form a chemical battery. The electrons collected by the anode 22 move to the cathode 24 side via the external resistance R, and oxygen in the air is supplied as an electron acceptor at the cathode 24, and an oxidation-reduction reaction involving oxygen and water occurs. . In the microbial fuel cell 1, the electrical energy generated by the power generation microorganism is collected from such an external circuit.

  The number of electrodes, the electrode area, the arrangement, and the like of the anode 22 and the cathode 24 are not particularly limited. For example, as shown in FIG. 1, a pair of the anode 22 and the cathode 24 are arranged in parallel. A plurality of pairs of anodes 22 and cathodes 24 constituting the electrodes can be arranged. In the plan view of the microbial fuel cell tank 20, each of the anode 22 and the cathode 24 has one end in the longitudinal direction abutting against the inner wall of the microbial fuel cell tank 20, and the other end from the inner wall of the microbial fuel cell tank 20. Arrange them so that they are separated. In other words, the microbial fuel cell tank 20 is partitioned by the anode 22 and the cathode 24 that are arranged in parallel so that the portions separated from the inner wall are alternately arranged on the left and right sides, and the horizontal detour in which the waste water is alternately diverted in the horizontal direction. It is possible to form a flow-type treatment tank. As described above, when the microbial fuel cell tank 20 is a bypass processing tank, the wastewater flows while being stirred, so that uneven distribution of the power generation microorganisms is reduced for each of the plurality of electrodes arranged in parallel. be able to. As a result, the efficiency of oxidative decomposition by the power generation microorganisms and the current collection by the anode 22 can be increased, and the efficiency of power recovery can be improved. Further, the residence time is easily secured and the uneven distribution of sludge is suppressed, so that anaerobic treatment and power recovery can be stabilized.

  The power generation microorganism is a microorganism that donates electrons to the anode 22 by oxidizing and decomposing a substrate such as an organic substance or an inorganic substance contained in waste water. As the power generation microorganism, a microorganism having the ability to use metal ions such as iron, manganese, vanadium, and oxides thereof as the final electron acceptor in the electron transfer system can be used. Examples of such microorganisms include microorganisms classified into the genus Shewanella, the genus Geobacter and the like, which have an electron transfer ability outside the cell. Among these, it is preferable to use Shewanella oneidensis, Geobacter sulfurreducens or Geobacter metallireducens among these. Such power-generating microorganisms can be used in the form of sludge containing anaerobic microorganisms, suspended in waste water introduced into the microbial fuel cell tank 20, or immobilized on the anode 22.

  In the microbial fuel cell tank 20, the wastewater whose oxidation-reduction potential is lowered in the anaerobic tank 10 is anaerobically treated under sludge containing power generation microorganisms under low free oxygen conditions or no free oxygen conditions, and is contained in the wastewater. Decompose the substrate oxidatively. Electrons generated in the process of oxidative decomposition of the substrate by the power generation microorganism are taken from the electron transfer system of the power generation microorganism, collected by the anode 22 and collected as electric power. It is possible to realize a redox potential suitable for the electron transfer system of the power generation microorganism by transferring the waste water having a reduced redox potential in the anaerobic tank 10 to the microbial fuel cell tank 20 while suppressing intrusion of air. It is. The oxidation-reduction potentiometer 14 may be installed in the microbial fuel cell tank 20 or a pipe between the anaerobic tank 10 and the microbial fuel cell tank 20.

  In such a microbial fuel cell tank 20, the anaerobically treated waste water is drained out of the microbial fuel cell system 1 as treated water. Usually, wastewater such as sewage introduced as raw water into the microbial fuel cell system 1 is difficult to ensure the quality of discharged water only by anaerobic treatment. An aerobic tank to be performed, an aerobic tank having an anaerobic tank and an aerobic tank, an anaerobic tank to perform anaerobic treatment of wastewater in the absence of free oxygen and bound oxygen, and aerobic The system may be configured such that a multiple-stage processing tank including a tank is installed.

  According to the microbial fuel cell system 1 according to the above-described embodiment, the anaerobic tank 10 that performs the anaerobic treatment of wastewater is provided in the front stage of the microbial fuel cell tank 20, so that the wastewater introduced into the microbial fuel cell tank 20. The redox potential of can be lowered in advance. By anaerobically treating the introduced wastewater, the oxidation-reduction potential of the wastewater flowing into the microbial fuel cell tank 20 can always be maintained at a low potential of about −200 mV or less. Oxidative decomposition and electron transfer proceed at a favorable reaction rate, so that the power density per electrode to be generated can be improved and the generated power can be maintained stably over time. In addition, the sludge can be prevented from flowing into the microbial fuel cell tank 20 from the previous stage by the design of the tank structure of the anaerobic tank 10 and the connection structure between the anaerobic tank 10 and the microbial fuel cell tank 20. Therefore, it can be avoided that the bacterial flora in which the power generation microorganisms are accumulated is fluctuated to reduce the amount of the power generation microorganisms, and it is possible to easily ensure the stability of the generated power with time.

  Next, a microbial fuel cell system according to Modification 1 will be described.

  FIG. 2 is a diagram illustrating an example of the configuration of the microbial fuel cell system according to the first modification.

  As shown in FIG. 2, the microbial fuel cell system 1 according to the embodiment is configured as a microbial fuel cell system 2 (microbial fuel cell system according to Modification 1) 2 in which the structure of the anaerobic tank is changed. You can also. The microbial fuel cell system 2 according to the first modification includes an up-and-down bypass type anaerobic tank 10 </ b> A instead of the single-chamber anaerobic tank 10.

  The anaerobic tank 10 </ b> A is a treatment tank that performs anaerobic treatment of wastewater containing organic matter. Like the anaerobic tank 10, wastewater containing organic matter is introduced as treated water and is supplied to the microbial fuel cell tank 20. It works to lower the oxidation-reduction potential of the wastewater introduced. As shown in FIG. 2, the anaerobic tank 10 </ b> A has an up-and-down bypass tank structure partitioned by a bypass wall 110 arranged along the vertical direction. The outlet of the wastewater in the anaerobic tank 10A is provided on the upper side of the processing chamber 102 where the upward flow is formed by the bypass wall 110.

  In the detour wall 110, one end in the vertical direction is in contact with the inner wall of the anaerobic tank 10A, while the other end is separated from the inner wall of the anaerobic tank 10A, and an opening is provided between the detour wall 10A. This opening forms a bypass channel f that communicates between the spaces on both sides separated by the bypass wall. In FIG. 2, the anaerobic tank 10 </ b> A includes two processing chambers 101 and 102 partitioned by a bypass wall 110, and the processing chambers communicate with each other through an opening provided on the lower end side of the bypass wall 110. However, the number of processing chambers partitioned by the bypass wall is not particularly limited. For example, a tank structure including three or more chambers may be provided such that openings provided on the lower end side of the bypass wall and openings provided on the upper end side are alternately arranged. Further, although the first processing chamber 101 is provided with the stirring means 12A, it can be omitted without installing the stirring means 12A.

  According to the microbial fuel cell system 2 according to Modification 1 described above, by providing the bypass wall 110 in the anaerobic tank 10A, the wastewater to be anaerobically treated in the anaerobic tank 10A can be weakly stirred by the water head. Can be stirred. Then, by providing an outlet of the waste water on the upper side of the processing chamber 102 where the upward flow is formed by the bypass wall 110, the supernatant waste water in which the sludge is prevented from floating can be transferred to the microbial fuel cell tank 20. it can. Therefore, it is possible to suppress the outflow of sludge required for anaerobic treatment from the anaerobic tank 10 </ b> A and the inflow of sludge from the previous stage into the microbial fuel cell tank 20. By suppressing the outflow of sludge from the anaerobic tank 10A, it is possible to stabilize the anaerobic treatment in the anaerobic tank 10A, and by suppressing the inflow of sludge into the microbial fuel cell tank 20, the power generation microorganisms accumulate. The decrease in the amount of power-generating microorganisms caused by fluctuations in the existing bacterial flora can be suppressed, so stable stabilization by power-generating microorganisms that maintain the amount of cells while reliably reducing the redox potential through stable anaerobic treatment Power generation can be performed, and more efficient power recovery can be realized.

  Next, a microbial fuel cell system according to Modification 2 will be described.

  FIG. 3 is a diagram illustrating an example of a configuration of a microbial fuel cell system according to Modification 2.

  As shown in FIG. 3, the microbial fuel cell system 1 according to the embodiment includes a microbial fuel cell system (a microbial fuel cell system according to Modification 2) 3 in which the connection structure between the anaerobic tank and the microbial fuel cell tank is changed. It is also possible to adopt a form such as The microbial fuel cell system 3 according to Modification 2 includes a connection pipe 120 and a control valve V10 between the anaerobic tank 10 and the microbial fuel cell tank 20. The tank configuration of the microbial fuel cell tank 20 is the same as that in the microbial fuel cell system 1 described above.

  The connecting pipe 120 communicates between the anaerobic tank 10 and the microbial fuel cell tank 20 to form a waste water flow path. The connecting pipe 120 connects the upper side of the anaerobic tank 10 and the microbial fuel cell tank 20, and transfers the supernatant of waste water held in the anaerobic tank 10 to the microbial fuel cell tank 20. When the wastewater is transferred by the connecting pipe 120, contact between the wastewater and the outside air is reduced, so that the oxidation-reduction potential of the wastewater can be easily maintained at a low potential. The connecting pipe 120 may be connected so that the wastewater flows down naturally by the head of water, or the wastewater pressurized by passing a pump (not shown) may flow therethrough.

  The control valve V <b> 10 is provided in the connection pipe 120 and has a function of controlling the flow rate of waste water in the connection pipe 120. The control valve V10 is connected to the oxidation-reduction potentiometer 14 via a signal line, and the opening degree is controlled based on the oxidation-reduction potential of wastewater measured by the oxidation-reduction potentiometer 14. . The opening degree of the control valve V10 is set in the controller of the control valve by setting a predetermined low potential value such that the oxidation-reduction potential of the wastewater introduced into the microbial fuel cell tank 20 is −200 mV or less, and the set value And the measured value measured by the oxidation-reduction potentiometer 14 can be controlled. Note that the oxidation-reduction potentiometer 14 is provided in the anaerobic tank 10 in FIG. 3, but may be provided in the microbial fuel cell tank 20, or between the anaerobic tank 10 and the microbial fuel cell tank 20. It may be provided on the connecting pipe 120.

  The control valve V10 opens the wastewater flow path at a predetermined opening when the oxidation-reduction potential of the wastewater measured by the oxidation-reduction potentiometer 14 is equal to or lower than a set value. The opening degree of the control valve V10 may be controlled based on the flow rate so that the wastewater is transferred to the microbial fuel cell tank 20 at a predetermined flow rate, or may be fully opened without being controlled based on the flow rate. In this way, when the redox potential of the wastewater is equal to or lower than the set value (predetermined low potential value), the microbial fuel cell tank 20 has a low redox potential by anaerobic treatment by opening the flow path. Reduced wastewater is transferred to

  On the other hand, when the oxidation-reduction potential of the wastewater measured by the oxidation-reduction potentiometer 14 exceeds the set value, the control valve V10 fully closes the wastewater flow path. As described above, when the oxidation-reduction potential of the wastewater exceeds the set value (predetermined low potential value), the wastewater whose oxidation-reduction potential is not lowered to the low potential is supplied to the microbial fuel cell tank 20 by closing the flow path. It can be restricted from being transferred.

  According to the microbial fuel cell system 3 according to Modification 2 described above, wastewater whose oxidation-reduction potential is not lowered to a low potential can be restricted from flowing into the microbial fuel cell tank 20, so that the microbial fuel cell The oxidation-reduction potential of the wastewater in the tank 20 can be reliably maintained at a low potential, and the generated power can be more stabilized over time. Further, since the residence time of the anaerobic treatment in the anaerobic tank 10 can be varied by controlling the opening and closing of the control valve V10, the microbial fuel is not affected by the oxidation-reduction potential of the wastewater introduced as raw water. The redox potential of the wastewater introduced into the battery tank 20 can be lowered to a desired low potential value.

  Next, a microbial fuel cell system according to Modification 3 will be described.

  FIG. 4 is a diagram illustrating an example of a configuration of a microbial fuel cell system according to Modification 3.

  As shown in FIG. 4, the microbial fuel cell system 1 according to the embodiment includes a microbial fuel cell system (microbial fuel cell system according to Modification 3) 4 in which the connection structure between the anaerobic tank and the microbial fuel cell tank is changed. It is also possible to adopt a form such as The microbial fuel cell system 4 according to Modification 3 includes a sedimentation tank 40, a sludge return pipe 130, and a sludge return pump 46 between the anaerobic tank 10 and the microbial fuel cell tank 20. The tank configuration of the microbial fuel cell tank 20 is the same as that in the microbial fuel cell system 1 described above.

  The sedimentation tank 40 is a treatment tank that is provided downstream of the anaerobic tank 10 and upstream of the microbial fuel cell tank 20 and performs a precipitation separation process of wastewater containing sludge. A sludge return pipe 130 is connected to the bottom of the sedimentation tank 40. Inside the sedimentation tank 40, an inclined plate and an inclined pipe (not shown) are arranged. It is possible to improve sludge sedimentation efficiency by installing an inclined plate or an inclined pipe and allowing the waste water to flow upward or horizontally. Moreover, a sludge scraper, a scum remover, etc. (not shown) can be installed. The sludge scraper and the scum remover may be provided with an appropriate device such as a traveling type or a rotating type according to the shape of the sedimentation tank 40. In addition, it is preferable that the tank structure of the settling tank 40 is a sealed type to prevent intrusion of oxygen in the outside air and release of odor.

  In the sedimentation tank 40, sludge in the wastewater transferred from the anaerobic tank 10 is settled and removed by causing the wastewater to stay at a slow speed. The wastewater from which the sludge has been removed is transferred to the microbial fuel cell tank 20 by overflowing the overflow weir provided on the upper side of the settling tank 40 while maintaining the reduced redox potential. . On the other hand, the sludge settled on the lower side of the settling tank 40 is drawn out to the sludge return pipe 130.

  The sludge return pipe 130 communicates between the settling tank 40 and the anaerobic tank 10, and returns the sludge separated in the settling tank 40 to the anaerobic tank 10. The sludge return pipe 130 is provided with a sludge return pump 46. When the sludge return pump 46 is operated, surplus sludge removed from the waste water in the settling tank 40 is returned to the anaerobic tank 10 and is anaerobic. Reused for processing.

  According to the microbial fuel cell system 4 according to Modification 3 described above, the sedimentation tank 40 is provided in the previous stage of the microbial fuel cell tank 20, thereby suppressing sludge from flowing into the microbial fuel cell tank 20 from the previous stage. Can do. Therefore, it can be avoided that the bacterial flora in which the power generation microorganisms are accumulated is fluctuated and the amount of the power generation microorganisms is reduced, and the stability of the generated power over time can be easily secured. Moreover, by providing the sludge return pipe 130, it becomes easy to ensure the amount of sludge in the anaerobic tank 10, and it becomes possible to maintain the efficiency of the anaerobic treatment for reducing the oxidation-reduction potential of the wastewater at a high level.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples of the present invention, but the present invention is not limited thereto.

  As an example, evaluation of power generated by the microbial fuel cell system according to the above embodiment was performed. In addition, as a control (comparative example), evaluation of power generated by a microbial fuel cell system not equipped with an anaerobic tank was also performed.

  FIG. 5 is a diagram illustrating an example of the configuration of the microbial fuel cell system according to the embodiment.

  As shown in FIG. 5, the microbial fuel cell system according to the embodiment includes an anaerobic tank 10 </ b> B that performs anaerobic treatment of wastewater containing organic matter, and a microbial fuel cell tank 20, and a subsequent stage of the microbial fuel cell tank 20. The microbial fuel cell system 5 provided with an aerobic tank 50 for performing an aerobic treatment of wastewater and a settling tank 60 for performing a precipitation separation process of wastewater containing sludge was used in this order. The tank configuration of the microbial fuel cell tank 20 is the same as that in the microbial fuel cell system 1 described above. The tank capacity ratio of each processing tank provided in the microbial fuel cell system 5 is set such that the anaerobic tank 10B: microbial fuel cell tank 20: aerobic tank 50: sedimentation tank 60 is 5: 2: 1: 2. Yes.

  As shown in FIG. 5, the anaerobic tank 10 </ b> B includes two processing chambers 103 and 104 partitioned by a bypass wall 210, and the processing chambers communicate with each other through an opening provided on the lower end side of the bypass wall 210. It has a vertical detour tank structure. The two processing chambers 103 and 104 have a double cylindrical structure, and are partitioned between the inner processing chamber 103 having a circular shape in a plan view and defined between the outer cylinder and the inner cylinder. The outer processing chamber 104 has an annular shape in plan view. Then, the inner processing chamber 103 and the outer processing chamber 104 communicate with each other through an opening provided on the lower end side of the bypass wall 210, and a bypass channel f is formed in the radial direction from the inner processing chamber 103 to the outer processing chamber 104. ing.

  The aerobic tank 50 is a treatment tank that performs aerobic treatment of wastewater. The aerobic tank 50 is provided with aeration means for aeration of wastewater to be aerobically treated. As shown in FIG. 5, the aeration unit is configured by a diffuser tube 52 and a blower 54. When air is supplied to the diffuser tube 52 by the blower 54, air is diffused from the diffuser tube 52 to waste water. The aerobic tank 50 holds sludge containing aerobic microorganisms. Therefore, the wastewater introduced into the aerobic tank 50 is subjected to aerobic treatment by aerobic microorganisms, the oxidation-reduction potential returns to the high potential side, and organic matter decomposition treatment and dephosphorization treatment are performed to obtain treated water with good water quality. It has come to be obtained.

  The sedimentation tank 60 is a treatment tank similar to the sedimentation tank 40 provided in the microbial fuel cell system 3 except that the sedimentation tank 60 has an open tank structure. A sludge extraction pipe 150 is connected to the lower side of the settling tank 60, and the sludge return pipe 150 is provided with a sludge return pump 66. The sludge removed from the waste water in the settling tank 60 is returned to the aerobic tank 50. It has come to be.

  In the Example, the treated water of the first sedimentation basin of the sewage treatment plant was introduced into the anaerobic tank 10B of the microbial fuel cell system 5 shown in FIG. And after reducing the oxidation-reduction potential of wastewater in the anaerobic tank 10B, the microbial fuel cell tank 20 recovered the electrical energy. At this time, the generated power generated in the microbial fuel cell tank 20 is measured via an external circuit, and the oxidation-reduction potential of the wastewater is periodically measured by the oxidation-reduction potentiometer 14 installed in the microbial fuel cell tank 20. . These results are shown in FIGS.

  On the other hand, in the comparative example, in place of the microbial fuel cell system 5 shown in FIG. 5, the microbial fuel cell tank 20 of the microbial fuel cell system that does not include the anaerobic tank (10B) is used as a sewage treatment plant. The treated water of the first sedimentation basin was introduced. Then, electric energy was recovered in the microbial fuel cell tank 20 without reducing the oxidation-reduction potential of the wastewater. At this time, the generated power generated and the oxidation-reduction potential of the wastewater were periodically measured as in the example. These results are shown in FIGS.

  FIG. 6 is a diagram illustrating a change with time of oxidation-reduction potential of wastewater in the microbial fuel cell system according to the example and the microbial fuel cell system according to the comparative example.

  In FIG. 6, the vertical axis represents the oxidation-reduction potential (mV) of the wastewater introduced into the microbial fuel cell tank 20, and the horizontal axis represents the treatment time of the wastewater in the microbial fuel cell tank 20. Moreover, ■ indicates the measurement result in the example, and ◆ indicates the measurement result in the comparative example.

  As shown in FIG. 6, in the microbial fuel cell system according to the comparative example that does not include the anaerobic tank (10B), the rate of reduction of the oxidation-reduction potential is small, and it takes a long time for the oxidation-reduction potential to become low. I understand that. Moreover, it turns out that it is difficult to implement | achieve a low electric potential below -200mV, when an oxidation-reduction potential becomes equilibrium in the range of -100mV--200mV. In contrast, in the microbial fuel cell system 5 according to the example in which the anaerobic treatment of the wastewater was previously performed in the anaerobic tank 10B, the rate of reduction of the oxidation-reduction potential is large, and the oxidation-reduction potential rapidly becomes a low potential. Yes. Further, the oxidation-reduction potential is substantially in the range of −300 mV to −500 mV, particularly around −400 mV, and it can be confirmed that the oxidation-reduction potential is lowered to a lower potential. Thus, it is recognized that a low potential suitable for power generation by power generation microorganisms is realized for the first time by performing anaerobic treatment of wastewater in an anaerobic tank in advance.

  FIG. 7 is a diagram illustrating a change over time in the power density of power generation by the microbial fuel cell system according to the example and the microbial fuel cell system according to the comparative example.

In FIG. 7, the vertical axis represents the power density per anode of power generation (mW / m ² −anode) in the microbial fuel cell tank 20, and the horizontal axis represents the wastewater treatment time in the microbial fuel cell tank 20. Moreover, ■ indicates the measurement result in the example, and ◆ indicates the measurement result in the comparative example.

As shown in FIG. 7, in the microbial fuel cell system which concerns on the comparative example which is not equipped with the anaerobic tank (10B), it can confirm that the speed | rate of increase of an electric power density is small and generated electric power is comparatively small. In contrast, in the microbial fuel cell system 5 according to the example in which the anaerobic treatment of the wastewater was previously performed in the anaerobic tank 10B, the power density rapidly increased after the start of the treatment, and the power density was 300 (mW / m ^2). -Anode) level is reached. Thus, it can be seen that the generated electric power can be greatly increased by performing anaerobic treatment to reduce the oxidation-reduction potential of the wastewater. Therefore, it is recognized that an anaerobic tank that performs anaerobic treatment of wastewater is provided in the front stage of the microbial fuel cell tank, so that the recovery efficiency of electric energy can be improved and stable power generation can be performed with good power at the time of transit. It is done.

1 Microbial fuel cell system 2, 3, 4 Microbial fuel cell system (modified)
DESCRIPTION OF SYMBOLS 10 Anaerobic tank 12 Stirring means 14 Oxidation reduction electrometer 20 Microbial fuel cell tank 22 Anode 24 Cathode 26 Box (air cathode)
40 sedimentation tank 46 sludge return pump 50 aerobic tank 52 aeration pipe 54 blower 60 sedimentation tank 66 sludge return pump 110 bypass wall 120 connecting pipe 130 sludge return pipe 150 sludge return pipe 210 bypass wall

Claims (6)

An anaerobic tank for anaerobic treatment of wastewater containing organic matter;
A microbial fuel cell tank, which is installed in a subsequent stage of the anaerobic tank, includes an anode, a cathode, and a microorganism that oxidizes and decomposes a substrate contained in the wastewater to donate electrons to the anode. Microbial fuel cell system.   The microbial fuel cell system according to claim 1, wherein the redox potential of the wastewater is reduced to -200 mV or less in the anaerobic tank.   The microbial fuel cell system according to claim 1 or 2, wherein the anaerobic tank has a vertical detour tank structure partitioned by a detour wall disposed along a vertical direction.   The microbial fuel cell system according to claim 1 or 2, wherein the anaerobic tank holds a floating carrier on which anaerobic microorganisms that perform anaerobic treatment are supported. An oxidation-reduction potentiometer that measures the oxidation-reduction potential of the wastewater subjected to anaerobic treatment;
A connection pipe that connects between the anaerobic tank and the microbial fuel cell tank, and forms a flow path for the waste water,
A control valve for controlling the flow rate of the wastewater in the connection pipe,
The control valve is opened when the oxidation-reduction potential of the wastewater measured by the oxidation-reduction potentiometer is lower than a set value, and is closed when the oxidation-reduction potential exceeds a set value. The microbial fuel cell system according to claim 1 or 2. A settling tank that is provided between the anaerobic tank and the microbial fuel cell tank, and that performs precipitation separation treatment of wastewater containing sludge;
The microbial fuel cell system according to any one of claims 1 to 5, further comprising a sludge return pipe for returning the sludge separated in the settling tank to the anaerobic tank.

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