Activated sludge treatment facility and activated sludge treatment method

Abstract

To provide activated sludge treatment equipment having high energy efficiency by reducing the area of a sedimentation basin even when the daily fluctuation of inflow sewage is large.SOLUTION: An activated sludge treatment facility comprising: a biological treatment tank for biologically treating inflow wastewater; and a final sedimentation basin for solid-liquid separating treated water biologically treated in the biological treatment tank, wherein the activated sludge treatment facility comprises: a communication passage provided at a position lower than a minimum water level of the biological treatment tank and allowing the treated water to flow from the biological treatment tank to the final sedimentation basin; a sludge return passage for returning a part of the activated sludge taken out from the final sedimentation basin to an upstream section as return sludge; and a constant flow-out section for constant-flowing treated water out of the final sedimentation basin.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an activated sludge treatment facility and an activated sludge treatment method. [Background technology]

[0002] As shown in Figure 1, activated sludge treatment equipment comprises a primary sedimentation tank, a biological treatment tank, and a final sedimentation tank. Organic wastewater, from which suspended solids have been settled and removed in the primary sedimentation tank, flows into the biological treatment tank, where the dissolved organic matter is purified by the activated sludge in the tank and then flows down to the final sedimentation tank. The activated sludge settles and separates in the final sedimentation tank, and the clear supernatant treated water is disinfected and then released into the river. A portion of the activated sludge that settles in the final sedimentation tank is returned to the biological treatment tank via the sludge return line.

[0003] The biological treatment tank is divided into four compartments by partitions with openings at the bottom along the flow direction of the inflowing wastewater, and each compartment is equipped with aeration devices, agitation blades, etc. In the compartments where the aeration devices are driven, aerobic treatment occurs, where aerobic microorganisms break down BOD or nitrify ammonia, while in the compartments where agitation blades are rotated instead of aeration devices, anaerobic treatment occurs, where anaerobic microorganisms perform denitrification and phosphorus removal reactions.

[0004] Generally, the pollution load of wastewater flowing into a sewage treatment facility, which is expressed as the product of the water quality, such as BOD and ammonia concentration, contained in the inflowing wastewater and the water volume, fluctuates with the seasons. Therefore, the facility is operated to efficiently purify the wastewater by appropriately determining which sections are to be treated aerobically and which sections are to be treated anaerobically in response to seasonal fluctuations.

[0005] In addition, the pollution load of influent wastewater fluctuates throughout the day, and in many cases the peaks in influent volume and pollution concentration occur twice a day, in the morning and at night. Because the peak and bottom times of the influent load change in a short period of time, it is not possible to make adjustments such as changing the number of biological treatment lines in operation, and all lines must be operated.

[0006] For this reason, the total amount of activated sludge to be held in the biological treatment tank must be an amount that can handle the maximum hourly load, and outside of peak hours, oxygen is wasted in the form of an increase in endogenous respiration required to hold the unnecessary activated sludge. Because the dissolved oxygen concentration needs to be kept constant, it is difficult to stop the aeration device in the biological treatment tank, which results in energy loss.

[0007] Furthermore, the surface area load V of the final sedimentation tank is a value expressed as the upward flow velocity obtained by dividing the inflow water volume by the surface area of ​​the sedimentation tank, and the surface area of ​​the sedimentation tank is set to a large value taking into account the daily fluctuation rate so that it is smaller than the particle settling velocity Vs. As a result, the operating rate of the final sedimentation tank is low outside of peak hours, resulting in waste.

[0008] In the past, the installation of a flow equalization tank to absorb and equalize daily fluctuations has been proposed as a way to eliminate waste in the final settling tank. However, this requires pumping equipment to pump the wastewater out of the flow equalization tank again, which increases power consumption, as well as the need to deal with odors and clean the tank when it is not in use.

[0009] Patent Document 1 discloses a wastewater treatment method characterized by the provision of a float-type flow control device inside a wastewater treatment reaction tank that discharges a fixed amount of wastewater into a final settling tank, and by raising and lowering the water level in the reaction tank in response to fluctuations in the amount of wastewater flowing into the wastewater treatment reaction tank, the reaction time of the inflowing wastewater is maintained at a fixed level or above and the water volume load on the final settling tank is equalized. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 04-197494 Summary of the Invention [Problem to be solved by the invention]

[0011] However, the wastewater treatment method described in Patent Document 1 had the problem that, as a result of raising and lowering the water level in the reaction tank, the actual head of the pump that returns sludge from the final settling tank through the sludge return line increases, resulting in increased power consumption.

[0012] An object of the present invention is to provide an activated sludge treatment facility and an activated sludge treatment method that are highly energy efficient and reduce the area of ​​the settling tank even when the amount of influent wastewater varies greatly from day to day. [Means for solving the problem]

[0013] In order to achieve the above-mentioned object, the first characteristic configuration of the activated sludge treatment equipment of the present invention is an activated sludge treatment equipment comprising a biological treatment tank for biologically treating inflowing wastewater and a final sedimentation tank for solid-liquid separation of the treated water biologically treated in the biological treatment tank, and comprising a connecting passage installed at a position below the minimum water level of the biological treatment tank for flowing the treated water from the biological treatment tank to the final sedimentation tank, a sludge return path for returning a portion of the activated sludge extracted from the final sedimentation tank to the upstream section as returned sludge, and a fixed amount outflow section for outflowing a fixed amount of treated water from the final sedimentation tank.

[0014] Since biological treatment can be carried out while the water level in the biological treatment tank remains consistent with the water level in the final sedimentation tank in response to fluctuations in the amount of inflow wastewater into the biological treatment tank, the actual head of the pump does not increase even when sludge is returned from the final sedimentation tank via the sludge return line. Furthermore, since the water levels in the biological treatment tank and the final sedimentation tank are adjusted in response to fluctuations in the amount of inflow wastewater, the water surface load on the final sedimentation tank during peak inflow periods can be reduced. Furthermore, the HRT of the reaction tank is increased, stabilizing the quality of the treated water.

[0015] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the biological treatment tanks are installed in multiple series so that they can be operated in parallel, and the inflow water channel from the primary sedimentation tank and each biological treatment tank are connected by submerged gates equipped with opening and closing mechanisms.

[0016] In conventional distribution systems, wastewater is supplied through a common outflow channel from the overflow weir at the outflow point of the primary sedimentation tank. This system distributes the amount of wastewater supplied to each system evenly by installing movable weirs at the inlets of each biological treatment tank. This system wastes pumping power when the water level is low. However, this system saves energy by reducing the actual head of the pump that pumps water to the primary sedimentation tank. It also makes it possible to add a flow control function to the primary sedimentation tank, further increasing its resistance to flow rate fluctuations. Furthermore, because all tanks are connected by the aforementioned common outflow channel, the water level remains consistent even when the water level fluctuates. This prevents uneven aeration caused by differences in water levels in the biological treatment tank.

[0017] The third characteristic configuration is that, in addition to the first characteristic configuration described above, the biological treatment tank is equipped with a partition wall that divides the biological treatment tank into at least two compartments along the flow direction of the inflow wastewater, and an activated sludge storage mechanism that can store at least a portion of the returned sludge in the upstream compartment, and is equipped with a control mechanism that adjusts the amount of activated sludge stored by the activated sludge storage mechanism based on the pollution load of the inflow wastewater.

[0018] At least a portion of the activated sludge returned to the upstream compartment via the sludge return line is stored in the upstream compartment by the activated sludge storage mechanism, and the control mechanism adjusts the amount of activated sludge stored in the upstream compartment, allowing the activated sludge concentration in the downstream compartment to be appropriately adjusted. Simply lowering the water level would reduce the volume of the biological treatment tank, which would increase the activated sludge concentration and worsen settling, potentially resulting in a decrease in solid-liquid separation performance in the final sedimentation tank. However, using the activated sludge storage mechanism can suppress the increase in activated sludge concentration and avoid the deterioration of settling.

[0019] When the pollutant load of influent wastewater is low, e.g., when the wastewater volume is low or the pollutant concentration (e.g., BOD or ammonia concentration) is low, the control mechanism controls the activated sludge storage mechanism to increase the amount of activated sludge stored in the upstream compartment, thereby adjusting the activated sludge concentration in the downstream treatment tank to a lower level. Because the activated sludge stored in the upstream compartment does not require oxygen for endogenous respiration, the aeration power required to supply oxygen for endogenous respiration in the downstream compartment can be reduced. Furthermore, the activated sludge stored in the upstream compartment is gradually replaced as it is returned through the sludge return line and flows down the overflow section to the downstream compartment, so it does not decay. Furthermore, when the pollutant load of influent wastewater is high, e.g., when the wastewater volume is high or the pollutant concentration is high, the control mechanism controls the activated sludge storage mechanism to decrease the amount of activated sludge stored in the upstream compartment, thereby adjusting the activated sludge concentration in the downstream treatment tank to a higher level. As a result, the wastewater is efficiently purified.

[0020] The fourth characteristic configuration is that, in addition to the first characteristic configuration described above, the constant volume outflow section is configured to be able to adjust the outflow volume based on the amount of sewage flowing into the biological treatment tank.

[0021] The outflow rate of the final settling tank can be freely adjusted according to the inflow of wastewater into the biological treatment tank, and the water levels of the biological treatment tank and the final settling tank can be appropriately adjusted to achieve good wastewater treatment efficiency.

[0022] The fifth characteristic feature of the present invention is that, in addition to the first characteristic feature described above, an air lift pump is provided to return activated sludge through the sludge return path.

[0023] Compared to pumping using a mechanical pump, the power required to return activated sludge through the sludge return line can be significantly reduced.

[0024] The first characteristic feature of the activated sludge treatment method of the present invention is an activated sludge treatment method for an activated sludge treatment facility equipped with a biological treatment tank for biologically treating inflowing wastewater and a final sedimentation tank for solid-liquid separation of the water to be treated that has been biologically treated in the biological treatment tank, in which a connecting passage for flowing the water to be treated from the biological treatment tank to the final sedimentation tank is installed at a position below the minimum water level of the biological treatment tank, a sludge return line for returning a portion of the activated sludge extracted from the final sedimentation tank to the upstream section as returned sludge, and a constant volume outflow section for outflowing a constant amount of treated water from the final sedimentation tank, and biological treatment is carried out by fluctuating the water level of the biological treatment tank while keeping it consistent with the water level of the final sedimentation tank in accordance with fluctuations in the inflow rate of inflowing wastewater into the biological treatment tank.

[0025] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the amount of treated water flowing out from the constant volume outflow section is adjusted based on the amount of inflow wastewater into the biological treatment tank.

[0026] The third characteristic configuration, in addition to the first characteristic configuration described above, is provided with a partition wall that divides the biological treatment tank into at least two compartments along the flow direction of the inflow wastewater, and an activated sludge storage mechanism that can store at least a portion of the returned sludge in the upstream compartment, and the amount of activated sludge stored by the activated sludge storage mechanism is adjusted based on the pollution load of the inflow wastewater. [Effects of the Invention]

[0027] As described above, according to the present invention, it is possible to provide an activated sludge treatment facility and an activated sludge treatment method that are highly energy efficient by reducing the area of ​​the settling tank, even when the inflow wastewater fluctuates greatly from day to day. [Brief explanation of the drawings]

[0028] [Figure 1] Diagram of activated sludge treatment facility using conventional standard activated sludge method [Figure 2]1(a) is an explanatory diagram of a first embodiment of activated sludge treatment equipment according to the present invention; FIG. 1(b) is an explanatory diagram of a state in which sludge is stored in an upstream compartment; and FIG. 1(c) is a plan view of a biological treatment tank and an explanatory diagram of an overflow section formed in a partition wall. [Figure 3] 2 is an explanatory diagram of a second embodiment of the activated sludge treatment facility according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an activated sludge treatment facility and an activated sludge treatment method according to the present invention will now be described with reference to the accompanying drawings. [First aspect] Figures 2(a), (b), and (c) show a first embodiment of an activated sludge treatment facility. The activated sludge treatment facility includes a primary sedimentation tank, a biological treatment tank, a final sedimentation tank, and a sludge return line equipped with an electric pump that returns a portion of the activated sludge settled in the final sedimentation tank to the biological treatment tank as return sludge. The MLSS concentrations shown in Figures 2(a) and (b) are examples of control values.

[0030] Sediment and other debris contained in wastewater entering a sewage treatment plant settles in a grit basin, and large impurities are removed by a screen before being pumped to a primary sedimentation basin. After small particles of sand, trash, and solid organic matter are removed in the primary sedimentation basin, the wastewater flows into a biological treatment tank, where activated sludge breaks down soluble organic matter. The activated sludge then flows into a final sedimentation basin. The activated sludge settles in the final sedimentation basin, and the supernatant flows into a treated water tank. After being disinfected in a disinfection tank, the treated water is either released into a river or reused as treated water within the plant. The activated sludge that settles in the final sedimentation basin is guided by a sludge collector to a sludge pit at the base end and concentrated. The activated sludge is then removed from the sludge pit; some is returned to the biological treatment tank via a sludge return line, and some is left as excess sludge for final treatment.

[0031] The connecting passage for the treated water flowing from the biological treatment tank to the final sedimentation tank is installed at a position below the minimum water level set in the biological treatment tank, and the final sedimentation tank is provided with a fixed quantity outflow section that discharges a fixed quantity of treated water, which is the supernatant of solid-liquid separation.

[0032] As a fixed quantity outflow section, an overflow device equipped with a weir linked to a float that rises and falls according to the water level in the final sedimentation tank, a flow control mechanism equipped with a flow meter and an electric valve and capable of adjusting the valve opening using the electric valve based on the flow meter measurement value, or a pressure-regulating flow control mechanism capable of adjusting the flow rate using pressure can be used.

[0033] Instead of the conventional overflow weir that overflows from the biological treatment tank into the final settling tank, the system is designed so that the water to be treated flows from the biological treatment tank into the final settling tank through a connecting passage installed below the biological treatment tank's minimum water level. This allows biological treatment to be carried out while the water level in the biological treatment tank fluctuates to match the water level in the final settling tank in response to fluctuations in the amount of wastewater entering the biological treatment tank. The water level fluctuation range is adjustable between 0.5 and 2 meters. The biological treatment tank is approximately 5 meters deep.

[0034] Therefore, the water levels in the biological treatment tank and final settling tank are adjusted according to fluctuations in the amount of wastewater inflow, significantly reducing the surface area load on the final settling tank during peak water inflow periods. Furthermore, even when activated sludge is returned from the final settling tank via the sludge return line, the actual head of the pump does not increase. Furthermore, the HRT of the reaction tank also increases as the amount of wastewater inflow increases, stabilizing the quality of the treated water.

[0035] It is preferable to provide a control mechanism that adjusts the outflow rate from the fixed-quantity outflow section based on the amount of wastewater flowing into the biological treatment tank. This allows the outflow rate of the final settling tank to be freely adjusted according to the amount of wastewater flowing into the biological treatment tank, and makes it possible to appropriately adjust the water levels in the biological treatment tank and the final settling tank to achieve good wastewater treatment efficiency.

[0036] Furthermore, instead of using a mechanical pump to return sludge, it is preferable to provide an air lift pump in the final settling tank and a sludge return line that returns activated sludge lifted from the sludge pit by air bubbles from the air lift pump to the biological treatment tank. This allows for a significant reduction in the power required to return activated sludge via the sludge return line.

[0037] As shown in Figure 2(a), the biological treatment tank is made up of a rectangular concrete frame in plan view, and is divided into four compartments by partitions W1, W2, and W3 along the flow direction of the inflowing wastewater. A portion of the activated sludge removed from the biological treatment tank and separated in the final sedimentation tank is returned to the most upstream compartment. In this example, an activated sludge storage mechanism is installed in the most upstream compartment so that the returned sludge can be stored in the most upstream compartment. Partitions W2 and W3 have openings on the bottom side through which the wastewater and activated sludge flow.

[0038] The activated sludge storage mechanism is composed of a partition W1 installed between the most upstream compartment and the downstream compartment, an overflow section O formed in the partition W1, and an agitation mechanism installed in the most upstream compartment. The agitation mechanism can be an aeration device that supplies air bubbles into the tank to agitate the wastewater and activated sludge, or an agitation device equipped with a motor-driven agitator blade that agitates the wastewater and activated sludge in the tank.

[0039] By stopping the agitation mechanism, the activated sludge returned through the sludge return line settles and is stored in the most upstream compartment, while the influent wastewater mainly flows down to the downstream compartment through the overflow section O formed in the partition W1. In addition, by driving the agitation mechanism, the activated sludge that settled in the most upstream compartment is agitated within the tank and flows down to the downstream compartment through the overflow section O together with the influent wastewater.

[0040] For example, by driving the air diffuser, the settled activated sludge is stirred upward by air bubbles and supplied to the downstream compartment from the overflow section O, or by driving the stirring device, the settled sludge is stirred by the stirring blades and supplied to the downstream compartment from the overflow section O, and the amount of activated sludge supplied to the downstream compartment is adjusted depending on the degree of stirring.

[0041] In other words, activated sludge returned to the upstream compartment is received by the partition W1 and prevented from flowing downward to the downstream compartment, and is only allowed to flow downward to the downstream compartment through the overflow section O formed in the partition W1. The amount of sludge flowing downward to the downstream compartment through the overflow section O is adjusted according to the agitation state of the agitation mechanism installed in the upstream compartment, thereby adjusting the sludge concentration in the downstream compartment.

[0042] For example, as shown in Figure 2(a), by operating the agitation mechanism (aeration device) in the morning and evening when the pollution load of the influent sewage is at its peak in response to daily fluctuations in the influent sewage, the concentration of activated sludge that contributes to biological treatment can be increased throughout the biological treatment tank, allowing for efficient purification of the sewage.As shown in Figure 2(b), by stopping the agitation mechanism (aeration device or agitation device) during the day or night when the pollution load of the influent sewage is lower, activated sludge can be stored in the most upstream compartment, suppressing the aeration required for endogenous respiration of the activated sludge that does not contribute to wastewater purification, thereby reducing the power required for aeration.The activated sludge stored in the upstream compartment does not decay because it is gradually replaced as it is returned through the sludge return line and flows down from the overflow to the downstream compartment.

[0043] A control mechanism may be provided that monitors the pollution load of influent wastewater and controls the activated sludge storage mechanism so that when the pollution load is low, a larger amount of activated sludge is stored in the upstream compartment, and when the pollution load of influent wastewater is high, a smaller amount of activated sludge is stored in the upstream compartment.The control mechanism may be a control panel that allows an operator who monitors the pollution load to manually operate the agitation mechanism, or a control panel equipped with an electronic control unit that automatically controls the agitation mechanism based on the measured pollution load.

[0044] The pollution load of influent wastewater can be calculated by multiplying the normalized values ​​of the influent wastewater volume and the pollution concentration. The pollution concentration can be calculated by the BOD or ammonia concentration of the wastewater.

[0045] It is preferable to control the activated sludge storage mechanism via a control mechanism so that the activated sludge concentration reaches a target value based on the detection value of the activated sludge concentration meter installed in the downstream compartment. When a fluctuation in the activated sludge concentration in the downstream compartment is detected, the agitation mechanism in the upstream compartment is controlled to adjust the activated sludge concentration in the downstream compartment to an appropriate value, thereby preventing deterioration of treated water quality. At the same time, the control mechanism may adjust the outflow rate from the fixed-volume outflow section based on the inflow rate of wastewater. Note that it is not necessary to use an expensive MLSS concentration meter as the activated sludge concentration meter; any type that can measure activated sludge concentration will do.

[0046] As shown in Figure 2(c), the installation position of the sludge concentration meter is preferably downstream of the overflow section O at a position where it can measure the average sludge concentration of the downstream compartment. For example, in an example where the sewage inlet section formed in the upstream compartment is formed at the end, and the overflow section O is formed above the partition wall W1 diagonally spaced from the sewage inlet section, it is preferable to set the sludge concentration meter at a position not immediately adjacent to the overflow section O (the hatched area in Figure 2(c)) where it is thought that the sludge flowing in from the overflow section O will be sufficiently mixed within the compartment.

[0047] [Second aspect] The activated sludge treatment facility shown in Figure 3 is an example of a system equipped with multiple sludge treatment systems, each with a biological treatment tank and a final settling tank integrated together. In this example, multiple biological treatment tanks are installed in parallel, and the inflow channel from the primary settling tank is connected to each biological treatment tank by a submerged gate equipped with an opening and closing mechanism. With the conventional distribution system, pumping power is wasted when the water level is low, but with this system, the actual head of the pump that pumps water to the primary settling tank can be reduced, resulting in energy savings. The conventional distribution system distributes wastewater supplied from the overflow weir at the outflow of the primary settling tank via a common outflow channel by installing movable weirs at the inlets of the biological treatment tanks in each system, so that the amount of wastewater supplied is equal.

[0048] In this example, a pressure-regulating flow control mechanism that can adjust the flow rate by pressure is used as the constant-volume outflow section. The pressure-regulating flow control mechanism is equipped with a treated water outlet E formed in the tank wall of the final sedimentation tank, a pressure tank T tightly connected to the outlet E, an air supply pipe A that supplies compressed air from a compressor C, an air purge pipe B, a drain pipe D, etc.

[0049] Outlet E is formed on the wall of the final settling tank below the standard water level of the tank, and a sealed pressure tank T is installed and connected to outlet E. Compressed air from compressor C is supplied through compressed air intake pipe A, which is connected to the top of pressure tank T. Air purge pipe B, which is installed so that its tip opens at a height near the top of outlet E of the final settling tank, is connected to intake pipe A, and drain pipe D, which discharges treated water that has flowed into pressure tank T to the outside of pressure tank T, is installed at the bottom of pressure tank T so that it opens below the bottom of outlet E.

[0050] When compressed air is sent to pressure tank T via air supply pipe A, and the water level in the final settling tank is above the bottom end of air purge pipe B, the pressure in the sealed internal space of pressure tank T will be equal to the water pressure at the submerged depth of air purge pipe B. When the water level in the final settling tank fluctuates, the submerged depth of air purge pipe B also fluctuates, and the pressure in the internal space of pressure tank T fluctuates accordingly, so that the overflow water level from the bottom end of outlet E is always constant, and the amount of overflow water is always kept constant even if the water level in the final settling tank fluctuates. By adjusting the submerged depth of air purge pipe B, the amount of overflow water can be adjusted.

[0051] An on-off valve G is installed in the drainage pipe D, and when a sensor such as a turbidity meter detects that the sludge interface in the final settling tank has risen, the control mechanism closes the on-off valve G, and when the amount of wastewater flowing into the biological treatment tank peaks and there is a risk of overflow, the treated water overflows from an overflow weir installed in the final settling tank and flows into the treated water tank.The HRT can also be controlled by switching the compressor C on / off and the pressure relief valve F on / off.

[0052] [Activated sludge treatment method] The activated sludge treatment method of the present invention is an activated sludge treatment method for an activated sludge treatment facility equipped with a biological treatment tank for biologically treating inflowing wastewater and a final sedimentation tank for solid-liquid separation of the water to be treated that has been biologically treated in the biological treatment tank, and is characterized in that a connecting passage for flowing the water to be treated from the biological treatment tank to the final sedimentation tank is installed at a position below the minimum water level of the biological treatment tank, a sludge return line for returning a portion of the activated sludge removed from the final sedimentation tank to the upstream section as returned sludge, and a constant volume outflow section for outflowing a constant amount of treated water from the final sedimentation tank, and biological treatment is carried out by fluctuating the water level of the biological treatment tank while keeping it consistent with the water level of the final sedimentation tank in accordance with fluctuations in the inflow rate of inflowing wastewater into the biological treatment tank.

[0053] It is preferable to adjust the amount of treated water that flows out from the constant flow outlet based on the amount of inflow wastewater into the biological treatment tank.

[0054] It is also preferable to provide a partition wall that divides the biological treatment tank into at least two compartments along the flow direction of the inflow wastewater, and an activated sludge storage mechanism that can store at least a portion of the returned sludge in the upstream compartment, and to adjust the amount of activated sludge stored by the activated sludge storage mechanism based on the pollution load of the inflow wastewater.

[0055] The activated sludge treatment equipment and method according to the present invention described above makes it possible to significantly reduce the area of ​​the final settling tank compared to conventional activated sludge processes, and reduces the pumping power for wastewater outside of peak inflow wastewater periods (high water level periods) by the amount of head equivalent to the lower water level, thereby realizing energy savings. Furthermore, by adding a flow control mechanism, the water level can be raised during peak inflow periods, increasing the HRT, and the activated sludge concentration during normal times can be lowered compared to conventional designs.

[0056] The above-described embodiments are all examples of the present invention, and the present invention is not limited to these descriptions. It goes without saying that the specific configuration of each part can be appropriately modified and designed within the scope of the effects of the present invention. [Explanation of symbols]

[0057] A: Air supply pipe B: Air purge pipe C: Compressor D: Drain pipe E: Outlet T: Pressure tank W1,W2,W3: Bulkhead O: Overflow section

Claims

1. An activated sludge treatment facility comprising a biological treatment tank for biologically treating inflow wastewater and a final sedimentation tank for solid-liquid separation of the water to be treated that has been biologically treated in the biological treatment tank, a communication passage installed at a position below the minimum water level of the biological treatment tank and allowing the water to be treated to flow from the biological treatment tank to the final sedimentation tank; a sludge return line for returning a portion of the activated sludge removed from the final sedimentation tank to an upstream section as returned sludge; a constant-quantity outflow section for causing a constant amount of treated water to flow out from the final sedimentation tank; Activated sludge treatment facility equipped with:

2. The biological treatment tanks are installed in multiple series so as to be operable in parallel, 2. The activated sludge treatment facility according to claim 1, wherein the inflow channel from the primary sedimentation tank and each biological treatment tank are connected by submerged gates equipped with opening and closing mechanisms.

3. a partition wall that divides the biological treatment tank into at least two compartments along the flow direction of the inflow wastewater, and an activated sludge storage mechanism that can store at least a portion of the returned sludge in the upstream compartment, 2. The activated sludge treatment facility according to claim 1, further comprising a control mechanism for adjusting the amount of activated sludge stored by said activated sludge storage mechanism based on the pollution load of said influent wastewater.

4. 2. The activated sludge treatment facility according to claim 1, wherein the constant volume outflow section is configured to be able to adjust the outflow rate based on the amount of sewage inflowing into the biological treatment tank.

5. 2. The activated sludge treatment facility according to claim 1, further comprising an air lift pump for returning activated sludge through said sludge return line.

6. An activated sludge treatment method for an activated sludge treatment facility including a biological treatment tank for biologically treating inflow wastewater and a final sedimentation tank for solid-liquid separation of the water to be treated that has been biologically treated in the biological treatment tank, a communication passage at a position below the minimum water level of the biological treatment tank for passing the water to be treated from the biological treatment tank to the final sedimentation tank; a sludge return line for returning a portion of the activated sludge removed from the final sedimentation tank to an upstream section as returned sludge; a constant-quantity outflow section for causing a constant amount of treated water to flow out from the final sedimentation tank; Installed An activated sludge treatment method in which biological treatment is carried out by changing the water level of the biological treatment tank while keeping it consistent with the water level of the final sedimentation tank in response to fluctuations in the amount of inflow wastewater into the biological treatment tank.

7. 7. The activated sludge treatment method according to claim 6, wherein the amount of treated water that flows out from the constant volume outflow section is adjusted based on the amount of inflow of the influent wastewater into the biological treatment tank.

8. a partition wall that divides the biological treatment tank into at least two compartments along the flow direction of the inflow wastewater, and an activated sludge storage mechanism that can store at least a portion of the returned sludge in the upstream compartment, 7. The activated sludge treatment method according to claim 6, wherein the amount of activated sludge stored in said activated sludge storage mechanism is adjusted based on the pollution load of said influent wastewater.

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