JP5717187B2 - Waste water treatment method and waste water treatment equipment - Google Patents

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 Documents 1 to 3). 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. 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.

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)
NO ₃ ⁻ + H ⁺ +5 (H) → 0.5N ₂ + 3H ₂ O (8)

JP-A-6-63588 JP 2009-131854 A JP-A-8-168793

  However, in the above-described 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 reduction reaction becomes insufficient and complete decomposition into nitrogen does 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) → 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)

  Moreover, in the above-mentioned wastewater treatment method, in order to isolate | separate the solid-liquid of the nitrogen-containing wastewater after a nitrification process, nitrogen-containing wastewater is left still in a solid-liquid separation tank, and activated sludge is settled. A part of the precipitated activated sludge is returned to the upstream raw water of the nitrification tank or before it through the return route, and the remaining activated sludge is returned to the outside of the device as excess sludge via the discharge pipe. Discharged. Since the inside of the activated sludge is in an oxygen-free state or a state close thereto, it is in an environmental condition where a reduction reaction of nitric acid or nitrous acid generated by the nitrification reaction is likely to occur.

  However, because activated sludge has already been treated aerobically, due to the lack of organic matter necessary for the reduction reaction, the reduction reaction does not proceed sufficiently until it becomes nitrogen, and nitrous oxide is produced. May be. When activated sludge containing nitrous oxide is returned to the nitrification tank via the return route, nitrous oxide is volatilized due to the influence of air diffused in the nitrification tank, and dissolved nitrous oxide enters the atmosphere. Released.

  In order to solve such a problem, Patent Document 3 proposes a technique of temporarily storing a part of activated sludge in a storage tank and storing the activated sludge until the oxidation-reduction potential becomes −190 mV or less. ing. However, the prior art is intended to improve the dispersibility of the returned sludge, and is not intended to reduce the amount of nitrous oxide generated or the amount of volatilization. For this reason, provision of the technique which can reduce the generation amount and volatilization amount of nitrous oxide was anticipated.

  This invention is made | formed in view of the said subject, The objective is to provide the waste water treatment method and waste water treatment apparatus which can reduce the generation amount and volatilization amount of nitrous oxide.

  In order to solve the above problems, a wastewater treatment method according to the first aspect of the present invention includes a denitrification step of reducing nitrogen oxides contained in nitrogen-containing wastewater in a denitrification tank, and a most downstream position of the denitrification tank. A measurement step of measuring the oxidation-reduction potential in the vicinity, and an organic substance addition step of adding an organic substance into the denitrification tank when the oxidation-reduction potential measured in the measurement step is equal to or greater than a predetermined value.

  In order to solve the above problems, a wastewater treatment apparatus according to the first aspect of the present invention includes a denitrification tank that reduces nitrogen oxides contained in nitrogen-containing wastewater, and a redox near the most downstream position of the denitrification tank. Measuring means for measuring the potential, and organic substance adding means for adding an organic substance into the denitrification tank when the oxidation-reduction potential measured by the measuring means is a predetermined value or more.

In order to solve the above problems, a wastewater treatment method according to a second aspect of the present invention includes a nitrification step of nitrifying ammonia nitrogen in nitrogen-containing wastewater in an aerobic tank, and a downstream side of the aerobic tank. A solid-liquid separation step for solid-liquid separation of the nitrogen-containing wastewater that has been nitrified in the settling tank, and a return step for returning a part of the sludge generated by the solid-liquid separation step to the aerobic tank via a return path And a measurement step for measuring the oxidation-reduction potential in the return path , and an organic substance addition step for adding an organic substance in the return path when the oxidation-reduction potential measured in the measurement step is a predetermined value or more. Including. Further, the waste water treatment method according to another example of the second aspect of the present invention includes a nitrification step for nitrifying ammonia nitrogen in nitrogen-containing waste water in an aerobic tank, and a precipitation located downstream of the aerobic tank. A solid-liquid separation step for solid-liquid separation of the nitrogen-containing wastewater that has been nitrified in the tank; a return step for returning a part of the sludge generated by the solid-liquid separation step to the aerobic tank via a return path; A measurement step of measuring the oxidation-reduction potential in the precipitation tank; and an organic substance addition step of adding an organic substance into the precipitation tank when the oxidation-reduction potential measured in the measurement step is a predetermined value or more.

In order to solve the above problems, a wastewater treatment apparatus according to a second aspect of the present invention is an aerobic tank for nitrifying ammonia nitrogen in nitrogen-containing wastewater, and is located downstream of the aerobic tank, and is nitrified. oxidation of but a sedimentation tank for the nitrogen-containing wastewater to solid-liquid separation was complete, solid-liquid and return path for a part of the sludge produced by the separation is returned to the aerobic tank, said return path or the settling tank Measuring means for measuring the reduction potential , and organic substance adding means for adding an organic substance into the return path when the oxidation-reduction potential measured by the measuring means is a predetermined value or more. Further, a wastewater treatment apparatus according to another example of the second aspect of the present invention is located in an aerobic tank for nitrifying ammonia nitrogen in nitrogen-containing wastewater, and downstream of the aerobic tank, and nitrification is completed. A precipitation tank for solid-liquid separation of the nitrogen-containing wastewater, a return path for returning a part of sludge generated by solid-liquid separation to the aerobic tank, and a measuring means for measuring the oxidation-reduction potential in the precipitation tank; And an organic substance addition means for adding an organic substance into the precipitation tank when the oxidation-reduction potential measured by the measurement means is equal to or greater than a predetermined value.

  According to the waste water treatment method and waste water treatment apparatus according to the present invention, the amount of nitrous oxide generated and the amount of volatilization can be reduced.

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 an explanatory diagram showing the relationship between the ORP value and the progress of the denitrification reaction in the denitrification tank. FIG. 3 is a schematic diagram showing a configuration of a modified example of the waste water treatment apparatus according to the first embodiment of the present invention. FIG. 4 is a schematic view showing a configuration of a waste water treatment apparatus according to the second embodiment of the present invention. FIG. 5 is a schematic diagram showing the internal configuration of the return path. FIG. 6 is an explanatory diagram showing the relationship between the ORP value and the progress of the denitrification reaction in the return path. FIG. 7 is a schematic diagram illustrating a modified example of the internal configuration of the return path. FIG. 8 is a schematic diagram showing a modification of the internal configuration of the return path. FIG. 9 is a schematic diagram showing a modification of the internal configuration of the return path.

  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, with reference to FIG. 1 thru | or FIG. 3, the waste water treatment apparatus which is the 1st Embodiment of this invention, and its waste water treatment method are demonstrated.

  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, and an aerobic (nitrification) tank 6 arranged along the flow direction of nitrogen-containing wastewater. , And a solid-liquid separation tank (precipitation tank) 10 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 as a result of the nitrification solution in the aerobic tank 6 being 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. 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.

  An ORP meter 24 for measuring the oxidation-reduction potential (ORP value) of the nitrogen-containing wastewater is provided at the tank end position (the position near the most downstream) 4a of the denitrification tank 4, that is, the position immediately before reaching the aerobic tank 6. Yes. On the upstream side of the denitrification tank 4, there is provided an organic substance addition means 26 for adding organic substances stored in a storage tank (not shown) to the upstream side of the denitrification tank 4. Examples of the organic substance added by the organic substance adding means 26 include alcohols such as methanol and ethanol, volatile fatty acids such as acetic acid, and easily degradable carbohydrates such as glucose.

  The organic substance addition means 26 may add nitrogen-containing wastewater as an organic substance to the upstream side of the denitrification tank 4. In this case, for example, it is necessary to guide the nitrogen-containing wastewater before flowing into the anaerobic tank 2 to the organic substance adding means 26 by the branch path V indicated by a virtual line in FIG. The organic substance adding means 26 includes a flow rate adjusting valve capable of adjusting the flow rate of the organic substance in accordance with the content of the control command D2 from the computer 28. The ORP meter 24 and the organic substance adding means 26 are connected to a computer 28.

  The aerobic tank 6 is a tank that is arranged on the downstream side of the denitrification tank 4 and into which treated water that has flowed out of the denitrification tank 4 flows. At the bottom of the aerobic tank 6, an air diffuser 16 for supplying air to the stored treated water is provided. The amount of air diffused by the air diffuser 16 is controlled by the controller 22. The controller 22 includes a blower 20 and a flow rate adjustment valve (not shown), and adjusts the amount of air diffused by the air diffuser 16 in accordance with a control command from the computer 28. In the aerobic tank 6, the air diffused by the air diffuser 16 is sufficiently performed, and the treated water is nitrified by the action of nitrifying bacteria in an environment where the dissolved oxygen concentration is high.

  The solid-liquid separation tank 10 is located on the downstream side of the aerobic tank 6 and is a tank into which treated water that has flowed out of the aerobic 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 includes an arithmetic processing unit and a memory (not shown) inside, and data of a critical ORP value Dc as a predetermined critical value is stored in the memory. The computer 28 has a function of receiving the ORP value D1 from the ORP meter 24 and comparing the ORP value D1 with the critical ORP value Dc in the memory. The computer 28 has a function of sending a control command D2 for causing the organic material adding means 26 to execute control for increasing or decreasing the amount of organic material added (including addition start / addition stop). When the ORP value D1 is greater than or equal to the critical ORP value Dc, the computer 28 sends a control command D2 for increasing the amount of organic matter added to the organic matter adding means 26.

  FIG. 2 is a diagram showing the relationship between the ORP value D1 and the progress of the denitrification reaction (chemical reaction formulas (9) to (12)) in the denitrification tank 4. When the ORP value D1 is about -180 mV, the denitrification reaction does not proceed until the chemical reaction formula (10) in the denitrification tank 4, and when the ORP value D1 is about -200 mV, the chemical reaction formula (11 It can be seen that the denitrification reaction proceeds only up to the formula. For this reason, in this state, nitrous oxide is produced in a large amount without being decomposed to nitrogen. On the other hand, when the ORP value D1 decreases to about −220 mV or less, the denitrification reaction proceeds sufficiently to the chemical reaction formula (12), and the decomposition of nitrous oxide into nitrogen can be promoted. As a result, the amount of nitrous oxide generated can be reduced.

  From the above, in this embodiment, the critical ORP value Dc in the memory is set to −220 mV, and the computer 28 outputs the control command D2 for increasing the amount of organic matter added when the ORP value D1 exceeds −220 mV. Send it out. When the amount of organic matter added to the denitrification tank 4 increases, the activity of denitrifying bacteria (nitrate reducing bacteria) in the denitrifying tank 4 becomes active, the denitrification reaction is promoted, and the generation amount of nitrous oxide is reduced. The ORP value D1 decreases. Thereby, the generation amount and volatilization amount of nitrous oxide can be reduced. In addition, the value of the critical ORP value Dc is a value that changes according to the quality of the raw water such as the organic substance concentration, and is not limited to -220 mV.

  As is apparent from the above description, the waste water treatment apparatus according to one embodiment of the present invention measures the ORP value D1 in the vicinity of the most downstream position of the denitrification tank 4, and the measured ORP value D1 is equal to or greater than the critical ORP value Dc. In this case, an organic substance is added into the denitrification tank 4. When the amount of organic matter added to the denitrification tank 4 increases, the activity of denitrifying bacteria in the denitrification tank 4 becomes active, the denitrification reaction is promoted, the amount of nitrous oxide generated is reduced, and the ORP value D1 decreases. . Thereby, the generation amount and volatilization amount of nitrous oxide can be reduced.

[Modification]
FIG. 3 is a schematic diagram showing a configuration of a modified example of the waste water treatment apparatus according to the first embodiment of the present invention. As shown in FIG. 3, in this modification, a circulation pump 9 that circulates the nitrification liquid to the denitrification tank 4 and an ORP meter 24 are connected to a computer 28. In this modification, the computer 28 sends a control command D2 for increasing / decreasing the circulation amount of the nitrating liquid to the circulation pump 9 according to the comparison result between the ORP value D1 and the critical ORP value Dc. Specifically, when the ORP value D1 is equal to or higher than the critical ORP value Dc, the computer 28 sends a control command D2 for reducing the circulation amount of the nitrification liquid to the circulation pump 9. By reducing the circulation amount of the nitrification liquid, the inflow amount of the nitrification liquid into the denitrification tank 4 is reduced, and the dissolved oxygen amount in the denitrification tank 4 is reduced. As a result, the denitrification reaction is promoted, and the amount of nitrous oxide generated can be reduced.

  Even if the computer 28 controls not a circulating pump 9 but a flow rate adjusting valve (not shown) provided separately in the middle of the circulation path 8, the same effect can be realized. In this modification, the computer 28 and the circulation pump 9 are connected to adjust the circulation amount of the nitrification liquid, but the computer 28 and a sludge return pump (not shown) are adjusted to adjust the return amount of the sludge from the solid-liquid separation tank 10. And may be connected to each other. When the ORP value D1 is equal to or greater than the critical ORP value Dc, the same effect can be realized even if the computer 28 performs control to reduce the sludge return amount. In addition, the organic substance addition amount adjustment described in the first embodiment, the circulation amount adjustment and the sludge return amount adjustment described in the present modification may employ any one method, or a plurality of these methods. Of course, a combination of these methods may be adopted.

  In the said 1st Embodiment and modification, although the waste water treatment apparatus which implement | achieves A2O method which has an anaerobic tank, an anaerobic tank, and an aerobic tank was demonstrated, the range which can apply this invention is to the apparatus which concerns on A2O method. It is not limited. That is, the present invention can be applied to any wastewater treatment apparatus having a denitrification tank having a denitrification function and an aerobic tank having a nitrification function. The present invention can also be applied to a wastewater treatment apparatus according to the AO method that includes an anaerobic tank and an aerobic tank. That is, the ORP value in the position near the most downstream of the anaerobic tank is measured, and when the ORP value exceeds a predetermined critical value, the amount of organic matter added to the anaerobic tank by the organic matter adding means is increased, The amount of nitrous oxide generated can be reduced. Of course, in this case, the ORP meter is installed at the tank end position of the anaerobic tank, and the organic substance adding means is configured to be able to add the organic substance toward the relatively upstream side of the anaerobic tank. In addition, the circulation path from the aerobic tank is also configured to be able to circulate waste water toward a relatively upstream side of the anaerobic tank.

[Second Embodiment]
Next, with reference to FIG. 4 thru | or FIG. 9, the waste water treatment apparatus which is the 2nd Embodiment of this invention, and its waste water treatment method are demonstrated.

FIG. 4 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. 4, the wastewater treatment apparatus S according to the second embodiment of the present invention includes an aerobic tank 102, a solid-liquid separation tank ( precipitation tank ) 110, a return path 112, an ORP meter 124, and an organic substance addition unit 122. , And a computer 128 as main components.

  The aerobic tank 102 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. A diffuser 126 for supplying air to the stored treated water is provided at the bottom of the aerobic tank 102. In the aerobic tank 102, aeration by the aeration device 126 is sufficiently performed, and nitrification of the nitrogen-containing wastewater is performed by the action of nitrifying bacteria in an environment where the dissolved oxygen concentration is high.

  The solid-liquid separation tank 110 is located on the downstream side of the aerobic tank 102 and is a tank into which treated water flowing out from the aerobic tank 102 flows. The solid-liquid separation tank 110 is for solid-liquid separation of treated water that has undergone biological treatment. In the solid-liquid separation tank 110, 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 upstream side of the aerobic tank 102 via the return path 112, and the biomass in the aerobic tank 102 is maintained.

The remaining sludge generated by the solid-liquid separation is discharged out of the apparatus through the discharge pipe 114 as excess sludge. In the present embodiment, the sludge is returned from the solid-liquid separation tank 110 to the aerobic tank 102 through the return path 112, but the sludge floating or partially settled in the aerobic tank 102 is returned to the aerobic tank. You may comprise so that it may return from the downstream of 102 to the upstream of the aerobic tank 102. In the configuration in which the waste water treatment apparatus S includes a plurality of aerobic tanks 102, sludge may be returned from the aerobic tank on the downstream side to the aerobic tank on the upstream side.

FIG. 5 is a schematic diagram showing the internal configuration of the return path 112. An organic substance adding means 122 is installed on the upstream side of the return path 1 1 2. The organic substance addition means 122 adds an organic substance to the sludge returned via the return path 1 1 2. The organic substance addition means 122 is connected to the computer 128 and adjusts the addition amount of the organic substance based on a control command D2 from the computer 128. Examples of the organic substance added by the organic substance adding means 122 include alcohols such as methanol and ethanol, volatile fatty acids such as acetic acid, and easily degradable carbohydrates such as glucose. Moreover, the organic substance addition means 122 may add nitrogen-containing waste water as an organic substance. In this case, it is necessary to guide the nitrogen-containing wastewater before flowing into the aerobic tank 102 to the organic substance adding means 122 by, for example, the branch path V indicated by a virtual line in FIG.

  A screw 113 is installed at a position downstream of the organic substance addition means 122 in the return path 112. The screw 113 stirs the organic matter added by the organic matter addition means 122 and the sludge. By stirring the organic matter and the sludge, the contact opportunity between the denitrifying bacteria and the organic matter can be increased, and the denitrification reaction can proceed efficiently. In addition, you may stir organic substance and sludge using a diffuser instead of the screw 113. FIG.

  An ORP meter 124 is installed at a position 112 a downstream of the screw 113 in the return path 112. The ORP meter 124 is for measuring the oxidation-reduction potential (ORP value) D1 of the sludge returned through the return path 112. The ORP meter 124 is connected to the computer 128 and sends the measured ORP value D1 to the computer 128. By installing the ORP meter 124 at a position downstream of the screw 113, the ORP value D1 can be measured after the sludge and the organic matter are sufficiently stirred.

  In the present embodiment, the ORP meter 124 is installed at the downstream position 112a of the return path 112, and the organic substance adding unit 122 is installed on the upstream side thereof. However, the ORP meter 124 and the organic substance adding unit 122 are installed in the solid-liquid separation tank 110. May be. However, when adding an organic substance in the solid-liquid separation tank 110, it is desirable to add it near the sludge interface so as not to disturb the tank flow.

  The computer 128 includes an arithmetic processing unit and a memory (not shown) therein, and data of a critical ORP value Dc1 as a predetermined critical value is stored in the memory. The computer 128 has a function of receiving the ORP value D1 from the ORP meter 124 and comparing the ORP value D1 with the critical ORP value Dc1 in the memory. The computer 128 has a function of sending a control command D2 for executing control for increasing or decreasing the amount of organic substance added (including addition start / stop of addition) to the organic substance addition means 122. When the ORP value D1 is equal to or greater than the critical ORP value Dc1, the computer 128 sends a control command D2 for increasing the amount of organic matter added to the organic matter adding means 122.

  FIG. 6 is a diagram showing the relationship between the ORP value D1 and the progress of the denitrification reaction (chemical reaction formulas (9) to (12)) in the return path 112. When the ORP value D1 is about +50 mV, the denitrification reaction does not proceed only up to the chemical reaction formula (10) in the return path 112, and when the ORP value D1 is about −50 mV, the chemical reaction formula (11) It can be seen that the denitrification reaction proceeds only up to the formula. For this reason, in this state, nitrous oxide is produced in a large amount without being decomposed to nitrogen. On the other hand, when the ORP value D1 is lowered to about −100 mV or less, the denitrification reaction proceeds sufficiently to the chemical reaction formula (12), and the decomposition of nitrous oxide into nitrogen can be promoted. As a result, the amount of nitrous oxide generated can be reduced.

  From the above, in this embodiment, the critical ORP value Dc1 in the memory is set to −100 mV, and the computer 128 outputs the control command D2 for increasing the amount of organic matter added when the ORP value D1 exceeds −100 mV. Send it out. When the amount of organic matter added to the return path 112 increases, the activity of denitrifying bacteria (nitrate-reducing bacteria) in the return path 112 becomes active, the denitrification reaction is promoted, and the amount of nitrous oxide generated is reduced. The ORP value D1 decreases. Moreover, the dissolved nitrous oxide concentration of sludge can be reduced, and even when the sludge is returned to the aerobic tank 102, the amount of nitrous oxide volatilized from the aerobic tank 102 can be reduced. Thereby, the generation amount and volatilization amount of nitrous oxide can be reduced. In addition, the value of the critical ORP value Dc1 is a value that changes according to the quality of the raw water such as the organic substance concentration, and is not limited to −100 mV.

  As is clear from the above description, the waste water treatment apparatus S according to the second embodiment of the present invention measures the ORP value D1 in the return path 112, and the measured ORP value D1 is equal to or higher than the critical ORP value Dc1. In some cases, organic matter is added into the return path 112. When the amount of organic substances added to the return path 112 increases, the activity of denitrifying bacteria in the return path 112 becomes active, the denitrification reaction is promoted, the amount of nitrous oxide generated is reduced, and the ORP value D1 decreases. To do. Moreover, the dissolved nitrous oxide concentration of sludge can be reduced, and even when the sludge is returned to the aerobic tank 102, the amount of nitrous oxide volatilized from the aerobic tank 102 can be reduced. Thereby, the generation amount and volatilization amount of nitrous oxide can be reduced.

[Modification]
FIG. 7 is a schematic diagram illustrating a modified example of the internal configuration of the return path 112. In this modification, the return path 112 has a reaction chamber 104 in the middle of the path. An ORP meter 124 and a screw 113 are installed in the reaction chamber 104, and the organic substance adding means 122 is configured to add an organic substance into the reaction chamber 104. As described above, the reaction chamber 104 is arranged in the middle of the path, and the ORP value D1, the addition of organic substances, and the agitation are performed inside the reaction chamber 104. Thus, more accurate feedback control and more efficient denitrification reaction are promoted. Can be realized. The ORP meter 124 is desirably disposed at a downstream position in the reaction chamber 104, and may be disposed in the return path 112 downstream from the reaction chamber 104 as necessary.

  FIG. 8 is a schematic diagram showing a modification of the internal configuration of the return path 112. In this modification, the return path 112 is formed in a spiral shape. According to such a configuration, the shape of the return path 112 itself functions as a stirring means without the need for the screw 113. FIG. 9 is a schematic diagram illustrating a modified example of the internal configuration of the return path 112. In this modification, the return path 112 is formed in a generally bellows shape so that the cross section of the return path 112 changes in the length direction. According to such a configuration, the flow rate of the sludge moving in the return path 112 can be changed, and the shape of the return path 112 itself can function as a stirring means without the need for the screw 113. become. Also in the configuration shown in FIG. 8 or FIG. 9, the arrangement position of the ORP meter 124 is preferably a position after the added organic matter and the return sludge are sufficiently stirred, and is the downstream position in the return path 112. Good.

  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 Denitrification tank 4a Tank end position (nearest downstream position)
6 Aerobic (nitrification) tank 8 Circulation route 9 Circulation pump 10 Solid-liquid separation tank (precipitation tank)
DESCRIPTION OF SYMBOLS 12 Return route 14 Drain pipe 16 Air diffuser 20 Blower 22 Controller 24 ORP meter 26 Organic substance addition means 28 Computer 102 Aerobic (nitrification) tank 104 Reaction chamber 110 Solid-liquid separation tank (precipitation tank)
112 Return path 112a Downstream position 113 Screw 114 Discharge pipe 122 Organic substance addition means 124 ORP meter 126 Aeration device 128 Computer S Biological treatment device V Branch path

Claims (7)

A nitrification step for nitrifying ammonia nitrogen in the nitrogen-containing wastewater in an aerobic tank;
A solid-liquid separation step for solid-liquid separation of nitrogen-containing wastewater that has been nitrified in a precipitation tank located downstream of the aerobic tank;
A return step of returning a part of the sludge generated by the solid-liquid separation step to the aerobic tank via a return path;
A measuring step for measuring an oxidation-reduction potential in the return path;
If the redox potential measured by the measuring step is a predetermined value or more, and an organic material added step of adding an organic substance into the return path,
The waste water treatment method characterized by including. The measurement step is a step of measuring an oxidation-reduction potential in a reaction chamber provided in the return path, and the organic substance addition step is a step of adding an organic substance in the reaction chamber. Item 2. A wastewater treatment method according to Item 1. A nitrification step for nitrifying ammonia nitrogen in the nitrogen-containing wastewater in an aerobic tank;
A solid-liquid separation step for solid-liquid separation of nitrogen-containing wastewater that has been nitrified in a precipitation tank located downstream of the aerobic tank;
A return step of returning a part of the sludge generated by the solid-liquid separation step to the aerobic tank via a return path ;
A step of measuring the redox potential before Symbol settling tank,
If the redox potential measured by the measuring step is a predetermined value or more, and an organic material added step of adding an organic substance before Symbol settling tank,
The waste water treatment method characterized by including. The waste water treatment method according to any one of claims 1 to 3, further comprising a stirring step of stirring the sludge and the added organic matter. An aerobic tank that nitrifies ammoniacal nitrogen in nitrogen-containing wastewater;
A settling tank in which the located downstream of the aerobic tank, solid-liquid separating nitrogen-containing waste water nitrification is complete,
A return path for returning a part of the sludge generated by solid-liquid separation to the aerobic tank;
Measuring means for measuring the oxidation-reduction potential in the return path;
If the redox potential measured by the measuring means is a predetermined value or more, and an organic additive means for adding an organic substance into the return path,
A wastewater treatment apparatus comprising: A reaction chamber is provided in the middle of the return path, the measuring means is provided in the reaction chamber, and the organic substance adding means is configured to add the organic substance into the reaction chamber. The waste water treatment apparatus according to claim 5. An aerobic tank that nitrifies ammoniacal nitrogen in nitrogen-containing wastewater;
A precipitation tank located on the downstream side of the aerobic tank for solid-liquid separation of the nitrogen-containing wastewater that has been nitrified;
A return path for returning a part of the sludge generated by solid-liquid separation to the aerobic tank ;
Measuring means for measuring the redox potential before Symbol settling tank,
If oxidation-reduction potential measured by the measuring means is a predetermined value or more, and an organic additive means for adding an organic substance before Symbol settling tank,
A wastewater treatment apparatus comprising:

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