Activated sludge treatment facility and activated sludge treatment method

Abstract

To provide activated sludge treatment equipment having high energy efficiency by properly adjusting the MLSS concentration of a biological treatment tank corresponding to the fluctuations of the pollution load quantity of inflow sewage.SOLUTION: The activated sludge treatment apparatus includes a biological treatment tank divided into at least two sections along a flow direction of inflow wastewater, a sludge return passage for returning a part of activated sludge taken out from the biological treatment tank to an upstream section as return sludge, and an activated sludge storage mechanism capable of storing at least a part of the return sludge in the upstream section, wherein the activated sludge storage mechanism includes a partition wall installed between the upstream section and the downstream section, an overflow section formed in the partition wall, and an agitation mechanism installed in the upstream section.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] Non-Patent Document 1 discloses an activated sludge treatment facility that purifies sewage sludge using the standard activated sludge method. As shown in Figure 1, the activated sludge treatment facility includes 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 dissolved organic matter is purified by the activated sludge in the tank and then flows down to the final sedimentation tank. Activated sludge is settled and separated in the final sedimentation tank, and the clear supernatant treated water is disinfected and then released into a river. A portion of the activated sludge that settles in the final sedimentation tank is returned to the biological treatment tank via a 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, so 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. Figure 1 shows an example where all sections are set to be treated aerobically. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Sewerage Facility Planning and Design Guidelines and Commentary, Part 2, 2019 Edition, Japan Sewage Works Association, Published October 11, 2019 Summary of the Invention [Problem to be solved by the invention]

[0006] The pollution load of influent wastewater fluctuates daily, with peaks in influent volume and pollution concentrations often occurring twice a day, in the morning and evening. Because the peak and bottom times of the influent load alternate in a short period of time, adjustments such as changing the number of biological treatment lines in operation are not possible, and all lines must be operated. Therefore, the total amount of activated sludge to be retained in the biological treatment tank must be sufficient to handle the maximum hourly load. Outside of peak hours, oxygen is wasted in the form of increased endogenous respiration, which is required to retain the excess activated sludge. Because the dissolved oxygen concentration must be maintained at a constant level, it is difficult to shut down the aeration system in the biological treatment tank, resulting in energy loss.

[0007] In the conventional activated sludge process, power consumption can be reduced by operating in nitrification inhibition mode, but once the water temperature rises to a certain level, nitrification progresses, resulting in an increase in power consumption.It is not possible to control the temperature of the inflowing wastewater, and it is difficult to reliably switch the environment for nitrification progress in a short period of time.If the system is placed in an intermediate state between nitrification promotion mode and nitrification inhibition mode, there is a risk that the amount of nitrous oxide, a greenhouse gas, will increase.

[0008] Therefore, it is conceivable to withdraw sludge from the biological treatment tank when the pollution load becomes low, and to supply activated sludge to the biological treatment tank when the pollution load becomes high. However, this has been difficult to implement because it requires the space required for a sludge storage tank to temporarily store the activated sludge held in the biological treatment tank, as well as the sludge transport equipment and the electricity required for it to transport the activated sludge between the biological treatment tank and the sludge storage tank.

[0009] Furthermore, the pollution load of influent wastewater fluctuates with the seasons. Efficient operation can be achieved by increasing or decreasing the number of biological treatment lines in operation in response to seasonal fluctuations. However, when the operation of the biological treatment tank is stopped, the pond must be drained to prevent the activated sludge from decaying. In addition to the difficulty of completely draining the activated sludge, it is necessary to fill the biological treatment tank with fresh water to protect the aeration device installed there from ultraviolet rays, making the work extremely cumbersome. For this reason, the reality is that operation continues with the number of lines corresponding to the peak load.

[0010] Furthermore, the solid-liquid separation performance in the final settling tank is affected by the concentration of activated sludge (MLSS); if the MLSS concentration is low, the solid-liquid separation performance increases, and if the MLSS concentration is high, the solid-liquid separation performance decreases. In order to maintain good treated water quality, the top priority is to prevent activated sludge from flowing out of the final settling tank. In a situation where the amount of inflowing wastewater is increasing but the pollutant concentration is decreasing, it is desirable to be able to lower the MLSS concentration in terms of operating and managing the final settling tank, but it has been difficult to increase or decrease the MLSS concentration in a short period of time.

[0011] The amount of wastewater flowing into a sewage treatment plant generally increases due to the effects of infiltration during rainfall. This is a common situation in both combined and separate sewer systems. Because wastewater containing infiltration during rainfall is diluted with rainwater, there is a large amount of water, but no increase in the amount of activated sludge required to decompose organic matter is required. For this reason, it is desirable to be able to temporarily reduce the MLSS concentration during rainfall in order to prioritize ensuring the solid-liquid separation performance of the final settling tank.

[0012] The object of the present invention is to provide an activated sludge treatment facility and an activated sludge treatment method that are highly energy efficient by making it possible to appropriately adjust the MLSS concentration in the biological treatment tank in accordance with fluctuations in the pollution load of inflowing wastewater. [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 that it comprises a biological treatment tank divided into at least two compartments along the flow direction of the inflow wastewater, a sludge return path for returning a portion of the activated sludge extracted from the biological treatment tank to the upstream compartment as returned sludge, and an activated sludge storage mechanism capable of storing at least a portion of the returned sludge in the upstream compartment.

[0014] A portion of the activated sludge removed from the biological treatment tank is returned to the upstream compartment via the sludge return line. At least a portion of the returned activated sludge is stored in the upstream compartment by the activated sludge storage mechanism, making it possible to adjust the activated sludge concentration in the downstream compartment.

[0015] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the activated sludge storage mechanism is composed of a partition installed between the upstream compartment and the downstream compartment, an overflow section formed in the partition, and a stirring mechanism installed in the upstream compartment.

[0016] In this activated sludge storage mechanism, activated sludge returned to the upstream compartment is received by a partition wall, preventing it from flowing downstream. It is only allowed to flow downstream through an overflow section formed in the partition wall. The amount of activated sludge flowing downstream through the overflow section is adjusted based on the agitation state of the agitation mechanism installed in the upstream compartment. For example, an aeration device or an agitation device equipped with agitating blades can function as the agitation mechanism. When the upstream compartment functions as an aerobic tank, the aeration device is activated to agitate the returned sludge, causing it to flow from the overflow section to the downstream compartment. When the upstream compartment functions as an anaerobic tank, the agitation blades are activated instead of the aeration device, causing the returned sludge to agitate and flow from the overflow section to the downstream compartment.

[0017] The third characteristic configuration is that, in addition to the second characteristic configuration described above, it is equipped with a control mechanism that controls the activated sludge storage mechanism so that when the pollution load of the inflow wastewater is low, the amount of activated sludge stored in the upstream compartment is increased, and when the pollution load of the inflow wastewater is high, the amount of activated sludge stored in the upstream compartment is decreased.

[0018] When the pollutant load of influent wastewater is low, e.g., when the wastewater volume is low or the pollutant concentration (e.g., BOD and 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 activated sludge 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 downstream from the overflow section, preventing it from decaying. 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.

[0019] For example, when the pollution load is high, by operating the aeration devices in the upstream and downstream compartments, the entire amount of stored activated sludge can be effectively used for water treatment, and when the pollution load is low, oxygen is supplied only to the minimum amount of activated sludge necessary, thereby reducing the power required for aeration.

[0020] The fourth characteristic configuration is that, in addition to the third characteristic configuration described above, the control mechanism controls the activated sludge storage mechanism based on the detection value of an activated sludge concentration meter installed in the downstream section.

[0021] The control mechanism monitors the detection value of the sludge concentration meter and, when it detects a change in the activated sludge concentration in the downstream compartment, controls the stirring mechanism in the upstream compartment to adjust the activated sludge concentration in the downstream compartment to an appropriate value, thereby avoiding a deterioration in the quality of the treated water.

[0022] The fifth characteristic configuration is that, in addition to the third characteristic configuration described above, a final sedimentation tank is provided downstream of the biological treatment tank, and the control mechanism controls the activated sludge storage mechanism based on the level of the sludge interface in the final sedimentation tank or the state of activated sludge mixed with the overflow water of the final sedimentation tank.

[0023] When activated sludge is mixed into the overflow water of the final sedimentation tank, it can be determined that the final sedimentation tank's allowable water surface load has been exceeded. By controlling the activated sludge storage mechanism to store activated sludge in the upstream section, the concentration of activated sludge flowing into the final sedimentation tank can be reduced, resulting in improved solid-liquid separation performance in the final sedimentation tank and the recovery of treated water quality.

[0024] The sixth characteristic configuration is that, in addition to the third characteristic configuration described above, a final sedimentation tank is provided downstream of the biological treatment tank, and the control mechanism adjusts the water level of the biological treatment tank based on the pollution load of the inflow wastewater, while keeping the water level of the biological treatment tank and the water level of the final sedimentation tank the same.

[0025] The system achieves a flow rate adjustment function by raising the water levels in the biological treatment tank and the final settling tank when the influent wastewater pollution load is high and lowering them when the influent wastewater pollution load is low, thereby equalizing the influent load. In other words, because peak loads are suppressed, the total amount of activated sludge to be held in the biological treatment tank can be reduced compared to conventional systems, further reducing oxygen consumption due to endogenous respiration. Because the water levels in the biological treatment tank and the final settling tank are consistent, fluctuations in the water level in the biological treatment tank do not change the actual head of sludge return or increase power consumption. Simply lowering the water level would reduce the capacity of the biological treatment tank, which could increase the activated sludge concentration and worsen settling, potentially resulting in poor solid-liquid separation performance in the final settling tank. However, the use of the activated sludge storage mechanism prevents the increase in activated sludge concentration, thereby avoiding poor settling.

[0026] The seventh characteristic configuration is that, in addition to the third characteristic configuration described above, a final sedimentation tank is provided downstream of the biological treatment tank, and the control mechanism is provided with a target value calculation unit that calculates a target value for the time-series activated sludge concentration in the downstream section based on a predicted value of the pollution load of the inflowing wastewater, and a target control value calculation unit that calculates a time-series control value for the activated sludge storage mechanism so that the final sedimentation tank falls within the allowable water area load when sludge having the activated sludge concentration calculated by the target value calculation unit flows into the final sedimentation tank.

[0027] The target value calculation unit calculates a time-series target value for the activated sludge concentration in the downstream section based on the predicted value of the pollution load of the inflowing wastewater, and the target control value calculation unit calculates a time-series control value for the activated sludge storage mechanism so that the final sedimentation tank falls within the allowable water area load when activated sludge of the concentration calculated by the target value calculation unit flows into the final sedimentation tank.

[0028] 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 divided into at least two compartments along the flow direction of inflow wastewater, a sludge return line for returning a portion of the activated sludge removed from the biological treatment tank to the upstream compartment as returned sludge, and an activated sludge storage mechanism capable of storing at least a portion of the returned sludge in the upstream compartment, wherein the amount of activated sludge stored in the upstream compartment by the activated sludge storage mechanism is adjusted based on the pollution load of the inflow wastewater.

[0029] The second characteristic configuration, in addition to the first characteristic configuration described above, is that the activated sludge storage mechanism is adjusted so that when the pollution load of the inflow wastewater is low, the amount of sludge stored in the upstream compartment is large, and when the pollution load of the inflow wastewater is high, the amount of sludge stored in the upstream compartment is small.

[0030] The third characteristic configuration is that, in addition to the first characteristic configuration described above, the activated sludge storage mechanism is adjusted based on the detection value of an activated sludge concentration meter installed in the downstream section.

[0031] The fourth characteristic configuration is that, in addition to the first characteristic configuration described above, the activated sludge treatment equipment is provided with a final sedimentation tank downstream of the biological treatment tank, and the activated sludge storage mechanism is adjusted based on the level of the sludge interface in the final sedimentation tank or the state of activated sludge mixed with the overflow water of the final sedimentation tank.

[0032] The fifth characteristic configuration is that, in addition to the first characteristic configuration described above, the activated sludge treatment equipment is provided with a final settling tank downstream of the biological treatment tank, and the water level of the biological treatment tank is adjusted based on the pollution load of the inflow wastewater, while keeping the water level of the biological treatment tank and the water level of the final settling tank the same. [Effects of the Invention]

[0033] 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 making it possible to appropriately adjust the MLSS concentration in the biological treatment tank in accordance with fluctuations in the pollution load of inflowing wastewater. [Brief explanation of the drawings]

[0034] [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 the activated sludge treatment equipment according to the present invention; FIG. 1(b) is an explanatory diagram of activated sludge stored in the upstream compartment; and FIG. 1(c) is a plan view of the biological treatment tank and an explanatory diagram of an overflow section formed in the partition wall. [Figure 3] FIG. 1(a) is an explanatory diagram of a second embodiment of the activated sludge treatment facility according to the present invention, and FIG. 1(b) is an explanatory diagram of the state in which sludge is stored in the upstream compartment. [Figure 4] FIG. 1(a) is an explanatory diagram of a third embodiment of the activated sludge treatment facility according to the present invention, and FIG. 1(b) is an explanatory diagram of the state in which sludge is stored in the upstream compartment. [Figure 5] (a) is an explanatory diagram of a third embodiment of the activated sludge treatment facility according to the present invention, (b) is an explanatory diagram of activated sludge stored in the upstream compartment, and (c) is an explanatory diagram of the MABR. DETAILED DESCRIPTION OF THE INVENTION

[0035] 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 that returns a portion of the excess 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.

[0036] Sewage that flows into 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 is discharged 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.

[0037] 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 activated sludge can be stored in the most upstream compartment. Partitions W2 and W3 have openings at the bottom through which 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] In other words, the 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 activated 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 activated sludge concentration in the downstream compartment.

[0041] In response to daily fluctuations in influent wastewater, for example, as shown in Figure 2(a), by operating the agitation mechanism in the morning and evening when the pollution load of influent wastewater is at its peak, the concentration of activated sludge that contributes to biological treatment throughout the biological treatment tank can be increased, allowing for efficient purification of the wastewater.As shown in Figure 2(b), by stopping the agitation mechanism during the day or night when the pollution load of influent wastewater is lower, activated sludge can be stored in the most upstream compartment, suppressing the aeration required for endogenous respiration of activated sludge that does not contribute to wastewater purification, thereby reducing the power required for aeration.The activated sludge stored in the upstream compartment is gradually replaced as it is returned through the sludge return line and flows down from the overflow section O to the downstream compartment, so it does not decay.

[0042] 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.

[0043] 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.

[0044] It is preferable to control the activated sludge storage mechanism via a control mechanism based on the detected value of the activated sludge concentration meter installed in the downstream compartment so that the activated sludge concentration reaches the target value, and when a fluctuation in the activated sludge concentration in the downstream compartment is detected, the stirring 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 the treated water quality. Note that it is not necessary to use an expensive MLSS concentration meter as the activated sludge concentration meter, and any type that can measure activated sludge concentration will be acceptable.

[0045] 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.

[0046] It is also preferable to monitor the amount of activated sludge mixed into the overflow water of the final settling tank using, for example, a turbidity meter, or to monitor the sludge interface in the final settling tank using, for example, a sludge interface meter, via a control mechanism, and control the activated sludge storage mechanism based on the values. When sludge is mixed into the overflow water of the final settling tank, or when the level of the sludge interface rises to a level higher than normal, it can be determined that the allowable water area load of the final settling tank has been exceeded, and by controlling the activated sludge storage mechanism to store activated sludge in the upstream section, the concentration of activated sludge flowing into the final settling tank can be reduced, resulting in improved solid-liquid separation performance in the final settling tank and recovery of treated water quality.

[0047] Furthermore, it is preferable that the control mechanism includes a target value calculation unit that calculates a target value for the time-series activated sludge concentration in the downstream section based on a predicted value of the pollution load of the inflowing wastewater, and a target control value calculation unit that calculates a time-series control value for the activated sludge storage mechanism so that the final sedimentation tank falls within the allowable water area load when activated sludge of the concentration calculated by the target value calculation unit flows into the final sedimentation tank.

[0048] The predicted value of the pollution load of influent wastewater can be, for example, time-series data of influent water volume sampled in the past, or data that adds rainfall forecast information to the time-series data. The predicted value can be obtained by correcting the time-series data of the pollution load of influent wastewater using a correction formula based on a predetermined rainfall amount.

[0049] The target value calculation unit can calculate an appropriate target value for the MLSS concentration over time based on the data, the current MLSS concentration, the returned sludge volume, and the returned sludge concentration, and based on indicators such as the BOD-SS load in activated sludge under aerobic conditions.

[0050] The target control value calculation unit calculates the control value of the agitation mechanism required to control the MLSS concentration to the target value, and predicts the concentration of activated sludge that will flow into the final settling tank when the agitation mechanism is controlled at that control value. The control value of the agitation mechanism for adjusting the MLSS concentration can be obtained in advance through experiments or simulations.

[0051] The target control value calculation unit predicts the concentration of activated sludge flowing into the final settling tank when the agitation mechanism is controlled based on the control value, and if the predicted value deviates from a preset allowable range for the water surface load of the final settling tank, calculates a target control value by correcting the control value for the agitation mechanism.By controlling the agitation mechanism using the target control value, the amount of activated sludge stored in the upstream compartment is appropriately controlled as a result.

[0052] 2(a), (b), and (c) show an example in which the biological treatment tank is divided into four compartments along the flow of inflow wastewater, with the most upstream compartment being used for sludge storage, but any of the three upstream compartments other than the most downstream compartment may be used for activated sludge storage. However, the partition downstream of the compartment used for sludge storage must have an overflow section O formed.

[0053] Furthermore, the compartments other than the compartment used for sludge storage may be used for either aerobic or anaerobic treatment. For example, if the most upstream compartment is used for sludge storage, the aeration devices of all three downstream compartments can be driven to turn all tanks into aerobic tanks, and the three compartments can be used as anoxic tanks, anaerobic tanks, and aerobic tanks, from the upstream side.

[0054] When the pollution load is high, all four compartments can be used as aerobic tanks, or nitrification promotion operation can be performed by configuring the compartments in the following order, starting from the upstream compartment: anaerobic tank, aerobic tank, anaerobic tank, aerobic tank.In addition, because it becomes possible to control the amount of activated sludge under aerobic conditions, by controlling the amount of sludge stored in the upstream compartments according to the needs for nitrification promotion and nitrification suppression, it is possible to shorten the transition period between continued nitrification suppression operation and switching to nitrification promotion operation, and to suppress the generation of nitrous oxide, a greenhouse gas.

[0055] The biological treatment tank divided into four compartments as shown in Figures 2(a), (b), and (c) is an example, and the number of compartments in the biological treatment tank is not limited to 4. In other words, the activated sludge treatment facility according to the present invention only needs to divide the biological treatment tank into at least two compartments along the flow direction of the inflowing wastewater and be equipped with an activated sludge storage mechanism that can store at least a portion of the activated sludge returned via the sludge return line in the upstream compartment.

[0056] [Second aspect] Figures 3(a) and (b) show a second embodiment of an activated sludge treatment facility. In this activated sludge treatment facility, a control mechanism adjusts the water level in the biological treatment tank based on the pollution load of inflowing wastewater, keeping the water level in the biological treatment tank and the water level in the final sedimentation tank consistent. The connection between the biological treatment tank and the final sedimentation tank is replaced by an overflow weir, and a communication passage is used to maintain communication between the two even when the water level drops. The MLSS concentrations shown in Figures 3(a) and (b) are an example of control values.

[0057] As shown in Figure 3(a), when the pollution load of the inflowing wastewater is high, the water level of the biological treatment tank and the water level of the final sedimentation tank are raised, and as shown in Figure 3(b), when the pollution load of the inflowing wastewater is low, the water level of the biological treatment tank and the water level of the final sedimentation tank are lowered within a specified range, thereby realizing a flow rate adjustment function and equalizing the inflow load.

[0058] The specified range is preferably 0.5 to 1.0 m. To ensure constant flow, the outflow section of treated water from the final settling tank can be equipped with an overflow device for a batch activated sludge process in which a weir is raised and lowered by a float, an overflow device for a long-term aeration process (single-tank anaerobic aerobic operation), or a drainage device combining a flow meter and a motor-operated valve. When an overflow device for a long-term aeration process (single-tank anaerobic aerobic operation) or a drainage device combining a flow meter and a motor-operated valve is used, the amount of effluent water from the final settling tank can be freely adjusted depending on the inflow status of the wastewater.

[0059] In other words, when the inflow load changes from low to high, the increase in the amount of wastewater inflow is consumed as a rise in the water level of the final sedimentation tank, which suppresses the amount of treated water outflow from the final sedimentation tank during peak times, reducing the water surface load of the final sedimentation tank compared to conventional methods and reducing the required water surface load.Since the water level in the biological treatment tank and the water level in the final sedimentation tank are the same, even if the water level in the biological treatment tank fluctuates, the actual head of the sludge return does not change and there is no increase in power consumption.

[0060] [Third aspect] Figures 4(a) and (b) show a third embodiment of an activated sludge treatment facility. This activated sludge treatment facility employs an MBR (membrane bioreactor) system, in which a membrane separator replaces the final settling tank. The biological treatment tank is divided into two compartments, with the upstream compartment functioning as an anoxic tank or sludge storage tank, and the downstream compartment functioning as an auxiliary aeration tank and membrane separation tank. The MLSS concentrations shown in Figures 4(a) and (b) are examples of control values.

[0061] The partitions separating the compartments have an overflow section, and the upstream compartment is equipped with a motor-driven agitator with impellers as a stirring mechanism. As shown in Figure 4(a), when the pollution load of the inflowing wastewater is low, the agitator is activated and the upstream compartment functions as an anoxic tank. When the pollution load of the inflowing wastewater is high, the agitator is stopped and the upstream compartment functions as a sludge storage tank.

[0062] [Fourth aspect] Figures 5(a) and (b) show a fourth embodiment of an activated sludge treatment facility. This activated sludge treatment facility uses a hybrid membrane aerated biofilm reactor (MABR) instead of a final settling tank. The biological treatment tank is divided into two compartments: the upstream compartment functions as a MABR tank or sludge storage tank, and the downstream compartment functions as an auxiliary nitrification tank. The MLSS concentrations shown in Figures 5(a) and (b) are examples of control values.

[0063] As shown in Figure 5(c), the MABR is a module made up of bundled hollow fiber membranes, with a biological film formed on the outer surface of the hollow fiber membranes. By supplying oxygen to the biological film from within the hollow fiber membranes, aerobic treatment occurs on the membrane surface, allowing organic matter treatment and nitrification / denitrification to occur in a single tank. The MABR is placed in the upstream compartment to treat organic matter and nitrification / denitrification, while an aeration device is installed in the downstream compartment and functions as an auxiliary nitrification tank. The aeration device placed in the upstream compartment is used to prevent the biological film from growing thicker.

[0064] When the pollution load of the inflowing wastewater is low, return sludge is stored in the upstream compartment, and the activated sludge concentration in the downstream compartment is lowered, thereby suppressing the oxygen consumption by endogenous respiration in the downstream compartment.

[0065] [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 divided into at least two compartments along the flow direction of inflow wastewater, a sludge return line for returning a portion of the activated sludge removed from the biological treatment tank to the upstream compartment as returned sludge, and an activated sludge storage mechanism capable of storing at least a portion of the returned sludge in the upstream compartment. That is, the activated sludge storage mechanism is configured to adjust the amount of activated sludge stored in the upstream compartment based on the pollution load of inflowing wastewater.

[0066] The activated sludge storage mechanism is configured to adjust so that when the pollution load of the inflowing wastewater is low, the amount of activated sludge stored in the upstream compartment is large, and when the pollution load of the inflowing wastewater is high, the amount of activated sludge stored in the upstream compartment is small.

[0067] The activated sludge storage mechanism is also configured to adjust based on the detected value of the activated sludge concentration meter installed in the downstream section.

[0068] Furthermore, if the activated sludge treatment facility is equipped with a final sedimentation tank downstream of the biological treatment tank, the activated sludge storage mechanism is configured to be adjusted based on the state of activated sludge mixed with the overflow water of the final sedimentation tank.

[0069] The water level in the biological treatment tank is adjusted based on the pollution load of the inflowing wastewater, while keeping the water level in the biological treatment tank and the water level in the final sedimentation tank consistent.

[0070] The activated sludge treatment system and method according to the present invention, as described above, are expected to contribute to energy savings by reducing endogenous respiration compared to conventional activated sludge processes. Furthermore, in systems equipped with power generation equipment using biogas obtained by digesting solid organic matter removed in the primary sedimentation tank, the suppression of endogenous respiration increases the amount of excess sludge produced, improving the overall efficiency of digester gas power generation. Furthermore, by periodically placing activated sludge in an anaerobic state, the occurrence of bulking due to the proliferation of filamentous bacteria can be suppressed. Furthermore, the denitrification reaction occurs in the anaerobic tank, consuming BOD, further reducing the amount of air diffused in the downstream stage.

[0071] The above-described embodiments are merely 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. Furthermore, any one or more of the above-described embodiments may be appropriately combined. [Explanation of symbols]

[0072] W1,W2,W3: Bulkhead O: Overflow section

Claims

1. a biological treatment tank divided into at least two compartments along the flow direction of inflow wastewater; a sludge return line for returning a portion of the activated sludge removed from the biological treatment tank to an upstream section as returned sludge; an activated sludge storage mechanism capable of storing at least a portion of the returned sludge in the upstream compartment; Activated sludge treatment facility equipped with:

2. 2. The activated sludge treatment facility according to claim 1, wherein the activated sludge storage mechanism comprises a partition wall installed between the upstream compartment and the downstream compartment, an overflow section formed in the partition wall, and an agitation mechanism installed in the upstream compartment.

3. 3. The activated sludge treatment facility according to claim 2, further comprising a control mechanism for controlling the activated sludge storage mechanism so that a larger amount of activated sludge is stored in the upstream compartment when the pollution load of the influent wastewater is low, and a smaller amount of activated sludge is stored in the upstream compartment when the pollution load of the influent wastewater is high.

4. 4. The activated sludge treatment facility according to claim 3, wherein the control mechanism controls the activated sludge storage mechanism based on a detected value of an activated sludge concentration meter installed in the downstream section.

5. A final sedimentation tank is provided downstream of the biological treatment tank, 4. The activated sludge treatment facility according to claim 3, wherein the control mechanism controls the activated sludge storage mechanism based on the level of the sludge interface in the final sedimentation tank or the state of activated sludge mixed with the overflow water in the final sedimentation tank.

6. A final sedimentation tank is provided downstream of the biological treatment tank, 4. The activated sludge treatment facility according to claim 3, wherein the control mechanism adjusts the water level of the biological treatment tank based on the pollution load of the inflow wastewater while keeping the water level of the biological treatment tank and the water level of the final sedimentation tank the same.

7. A final sedimentation tank is provided downstream of the biological treatment tank, 4. The activated sludge treatment facility according to claim 3, wherein the control mechanism comprises: a target value calculation unit that calculates a target value of the activated sludge concentration in the downstream section over time based on a predicted value of the pollution load of the inflowing wastewater; and a target control value calculation unit that calculates a control value for the activated sludge storage mechanism over time so that the final sedimentation tank falls within the allowable water area load when sludge having the activated sludge concentration calculated by the target value calculation unit flows into the final sedimentation tank.

8. a biological treatment tank divided into at least two compartments along the flow direction of inflow wastewater; a sludge return line for returning a portion of the activated sludge removed from the biological treatment tank to an upstream section as returned sludge; an activated sludge storage mechanism capable of storing at least a portion of the returned sludge in the upstream compartment; An activated sludge treatment method for an activated sludge treatment facility comprising: an activated sludge treatment method for adjusting the amount of activated sludge stored in the upstream compartment by the activated sludge storage mechanism based on the pollution load of the inflowing wastewater.

9. 9. The activated sludge treatment method according to claim 8, wherein the activated sludge storage mechanism is adjusted so that when the pollution load of the inflow wastewater is low, the amount of sludge stored in the upstream compartment is increased, and when the pollution load of the inflow wastewater is high, the amount of sludge stored in the upstream compartment is decreased.

10. 9. The activated sludge treatment method according to claim 8, wherein the activated sludge storage mechanism is adjusted based on the detected value of an activated sludge concentration meter installed in the downstream section.

11. The activated sludge treatment facility includes a final settling tank downstream of the biological treatment tank, 9. The activated sludge treatment method according to claim 8, wherein the activated sludge storage mechanism is adjusted based on the level of the sludge interface in the final settling tank or the state of activated sludge mixed with the overflow water of the final settling tank.

12. The activated sludge treatment facility includes a final settling tank downstream of the biological treatment tank, 9. The activated sludge treatment method according to claim 8, wherein the water level of the biological treatment tank is adjusted based on the pollution load of the inflow wastewater while the water level of the biological treatment tank and the water level of the final sedimentation tank are made equal.

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