JP6422639B2 - Waste water treatment device, waste water treatment method, waste water treatment system, control device, and program - Google Patents

Description

  The present invention relates to a wastewater treatment device, a wastewater treatment method, a wastewater treatment system, a control device, a control method, and a program for controlling the amount of aeration air in an aerobic tank in combined sewage treatment.

  Conventionally, as a sewage treatment system for treating sewage such as domestic wastewater or factory effluent, various sewage treatment systems such as those using a standard activated sludge method and those using a trickling filter method have been put into practical use.

  In the sewage treatment system based on the standard activated sludge method, aeration treatment is performed in which oxygen is supplied to various types of aerobic microorganisms existing in the reaction tank while flowing the sewage to be treated into the reaction tank. As a result, the organic matter contained in the sewage in the reaction tank is decomposed by the action of the aerobic microorganism, and a stable treated water quality is obtained.

In the aeration process in the reaction tank, inflow water proportional control, DO (dissolved oxygen) control, or ammonia control (see Patent Document 1) is performed on the diffuser that performs aeration. The inflow water proportional control is a control for supplying an amount of air proportional to the amount of inflow water flowing into the reaction tank to the air diffuser using a flow meter installed on the inflow side of the reaction tank. The DO control measures the dissolved oxygen concentration using a dissolved oxygen meter (DO meter) installed at the end on the outflow side of the reaction tank, and supplies air to the air diffuser so as to maintain this dissolved oxygen concentration at a predetermined concentration. This is the supply control. Ammonia control uses an ammonia meter installed at the end on the outflow side of the reaction tank to supply air to the diffuser so that ammonia nitrogen (NH ₄ -N) at the end of the reaction tank is maintained at a predetermined concentration. It is control to do.

JP 2005-199116 A

  However, the various controls described above have the following problems. That is, in the influent water proportional control, the organic matter load and ammonia load of the influent water containing nitrogen changes, and the water quality fluctuates. Therefore, if the air amount is controlled in proportion to the influent water amount, excess or deficiency of the air amount occurs. End up. In addition, in the DO control, the organic load and ammonia load of the inflowing water containing nitrogen change, and when these loads decrease, the air volume tends to become excessive, and conversely, when the load increases, the air volume is insufficient. It becomes easy to do. In addition, in the ammonia control, an appropriate amount of air can be supplied to the aeration device according to the ammonia load of the inflowing water containing nitrogen, but on the other hand, it is possible to control the denitrification process in the previous stage of performing ammonia control. It was difficult.

  Furthermore, when biological treatment using activated sludge is performed in a combined sewage treatment plant, it is necessary to consider a significant increase in influent water during rainy weather. That is, when the amount of inflow water increases during rainy weather, the nitrogen concentration in the inflow water rapidly decreases, so that the amount of air supplied to the reaction tank becomes excessive and the nitrogen removal rate may decrease.

  The present invention has been made in view of the above, and its purpose is to increase the amount of inflow water during rainy weather in a combined sewage treatment plant, and the amount of nitrogen-containing water flowing into the reaction tank has changed abruptly. Even in this case, it is possible to supply an appropriate amount of oxygen to the reaction tank, to appropriately control the denitrification treatment, and to improve the quality of treated water by improving the nitrogen removal rate. A treatment apparatus, a wastewater treatment method, a wastewater treatment system, a control apparatus, a control method, and a program are provided.

  In order to solve the above-described problems and achieve the above object, the wastewater treatment apparatus according to the present invention is configured such that ammonia contained in nitrogen-containing water is nitrified into nitric acid in accordance with the flow of nitrogen-containing water in the reaction tank, and contains nitrogen. Aeration means for supplying gas over substantially the entire area in the flow direction to the nitrogen-containing water so that each desired ratio of nitric acid is denitrified at each position along the water flow direction, and the flow of nitrogen-containing water In order to obtain the final required nitrification water quality downstream of the upstream denitrification section and the upstream denitrification section where the nitrification reaction for obtaining the minimum necessary denitrification amount along the direction can occur Denitrification confirmation means for confirming the denitrification state provided at a midway position between the downstream nitrification section where denitrification reaction can occur and whether or not a desired ratio of nitric acid is denitrified at the midway position; , Provided upstream of the denitrification confirmation means, Ammonia concentration measuring means configured to be able to measure the ammonia concentration of the contained water, and a desired ratio of nitric acid at the midpoint based on the ammonia concentration measured by the ammonia concentration measuring means, and the specified desired ratio of nitric acid Denitrification confirmation along the flow direction of nitrogen-containing water so that nitric acid is denitrified at the desired ratio of nitric acid specified in the middle position based on the denitrification state confirmed by the denitrification confirmation means Gas supply amount control means for controlling the gas supply amount by the air diffusion means at least upstream from the means.

  The wastewater treatment apparatus according to the present invention is characterized in that, in the above invention, the ammonia concentration measuring means is installed in the vicinity of the inflow side of the nitrogen-containing water in the reaction tank.

  The wastewater treatment apparatus according to the present invention is the wastewater treatment apparatus according to the above invention, wherein the aeration means sequentially performs a region where the nitrification reaction is performed and a region where the denitrification reaction is performed according to the passage of time or the flow direction of the nitrogen-containing water. It is characterized by being able to supply gas so as to be alternately or repeatedly formed.

  The wastewater treatment apparatus according to the present invention is the above-described invention, wherein the gas supply amount control means contains nitrogen when the denitrification confirmation means cannot confirm the desired ratio of denitrification with respect to nitric acid generated by nitrification by the nitrification reaction. The flow rate of the gas supplied from the air diffuser at least upstream of the denitrification confirming unit is controlled to increase or decrease along the water flow direction.

  In the waste water treatment apparatus according to the present invention, in the above invention, the denitrification confirmation unit is a nitric acid concentration measurement unit configured to be capable of measuring a nitric acid concentration, and whether or not a desired ratio of nitric acid is denitrified. The confirmation is performed by measuring the nitric acid concentration, and the gas supply amount control means sets the control concentration range in the nitric acid concentration based on the ammonia concentration measured by the ammonia concentration measuring means, and is measured by the nitric acid concentration measuring means. Controlling the aeration means so that the concentration of nitric acid is within the control concentration range, and controlling the amount of gas supplied from the aeration means upstream of the nitric acid concentration measurement means along at least the flow direction of the nitrogen-containing water. Features. In this configuration, the wastewater treatment apparatus according to the present invention is configured so that the gas supply amount control means supplies the gas so that the nitric acid concentration is not less than 3% and not more than 20% of the ammonia concentration measured by the ammonia concentration measuring means. It is configured to control the amount.

  The wastewater treatment apparatus according to the present invention is the waste water treatment apparatus according to the above invention, wherein the gas supply amount control means moves the air diffusion means from the air diffusion means at least upstream from the denitrification confirmation means along the flow direction of the nitrogen-containing water. The gas supply amount is controlled so as to be substantially uniform.

  The wastewater treatment method according to the present invention includes a biological treatment step for performing biological treatment by nitrification reaction and denitrification reaction on nitrogen-containing water flowing in a reaction tank, and ammonia contained in nitrogen-containing water according to the flow of nitrogen-containing water. Aeration to supply gas to the nitrogen-containing water over almost the entire flow direction so that each desired proportion of nitric acid is denitrified at each position along the flow direction of the nitrogen-containing water. A step, an upstream denitrification section in which a nitrification reaction for obtaining a minimum amount of denitrification nitrogen along the flow direction of the nitrogen-containing water can occur, and a final downstream following the upstream denitrification section Denitrification to confirm whether or not the desired proportion of nitric acid has been denitrified at an intermediate position between the downstream nitrification section where denitrification reaction for obtaining the nitrification water quality necessary for the reaction can occur Confirmation step and in reaction tank The ammonia concentration measuring step for measuring the ammonia concentration at a position upstream from the middle position along the flow direction of the nitrogen-containing water, and the desired ratio of nitric acid is defined based on the ammonia concentration measured in the ammonia concentration measuring step In addition, based on the desired ratio of the specified nitric acid and the denitrification state confirmed in the denitrification confirmation step, the nitrogen-containing water is denitrified at the midpoint at the desired ratio of the specified nitric acid. A gas supply amount control step for controlling a gas supply amount at least upstream from the midway position along the flow direction.

  The wastewater treatment method according to the present invention is characterized in that, in the above-described invention, the ammonia concentration is measured at a position near the inflow side of the nitrogen-containing water in the reaction tank in the ammonia concentration measurement step.

  According to the wastewater treatment method of the present invention, in the above-described invention, the region where the nitrification reaction is performed and the region where the denitrification reaction is performed are sequentially, alternately or repeatedly according to the passage of time or the flow direction of the nitrogen-containing water. A gas is supplied to the nitrogen-containing water so as to be formed.

  In the wastewater treatment method according to the present invention, in the above-described invention, the denitrification state confirmed in the denitrification confirmation step is a nitric acid concentration at an intermediate position, and in the gas supply amount control step, the nitric acid concentration is an ammonia concentration measurement step. Characterized in that the gas supply amount is controlled at least upstream along the flow direction of nitrogen-containing water from an intermediate position in a direction falling within a set concentration range of nitric acid concentration set based on the ammonia concentration measured in To do.

  In the wastewater treatment method according to the present invention, in the above invention, in the gas supply amount control step, the nitric acid concentration is not less than 3% and not more than 20% of the ammonia concentration measured in the ammonia concentration measurement step. The supply amount of gas is controlled.

  The wastewater treatment system according to the present invention includes an upstream denitrification section that can also undergo a nitrification reaction for obtaining a minimum amount of denitrification nitrogen along the flow direction of nitrogen-containing water, and an upstream denitrification section. Ammonia contained in the nitrogen-containing water according to the flow direction is provided at an intermediate position between the downstream nitrification section where the denitrification reaction for obtaining the finally required nitrified water quality following the downstream side can also occur. Nitrogen-containing nitric acid, and nitrogen-containing water to which gas is supplied over almost the entire area in the flow direction so that each desired ratio of nitric acid is denitrified at each position along the flow direction, the concentration of nitric acid at the intermediate position A denitrification confirmation means for confirming the denitrification state of whether or not a desired ratio has been denitrified, and an ammonia concentration measurement provided upstream of the denitrification confirmation means and capable of measuring the ammonia concentration of nitrogen-containing water Means and ammo A denitrification state is defined on the basis of the ammonia concentration measured by the concentration measuring means, and nitric acid is detected at an intermediate position based on the desired ratio of the specified nitric acid and the denitrification state confirmed by the denitrification confirmation means. A gas supply amount that controls the supply amount of the gas supplied to the nitrogen-containing water at least upstream from the denitrification confirmation means along the flow direction of the nitrogen-containing water so that it is denitrified at the desired ratio of the specified nitric acid. And a control means.

  The control device according to the present invention is such that ammonia contained in nitrogen-containing water is nitrified into nitric acid according to the flow of nitrogen-containing water, and each desired ratio of nitric acid is denitrified at each position along the flow direction of nitrogen-containing water. Nitrogen-containing reaction for supplying gas to the nitrogen-containing water over almost the entire flow direction also causes a nitrification reaction to obtain the minimum amount of denitrified nitrogen along the flow direction of the nitrogen-containing water. Provided at an intermediate position between the upstream denitrification section and the downstream nitrification section that can also undergo the denitrification reaction to obtain the final required nitrification water quality downstream of the upstream denitrification section. The denitrification state is confirmed by the denitrification confirmation means that confirms the denitrification state whether or not the desired ratio of nitric acid is denitrified at the middle position, and denitrified along the flow direction of the nitrogen-containing water. Provided upstream from the confirmation means and contains nitrogen Based on the desired ratio of nitric acid at the intermediate position defined based on the ammonia concentration measured by the ammonia concentration measuring means configured to be capable of measuring the ammonia concentration of the nitric acid at the desired ratio of nitric acid at which the nitric acid is defined at the intermediate position The supply amount of the gas is controlled at least upstream from the denitrification confirmation means along the flow direction of the nitrogen-containing water so as to be denitrified.

  The control method according to the present invention is a control method by a control device that controls the amount of gas supplied to nitrogen-containing water, and the nitrification reaction for obtaining the minimum amount of denitrified nitrogen along the flow direction of nitrogen-containing water is also performed. At an intermediate position between a possible upstream denitrification section and a downstream nitrification section that can also undergo a denitrification reaction to obtain the final required nitrified water quality downstream of the upstream denitrification section In accordance with the flow direction, ammonia contained in the nitrogen-containing water is nitrified into nitric acid, and gas is supplied over substantially the entire region in the flow direction so that each desired proportion of nitric acid is denitrified at each position along the flow direction. A denitrification confirmation step for confirming whether or not a desired ratio of nitric acid has been denitrified with respect to the nitrogen-containing water, and a position upstream from a middle position along the flow direction of the nitrogen-containing water. Measure ammonia concentration The desired concentration of nitric acid based on the ammonia concentration measured in the ammonia concentration measurement step, and the desired ratio of nitric acid and the denitrification state confirmed in the denitrification confirmation step. Based on the supply amount of gas supplied to the nitrogen-containing water at least upstream from the intermediate position along the flow direction of the nitrogen-containing water, so that the nitric acid is denitrified at the desired ratio of the specified nitric acid at the intermediate position And a gas supply amount control step for controlling.

  The program according to the present invention includes an upstream denitrification section in which a nitrification reaction for obtaining a minimum amount of denitrification nitrogen along the flow direction of nitrogen-containing water can occur, and a downstream side of the upstream denitrification section. The ammonia contained in the nitrogen-containing water is nitrified into nitric acid according to the flow direction at a midway position between the downstream nitrification section where the denitrification reaction for obtaining the final required nitrified water quality can occur, and the flow Whether or not the desired ratio of nitric acid is denitrified with respect to nitrogen-containing water in which gas is supplied over substantially the entire flow direction so that each desired ratio of nitric acid is denitrified at each position along the direction In the denitrification confirmation step for confirming the denitrification state, the ammonia concentration measurement step for measuring the ammonia concentration at a position upstream from the midway position along the flow direction of the nitrogen-containing water, and the ammonia concentration measurement step The desired ratio of nitric acid is defined on the basis of the measured ammonia concentration, and nitric acid is defined in the middle position based on the desired ratio of nitric acid and the denitrification state confirmed in the denitrification confirmation step. A gas supply amount control step for controlling the supply amount of the gas supplied to the nitrogen-containing water at least upstream from the midway position along the flow direction of the nitrogen-containing water so as to be denitrified at a desired ratio of It is made to perform.

  According to the wastewater treatment apparatus, the wastewater treatment method, the wastewater treatment system, the control apparatus, the control method, and the program according to the present invention, the gas according to the load of nitrogen-containing water flowing into the reaction tank for aeration Since the supply amount can be appropriately controlled, the power consumption can be reduced while supplying an appropriate amount of oxygen to the reaction tank, and denitrification treatment can be performed even in an emergency when the quality of the raw water for treatment has changed significantly. It is possible to appropriately control, and it is possible to improve the treated water quality by improving the nitrogen removal rate.

FIG. 1 is a configuration diagram showing a wastewater treatment apparatus according to a first embodiment of the present invention. FIG. 2A is a plan view showing a reaction tank in the waste water treatment apparatus according to the first embodiment of the present invention. FIG. 2B is a plan view showing another modification of the reaction tank in the wastewater treatment apparatus according to the first embodiment of the present invention. FIG. 3 is a configuration diagram showing a modified example of the waste water treatment apparatus according to the first embodiment of the present invention. FIG. 4A shows NH ₄ —N, NO ₂ —N, and NO ₃ —N of Example 1 measured along the flow of water to be treated in the reaction tank in the wastewater treatment apparatus according to the first embodiment. It is a graph which shows each nitrogen concentration and total nitrogen concentration. FIG. 4B shows NH ₄ —N, NO ₂ —N, and NO ₃ —N according to Example 2 measured along the flow of water to be treated in the reaction tank in the wastewater treatment apparatus according to the first embodiment. It is a graph which shows each nitrogen concentration and total nitrogen concentration. FIG. 5 is a flowchart showing a wastewater treatment method according to the first embodiment of the present invention. FIG. 6 is a block diagram showing a wastewater treatment apparatus according to the second embodiment of the present invention. FIG. 7 is a perspective perspective view showing a reaction tank according to the third embodiment of the present invention. 8A is a cross-sectional view taken along the line AA in the reaction tank shown in FIG. 8B is a cross-sectional view taken along line BB in the reaction tank shown in FIG. FIG. 9A is a configuration diagram showing another modification of the reaction vessel according to the embodiment of the present invention. FIG. 9B is a configuration diagram showing another modification of the reaction vessel according to the embodiment of the present invention. FIG. 9C is a configuration diagram showing another modification of the reaction vessel according to the embodiment of the present invention. FIG. 9D is a timing chart showing the timing of aeration with the passage of time in the aeration unit in the reaction tank shown in FIG. 9C. FIG. 9E is a block diagram showing another modification of the reaction vessel according to the embodiment of the present invention. FIG. 9F is a schematic cross-sectional view of a carrier carrying microorganisms suspended in the reaction tank shown in FIG. 9E. FIG. 10A is a cross-sectional view at an installation position when a pair of DO meters is installed in the reaction tank shown in FIG. 7. FIG. 10B is a graph showing the dependency of the denitrification rate and nitrification rate on the dissolved oxygen concentration. FIG. 11A is a cross-sectional view at an installation position when a pair of ORP meters is installed in the reaction tank shown in FIG. 7. FIG. 11B is a graph showing the redox potential dependence of the denitrification rate and nitrification rate. FIG. 12A is a configuration diagram illustrating a case where an ammonia meter is installed in the wastewater treatment apparatus illustrated in FIG. 6. FIG. 12B shows each nitrogen of NH ₄ —N, NO ₂ —N, and NO ₃ —N measured along the flow of water to be treated in the reaction tank for explaining the target nitrification rate and the measured nitrification rate. It is a graph which shows a density | concentration and a total nitrogen concentration.

  Embodiments of the present invention will be described below with reference to the drawings. In all the drawings of the following embodiments, the same or corresponding parts are denoted by the same reference numerals. Further, the present invention is not limited to the embodiments described below.

(First embodiment)
(Configuration of wastewater treatment equipment)
First, the structure of the waste water treatment apparatus including the control device according to the first embodiment of the present invention will be described. 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 waste water treatment apparatus according to the first embodiment of the present invention includes an initial settling basin 1 and a plurality of aerobic tanks 2a, 2b, 2c, and 2d that are sequentially communicated (first tank to fourth tank). A reaction tank 2, a solid-liquid separation tank 3, a sludge return path 5, and a control unit 9.

  Nitrogen-containing raw water (hereinafter, raw water) flows into the first sedimentation basin 1. In the first settling basin 1, raw water is allowed to flow gently to deposit dust with relatively small particles.

  To-be-treated water that is nitrogen-containing water that has flowed out of the sedimentation tank 1 first flows into the reaction tank 2. A plurality of aerobic tanks 2a to 2d constituting the reaction tank 2 are arranged along the flow direction of the water to be treated. Here, a BOD oxidation region may be generated on the inflow side of the water to be treated in the reaction tank 2. Moreover, each of the aerobic tanks 2a to 2d includes air diffusers 6a, 6b, 6c, and 6d as air diffusers. The air diffusers 6a to 6d diffuse gas into the aerobic tanks 2a to 2d using a gas such as air supplied by the blower 8 to aerate the activated sludge inside the reaction tank 2. In each of the aerobic tanks 2a to 2d, ammonia nitrogen contained in the water to be treated is mainly nitrified into nitrite nitrogen and nitrate nitrogen under aerobic conditions. The aerobic tanks 2a to 2d provided with the respective air diffusers 6a to 6d may be arranged linearly, and are folded back halfway as shown in FIG. It is good also as a detour channel arranged in order.

  Moreover, as shown in FIG. 1, each of the air diffusers 6a to 6d is provided with gas supply amount control units 10a, 10b, 10c, and 10d as part of the gas supply amount control means constituting the control device. Yes. Each of the gas supply amount control units 10a to 10d is composed of an air flow rate control valve or the like, and each aerobic tank 2a according to a control signal from the control unit 9 as a part of the gas supply amount control means constituting the control device. The gas supply amount from the air diffusers 6a to 6d at ˜2d is controlled uniformly or individually.

  The control unit 9 as a control device includes, for example, a computer (PC) configured to include a CPU, a storage medium such as a ROM and a RAM, and a recording medium such as a hard disk. In the control unit 9, a predetermined program capable of executing a wastewater treatment method and a control method described later is stored in a recording medium. As will be described later, the control unit 9 outputs the control signal according to the stored program in response to the confirmation signal such as the measurement value data of the input nitric acid concentration, thereby allowing the gas supply amount control units 10a to 10d to operate. The amount of gas supplied from the air diffusers 6a to 6d is controlled.

  A nitric acid meter 7 as a denitrification confirmation means is provided at a desired position along the flow of the water to be treated in the reaction tank 2. This nitric acid meter 7 is a nitric acid concentration measuring means for measuring the nitric acid concentration of the water to be treated at a desired position for controlling denitrification. In this 1st Embodiment, the nitric acid meter 7 is installed in the outflow position of the aerobic tank 2b which is a substantially intermediate position of the reaction tank 2, for example. Here, the installation position of the nitric acid meter 7 can be set to a desired position, and it is used for controlling the denitrification reaction as will be described later, so that the desired water quality can be finally obtained by the denitrification reaction. And the upstream side from the position where the nitrification reaction can be sufficiently carried out inside the reaction tank 2 is desirable. Furthermore, the installation position of the nitric acid meter 7 can be determined based on the position dependency of the reaction tank 2 regarding the total nitrogen concentration, nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen measured in advance. .

  In this case, in consideration of controlling the denitrification reaction in the reaction tank 2, the nitric acid meter 7 has a minimum denitrification nitrogen amount that is a denitrification nitrogen amount capable of finally obtaining a desired water quality. It can be installed at a midway position between the upstream denitrification section for obtaining and the downstream nitrification section for obtaining the finally required nitrified water quality downstream of the upstream denitrification section. desirable. In other words, the nitric acid meter 7 needs to advance the denitrification reaction while suppressing the generation of nitric acid due to the nitrification reaction, for example, in the region where the denitrification reaction and the nitrification reaction coexist. It is more preferable to install in the vicinity of the most downstream side of the region in the reaction tank 2 where there is.

  Here, the “upstream denitrification section” can be defined as follows. That is, first, the reaction tank 2 is in an environmental state in which the amount of dissolved oxygen contained in the nitrogen-containing water gradually increases from the upstream side toward the downstream side. Therefore, assuming such an environmental state as a precondition, if it can be confirmed that the desired ratio of nitric acid is denitrified at a midway position in the flow direction of the nitrogen-containing water, the desired ratio of nitric acid upstream from this midway position It can be presumed that the section where is denitrified is continuously secured. Second, the amount of denitrified nitrogen that will be denitrified to the intermediate position described above as the length of the continuous section where the desired proportion of nitric acid is denitrified upstream from the intermediate position described above becomes longer. Is in an increasing relationship. Thirdly, the nitrogen gas released into the atmosphere by denitrification of the desired proportion of nitric acid is not dissolved again in the nitrogen-containing water. Therefore, the “upstream denitrification section” is a section in the reaction tank along the flow direction of the nitrogen-containing water determined in consideration of the above, and the denitrification confirmation installed at the position immediately after the section. Based on the denitrification state confirmed by the means, the minimum necessary denitrification is achieved when the gas supply amount by the aeration means is controlled so that the desired denitrification state upstream of the installation position is maintained. This is the section where the amount of nitrogen is obtained.

  Further, the “downstream nitrification section” is a section in the reaction tank along the flow direction of the nitrogen-containing water, and is in a denitrification state confirmed by the denitrification confirmation means installed at a position immediately before this section. Based on this, when the supply amount of the oxygen-containing gas from the air diffuser is controlled so that the desired denitrification state is maintained on the upstream side of the installation position of the denitrification confirmation unit, the flow from the upstream side to the downstream side is controlled. This is a section where it is expected that the water quality in the final nitrification state will be obtained in combination with the environmental condition in the reaction tank where the amount of dissolved oxygen contained in the nitrogen-containing water gradually increases.

  Further, an ammonia meter 11 as an ammonia concentration measuring means capable of measuring the ammonia concentration is provided upstream of the installation position of the nitric acid meter 7 along the flow of the water to be treated in the reaction tank 2. The ammonia meter 11 can be provided at any desired position as long as it is upstream of the nitric acid meter 7. In the first embodiment, it is important to measure the ammonia concentration when the load of the water to be treated is changed when the inflow amount of the water to be treated is greatly increased during rainy weather or the like. It is preferable to provide in the vicinity of the inflow side of the aerobic tank 2a which is the inflow side (inlet side) of the reaction tank 2 or in the vicinity of the inflow side outside the reaction tank 2. The ammonia meter 11 supplies the measured ammonia concentration value to the control unit 9.

  The controller 9 to which the ammonia concentration value measured by the ammonia meter 11 and the nitric acid concentration value measured by the nitric acid meter 7 are supplied controls the gas supply amount based on these ammonia concentration and nitric acid concentration values. A control signal is supplied to the units 10a to 10d to control the gas supply amount by the air diffusers 6a to 6d. That is, the gas supply amount control means is configured by the control unit 9 and the gas supply amount control units 10a to 10d. Details of the control by the control unit 9 will be described later. The control unit 9, the gas supply amount control unit 10, the nitric acid meter 7, and the ammonia meter 11 constitute a wastewater treatment system.

In this specification, nitric acid means nitric acid (HNO ₃ ), nitrous acid (HNO ₂ ), nitrate nitrogen (NO ₃ —N), nitrite nitrogen (NO ₂ —N), nitrate nitrogen and nitrous acid. It is a concept that includes NO _x that represents a collection of nitrogen and both nitric acid and nitrous acid. Further, in this specification, ammonia is a concept including ammonia and ammoniacal nitrogen. That is, in this specification, the nitric acid concentration is any one of nitric acid, nitrous acid, nitrate nitrogen, nitrite nitrogen, aggregation of nitrate nitrogen and nitrite nitrogen, and NO _x indicating both nitric acid and nitrite. The ammonia concentration may be any one of ammonia (NH ₃ ) and ammoniacal nitrogen (NH ₄ —N).

  Further, even when a plurality of aerobic tanks 2a to 2d constituting the reaction tank 2 are arranged in a folded manner as shown in FIG. 2A, the nitric acid meter 7 follows the flow of water to be treated in the reaction tank 2. It is provided at a desired position, for example, the outflow position of the aerobic tank 2b. In addition, the ammonia meter 11 is provided at a desired position upstream of the nitric acid meter 7 along the flow of water to be treated in the reaction tank 2, for example, an inflow position of the aerobic tank 2a. Details regarding the installation positions of the nitric acid meter 7 and the ammonia meter 11 will be described later.

  To-be-treated water that has flowed out of the most downstream aerobic tank 2d flows into the solid-liquid separation tank 3. In the solid-liquid separation tank 3, the water to be treated is separated into the separation liquid 4a and the activated sludge 4b. A pipe (not shown) is connected to the side wall of the solid-liquid separation tank 3, and the separation liquid 4a is sent to the disinfection process through this pipe. The sludge return path 5 is connected to the bottom of the solid-liquid separation tank 3 so that the activated sludge 4b deposited on the bottom of the solid-liquid separation tank 3 can be returned to the aerobic tank 2a. Thereby, the biomass in the aerobic tank 2a and the downstream aerobic tanks 2b, 2c, and 2d can be maintained at a predetermined amount.

(Gas supply control in wastewater treatment methods)
Next, a wastewater treatment method performed in the aerobic tanks 2a to 2d, a control method associated therewith, and a gas supply amount control by a program executed by the control unit 9 will be described. FIG. 5 is a flowchart showing the processing method according to the first embodiment.

In the wastewater treatment method performed in the aerobic tanks 2a to 2d, first, water to be treated from the first sedimentation basin 1 shown in FIG. 1 is sequentially sent from the aerobic tank 2a to the aerobic tank 2d. In each of the aerobic tanks 2a to 2d, ammonia nitrogen (NH ₄ -N) in the water to be treated is converted into the following reaction formula (1) by nitrifying bacteria that are aerobic microorganisms in activated sludge under aerobic conditions. ) To (3), and nitrified to nitrite nitrogen (NO ₂ —N) or nitrate nitrogen (NO ₃ —N) (step ST 1 and step ST 2 in FIG. 5).

NH ₃ + O ₂ + 2e ⁻ + 2H ⁺ → 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)

  On the other hand, in the reaction tank 2, an environment is formed in which the amount of dissolved oxygen contained in the nitrogen-containing water gradually increases from the upstream side toward the downstream side. Therefore, particularly in the upstream side of the reaction tank 2, there is a region where the amount of dissolved oxygen in the water to be treated is small. In such a region where the amount of oxygen in the water to be treated in the reaction tank 2 is small, or even in a nitrification tank or the like, a denitrification reaction (anaerobic reaction) due to denitrifying bacteria occurs because the amount of oxygen is small. Therefore, if a sufficient carbon source is supplied to a region where the denitrification reaction occurs (denitrification reaction region), the denitrification reaction can be sufficiently advanced. As a result, even in the reaction tank 2 which is an aerobic tank, a region where a partial denitrification reaction is performed occurs.

  Specifically, for example, when the reaction tank 2 is a deep-layer swirl reaction tank to be described later, a swirl flow is formed in a plane direction perpendicular to the overall flow direction of the water to be treated in the reaction tank 2. In this case, oxygen is supplied to the upper layer side in the reaction tank 2 that is upstream of the swirl flow, so that the dissolved oxygen increases. Therefore, oxygen is consumed on this upper layer side, and the reaction formulas (1) to (3) A nitrification reaction region where the nitrification reaction due to the above becomes relatively dominant is formed. On the other hand, the lower layer side in the reaction tank 2 on the downstream side of the swirl flow is inclined to an anaerobic state because oxygen is consumed on the upper layer side, so that the denitrification reaction increases. Thus, a denitrification reaction region is formed. Thereby, the state in which the nitrification reaction and the denitrification reaction coexist in the reaction tank 2 is obtained.

  Furthermore, specifically, for example, when the reaction tank 2 is a deep tank swirl reaction tank or a shallow tank reaction tank, the supply of oxygen to the water to be treated by the air diffuser may be varied over time or the supply area may be By dividing each section, the nitrification reaction area and the denitrification reaction area can coexist. That is, by changing the supply of oxygen over time or by dividing the supply region into sections, a state or region with a large amount of oxygen and a state or region with a small amount of oxygen are formed in the reaction tank 2, and the amount of oxygen is large. A nitrification reaction region is formed depending on the state and region, and a denitrification reaction region is formed depending on the state and region where oxygen is low. Thereby, the state in which the nitrification reaction and the denitrification reaction coexist in the reaction tank 2 is obtained.

Then, in the denitrifying reaction region of the reaction vessel 2 is aerobic tank, as in the following reaction formula (4) to (10), nitrous oxide generated by nitrification is insufficient (N ₂ O) Gas is decomposed or nitrous acid is reduced without generating nitrous oxide to decompose nitrogen and carbon dioxide to remove nitrogen.

NO ₂ ⁻ + 3H ⁺ + 2e ⁻ → 0.5N ₂ O + 1.5H ₂ O (4)
NO ₂ ⁻ + H ⁺ +2 (H) → 0.5N ₂ O + 1.5H ₂ O (5)
NO ₃ ⁻ + H ⁺ +5 (H) → 0.5N ₂ + 3H ₂ O (6)
NO ₃ ⁻ + 2H → NO ₂ ⁻ + H ₂ O (7)
NO ₂ ⁻ + H ⁺ + (H) → NO + H ₂ O (8)
NO + (H) → 0.5N ₂ O + 0.5H ₂ O (9)
N ₂ O + 2 (H) → N ₂ + H ₂ O (10)

Here, in the case where the denitrification reaction and the nitrification reaction proceed in parallel, the present inventor is directed from the inflow side of the aerobic tank 2a to the outflow side of the aerobic tank 2d in the reaction tank 2, that is, Each of ammonia nitrogen (NH ₄ -N), nitrite nitrogen (NO ₂ -N), and nitrate nitrogen (NO ₃ -N) at a plurality of positions along the direction of the water to be treated And the total nitrogen concentration of these were measured. FIG. 4A shows the nitrogen concentration and total nitrogen concentration of NH ₄ —N, NO ₂ —N, and NO ₃ —N according to the first embodiment, depending on the position along the flow direction of the water to be treated in the reaction tank 2. It is a graph which shows the measurement result.

As shown in FIG. 4A, from the inflow side of the aerobic tank 2a, which is a relatively first half side of the reaction tank 2, to the position on the outflow side of the aerobic tank 2b, NO ₂ -N and NO The nitrogen concentration of _3- N does not increase very much and the total nitrogen concentration decreases. That is, in the aerobic tanks 2a and 2b on the upstream side of the reaction tank 2, there are a nitrification reaction region and a denitrification reaction region, and the denitrification process is proceeding mainly while the nitrification process proceeds. Furthermore, since the return sludge returned from the solid-liquid separation tank 3 also flows into the aerobic tank 2a on the upstream side of the reaction tank 2, the downstream side of the reaction tank 2 contained in this return sludge. Denitrification treatment is also performed on nitric acid (NO ₂ —N and NO ₃ —N) produced by nitrification treatment in FIG. Combined with these phenomena, it is considered that the nitrogen removal rate is improved on the upstream side of the reaction tank 2 and the total nitrogen concentration is reduced. Further, from the outflow side of the aerobic tank 2b, which is a relatively second half side in the reaction tank 2, to the position of the outflow side of the aerobic tank 2d, the total nitrogen concentration is slightly reduced or maintained constant, while NO. Nitric acid concentrations of _2- N and NO ₃ -N are increasing. That is, the present inventor considered that in the aerobic tanks 2c and 2d on the downstream side of the reaction tank 2, the nitrification reaction proceeded mainly rapidly while the denitrification reaction continued.

  Therefore, the inventor first installs the nitric acid meter 7 at a desired position where the nitrogen concentration in the reaction tank 2 decreases, and supplies gas at least upstream from the nitric acid meter 7 based on the nitric acid concentration at this position. It was recalled that the denitrification reaction occurring upstream of the nitric acid meter 7 can be controlled by controlling the amount substantially uniformly or individually, and the nitrification reaction can be controlled accordingly.

  Further, the present inventor can install the ammonia meter 11 on the upstream side of the nitric acid meter 7 in order to cope with the case where the inflow amount of the water to be treated is increased and the ammonia concentration is greatly reduced in rainy weather. It was recalled that it is preferable to reset the control concentration range of the downstream nitric acid concentration according to the variation of the ammonia concentration measured by the ammonia meter 11. Then, the inventor conducted various experiments to confirm that nitrogen removal can be stably performed by controlling the nitric acid concentration based on the control concentration value of the set nitric acid concentration.

Specifically, as the water to be treated flows down in the reaction tank 2, the present inventor gradually added ammonia (NH ₄ ) contained in the water to be treated by the air diffusers 6a to 6d to nitric acid (nitrite nitrogen (NO). _2- N) and nitrate nitrogen (NO ₃ -N)), by supplying gas to the water to be treated in the reaction tank 2 over substantially the entire flow direction thereof, It was found that each desired ratio of nitric acid produced by nitrification at each position in the flow direction of the water to be treated in the reaction tank 2 can be denitrified. Therefore, the present inventor installs the nitric acid meter 7 at a desired position, installs the ammonia meter 11 upstream of the nitric acid meter 7, and sets the nitric acid meter 7 at the installation position based on the ammonia concentration measured by the ammonia meter 11. A control concentration range of nitric acid concentration is set, and at least the gas supply amount from the air diffuser 6 upstream of the nitric acid meter 7 is uniform so that the measurement value measured by the nitric acid meter 7 falls within this control concentration range. Alternatively, it has been found that the nitrification reaction can be controlled by controlling the denitrification reaction upstream of the nitric acid meter 7 by controlling individually.

  Therefore, in the present invention, the controller 9 performs monitoring of the ammonia concentration by the ammonia meter 11 upstream of the nitric acid meter 7 and monitoring of the nitric acid concentration by the nitric acid meter 7 installed on the outflow side of the aerobic tank 2b. Based on the ammonia concentration and nitric acid concentration, the gas supply amount control units 10a and 10b at least upstream of the nitric acid meter 7 along the flow direction of the water to be treated are controlled. Further, in the present invention, the gas supply amount in the reaction tank 2, that is, the gas supply amounts of the respective aerobic tanks 2 a to 2 d are adjusted by the gas supply amount control units 10 a to 10 d.

Therefore, in the first embodiment, it is desirable to install the nitric acid meter 7 on the outflow side of the aerobic tank 2b and the ammonia meter 11 on the inflow side of the aerobic tank 2a. When the ammonia meter 11 measures the NH ₄ —N concentration (ammonia concentration) on the inflow side of the reaction tank 2 and supplies the measured value to the control unit 9, the control unit 9 determines the concentration based on the ammonia concentration value. The range is set to the control concentration range in the total nitric acid concentration of NO ₂ —N and NO ₃ —N on the outflow side of the aerobic tank 2 b so that the nitric acid concentration measured by the nitric acid meter 7 falls within this control concentration range. The control unit 9 controls at least the gas supply amount control units 10a and 10b on the upstream side of the nitric acid meter 7 along the flow direction of the water to be treated. In addition, the control part 9 supplies a control signal to the gas supply amount control parts 10c and 10d as needed. Thereby, the control part 9 controls the gas supply amount in each aerobic tank 2a, 2b and also aerobic tank 2c, 2d individually or substantially uniformly.

And when the denitrification of the desired ratio with respect to the nitric acid produced | generated by nitrification by the nitrification reaction cannot be confirmed by the nitric acid meter 7, the air diffusers 6a and 6b at least upstream from the nitric acid meter 7 along the flow direction of the water to be treated. Increase or decrease the gas supply amount individually or uniformly. By controlling the gas supply amount by the control unit 9 in this way, the denitrification reaction can be advanced while suppressing the nitrification reaction in the treated water upstream of the nitric acid meter 7 in the reaction tank 2. On the downstream side of the nitric acid meter 7, the amount of dissolved oxygen in the treated water increases along the flow from the upstream side to the downstream side of the treated water, so that the treated water is more favorable while the denitrification reaction proceeds. As the nitrification reaction proceeds rapidly under atmospheric conditions, ammonia (NH ₄ ) decreases rapidly and nitric acid (nitrite nitrogen (NO ₂ -N) and nitrate nitrogen (NO ₃ -N)) Concentration increases rapidly. In addition, in the control of the gas supply amount, aeration may be performed continuously as described later, or may be performed intermittently including aeration stop control in which the gas supply amount is zero.

  Specifically, first, the ammonia meter 11 measures the ammonia concentration on the inflow side of the aerobic tank 2a (step ST3 in FIG. 5), and supplies the measured value of the ammonia concentration to the control unit 9. The control unit 9 sets, for example, a concentration range of 3 to 20% as the control concentration range of the nitric acid concentration with respect to the measured value of the supplied ammonia concentration (step ST4 in FIG. 5). In addition, about this control concentration range, the optimal control concentration range is set for every reaction tank according to design, such as the shape of the reaction tank 2, and a dimension.

  Specifically, the configuration according to the present invention corresponds to, for example, a case where the ammonia concentration of the water to be treated flowing in due to an increase in influent water is reduced from about 15 to 30 mg / L to about 5 to 15 mg / L. Is preferred. Therefore, when the ammonia concentration of the water to be treated becomes 5 to 15 mg / L, the control concentration range is within a concentration range of 3 to 20% with respect to the ammonia concentration, that is, within a range of 0.15 to 3 mg / L. Is preferably set.

On the other hand, the nitric acid meter 7 measures the total nitric acid concentration of NO ₂ —N and NO ₃ —N on the outflow side of the aerobic tank 2 b (step ST 5 in FIG. 5). The nitric acid meter 7 supplies the measured value of the nitric acid concentration to the control unit 9. The controller 9 determines whether or not the supplied concentration of nitric acid is within the control concentration range (step ST6 in FIG. 5).

  Here, according to the knowledge of the present inventor, when the nitric acid concentration in the reaction tank 2 exceeds 20% of the ammonia concentration which is the predetermined control concentration range described above, nitrification proceeds rapidly, and the amount of air is reduced. Even if it is reduced, it becomes difficult to control the state inside the reaction tank 2, so the set concentration range is preferably 20% or less of the ammonia concentration. Then, when the measured value of the supplied nitric acid concentration is within the control concentration range (step ST6: Yes in FIG. 5), the control unit 9 monitors the nitric acid concentration by the nitric acid meter 7, and the control concentration range of the nitric acid concentration. The setting and monitoring of the ammonia concentration by the ammonia meter 11 are continued (steps ST3 to ST5 in FIG. 5).

  On the other hand, the control unit 9 determines that the measured value of the nitric acid concentration supplied from the nitric acid meter 7 is, for example, less than the control concentration range of less than 3% of the ammonia concentration, that is, less than the lower limit of the control concentration range (in FIG. 5, Step ST6: No), and supply a control signal to the gas supply amount control units 10a to 10d to supply gas from at least the air diffusers 6a and 6b so as to increase the nitric acid concentration in at least the aerobic tanks 2a and 2b. Control to increase the amount is performed (step ST7 in FIG. 5). At this time, in the aerobic tanks 2c and 2d, control for increasing the gas supply amount by the air diffusers 6c and 6d may be performed similarly to the air diffusers 6a and 6b, or control not changing may be performed.

  In addition, the control unit 9 also detects the concentration of nitric acid supplied from the nitric acid meter 7 when the measured value exceeds 20% of the ammonia concentration, that is, exceeds the upper limit of the control concentration range. It is determined that the measured concentration value is outside the control concentration range (step ST6: No in FIG. 5), a control signal is supplied to the gas supply amount control units 10a to 10d, and at least nitric acid in the aerobic tanks 2a and 2b Control is performed to reduce the gas supply amount by at least the air diffusers 6a and 6b so as to reduce the concentration (step ST7 in FIG. 5). At this time, in the aerobic tanks 2c and 2d, the control unit 9 performs control that does not change even if control is performed to reduce the gas supply amount by the air diffusion units 6c and 6d in the same manner as the air diffusion units 6a and 6b. You can go.

  Moreover, in control of these gas supply amount, the control part 9 may perform the independent control for each gas supply amount control part 10a-10d with respect to each aeration part 6a-6d, mutually. The same control may be performed. That is, in the above-described control of the air diffusers 6a to 6d, the gas supply amount from the air diffusers 6a to 6d is uniformly increased or decreased, or the gas supply amount from the air diffusers 6a and 6b is increased or decreased. It is possible to keep the gas supply amount from the gas parts 6c and 6d constant.

  In addition, according to the installation position of the nitric acid meter 7, the aeration part 6 which needs to perform increase / decrease control is selected. Specifically, when the nitric acid meter 7 is installed on the downstream side of the aerobic tank 2a or the upstream side of the aerobic tank 2b, the control unit 9 is controlled by the gas supply amount control unit 10a from the aeration unit 6a. The gas supply amount is controlled. On the other hand, when the nitric acid meter 7 is installed on the downstream side of the aerobic tank 2c or the upstream side of the aerobic tank 2d, the control unit 9 uses at least the gas supply amount control units 10a to 10c to distribute the aeration units 6a to 6a. Each gas supply amount from 6c is controlled. In the control of these gas supply amounts, the control unit 9 may perform independent control for each of the gas supply amount control units 10a to 10d with respect to the respective air diffusion units 6a to 6d. Control may be performed, and a plurality of diffuser portions may be appropriately selected and grouped in the diffuser portions 6a, 6b, 6c, and 6d, and control may be performed independently for each group.

  Thus, the control part 9 supplies a control signal to each gas supply amount control part 10a-10d, and controls the gas supply quantity in each aeration part 6a-6d, and aerobic tank 2a, 2b It is possible to control the production of the denitrification reaction inside the reaction tank 2 by appropriately coexisting the denitrification reaction and the nitrification reaction. Further, since the controller 9 optimally controls the gas supply amount, the gas supply amount by the air diffusers 6a to 6d can be controlled to a necessary and sufficient amount, and the power consumption of the blower 8 can be reduced. Thus, it is possible to reduce power consumption in wastewater treatment.

(Examples 1 and 2)
Next, Examples 1 and 2 based on the first embodiment will be described. In FIG. 4A described above, as Example 1 of the first embodiment, when the ammonia concentration in the water to be treated flowing into the reaction tank 2 is 8 mg / L, the control concentration range of the nitric acid concentration is 20% of the ammonia concentration. in the following 16% before and after the 1.3 mg / L before and after the criteria is a graph showing NH ₄ -N, _NO 2 -N, and _NO 3 nitrogen concentration and total nitrogen concentration -N. FIG. 4B shows the control concentration range of the nitric acid concentration as 20% of the ammonia concentration when the ammonia concentration in the treated water flowing into the reaction tank 2 is 8 mg / L as Example 2 in the first embodiment. 41% before and beyond, i.e. in the case of a 3.3 mg / L before and after _is a graph showing NH 4 -N, _NO 2 -N, and _NO 3 nitrogen concentration and total nitrogen concentration -N.

  From FIG. 4A, the nitrogen concentration of the water to be treated on the inflow side of the reaction tank 2 is 8 mg / L, whereas the nitrogen concentration of the water to be treated on the final outflow side is reduced to about 4 mg / L. I understand that From FIG. 4B, the nitrogen concentration of the water to be treated on the inflow side of the reaction tank 2 is 8 mg / L, whereas the nitrogen concentration of the water to be treated on the final outflow side is about 6 mg / L. It turns out that it has decreased. Therefore, when FIG. 4A is compared with FIG. 4B, a concentration range of 3 to 20% is set as the control concentration range of the nitric acid concentration with respect to the measured value of the supplied ammonia concentration. It can be seen that the nitrogen removal effect can be further improved by controlling the gas supply amount to be supplied.

  According to the first embodiment of the present invention described above, in the plurality of aerobic tanks 2a to 2d constituting the reaction tank 2, the ammonia meter 11 is installed on the inflow side of the aerobic tank 2a, and the reaction tank 2 The nitric acid meter 7 is installed at a desired midway position along the flow direction of the water to be treated in FIG. 1, for example, on the outflow side of the aerobic tank 2b, which is an intermediate position of the reaction tank 2, and the control unit 9 The control concentration range of nitric acid concentration is set based on the ammonia concentration measured by the above, and at least the air diffusers 6a and 6b, as necessary, so that the nitric acid concentration falls within the set concentration range determined based on the ammonia concentration. The gas supply amounts in the aerobic tanks 2a to 2d are controlled by the air diffusers 6a to 6d. As a result, even when the amount of water to be treated flowing into the reaction tank 2 greatly increases and the ammonia concentration greatly decreases during rainy weather, the controller 9 appropriately controls the gas supply amount. The amount of gas supplied by the air diffusers 6a to 6d can be controlled to a necessary and sufficient amount, and an appropriate amount of oxygen can be supplied to the reaction tank 2 according to the organic load or nitrogen load of the water to be treated. Therefore, the denitrification reaction mainly performed in the aerobic tanks 2a and 2b, which are relatively first half of the reaction tank 2, can be controlled together with the nitrification reaction, and the nitrogen removal rate can be improved. Since an appropriate amount of oxygen can be supplied to the reaction tank 2 in accordance with the organic load and nitrogen load, it is possible to reduce the power consumption of the blower 8 and reduce the power consumption in the waste water treatment. . In addition, if there is another reaction tank of the same shape as the reaction tank 2 and there is inflow of wastewater and return of return sludge under the same conditions, the other reaction tank also controls the gas supply amount under the same conditions as the reaction tank 2. Thus, an appropriate amount of oxygen can be supplied.

(Modification 1 of the first embodiment)
Moreover, in this 1st Embodiment, although the reaction tank 2 was comprised from the four aerobic tanks 2a-2d, it is also possible to make this reaction tank 2 into the single tank from which the flow of to-be-processed water arises. is there. FIG. 2B is a plan view in the case where the reaction tank 2 is configured as a single tank as Modification 1 of the first embodiment. As shown in FIG. 2B, the air diffuser may be constituted by a single air diffuser 6 instead of the plurality of air diffusers 6a to 6d. Even in this case, the nitric acid meter 7 flows along the flow direction of the water to be treated at a desired position on the most downstream side of the region where the denitrification reaction needs to be controlled, here, the flow of the water to be treated in the reaction tank 2. The ammonia meter 11 is provided at a desired position upstream of the nitric acid meter 7, preferably at a position near the inflow side of the water to be treated in the reaction tank 2. In addition, even if it is a case where an aeration means is comprised from the single aeration part 6, you may comprise so that a gas supply amount can be controlled for every gas supply part in the reaction tank 2 in the aeration part 6. FIG. . Even when the reaction tank 2 is a single tank, the air diffuser may be composed of a plurality of air diffusers as in the first embodiment described above. And also when making the reaction tank 2 into a single tank and comprising an aeration means from several aeration parts, you may control a some aeration part mutually independently, or you may control mutually the same. .

(Modification 2 of the first embodiment)
In the first embodiment described above, the ammonia meter 11 is provided near the inflow side of the water to be treated in the reaction tank 2, and the installation position of the ammonia meter 11 is provided outside the reaction tank 2. It is also possible. FIG. 3 is a configuration diagram in a case where an ammonia meter 11 is provided outside the reaction tank 2 as a modified example 2 of the first embodiment. As shown in FIG. 3, the ammonia meter 11 is located at a desired position upstream of the nitric acid meter 7 along the flow direction of the treated water, specifically, near the inflow side of the treated water outside the reaction tank 2. It is provided at a position downstream of the first sedimentation site 1 along the flow direction of the water to be treated.

なお、Ｑ_r：反応槽２の後段からの返送汚泥、Ｑ_in：流入水量、Ｃ_NH4out：反応槽２の外部で計測されたアンモニア濃度、Ｃ_NH4in：反応槽２における被処理水の流入側近傍の位置での換算アンモニア濃度である。 In this case, the ammonia concentration outside the reaction vessel 2 measured by the ammonia meter 11 is converted into the ammonia concentration in the vicinity of the inflow side of the water to be treated in the reaction vessel 2 by a conversion equation such as the following equation (11). Convert. Then, the converted value of the ammonia concentration is adopted as the measured value of the ammonia meter 11 according to the first embodiment, and the control concentration range of the nitric acid concentration at the position of the nitric acid meter 7 is set based on the converted value. .

Incidentally, Q _r: return sludge from the subsequent reaction vessel 2, Q _in: inflow water amount, C _NH4out: ammonia concentration measured at the outside of the reaction vessel 2, C _NH4in: inflow side vicinity of the water to be treated in the reaction vessel 2 It is the converted ammonia concentration at the position.

(Second Embodiment)
Next, a wastewater treatment apparatus including a control device according to a second embodiment of the present invention will be described. FIG. 6 is a block diagram showing a wastewater treatment apparatus according to the second embodiment.

  As shown in FIG. 6, in the wastewater treatment apparatus according to the second embodiment, unlike the first embodiment, the reaction tank 2 is not a multi-stage aerobic tank but a single aerobic tank. It consists of a nitrification denitrification reactor. In addition, a nitric acid meter 7 is installed at a desired position in the flow direction of the water to be treated in the reaction tank 2, that is, an intermediate position for controlling the denitrification reaction in the water to be treated further upstream. The nitric acid meter 7 measures the nitric acid concentration at the predetermined position and supplies the measurement result to the control unit 9. The control unit 9 sets a control concentration range from the ammonia concentration measured by the ammonia meter 11 provided on the upstream side, and at least upstream from the nitric acid meter 7 based on the control concentration range and the supplied nitric acid concentration. The gas supply amount (aeration amount) of the air diffusers 6a and 6b is controlled. In addition, the control part 9 can also control the aeration parts 6a-6d over the reaction tank 2 so that gas supply amount may become uniform, and the aeration parts 6a and 6b and the aeration part 6c. , 6d can be individually controlled.

  An anaerobic tank 12 is provided upstream of the reaction tank 2 along the flow direction of the water to be treated. The anaerobic tank 12 is a tank into which treated water, which is nitrogen-containing water, first flows through the settling tank 1. In the anaerobic tank 12, a stirring unit 12b that can be rotated by an external motor 12a is provided, and the activated sludge in the anaerobic tank 12 is stirred by the stirring unit 12b. Depending on the configuration of the sewage treatment plant, the initial sedimentation basin 1 may not be provided. In this case, the raw water first flows into the anaerobic tank 12. The anaerobic tank 12 is a tank for performing dephosphorization treatment (anaerobic treatment) on the water to be treated by the action of phosphorus-accumulating bacteria in an anaerobic environment. And in the anaerobic tank 12, while the organic substance contained in to-be-processed water under anaerobic conditions is taken in into activated sludge, the phosphorus contained in activated sludge is discharge | released into raw | natural water.

  In addition, the activated sludge 4 b deposited on the bottom of the solid-liquid separation tank 3 is returned to the anaerobic tank 12 by the sludge return path 5 connected to the bottom of the solid-liquid separation tank 3. Thereby, the biomass in the anaerobic tank 12 and the downstream reaction tank 2 can be maintained at a predetermined amount. In addition, the remainder of the activated sludge 4b produced | generated in the solid-liquid separation tank 3 is discharged | emitted outside as excess sludge. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

  In the second embodiment, a nitric acid meter 7 for supplying the measured nitric acid concentration to the control unit 9 is installed at a desired position in the reaction tank 2 composed of a single tank, and is measured upstream of the nitric acid meter 7. By installing an ammonia meter 11 for supplying the ammonia concentration to the control unit 9 and determining a control concentration range of the nitric acid concentration based on the ammonia concentration measured by the ammonia meter 11, the same as in the first embodiment An effect can be obtained.

(Third embodiment)
Next, a wastewater treatment apparatus including a control device according to a third embodiment of the present invention will be described. FIG. 7 is a perspective transparent view showing the anaerobic tank 12 and the reaction tank 2 in the wastewater treatment apparatus according to the third embodiment. In FIG. 7, the side walls on the near side of the drawing in the anaerobic tank 12 and the reaction tank 2 are not shown for the following explanation. 8A and 8B are cross-sectional views of the reaction tank 2 along the lines AA and BB in FIG. 7, respectively.

  As shown in FIG. 7, the reaction tank 2 is composed of a single tank, and an anaerobic tank 12 is provided upstream of the reaction tank 2 along the flow direction of the water to be treated. Raw water flows into the anaerobic tank 12 from one side, and the water to be treated that has been anaerobically treated in the anaerobic tank 12 is supplied to the reaction tank 2 from the other side.

  In addition, a plate-like air diffuser 6 is provided in the reaction tank 2 approximately in the middle along the height direction of the reaction tank 2. The air diffuser 6 is configured such that the gas supply amount control unit 10 can adjust the gas supply amount for each predetermined section along the flow direction of the water to be treated which is the longitudinal direction of the reaction tank 2.

  A nitric acid meter 7 capable of measuring the nitric acid concentration is installed at a predetermined position along the flow direction of the water to be treated in the reaction tank 2, that is, the longitudinal direction of the reaction tank 2. The nitric acid meter 7 supplies the measured nitric acid concentration to the control unit 9. The control unit 9 supplies a control signal to the gas supply amount control unit 10 according to a predetermined program according to the measurement value of the supplied nitric acid concentration. The gas supply amount control unit 10 controls the gas supply amount so as to be uniform over the entire air diffuser 6 according to the supplied control signal, or for each predetermined section of the air diffuser 6. Control the gas supply rate.

  In addition, a partition plate 13 is provided in the central portion of the reaction tank 2 along the longitudinal direction of the reaction tank 2. The partition plate 13 is installed so that its thickness direction is substantially parallel to the bottom surface of the reaction tank 2. In other words, the partition plate 13 is installed such that its surface is perpendicular to the bottom surface of the reaction tank 2. By this partition plate 13, the inside of the reaction tank 2 is in a state of being partially partitioned with the upper and lower portions of the partition plate 13 opened.

  In the reaction tank 2 configured as described above, when aeration is performed by supplying a gas to the water to be treated from the aeration unit 6 while flowing the water to be treated, the aerated gas flows along the partition plate 13. Ascend and turn to the opposite side while being partitioned by the partition plate 13. At the same time, since the water to be treated is flowing along the longitudinal direction of the reaction tank 2, the aerated gas forms a spiral swirl flow C as shown in FIG. It will dissolve. Similarly, the water to be treated advances along the longitudinal direction of the reaction tank 2 while swirling spirally so that the longitudinal axis of the reaction tank 2 is substantially centered. The gas supply amount from the air diffuser 6 is appropriately set according to conditions such as the inflow amount of the water to be treated and the size and shape of the reaction tank 2.

  And it is sectional drawing along the BB line in the swirl | vortex flow C in FIG. 8A which is sectional drawing along the AA line in the position in which the ammonia meter 11 was provided, and the position in which the nitric acid meter 7 was provided. As shown in a swirl flow C in FIG. 8B, oxygen-containing gas such as air diffused from the air diffuser 6 passes through the gap in the upper part of the partition plate 13 together with the water to be treated to the opposite side. Turn. Further, the water to be treated accompanying the swirling of air passes through the gap in the lower part of the partition plate 13 and reaches the lower part of the air diffuser 6. In this case, the upstream aerobic region 31 and the downstream anaerobic region 32 coexist along the flow direction of the swirling flow C of the water to be treated. The aerobic region 31 has a nitrification reaction promoted by an aerobic nitrifying bacterium, and constitutes a nitrification region. On the other hand, the anaerobic region 32 has a denitrification reaction promoted by an anaerobic denitrifying bacterium. Configure.

  Moreover, in FIG. 8A and FIG. 8B, the flow of the air by the aeration from the aeration part 6, and the state of an anaerobic region are shown. Then, as shown in FIGS. 7, 8 </ b> A, and 8 </ b> B, on the upstream side in the longitudinal direction of the reaction tank 2, the diffused portion upstream of the position where the nitric acid meter 7 is installed in the water to be treated. Oxygen based on the gas supply amount from 6 is dissolved. On the other hand, the position where the ammonia meter 11 is installed is on the upstream side in the flow direction of the water to be treated, which is the longitudinal direction of the reaction tank 2, and therefore, compared with the position where the nitric acid meter 7 is installed. Therefore, the amount of dissolved oxygen is low. Therefore, the anaerobic region 32 shown in FIG. 8A is larger than the anaerobic region 32 shown in FIG. 8B. In other words, since the water to be treated flows from the upstream side to the downstream side along the longitudinal direction of the reaction tank 2, the amount of contact with oxygen increases as it goes downstream, so the ammonia meter 11 shown in FIG. 8A. From the installation position to the installation position of the nitric acid meter 7 shown in FIG. 8B, the dissolved oxygen increases and the aerobic region 31 expands. Thereby, in the to-be-processed water in this reaction tank 2, a denitrification area | region tends to reduce as it goes downstream from an upstream side. On the other hand, the nitrification region tends to increase from the upstream side to the downstream side. The anoxic anaerobic region 32 is not a complete anaerobic state, but means a region inclined to an anaerobic state where predominantly anaerobic denitrifying bacteria predominate, that is, a region where the denitrifying reaction is proceeding.

From the above, the denitrification reaction is promoted while the nitrification reaction coexists on the upstream side of the reaction tank 2, and the nitrification reaction is promoted while the denitrification reaction occurs on the downstream side. As a result, as shown in FIG. 4, denitrification proceeds immediately after the nitrification reaction on the upstream side of the reaction tank 2, so that nitrate nitrogen (NO ₃ -N) or nitrite nitrogen ( nO ₂ -N) is hardly emerge. And as it progresses to the downstream side of the reaction tank 2, the concentration of nitric acid increases as the nitrification reaction is promoted while the total nitrogen concentration decreases due to the denitrification reaction. Since other configurations are the same as those in the first and second embodiments, the description thereof is omitted.

  According to the third embodiment described above, the surface perpendicular to the overall flow direction of the water to be treated is provided inside the reaction tank 2 by supplying the gas from the air diffuser 6 while providing the partition plate 13. Since the swirl flow is formed in the direction, oxygen is supplied and the dissolved oxygen increases on the upper layer side in the reaction tank 2 that is upstream of the swirl flow. While a nitrification reaction region in which the reaction becomes relatively dominant is formed, the lower layer side in the reaction tank 2 downstream of the swirl flow dissolves in comparison with the upper layer side due to the consumption of oxygen on the upper layer side. Since oxygen decreases, it tends to an anaerobic state, a denitrification reaction increases, and a denitrification reaction area | region is formed. Thereby, the state in which the nitrification reaction and the denitrification reaction coexist in the reaction tank 2 is obtained. Therefore, the nitrification reaction and the denitrification reaction can coexist with good controllability, and the nitrification reaction can be more efficiently suppressed as the denitrification reaction is controlled on the upstream side along the overall flow direction of the water to be treated. At the same time, the nitrification reaction can be promoted on the downstream side. Therefore, while measuring the ammonia concentration with the ammonia meter 11 and the nitric acid concentration with the nitric acid meter 7, the aeration is performed so that the nitric acid concentration falls within the control concentration range set by the ammonia concentration measured by the ammonia meter 11. By controlling the part 6, it is possible to more accurately control the denitrification reaction and the nitrification reaction in the reaction tank 2.

(Modification of reaction tank and diffuser)
Next, the modification regarding the reaction tank 2 and the inside aeration part 6 in each embodiment of this invention mentioned above is demonstrated.

(Modification 3)
FIG. 9A is a configuration diagram showing a reaction tank 2 according to Modification 3. As shown in FIG. 9A, in the reaction tank 2 according to the modified example 3, a plurality of air diffusers 16a, 16b, and 16c are provided inside the reaction tank 2 as in the second embodiment. Each of these air diffusers 16a to 16c is controlled by gas supply amount control units 19a, 19b and 19c for controlling the gas supply amount based on a control signal from the control unit 9 (not shown in FIG. 9A). The Moreover, unlike 2nd Embodiment, between each aeration part 16a-16c is provided at predetermined intervals. That is, while the gas is supplied as a whole of the reaction tank 2, the region where the gas is supplied and the region where the gas is not supplied are sequentially alternately or repeatedly locally along the flow direction of the water to be treated. It is formed. Thereby, in the reaction tank 2, since the nitrifying bacteria of the aerobic bacteria and the facultative anaerobic denitrifying bacteria can coexist, their activities can be activated alternately, which will be described in the third embodiment. Like the reaction tank 2, the region where the nitrification reaction occurs and the region where the denitrification reaction occur can be formed with good controllability in the reaction tank 2.

(Modification 4)
FIG. 9B is a configuration diagram showing the reaction tank 2 according to the fourth modification. As shown in FIG. 9B, in the reaction tank 2 according to the modified example 4, a plurality of air diffusers 26a, 26b, 26c, 26d, and 26e are provided in the reaction tank 2 as in the second embodiment. Yes. The air diffusers 26a to 26e are respectively supplied with gas supply amount control units 29a, 29b, 29c, which control the gas supply amount based on a control signal from the control unit 9 (not shown in FIG. 9B). It is controlled by 29d and 29e. Further, unlike the second embodiment, the control unit 9 selectively sets an aeration unit that performs aeration and an aeration unit that does not perform aeration for the plurality of aeration units 26a to 26e. . In FIG. 9B, the air diffusers 26a, 26c, and 26e are controlled to perform aeration, and the air diffusers 26b and 26d are controlled not to perform aeration. Of these diffusers 26a to 26e, the diffuser that performs aeration and the diffuser that does not perform aeration are appropriately selected according to the quality of water to be treated flowing in the reaction tank 2. That is, while the gas is supplied as a whole of the reaction tank 2, the region where the gas is supplied and the region where the gas is not supplied are sequentially alternately or repeatedly locally along the flow direction of the water to be treated. It is formed. Thereby, in the reaction tank 2, since the nitrifying bacteria of the aerobic bacteria and the facultative anaerobic denitrifying bacteria can coexist, their activities can be activated sequentially, alternately or repeatedly. Similarly to the reaction tank 2 according to the embodiment, in the reaction tank 2, a region where the nitrification reaction occurs and a region where the denitrification reaction occur can be formed with good controllability.

(Modification 5)
FIG. 9C is a configuration diagram showing a reaction tank 2 according to Modification 5. As shown in FIG. 9C, in the reaction tank 2 according to Modification 5, a single air diffuser 36 is provided inside the reaction tank 2 as in Modification 1 in the first embodiment. The air diffuser 36 is controlled by a gas supply amount controller 39 that controls the gas supply amount based on a control signal from the controller 9 (not shown in FIG. 9C). Further, unlike the fourth modification, the aeration unit 36 is controlled by the control unit 9 so as to perform aeration or no aeration sequentially, alternately or repeatedly as time elapses.

  FIG. 9D is an example of a timing chart showing the timing of the presence or absence of this aeration. As shown in FIG. 9D, the time during which aeration is performed by the air diffuser 36 (ON in FIG. 9D) and the time during which aeration is not performed (OFF in FIG. 9D) are the water to be treated flowing in the reaction tank 2. It is appropriately set according to various conditions such as water quality. That is, while the gas is supplied to the reaction tank 2 as a whole, the time during which the gas is supplied to the water to be treated and the time during which the gas is not supplied are sequentially or alternately set as time passes. Thereby, in the reaction tank 2, nitrifying bacteria of aerobic bacteria and facultative anaerobic denitrifying bacteria can coexist, and their activities can be activated sequentially, alternately or repeatedly over time. Therefore, similarly to the reaction tank 2 described in the third embodiment, the region where the nitrification reaction occurs and the region where the denitrification reaction occurs can be formed with good controllability in the reaction tank 2.

(Modification 6)
Further, FIG. 9E is a configuration diagram showing the reaction tank 2 according to Modification 6. As shown in FIG. 9E, in the reaction tank 2 according to the modified example 6, a single aeration unit 46 is provided inside the reaction tank 2 as in the modified example 5. And this aeration part 46 is controlled by the gas supply amount control part 49 which controls a gas supply amount based on the control signal from the control part 9 (not shown in FIG. 9E). A plurality of carriers 43 carrying both aerobic nitrifying bacteria and facultative anaerobic denitrifying bacteria are introduced into the reaction tank 2. When the gas is supplied from the air diffuser 46 into the reaction tank 2, the inside of the reaction tank 2 is stirred, the carrier 43 flows in the water to be treated, and the carrier 43 is distributed substantially uniformly in the water to be treated. . FIG. 9F is a sectional view showing a sectional structure of the carrier 43.

  As shown in FIG. 9F, the carrier 43 is composed of a granular resin carrier, and the size and shape of the carrier 43 are various sizes and shapes as long as the carrier 43 can retain bacteria even when flowing in the water to be treated. Can be adopted. For example, a cylindrical shape, a spherical shape or the like having an outer diameter of about several millimeters is preferable. In addition, aerobic nitrifying bacteria are mainly carried in the nitrification reaction zone on the surface of the carrier 43, and facultative anaerobic denitrifying bacteria are mainly carried in the denitrification reaction zone. Specifically, the carrier 43 contains aerobic nitrifying bacteria contributing to the nitrification reaction in the outer region 43a, and facultative anaerobic denitrifying bacteria contributing to the anaerobic denitrification reaction in a form surrounded by the nitrifying bacteria. As the dominant species, two layers of microbial membranes to be present in the inner region 43b are supported on the surface portion. As a result, in the carrier 43 in the water to be treated, nitrifying bacteria located on the outer side are set as aerobic conditions as dominant species, and denitrifying bacteria located on the inner side have anaerobic conditions surrounded by the nitrifying bacteria. Secured.

  That is, while the gas is supplied to the entire reaction tank 2, the aerobic nitrifying bacteria and the anaerobic denitrifying bacteria coexist by the carrier 43 itself in the water to be treated in the reaction tank 2, and the nitrification reaction is performed. A state in which the denitrification reaction coexists can be formed. As a result, the nitrification reaction of the aerobic bacteria and the facultative anaerobic denitrification bacteria can be activated in the reaction tank 2 together, so that the nitrification reaction is performed in the reaction tank 2. And denitrification can coexist with good controllability.

(Modification of denitrification confirmation means)
Next, a modified example related to a meter used as a denitrification confirmation unit in each embodiment of the present invention described above will be described.

(Modification 7)
First, Modification 7 will be described. FIG. 10A is a cross-sectional view of the reaction vessel 2 according to the modified example 7 corresponding to FIG. 8A showing the reaction vessel 2 according to the third embodiment. FIG. 10B is a graph showing the dissolved oxygen concentration dependence of the denitrification rate and nitrification rate. In this modified example 7, a pair of dissolved oxygen (DO) meters are used as denitrification confirmation means.

  That is, as shown in FIG. 10A, in the reaction tank 2 that forms a swirling flow, the aerobic region 31 and the anaerobic region 32 are respectively sequentially upstream and downstream along the swirling flow of the water to be treated. It is formed. In the modified example 7, unlike the third embodiment, the dissolved oxygen concentration (DO concentration) is measured in each of the aerobic region 31 and the anaerobic anaerobic region 32 whose formation is known in advance. The DO meter 51a and the second DO meter 51b are installed as a pair. In addition, since the swirl | vortex flow in the reaction tank 2 is generally helical, the 1st DO meter 51a and the 2nd DO meter 51b are installed in the position shifted a little along the longitudinal direction of the reaction tank 2. Although it is preferable, in FIG. 10A, it has described in the same position along the longitudinal direction of the reaction tank 2 for convenience. Further, the measured values of the DO concentration measured by the first DO meter 51a and the second DO meter 51b are respectively supplied to the control unit 9. Other configurations are the same as those of the third embodiment, and thus the description thereof is omitted.

  Next, a control method by the control unit 9 when a DO meter is used as the denitrification confirmation unit will be described. First, the second DO meter 51b measures the DO concentration DO2 in the anaerobic region 32. The second DO meter 51b supplies the DO concentration DO2 to the control unit 9. Then, or together with this, the first DO meter 51a measures the DO concentration DO1 in the aerobic region 31. The first DO meter 51a supplies the DO concentration DO1 to the control unit 9.

  The control unit 9 determines that the DO concentration DO2 in the anaerobic region 32 is within a predetermined DO concentration range calculated as a predetermined ratio with respect to the ammonia concentration measured by the preceding ammonia meter 11, specifically, for example, 0 mg / L. It is determined whether or not it is greater than or equal to 0.5 mg / L (0 mg / L <DO2 ≦ 0.5 mg / L). Here, as shown in FIG. 10B, when the DO concentration is 0.5 mg / L or less, the DO concentration dependency of the denitrification rate is an upwardly convex graph, and the processing rate increases as the DO concentration decreases. To do. When the DO concentration is 0.5 mg / L or less, the DO concentration dependency of the nitrification rate is a very small rate. Therefore, if DO concentration DO2 of the to-be-processed water in the anoxic anaerobic area | region 32 measured by the 2nd DO meter 51b is 0.5 mg / L or less, the longitudinal direction of the reaction tank 2 from this 2nd DO meter 51b It can be confirmed that the denitrification process is performed efficiently while the nitrification process is suppressed on the upstream side along the line.

  When the DO concentration DO2 in the anoxic anaerobic region 32 shown in FIG. 10A is outside the predetermined DO concentration range, the control unit 9 controls the gas supply amount from the aeration unit 6 to thereby make the anaerobic anaerobic condition. Control is performed so that the DO concentration in the region 32 falls within a predetermined DO concentration range. Specifically, when the DO concentration DO2 exceeds the upper limit (for example, 0.5 mg / L) of a predetermined DO concentration range, at least upstream of the second DO meter 51b along the flow direction of the water to be treated. Reduce gas supply. On the other hand, when the DO concentration DO2 falls below the lower limit of the predetermined DO concentration range, the gas supply amount at least upstream from the second DO meter 51b along the flow direction of the water to be treated is increased.

  Further, the control unit 9 determines that the DO concentration DO1 in the aerobic region 31 is higher than the DO concentration DO2 in the anaerobic region 32 by a predetermined DO concentration, specifically, a DO concentration higher by 0.5 mg / L, for example. It is determined whether or not (DO2 + 0.5 mg / L ≦ DO1). Here, as shown in FIG. 10B, as the range of DO2 + 0.5 mg / L, when the DO concentration is larger than 0.5 mg / L, the DO concentration dependency of the nitrification rate increases monotonously, and the DO concentration increases. As the process proceeds, the processing speed also increases. Therefore, if the DO concentration DO1 of the water to be treated in the aerobic region 31 measured by the first DO meter 51a is larger than the DO concentration DO2 of the water to be treated in the anaerobic region 32 by 0.5 mg / L or more, It can be confirmed that the nitrification treatment is promoted while the denitrification treatment is performed on the downstream side along the longitudinal direction of the reaction tank 2 from the first DO meter 51a.

  When the DO concentration DO1 in the aerobic region 31 shown in FIG. 10A is less than the DO concentration obtained by adding a predetermined DO concentration (for example, 0.5 mg / L) to the DO concentration DO2 in the anaerobic region 32, control is performed. The unit 9 controls the gas supply amount from the air diffuser 6 so that the DO concentration DO1 in the aerobic region 31 is higher than the DO concentration DO2 by a predetermined DO concentration or higher. Specifically, when the DO concentration DO1 is less than the DO concentration obtained by adding a predetermined DO concentration (for example, 0.5 mg / L) to the DO concentration DO2, at least the first DO along the flow direction of the water to be treated. The gas supply amount upstream of the total 51a is increased.

  In the modified example 7 demonstrated above, control of the denitrification process performed with the nitric acid meter in embodiment mentioned above is performed using a pair of DO meter. As a result, the nitrification reaction of the aerobic bacteria and the facultative anaerobic denitrification bacteria can be activated in the reaction tank 2 together, so that the nitrification reaction is performed in the reaction tank 2. And denitrification can coexist with good controllability.

(Modification 8)
Next, Modification 8 will be described. FIG. 11A is a cross-sectional view of a reaction vessel 2 according to Modification 8 corresponding to FIG. 8A showing the reaction vessel 2 according to the third embodiment. FIG. 11B is a graph showing the redox potential dependence of the denitrification rate and nitrification rate. In this modification 8, a pair of redox potential (ORP) meters are used as denitrification confirmation means.

  That is, as shown in FIG. 11A, in the modified example 8, unlike the third embodiment, an aerobic region that has been found to be formed in advance inside the reaction tank 2 that forms a swirling flow. A pair of a first ORP meter 55a and a second ORP meter 55b capable of measuring an oxidation-reduction potential (ORP value) are installed in the 31 and the anaerobic region 32, respectively. Since the swirl flow in the reaction vessel 2 is generally spiral, the first ORP meter 55a and the second ORP meter 55b are installed at positions slightly shifted along the longitudinal direction of the reaction vessel 2. Although it is preferable, in FIG. 11A, it has described in the same position along the longitudinal direction of the reaction tank 2 for convenience. The measured value of the ORP value measured by the first ORP meter 55 a and the second ORP meter 55 b is supplied to the control unit 9. Other configurations are the same as those of the third embodiment, and thus the description thereof is omitted.

  Next, a control method by the control unit 9 when a pair of ORP meters is used as denitrification confirmation means will be described. First, the second ORP meter 55b measures the ORP value ORP2 in the anoxic anaerobic region 32. The second ORP meter 55b supplies the ORP value ORP2 to the control unit 9. Then, or together with this, the first ORP meter 55a measures the ORP value ORP1 in the aerobic region 31. The first ORP meter 55a supplies the ORP value ORP1 to the control unit 9.

  The control unit 9 determines that the ORP value ORP2 in the anaerobic anaerobic region 32 is within a predetermined ORP value range calculated as a predetermined ratio with respect to the ammonia concentration measured by the preceding ammonia meter 11, specifically, for example −50 mV or less. It is determined whether or not (ORP2 ≦ −50 mV). Here, as shown in FIG. 11B, when the ORP value is −50 mV or less, the dependency of the denitrification rate on the ORP value is a convex graph, and the processing rate increases as the ORP value decreases. Further, when the ORP value is −50 mV or less, the nitrification rate is almost zero. Therefore, if the ORP value of the water to be treated in the anaerobic anaerobic region 32 measured by the second ORP meter 55b is -50 mV or less, the upstream along the longitudinal direction of the reaction tank 2 from the second ORP meter 55b. On the side, it can be confirmed that the denitrification treatment is efficiently performed while the nitrification treatment is suppressed.

  When the ORP value ORP2 in the anaerobic anaerobic region 32 shown in FIG. 11A falls outside the predetermined ORP value range, the control unit 9 controls the gas supply amount from the aeration unit 6 to thereby make anaerobic anaerobic. Control is performed so that the ORP value in the region 32 falls within a predetermined ORP value range. Specifically, when the ORP value ORP2 exceeds the upper limit (for example, −50 mV) of a predetermined ORP value range, the gas supply amount upstream of at least the second ORP meter 55b along the flow direction of the water to be treated. Decrease. On the other hand, when the ORP value ORP2 falls below the lower limit (for example, −100 mV) of the predetermined ORP value range, the gas supply amount upstream of at least the second ORP meter 55b along the flow direction of the water to be treated is increased. .

  Further, the controller 9 determines that the ORP value ORP1 in the aerobic region 31 is equal to or higher than the ORP value ORP2 in the anaerobic region 32 by a predetermined ORP value, specifically, 50 mV higher than the ORP value (ORP2 + 50 mV ≦ ORP1). ) Or not. Here, as shown in FIG. 11B, when the ORP value is larger than −50 mV as a possible range of ORP2 + 50 mV, the dependency of the nitrification rate on the ORP value increases monotonously, and the processing rate increases as the ORP value increases. Therefore, if the ORP value ORP1 of the treated water in the aerobic region 31 measured by the first ORP meter 55a is 50 mV or more larger than the ORP value ORP2 of the treated water in the anaerobic region 32, the first ORP. It can be confirmed that the nitrification process is promoted while the denitrification process is performed on the downstream side along the longitudinal direction of the reaction tank 2 from the total 55a.

  When the ORP value ORP1 in the aerobic region 31 shown in FIG. 11A is less than the ORP value obtained by adding a predetermined ORP value (for example, 50 mV) to the ORP value ORP2 in the anaerobic region 32, the control unit 9 By controlling the gas supply amount from the air diffuser 6, the ORP value ORP1 in the aerobic region 31 is controlled to be an ORP value that is higher than the ORP value ORP2 by a predetermined ORP value or more. Specifically, when the ORP value ORP1 becomes less than the ORP value obtained by adding a predetermined ORP value (for example, 50 mV) to the ORP value ORP2, at least upstream from the first ORP meter 55a along the flow direction of the water to be treated. Increase the gas supply on the side.

  In the modification 8 demonstrated above, control of the denitrification process performed with the nitric acid meter in embodiment mentioned above is performed using a pair of ORP meter. As a result, the nitrification reaction of the aerobic bacteria and the facultative anaerobic denitrification bacteria can be activated in the reaction tank 2 together, so that the nitrification reaction is performed in the reaction tank 2. And denitrification can coexist with good controllability.

(Modification 9)
Next, Modification 9 will be described. FIG. 12A is a configuration diagram of a wastewater treatment apparatus according to Modification 9 corresponding to FIG. 6 in the second embodiment. FIG. 12B shows NH ₄ —N, NO ₂ —N, and NO ₃ corresponding to FIG. 4 measured along the flow of water to be treated in the reaction tank for explaining the target nitrification rate and the measured nitrification rate. It is a graph which shows each nitrogen concentration of -N, and a total nitrogen concentration. In this modified example 9, a pair of ammonia meters is used as denitrification confirmation means.

  That is, as shown in FIG. 12A, in the modified example 9, unlike the second embodiment, instead of the nitric acid meter 7 in the reaction tank 2, the first upstream side along the flow direction of the water to be treated is used. A nitrification rate meter 58 comprising a pair of ammonia meters of an ammonia meter 58a and a second ammonia meter 58b on the downstream side is installed. The measured values of the ammonia concentration measured by the first ammonia meter 58a and the second ammonia meter 58b are respectively supplied to the control unit 9. Since other configurations are the same as those of the second embodiment, the description thereof is omitted.

Next, a control method by the control unit 9 in the case of using a nitrification rate meter 58 including a pair of first ammonia meter 58a and second ammonia meter 58b as denitrification confirmation means will be described. First, the first ammonia meter 58a and the second ammonia meter 58b measure the first ammonia concentration NH1 and the second ammonia concentration NH2, respectively. Each of the first ammonia concentration NH1 and the second ammonia concentration NH2 is supplied to the control unit 9. The controller 9 calculates the measured nitrification rate from the supplied first ammonia concentration NH1 and second ammonia concentration NH2 (NH1> NH2). Specifically, the measured nitrification rate is calculated from the ammonia concentration NH1 measured by the first ammonia meter 58a on the upstream side and the ammonia concentration NH2 on the downstream side based on the following equation (12). The measured nitrification speed corresponds to the absolute value of the slope of the solid line shown in FIG. 12B, and the measured nitrification speed may vary as shown by two solid lines depending on the installation position of the nitrification speed meter 58.

On the other hand, the final ammonia concentration (target ammonia concentration) NH3 as the treated water target value is set in advance for each of the various reaction vessels 2. The control unit 9 calculates a reference nitrification rate (target nitrification rate) from the target ammonia concentration NH3 and the ammonia concentration NH1 measured at the position of the first ammonia meter 58a, and records it in the control unit 9 Store in an area (not shown). This target nitrification speed is calculated based on the following equation (13). This target nitrification speed corresponds to the absolute value of the slope of the dotted line shown in FIG. 12B.

Then, as shown in FIG. 12A, the controller 9 determines that the measured nitrification rate between the first ammonia meter 58a and the second ammonia meter 58b, that is, the measured nitrification rate measured by the nitrification rate meter 58 is The amount of gas supplied from the air diffuser 6 upstream of at least the second ammonia meter 58b is controlled so as to be less than the target nitrification rate calculated as a predetermined ratio with respect to the ammonia concentration measured by the ammonia meter 11. . Thereby, the progress of the nitrification reaction on the upstream side of the second ammonia meter 58b can be suppressed, and the denitrification reaction in this region can be promoted. Even if the measured nitrification rate is less than the target nitrification rate, if it becomes too slow, the ammonia concentration may not decrease to the desired target ammonia concentration NH3 on the outflow side of the reaction tank 2. Therefore, according to the knowledge obtained from the experiment of the present inventor, it is preferable that the measured nitrification rate is larger than half of the target nitrification rate. That is, the control unit 9 controls the gas supply amount from the air diffusion unit 6 so that the following expression (14) is satisfied.

  Specifically, when the measured nitrification rate with respect to the target nitrification rate is larger than the range set by the equation (14), that is, when the measured nitrification rate is equal to or higher than the target nitrification rate, the nitrification reaction proceeds. It will be too much. Therefore, the controller 9 reduces the amount of air supplied from the air diffusers 6a, 6b at least upstream of the second ammonia meter 58b along the flow direction of the water to be treated in the reaction tank 2. Thereby, the control unit 9 controls the reaction tank 2 so that the nitrification reaction does not proceed excessively. On the other hand, when the measured nitrification rate with respect to the target nitrification rate is smaller than the range set by the equation (14), that is, when the measured nitrification rate is less than half of the target nitrification rate, the nitrification reaction is suppressed. It will be too much. Therefore, the controller 9 increases the amount of air supplied from the air diffusers 6a and 6b at least upstream of the second ammonia meter 58b along the flow direction of the water to be treated in the reaction tank 2. Thereby, the control unit 9 controls the reaction tank 2 to perform the nitrification reaction at a desired nitrification rate.

  In the modification 9 demonstrated above, control of the denitrification process which was performed with the nitric acid meter in embodiment mentioned above is performed using a pair of ammonia meter. Thereby, in the reaction tank 2, nitrifying bacteria of aerobic bacteria and facultative anaerobic denitrifying bacteria can coexist and their activities can be activated together. Thereby, the nitrification reaction and the denitrification reaction can coexist in the reaction tank 2 with good controllability.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, Various deformation | transformation based on the technical idea of this invention is possible. For example, the numerical values given in the above-described embodiment are merely examples, and different numerical values may be used as necessary.

In the above-described embodiment, biological treatment of wastewater by the so-called standard activated sludge method has been described. However, the present invention is not necessarily limited to this method, and is applied to various treatment methods using an aerobic tank. can do. Specifically, the present invention relates to an AO (anaerobic-aerobic) method, an A ₂ O (anaerobic-anoxic-aerobic) method, a nitrification + endogenous denitrification method, a multi-step inflow nitrification denitrification method, and a multi-step inflow. It can be applied to various wastewater treatment methods using an aerobic tank such as the formula A ₂ O method.

  Moreover, as the reaction tank 2, it is also possible to employ a deep tank swirl reaction tank having a depth of about 10 m or a shallow tank reaction tank having a depth of about 5 m.

  Further, in the above-described embodiment, a nitric acid meter, a dissolved oxygen (DO) meter, an oxidation-reduction potential (ORP) meter, an ammonia meter, and a flow meter are used as the denitrification confirmation means, but it is not necessarily limited to these instruments. However, a BOD meter, a COD meter, a TOC meter, an Rr meter, an ATU-Rr meter, a UV meter, and the like can be employed.

  Moreover, in the above-described embodiment, the control unit and the gas supply amount control unit are separated, but these control unit and the gas supply amount control unit can also be configured from the same control unit, It is also possible to configure three or more separate bodies having similar functions.

  Moreover, in the above-described modified examples 7 and 8, the DO meter and the ORP meter are installed in the swirl flow reaction tank, but the present invention is not necessarily limited to the swirl flow reaction tank. If the reaction tank is capable of confirming the coexistence of the nitrification region, the DO concentration and ORP value in the denitrification region are measured with one instrument using a pair of DO meters and a pair of ORP meters, while the other By measuring the DO concentration and ORP value in the nitrification region with the instrument, the formation of the denitrification region and the nitrification region similar to the above can be controlled. Furthermore, in the reaction tank in which the denitrification region and the nitrification region appear alternately with time, as in the reaction tank 2 described in the modified example 5 described above, measurement with a pair of DO meters and ORP meters, It is also possible to use a single DO meter or ORP meter.

  Moreover, in the above-mentioned modified examples 7 and 8, the reaction tank 2 according to the third embodiment is used, and in the modified examples 9 and 10, the reaction tank 2 according to the second embodiment is used. 10, it is also possible to employ the reaction vessel 2 in the modified examples 3 to 6. In this case, by installing a meter installed in the denitrification region and a meter installed in the nitrification region in the nitrification region and the denitrification region that are confirmed to be formed in each reaction tank 2, respectively. The same effect as that of the embodiment can be obtained.

  Moreover, in the above-mentioned modification 9, the nitrification rate meter is composed of a plurality of ammonia meters, specifically a pair of ammonia meters, and the nitrification rate in the water to be treated in the reaction tank 2 is determined using this nitrification rate meter. Although the nitrification rate meter is measured, the nitrification rate meter is not necessarily limited to a pair of ammonia meters. Even if three or more ammonia meters are employed, various devices capable of measuring the nitrification rate may be employed. good.

DESCRIPTION OF SYMBOLS 1 First sedimentation tank 2 Reaction tank 2a, 2b, 2c, 2d Aerobic tank 3 Solid-liquid separation tank 4a Separation liquid 4b Activated sludge 5 Sludge return path 6, 6a, 6b, 6c, 6d, 16a, 16b, 16c, 26a, 26b, 26c, 26d, 26e, 36, 46 Aeration unit 7 Nitric acid meter 8 Blower 9 Control unit 10, 10a, 10b, 10c, 10d, 19a, 19b, 19c, 29a, 29b, 29c, 29d, 29e, 39, 49 Gas supply control unit 11 Ammonia meter 12 Anaerobic tank 12a Motor 12b Stirrer 13 Partition plate 31 Aerobic region 32 Anoxic anaerobic region 43 Carrier 43a Outer region 43b Inner region 51a First DO meter 51b Second DO meter 55a First ORP meter 55b Second ORP meter 58 Nitrification rate meter 58a First ammonia meter 58b Second ammonia meter

Claims (9)

In the reaction tank in which the nitrification reaction and the denitrification reaction are performed in parallel, the ammonia contained in the nitrogen-containing water is nitrified into nitric acid according to the flow of the nitrogen-containing water, and up to each position along the flow direction of the nitrogen-containing water. An aeration means for supplying a gas over substantially the entire region of the flow direction to the nitrogen-containing water so that the nitric acid is denitrified at a desired degree of progress of the denitrification reaction;
And a predetermined provided a is the middle position position, the nitric acid concentration measuring means for measuring the nitric acid concentration of the nitrogen-containing water definitive in the middle position location in the flow direction of the nitrogen-containing water,
An ammonia concentration measuring means provided upstream of the nitric acid concentration measuring means and configured to measure the ammonia concentration of the nitrogen-containing water flowing into the reaction tank ;
Based on the ammonia concentration measured by the ammonia concentration measuring means, the control concentration range of the nitric acid concentration at the middle position is specified, and the nitric acid concentration measured by the nitric acid concentration measuring means is within the control concentration range. A gas supply amount control means for controlling the gas supply means to control the gas supply amount by the air diffusion means at least upstream from the nitric acid concentration measurement means along the flow direction of the nitrogen-containing water;
Equipped with a,
The intermediate position is a position where the nitric acid concentration of the nitrogen-containing water can be controlled to 3% or more and 20% or less of the ammonia concentration measured by the ammonia concentration measuring means .   The wastewater treatment apparatus according to claim 1, wherein the ammonia concentration measuring means is installed in the vicinity of the inflow side of the nitrogen-containing water in the reaction tank.   The gas supply amount control means is configured to control the gas supply amount so that the nitric acid concentration is not less than 3% and not more than 20% of the ammonia concentration measured by the ammonia concentration measuring means. The wastewater treatment apparatus according to claim 1 or 2, characterized by the above. A biological treatment step of performing biological treatment by nitrification reaction and denitrification reaction on nitrogen-containing water flowing in the reaction tank;
According to the flow of the nitrogen-containing water, ammonia contained in the nitrogen-containing water is nitrified into nitric acid, and the nitric acid is denitrified at each degree along the flow direction of the nitrogen-containing water according to the degree of progress of the denitrification reaction. An air diffusion step for supplying a gas over the substantially entire region in the flow direction to the nitrogen-containing water,
A nitric acid concentration measuring step for measuring the nitric acid concentration of the nitrogen-containing water at a midway position that is a predetermined position in the flow direction of the nitrogen-containing water;
An ammonia concentration measuring step for measuring an ammonia concentration of the nitrogen-containing water flowing into the reaction tank at a position upstream of the intermediate position along the flow direction of the nitrogen-containing water in the reaction tank ;
Based on the ammonia concentration measured in the ammonia concentration measuring step, the control concentration range of the nitric acid concentration at the intermediate position is specified, and the nitric acid concentration measured in the nitric acid concentration measuring step is within the control concentration range . A gas supply amount control step for controlling a gas supply amount at least upstream from the intermediate position along the flow direction of the nitrogen-containing water;
Only including,
The intermediate position is a position where the concentration of nitric acid in the nitrogen-containing water can be controlled to 3% or more and 20% or less of the ammonia concentration measured in the ammonia concentration measuring step .   According to the passage of time or the flow direction of the nitrogen-containing water, a gas is supplied to the nitrogen-containing water so that a region where the nitrification reaction is performed and a region where the denitrification reaction is performed are sequentially or alternately formed. The wastewater treatment method according to claim 4.   In the gas supply amount control step, the gas supply amount is controlled so that the nitric acid concentration is 3% or more and 20% or less of the ammonia concentration measured in the ammonia concentration measurement step. The wastewater treatment method according to claim 4 or 5. Each position along the flow direction is provided at an intermediate position that is a predetermined position in the flow direction of the nitrogen-containing water flowing in the reaction tank, and ammonia contained in the nitrogen-containing water is nitrified into nitric acid according to the flow direction. The nitrogen-containing water nitric acid is supplied at the intermediate position with respect to the nitrogen-containing water to which the gas is supplied over substantially the entire region of the flow direction so that the nitric acid is denitrified at a predetermined degree of denitrification. Nitric acid concentration measuring means for measuring the concentration;
An ammonia concentration measuring means provided upstream of the nitric acid concentration measuring means and configured to measure the ammonia concentration of the nitrogen-containing water flowing into the reaction tank ;
Based on the ammonia concentration measured by the ammonia concentration measuring means, the control concentration range of the nitric acid concentration at the middle position is specified, and the nitric acid concentration measured by the nitric acid concentration measuring means is within the control concentration range . Gas supply amount control means for controlling the supply amount of gas supplied to the nitrogen-containing water at least upstream from the nitric acid concentration measurement means along the flow direction of the nitrogen-containing water;
Equipped with a,
The intermediate position is a position where the concentration of nitric acid in the nitrogen-containing water can be controlled to 3% or more and 20% or less of the ammonia concentration measured by the ammonia concentration measuring means . Degree of progress of the denitrification reaction in which ammonia contained in the nitrogen-containing water is nitrified into nitric acid according to the flow of nitrogen-containing water flowing in the reaction tank, and nitric acid is defined up to each position along the flow direction of the nitrogen-containing water With respect to the aeration means for supplying gas to the nitrogen-containing water over substantially the entire region in the flow direction so as to be denitrified at
The nitric acid concentration, which is provided at a predetermined position in the flow direction of the nitrogen-containing water and confirmed by the nitric acid concentration measuring means for measuring the nitric acid concentration of the nitrogen-containing water at the intermediate position, and the nitrogen-containing water Based on the ammonia concentration measured by the ammonia concentration measuring means provided upstream of the nitric acid concentration measuring means along the flow direction and configured to measure the ammonia concentration of the nitrogen-containing water flowing into the reaction vessel. Based on the control concentration range of nitric acid concentration at the intermediate position to be defined, along the flow direction of the nitrogen-containing water so that the nitric acid concentration measured by the nitric acid concentration measuring means is within the control concentration range, Control the gas supply amount at least upstream from the nitric acid concentration measuring means ,
The intermediate position is a position where the concentration of nitric acid in the nitrogen-containing water can be controlled to 3% or more and 20% or less of the ammonia concentration measured by the ammonia concentration measuring means . In the middle position which is a predetermined position in the flow direction of the nitrogen-containing water flowing in the reaction tank, ammonia contained in the nitrogen-containing water is nitrified according to the flow direction, and nitric acid is nitrated up to each position along the flow direction. The nitrogen concentration of the nitrogen-containing water is set at the intermediate position with respect to the nitrogen-containing water in which gas is supplied over substantially the entire region in the flow direction so that the nitrogen is denitrified at the specified degree of progress of the denitrification reaction. A nitric acid concentration measuring step to be measured;
An ammonia concentration measuring step for measuring the ammonia concentration of the nitrogen-containing water flowing into the reaction tank at a position upstream from the intermediate position along the flow direction of the nitrogen-containing water ;
Based on the ammonia concentration measured in the ammonia concentration measuring step, the control concentration range of the nitric acid concentration at the intermediate position is specified, and the nitric acid concentration measured in the nitric acid concentration measuring step is within the control concentration range . A gas supply amount control step for controlling a supply amount of gas supplied to the nitrogen-containing water at least upstream from the intermediate position along the flow direction of the nitrogen-containing water;
To the computer ,
The program is characterized in that the intermediate position is a position where the nitric acid concentration of the nitrogen-containing water can be controlled to 3% or more and 20% or less of the ammonia concentration measured in the ammonia concentration measuring step .

Images