JP2017159210A - Nitrification denitration type wastewater treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for supplying an alkali component which is environment friendly and economically excellent without using chemical agent in a biological nitrification denitration type wastewater treatment system.SOLUTION: There is provided a nitrification denitration type wastewater treatment system including at least an anaerobic tank 2, an aerobic tank 3 and a microbial fuel cell 1, the microbial fuel cell 1 has an anode electrode 11 to which electrically produced microbial is fixed, a cathode zone 15 with a cathode electrode 14 and an ion permeable barrier 13 separating a zone 12 having the anode electrode 11 and the cathode zone, OHgenerated in the cathode zone 14 is supplied to the anaerobic tank 2 and a nitration liquid of the aerobic tank 3 is supplied to the cathode zone 14.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nitrification / denitrification wastewater treatment system and a wastewater treatment method based on a biological nitrification / denitrification method.

  Biological nitrification and denitrification is a nitrification process in which ammonia nitrogen is treated with microorganisms under aerobic conditions and oxidized to nitrous acid or nitrate nitrogen, and nitrous acid and nitrate nitrogen are reduced as nitrogen gas under anaerobic conditions. It consists of a denitrification step to be removed.

A general biological nitrification denitrification method will be briefly described with reference to the flowchart shown in FIG. In the figure, S1 is a step for mineralizing organic nitrogen to ammonia nitrogen (NH ₄ —N). In this step, the alkalinity of 3.57 mg / L increases with respect to 1 mg / L of nitrogen. In addition, alkalinity here is M alkalinity measured by the method of JISK0102-15.1. S2 is a step of nitrifying NH ₄ -N under aerobic conditions to produce NO ₃ -N. In this step, the alkalinity of 7.14 mg / L decreases with respect to 1 mg / L of nitrogen. Finally, S3 is a step of denitrifying NO ₃ —N under anaerobic conditions to generate N ₂ gas and releasing it into the atmosphere. At this time, the alkalinity of 3.57 mg / L increases with respect to 1 mg / L of nitrogen.

  For this reason, in the step in which the alkalinity decreases, it may be necessary to examine and add the alkali agent addition amount based on the alkalinity balance calculation according to the nitrogen concentration and alkalinity of the influent water (for example, Patent Document 1). As an alkaline agent, sodium bicarbonate and sodium carbonate are widely used from the viewpoint of maintaining stable nitrite type nitrification. In addition, a process is also used in which cheaper sodium hydroxide is used in combination or alone.

JP 2006-88092 A

  Conventionally, in the biological nitrification denitrification method, in order to supply an alkaline component to the nitrification process, it is indispensable to input chemicals. For this reason, the ion concentration in a processing tank and effluent water became high, and there existed a bad influence on biological treatment and an environment. Also, chemicals are expensive and the production process is at risk of polluting the environment. In order to solve these problems, it is necessary to develop technology for supplying environmentally friendly and economically superior alkaline components without using chemicals in biological nitrification denitrification wastewater treatment systems. .

The present inventors have conceived of supplying the alkali component OH ⁻ generated from the electrochemical reaction at the cathode during the nitrification / denitrogenation reaction, particularly during the nitrification reaction, using the principle of a microbial fuel cell. It came to solve the problem.

According to one embodiment of the present invention, [1] a nitrification / denitrification wastewater treatment system comprising at least an anaerobic tank, an aerobic tank, and a microbial fuel cell, wherein the microbial fuel cell is an electric generator OH ⁻ generated in the aerobic tank in the cathode region, comprising: an anode electrode in which microorganisms are fixed; a cathode region having a cathode electrode; and an ion-permeable diaphragm that separates the region having the anode electrode from the cathode region. Is supplied, and the aerobic tank nitrification solution is supplied to the cathode region.

  [2] In the nitrification / denitrification wastewater treatment system according to [1], the microbial fuel cell may be provided inside the anaerobic tank, and may include means for sending a nitrification solution from the aerobic tank to the cathode region. preferable.

  [3] In the nitrification / denitrification wastewater treatment system according to [1], the microbial fuel cell is provided outside the anaerobic tank and the aerobic tank, and sends the nitrification solution from the aerobic tank to the cathode region. Means for sending catholyte from the cathode region to the aerobic tank, means for sending water to be treated to the region having the anode electrode (anode region), and from the region having the anode electrode (anode region) It is preferable to provide a means for feeding the anolyte to the anaerobic tank.

  [4] The nitrification denitrification wastewater treatment system according to [1], further comprising an anoxic tank between the anaerobic tank and the aerobic tank, wherein the microbial fuel cell is provided inside the anaerobic tank. And a means for sending the nitrification solution from the aerobic tank to the cathode region, and a means for sending the catholyte from the cathode region to the aerobic tank or an oxygen-free tank.

  [5] The nitrification / denitrification wastewater treatment system according to [1], further comprising an anoxic tank between the anaerobic tank and the aerobic tank, wherein the microbial fuel cell includes the anaerobic tank and the aerobic tank. A means for sending a nitrification liquid from the aerobic tank to the cathode region, a means for sending a catholyte from the cathode region to the aerobic tank or an oxygen-free tank, and the anode electrode. It is preferable to include means for sending the water to be treated to the area having the anode (anode area) and means for sending the anolyte from the area having the anode electrode (anode area) to the anaerobic tank.

  [6] In the nitrification / denitrification wastewater treatment system according to [2] or [4], it is preferable that the anode electrode is immersed in water to be treated inside the anaerobic tank.

  [7] In the nitrification / denitrification wastewater treatment system according to [3] or [5], the means for sending the water to be treated to the region having the anode electrode (anode region) may pass through the inside of the anaerobic tank. preferable.

  [8] In the nitrification denitrification wastewater treatment system according to any one of [1] to [7], the microbial fuel cell can be replaced in an electric circuit connecting the anode electrode and the cathode electrode. It is preferable to provide an external resistor or a variable external resistor.

According to another aspect of the present invention, there is [9] a nitrification denitrification wastewater treatment method, wherein a denitrification step of generating nitrogen by reducing nitric acid or nitrous acid in treated water; It comprises at least a nitrification step in which an ammonium compound is converted to nitric acid or nitrous acid by a nitrifying bacterium, and an alkali generation step for generating OH ⁻ at the cathode of the microbial fuel cell. The nitrification step is obtained in the alkali generation step. OH ⁻ is added, and the nitrification liquid in the nitrification step is supplied to the cathode of the microbial fuel cell.

[10] In the nitrification / denitrification wastewater treatment method according to [9], it is preferable to adjust the production amount of OH ⁻ in the alkali production step by changing an external resistance of the microbial fuel cell.

  According to the wastewater treatment system and the wastewater treatment method according to the present invention, by incorporating a microbial fuel cell into a general wastewater treatment system using a nitrification denitrification method, it is possible to supply an alkaline component without using chemicals or the like. Become. In such a system, the circuit current can be adjusted by replacing the external resistance of the microbial fuel cell, whereby the production amount of the alkaline component can be adjusted in the cathode tank of the microbial fuel cell. Since the microbial fuel cell does not consume power and does not require the input of chemicals, it is possible to provide a wastewater treatment system and a wastewater treatment method that are environmentally friendly and have sufficient treatment characteristics.

FIG. 1 (A) is a conceptual diagram showing a wastewater treatment method and system according to a first embodiment of the present invention, and (B) is an enlarged view of a microbial fuel cell in (A). FIG. 2 is a conceptual diagram showing a wastewater treatment method and system according to a second embodiment of the present invention. FIG. 3 is a conceptual diagram showing a wastewater treatment method and system according to a third embodiment of the present invention. FIG. 4 is a conceptual diagram showing a wastewater treatment method and system according to a fourth embodiment of the present invention. FIG. 5 is a conceptual diagram showing an experimental system used in an experimental example. FIG. 6 is a graph showing the relationship between the pH of the circulating solution and the circuit current with respect to the treatment time in the experimental example. FIG. 7 is a graph comparing the measured value of the OH ⁻ production amount and the theoretical value in the experimental example. FIG. 8 is a flow diagram illustrating a general biological nitrification denitrification method.

  Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the embodiments described below. The drawings are exemplary schematic diagrams for explaining the present invention and are not intended to limit the present invention.

[First Embodiment]
The present invention is a wastewater treatment system according to the first embodiment, and is mainly composed of an anaerobic tank, an aerobic tank, a sedimentation tank, and a microbial fuel cell provided inside the anaerobic tank.

  FIG. 1 is a diagram conceptually showing a wastewater treatment system according to this embodiment. The wastewater treatment system shown in FIG. 1 (A) includes an anaerobic tank 2, an aerobic tank 3, and a sedimentation tank 5 based on a wastewater treatment system using an anaerobic / aerobic method (hereinafter also referred to as AO method). The microbial fuel cell 1 is provided inside the anaerobic tank 2.

The anaerobic tank 2 is a treatment tank into which water to be treated containing organic nitrogen first flows, and is a denitrification tank in which a denitrification step is performed in which nitric acid or nitrous acid in the water to be treated is reduced to generate nitrogen. It may be. The anaerobic tank 2 can be configured to include activated sludge containing denitrifying bacteria. When water to be treated is introduced into the anaerobic tank 2 (L ₁ ), it is treated in the anaerobic tank 2 and then sent to the aerobic tank 3 (L ₂ ). The display L _n in each embodiment of the present invention shows a means for flowing a stream or treated water of the water to be treated between the treatment tank or between the processing tank and the microbial fuel anode or cathode region of the cell. The means for flowing the water to be treated may be transfer means such as pipes, flow paths, and pumps, but is not limited to a specific configuration.

The aerobic tank 3 is a treatment tank into which water to be treated is introduced from the anaerobic tank 2, and may be a nitrification tank in which a nitrification step is performed in which an ammonium compound is converted into nitric acid or nitrous acid by nitrifying bacteria. The aerobic tank 3 can be configured to include an activated sludge containing nitrifying bacteria and an aeration apparatus for introducing air containing oxygen. The water to be treated that has been treated in the aerobic tank 3 is sent to the next process (L ₃ ).

The settling tank 5 is a tank into which treated water is introduced from the aerobic tank 3 and is also referred to as a settling tank. In the settling tank 5, the activated sludge containing microorganisms is precipitated and separated from the supernatant treated water. The activated sludge is returned to the anaerobic tank 2 (L ₇ ) and used again for processing. The treated water in the supernatant of the sedimentation tank 5 is sent to the next step by means not shown, and further processed and discharged.

  The microbial fuel cell 1 is provided inside the anaerobic tank 2. Referring to FIG. 1 (B), the microbial fuel cell 1 includes an anode region 12 including an anode electrode 11 on which an electricity-generating microorganism is fixed, a cathode region 15 including a cathode electrode 14, the anode region 12 and the cathode region 15; Are formed of an ion permeable diaphragm 13 and an external resistor 16.

  The electrogenerated microorganisms fixed to the anode electrode 11 are not particularly limited, and one or more fungi generally used in microbial fuel cells can be used. For example, Geobactor, Saccharomyces, Hansenula, Candida, Micrococcus, Staphylococcus, Streptococcus, Leuconostoa, Lactobacillus, Corynebacterium, Arthrobacter, Bacillus, Clostridium, Neisseria, Escherichia, Enterobacter, Serigenia, ellaactor It can be selected from, but not limited to, fungi belonging to the genus Thiobacillus, Gluconobacter, Pseudomonas, Xanthomonas, Vibrio, Comamonas and Proteus (Proteusvulgaris). In addition to this, the anode electrode 11 may optionally include an electron mediator. Further, the anode and cathode electrodes 11 and 14 can be made of a general electrode material, and may be a metal such as carbon or platinum, a conductive polymer, a conductive inorganic material, or the like, but is not limited thereto. Not. As the ion permeable membrane 13, a cation exchange membrane can be used.

Referring to FIG. 1 (A), in this embodiment, the microbial fuel cell 1 is such that at least the anode electrode 11 and the cathode electrode 14 are immersed in the water to be treated, and preferably the anode region 12 and the cathode region 15 are treated. It is provided inside the anaerobic tank 2 in such a manner that it is immersed in water. The cathode region 15 is isolated from the anaerobic tank 2 by a film, a partition wall or the like through which no substance can permeate. Therefore, the water to be treated in the anaerobic tank 2 does not flow into the cathode region 15. The cathode region 15 is provided with means L ₁₁ for flowing the nitrating liquid from the aerobic tank 3 into the cathode region 15 and means for flowing the catholyte from the cathode region 15 into the aerobic tank 3. The apparatus (L ₁₁ ) that causes the return liquid from the nitrification tank to flow into the cathode region 15 may be a pump, piping, or the like. In order to realize such a flow of water to be treated, specifically, a cathode tank can be provided at the outlet of the nitrification liquid return line for denitrification of an existing (general) sewage treatment plant. The specific embodiment is not limited. In FIG. 1 (A), the flow L ₁₂ into which the catholyte flows into the aerobic tank 3 is described as joining the L ₂ , but it is directly connected to the aerobic tank 3 separately from L _2. You may do it.

On the other hand, the anode region 12 is a region separated from the cathode region 15 by a partition wall and having an anode electrode. The anode area | region 12 should just be an area | region which exists in the state which the anode electrode 11 can contact with to-be-processed water. Therefore, there may not be a partition wall or a diaphragm that delimits the anode region 12 indicated by a phantom line in FIG. 1, or it may be a film or a partition wall through which water to be treated can permeate or flow. Therefore, in a preferred embodiment, the anode electrode is immersed in the anaerobic tank 2, and the anaerobic tank 2 itself can be referred to as an anode region. In this case, it is not necessary to include the means L ₁₃ for flowing the water to be treated into the anode region 12 indicated by the phantom line in FIG. 1 and the means L ₁₄ for flowing the anolyte of the anode region 12 into the anaerobic tank 2. In another embodiment, the anaerobic tank 2 may have a partition wall or a diaphragm that defines the anode region. In this case, means L ₁₃ for causing the water to be treated in the anaerobic tank 2 to flow into the anode region 12. Means L ₁₄ for allowing the anolyte in the anode region 12 to flow into the anaerobic tank 2 may be provided, and specific means may include a pump and piping.

A waste water treatment method in the nitrification denitrification waste water treatment system shown in FIG. A treated water stream L ₁ containing organic nitrogen flows into the anaerobic tank 2. In the anaerobic tank 2, the denitrification process which reduces | restores nitric acid or nitrous acid in to-be-processed water, and produces | generates nitrogen is performed. Further, the water to be treated containing a large amount of organic matter comes into contact with the anode electrode disposed in the anaerobic tank 2 or flows into the anode region 12 of the microbial fuel cell 1 (L ₁₃ ), thereby providing nutrient sources for the electrogenerated microorganisms. It can be. When the defined anode region 12 is present, the anolyte in the anode region 12 is circulated to the anaerobic tank 2 (L ₁₄ ). On the other hand, the nitrification liquid is caused to flow into the cathode region 15 of the microbial fuel cell 1 from the aerobic tank 3 (L ₁₁ ). The nitrification solution in the aerobic tank 3 has a large amount of dissolved oxygen, which is advantageous for supplying oxygen necessary for the following cathode reaction to the cathode electrode 14.
O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻
Then, the catholyte containing a lot of OH ⁻ produced by the cathode electrode 14 is sent to the aerobic tank 3. And the alkalinity can be increased and the pH of the aerobic tank 3 can be adjusted to the optimal range, for example, 6.5-9.0. Conventionally, in the aerobic tank 3 in which it has been necessary to lower the pH by adding an alkaline agent made of a chemical, the pH is adjusted without adding a chemical and without increasing the salt derived from the chemical. This is advantageous.

In the present embodiment, the amount of OH ⁻ produced at the cathode electrode 14 can be adjusted by changing the external resistance 16 of the microbial fuel cell 1. In order to achieve such a configuration, the external resistor 16 can be configured with a replaceable resistor or a variable resistor. In addition, the aerobic tank 3 may be provided with a device for measuring the pH of the nitrating solution, and the amount of OH ⁻ produced in the cathode electrode 14 may be adjusted according to the pH measurement result of the nitrating solution.

  According to the waste water treatment system and waste water treatment method according to the first embodiment of the present invention, by installing the microbial fuel cell 1 in the anaerobic tank 2, the waste water treatment system by the conventional AO method and the liquid to be treated are used. Thus, the alkali component can be supplied without using chemicals.

[Second Embodiment]
The present invention is a wastewater treatment system according to the second embodiment, and is an anaerobic tank, an aerobic tank, a precipitation tank, and a microbial fuel cell provided independently of the anaerobic tank and the aerobic tank. Consists mainly of.

  FIG. 2 is a diagram conceptually illustrating the waste water treatment system according to the present embodiment. The wastewater treatment system shown in FIG. 2 includes an anaerobic tank 2, an aerobic tank 3, and a settling tank 5 based on a wastewater treatment system based on the AO method, and a microbial fuel cell 1 separately from these tanks. .

About the structure of the anaerobic tank 2, the aerobic tank 3, and the sedimentation tank 5, it is as having demonstrated in 1st Embodiment, and abbreviate | omits description here. Also for the microbial fuel cell 1, as shown in FIG. 1 (B), an anode region 12 including an anode electrode 11 to which an electrogenerated microorganism is fixed, a cathode region 15 including a cathode electrode 14, and the anode region 12 and the cathode region. 15 is common in that it is composed of an ion-permeable diaphragm 13 that separates 15 and an external resistor 16. However, the microbial fuel cell 1 is disposed independently of the anaerobic tank 2, and each of the anode region 12 and the cathode region 15 is configured to be defined by a partition wall that does not allow water or a substance to permeate outside. Is different. The means L ₂₁ and L ₂₂ for flowing the water to be treated between the cathode region 15 and the aerobic tank 3 can have the same configuration as described in the first embodiment. Alternatively, the means L _21, may be used airlift. On the other hand, in the present embodiment, the anode region 12 is a region defined independently of the anaerobic tank 2, it means L ₂₃ for flowing water to be treated not undergone anaerobic tank 2, from the anode region 12 to the anaerobic tank Means L ₂₄ for flowing the water to be treated is provided. These means L ₂₃ and L ₂₄ may typically be pipes and pumps, but are not limited to these as long as they can circulate the water to be treated.

The wastewater treatment method in the nitrification / denitrification wastewater treatment system shown in FIG. 2 is the same as that of the first embodiment in that the denitrification process is performed in the anaerobic tank 2 and the nitrification process is performed in the aerobic tank 3. is there. In the second embodiment, to-be-treated water that serves as a nutrient source for the electricity-generated microorganisms is sent to the anode region 12 of the microbial fuel cell 1 without passing through the anaerobic tank 2 (L ₂₃ ) and is present in the anode region 12. The anolyte to be sent is sent to the anaerobic tank 2 (L ₂₄ ). On the other hand, the nitrification liquid sent from the aerobic tank 3 is caused to flow into the cathode region 15 of the microbial fuel cell 1 (L ₂₁ ), and the catholyte containing a lot of OH ⁻ generated at the cathode electrode 14 is added to the aerobic tank 3. (L ₂₂ ). In order to cause the water to be treated in the anaerobic tank 2 to flow into the anode region 12 instead of or in addition to the mode (L ₂₃ ) in which the water to be treated before flowing into the anaerobic tank 2 is directly supplied to the anode region 12. The means may be provided. By such a flow of water to be treated, OH ⁻ generated in the microbial fuel cell 1 is supplied to the aerobic tank 3 to prevent the pH of the aerobic tank 3 from being lowered and adjusted to a suitable pH range. be able to. In addition, since the treated water rich in organic matter is supplied to the anode region 12 of the microbial fuel cell 1, the nutrient source of the microorganisms fixed to the anode electrode 11 can be continuously supplied. Thus, in the aerobic tank 3, the pH can be adjusted without introducing chemicals. Moreover, the organic substance in to-be-processed water can be utilized as a nutrient source of microorganisms required in order to make the microbial fuel cell 1 function.

Also in the present embodiment, by adjusting the external resistance 16 of the microbial fuel cell 1, the amount of OH ⁻ produced can be adjusted, and optionally, an aerobic tank 3 is provided with a device for measuring pH. Depending on the measurement result, the production amount of OH ⁻ can be adjusted.

  According to the waste water treatment system and waste water treatment method according to the second embodiment of the present invention, even if the microbial fuel cell 1 is configured independently of the anaerobic tank 2, the same effects as those of the first embodiment can be obtained. In addition, maintenance and replacement of the anode, cathode, etc. are facilitated. Furthermore, it can be set as the structure where a microbe does not enter into an anode area | region by setting it as the aspect which sends liquid to be treated before flowing into an anaerobic tank directly to an anode area | region.

[Third Embodiment]
The present invention is a wastewater treatment system according to the third embodiment, comprising an anaerobic tank, an oxygen-free tank, an aerobic tank, a sedimentation tank 5, and a microbial fuel cell provided inside the anaerobic tank. Mainly composed.

  FIG. 3 is a diagram conceptually showing the wastewater treatment system according to the present embodiment. The wastewater treatment system shown in FIG. 3 is based on a wastewater treatment system using an anaerobic / anoxic / aerobic method (hereinafter also referred to as A2O method), an anaerobic tank 2, an anaerobic tank 4, an aerobic tank 3, and a sedimentation tank. 5 and a microbial fuel cell 1 in the anaerobic tank 2.

About the structure of the anaerobic tank 2, the aerobic tank 3, and the sedimentation tank 5, it is as having demonstrated in 1st Embodiment, and abbreviate | omits description here. The configuration of the microbial fuel cell 1 and the manner of installation in the anaerobic tank 2 can be the same as described in the first embodiment. The anaerobic tank 4 is located between the anaerobic tank 2 and the aerobic tank 3, and is a processing tank into which treated water from the anaerobic tank 2 flows (L ₄ ). In the anaerobic tank 4, a denitrification step is performed in which nitric acid or nitrous acid in the water to be treated is reduced to generate nitrogen. The nitrification solution from the aerobic tank 3 is returned to the anaerobic tank 4 (L ₈ ).

Also in the present embodiment, the configuration for sending the nitrification liquid from the aerobic tank 3 to the cathode region 15 of the microbial fuel cell 1 (L ₃₁ ) is the same as in the first and second embodiments. On the other hand, the catholyte of the microbial fuel cell 1 is sent to the aerobic tank 3 (L ₃₂ ). When the anode electrode is directly immersed in the anaerobic tank 2 and the anode electrode and the water to be treated are configured to come into contact with each other, or when the anode area is defined in the anaerobic tank 2, the process proceeds to the anode area 12 of the microbial fuel cell 1. treatment water flow (L _33), the points forming the flow to the anaerobic tank 2 of the anolyte in the anode region 12 (L ₃₄₎ is the same as in the first embodiment. As described in the first embodiment, when the anode electrode is directly immersed in the anaerobic tank 2, the flow L ₃₃ and the flow L ₃₄ are not necessary. By such a flow of water to be treated, the alkaline component generated in the cathode region can be supplied to the aerobic tank 3 in which the alkalinity decreases, and the aerobic tank 3 can be adjusted to a suitable pH region. . In addition, since the anode electrode 11 is disposed in such a manner that it can be sufficiently brought into contact with the water to be treated rich in organic matter, it is possible to continue supplying the nutrient source of the microorganisms fixed to the anode electrode 11. And similarly to 1st, 2nd embodiment, in the aerobic tank 3, pH can be adjusted, without throwing in a chemical. Moreover, the organic substance in to-be-processed water can be utilized as a nutrient source of microorganisms required in order to make the microbial fuel cell 1 function.

As a modification of the present embodiment, a mode in which the catholyte is sent to the anaerobic tank 4 instead of or in addition to sending the catholyte to the aerobic tank 3 is also included in the present invention. In the anaerobic tank 4, the alkali component is not consumed. Accordingly, alkaline components generated at the cathode electrode is sent to the anoxic tank 4, with the flow of the water to be treated (L _5), it is sent to the aerobic tank 3, by adjusting the alkalinity of the aerobic tank 3 Can do.

Also in this embodiment, the amount of OH ⁻ produced can be adjusted by adjusting the external resistance. Optionally, a device for pH measurement is provided in the aerobic tank 3, depending on the measurement result. , OH ⁻ production amount can be adjusted.

  According to the waste water treatment system and waste water treatment method according to the third embodiment of the present invention, the microbial fuel cell 1 is installed in the anaerobic tank 2 to use the conventional waste water treatment system by the A2O method and the liquid to be treated. Thus, the alkali component can be supplied without using chemicals. Moreover, the phosphorus released into the anaerobic tank permeates the ion permeable membrane of the microbial fuel cell, and the concentrated phosphorus is sent to the aerobic tank. For this reason, the microbe in an aerobic tank becomes easy to take in phosphorus, and the advantage that a phosphorus removal rate improves is also acquired.

[Fourth Embodiment]
The present invention is a wastewater treatment system according to the fourth embodiment, and is independent of an anaerobic tank, an anaerobic tank, an aerobic tank, a precipitation tank, an anaerobic tank, an anaerobic tank, and an aerobic tank. And a microbial fuel cell provided as a main component.

  FIG. 4 is a diagram conceptually showing the wastewater treatment system according to the present embodiment. The wastewater treatment system shown in FIG. 4 is based on a wastewater treatment system using an anaerobic / anoxic / aerobic method (hereinafter also referred to as A2O method), an anaerobic tank 2, an anaerobic tank 4, an aerobic tank 3, and a sedimentation system. A tank 5 is provided, and a microbial fuel cell 1 is provided outside the tank 5.

  About the structure of the anaerobic tank 2, the anoxic tank 4, the aerobic tank 3, and the sedimentation tank 5, it is as having demonstrated in 3rd Embodiment. The configuration of the microbial fuel cell 1 provided independently of the anaerobic tank 2 is as described in the second embodiment.

Also in the present embodiment, the configuration for sending the nitrification liquid from the aerobic tank 3 to the cathode region 15 of the microbial fuel cell 1 (L ₄₁ ) is the same as in the first to third embodiments. On the other hand, the catholyte of the microbial fuel cell 1 is sent to the aerobic tank 3 (L ₄₂ ) as in the third embodiment. Flow of the water to be treated from the water to be treated before flowing into the anaerobic tank 2 to the anode region 12 of the microbial fuel cell 1 (L ₄₃ ), flow of the anolyte in the anode region 12 to the anaerobic tank 2 (L ₄₄ ) Is the same as in the second embodiment. Such a flow of water to be treated can prevent the pH of the aerobic tank 3 from being lowered and can be adjusted to a suitable pH region as in the third embodiment. In addition, since the treated water rich in organic matter is supplied to the anode region 12 of the microbial fuel cell 1, the nutrient source of the microorganisms fixed to the anode electrode 11 can be continuously supplied. And similarly to the 1st-3rd embodiment, in the aerobic tank 3, pH can be adjusted, without throwing in a chemical. Moreover, the organic substance in to-be-processed water can be utilized as a nutrient source of microorganisms required in order to make the microbial fuel cell 1 function.

Also in this embodiment, the treated water before flowing into the anaerobic tank 2 is directly sent to the anode region 12 of the microbial fuel cell 1 (L ₄₃ ), and the treated water in the anaerobic tank 2 is sent to the anode region 12. May be sent to Further, the cathode solution in place of the (L ₄₂₎ manner to send to the aerobic tank 3, or in addition, the catholyte may be manner to send to the anoxic tank 4. Even in these embodiments, similar effects can be obtained.

Also in this embodiment, the amount of OH ⁻ produced can be adjusted by adjusting the external resistance. Optionally, a device for pH measurement is provided in the aerobic tank 3, depending on the measurement result. , OH ⁻ production amount can be adjusted.

  According to the waste water treatment system and waste water treatment method according to the fourth embodiment of the present invention, even if the microbial fuel cell 1 is configured independently of the anaerobic tank 2, the same effects as those of the third embodiment can be obtained. In addition, maintenance and replacement of the anode, cathode, etc. are facilitated. Further, by adopting a mode in which the water to be treated is directly fed to the anode region, there can be obtained an advantage that a structure in which various bacteria are difficult to enter the anode region can be obtained.

  Hereinafter, the present invention will be described in more detail with reference to the following experimental examples. However, the present invention is not limited to the following experimental examples.

The test apparatus shown in FIG. 5 was assembled, and the production of OH ⁻ in the microbial fuel cell and the nitrification / denitrification wastewater treatment system according to the present invention were verified. This test apparatus includes a simulated anode tank 12 for an anaerobic tank, a cathode tank 15, and a simulated aeration tank 31 for the aerobic tank 3. The anode tank 12 was provided with an anode electrode 11 for taking out electrons. The cathode tank 15 is provided with a diaphragm 13 separating from the anode tank and a cathode electrode 14 for reacting electrons, oxygen and H ⁺ . A resistor 16 was connected to an external circuit connecting the anode electrode 11 and the cathode electrode 14 for current adjustment. The simulated aeration tank 31 of the aerobic tank 3 is provided with an aeration device 32 and circulation pumps 33 and 34 for solution circulation.

  Using this test apparatus, in order to confirm the relationship between the production amount of the alkali component and the circuit current, the relationship between the pH change of the circulating solution in the cathode tank 15 and the aeration tank 31 and the circuit current was examined. As the circulating solution, acidic automobile wastewater (pH 3.63, volume 0.4 L) was used. The current was calculated by measuring the voltage of the external resistance using a voltmeter. Further, the pH of the circulating fluid was measured using a pH meter, and the test was terminated when the pH reached 7. The results are shown in the graph of FIG.

Next, the charge amount during the experiment was calculated from the current data. Further, the theoretical value of the amount of OH ⁻ produced was calculated from the reaction formula of the cathode shown in the first embodiment. On the other hand, using sodium hydroxide, the same amount of acidic automobile wastewater (pH 3.63, volume 0.4 L) was adjusted to pH 7, and the amount of OH ⁻ necessary for neutralization was calculated from the amount of sodium hydroxide consumed. . The OH ^- amount of OH actually generated from the cathode reaction ^- is the same amount of.

As shown in the graph of FIG. 7, the theoretical value of the amount of OH ⁻ generated from the charge amount was 3.75 mmol, whereas the amount of OH ⁻ actually generated was 3.54 mmol. OH ^- to the theoretical value of the amount of actually generated OH ^- proportions of are called alkali component generating efficiency, the alkali component generating efficiency by this study was 94.4%. From this result, since the theoretical value and the experimental value of the amount of OH ⁻ produced are almost the same, it can be seen that the amount of OH ⁻ produced can be controlled by adjusting the external resistance. From this, it is considered that by using the system of the present invention, it is not necessary to separately supply chemical-derived OH ⁻ .

DESCRIPTION OF SYMBOLS 1 Microbial fuel cell 11 Anode electrode 12 Anode area | region (area | region which has an anode electrode)
13 Ion-permeable membrane 14 Cathode electrode 15 Cathode region 16 External resistance 2 Anaerobic tank 3 Aerobic tank 4 Oxygen-free tank 5 Precipitation tank

Claims (10)

A nitrification denitrification wastewater treatment system comprising at least an anaerobic tank, an aerobic tank, and a microbial fuel cell,
The microbial fuel cell includes an anode electrode on which an electrogenic microorganism is fixed, a cathode region having a cathode electrode, and an ion-permeable diaphragm that separates the region having the anode electrode and the cathode region,
A system in which OH ⁻ generated in the cathode region is supplied to the aerobic tank, and a nitrating solution of the aerobic tank is supplied to the cathode region. The microbial fuel cell is provided inside the anaerobic tank,
The nitrification denitrification waste water treatment system according to claim 1, further comprising means for sending a nitrification solution from the aerobic tank to the cathode region. The microbial fuel cell is provided outside the anaerobic tank and aerobic tank,
Means for sending a nitrating solution from the aerobic tank to the cathode region; means for sending a catholyte from the cathode region to the aerobic tank;
2. The nitrification / denitrification wastewater treatment system according to claim 1, further comprising: means for sending the water to be treated to the area having the anode electrode; and means for sending the anolyte from the area having the anode electrode to the anaerobic tank. An anaerobic tank is further provided between the anaerobic tank and the aerobic tank,
The microbial fuel cell is provided inside the anaerobic tank,
2. The nitrification / denitrification wastewater treatment system according to claim 1, comprising: means for sending a nitrating solution from the aerobic tank to the cathode region; and means for sending a catholyte from the cathode region to the aerobic tank or an oxygen-free tank. . An anaerobic tank is further provided between the anaerobic tank and the aerobic tank,
The microbial fuel cell is provided outside the anaerobic tank, aerobic tank and anoxic tank,
Means for sending nitrification liquid from the aerobic tank to the cathode region; means for sending catholyte from the cathode region to the aerobic or anoxic tank;
2. The nitrification / denitrification wastewater treatment system according to claim 1, further comprising: means for sending the water to be treated to the area having the anode electrode; and means for sending the anolyte from the area having the anode electrode to the anaerobic tank.   The nitrification denitrification wastewater treatment system according to claim 2 or 4, wherein the anode electrode is immersed in water to be treated inside the anaerobic tank.   The nitrification denitrification wastewater treatment system according to claim 3 or 5, wherein means for sending the water to be treated to the region having the anode electrode passes through the inside of the anaerobic tank.   8. The nitrification / denitrification according to claim 1, wherein the microbial fuel cell has a replaceable external resistance or a variable external resistance in an electric circuit connecting the anode electrode and the cathode electrode. 9. Nitrogen wastewater treatment system. A denitrification step of reducing nitric acid or nitrous acid in the water to be treated to generate nitrogen;
A nitrification step of converting ammonium compounds in the water to be treated into nitric acid or nitrite by nitrifying bacteria,
A nitrification denitrification wastewater treatment method comprising at least an alkali production step of producing OH ⁻ at a cathode of a microbial fuel cell,
A nitrification denitrification wastewater treatment method, wherein OH ⁻ obtained in the alkali generation step is added to the nitrification step, and the nitrification liquid in the nitrification step is supplied to the cathode of the microbial fuel cell. The method according to claim 9, wherein the amount of OH ⁻ produced in the alkali production step is adjusted by changing an external resistance of the microbial fuel cell.

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