JP7734370B2 - Water treatment device and water treatment method - Google Patents

Description

The present invention relates to a water treatment device and a water treatment method.

A variety of water treatment methods have been proposed to remove organic matter from wastewater. Specifically, these methods include the activated sludge process, which utilizes the aerobic respiration of microorganisms, and the anaerobic treatment process, which utilizes the anaerobic respiration of microorganisms.

In the activated sludge process, wastewater is purified by mixing mud containing microorganisms (activated sludge) with wastewater in a biological reactor, and then sending air into the reactor, which is necessary for the microorganisms to oxidize and decompose the organic matter in the wastewater, and stirring the mixture. However, the activated sludge process requires a huge amount of electricity to aerate the biological reactor. In addition, as the microorganisms breathe oxygen and actively metabolize, large amounts of sludge (dead microorganisms) are generated as industrial waste.

In contrast, anaerobic treatment does not require aeration, so the amount of electricity required can be significantly reduced compared to activated sludge treatment. Furthermore, because the free energy acquired by microorganisms is small, the amount of sludge produced is reduced. Patent Document 1 discloses a microbial fuel cell as an example of a water treatment device that utilizes this type of anaerobic treatment.

A microbial fuel cell has a negative electrode that supports microorganisms and a positive electrode that comes into contact with an oxygen-containing gas phase and wastewater. Wastewater containing organic matter is supplied to the negative electrode, and oxygen-containing gas is supplied to the positive electrode. The negative and positive electrodes are connected to each other via a load circuit to form a closed circuit. At the negative electrode, hydrogen ions and electrons are generated from the wastewater through the catalytic action of the microorganisms. The generated hydrogen ions then move to the positive electrode, and the electrons move to the positive electrode via the load circuit. The hydrogen ions and electrons that move from the negative electrode combine with oxygen at the positive electrode to become water, which is consumed. In this process, the electrical energy flowing through the closed circuit can be recovered.

Patent Document 1 discloses a microbial fuel cell that includes a negative electrode that is immersed in an organic substrate and supports anaerobic microorganisms, and a positive electrode that is enclosed together with an electrolyte in a sealed hollow cassette that has an outer shell formed from an ion-permeable diaphragm and an inlet/outlet hole and is inserted into the organic substrate. In this microbial fuel cell, oxygen is supplied into the cassette via the inlet/outlet hole, while electricity is extracted via a circuit that electrically connects the negative and positive electrodes.

JP 2009-93861 A

Conventional water treatment systems that use microbial fuel cells can treat organic matter in wastewater to a certain extent. However, there is a demand for water treatment systems that can more efficiently treat organic matter in wastewater and produce water of good quality.

The present invention was made in consideration of these problems with the prior art. The object of the present invention is to provide a water treatment device and water treatment method that can efficiently remove organic matter from wastewater using anaerobic treatment, thereby achieving good water quality.

To solve the above problems, a water treatment device according to one aspect of the present invention comprises a water treatment structure including: a negative electrode that contacts the water to be treated inhabited by anaerobic microorganisms, including facultative anaerobes and obligate anaerobes, and to which the anaerobic microorganisms adhere; and a positive electrode that is electrically connected to the negative electrode and contacts an oxygen-containing gas phase and the water to be treated. The water treatment device further comprises an aeration device that intermittently aerates the water to be treated with an oxygen-containing gas. The aeration device alternates between an active aeration state and an inactive aeration state, and during the active aeration state, the oxygen-containing gas is brought into contact with the anaerobic microorganisms.

The water treatment device may further include a treatment tank that holds the water treatment structure, the water to be treated, and at least a portion of the aeration device.

In water treatment devices, it is preferable to bring oxygen-containing gas into contact with anaerobic microorganisms, so that facultative anaerobes remain in the water being treated and obligate anaerobes are removed from the water being treated.

In the water treatment device, the aeration device may alternate between an aeration state and a stopped state at regular intervals.

In a water treatment device, the aeration period can be 10 to 20 minutes, and the aeration period can be 40 minutes to 3 hours.

In the water treatment device, the positive electrode may have aerobic microorganisms attached thereto or may carry an oxygen reduction catalyst.

In the water treatment structure, the negative electrode and positive electrode are integrated, and the shape of the water treatment structure may be plate-like, rod-like, or string-like.

A water treatment method according to one aspect of the present invention uses a water treatment structure that includes a negative electrode that contacts water to be treated inhabited by anaerobic microorganisms, including facultative anaerobes and obligate anaerobes, and to which the anaerobic microorganisms adhere, and a positive electrode that is electrically connected to the negative electrode and contacts an oxygen-containing gas phase and the water to be treated. The water treatment method alternates between an aeration state in which an oxygen-containing gas is aerated into the water to be treated, bringing the gas into contact with the anaerobic microorganisms, and an aeration stop state in which aeration of the gas is stopped.

The present invention provides a water treatment device and water treatment method that can efficiently remove organic matter from wastewater using anaerobic treatment, thereby achieving good water quality.

1 is a perspective view showing an example of a water treatment device according to a first embodiment. FIG. 2 is a cross-sectional view taken along line AA in FIG. FIG. 2 is a cross-sectional view taken along line BB in FIG. 1 is a cross-sectional view illustrating a mechanism for purifying water to be treated by the water treatment structure. FIG. 1 is a cross-sectional view illustrating a mechanism for purifying water to be treated by the water treatment structure. FIG. FIG. 10 is a perspective view showing an example of a water treatment device according to a second embodiment. FIG. 10 is an exploded perspective view showing a stack formed by stacking a positive electrode, a spacer member, and a plate member in a water treatment device according to a second embodiment. 7 is a cross-sectional view taken along line CC in FIG. 6. 1 is a photograph showing a state before treatment of water to be treated in the water treatment structure of Example 1. FIG. 1 is a schematic diagram showing a water treatment system of an example and a comparative example. (a) is a photograph showing the state of the negative electrode surface after treating the water to be treated in the water treatment structure of Example 1. (b) is a photograph showing the state of the negative electrode surface after treating the water to be treated in the water treatment structure of Example 2. (c) is a photograph showing the state of the negative electrode surface after treating the water to be treated in the water treatment structure of Comparative Example 1.

The water treatment device and water treatment method according to this embodiment will be described in detail below using the drawings. Note that the dimensional proportions in the drawings have been exaggerated for the sake of explanation and may differ from the actual proportions.

[First embodiment]
1 to 3, the water treatment device 100 according to this embodiment includes a water treatment structure 10 and a treatment tank 20 that holds the water treatment structure 10 and the water to be treated 30 that is purified by the water treatment structure 10. The water treatment device 100 further includes an aeration device 50 that aerates the water to be treated 30 with an oxygen-containing gas.

(Water treatment structure)
In this embodiment, the water treatment structure 10 includes a conductor 1. As shown in Figures 1 to 3, the conductor 1 is made of a conductive material and is a flat plate member having a substantially rectangular parallelepiped shape.

The water treatment structure 10 has a region where an oxygen reduction reaction occurs, reducing oxygen in the gas phase 40, and a region where an organic matter oxidation reaction occurs, oxidizing organic matter in the water to be treated 30 to produce hydrogen ions and electrons. Specifically, in the water treatment structure 10, the region where the oxygen reduction reaction occurs is the upper portion (cathode 11) that is in contact with the gas phase 40 and the water to be treated 30, and the region where the organic matter oxidation reaction occurs is the lower portion (negative electrode 12) that is in contact with the water to be treated 30. In this way, in the water treatment structure 10, the positive electrode 11 and negative electrode 12 are integrally configured.

The conductor 1 constituting the water treatment structure 10 has an internal space for hydrogen ions (H ⁺ ) to move between the positive electrode 11 where an oxygen reduction reaction occurs and the negative electrode 12 where an organic matter oxidation reaction occurs. Due to the existence of a continuous space inside the conductor 1, as will be described later, hydrogen ions generated at the negative electrode 12 can move to the positive electrode 11 through the internal space.

The material of the conductor 1 is not particularly limited as long as it can ensure conductivity, but can be, for example, at least one selected from the group consisting of conductive metals, carbon materials, and conductive polymer materials. The conductive metal can be, for example, at least one selected from the group consisting of aluminum, copper, stainless steel, nickel, and titanium. The carbon material can be, for example, at least one selected from the group consisting of carbon paper, carbon felt, carbon cloth, and graphite sheet. The conductive polymer material can be, for example, at least one selected from the group consisting of polyacetylene, polythiophene, polyaniline, poly(p-phenylene vinylene), polypyrrole, and poly(p-phenylene sulfide).

As mentioned above, the conductor 1 has an internal space between the positive electrode 11 and the negative electrode 12 for hydrogen ions to move between, so it preferably has a continuous space from the negative electrode 12 to the positive electrode 11. To ensure this internal space, the conductor 1 preferably includes a porous conductive sheet. It is more preferable that the conductor 1 be made of a porous conductive sheet. Such a porous conductive sheet has many pores inside, allowing hydrogen ions to move easily.

The conductor 1 preferably comprises at least one of a woven conductive sheet and a nonwoven conductive sheet. Woven conductive sheets and nonwoven conductive sheets have numerous pores, which facilitate the movement of hydrogen ions. Alternatively, the conductor 1 may be a metal plate with multiple through-holes extending from the negative electrode 12 to the positive electrode 11.

The conductor 1 preferably comprises a nonwoven conductive sheet, and particularly preferably consists of a nonwoven conductive sheet. Because the thickness and porosity of nonwoven fabric can be easily adjusted, as described below, it is easy to achieve a configuration in which anaerobic microorganisms are attached to the negative electrode 12 of the conductor 1 and an oxygen reduction catalyst or aerobic microorganisms are supported on the positive electrode 11. The pore size of the spaces in the conductor 1 is not particularly limited as long as hydrogen ions can move from the negative electrode 12 to the positive electrode 11.

From the above perspective, it is particularly preferable that the conductive material constituting the conductor 1 be at least one selected from the group consisting of graphite sheet, carbon paper, carbon cloth, carbon felt, and stainless steel (SUS).

As shown in Figures 1 to 3, the length L1 of the water treatment structure 10 in the vertical direction Y is preferably longer than the length L2 of the water treatment structure 10 in the width direction Z perpendicular to the vertical direction Y. It is particularly preferable that the water treatment structure 10 be plate-shaped. This increases the distance between the negative electrode 12 in the water treatment structure 10 and the water surface 30a of the water to be treated 30, creating anaerobic conditions around the negative electrode 12. This allows anaerobic microorganisms to adhere to the negative electrode 12 of the water treatment structure 10, allowing efficient oxidation of organic matter. Furthermore, in the water treatment structure 10, a potential difference is generated between the site where the oxygen reduction reaction occurs (positive electrode 11) and the site where the organic matter oxidation reaction occurs (negative electrode 12), allowing electrons to be efficiently conducted from the negative electrode 12 to the positive electrode 11 via the conductor 1.

The length L1 in the vertical direction Y of the water treatment structure 10 is preferably at least twice the length L2 in the width direction Z, more preferably at least five times, even more preferably at least eight times, and particularly preferably at least ten times. There is no particular upper limit to the length L1 in the vertical direction Y of the water treatment structure 10, but it is preferably, for example, no more than 50 times the length L2 in the width direction Z.

As mentioned above, it is more preferable that the water treatment structure 10 be plate-shaped. However, the shape of the water treatment structure 10 is not limited to this, and it may be rod-shaped or string-shaped as long as the length L1 in the vertical direction Y can be longer than the length L2 in the width direction Z. When the water treatment structure is plate-shaped, rod-shaped, or string-shaped, the distance between the negative electrode 12 in the water treatment structure 10 and the water surface 30a of the water to be treated 30 is increased, allowing more anaerobic microorganisms to adhere to the negative electrode 12. Furthermore, in the water treatment structure 10, a potential difference can be generated between the positive electrode 11, where an oxygen reduction reaction occurs, and the negative electrode 12, where an organic matter oxidation reaction occurs, thereby controlling the metabolism of the microorganisms. Note that when the water treatment structure 10 is rod-shaped or string-shaped, the length L2 in the width direction Z, which is perpendicular to the vertical direction Y, refers to the maximum linear distance between two points on the periphery of the water treatment structure 10.

As shown in FIG. 4, an oxygen reduction catalyst 2 is preferably supported on the site (positive electrode 11) where the oxygen reduction reaction occurs in the water treatment structure 10. Supporting the oxygen reduction catalyst 2 allows the oxygen reduction reaction involving oxygen, hydrogen ions, and electrons to proceed efficiently at the positive electrode 11. The oxygen reduction catalyst 2 may be supported on the surface of the conductor 1 or inside the conductor 1.

The oxygen reduction catalyst 2 that can be supported on the conductor 1 is not particularly limited, but may contain platinum. Alternatively, the oxygen reduction catalyst 2 may include carbon particles doped with at least one non-metallic atom and a metal atom. The atoms doped into the carbon particles are not particularly limited. The non-metallic atom is preferably at least one selected from the group consisting of nitrogen, boron, sulfur, and phosphorus atoms. The metal atom is preferably at least one of iron and copper atoms.

The oxygen reduction catalyst 2 may be bound to the conductor 1 using a binder. In other words, the oxygen reduction catalyst 2 may be supported on the surface and inside the pores of the conductor 1 using a binder. This prevents the oxygen reduction catalyst 2 from detaching from the conductor 1 and reducing its oxygen reduction properties. The binder may be, for example, at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), and ethylene-propylene-diene copolymer (EPDM). NAFION (registered trademark) may also be used as the binder.

Anaerobic microorganisms that decompose organic matter in the water to be treated 30 and generate hydrogen ions and electrons are attached to the area (negative electrode 12) in the water treatment structure 10 where the organic matter oxidation reaction occurs. The anaerobic microorganisms 3 do not require oxygen to grow, and do not require air to oxidize and decompose the organic matter in the water to be treated 30. This allows for a significant reduction in the amount of electricity required to supply air. Furthermore, because the free energy acquired by the microorganisms is small, it is possible to reduce the amount of sludge generated.

The anaerobic microorganisms attached to the negative electrode 12 of the water treatment structure 10 are preferably, for example, electricity-producing bacteria with an extracellular electron transport mechanism. Specific examples of anaerobic microorganisms include bacteria of the genus Geobacter, Shewanella, Aeromonas, Geothrix, and Saccharomyces.

A biofilm containing anaerobic microorganisms may be layered and fixed on the negative electrode 12 of the water treatment structure 10, thereby allowing the anaerobic microorganisms to adhere to the negative electrode 12. Note that a biofilm generally refers to a three-dimensional structure containing a microbial population and extracellular polymeric substances (EPS) produced by the microbial population. However, the anaerobic microorganisms may also adhere to the negative electrode 12 without using a biofilm. Furthermore, the anaerobic microorganisms may adhere not only to the surface of the negative electrode 12, but also to the interior thereof.

Anaerobic microorganisms include facultative anaerobes and obligate anaerobes. Facultative anaerobes are anaerobic bacteria that can survive even in the absence of oxygen. Absolute anaerobes are anaerobic bacteria that cannot survive in the presence of oxygen and will die out. Both facultative anaerobes and obligate anaerobes are attached to the negative electrode 12.

Aerobic microorganisms that produce water by reacting oxygen in the gas phase 40 with hydrogen ions and electrons may be attached to the site (cathode 11) in the water treatment structure 10 where the oxygen reduction reaction occurs. Examples of such aerobic microorganisms 4 include bacteria of the genus Sphingobacterium, Acinetobacterium, and Acinetobacter.

The water treatment structure 10 may consist only of the conductor 1, without supporting the oxygen reduction catalyst 2 on the positive electrode 11. As described below, when both anaerobic microorganisms 3 and aerobic microorganisms 4 are present in the water to be treated 30, the anaerobic microorganisms 3 will adhere to the positive electrode 11 and the aerobic microorganisms 4 will adhere to the negative electrode 12, causing a local cell reaction and enabling the oxidative decomposition of organic matter.

(Treatment tank)
The water treatment device 100 includes a substantially rectangular parallelepiped treatment tank 20 that holds organic matter-containing water to be treated 30 inside. A front wall 23 of the treatment tank 20 is provided with an inlet 21 for supplying the water to be treated 30 to the treatment tank 20. A rear wall 24 of the treatment tank 20 is provided with an outlet 22 for discharging the treated water 30 from the treatment tank 20.

The water to be treated 30 is continuously supplied into the treatment tank 20 through the inlet 21. As shown in Figures 1 and 2, the water treatment structure 10 is disposed inside the treatment tank 20 so that the negative electrode 12 and a portion of the positive electrode 11 are immersed in the water to be treated 30. Therefore, the water to be treated 30 supplied from the inlet 21 of the treatment tank 20 flows while coming into contact with the water treatment structure 10, and is then discharged from the outlet 22.

(Aeration device)
Water treatment device 100 further includes an aeration device 50 that intermittently aerates oxygen-containing gas into water to be treated 30. Aeration device 50 includes an aeration member 51 having holes for diffusing the gas, an aeration blower 52 for pressurizing the gas, and piping 53 for supplying the gas from aeration blower 52 to aeration member 51. Aeration device 50 further includes a control unit 54 that is electrically connected to aeration blower 52 and controls the operation of aeration blower 52.

The diffusing member 51 is a member with many holes that allow gas to flow through. The diffusing member 51 is not particularly limited, but examples include a porous ceramic diffusing plate made of large ceramic particles bonded together with a binder or a synthetic resin diffusing plate. A membrane diffuser can also be used as the diffusing member 51.

A pipe 53 for supplying gas from outside the treatment tank 20 is connected to the air diffuser 51. Specifically, one end of the hollow pipe 53 is connected to the lower part of the air diffuser 51. The pipe 53 penetrates the rear wall 24 of the treatment tank 20 and extends to the outside of the treatment tank 20. An aeration blower 52 for pressurizing the gas is connected to the other end of the pipe 53.

The control unit 54 is electrically connected to the aeration blower 52 and is composed of a microcomputer consisting of a CPU, RAM, ROM, hard disk, etc., and electronic circuits, etc. The control unit 54 controls the operation and stop of the aeration blower 52, the operation and stop times, and the volume of gas supplied to the aeration member 51.

The gas aerated from the aeration device 50 into the water to be treated 30 is an oxygen-containing gas, such as air.

Next, the operation of the water treatment device 100 of this embodiment will be described. In the water treatment device 100, the water treatment structure 10 is installed inside the treatment tank 20, which holds the water to be treated 30. In this case, as shown in FIG. 2, the water treatment structure 10 is installed inside the treatment tank 20 so that the main surface 1a of the conductor 1 is approximately parallel to the vertical direction Y.

When the water treatment structure 10 is installed inside the treatment tank 20, as shown in Figures 4 and 5, the positive electrode 11 of the water treatment structure 10 is in contact with the gas phase 40 and the water surface 30a of the water to be treated 30. Furthermore, the positive electrode 11 of the water treatment structure 10 is also in contact with the water to be treated 30. Note that the water to be treated 30 in contact with the positive electrode 11 is located near the gas phase 40, and therefore has a high dissolved oxygen concentration.

The negative electrode 12 of the water treatment structure 10 is immersed inside the water to be treated 30. Note that since the length L1 of the water treatment structure 10 in the vertical direction Y is longer than the length L2 in the width direction Z, the negative electrode 12 is separated from the water surface 30a, resulting in a low dissolved oxygen concentration.

As described above, the water to be treated 30 that comes into contact with the positive electrode 11 of the water treatment structure 10 has a high dissolved oxygen concentration, so if the water to be treated 30 contains aerobic microorganisms 4, the aerobic microorganisms 4 will adhere to the positive electrode 11. Here, if the conductor 1 is porous, for example, the water to be treated 30 will rise due to capillary action, and the water to be treated 30 can be held up to the upper end of the conductor 1. Therefore, the aerobic microorganisms 4 can adhere to the entire upper part of the water treatment structure 10.

In addition, the negative electrode 12 of the water treatment structure 10 is located away from the water surface 30a, and since the surrounding oxygen concentration is low, anaerobic microorganisms 3 adhere to the negative electrode 12.

In the water treatment device 100 configured as described above, an oxidation reaction of organic matter contained in the water to be treated 30 progresses due to the metabolism of anaerobic microorganisms 3 at the negative electrode 12 of the water treatment structure 10, producing hydrogen ions (H ⁺ ) and electrons (e ⁻ ). The hydrogen ions produced by the oxidation reaction pass through the internal space of the conductor 1 and move to the positive electrode 11. Furthermore, the electrons produced by the oxidation reaction move to the positive electrode 11 via the conductor 1.

Then, at the positive electrode 11, the electrons and hydrogen ions transferred from the negative electrode 12 react with oxygen molecules through the action of an oxygen reduction catalyst and/or aerobic microorganisms to produce water. In this way, an oxidation reaction of organic matter progresses at the negative electrode 12, and an oxygen reduction reaction progresses at the positive electrode 11, forming a local battery circuit for the entire water treatment structure. In this way, the catalytic action of the anaerobic microorganisms 3 at the negative electrode 12 decomposes organic matter in the water to be treated 30, making it possible to purify the water to be treated 30.

In the water treatment structure 10, a potential difference occurs between the positive electrode 11, where an oxygen reduction reaction occurs, and the negative electrode 12, where an organic matter oxidation reaction occurs. As a result, electrons are conducted from the negative electrode 12 to the positive electrode 11 through the conductor 1. Specifically, the length L1 of the water treatment structure 10 in the vertical direction Y is longer than the length L2 in the width direction Z, so the positive electrode 11 and the negative electrode 12 are separated from each other. The conductor 1 between the positive electrode 11 and the negative electrode 12 has a high electrical resistivity, which creates a potential difference between the positive electrode 11 and the negative electrode 12. In other words, the relatively high electrical resistivity of the conductor 1 between the positive electrode 11 and the negative electrode 12 allows the positive electrode 11 and the negative electrode 12 to be controlled to an appropriate potential, thereby ensuring a sufficient potential difference between the positive electrode 11 and the negative electrode 12. By ensuring the potential difference, the metabolism of the microorganisms is controlled, allowing electrons to be efficiently conducted from the negative electrode 12 to the positive electrode 11 through the conductor 1, further increasing the efficiency of decomposing organic matter in the water to be treated 30. Furthermore, the water treatment structure 10 does not require the installation of external circuitry such as wiring or a booster system to ensure the potential difference, and since the positive electrode 11 and negative electrode 12 are short-circuited, it can be configured simply.

The water to be treated 30 is inhabited by anaerobic microorganisms, including both facultative anaerobes (Geobacter), which are electricity-generating bacteria, and obligate anaerobes. Therefore, both facultative anaerobes and obligate anaerobes are attached to the negative electrode 12 as anaerobic microorganisms. Facultative anaerobes have a greater ability than obligate anaerobes to decompose organic matter in the water to be treated 30 and generate hydrogen ions and electrons. Therefore, it is preferable that the anaerobic microorganisms inhabiting the water to be treated 30 and the anaerobic microorganisms attached to the negative electrode 12 be more facultative anaerobes than obligate anaerobes.

Therefore, in this embodiment, the aeration device 50 is used to intermittently aerate the water to be treated 30 with oxygen-containing gas. In other words, the aeration device 50 alternately switches between active and inactive aeration of the water to be treated 30. During the aeration state, the oxygen-containing gas is brought into contact with the facultative anaerobic bacteria and the obligate anaerobic bacteria. As a result, the facultative anaerobic bacteria remain inhabiting the water to be treated 30, but most of the obligate anaerobic bacteria are killed. Furthermore, while the facultative anaerobic bacteria attached to the negative electrode 12 remain, some of the obligate anaerobic bacteria are killed, resulting in a decrease in the amount of obligate anaerobic bacteria. Therefore, facultative anaerobic bacteria can predominate in the water to be treated 30 and the negative electrode 12. This makes it easier for the facultative anaerobic bacteria to decompose organic matter in the water to be treated 30, thereby enabling efficient purification of the water to be treated 30.

Here, if the water to be treated 30 is continuously aerated, the amount of dissolved oxygen in the water to be treated 30 increases, making it difficult to maintain an anaerobic atmosphere around the anode 12. Therefore, the water to be treated 30 is aerated intermittently. Specifically, it is preferable for the aeration device 50 to alternate between active and inactive aeration at regular intervals. The duration of the active and inactive aeration states can be adjusted based on the flow rate of the water to be treated 30 and the amount and ratio of facultative anaerobic bacteria and obligate anaerobic bacteria living in the water to be treated 30. However, the duration of the active aeration state can be set to 10 to 20 minutes, and the duration of the inactive aeration state can be set to 40 to 3 hours. For example, it is preferable to set the active aeration state to 20 minutes and the inactive aeration state to 40 minutes, alternating between 20 minutes of aeration and 40 minutes of inactive aeration.

Furthermore, the aeration air volume during aeration is not particularly limited as long as it is an amount that allows facultative anaerobic bacteria to predominate, but it is preferable that it does not exceed the aeration air volume used in general aerobic treatment, for example.

Intermittent aeration of the water to be treated 30 may be performed from the beginning when the water treatment structure 10 begins to purify the water to be treated 30, or may be performed when the purification efficiency of the water to be treated 30 by the water treatment structure 10 has decreased. Furthermore, intermittent aeration of the water to be treated 30 may be performed continuously while the water treatment structure 10 is purifying the water to be treated 30, or may be stopped when the purification efficiency of the water to be treated 30 by the water treatment structure 10 has improved.

As such, the water treatment device 100 of this embodiment includes a water treatment structure 10 having a negative electrode 12 that contacts the water to be treated 30 inhabited by anaerobic microorganisms 3, including facultative anaerobes and obligate anaerobes, and to which the anaerobic microorganisms 3 adhere, and a positive electrode 11 that is electrically connected to the negative electrode 12 and contacts the oxygen-containing gas phase 40 and the water to be treated 30. The water treatment device 100 further includes an aeration device 50 that intermittently aerates the water to be treated 30 with an oxygen-containing gas. The aeration device 50 alternates between an active aeration state and an inactive aeration state, and when in the active aeration state, the oxygen-containing gas is brought into contact with the anaerobic microorganisms 3.

The water treatment method of this embodiment uses a water treatment structure 10 that includes a negative electrode 12 that contacts the water to be treated 30 inhabited by anaerobic microorganisms 3, including facultative anaerobes and obligate anaerobes, and to which the anaerobic microorganisms 3 adhere, and a positive electrode 11 that is electrically connected to the negative electrode 12 and contacts the oxygen-containing gas phase 40 and the water to be treated 30. The water treatment method alternates between an aeration state in which an oxygen-containing gas is aerated into the water to be treated 30, bringing the gas into contact with the anaerobic microorganisms 3, and an aeration stop state in which aeration of the gas is stopped.

In the water treatment device 100 and water treatment method of this embodiment, aeration and non-aeration of the water to be treated 30 are alternately repeated. During aeration, oxygen-containing gas is brought into contact with facultative anaerobic bacteria and obligate anaerobic bacteria. As a result, of the anaerobic microorganisms 3 inhabiting the water to be treated 30 in the treatment tank 20, obligate anaerobic bacteria are removed, while facultative anaerobic bacteria remain. Furthermore, while facultative anaerobic bacteria attached to the negative electrode 12 remain, some of the obligate anaerobic bacteria are killed, resulting in a decrease in the amount of obligate anaerobic bacteria. As a result, facultative anaerobic bacteria predominate on the surfaces of the water to be treated 30 and the negative electrode 12, making it easier for the facultative anaerobic bacteria to decompose organic matter in the water to be treated 30, thereby enabling efficient purification of the water to be treated 30.

In this embodiment, oxygen-containing gas may be aerated throughout the entire water to be treated 30. Alternatively, as shown in Figures 2 and 3, an aeration member 51 may be disposed below the negative electrode 12 to aerate the area around the negative electrode 12. Alternatively, the aeration member 51 may be disposed upstream of the negative electrode 12, for example, near the front wall 23 of the treatment tank 20.

In the water treatment device 100 shown in Figures 1 to 3, one water treatment structure 10 is installed inside one treatment tank 20. However, this embodiment is not limited to this configuration, and multiple water treatment structures 10 may be installed inside the treatment tank 20. By installing multiple water treatment structures 10 inside one treatment tank 20, it is possible to more efficiently purify organic matter in the water to be treated 30.

The negative electrode 12 of the water treatment structure 10 may be modified with electron transfer mediator molecules. Alternatively, the water to be treated 30 in the treatment tank 20 may contain electron transfer mediator molecules. This promotes electron transfer from the anaerobic microorganisms 3 to the negative electrode 12, enabling more efficient liquid treatment.

The water treatment device of this embodiment is equipped with the water treatment structure 10 and the aeration device 50, which allows for efficient removal of organic matter from wastewater using anaerobic treatment, thereby achieving good water quality. Therefore, the treatment tank 20 is not an essential component of the water treatment device in order to achieve the above-mentioned effects.

[Second embodiment]
Next, a water treatment device according to a second embodiment will be described. In the water treatment device 100 according to the first embodiment, the water treatment structure 10 has an integral structure in which the positive electrode 11 and the negative electrode 12 are integrated. In other words, the water treatment structure 10 is composed of a plate-like member having the positive electrode 11 and the negative electrode 12. However, the water treatment structure is not limited to this structure and may be a so-called cassette type.

As shown in Figures 6 to 8, the water treatment device 200 according to this embodiment includes a water treatment structure 110 having a positive electrode 111 and a negative electrode 112. The water treatment device 200 further includes a treatment tank 120 in which the water treatment structure 110 is arranged so as to be immersed in the water to be treated 130.

(Water treatment structure)
The water treatment structure 110 includes a positive electrode 111 and a negative electrode 112 electrically connected to the positive electrode 111 and having anaerobic microorganisms attached thereto. In the water treatment structure 110, the positive electrode 111 and the negative electrode 112 are disposed so as to face each other, and further, a gap exists between the positive electrode 111 and the negative electrode 112.

As shown in Figure 7, the positive electrode 111 is stacked and fixed on a spacer member 115. The spacer member 115 is a U-shaped frame member that fits along the outer periphery of the surface 111a of the positive electrode 111 and is open at the top. The side surface 115a of the spacer member 115 is joined to the outer periphery of the surface 111a of the positive electrode 111, and the side surface opposite the side surface 115a is joined to the outer periphery of the surface 116a of the plate member 116.

As shown in Figures 6 and 8, a laminate consisting of a positive electrode 111, a spacer member 115, and a plate member 116 is placed inside a treatment tank 120 so that a gas phase 140 communicating with the atmosphere is formed. Water to be treated 130 is held inside the treatment tank 120, and the gas diffusion layer 114 of the positive electrode 111 and the negative electrode 112 are immersed in the water to be treated 130.

The positive electrode 111 is provided with a water-repellent layer 113, and the plate member 116 is made of a flat plate material that is impermeable to the water to be treated 130. As a result, the water to be treated 130 held inside the treatment tank 120 is separated from the internal space formed by the positive electrode 111, spacer member 115, and plate member 116, and this internal space becomes a gas phase 140. The water treatment device 200 is configured so that this gas phase 140 is either released to the outside air, or air is supplied to the gas phase 140 from the outside, for example, by a pump.

The positive electrode 111 consists of a gas diffusion electrode including a water-repellent layer 113 and a gas diffusion layer 114 that is overlaid so as to be in contact with the water-repellent layer 113. By using such a thin-plate gas diffusion electrode, oxygen in the gas phase 140 can be easily supplied to the catalyst in the positive electrode 111.

The water-repellent layer 113 is a layer that is both water-repellent and oxygen-permeable. The water-repellent layer 113 effectively separates the gas phase 140 and the water to be treated 130 in the water treatment structure 110, while allowing oxygen to move from the gas phase 140 to the water to be treated 130. The water-repellent layer 113 is in contact with the oxygen-containing gas phase 140, and supplies oxygen to the gas diffusion layer 114 in a substantially uniform manner.

The water-repellent layer 113 is preferably porous so that the oxygen can diffuse. Furthermore, the material that constitutes the water-repellent layer 113 is not particularly limited as long as it is water-repellent and can diffuse the oxygen in the gas phase 140. For example, the material that constitutes the water-repellent layer 113 can be at least one selected from the group consisting of polyethylene, polypropylene, polybutadiene, nylon, polytetrafluoroethylene (PTFE), ethyl cellulose, poly-4-methylpentene-1, butyl rubber, and polydimethylsiloxane (PDMS).

The gas diffusion layer 114 comprises a porous conductive material and an oxygen reduction catalyst supported on the conductive material. By providing such a gas diffusion layer 114 on the positive electrode 111, electrons generated by the local cell reaction (described below) can be conducted between the catalyst and the external circuit 160.

The conductive material in the gas diffusion layer 114 can be composed of one or more materials selected from the group consisting of carbon-based substances, conductive polymers, semiconductors, and metals. Furthermore, the oxygen reduction catalyst in the gas diffusion layer 114 can be the same as that in the first embodiment.

The negative electrode 112 of this embodiment, like the first embodiment, supports anaerobic microorganisms, and further generates hydrogen ions and electrons from organic matter in the water to be treated 130 through the catalytic action of the anaerobic microorganisms.

The negative electrode 112 has a structure in which anaerobic microorganisms are supported on a conductive sheet. The conductive sheet may be a metal plate with multiple through-holes in the thickness direction. Alternatively, a graphite sheet may be used as the conductive sheet for the negative electrode 112.

The water treatment structure 110 may further include a proton-permeable ion migration layer (not shown) disposed between the positive electrode 111 and the negative electrode 112. The ion migration layer is electrically insulating and has the function of allowing hydrogen ions generated at the negative electrode 112 to pass through and migrate to the positive electrode 111. For example, an ion exchange membrane using an ion exchange resin can be used as the ion migration layer. Alternatively, a porous membrane with pores that allow hydrogen ions to pass through can also be used as the ion migration layer.

(external circuit)
6 and 8 , the positive electrode 111 and the negative electrode 112 are electrically connected via an external circuit 160. As will be described later, organic matter in the water to be treated 130 is decomposed by the catalytic action of anaerobic microorganisms supported on the negative electrode 112, generating electrons. The electrons generated at the negative electrode 112 move to the external circuit 160 and then move from the external circuit 160 to the positive electrode 111. At this time, the external circuit 160 can recover electrical energy flowing in the closed circuit.

(Treatment tank and aeration device)
The water treatment device 200 includes a treatment tank 120 having an inlet 121 provided in a front wall 123 and an outlet 122 provided in a rear wall 124, similar to the first embodiment.

Furthermore, as in the first embodiment, the water treatment device 200 includes an aeration device 150 that includes an aeration member 151 that diffuses gas, an aeration blower 152 that pressurizes the gas, and a piping 153 that supplies gas from the aeration blower 152 to the aeration member 151. The aeration device 150 further includes a control unit 154 that is electrically connected to the aeration blower 152 and controls the operation of the aeration blower 152. Note that, although the aeration member 51 is disposed below the negative electrode 112 in Figure 8, the aeration member 51 may also be disposed upstream of the negative electrode 112.

Next, the operation of the water treatment device 200 of this embodiment will be described. As shown in Figures 6 and 8, when a water treatment structure 110 equipped with a positive electrode 111 and a negative electrode 112 is immersed in the water to be treated 130, the gas diffusion layer 114 of the positive electrode 111 and the negative electrode 112 are immersed in the water to be treated 130, and a portion of the water-repellent layer 113 is exposed to the gas phase 140.

When the water treatment device 200 is operating, water to be treated 130 containing organic matter is supplied to the negative electrode 112, and air is supplied to the positive electrode 111. At this time, air is continuously supplied through an opening provided at the top of the spacer member 115.

At the positive electrode 111, oxygen diffuses through the water-repellent layer 113 to the gas diffusion layer 114. At the negative electrode 112, the catalytic action of anaerobic microorganisms generates hydrogen ions and electrons from organic matter in the water to be treated 130. The hydrogen ions generated at the negative electrode 112 migrate toward the positive electrode 111 and reach the gas diffusion layer 114 within the positive electrode 111. The generated electrons migrate to the external circuit 160 through the conductive sheet of the negative electrode 112, and then from the external circuit 160 to the gas diffusion layer 114 of the positive electrode 111. The hydrogen ions and electrons then combine with oxygen through the action of the oxygen reduction catalyst in the gas diffusion layer 114, becoming water, which is then consumed. At this time, the external circuit 160 recovers the electrical energy flowing through the closed circuit. In this way, the water treatment structure 110 can decompose organic matter in the water to be treated 130 through the action of anaerobic microorganisms at the negative electrode 112.

In the water treatment device 200 of this embodiment, as in the first embodiment, both facultative anaerobes and obligate anaerobes inhabit the water to be treated 130 as anaerobic microorganisms. Furthermore, both facultative anaerobes and obligate anaerobes are attached to the negative electrode 112 as anaerobic microorganisms. Therefore, the aeration device 150 alternates between active and inactive aeration of the water to be treated 130. During the active aeration state, oxygen-containing gas is brought into contact with the facultative anaerobes and obligate anaerobes. As a result, while the facultative anaerobes remain inhabiting the water to be treated 130, most of the obligate anaerobes are killed, allowing the facultative anaerobes to predominate. Furthermore, while the facultative anaerobes remain attached to the negative electrode 112, some of the obligate anaerobes are killed, resulting in a decrease in the amount of obligate anaerobes. This makes it easier for the facultative anaerobic bacteria to decompose organic matter in the water to be treated 130, allowing the water to be treated 130 to be purified efficiently.

In this embodiment, it is preferable that the aeration device 150 alternate between an active aeration state and an inactive aeration state at regular intervals. The active aeration state can last for 10 to 20 minutes, and the inactive aeration state can last for 40 minutes to 3 hours.

The present embodiment will be described in more detail below using examples and comparative examples, but the present embodiment is not limited to these examples.

[Fabrication of water treatment structure]
First, the water treatment structures used in Example 1 and Comparative Example 1, and the water treatment structure used in Example 2 were fabricated.

(Example 1 and Comparative Example 1)
First, two graphite sheets (conductors) were prepared, each measuring 68 cm in length, 30 cm in width, and 0.5 cm in thickness. A plurality of through holes were formed in the graphite sheets, except for the top 8 cm of each sheet. The through holes were drilled along the thickness direction of the graphite sheets.

Next, an iron-based catalyst consisting of iron- and nitrogen-loaded carbon black was dispersed in a mixed solution of Nafion solution and ethanol to prepare a catalyst slurry. The resulting catalyst slurry was then applied to the top 8 cm of a graphite sheet and allowed to dry. This resulted in two water treatment structures with an iron-based catalyst loaded on top of the graphite sheet. Figure 9 shows an example of a water treatment structure in which an iron-based catalyst is loaded on top of a graphite sheet with through-holes, with the upper black area being the area where the iron-based catalyst is loaded.

Example 2
The graphite sheets having through holes formed therein in Example 1 and Comparative Example 1 were used as they were as water treatment structures. In other words, the water treatment structure of Example 2 was the same as the water treatment structures of Example 1 and Comparative Example 1 in that no iron-based catalyst was supported thereon.

[evaluation]
Example 1
A treatment tank having an inlet and an outlet and a capacity of approximately 20 L was prepared. Furthermore, an aeration device for aerating the water to be treated was installed in the treatment tank. The water treatment structure fabricated as described above was then disposed inside the treatment tank, thereby obtaining a water treatment device 100.

Next, as shown in FIG. 10, a high-speed filtration device 210 for filtering the water to be treated and a high-speed filtration treatment tank 220 for storing the high-speed filtered water to be treated were installed upstream of the water treatment device 100. Furthermore, a sludge storage tank 240 for removing sludge from the treated water purified by the water treatment device 100 was installed downstream of the water treatment device 100. Note that a diaphragm pump 230 was installed between the high-speed filtration treatment tank 220 and the water treatment device 100 to send the high-speed filtered water to be treated from the high-speed filtration treatment tank 220 to the inlet of the water treatment device 100. Note that sewage (actual sewage) was used as the water to be treated. In this way, the experimental device of Example 1 was constructed.

The water to be treated was then sent to the high-speed filtration device 210 to remove solids from the sewage, and the high-speed filtered water was stored in the high-speed filtration treatment tank 220. A diaphragm pump was then used to send the high-speed filtered water to the water treatment device 100 from the high-speed filtration treatment tank 220. The amount of water to be treated sent to the water treatment device 100 was adjusted so that the hydraulic retention time (HRT) in the treatment tank was 4 hours. The water treated in the water treatment device 100 was then discharged into the sludge storage tank.

This purification process for the water (sewage) was carried out for approximately four months. During this period, the water treatment device 100 continuously performed intermittent aeration on the water to be treated, intermittently bringing the water into contact with air. The intermittent aeration consisted of alternating periods of 10 minutes of aeration and 50 minutes of no aeration.

During the final 54 days of the purification process, the high-speed filtered water to be treated and the treated water discharged from the water treatment device 100 were sampled approximately once a week, and the biological oxygen demand (SC-BOD) for the dissolved carbonaceous organic matter contained in the water to be treated and the treated water were measured.

Furthermore, the SC-BOD removal rate was calculated from the average value of the SC-BOD concentration of the high-speed filtered water to be treated and the average value of the SC-BOD concentration of the treated water discharged from the water treatment device according to Equation 1. Note that a higher SC-BOD removal rate indicates a higher organic matter purification capability in the water treatment device.
[Equation 1]
[SC-BOD removal rate] = (A-B)/A
A: Average value of SC-BOD concentration in treated water after high-speed filtration. B: Average value of SC-BOD concentration in treated water discharged from water treatment equipment.

Example 2
The SC-BOD concentration of the high-speed filtered treated water and the SC-BOD concentration of the treated water discharged from the water treatment device were measured in the same manner as in Example 1, except that the water treatment structure of Example 2 was used, and the SC-BOD removal rate was calculated.

(Comparative Example 1)
In the water treatment device 100 of Example 1, the SC-BOD concentration of the high-speed filtered water to be treated and the SC-BOD concentration of the treated water discharged from the water treatment device were measured in the same manner as in Example 1, except that intermittent aeration was not performed at all, and the SC-BOD removal rate was calculated.

(Comparative Example 2)
A purification treatment was carried out in the same manner as in Example 1, except that the water treatment structure of Example 1 was replaced with a trical net. The trical net is a non-woven, square-mesh resin net that is not conductive and has no water purification function. In other words, Comparative Example 2 is an example in which only intermittent aeration was performed on the high-speed filtered water to be treated. Then, in the same manner as in Example 1, the SC-BOD concentrations of the high-speed filtered water to be treated and the treated water discharged from the water treatment device were measured, and the SC-BOD removal rate was calculated.

The average SC-BOD concentration of the high-speed filtered treated water and the average SC-BOD concentration of the treated water discharged from the water treatment device 100 for each example, as well as their standard deviations, are shown in Table 1. Furthermore, the SC-BOD removal rate for each example is also shown in Table 1.

Table 1 shows that Examples 1 and 2, which used a water treatment structure and performed intermittent aeration, achieved an SC-BOD removal rate of 74% or more for raw water (high-speed filtered water to be treated). Furthermore, Examples 1 and 2 achieved SC-BOD concentrations of less than 15 mg/L, demonstrating good purification performance. In contrast, Comparative Example 1, which used a water treatment structure but did not perform intermittent aeration, achieved an SC-BOD removal rate of 70%. This demonstrates that intermittent aeration increases the purification efficiency of the water to be treated. Furthermore, Comparative Example 2, which only performed intermittent aeration, achieved an SC-BOD removal rate of 63%. This demonstrates that combining a water treatment structure with intermittent aeration significantly improves purification efficiency.

Note that, from Examples 1 and 2, although the SC-BOD removal rate improves when an oxygen reduction catalyst is supported on the positive electrode, it can also be seen that the SC-BOD removal rate is increased even without the support of an oxygen reduction catalyst. This is thought to be because aerobic microorganisms adhere to the positive electrode and react oxygen in the gas phase with hydrogen ions and electrons to produce water. Therefore, it can be seen that, regardless of the presence or absence of an oxygen reduction catalyst, combining a water treatment structure with intermittent aeration improves purification efficiency. Furthermore, because purification efficiency is improved even without the use of a catalyst, the cost of the water treatment structure can be reduced. Furthermore, the catalyst in the water treatment structure may deteriorate, in which case the water treatment structure must be replaced. However, if a catalyst is not used, there is no need to replace the water treatment structure, further reducing costs.

Figure 11 shows the results of observing the surface of the water treatment structure of each example after purification of the treated water. Figure 11(a) is a photograph showing the surface of the water treatment structure of Example 1, Figure 11(b) is a photograph showing the surface of the water treatment structure of Example 2, and Figure 11(c) is a photograph showing the surface of the water treatment structure of Comparative Example 1. Figure 11 shows that in each example, the water treatment structure had a large amount of microorganisms attached to the entire negative electrode. Furthermore, Figure 11(a) shows that the attached microorganisms in Example 1 were brown. Figure 11(b) shows that the attached microorganisms in Example 2 were gray. In contrast, Figure 11(c) shows that the attached microorganisms in Comparative Example 1, which did not undergo intermittent aeration, were dark green. Thus, the different colors of the attached microorganisms in each example of the water treatment structure indicate that the microbial species are different.

In each water treatment structure, the negative electrode is immersed in the water to be treated. Furthermore, as shown in Table 1, microorganisms contribute to the purification of the water to be treated. Therefore, the microorganisms adhering to the entire negative electrode are thought to be anaerobic microorganisms, which are electricity-generating bacteria, and their symbiotic microorganisms. Furthermore, since intermittent aeration was performed in Examples 1 and 2, the anaerobic microorganisms adhering to the negative electrode are thought to be facultative anaerobes, rather than obligate anaerobes. In contrast, since intermittent aeration was not performed in Comparative Example 1, the anaerobic microorganisms adhering to the negative electrode are thought to be both obligate anaerobes and facultative anaerobes.

In this way, by intermittently aerating the water to be treated with oxygen-containing gas, facultative anaerobic bacteria become dominant in the water to be treated and in the negative electrode, making it possible to efficiently purify the water to be treated.

The present embodiment has been described above, but it is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

2 oxygen reduction catalyst 3 anaerobic microorganism 4 aerobic microorganism 10, 110 water treatment structure 11, 111 positive electrode 12, 112 negative electrode 20, 120 treatment tank 30, 130 water to be treated 40, 140 gas phase 50, 150 aeration device 100, 200 water treatment device

Claims (8)

a water treatment structure including: a negative electrode that contacts water to be treated inhabited by anaerobic microorganisms having facultative anaerobes and obligate anaerobes, and to which the anaerobic microorganisms are attached; and a positive electrode that is electrically connected to the negative electrode and contacts an oxygen-containing gas phase and the water to be treated;
an aeration device that intermittently aerates the water to be treated with an oxygen-containing gas;
Equipped with
the anaerobic microorganisms decompose organic matter in the water to be treated to generate hydrogen ions and electrons, and further have an extracellular electron transport mechanism;
The water treatment structure includes a conductor,
The aeration device alternately repeats an aeration state and a non-aeration state, and in the aeration state, the gas is brought into contact with the anaerobic microorganisms. The water treatment device of claim 1 further comprises a treatment tank that holds the water treatment structure, the water to be treated, and at least a portion of the aeration device. The water treatment device according to claim 1 or 2, wherein the gas is brought into contact with the anaerobic microorganisms, so that the facultative anaerobic bacteria remain in the water to be treated and the obligate anaerobic bacteria are removed from the water to be treated. A water treatment device according to any one of claims 1 to 3, wherein the aeration device alternates between an active aeration state and an inactive aeration state at regular intervals. A water treatment device according to any one of claims 1 to 4, wherein the duration of the aeration state is 10 to 20 minutes, and the duration of the aeration state is 40 minutes to 3 hours. The water treatment device described in any one of claims 1 to 5, wherein the positive electrode has aerobic microorganisms attached thereto or an oxygen reduction catalyst supported thereon. the water treatment structure is composed of the negative electrode , the positive electrode, and an internal space existing between the negative electrode and the positive electrode,
The water treatment device according to claim 1 , wherein the water treatment structure has a plate-like, rod-like, or string-like shape. A water treatment method using a water treatment structure including: a negative electrode that contacts water to be treated inhabited by anaerobic microorganisms having facultative anaerobes and obligate anaerobes, and to which the anaerobic microorganisms are attached; and a positive electrode that is electrically connected to the negative electrode and contacts an oxygen-containing gas phase and the water to be treated,
the anaerobic microorganisms decompose organic matter in the water to be treated to generate hydrogen ions and electrons, and further have an extracellular electron transport mechanism;
The water treatment structure includes a conductor,
A water treatment method that alternately repeats an aeration state in which an oxygen-containing gas is aerated into the water to be treated, thereby bringing the gas into contact with the anaerobic microorganisms, and an aeration stop state in which aeration of the gas is stopped.