Water treatment method and water treatment apparatus

Abstract

This invention provides a water treatment method that allows for the calculation of the sedimentation rate of biological sludge in a reaction tank while operating a semi-batch treatment system. [Solution] One aspect of the present disclosure is a water treatment method comprising: an inflow step of introducing water to be treated into a reaction tank; a biological treatment step of biologically treating the water to be treated in the reaction tank with biological sludge; a sedimentation step of allowing the biological sludge in the reaction tank to settle; and a discharge step of discharging the biologically treated water from the reaction tank; a first detection step of detecting the sludge interface position or sludge concentration in the reaction tank during the sedimentation step; and a calculation step of calculating the sedimentation rate of the biological sludge based on the sludge interface position or sludge concentration detected in the first detection step.

Description

[Technical Field]

[0001] This disclosure relates to water treatment methods and water treatment equipment technologies. [Background technology]

[0002] Traditionally, biological wastewater treatment has employed the activated sludge method, which utilizes microbial aggregates called flocs (aerobic biological sludge). However, in the activated sludge method, when separating the flocs (aerobic biological sludge) from the treated water in the sedimentation tank, the slow settling rate of the flocs sometimes necessitates a very large surface area in the sedimentation tank. Furthermore, the treatment rate of the activated sludge method depends on the sludge concentration in the biological treatment tank. While increasing the sludge concentration can increase the treatment rate, this can lead to problems such as bulking in the sedimentation tank, which can cause solid-liquid separation failures and make it impossible to maintain treatment.

[0003] On the other hand, anaerobic biological treatment typically utilizes granules, which are dense aggregates of microorganisms. Granules have a very fast settling rate, and because the microorganisms are densely aggregated, it is possible to increase the sludge concentration in the biological treatment tank, enabling high-speed wastewater treatment. However, anaerobic biological treatment has drawbacks compared to aerobic treatment (activated sludge method), such as being limited to certain types of wastewater that can be treated and requiring the treatment water temperature to be maintained at around 30-35°C. Furthermore, anaerobic biological treatment alone may result in poor water quality, and if the treated water is to be discharged into rivers or other bodies of water, it may be necessary to carry out aerobic treatment such as the activated sludge method separately.

[0004] In recent years, it has become clear that by treating wastewater under special conditions using a semi-batch treatment system that intermittently infuses wastewater into a reaction tank, it is possible to form granulated biological sludge with good settling properties not only from anaerobic biological sludge but also from aerobic biological sludge (see, for example, Patent Documents 1-4). The granulated biological sludge has, for example, an average particle size of 0.1 mm or more and a settling velocity of 3 m / h or more. In semi-batch biological treatment, it is common to repeatedly perform the following steps in a single reaction tank: (1) inflow of wastewater, (2) biological treatment of wastewater with biological sludge, (3) settling of the biological sludge, and (4) discharge of treated water.

[0005] Furthermore, Patent Document 5 discloses a biological treatment method that repeatedly performs the following steps: (1) inflow of wastewater and discharge of treated water, (2) biological treatment of wastewater with biological sludge, and (3) sedimentation of the biological sludge. This makes it possible to obtain biological sludge with high sedimentation properties, such as granulated biological sludge. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2004 / 024638 [Patent Document 2] Japanese Patent Publication No. 2008-212878 [Patent Document 3] Patent No. 4975541 [Patent Document 4] Patent No. 4804888 [Patent Document 5] Japanese Patent Publication No. 2016-77931 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, calculating the settling rate of biological sludge in the reaction tank while operating a semi-batch processing system is important for understanding the properties of the biological sludge in the reaction tank. Previously, understanding the properties of biological sludge required complicated procedures, skilled operators, or expensive analytical equipment.

[0008] The purpose of this disclosure is to provide a water treatment method and a water treatment apparatus that can calculate the settling rate of biological sludge in a reaction tank while operating a semi-batch treatment apparatus. [Means for solving the problem]

[0009] One aspect of the present disclosure is a water treatment method characterized by comprising: an inflow step of introducing water to be treated into a reaction tank; a biological treatment step of biologically treating the water to be treated in the reaction tank with biological sludge; a sedimentation step of allowing the biological sludge in the reaction tank to settle; and a discharge step of discharging the biologically treated water from the reaction tank; a first detection step of detecting the sludge interface position or sludge concentration in the reaction tank during the sedimentation step; and a calculation step of calculating the sedimentation rate of the biological sludge based on the sludge interface position or sludge concentration detected in the first detection step.

[0010] Furthermore, it is preferable that the water treatment method includes a sludge property determination step in which the properties of the biological sludge are determined based on the settling velocity of the biological sludge calculated in the calculation step.

[0011] Furthermore, the water treatment method preferably includes a second detection step for detecting the sludge concentration in the reaction tank during the biological treatment step, and in the sludge property determination step, it is preferable to determine the properties of the biological sludge based on the settling rate of the biological sludge and the sludge concentration detected in the second detection step.

[0012] In addition, one aspect of the present disclosure is a semi-batch treatment apparatus that has a reaction tank and performs an inflow step of flowing untreated water into the reaction tank, a biological treatment step of biologically treating the untreated water in the reaction tank with biological sludge, a sedimentation step of sedimenting the biological sludge in the reaction tank, and a discharge step of discharging the biologically treated water in the reaction tank, and a first detection means for detecting the sludge interface position or sludge concentration in the reaction tank during the sedimentation step, and a calculation means for calculating the sedimentation rate of the biological sludge based on the sludge interface position or sludge concentration detected by the first detection means. The water treatment apparatus is characterized by having these components.

[0013] In addition, in the water treatment apparatus, it is preferable to have sludge property grasping means for grasping the property of the biological sludge based on the sedimentation rate of the biological sludge calculated by the calculation means.

[0014] In addition, in the water treatment apparatus, it has second detection means for detecting the sludge concentration in the reaction tank during the biological treatment step, and it is preferable that the sludge property grasping means grasps the property of the biological sludge based on the sedimentation rate of the biological sludge and the sludge concentration detected by the second detection means.

Advantages of the Invention

[0015] According to the present disclosure, it is possible to provide a water treatment method and a water treatment apparatus capable of calculating the sedimentation rate of biological sludge in a reaction tank while operating a semi-batch treatment apparatus.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic configuration diagram showing an example of the water treatment apparatus according to this embodiment. [Figure 2] It is a schematic configuration diagram showing another example of the water treatment apparatus according to this embodiment. [Figure 3] It is a sedimentation characteristic curve of granular sludge and an activated sludge sedimentation characteristic curve based on the exponential function formula (V = V0·e(-k·X)). [Figure 4] It is a diagram showing the change in sludge concentration in the reaction tank during the sedimentation step in Examples 1 and 2.

Mode for Carrying Out the Invention

[0017] Embodiments of the present disclosure will be described below. This embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to this embodiment.

[0018] <Water treatment method and water treatment apparatus> FIG. 1 is a schematic configuration diagram showing an example of a water treatment apparatus according to this embodiment. The water treatment apparatus 1 includes a semi-batch treatment apparatus 10, a sludge concentration meter 12, and an arithmetic unit 14. The semi-batch treatment apparatus 10 includes a reaction tank 16. A drainage supply pipe 18 is connected to the drainage inlet of the reaction tank 16. A pump 20 and a valve 22 are installed in the drainage supply pipe 18. Further, a treated water pipe 26 is connected to the treated water outlet of the reaction tank 16. A valve 28 is provided in the treated water pipe 26. An aeration device 32 connected to an aeration blower 30 is installed at the lower part in the reaction tank 16.

[0019] The sludge concentration meter 12 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 position to 2 m below the water surface, preferably in the range from the water surface position to 1 m below the water surface. The sludge concentration meter 12 is connected to the arithmetic unit 14 and is configured such that the sludge concentration detected by the sludge concentration meter 12 is transmitted to the arithmetic unit 14.

[0020] The arithmetic unit 14 is composed of, for example, a microcomputer and an electronic circuit including a CPU that executes a predetermined program, a ROM and a RAM that store programs, calculation results, etc. The arithmetic unit 14 functions as a calculation means for calculating the sedimentation rate of biological sludge based on the sludge concentration in the reaction tank 16 detected by the sludge concentration meter 12, as will be described later. Further, the arithmetic unit 14 functions as a sludge property grasping means for grasping the properties of biological sludge based on the calculated sedimentation rate of biological sludge, etc., as will be described later.

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

[0022] <(1) Inflow process> The pump 20 is activated and the valve 22 is opened to allow a predetermined amount of water to be treated to flow from the wastewater supply pipe 18 into the reaction tank 16. Examples of water to be treated include wastewater containing organic matter, and specifically include organic wastewater containing biodegradable organic matter such as wastewater from food processing plants, chemical plants, semiconductor plants, machinery plants, sewage, and human waste.

[0023] <(2) Biological treatment process> After stopping the pump 20 and closing the valve 22, the aeration blower 30 is activated, and oxygen-containing gas such as air supplied from the aeration blower 30 is supplied to the reaction tank 16 through the aeration device 32. As a result, the water to be treated is biologically treated by biological sludge in the reaction tank 16. The biological reaction is not limited to an aerobic reaction; it is also possible to perform an anaerobic reaction by stirring without supplying air, etc., or a combination of aerobic and anaerobic reactions is possible. An anaerobic state refers to a state in which dissolved oxygen is not present, but oxygen derived from nitrite or nitrate is present. For example, as shown in Figure 2, a stirring device consisting of a motor 34, a stirring blade 36, a shaft connecting the motor 34 and the stirring blade 36, etc., can be installed in the reaction tank 16, and stirring can be performed by stopping the aeration blower 30 and using the stirring device. Note that the stirring device is not limited to the above configuration.

[0024] Furthermore, in the biological treatment process, it is desirable to detect the sludge concentration in the reaction tank 16 using a sludge concentration meter 12. The calculation unit 14 receives and stores the sludge concentration detected by the sludge concentration meter 12. The detection of sludge concentration by the sludge concentration meter 12 may be performed multiple times at predetermined time intervals. The calculation unit 14 may then, for example, calculate the average value from the multiple detected sludge concentrations and store that average sludge concentration.

[0025] <(3) Settlement Process> The aeration blower 30 is stopped, and the tank is left to stand for a predetermined time to allow the biological sludge in the reaction tank 16 to settle.

[0026] Furthermore, during the sedimentation process, the sludge concentration in the reaction tank 16 is detected by the sludge concentration meter 12. The calculation unit 14 then calculates the sedimentation rate of the biological sludge based on the change in sludge concentration detected by the sludge concentration meter 12. The specific calculation method is described below.

[0027] For example, at the start of the sedimentation process, the sludge concentration detected by the sludge concentration meter 12 is about the same as the sludge concentration during the biological treatment process. However, as the biological sludge begins to settle, it becomes concentrated, and the sludge concentration detected by the sludge concentration meter 12 increases. Furthermore, as the biological sludge settles, the sludge interface of the biological sludge falls below the position of the sludge concentration meter 12, causing the sludge concentration detected by the sludge concentration meter 12 to decrease rapidly. Therefore, the time from the start of the sedimentation process until the sludge concentration detected by the sludge concentration meter 12 decreases rapidly can be estimated as the time from the start of the sedimentation process until the sludge interface of the biological sludge falls below the position of the sludge concentration meter 12. Thus, the value obtained by dividing the distance from the water surface to the sludge concentration meter 12 by the above time can be estimated as the sedimentation velocity of the biological sludge. The calculation device 14 receives the sludge concentration in the reaction tank 16, which is sequentially detected by the sludge concentration meter 12, and measures the time it takes for the sludge concentration detected by the sludge concentration meter 12 to fall below a predetermined concentration. The predetermined concentration is preferably set to 1 / 4 of the sludge concentration initially detected by the sludge concentration meter 12, and more preferably to 1 / 10. The calculation device 14 then calculates the settling velocity of the biological sludge from the measured time and the predetermined distance from the water surface to the sludge concentration meter 12.

[0028] The calculation unit 14 may further determine the properties of the biological sludge based on the calculated settling velocity of the biological sludge (hereinafter sometimes referred to as the settling velocity of the biological sludge (A)) and the sludge concentration during the biological treatment process (the average sludge concentration may also be used). This will be explained in detail below.

[0029] The relationship between the settling rate of biological sludge in the settling process and the sludge concentration in the biological treatment process is expressed by the following exponential function. V = V0·e (-k·X) V: Settlement velocity of biological sludge in the settling process (m / h) X: Sludge concentration in the biological treatment process k,V0: Constant

[0030] Figure 3 shows the exponential function equation (V=V0·e (-k·X) The settling characteristic curves of granular sludge and activated sludge based on the following are shown. As shown in Figure 3, the settling velocity of granular sludge is faster than that of activated sludge containing a large amount of flocs, but it tends to slow down if the sludge concentration is high, similar to the settling velocity of activated sludge. Therefore, to understand the properties of biological sludge, it is preferable to consider not only the settling velocity but also the sludge concentration.

[0031] The calculation unit 14 stores information regarding the relationship between sludge concentration and sedimentation velocity related to the sedimentation characteristics of granular sludge (an exponential function representing the sedimentation characteristics of granular sludge). From the measured sludge concentration during the biological treatment process and the pre-stored sedimentation characteristics of granular sludge, the sedimentation velocity (A) is calculated to determine the properties of the granular sludge at the current sludge concentration.

[0032] The calculation unit 14 compares the calculated biological sludge settling velocity (Vm) with the range of the settling velocity (Vg) calculated from the settling characteristics and sludge concentration of the granular sludge to determine the properties of the biological sludge. Specifically, it compares the calculated biological sludge settling velocity (Vm) with the range of the biological sludge settling velocity (Vg) calculated to determine the granular properties. If (Vm) is greater than or equal to (Vg), it can be determined that the biological sludge has good settling properties and is granulated, and therefore the condition of the biological sludge is judged to be good. On the other hand, if Vm is less than Vg, it can be determined that the biological sludge has poor settling properties and is not sufficiently granulated, and therefore the condition of the biological sludge is judged to be poor.

[0033] By recording the relationship between (Vg) and (Vm) over time, it is possible to understand the trend of deterioration or improvement in sludge properties from the trend. If there is a deterioration trend, it is possible to adjust the operating conditions of the semi-batch treatment device to improve the sludge properties, and if there is an improvement trend, it is possible to determine that it is preferable to maintain the current operating conditions.

[0034] Furthermore, by pre-storing the sedimentation characteristics of the granular sludge according to its SVI in the calculation device 14, it is possible to output a predicted SVI value for the granular sludge from the measured Vm and calculated Vg. This eliminates the need to perform daily SVI measurements in operation management, contributing to reduced manpower in operation management.

[0035] In this embodiment, for example, when the sludge concentration is operating within a certain range, or when the calculated settling velocity (Vg) of the biological sludge is in a range that is not possible for normal activated sludge, the properties of the biological sludge may be determined based solely on the calculated settling velocity (Vm). Specifically, if the calculated settling velocity (Vm) of the biological sludge is above a predetermined value, the condition of the biological sludge is determined to be good, and if it is below the predetermined value, the condition of the biological sludge is determined to be poor.

[0036] <(4) Discharge process> Depending on the predetermined end time of the sedimentation process, the valve 28 is opened, and the supernatant water obtained in the sedimentation process is discharged from the reaction tank 16 to the treated water piping 26 as treated water.

[0037] The treatment process consists of four steps: (1) inflow, (2) biological treatment, (3) sedimentation, and (4) discharge. This process is repeated to treat the water to be treated.

[0038] In this embodiment, the inflow process and discharge process are not limited to separate processes; the discharge process may be performed simultaneously with the inflow process. That is, the treatment of the water to be treated may be carried out in a cycle consisting of (1) inflow / discharge process, (2) biological treatment process, and (3) sedimentation process, and this cycle may be repeated.

[0039] Taking the water treatment device 1 in Figure 1 as an example, the pump 20 is operated and valve 22 is opened to allow the water to be treated to flow from the wastewater supply pipe 18 into the reaction tank 16, while valve 28 is opened to discharge the treated water in the reaction tank 16 into the treated water pipe 26 ((1) Inflow process / Discharge process). After a predetermined time has elapsed, valves 22 and 28 are closed and the aeration blower 30 is operated, and oxygen-containing gas such as air supplied from the aeration blower 30 is supplied to the reaction tank 16 through the aeration device 32, and the water to be treated is biologically treated with biological sludge ((2) Biological treatment process). Next, the operation of the aeration blower 30 is stopped and the reaction tank 16 is left to stand for a predetermined time to allow the biological sludge in the reaction tank 16 to settle ((3) Settlement process). Detection of the sludge concentration in the reaction tank 16, calculation of the settling rate of the biological sludge, and understanding of the properties of the biological sludge are as described above.

[0040] Examples of conventionally known methods for detecting sludge concentration include transmitted light type, scattered light type, microwave type, and ultrasonic type. Furthermore, instruments correlated with sludge concentration, such as viscometers and turbidimeters, may be used as detectors for detecting sludge concentration in the reaction tank 16. That is, the sludge concentration in the reaction tank 16 may be estimated from the detected values ​​obtained from instruments correlated with sludge concentration, such as viscometers and turbidimeters.

[0041] Furthermore, in the water treatment apparatus 1 shown in Figure 1, a sludge concentration meter 12 is used as a detector (first detection means) for detecting the sludge concentration in the reaction tank 16 during the sedimentation process. However, a sludge interface meter that detects the position of the sludge interface in the reaction tank 16 during the sedimentation process may also be used. Examples of conventionally known sludge interface meters include ultrasonic, turbidity detection, and transmitted light types. The calculation device 14 calculates the sedimentation velocity (m / h) of the biological sludge from the position of the sludge interface in the reaction tank 16 detected by the sludge interface meter after a predetermined time has elapsed from the start of the sedimentation process.

[0042] According to this embodiment, the settling velocity of the biological sludge can be calculated while the water treatment device is in operation, and the properties of the biological sludge can be understood based on the calculation results. Therefore, it is possible to change the operating conditions of the water treatment device in accordance with changes in the properties of the biological sludge. For example, if the calculated settling velocity of the biological sludge indicates that the condition of the biological sludge is good, the volumetric load or sludge load of the reaction tank can be increased to improve the water treatment efficiency.

[0043] In this embodiment, if the condition of the biological sludge is determined to be good, it can be inferred that self-granulated biological sludge (so-called granular sludge) has been formed in the reaction tank 16. Granular sludge is, for example, sludge with an average particle size of 0.2 mm or more, or a settling index SVI5 of 80 mL / g or less. SVI is a settling index of biological sludge and is determined by the following method. First, 1 L of sludge is placed in a 1 L graduated cylinder, and after gently stirring to make the sludge concentration as uniform as possible, the sludge interface is measured after standing for 5 minutes. Then, the volume percentage (%) occupied by the sludge in the graduated cylinder is calculated. Next, the MLSS (mg / L) of the sludge is measured. These are then applied to the following formula to calculate SVI5. To calculate SVI30, the 5 minutes of standing time should be changed to 30 minutes. SVI5 (mL / g) = Volume percentage occupied by sludge × 10,000 / MLSS

[0044] The volumetric load of reaction vessel 16 is 0.15 kg BOD / m³. 3 / day ~1.00kgBOD / m 3 It is preferable that the range be within / day, and 0.30 kg BOD / m³ 3 / day ~0.60kgBOD / m 3 A range of / day is more preferable. By setting the volumetric load of the reaction vessel 16 within the above range, it becomes possible to form better granules.

[0045] The sludge load in the reaction tank 16 is preferably in the range of 0.05 kg BOD / kg MLSS / day to 0.30 kg BOD / kg MLSS / day, and more preferably in the range of 0.10 kg BOD / kg MLSS / day to 0.20 kg BOD / kg MLSS / day. By setting the sludge load in the reaction tank 16 within the above range, it becomes possible to form better granules.

[0046] The dissolved oxygen (DO) in the reaction tank 16 is preferably 0.5 mg / L or more, particularly preferably 1 mg / L or more under aerobic conditions.

[0047] In terms of promoting the granulation of biological sludge, Fe 2+ 、Fe 3+ 、Ca 2+ 、Mg 2+ etc., ions capable of forming hydroxides may be added to the treated water in the reaction tank 16 or the treated water before being introduced into the reaction tank 16. By adding the above ions, it becomes possible to promote the nucleation of granules.

Examples

[0048] Hereinafter, examples will be given to explain the present disclosure in more specific detail, but the present disclosure is not limited to the following examples.

[0049] A semi-batch treatment device having a reaction tank with an effective volume of 1.4 m 3 was used to conduct a water flow test. The wastewater used in the test was the primary-treated sewage by sedimentation treatment at a sewage treatment plant.

[0050] The operation cycle of the reaction tank was carried out as follows. (1) Inflow / discharge process: The wastewater was introduced into the reaction tank over 90 minutes, and at the same time, the supernatant was discharged as treated water. (2) Biological treatment process: Air was supplied from the aeration device installed at the bottom of the reaction tank for 460 minutes to perform biological treatment of the wastewater. (3) Sedimentation process: The supply of air from the aeration device was stopped, and the reaction tank was left standing for 8 minutes to sediment the biological sludge in the reaction tank. The above operating cycles (1) to (3) were repeated as one cycle.

[0051] <Calculation of the settling velocity of biological sludge> In Example 1, biological sludge with SVI5: 50 mL / g, SVI30: 37 mL / g, and average particle size: 650 μm was added to the reaction tank so that the MLSS in the reaction tank was 4000 mg / L, and the above operating cycle was performed. In Example 2, biological sludge with SVI5: 260 mL / g, SVI30: 120 mL / g, and average particle size: 180 μm was added to the reaction tank so that the MLSS in the reaction tank was 2500 mg / L, and the above operating cycle was performed. In both Examples 1 and 2, the sludge concentration in the reaction tank during the settling process was sequentially detected using a sludge concentration meter installed 1 m below the water surface in the reaction tank.

[0052] Figure 4 shows the changes in sludge concentration in the reaction tank during the sedimentation process in Examples 1 and 2. The horizontal axis of Figure 4 represents the elapsed time of the sedimentation process, and the vertical axis represents the sludge concentration in the reaction tank detected by a sludge concentration meter installed 1 m below the water surface of the reaction tank. In Example 1, the sludge concentration in the reaction tank gradually increased from the start of the sedimentation process, reaching 6350 mg / L 75 seconds after the start of the sedimentation process. Subsequently, the sludge concentration in the reaction tank decreased rapidly, falling to 800 mg / L 2 minutes after the start of the sedimentation process, which was less than 1 / 4 of the sludge concentration immediately after the start of the sedimentation process. The sludge concentration meter was located 1 m below the water surface of the reaction tank, and it took 2 minutes for the sludge concentration to decrease to 1 / 4 of the sludge concentration immediately after the start of the sedimentation process, so the sedimentation velocity of the biological sludge was calculated to be 30 m / hr. In Example 2, the sludge concentration in the reaction tank gradually increased from the start of the sedimentation process, then decreased sharply to 0 mg / L 10 minutes after the start of the sedimentation process. From this result, the sedimentation velocity of the biological sludge was calculated to be 6 m / hr. As mentioned above, if the sedimentation velocity of the biological sludge can be calculated, it is also possible to understand the properties of the biological sludge. [Explanation of Symbols]

[0053] 1 water treatment device, 10 semi-batch treatment devices, 12 sludge concentration meter, 14 calculation device, 16 reaction tank, 18 wastewater supply piping, 20 pump, 22, 28 valves, 26 treated water piping, 30 aeration blower, 32 aeration device, 34 motor, 36 stirring blade.

Claims

1. A semi-batch treatment process comprising: an inflow step of introducing water to be treated into a reaction tank; a biological treatment step of biologically treating the water to be treated in the reaction tank with biological sludge; a sedimentation step of allowing the biological sludge in the reaction tank to settle; and a discharge step of discharging the biologically treated water from the reaction tank. A first detection step for detecting the sludge interface position or sludge concentration in the reaction tank during the sedimentation process, A water treatment method characterized by comprising: a calculation step of calculating the sedimentation velocity of biological sludge based on the sludge interface position or sludge concentration detected in the first detection step.

2. The water treatment method according to claim 1, further comprising a sludge property determination step for determining the properties of the biological sludge based on the settling velocity of the biological sludge calculated by the calculation step.

3. The process includes a second detection step for detecting the sludge concentration in the reaction tank during the biological treatment process, The water treatment method according to claim 2, characterized in that the sludge properties determination step determines the properties of the biological sludge based on the sedimentation rate of the biological sludge and the sludge concentration detected in the second detection step.

4. A semi-batch processing apparatus having a reaction tank, which performs an inflow step of introducing water to be treated into the reaction tank, a biological treatment step of biologically treating the water to be treated in the reaction tank with biological sludge, a sedimentation step of allowing the biological sludge in the reaction tank to settle, and a discharge step of discharging the biologically treated water from the reaction tank, A first detection means for detecting the sludge interface position or sludge concentration in the reaction tank during the sedimentation process, A water treatment apparatus comprising: a calculation means for calculating the sedimentation velocity of biological sludge based on the sludge interface position or sludge concentration detected by the first detection means.

5. The water treatment apparatus according to claim 4, further comprising a sludge property determination means for determining the properties of the biological sludge based on the settling velocity of the biological sludge calculated by the calculation means.

6. The system includes a second detection means for detecting the sludge concentration in the reaction tank during the biological treatment process, The water treatment apparatus according to claim 5, characterized in that the sludge property determination means determines the properties of the biological sludge based on the settling velocity of the biological sludge and the sludge concentration detected by the second detection means.

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