Wastewater treatment system and wastewater treatment method

Abstract

A sewage treatment system and a sewage treatment method are provided that enable simple and efficient operation control of a blower. [Solution] The wastewater treatment system 1 of the present invention purifies wastewater by using activated sludge. The wastewater treatment system 1 includes an aeration tank 30 that stores and aerates wastewater together with activated sludge, an inflow pump 21 for inflowing wastewater into the aeration tank 30, a blower 40 for blowing air into the aeration tank 30, a pH measuring means 31 for measuring the pH value of the wastewater in the aeration tank 30, and an operation control means 81 for controlling the start and stop of the operation of the blower 40. The operation control means 81 starts the operation of the blower 40 in response to the operation of the inflow pump 21 or when a 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 measuring means 31.

Description

[Technical field]

[0001] The present invention relates to a wastewater treatment system and a wastewater treatment method for microbially treating organic pollutants contained in wastewater. [Background technology]

[0002] One method of treating wastewater such as domestic wastewater (e.g., wastewater from kitchen equipment and toilets) is to have microorganisms decompose organic matter. In wastewater treatment facilities that employ this method, for example, wastewater is temporarily stored in a wastewater inflow pump tank (adjustment tank), then sent to an aeration tank for aeration, and dirt is removed using activated sludge. The sludge suspension is then transferred to a settling tank where it is retained, and the supernatant water is disinfected by settling and separated before being released. The blower that sends air to the aeration tank is operated according to the amount of wastewater inflow load, and for example, the operation time of the blower is set by a timer, and the blowing of air to the aeration tank is controlled by time.

[0003] Depending on the installation location of the sewage treatment equipment, the amount of sewage inflowing into the equipment may vary greatly depending on the season, weather, time of day, etc. For example, if the sewage treatment equipment is installed in a rest facility such as a service area on a highway, the amount of sewage inflow will vary depending on the traffic volume using that road, and if it is installed in a large commercial facility or a venue used for sports events, concerts, etc., similar fluctuations will occur depending on the time of day. However, when the amount of sewage inflow varies greatly like this, simply controlling the operation of the blower using a timer will result in the blower operating repeatedly with the same timer setting until it is reset, making it impossible to balance the amount of sewage inflow and the amount of aeration air, resulting in over- or under-aeration. In order to solve this problem, for example, Patent Document 1 proposes a sewage treatment equipment in which a pH meter is installed in the aeration tank and the start and stop of the operation of the blower is controlled according to the measured pH value of the sewage in the aeration tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-217375 A Summary of the Invention [Problem to be solved by the invention]

[0005] The wastewater treatment device in Patent Document 1 measures the pH value of the wastewater in the aeration tank, and when the pH value rises, starts the operation of a blower to send air into the aeration tank, and when the pH value falls, stops sending air to the aeration tank, thereby responding to fluctuations in the inflow of wastewater. Specifically, the start and stop of the blower operation is controlled by two points, the upper and lower limits of the pH value, and the control width is about 0.3.

[0006] However, in reality, the pH in the aeration tank does not fluctuate significantly, and considering the general measurement accuracy of pH measuring devices, it is difficult to control the pH value at two points, above and below, with a control width of 0.3. Therefore, there is a demand for a wastewater treatment system that allows for simpler and more efficient control of the blower operation.

[0007] The present invention has been made in consideration of the above problems, and has an object to provide a sewage treatment system and a sewage treatment method that enable simple and efficient operation control of a blower. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, firstly, the present invention provides a sewage treatment system that purifies sewage by utilizing activated sludge, comprising an aeration tank for storing and aerating sewage together with activated sludge, an inflow pump for inflowing sewage into the aeration tank, a blower for blowing air into the aeration tank, a pH measuring means for measuring the pH value of the sewage in the aeration tank, and an operation control means for controlling the start and stop of operation of the blower, wherein the operation control means starts operation of the blower in response to the operation of the inflow pump or when a preset operation start time is reached, and stops operation of the blower in response to the pH measurement value measured by the pH measuring means (Invention 1).

[0009] According to this invention (Invention 1), the operation control means starts the operation of the blower using the operation of the inflow pump or a preset time as a trigger, and stops the operation of the blower using the pH value measured by the pH measurement means as a trigger, so that simple and efficient operation control of the blower is possible. In particular, the start and stop of the blower can be managed by a single point, the lower limit value of the pH value, which makes it easy to maintain and manage the system.

[0010] The rise in the pH value in the aeration tank occurs when wastewater flows into the aeration tank by the inflow pump. In other words, it is possible to know that the pH value in the aeration tank is rising by monitoring the operation status of the inflow pump without measuring the pH value of the wastewater in the aeration tank. In addition, during times when the inflow of wastewater into the aeration tank decreases, it is possible to set the fan to start operation at a specified time regardless of the operation of the inflow pump, or to predict the timing of the inflow of wastewater from past data, etc., and to start operation at a time set based on the prediction. In this way, the timing of starting the operation of the blower is triggered by the operation of the inflow pump or the operation start time set in advance, and regardless of the trigger used to start the operation, the operation is stopped based on the pH measurement value measured by the pH measuring means, thereby enabling efficient operation control of the blower.

[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 inflow pump starts to inflow sewage into the aeration tank (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 value measured by the pH measuring means becomes equal to or less than a first set value (Invention 3).

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

[0014] In the above invention (Invention 4), it is preferable that the air amount adjusting means adjusts the amount of air for aeration based on an aeration intensity D defined by the following formula (1) (Invention 5). 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 )

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

[0016] Secondly, the present invention provides a sewage treatment method for purifying the sewage by using activated sludge, by using an inflow pump to introduce sewage into an aeration tank, storing the introduced sewage together with activated sludge in the aeration tank, and aerating the sewage by sending air into the aeration tank with a blower, wherein the operation of the blower is started to start sending air to the aeration tank in response to the operation of the inflow pump or when a preset operation start time is reached, the pH value of the sewage in the aeration tank is measured, and the operation of the blower is stopped in response to the measured pH value to stop the sending of air to the aeration tank (Invention 8). Effect of the Invention

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

[0018] [Figure 1] 1 is an explanatory diagram illustrating a basic configuration of a wastewater treatment system according to one embodiment of the present invention. [Diagram 2] 1 is a graph showing the relationship between aeration intensity, aeration time, and dissolved oxygen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] An embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiment described below, and the described embodiment is merely an example for explaining the technical features of the present invention. In addition, the shapes and dimensions shown in each drawing are shown only to facilitate understanding of the contents of the present invention, and do not accurately reflect the actual shapes and dimensions.

[0020] <Sewage treatment system> 1 is an explanatory diagram showing a schematic basic configuration of a sewage treatment system 1 according to one embodiment of the present invention. This sewage treatment system 1 is a sewage treatment system that purifies sewage by using activated sludge, and can be suitably used in facilities that are used by an unspecified number of customers and where the inflow of sewage fluctuates greatly, such as rest facilities such as service areas on expressways, large commercial facilities, and venues used for sporting events, concerts, and the like.

[0021] As shown in Fig. 1, the wastewater treatment system 1 includes a raw water pump tank 10, a wastewater inflow pump tank 20, an aeration tank 30, a sedimentation tank 50, a disinfection tank 60, and a discharge pump tank 70, which are connected in series. The wastewater treatment system 1 includes an inflow pump 21 for inflowing wastewater into the aeration tank 30, which contains and aerates wastewater together with activated sludge, a blower 40 for blowing air into the aeration tank 30, a pH meter 31 as a pH measuring means for measuring the pH value of the wastewater 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 wastewater delivered from various locations in the installation site of the wastewater treatment system 1, and is provided for the purpose of making the amount and quality of the wastewater as uniform as possible. The wastewater stored in the raw water pump tank 10 is pumped by the raw water pump 11 through the piping 12 to the wastewater inflow pump tank 20 at an appropriate time.

[0023] The wastewater inflow pump tank 20 is provided for the purpose of adjusting the amount of wastewater sent to the aeration tank 30 and the timing of sending. In the wastewater inflow pump tank 20, an inflow pump 21 for sending wastewater to the aeration tank 30 via piping 22, and a first water level sensor 23a and a second water level sensor 23b for detecting the water level in the wastewater inflow pump tank 20 are installed. The first water level sensor 23a detects a high water level for starting the inflow pump 21, and the second water level sensor 23b detects a low water level for stopping the inflow pump 21. For example, when the first water level sensor 23a detects that the level of sewage in the sewage inlet pump tank 20 is higher than a predetermined reference water level, the inlet pump 21 starts up and sends the sewage in the sewage inlet pump tank 20 to the aeration tank 30 via the piping 22, and when, for example, the second water level sensor 23b detects that the level of sewage in the sewage inlet pump tank 20 is lower than a predetermined reference water level, the inlet pump 21 stops and the sending of sewage to the aeration tank 30 also ends.

[0024] The aeration tank 30 contains activated sludge together with wastewater, and is configured to aerate the wastewater in the aeration tank 30 with air sent in from a blower 40. A pH meter 31 is disposed inside the aeration tank 30 to measure the pH value of the wastewater contained in the aeration tank 30. The aeration tank 30 is connected to a settling tank 40 by a piping 32, and is configured so that the wastewater in the aeration tank 30 flows into the settling tank 40.

[0025] In the aeration tank 30, activated sludge is used to purify the wastewater. The wastewater that is introduced into the aeration tank 30 by the inflow pump 21 contains, for example, organic contaminants and ammonia (NH 4 + ) is included, for example, as organic matter C 6H 12 O 6 The reaction equation in the aeration tank 30 using glucose is shown below: (a) anabolism, (b) catabolism, and (c) internal respiration. (A) Anabolic action C 6 H 12 O 6 (organic matter)+NH 3 +O 2 → C 5 H 7 NO 2 (New sludge) + CO 2 +4H 2 O (a) Catabolism C 6 H 12 O 6 (Organic matter) +6O 2 → 6CO 2 +6H 2 O+heat (C) Internal respiration C 5 H 7 NO 2 (Sludge) +7O 2 → 5CO 2 +3H 2 O+HNO 3 (nitric acid)

[0026] When the amount of air is insufficient in the aeration tank 30, specifically when the aeration intensity D described later falls below approximately 0.50, assimilation increases, catabolism and endogenous respiration decrease, and excess sludge increases. On the other hand, when the amount of air is appropriate, catabolism and endogenous respiration increase, and sludge decreases. In other words, in wastewater treatment using activated sludge, it is important to appropriately control the amount of air. The wastewater flowing into the aeration tank 30 contains ammonia (NH 4 + As purification progresses in the aeration tank 30, ammonia is nitrified (oxidized) and combined with oxygen through assimilation and internal respiration, and the nitrogen form is converted to NH 4 + (ammonia nitrogen) → NO 2 -(Nitrite nitrogen) → NO 3 - (nitrate nitrogen), the pH value drops, for example, from PH 6.2 to around PH 6.8.

[0027] In conventional technology (a method in which the start and stop of the blower for aeration is controlled by a timer, and not by monitoring the pH value), purification is mainly by assimilation reaction (adsorption reaction). In other words, the dirt (organic matter) contained in the wastewater is purified by the generation of new sludge, but the increase in dissolved oxygen (DO) caused by aeration significantly reduces the pH value, significantly worsening the quality of the discharged water, so the amount of aeration air supplied by aeration must be restricted.

[0028] In catabolism, organic matter (dirt) is removed by converting it into heat using large amounts of oxygen, and CO 2 In this case, no new sludge is generated, which leads to a reduction in excess sludge, but a high DO is required. In the internal respiration process, when organic matter becomes diluted, the sludge decreases due to cannibalism, and nitrate NO 3 - The production of nitrate causes the pH value to drop, so monitoring this pH value makes it possible to manage the supply of oxygen. If the aeration is too strong, the sludge will be finely crushed and will flow out, causing the quality of the effluent to deteriorate rapidly, so it is necessary to avoid a drop in the pH value.

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

[0030] The blower 40 is used to send air into the aeration tank 30, and is connected to a blower pipe 41 that supplies air to the aeration tank 30. A branch pipe 42 that exhausts air to the outside of the system is connected to the blower pipe 41. A plurality of air diffuser pipes 43 are connected to the blower pipe 41 on the aeration tank 30 side of the branch pipe 42, and the plurality of air diffuser pipes 43 are disposed inside the aeration tank 30.

[0031] An adjustment valve 44 with a discharge air amount meter is provided on the blower 40 side of the branch pipe 42 of the blower pipe 41, and is configured to measure the amount of air passing through and adjust the amount of air. Also, an adjustment valve 45 with an aeration air amount meter is provided on the aeration tank 30 side of the branch pipe 42 of the blower pipe 41 (before the branch pipes 43 are branched) and is configured to measure the amount of air passing through and adjust the amount of air. The air passing through the adjustment valve 45 with aeration air amount meter is aeration air that is sent to the aeration tank 30 and used for aeration. On the other hand, an adjustment valve 46 with a release air amount meter is provided on the branch pipe 42, and is configured to measure the amount of air passing through and adjust the amount of air. The air passing through the adjustment valve 46 with a release air amount meter is release air that is discharged to the outside of the system. The adjusting valve 45 with an aeration air volume meter and the adjusting valve 46 with a release air volume meter function as air volume adjustment means for adjusting the volume of aeration air supplied from the blower 40 to the aeration tank 30 and the volume of release air discharged from the branch pipe 42 to the outside of the system.

[0032] The settling tank 50 is for settling the sludge contained in the wastewater and separating it from the supernatant water. The settling tank 50 is connected to the disinfection tank 60 by a pipe 51, and the separated supernatant water flows into the overflow weir and is discharged into the disinfection tank 60 via the pipe 51. 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 transported to the outside of the system through a sludge withdrawal pipe 53 connected midway to the sludge return pipe 52.

[0033] The disinfection tank 60 disinfects the supernatant water discharged from the settling tank 50 using a known disinfection means (not shown). The disinfection tank 60 is connected to the discharge pump tank 70 by a pipe 61, and is configured so 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 to the outside of the system via a pipe 72 by the discharge pump 71. The disinfection tank 60 may be arranged at successively lower locations to allow the supernatant water to flow from the disinfection tank 60 to the discharge pump tank 70 due to a difference in head.

[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 obtained by the PH meter 31 into a PH value, and an operation control timer 83 for sending an operation start signal for the blower 40 when a set time has elapsed. The set time at which the operation control timer 83 sends out the operation start signal may be a certain fixed time that is simply set in advance as the operation start time, or it may be possible to generate sewage inflow prediction information based on past sewage inflow data and the like, and set the operation start time in advance to correspond to the generated inflow prediction information.

[0035] <Controlling start / stop of blower operation> 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 at a preset operation start time. In either case, the operation control means 81 stops the operation of the blower 40 in response to the pH value measured by the pH meter 31.

[0036] When operation of the blower 40 is started in response to the operation of the inflow pump 21, the operation control means 81 sends an instruction to the blower 40 to start operation after a predetermined delay time has elapsed since the inflow pump 21 started to inflow sewage into the aeration tank 30. Upon receiving the instruction, the blower 40 starts operation and starts sending air into the aeration tank 30. 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 the operation of the blower 40 is to be started at a preset operation start time, the operation control means 81, upon receiving an operation start signal sent out by the operation control timer 83, sends an instruction to the blower 40 to start operating the blower 40. Upon receiving the instruction, the blower 40 starts operating, and starts sending air into the aeration tank 30.

[0038] When the operation of the blower 40 is stopped according to the pH measured by the pH measuring device 31, the operation control means 81 sends an instruction to the blower 40 to stop the operation of the blower 40 when the pH measured by the pH measuring device 31 becomes equal to or less than the first set value. The blower 40 stops the operation upon receiving the instruction and stops sending air to the aeration tank 30. Here, the first set value is preferably a pH value at which the catabolic reaction and the internal respiratory reaction are almost completed. The first set value is determined based on the coagulation property of the sludge in the aeration tank 30, the state of the discharged water quality, the sludge conversion rate, etc., and is preferably set to, for example, about pH 5.7 to pH 7.0, particularly about pH 6.0 to pH 6.6. It is extremely important in the wastewater treatment system 1 of this embodiment to constantly manage this first set value as the lower limit pH value of the wastewater 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 using the operation of the inflow pump 21 or a preset time as a trigger, and stops the operation of the blower 40 using a pH measurement value measured by the pH meter 31 as a trigger, so that simple and efficient operation control of the blower 40 is possible. The start and stop of the operation of the blower 40 can be managed by a single point of the lower limit value of the pH value, so that the maintenance and management of the system is also easy. In addition, when the start and stop of the operation of the blower 40 is controlled using a conventional timer control method, it is necessary to determine the operation time based on the inflow prediction. If the inflow prediction is incorrect, the pH in the aeration tank may drop too much, causing the discharge water quality to fall below the discharge standard, or there may be over- or under-aeration. By stopping the operation of the blower 40 using a pH measurement value measured by the pH meter 31 as a trigger, such problems are eliminated.

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

[0041] The rise in the pH value in the aeration tank 30 occurs when wastewater flows into the aeration tank 30 by the inflow pump 21. That is, even without measuring the pH value of the wastewater in the aeration tank 30, it is possible to know that the pH value in the aeration tank 30 is rising (will rise) by monitoring the operation status of the inflow pump 21. In addition, during a time period when the inflow of wastewater into the aeration tank 30 decreases, it is possible to set the pump to start operation at a predetermined time regardless of the operation of the inflow pump 21, or to predict the timing of the inflow of wastewater from past data, etc., and to start operation at a time set based on the prediction. In this way, the timing of starting the operation of the blower 40 is triggered by the operation of the inflow pump 21 or a preset operation start time, but regardless of what trigger is used to start the operation of the blower 40, the operation of the blower 40 is stopped based on the pH measured by the pH meter 31, thereby enabling efficient operation control of the blower 40.

[0042] The above-mentioned sewage treatment system 1 is suitably used in a sewage treatment method in which sewage is introduced into the aeration tank 30 using the inflow pump 21, the introduced sewage is stored in the aeration tank 30 together with activated sludge, and air is sent into the aeration tank 30 by the blower 40 to aerate the sewage, thereby purifying the sewage using activated sludge. In this sewage treatment method, the operation of the blower 40 is started to start sending air into the aeration tank 30 in response to the operation of the inflow pump 21 or when a preset operation start time is reached. In addition, the pH value of the sewage in the aeration tank 30 is measured, and the operation of the blower 40 is stopped in response to the measured pH value to stop sending air into the aeration tank 30.

[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 wastewater treatment system 1, the air amount adjusting means (the adjusting valve 45 with an aeration air amount measuring meter and the adjusting valve 46 with a release air amount measuring meter) adjusts the amount of aeration air so that the aeration intensity D is 0.50 or more and 1.50 or less. If the aeration intensity D is less than 0.50, the amount of air in the aeration tank 30 is insufficient, and while the assimilation of the activated sludge increases, the catabolism and internal respiration decrease, and the excess sludge increases. If the aeration intensity D exceeds 1.50, the aeration force is too strong and the sludge is finely crushed, and the sludge does not settle in the settling tank 50. If the sludge does not settle, the crushed fine sludge will float in the supernatant water, leading to a deterioration in the quality of the effluent water. In the wastewater treatment system 1, it is preferable to control the amount of aeration air 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] FIG. 2 is a graph showing the relationship between aeration intensity, aeration time, and dissolved oxygen. The vertical axis of FIG. 2 is the amount of dissolved oxygen (mg / L), and the horizontal axis is the aeration time (minutes). In this graph, sewage is stored in the aeration tank 30 of the sewage treatment system 1, air is supplied to the aeration tank 30 using the blower 40 while the inflow pump 21 is stopped, and the amount of dissolved oxygen (DO value) in the aeration tank 30 is measured and plotted every 5 minutes of the aeration time. The aeration intensity D is changed from 0.50 to 1.50 in increments of 0.25, and the relationship between the passage of aeration time and the transition of the DO value is shown by connecting the plots of the DO value at each aeration intensity D with a line. For reference, the DO value in the aeration tank 30 is measured and plotted every 5 minutes after aeration is stopped, and is also shown in FIG. 2, which is connected with a line. The water temperature in the aeration tank 30 was 19°C.

[0048] As shown in Fig. 2, when the blower 40 is operated with an aeration intensity D = 0.5, the DO value in the aeration tank 30 changes very little. If the blower 40 is stopped in this state, the DO value will soon approach zero, and the activated sludge suspended solids (Mixed Liquor Suspended Solids, MLSS) in the aeration tank 30 will always be in an oxygen-deficient state, resulting in sludge with low settling properties and difficult solid-liquid separation. If the blower 40 is operated with an aeration intensity D = 0.75 or D = 1.00, the DO value will gradually increase over the aeration time in the aeration tank 30, and the DO dissolution efficiency can be increased.

[0049] 2, the time required for the DO value to reach 3.0 by operation at each aeration intensity is 55 minutes for the aeration intensity D=0.75 (the operation time of the blower 40), 25 minutes for the aeration intensity D=1.00, 18 minutes for the aeration intensity D=1.25, and 12 minutes for the aeration intensity D=1.50. At the aeration intensity D=0.50, the DO does not increase even if 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 D=1.50, the DO value can be raised to 3.0 within an aeration time of 20 minutes. By increasing the aeration intensity D, the aeration time is shortened, and the operation time of the blower 40 can be reduced, which enables efficient operation control of the blower with reduced operating costs.

[0050] Here, the aeration time (55 minutes) required to reach a DO value of 3.0 when the aeration intensity D is 0.75 was used as the standard, and the reduction in aeration time was calculated as a reduction rate (%) when the aeration intensity D is increased to 1.00, 1.25, and 1.50. These values ​​are shown in Table 1.

[0051] [Table 1]

[0052] According to Table 1, for example, when the aeration intensity D is 1.00, the aeration time is 25 minutes, and when the aeration intensity D is 0.75, the reduction rate can be estimated as 45%. By increasing the aeration intensity D in this way, the operation time of the blower 40 can be shortened, resulting in a significant power saving effect. Furthermore, the more the power consumption is reduced, the more the CO 2 Since the amount of wastewater generated will also decrease, increasing the aeration intensity D will lead to the realization of an environmentally friendly wastewater treatment system.

[0053] When controlling the operation of the blower using the conventional timer control method, there is a risk that the pH will drop significantly if the aeration intensity is increased, so the blower is operated with the idea of ​​aeration for a long time without increasing the aeration intensity (for example, by keeping the aeration intensity at around 0.50). In this case, the aeration intensity is reduced by increasing the amount of air released outside the system, so the power required to operate the blower remains the same but it operates for a long time, which increases costs.

[0054] In addition, in the conventional PH interlocking method, the blower operation start / stop was controlled by the upper and lower limits of the PH value only during the period when the inflow of sewage was large. On the other hand, during the period when the inflow was small (for example, at night, etc.), the PH fluctuation was not so large that the start / stop of the blower operation by the PH value management was effective, so in order to secure the minimum amount of oxygen necessary for microorganisms to live and maintain their activity even during the period when the inflow was small, it was necessary to operate the blower intermittently by setting a timer. This timer setting had to be based on prediction, and the PH value of the aeration tank may fall below the lower limit value, which may deteriorate the quality of the discharged water, but there is a concern that if the aeration intensity is increased, it may fall far below the lower limit value. Therefore, even in the PH interlocking method, aeration is performed without increasing the aeration intensity very much (for example, the aeration intensity is suppressed to about 0.75), so the operation time is accordingly long. By increasing the aeration intensity D and operating, the sewage treatment system 1 of this embodiment enables more efficient operation control of the blower.

[0055] According to data measured by the inventors in the past, the operation time of the blower using the PH interlocking method (aeration strength 0.75) is 3,627 hours / year. If the blower is operated with an aeration strength D of 1.00 using the method of the present application, the operation time of the blower is 3,627 hours / year x reduction rate 0.45 = 1,632 hours, and the reduction time is expected to be 1,995 hours / year. In order to explain the power saving effect of adopting the method of the present application, the data on the operation time, power consumption, and electricity charges of the blower when the timer control method and the PH interlocking method are adopted, as well as 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-term aeration method), the blower operation time is extremely long at 6,166 hours / year, 16.9 hours / day on average. In this method, the aeration intensity is set to D=0.50 or less, and the excess sludge conversion rate is low and the function cannot be exerted, so air is released in large amounts to avoid a drop in pH. In the pH-linked method, the aeration intensity is increased to D=0.75 and controlled by the pH value, so the blower operation time is improved to 9.9 hours / day. In the method of the present application, the operation time can be reduced by setting D=1.00, and if the aeration intensity is increased beyond that, further reduction in operation time and power saving effects are expected. The power saving effect is that the electricity bill for the timer control method was about 2.4 million yen, while the PH-linked method was about 1.41 million yen, and the method of the present application (lower limit pH management method) was about 640,000 yen.

[0058] CO by adopting the method of this application 2 In order to explain the reduction in emissions, we measured the operating time of the blower, power consumption, and CO2 emissions when the timer control method and the PH interlocking method were adopted. 2 Table 3 summarizes the data on the amount of waste generated and the data when the method of the present application (lower limit pH control method) is adopted.

[0059] [Table 3]

[0060] As shown in Table 3, the timer control method 2 The amount of CO generated is 41 tons / year, compared with 24.5 tons / year for the PH linked system and 11 tons / year for the system proposed in this application. 2 The reduction amount is 17 tons / year with the PH interlocking method and 31 tons / year with the method of this application. 2 Reductions can be achieved.

[0061] The control unit 80 of the sewage treatment system 1 is housed in a portable control panel, which is installed in an existing large-scale septic tank or large-scale sewage treatment facility, and the PH meter 31, blower on-off signal, etc. are connected to monitor the operation status and collect data before and after installation, making it possible to visualize the effects. As a result, it is possible to prove to managers of existing large-scale septic tanks that this is an inexpensive sewage treatment system with high power-saving effects, making it easier to promote the introduction of the system.

[0062] The sewage treatment system and the sewage treatment method using the system according to the present invention have been described above with reference to the drawings, but the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the sewage treatment system has only one aeration tank, but the sewage treatment system may have multiple aeration tanks. In addition, the sewage treatment system does not need to have all the components, and may be, for example, a sewage treatment system that does not have a raw water pump tank or a disinfection tank, or a sewage treatment system that has other components (tanks) as necessary. [Explanation of symbols]

[0063] 1. Wastewater treatment system 10 Raw water pump tank 11 Raw water pump 20 Sewage inflow pump tank 21 Inflow pump 23a No. 1 water level sensor 23b Second water level sensor 30 Aeration tank 31 PH measuring device (PH measuring means) 40 Blower 41 Air pipe 42 Regulating valve with discharge air volume measuring gauge 43 Regulating valve with aeration air volume measuring meter 44 Air diffuser 45 Branch pipe 46 Regulating valve with air release meter 50 Sedimentation tank 52 Sludge return pipe 53 Sludge extraction pipe 60 Disinfection tank 70 Discharge Pump Tank 71 Discharge Pump 80 Control section 81 Operation control means 82 pH converter 83 Operation control timer 12, 22, 32, 51, 61, 72 Piping

Claims

1. A wastewater treatment system for purifying domestic wastewater using activated sludge, comprising: an adjustment tank for storing wastewater; an aeration tank for storing and aerating the wastewater sent from the adjustment tank together with activated sludge; and a settling tank for settling the sludge contained in the wastewater flowing in from the aeration tank and separating it from the supernatant water, the system being configured to be connected in series; an inflow pump for inflowing wastewater from the adjustment tank into the aeration tank, the inflow pump being activated when it is detected that the wastewater level in the adjustment tank is higher than a predetermined reference water level and being stopped when it is detected that the water level is lower than the reference water level; A blower for blowing air into the aeration tank; A pH measuring means for measuring the pH value of the wastewater in the aeration tank; An operation control means for controlling the start and stop of the operation of the blower, A wastewater treatment system, wherein the operation control means starts operation of the blower after a predetermined delay time has elapsed since the inflow pump starts to inflow sewage into the aeration tank, and stops operation of the blower depending on the pH measurement value measured by the pH measurement means.

2. 2. The wastewater treatment system according to claim 1, wherein the operation control means stops the operation of the blower when the pH value measured by the pH measuring means becomes equal to or lower than a first set value.

3. A branch pipe for discharging air to the outside of the system is connected to the middle of the air blower pipe for supplying air from the blower to the aeration tank, The system further includes an air amount adjusting means for adjusting the amount of aeration air supplied from the blower to the aeration tank and the amount of escape air discharged from the branch pipe to the outside of the system, 3. The wastewater treatment system according to claim 1, wherein the air amount adjusting means adjusts the amount of air for aeration based on an aeration intensity D defined by the following formula (1): D=V / C...(1) V: Amount of aeration air blown per 1 m3 of aeration tank volume per hour (m3 / h) C: Capacity of the aeration tank (m 3 )

4. 4. The wastewater treatment system according to claim 3, wherein the air amount adjusting means adjusts the amount of air for aeration so that the aeration intensity D is 0.50 or more and 1.50 or less.

5. A sewage treatment system as described in claim 4, wherein the air volume adjustment means adjusts the amount of air for aeration so that the aeration intensity D is greater than or equal to 0.75 and less than or equal to 1.

00.

6. A sewage treatment system comprising an adjustment tank for storing sewage, an aeration tank for storing and aerating the sewage sent from the adjustment tank together with activated sludge, and a settling tank for settling the sludge contained in the sewage flowing in from the aeration tank and separating it from the supernatant water, all connected in series; an inflow pump which starts when it detects that the sewage level in the adjustment tank is higher than a predetermined reference water level and stops when it detects that the water level is lower than the reference water level, is used to flow sewage from the adjustment tank into the aeration tank, the flowed-in sewage is stored in the aeration tank together with the activated sludge, and aeration is performed by blowing air into the aeration tank with a blower, thereby purifying sewage, which is domestic wastewater, using activated sludge, After a predetermined delay time has elapsed since the inflow pump started to inflow sewage into the aeration tank, the blower is started to operate to start sending air into the aeration tank; The method for treating wastewater comprises measuring the pH value of the wastewater in the aeration tank, and stopping the operation of the blower in accordance with the measured pH value to stop the supply of air to the aeration tank.

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