JP2006272261A - Sewage treatment method and sewage treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sewage treatment method which enables the alternate execution of not only aerobic treatment and oxygen-free treatment but also temporary aeration under a proper condition for the purpose of stirring at the time of oxygen-free treatment and the development of a stable nitrogen removing capacity, and a sewage treatment apparatus. <P>SOLUTION: The sewage treatment apparatus 10 is equipped with a biological treatment tank 12 for biologically treating sewage by activated sludge and a blower 24 for sending air to an air diffuser 22 to alternately perform aerobic treatment for continuously driving the blower 24 and oxygen-free treatment for temporarily treating the blower 24 and also equipped with a sludge interface meter 16 for detecting the interface of sludge, a dissolved oxygen densitometer 18 for measuring the concentration of dissolved oxygen, a lifting device 20 for raising and lowering the sludge interface meter 16 and the dissolved oxygen densitometer 18 and a control unit 26 for controlling the temporary driving of the blower 24 on the basis of the measuring results of the sludge interface meter 16 and the dissolved oxygen densitometer 18. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sewage treatment method and apparatus, and more particularly to a sewage treatment method and apparatus for treating sewage containing organic matter such as domestic wastewater and nitrogen.

  Conventionally, a biological treatment method using activated sludge has been used as a treatment method for sewage such as domestic wastewater. In this biological treatment method, organic matter in sewage is decomposed by microorganisms that live in activated sludge.

  When treating organic matter and nitrogen in sewage by a biological treatment method, a method is generally adopted in which an aerobic treatment that supplies oxygen to a biological treatment tank that holds activated sludge and an oxygen-free treatment that does not supply oxygen are alternately performed. (For example, refer to Patent Document 1). This is a nitrification reaction that converts ammonia nitrogen to nitrite nitrogen or nitrate nitrogen in the presence of dissolved oxygen, and nitrite nitrogen or nitrate nitrogen to nitrogen gas in the absence of dissolved oxygen. This is because a denitrification reaction is necessary to biologically treat nitrogen in sewage.

  By the way, in order to increase the reaction efficiency in the oxygen-free treatment, a method of stirring by providing a stirrer in the biological treatment tank is generally employed. However, in recent years, a method for performing oxygen-free treatment without providing a stirrer has been put into practical use.

  However, in this method, since agitation is not performed, the activated sludge settles with time and a supernatant liquid is generated. Since there is almost no microorganisms in the supernatant, there is a problem in that denitrification of nitrite nitrogen or nitrate nitrogen contained in the supernatant is insufficient and a large amount of nitrogen remains in the treated water.

For this reason, when an oxygen-free process is performed without providing a stirrer, the blower is periodically operated for a short time during the oxygen-free process. Thereby, the inside of a biological treatment tank is aerated and agitation is performed, the fall of a sludge interface can be prevented, and a denitrification process can fully be advanced.
JP 2004-243248 A

  However, in the conventional treatment method, when the amount of aeration at the time of oxygen-free treatment becomes excessive, the dissolved oxygen concentration in the biological treatment tank rises and becomes an unsuitable environment for performing the denitrification reaction. For this reason, it is difficult to set a time interval for performing aeration (hereinafter referred to as an aeration interval) and a single aeration time (hereinafter simply referred to as an aeration time), and it is difficult to improve processing performance. That is, the aeration interval and aeration time have different values depending on the load of organic matter and nitrogen flowing into the tank and the sedimentation property of activated sludge, and there is a problem that it is difficult to set appropriately considering these factors. .

  For example, when the sedimentation rate is slow, the sludge interface is always high, so the denitrification reaction proceeds in many areas in the tank, and stirring is not necessary, and the appropriate value of the aeration interval increases. On the other hand, when the sedimentation rate is high, the sludge interface is immediately lowered, so that the denitrification reaction is performed only at the bottom of the tank, and the denitrification treatment is insufficient. For this reason, when the sedimentation rate is fast, it is necessary to set the aeration interval shorter than when the sedimentation rate is slow and to stir frequently.

  In addition, when the dissolved oxygen concentration of activated sludge is high, oxygen is further supplied to the activated sludge by stirring by aeration, so that the denitrification reaction that proceeds under anoxic conditions is hindered, and nitrogen removal performance Gets worse. Therefore, when the dissolved oxygen concentration of activated sludge is high, it is necessary to set the aeration interval longer and the aeration time shorter.

  As described above, the appropriate values of the aeration interval and the aeration time change according to the sedimentation rate of the activated sludge, the dissolved oxygen concentration, and the like, and it is difficult to set the optimum values. In particular, the aeration interval must be set to an appropriate value after measuring the sludge settling speed and dissolved oxygen concentration for a long time, and is difficult to set to an optimum value. For this reason, conventionally, the problem that high nitrogen treatment performance cannot be maintained, and the problem that the aeration interval and aeration time are outside the appropriate range when the amount of sewage inflow into the tank fluctuates and the quality of the treated water deteriorates. was there. Furthermore, conventionally, since the optimum values of the aeration interval and the aeration time are not known, wasteful aeration is often performed, which increases the burden on the blower and increases the incidence of blower failure. .

  The present invention has been made in view of such circumstances, and performs aerobic treatment and oxygen-free treatment alternately, and performs temporary aeration for the purpose of stirring during oxygen-free treatment under appropriate conditions. An object of the present invention is to provide a wastewater treatment method and apparatus capable of exhibiting stable nitrogen removal performance.

  In order to achieve the above object, the invention according to claim 1 performs biological treatment of sewage (treated water) with activated sludge and alternately performs aerobic treatment for continuous aeration and oxygen-free treatment for temporary aeration. In the sewage treatment method to be performed, the interface position of the activated sludge is detected at the time of the oxygen-free treatment, the dissolved oxygen concentration of the activated sludge is detected, and according to the detection result of the interface position and the dissolved oxygen concentration, It is characterized by controlling temporary aeration.

  According to the first aspect of the present invention, since the temporary aeration is controlled according to the interface position of the activated sludge and the dissolved oxygen concentration, the temporary aeration can be performed under optimum conditions. Accordingly, it is possible to prevent the denitrification process from being insufficient due to insufficient aeration due to insufficient aeration, or the concentration of dissolved oxygen from being increased due to excessive aeration to prevent the denitrification process from being hindered.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, the temporary aeration is started when the detection result of the interface position becomes a threshold value or less.

  Since the activated sludge does not exist in the supernatant portion above the interface position, the denitrification reaction does not proceed, and the denitrification reaction proceeds in the activated sludge portion below the interface position. Therefore, when the interface position is high, the denitrification reaction proceeds in a wide range in the tank, so that stirring is not necessary. On the contrary, when the interface position is low, the denitrification reaction proceeds only in a narrow range in the tank, and the denitrification treatment becomes insufficient. Therefore, when the interface position is low, temporary aeration and stirring are performed, so that the interface position can be raised and the range for performing the denitrification reaction can be expanded. Thus, according to the second aspect of the present invention, since temporary aeration is performed according to the interface position of the activated sludge, the denitrification reaction can sufficiently proceed without wasteful aeration.

  A third aspect of the present invention is characterized in that, in the first or second aspect of the invention, the temporary aeration is performed when the detected value of the dissolved oxygen concentration of the sewage falls below a threshold value.

  When the dissolved oxygen concentration is high, the denitrification reaction hardly proceeds. Therefore, if aeration is performed when the dissolved oxygen concentration is high, the denitrification reaction does not proceed further. Conversely, when the dissolved oxygen concentration is low, the denitrification reaction is not greatly hindered even if temporary aeration is performed. According to the invention of claim 3, since temporary aeration is performed when the dissolved oxygen concentration is low, it is possible to minimize a decrease in denitrification treatment due to aeration.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the dissolved oxygen concentration is detected at a plurality of locations in the height direction after the temporary aeration is started, and the plurality of detections are performed. The temporary aeration is controlled based on a value. According to the invention of claim 4, after the temporary aeration is started, the dissolved oxygen concentration is measured at a plurality of locations in the height direction, and the temporary aeration is controlled based on the plurality of detected values. Can be prevented. For example, excessive aeration can be prevented by stopping the temporary aeration when the difference between the maximum value and the minimum value of the plurality of measurement values is less than or equal to the threshold value. Thereby, it can prevent that denitrification reaction is prevented by excessive aeration, and can maintain high nitrogen removal performance.

  In order to achieve the above-mentioned object, the invention according to claim 5 provides a biological treatment tank that biologically treats sewage with activated sludge, and an air supply that feeds gas to an air diffuser arranged in the biological treatment tank. A sewage treatment apparatus that alternately performs an aerobic treatment for continuously driving the air supply means and an oxygen-free treatment for temporarily driving the air supply means. An interface detecting means for detecting, a dissolved oxygen concentration meter for measuring the dissolved oxygen concentration in the biological treatment tank, an elevating means for raising and lowering the interface detecting means and the dissolved oxygen concentration meter, and when being raised and lowered by the raising and lowering means And a control device for controlling the temporary drive of the air supply means based on the detection result of the interface detection means and the measured value of the dissolved oxygen concentration meter.

  According to the invention of claim 5, the height position of the sludge interface and the dissolved oxygen concentration in the vicinity of the interface are detected by moving up and down the interface detecting means and the dissolved oxygen concentration meter. And according to the height position of a sludge interface and dissolved oxygen concentration, an air supply means is temporarily driven. Thus, if the air supply means is controlled according to the height position of the sludge interface and the dissolved oxygen concentration, temporary aeration can be performed under optimum conditions. Accordingly, it is possible to prevent agitation due to insufficient aeration and a decrease in denitrification ability, or an increase in dissolved oxygen concentration due to excessive aeration and a decrease in anaerobic ability.

  According to the method and apparatus for treating sewage according to the present invention, the interface position of activated sludge and the dissolved oxygen concentration of sewage are detected, and temporary aeration during oxygen-free treatment is controlled according to the detected value. Therefore, temporary aeration can be performed under optimum conditions, and stable nitrogen removal performance can be exhibited.

  Hereinafter, preferred embodiments of a sewage treatment method and apparatus according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a schematic configuration of a sewage treatment apparatus. As shown in the figure, the sewage treatment apparatus 10 is mainly composed of a biological treatment tank 12, a sedimentation tank 14, a sludge interface meter 16, a dissolved oxygen concentration meter 18, an elevating device 20, an air diffuser 22, a blower 24, and a control device 26. Consists of.

  An inflow pipe 28 is connected to the biological treatment tank 12, and sewage flows into the biological treatment tank 12 from the inflow pipe 28. In the biological treatment tank 12, sewage and activated sludge are mixed, and organic matter and nitrogen in the sewage are biologically treated by microorganisms in the activated sludge.

  The biological treatment tank 12 is connected to the sedimentation tank 14 via a transfer pipe 30, and the treated water treated in the biological treatment tank 12 is transferred to the precipitation tank 14. In the settling tank 14, sludge contained in the treated water is precipitated, and the supernatant liquid is drained from the treated water outflow pipe 32. The bottom of the sedimentation tank 14 is formed in a hopper shape, and a sludge return pipe 36 is connected to the lower end thereof. Then, the activated sludge precipitated in the settling tank 14 is returned to the biological reaction tank 12 from the sludge return pipe 36 as return sludge. A sludge extraction pipe 34 is connected to the return sludge pipe 36, and a part of the return sludge is periodically extracted.

  An air diffuser 22 is provided at the bottom of the biological treatment tank 12. The air diffuser 22 is connected to a blower (corresponding to an air supply means) 24. By driving the blower 24, air is supplied to the air diffuser 22 and aeration in the biological treatment tank 12 is performed. . That is, bubbles are generated from the air diffuser 22 and the bubbles rise in the sewage, whereby the inside of the biological treatment tank 12 is agitated and oxygen is supplied to the activated sludge in the biological treatment tank 12. The shape and configuration of the air diffuser 22 are not particularly limited. For example, an air diffuser tube in which a large number of holes are formed is used.

  The blower 24 is connected to the control device 26, and the control device 26 controls the drive and stop of the blower 24. Aerobic processing is performed by continuously driving the blower 24, and oxygen-free processing is performed by intermittently driving the blower 24. The aerobic treatment and the oxygen-free treatment are performed alternately, and the operation time for each treatment is set to several tens of minutes.

  The lifting device 20 is a device that moves the sludge interface meter 16 and the dissolved oxygen concentration meter 18 up and down to adjust the height position in the biological treatment tank 12. The sludge interface meter 16 and the dissolved oxygen concentration meter 18 may be fixed and moved up and down at the same time, or may be moved up and down separately. Moreover, although the raising / lowering method by the raising / lowering apparatus 20 is not specifically limited, For example, the roller (not shown) around which the cable wire of the sludge interface meter 16 or the dissolved oxygen concentration meter 18 is rotationally driven is moved up and down. Good. Alternatively, the sludge interface meter 16 and the dissolved oxygen concentration meter 18 may be supported by a rod-shaped member (not shown), and the rod-shaped member may be moved up and down by a linear motor or the like.

  The sludge interface meter 16 is a device that detects the interface position of sludge. For example, the sludge interface meter 16 has a light projecting unit (not shown) and a light receiving unit (not shown) arranged at a predetermined interval. The amount of light that has been projected and received by the light receiving unit (the amount of transmitted light) is measured. And when this transmitted light quantity exceeds a threshold value, the presence of sludge is detected. The height position of the sludge interface can be detected by detecting the presence of sludge while raising and lowering the sludge interface meter 16 in the biological treatment tank 12.

  The sludge interface meter 16 and the dissolved oxygen concentration meter 18 are electrically connected to the control device 26 described above, and the detected value is output to the control device 26. The control device 26 is connected to the lifting device 20 and can detect the height positions of the dissolved oxygen concentration meter 18 and the sludge interface meter 16 when lifted and lowered by the lifting device 20.

  The control device 26 switches between an aerobic process and an oxygen-free process by switching between the continuous drive and the drive stop of the blower 24 described above. Moreover, the control apparatus 26 drives the blower 24 temporarily based on the measured value of the sludge interface meter 16 and the dissolved oxygen concentration meter 18 at the time of an oxygen-free process, and stirs in the biological treatment tank 12. FIG. Below, the control flow by the control apparatus 26 is demonstrated based on FIG.

  First, the time T1 of the first timer for measuring time is reset to 0 (step S1), and then the blower 24 is continuously driven until the time T1 of the first timer reaches a set value (for example, 25 minutes). Then, an aerobic process is performed (steps S2 and S3).

  Then, when the time T1 of the first timer reaches the set value, the operation is switched to the oxygen-free process. In the oxygen-free treatment, first, the time T2 of the second timer is reset to 0 (step S4), and then the blower 24 is stopped and the oxygen-free treatment is started (step 5). This anaerobic treatment is performed until the above-described first timer T1 reaches a set value (for example, 60 minutes, that is, the anaerobic treatment time is 35 minutes) (step S6). Steps S1 to S3) are repeated.

  When the second timer T2 reaches the set value of the aeration interval (for example, 10 minutes) during the oxygen-free treatment (step S7), the height position of the sludge interface and the dissolved oxygen concentration are measured (step S8). That is, the sludge interface meter 16 and the dissolved oxygen concentration meter 18 are lowered by the lifting device 20, the height position of the sludge interface is detected by the sludge interface meter 16, and the dissolved oxygen concentration of the activated sludge is determined by the dissolved oxygen concentration meter 18. taking measurement.

  If the measured height position of the sludge interface is larger (higher) than the threshold value, the temporary stirring process is skipped for one cycle, and the process returns to step S4 to reset the second timer for measuring the aeration interval to zero. . Conversely, when the height position of the sludge interface is smaller (lower) than the threshold value, the process proceeds to the next step. Then, the measured dissolved oxygen concentration is compared with the threshold value (step S10). If the dissolved oxygen concentration is larger than the threshold value, the temporary aeration process is skipped for one cycle, and the process returns to step S4. Conversely, when the dissolved oxygen concentration is smaller than the threshold value, the blower 24 is temporarily driven for a predetermined time (for example, 30 seconds) to perform aeration (step S11). After the aeration is completed, the process returns to step S4, the second timer is reset to 0, and the measurement of the aeration interval is started. Thus, temporary aeration processing is performed as necessary, and this is repeated periodically.

  Next, each process will be described with reference to FIGS. 2 (A) to 2 (C).

  When the aerobic treatment is performed, the sludge interface meter 16 and the dissolved oxygen concentration meter 18 are arranged in the vicinity of the water surface of the biological treatment tank 12 as shown in FIG. In this state, the control device 26 continuously drives the blower 24 to aerate the inside of the biological treatment tank 12. Thereby, since the whole inside of the biological treatment tank 12 is maintained in an aerobic state, the nitrification reaction which is an aerobic process is performed efficiently. The positions of the sludge interface meter 16 and the dissolved oxygen concentration meter 18 during the aerobic treatment are not particularly limited, but if placed in the sewage, there is a risk of shaking and colliding with the wall, If placed on the water surface, the sludge may be agitated when lowered into the water, so it is preferable to place it on the water surface.

  On the other hand, in the oxygen-free treatment, the blower 24 is stopped, aeration is stopped, and an oxygen-free state is formed. At this time, since agitation by aeration is also stopped, the activated sludge gradually settles with time, and the sludge interface descends as shown in FIG. 2B and FIG. 2C. At this time, since there is almost no activated sludge in the supernatant portion above the sludge interface, the denitrification reaction hardly proceeds, and the denitrification treatment is performed in the activated sludge below the sludge interface. Therefore, since the range where denitrification processing is performed decreases by the sludge interface decreasing, the ability of denitrification processing in the biological treatment tank 12 as a whole decreases.

  Therefore, in the present embodiment, while the oxygen-free treatment is performed, the lifting device 20 is driven periodically (for example, every 5 minutes or every 10 minutes), and the sludge interface meter 16 and the dissolved oxygen concentration meter 18 are lowered. Let Then, the height of the sludge interface is detected by the sludge interface meter 16, and further activated by the dissolved oxygen concentration meter 18 at a position below this sludge interface (for example, a position 0.1 m below the sludge interface). Measure the dissolved oxygen concentration of sludge.

  The control device 26 determines whether or not to temporarily drive the blower 24 based on the height position of the sludge interface and the dissolved oxygen concentration thus measured. Specifically, when the height position of the sludge interface becomes a predetermined value or less and the dissolved oxygen concentration becomes a predetermined value or less, the blower 24 is driven to perform temporary driving. By performing temporary driving, aeration is performed from the air diffuser 22, the activated sludge that has settled is wound up, and the inside of the biological treatment tank 12 is agitated. Thereby, a denitrification reaction will advance in the whole inside of the biological treatment tank 12, and the capability of a denitrification process will improve. The time for temporarily driving the blower 24 is the time required until the concentration of activated sludge becomes substantially uniform inside the biological treatment tank 12, and the time until the environment suitable for the denitrification reaction is formed. It is. The standard of the driving time is, for example, about several tens of seconds, and is actually adjusted according to the situation of the sewage treatment facility.

  The lowering of the sludge interface meter 16 and the dissolved oxygen concentration meter 18 by the elevating device 20 as described above, and the measurement by the sludge interface meter 16 and the dissolved oxygen concentration meter 18 at that time are periodically repeated, and if necessary, the blower 24 Is temporarily driven to stir the inside of the biological treatment tank 12. Thus, denitrification can be efficiently performed by controlling temporary aeration based on the height position of the sludge interface and the dissolved oxygen concentration.

  Hereinafter, the relationship between the height position of the sludge interface, the dissolved oxygen concentration, and the denitrification efficiency will be described.

  As shown in FIG. 2B, when the sludge interface is high, the oxygen-free state is maintained over a wide range in the biological treatment tank 12, and the denitrification reaction proceeds efficiently. Therefore, the denitrification process proceeds sufficiently without performing temporary aeration. Therefore, when the sludge interface is sufficiently high, the environment suitable for the denitrification reaction is maintained by not temporarily driving the blower 24.

  As shown in FIG. 2C, when the sludge interface is low, the denitrification reaction proceeds only in a narrow range below the sludge interface, so that the denitrification treatment is insufficient. Therefore, when the sludge interface detected by the sludge interface meter 16 is lower than a predetermined value, the blower 24 is temporarily driven, the inside of the biological treatment tank 12 is stirred, and denitrification is performed in a wide range within the biological treatment tank 12. Do processing. Thereby, denitrification processing can be performed efficiently. In addition, as a standard of the height position of the sludge interface at the time of driving the blower 24 temporarily, although it changes with load amounts of organic matter and nitrogen, about 3/4 to 2/3 of the water depth of the biological treatment tank 12 is preferable. .

  On the other hand, regardless of the height position of the sludge interface, when the dissolved oxygen concentration is high (that is, in an aerobic environment), the denitrification reaction that requires anoxic conditions hardly proceeds. Therefore, when the blower 24 is temporarily driven and stirred when the dissolved oxygen concentration is high, the dissolved oxygen concentration of the activated sludge increases due to the oxygen supply by the blower 24 and the entrainment of oxygen remaining in the supernatant. There is a risk that the oxygen-free treatment time will end without the denitrification reaction proceeding. For this reason, when the measured value of the dissolved oxygen concentration meter 18 has not decreased to a predetermined value or less, the blower 24 is temporarily not driven without being temporarily driven. And stir. Thereby, the environment suitable for denitrification reaction can always be prepared in the biological treatment tank 12. Note that the dissolved oxygen concentration of the activated sludge when the blower 24 is temporarily driven is preferably as close to 0 mg / L as possible, for example, set to 0.5 mg / L.

  As described above, according to the present embodiment, the blower 24 is temporarily driven based on the height position of the sludge interface and the dissolved oxygen concentration of the activated sludge, and the agitation during the oxygen-free treatment is performed. The inside of the biological treatment tank 12 can always be maintained in an environment suitable for the denitrification treatment, and the denitrification treatment can be performed efficiently.

  Further, according to the present embodiment, since temporary aeration is performed based on the height position of the sludge interface and the dissolved oxygen concentration of the activated sludge, the difficulty of adjusting the aeration time and the aeration interval is reduced, and high processing performance is achieved. Can be easily secured. Therefore, according to the present embodiment, automation of all the processes is facilitated, and stable nitrogen treatment performance can be ensured even when the processes are automated.

  Further, in this embodiment, since the blower 24 can be operated with the minimum necessary, the mechanical burden on the blower 24 can be reduced.

  Further, since the sewage treatment apparatus 10 of the present embodiment also uses the aeration apparatus 22 and the blower 24 for aerobic treatment as a stirring means at the time of oxygen-free treatment, a mechanical stirring means such as a stirring blade is unnecessary. Therefore, the cost can be reduced.

  In the above-described embodiment, the temporary aeration process is automatically stopped after a predetermined time, but the control method of the temporary aeration process is not limited to this. For example, after the start of the temporary aeration process, the dissolved oxygen concentration may be measured at a plurality of locations in the height direction, and the temporary aeration process may be stopped based on this measured value. FIG. 4 is a flowchart showing details of the temporary aeration process (step S11) of FIG.

  First, the time T3 of the third timer for timing the temporary aeration process is reset to 0 (step S21), and the time T4 of the fourth timer for timing the DO measurement time interval is reset to 0. (Step S22).

  Next, the blower 24 is turned on and a temporary aeration process is performed (step S23). Then, except for the case where the temporary aeration processing time T3 exceeds the set time (step S24), the following processing is performed. That is, the driving state of the blower 24 is maintained until the time T4 of the DO measurement time interval reaches the set time, and when the time T4 of the measurement time interval reaches the set time (step S25), a plurality of height directions are set. The dissolved oxygen concentration is measured at the location (step S26). The dissolved oxygen concentration is measured at a plurality of locations in the height direction by moving the dissolved oxygen concentration meter 18 up and down by the lifting device 20.

  Next, a maximum value and a minimum value are obtained from a plurality of measured values, and a difference between the maximum value and the minimum value is calculated (step S27). Then, the calculated difference value is compared with a threshold value (step S28), and if the calculated difference value is larger than the threshold value, it is determined that stirring is not sufficiently performed, and the process returns to step S22. When the time T4 reaches the set time, the dissolved oxygen concentration is measured again at a plurality of locations, and the same processing is performed. If the calculated value of the difference is less than or equal to the threshold value, it is determined that the agitation has been sufficiently performed and the dissolved oxygen concentration has become uniform, the blower 24 is turned off, and the temporary aeration process is terminated. Even if the calculated value of the difference does not fall below the threshold value, if the time T3 of the temporary aeration process exceeds the set time (step S24), the blower 24 is turned off and the temporary aeration process is performed. Exit.

  As described above, after starting the temporary aeration treatment, the dissolved oxygen concentration was measured at a plurality of locations in the height direction, and the difference between the maximum value and the minimum value was obtained, and this difference was below the threshold value. At this time, since the temporary aeration process is ended, the aeration amount can be controlled to an appropriate amount. That is, the temporary aeration process is stopped when it is determined that the difference between the plurality of measured values of the dissolved oxygen concentration is small and the stirring is sufficiently performed, so that the amount of aeration can be controlled to an appropriate amount. Thereby, excessive aeration can be prevented and it can prevent that the dissolved oxygen concentration after stirring rises too much. Therefore, the denitrification reaction after the temporary aeration treatment can sufficiently proceed. Further, in the above control method, since it is possible to control to an appropriate aeration amount, the driving time of the blower 24 can be shortened, the burden on the blower 24 can be reduced, and the failure occurrence rate of the blower 24 can be reduced. Can do.

  Instead of moving the dissolved oxygen concentration meter 18 up and down and measuring at a plurality of measurement points, a plurality of dissolved oxygen concentration meters 18 may be provided in advance and measured simultaneously.

The schematic diagram which shows the structure of the sewage treatment apparatus which concerns on this invention. Schematic showing the biological treatment tank at the time of each treatment Flow chart showing control flow of sewage treatment equipment Flow chart showing control flow of temporary aeration processing

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Sewage treatment apparatus, 12 ... Biological treatment tank, 14 ... Precipitation tank, 16 ... Sludge interface meter, 18 ... Dissolved oxygen concentration meter, 20 ... Lifting device, 22 ... Aeration device, 24 ... Blower, 26 ... Control device, 28 ... Inflow pipe, 30 ... Transfer pipe, 32 ... Treated water outflow pipe, 34 ... Sludge extraction pipe, 36 ... Sludge return pipe

Claims (5)

In a sewage treatment method in which sewage is biologically treated with activated sludge, and aerobic treatment in which continuous aeration is performed and oxygen-free treatment in which temporary aeration is performed alternately.
While detecting the interface position of the activated sludge during the oxygen-free treatment, the dissolved oxygen concentration of the activated sludge is detected,
The sewage treatment method, wherein the temporary aeration is controlled according to the detection result of the interface position and the dissolved oxygen concentration.   The sewage treatment method according to claim 1, wherein the temporary aeration is performed when a detection value of the interface position becomes a threshold value or less.   The sewage treatment method according to claim 1 or 2, wherein the temporary aeration is performed when a detected value of a dissolved oxygen concentration of the activated sludge becomes a threshold value or less.   4. The dissolved oxygen concentration is detected at a plurality of locations in the height direction after the temporary aeration is started, and the temporary aeration is controlled based on the plurality of detection values. The sewage treatment method according to any one of the above. An aerobic system comprising: a biological treatment tank for biologically treating sewage with activated sludge; and an air supply means for supplying gas to an air diffuser disposed in the biological treatment tank, wherein the air supply means is continuously driven. In a sewage treatment apparatus that alternately performs treatment and oxygen-free treatment that temporarily drives the air supply means,
An interface detecting means for detecting a sludge interface of the biological treatment tank;
A dissolved oxygen concentration meter for measuring the dissolved oxygen concentration in the biological treatment tank;
Elevating means for elevating and lowering the interface detecting means and the dissolved oxygen concentration meter;
A control device for controlling the temporary driving of the air supply means based on the detection result of the interface detection means and the measured value of the dissolved oxygen concentration meter when the elevating means is moved up and down;
A sewage treatment apparatus comprising:

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