JP5377224B2 - Gas generation amount reduction system and gas generation amount reduction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and method for reducing amount of generated gas capable of simply reducing amount of nitrous oxide gas generated from a nitrification tank at a low cost on the basis of an unprecedented idea to accelerate a denitrification reaction in the nitrification tank. <P>SOLUTION: The system S for reducing the amount of generated gas which reduces the amount of nitrous oxide gas G generated from sewage W in an aerobic tank 2 for a sewage treatment using microorganisms includes: a gas concentration sensor 6 for detecting the concentration of the nitrous oxide gas G generated from the sewage W in the aeration tank 2; a methanol supply device 4 for supplying methanol M to the sewage W; and a computer 5 for controlling the amount of the methanol M to be supplied to the sewage W in the aeration tank 2 according to the variation of the concentration measured by the gas concentration sensor 6. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a gas generation amount reduction system and a gas generation amount reduction method, and more particularly, to a system for reducing the generation amount of nitrous oxide gas generated in a reaction tank that performs sewage treatment using 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, a method has been proposed in which gaseous nitrous oxide generated by nitrification treatment is recovered and dissolved in an absorbing solution, and then the absorbing solution is denitrified (see, for example, Patent Document 1). In addition, a method has been proposed in which oxygen that inhibits the reaction of denitrifying bacteria is removed by an oxygen removing device before introducing a gas containing nitrous oxide gas generated in the nitrification tank into an anaerobic denitrifying tank and performing a reduction treatment. Yes. (For example, see Patent Document 2). Furthermore, a method for removing nitrous oxide in the gas by dissolving a gas containing nitrous oxide in the absorbing liquid and treating the absorbing liquid under anaerobic conditions has been proposed (for example, , See Patent Document 3).

JP-A-10-128389 JP 2000-246055 A JP 2002-204926 A

  However, in Patent Documents 1 and 3 and the like, nitrous oxide generated in the nitrification treatment is separately moved to an anaerobic tank by interposing an absorbing solution or the like, and denitrification treatment is performed in the anaerobic tank. . Therefore, there is a problem that it is necessary to separately prepare a transfer means for transferring nitrous oxide.

  Moreover, in the said patent document 2, since oxygen inhibits reaction of denitrifying bacteria, it is premised on removing oxygen before the denitrification process of nitrous oxide. Therefore, there is a need for an oxygen removal device that removes oxygen from the gas generated in the nitrification tank.

  The present invention has been made in view of the above circumstances, and based on an unprecedented idea of promoting the denitrification reaction in the nitrification tank, the amount of nitrous oxide gas generated from the nitrification tank can be simply and low-cost. An object of the present invention is to provide a gas generation amount reduction system and a gas generation amount reduction method that can be reduced to a minimum.

In order to solve the above problems, a gas generation amount reduction system as an exemplary aspect of the present invention is a gas that reduces the generation amount of nitrous oxide gas from sewage in a reaction tank that performs sewage treatment using microorganisms. A generation amount reduction system, a concentration detection means for detecting the concentration of nitrous oxide gas generated from sewage in the reaction tank, a carbon source supply means for supplying a carbon source into the sewage, and sewage retention in the reaction tank Residence time detection means for detecting time, and control means for controlling the amount of carbon source supplied to the sewage in the reaction tank based on the change in concentration detected by the concentration detection means and the change in residence time detected by the residence time detection means If, Ru equipped with.

  The concentration of nitrous oxide gas generated from the sewage in the reaction tank (aerobic tank, that is, the nitrification tank) is detected, and the supply amount of the carbon source is controlled based on the change in the detected concentration. The denitrification reaction can be promoted by supplying a carbon source. An increase in nitrous oxide gas due to insufficient denitrification in the aerobic tank can be prevented, and the amount of nitrous oxide gas generated from sewage can be finely controlled. As a result, it is possible to contribute to a reduction in the amount of nitrous oxide gas generated.

  More specifically, a nitrification reaction by an aerobic microorganism is performed in a reaction tank, that is, an aerobic tank, and at the same time, a denitrification reaction by an anaerobic microorganism (denitrifying bacteria) is also performed. Nitrous acid and nitric acid are generated from ammoniacal nitrogen by a nitrification reaction by an aerobic microorganism, and nitrous acid and the like are denitrified by a denitrification reaction by an anaerobic microorganism to generate nitrogen and carbon dioxide.

  However, when the denitrification reaction is insufficient, nitrous acid and the like are only denitrified to nitrous oxide, and the amount of nitrous oxide gas generated increases. However, if the concentration of nitrous oxide gas is detected and a carbon source that promotes denitrification is supplied to the aerobic tank according to the detected concentration, sufficient denitrification is performed, and generation of nitrous oxide gas is prevented. It is suppressed.

  The gas generation amount reduction system according to the present invention can be applied to an aerobic tank in a sewage treatment facility, and as the sewage treatment facility, non-nitrification type, nitric acid type, nitrite type, nitrification denitrification type, etc. Various facilities 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.

  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 carbon source may be alcohol.

  By supplying alcohol, the reaction of anaerobic microorganisms can be efficiently promoted, and denitrification of nitrous acid, nitric acid, and nitrous oxide can be performed efficiently. The alcohol includes methanol and ethanol. The chemical reaction when alcohol is supplied as a carbon source in the nitric acid denitrification process is represented by the following chemical formula.

<Chemical formula 1>
^{_{6NO 3 - + 5CH 3 OH →}} 3N 2 + 5CO 2 + 7H 2 O + 6OH -
On the other hand, the chemical reaction when alcohol is supplied as a carbon source in the denitrification process of nitrous oxide is represented by the following chemical formula.

<Chemical formula 2>
3N ₂ O + CH ₃ OH → 3N ₂ + CO ₂ + 2H ₂ O
The supply position of the carbon source may be near the denitrification reaction region in the sewage in the reaction tank.

  In the aerobic tank, the nitrification reaction does not always occur uniformly and uniformly. Generally, air is supplied to the aerobic tank by aeration. However, even if the aerobic tank is agitated, the dissolved oxygen amount (air amount) may vary. A sufficient nitrification reaction is performed in a region where the amount of dissolved oxygen in the sewage in the aerobic tank is high, and the generation amount of nitrous oxide gas is suppressed.

  However, the nitrification reaction is insufficient in a region where the dissolved oxygen amount is low in the aerobic tank, and a large amount of nitrous oxide gas is generated as shown in the following chemical formula.

<Chemical Formula 3>
NH ₄ -N → NO ₂ -N + N ₂ O

<Chemical formula 4>
NO ₂ -N → N ₂ O → N ₂
Here, it is considered that a denitrification reaction occurs in a region where the amount of dissolved oxygen is low. That is, the region where the dissolved oxygen amount is low can be rephrased as the denitrification reaction region. When a sufficient denitrification reaction is performed in this denitrification reaction region, as shown in the chemical formula 2, nitrous oxide is also denitrified to generate nitrogen and carbon dioxide.

  However, if denitrification is insufficient, nitrous oxide generated by nitrification is not decomposed, and the amount of nitrous oxide gas generated increases. In addition, nitrous acid and the like produced by nitrification can be denitrified only to nitrous oxide. By supplying a carbon source in the vicinity of the denitrification reaction region, the denitrification reaction can be efficiently promoted. As a result, a reduction in the amount of nitrous oxide gas generated can be realized by promoting the denitrification reaction in the aerobic tank.

  The reaction tank is a swirl type reaction tank in which sewage is swirled by air supply, and the distance along the swirl path from the air supply position to the carbon source supply position is a turn from the carbon source supply position to the air supply position. It may be set longer than the distance along the trajectory.

  By aeration (air supply), the nitrification reaction of sewage in the aerobic tank can be promoted. Moreover, since this aerobic tank is a swirling flow type, a stirring effect can be obtained and air can be sufficiently distributed into the sewage.

  However, as dissolved oxygen is consumed by the nitrification reaction, the inside of the sewage becomes anoxic (or hypoxic). The region immediately before the air supply position along the turning trajectory is the region with the lowest oxygen concentration. Therefore, the denitrification reaction region is the latter half partial region along the turning trajectory as viewed from the air supply position.

  When the carbon source supply position is arranged in the second half region along the turning trajectory as viewed from the air supply position, that is, the distance along the turning trajectory from the air supply position to the carbon source supply position is the carbon source supply position. When the distance from the air supply position to the air supply position is longer than the distance along the turning trajectory, the supply carbon source is effectively consumed in the denitrification reaction and the denitrification can be promoted. As a result, the amount of nitrous oxide gas generated can be reduced.

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

  The reaction tank may have a partition for shaping the swirling of the sewage in the tank, and the air supply position and the carbon source supply position may be arranged on the opposite side across the partition wall.

  If a partition is provided in the aerobic tank, preferably at a substantially central portion, and air is supplied to one side of the partition, a swirling flow that rotates around the partition can be shaped. In that case, if the carbon source supply position is set on the other side of the partition wall, the denitrification reaction in an oxygen-free or low-oxygen region can be efficiently promoted.

  The control means may perform control to increase the carbon source amount based on a volume ratio decrease of the air supply amount with respect to the sewage.

  When the amount of air supplied to the sewage is reduced by the volume ratio, the contact time between the nitrifying bacteria and oxygen is shortened, and the nitrification reaction is likely to be insufficient, leading to an increase in the amount of nitrous oxide gas generated. Here, if the denitrification reaction is promoted by increasing the carbon source supply, denitrification of nitrous acid and nitrous oxide, that is, decomposition into nitrogen and carbon dioxide proceeds, resulting in a reduction in the amount of nitrous oxide gas generated. Can contribute.

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

  Since the amount of carbon source is increased based on the increase in the detected concentration of nitrous oxide gas, the denitrification reaction is promoted, and denitrification of nitrous acid and nitrous oxide, that is, decomposition into nitrogen and carbon dioxide proceeds, Control which suppresses generation | occurrence | production of nitrous oxide gas is realizable.

  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. Then, based on the change in the residence time and the change in the detected concentration, the amount of carbon source supplied to the sewage in the aerobic tank is controlled, so that the denitrification reaction in the aerobic tank is properly performed and nitrous oxide is performed. The amount of gas generated can be reduced.

  The control means may perform control to increase the amount of carbon source based on a decrease in residence time and an increase in detected concentration.

  If the detection concentration increases when the residence time decreases, it can be determined that sufficient nitrification and denitrification reactions are not performed in the aerobic tank, and as a result, nitrous oxide gas has increased. . Therefore, if the control for increasing the amount of the carbon source is performed in such a case, the denitrification reaction can be promoted and sufficiently progressed, and the amount of nitrous oxide gas generated can be reduced.

  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 aerobic tank is a fixed capacity in a specific sewage treatment facility, the flow rate of sewage in the aerobic tank (that is, the amount of sewage flowing into or out of the aerobic tank) Is detected, the residence time of sewage in the aerobic tank 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 inflow of sewage into the aerobic tank and the outflow of sewage from the aerobic tank are approximately the same, which is approximately equivalent to the flow rate of sewage in the aerobic tank. . In addition, for example, in a system in which sewage is sent to the first sedimentation basin by a pump and sewage is fed from the first sedimentation basin to the reaction tank, the amount of water delivered by the pump is equivalent to the flow rate in the aerobic tank. .

  For example, when detecting the flow rate of sewage in the aerobic tank with a flow meter, if the capacity V of the aerobic tank and the flow rate (measured value by the flow meter) Q are set, the residence time T is calculated by the flow rate calculation means as T = V / Q 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 aerobic tank is calculated by the flow rate calculation means without using the flow meter based on the rotation 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.

  A cover for covering the opening of the reaction tank to collect nitrous oxide gas generated from the sewage in the reaction tank; and a derivation means for guiding the nitrous oxide gas collected by the cover to the concentration detection means. May be.

  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 aerobic tank is hardly leaked to the concentration detection means. Can lead to. The accuracy of concentration detection by the concentration detection means can be improved, and the efficiency of nitrous oxide gas reduction by this gas generation amount reduction system can be improved.

A gas generation amount reduction method as another exemplary aspect of the present invention is a gas generation amount reduction method for reducing the generation amount of nitrous oxide gas from sewage in a reaction tank that performs sewage treatment using microorganisms. A concentration detecting step for detecting the concentration of nitrous oxide gas generated from sewage in the reaction tank by a concentration detecting means; a residence time detecting step for detecting a residence time of sewage in the reaction tank by a residence time detecting means; to include a carbon source supplying step of supplying a carbon source, based on a change in the change and the detected residence time of the detected concentration, and a control step of controlling the amount of carbon source supplied to the sewage in the reaction vessel, the.

  The concentration of nitrous oxide gas generated from the sewage in the reaction tank (aerobic tank) is detected, and the supply amount of the carbon source is controlled based on the change in the detected concentration, so the denitrification reaction in the aerobic tank This can be promoted by supplying a carbon source. An increase in nitrous oxide gas due to insufficient denitrification in the aerobic tank can be prevented, and the amount of nitrous oxide gas generated from sewage can be finely controlled. As a result, it is possible to 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, the concentration of the nitrous oxide gas generated from the reaction tank is detected, and the supply amount of the carbon source is controlled based on the change in the detected concentration, so that the reaction is performed by controlling the denitrification reaction in the reaction tank. The amount of nitrous oxide gas generated from the tank can be finely controlled, and the amount of nitrous oxide gas generated can be reduced with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows typically the outline of the whole structure of the sewage treatment facility to which the gas generation amount reduction system which concerns on Embodiment 1 of this invention is applied. It is a schematic block diagram which shows typically the outline of the aerobic tank and its peripheral part in the sewage treatment facility shown in FIG. It is a graph which shows the relationship between the amount of nitrous oxide gas which generate | occur | produces from the sewage W of a unit volume, and the supply amount of methanol M required for denitrification of the nitrous oxide gas. It is a schematic block diagram which shows typically the schematic structure of the gas generation amount reduction system which concerns on Embodiment 2 of this invention. It is a flowchart explaining operation | movement of the gas generation amount reduction system shown in FIG.

[Embodiment 1]
Hereinafter, the gas generation amount reduction system S according to the first embodiment 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 a gas generation amount reduction system S according to Embodiment 1 of the present invention is applied. This sewage treatment facility A has a first settling basin 1, an aerobic tank (reaction tank) 2, and a final settling basin 3, and performs nitric acid-type sewage treatment by a so-called standard activated sludge method. By setting the residence time of W to be relatively long, the nitrification reaction by nitrifying bacteria is actively advanced in the aerobic tank 2.

  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 aerobic tank 2 of the downstream from the sedimentation tank 1 initially.

  The aerobic 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 aerobic tank 2, there are heterotrophic bacteria and autotrophic bacteria (nitrifying bacteria) as aerobic microorganisms. The heterotrophic bacteria grow while decomposing organic matter in the sewage W while consuming oxygen, form flocs, stay in the aerobic tank 2 and settle at the bottom of the final sedimentation basin.

  Nitrifying bacteria also nitrify ammonia nitrogen in sewage W while consuming oxygen. However, for example, due to various factors such as an imbalance in dissolved oxygen concentration in the aerobic tank 2 and an increase in the amount of treated sewage, the contact time between nitrifying bacteria and oxygen may not be sufficiently secured. In such a case, the nitrification reaction by nitrifying bacteria does not proceed sufficiently, and as a result, nitrous oxide gas is generated from the aerobic tank 2 due to insufficient nitrification.

  In addition, as will be described later, in the aerobic tank 2, in the region where the amount of oxygen in the sewage W is small, anaerobic reaction (denitrification reaction) of denitrifying bacteria due to anoxia occurs. If a sufficient carbon source is supplied in this region (denitrification reaction region), the denitrification reaction can proceed sufficiently. As a result, nitrous oxide gas generated due to insufficient nitrification can be decomposed, or nitrous acid can be reduced (without generating nitrous oxide) and decomposed into nitrogen and carbon dioxide.

  A gas generation amount reduction system S according to Embodiment 1 of the present invention is applied to the aerobic tank 2. FIG. 2 is a schematic configuration diagram schematically showing the outline of the aerobic tank 2 and its peripheral portion in the sewage treatment facility A. This gas generation amount reduction system S has a methanol supply device (carbon source supply means) 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. It is roughly structured. Further, the aerobic tank 2 is provided with an air diffuser (air supply means) 2a and a partition wall 2b, which is a swirling flow type reaction tank.

  The air diffuser 2a is a device that is installed in the aerobic 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. Note that an air flow meter 2 c that measures the air supply amount per unit time and transmits the measurement data D 4 to the computer 5 is attached to the air diffuser 2 a. Thereby, increase / decrease in the supply amount of the air B can be measured, and the supply amount of the methanol (carbon source) E based on the measurement data D4 can be adjusted.

  The partition wall 2b is a wall surface member installed at substantially the center of the aerobic tank 2 and extends in the direction perpendicular to the paper surface in FIG. 2, and shapes the swirl flow of the sewage W in the aerobic tank 2. Is for. The partition wall 2 b is provided with a gap between the lower portion thereof and the bottom surface of the aerobic tank 2 without blocking the sewage W in the aerobic tank 2 to the left and right. The water surface of the sewage W is also set at a position higher than the partition wall 2b, and a gap is provided between the upper portion of the partition wall 2b and the sewage W water surface.

  The air diffuser 2a is disposed near the bottom surface of the aerobic tank 2 and at the left side position (air supply position) of the partition wall 2b in FIG. A swirling flow C is generated in the sewage W by aeration (air supply) from the air diffuser 2a. The swirling flow C rises from the air diffuser 2a and flows in the vicinity of the upper part of the partition wall 2b from the left side to the right side. The swirl flow C that reaches the right side of the partition wall 2b descends on the right side of the partition wall 2b, flows in the vicinity of the lower part of the partition wall 2b from the right side to the left side, and rises again by the air B from the diffuser 2a. .

  In this manner, the aeration device 2a and the partition wall 2b generate a swirling flow C as shown in FIG. 2 in the aerobic tank 2, and an agitation effect is obtained.

  The methanol supply device 4 is a device for supplying methanol M as a carbon source to the sewage W in the aerobic tank 2, and has a tank 4a, a control valve 4b, and a supply pipe 4c. The control valve 4b is connected to the computer 5, and is configured to be able to open and close the valve and adjust the opening degree based on a control command from the computer 5. The amount of methanol M stored in the tank 4a is adjusted by the control valve 4b based on a control command from the computer 5, and is supplied into the sewage W from the supply pipe 4c.

  In addition, the front-end | tip part of the supply pipe | tube 4c is arrange | positioned so that methanol M may be supplied in the supply position (carbon source supply position) 4d in the sewage W in the aerobic tank 2. FIG. The supply position 4d is on the opposite side of the partition 2b with respect to the arrangement position of the air diffuser 2a, and is on the right side of the partition 2b in FIG.

  The left region of the partition wall 2b is a region where the air B is sufficiently supplied by the air diffuser 2a and the dissolved oxygen concentration is high. In this region, the nitrification reaction is mainly performed. On the other hand, the right region of the partition wall 2b is a region where the sewage W in which oxygen has already been consumed by the nitrification reaction in the left region is swirling, and is a region where the dissolved oxygen concentration is little or extremely low (denitrification reaction region). is there. In the denitrification reaction region R, an oxygen-free denitrification reaction by denitrifying bacteria is mainly performed, and methanol M as a carbon source is used in the denitrification reaction.

  Therefore, it is desirable that the supply position 4d be arranged in the vicinity of the denitrification reaction region R or in the region R. Furthermore, the supply position 4d is more preferably a position immediately before the air supply position along the trajectory of the swirl flow C, that is, the right side of the partition wall 2b and the vicinity of the bottom surface of the aerobic tank 2.

  The computer 5 is for controlling the amount of methanol M supplied by the methanol supply device 4. The computer 5 is connected to the control valve 4b of the methanol supply device 4 and the gas concentration sensor 6, and controls the supply amount of methanol M toward the control valve 4b based on the concentration data D1 from the gas concentration sensor 6. It has a function of sending out a control command D2. The control valve 4b is capable of opening / closing control and opening adjustment based on a control command D2.

  For example, the computer 5 has a CPU and a storage device. A methanol 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 methanol supply apparatus 4 according to the determination result of a density | concentration change may be exhibited.

  The computer 5 is also connected to the air flow meter 2c. And based on the measurement data D4 from the air flowmeter 2c, it has the function to send out the control command D2 toward the methanol supply apparatus 4.

  The gas concentration sensor 6 is for detecting the gas concentration of the nitrous oxide gas G generated from the aerobic tank 2. Here, the gas concentration of the nitrous oxide gas G generated from the aerobic tank 2 means that the nitrous oxide generated in the liquid phase in the aerobic tank 2 is phase-transferred to the gas phase, and as a result, aerobic. It means the concentration of the nitrous oxide gas G released from the tank 2 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. If the residence time of the sewage W in the aerobic tank 2 becomes short, the nitrification reaction by the nitrifying bacteria in the aerobic tank 2 becomes insufficient, the generation amount of nitrous oxide gas G increases, and consequently the gas concentration sensor The detection density due to 6 increases.

  The cover portion 7 is a lid member that covers the opening of the aerobic tank 2 and collects the nitrous oxide gas G from the aerobic 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 aerobic tank 2 is sent to the final settling basin 3 on the downstream side. In the final sedimentation basin 3, flocs generated in the aerobic tank 2 are settled. The precipitate is condensed and partly incinerated as excess sludge, or returned to the aerobic 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 gas generation amount reduction system S will be described.

  When the concentration of the nitrous oxide gas G generated from the aerobic tank 2 is detected by the gas concentration sensor 6, the gas concentration sensor 6 transmits concentration data D 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 aerobic tank 2 becomes short and the nitrification reaction becomes insufficient, the concentration data D1 tends to increase. Therefore, the computer 5 determines whether or not the concentration data D1 is increasing, and when it is increasing, the control command for increasing the supply amount of methanol M toward the control valve 4b of the methanol supply device 4 is provided. D2 is transmitted. When the methanol supply device 4 that has received the control command D2 increases the supply amount of methanol M, the denitrification reaction in the vicinity of the denitrification reaction region R in the aerobic tank 2 is promoted. 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 amount of methanol M, and directs the control command D2 for maintaining or decreasing the supply amount of methanol M to the methanol supply device 4, for example. To send.

  FIG. 3 shows the relationship between the amount of nitrous oxide gas generated from the unit volume of sewage W and the supply amount of methanol M necessary for denitrification of the nitrous oxide gas. Here, the amount of nitrous oxide gas generated from the unit volume of sewage W is equivalent to the concentration of nitrous oxide gas × the amount of supplied air × the amount of water that the gas permeates.

  As shown in this graph, the amount of nitrous oxide gas generated and the supply amount of methanol M necessary for the denitrification are approximately proportional. The reason is that the theoretical methanol supply required for denitrification of activated sludge by sewage W is given by the denitrification consumption of nitrate nitrogen + the denitrification consumption of nitrite nitrogen + the consumption of dissolved oxygen. On the other hand, when nitrous oxide gas is generated, the theoretical methanol supply required for denitrification is the denitrification consumption of nitrate nitrogen + the denitrification consumption of nitrite nitrogen + the consumption of dissolved oxygen + By being given by the denitrification consumption of dissolved nitrous oxide.

  Furthermore, more appropriate nitrous oxide gas reduction control can be performed by taking into account the measurement data D4 obtained by the air flow meter 2c. For example, the air supply amount by the air diffuser 2a may decrease due to a malfunction of the apparatus, an external fluctuation factor, or the like. In that case, the computer 5 can grasp the decrease in the air supply amount by the measurement data D4 from the air flow meter 2c. The decrease in the air supply amount induces a decrease in the nitrification reaction, and as a result, there is a high possibility that it will lead to an increase in the amount of nitrous oxide gas G generated. Therefore, even if the concentration data D1 obtained by the gas concentration sensor 6 has not decreased, the computer 5 may increase the supply amount of methanol M if the measurement data D4 of the air flow rate has decreased. .

  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 increasing the supply amount of methanol M 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 reducing the supply amount of methanol M by a predetermined amount can be transmitted.

  Further, a reference value (reference speed) of the concentration increase rate (concentration increase per hour) is determined in advance, and when the concentration increase rate based on the detected concentration data D1 exceeds the reference rate, the methanol supply amount It is also possible to adopt a configuration in which a control command D2 for increasing the value by a predetermined amount. 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 decreasing the methanol supply amount by a predetermined amount can be transmitted.

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

[Embodiment 2]
FIG. 4 is a schematic configuration diagram schematically showing a schematic configuration of a gas generation amount reduction system S2 according to Embodiment 2 of the present invention. This gas generation amount reduction system S2 includes a flow meter (residence time) in addition to a methanol supply device 4, a computer (control means) 5, a gas concentration sensor (concentration detection means) 6, a cover 7 and a guide pipe (derivation means) 8. Detection means) 9 is provided.

  The flow meter 9 is disposed in the middle of the flow path from the settling basin 1 to the aerobic tank 2 at first, and can measure the flow rate of the sewage W flowing into the aerobic tank 2. 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 basin 1 by a pump (not shown), the flow rate to the aerobic tank 2 can be calculated based on the rotation speed of the pump and the HQ curve.

  Since the capacity of the aerobic 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 aerobic tank 2 can be roughly calculated. For example, if 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 aerobic tank 2 is T = V / Q, and the flow rate Q and the residence time T are inversely related. It becomes.

  The gas generation amount reduction system S2 controls the amount of air supplied into the aerobic tank 2 based on information on both the residence time T and the concentration detected by the gas concentration sensor 6. That is, when the residence time T is decreasing and the detected concentration by the gas concentration sensor 6 is increasing, it can be determined that the nitrification reaction in the sewage treatment facility A is insufficient, and nitrous oxide. In order to reduce the amount of gas G generated, control is performed to increase the supply amount of methanol M.

  Specifically, the gas generation amount reduction system S2 performs an operation based on the flowchart shown in FIG.

  When the concentration of the nitrous oxide gas G generated from the aerobic 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 aerobic tank 2 is measured by the flow meter 9, the flow meter 9 transmits 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 tends to increase (S.3). And when it determines with the flow volume data D3 having an increasing tendency (decreasing tendency of the residence time T) (S.3: Y), possibility that the nitrification reaction in the aerobic tank 2 will become inadequate is high. The control command D2 for increasing the supply amount of methanol M is transmitted to the methanol supply device 4 (S.4).

  On the other hand, when the flow rate data D3 is not increasing (S.3: N), the computer 5 determines whether or not the concentration data D1 is increasing (S.5). When it is determined that the concentration data D1 is increasing (S.5: Y), a control command D2 for increasing the supply amount of methanol M is also transmitted to the methanol supply device 4 (S.6). .

  Thus, when the flow rate data D3 is increasing or when the concentration data D1 is increasing, it can be determined that the amount of nitrous oxide gas G generated is increasing. Accordingly, in this case, by increasing the supply amount of methanol M, the denitrification reaction in the aerobic tank 2 is promoted, and the generation amount of the nitrous oxide gas G is reduced.

  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.

A: Sewage treatment equipment B: Air (supply air)
C: Swirl D1: Concentration data D2: Control command D3: Flow rate data D4: Measurement data M: Methanol (carbon source)
G: Nitrous oxide gas Q: Flow rate R: Denitrification reaction area S, S2: Gas generation amount reduction system T: Residence time V: Capacity W: Sewage 1: First sedimentation tank 2: Aerobic tank (reaction tank)
2a: Air diffuser (air supply means)
2b: Partition 2c: Air flow meter 3: Final sedimentation tank 4: Methanol supply device (carbon source supply means)
4a: Tank 4b: Control valve 4c: Supply pipe 4d: Supply position (carbon source supply position)
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)

Claims (11)

A gas generation amount reduction system that reduces the amount of nitrous oxide gas generated from sewage in a reaction tank that performs sewage treatment using microorganisms,
Concentration detecting means for detecting the concentration of nitrous oxide gas generated from sewage in the reaction vessel;
A carbon source supply means for supplying a carbon source into the sewage,
A residence time detecting means for detecting a residence time of sewage in the reaction vessel;
And control means based on a change of the detected residence time, to control the amount of carbon source supplied to the sewage in the reaction vessel by the concentration detection means according to the detected concentration and the change in the residence time detecting means,
Gas generation amount reducing system characterized by Ru with a. The gas generation amount reduction system according to claim 1, wherein the carbon source is alcohol. The gas generation amount reduction system according to claim 1 or 2 , wherein a supply position of the carbon source is in the vicinity of a denitrification reaction region in sewage in the reaction tank. The reactor is a swirling flow type reaction vessel for pivoting the sewage by the supply of air, and the distance along the swing trajectory from the supply position before Symbol air to the supply position of the carbon source, the carbon gas generation amount reduction system according to claims 1 to 3, Neu Zureka 1 wherein characterized in that it is longer than the distance along the swing trajectory to the air supply position from the source supply position. The reaction vessel, which has a partition wall for shaping the pivoting of the sewage, and supply position before Symbol air supply position of the carbon source, and being disposed on opposite sides of the partition wall The gas generation amount reduction system according to claim 4. Gas generation amount reduction system according to claim 4 or 5 wherein said control means, and performs a control for increasing the amount of carbon source on the basis of the volume reduction ratio of the air supply amount for the previous SL sewage. Said control means, said detecting concentration gas generation amount reduction system according to claim 1-6 Neu Zureka paragraph (1), characterized by performing control for increasing the amount of carbon source on the basis of the rise in. Said control means, reducing the amount of gas generated according to any one of claims 1 to 7, characterized in that the control for increasing the amount of carbon source on the basis of the increase of the reduction and the detected concentration of the residence time System . The said residence time detection means is comprised including the flowmeter which measures the flow volume of the said sewage in the said reaction tank, or the flow volume calculation means which calculates this flow volume, The any one of Claims 1-8 characterized by the above-mentioned. The gas generation amount reduction system according to Item 1 . A cover part covering the opening of the reaction tank to collect the nitrous oxide gas generated from the sewage in the reaction tank, and a derivation for guiding the nitrous oxide gas collected by the cover part to the concentration detection means claim 1-9 Neu Zureka gas generation rate reduction system according to item 1, characterized in that it comprises a means. A gas generation amount reduction method for reducing generation amount of nitrous oxide gas from sewage in a reaction tank that performs sewage treatment using microorganisms,
A concentration detecting step for detecting the concentration of nitrous oxide gas generated from sewage in the reaction tank by a concentration detecting means ;
A residence time detection step of detecting a residence time of sewage in the reaction tank by a residence time detection means;
A carbon source supply step for supplying a carbon source into the sewage,
A control step of based on said change and said detected dwell time change in the detected concentration, to control the amount of carbon source supplied to the sewage in the reaction vessel,
Gas generation amount reducing method characterized in that it comprises a.

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