JP2010099560A - Air supply system and air supply method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air supply system and an air supply method detecting the concentration of nitrous oxide gas in a reactor supplied with air, and highly precisely controlling a generation amount of nitrous oxide gas. <P>SOLUTION: The air supply system S supplies air into the reactor 2 for sewage treatment using aerobic microorganisms, and includes a gas concentration sensor 6 detecting the concentration of nitrous oxide gas G generated from the reactor 2, and a computer 5 controlling the amount of air B supplied to the reactor 2 based on the variation of concentration data 1 by the gas concentration sensor 6. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an air supply system and an air supply method, and more particularly to an air supply system that supplies air for promoting reaction into a reaction tank in sewage treatment using aerobic microorganisms.

  In sewage treatment, so-called aerobic treatment using aerobic microorganisms has been conventionally performed for nitrification of ammonia nitrogen contained in sewage such as domestic wastewater and factory wastewater. In this aerobic treatment, aerobic microorganisms such as nitrifying bacteria are introduced into sewage in a reaction tank, or decomposition treatment is performed in an oxygen environment using aerobic microorganisms originally present in sewage.

  For example, the sewage from which the precipitated sludge has been removed in the first settling tank is sent to the reaction tank and subjected to aerobic treatment in the reaction tank. At that time, aerobic microorganisms nitrify ammoniacal nitrogen using oxygen to produce nitric acid or nitrous acid while growing. The grown aerobic microorganisms form flocs, stay in the reaction tank as activated sludge, and settle in the final sedimentation tank. Part of the activated sludge is collected and removed, and incinerated in the sludge incineration process. The supernatant water from which the activated sludge has been removed is sent to the final sedimentation basin for the next treatment.

  In this reaction tank, aeration is often performed to promote the nitrification reaction. Aeration is performed by supplying air or oxygen to the sewage in the reaction tank, thereby increasing the dissolved oxygen concentration of the sewage and promoting the reaction of aerobic microorganisms.

On the other hand, it is known that nitrous oxide gas (also referred to as N ₂ O gas or dinitrogen monoxide gas) is generated in the aerobic treatment in the reaction tank. This nitrous oxide gas is a greenhouse gas, and its greenhouse effect is as high as about 310 times that of carbon dioxide (CO ₂ ) gas. Therefore, in the treatment in the reaction tank, suppressing the generation of nitrous oxide gas is urgently required from the viewpoint of protecting the global environment.

  For example, in Patent Document 1, in AOSBR (anoxic / aerobic batch activated sludge process), nitrous oxide gas is monitored, and the end of nitrification reaction is determined by detecting the end of its generation. A proposal for determining energy allocation is disclosed. In addition, a proposal for determining whether the nitrification reaction is stagnant or worsened based on the generation time of nitrous oxide gas is also disclosed. Thereby, based on the presence or absence of nitrous oxide gas and the generation time thereof, it is possible to detect whether the process is good or bad, and contribute to optimal system operation.

JP 2007-244949 A

  However, what is disclosed in the above-mentioned Patent Document 1 is to detect whether processing is good / bad based on the presence or absence of nitrous oxide gas or the generation time thereof, and based on the concentration of nitrous oxide gas, It does not precisely control (reduce) the generation amount. Further, Patent Document 1 does not disclose a method for reducing nitrous oxide gas generated in a reaction tank in a treatment method other than AOSBR (for example, a standard method).

  Therefore, for example, in a sewage treatment system based on a general standard method having a first settling basin, a reaction tank, and a final settling basin, the amount of nitrous oxide gas generated in a reaction tank where aerobic treatment is performed by air supply is accurately determined. Proposals to control are needed.

  The present invention has been made in view of the above circumstances, and is capable of detecting the concentration of nitrous oxide gas in a reaction tank in which air is supplied, and controlling the amount of nitrous oxide gas generated with high accuracy. It is an exemplary problem to provide a supply system and an air supply method.

  In order to solve the above-described problems, an air supply system as an exemplary aspect of the present invention is an air supply system that supplies air into a reaction tank for performing sewage treatment using aerobic microorganisms. Concentration detection means for detecting the concentration of nitrous oxide gas generated from the tank, and control means for controlling the amount of air supplied into the reaction tank based on a change in detected concentration by the concentration detection means.

  Since the concentration of nitrous oxide gas generated from the reaction tank is detected and the amount of supplied air is controlled based on the change in the detected concentration, the amount of nitrous oxide gas generated from the reaction tank can be finely controlled, This can contribute to a reduction in the amount of nitrous oxide gas generated.

  More specifically, when the amount of air supplied into the reaction tank is an appropriate amount, the nitrification reaction by aerobic microorganisms is performed appropriately. As a result, the amount of nitrous oxide gas generated in the reaction tank is reduced. Less gas concentration is low. However, even if the supply air amount is constant, the dissolved oxygen concentration in the sewage is appropriate depending on external factors such as the amount of sewage flowing into the reaction tank (sewage treatment amount), the degree of stirring, the temperature, and the amount of activated sludge. In some cases, the nitrification reaction may not be performed properly due to excessive or insufficient reaction.

  If the nitrification reaction is not performed properly, the amount of nitrous oxide gas generated increases as a result, and the detected nitrous oxide gas concentration also becomes high. Therefore, if the amount of air supplied to the reaction tank is controlled to adjust the dissolved oxygen concentration in the sewage based on the change in the detected concentration by the concentration detection means (for example, an increase in the detected concentration), the nitrification reaction is again appropriate. Heading to the reaction, the amount of nitrous oxide gas generated can be reduced.

  In addition, the nitrification reaction being appropriately performed means that the nitrification reaction proceeds as designed according to the purpose of treatment in the sewage treatment facility. Specifically, the nitrification reaction is sufficiently advanced to be ammoniacal. This includes a case where most of nitrogen is changed to nitric acid and a case where nitric acid or nitrous acid is hardly generated without causing a nitrification reaction to proceed. When this nitrification reaction is optimized, the amount of nitrous oxide gas generated is small. Aerobic microorganisms include bacteria (nitrifying bacteria) that nitrify ammonia nitrogen into nitric acid or nitrous acid by oxygen respiration, and heterotrophic bacteria that decompose organic substances using oxygen.

  In addition, the air supply system according to the present invention can be applied to a reaction tank in a sewage treatment facility, and the sewage treatment facility includes various types such as non-nitrification type, nitric acid type, nitrite type, and nitrification denitrification type. Can be included. The sewage treatment facilities include those in which sewage is sent from the first settling tank to the final settling tank via the reaction tank and those having a batch type reaction tank that also serves as the settling tank. In addition to the standard method in which only the aerobic treatment is performed in the reaction tank, an advanced treatment method (AO method, A2O method, AOAA law etc.) are also included. It also includes treatment facilities related to the so-called standard activated sludge method, circulating nitrification denitrification method, step inflow type AOAO method, and step inflow type A2O method.

  The air supply to the reaction tank includes a case where it is performed by an air diffuser that discharges air from a porous head disposed in the sewage, and a case where it is performed by an aerator that performs air injection and agitation into the sewage. Further, since oxygen is required for the nitrification reaction in the reaction tank, oxygen supply may be performed instead of air supply.

  As the concentration detection means, a known concentration sensor capable of detecting the nitrous oxide gas concentration can be applied. The control means is typically a computer, but may of course be a general-purpose computer or a dedicated computer (CPU) that sends an operation command based on the control algorithm according to the present invention.

  The control means may perform control to reduce the amount of air based on an increase in the detected concentration.

  Some sewage treatment facilities perform an operation with a relatively short residence time in the reaction tank (that is, an undigested type). This non-nitrification type sewage treatment facility does not aim at nitrification of sewage but aims at treatment by the so-called standard activated sludge method for the purpose of decomposing organic substances contained in sewage. Therefore, the organic matter is decomposed by aerobic microorganisms, but the sewage residence time in the reaction tank is short so that ammonia nitrogen is not much nitrified (that is, the reaction tank is small relative to the flow rate of sewage). Designed. In such a processing facility, the nitrification reaction does not progress so much in a normal state, so that the generation of nitrous oxide gas from the reaction tank is small.

  However, the amount of sewage to be treated in the sewage treatment plant is not always constant, and generally varies according to time. For example, when the amount of sewage to be treated decreases in the night time zone, the sewage flow rate decreases and the sewage residence time in the reaction tank becomes longer. If it does so, the nitrification reaction of ammonia nitrogen by the aerobic microorganism in the reaction tank which should not have progressed much progresses, and nitrous oxide gas is generated as shown in the following reaction formula.

  However, in the present invention, since the amount of air supplied into the reaction tank is reduced based on the increase in the nitrous oxide gas concentration, the progress of the nitrification reaction can be decelerated or stopped even when the sewage flow rate is small. As a result, the nitrification reaction does not proceed and the amount of nitrous oxide gas generated can be reduced. Even if the residence time of the sewage is unexpectedly long, the progress of the nitrification reaction can be prevented and the generation of nitrous oxide gas can be suppressed.

  The control means may perform control to increase the amount of air based on an increase in the detected concentration.

  Some sewage treatment facilities perform an operation with a relatively long residence time in the reaction tank (for example, nitric acid type, nitrification denitrification type). This nitric acid type sewage treatment facility aims to nitrify sewage in a reaction tank. Further, the nitrification and denitrification type sewage treatment facility is intended to nitrify and denitrify sewage in a reaction tank. Therefore, the residence time of the sewage in the reaction tank is designed to be long (that is, the reaction tank is larger than the flow rate of the sewage) so that the nitrification reaction by the aerobic microorganism is sufficiently performed. In such a processing facility, the nitrification reaction proceeds almost completely in a normal state, so that the generation of nitrous oxide gas from the reaction tank is small.

  However, for example, when the amount of sewage to be treated increases in the daytime period, the sewage flow rate increases and the sewage residence time in the reaction tank becomes shorter. As a result, the contact time between the aerobic microorganism and the dissolved oxygen in the reaction tank is shortened, and anaerobic denitrification reaction occurs partially, resulting in an insufficient nitrification reaction of ammonia nitrogen. As a result, nitrous oxide gas is generated as shown in the following reaction formula.

  However, in the present invention, the amount of air supplied into the reaction tank is increased based on the increase in the concentration of nitrous oxide gas, so that the contact time between the aerobic microorganism and dissolved oxygen is sufficiently increased even when the flow rate of sewage is large. It can be secured for a long time. As a result, the nitrification reaction can be promoted and sufficiently progressed, and the amount of nitrous oxide gas generated can be reduced. Even if the residence time of sewage is shortened unexpectedly, the nitrification reaction can be sufficiently advanced to suppress the generation of nitrous oxide gas.

  The air supply system further includes a residence time detecting means for detecting the residence time of the sewage in the reaction tank, and the control means supplies the air supplied into the reaction tank based on the detected change in the residence time and the detected concentration. The amount may be controlled.

  Since the residence time detection means detects the residence time of the sewage in the reaction tank, it is possible to grasp the change of the residence time, that is, whether the residence time is increasing or decreasing. And by controlling the amount of air supplied into the reaction tank based on the change in the residence time and the change in the detected concentration, the sewage treatment equipment such as nitric acid type and nitrification denitrification type is also used in the non-nitrification type sewage treatment equipment. Also, the nitrification reaction can be optimized and the amount of nitrous oxide gas generated can be reduced.

  The control means may perform control to decrease the air amount based on increase in residence time and increase in detected concentration, and control to increase air amount based on decrease in residence time and increase in detected concentration.

  If the detected concentration increases when the residence time increases, it can be determined that the sewage treatment facility is a facility that is operating with a short residence time, that is, an unnitrified facility. If the control for reducing the amount of air is performed based on the determination, the progress of the nitrification reaction can be decelerated or stopped to reduce the generation amount of nitrous oxide gas.

  On the other hand, if the detected concentration increases when the residence time decreases, it is determined that the sewage treatment facility is a facility that operates for a long residence time, that is, a nitrate type, nitrification denitrification type, etc. Can do. If control for increasing the amount of air is performed based on the determination, the nitrification reaction can be promoted and sufficiently progressed, and the amount of nitrous oxide gas generated can be reduced.

  Without having to change the control mode for each processing mode in the sewage treatment facility, it is possible to automatically determine a plurality of processing modes and appropriately control the supply air amount for each processing mode.

  The residence time detection means may include a flow meter that measures the flow rate of sewage in the reaction tank, or a flow rate calculation means that calculates the flow rate.

  Since the capacity of the reaction tank is constant in a specific sewage treatment facility, if the flow rate of sewage in the reaction tank (that is, the amount of sewage flowing into the reaction tank or the amount of sewage flowing out of the reaction tank) is detected. The residence time of sewage in the reaction vessel can be detected based on the flow rate. For example, if the residence time detecting means is configured using a flow meter, the system according to the present invention can be configured with a simple configuration at low cost.

  In a stable system, the amount of sewage flowing into the reaction tank and the amount of sewage outflow from the reaction tank are substantially the same, which is substantially equivalent to the flow rate of sewage in the reaction tank. Further, for example, in a system in which sewage is fed to a first sedimentation basin by a pump and sewage is fed from the first sedimentation basin to a reaction tank, the amount of water fed by the pump is equivalent to the flow rate in the reaction tank.

  For example, when the flow rate of sewage in the reaction vessel is detected by a flow meter, if the capacity V and flow rate (measured value by the flow meter) Q of the reaction vessel are set, the residence time T is set to T = V / Q by the flow rate calculation means. Can be calculated. The flow rate calculation means may be, for example, a computer having a CPU, or a control device that records a specific calculation procedure as a program as described above and outputs a residence time in response to an input of a flow rate measurement value. Also good.

  In addition, when the absolute value of the residence time is not necessarily required and only the change (increase or decrease) of the residence time needs to be detected, the flow rate Q and the residence time T are in an inversely proportional relationship. No calculation by the calculation means is required. It is also possible to detect a change in residence time based only on the measurement value of the flow meter.

  On the other hand, when the sewage is first sent to the settling basin by the pump, the flow rate in the reaction vessel is calculated by the flow rate calculation means without using a flow meter based on the rotational speed of the pump and the HQ curve. You can also According to this method, since the flow rate of sewage and hence the residence time of sewage based on the flow rate can be detected without using a flow meter, the system can be made simple and inexpensive.

  The air supply system further has a nitrification rate detection means for detecting the nitrification rate of sewage in the reaction tank, and the control means supplies the air supplied into the reaction tank based on the detected change in nitrification rate and change in detected concentration. The amount may be controlled.

  Since the nitrification rate detection means detects the nitrification rate of the sewage in the reaction tank, it is possible to grasp the change in the nitrification rate, that is, whether the nitrification rate tends to increase (acceleration) or decrease (deceleration). . And by controlling the amount of air supplied into the reaction tank based on the change in the nitrification speed and the change in the detected concentration, the sewage treatment facilities such as nitric acid type and nitrification denitrification type are also used in the non-nitrification type sewage treatment facilities. Also, the nitrification reaction can be optimized and the amount of nitrous oxide gas generated can be reduced.

  The control means may perform control to decrease the air amount based on an increase in nitrification speed and increase in detected concentration, and control to increase the air amount based on decrease in nitrification speed and increase in detected concentration.

  When the detected concentration increases when the nitrification rate increases, it can be determined that the sewage treatment facility is a facility that operates with a short residence time, that is, an unnitrified facility. If the control for reducing the amount of air is performed based on the determination, the progress of the nitrification reaction can be decelerated or stopped to reduce the generation amount of nitrous oxide gas.

  On the other hand, if the detected concentration increases when the nitrification rate decreases, it is judged that the sewage treatment facility is a facility that operates for a long residence time, that is, a nitrate type, nitrification denitrification type, etc. Can do. If control for increasing the amount of air is performed based on the determination, the nitrification reaction can be promoted and sufficiently progressed, and the amount of nitrous oxide gas generated can be reduced.

  Without having to change the control mode for each processing mode in the sewage treatment facility, it is possible to automatically determine a plurality of processing modes and appropriately control the supply air amount for each processing mode.

  The nitrification rate detection means may include a respiration rate meter that measures oxygen uptake by sewage in the reaction tank.

By using a respiration rate meter, oxygen uptake by sewage in the reaction tank can be measured. Since the change in the rate of oxygen uptake substantially indicates the change in the rate of nitrification reaction by aerobic microorganisms in the reaction tank, a nitrification rate detection means can be configured by a respiration rate meter. Therefore, the system according to the present invention can be configured at a low cost with a simple configuration. The nitrification rate can also be detected by detecting the concentration of NH ₄ —N, NO ₂ —N or NO ₃ —N in the reaction tank.

  You may have a cover part which covers the opening of a reaction tank in order to collect the nitrous oxide gas which generate | occur | produces from a reaction tank, and the derivation | leading-out means which guides the nitrous oxide gas collected by the cover part to a density | concentration detection means.

  The cover portion covers the opening of the reaction tank and collects nitrous oxide gas, and the derivation means guides it to the concentration detection means, so that the nitrous oxide gas generated from the reaction tank is hardly leaked to the concentration detection means. Can lead. The accuracy of concentration detection by the concentration detection means can be improved, and the efficiency of nitrous oxide gas reduction by this air supply system can be improved.

  An air supply method according to another exemplary aspect of the present invention is an air supply method for supplying air into a reaction tank for performing sewage treatment using aerobic microorganisms, the nitrous oxide generated from the reaction tank. A step of detecting the concentration of the gas, and a step of controlling the amount of air supplied into the reaction tank based on a change in the detected concentration by the concentration detecting means.

  According to this air supply method, the same effect as the above air supply system can be obtained. That is, since the concentration of nitrous oxide gas generated from the reaction tank is detected and the amount of supplied air is controlled based on the change in the detected concentration, the amount of nitrous oxide gas generated from the reaction tank can be finely controlled. This can contribute to a reduction in the amount of nitrous oxide gas generated.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, since the concentration of nitrous oxide gas generated from the reaction tank is detected and the amount of supplied air is controlled based on the change in the detected concentration, the amount of nitrous oxide gas generated from the reaction tank is finely defined. The amount of nitrous oxide gas generated can be reduced with high accuracy.

[Embodiment 1]
<Sewage treatment plant with short residence time>
Hereinafter, an air supply system S according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram schematically showing an outline of the overall configuration of a sewage treatment facility A to which an air supply system S according to Embodiment 1 of the present invention is applied. This sewage treatment facility A has an initial settling basin 1, a reaction tank 2, and a final settling basin 3, and performs unnitrified sewage treatment by a so-called standard activated sludge method. Is set relatively short.

  The first sedimentation basin 1 is a sedimentation basin into which sewage W flows as a supernatant from which large particles of dust, sand, and the like have been removed in the upstream sedimentation basin. In the first sedimentation basin 1, the sewage W is allowed to flow gently to deposit dust with relatively small particles. And the sewage W as a supernatant from which the dust etc. of the particle | grains were removed is sent to the reaction tank 2 of the downstream from the sedimentation tank 1 initially.

  The reaction tank 2 is for purifying the sewage W initially sent from the settling basin 1 by performing an aerobic treatment with an aerobic microorganism. In the reaction tank 2, there are heterotrophic bacteria and autotrophic bacteria (nitrifying bacteria) as aerobic microorganisms. The heterotrophic bacteria grow while decomposing organic substances in the sewage W while consuming oxygen, form flocs, stay in the reaction tank 2, and settle at the bottom of the final sedimentation basin. Nitrifying bacteria also nitrify ammonia nitrogen in the sewage W while consuming oxygen. However, since the nitrification reaction is slower than the decomposition of organic matter, the residence time of the sewage W in the reaction tank 2 is set short. As a result, the nitrification reaction can be made to hardly proceed. The sewage treatment facility A according to the first embodiment is a treatment facility that has a short residence time and is mainly intended for decomposition of organic substances, but does not aim at nitrification.

  The air supply system S according to Embodiment 1 of the present invention is applied to the reaction tank 2. FIG. 2 is a schematic configuration diagram schematically showing an outline of the reaction tank 2 and its peripheral portion in the sewage treatment facility A. This air supply system S is roughly configured to include an air diffuser 4, a computer (control means) 5, a gas concentration sensor (concentration detection means) 6, a cover portion 7, and a guide tube (lead-out means) 8.

  The air diffuser 4 is a device that is installed in the reaction tank 2 and discharges air B into the sewage W. For example, an air pump, a porous member, an intake pipe, and the like are configured. The air is sucked into the sewage W from the porous member through the intake pipe, and the details are omitted. The air diffuser 4 can control the amount of air to be supplied based on a control command from the computer 5.

  The computer 5 is for controlling the amount of air released (amount of supply air) by the air diffuser 4. The computer 5 is connected to the air diffuser 4 and the gas concentration sensor 6, and sends out a control command D <b> 2 for controlling the amount of supplied air toward the air diffuser 4 based on the concentration data D <b> 1 from the gas concentration sensor 6. Has the function of For example, the computer 5 has a CPU and a storage device. An air supply program is stored in the storage device. Based on the function of the program, the CPU as the main part of the computer 5 receives the concentration data D1 from the gas concentration sensor 6, and based on the concentration data D1. You may be comprised so that the function which determines the density | concentration change of the nitrous oxide gas G mentioned later and the function which transmits control instruction | command D2 toward the diffuser 4 according to the determination result of a density | concentration change may be exhibited.

  The gas concentration sensor 6 is for detecting the gas concentration of the nitrous oxide gas G generated from the reaction tank 2. Here, the gas concentration of the nitrous oxide gas G generated from the reaction tank 2 means that the nitrous oxide generated in the liquid phase in the reaction tank 2 causes a phase transfer to the gas phase, and as a result, from the reaction tank 2 It means the concentration of nitrous oxide gas G released in the gas state. The phase transfer of nitrous oxide occurs due to a concentration difference between the nitrous oxide concentration in the liquid phase and the nitrous oxide gas concentration in the supplied air B.

  The gas concentration sensor 6 constantly or continuously monitors the concentration of the nitrous oxide gas G, and transmits the concentration data D1 to the computer 5 constantly or continuously. Nitrous oxide gas G is not generated in the decomposition reaction of organic matter by heterotrophic bacteria in the reaction tank 2, but the nitrifying bacteria in the reaction tank 2 become longer as the residence time of the sewage W in the reaction tank 2 becomes longer. As a result, the amount of nitrous oxide gas G generated increases, and as a result, the concentration detected by the gas concentration sensor 6 increases.

  The cover portion 7 is a lid member that covers the opening of the reaction tank 2 and collects the nitrous oxide gas G from the reaction tank 2. One end of the guide tube 8 is connected to a part of the cover portion 7, and the other end of the guide tube 8 is connected to the gas concentration sensor 6. And the nitrous oxide gas G collected by the cover part 7 can be guide | induced to the gas concentration sensor 6 almost without leaking outside.

  The sewage W purified by the decomposition of the organic matter by the aerobic treatment in the reaction tank 2 is sent to the final settling basin 3 on the downstream side. In the final sedimentation basin 3, flocs generated in the reaction tank 2 are settled. The precipitate is condensed and partly incinerated as surplus sludge, or returned to the reaction tank 2 and used as an aerobic microorganism source. The sewage W as a supernatant is subjected to sterilization and pH adjustment and discharged into rivers and open seas.

  Next, the operation of the air supply system S will be described.

  When the concentration of the nitrous oxide gas G generated from the reaction tank 2 is detected by the gas concentration sensor 6, the gas concentration sensor 6 transmits concentration data D <b> 1 to the computer 5. The computer 5 receives the concentration data D1 from the gas concentration sensor 6 constantly or continuously, and determines the concentration change.

  Specifically, when the residence time of the sewage W in the reaction tank 2 becomes longer and the nitrification reaction proceeds, the concentration data D1 tends to increase. Therefore, the computer 5 determines whether or not the concentration data D1 is increasing, and transmits a control command D2 for reducing the amount of supplied air to the air diffuser 4 when the concentration data D1 is increasing. When the air diffuser 4 that has received the control command D2 reduces the supply air amount, the nitrification reaction in the reaction tank 2 is decelerated or stopped. Then, the generation amount of the nitrous oxide gas G decreases, and the concentration data D1 obtained by the gas concentration sensor 6 also starts to decrease. When determining the decreasing tendency of the concentration data D1, the computer 5 stops transmission of the control command D2 for decreasing the supply air amount, and transmits, for example, a control command D2 for maintaining or increasing the supply air amount to the aeration device 4.

  Various modes can be considered for the transmission mode of the control command D2 based on the density data D1. For example, an upper limit value of the concentration may be determined in advance, and when the detected concentration data D1 exceeds the upper limit value, a control command D2 for reducing the supply air amount by a predetermined amount may be transmitted. In this case, when the concentration data D1 is less than a preset lower limit value, a control command D2 for increasing the supply air amount by a predetermined amount can be transmitted.

  In addition, a reference value (reference speed) of the concentration increase rate (concentration increase amount per hour) is set in advance, and when the concentration increase rate based on the detected concentration data D1 exceeds the reference speed, the amount of supplied air It is also possible to adopt a configuration in which a control command D2 for reducing the predetermined amount is transmitted. In this case, when the concentration decrease rate based on the detected concentration data D1 is less than a preset reference deceleration, a control command D2 for increasing the supply air amount by a predetermined amount can be transmitted.

  The control command D2 may be transmitted so as to set the decrease amount of the supply air amount in accordance with the increment of the concentration data D1 (for example, in proportion). That is, it can be set so that the decrease in the supply air amount is small when the increase in the concentration data D1 is small, and the decrease in the supply air amount is large when the increase in the concentration data D1 is large. Of course, in this case, the control command D2 is transmitted so as to set the increase amount of the supply air amount in accordance with the decrease amount of the concentration data D1.

[Embodiment 2]
<Sewage treatment plant with long residence time>
An air supply system S according to Embodiment 2 of the present invention will be described. The configuration of the air supply system S and the sewage treatment facility A to which the air supply system S is applied is substantially the same as that described in the first embodiment, and will be described based on the same reference numerals with reference to FIGS. 1 and 2. To do. This sewage treatment facility A performs nitric acid-type sewage treatment by a so-called standard activated sludge method. By setting the residence time of the sewage W to be relatively long, nitrification by nitrifying bacteria is actively carried out in the reaction tank 2. The reaction proceeds.

  In the reaction tank 2, there are nitrifying bacteria as autotrophic bacteria together with heterotrophic bacteria. Then, heterotrophic bacteria decompose organic substances in the sewage W, and nitrifying bacteria nitrify ammoniacal nitrogen in the sewage W. Since the residence time of the sewage W in the reaction tank 2 is long, the nitrification reaction proceeds sufficiently. In this processing state, the generation of nitrous oxide gas G from the reaction tank 2 is only accompanied by the nitrification reaction.

  However, if the residence time in the reaction tank 2 is shortened due to an external factor such as an increase in the amount of treated sewage, sufficient contact time between the supply air B from the air diffuser 4 and the nitrifying bacteria in the sewage W is secured. It becomes difficult to do. As a result, the amount of supplied oxygen is insufficient, the nitrification reaction cannot proceed sufficiently, and an anaerobic reaction (denitrification reaction) due to anoxia occurs in a part of the sewage W. Nitrous oxide gas G is generated by this denitrification reaction, and the concentration detected by the gas concentration sensor 6 increases.

  Therefore, in the air supply system S according to the second embodiment, the computer 5 diffuses the control command D2 for increasing the supply air amount in accordance with the increase in the detected concentration of the nitrous oxide gas G by the gas concentration sensor 6. Transmit to the device 4. When the amount of supply air increases, a sufficient contact time between dissolved oxygen and nitrifying bacteria caused by the supply air B can be secured, the nitrification reaction is promoted and proceeds sufficiently, and the nitrous oxide gas G Generation can be reduced.

  For example, in the air supply system S, when the concentration of the nitrous oxide gas G generated from the reaction tank 2 is detected by the gas concentration sensor 6, the gas concentration sensor 6 transmits the concentration data D <b> 1 to the computer 5. . The computer 5 receives the concentration data D1 from the gas concentration sensor 6 constantly or continuously, and determines the concentration change.

  Specifically, when the residence time of the sewage W in the reaction tank 2 is shortened and the nitrification reaction does not proceed sufficiently, the concentration data D1 tends to increase. Therefore, the computer 5 determines whether or not the concentration data D1 is increasing, and transmits a control command D2 for increasing the supply air amount to the air diffuser 4 when the concentration data D1 is increasing. When the air diffuser 4 that has received the control command D2 increases the supply air amount, the nitrification reaction in the reaction tank 2 is transmitted and proceeds sufficiently. Then, the generation amount of the nitrous oxide gas G decreases, and the concentration data D1 obtained by the gas concentration sensor 6 also starts to decrease. When determining the decreasing tendency of the concentration data D1, the computer 5 stops transmission of the control command D2 for increasing the supply air amount, and transmits, for example, a control command D2 for maintaining or decreasing the supply air amount to the aeration device 4.

[Embodiment 3]
FIG. 3 is a schematic configuration diagram schematically showing a schematic configuration of an air supply system S3 according to Embodiment 3 of the present invention. This air supply system S3 includes a diffuser 4, a computer (control means) 5, a gas concentration sensor (concentration detection means) 6, a cover 7 and a guide tube (lead-out means) 8, and a flow meter (residence time detection means). ) 9.

  The flow meter 9 is disposed in the middle of the flow path from the first sedimentation basin 1 to the reaction tank 2 so that the flow rate of the sewage W flowing into the reaction tank 2 can be measured. The flow meter 9 and the computer 5 are connected to each other so that flow rate data D3 from the flow meter 9 can be transmitted to the computer 5.

  Further, when the sewage W is first sent to the settling tank 1 by a pump (not shown), the flow rate to the reaction tank 2 can be calculated based on the rotation speed of the pump and the HQ curve.

  Since the capacity of the reaction tank 2 is constant, if the flow rate of the sewage W can be measured by the flow meter 9, the residence time of the sewage W in the reaction tank 2 can be roughly calculated. For example, when the flow rate Q of the sewage W and the capacity of the reaction tank are V, the residence time T of the sewage W in the reaction tank 2 is T = V / Q, and the flow rate Q and the residence time T are inversely related. Become.

  The air supply system S3 controls the amount of air supplied into the reaction tank 2 based on information on both the residence time T and the concentration detected by the gas concentration sensor 6. That is, as shown in Table 1, when the residence time T is increasing and the detected concentration by the gas concentration sensor 6 is increasing, it can be determined that the sewage treatment facility is non-nitrating. In order to reduce the generation amount of nitrous oxide gas, control is performed to reduce the supply air amount. On the other hand, when the concentration detected by the gas concentration sensor 6 is increasing when the residence time T is decreasing, it can be determined that the sewage treatment facility is a nitric acid type, and the amount of nitrous oxide gas generated In order to reduce the amount of air, control is performed to increase the amount of supplied air.

  Specifically, the air supply system S3 performs an operation based on the flowchart shown in FIG.

  When the concentration of the nitrous oxide gas G generated from the reaction tank 2 is detected by the gas concentration sensor 6, the gas concentration sensor 6 transmits concentration data D1 to the computer 5 (S.1). When the flow rate of the sewage W flowing into the reaction tank 2 is measured by the flow meter 9, the flow meter 9 transmits the flow rate data D3 to the computer 5 (S.2). The computer 5 receives the concentration data D1 and the flow rate data D3 constantly or continuously.

  The computer 5 determines whether or not the flow rate data D3 is decreasing (S.3). When it is determined that the flow rate data D3 is in a decreasing trend (increase in residence time T) (S.3: Y), it is further determined whether or not the concentration data D1 is in an increasing trend (S.4). ). When it is determined that the concentration data D1 is increasing (S.4: Y), it is determined that the treatment mode of the sewage treatment facility is the non-nitrification type (S.5), and the supply is directed to the air diffuser 4 A control command D2 for reducing the air amount is transmitted (S.6). The fact that the flow rate data D3 is decreasing is synonymous with the tendency that the residence time T is increasing, and that the flow rate data D3 is increasing and that the residence time T is decreasing. It is synonymous. Further, the degree of decrease in the supply air amount may be set based on the decrease amount or decrease rate of the flow rate data D3, or the increase amount or increase rate of the concentration data D1. On the other hand, when it is determined that the flow rate data D3 is decreasing (S.3: Y) and the concentration data D1 is decreasing (S.4: N), the sewage treatment facility is a nitric acid type. (S.7).

  When the computer 5 determines that the flow rate data D3 has an increasing tendency (decreasing tendency of the residence time T) (S.3: N), and further determines that the concentration data D1 has an increasing tendency (S .8: Y), it is determined that the treatment mode of the sewage treatment facility is a nitric acid type (S.9), and a control command D2 for increasing the amount of supplied air is transmitted to the air diffuser 4 (S.10). . On the other hand, when it is determined that the flow rate data D3 is increasing (decreasing tendency of the residence time T) (S.3: N), when it is further determined that the concentration data D1 is decreasing (S.8). : N), it is determined that the treatment mode of the sewage treatment facility is the non-nitrification type (S.11).

[Embodiment 4]
FIG. 5 is a schematic configuration diagram schematically showing a schematic configuration of an air supply system S4 according to Embodiment 4 of the present invention. The air supply system S3 includes a diffuser 4, a computer (control means) 5, a gas concentration sensor (concentration detection means) 6, a cover 7 and a guide tube (lead-out means) 8, and a respiration rate meter (nitrification rate detection). Means) 10.

  The respiration rate meter 10 is arranged in the reaction tank 2 and can measure the oxygen intake amount and / or the oxygen intake rate in the reaction tank 2. The respiration rate meter 10 and the computer 5 are connected so that measurement data D4 from the respiration rate meter 10 can be transmitted to the computer 5.

  This oxygen intake indicates the activity of nitrifying bacteria in the reaction tank 2. That is, if the nitrification reaction by nitrifying bacteria is promoted, the oxygen consumption increases, and the numerical value of the measurement data D4 by the respiration rate meter 10 also increases. Conversely, if the nitrification reaction by the nitrifying bacteria slows down, the oxygen consumption decreases, and the numerical value of the measurement data D4 by the respiration rate meter 10 also decreases. Therefore, the measurement data D4 is data indicating the nitrification rate. In the present application, the increase in the nitrification rate and the increase in the measurement data D4, and the decrease in the nitrification rate and the decrease in the measurement data D4 are treated as synonymous.

  The air supply system S4 controls the amount of air supplied into the reaction tank 2 based on information on both the nitrification rate and the concentration detected by the gas concentration sensor 6. That is, as shown in Table 2, when the concentration detected by the gas concentration sensor 6 is increasing when the nitrification rate is increasing, it can be determined that the sewage treatment facility is not nitrified, Control is performed to reduce the amount of supplied air in order to reduce the amount of nitrous oxide gas generated. On the other hand, if the detected concentration by the gas concentration sensor 6 is increasing when the nitrification rate is decreasing, it can be determined that the sewage treatment facility is of the nitric acid type, and the amount of nitrous oxide gas generated is In order to decrease, control is performed to increase the amount of supplied air.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these, A various deformation | transformation and change are possible within the range of the summary.

It is a schematic block diagram which shows typically the outline of the whole structure of the sewage treatment equipment to which the air supply system which concerns on Embodiment 1 of this invention is applied. It is a schematic block diagram which shows typically the outline of the reaction tank and its peripheral part in the sewage treatment facility shown in FIG. It is a schematic block diagram which shows typically the schematic structure of the air supply system which concerns on Embodiment 3 of this invention. It is a flowchart explaining operation | movement of the air supply system shown in FIG. It is a schematic block diagram which shows typically the schematic structure of the air supply system which concerns on Embodiment 4 of this invention.

Explanation of symbols

A: Sewage treatment equipment B: Air (supply air)
D1: Concentration data D2: Control command D3: Flow rate data D4: Measurement data G: Nitrous oxide gas Q: Flow rate S, S3, S4: Air supply system T: Residence time V: Capacity W: Sewage 1: First sedimentation basin 2 : Reaction tank 3: Final sedimentation tank 4: Aeration device 5: Computer (control means)
6: Gas concentration sensor (concentration detection means)
7: Covering part 8: Guide tube (lead-out means)
9: Flow meter (residence time detection means)
10: Respiration rate meter (nitrification rate detection means)

Claims (11)

An air supply system for supplying air into a reaction tank for sewage treatment using aerobic microorganisms,
Concentration detecting means for detecting the concentration of nitrous oxide gas generated from the reaction vessel;
An air supply system comprising: control means for controlling the amount of air supplied into the reaction tank based on a change in the detected concentration by the concentration detection means.   The air supply system according to claim 1, wherein the control unit performs control to reduce the amount of air based on an increase in the detected concentration.   The air supply system according to claim 1, wherein the control unit performs control to increase the amount of air based on an increase in the detected concentration. It further has a residence time detecting means for detecting the residence time of sewage in the reaction tank,
The air supply system according to claim 1, wherein the control means controls the amount of air supplied into the reaction tank based on the detected change in residence time and change in the detected concentration.   The control means performs control to decrease the air amount based on the increase of the residence time and increase of the detected concentration, and control to increase the air amount based on the decrease of the residence time and increase of the detected concentration. The air supply system according to claim 4 to be performed.   The air supply system according to claim 4 or 5, wherein the residence time detection means includes a flow meter that measures the flow rate of the sewage in the reaction tank, or a flow rate calculation unit that calculates the flow rate. . Nitrification rate detection means for detecting the nitrification rate of sewage in the reaction tank,
The air supply system according to claim 1, wherein the control means controls the amount of air supplied into the reaction tank based on the detected change in nitrification rate and change in the detected concentration.   The control means performs control to decrease the amount of air based on the increase in the nitrification speed and increase in the detected concentration, and control to increase the amount of air based on the decrease in the nitrification speed and increase in the detected concentration. The air supply system according to claim 7 to be performed.   The air supply system according to claim 7 or 8, wherein the nitrification rate detection means includes a respiration rate meter that measures oxygen uptake by the sewage in the reaction tank. A cover for covering the opening of the reaction tank to collect the nitrous oxide gas generated from the reaction tank;
The air supply system according to any one of claims 1 to 9, further comprising a derivation unit that guides the nitrous oxide gas collected by the cover unit to the concentration detection unit. An air supply method for supplying air into a reaction tank for sewage treatment using aerobic microorganisms,
Detecting the concentration of nitrous oxide gas generated from the reaction vessel;
Controlling the amount of air supplied into the reaction tank based on a change in detected concentration by the concentration detecting means.

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