JP2011218346A - Method and apparatus for treating wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both of the efficiency of the whole wastewater treatment, and the reduction of generation and emitting amount of nitrous oxide.SOLUTION: An apparatus S for treating wastewater measures an ORP value D1 in the position near the downmost stream of the diversion tanks 61 to 64, and the diversion tank whose ORP value D1 is within a first prescribed range Dc1 is determined to be a specific diversion tank. Air is supplied into the specific diversion tank and the diversion tank at a side upstream therefrom by an air diffuser 16, and the air content to be supplied into the diversion tank downstream of the specific diversion tank is reduced from that to be supplied into the specific diversion tank and the tank upstream thereof. Thereby, since the air diffusers can be operated at low electric power in a downstream tank, energy saving can be achieved and besides, the generation and emitting amount of nitrous oxide can be reduced in the downstream tank.

Description

  The present invention relates to a wastewater treatment method and wastewater treatment apparatus for biologically treating wastewater containing nitrogen.

It is known that nitrous oxide gas (N ₂ O) is generated as a reaction byproduct when biologically treating wastewater containing nitrogen (hereinafter abbreviated as nitrogen-containing wastewater). Nitrous oxide gas is a greenhouse gas, and its greenhouse effect is as high as about 310 times that of carbon dioxide gas. Nitrous oxide gas is also regarded as a problem as an ozone depleting gas that destroys the stratospheric ozone layer, like chlorofluorocarbon gas. For this reason, when biologically treating nitrogen-containing wastewater, it is an urgent task to suppress the diffusion of nitrous oxide gas into the atmosphere from the viewpoint of protecting the global environment. Nitrogen-containing wastewater includes raw water supplied from the first sedimentation basin of the sewage treatment plant, general sewage and sewage, human waste, industrial wastewater, agricultural village wastewater, fishery village wastewater, aquaculture wastewater, etc. Can be illustrated.

  In general, biological treatment of nitrogen-containing wastewater (hereinafter referred to as wastewater treatment method) involves nitrification using nitrifying bacteria to oxidize ammonia nitrogen in nitrogen-containing wastewater, and nitrogen containing using denitrifying bacteria. A denitrification step of reducing nitrogen oxides contained in the waste water (see Patent Document 1). The nitrification step is a step in which ammonia is oxidized into nitrous acid according to chemical reaction formulas (1) and (2) shown below, and a step in which nitrous acid is oxidized into nitric acid in accordance with chemical reaction formula (3) shown below. And including.

NH ₄ ⁺ + O ₂ + H ⁺ + 2e ⁻ → NH ₂ OH + H ₂ O (1)
NH ₂ OH + H ₂ O → NO ₂ ⁻ + 5H ⁺ + 4e ⁻ (2)
NO ₂ ⁻ + 0.5O ₂ → NO ₃ ⁻ (3)

The chemical reaction formulas (1) and (2) essentially proceed continuously as a pair of reactions, and surplus electrons are transferred to oxygen as shown in the following chemical reaction formula (4). However, a part of NH ₂ OH generated according to the chemical reaction formula (1) is oxidized according to the chemical reaction formula (5) shown below without passing through the reaction path of the chemical reaction formula (2). Nitrogen may be produced. In addition, when the amount of oxygen necessary for the nitrification process cannot be secured due to a shortage of aeration, the reaction does not proceed sufficiently, NO ₂ ⁻ accumulates in the waste water, and the chemical reaction formulas (6) and (7) shown below: ) Reaction, and the nitrification rate decreases, the conversion rate to nitrous oxide may increase.

0.5O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (4)
NH ₂ OH + NO ₂ ⁻ → N ₂ O + H ₂ O + OH ⁻ (5)
NO ₂ ⁻ + 3H ⁺ + 2e ⁻ → 0.5N ₂ O + 1.5H ₂ O (6)
NO ₂ ⁻ + H ⁺ +2 (H) → 0.5N ₂ O + 1.5H ₂ O (7)

  On the other hand, the denitrification process proceeds according to the chemical reaction formula (8) shown below using an organic substance. (H) in the chemical reaction formula (8) represents ethanol and other organic substances. However, in this denitrification step, if the reaction environment is not good, such as a small amount of organic matter or a large amount of dissolved oxygen, the denitrification reaction will be insufficient and complete decomposition into nitrogen will not proceed. As a result, among the chemical reaction formulas (9) to (12) shown below, the reaction may be completed up to the chemical reaction formula (11), and the amount of nitrous oxide generated may increase.

NO ₃ ⁻ + H ⁺ +5 (H) → 0.5N ₂ + 3H ₂ O (8)
NO ₃ ⁻ + H ⁺ +5 (H) → NO ₂ ⁻ + H ₂ O (9)
NO ₂ ⁻ + H ⁺ + (H) → NO + H ₂ O (10)
NO + (H) → 0.5N ₂ O + 0.5H ₂ O (11)
N ₂ O + 2 (H) → N ₂ + H ₂ O (12)

  By the way, in order to improve the nitrogen removal rate in wastewater treatment methods such as anaerobic aerobic method (AO method), anaerobic anaerobic aerobic method (A2O method), circulation type nitrification denitrification method, nitrification generated in nitrification tank It is necessary to circulate the liquid to a denitrification tank (anaerobic tank or anoxic tank) and promote nitrogenation by biological reduction reaction. However, energy is required to circulate the nitrification liquid, and the efficiency of the denitrification reaction in the denitrification tank deteriorates when the nitrification liquid in which oxygen is dissolved flows into the denitrification tank. Accordingly, if a plurality of aerobic tanks are provided, and a tank in which the nitrification reaction is sufficiently completed is identified, and the subsequent tanks can be used for the denitrification reaction, it is preferable that the circulation amount of the nitrification liquid need not be increased unnecessarily. . From such a background, Patent Document 2 discloses a technique in which a part of a plurality of aerobic tanks is switched to an anaerobic tank based on the value of the oxidation-reduction potential.

JP-A-6-63588 Japanese Utility Model Publication No. 5-18699

  However, the technique described in Patent Document 2 is aimed at improving the efficiency of wastewater treatment including energy saving, but does not take into account the reduction in the amount of nitrous oxide generated. In particular, no consideration has been given to the adverse effect that dissolved nitrous oxide easily volatilizes into the atmosphere with aeration (air supply) in an aerobic tank.

  The present invention has been made in view of the above problems, and its purpose is to provide a wastewater treatment method and a wastewater treatment apparatus that can achieve both the efficiency of the entire wastewater treatment and the reduction of the amount of nitrous oxide generated and the amount of volatilization. Is to provide.

  In order to solve the above-mentioned problem, a wastewater treatment method according to the first aspect of the present invention includes a wastewater treatment comprising a plurality of diversion tanks arranged along the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater. A wastewater treatment method in the apparatus, the step of measuring a redox potential or dissolved oxygen concentration at a position near the most downstream of each diversion tank, and a nitrification reaction of the nitrogen-containing wastewater based on the redox potential or dissolved oxygen concentration Identifying a diversion tank that has been substantially completed as a specific diversion tank, supplying a first supply amount of air into the specific diversion tank and a diversion tank upstream of the specific diversion tank, and the identification Supplying a second supply amount of air less than the first supply amount into the diversion tank downstream of the diversion tank.

  In order to solve the above-described problem, a wastewater treatment apparatus according to the first aspect of the present invention includes a wastewater treatment system including a plurality of diversion tanks arranged along the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater. A measuring means for measuring a redox potential or dissolved oxygen concentration at a position near the most downstream of each diversion tank, and the nitrogen-containing wastewater based on the redox potential or dissolved oxygen concentration measured by the measuring means. Means for identifying a diversion tank in which the nitrification reaction of the nitrification reaction is substantially completed as a specific diversion tank, and means for supplying a first supply amount of air into the specific diversion tank and into a diversion tank upstream of the specific diversion tank; And means for supplying a second supply amount of air smaller than the first supply amount into the diversion tank on the downstream side of the specific diversion tank.

  In order to solve the above-mentioned problem, a wastewater treatment method according to the second aspect of the present invention includes a wastewater treatment comprising a plurality of diversion tanks arranged along the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater. A wastewater treatment method in the apparatus, the step of measuring a redox potential or dissolved oxygen concentration at a position near the most downstream of each diversion tank, and a nitrification reaction of the nitrogen-containing wastewater based on the redox potential or dissolved oxygen concentration Identifying a diversion tank that has been substantially completed as a specific diversion tank, supplying a first supply amount of air into the specific diversion tank and a diversion tank upstream of the specific diversion tank, and the identification Adding an organic substance into a diversion tank on the downstream side of the diversion tank, and stirring the diversion tank to which the organic substance is added.

  In order to solve the above-mentioned problem, a wastewater treatment apparatus according to a second aspect of the present invention is a wastewater treatment apparatus comprising a plurality of diversion tanks arranged along the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater. A measuring means for measuring a redox potential or dissolved oxygen concentration at a position near the most downstream of each diversion tank, and the nitrogen-containing wastewater based on the redox potential or dissolved oxygen concentration measured by the measuring means. Means for identifying a diversion tank in which the nitrification reaction of the nitrification reaction is substantially completed as a specific diversion tank, and means for supplying a first supply amount of air into the specific diversion tank and into a diversion tank upstream of the specific diversion tank; And means for adding an organic substance into a diversion tank downstream from the specific diversion tank and stirring the diversion tank to which the organic substance is added.

  According to the waste water treatment method and the waste water treatment apparatus according to the present invention, it is possible to achieve both the efficiency of the whole waste water treatment and the reduction in the amount of nitrous oxide generated and the amount of volatilization.

FIG. 1 is a schematic diagram showing a configuration of a wastewater treatment apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of a modified example of the waste water treatment apparatus illustrated in FIG. 1. FIG. 3 is a schematic view showing a configuration of a waste water treatment apparatus according to the second embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the ORP value and the ammonia concentration in the diversion tank. FIG. 5 is a schematic diagram illustrating a configuration of a modified example of the waste water treatment apparatus illustrated in FIG. 3.

  Hereinafter, a waste water treatment apparatus and a waste water treatment method thereof according to first and second embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
First, the waste water treatment apparatus and the waste water treatment method according to the first embodiment of the present invention will be described with reference to FIGS.

[Configuration of wastewater treatment equipment]
FIG. 1 is a schematic diagram showing a configuration of a wastewater treatment apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the wastewater treatment apparatus S according to the first embodiment of the present invention includes an anaerobic tank 2, a denitrification tank 4, a diversion tank 6, a solid-liquid separation tank (precipitation tank) 10, an air diffuser 16, An ORP meter 24 and a computer 28 are provided as main components. The anaerobic tank 2 is a tank into which nitrogen-containing wastewater flows first or through a first sedimentation basin (not shown) depending on the configuration of the sewage treatment plant. The anaerobic tank 2 is for performing a dephosphorization process (anaerobic treatment) on the nitrogen-containing wastewater by the action of phosphorus-accumulating bacteria in an anaerobic environment.

  The denitrification tank 4 is a tank that is arranged on the downstream side of the anaerobic tank 2 and into which treated water that has flowed out of the anaerobic tank 2 flows. The denitrification tank 4 is for denitrifying the treated water by the action of denitrifying bacteria in an oxygen-free environment. The treated water in the denitrification tank 4 contains nitric acid by circulating the nitrification liquid in the diversion tank 64 (6) through the circulation path 8. This nitric acid is decomposed into nitrogen by the chemical reaction according to the chemical reaction formulas (9) to (12) already described. Denitrification efficiency in the denitrification tank 4 can be improved by circulating the nitrification liquid in the denitrification tank 4 via the circulation path 8.

  The diversion tank 6 is a tank that is disposed on the downstream side of the denitrification tank 4 and into which treated water that has flowed out of the denitrification tank 4 flows. The diversion tank 6 includes a plurality of diversion tanks 61 to 64. The plurality of diversion tanks 61 to 64 may be physically separated, or may be one in which one diversion tank is virtually divided into a plurality of partition walls or a flow in the tank. A diffuser 16 for supplying air to the stored treated water is provided at the bottom of each diversion tank. The amount of air diffused by each air diffuser 16 is controlled by an individual controller 18. Each controller 18 includes a blower and a flow rate adjustment valve, and adjusts the amount of air diffused by each air diffuser 16 in accordance with a control command from the computer 28. An ORP meter 24 for measuring the oxidation-reduction potential (ORP value) of the treated water stored in each tank is installed at the terminal position (most downstream vicinity position) 6a of each tank.

  The first-stage (most upstream) diversion tank 61 is used as an aerobic (nitrification) tank. That is, in the diversion tank 61, the aeration by the aeration device 16 is sufficiently performed, and nitrification of the treated water is performed by the action of nitrifying bacteria in an environment where the dissolved oxygen concentration is high. On the other hand, the diversion tanks 62 to 64 in the subsequent stages are used by switching to either the aerobic tank or the downstream tank according to the measured value of the ORP value by each ORP meter 24. More specifically, when the computer 28 determines that any one of the conversion tanks 62 to 64 is the specific conversion tank, the specific conversion tank and the conversion tank upstream thereof are used as the aerobic tank. The diversion tank on the downstream side of the specific diversion tank is used as the downstream tank. In the present specification, the specific diversion tank means a diversion tank that can be “determined that the nitrification reaction has been substantially completed up to the diversion tank”. In the initial operation, it is preferable to use all the diversion tanks 61 to 64 as aerobic tanks.

  The solid-liquid separation tank 10 is located on the downstream side of the diversion tank 6 and is a tank into which treated water that has flowed out of the diversion tank 6 flows. The solid-liquid separation tank 10 is for solid-liquid separation of treated water that has undergone biological treatment. In the solid-liquid separation tank 10, the supernatant water generated by the solid-liquid separation is discharged out of the apparatus. Part of the sludge generated by the solid-liquid separation is returned to the anaerobic tank 2 and the position where it merges with the nitrogen-containing wastewater before flowing into the anaerobic tank 2 via the return path 12, and the biomass in the anaerobic tank 2 Is maintained. The remainder of the sludge generated by solid-liquid separation is discharged out of the apparatus through the discharge pipe 14 as excess sludge.

  The computer 28 determines which of the diversion tanks 61 to 64 is the specific diversion tank based on the ORP value from the ORP meter 24 installed in each diversion tank 61 to 64. In the present embodiment, the numerical value range information indicating the first predetermined range Dc1 is stored in advance in the memory in the computer 28, and the computer 28 compares this numerical value range with the ORP value D1 from each ORP meter 24. Then, the diversion tank having the ORP value D1 within this numerical range is determined as the specific diversion tank.

  The computer 28 sends out a control command D2 so as to continue the aeration by the aeration device 16 to each controller 18 of the specific diversion tank and the diversion tank upstream thereof. Thereby, the specific diversion tank and the diversion tank on the upstream side are used as an aerobic tank. On the other hand, the computer 28 controls the controller 18 of the diversion tank downstream of the specific diversion tank so as to supply an air amount smaller than the air amount supplied by the air diffuser 16 in the aerobic tank. D2 is sent out. Thereby, the diversion tank on the downstream side of the specific diversion tank is used as a downstream denitrification tank. The downstream denitrification tank is a tank that realizes an in-tank environment in which the denitrification reaction and the nitrification reaction do not proceed as much as possible in order to reduce the generation amount and volatilization amount of nitrous oxide. As a result, the amount of power required for aeration can be reduced, and the wastewater treatment device can be effectively utilized.

  When the aeration to the downstream tank is completely stopped, the downstream tank is in an oxygen-free state, but since the amount of organic substances is insufficient, it is difficult to perform a sufficient denitrification reaction. For this reason, the denitrification reaction partly proceeds, resulting in a semi-denitrification state, and the amount of nitrous oxide generated may increase. On the other hand, when a large amount of air is supplied to the downstream tank, unnecessary nitrification reaction is promoted using unnecessary energy, and dissolved nitrous oxide is volatilized. For this reason, it is desirable to supply air to such an extent that denitrification reaction and nitrification reaction do not proceed and dissolved nitrous oxide is not volatilized.

  It is preferable to control the amount of air for the diversion tank downstream of the specific diversion tank based on the ORP value D1 of the diversion tank downstream of the specific diversion tank. Specifically, in the present embodiment, the information in the second predetermined range Dc2 is stored in the memory in the computer 28, and the computer 28 determines the ORP value D1 from the diversion tank downstream of the specific diversion tank and this The second predetermined range Dc2 is compared. When the ORP value D1 from the diversion tank downstream of the specific diversion tank is equal to or greater than the second predetermined range Dc2, the computer 28 supplies the amount of air supplied to the controller 18 of the diversion tank downstream of the specific diversion tank. Sends a control command to further reduce the.

  On the other hand, when the ORP value D1 from the diversion tank downstream of the specific diversion tank is less than the second predetermined range Dc2, the computer 28 supplies the air amount to the controller 18 of the diversion tank downstream of the specific diversion tank. Sends a control command that further increases. As a result, the ORP value D1 from the diversion tank on the downstream side of the specific diversion tank is feedback-controlled so as to fall within the second predetermined range Dc2.

[Wastewater treatment method]
Next, a wastewater treatment method by the wastewater treatment apparatus S according to the first embodiment of the present invention will be described.

  In the waste water treatment apparatus S which is the first embodiment of the present invention, first, the nitrogen-containing waste water flows into the anaerobic tank 2 and is subjected to dephosphorization treatment. Next, the treated water flows into the upstream denitrification tank 4 and is denitrified. Next, the treated water flows into the diversion tank 6 and is nitrified. Next, the ORP value D 1 at the tank terminal position 6 a of the diversion tanks 61 to 64 is measured by the ORP meter 24, and the measured ORP value D 1 is sent to the computer 28. Next, the computer 28 specifies the specific diversion tank by comparing the ORP value D1 with the predetermined range Dc1.

  Next, the computer 28 sends a control command D2 for reducing the air supply amount to the specific diversion tank and the diversion tank upstream of the specific diversion tank to the controller 18 of the diversion tank downstream from the specific diversion tank. Send it out. Further, the computer 28 compares the ORP value D1 of the diversion tank downstream from the specific diversion tank with the second predetermined range Dc2. When the ORP value D1 of the diversion tank downstream of the specific diversion tank is equal to or greater than the second predetermined range Dc2, the computer 28 further reduces the amount of air supplied to the diversion tank downstream of the specific diversion tank. A control command D2 is sent out. On the other hand, when the ORP value D1 of the diversion tank downstream from the specific diversion tank is less than the second predetermined range Dc2, the computer 28 increases the amount of air supplied to the diversion tank downstream from the specific diversion tank. A control command D2 is sent to the controller 18 of the diversion tank 64.

  As is apparent from the above description, in the wastewater treatment method according to the first embodiment of the present invention, the wastewater treatment apparatus S measures the ORP value D1 at the position closest to the downstream of the diversion tanks 61 to 64, and the ORP value. The diversion tank in which D1 is within the first predetermined range Dc1 is determined as the specific diversion tank, and air is supplied to the diversion tank 16 in the specific diversion tank and upstream from the specific diversion tank, and downstream from the specific diversion tank. The amount of air supplied into the diversion tank on the side is reduced below the amount of air supplied into the specific diversion tank and the diversion tank on the upstream side. According to such a wastewater treatment method, since the diffuser can be operated with low power in the downstream tank, energy saving can be realized. Moreover, the generation amount and volatilization amount of nitrous oxide in a downstream tank can be reduced. That is, according to such a waste water treatment method, it is possible to achieve both the efficiency of the whole waste water treatment and the reduction of the amount of nitrous oxide generated and the amount of volatilization.

  Further, in the wastewater treatment method according to the first embodiment of the present invention, the wastewater treatment apparatus S has a specific diversion tank so that the ORP value in the diversion tank downstream from the specific diversion tank is within the second predetermined range Dc2. Since the amount of air supplied into the conversion tank on the further downstream side is adjusted, it is possible to suppress the progress of the denitrification reaction or nitrification reaction in the conversion tank on the downstream side of the specific conversion tank.

[Modification]
In the present embodiment, the computer 28 specifies the specific diversion tank based on whether the ORP value D1 in the diversion tank is within the first predetermined range Dc1, but the computer 28 of the ORP meter 24 that is continuous in the upstream and downstream directions. You may identify a specific diversion tank based on whether the difference value of ORP value D1 is more than a predetermined difference value. More specifically, in this case, the computer 28 continues in the upstream / downstream direction when the difference value of the ORP value D1 of the diversion tanks continuous in the upstream / downstream direction is less than a predetermined difference value stored in the memory. It is determined that the diversion tank is not a specific diversion tank. On the other hand, when the difference value of the ORP value D1 of the diversion tanks continuous in the upstream / downstream direction is equal to or larger than the predetermined difference value stored in the memory, the computer 28 determines that the downstream diversion tank is the specific diversion tank. To do.

  In the present embodiment, the specific diversion tank is identified based on whether or not the ORP value D1 in the diversion tank is within the first predetermined range Dc1, but as shown in FIG. In addition to the ORP meter 24, a DO meter 34 for measuring the dissolved oxygen concentration (DO value) is provided at the tank end position 6a, and the difference value of the DO value D3 of the DO meter 34 continuous in the upstream and downstream directions is equal to or greater than a predetermined difference value Dc3. The specific diversion tank may be specified based on whether or not there is. More specifically, in this case, when the difference value of the DO value D3 of the diversion tank continuous in the upstream / downstream direction is less than the predetermined difference value Dc3 stored in the memory, the computer 28 continues in the upstream / downstream direction. It is determined that the diversion tank to be used is not a specific diversion tank. On the other hand, when the difference value of the DO value D3 of the diversion tanks continuous in the upstream / downstream direction is equal to or larger than the predetermined difference value Dc3 stored in the memory, the computer 28 determines that the downstream diversion tank is the specific diversion tank. . The predetermined difference value Dc3 is preferably about 0.3 mg / L. Also in this modified example, the feedback control of the air supply amount to the downstream conversion tank downstream of the specific conversion tank is performed based on the comparison between the ORP value D1 and the second predetermined range Dc2.

  In the present embodiment and the modification, the case where the waste water treatment apparatus S includes the anaerobic tank 2 and the denitrification tank 4 has been described, but the waste water treatment apparatus S includes neither the anaerobic tank 2 nor the upstream denitrification tank 4, drainage The present invention can be applied to a configuration in which the processing apparatus S includes only one of the anaerobic tank 2 or the denitrification tank 4.

[Second Embodiment]
Next, with reference to FIG. 3 thru | or FIG. 5, the waste water treatment apparatus which is the 2nd Embodiment of this invention, and its waste water treatment method are demonstrated.

[Configuration of wastewater treatment equipment]
FIG. 3 is a schematic view showing a configuration of a waste water treatment apparatus according to the second embodiment of the present invention. As shown in FIG. 3, the waste water treatment apparatus S according to the second embodiment of the present invention includes an anaerobic tank 2, an upstream denitrification tank (denitrification tank) 4, a diversion tank 6, and a solid-liquid separation tank (precipitation tank) 10. , ORP meter 24, organic substance adding means 26, and computer 28 as main components. The anaerobic tank 2 is a tank into which nitrogen-containing wastewater flows first or through a first sedimentation basin (not shown) depending on the configuration of the sewage treatment plant. The anaerobic tank 2 is for performing a dephosphorization process (anaerobic treatment) on the nitrogen-containing wastewater by the action of phosphorus-accumulating bacteria in an anaerobic environment.

  The upstream denitrification tank 4 is a tank that is disposed on the downstream side of the anaerobic tank 2 and into which treated water that has flowed out of the anaerobic tank 2 flows. The upstream denitrification tank 4 is for performing denitrification treatment on the treated water by the action of denitrifying bacteria in an oxygen-free environment. The treated water in the upstream denitrification tank 4 contains nitric acid as the nitrification liquid in the diversion tank 64 (6) is circulated through the circulation path 8. This nitric acid is decomposed into nitrogen by the chemical reaction according to the chemical reaction formulas (9) to (12) already described. By circulating the nitrification liquid in the upstream denitrification tank 4 via the circulation path 8, the denitrification efficiency in the upstream denitrification tank 4 can be improved.

  The diversion tank 6 is a tank that is disposed on the downstream side of the denitrification tank 4 and into which treated water that has flowed out of the denitrification tank 4 flows. The diversion tank 6 includes a plurality of diversion tanks 61 to 64. The plurality of diversion tanks 61 to 64 may be physically separated, or may be one in which one diversion tank is virtually divided into a plurality of partition walls or a flow in the tank. A diffuser 16 for supplying air to the stored treated water is provided at the bottom of each diversion tank. The amount of air diffused by each air diffuser 16 is controlled by an individual controller 18. Each controller 18 includes a blower and a flow rate adjustment valve, and adjusts the amount of air diffused by each air diffuser 16 in accordance with a control command from the computer 28. An ORP meter 24 for measuring the oxidation-reduction potential (ORP value) of the treated water stored in each tank is installed at the terminal position (most downstream vicinity position) 6a of each tank.

  The first-stage (most upstream) diversion tank 61 is used as an aerobic (nitrification) tank. Therefore, in the diversion tank 61, the air diffused by the air diffuser 16 is sufficiently performed, and the nitrogen-containing wastewater is nitrified by the action of nitrifying bacteria in an environment with a high dissolved oxygen concentration. On the other hand, the diversion tanks 62 to 64 in the subsequent stages are used by switching to either an aerobic tank or a denitrification tank according to the ORP value measured by each ORP meter 24. More specifically, when the computer 28 determines that any one of the diversion tanks 62 to 64 is a specific diversion tank, the specific diversion tank and the diversion tank upstream of the diversion tank are defined as aerobic tanks. The diversion tank downstream from the specific diversion tank is used as a denitrification tank.

  In this embodiment, since the denitrification tank is arranged not only in the upstream denitrification tank 4 but also in the downstream side of the diversion tank 61 which is an aerobic tank, the circulation amount of the nitrification liquid via the circulation path 8 is reduced. Can be reduced. As a result, it is possible to reduce the energy required for the circulation of the nitrification solution, and it is possible to suppress a decrease in the denitrification efficiency due to a large amount of the nitrification solution containing a large amount of dissolved oxygen flowing into the upstream denitrification tank 4. In the present specification, the specific diversion tank means a diversion tank that can be “determined that the nitrification reaction has been substantially completed up to the diversion tank”. In the initial operation, it is preferable to use all the diversion tanks 61 to 64 as aerobic tanks.

  The solid-liquid separation tank 10 is located on the downstream side of the diversion tank 6 and is a tank into which treated water that has flowed out of the diversion tank 6 flows. The solid-liquid separation tank 10 is for solid-liquid separation of treated water that has undergone biological treatment. In the solid-liquid separation tank 10, the supernatant water generated by the solid-liquid separation is discharged out of the apparatus. Part of the sludge generated by the solid-liquid separation is returned to the anaerobic tank 2 and the position where it merges with the nitrogen-containing wastewater before flowing into the anaerobic tank 2 via the return path 12, and the biomass in the anaerobic tank 2 Is maintained. The remainder of the sludge generated by solid-liquid separation is discharged out of the apparatus through the discharge pipe 14 as excess sludge.

  The organic substance addition means 26 adds an organic substance to a position close to the upstream side of the diversion tanks 62 to 64 excluding the first-stage diversion tank 61. The organic substance addition means 26 has an open / close and flow rate adjustment valve, and can switch the diversion tanks 62 to 64 to which the organic substance is added in accordance with a control command from the computer 28. The organic substance adding means 26 can also adjust the amount of organic substance added in accordance with a control command from the computer 28. Examples of the organic substance to be added include nitrogen-containing wastewater before flowing into the anaerobic tank 2, such as alcohols such as methanol and ethanol, volatile fatty acids such as acetic acid, easily decomposable carbohydrates such as glucose, and the like.

  The computer 28 determines which of the diversion tanks 61 to 64 is the specific diversion tank based on the ORP value from the ORP meter 24 installed in each diversion tank 61 to 64. In the present embodiment, the numerical value range information indicating the first predetermined range Dc1 is stored in advance in the memory in the computer 28, and the computer 28 compares this numerical value range with the ORP value D1 from each ORP meter 24. Then, the diversion tank having the ORP value D1 within this numerical range is determined as the specific diversion tank. According to the study by the present inventors, as shown in FIG. 4, when the ORP value is 40 mV or more, the ammonia concentration greatly decreases. For this reason, the first predetermined range Dc1 is desirably a range in which the ORP value is approximately 40 mV or more and approximately 60 mV or less.

  The computer 28 sends out a control command D2 so as to continue the aeration by the aeration device 16 to each controller 18 of the specific diversion tank and the diversion tank upstream thereof. Thereby, the specific diversion tank and the diversion tank on the upstream side are used as an aerobic tank. On the other hand, the computer 28 sends a control command D2 to each controller 18 of the diversion tank on the downstream side of the specific diversion tank so as to stop the aeration. Thereby, the diversion tank on the downstream side of the specific diversion tank becomes oxygen-free and is used as a downstream denitrification tank. Moreover, even if a slight amount of nitrous oxide is dissolved in the diversion tank on the downstream side of the specific diversion tank, it is possible to suppress nitrous oxide from evaporating into the atmosphere. In addition, the amount of power for air diffusion can be reduced, and energy saving can be realized. Further, since denitrification can be performed in the downstream denitrification tank, the amount of nitrification liquid to be circulated in the upstream denitrification tank 4 can be reduced, and the amount of energy required for circulation of the nitrification liquid can be reduced.

  In addition, when the stirring apparatus is installed in the diversion tank on the downstream side of the specific diversion tank, the computer 28 promotes the denitrification reaction by stirring the treated water in the diversion tank by driving the stirring apparatus. Also good. In this case, the air diffuser 16 and the controller 18 may have a stirring function. That is, the computer 28 does not stop the air supply completely, but sends a control command D2 for supplying a very small amount of air to the controller 18 and realizes the stirring function in the tank within a range in which the amount of dissolved oxygen is not increased so much. May be. In this case, since the amount of aeration for stirring is very small, there is almost no adverse effect on the denitrification reaction. Even if dissolved nitrous oxide exists, the amount of air diffused is very small, so that nitrous oxide is hardly volatilized.

  Organic substances are added from the organic substance addition means 26 to the diversion tank on the downstream side of the specific diversion tank. That is, the computer 28 sends a control command D2 for adding an organic substance to the diversion tank downstream of the specific diversion tank to the organic substance addition means 26. At this time, the amount of the organic substance added is adjusted based on the ORP value D1 of the diversion tank on the downstream side of the specific diversion tank. That is, the predetermined critical value Dc2 is stored in the memory of the computer 28, and the computer 28 compares the ORP value D1 of the diversion tank downstream of the specific diversion tank with the predetermined critical value Dc2. When the ORP value D1 of the diversion tank on the downstream side of the specific diversion tank is equal to or greater than the predetermined critical value Dc2, the computer 28 sends a control command D2 for increasing the organic substance addition amount to the organic substance addition means 26. As a result, even if the efficiency of the denitrification reaction deteriorates, the amount of organic matter in the diversion tank downstream of the specific diversion tank increases, the denitrification reaction is promoted, and the amount of nitrous oxide generated is reduced. it can.

[Wastewater treatment method]
Next, a wastewater treatment method by the wastewater treatment apparatus S according to the second embodiment of the present invention will be described.

  In the waste water treatment apparatus S that is the second embodiment of the present invention, first, the nitrogen-containing waste water flows into the anaerobic tank 2 and is subjected to dephosphorization treatment. Next, the treated water flows into the upstream denitrification tank 4 and is denitrified. Next, the treated water flows into the diversion tank 6 and is nitrified. Next, the ORP value D 1 at the tank terminal position 6 a of the diversion tanks 61 to 64 is measured by the ORP meter 24, and the measured ORP value D 1 is sent to the computer 28. Next, the computer 28 specifies the specific diversion tank by comparing the ORP value D1 with the predetermined range Dc1.

  Next, the computer 28 sends a control command D2 for operating the air diffuser 16 to such an extent that the agitating function is exhibited instead of the air diffuser function, to the diverter tank controller 18 on the downstream side of the specific diverter tank. Further, the computer 28 sends a control command for adding the organic substance to the diversion tank downstream of the specific diversion tank to the organic substance addition means 26. Then, the computer 28 compares the ORP value D1 of the diversion tank downstream of the specific diversion tank with the predetermined critical value Dc2, and the ORP value D1 of the diversion tank downstream of the specific diversion tank is equal to or greater than the predetermined critical value Dc2. In this case, a control command D2 for increasing the amount of organic matter added to the diversion tank downstream from the specific diversion tank is sent to the organic substance addition means 26.

  As is clear from the above description, in the wastewater treatment method according to the second embodiment of the present invention, the wastewater treatment device S measures the ORP value in the position near the most downstream of the diversion tanks 61 to 64, and the ORP value is The diversion tank in the first predetermined range is determined as the specific diversion tank, air is supplied to the diversion tank 16 in the specific diversion tank and the diversion tank upstream from the diversion tank, and the diversion downstream from the specific diversion tank. An organic substance is added to the tank, and the inside of the diversion tank to which the organic substance is added is stirred. According to such a wastewater treatment method, since the operation of the air diffuser can be stopped in the downstream tank, energy saving can be realized. Moreover, the generation amount and volatilization amount of nitrous oxide in a downstream tank can be reduced. That is, according to such a wastewater treatment method, it is possible to achieve both the efficiency of the whole wastewater treatment and the reduction of the amount of nitrous oxide generated.

  Further, in the wastewater treatment method according to the second embodiment of the present invention, when the wastewater treatment apparatus S has an ORP value in the diversion tank downstream from the specific diversion tank, the amount of organic matter added is increased. Therefore, the denitrification reaction in the downstream tank is promoted, and the amount of nitrous oxide generated can be reduced.

[Modification]
In the present embodiment, the computer 28 specifies the specific diversion tank based on whether the ORP value D1 in the diversion tank is within the first predetermined range Dc1, but the computer 28 of the ORP meter 24 that is continuous in the upstream and downstream directions. You may identify a specific diversion tank based on whether the difference value of ORP value D1 is more than a predetermined difference value. More specifically, in this case, the computer 28 continues in the upstream / downstream direction when the difference value of the ORP value D1 of the diversion tanks continuous in the upstream / downstream direction is less than a predetermined difference value stored in the memory. It is determined that the diversion tank is not a specific diversion tank. On the other hand, when the difference value of the ORP value D1 of the diversion tanks continuous in the upstream / downstream direction is equal to or larger than the predetermined difference value stored in the memory, the computer 28 determines that the downstream diversion tank is the specific diversion tank. To do.

  In the present embodiment, the specific diversion tank is identified based on whether or not the ORP value D1 in the diversion tank is within the first predetermined range Dc1, but as shown in FIG. In addition to the ORP meter 24, a DO meter 34 for measuring the dissolved oxygen concentration (DO value) is provided at the tank end position 6a, and the difference value of the DO value D3 of the DO meter 34 continuous in the upstream and downstream directions is equal to or greater than a predetermined difference value Dc3. The specific diversion tank may be specified based on whether or not there is. More specifically, in this case, when the difference value of the DO value D3 of the diversion tank continuous in the upstream / downstream direction is less than the predetermined difference value Dc3 stored in the memory, the computer 28 continues in the upstream / downstream direction. It is determined that the diversion tank to be used is not a specific diversion tank. On the other hand, when the difference value of the DO value D3 of the diversion tanks continuous in the upstream / downstream direction is equal to or larger than the predetermined difference value Dc3 stored in the memory, the computer 28 determines that the downstream diversion tank is the specific diversion tank. .

  The embodiment to which the invention made by the present inventors is applied has been described above, but the present invention is not limited by the description and the drawings that constitute a part of the disclosure of the present invention. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

2 Anaerobic tank 4 Upstream denitrification tank (denitrification tank)
6, 61-64: Diversion tank 6a Tank end position (position near the most downstream)
8 Circulation path 10 Solid-liquid separation tank (precipitation tank)
DESCRIPTION OF SYMBOLS 12 Return path 14 Drain pipe 16 Air diffuser 18 Controller 24 ORP meter 26 Organic substance addition means 28 Computer 34 DO meter S Biological processing device

Claims (12)

A wastewater treatment method in a wastewater treatment apparatus comprising a plurality of diversion tanks arranged in the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater,
Measuring a redox potential or dissolved oxygen concentration at a position near the most downstream of each diversion tank;
Identifying a diversion tank in which the nitrification reaction of the nitrogen-containing wastewater is substantially completed as a specific diversion tank based on the redox potential or dissolved oxygen concentration;
Supplying a first supply amount of air into the specific diversion tank and into the diversion tank upstream of the specific diversion tank;
Supplying a second supply amount of air less than the first supply amount into the diversion tank downstream of the specific diversion tank;
The waste water treatment method characterized by including.   2. The wastewater treatment method according to claim 1, wherein the step of specifying the specific diversion tank includes the step of specifying, as the specific diversion tank, a diversion tank in which the oxidation-reduction potential is within a first predetermined range.   In the step of identifying the specific diversion tank, when the difference value of the oxidation-reduction potential at the position near the most downstream of the two diversion tanks continuous in the flow direction of the nitrogen-containing wastewater is a predetermined difference value or more, the diversion tank on the downstream side The wastewater treatment method according to claim 1, further comprising a step of identifying the specific diversion tank.   In the step of identifying the specific diversion tank, if the difference value of the dissolved oxygen concentration in the vicinity of the most downstream of two diversion tanks continuous in the flow direction of the nitrogen-containing wastewater is equal to or greater than a predetermined difference value, the diversion tank on the downstream side The wastewater treatment method according to claim 1, further comprising a step of identifying the specific diversion tank.   Adjusting the amount of air supplied into the diversion tank downstream from the specific diversion tank so that the oxidation-reduction potential in the diversion tank downstream from the specific diversion tank is within a second predetermined range. The wastewater treatment method according to any one of claims 1 to 4. A wastewater treatment apparatus comprising a plurality of diversion tanks arranged in the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater,
A measuring means for measuring the redox potential or dissolved oxygen concentration at the position near the most downstream of each diversion tank;
Based on the oxidation-reduction potential or dissolved oxygen concentration measured by the measuring means, means for specifying a diversion tank in which the nitrification reaction of the nitrogen-containing wastewater is substantially completed as a specific diversion tank;
Means for supplying a first supply amount of air into the specific diversion tank and into the diversion tank upstream of the specific diversion tank;
Means for supplying a second supply amount of air less than the first supply amount into the diversion tank downstream of the specific diversion tank;
A wastewater treatment apparatus comprising: A wastewater treatment method in a wastewater treatment apparatus comprising a plurality of diversion tanks arranged in the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater,
Measuring a redox potential or dissolved oxygen concentration at a position near the most downstream of each diversion tank;
Identifying a diversion tank in which the nitrification reaction of the nitrogen-containing wastewater is substantially completed as a specific diversion tank based on the redox potential or dissolved oxygen concentration;
Supplying a first supply amount of air into the specific diversion tank and into the diversion tank upstream of the specific diversion tank;
Adding an organic substance in a diversion tank downstream from the specific diversion tank, and stirring the diversion tank to which the organic substance is added;
The waste water treatment method characterized by including.   The wastewater treatment method according to claim 7, wherein the step of specifying the specific diversion tank includes the step of specifying a diversion tank having the oxidation-reduction potential within a first predetermined range as the specific diversion tank.   In the step of identifying the specific diversion tank, when the difference value of the oxidation-reduction potential at the position near the most downstream of the two diversion tanks continuous in the flow direction of the nitrogen-containing wastewater is a predetermined difference value or more, the diversion tank on the downstream side The wastewater treatment method according to claim 7, further comprising a step of identifying the specific diversion tank.   In the step of identifying the specific diversion tank, if the difference value of the dissolved oxygen concentration in the vicinity of the most downstream of two diversion tanks continuous in the flow direction of the nitrogen-containing wastewater is equal to or greater than a predetermined difference value, the diversion tank on the downstream side The wastewater treatment method according to claim 7, further comprising a step of identifying the specific diversion tank.   11. The method according to claim 7, further comprising a step of increasing the amount of the organic substance added when an oxidation-reduction potential in a diversion tank downstream from the specific diversion tank is a predetermined critical value or more. The waste water treatment method as described in a term. A wastewater treatment apparatus comprising a plurality of diversion tanks arranged in the flow direction of nitrogen-containing wastewater to nitrify the nitrogen-containing wastewater,
A measuring means for measuring the redox potential or dissolved oxygen concentration at the position near the most downstream of each diversion tank;
Based on the oxidation-reduction potential or dissolved oxygen concentration measured by the measuring means, means for specifying a diversion tank in which the nitrification reaction of the nitrogen-containing wastewater is substantially completed as a specific diversion tank;
Means for supplying a first supply amount of air into the specific diversion tank and into the diversion tank upstream of the specific diversion tank;
Means for adding an organic substance in a diversion tank downstream from the specific diversion tank, and stirring the diversion tank to which the organic substance is added;
A wastewater treatment apparatus comprising:

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