Sewage treatment system and sewage treatment method

Abstract

To provide a sewage treatment system and sewage treatment method capable of simply and efficiently controlling an operation of a blower.SOLUTION: A sewage treatment system 1 of the present invention purifies sewage using activated sludge. The sewage treatment system 1 includes an aeration tank 30 for storing sewage together with activated sludge and aerating the same, an inlet pump 21 for feeding sewage into the aeration tank 30, a blower 40 for supplying air into the aeration tank 30, pH measurement means 31 for measuring the pH value of the sewage in the aeration tank 30, and operation control means 81 for controlling the start and stop of the blower 40. The operation control means 81 starts the operation of the blower 40 in response to the operation of the inlet pump 21 or when the preset operation start time is reached, and stops the operation of the blower 40 in response to the pH measurement value measured by the pH measurement means 31.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sewage treatment system and a sewage treatment method for microbiologically treating organic pollutants contained in sewage.

Background Art

[0002] As one of the methods for treating sewage such as domestic wastewater (e.g., wastewater from kitchen facilities and toilets), a method of decomposing organic matter by microorganisms is known. In sewage treatment facilities adopting this method, for example, sewage is once stored in a sewage inflow pump tank (regulation tank), then sent to an aeration tank for aeration, and the dirt is removed by activated sludge. Next, the sludge suspension is transferred to a sedimentation tank and retained, and the supernatant water is disinfected and discharged after sedimentation separation. The blower that sends air to the aeration tank is operated according to the sewage inflow load. For example, the operation time of the blower is set by a timer, and the air supply to the aeration tank is controlled by time.

[0003] Depending on the installation location of the sewage treatment facility, the amount of sewage flowing into the facility may vary greatly depending on the season, weather, time of day, etc. For example, when the sewage treatment facility is installed in a rest facility such as a service area on a highway, the amount of sewage flowing in varies due to changes in the traffic volume using that road. Similarly, when installed in a venue used in large commercial facilities, sports events, concerts, etc., the same variation occurs depending on the time of day. However, when the variation in the amount of sewage flowing in is large in this way, simply controlling the operation of the blower by a timer will result in repeating the operation of the blower with the same timer setting until it is reset, and it is impossible to balance the amount of sewage flowing in and the amount of aeration air, resulting in an excess or deficiency of aeration. To solve such problems, for example, Patent Document 1 proposes a sewage treatment apparatus in which a pH meter is installed in the aeration tank, and the start and stop of the operation of the blower are controlled according to the measured pH value of the sewage in the aeration tank.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the sewage treatment apparatus of Patent Document 1, the pH value of the sewage in the aeration tank is measured. When the pH value rises, the operation of the blower is started to send air into the aeration tank, and when the pH value drops, the supply of air to the aeration tank is stopped to cope with fluctuations in the inflow of sewage. Specifically, the start and stop of the operation of the blower are controlled by two-point management of the upper and lower limits of the pH value, and the management width is about 0.3.

[0006] However, in reality, the pH in the aeration tank does not fluctuate so much. Considering the general measurement accuracy of the pH measuring instrument, it is difficult to manage the pH value at two points (upper and lower) with a management width of 0.3. There is a need for a sewage treatment system that enables simpler and more efficient operation control of the blower.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a sewage treatment system and a sewage treatment method capable of simple and efficient operation control of a blower.

Means for Solving the Problems

[0008] To achieve the above object, first, the present invention provides a sewage treatment system for purifying sewage using activated sludge, comprising an aeration tank for containing sewage together with activated sludge and aerating it, an inflow pump for flowing sewage into the aeration tank, a blower for sending air into the aeration tank, pH measuring means for measuring the pH value of the sewage in the aeration tank, and operation control means for controlling the start and stop of the operation of the blower. The operation control means starts the operation of the blower in response to the operation of the inflow pump or when a preset operation start time is reached, and stops the operation of the blower according to the pH measurement value measured by the pH measuring means (Invention 1).

[0009] According to such an invention (Invention 1), since the operation control means starts the operation of the blower triggered by the operation of the inflow pump or a preset time, and stops the operation of the blower triggered by the PH measurement value measured by the PH measurement means, simple and efficient operation control of the blower becomes possible. In particular, since the start and stop of the operation of the blower can be managed based on only the lower limit value of the PH value, the maintenance and management of the system become easy.

[0010] The increase in the PH value in the aeration tank is caused by the inflow of sewage into the aeration tank by the inflow pump. That is, even without measuring the PH value of the sewage in the aeration tank, it is possible to grasp that the PH value in the aeration tank rises by monitoring the operation status of the inflow pump. Also, in a time period when the inflow of sewage into the aeration tank decreases, etc., it can be set to start the operation at a predetermined time regardless of the operation of the inflow pump, or it is also possible to predict the inflow timing of the sewage from past data, etc., and set it to start the operation when the set time based on the prediction arrives. Thus, the timing of starting the operation of the blower is triggered by the operation of the inflow pump or the preset operation start time, and regardless of what trigger is used to start the operation, by setting the operation stop to the PH measurement value measured by the PH measurement means, efficient operation control of the blower becomes possible.

[0011] In the above invention (Invention 1), it is preferable that the operation control means starts the operation of the blower after a predetermined delay time has elapsed since the start of the inflow of sewage into the aeration tank by the inflow pump (Invention 2)

[0012] In the above inventions (Inventions 1 and 2), it is preferable that the operation control means stops the operation of the blower when the PH measurement value measured by the PH measurement means becomes equal to or less than a first set value (Invention 3)

[0013] In the above invention (Inventions 1-3), a branch pipe for discharging air to the outside of the system is connected in the middle of the air supply pipe for supplying air from the blower to the aeration tank, and an air volume adjustment means for adjusting the amount of aeration air supplied from the blower to the aeration tank and the amount of bypass air discharged from the branch pipe to the outside of the system may be further provided (Invention 4).

[0014] In the above invention (Invention 4), it is preferable that the air volume adjustment means adjusts the amount of aeration air based on the aeration intensity D defined by the following formula (1) (Invention 5). D = V / C ··· (1) V: The amount of aeration air blown per cubic meter of the aeration tank capacity per hour (m 3 / h) 3 / h) C: The capacity of the aeration tank (m 3 )

[0015] In the above invention (Invention 5), it is preferable that the air volume adjustment means adjusts the amount of aeration air so that the aeration intensity D is 0.50 or more and 1.50 or less (Invention 6).

[0016] Second, the present invention is a sewage treatment method for purifying sewage using activated sludge by flowing sewage into an aeration tank using an inflow pump, accommodating the flowed sewage together with activated sludge in the aeration tank, and blowing air into the aeration tank by a blower for aeration. When the operation of the inflow pump is triggered or when a preset operation start time is reached, the operation of the blower is started to start sending air into the aeration tank, the pH value of the sewage in the aeration tank is measured, and the operation of the blower is stopped and the air supply to the aeration tank is stopped according to the measured pH value (Invention 8).

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a sewage treatment system and a sewage treatment method capable of simple and efficient operation control of a blower.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited only to the embodiments described below, and the described embodiments are merely examples for explaining the technical features of the present invention. Also, the shapes and dimensions shown in each drawing are only shown to facilitate the understanding of the content of the present invention, and do not correctly reflect the actual shapes and dimensions.

[0020] <Sewage treatment system> FIG. 1 is an explanatory diagram schematically showing the basic configuration of a sewage treatment system 1 according to an embodiment of the present invention. This sewage treatment system 1 is a sewage treatment system that purifies sewage using activated sludge, and is particularly suitable for use in facilities where an unspecified number of users use it and the inflow of sewage fluctuates violently, such as rest facilities such as service areas on highways, large commercial facilities, and venues used in sports events and concerts.

[0021] As shown in FIG. 1, the sewage treatment system 1 includes a raw water pump tank 10, a sewage inflow pump tank 20, an aeration tank 30, a sedimentation tank 50, a disinfection tank 60, and a discharge pump tank 70, and these tanks are connected in series. The sewage treatment system 1 includes an inflow pump 21 for allowing sewage to flow into the aeration tank 30 that stores sewage together with activated sludge and aerates it, a blower 40 for sending air into the aeration tank 30, a pH meter 31 as pH measurement means for measuring the pH value of the sewage in the aeration tank 30, and a control unit 80 having an operation control means 81 for controlling the start and stop of the operation of the blower.

[0022] The raw water pump tank 10 temporarily stores the sewage fed from various locations of the installation site of the sewage treatment system 1, and is provided for the purpose of making the quantity and quality of the sewage as uniform as possible. The sewage stored in the raw water pump tank 10 is fed into the sewage inflow pump tank 20 via the pipe 12 by the raw water pump 11 at an appropriate timing.

[0023] The sewage inflow pump tank 20 is provided for the purpose of adjusting the quantity and feeding timing of the sewage to be fed into the aeration tank 30. Inside the sewage inflow pump tank 20, an inflow pump 21 for feeding the sewage into the aeration tank 30 via the pipe 22, a first water level sensor 23a and a second water level sensor 23b for detecting the water level in the sewage inflow pump tank 20 are installed. The first water level sensor 23a detects the high water level for starting the inflow pump 21, and the second water level sensor 23b detects the low water level for stopping the inflow pump 21. For example, when the first water level sensor 23a detects that the water level of the sewage in the sewage inflow pump tank 20 is higher than a predetermined reference water level, the inflow pump 21 is started to feed the sewage in the sewage inflow pump tank 20 into the aeration tank 30 via the pipe 22. For example, when the second water level sensor 23b detects that the water level of the sewage in the sewage inflow pump tank 20 is lower than a predetermined reference water level, the inflow pump 21 stops and the feeding of the sewage into the aeration tank 30 also ends.

[0024] The aeration tank 30 contains activated sludge together with the sewage, and is configured to aerate the sewage in the aeration tank 30 with the air fed from the blower 40. Inside the aeration tank 30, a pH meter 31 for measuring the pH value of the sewage contained in the aeration tank 30 is arranged. The aeration tank 30 is connected to the sedimentation tank 40 by the pipe 32, and is configured such that the sewage in the aeration tank 30 flows into the sedimentation tank 40.

[0025] In the aeration tank 30, purification of the sewage using activated sludge is performed. The sewage fed into the aeration tank 30 by the inflow pump 21 contains, for example, organic matter dirt and ammonia (NH4 + ), and, for example, as the organic matter, C6H 12When showing the reaction formula in the aeration tank 30 using O6 (glucose), it is purified by the following (a) assimilation, (b) dissimilation, and (c) internal respiration. (a) Assimilation C6H 12 O6 (organic matter) + NH3 + O2 → C5H7NO2 (new sludge) + CO2 + 4H2O (b) Dissimilation C6H 12 O6 (organic matter) + 6O2 → 6CO2 + 6H2O + heat (c) Internal respiration C5H7NO2 (sludge) + 7O2 → 5CO2 + 3H2O + HNO3 (nitric acid)

[0026] In the aeration tank 30, when the air volume is insufficient, specifically, when the aeration intensity D described later is less than approximately 0.50, assimilation increases, dissimilation and internal respiration decrease, and excess sludge increases. On the other hand, when the air volume is appropriate, dissimilation and internal respiration increase and the sludge decreases. That is, appropriately controlling the air volume is important in wastewater treatment using activated sludge. The wastewater flowing into the aeration tank 30 shows a weakly alkaline pH value of about pH 7.5 to pH 8.5 because it contains ammonia (NH4 + ). As purification progresses in the aeration tank 30, ammonia is nitrified (oxidized) and combined with oxygen by assimilation and internal respiration, and the nitrogen state changes from NH4 + (ammonia nitrogen) → NO2 - (nitrous nitrogen) → NO3 - (nitrate nitrogen), and the pH value decreases to about pH 6.2 to pH 6.8, for example.

[0027] In the conventional technology (a method of controlling the start and stop of the operation of the blower for aeration by a timer and not controlling by monitoring the pH value), purification is mainly carried out by the assimilation reaction (adsorption reaction). That is, the dirt (organic matter) contained in the wastewater is purified by generating new sludge, but the increase in dissolved oxygen (DO) by aeration significantly reduces the pH value and significantly deteriorates the quality of the discharged water. Therefore, the amount of aeration air supplied by aeration has to be suppressed.

[0028] In the process of catabolism, organic matter (dirt) is removed by being converted into heat using a large amount of oxygen and turns into CO2. At this time, no new sludge is generated, which leads to a reduction in excess sludge. However, for this purpose, a very high DO is required. In the process of endogenous respiration, as the organic matter becomes diluted, cannibalism occurs and the sludge decreases, and nitric acid NO3 - is generated, causing the pH value to decrease. Therefore, by monitoring this pH value, the supply of oxygen can be managed. If the aeration is too strong, the sludge will be finely pulverized and flow out, and the quality of the effluent water will deteriorate rapidly. Therefore, it is necessary to avoid a decrease in the pH value.

[0029] The pH value in the aeration tank 30 is monitored by the pH measuring device 31. The pH measuring device 31 is preferably disposed, for example, near the outflow part of the aeration tank 30. The measurement result measured by the pH measuring device 31 is sent to a control unit 80 described later and converted into a pH value by a pH converter 82. When the aeration tanks are connected in multiple stages, the pH measuring device 31 is preferably disposed near the outflow part of the foremost aeration tank.

[0030] The blower 40 is for sending air into the aeration tank 30, and an air supply pipe 41 for supplying air to the aeration tank 30 is connected. In the middle of the air supply pipe 41, a branch pipe 42 for discharging air to the outside of the system is connected. On the side of the aeration tank 30 rather than the branch pipe 42, a plurality of air diffuser pipes 43 are connected to the air supply pipe 41, and those plurality of air diffuser pipes 43 are disposed inside the aeration tank 30.

[0031] A regulating valve 44 with a discharge air volume meter is provided in the middle of the blower 40 side rather than at the branch to the branch pipe 42 of the air supply pipe 41. It is configured to measure the amount of air passing through and to be able to adjust the amount of the air. Further, a regulating valve 45 with an aeration air volume meter is provided in the middle of the aeration tank 30 side (before branching to a plurality of diffuser pipes 43) rather than at the branch to the branch pipe 42 of the air supply pipe 41. It is configured to measure the amount of air passing through and to be able to adjust the amount of the air. The air passing through the regulating valve 45 with an aeration air volume meter is the aeration air that is supplied to the aeration tank 30 and used for aeration. On the other hand, a regulating valve 46 with a bypass air volume meter is provided in the middle of the branch pipe 42. It is configured to measure the amount of air passing through and to be able to adjust the amount of the air. The air passing through the regulating valve 46 with a bypass air volume meter is the bypass air that is discharged to the outside of the system. The regulating valve 45 with an aeration air volume meter and the regulating valve 46 with a bypass air volume meter function as air volume adjusting means for adjusting the amount of aeration air supplied from the blower 40 to the aeration tank 30 and the amount of bypass air discharged from the branch pipe 42 to the outside of the system.

[0032] The sedimentation tank 50 is for sedimenting the sludge contained in the sewage and separating it from the supernatant water. The sedimentation tank 50 is connected to the disinfection tank 60 by a pipe 51, and is configured such that the separated supernatant water flows to the overflow weir and is discharged to the disinfection tank 60 via the pipe 51. Also, a part of the separated sludge is returned to the vicinity of the inlet of the aeration tank 30 by a sludge return pipe 52, and a part of the excess sludge can be carried out of the system from a sludge extraction pipe 53 connected in the middle of the sludge return pipe 52.

[0033] The disinfection tank 60 is for disinfecting the supernatant water discharged from the sedimentation tank 50 using known disinfection means (not shown). The disinfection tank 60 is connected to the discharge pump tank 70 by a pipe 61, and is configured such that the supernatant water disinfected in the disinfection tank 60 is discharged to the discharge pump tank 70 via the pipe 61. The supernatant water stored in the discharge pump tank 70 is discharged outside the system through a pipe 72 by a discharge pump 71. The disinfection tank 60 and the discharge pump tank 70 may be arranged such that the supernatant water flows due to the head difference and their arrangement locations gradually become lower in sequence.

[0034] The control unit 80 includes an operation control means 81 for controlling the start and stop of the operation of the blower 40, a PH converter 82 for converting the measurement result measured by the PH meter 31 into a PH value, and an operation control timer 83 for sending out an operation start signal of the blower 40 when the set time is reached. The set time at which the operation control timer 83 sends out the operation start signal may be simply set in advance with a certain fixed time as the operation start time, or the inflow prediction information of the sewage may be generated based on the past sewage inflow volume data, etc., and the operation start time may be set in advance so as to correspond to the generated inflow prediction information.

[0035] <Control of the start and stop of the operation of the blower> The operation control means 81 may start the operation of the blower 40 in response to the operation of the inflow pump 21, or may start the operation of the blower 40 when the preset operation start time is reached. In any case, the operation control means 81 stops the operation of the blower 40 according to the PH measurement value measured by the PH meter 31.

[0036] When starting the operation of the blower 40 in response to the operation of the inflow pump 21, the operation control means 81 sends an instruction to the blower 40 to start the operation of the blower 40 after a predetermined delay time has elapsed since the start of the inflow of sewage into the aeration tank 30 by the inflow pump 21. The blower 40 that receives the instruction starts the operation, and the supply of air into the aeration tank 30 is started. It is appropriate to determine the delay time based on the capacity of the aeration tank 30, the performance of the inflow pump 21, etc.

[0037] When starting the operation of the blower 40 when the pre-set operation start time is reached, upon receiving the operation start signal sent by the operation control timer 83, the operation control means 81 sends an instruction to the blower 40 to start the operation of the blower 40. The blower 40 that has received the instruction starts the operation, and the supply of air to the aeration tank 30 is started.

[0038] When stopping the operation of the blower 40 according to the pH measurement value measured by the pH meter 31, the operation control means 81 sends an instruction to the blower 40 to stop the operation of the blower 40 when the pH measurement value measured by the pH meter 31 becomes equal to or less than the first set value. The blower 40 that has received the instruction stops the operation and stops the supply of air to the aeration tank 30. Here, the first set value is preferably a pH value at which the dissimilation reaction and the endogenous respiration reaction are almost completed. The first set value is determined based on the cohesiveness of the sludge in the aeration tank 30, the state of the treated water quality, the sludge conversion rate, etc., but is preferably set to about pH 5.7 to pH 7.0, particularly around pH 6.0 to pH 6.6. It is extremely important in the sewage treatment system 1 of this embodiment to constantly manage this first set value as the lower limit pH value of the sewage in the aeration tank 30.

[0039] By controlling the start and stop of the blower 40 in this way, the operation control means 81 starts the operation of the blower 40 triggered by the operation of the inflow pump 21 or a preset time, and stops the operation of the blower 40 triggered by the PH measurement value measured by the PH meter 31. Therefore, it is possible to perform simple and efficient operation control of the blower 40. Since the start and stop of the operation of the blower 40 can be managed based on only the lower limit value of the PH value, the maintenance and management of the system are also facilitated. In addition, when controlling the start and stop of the operation of the blower 40 using the conventional timer control method, it is necessary to determine the operation time based on the inflow prediction. And when the inflow prediction is off, the PH in the aeration tank may drop too much, resulting in the discharged water quality falling below the discharge standard or the occurrence of excessive or insufficient aeration. By using the PH measurement value measured by the PH meter 31 as a trigger to stop the operation of the blower 40, such problems are solved.

[0040] In the sewage treatment system 1 equipped with such operation control means 81, during the day when a large amount of sewage inflow is expected, the operation of the inflow pump 21 can be used as a trigger for starting the operation of the blower 40, and at night when a small amount of sewage inflow is expected, the trigger for starting the operation of the blower 40 can be the operation start signal from the operation control timer 83. And the stop of the operation of the blower 40 is controlled based on the PH measurement value measured by the PH meter 31. Regardless of what the trigger for starting the operation of the blower 40 is, by always controlling the stop of the operation with the PH measurement value of the sewage in the aeration tank 30, it is possible to avoid a situation where the discharged water quality deteriorates even when the aeration intensity is increased.

[0041] The increase in the pH value in the aeration tank 30 is caused by the inflow of sewage into the aeration tank 30 by the influent pump 21. That is, even without measuring the pH value of the sewage in the aeration tank 30, it is possible to grasp that the pH value in the aeration tank 30 will increase (or is likely to increase) by monitoring the operating status of the influent pump 21. Also, in a time period when the inflow of sewage into the aeration tank 30 decreases, etc., it can be set to start the operation at a predetermined time regardless of the operation of the influent pump 21, or it is also possible to predict the inflow timing of the sewage from past data, etc., and set it to start the operation when the set time based on the prediction is reached. In this way, the timing of starting the operation of the blower 40 is triggered by the operation of the influent pump 21 or the preset operation start time. However, regardless of what trigger is used to start the operation of the blower 40, the operation stop of the blower 40 is performed based on the pH measurement value measured by the pH meter 31, enabling efficient operation control of the blower 40.

[0042] The above sewage treatment system 1 is suitably used for a sewage treatment method that uses activated sludge to purify sewage by flowing sewage into the aeration tank 30 using the influent pump 21, storing the influent sewage together with the activated sludge in the aeration tank 30, and blowing air into the aeration tank 30 by the blower 40 for aeration. In this sewage treatment method, the operation of the blower 40 is started to start blowing air into the aeration tank 30 in response to the operation of the influent pump 21 or when the preset operation start time is reached. Also, the pH value of the sewage in the aeration tank 30 is measured, and the operation of the blower 40 is stopped to stop blowing air into the aeration tank 30 according to the measured pH measurement value.

[0043] <Control of Aeration Air Volume Based on Aeration Intensity> Because oxygen (air) is required to purify wastewater using activated sludge, in the wastewater treatment system 1, oxygen is supplied by operating the blower 40 to send air into the aeration tank 30. As described above, when the amount of air is insufficient in the aeration tank 30, assimilation increases, catabolism and internal respiration decrease, and excess sludge increases. On the other hand, when the amount of air is appropriate, catabolism and internal respiration increase, and sludge decreases. In the wastewater treatment system 1, the concept of aeration intensity is introduced to appropriately control the amount of air in the aeration tank 30.

[0044] The aeration intensity D is defined by the following formula (1). D = V / C (1) V: Aeration tank volume per hour (1 m) 3 Aeration air volume per unit (m 3 / h) C: Capacity of the aeration tank (m 3 )

[0045] As can be seen from the above formula (1), the aeration intensity is a concept for controlling the amount of air to be supplied to the capacity of the aeration tank. 3 This indicates the amount of air aerated per hour per unit area. In this embodiment, the regulating valve 45 with an aeration air volume meter and the regulating valve 46 with a release air volume meter function as air volume adjustment means for adjusting the amount of aeration air supplied from the blower 40 to the aeration tank 30 and the amount of release air discharged to the outside of the system from the branch pipe 42. By changing the opening and closing degree of the regulating valve 45 with an aeration air volume meter and the regulating valve 46 with a release air volume meter, the amount of aeration air can be adjusted based on the aeration intensity D.

[0046] In the sewage treatment system 1, the air volume adjusting means (adjusting valve 45 with an aeration air volume meter and adjusting valve 46 with a bypass air volume meter) adjusts the aeration air volume so that the aeration intensity D is 0.50 or more and 1.50 or less. When the aeration intensity D is less than 0.50, the air volume in the aeration tank 30 is insufficient. While the assimilation of activated sludge increases, the dissimilation and endogenous respiration decrease, resulting in an increase in excess sludge. When the aeration intensity D exceeds 1.50, the aeration force is too strong and the sludge is finely pulverized, causing the sludge not to settle in the sedimentation tank 50. If the sludge does not settle, the pulverized fine sludge floats in the supernatant water, leading to deterioration of the effluent quality. In the sewage treatment system 1, it is particularly preferable to control the aeration air volume supplied from the blower 40 to the aeration tank 30 so that the aeration intensity D is 0.75 or more and 1.25 or less.

[0047] Figure 2 is a graph showing the relationship between the aeration intensity, aeration time, and dissolved oxygen. The vertical axis of Figure 2 is the dissolved oxygen amount (mg / L), and the horizontal axis is the aeration time (minutes). This graph is obtained by storing sewage in the aeration tank 30 of the sewage treatment system 1, supplying air to the aeration tank 30 using the blower 40 with the inflow pump 21 stopped, and measuring and plotting the dissolved oxygen amount (DO value) in the aeration tank 30 every 5 minutes. The aeration intensity D is changed from 0.50 in 0.25 increments up to 1.50, and the plots of the DO values at each aeration intensity D are connected by lines to show the relationship between the passage of aeration time and the change in the DO value. Also, for reference, the change in the DO value in the aeration tank 30 after aeration stops is measured and plotted every 5 minutes, and the lines connecting them are combined and shown in Figure 2. The water temperature in the aeration tank 30 was 19°C.

[0048] As shown in Fig. 2, when the blower 40 is operated at an aeration intensity D = 0.5, the DO value in the aeration tank 30 hardly changes. When the blower 40 is stopped in this state, the DO value immediately approaches zero, and the activated sludge suspended solids (Mixed Liquor Suspended Solids, MLSS) in the aeration tank 30 are always in an anoxic state, becoming sludge with low sedimentation performance and difficult solid-liquid separation. When the blower 40 is operated at an aeration intensity D = 0.75 or an aeration intensity D = 1.00, the DO value gradually increases with the passage of aeration time in the aeration tank 30, so the dissolution efficiency of DO can be increased.

[0049] When reading from Fig. 2 the time required for the DO value to reach 3.0 during operation at each aeration intensity, it can be seen that at an aeration intensity D = 0.75, the aeration time (operation time of the blower 40) is 55 minutes, at an aeration intensity D = 1.00, the aeration time is 25 minutes, at an aeration intensity D = 1.25, the aeration time is 18 minutes, and at an aeration intensity D = 1.50, the aeration time is 12 minutes. At an aeration intensity D = 0.50, the DO does not increase even when the aeration time is 60 minutes or more. On the other hand, when the blower 40 is operated at an aeration intensity D = 1.25 or an aeration intensity D = 1.50, the DO value can be increased to 3.0 within 20 minutes of aeration time. By increasing the aeration intensity D, the aeration time is shortened, and the operation time of the blower 40 can be reduced, so efficient operation control of the blower 40 with reduced operation cost can be achieved.

[0050] Here, based on the aeration time (55 minutes) required for the DO value to reach 3.0 when the aeration intensity D is 0.75, the reduction rate (%) is calculated for how much the aeration time can be reduced when the aeration intensity D is increased to 1.00, 1.25, and 1.50, and the numerical values are shown in Table 1.

[0051]

Table 1

[0052] According to Table 1, for example, when the aeration intensity D = 1.00, the aeration time is 25 minutes. Based on the aeration intensity D = 0.75, the reduction rate can be estimated to be 45%. By increasing the aeration intensity D in this way, the operating time of the blower 40 can be shortened, so a significant power-saving effect can be obtained. Also, if the power consumption is reduced, the amount of CO2 generated will also decrease accordingly. Therefore, increasing the aeration intensity D also leads to the realization of an environmentally friendly sewage treatment system.

[0053] When controlling the operation of the blower by adopting the conventional timer control method, if the aeration intensity is increased, there is a risk that the PH will drop significantly. Therefore, the blower is operated based on the idea of long-term aeration without increasing the aeration intensity (for example, keeping the aeration intensity at about 0.50). In this case, since the aeration intensity is reduced by increasing the amount of air escaping to the outside of the system, the power required for the operation of the blower remains unchanged and it will operate for a long time, resulting in an increase in cost.

[0054] Also, in the conventional PH interlocking method, the start and stop of the blower operation were controlled only at the upper and lower limits of the PH value only during the time period when the inflow of sewage was large. On the other hand, in the time period when the inflow is small (for example, at night, etc.), since there is not enough PH fluctuation for the start and stop of the blower operation by PH value management to be effective, in order to ensure the minimum amount of oxygen required for the survival of microorganisms and maintain their activity even in the time period when the inflow is small, it was necessary to operate the blower intermittently by timer setting. This timer setting has to be based on prediction, and there is a possibility that the PH value of the aeration tank will fall below the lower limit value and deteriorate the quality of the treated water. However, if the aeration intensity is increased, there is a concern that it will fall significantly below the lower limit value. Therefore, even in the PH interlocking method, the aeration is carried out without increasing the aeration intensity so much (for example, keeping the aeration intensity at about 0.75), resulting in an appropriate operating time. By operating with an increased aeration intensity D, in the sewage treatment system 1 of this embodiment, more efficient operation control of the blower is possible.

[0055] According to the data measured by the inventor in the past, the operating time of the blower by the pH interlock method (aeration intensity 0.75) is 3,627 hours / year. If the blower is operated with an aeration intensity D = 1.00 in the method of the present application, the operating time of the blower is expected to be 3,627 hours / year × reduction rate 0.45 = 1,632 hours, and the reduction time is 1,995 hours / year. In order to explain the power-saving effect by adopting the method of the present application, the data of the operating time, power consumption, and electricity charge of the blower when the timer control method and the pH interlock method are adopted, and the data when the method of the present application is adopted are summarized in Table 2.

[0056]

Table 2

[0057] From Table 2, in the conventional timer control method (activated sludge method, long-time aeration method), the blower operating time is extremely long at 6,166 hours / year and 16.9 hours / day on average. In this method, the aeration intensity is set to D = 0.50 or less, the excess sludge conversion rate is low and the function cannot be exerted, and in order to avoid a decrease in pH, a large amount of air is vented. In the pH interlock method, since the aeration intensity is increased to D = 0.75 and controlled by the pH value, the operating time of the blower has been improved to 9.9 hours / day. In the method of the present application, by setting D = 1.00, the operating time can be reduced, and further reduction in the operating time and power-saving effect are expected with a higher aeration intensity. The power-saving effect is about 2.4 million yen for the electricity charge in the timer control method, about 1.41 million yen in the pH interlock method, and about 0.64 million yen in the method of the present application (lower limit pH management method).

[0058] In order to explain the reduction effect of CO2 generation amount by adopting the method of the present application, the data of the operating time, power consumption, and CO2 generation amount of the blower when the timer control method and the pH interlock method are adopted, and the data when the method of the present application (lower limit pH management method) is adopted are summarized in Table 3.

[0059]

Table 3

[0060] As shown in Table 3, in the timer control method, the amount of CO2 generated is 41 tons / year, in the pH interlock method it is 24.5 tons / year, and in the method of the present application it is 11 tons / year. Along with the reduction in power consumption, the reduction in the greenhouse gas CO2 can be achieved at 17 tons / year in the pH interlock method and 31 tons / year in the method of the present application. It is possible to achieve the reduction of the greenhouse gas CO2 in the management of sewage treatment facilities.

[0061] The control unit 80 of the sewage treatment system 1 is housed in a portable control panel, installed in an existing large-scale septic tank or large-scale sewage treatment facility, connected to the pH measuring instrument 31, the blower on-off signal, etc., and monitors the operation status to collect data before and after installation, so that the effect can be visualized. As a result, it can be proved to the manager of the existing large-scale septic tank that it is a sewage treatment system with low cost and high power-saving effect, and it becomes easy to promote the system introduction.

[0062] As described above, the sewage treatment system according to the present invention and the sewage treatment method using the system have been described based on the drawings. However, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, in the above-described embodiment, the sewage treatment system includes only one aeration tank, but a sewage treatment system including a plurality of aeration tanks may also be used. Further, the sewage treatment system does not necessarily include all the components. For example, a sewage treatment system that does not include a raw water pump tank or a disinfection tank may be used, or a sewage treatment system that includes other components (tanks) as necessary may also be used.

Explanation of Signs

[0063] 1 Sewage treatment system 10 Raw water pump tank 11 Raw water pump 20 Sewage inflow pump tank 21 Inflow pump 23a First water level sensor 23b Second water level sensor 30 Aeration tank 31 pH meter (pH measurement means) 40 Blower 41 Air delivery pipe 42 Control valve with air discharge volume meter 43 Control valve with aeration air volume meter 44 Diffuser pipe 45 Branch pipe 46 Control valve with bypass air volume meter 50 Settling tank 52 Sludge return pipe 53 Sludge extraction pipe 60 Disinfection tank 70 Discharge pump tank 71 Discharge pump 80 Control unit 81 Operation control means 82 pH converter 83 Operation control timer 12, 22, 32, 51, 61, 72 Pipes

Claims

1. A sewage treatment system for purifying sewage using activated sludge, comprising: An aeration tank for containing sewage together with activated sludge and aerating it; An inflow pump for allowing sewage to flow into the aeration tank; A blower for sending air into the aeration tank; PH measurement means for measuring the PH value of the sewage in the aeration tank; Operation control means for controlling the start and stop of the operation of the blower, wherein the operation control means starts the operation of the blower in response to the operation of the inflow pump or when a preset operation start time is reached, and stops the operation of the blower according to the PH measurement value measured by the PH measurement means.

2. The sewage treatment system according to claim 1, wherein the operation control means starts the operation of the blower after a predetermined delay time has elapsed since the start of the inflow of sewage into the aeration tank by the inflow pump.

3. The sewage treatment system according to claim 1, wherein the operation control means stops the operation of the blower when the PH measurement value measured by the PH measurement means becomes equal to or less than a first set value.

4. A branch pipe for discharging air to the outside of the system is connected in the middle of the air supply pipe for supplying air from the blower to the aeration tank, The sewage treatment system according to any one of claims 1 to 3, further comprising air volume adjustment means for adjusting the amount of aeration air supplied from the blower to the aeration tank and the amount of bypass air discharged from the branch pipe to the outside of the system.

5. The sewage treatment system according to claim 4, wherein the air volume adjustment means adjusts the amount of aeration air based on the aeration intensity D defined by the following formula (1). D = V / C... (1) V: Aeration air volume (m ３ per hour) blown into per 1 m of aeration tank volume per hour ３ / h C: Volume of the aeration tank (m ３ )

6. The sewage treatment system according to claim 5, wherein the air volume adjustment means adjusts the amount of aeration air so that the aeration intensity D is 0.50 or more and 1.50 or less.

7. A sewage treatment method for purifying sewage using activated sludge, comprising flowing sewage into an aeration tank using an inflow pump, containing the flowed sewage together with activated sludge in the aeration tank, and sending air into the aeration tank by a blower for aeration, starting the operation of the blower and starting the supply of air to the aeration tank in response to the operation of the inflow pump or when a preset operation start time is reached, measuring the PH value of the sewage in the aeration tank, and stopping the operation of the blower and stopping the supply of air to the aeration tank according to the measured PH measurement value.

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