Water treatment system and water treatment method

Abstract

To provide a water treatment system that is capable of forming granular sludge with high settling properties even when a water quality of water to be treated fluctuates.SOLUTION: A water treatment system 1 includes: a semi-batch treatment apparatus 10 that includes a reaction tank 16 and performs an inflow process of inflowing water to be treated into the reaction tank 16, a biological treatment process of biologically treating the water to be treated in the reaction tank 16 with biological sludge, a sedimentation process of sedimenting the biological sludge in the reaction tank 16, a discharge process of discharging biologically treated water in the reaction tank 16, and a sludge discharge process of discharging the biological sludge in the reaction tank 16; a water quality estimation unit 34 that calculates a representative value of a water quality of the water to be treated from time-series data of the water quality of the water to be treated flowing into the reaction tank 16 for a predetermined period of time; and a control unit 36 that determines a target value of a sludge concentration in the reaction tank 16 from the water quality representative value, and controls an amount of the biological sludge discharged from the reaction tank 16 in the sludge discharge process based on the target value of the sludge concentration and the sludge concentration in the reaction tank 16.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a technique for a water treatment system and a water treatment method. [Background technology]

[0002] Conventionally, biological wastewater treatment has used the activated sludge method, which utilizes a collection of microorganisms called flocs (aerobic biological sludge). However, in the activated sludge method, when separating the flocs (aerobic biological sludge) from the treated water in the settling tank, the surface area of ​​the settling tank may need to be very large because the settling speed of the flocs is slow. In addition, the treatment speed of the activated sludge method depends on the sludge concentration in the biological treatment tank, and although the treatment speed can be increased by increasing the sludge concentration, there are cases where the treatment cannot be maintained due to solid-liquid separation problems caused by bulking in the settling tank, etc.

[0003] On the other hand, in anaerobic biological treatment, it is common to utilize a dense collection of microorganisms called granules. Granules have a very fast settling rate and the microorganisms are densely packed together, so the sludge concentration in the biological treatment tank can be increased, making it possible to realize high-speed wastewater treatment. However, anaerobic biological treatment may have problems such as the fact that the types of wastewater to be treated are limited compared to aerobic treatment (activated sludge method) and that the treated water temperature needs to be maintained at about 30 to 35°C. In addition, when anaerobic biological treatment alone is used, the quality of the treated water is poor, and when the treated water is to be discharged into a river or the like, it may be necessary to separately carry out aerobic treatment such as the activated sludge method.

[0004] In recent years, it has become clear that by using a semi-batch treatment apparatus in which wastewater is intermittently introduced into a reaction tank, it is possible to form a granulated biological sludge (hereinafter referred to as granular sludge) with good settling properties not only from anaerobic biological sludge but also from aerobic biological sludge (see, for example, Patent Documents 1 to 4). Granular sludge has an average particle size of, for example, 0.2 mm or more. In semi-batch biological treatment, it is common to repeatedly carry out the following steps in one reaction tank: (1) introduction of wastewater, (2) biological treatment of the wastewater using biological sludge, (3) settling of the biological sludge, and (4) discharge of biologically treated water.

[0005] Patent Document 5 discloses a biological treatment method that repeats the steps of (1) inflow of wastewater and discharge of biologically treated water, (2) biological treatment of the wastewater using biological sludge, and (3) settling of the biological sludge. This allows the production of biological sludge with high settling properties like granular sludge. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2004 / 024638 [Patent Document 2] JP 2008-212878 A [Patent Document 3] Patent No. 4975541 [Patent Document 4] Patent No. 4804888 [Patent Document 5] JP 2016-77931 A Summary of the Invention [Problem to be solved by the invention]

[0007] In a semi-batch treatment apparatus, if there is a change in the quality of the water to be treated, the properties of the granular sludge may deteriorate, which may result in a decrease in the performance of the biological treatment.

[0008] An object of the present disclosure is to provide a water treatment system and a water treatment method that are capable of forming granular sludge with high settling properties even if the water quality of the water to be treated fluctuates. [Means for solving the problem]

[0009] One aspect of the present disclosure is a water treatment system comprising: a semi-batch treatment apparatus having a reaction tank and performing an inflow process of inflowing water to be treated into the reaction tank, a biological treatment process of biologically treating the water to be treated in the reaction tank using biological sludge, a sedimentation process of settling the biological sludge in the reaction tank, a discharge process of discharging the biologically treated water in the reaction tank, and a sludge discharge process of discharging the biological sludge in the reaction tank; a water quality estimation unit that calculates a representative water quality value of the water to be treated from time series data over a predetermined period of time of the water quality of the water to be treated flowing into the reaction tank; and a control unit that determines a target value of a sludge concentration in the reaction tank from the representative water quality value, and controls the amount of the biological sludge discharged from the reaction tank in the sludge discharge process based on the target value of the sludge concentration and the sludge concentration in the reaction tank.

[0010] In addition, in the above water treatment system, it is preferable that the water quality estimation unit includes an acquisition unit that acquires the water quality of the treated water for a specific period including the first day within the specified period, a prediction unit that predicts time series data of the water quality of the treated water for the specified period by inputting the water quality of the treated water for the specific period including the first day acquired by the acquisition unit into a pre-trained model for predicting time series data of the water quality of the treated water for the specified period from the water quality of the treated water for the specific period including the first day, and a calculation unit that calculates a representative water quality value of the treated water from the predicted time series data.

[0011] Moreover, one aspect of the present disclosure is a water treatment method comprising: an inflow process for inflowing water to be treated into a reaction tank; a biological treatment process for biologically treating the water to be treated in the reaction tank with biological sludge; a sedimentation process for sedimenting the biological sludge in the reaction tank; a discharge process for discharging the biologically treated water in the reaction tank; and a sludge discharge process for discharging the biological sludge in the reaction tank; a water quality estimation process for calculating a representative water quality value of the water to be treated from time-series data of the water quality of the water to be treated flowing into the reaction tank over a predetermined period of time; and a control process for determining a target value of a sludge concentration in the reaction tank from the representative water quality value, and controlling the amount of the biological sludge discharged from the reaction tank in the sludge discharge process based on the target value of the sludge concentration and the sludge concentration in the reaction tank. Effect of the Invention

[0012] According to the present disclosure, it is possible to provide a water treatment method and a water treatment system that are capable of forming granular sludge with high settling properties even when the water quality of the water to be treated fluctuates. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram illustrating an example of a water treatment system according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a block diagram showing a water quality estimation unit. [Diagram 3] FIG. 2 is a schematic configuration diagram showing another example of the water treatment system according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] An embodiment of the present disclosure will be described below. The embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to the embodiment.

[0015] 1 is a schematic diagram showing an example of a water treatment system according to the present embodiment. The water treatment system 1 includes a semi-batch treatment device 10, a sludge concentration meter 12, a water quality meter 13, and a calculation device 14. The semi-batch treatment device 10 includes a reaction tank 16. A supply pipe 18 is connected to the inlet of the reaction tank 16. A pump 20 and a valve 22 are installed in the supply pipe 18. A treated water pipe 26 is connected to the outlet of the reaction tank 16. A valve 28 is installed in the treated water pipe 26. A sludge outlet of the reaction tank 16 is connected to a sludge discharge pipe 30. A sludge discharge pump 32 and a valve 33 are installed in the sludge discharge pipe 30.

[0016] The sludge concentration meter 12 functions as a sludge concentration measuring means for measuring the sludge concentration in the reaction tank 16, and is installed at a predetermined height in the reaction tank 16. The installation position of the sludge concentration meter 12 is, for example, in the range from the water surface to 2 m below the water surface. The sludge concentration meter 12 may be of a conventionally known type, such as a transmitted light type, a scattered light type, a microwave type, or an ultrasonic type. In addition, as a sludge concentration measuring means for acquiring the sludge concentration in the reaction tank 16, a meter that is correlated with the sludge concentration, such as a viscometer or a turbidity meter, may be used. For example, the sludge concentration in the reaction tank 16 may be estimated from a detection value detected by a meter that is correlated with the sludge concentration, such as a viscometer or a turbidity meter. The sludge concentration meter 12 is connected to the calculation device 14, and is configured so that the sludge concentration measured by the sludge concentration meter 12 is transmitted to the calculation device 14.

[0017] The water quality meter 13 functions as a water quality measuring means for measuring the water quality of the water to be treated flowing into the reaction tank 16, and is installed, for example, in the supply pipe 18. The water quality of the water to be treated measured by the water quality meter 13 includes, for example, BOD (biochemical oxygen demand), COD (chemical oxygen demand), TOC (total organic carbon), DO (dissolved oxygen), SS (suspended solids), phosphorus concentration, nitrogen concentration, ammonia concentration, and the like. Among these, BOD is preferable. Note that, for BOD, other water qualities that are correlated with BOD, such as TOC, SS, and COD concentration, may be measured by the water quality meter, and the BOD concentration may be estimated from the measured value. The water quality meter 13 is connected to the calculation device 14, and is configured so that the water quality of the water to be treated measured by the water quality meter 13 is transmitted to the calculation device 14.

[0018] In this embodiment, it is desirable to use values ​​measured by a sludge concentration meter 12 or a water quality meter 13, etc., installed in the water treatment system 1 for the water quality of the water to be treated and the sludge concentration in the reaction tank 16, but this is not limited to this, and for example, values ​​measured by an operator using an official method, etc. may be used.

[0019] The calculation device 14 is composed of, for example, a microcomputer composed of a CPU that executes a predetermined program, and a ROM and RAM that store the program, calculation results, etc., and electronic circuits, etc. As shown in Fig. 1, the calculation device 14 functionally has a water quality estimation unit 34 and a control unit 36. The calculation device 14 is connected to each valve and pump.

[0020] The water quality estimation unit 34 calculates a representative water quality value of the water to be treated from time series data of the water quality of the water to be treated for a predetermined period. The representative water quality value is, for example, an average value or a median value of the water quality in the time series data for a predetermined period. The control unit 36 ​​controls the operation and stopping of each pump and the opening and closing of each valve. The control unit 36 ​​also determines a target value of the sludge concentration in the reaction tank 16 from the representative water quality value, and controls the amount of sludge to be discharged from the reaction tank 16 based on the target value of the sludge concentration and the sludge concentration in the reaction tank 16.

[0021] An example of the operation of the water treatment system 1 will be described below.

[0022] <(1) Inflow process> By operating the pump 20 and opening the valve 22, a predetermined amount of water to be treated is supplied from the supply pipe 18 into the reaction tank 16. The water to be treated may be, for example, wastewater containing organic matter, and specific examples thereof include organic wastewater containing biodegradable organic matter, such as wastewater from food processing plants, chemical plants, semiconductor plants, machine factories, sewage, and human waste.

[0023] <(2) Biological treatment process> The pump 20 is stopped and the valve 22 is closed. An oxygen-containing gas such as air is supplied from an aeration device (not shown) into the reaction tank 16, and the water to be treated is biologically treated by the biological sludge under aerobic conditions. The biological treatment is not limited to aerobic conditions, but may be anaerobic conditions, or a combination of aerobic and anaerobic conditions. When biological treatment is performed under anaerobic conditions, it is desirable to agitate the water to be treated, biological sludge, etc., for example, by an agitator (not shown) without supplying air, etc., into the reaction tank 16.

[0024] <(3) Sedimentation process> The supply of oxygen-containing gas and stirring by the stirrer are stopped, and the inside of the reaction tank 16 is left to stand for a predetermined period of time to allow the biological sludge in the reaction tank 16 to settle. This yields biologically treated supernatant water.

[0025] <(4) Discharge process> Depending on a predetermined end time of the settling process, the valve 28 is opened and the supernatant water obtained in the settling process is discharged from the reaction tank 16 to the treated water pipe 26 as treated water.

[0026] In the water treatment system 1 shown in FIG. 1, an operation cycle including steps (1) to (4) is repeatedly performed, whereby the water to be treated is treated in the reaction tank 16 and granular sludge that has undergone self-granulation is formed.

[0027] In addition, in the water treatment system 1 shown in FIG. 1, a sludge discharge process is periodically performed to discharge biological sludge (including granular sludge) in the reaction tank 16. The sludge discharge process is performed, for example, four times a day to once every two weeks. When the sludge discharge process is performed, the sludge discharge pump 32 is operated and the valve 33 is opened. As a result, a predetermined amount of biological sludge in the reaction tank 16 is extracted from the sludge discharge pipe 30. The biological sludge may be discharged by leaving the reaction tank 16 in a stationary state and discharging the biological sludge deposited at the bottom of the reaction tank 16, or by supplying a gas such as an oxygen-containing gas into the reaction tank 16 or operating an agitator or the like to discharge the biological sludge in the reaction tank 16 in an agitated state.

[0028] Here, if a constant amount of biological sludge is periodically discharged from the reaction tank 16 despite fluctuations in the quality of the water to be treated, the granular sludge formed in the reaction tank 16 may collapse, causing a decrease in the settling property of the granular sludge. Therefore, in this embodiment, the discharge amount of biological sludge discharged from the reaction tank 16 in the sludge discharge step is controlled as follows.

[0029] The water quality of the water to be treated is measured at any time by the water quality meter 13. The measured water quality is transmitted to the calculation device 14 together with the date and time of measurement, and is stored in the water quality estimation unit 34 as time-series data of the water quality of the water to be treated (data consisting of the water quality of the water to be treated and the date and time of measurement). The water quality estimation unit 34 also calculates a representative water quality value of the water to be treated from the time-series data for a predetermined period (set, for example, between 10 days or more and 6 months or less). The representative value is, for example, the average value or median value of the water quality in the time-series data for the predetermined period.

[0030] The control unit 36 ​​determines a target value of the sludge concentration in the reaction tank 16 from the representative water quality value of the water to be treated. The target value is determined, for example, by previously preparing correlation information that specifies the target value of the sludge concentration relative to the representative water quality value of the water to be treated, and applying the representative water quality value of the water to be treated calculated by the water quality estimation unit 34 to the correlation information.

[0031] Then, the control unit 36 ​​controls the amount of biological sludge discharged from the reaction tank 16 based on the determined target value of the sludge concentration and the sludge concentration in the reaction tank 16. For example, the control unit 36 ​​acquires the sludge concentration in the reaction tank 16 measured by the sludge concentration meter 12. The sludge concentration in the reaction tank 16 is preferably measured in a state in which the biological sludge is being stirred. When the acquired sludge concentration in the reaction tank 16 is below the determined target value of the sludge concentration, the control unit 36 ​​controls, for example, the operating time, output, etc. of the sludge discharge pump 32 so that the amount of biological sludge discharged from the reaction tank 16 is less than a preset reference amount (the amount of biological sludge discharged may be zero). Furthermore, when the acquired sludge concentration in the reaction tank 16 exceeds the target value of the sludge concentration determined above, the control unit 36 ​​controls, for example, the operating time and output of the sludge discharge pump 32 so that the amount of biological sludge discharged from the reaction tank 16 is equal to or greater than a preset reference amount. When the amount of biological sludge discharged from the reaction tank 16 is to be greater than the reference amount, it is preferable to discharge an increased amount of biological sludge over a period of, for example, three days to one week, rather than discharging the increased amount of biological sludge in a short period of time.

[0032] By controlling the amount of biological sludge discharged from the reaction tank 16 in this way, even if the quality of the water to be treated fluctuates, the collapse of the granular sludge is suppressed, and granular sludge with high settling properties can be formed. As a result, the deterioration of the biological treatment performance in the reaction tank 16 is suppressed.

[0033] 2, the water quality estimation unit 34 may include a learning data storage unit 38, a learning unit 40, a learned model storage unit 42, an acquisition unit 44, a prediction unit 46, and a calculation unit 48. An example of a method for calculating the representative water quality value of the water to be treated by the water quality estimation unit 34 shown in FIG. 2 will be described below.

[0034] The learning data storage unit 38 stores learning data. The input teacher data of the learning data is, for example, the water quality of the water to be treated, the water temperature of the water to be treated, environmental information such as outside air temperature, precipitation, and humidity, device operation information such as aeration air volume, inflow water volume, dissolved oxygen concentration in the reaction tank, pH in the reaction tank, and water temperature in the reaction tank, water consumption for daily use in the treatment area, and dates, etc. The specific period may be only the first day. The output teacher data of the learning data is time-series data of the water quality of the water to be treated in a predetermined period. For example, if the predetermined period is five days, it is the dates from the first day to the fifth day and the water quality of the water to be treated.

[0035] The learning unit 40 executes a known supervised machine learning algorithm based on the learning data stored in the learning data storage unit 38 to generate a trained model that predicts time series data of the water quality of the water to be treated during a predetermined period from the water quality information of the water to be treated during a specific period including the first day within the predetermined period. For example, a trained model that predicts time series data of the water quality of the water to be treated during a predetermined period from the water quality information of the water to be treated during the first day within the predetermined period is generated using input side teacher data of the water quality of the water to be treated during the first day within the predetermined period, and output side teacher data that is time series data of the water quality of the water to be treated during the predetermined period. Also, for example, a trained model that predicts time series data of the water quality of the water to be treated during a predetermined period from the water quality information of the water to be treated during the first day to several days within the predetermined period may be generated using input side teacher data of the water quality of the water to be treated during the first day to several days within the predetermined period, and output side teacher data that is time series data of the water quality of the water to be treated during the predetermined period. The learning unit 40 stores the generated trained model in the trained model storage unit 42. The trained model itself is a known model, such as a neural network model, a support vector machine, or a logistic regression model. The neural network model also includes a deep neural network model obtained by deep learning.

[0036] The trained model storage unit 42 stores the trained model generated by the training unit 40.

[0037] The acquisition unit 44 acquires water quality information of the water to be treated for a specific period including the first day of the predetermined period. The water quality information of the water to be treated is composed of the water quality of the water to be treated measured by the water quality meter 13 and the date of measurement.

[0038] The prediction unit 46 inputs the water quality information of the water to be treated for a specific period including the first day within the predetermined period acquired by the acquisition unit 44 into the trained model stored in the trained model storage unit 42, and predicts the time series data of the water quality of the water to be treated for the predetermined period. For example, the water quality information of the water to be treated for the first day within the predetermined period acquired by the acquisition unit 44 is input into a trained model that predicts the time series data of the water quality of the water to be treated for the predetermined period from the water quality information of the water to be treated for the first day within the predetermined period, and predicts the time series data of the water quality of the water to be treated for the predetermined period. Here, when the water quality of the water to be treated on the second day within the predetermined period acquired by the acquisition unit 44 is higher than the water quality of the water to be treated on the second day in the time series data of the water quality of the water to be treated for the above-mentioned predicted time series data of the water quality of the water to be treated for the predetermined period, it is preferable that the prediction unit 46 inputs the water quality information of the water to be treated for the period from the first day to several days (at least two days) within the predetermined period into a trained model that predicts the time series data of the water quality of the water to be treated for the predetermined period, and predicts the time series data of the water quality of the water to be treated for the predetermined period. The time series data predicted by the prediction unit may be a function representing the time series data.

[0039] The calculation unit 48 calculates a representative value of the water quality of the water to be treated (for example, an average value, a median value, etc.) from the time-series data of the water quality of the water to be treated predicted by the prediction unit 46 for a predetermined period.

[0040] Fig. 3 is a schematic diagram showing another example of a water treatment system according to an embodiment. In the water treatment system 2 shown in Fig. 3, the same components as those in the water treatment system 1 shown in Fig. 1 are denoted by the same reference numerals. In the water treatment system 2 shown in Fig. 3, the outlet to which the treated water pipe 26 is connected is provided at a position at the water level height of the reaction tank 16. Note that the water treatment system 2 shown in Fig. 3 does not have a sludge discharge pipe 30 connected to the sludge outlet of the reaction tank 16.

[0041] An example of the operation of the water treatment system 2 shown in FIG. 3 will be described.

[0042] (1) Inflow process and discharge process: The pump 20 is operated and the valve 22 is opened, so that the water to be treated is supplied from the supply pipe 18 into the reaction tank 16. When the water to be treated flows in, the valve 28 is opened and the treated water (supernatant water) in the reaction tank 16 obtained in the settling process is pushed out by the inflowing water to be treated and discharged to the treated water pipe 26.

[0043] (2) Biological treatment step: The pump 20 is stopped, and the valves 22 and 28 are closed. In the reaction tank 16, the water to be treated is biologically treated by the biological sludge. As described above, the biological treatment is carried out, for example, under aerobic conditions, anaerobic conditions, or a combination thereof.

[0044] (3) Settling step: The supply of oxygen-containing gas and stirring by the stirrer are stopped, and the inside of the reaction tank 16 is left in a static state for a predetermined period of time to allow the biological sludge in the reaction tank 16 to settle. As a result, biologically treated supernatant water is obtained.

[0045] In the water treatment system 2 shown in FIG. 3, an operation cycle including steps (1) to (3) is repeatedly performed, whereby the water to be treated is treated in the reaction tank 16 and granular sludge that has undergone self-granulation is formed.

[0046] Also, in the water treatment system 2 shown in FIG. 3, a sludge discharge step is periodically performed to discharge biological sludge (including granular sludge) in the reaction tank 16. When the sludge discharge step is performed, a gas such as an oxygen-containing gas is supplied into the reaction tank 16, an agitator or the like is operated, and the biological sludge in the reaction tank 16 is stirred. The pump 20 is operated and the valves 22 and 28 are opened. As a result, the biological sludge in the reaction tank 16 is pushed out by the incoming treated water and discharged from the treated water pipe 26. The discharge amount of biological sludge discharged from the reaction tank 16 can be controlled by controlling the operation time, output, etc. of the pump 20. The method for controlling the discharge amount of biological sludge discharged from the reaction tank 16 is as described above.

[0047] The granular sludge formed by this embodiment is, for example, sludge with an average particle size of 0.1 mm or more, or with a settling index SVI5 of 80 mL / g or less. SVI is a settling index of biological sludge, and is calculated by the following method. First, 1 L of sludge is put into a 1 L measuring cylinder, gently stirred so that the sludge concentration becomes as uniform as possible, and then the sludge interface is measured after leaving it to stand for 5 minutes. Then, the volume ratio (%) of the sludge in the measuring cylinder is calculated. Next, the MLSS (mg / L) of the sludge is measured. These are applied to the following formula to calculate SVI5. To calculate SVI30, the above 5 minutes of standing can be changed to 30 minutes of standing. SVI5 (mL / g) = Volume ratio of sludge x 10,000 / MLSS

[0048] The volumetric load of the reactor 16 is 0.15 kg BOD / m 3 / day ~ 1.00kgBOD / m 3 / day, and preferably in the range of 0.30 kg BOD / m 3 / day ~ 0.60kgBOD / m 3 By setting the volume load of the reaction vessel 16 in the above range, it is possible to form better granules.

[0049] The dissolved oxygen (DO) in the reaction tank 16 is preferably set to 0.5 mg / L or more, particularly 1 mg / L or more, under aerobic conditions.

[0050] In order to promote the granulation of biological sludge, Fe is added to the water to be treated in the reaction tank 16 or to the water to be treated before being introduced into the reaction tank 16. 2+ , Fe 3+ , Ca 2+ , Mg 2+ It is also possible to add ions that can form hydroxides, including the above ions. By adding the above ions, it is possible to promote the nucleation of granules. [Explanation of symbols]

[0051] 1, 2 water treatment system, 10 semi-batch treatment device, 12 sludge concentration meter, 13 water quality meter, 14 calculation device, 16 reaction tank, 18 supply piping, 20 pump, 22, 28, 33 valve, 26 treated water piping, 30 sludge discharge piping, 32 sludge discharge pump, 34 water quality estimation unit, 36 control unit, 38 learning data memory unit, 40 learning unit, 42 learned model memory unit, 44 acquisition unit, 46 prediction unit, 48 calculation unit.

Claims

1. a semi-batch treatment apparatus having a reaction tank, the apparatus carrying out an inflow process of inflowing water to be treated into the reaction tank, a biological treatment process of biologically treating the water to be treated in the reaction tank with biological sludge, a sedimentation process of sedimenting the biological sludge in the reaction tank, a discharge process of discharging the biologically treated water in the reaction tank, and a sludge discharge process of discharging the biological sludge in the reaction tank; A water quality estimation unit that calculates a representative value of the water quality of the water to be treated from time series data of the water quality of the water to be treated flowing into the reaction tank for a predetermined period of time; a control unit that determines a target value of the sludge concentration in the reaction tank from the water quality representative value, and controls the amount of the biological sludge discharged from the reaction tank in the sludge discharge process based on the target value of the sludge concentration and the sludge concentration in the reaction tank.

2. The water quality estimation unit includes an acquisition unit that acquires water quality information of the treated water for a specific period including the first day within the specified period, a prediction unit that inputs the water quality information of the treated water for a specific period including the first day acquired by the acquisition unit into a pre-trained model for predicting time series data of the water quality of the treated water for the specified period from the water quality information of the treated water for the specific period including the first day, and predicts time series data of the water quality of the treated water for the specified period, and a calculation unit that calculates a representative water quality value of the treated water from the predicted time series data.

3. A semi-batch treatment process includes an inflow process of inflowing water to be treated into a reaction tank, a biological treatment process of biologically treating the water to be treated in the reaction tank with biological sludge, a sedimentation process of sedimenting the biological sludge in the reaction tank, a discharge process of discharging the biologically treated water in the reaction tank, and a sludge discharge process of discharging the biological sludge in the reaction tank; A water quality estimation step of calculating a representative value of the water quality of the water to be treated from time series data of the water quality of the water to be treated flowing into the reaction tank for a predetermined period of time; a control process for determining a target value of the sludge concentration in the reaction tank from the water quality representative value, and controlling the amount of the biological sludge discharged from the reaction tank in the sludge discharge process based on the target value of the sludge concentration and the sludge concentration in the reaction tank.

Images