Power generation device and power generation method

Abstract

To provide a power generator capable of being used as a stable power supply source in the recovery and utilization of energy by electrode reaction using treated water after anaerobic treatment, and provide a power generation method.SOLUTION: There is provided a power generator which includes: a power generation unit that generates power through an electrode reaction using reducing substances in the treated water after anaerobic treatment as electron donors; and a control unit that controls the power generation unit to maintain the power generation output within the specified range. A power generation method using the power generator is also provided. With this, constant electrical energy can be obtained regardless of the properties of the treated water by maintaining the power generation output within the specified range. Accordingly, the power generator can be used as a stable power supply source.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power generation device and a power generation method. More specifically, the present invention relates to a power generation device and a power generation method using treated water after anaerobic treatment.

Background Art

[0002] Generally, as a method for treating wastewater containing organic substances, biological treatment using various microorganisms is known. In particular, biological treatment under an anaerobic environment (hereinafter referred to as "anaerobic treatment") is widely used because of its high introduction merits such as no need for aeration power and almost no generation of excess sludge. In addition, various technologies for utilizing the products generated in the wastewater treatment process by anaerobic treatment have also been studied. For example, as one of the technologies for utilizing the products generated by anaerobic treatment, it is known to use biogas such as methane generated by anaerobic treatment as fuel for power generation.

[0003] On the other hand, a microbial fuel cell is known as a technology for generating electricity by utilizing the oxidation-reduction reaction of microorganisms. A microbial fuel cell obtains electrical energy by utilizing the metabolic ability of microorganisms. More specifically, a microbial fuel cell has a configuration in which electrons generated during the process of oxidatively decomposing a substrate such as an organic substance by microorganisms are recovered on the anode side and the electrons are transferred to the cathode side to obtain an electric current.

[0004] For example, Patent Document 1 describes a power generation device in which one of a pair of electrodes is used as an anode and is brought into contact with a solution (suspension) containing microorganisms capable of growing under anaerobic conditions and organic substances, the other electrode is used as a cathode and is formed of a material having structural voids and is brought into contact with air, and the anode and the cathode are electrically connected to form a closed circuit. Patent Document 1 also describes attaching microorganisms to the anode surface. Furthermore, Patent Document 1 also describes a power generation method in which, by this power generation device, an oxidation reaction by microorganisms using an organic substance at the anode as an electron donor and a reduction reaction using oxygen at the cathode as an electron acceptor proceed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2004-342412 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Power generation using microbial fuel cells, as described in Patent Document 1, has low energy conversion efficiency, and improving power output is a major challenge for practical application. This is presumed to be due to the fact that the transfer of mass to the electrodes is inhibited by the microorganisms, as the microorganisms are in direct contact with or supported on the electrodes, and the metabolic rate of the microorganisms becomes the rate-limiting factor.

[0007] Furthermore, in recent years, in order to reduce the power consumption required to drive equipment during wastewater treatment and to achieve superior energy conservation, there has been a demand for technologies that enable efficient energy recovery and utilization as an accessory to wastewater treatment. As one such technology, a technology that applies microbial fuel cells to wastewater treatment and generates electricity simultaneously is being considered, but as mentioned above, there is a challenge in obtaining sufficient power output.

[0008] One possible technique for easily and efficiently recovering energy in wastewater treatment is to install electrodes in the wastewater treatment process and directly recover electrical energy through electrode reactions. The inventors have already discovered that by using reducing substances (mainly hydrogen sulfide) generated during anaerobic treatment as electron donors, energy recovery (power generation) through electrode reactions becomes possible.

[0009] On the other hand, through repeated studies, the inventors discovered that when electrodes are placed on the anaerobic treatment process to carry out an electrode reaction, the properties of the treated water after anaerobic treatment vary depending on the anaerobic treatment conditions, which affects the power output and makes it difficult to stably utilize the recovered energy (electricity).

[0010] The object of the present invention is to provide a power generation device and a power generation method that enable the recovery and utilization of energy from electrode reactions using treated water after anaerobic treatment as a stable power supply source. [Means for solving the problem]

[0011] As a result of diligent research into the above-mentioned problems, the inventors of the present invention have found that by controlling the power generation output from the electrode reaction using treated water after anaerobic treatment to maintain it within a predetermined range, it is possible to stably supply and utilize the generated energy, and have completed the present invention. In other words, the present invention relates to the following power generation device and power generation method.

[0012] The present invention, which solves the above problems, is characterized by comprising a power generation unit that generates electricity by an electrode reaction using a reducing substance in the treated water after anaerobic treatment as an electron donor, and a control unit that controls the power output of the power generation unit to maintain it within a predetermined range. The power generation device of the present invention generates electricity by directly using reducing substances contained in treated water after anaerobic treatment as electron donors, thus avoiding inhibition of mass transfer by microorganisms. This allows for more efficient power generation compared to power generation using microbial fuel cells. Furthermore, by maintaining the power output within a predetermined range, a constant amount of electrical energy can be obtained regardless of the properties of the treated water, making it possible to use it as a stable power supply source.

[0013] Furthermore, in one embodiment of the power generation device of the present invention, the control unit is characterized by controlling the flow rate of treated water supplied to the power generation unit. Through repeated investigations, the inventors discovered that in power generation using electrode reactions with treated water after anaerobic treatment, the flow rate of the treated water affects the power output. Therefore, this feature makes it easy to maintain the power output within a predetermined range by controlling the flow rate of treated water supplied to the power generation unit.

[0014] Furthermore, in one embodiment of the power generation device of the present invention, the control unit is characterized by controlling the concentration of reducing substances in the treated water after anaerobic treatment. Through repeated investigations, the inventors discovered that in power generation using electrode reactions with treated water after anaerobic treatment, the concentration of reducing substances in the treated water affects the power output. Therefore, this feature makes it easy to maintain the power output within a predetermined range by controlling the concentration of reducing substances in the treated water supplied to the power generation unit.

[0015] Furthermore, one embodiment of the power generation device of the present invention is characterized by having a branching path that supplies a portion of the treated water after anaerobic treatment to the power generation unit. If further treatment is required for the treated water after anaerobic treatment, it can be difficult to simultaneously ensure a smooth supply of the treated water to the subsequent treatment and control the flow rate of the treated water to maintain a constant power output in the power generation equipment. On the other hand, this feature allows for the smooth supply of treated water to subsequent treatments and facilitates control of the power output in the power generation device by supplying only a portion of the treated water to the power generation unit, rather than supplying all of it after anaerobic treatment.

[0016] Furthermore, the present invention, which solves the above problems, is characterized by comprising a power generation step in which power is generated by an electrode reaction using a reducing substance in the treated water after anaerobic treatment as an electron donor, and a control step in which the power output in the power generation step is controlled to be maintained within a predetermined range. The power generation method of the present invention uses the reducing substances contained in the treated water after anaerobic treatment as direct electron donors for power generation, so that the inhibition of mass transfer by microorganisms does not occur, and thus more efficient power generation is possible compared to power generation by a microbial fuel cell. Also, by maintaining the power generation output within a predetermined range, a certain amount of power can be obtained regardless of the properties of the treated water, and stable power supply can be achieved.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a power generation device and a power generation method that enable utilization as a stable power supply source in the recovery and utilization of energy by an electrode reaction using treated water after anaerobic treatment.

Brief Description of the Drawings

[0018] [Figure 1] It is a schematic explanatory diagram of the power generation device in the first embodiment of the present invention. [Figure 2] It is a graph showing the relationship between the flow rate of the treated water and the power generation output in the power generation by the power generation unit of the power generation device according to the first embodiment of the present invention. [Figure 3] It is a schematic explanatory diagram of the power generation device in the second embodiment of the present invention. [Figure 4] It is a schematic explanatory diagram of the power generation device in the third embodiment of the present invention. [[ID=2"]] [Figure 5] It is a graph showing the relationship between the concentration of reducing substances in the treated water and the power generation output in the power generation by the power generation unit of the power generation device according to the third embodiment of the present invention. [Figure 6] It is a schematic explanatory diagram of the power generation device in the fourth embodiment of the present invention.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the power generation device and the power generation method according to the present invention will be described in detail with reference to the drawings. The power generation method in the present invention shall be replaced with the description of the operation of the power generation device in the present invention. The power generation apparatus and power generation method described in the embodiments are merely illustrative examples for explaining the power generation apparatus and power generation method according to the present invention, and are not limited thereto.

[0020] In the present invention, the reducing substance contained in the treated water introduced into the power generation section of the power generation device is not particularly limited, as long as it functions as an electron donor. Whether or not a substance functions as an electron donor is relatively determined by its combination with a substance that functions as an electron acceptor (hereinafter simply referred to as "electron acceptor"). In other words, the reducing substance in the present invention is one that is more likely to release electrons than an electron acceptor, that is, one with a lower oxidation-reduction potential than an electron acceptor. For example, when oxygen is used as an electron acceptor, the reducing substance in the present invention is one with a lower oxidation-reduction potential than oxygen, and examples of such reducing substances include hydrogen sulfide, hydrogen, and ammonia.

[0021] [First Embodiment] Figure 1 is a schematic diagram illustrating the structure of a power generation device in a first embodiment of the present invention. As shown in Figure 1, the power generation device 1A in this embodiment is applied to a wastewater treatment facility that performs anaerobic treatment on the water to be treated W. It is located downstream of the anaerobic treatment tank 2 and comprises a power generation unit 3 and a control unit 4. The anaerobic treatment tank 2 is provided with a pipe L1 for introducing the water to be treated W, and a pipe L2 connects the anaerobic treatment tank 2 to the power generation device 1A. The pipe L2 introduces the treated water W1, which has been treated by the anaerobic treatment tank 2, into the power generation unit 3, and a pipe L3 discharges the treated water W2 from the power generation unit 3. In Figure 1, the dashed-dotted arrows indicate that the device is connected in a controllable or inputtable manner.

[0022] In this embodiment, the anaerobic treatment tank 2 is a tank for treating the water to be treated W, and also functions to supply treated water W1 containing reducing substances to the power generation device 1A. The treatment performed in the anaerobic treatment tank 2 is not particularly limited as long as it is appropriate to the target substance contained in the water to be treated W, and the treated water W1 after treatment contains reducing substances. For example, treatments performed in the anaerobic treatment tank 2 include methane fermentation by acid-producing bacteria and methane-producing bacteria, denitrification treatment in which nitrates and nitrites are reduced by denitrifying bacteria, and sulfate reduction treatment in which sulfates are reduced by sulfate-reducing bacteria. From the viewpoint of treatment costs and the usefulness of the produced gas, methane fermentation that produces methane is particularly preferred.

[0023] The water to be treated W in the anaerobic treatment tank 2 is not particularly limited as long as it generates reducing substances during the treatment process. The reducing substances only need to be present in the treated water W1, and may be present in the water to be treated W before it is introduced into the anaerobic treatment tank 2. Specific examples of the water to be treated W include industrial wastewater discharged from various factories such as food processing plants, chemical plants, and paper and pulp mills, as well as domestic wastewater such as sewage. The following description will primarily focus on water to be treated W that generates reducing substances through treatment, but is not limited to this.

[0024] In the anaerobic treatment tank 2, when methane fermentation is performed as part of the anaerobic treatment, in addition to methane, hydrogen sulfide, hydrogen, ammonia, etc., are generated in the treated water W. These products correspond to the reducing substances in this invention.

[0025] The treated water W, processed in the anaerobic treatment tank 2, becomes treated water W1 containing reducing substances, which is then introduced to the power generation device 1A via piping L2.

[0026] [Power generation equipment] (Power Generation Department) The power generation unit 3 is for performing a power generation step in which reducing substances in the treated water W1 are used as electron donors to generate electricity. As shown in Figure 1, the power generation unit 3 of this embodiment is located downstream of the anaerobic treatment tank 2 and comprises a first cell 31a and a second cell 31b, an ion exchanger 35 provided to partition the cells 31a and 31b, and electrodes 33a and 33b arranged in cells 31a and 31b, respectively. Here, the first cell 31a is formed so that treated water W1 introduced from the anaerobic treatment tank 2 via piping L2 comes into contact with the electrode 33a, and the electrode 33a located in the first cell 31a functions as an anode. On the other hand, the second cell 31b is formed to store or supply electron acceptors, and the electrode 33b located in the second cell 31b functions as a cathode. Furthermore, electrodes 33a and 33b are connected to an external circuit C by a conductor. This makes it possible to recover and utilize the electrical energy generated in the power generation unit 3 by the action of reducing substances as electron donors.

[0027] The first cell 31a is equipped with an electrode 33a and is formed so that the treated water W1 comes into contact with the electrode 33a; its material and shape are not particularly limited. For example, as shown in Figure 1, it may have a space that can temporarily store the treated water W1 introduced from the treated water inlet 32a via piping L2, and piping L3 for discharging the treated water W2 after it has come into contact with the electrode 33a from the treated water outlet 32b. As a result, the reducing substances in the treated water W1 donate electrons to the electrode 33a as electron donors and are then quickly discharged via piping L3.

[0028] The treated water W2 discharged through piping L3 can be discharged directly into rivers or other bodies of water if it meets the water quality requirements for discharge. Alternatively, treatment equipment may be installed downstream of piping L3 to further treat the treated water W2 before discharging it from the system. Such treatment equipment is not particularly limited as long as it can treat the treated water W2 to a water quality suitable for discharge from the system or into rivers. Examples include aeration tanks and pH adjustment tanks.

[0029] The second cell 31b is equipped with an electrode 33b and is formed to store or supply electron acceptors to reducing substances in the treated water W1, and is not limited in terms of material or shape.

[0030] Here, the electron acceptor may be in the form of either a gas or a liquid. The liquid may be a solution in which a solid drug is dissolved, or a solution in which a gas is mixed (dissolved). In this embodiment, specific examples of electron acceptors include, for example, gases such as oxygen and oxygen-containing gases. Oxygen-containing gases include those that contain oxygen as a mixture, such as air, and those that contain oxygen as an element constituting a compound, such as carbon dioxide. When a gas is used as an electron acceptor, there are advantages such as the fact that the treatment of waste products after the reaction is unnecessary (or easy) and the cost of obtaining the gas can be reduced. In order to make the most of these advantages, it is particularly preferable to use air as the electron acceptor. Furthermore, other examples of electron acceptors in this embodiment include, for example, solutions containing dissolved oxygen or aqueous solutions of oxidizing agents such as potassium ferricyanide, as liquids. When a liquid is used as the electron acceptor, it has the advantage of making it easier to handle compounds (oxidizing agents) that are highly effective as electron acceptors, thereby further improving power generation efficiency. From the viewpoint of improving power generation efficiency, it is particularly preferable to use an aqueous solution of potassium ferricyanide as the electron acceptor.

[0031] As an example of the second cell 31b, as shown in Figure 1, the second cell 31b may be provided with an electron acceptor supply port 34a for supplying gaseous electron acceptors (oxygen, air, etc.) to the electrode 33b via piping L4, and an electron acceptor outlet 34b for discharging the gas after the reaction via piping L5. Another example of the second cell 31b is to provide a space in the second cell 31b that can store liquid, and to provide an electron acceptor supply port 34a and an electron acceptor outlet 34b that can supply the electron acceptor solution and discharge the solution after the reaction, respectively. As a result, electrons from electrode 33a can be received by the electron acceptor via electrode 33b, and an electric current flows between electrode 33a and electrode 33b to generate electricity. The electron acceptor after the reaction is then quickly discharged to the outside of the power generation unit 3 via the electron acceptor outlet 34b and piping L5. Furthermore, a flow rate adjustment mechanism such as a valve may be provided in the electron acceptor supply port 34a and / or electron acceptor outlet port 34b, or in the piping L4 and / or piping L5, to adjust the concentration of the electron acceptor in the second cell 31b. In addition, a control mechanism may be provided to control the flow rate adjustment mechanism so that the electron acceptor concentration is maintained in proportion to the amount of electrons generated by the reaction at electrode 33a. This makes it possible to suppress the decrease in reaction efficiency related to electron transfer between electrode 33a and electrode 33b, and thereby suppress the decrease in power generation efficiency.

[0032] In Figure 1, the electron acceptor supply port 34a and electron acceptor outlet 34b are shown as one each, but the design is not limited to this. For example, multiple electron acceptor supply ports 34a and electron acceptor outlets 34b may be provided. In particular, when an oxygen-containing gas is used as the electron acceptor, water is produced by the reaction at electrode 33b, as will be described later. Therefore, when multiple electron acceptor outlets 34b are provided, for example, one can be provided to discharge gas and the other to discharge liquid.

[0033] The ion exchanger 35 can be any known configuration that allows ions to pass through, and is not particularly limited. In particular, it is preferable to use a cation exchange membrane that can allow hydrogen ions generated at electrode 33a (anode side) to pass through. This allows hydrogen ions to move from electrode 33a (anode side) to electrode 33b (cathode side), thereby increasing the reaction efficiency of the electron acceptor at electrode 33b and improving the electrode reaction efficiency. Furthermore, it is more preferable that the ion exchanger 35 has low oxygen permeability. This suppresses the movement of electron acceptors (especially oxygen) supplied to electrode 33b (cathode side) to electrode 33a, and prevents the reaction efficiency of the electron donor at electrode 33a from decreasing due to oxygen. In Figure 1, the ion exchanger 35 is shown as being provided separately from electrodes 33a and 33b, but this is not the only option. For example, the ion exchange material can be integrated with electrodes 33a and / or 33b. This makes it possible to miniaturize the entire power generation unit 3 and reduce the time required for maintenance work.

[0034] Electrode 33a is an electrode that recovers electrons from reducing substances in the treated water W1, and functions as a so-called anode. In this embodiment, electrode 33a is positioned in the first cell 31a so as to be in contact with the treated water W1 after it has been treated in the anaerobic treatment tank 2.

[0035] The electrode 33a can function as an anode, and its material and shape are not particularly limited. The material and shape of the electrode 33a can be appropriately selected considering the cost of material procurement and processing, the reaction efficiency of reducing substances in the electrode 33a, etc. Examples of materials for the electrode 33a include carbon and metals (stainless steel, platinum, copper, etc.) which are widely used as electrode materials in the field of electrochemistry. Examples of shapes for the electrode 33a include flat plates, rods, meshes, etc. In particular, considering the electrode reaction efficiency, it is preferable to use a porous material as the electrode 33a in this embodiment. For example, as the electrode 33a, in addition to using carbon fibers such as carbon paper, carbon cloth, and carbon felt, which are porous materials, foamed metal, porous metal, and metal mesh may be used.

[0036] In this embodiment, the electrode 33a does not have microorganisms in contact with or supported on its surface. Therefore, the mass transfer of reducing substances is not inhibited by microorganisms, the reaction efficiency as an electron donor (the mass transfer rate of reducing substances to the electrode 33a) can be improved, and the power generation efficiency can be improved. Furthermore, in this embodiment, electrode 33a does not recover electrons generated by the metabolism of microorganisms, but rather recovers electrons directly from reducing substances. Therefore, the metabolism of microorganisms does not become the rate-limiting factor, the reaction efficiency as an electron donor (the rate of electron recovery at electrode 33a) is improved, and the power generation efficiency can be improved.

[0037] Electrode 33b is the counter electrode to electrode 33a and is the electrode that transfers electrons to the electron acceptor, functioning as a so-called cathode. Furthermore, in this embodiment, electrode 33b is located within the second cell 31b.

[0038] The electrode 33b can function as a cathode, and its material and shape are not particularly limited. The material and shape of the electrode 33b can be appropriately selected considering the cost of material procurement and processing, the reaction efficiency of the electron acceptor in the electrode 33b, etc. Examples of materials for the electrode 33b include carbon and metals (stainless steel, platinum, copper, etc.) which are widely used as electrode materials in the field of electrochemistry. Examples of shapes for the electrode 33b include flat plates, rods, meshes, etc. In particular, considering the electrode reaction efficiency, it is preferable to use a porous material as the electrode 33b in this embodiment. For example, as the electrode 33b, in addition to using carbon fibers such as carbon paper, carbon cloth, and carbon felt, which are porous materials, foamed metal, porous metal, and metal mesh may be used.

[0039] When the electron acceptor supplied to the second cell 31b is a gas (air), one side of the electrode 33b is in contact with the gas, while the other side is in contact with the treated water W1. For this reason, it is preferable that the electrode 33b be in a form suitable as a so-called air cathode. A suitable form for an air cathode is, for example, one that possesses both gas permeability and water impermeability. By making the electrode 33b gas permeable, it becomes possible to effectively react the gas, which is the electron acceptor, at the electrode 33b. Furthermore, by making the electrode 33b water impermeable, it becomes possible to suppress the treated water W1 in the first cell 31a from permeating through the electrode 33b and flowing into the second cell 31b. Specific examples of such an electrode 33b include one made of carbon fiber, or one in which a metal mesh surface has been treated by coating it with a material that has gas permeability and water impermeability, or by laminating a film. In this context, impermeability refers to the inability to allow water to pass through. For example, waterproofing, water-repellenting, hydrophobicating, or water-stopping the electrode 33b is also included in the definition of impermeability.

[0040] The reactions and processes related to the electrode reaction in the power generation device of the first embodiment of the present invention will be described below with reference to Figure 1. The reactions and processes related to the electrode reaction in the power generation device 1A of this embodiment are described in which a reducing substance contained in the treated water W1 after anaerobic treatment is used as an electron donor, and a solution containing an oxidizing agent or oxygen is used as an electron acceptor. The description of the reactions and processes based on Figure 1 is an example of the electrode reaction in this embodiment and is not limited to it. Furthermore, the following description mainly concerns the reactions and processes related to the power generation section 3 of the power generation device 1A, and the description of the reactions and processes related to the anaerobic treatment tank 2 that generates the treated water W1 introduced into the power generation device 1A has been simplified. In addition, the notations for reactions R1 to R4 and processes S1 to S3 are numbered for explanatory purposes and do not specify the order of the reactions and processes.

[0041] As shown in Figure 1, the water to be treated W introduced into the anaerobic treatment tank 2 is subjected to anaerobic treatment by anaerobic microorganisms (acid-producing bacteria and methane-producing bacteria) in the anaerobic treatment tank 2 (step S1). At this time, in addition to methane, reducing substances (hydrogen, hydrogen sulfide, ammonia, etc.) are produced.

[0042] The treated water W1, which has been treated in the anaerobic treatment tank 2 and contains reducing substances, is introduced into the first cell 31a in the power generation unit 3 via piping L2 (step S2). Here, when the reducing substance (hydrogen, hydrogen sulfide, ammonia, etc.) comes into contact with the electrode 33a, the reducing substance functions as an electron donor and donates electrons to the electrode 33a. Taking hydrogen sulfide as an example of the reducing substance that functions as an electron donor, the reaction at the electrode 33a (reaction R1) is shown by the following reaction equation (equation 1).

number

[0043] Furthermore, some of the hydrogen sulfide reacts as hydrogen sulfide ions. This reaction is represented by the following reaction equation (Equation 2).

number

[0044] As shown in Equations 1 and 2, in reaction R1, the hydrogen sulfide contained in the treated water W1 after treatment in the anaerobic treatment tank 2 donates electrons to the electrode 33a, and the hydrogen sulfide itself is oxidized, rendering it harmless and odorless. Therefore, the power generation device 1A of this embodiment can perform desulfurization and deodorization treatment in addition to power generation. Furthermore, reducing substances (such as ammonia), which are harmful and odorous substances other than hydrogen sulfide, also function as electron donors, and as the reaction proceeds, they can be rendered harmless and odorless.

[0045] Based on the reaction equations shown in Equations 1 and 2, after the reaction at electrode 33a proceeds, electrons move from electrode 33a to electrode 33b via the wire (reaction R2). At this time, the hydrogen ions generated in the reaction at electrode 33a move to the second cell 31b side via the ion exchanger 35 (reaction R3).

[0046] Meanwhile, an electron acceptor (solution) is introduced into the second cell 31b from the electron acceptor supply port 34a (step S3). Here, in reaction R2, electrons that have moved from electrode 33a to electrode 33b are received by the electron acceptor via electrode 33b. At the same time, in reaction R3, hydrogen ions that have moved to the second cell 31b side via the ion exchanger 35 also react with the electron acceptor. The reaction at electrode 33b at this time (reaction R4) is shown by the following reaction equation (equation 3). In equation 3, oxygen corresponds to the electron acceptor.

number

[0047] Based on the reactions R1 to R4 and steps S1 to S3 described above, an electric current flows between electrodes 33a and 33b. This causes a reaction to proceed using the reducing substance in the treated water W1 as an electron donor, and power is generated in the power generation device 1A of this embodiment.

[0048] In conventional power generation using microbial fuel cells, increasing the concentration of microorganisms required for wastewater treatment further inhibits mass transfer to the electrodes, resulting in a trade-off between wastewater treatment efficiency and power generation efficiency. On the other hand, the power generation device 1A and power generation method using power generation device 1A of this embodiment allow for separate wastewater treatment (anaerobic treatment tank 2) and power generation (power generation device 1A). Therefore, in the power generation device 1A and power generation method of this embodiment, there is no trade-off between wastewater treatment efficiency and power generation efficiency, enabling efficient power generation.

[0049] Furthermore, the electrical energy generated by the power generation device 1A of this embodiment can be recovered and utilized through an external circuit C connected to electrodes 33a and 33b. The utilization of the electrical energy is not particularly limited. For example, it may be used to drive equipment in the wastewater treatment facility where the power generation device 1A is located, such as the anaerobic treatment tank 2, or it may be used outside the wastewater treatment facility.

[0050] Here, the relationship between the power output of the power generation unit 3 and the flow rate of the treated water W1 supplied to the first cell 31a via the piping L2 will be explained based on an embodiment. Figure 2 is a graph showing the relationship between the flow rate of treated water supplied to the power generation unit 3 and the power output in power generation using the power generation unit 3 of the power generation device 1A of this embodiment. In Figure 2, the measurement conditions involved using carbon felt electrodes for electrodes 33a and 33b, and a cation exchange membrane for the ion exchanger 35. A solution of potassium ferricyanide dissolved in phosphate buffer was supplied to the second cell 31b at a constant flow rate, while a sample solution of sodium hydrogen sulfide dissolved in phosphate buffer, corresponding to the treated water W1 in this embodiment, was supplied to the first cell 31a at different flow rates (unit: mL / min). The voltage flowing between electrodes 33a and 33b was measured using a potentiostat, and the maximum output ratio was determined using the zero flow rate (no inflow or outflow of the sample solution into the first cell 31a, simply stored) as the reference point.

[0051] As shown in Figure 2, it was found that the power output ratio increases with increasing flow rate of the sample solution (corresponding to treated water W1) supplied to the power generation unit 3, and gradually approaches a constant value. Here, depending on the treatment conditions in the anaerobic treatment tank 2, the flow rate of treated water W1 discharged from the anaerobic treatment tank 2 may change, so the power output of the power generation unit 3 will fluctuate in accordance with the flow rate of treated water W1 discharged from the anaerobic treatment tank 2. On the other hand, when the power output obtained from the power generation unit 3 is used as electrical energy outside the power generation device 1A via an external circuit C, the fluctuations in both the strength and strength of the power output, as well as the power output itself, become a problem in terms of stable use as a power supply source. Therefore, in order to use the power generation device 1A in this embodiment as a stable power supply source, it is necessary that a constant amount of electrical energy can be obtained from the power generation unit 3 regardless of fluctuations in the properties (flow rate of treated water W1) of the treated water W1 discharged from the anaerobic treatment tank 2.

[0052] (Control Unit) The control unit 4 is for performing control steps to maintain the power output of the power generation unit 3 within a predetermined range. In this embodiment, the control unit 4 controls the flow rate of treated water W1 supplied to the power generation unit 3 so as to maintain the power generation output of the power generation unit 3 within a predetermined range, based on the relationship between the power generation output and the flow rate of treated water W1 as described above. More specifically, as shown in Figure 1, the control unit 4 may include a calculation control unit 41 and a flow rate adjustment mechanism 42.

[0053] The calculation control unit 41 is connected to the external circuit C and receives the power output from the power generation unit 3 as input. It calculates the flow rate of treated water W1 necessary to maintain this power output within a predetermined range, and controls the operation of the flow rate adjustment mechanism 42 based on the calculation result. Furthermore, the flow rate adjustment mechanism 42 is for adjusting the flow rate of treated water W1 supplied to the power generation unit 3 via the piping L2, and known mechanisms for adjusting the flow rate, such as on-off valves and valves, can be used.

[0054] In this embodiment, the calculation control unit 41 may, for example, include manual operation by an operator, but it is preferable to use a computing device that has data input / output functions for acquiring information and executes a program for performing calculations and sending control signals related to the operation control of the flow rate adjustment mechanism 42 using a processor such as a CPU, thereby enabling automatic control. This makes it easier to optimize the control for maintaining the power output from the power generation unit 3 within a predetermined range. The control unit 4 may also be equipped with a display means for displaying parameters used for control, such as the power output and the flow rate of the treated water W1, as well as an input means for the display means.

[0055] As described above, by using the power generation device 1A of this embodiment and directly using reducing substances contained in the treated water after anaerobic treatment as electron donors to generate electricity, there is no inhibition of mass transfer by microorganisms, making it possible to generate electricity more efficiently than with microbial fuel cells. Furthermore, by using the power generation device 1A of this embodiment and maintaining the power output within a predetermined range based on the relationship between the flow rate of treated water supplied to the power generation device and the power output, a constant amount of electrical energy can be obtained regardless of the flow rate of treated water, making it possible to use it as a stable power supply source.

[0056] In this embodiment, the power generation device 1A uses a reducing substance in the treated water W1 as an electron donor and generates electricity through an electrochemical reaction (electrode reaction). Generally, when performing an electrochemical reaction, a problem arises in which the efficiency of the electrochemical reaction decreases due to the movement of electrons to areas other than the area where the electrochemical reaction actually takes place (power generation unit 3). Therefore, in this embodiment, it is preferable to insulate areas other than the area where the electrochemical reaction takes place (power generation unit 3) of the power generation device 1A. Specific examples of insulation treatment include, for example, installing the anaerobic treatment tank 2 on top of an insulator, constructing the outer or inner wall of the anaerobic treatment tank 2 from an insulator, or coating the outer or inner wall of the anaerobic treatment tank 2 with an insulating material. Furthermore, as for the insulation treatment of the introduction pipe L1, connecting pipe L2, and discharge pipe L3, for example, each pipe may be made of an insulator, or each pipe may be coated with an insulating material.

[0057] [Second Embodiment] Figure 3 is a schematic diagram illustrating a power generation device in a second embodiment of the present invention. The power generation device 1B according to the second embodiment is applied to a wastewater treatment facility that includes an anaerobic treatment tank 2 for treating the water to be treated W, as well as a reaction tank 5 for further wastewater treatment of the treated water discharged from the anaerobic treatment tank 2. Compared to the power generation device 1A in the first embodiment, it is equipped with a branching path 43 for branching the treated water discharged from the anaerobic treatment tank 2 into water supplied to the power generation unit 3 (treated water W1) and water supplied to the reaction tank 5 (treated water W1'). The explanation of components that are the same as those in the first embodiment will be omitted.

[0058] As shown in Figure 3, the power generation device 1B in this embodiment generates electricity using treated water (treated water W1) that is supplied to the power generation unit 3 via piping L2, which serves as a branch line 43, from the treated water discharged from the anaerobic treatment tank 2.

[0059] The reaction tank 5 is used to further treat the treated water discharged from the anaerobic treatment tank 2 to meet the water quality requirements for discharge into rivers, etc. Specifically, this could be an aeration tank or an aerobic treatment tank. Furthermore, it is preferable that the reaction tank 5 receives not only the treated water W1' supplied via piping L6 from the anaerobic treatment tank 2, but also treated water W2 discharged from the power generation unit 3 via piping L3, and treats it. This makes it possible to improve the wastewater treatment efficiency for the water to be treated W as a whole wastewater treatment facility to which the power generation device 1B is applied. The treated water W3 that is treated and discharged in the reaction tank 5 is then discharged outside the treatment system via piping L7.

[0060] The branch line 43 branches off from the piping L6 that connects the anaerobic treatment tank 2 and the reaction tank 5, and connects the anaerobic treatment tank 2 and the power generation unit 3 of the power generation device 1B. As shown in Figure 3, it consists of piping L2. Furthermore, as shown in Figure 3, by providing a flow rate adjustment mechanism 42 at the starting point of the branch line 43 and controlling the ratio of treated water W1' supplied to the pipe L6 side and treated water W1 supplied to the branch line 43 side (pipe L2 side) with the calculation control unit 41, it becomes easy to control the flow rate of treated water W1 supplied to the power generation unit 3 so as to maintain the power output of the power generation unit 3 within a predetermined range.

[0061] As shown in Figure 3, when further treatment is required for the treated water W1 after anaerobic treatment, it can be difficult to simultaneously supply the treated water W1 smoothly to the subsequent treatment and control the flow rate of the treated water W1 in order to maintain a constant power output in the power generation equipment. On the other hand, in the power generation device 1B of this embodiment, instead of supplying all of the treated water W1 after anaerobic treatment to the power generation unit 3, a portion of the treated water W1 is supplied to the power generation unit 3. This allows for the smooth supply of the treated water W1' after anaerobic treatment to the reaction tank 5, which is the subsequent treatment stage, and also facilitates the control of the power output in the power generation device 1B.

[0062] [Third Embodiment] Figure 4 is a schematic diagram illustrating a power generation device in a third embodiment of the present invention. As shown in Figure 4, the power generation device 1C according to the third embodiment is provided with a calculation control unit 44 and a concentration control mechanism 45 that control the concentration of reducing substances in the treated water W1, in place of the calculation control unit 41 and flow rate adjustment mechanism 42, which are components of the control unit 4 that control the flow rate of the treated water W1, as shown in Figure 4 of the power generation device 1A according to the first embodiment. The same components as those in the first embodiment will not be described.

[0063] In this embodiment, the power generation device 1C focuses on factors other than the flow rate of treated water W1 shown in the power generation device 1A of the first embodiment as properties of treated water W1 that affect power output, and more specifically, focuses on the concentration of reducing substances in treated water W1.

[0064] Here, the relationship between the power output of the power generation unit 3 and the concentration of reducing substances in the treated water W1 supplied to the first cell 31a via the piping L2 will be explained based on an example. Figure 5 is a graph showing the relationship between the concentration of reducing substances (sulfide concentration) in the treated water supplied to the power generation unit 3 and the power output in the power generation by the power generation unit 3 of the power generation device 1C of this embodiment.

[0065] In Figure 5, the measurement conditions involved using carbon felt electrodes as electrodes 33a and 33b, and a cation exchange membrane as the ion exchanger 35. A solution of potassium ferricyanide dissolved in phosphate buffer was supplied to the second cell 31b at a constant flow rate, while the first cell 31a was supplied with a sample solution equivalent to the treated water W1 in this embodiment, consisting of sodium hydrogen sulfide dissolved in phosphate buffer at different amounts, at a constant flow rate for each sulfide concentration (unit: mM). The voltage flowing between electrodes 33a and 33b was measured using a potentiostat, and the maximum output ratio was determined using the zero sulfide concentration as the reference.

[0066] As shown in Figure 5, it was found that the power output ratio tends to increase with increasing sulfide concentration (corresponding to reducing substance concentration) in the sample solution (corresponding to treated water W1). Here, depending on the treatment conditions in the anaerobic treatment tank 2, the reducing substance concentration in the treated water W1 discharged from the anaerobic treatment tank 2 may change, so the power output in the power generation unit 3 will fluctuate according to the reducing substance concentration of the treated water W1 discharged from the anaerobic treatment tank 2. Therefore, in order to utilize the power generation device 1C in this embodiment as a stable power supply source, it is necessary that a constant amount of electrical energy can be obtained from the power generation unit 3 regardless of fluctuations in the properties of the treated water W1 discharged from the anaerobic treatment tank 2 (concentration of reducing substances in the treated water W1).

[0067] In this embodiment, the control unit 4 controls the concentration of reducing substances in the treated water W1 supplied to the power generation unit 3 so as to maintain the power generation output of the power generation unit 3 within a predetermined range, based on the relationship between the power generation output and the concentration of reducing substances in the treated water W1 as described above. More specifically, as shown in Figure 4, the control unit 4 may include a calculation control unit 44 and a concentration control mechanism 45.

[0068] The calculation control unit 44 is connected to the external circuit C and receives the power output from the power generation unit 3 as input. It calculates the concentration of reducing substances in the treated water W1 necessary to maintain this power output within a predetermined range, and controls the operation of the concentration control mechanism 45 based on the calculation result. In this embodiment, the calculation control unit 44 may, like the calculation control unit 41 in the first embodiment, include, for example, manual operation by an operator. However, it is preferable to use a computing device that has data input / output functions for acquiring information and executes a program for performing calculations and sending control signals related to the operation control of the concentration control mechanism 45 using a processor such as a CPU, thereby enabling automatic control. This makes it easier to optimize the control for maintaining the power output from the power generation unit 3 within a predetermined range.

[0069] The concentration control mechanism 45 is for adjusting the concentration of reducing substances in the treated water W1 supplied to the power generation unit 3 via the piping L2. In this embodiment, the concentration control mechanism 45 can, for example, increase the amount of reducing substances generated by treatment in the anaerobic treatment tank 2 in order to increase the concentration of reducing substances in the treated water W1 when the power output tends to fall below a predetermined range, and decrease the amount of reducing substances generated by treatment in the anaerobic treatment tank 2 in order to decrease the concentration of reducing substances in the treated water W1 when the power output tends to rise above a predetermined range.

[0070] More specifically, one of the concentration control mechanisms 45 is to provide a sulfur addition means for adding sulfur to the anaerobic treatment tank 2, thereby increasing the concentration of reducing substances (hydrogen sulfide) contained in the treated water W1. In this case, the sulfur addition means can be any means capable of adding sulfur to the anaerobic treatment tank 2 and is not particularly limited, but it is preferable to utilize the sulfur generated in the power generation unit 3 based on equations 1 and 2. For example, in order to utilize the sulfur contained in the treated water W2 discharged from the power generation unit 3, a line is formed to introduce a portion of the treated water W2 into the anaerobic treatment tank 2 (not shown), or a means is provided to remove sulfur adhering to the electrode 33a of the power generation unit 3 (not shown), thereby increasing the total amount of sulfur contained in the treated water W2 and introducing this treated water W2 into the anaerobic treatment tank 2. In addition, a flow rate adjustment mechanism may be provided to control the flow rate of the treated water W2 introduced into the anaerobic treatment tank 2. This makes it possible to control the concentration of reducing substances and reduce the cost of processing the sulfur generated in the power generation unit 3.

[0071] Another example of the concentration control mechanism 45 is to provide a dilution water addition means for adding dilution water to the treated water W1, thereby lowering the concentration of reducing substances (hydrogen sulfide) contained in the treated water W1. In this case, the dilution water added by the dilution water addition means can be any water that can lower the concentration of reducing substances in the treated water W1, and can be pure water, water for use, or other treated water from a wastewater treatment facility (especially treated water that can be discharged into rivers, etc.).

[0072] In this embodiment, the control unit 4 may also be equipped with a display means for displaying parameters used for control, such as the power output and the concentration of reducing substances in the treated water W1, as well as an input means for the display means.

[0073] In the power generation device 1C of this embodiment, power generation can be performed by the same process as in the first embodiment. Furthermore, by using the power generation device 1C of this embodiment and maintaining the power output within a predetermined range based on the relationship between the concentration of reducing substances in the treated water supplied to the power generation device and the power output, it is possible to obtain a constant amount of electrical energy regardless of the concentration of reducing substances in the treated water, making it possible to use it as a stable power supply source.

[0074] [Fourth Embodiment] Figure 6 is a schematic diagram illustrating a power generation device in a fourth embodiment of the present invention. The power generation device 1D according to the fourth embodiment is applied to a wastewater treatment facility that includes an anaerobic treatment tank 2 for anaerobic treatment of the water to be treated W, as well as a reaction tank 5 for further wastewater treatment of the treated water discharged from the anaerobic treatment tank 2. Compared to the power generation device 1C in the third embodiment, it is equipped with a branching path 43 for branching the treated water discharged from the anaerobic treatment tank 2 into water supplied to the power generation unit 3 (treated water W1) and water supplied to the reaction tank 5 (treated water W1'). The explanation of components that are the same as those in the third embodiment will be omitted.

[0075] As shown in Figure 6, the power generation device 1D in this embodiment generates electricity using treated water (treated water W1) that is supplied to the power generation unit 3 via piping L2, which serves as a branch line 43, from the treated water discharged from the anaerobic treatment tank 2. The reaction vessel 5 has the same structure as that shown in the second embodiment described above, so its explanation will be omitted.

[0076] The branch line 43 branches off from the piping L6 that connects the anaerobic treatment tank 2 and the reaction tank 5, and connects the anaerobic treatment tank 2 and the power generation unit 3 of the power generation device 1D. As shown in Figure 6, it consists of piping L2. Furthermore, as shown in Figure 6, a dilution water addition means, which is one of the concentration control mechanisms 45, is provided on the branch line 43. By controlling only the concentration of reducing substances in the treated water W1 supplied to the branch line 43 side (pipe L2 side) and supplying the treated water W1' supplied to the reaction tank 5 via pipe L6 without changing its properties, it is not necessary to control the concentration of reducing substances in the entire amount of treated water discharged from the anaerobic treatment tank 2. This makes it easy to control the concentration of reducing substances in the treated water W1 supplied to the power generation unit 3 so as to maintain the power output of the power generation unit 3 within a predetermined range.

[0077] In particular, in the power generation device 1D of this embodiment, when diluting treated water W1 as the concentration control mechanism 45, a portion of the treated water W3 after treatment in the reaction tank 5 is used as the water for dilution. This allows the configuration related to the concentration control mechanism 45 to be shared with the existing configuration within the wastewater treatment facility, eliminating the need to supply water from an external source, thus enabling cost reduction.

[0078] In the power generation device 1D of this embodiment, instead of supplying all of the treated water W1 after anaerobic treatment to the power generation unit 3, a portion of the treated water W1 is supplied to the power generation unit 3. This allows for the smooth supply of the treated water W1' after anaerobic treatment to the reaction tank 5, which is a subsequent treatment, and also facilitates the control of the power output in the power generation device 1D.

[0079] The embodiments described above are merely examples of power generation devices and power generation methods. The power generation devices and power generation methods according to the present invention are not limited to the embodiments described above, and the power generation devices and power generation methods according to the embodiments described above may be modified without changing the gist of the claims.

[0080] For example, the power generation device in this embodiment may be equipped with multiple power generation units. Alternatively, multiple power generation devices of this embodiment may be installed within a wastewater treatment facility. This makes it possible to generate electricity at multiple locations by effectively utilizing the treatment process within the wastewater treatment facility, and also improves both the wastewater treatment efficiency and the power generation efficiency.

[0081] Furthermore, the power generation device in this embodiment may be configured to handle multiple elements as a control unit that controls the power output in response to changes in the properties of the treated water. For example, a flow rate adjustment mechanism for controlling the flow rate of the treated water and a concentration control mechanism for controlling the concentration of reducing substances in the treated water may be provided in combination, and each mechanism may be controlled to maintain the power output within a predetermined range. [Industrial applicability]

[0082] The power generation apparatus and power generation method of the present invention are suitable for use as a stable power supply source when applied to wastewater treatment involving anaerobic treatment, which generates reducing substances by treating the water to be treated. [Explanation of symbols]

[0083] 1A, 1B, 1C, 1D Power generation device, 2 Anaerobic treatment tank, 3 Power generation section, 31a First cell, 31b Second cell, 32a Treated water inlet, 32b Treated water outlet, 33a, 33b Electrodes, 34a Electron acceptor supply port, 34b Electron acceptor outlet, 35 Ion exchanger, 4 Control unit, 41 Calculation control unit, 42 Flow rate adjustment mechanism, 43 Branch line, 44 Calculation control unit, 45 Concentration control mechanism, 5 Reaction tank, C External circuit, L1~L6 Piping, W Water to be treated, W1, W1', W2, W3 Treated water

Claims

1. A power generation unit that generates electricity through an electrode reaction using reducing substances in the treated water after anaerobic treatment as electron donors, The system includes a control unit that controls the power output of the power generation unit to maintain it within a predetermined range, The power generation device is characterized in that the control unit performs control based on the power output generated by the power generation unit.

2. The power generation apparatus according to claim 1, characterized in that the control unit controls the flow rate of treated water supplied to the power generation unit.

3. The power generation apparatus according to claim 1, characterized in that the control unit controls the concentration of reducing substances in the treated water after anaerobic treatment.

4. The power generation apparatus according to any one of claims 1 to 3, characterized in that it includes a branching path for supplying a portion of the treated water after anaerobic treatment to the power generation unit.

5. A power generation step in which electricity is generated by an electrode reaction using reducing substances in the treated water after anaerobic treatment as electron donors, The system includes a control step for controlling the power output in the power generation step to maintain it within a predetermined range, The power generation method is characterized in that the control step is performed based on the power output generated in the power generation step.

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