JP2020082006A - Liquid treatment system - Google Patents

Abstract

To provide a liquid treatment system capable of removing organic substances from an electrolytic solution and removing phosphorus.SOLUTION: Liquid treatment system A includes a first electrolytic solution tank 1, a first supply part 5 which supplies an electrolytic solution 3 to the first electrolytic tank 1 and a first discharge part 6 which discharges the electrolytic solution 3 in the first electrolytic solution tank 1 from the first electrolyte tank 1. The liquid treatment system A includes a second electrolytic solution tank 2 which is provided downstream of the first electrolytic solution tank 1 and holds the electrolytic solution 3 discharged from the first electrolytic solution tank 1. The liquid treatment system A has a second supply unit 7 which supplies an electrolytic solution 3 discharged from the first electrolytic solution tank 1 to the second electrolytic solution tank 2 and a second discharge part 8 which discharges the electrolytic solution 3 in the second electrolyte tank 2, and an oxygen supply unit 200 which supplies oxygen to an electrolytic solution 3 in the second electrolytic solution tank 2. The phosphate ion concentration of the electrolytic solution 3 passing through the second discharge part 8 is lower than the phosphate ion concentration of the electrolytic solution 3 passing through the first supply part 5.SELECTED DRAWING: Figure 2

Description

The present invention relates to liquid treatment systems.

In recent years, microbial fuel cells that generate electricity using biomass have been attracting attention as sustainable energy. A microbial fuel cell is a wastewater treatment device that converts chemical energy of organic substances contained in domestic wastewater and industrial wastewater into electric energy, and oxidatively decomposes and treats the organic substances. In addition, the microbial fuel cell has features that the amount of sludge generated is small and the energy consumption is small.

The microbial fuel cell has a negative electrode supporting microorganisms, and a positive electrode in contact with a gas phase containing oxygen and an electrolytic solution (wastewater). Then, while supplying an electrolytic solution containing an organic substance and the like to the negative electrode, a gas containing oxygen is supplied to the positive electrode. The negative electrode and the positive electrode form a closed circuit by connecting to each other via a load circuit. At the negative electrode, hydrogen ions and electrons are generated from the electrolytic solution by the catalytic action of anaerobic microorganisms. Then, the generated hydrogen ions move to the positive electrode via the electrolytic solution, and the electrons move to the positive electrode via the load circuit. Hydrogen ions and electrons transferred from the negative electrode combine with oxygen in the positive electrode and are consumed as water. At that time, the electric energy flowing through the closed circuit is recovered.

As the above-mentioned microbial fuel cell, the microbial fuel cell described in Patent Document 1 is known. Patent Document 1 discloses a microbial fuel that includes a negative electrode and a positive electrode, and supplies electricity to a closed hollow cassette through an inlet/outlet hole while extracting electricity through a circuit that electrically connects the negative electrode and the positive electrode. Batteries are listed. The negative electrode is immersed in an organic substrate and carries anaerobic microorganisms. The positive electrode is enclosed with an electrolytic solution in a closed hollow cassette having an outer shell and an inlet/outlet hole formed at least in part by an ion-permeable diaphragm, or is bonded to the inside of the diaphragm of the cassette to form an organic substrate. Is plugged into.

Japanese Patent No. 5164511

According to the microbial fuel cell of Patent Document 1, the current-producing bacteria decompose the organic substances in the wastewater to generate an electric current. However, the wastewater contains a large amount of phosphorus compounds as well as organic substances. When phosphorus compounds in wastewater flow out into the natural environment, eutrophication progresses, causing red tides. Therefore, it is required to remove phosphorus from wastewater as well as organic substances.

The present invention has been made in view of the above problems of the conventional technology. Then, an object of the present invention is to provide a liquid treatment system capable of removing an organic substance in an electrolytic solution and also removing phosphorus.

In order to solve the above problems, a liquid processing system according to an aspect of the present invention includes a first electrolytic solution tank that holds an electrolytic solution containing an organic substance and a phosphorus compound. The liquid processing system includes a first supply unit that supplies the electrolytic solution to the first electrolytic solution tank, and a first discharge unit that discharges the electrolytic solution in the first electrolytic solution tank from the first electrolytic solution tank. The liquid processing system is in contact with the electrolytic solution in the first electrolytic solution tank, the positive electrode in contact with the gas phase containing oxygen, and the electrolytic solution in the first electrolytic solution tank, and is electrically connected to the positive electrode. A negative electrode carrying anaerobic microorganisms. The liquid processing system includes a second electrolytic solution tank that is provided on the downstream side of the first electrolytic solution tank and holds the electrolytic solution discharged from the first electrolytic solution tank. The liquid treatment system includes a second supply unit that supplies the electrolytic solution discharged from the first electrolytic solution tank to the second electrolytic solution tank, a second discharge unit that discharges the electrolytic solution in the second electrolytic solution tank, and (2) An oxygen supply unit that supplies oxygen to the electrolytic solution in the electrolytic solution tank. The phosphate ion concentration of the electrolytic solution passing through the second discharging part is lower than the phosphate ion concentration of the electrolytic solution passing through the first supplying part.

According to the present disclosure, it is possible to provide a liquid treatment system capable of removing an organic substance in an electrolytic solution and also removing phosphorus.

It is a perspective view which shows roughly an example of the liquid treatment system which concerns on 1st embodiment. It is sectional drawing which followed the AA line in FIG. It is an exploded perspective view showing an example of an electrode cassette in a liquid treatment system. It is an exploded perspective view showing an example of an oxygen supply part in a liquid treatment system. It is sectional drawing which shows another example of a liquid treatment system schematically. It is a perspective view which shows roughly an example of the liquid processing system which concerns on 2nd embodiment. It is sectional drawing which followed the BB line in FIG.

Hereinafter, the liquid processing system according to this embodiment will be described in detail. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

[First embodiment]
As a method of removing phosphorus from an electrolytic solution, a physicochemical removal method of precipitating and separating phosphorus using a drug, and a biological removal method of utilizing polyphosphate-accumulating bacteria are known. Physicochemical removal can remove phosphorus in a stable manner, but it requires the use of chemicals and tends to increase the amount of sludge generated.

Therefore, in the liquid treatment system according to this embodiment, phosphorus is removed from the electrolytic solution by the biological removal method. Specifically, as shown in FIGS. 1 and 2, the liquid processing system A includes a first electrolytic solution tank 1 that holds an electrolytic solution 3 containing an organic substance and a phosphorus compound. The electrolytic solution 3 held in the first electrolytic solution tank 1 is waste water such as domestic waste water or factory waste water.

The liquid processing system A includes a first supply unit 5 that supplies the electrolytic solution 3 to the first electrolytic solution tank 1. The liquid processing system A includes a first discharging unit 6 that discharges the electrolytic solution 3 in the first electrolytic solution tank 1 from the first electrolytic solution tank 1. The first electrolytic solution tank 1 is a substantially rectangular parallelepiped-shaped container, and a first supply unit 5 is provided above the front wall 1 a of the first electrolytic solution tank 1. Further, a first discharge part 6 is provided on the upper part of the rear wall 1b of the first electrolytic solution tank 1.

The liquid processing system A includes a positive electrode 10 that contacts the electrolytic solution 3 in the first electrolytic solution tank 1 and contacts the gas phase G containing oxygen. Specifically, the positive electrode is immersed in the electrolytic solution in the first electrolytic solution tank 1. Further, the liquid processing system A includes a negative electrode 20 that comes into contact with the electrolytic solution 3 in the first electrolytic solution tank 1 and is electrically connected to the positive electrode 10 and carries anaerobic microorganisms. Specifically, the negative electrode 20 is immersed in the electrolytic solution 3 in the first electrolytic solution tank 1. Specifically, the liquid processing system A includes an electrode cassette 100 having a positive electrode 10 and a negative electrode 20, and the electrode cassette 100 is arranged so as to be immersed in the electrolytic solution 3 inside the first electrolytic solution tank 1. There is. Then, as described below, the electrode cassette 100 decomposes the organic substance contained in the electrolytic solution 3 in the first electrolytic solution tank 1. The electrolytic solution 3 held in the first electrolytic solution tank 1 is under an anaerobic condition so that anaerobic microorganisms can act.

The liquid processing system A includes a second electrolytic solution tank 2 which is provided on the downstream side of the first electrolytic solution tank 1 and holds the electrolytic solution 3 discharged from the first electrolytic solution tank 1. Then, the liquid processing system A includes a second supply unit 7 for supplying the electrolytic solution 3 discharged from the first electrolytic solution tank 1 to the second electrolytic solution tank 2 and the electrolytic solution 3 in the second electrolytic solution tank 2. And a second discharging portion 8 for discharging. The second electrolytic solution tank 2 is a substantially rectangular parallelepiped container, and the second supply unit 7 is provided on the upper portion of the front wall 2 a of the second electrolytic solution tank 2. Further, a second discharge part 8 is provided on the upper part of the rear wall 2b of the second electrolytic solution tank 2.

Then, the electrolytic solution 3 passes through the first supply unit 5, the first electrolytic solution tank 1, the first discharge unit 6, the second supply unit 7, the second electrolytic solution tank 2, and the second discharge unit 8 in order. Further, the liquid processing system A is configured. The first supply unit 5, the first discharge unit 6, the second supply unit 7, and the second discharge unit 8 supply or discharge the electrolytic solution 3 to the first electrolytic solution tank 1 or the second electrolytic solution tank 2. If it is possible, it is not necessary to be provided on the walls of the first electrolytic solution tank 1 and the second electrolytic solution tank 2. The 1st supply part 5, the 1st discharge part 6, the 2nd supply part 7, and the 2nd discharge part 8 may be arrange|positioned above the 1st electrolytic solution tank 1 and the 2nd electrolytic solution tank 2, for example. In addition, in the present embodiment, the first discharge part 6 and the second supply part 7 are configured by the cylindrical connecting pipe 4, but the first discharge part 6 and the second supply part 7 are configured by different members. Alternatively, the connecting pipe 4 may be formed of a single member.

The liquid processing system A includes an oxygen supply unit 200 that supplies oxygen to the electrolytic solution 3 in the second electrolytic solution tank 2. Specifically, the oxygen supply unit 200 is arranged so as to be immersed in the electrolytic solution 3 inside the second electrolytic solution tank 2. Therefore, oxygen is supplied to the electrolytic solution 3 held in the second electrolytic solution tank 2 by the oxygen supply unit 200, and the electrolytic solution 3 held in the second electrolytic solution tank 2 becomes an aerobic condition. There is.

In the liquid processing system A according to this embodiment, phosphorus is removed from the electrolytic solution 3 by the bacteria that accumulate phosphorus. Specifically, the phosphorus in the electrolytic solution 3 is removed by a biological phosphorus removal method using a microorganism such as polyphosphate accumulating organisms. The polyphosphate-accumulating bacterium may be any bacterium capable of accumulating high-concentration polyphosphate in the body, for example, at least one kind selected from the group consisting of Acinetobacter genus bacterium, Arthrobacter genus bacterium and Pseudomonas genus bacterium. It may be a bacterium.

The polyphosphate-accumulating bacterium has the property of releasing phosphorus to the outside of the body under anaerobic conditions where the oxygen concentration is low, and taking up phosphorus into the body under aerobic conditions where the oxygen concentration is high. As described above, in the liquid processing system A according to the present embodiment, the electrolytic solution 3 in the first electrolytic solution tank 1 provided on the upstream side is subjected to anaerobic conditions, and the second electrolytic solution tank 2 provided on the downstream side is used. The electrolytic solution 3 therein is aerobic. The polyphosphate-accumulating bacteria are contained in the electrolytic solution 3 held in the first electrolytic solution tank 1 and the electrolytic solution 3 held in the second electrolytic solution tank 2.

Therefore, the polyphosphoric acid-accumulating bacteria release phosphorus outside the body in the electrolytic solution 3 held in the first electrolytic solution tank 1, but in the electrolytic solution 3 held in the second electrolytic solution tank 2, the first electrolytic solution. The amount of phosphorus released from the tank 1 is taken into the body. Since the phosphorus in the electrolytic solution 3 is concentrated in the polyphosphate-accumulating bacteria, the phosphorus in the electrolytic solution 3 is removed by removing the polyphosphate-accumulating bacteria from the electrolytic solution 3.

Therefore, the phosphate ion concentration of the electrolytic solution 3 passing through the second discharging part 8 is lower than the phosphate ion concentration of the electrolytic solution 3 passing through the first discharging part 6. Further, the phosphate ion concentration of the electrolytic solution 3 passing through the second discharging part 8 is lower than the phosphate ion concentration of the electrolytic solution 3 passing through the first supplying part 5. The phosphate ion concentration is the concentration of phosphate ions dissolved in the filtered electrolytic solution 3. The phosphate ion concentration can be measured by a method such as molybdenum blue absorptiometry according to Japanese Industrial Standard JIS K0102:2016 (factory drainage test method).

[Electrode cassette]
As shown in FIGS. 1 to 3, the electrode cassette 100 includes an electrode assembly 40 including a positive electrode 10, a negative electrode 20, and an ion transfer layer 30. In the electrode cassette 100, the negative electrode 20 is arranged so as to contact one surface 30a of the ion transfer layer 30, and the positive electrode 10 is arranged so as to contact the surface 30b of the ion transfer layer 30 opposite to the surface 30a. ing.

As shown in FIG. 3, the electrode assembly 40 is laminated on the cassette base material 50A. The cassette base 50A is a U-shaped frame member that extends along the outer periphery of the surface 10a of the positive electrode 10, and has an open top. That is, the cassette base material 50A is a frame member in which the bottom surfaces of the two first columnar members 51 are connected by the second columnar member 52. Then, as shown in FIG. 2, the side surface 53 of the cassette base material 50A is joined to the outer peripheral portion of the surface 10a of the positive electrode 10.

As shown in FIG. 2, the electrode cassette 100 formed by stacking two sets of the electrode assembly 40 and the cassette base 50A has the first electrolytic solution tank 1 so that the gas phase G communicating with the atmosphere is formed. Placed inside. An electrolytic solution 3, which is water to be treated, is held inside the first electrolytic solution tank 1, and the gas diffusion layer 12, the negative electrode 20, and the ion transfer layer 30 of the positive electrode 10 are immersed in the electrolytic solution 3.

As described below, the positive electrode 10 includes a water repellent layer 11 having water repellency. Therefore, the electrolytic solution 3 held inside the first electrolytic solution tank 1 is separated from the inside of the cassette base material 50A, and the internal space formed by the electrode assembly 40 and the cassette base material 50A becomes the gas phase G. ing. In the liquid processing system A, the gas phase G is opened to the outside air, or air is supplied to the gas phase G from the outside by, for example, a pump. Further, as shown in FIG. 2, the positive electrode 10 and the negative electrode 20 are electrically connected to the external circuit 60, respectively.

(Positive electrode)
As shown in FIG. 2, the positive electrode 10 according to the present embodiment is composed of a gas diffusion electrode including a water repellent layer 11 and a gas diffusion layer 12 that is stacked so as to contact the water repellent layer 11. The gas diffusion layer 12 of the positive electrode 10 is in contact with the ion transfer layer 30, and the water repellent layer 11 is exposed on the gas phase G side. By using such a thin plate-shaped gas diffusion electrode, it becomes possible to easily supply oxygen in the gas phase G to the catalyst in the positive electrode 10.

<Water repellent layer>
The water repellent layer 11 in the positive electrode 10 is a layer having both water repellency and oxygen permeability. The water-repellent layer 11 is configured to allow the movement of oxygen from the gas phase G to the liquid phase while favorably separating the gas phase G and the liquid phase in the electrochemical system in the electrode cassette 100. That is, the water-repellent layer 11 allows oxygen in the vapor phase G to permeate and move to the gas diffusion layer 12, while suppressing movement of the electrolytic solution 3 to the vapor phase G side. The term "separation" as used herein means to physically cut off.

The water-repellent layer 11 is in contact with the gas phase G containing oxygen and diffuses oxygen in the gas phase G. In the structure shown in FIG. 2, the water repellent layer 11 supplies oxygen to the gas diffusion layer 12 substantially uniformly. Therefore, the water repellent layer 11 is preferably a porous body so that the oxygen can be diffused. Since the water-repellent layer 11 has water repellency, it is possible to prevent the pores of the porous body from being clogged due to dew condensation or the like, thereby reducing the oxygen diffusivity. Further, since the electrolytic solution 3 is less likely to soak into the water repellent layer 11, oxygen can be efficiently circulated from the surface of the water repellent layer 11 that contacts the gas phase G to the surface that faces the gas diffusion layer 12. Becomes

The water-repellent layer 11 is preferably formed of a woven or non-woven fabric into a sheet shape. The material forming the water-repellent layer 11 is not particularly limited as long as it has water repellency and can diffuse oxygen in the gas phase G. Examples of the material forming the water repellent layer 11 include polyethylene, polypropylene, polybutadiene, nylon, polytetrafluoroethylene (PTFE), ethyl cellulose, poly-4-methylpentene-1, butyl rubber and polydimethylsiloxane (PDMS). At least one selected from the group consisting of silicone can be used. Since these materials easily form a porous body and have high water repellency, it is possible to suppress clogging of pores and improve gas diffusivity. The water-repellent layer 11 preferably has a plurality of through holes penetrating in the stacking direction X of the water-repellent layer 11 and the gas diffusion layer 12.

The water-repellent layer 11 may be subjected to water-repellent treatment using a water-repellent agent, if necessary, in order to enhance the water repellency. Specifically, water repellency may be improved by attaching a water repellent agent such as polytetrafluoroethylene to the porous body forming the water repellent layer 11.

<Gas diffusion layer>
The gas diffusion layer 12 in the positive electrode 10 preferably includes a porous conductive material and a catalyst carried by the conductive material. The gas diffusion layer 12 may be composed of a porous catalyst having conductivity. By using such a gas diffusion layer 12 for the positive electrode 10, it becomes possible to conduct electrons generated by a local cell reaction described later between the catalyst and the external circuit 60. That is, as will be described later, the gas diffusion layer 12 carries a catalyst, and the catalyst is an oxygen reduction catalyst. Then, the electrons move from the external circuit 60 to the catalyst through the gas diffusion layer 12, whereby the oxygen reduction reaction by oxygen, hydrogen ions and electrons can be advanced by the catalyst.

In the positive electrode 10, it is preferable that oxygen permeates the water repellent layer 11 and the gas diffusion layer 12 efficiently and is supplied to the catalyst in order to ensure stable performance. Therefore, the gas diffusion layer 12 is preferably a porous body having a large number of pores through which oxygen permeates, from the surface facing the water repellent layer 11 to the surface opposite thereto. Further, it is particularly preferable that the shape of the gas diffusion layer 12 is a three-dimensional mesh shape. Such a mesh shape makes it possible to impart high oxygen permeability and conductivity to the gas diffusion layer 12.

In the positive electrode 10, in order to efficiently supply oxygen to the gas diffusion layer 12, the water repellent layer 11 is preferably joined to the gas diffusion layer 12 via an adhesive. Thereby, the diffused oxygen is directly supplied to the gas diffusion layer 12, and the oxygen reduction reaction can be efficiently performed. From the viewpoint of ensuring the adhesiveness between the water repellent layer 11 and the gas diffusion layer 12, the adhesive is preferably provided on at least a part of the water repellent layer 11 and the gas diffusion layer 12. However, from the viewpoint of enhancing the adhesiveness between the water repellent layer 11 and the gas diffusion layer 12 and stably supplying oxygen to the gas diffusion layer 12 for a long period of time, the adhesive is the water repellent layer 11 and the gas diffusion layer 12. It is more preferable that it is provided on the entire surface between 12 and 12.

The adhesive preferably has oxygen permeability and contains at least one selected from the group consisting of polymethylmethacrylate, methacrylic acid-styrene copolymer, styrene-butadiene rubber, butyl rubber, nitrile rubber, chloroprene rubber and silicone. A resin can be used.

Here, the gas diffusion layer 12 of the positive electrode 10 in the present embodiment will be described in more detail. As described above, the gas diffusion layer 12 can be configured to include the porous conductive material and the catalyst carried by the conductive material.

The conductive material in the gas diffusion layer 12 can be composed of, for example, one or more materials selected from the group consisting of carbon-based substances, conductive polymers, semiconductors and metals. Here, the carbon-based substance means a substance having carbon as a constituent component. Examples of the carbon-based substance include, for example, graphite, activated carbon, carbon black, Vulcan (registered trademark) XC-72R, acetylene black, furnace black, carbon powder such as Denka black, graphite felt, carbon wool, carbon woven cloth, and the like. Examples thereof include carbon fibers, carbon plates, carbon paper, carbon disks, carbon cloth, carbon foil, and carbon-based materials obtained by compression-molding carbon particles. Further, examples of the carbon-based material also include fine-structured materials such as carbon nanotubes, carbon nanohorns, and carbon nanoclusters. Furthermore, as the conductive material in the gas diffusion layer 12, a metal material such as mesh and foam can be used.

The conductive polymer is a general term for polymer compounds having conductivity. Examples of the conductive polymer include aniline, aminophenol, diaminophenol, pyrrole, thiophene, paraphenylene, fluorene, furan, acetylene, or a single monomer having a derivative thereof as a constituent unit or a polymer of two or more kinds of monomers. Can be mentioned. Specific examples of the conductive polymer include polyaniline, polyaminophenol, polydiaminophenol, polypyrrole, polythiophene, polyparaphenylene, polyfluorene, polyfuran, and polyacetylene. Examples of the conductive material made of metal include aluminum, copper, stainless steel, nickel and titanium. In consideration of availability, cost, corrosion resistance, durability, etc., the conductive material is preferably a carbon-based substance.

The shape of the conductive material is preferably a powder shape or a fiber shape. Further, the conductive material may be supported by the support. The support means a member which has rigidity by itself and can give a certain shape to the gas diffusion electrode. The support may be an insulator or a conductor. When the support is an insulator, examples of the support include glass, plastic, synthetic rubber, ceramics, water-resistant or water-repellent treated paper, plant pieces such as wood pieces, bone pieces, animal pieces such as shells, and the like. .. Examples of the support having a porous structure include porous ceramics, porous plastics and sponges. When the support is a conductor, examples of the support include carbon paper, carbon fiber, carbon-based substances such as carbon rods, metals, and conductive polymers. When the support is a conductor, the support can also function as a current collector by disposing a conductive material supporting a carbon-based material on the surface of the support.

The catalyst in the gas diffusion layer 12 is a platinum-based catalyst, a carbon-based catalyst using iron or cobalt, a transition metal oxide-based catalyst such as partially oxidized tantalum carbonitride (TaCNO) and zirconium carbonitride (ZrCNO), and tungsten. Alternatively, a carbide-based catalyst using molybdenum, activated carbon, or the like can be used.

The catalyst in the gas diffusion layer 12 is preferably a carbon-based material doped with metal atoms. The metal atom is not particularly limited, but titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium. It is preferably an atom of at least one metal selected from the group consisting of platinum and gold. In this case, the carbon-based material exhibits excellent performance as a catalyst for promoting the oxygen reduction reaction. The amount of metal atoms contained in the carbon-based material may be appropriately set so that the carbon-based material has excellent catalytic performance.

It is preferable that the carbon-based material is further doped with one or more non-metal atoms selected from nitrogen, boron, sulfur and phosphorus. The amount of non-metal atoms doped in the carbon-based material may be appropriately set so that the carbon-based material has excellent catalytic performance.

The carbon-based material is based on a carbon source material such as graphite and amorphous carbon, and the carbon source material is doped with a metal atom and one or more non-metal atoms selected from nitrogen, boron, sulfur and phosphorus. It can be obtained.

The combination of metal atoms and non-metal atoms doped in the carbon-based material is appropriately selected. In particular, it is preferable that the non-metal atom contains nitrogen and the metal atom contains iron. In this case, the carbon-based material can have a particularly excellent catalytic activity. The non-metal atom may be only nitrogen, and the metal atom may be only iron.

The non-metal atom may include nitrogen and the metal atom may include at least one of cobalt and manganese. Also in this case, the carbon-based material can have a particularly excellent catalytic activity. The non-metal atom may be nitrogen only. Further, the metal atom may be only cobalt, only manganese, or only cobalt and manganese.

The shape of the carbon-based material is not particularly limited. For example, the carbon-based material may have a particle shape or a sheet shape. The size of the carbon-based material having a sheet shape is not particularly limited, and for example, the carbon-based material may have a minute size. The carbonaceous material having a sheet shape may be porous. The sheet-shaped and porous carbon-based material preferably has, for example, a woven cloth shape, a non-woven cloth shape, or the like. Such a carbon-based material can form the gas diffusion layer 12 without a conductive material.

The carbon-based material configured as the catalyst in the gas diffusion layer 12 can be prepared as follows. First, a mixture containing a non-metal compound containing at least one non-metal selected from the group consisting of nitrogen, boron, sulfur and phosphorus, a metal compound and a carbon source material is prepared. Then, this mixture is heated at a temperature of 800° C. or higher and 1000° C. or lower for 45 seconds or more and less than 600 seconds. As a result, it is possible to obtain a carbon-based material configured as a catalyst.

Here, as the carbon source material, for example, graphite or amorphous carbon can be used as described above. Furthermore, the metal compound is not particularly limited as long as it is a compound containing a metal atom capable of coordinatively bonding with a non-metal atom doped in the carbon source material. Examples of the metal compound include inorganic metal salts such as metal chlorides, nitrates, sulfates, bromides, iodides, and fluorides, organic metal salts such as acetates, hydrates of inorganic metal salts, and organic metal salts. It is possible to use at least one selected from the group consisting of hydrates of For example, when graphite is doped with iron, the metal compound preferably contains iron(III) chloride. When the graphite is doped with cobalt, the metal compound preferably contains cobalt chloride. When the carbon source material is doped with manganese, the metal compound preferably contains manganese acetate. The amount of the metal compound used is preferably determined such that the ratio of metal atoms in the metal compound to the carbon source material is within the range of 5 to 30% by mass, and the ratio is 5 to 20% by mass. More preferably, it is determined to be within the range.

As described above, the non-metal compound is preferably at least one non-metal compound selected from the group consisting of nitrogen, boron, sulfur and phosphorus. Examples of the nonmetallic compound include pentaethylenehexamine, ethylenediamine, tetraethylenepentamine, triethylenetetramine, octylboronic acid, 1,2-bis(diethylphosphinoethane), triphenylphosphite, and benzyldisulfide. At least one compound selected from the group consisting of can be used. The amount of the non-metal compound used is appropriately set according to the amount of the non-metal atom doped into the carbon source material. The amount of the non-metal compound used is preferably determined such that the molar ratio of the metal atom in the metal compound to the non-metal atom in the non-metal compound is in the range of 1:1 to 1:2. , 1:1.5 to 1:1.8 is more preferably determined.

A mixture containing a non-metal compound, a metal compound, and a carbon source raw material when a carbon-based material configured as a catalyst is prepared is obtained, for example, as follows. First, a carbon source raw material, a metal compound and a non-metal compound are mixed, and a solvent such as ethanol is further added if necessary to prepare the total amount. These are further dispersed by an ultrasonic dispersion method. Then, after heating these at an appropriate temperature (for example, 60° C.), the mixture is dried to remove the solvent. As a result, a mixture containing the non-metal compound, the metal compound and the carbon source material is obtained.

Next, the obtained mixture is heated, for example, under a reducing atmosphere or an inert gas atmosphere. As a result, the carbon source material is doped with a non-metal atom, and the non-metal atom and the metal atom are coordinate-bonded to each other, thereby doping the metal atom. The heating temperature is preferably in the range of 800° C. to 1000° C., and the heating time is preferably in the range of 45 seconds to less than 600 seconds. Since the heating time is short, the carbon-based material is efficiently produced, and the catalytic activity of the carbon-based material is further increased. In the heat treatment, the temperature rising rate of the mixture at the start of heating is preferably 50°C/s or more. Such rapid heating further improves the catalytic activity of the carbon-based material.

Further, the carbonaceous material may be further acid washed. For example, the carbon-based material may be dispersed in pure water for 30 minutes with a homogenizer, and then the carbon-based material may be put into 2M sulfuric acid and stirred at 80° C. for 3 hours. In this case, elution of the metal component from the carbon-based material is suppressed.

By such a manufacturing method, a carbon-based material having a remarkably low content of an inert metal compound and a metal crystal and high conductivity can be obtained.

In the gas diffusion layer 12, the catalyst may be bound to the conductive material using a binder. That is, the catalyst may be supported on the surface of the conductive material and inside the pores by using a binder. This can prevent the catalyst from being desorbed from the conductive material and deteriorating the oxygen reduction property. As the binder, for example, at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), and ethylene-propylene-diene copolymer (EPDM) is preferably used. It is also preferable to use NAFION (registered trademark) as the binder.

(Negative electrode)
The negative electrode 20 in the present embodiment carries an anaerobic microorganism described later, and further has a function of generating hydrogen ions and electrons from the organic substance in the electrolytic solution 3 by the catalytic action of the anaerobic microorganism. Therefore, the negative electrode 20 is not particularly limited as long as it has a configuration that causes such a function.

The negative electrode 20 has a structure in which an anaerobic microorganism is carried on a conductive sheet having conductivity. As the conductor sheet, at least one selected from the group consisting of a porous conductor sheet, a woven cloth-like conductor sheet and a non-woven cloth-like conductor sheet can be used. Further, the conductor sheet may be a laminated body in which a plurality of sheets are laminated. By using such a sheet having a plurality of pores as the conductor sheet of the negative electrode 20, hydrogen ions generated by a local cell reaction described later easily move toward the ion transfer layer 30, and the oxygen reduction reaction It is possible to increase the speed. Further, from the viewpoint of improving the ion permeability, the conductor sheet of the negative electrode 20 has a continuous space (void) in the stacking direction X of the positive electrode 10, the ion transfer layer 30, and the negative electrode 20, that is, the thickness direction. Preferably.

The conductor sheet may be a metal plate having a plurality of through holes penetrating in the thickness direction. Therefore, as the material forming the conductor sheet of the negative electrode 20, for example, at least one selected from the group consisting of aluminum, copper, stainless steel, conductive metals such as nickel and titanium, and carbon paper and carbon felt is used. be able to.

A graphite sheet that can be used for the positive electrode 10 may be used as the conductor sheet of the negative electrode 20. In addition, it is preferable that the negative electrode 20 contains graphite, and that the graphene layers in the graphite are arranged along a plane in the direction YZ perpendicular to the stacking direction X of the positive electrode 10, the ion transfer layer 30, and the negative electrode 20. By arranging the graphene layers in this manner, the conductivity in the direction YZ perpendicular to the stacking direction X is improved rather than the conductivity in the stacking direction X. Therefore, the electrons generated by the local battery reaction of the negative electrode 20 are easily conducted to the external circuit 60, and the efficiency of the battery reaction can be further improved.

The anaerobic microorganism supported on the negative electrode 20 is not particularly limited as long as it is a current-producing bacterium that decomposes an organic substance in the electrolytic solution 3 to generate hydrogen ions and electrons. Anaerobic microorganisms do not need oxygen for oxidatively decomposing the organic substance in the electrolytic solution 3. Therefore, the electric power required to send oxygen can be significantly reduced. In addition, since the anaerobic microorganisms acquire a small amount of free energy, it is possible to reduce the amount of sludge generated.

The anaerobic microorganisms retained on the negative electrode 20 are preferably, for example, electro-producing bacteria having an extracellular electron transfer mechanism. Specifically, examples of the anaerobic microorganisms include Geobacter genus bacteria, Shewanella genus bacteria, Aeromonas genus bacteria, Geothrix genus bacteria, and Saccharomyces genus bacteria.

The anaerobic microorganisms may be retained in the negative electrode 20 by stacking and fixing the biofilm containing the anaerobic microorganisms on the negative electrode 20. In addition, a biofilm generally refers to a three-dimensional structure containing a microbial population and an extracellular polymeric substance (EPS) produced by the microbial population. However, the anaerobic microorganisms may be retained on the negative electrode 20 without depending on the biofilm. Further, the anaerobic microorganisms may be retained not only on the surface of the negative electrode 20 but also inside.

The negative electrode 20 may be modified with, for example, an electron transfer mediator molecule. Alternatively, the electrolytic solution 3 in the first electrolytic solution tank 1 may contain an electron transfer mediator molecule. As a result, electron transfer from the anaerobic microorganisms to the negative electrode 20 is promoted, and more efficient liquid treatment can be realized.

Specifically, in the metabolic mechanism of anaerobic microorganisms, electrons are exchanged within cells or with the final electron acceptor. When the mediator molecule is introduced into the electrolytic solution 3, the mediator molecule acts as the final electron acceptor for metabolism, and transfers the received electron to the negative electrode 20. As a result, it becomes possible to increase the rate of oxidative decomposition of organic substances in the electrolytic solution 3. Such an electron transfer mediator molecule is not particularly limited. As the electron transfer mediator molecule, for example, at least one selected from the group consisting of neutral red, anthraquinone-2,6-disulfonic acid (AQDS), thionine, potassium ferricyanide, and methyl viologen can be used.

(Ion transfer layer)
The electrode cassette 100 of the present embodiment further includes an ion transfer layer 30 having proton permeability, which is provided between the positive electrode 10 and the negative electrode 20. Then, as shown in FIGS. 1 and 2, the negative electrode 20 is separated from the positive electrode 10 via the ion transfer layer 30. The ion transfer layer 30 has a function of transmitting hydrogen ions generated in the negative electrode 20 and moving the hydrogen ions to the positive electrode 10 side.

As the ion transfer layer 30, for example, an ion exchange membrane using an ion exchange resin can be used. As the ion exchange resin, for example, NAFION (registered trademark) manufactured by DuPont Co., Ltd., and Flemion (registered trademark) and Selemion (registered trademark) manufactured by Asahi Glass Co., Ltd. can be used.

Further, as the ion transfer layer 30, a porous film having pores through which hydrogen ions can permeate may be used. That is, the ion transfer layer 30 may be a sheet having a space (void) for hydrogen ions to move from the negative electrode 20 to the positive electrode 10. Therefore, the ion transfer layer 30 preferably includes at least one selected from the group consisting of a porous sheet, a woven sheet, and a non-woven sheet. Further, the ion transfer layer 30 can use at least one selected from the group consisting of a glass fiber membrane, a synthetic fiber membrane, and a plastic non-woven fabric, and may be a laminate formed by laminating a plurality of these. Since such a porous sheet has a large number of pores inside, hydrogen ions can easily move. The pore size of the ion transfer layer 30 is not particularly limited as long as hydrogen ions can move from the negative electrode 20 to the positive electrode 10. The ion transfer layer 30 is not limited to a film as long as hydrogen ions can be transferred from the negative electrode 20 to the positive electrode 10, and may be appropriately changed and used according to the shapes of the negative electrode 20 and the positive electrode 10.

As described above, the ion transfer layer 30 has a function of transmitting hydrogen ions generated in the negative electrode 20 and moving the hydrogen ions to the positive electrode 10 side. However, for example, if the negative electrode 20 and the positive electrode 10 are close to each other without making contact, hydrogen ions can move from the negative electrode 20 to the positive electrode 10. Therefore, in the liquid processing system A, the ion transfer layer 30 is not an essential component. However, by providing the ion transfer layer 30, hydrogen ions can be efficiently transferred from the negative electrode 20 to the positive electrode 10. Therefore, it is preferable to provide the ion transfer layer 30 from the viewpoint of improving the output. It should be noted that a space may be provided between the positive electrode 10 and the ion transfer layer 30, and a space may also be provided between the negative electrode 20 and the ion transfer layer 30.

As shown in FIG. 2, the electrode cassette 100 includes an external circuit 60 that is electrically connected to the negative electrode 20 and the positive electrode 10. However, in the electrode cassette 100, the negative electrode 20 and the positive electrode 10 may be directly electrically connected by using a conductive member without using the external circuit 60. Further, in the electrode cassette 100, the entire upper portion of the cassette base material 50A is opened, but it may be partially opened as long as it is possible to introduce air (oxygen) into the inside, and it is closed. May be.

[Oxygen supply section]
The oxygen supply unit 200 supplies oxygen to the electrolytic solution 3 that has moved to the second electrolytic solution tank 2 to increase the dissolved oxygen concentration of the electrolytic solution 3 and bring the electrolytic solution 3 into an aerobic condition. By making the electrolytic solution 3 in the second electrolytic solution tank 2 aerobic, the polyphosphoric acid-accumulating bacteria can take in more phosphorus than the amount released in the first electrolytic solution tank 1 into the body. As a result, phosphorus is highly accumulated in the body of the polyphosphate-accumulating bacteria. Therefore, phosphorus in the electrolytic solution 3 can be removed by removing the polyphosphate-accumulating bacteria from the electrolytic solution 3.

Specifically, as shown in FIG. 4, the oxygen supply unit 200 is formed by laminating a cassette base material 50B and two water repellent layers 110. As the cassette base material 50B and the water repellent layer 110, the same materials as the water repellent layer 11 and the cassette base material 50A in the electrode cassette 100 described above can be used. Then, as shown in FIG. 4, the side surface 53 of the cassette base material 50B is joined to the outer peripheral portion of the surface 110a of the water repellent layer 110. Therefore, the electrolytic solution 3 held inside the second electrolytic solution tank 2 is separated from the inside of the cassette base material 50B, and the internal space formed by the water repellent layer 110 and the cassette base material 50B is in the vapor phase G. ing. In the liquid processing system A, the gas phase G is opened to the outside air, or air is supplied to the gas phase G from the outside by, for example, a pump.

However, the oxygen supply unit 200 is not limited to such a mode as long as the electrolytic solution 3 held in the second electrolytic solution tank 2 is in an aerobic condition and phosphorus in the electrolytic solution 3 is taken up by the polyphosphate-accumulating bacteria. .. The oxygen supply unit 200 may be, for example, a bag shape in which the tops of the two water-repellent layers 110 are joined to each other and the top of the water-repellent layer 110 is open so that the gas phase G is inside. Further, the oxygen supply unit 200 may be a known aerator that supplies air from the outside by a pump.

For example, as shown in FIG. 5, the liquid treatment system A may include an oxygen supply unit 200A that supplies oxygen to the electrolytic solution 3 in the second electrolytic solution tank 2 instead of the oxygen supply unit 200. The oxygen supply unit 200A preferably includes an air diffuser 151 having a hole for diffusing gas, and a gas supply member 152 for supplying gas to the hole.

The air diffuser 151 is a member having a large number of holes through which gas can flow. The air diffusing member 151 is not particularly limited, but for example, a porous ceramic air diffusing plate in which coarse ceramic particles are bonded with a binder or the like, or a synthetic resin diffusing plate can be used. A membrane diffuser can also be used as the air diffuser 151.

The gas supply member 152 is a hollow member that holds the air diffuser 151 and further supplies gas to the holes of the air diffuser 151. Then, the gas supplied from the gas supply member 152 passes through the holes of the air diffusing member 151, becomes bubbles, and diffuses into the electrolytic solution 3.

A pipe 153 for supplying gas from the outside of the second electrolytic solution tank 2 is preferably connected to the oxygen supply unit 200A. Specifically, it is preferable that a hollow pipe 153 is connected to the lower surface of the gas supply member 152. The pipe 153 penetrates the rear wall 2b of the second electrolytic solution tank 2 and extends to the outside of the second electrolytic solution tank 2. A compressor 154 for pumping gas is connected to the end of the pipe 153.

As shown in FIG. 5, the oxygen supply unit 200A is preferably provided on the lower side of the second electrolytic solution tank 2 in the vertical direction Y. Thereby, the bubbles generated from the oxygen supply unit 200A float above the lower portion of the electrolytic solution 3 held in the second electrolytic solution tank 2. Therefore, the time during which oxygen is in contact with the electrolytic solution 3 becomes long, and the electrolytic solution 3 is agitated, so that the electrolytic solution 3 held in the second electrolytic solution tank 2 can be efficiently put into an aerobic condition. it can.

The number of air diffusers 151 included in the oxygen supply unit 200A is not particularly limited, and a single air diffuser 151 may be provided inside the second electrolytic solution tank 2. As shown in FIG. The air diffusing member 151 may be provided.

The method of discharging bubbles from the oxygen supply unit 200A to the electrolytic solution 3 is not particularly limited, and the compressor 154 may be operated to pressure-feed the gas to the pipe 153. The gas fed under pressure passes through the inside of the pipe 153 and reaches the gas supply member 152 of the oxygen supply unit 200A. The gas supplied to the gas supply member 152 passes through the holes of the air diffusing member 151, becomes bubbles, and diffuses into the electrolytic solution 3. The timing of air diffusion in the oxygen supply unit 200A is not particularly limited, and it may be continuously or intermittently diffused.

The configuration of the oxygen supply unit 200A is not limited to the configuration including the air diffusion member 151 and the gas supply member 152 described above, and any configuration capable of air diffusion to the electrolytic solution 3 can be applied. Specifically, when coarse bubbles are generated, a metal or synthetic resin porous tube or a disc diffuser may be used as the oxygen supply unit 200A.

As described above, the pipe 153 for supplying gas from the outside of the second electrolytic solution tank 2 is connected to the oxygen supply unit 200A. The method of disposing the pipe 153 is not particularly limited, but may be disposed, for example, in contact with the bottom wall 2c of the second electrolytic solution tank 2. Further, in FIG. 5, the pipe 153 is arranged on the bottom wall 2c so as to penetrate the rear wall 2b. However, the configuration is not limited to such an aspect, and, for example, the pipe 153 may be penetrated from the lower surface of the bottom wall 2c and directly connected to the oxygen supply unit 200A. Further, the pipe 153 may be arranged along the bottom wall 2c and the rear wall 2b and may be directly connected to the oxygen supply unit 200A. That is, the pipe 153 may be arranged along the wall of the second electrolytic solution tank 2 without penetrating the wall portion of the second electrolytic solution tank 2.

As described above, the liquid processing system A includes the first electrolytic solution tank 1 that holds the electrolytic solution 3 containing the organic substance and the phosphorus compound. The liquid processing system A includes a first supply unit 5 for supplying the electrolytic solution 3 to the first electrolytic solution tank 1 and a first discharge for discharging the electrolytic solution 3 in the first electrolytic solution tank 1 from the first electrolytic solution tank 1. And a section 6. The liquid processing system A includes a positive electrode 10 that contacts the electrolytic solution 3 in the first electrolytic solution tank 1 and a gas phase G containing oxygen, and a positive electrode 10 that contacts the electrolytic solution 3 in the first electrolytic solution tank 1. And a negative electrode 20 that is electrically connected to the negative electrode 10 and carries anaerobic microorganisms. The liquid processing system A includes a second electrolytic solution tank 2 which is provided on the downstream side of the first electrolytic solution tank 1 and holds the electrolytic solution 3 discharged from the first electrolytic solution tank 1. The liquid processing system A discharges the electrolyte solution 3 discharged from the first electrolyte solution tank 1 into the second supply unit 7 that supplies the electrolyte solution 3 discharged from the first electrolyte solution tank 1 to the second electrolyte solution tank 2. A second discharge part 8 and an oxygen supply part 200 for supplying oxygen to the electrolytic solution 3 in the second electrolytic solution tank 2 are provided. The phosphate ion concentration of the electrolytic solution 3 passing through the second discharging part 8 is lower than the phosphate ion concentration of the electrolytic solution 3 passing through the first supplying part 5.

The electrolytic solution 3 in the first electrolytic solution tank 1 is in contact with the positive electrode 10 that comes into contact with the gas phase G containing oxygen and the negative electrode 20 that carries anaerobic microorganisms. Therefore, in the negative electrode 20, hydrogen ions and electrons are generated from the organic substance in the electrolytic solution 3 by the catalytic action of the anaerobic microorganisms, the organic substance in the electrolytic solution 3 is decomposed, and the external circuit 60 causes The electrical energy flowing in the closed circuit is recovered.

The electrolytic solution 3 treated in the first electrolytic solution tank 1 passes through the first discharge part 6 and the second supply part 7 and is continuously supplied to the inside of the second electrolytic solution tank 2. Oxygen is supplied to the electrolytic solution 3 supplied to the second electrolytic solution tank 2 by the oxygen supply unit 200. Therefore, the electrolytic solution 3 in the first electrolytic solution tank 1 is in an anaerobic condition, and the electrolytic solution 3 in the second electrolytic solution tank 2 is in an aerobic condition.

Therefore, the polyphosphoric acid-accumulating bacteria release phosphorus outside the body in the electrolytic solution 3 held in the first electrolytic solution tank 1, but in the electrolytic solution 3 held in the second electrolytic solution tank 2, the first electrolytic solution. The amount of phosphorus released from the tank 1 is taken into the body. Then, the electrolytic solution 3 processed in the second electrolytic solution tank 2 is discharged to the outside of the liquid processing system A through the second discharging unit 8. Therefore, according to the liquid processing system A of the present embodiment, it is possible to remove the organic substance in the electrolytic solution 3 and also remove phosphorus.

Further, by adjusting the amount of air supplied to the gas phase G of the electrode cassette 100 and the oxygen supply unit 200, dissolved oxygen in the electrolytic solution 3 held in the first electrolytic solution tank 1 and the second electrolytic solution tank 2 is adjusted. The concentration can be optimized in each tank. Therefore, by adjusting the dissolved oxygen concentration suitable for the microorganism in each tank, it becomes possible to further improve the treatment efficiency of the organic substance and phosphorus.

The electrolytic solution 3 may contain a nitrogen compound in addition to the organic substance and the phosphorus compound. The nitrogen compound is, for example, an organic compound (organic nitrogen) such as an amino acid, an ammonium salt (ammonia nitrogen), a nitrite (nitrite nitrogen), or a nitrate (nitrate nitrogen). Therefore, the electrolytic solution 3 held in the first electrolytic solution tank 1 may further contain a nitrogen compound. In this case, it is preferable that the total nitrogen concentration of the electrolytic solution 3 passing through the first discharging unit 6 is lower than the total nitrogen concentration of the electrolytic solution 3 passing through the first supplying unit 5. When the electrolyte solution 3 held in the first electrolyte solution tank 1 further contains a nitrogen compound, the total nitrogen concentration of the electrolyte solution 3 passing through the first discharge part 6 is preferably 10 mg/L or less. The total nitrogen concentration of the electrolytic solution 3 passing through the first discharge part 6 is preferably 5 mg/L or less. Further, the total nitrogen concentration can be measured by a method such as an ultraviolet absorptiometry method according to JIS K0102:2016.

Specifically, as described above, the internal space formed by the electrode assembly 40 and the cassette base material 50A is in the vapor phase G. The electrode cassette 100 is configured such that the gas phase G is opened to the outside air, or air is supplied to the gas phase G from the outside by, for example, a pump. When the first electrolytic solution tank 1 contains nitrifying bacteria that perform a nitrifying reaction and denitrifying bacteria that perform a denitrifying reaction, which will be described later, the catalytic action of the nitrifying bacteria and the denitrifying bacteria is promoted and the electrolytic solution 3 is added. It is also possible to remove the contained nitrogen compounds.

The nitrifying bacterium is an aerobic microorganism and is preferably retained on the positive electrode 10. Examples of nitrifying bacteria include Nitrosomonas bacteria, Nitrosococcus bacteria, Nitrosospira bacteria, Nitrobacter bacteria and Nitrospira bacteria.

The denitrifying bacteria are anaerobic microorganisms, and are preferably retained on the surface of the positive electrode 10 excluding the portion exposed to the gas phase G and on the electrolytic solution 3. Examples of the denitrifying bacteria include Pseudomonas genus bacteria, Bacillus genus bacteria, Paracoccus genus bacteria, and Achromobater genus bacteria. In the present embodiment, an example in which both the surface of the positive electrode 10 and the electrolytic solution 3 hold denitrifying bacteria will be described. However, even if either the surface of the positive electrode 10 or the electrolytic solution 3 holds denitrifying bacteria. Good.

Here, nitrification reaction and denitrification reaction in the positive electrode 10 and its vicinity will be shown below.
[Nitrification reaction]
[Formula 1] 2NH ₄ ⁺ +3O ₂ → 2NO ₂ ⁻ +2H ₂ O+4H ⁺
[Formula 2] 2NO ₂ ⁻ +O ₂ →2NO ₃ ⁻
[Denitrification reaction]
[Formula 3] NO ₃ ⁻ +2H ⁺ +2e ⁻ →NO ₂ ⁻ +H ₂ O
[Formula 4] 2NO ₂ ⁻ +6H ⁺ +6e ⁻ → N ₂ +2H ₂ O+2OH ⁻

When nitrifying bacteria are held on the positive electrode 10, oxygen is supplied to the nitrifying bacteria from the surface of the water-repellent layer 11 exposed to the gas phase G through the water-repellent layer 11, and the nitrification is performed as shown in Reaction Formula 1 and Reaction Formula 2. Nitrogenation reaction of nitrogen compounds occurs due to the catalytic action of bacteria. The denitrifying bacteria retained in the electrolytic solution 3 gather near the positive electrode 10 and act as a catalyst.

The nitrite ion generated by the reaction of reaction formula 1 and the nitrate ion generated by the reaction of reaction formula 2 are desorbed by reacting with hydrogen ion by the catalytic action of denitrifying bacteria, as shown in reaction formulas 3 and 4, respectively. Nitrogen reaction occurs. As described above, in the electrode cassette 100, the nitrogen compound in the electrolytic solution 3 becomes nitrogen, water, and hydroxide ions by the metabolism of nitrifying bacteria and denitrifying bacteria, so that the nitrogen compound in the electrolytic solution 3 can be removed. it can.

Here, the reactions of the reaction formulas 1 and 2 are reactions by the catalytic action of nitrifying bacteria which are aerobic microorganisms, and the reactions of the reaction formulas 3 and 4 are reactions by the catalytic action of denitrifying bacteria which are anaerobic microorganisms. Therefore, the oxygen supplied from the gas phase G side of the water repellent layer 11 is consumed by the nitrifying bacteria. As a result, in the electrolytic solution 3, the electrolytic solution 3 becomes an anaerobic condition as it goes from the water-repellent layer 11 to the negative electrode 20, so that the reaction by the denitrifying bacteria can proceed.

Therefore, in the liquid processing system A, the dissolved oxygen concentration of at least a part of the electrolytic solution 3 held in the first electrolytic solution tank 1 is preferably 0.5 mg/L or less. As described above, in the oxygen supply unit 200, the nitrogen compounds in the electrolytic solution 3 are removed by the nitrification reaction of nitrifying bacteria that are aerobic microorganisms and the denitrifying reaction of denitrifying bacteria that are anaerobic microorganisms. Then, the denitrifying bacteria have a property of reducing nitrate ions and nitrite ions to nitrogen gas under the condition that the dissolved oxygen in the electrolytic solution 3 is small. Therefore, when the dissolved oxygen concentration of the electrolytic solution 3 in the second electrolytic solution tank 2 exceeds 0.5 mg/L, the denitrification reaction by the denitrifying bacteria becomes difficult to proceed, and the nitrogen compounds are efficiently removed. There is a possibility that there is no.

Therefore, in order to promote the denitrification reaction by the denitrifying bacteria, the dissolved oxygen concentration of at least a part of the electrolytic solution 3 in the second electrolytic solution tank 2 is preferably 0.5 mg/L or less, and 0.2 mg/L The following is more preferable. The method of measuring the dissolved oxygen concentration of the electrolytic solution 3 is not particularly limited, but it can be measured using, for example, a dissolved oxygen meter by the diaphragm electrode method. The dissolved oxygen concentration of the electrolytic solution 3 held in the first electrolytic solution tank 1 adjusts the amount of air supplied from the outside to the gas phase G of the oxygen supply unit 200, and the oxygen permeation of the water repellent layer 110. It can be controlled by adjusting the rate.

As described above, the liquid processing system A according to the present embodiment can be configured to remove not only the organic substance and the phosphorus compound but also the nitrogen compound.

[Second embodiment]
Next, a liquid treatment system according to the second embodiment will be described in detail with reference to the drawings. The same components as those in the first embodiment are designated by the same reference numerals, and overlapping description will be omitted.

As shown in FIG. 6, the liquid processing system B according to the present embodiment is similar to the first embodiment in that the liquid processing system B includes a first electrolytic solution tank 1, a first supply unit 5, and a first discharge unit 6. , A positive electrode 10, a negative electrode 20, a second electrolytic solution tank 2, a second supply unit 7, and a second discharge unit 8.

The liquid treatment system B according to this embodiment includes a settling tank 70 that is provided on the downstream side of the second electrolytic solution tank 2 and that precipitates polyphosphate-accumulating bacteria. As described above, the polyphosphoric acid-accumulating bacteria that have passed through the first electrolytic solution tank 1 and the second electrolytic solution tank 2 take in a high concentration of phosphorus into the body. Therefore, by providing the liquid treatment system B with such a precipitation tank 70, the treated electrolytic solution 3 and the polyphosphate-accumulating bacteria containing high concentration of phosphorus can be easily separated.

The liquid processing system B includes a third supply unit 71 that supplies the electrolytic solution 3 discharged from the second electrolytic solution tank 2 to the precipitation tank 70, above the side wall 70a on the front side of the precipitation tank 70. Further, the liquid processing system B includes a third discharge part 72 for discharging the electrolytic solution 3 held in the settling tank 70, above the side wall 70 b on the rear side of the settling tank 70.

Then, the liquid processing system B is configured such that the electrolytic solution 3 sequentially passes through the third supply unit 71, the precipitation tank 70, and the third discharge unit 72. The third supply part 71 and the third discharge part 72 need not be provided on the side wall of the precipitation tank 70 as long as the electrolytic solution 3 can be supplied to or discharged from the precipitation tank 70. It may be arranged above. In addition, in the present embodiment, the second discharge part 8 and the third supply part 71 are configured by the cylindrical connecting pipe 4A, but the second discharge part 8 and the third supply part 71 are configured by different members. Alternatively, it may be formed of a single member like the connecting pipe 4A.

The settling tank 70 holds the electrolytic solution 3 and a precipitate 74 containing polyphosphate-accumulating bacteria, and is formed to have a recessed shape toward the bottom wall 70c so that the precipitate 74 can be easily collected. There is. The bottom wall 70c is provided with a discharge port 73 for discharging the precipitate 74.

The liquid treatment system B further includes a return pipe 75 for returning the polyphosphate-accumulating bacteria precipitated in the settling tank 70 to the first electrolytic solution tank 1. The return pipe 75 connects the settling tank 70 and the first supply unit 5, and a discharge port 73 provided on the bottom wall 70 c of the settling tank 70 and a connection provided on the pipe wall of the first supply unit 5. It communicates with the mouth 76. Therefore, the precipitate 74 that has settled on the bottom wall 70c of the precipitation tank 70 can be transferred to the first electrolytic solution tank 1 via the return pipe 75 by a pump or the like not shown.

As described above, since the electrolytic solution 3 in the first electrolytic solution tank 1 is in an anaerobic state, the polyphosphate-accumulating bacteria returned to the first electrolytic solution tank 1 through the return pipe 75 are in the electrolytic solution 3. Releases phosphorus to. However, thereafter, the polyphosphate-accumulating bacteria are transferred again to the second electrolytic solution tank 2 through the first discharging part 6 and the second supplying part 7. Since the electrolytic solution 3 in the second electrolytic solution tank 2 is in an aerobic condition, the polyphosphoric acid-accumulating bacteria take in more phosphorus than the one released in the first electrolytic solution tank 1 into the body. Then, the electrolytic solution 3 processed in the second electrolytic solution tank 2 is discharged to the outside of the liquid processing system B through the second discharging unit 8.

The number of times the polyphosphate-accumulating bacteria are circulated from the settling tank 70 to the first electrolytic solution tank 1 through the return pipe 75 is not particularly limited, and may be circulated multiple times. In the present embodiment, the return pipe 75 connects the bottom wall 70c of the settling tank 70 and the first supply unit 5, but the first electrolytic solution tank 1 contains a precipitate containing polyphosphate-accumulating bacteria. These connection positions are not particularly limited as long as 74 can be transferred. For example, one of the return pipes 75 may be directly connected to the first electrolytic solution tank 1 instead of the first supply unit 5. Further, in the present embodiment, one side of the return pipe 75 is connected to the settling tank 70, but it is sufficient that the precipitate 74 can be transferred to the first electrolytic solution tank 1 and the return tube 75 is returned to the second electrolytic solution tank 2. One of the flow tubes 75 may be connected.

Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[Fabrication of liquid processing system]
First, a silicone water repellent layer is applied to a polyolefin water repellent layer, and then a graphite foil, which is a gas diffusion layer, is bonded to produce a laminated sheet consisting of a water repellent layer/silicone adhesive/gas diffusion layer. did. As the water-repellent layer, SERPUI (registered trademark) manufactured by Sekisui Chemical Co., Ltd. was used. As the silicone resin, one-pack type RTV rubber KE-3475-T manufactured by Shin-Etsu Chemical Co., Ltd. was used. The graphite foil used was made by Hitachi Chemical Co., Ltd.

Next, a gas diffusion electrode was produced by press-molding a catalyst layer formed by mixing an oxygen reduction catalyst and PTFE (manufactured by Aldrich) on the surface of the graphite foil opposite to the water-repellent layer. The oxygen reduction catalyst was press-molded so that the basis weight was 6 mg/cm ² .

The oxygen reduction catalyst was prepared as follows. First, a mixed solution was prepared by placing 3 g of carbon black, a 0.1 M aqueous solution of iron(III) chloride, and a 0.15 M solution of pentaethylenehexamine in ethanol in a container. As the carbon black, Ketjenblack ECP600JD manufactured by Lion Specialty Chemicals Co., Ltd. was used. The amount of the 0.1 M iron(III) chloride aqueous solution used was adjusted so that the ratio of iron atoms to carbon black was 10% by mass. The total amount was adjusted to 9 mL by further adding ethanol to this mixed solution. Then, this mixed liquid was ultrasonically dispersed and then dried at a temperature of 60° C. in a dryer. As a result, a sample containing carbon black, iron (III) chloride, and pentaethylenehexamine was obtained.

Then, this sample was packed into one end of the quartz tube, and then the inside of the quartz tube was replaced with argon. This quartz tube was put in a furnace at 900° C. and then withdrawn in 45 seconds. When inserting the quartz tube into the furnace, the quartz tube was inserted into the furnace for 3 seconds to adjust the heating rate of the sample at the start of heating to 300° C./s. Subsequently, the sample was cooled by circulating argon gas in the quartz tube. As a result, an oxygen reduction catalyst was obtained.

Further, the gas diffusion electrode obtained as described above was laminated on a cassette base material as shown in FIG. 1 to provide an air intake section, thereby producing a positive electrode. And the said positive electrode and the negative electrode which consists of carbon materials (graphite foil) were installed in the 1st electrolyte solution tank which has a 1st supply part and a 1st discharge part, and has a capacity of 300 mL. Further, a polyolefin nonwoven fabric was placed between the positive electrode and the negative electrode. Then, the positive electrode and the negative electrode were connected to a load circuit.

Next, as shown in FIG. 1, the water repellent layer made of polyolefin was laminated on the cassette base material to provide an air intake section, thereby producing an oxygen supply section. As the water-repellent layer, SERPUI (registered trademark) manufactured by Sekisui Chemical Co., Ltd. was used. And the oxygen supply part was installed in the 2nd electrolytic solution tank which has the 2nd supply part and the 2nd discharge part, and has a capacity of 300 mL.

Then, as shown in FIG. 1, a second electrolytic solution tank having an oxygen supply unit provided therein is connected to the downstream side of the first electrolytic solution tank having an electrode cassette provided therein (a first discharge unit and a second discharge unit). After connecting by the supply part), the insides of the first electrolytic solution tank and the second electrolytic solution tank were filled with the electrolytic solution. The electrolytic solution contains an organic substance having a total organic carbon (TOC) of 600 mg/L. Furthermore, soil microorganisms containing anaerobic microorganisms and polyphosphate-accumulating bacteria that generate electricity were planted in the first electrolytic solution tank and the second electrolytic solution tank. Then, the electrolytic solution was continuously supplied to the first electrolytic solution tank so that the residence time of the electrolytic solution was 48 hours in each tank. In this way, the liquid processing system of this example was obtained.

[Evaluation]
The electrolytic solution was collected from each of the first supply section of the first electrolytic solution tank, the first discharging section (connection pipe) and the second discharging section of the second electrolytic solution tank in the liquid treatment system, and by molybdenum blue absorptiometry, The phosphate ion concentration in each electrolytic solution was measured.

In the liquid treatment system, the phosphate ion concentrations of the electrolytic solutions collected from the first supply section, the first discharge section of the first electrolytic solution tank, and the second discharge section of the second electrolytic solution tank are 27 mg/L and 28 mg, respectively. /L and 22 mg/L. From this, the effect of removing phosphorus from the electrolytic solution by polyphosphate-accumulating bacteria was confirmed by providing a second electrolytic solution tank equipped with an oxygen supply unit downstream of the first electrolytic solution tank equipped with the electrode cassette. did it.

Although the present embodiment has been described above, the present embodiment is not limited to these, and various modifications can be made within the scope of the gist of the present embodiment. Specifically, in the drawings, the positive electrode 10, the negative electrode 20, the ion transfer layer 30 in the electrode cassette 100, and the water repellent layer 110 in the oxygen supply unit 200 are formed in a rectangular shape. However, these shapes are not particularly limited, and can be arbitrarily changed depending on the size of the liquid treatment system, desired purification performance, and the like. Also, the area of each layer can be arbitrarily changed as long as the desired function can be exhibited.

In the liquid processing systems A and B, the electrode cassette 100 includes a cassette base material 50A that forms a gas phase G that contacts the positive electrode 10. However, in the liquid processing systems A and B of this embodiment, the cassette base material 50A is not an essential component. That is, when the positive electrode 10 is in contact with the electrolytic solution 3 and the gas phase G, and the negative electrode 20 is in contact with the electrolytic solution 3, it is possible to obtain electric energy while decomposing the organic substances and/or nitrogen compounds in the electrolytic solution 3. it can. For example, by floating the positive electrode 10 on the water surface of the electrolytic solution 3 and submerging the negative electrode 20 in the electrolytic solution 3, a part of the positive electrode 10 may come into contact with the gas phase G and the negative electrode 20 may come into contact with the electrolytic solution 3. it can. In addition, in such a structure, the positive electrode 10 does not need to include the water-repellent layer 11.

The liquid treatment system according to the present embodiment can be widely applied to treatment of a liquid containing an organic substance and phosphorus, for example, waste water generated from factories of various industries, organic waste water such as sewage sludge, and the like. It can also be used to improve the water environment.

DESCRIPTION OF SYMBOLS 1 1st electrolyte solution tank 2 2nd electrolyte solution tank 3 Electrolyte 5 5 1st supply part 6 1st discharge part 7 2nd supply part 8 2nd discharge part 10 Positive electrode 20 Negative electrode 200,200A Oxygen supply part A, B Liquid treatment System G gas phase

Claims (4)

A first electrolytic solution tank for holding an electrolytic solution containing an organic substance and a phosphorus compound,
A first supply unit that supplies the electrolytic solution to the first electrolytic solution tank,
A first discharge part for discharging the electrolytic solution in the first electrolytic solution tank from the first electrolytic solution tank,
A positive electrode in contact with the electrolytic solution in the first electrolytic solution tank, and in contact with a gas phase containing oxygen,
In contact with the electrolytic solution in the first electrolytic solution tank, electrically connected to the positive electrode, a negative electrode carrying anaerobic microorganisms,
A second electrolytic solution tank, which is provided on the downstream side of the first electrolytic solution tank and holds the electrolytic solution discharged from the first electrolytic solution tank,
A second supply unit that supplies the electrolytic solution discharged from the first electrolytic solution tank to the second electrolytic solution tank,
A second discharge part for discharging the electrolytic solution in the second electrolytic solution tank,
An oxygen supply unit for supplying oxygen to the electrolytic solution in the second electrolytic solution tank,
Equipped with
The liquid treatment system, wherein the phosphate ion concentration of the electrolytic solution passing through the second discharging part is lower than the phosphate ion concentration of the electrolytic solution passing through the first supplying part. The electrolytic solution held in the first electrolytic solution tank further contains a nitrogen compound,
The liquid treatment system according to claim 1, wherein the total nitrogen concentration of the electrolytic solution passing through the first discharge part is lower than the total nitrogen concentration of the electrolytic solution passing through the first supply part. The electrolytic solution held in the first electrolytic solution tank further contains a nitrogen compound, and the total nitrogen concentration of the electrolytic solution passing through the first discharge part is 10 mg/L or less. Liquid handling system. The liquid treatment system according to any one of claims 1 to 3, wherein polyphosphate-accumulating bacteria are contained in the electrolytic solution held in the first electrolytic solution tank and the electrolytic solution held in the second electrolytic solution tank. ..

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