Method for operating water treatment device, and water treatment device

Abstract

The invention provides an operation method of a water treatment device, which can reduce the operation load of an operator and contribute to energy conservation. In a method for operating a water treatment device provided with a biological treatment tank including at least an aerobic tank in which a membrane separation device is immersed, an extraction coefficient K (K < 1) is set as a control factor such that a sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow amount Qraw * K, and the membrane separation device is operated, the filtration amount Qtrt from the membrane separation device satisfies the following equation: filtration amount Qtrt = raw water inflow amount Qraw * (1-K), and the excess sludge naturally overflows from an overflow path of the biological treatment tank.

Description

Technical Field

[0001] This invention relates to a method for operating a water treatment apparatus and to a water treatment apparatus. Background Technology

[0002] like Figure 5 As shown, in order to purify the treated water, such as organic wastewater, which is the raw water, a water treatment device 1 using the membrane bio-reactor process is adopted. The device has: a biological treatment tank 8 including at least an anoxic tank 2 and an aerobic tank 3 with a membrane separation device 4 impregnated; and a sludge circulation path 7 for circulating sludge from the aerobic tank 3 to the anoxic tank 2.

[0003] The raw water flowing into the anoxic tank 2 is mixed with the activated sludge in the tank by the stirring mechanism 2a, and then flows into the aerobic tank 3. In the aerobic tank 3, under the aerobic environment of the auxiliary aeration device 6, organic matter is oxidized and decomposed by aerobic microorganisms, and ammonia is nitrified. A portion of the purified treated water is pumped out as treated water via the membrane separation device 4. The treated water and sludge in the aerobic tank 3 are circulated to the anoxic tank 2 via the sludge pump P1 and the sludge circulation path 7. In the anoxic tank 2, anaerobic microorganisms denitrify the water under anaerobic conditions.

[0004] In the aforementioned membrane separation activated sludge process, operational procedures are required to control the amount of microorganisms and the viscosity of the circulating activated sludge within the target management range. At this point, the management indicator is the MLSS (Mixed Liquor Suspended Solids) concentration. Since the MLSS concentration within the system increases depending on the SS contained in the incoming raw water and the proliferation of microorganisms, it is necessary to continuously or intermittently remove a suitable amount of sludge from the system. Therefore, a sludge extraction pipe 11 with an extraction valve 10 is branched into the sludge circulation path 7.

[0005] Because it is difficult to accurately predict the increase in MLSS concentration, operators measure and monitor the MLSS concentration within the system. To maintain the MLSS concentration within the managed range, they rely on personal experience and expertise to determine and perform sludge removal. Typically, the sludge removal rate is set and managed based on a percentage of the raw water inflow.

[0006] Prior art related to the extraction of such residual sludge is disclosed in Patent Documents 1 and 2.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2010-194482

[0010] Patent Document 2: Japanese Patent Application Publication No. 2013-176710 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, in water treatment plants that employ membrane separation activated sludge process, unlike the sludge extraction treatment mentioned above, the operator monitors the water level in the system while adjusting the filtration capacity of the membrane separation device according to the inflow of raw water.

[0013] That is, the operator is required to monitor the inflow of raw water and independently perform the following two tedious operations: adjusting the amount of treated water extracted through the membrane separation unit; and adjusting the amount of residual sludge extracted through the sludge extraction pipe.

[0014] In addition, the increased power consumption of pumps driven to handle water extraction or the removal of residual sludge necessitates an operating method acceptable to a decarbonized society from an energy conservation perspective.

[0015] The purpose of this invention is to provide an operating method and a water treatment device that reduces the operator's workload and contributes to energy conservation.

[0016] Technical means to solve the problem

[0017] To achieve the above objectives, the first characteristic structure of the water treatment device operation method of the present invention is a method for operating a water treatment device, the water treatment device having a biological treatment tank, the biological treatment tank including at least an aerobic tank with an impregnated membrane separation device, in the operation method of the water treatment device, the extraction coefficient K (K < 1) is set as a control factor, such that the sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow amount Qraw × K, and the membrane separation device is operated such that the filtration amount Qtrt from the membrane separation device satisfies: filtration amount Qtrt = raw water inflow amount Qraw × (1 - K), so that the remaining sludge overflows naturally from the overflow path of the biological treatment tank.

[0018] In the biological treatment tank, in addition to the sludge extraction pipe, an overflow path is pre-installed to prevent sludge from overflowing from the tank in case of abnormalities. By using this overflow path for sludge extraction, the remaining sludge can overflow naturally, eliminating the need for sludge extraction using the existing sludge extraction pipe. Under stable conditions where the water level in the biological treatment tank is approximately constant, the sludge extraction rate Qwas is determined by the raw water inflow rate Qraw minus the filtration rate Qtrt. Therefore, if the filtration rate Qtrt is set as the operating factor for the raw water inflow rate Qraw, the remaining sludge can overflow naturally from the overflow path.

[0019] Specifically, the sludge extraction rate Qwas is managed by the formula: sludge extraction rate Qwas = raw water inflow rate Qraw × K (K is the extraction coefficient and K < 1), and the membrane separation device is operated to ensure that the filtration rate Qtrt satisfies Qtrt = raw water inflow rate Qraw × (1 - K). If K > 0, the water level in the biological treatment tank rises, and the remaining sludge overflows naturally from the overflow path. If K < 0, the water level in the biological treatment tank can be actively lowered. For the raw water inflow rate Qraw obtained by flow sensors, the extraction coefficient K can be appropriately set as a control factor, for example, it can be preset based on the sludge yield. The sludge yield refers to the amount of organic matter produced relative to the amount of sludge treated by the water treatment equipment. For example, the BOD sludge yield refers to the increase in sludge (kg) relative to the BOD inflow rate (kg), calculated as {residual sludge concentration (mg / L) × residual sludge extraction rate (m³ / kg)}. 3 / day)}÷{Wastewater BOD concentration (mg / L)×Wastewater volume (m³)} 3 The BOD sludge yield of activated sludge is generally 0.3 to 0.5, calculated using formulas such as ( / day).

[0020] The second feature structure, based on the first feature structure described above, updates and sets the filtration capacity Qtrt at the specified time intervals, based on the raw water inflow Qraw measured at specified time intervals.

[0021] Since the raw water inflow Qraw is constantly changing, it is preferable to update the set filtration volume Qtrt at specified time intervals based on the raw water inflow Qraw measured at specified time intervals.

[0022] The third feature structure, based on the second feature structure described above, periodically or irregularly measures the MLSS of the biological treatment tank, and adjusts the extraction coefficient K based on the measured MLSS.

[0023] When the MLSS in the biological treatment tank is below the appropriate range, the amount of sludge extracted is reduced by decreasing the extraction coefficient K (increasing the filtration volume), thereby bringing the MLSS back to the appropriate range. When the MLSS is above the appropriate range, the amount of sludge extracted is increased by increasing the extraction coefficient K (reducing the filtration volume), thereby bringing the MLSS back to the appropriate range, which enables the water treatment device to remain in a stable state and operate.

[0024] The fourth feature structure, based on the third feature structure described above, measures the water level in the biological treatment tank. When the measured water level deviates from the specified allowable range, the extraction coefficient K is increased or decreased.

[0025] Furthermore, if the water level in the biological treatment tank deviates from the specified allowable range, abnormal water levels can be prevented in advance by adjusting the extraction coefficient K. For example, when the filtration volume Qtrt is relatively large compared to the raw water inflow Qraw, the extraction coefficient K is set to a larger value to avoid a sharp drop in water level. Conversely, when the filtration volume Qtrt is relatively small compared to the raw water inflow Qraw, the extraction coefficient K is set to a smaller value to avoid a sharp rise in water level.

[0026] The fifth feature structure, based on the third or fourth feature structure mentioned above, measures the water level in the biological treatment tank. When the measured water level deviates from the specified allowable range, it notifies the abnormal state via a notification mechanism.

[0027] When the water level in the biological treatment tank deviates from the prescribed allowable range, the abnormal condition can be notified through a notification agency, thereby prompting the operator to take notice and preventing major accidents from occurring in advance.

[0028] The first characteristic structure of the water treatment device of the present invention comprises: a biological treatment tank, including at least an aerobic tank impregnated with a membrane separation device; and a control device that sets the extraction coefficient K (K < 1) as a control factor such that the sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow amount Qraw × K, and operates the membrane separation device such that the filtration amount Qtrt from the membrane separation device satisfies: filtration amount Qtrt = raw water inflow amount Qraw × (1 - K), thereby causing the remaining sludge to overflow naturally from the overflow path of the biological treatment tank.

[0029] Invention Effects

[0030] As described above, according to the present invention, an operation method and a water treatment device can be provided that reduce the operator's workload and contribute to energy conservation. Attached Figure Description

[0031] Figure 1 This is an explanatory diagram of the first embodiment of the water treatment apparatus of the present invention.

[0032] Figure 2 This is an explanatory diagram of a second embodiment of the water treatment apparatus of the present invention.

[0033] Figure 3A This is a partial cross-sectional perspective view of the third embodiment of the water treatment device of the present invention.

[0034] Figure 3B This is a top view illustration of the third embodiment.

[0035] Figure 4A yes Figure 3B An explanatory diagram of the first method of AA section view.

[0036] Figure 4B This is an explanatory diagram of the second cross-sectional view.

[0037] Figure 5 This is an illustrative diagram of an existing water treatment system. Detailed Implementation

[0038] The operation method and the water treatment apparatus of the present invention will be described below based on the accompanying drawings.

[0039] [First Implementation]

[0040] like Figure 1 As shown, the water treatment device 1 includes: a biological treatment tank 8 comprising an anoxic tank 2 and an aerobic tank 3 impregnated with a membrane separation device 4; a sludge circulation path 7 for circulating sludge from the aerobic tank 3 to the anoxic tank 2; and a control device C.

[0041] The control device C consists of a computer with a CPU board, a memory board, an input / output unit, a display unit, etc. The memory mounted on the memory board stores a control program for controlling the water treatment device 1. The CPU mounted on the CPU board executes the control program, thereby controlling the operation of the water treatment device 1.

[0042] The input / output unit receives signals from various sensors installed in the biological treatment tank 8, including flow sensors, MLSS sensors, DO sensors, water level sensors, and pressure sensors that detect the inter-membrane differential pressure of the membrane separation unit 4. It also outputs control signals to each load, such as filtration volume control signals to the membrane separation unit 4, aeration volume control signals to the aeration unit 5 and auxiliary aeration unit 6, and sludge circulation volume control signals to the sludge pump P1. The flow sensors include sensors that measure the inflow of raw water, the sludge circulation volume, and the flow rate of treated water. MLSS sensors, DO sensors, and water level sensors are installed in the aerobic tank 3. Furthermore, the display unit consists of a touch-panel LCD display, allowing the operator to input and set various information via the screen.

[0043] The raw water flowing into the anoxic tank 2 is mixed with the activated sludge in the tank by the stirring mechanism 2a, and then flows into the aerobic tank 3 through the lower opening of the partition wall 8W. In the aerobic tank 3, under the aerobic environment of the auxiliary aeration device 6, organic matter is oxidized and decomposed by aerobic microorganisms, and ammonia is nitrified. A portion of the purified treated water is extracted as treated water via the membrane separation device 4. The treated water and sludge in the aerobic tank 3 are circulated to the anoxic tank 2 via the sludge pump P1 and the sludge circulation path 7. The treated water circulated to the anoxic tank 2 along with the sludge is denitrified by anaerobic microorganisms under an anaerobic environment.

[0044] The sludge that grows in the biological treatment tank 8 flows out of the tank naturally along the overflow path 9. The overflow path 9 consists of an overflow hole 9h formed on the upper part of the side wall of the biological treatment tank 8, a flange pipe 9f provided in the overflow hole 9h, and a sludge extraction pipe 9t connected to the flange pipe 9f. The sludge is then treated in a sludge storage tank or other residual sludge treatment device (not shown).

[0045] A plurality of membrane separation devices 4 are immersed in the aerobic tank 3, and auxiliary aeration devices 6 for promoting aerobic treatment are provided on both sides of the membrane separation devices 4. Each membrane separation device 4 is configured such that: inside the membrane shell with openings at the top and bottom, multiple plate-shaped membrane elements are arranged at certain intervals with each membrane surface in a vertical orientation, and the membrane surface is purified by the upward flow generated by the aeration from the aeration device 5 located at the bottom of the membrane shell.

[0046] The aeration device 5 and the auxiliary aeration device 6 each have an aeration pipe with a plurality of aeration holes, and are connected to a blower located outside the tank via a main aeration pipe connected to the aeration pipe. Each membrane element is connected to a water collection pipe via a pipe, and the water collection pipe is connected to a pump P2 located outside the tank as a suction mechanism. By adjusting the suction pressure of pump P2, the differential pressure between the membranes is brought to a specified value, thereby controlling the filtration rate Qtrt of the membrane separation device 4.

[0047] Control device C sets the extraction coefficient K (K < 1) as the control factor, ensuring that the sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow Qraw × K; and operates membrane separation device 4, ensuring that the filtration amount Qtrt from membrane separation device 4 satisfies: filtration amount Qtrt = raw water inflow Qraw × (1 - K), thereby causing the remaining sludge to overflow naturally from the overflow path 9 of the biological treatment tank 8. The sludge rises with the upflow generated by the aeration device 5, while the treated water with high sludge concentration overflows from the overflow path 9.

[0048] To prevent sludge from overflowing from the biological treatment tank 8 in the event of an anomaly, an overflow path 9, which serves as a safety mechanism pre-installed in the biological treatment tank 8, is used for sludge extraction, allowing the remaining sludge to overflow naturally without requiring further intervention. Figure 5 The sludge extraction operation of the existing sludge extraction pipe 11 shown does not require the operator to operate the sludge pump P1 or open and close the extraction valve 10.

[0049] If the extraction coefficient K > 0, the water level in the biological treatment tank 8 will rise, and the remaining sludge will overflow naturally from the overflow path 9. If the extraction coefficient K is set to K < 0, the water level in the biological treatment tank 8 can also be actively reduced.

[0050] The extraction factor K can be appropriately set by the operator via a touch panel LCD display. For example, the extraction factor K can be set based on the sludge yield corresponding to the raw water inflow Qraw captured by a flow sensor, etc. Sludge yield refers to the amount of organic matter produced relative to the amount of sludge treated by the water treatment equipment. For example, BOD sludge yield refers to the increase in sludge (kg) relative to the BOD inflow (kg), calculated as {residual sludge concentration (mg / L) × residual sludge extraction amount (m³)}. 3 / day)}÷{Wastewater BOD concentration (mg / L)×Wastewater volume (m³)} 3 The formulas are used to calculate the result.

[0051] To handle the constantly changing raw water inflow Qraw, control device C measures the raw water inflow Qraw at specified time intervals and updates the set filtration volume Qtrt based on the measurement results at the same specified time intervals. The specified time is not particularly limited; it can be set within the range of 10 minutes to several hours.

[0052] In addition, the control device C periodically or irregularly measures the MLSS of the biological treatment tank 8 and adjusts the extraction coefficient K based on the measured MLSS.

[0053] When the MLSS in the biological treatment tank 8 is below the appropriate range, the sludge extraction amount is reduced by decreasing the extraction coefficient K (increasing the filtration amount), thereby bringing the MLSS back to the appropriate range; when the MLSS is above the appropriate range, the sludge extraction amount is increased by increasing the extraction coefficient K (reducing the filtration amount), thereby bringing the MLSS back to the appropriate range, enabling the water treatment device 1 to remain in a stable state and operate.

[0054] Furthermore, the control device C measures the water level in the biological treatment tank 8. When the measured water level deviates from the specified allowable range, it is preferable to control it by increasing or decreasing the extraction coefficient K.

[0055] If the water level in the biological treatment tank 8 deviates from the specified allowable range, abnormal water level fluctuations can be prevented in advance by adjusting the extraction coefficient K. For example, when the filtration volume Qtrt is relatively large compared to the raw water inflow Qraw, the extraction coefficient K is set to a larger value to avoid a sharp drop in water level. Conversely, when the filtration volume Qtrt is relatively small compared to the raw water inflow Qraw, the extraction coefficient K is set to a smaller value to avoid a sharp rise in water level.

[0056] Control device C is configured to notify the operator of any abnormal condition when the water level in the biological treatment tank 8 deviates from the specified allowable range. This notification mechanism may include a buzzer or an email device used to notify the operator of the abnormality. By notifying the operator of the abnormal condition via this mechanism, the operator is alerted, thus preventing major accidents from occurring in advance.

[0057] [Second Implementation]

[0058] In the above embodiment, an example was described where the overflow path 9 consists of an overflow hole 9h formed in the upper part of the side wall of the biological treatment tank 8, a flange pipe 9f disposed in the overflow hole 9h, and a sludge extraction pipe 9t connected to the flange pipe 9f. However, the structure of the overflow path 9 is not limited to this arrangement; for example, it could also be... Figure 2 As shown in the diagram.

[0059] That is, the overflow path 9 consists of a longitudinal pipe 9a arranged along the side wall of the biological treatment tank 8, a flange pipe 9f installed at the overflow hole 9h formed on the side wall of the biological treatment tank 8, and a sludge extraction pipe 9t. The upper end of the longitudinal pipe 9a, which is open at the lower end, is connected to one end of the flange pipe 9f, and the other end of the flange pipe 9f is connected to the sludge extraction pipe 9t. By opening a portion of the upper end of the longitudinal pipe 9a to the atmosphere, or by pre-filling the overflow path 9 with water, the sludge will naturally flow out when the liquid level of the treated water in the biological treatment tank 8 rises above the formation position of the overflow hole 9h.

[0060] [Third Implementation]

[0061] exist Figure 3A , Figure 3B and Figure 4A , Figure 4BThe diagram shows a water treatment device 1 with a biological treatment tank 8 formed of iron plates for the bottom and side walls. The biological treatment tank 8, which is rectangular in plan view, is divided into three regions R1, R2, and R3 along its length by two partition walls 8W. A membrane separation device 4, also rectangular in plan view, is immersed and disposed in the central region R2. The membrane separation device 4 is located at the center of the width of the central region R2. An upward flow of air from an aeration device 5 located at the bottom of the membrane separation device 4 creates a circulating flow where the treated water rises from the bottom of the membrane separation device 4 upwards and then descends from the top of the membrane separation device 4 to both sides.

[0062] At the bottom of the biological treatment tank 8, auxiliary aeration devices 6 are installed on both sides of the membrane separation device 4 (see reference). Figure 4A , Figure 4B The biological treatment is configured to be switchable: when the auxiliary aeration device 6 is in operation, the entire central region R2 of the biological treatment tank 8 functions as an aerobic tank 3; when the auxiliary aeration device 6 is stopped, the upper part of the central region R2 of the biological treatment tank 8 functions as an aerobic tank 3, and the lower part functions as an anoxic tank 2.

[0063] The lower parts of the two partition walls 8W are open, and the water to be treated from the central region R2 separated by the partition walls 8W flows into the two side regions R1 and R3 through the lower part of the partition walls 8W. The water flows into the lower part of the membrane separation device 4 from the lower part of the partition walls 8W, and a portion of it is taken out by the membrane separation device 4 as treated water.

[0064] A raw water inlet pipe 12 is horizontally mounted above the central part of the central region R2. Separated by a partition plate 12W extending from the center of the membrane separation device 4 along its length, raw water inlet branch pipes 12t are installed on both sides, supplying raw water to the bottom of the biological treatment tank 8. That is, in the biological treatment tank 8, a flow is formed where the treated water and sludge flow together from the central region R2 to the two side regions R1 and R3, then from the side regions R1 and R3 to the membrane separation device 4, and finally from below to above the central region R2.

[0065] like Figure 3A As shown, a device is installed on the side wall of the central region R2 of the biological treatment tank 8, which is similar to... Figure 1 The same overflow path 9 is described, and Figure 1 Similarly, the control device C sets the extraction coefficient K (K < 1) as the control factor so that the sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow amount Qraw × K, and operates the membrane separation device 4 so that the filtration amount Qtrt from the membrane separation device 4 satisfies: filtration amount Qtrt = raw water inflow amount Qraw × (1 - K), thereby causing the remaining sludge to overflow naturally from the overflow path 9 of the biological treatment tank 8.

[0066] like Figure 4A , Figure 4B As shown, control device C calculates the sludge circulation ratio based on the difference between the values ​​of the MLSS sensor in the upper layer of the central region R2 and the MLSS sensor in the lower layer (below the membrane separation device 4), and adjusts the aeration rate from the aeration device 5 to achieve the target circulation ratio. Additionally, control device C adjusts the aeration rate of the auxiliary aeration device 6 to ensure that the DO sensor value in the middle layer of the central region R2 reaches the target value. Then, the extraction coefficient K is adjusted based on the water level detected by the water level sensor and the value of the MLSS sensor in the lower layer of the central region R2 (below the membrane separation device 4).

[0067] [Fourth Implementation]

[0068] In the above embodiment, a water treatment apparatus 1 is described, comprising: a biological treatment tank 8 including an anoxic tank 2 and an aerobic tank 3 impregnated with a membrane separation device 4; and a sludge circulation path 7 for circulating sludge from the aerobic tank 3 to the anoxic tank 2. However, the biological treatment tank 8 of the present invention may also be configured to further include an anaerobic tank for phosphorus removal, with sludge being circulated from the aerobic tank 3 to the anaerobic tank via the sludge circulation path 7.

[0069] The above description describes the method of automatically operating the water treatment device 1 by the control device C, but the water treatment device 1 can also be operated by an operator in place of the control device C or in cooperation with the control device C.

[0070] That is, the operation method of the water treatment device of the present invention is characterized by the following operation method of the water treatment device, which includes: a biological treatment tank, including at least an anoxic tank and an aerobic tank equipped with a membrane separation device; and a sludge circulation path for circulating sludge from the aerobic tank to the anoxic tank. The extraction coefficient K (K < 1) is set as a control factor such that the sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow amount Qraw × K, and the membrane separation device is operated such that the filtration amount Qtrt from the membrane separation device satisfies: filtration amount Qtrt = raw water inflow amount Qraw × (1 - K), so that the remaining sludge overflows naturally from the overflow path of the biological treatment tank.

[0071] In addition, it is preferable to update the set filtration volume Qtrt at specified time intervals based on the raw water inflow Qraw measured at specified time intervals.

[0072] The MLSS of the biological treatment tank is measured periodically or irregularly, and the extraction factor K is preferably adjusted based on the measured MLSS.

[0073] When measuring the water level in the biological treatment tank, if the measured water level deviates from the specified allowable range, it is preferable to increase or decrease the extraction coefficient K.

[0074] The water level in the biological treatment tank is measured, and when the measured water level deviates from the specified allowable range, the abnormal condition is preferably notified through a notification agency.

[0075] The above-described embodiments are one aspect of the present invention. The present invention is not limited to the above description. Of course, the specific structure of each part can be appropriately modified within the scope of achieving the effects of the present invention.

[0076] Explanation of reference numerals in the attached figures

[0077] 1: Water treatment equipment

[0078] 2: Anoxic tank

[0079] 3: Aerobic tank

[0080] 4: Membrane separation device

[0081] 5: Ventilation device

[0082] 6: Auxiliary ventilation device

[0083] 7: Sludge Recycling Path

[0084] 8: Biological treatment tank

[0085] 9: Overflow path

Claims

1. A method for operating a water treatment device, characterized in that, The water treatment device includes a biological treatment tank, which at least comprises an aerobic tank equipped with a membrane separation device. In the operation method of the water treatment device, The extraction coefficient K is set as a control factor so that the sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow Qraw × K, where K < 1. Operate the membrane separation device such that the filtration volume Qtrt from the membrane separation device satisfies: filtration volume Qtrt = raw water inflow Qraw × (1 - K). The remaining sludge is allowed to overflow naturally from the overflow path of the biological treatment tank.

2. The method of operating the water treatment device according to claim 1, characterized in that, Based on the raw water inflow Qraw measured at specified time intervals, the filtration rate Qtrt is updated and set at the specified time intervals.

3. The method of operating the water treatment device according to claim 2, characterized in that, The suspended solids in the mixture of the biological treatment tank are measured periodically or irregularly, and the extraction coefficient K is adjusted based on the measured suspended solids in the mixture.

4. The method of operating the water treatment device according to claim 3, characterized in that, Measure the water level in the biological treatment tank, and adjust the extraction coefficient K by increasing or decreasing the measured water level when it deviates from the specified allowable range.

5. The method of operating the water treatment apparatus according to claim 3 or 4, characterized in that, The water level in the biological treatment tank is measured, and when the measured water level deviates from the specified allowable range, an abnormal status is notified via a notification mechanism.

6. A water treatment device, characterized in that, have: Biological treatment tanks include at least an aerobic tank impregnated with a membrane separation device; as well as Control device, The control device sets the extraction coefficient K as a control factor, such that the sludge extraction amount Qwas satisfies: sludge extraction amount Qwas = raw water inflow amount Qraw × K, where K < 1. The control device operates the membrane separation device so that the filtration amount Qtrt from the membrane separation device satisfies: filtration amount Qtrt = raw water inflow Qraw × (1 - K). The control device allows the remaining sludge to overflow naturally from the overflow path of the biological treatment tank.

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