Water treatment method and water treatment apparatus

Abstract

This invention provides a water treatment method that suppresses the growth of filamentous bacteria, forms granules with good settling properties, and furthermore, can obtain biologically treated water with good water quality. [Solution] A water treatment method in which an operating cycle is repeatedly performed in a semi-batch reaction tank, the cycle includes an inflow step of introducing water to be treated containing a substance to be treated; a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge while aerating and stirring the water to be treated with an aeration means; a sedimentation step of settling the microbial sludge; and a treated water discharge step of discharging the biologically treated water obtained in the biological treatment step, wherein the maximum flow velocity in the semi-batch reaction tank is set to 20 cm / s or more in the biological treatment step.

Description

Technical Field

[0001] The present disclosure relates to a water treatment method and a water treatment apparatus.

Background Art

[0002] Conventionally, for the biological wastewater treatment of organic wastewater containing organic substances and the like, the activated sludge method utilizing an aggregate of microorganisms called floc (aerobic activated sludge) has been used. However, in the activated sludge method, when separating the floc (aerobic activated sludge) and the treated water in the sedimentation tank, the sedimentation rate of the floc may be slow, and thus the surface area of the sedimentation tank may have to be made very large. In addition, the treatment rate of the activated sludge method depends on the sludge concentration in the biological treatment tank, and the treatment rate can be increased by increasing the sludge concentration. However, problems such as solid-liquid separation obstacles such as bulking in the sedimentation tank may occur, making it impossible to maintain the treatment.

[0003] On the other hand, in anaerobic biological treatment, it is common to utilize an aggregate in which microorganisms called granules are densely aggregated and granulated (anaerobic activated sludge). Granules have a very high sedimentation rate, and since the microorganisms are densely aggregated, the sludge concentration in the biological treatment tank can be increased, making it possible to achieve high-speed treatment of wastewater. However, anaerobic biological treatment may have problems such as the types of wastewater to be treated being limited compared to aerobic treatment (activated sludge method), and the need to maintain the treatment water temperature at about 30 to 35°C. In addition, when discharging the treated water into a river or the like, it may be necessary to separately perform aerobic treatment such as the activated sludge method because the quality of the treated water is poor in anaerobic biological treatment alone.

[0004] In recent years, it has become clear that by using a semi-batch treatment system that intermittently infuses wastewater into the 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 a semi-batch biological treatment system, it is common to repeatedly perform four steps in a single biological treatment tank: (1) inflow of wastewater, (2) biological treatment of wastewater with microbial sludge, (3) settling of the biological sludge, and (4) discharge of treated water.

[0005] Furthermore, Patent Document 5 discloses a method for generating aerobic biogranules using a high-concentration culture medium, which provides a surface upstream gas velocity exceeding 0.25 cm / s. [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] Special Publication No. 2005-517532 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, in semi-batch biological treatment, the settling ability of the granules may decrease. One of the reasons for this is the proliferation of filamentous bacteria in the reaction tank. For example, filamentous bacteria tend to proliferate when the concentration of the target substance in the water to be treated is low, or when they are present in large quantities in the seed sludge introduced into the reaction tank during the startup of the biological treatment. When filamentous bacteria proliferate around the granules, the granules cross-link with each other, reducing their settling ability. Generally, it is possible to suppress the proliferation of filamentous bacteria by increasing the amount of sludge discharged from the reaction tank, but doing so would significantly reduce the sludge concentration in the reaction tank, worsening the water quality of the biologically treated water obtained by the biological treatment.

[0008] Therefore, the purpose of this disclosure is to provide a water treatment method and a water treatment apparatus that can suppress the growth of filamentous bacteria, form granules with good settling properties, and further obtain biologically treated water with good water quality. [Means for solving the problem]

[0009] The present disclosure is a water treatment method that repeatedly performs an operating cycle in a semi-batch reaction tank, comprising: an inflow step of introducing water to be treated containing a substance to be treated; a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge while aerating and stirring the water to be treated with an aeration means; a sedimentation step of settling the microbial sludge; and a treated water discharge step of discharging the biologically treated water obtained in the biological treatment step, wherein the maximum flow velocity in the semi-batch reaction tank is set to 20 cm / s or more in the biological treatment step.

[0010] Furthermore, in the water treatment method of the present disclosure, it is preferable that the maximum flow velocity in the semi-batch reaction tank be 20 cm / s or more and 100 cm / s or less in the biological treatment step.

[0011] Furthermore, in the water treatment method of the present disclosure, it is preferable to set the average flow velocity in the semi-batch reaction tank to 10 cm / s or more in the biological treatment step.

[0012] Also, in the water treatment method of the present disclosure, it is preferable to perform the treated water discharge step while performing the inflow step.

[0013] The water treatment apparatus of the present disclosure includes an inflow step of introducing raw water containing a treatment target substance, a biological treatment step of biologically treating the treatment target substance in the raw water with microbial sludge while aerating and stirring the raw water by aeration means, a sedimentation step of sedimenting the microbial sludge, and a treated water discharge step of discharging the biologically treated water obtained by the biological treatment step. The water treatment apparatus is a semi-batch reaction tank that repeatedly performs an operation cycle including these steps, and in the biological treatment step, the maximum flow velocity in the semi-batch reaction tank is 20 cm / s or more.

Advantages of the Invention

[0014] According to the present disclosure, it is possible to provide a water treatment method and a water treatment apparatus that can suppress the growth of filamentous bacteria, form granules with good sedimentation properties, and further obtain biologically treated water with good water quality.

Brief Description of the Drawings

[0015] [Figure 1] It is a schematic configuration diagram showing an example of a water treatment apparatus according to an embodiment of the present disclosure. [Figure 2] It is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present disclosure. [Figure 3] It is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present disclosure.

Modes for Carrying Out the Invention

[0016] 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.

[0017] A schematic diagram of an example of a water treatment apparatus according to an embodiment of the present disclosure is shown in FIG. 1, and its configuration will be described. The water treatment apparatus 1 includes a semi-batch reaction tank 10. The semi-batch reaction tank 10 includes an aeration pump 14 and an aeration device 26 as aeration means. The aeration device 26 is connected to the aeration pump 14 and is installed at the lower part inside the semi-batch reaction tank 10. Further, the water treatment apparatus 1 includes a drainage supply pipe 28, a drainage inflow pump 12, and a drainage inflow valve 38. And the drainage supply pipe 28 is connected to a drainage inlet 40 at the lower part of the semi-batch reaction tank 10 via the drainage inflow pump 12 and the drainage inflow valve 38. Further, the water treatment apparatus 1 includes a biologically treated water pipe 30 and a biologically treated water discharge valve 18. And the biologically treated water pipe 30 is connected to a biologically treated water outlet 16 of the semi-batch reaction tank 10 via the biologically treated water discharge valve 18. Further, the water treatment apparatus 1 includes a sludge extraction pipe 32 and a sludge extraction pump 24. And the sludge extraction pipe 32 is connected to a sludge extraction port 22 at the lower part of the semi-batch reaction tank 10 via the sludge extraction pump 24.

[0018] The water treatment apparatus 1 includes a control device 20. The control device 20 is composed of, for example, a microcomputer and an electronic circuit including a CPU that calculates a program, a ROM and a RAM that store the program and the calculation result, reads out a predetermined program stored in the ROM, etc., and executes the program to control the operation of the water treatment apparatus 1. The control device 20 is electrically connected to each of the drainage inflow pump 12, the drainage inflow valve 38, the biologically treated water discharge valve 18, the sludge extraction pump 24, and the aeration pump 14, for example. And the control device 20 controls the operation / stop of each pump and the opening / closing of each valve during the operation of the water treatment apparatus 1.

[0019] In the water treatment apparatus 1, for example, the following operation cycle is performed.

[0020] (1) Inflow step: Open the drainage inflow valve 38 and operate the drainage inflow pump 12 to allow the water to be treated to flow into the semi-batch reaction tank 10 from the drainage inlet 40 through the drainage supply pipe 28.

[0021] The water to be treated includes, for example, wastewater from food processing plants, chemical plants, semiconductor plants, machinery plants, sewage, human waste, and river water. The water to be treated contains biodegradable substances. These substances include, for example, organic matter and nitrogen-containing substances, such as ammonia nitrogen and nitrate nitrogen. If the water contains organic matter that is difficult to decompose, it can be treated by first applying physicochemical treatments such as ozone treatment or Fenton treatment to convert it into biodegradable components. As for oil and grease, since they can adhere to microbial sludge and have adverse effects, it is preferable to remove them to a level of, for example, 150 mg / L or less using existing methods such as flotation separation, coagulation and pressurized flotation, or adsorption before introducing them into the semi-batch reaction tank 10.

[0022] (2) Biological treatment process: The wastewater inlet pump 12 is stopped and the aeration pump 14 is activated to supply oxygen-containing gas such as air to the semi-batch reaction tank 10 through the aeration device 26. As a result, in the semi-batch reaction tank 10, the water to be treated is aerated and stirred with oxygen-containing gas, and the substances to be treated in the water to be treated are biologically treated by microbial sludge. For example, if the water to be treated contains organic matter, the organic matter in the water to be treated is decomposed to carbon dioxide by the microbial sludge. Alternatively, as shown in Figure 2, for example, an agitator consisting of a motor 34, a stirring blade 36, and a shaft connecting the motor 34 and the stirring blade 36 may be installed in the semi-batch reaction tank 10. In the water treatment apparatus 1 shown in Figure 2, aeration and stirring by the aeration pump 14 and aeration device 26 may be used in combination with stirring by the agitator. The agitator is not limited to the above configuration.

[0023] In the biological treatment process, the maximum flow velocity in the semi-batch reaction tank 10 is set to 20 cm / s or more for biological treatment. The maximum flow velocity is adjusted by the aeration airflow rate from the aeration means. The maximum flow velocity in the semi-batch reaction tank 10 refers to the fastest flow velocity measured in the semi-batch reaction tank 10 during the biological treatment process. In the case of a full-surface aeration system, it is preferable to measure the flow velocity at at least two points, for example, at a predetermined horizontal distance (maximum 10 m) apart, at least two points within 100 mm from the water surface to the bottom of the semi-batch reaction tank and at least two points within 100 mm from the bottom towards the water surface. That is, it is preferable to measure the flow velocity at at least four points in total: two points within 100 mm from the water surface to the bottom at a predetermined horizontal distance apart, and two points within 100 mm from the bottom towards the water surface at a predetermined horizontal distance apart. If a full-surface aeration system is not used, in addition to the four points mentioned above, it is desirable to measure the flow velocity at least near the top of the aeration device 26.

[0024] (3) Settlement process: The aeration pump 14 and stirring device are stopped and left to stand for a predetermined time, allowing the microbial sludge in the semi-batch reaction tank 10 to settle. As a result, biologically treated supernatant water is obtained in the semi-batch reaction tank 10.

[0025] (4) Treated water discharge process: The biological treated water discharge valve 18 is opened and the supernatant water obtained in the sedimentation process is discharged as biological treated water from the biological treated water discharge port 16 into the biological treated water piping 30.

[0026] In this embodiment, the operation cycle including steps (1) to (4) is repeated. Additionally, a sludge discharge step may be performed to discharge the microbial sludge from the semi-batch reaction tank 10, if necessary. The sludge discharge step may be performed at any point during steps (1) to (4), or at any point between steps (1) to (4). Furthermore, the sludge discharge step may be performed after every cycle or every multiple cycles of the operation cycle.

[0027] The sludge discharge process involves operating the sludge extraction pump 24 to extract a predetermined amount of microbial sludge from the semi-batch reaction tank 10 through the sludge extraction piping 32. During the extraction of microbial sludge, it is preferable to operate the aeration pump 14 and the stirring device to agitate the microbial sludge.

[0028] The operation cycle of this embodiment is not limited to a configuration in which the inflow process and the treated water discharge process are performed separately, but may also be a configuration in which the treated water discharge process is performed while the inflow process is being carried out. A specific example will be given below.

[0029] Figure 3 shows a schematic of another example of a water treatment apparatus according to the embodiment of this disclosure, and its configuration will be described. In the water treatment apparatus 2 shown in Figure 3, the same reference numerals are used for components similar to those in the water treatment apparatus 1 shown in Figure 1. In the water treatment apparatus 2 shown in Figure 3, the biological treated water outlet 16 is located at the water level of the semi-batch reaction tank 10. The wastewater inlet 40 is preferably located at a lower position than the biological treated water outlet 16, for example, it is preferably located at a position lower than 50% of the water level of the semi-batch reaction tank 10. The water level of the semi-batch reaction tank 10 is the water level when the liquid in the semi-batch reaction tank 10 is in a stationary state during the sedimentation process.

[0030] In the water treatment apparatus 2 shown in Figure 3, for example, the following operating cycle is performed.

[0031] (1) Inflow process / Treated water discharge process: The wastewater inflow valve 38 is opened and the wastewater inflow pump 12 is activated, and the water to be treated flows into the semi-batch reaction tank 10 from the wastewater inlet 40 through the wastewater supply pipe 28. When the water to be treated flows in, the biological treated water discharge valve 18 is opened. As a result, the biological treated water (supernatant water) obtained in the sedimentation process is pushed out by the incoming water to be treated and discharged into the biological treated water pipe 30 from the biological treated water outlet 16.

[0032] (2) Biological treatment process: The wastewater inlet pump 12 is stopped and the aeration pump 14 is activated, supplying oxygen-containing gas such as air to the semi-batch reaction tank 10 through the aeration device 26. As a result, in the semi-batch reaction tank 10, the water to be treated is aerated and stirred by the oxygen-containing gas, and the substances to be treated in the water are biologically treated by microbial sludge. In addition, in the biological treatment process, the maximum flow velocity in the semi-batch reaction tank 10 is set to 20 cm / s or more to carry out the biological treatment.

[0033] (3) Settlement process: The aeration pump 14 is stopped (and if a stirring device is installed, the stirring device is also stopped), and the tank is left to stand for a predetermined time to allow the sludge in the semi-batch reaction tank 10 to settle. This yields biologically treated supernatant water.

[0034] In this embodiment, the operation cycle including steps (1) to (3) is repeated. In addition, as mentioned above, a sludge discharge step may be performed as needed.

[0035] By repeatedly performing the above operating cycle in this embodiment, self-granulating granules can be formed in the semi-batch reaction tank 10. In particular, in this embodiment, since the maximum flow rate in the semi-batch reaction tank 10 is set to 20 cm / s or more during the biological treatment process, the attachment and proliferation of filamentous bacteria around the granules is suppressed, and granules with good settling properties can be formed. Furthermore, since it is not necessary to discharge more sludge than necessary from the semi-batch reaction tank 10 in order to suppress the growth of filamentous bacteria, a certain amount of microbial sludge can be secured in the semi-batch reaction tank 10, so that biologically treated water with good water quality can be obtained.

[0036] The maximum flow rate in the semi-batch reaction vessel 10 should be 20 cm / s or more to suppress the growth of filamentous bacteria, but it is preferable to set the maximum flow rate between 20 cm / s and 100 cm / s. Note that if the maximum flow rate in the semi-batch reaction vessel 10 exceeds 100 cm / s, the granules may break down.

[0037] Furthermore, the average flow velocity in the semi-batch reaction tank 10 is preferably 10 cm / s or more, and the maximum flow velocity is preferably 20 cm / s or more and 100 cm / s or less. If the average flow velocity falls below 10 cm / sec, microbial sludge may accumulate locally in the semi-batch reaction tank 10, which may lead to the proliferation of filamentous bacteria and deterioration of treatment performance. The average flow velocity refers to the flow velocity obtained by averaging the results of flow velocity measurements taken at multiple locations (preferably at least four locations) during the aeration process in the semi-batch reaction tank 10.

[0038] The granules formed in the semi-batch reaction tank 10 are microbial sludge that has undergone self-granulation, and are, for example, microbial sludge with an average particle size of 0.2 mm or more, or with a sedimentation index SVI5 of 80 mL / g or less. In this embodiment, whether or not the microbial sludge in the semi-batch reaction tank 10 is granules is determined, for example, by measuring the SVI, which is a sedimentation index of microbial sludge. Specifically, if the value of SVI5 measured by a sedimentation test of the microbial sludge in the semi-batch reaction tank 10 is below a predetermined value (for example, 80 mL / g or less), it is possible to determine that the microbial sludge is granules. Alternatively, if the particle size distribution of the microbial sludge in the semi-batch reaction tank 10 is measured and the average particle size is above a predetermined value (for example, 0.2 mm or more), it is possible to determine that the microbial sludge is granules (note that the lower the SVI value and the larger the average particle size, the better the sedimentation of the granules).

[0039] The volumetric load of the semi-batch reaction vessel 10 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 semi-batch reaction vessel 10 within the above range, it becomes possible to promote granule formation.

[0040] The sludge load in the semi-batch reaction tank 10 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 semi-batch reaction tank 10 within the above range, it is possible to promote granule formation.

[0041] The dissolved oxygen (DO) in the semi-batch reaction vessel 10 is preferably 0.5 mg / L or more, and particularly preferably 1 mg / L or more, under aerobic conditions.

[0042] In this embodiment, it is preferable to use water to be treated in which the total BOD5 concentration is in the range of 50 to 250 mg / L.

[0043] In terms of promoting granule formation, Fe is added to the water to be treated in the semi-batch reactor 10 or to the water to be treated before it is introduced into the semi-batch reactor 10. 2+ Fe 3+ Ca 2+ Mg 2+ It is preferable to add ions that cause hydroxide formation, such as those mentioned above. While ordinary treated water contains fine particles that act as nuclei for granules, the addition of the above ions can further promote granule nucleation.

[0044] The inflow rate of treated water in the inflow / treated water discharge process is preferably in the range of 10% to 100%. The inflow rate of treated water is the ratio of the amount of treated water inflow to the effective volume in the semi-batch reaction tank 10. Here, in order to promote granule formation, it is better to have as high a inflow rate of treated water as possible, but on the other hand, the higher the inflow rate of treated water, the greater the concern about deterioration of the treated water due to short circuits of treated water. Therefore, considering these factors, it is more preferable to have a inflow rate of treated water in the range of 20% to 80%. However, if a treatment device such as an activated sludge tank is installed downstream of the semi-batch reaction tank 10, and the water quality of the final treated water after the downstream treatment device does not deteriorate, there is no particular restriction on the inflow rate of treated water, and it is possible to set it to, for example, more than 100%. When the inflow rate of treated water exceeds 100%, it is preferable to set the upper limit of the inflow rate of treated water to 200% or less in order to suppress a decrease in the number of operating cycles.

[0045] The linear velocity of the water to be treated in the inflow process / treated water discharge process (the amount of water to be treated relative to the cross-sectional area of ​​the semi-batch reaction tank 10) is preferably 5 m / h or less. If the linear velocity of the water to be treated exceeds 5 m / h, there is a concern that the treated water may deteriorate due to short circuits of the water to be treated, granule outflow, etc. There is no particular lower limit for the linear velocity of the water to be treated in the inflow process / treated water discharge process, but it is preferable to have a value of 0.5 m / h or more in terms of shortening the time of the inflow process / treated water discharge process.

[0046] In this embodiment, a predetermined amount of granulated microbial sludge may be added to the semi-batch reaction tank 10 at the start of operation. [Examples]

[0047] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0048] A water treatment test was conducted using a semi-batch reactor with an effective volume of 33 L (125 mm x 438 mm x effective water depth of 600 mm). A wastewater inlet was installed at the bottom of the semi-batch reactor, and a treated water outlet was installed at the water surface of the reactor. The treated water was artificial wastewater with a BOD concentration of 100-200 mg / L, mainly composed of bonito extract and peptone. The operating cycle of the semi-batch reactor consisted of a 51-minute inflow / treated water discharge cycle, a biological treatment cycle for a time until the sludge load reached 0.18 kg / (kg·d), and a sedimentation cycle of 25-30 minutes. At the start of operation, activated sludge collected from a sewage treatment plant was added to the semi-batch reactor as initial sludge.

[0049] The maximum flow velocity in the semi-batch reaction tank during the biological treatment process was set to 11.1 cm / s (average flow velocity of 9.6 cm / s), and a water treatment test was conducted for 113 days using the above operating cycle. Subsequently, the maximum flow velocity in the semi-batch reaction tank during the biological treatment process was set to 22.9 cm / s (average flow velocity of 11.7 cm / s), and a water treatment test was conducted for 10 days using the above operating cycle. The water treatment test from the start of the test to day 113 was designated as Comparative Example 1, and the water treatment test from the end of Comparative Example 1 to day 10 was designated as Example 1. After the tests of Comparative Example 1 and Example 1, microbial sludge was collected from the semi-batch reaction tank, and the average particle size, the settling index SVI30, and the amount of filamentous bacteria were measured. The flow velocity was measured at a total of 6 points: 3 points horizontally spaced at predetermined distances from the water surface to 100 mm from the bottom, and 3 points horizontally spaced at predetermined distances from the bottom to 100 mm from the water surface.

[0050] The average particle size of the sludge was measured using a particle size analyzer such as a laser diffraction type.

[0051] SVI30 was measured as follows: First, 1 liter of microbial sludge was placed in a 1 liter graduated cylinder and gently stirred to ensure the sludge concentration was as uniform as possible. After standing for 30 minutes, the sludge interface was measured. The volume percentage (%) of microbial sludge in the graduated cylinder was then calculated. Next, the MLSS (mg / L) of the microbial sludge was measured. These values ​​were then applied to the following formula to calculate SVI30. A smaller SVI30 value indicates sludge with higher settling properties. SVI30 (mL / g) = Volume percentage occupied by sludge × 10,000 / MLSS

[0052] The amount of filamentous bacteria was measured by microscopic observation.

[0053] Furthermore, the DOC (dissolved organic carbon) removal rate, ammonia nitrogen removal rate, and DN (dissolved nitrogen) removal rate were measured for Comparative Example 1 and Example 1. The DOC and DN removal rates were measured using a TOC-TN meter after filtering the samples. The ammonia nitrogen removal rate was measured in accordance with JIS K0102 42.

[0054] The maximum flow velocity in the semi-batch reaction tank during the biological treatment process was set to 15.4 cm / s (average flow velocity of 9.9 cm / s), and a water treatment test was conducted for 30 days using the above operating cycle. Then, the maximum flow velocity in the semi-batch reaction tank during the biological treatment process was set to 42.1 cm / s (average flow velocity of 13.9 cm / s), and a water treatment test was conducted for 15 days using the above operating cycle. The water treatment test from the start of the test to day 30 was designated as Comparative Example 2, and the water treatment test from the end of Comparative Example 2 to day 15 was designated as Example 2. After the tests of Comparative Example 2 and Example 2, microbial sludge was collected from the semi-batch reaction tank, and the average particle size, the settling index SVI30, and the amount of filamentous bacteria were measured. In addition, the DOC removal rate, ammonia nitrogen removal rate, and DN removal rate were measured for Comparative Example 2 and Example 2.

[0055] Table 1 summarizes the measurement results for the average particle size, sedimentation index (SVI30), and amount of filamentous bacteria in comparative examples 1-2 and examples 1-2. In Table 1, particle size of 212 μm or larger is marked with ○, and smaller than 212 μm is marked with ×. For sedimentation, an SVI30 of 150 mL / g or less is marked with ○, and higher than 150 mL / g is marked with ×. For the amount of filamentous bacteria, when observing the sludge under a microscope at 100x magnification with a radius of 4 mm, if filamentous bacteria were observed in one sludge, 20 or more was marked with high, and fewer than 20 was marked with low.

[0056] [Table 1]

[0057] Table 2 summarizes the measurement results for DOC removal rate, ammonia nitrogen removal rate, and DN removal rate in Comparative Examples 1-2 and Examples 1-2.

[0058] [Table 2]

[0059] In the biological treatment process, Examples 1 and 2, in which the maximum flow rate in the semi-batch reaction vessel was set to 20 cm / s or higher, showed a reduction in the amount of filamentous bacteria and a decrease in the SVI30 value compared to Comparative Examples 1 and 2, in which the maximum flow rate in the semi-batch reaction vessel was set to less than 20 cm / s. Furthermore, Examples 1 and 2 showed the same DOC removal rate, ammonia nitrogen removal rate, and DN removal rate as Comparative Examples 1 and 2. Therefore, it can be said that by setting the maximum flow rate in the semi-batch reaction vessel to 20 cm / s or higher, the growth of filamentous bacteria is suppressed, granules with good settling properties are formed, and biologically treated water with good treated water quality can be obtained. [Explanation of Symbols]

[0060] 1,2 Water treatment equipment, 10 Semi-batch reaction tank, 12 Wastewater inlet pump, 14 Aeration pump, 16 Biologically treated water outlet, 18 Biologically treated water discharge valve, 20 Control device, 22 Sludge extraction port, 24 Sludge extraction pump, 26 Aeration device, 28 Wastewater supply piping, 30 Biologically treated water piping, 32 Sludge extraction piping, 34 Motor, 36 Agitator, 38 Wastewater inlet valve, 40 Wastewater inlet.

Claims

1. A water treatment method that involves repeatedly performing an operating cycle in a semi-batch reaction tank, the cycle comprising: an inflow step of introducing water to be treated containing the substance to be treated; a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge while aerating and stirring the water to be treated with an aeration means; a sedimentation step of allowing the microbial sludge to settle; and a treated water discharge step of discharging the biologically treated water obtained from the biological treatment step, the method being performed The water treatment method is characterized in that, in the biological treatment step, the maximum flow velocity in the semi-batch reaction tank is set to 20 cm / s or more.

2. The water treatment method according to claim 1, characterized in that the maximum flow rate in the semi-batch reaction tank is set to 20 cm / s or more and 100 cm / s or less in the biological treatment step.

3. The water treatment method according to claim 1 or 2, characterized in that the average flow rate in the semi-batch reaction tank is 10 cm / s or more in the biological treatment step.

4. The water treatment method according to any one of claims 1 to 3, characterized in that the treated water discharge step is performed while the inflow step is performed.

5. A water treatment apparatus comprising a semi-batch reaction tank that repeatedly performs an operating cycle including an inflow step of introducing water to be treated containing a substance to be treated, a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge while aerating and stirring the water to be treated with an aeration means, a settling step of settling the microbial sludge, and a treated water discharge step of discharging the biologically treated water obtained from the biological treatment step, The water treatment apparatus is characterized in that, in the biological treatment step, the maximum flow velocity in the semi-batch reaction tank is 20 cm / s or more.

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