Method for forming granules and apparatus for forming granules

Abstract

This invention provides a granule formation method using a semi-batch reaction vessel that can form good quality granules even when the BOD concentration of organic matter-containing wastewater fluctuates. [Solution] The method for forming granules according to the present disclosure is a method for forming granules using a semi-batch reaction tank 10, which comprises an inflow step of introducing organic matter-containing wastewater, a biological treatment step of biologically treating the target substance in the organic matter-containing wastewater with microbial sludge under aerobic conditions, a sedimentation step of settling the microbial sludge, and a discharge step of discharging the biologically treated water, wherein in the biological treatment step, the dissolved oxygen concentration in the semi-batch reaction tank 10 is monitored, and the time of the biological treatment step is adjusted based on the information regarding the monitored dissolved oxygen concentration.

Description

[Technical Field]

[0001] This disclosure relates to a method for forming granules and a granule forming apparatus for stably forming granules. [Background technology]

[0002] Traditionally, the activated sludge method, which utilizes microbial aggregates called flocs (aerobic biological sludge), has been used for the biological treatment of organic matter-containing wastewater. 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 the treatment rate can be increased by increasing the sludge concentration, increasing the sludge concentration to the range of 1500-5000 mg / L or higher can make solid-liquid separation difficult due to bulking in the sedimentation tank, potentially making it impossible to maintain treatment.

[0003] On the other hand, anaerobic biological treatment typically utilizes granules, which are granular aggregates of microorganisms. These 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 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 implement aerobic treatment such as the activated sludge method separately.

[0004] In recent years, it has become clear that by using a semi-batch treatment system that intermittently infuses wastewater into the reaction tank, and by further shortening the sedimentation time of the biological sludge, it is possible to form granulated biological sludge with good settling properties not only for anaerobic biological sludge but also for aerobic biological sludge (see, for example, Patent Documents 1-4). By granulating the aerobic biological sludge, it is possible to achieve an average particle size of 0.2 mm or more and a sedimentation velocity of 5 m / h or more. In a semi-batch treatment system, treatment is carried out in a single biological treatment tank through the following steps: (1) inflow of wastewater, (2) biological treatment of the target substance, (3) sedimentation of the biological sludge, and (4) discharge of treated water. By forming granulated aerobic biological sludge with good settling properties as described above, it becomes possible to maintain a high sludge concentration in the tank, enabling high-speed treatment. [Prior art documents] [Patent Documents]

[0005] [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 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in granule formation methods using semi-batch reactors, if the BOD concentration of the wastewater introduced into the semi-batch reactor fluctuates over time or over time, it may become difficult to stably form highly sedimentable granule sludge.

[0007] The purpose of this disclosure is to provide a granule formation method and a granule formation apparatus that can form good granules even when the BOD concentration of organic matter-containing wastewater fluctuates, in a granule formation method using a semi-batch reaction vessel. [Means for solving the problem]

[0008] The method for forming granules according to the present disclosure is a method for forming granules using a semi-batch reactor, comprising an inflow step of introducing organic matter-containing wastewater, a biological treatment step of biologically treating the target substances in the organic matter-containing wastewater with microbial sludge under aerobic conditions, a sedimentation step of settling the microbial sludge, and a discharge step of discharging the biologically treated water, wherein the biological treatment step is characterized by monitoring the dissolved oxygen concentration in the semi-batch reactor and adjusting the time of the biological treatment step based on the information regarding the monitored dissolved oxygen concentration.

[0009] Furthermore, in the method for forming the granules, it is preferable to monitor the dissolved oxygen concentration in the semi-batch reaction vessel during the biological treatment step and adjust the duration of the biological treatment step based on the time from the start of the biological treatment step until the dissolved oxygen concentration rises to or above a predetermined value.

[0010] Furthermore, in the method for forming the granules, the duration of the biological treatment step is preferably in the range of 1 to 5 times the time from the start of the biological treatment step until the dissolved oxygen concentration rises to or above a predetermined value.

[0011] In addition, the granule forming apparatus of the present disclosure includes an inflow step of introducing organic matter-containing wastewater, a biological treatment step of biologically treating a target substance to be treated in the organic matter-containing wastewater with microbial sludge under aerobic conditions, a sedimentation step of sedimenting the microbial sludge, and a discharging step of discharging the biologically treated biological treatment water to form granules, a semi-batch reactor; and a control unit that monitors the dissolved oxygen concentration in the semi-batch reactor and adjusts the time of the biological treatment step based on information regarding the monitored dissolved oxygen concentration.

Advantages of the Invention

[0012] According to the present disclosure, in a granule formation method using a semi-batch reactor, it is possible to provide a granule formation method and a granule formation apparatus capable of forming good granules even when the BOD concentration of organic matter-containing wastewater fluctuates.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic configuration diagram showing an example of the granule forming apparatus according to the present embodiment. [Figure 2] It is a schematic configuration diagram showing another example of the granule forming apparatus according to the present embodiment. [Figure 3] It is a diagram showing an example of the transition of the dissolved oxygen concentration in the semi-batch reactor during the biological treatment step. [Figure 4] It is a schematic configuration diagram showing another example of the granule forming apparatus according to the present embodiment.

Embodiments for Carrying Out the Invention

[0014] 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.

[0015] <Granule Formation Method and Formation Apparatus> An example schematic of the granule forming apparatus according to this embodiment embodiment is shown in Fig. 1, and its configuration will be described. The granule forming apparatus 1 includes a semi-batch reaction tank 10. In the granule forming apparatus 1, a drainage supply pipe 22 is connected to the drainage inlet of the semi-batch reaction tank 10 via a drainage inflow pump 12. A biological treatment water pipe 24 is connected to the biological treatment water discharge port 16 of the semi-batch reaction tank 10 via a biological treatment water discharge valve 18. At the lower part inside the semi-batch reaction tank 10, an aeration device 26 connected to an aeration pump 14 is installed. A DO meter 40 is installed in the semi-batch reaction tank 10. The DO meter 40 measures the dissolved oxygen concentration contained in the organic matter-containing drainage in the semi-batch reaction tank 10.

[0016] The control device 20 is composed of, for example, a microcomputer and electronic circuits including a CPU that calculates programs, a ROM and a RAM that store programs and calculation results. It reads a predetermined program stored in the ROM or the like and executes the program to control the operation of the granule forming apparatus 1. The control device 20 and the DO meter 40 are, for example, electrically connected, and the control device 20 monitors the dissolved oxygen concentration in the semi-batch reaction tank 10 measured by the DO meter 40. Also, the control device 20 and the drainage inflow pump 12, the control device 20 and the biological treatment water discharge valve 18, and the control device 20 and the aeration pump 14 are, for example, electrically connected, and the control device 20 controls the operation / stop of the drainage inflow pump 12 and the aeration pump 14, the opening and closing of the biological treatment water discharge valve 18, etc.

[0017] The granule forming apparatus 1 is operated, for example, in the following cycle.

[0018] <(1) Inflow process> The drainage inflow pump 12 operates, and a predetermined amount of organic matter-containing drainage flows into the semi-batch reaction tank 10 through the drainage supply pipe 22.

[0019] <(2) Biological treatment process> As the wastewater inlet pump 12 stops, oxygen-containing gas such as air is supplied to the semi-batch reaction tank 10 from the aeration pump 14, and under aerobic conditions, the substances to be treated in the organic wastewater are biologically treated by microbial sludge in the semi-batch reaction tank 10. The biological treatment process may combine the above aerobic reaction with an anaerobic reaction in which stirring is performed in an oxygen-free state without supplying air or other gases. An anaerobic state means that 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 28, a stirring blade 30, and a shaft connecting the motor 28 and the stirring blade 30 is installed in the semi-batch reaction tank 10. When performing an anaerobic reaction, stirring is performed by the stirring device with the aeration pump 14 stopped, and when performing an aerobic reaction, the aeration pump 14 is operated (the stirring device is also operated as needed). Note that the stirring device is not limited to the above configuration.

[0020] In the biological treatment process, the dissolved oxygen concentration in the semi-batch reaction vessel 10 is measured by the DO meter 40. The control device 20 also monitors the dissolved oxygen concentration in the semi-batch reaction vessel 10, as measured by the DO meter 40, at predetermined intervals or continuously, and adjusts the biological treatment process time as described later. When the adjusted biological treatment process time is reached, for example, the control device 20 stops the aeration pump 14 (in the granule forming apparatus 1 shown in Figure 2, the stirring device is also stopped).

[0021] <(3) Settlement Process> After the aeration pump 14 is stopped, the sludge in the semi-batch reaction tank 10 is allowed to settle by leaving it undisturbed for a predetermined period of time.

[0022] <(4) Discharge process> By opening the biologically treated water discharge valve 18, the supernatant water obtained in the sedimentation process is discharged as biologically treated water from the biologically treated water outlet 16 through the biologically treated water piping 24. In this case, a pump may be used to discharge the biologically treated water instead of the biologically treated water discharge valve.

[0023] By repeating the above cycle (1) to (4), granules are formed, which are aggregates of microorganisms that have densely gathered together into granular structures. The operation and stopping of the wastewater inlet pump 12, the aeration pump 14, and the motor 28 of the stirring device, as well as the opening and closing of the biologically treated water discharge valve 18, may be controlled by the control device 20 or by an operator.

[0024] The granules formed in the semi-batch reactor 10 are sludge that has undergone self-granulation, and are, for example, biological sludge with an average particle size of 0.2 mm or more, or a sedimentation index SVI5 of 80 mL / g or less. In this embodiment, whether or not granules have been formed is determined, for example, by measuring the SVI, a sedimentation index of sludge. Specifically, the SV is measured periodically by a sedimentation test of the sludge in the semi-batch reactor 10, and it is possible to determine that granules have been formed when the SVI5 value calculated from the volume percentage after 5 minutes of sedimentation falls below a predetermined value (for example, 80 mL / g or less). Alternatively, the particle size distribution of the sludge in the semi-batch reactor 10 is measured, and it is possible to determine that granules have been formed when the average particle size is above a predetermined value (for example, 0.2 mm or more) (note that the lower the SVI value and the larger the average particle size, the better the granules are judged to be).

[0025] <Time adjustment for biological processing> For granular sludge formation in a semi-batch reactor, it is important to repeat the organic matter concentration gradient within the reactor during one cycle. This requires periods of high BOD concentration (saturation time) and periods of near-zero BOD concentration (starvation time). Therefore, it is desirable to set the biological treatment process time so that appropriate saturation and starvation times are ensured. However, since the biological treatment process time is generally fixed at the initial setting, fluctuations in the BOD concentration of organic matter-containing wastewater can occur. For example, if the saturation time is long, it may become impossible to ensure sufficient starvation time, and if the saturation time is short, the starvation time may become very long, making it difficult to form good granules. From the perspective of forming good granules, it is conceivable to monitor the BOD concentration of organic matter-containing wastewater fed into the reactor and adjust the biological treatment process time accordingly. However, since measuring BOD concentration is generally time-consuming, using BOD concentration to adjust the biological treatment process time is not practical. In this embodiment, by monitoring the dissolved oxygen concentration in the semi-batch reaction vessel and adjusting the timing of the biological treatment process, it is possible to appropriately ensure both the satiety and starvation periods, even if the BOD concentration of the organic matter-containing wastewater fluctuates, thereby enabling the formation of good granules.

[0026] Figure 3 shows an example of the change in dissolved oxygen concentration in the semi-batch reactor during the biological treatment process. As shown in Figure 3, in the initial stages of the biological treatment process, the dissolved oxygen concentration in the semi-batch reactor 10 is maintained at a low level. This is thought to be because, as the organic matter in the organic matter-containing wastewater is decomposed by the microbial sludge, the dissolved oxygen in the organic matter-containing water is consumed by the microbial sludge. Then, as the biological treatment process progresses and reaches a certain point, the dissolved oxygen concentration in the semi-batch reactor 10 rises sharply. This is thought to be because, as the decomposition of organic matter by the microbial sludge progresses and the amount of organic matter in the organic matter-containing wastewater decreases, the dissolved oxygen in the organic matter-containing wastewater that was consumed by the microbial sludge is no longer consumed by the microbial sludge. In other words, it is thought that the oxygen supplied by the aeration device 26 remains in the organic matter-containing water, and the rate of consumption by the microbial sludge becomes very slow. Therefore, the time from the start of the biological treatment process until the dissolved oxygen concentration rises sharply corresponds to the time when the BOD concentration in the reaction vessel is high (saturation time), and the time from the point when the dissolved oxygen concentration rises sharply onward corresponds to the time when the BOD concentration is almost zero (starvation time).

[0027] In this embodiment, for example, the control device 20 monitors the dissolved oxygen concentration in the semi-batch reaction vessel 10, measured by the DO meter 40, at predetermined intervals, and the time of the biological treatment process is adjusted based on the monitored information regarding the dissolved oxygen concentration.

[0028] The above-mentioned information regarding dissolved oxygen concentration includes, for example, the time from the start of the biological treatment process until the dissolved oxygen concentration measured by the DO meter 40 rises to a predetermined value or higher. For example, the control device 20 is pre-programmed to store the ratio of the biological treatment process time to the time from the start of the biological treatment process until the dissolved oxygen concentration measured by the DO meter 40 rises to a predetermined value or higher. The control device 20 then monitors the dissolved oxygen concentration measured by the DO meter 40 to measure the time from the start of the biological treatment process until the dissolved oxygen concentration measured by the DO meter 40 rises to a predetermined value or higher, and sets the biological treatment process time based on the above ratio. By operating the aeration device 26 from the start of the biological treatment process until the set time, the biological treatment process is carried out, and even if the BOD concentration of the organic matter-containing wastewater introduced into the semi-batch reaction tank 10 fluctuates and the satiety time increases or decreases, an appropriate starvation time can be ensured, making it possible to form good granules. From the viewpoint of good granule formation, the duration of the biological treatment process is preferably in the range of 1 to 5 times the time from the start of the biological treatment process until the dissolved oxygen concentration measured by the DO meter 40 rises to or above a predetermined value.

[0029] Furthermore, the information regarding the dissolved oxygen concentration may also be, for example, the time from the start of the biological treatment process until the rate of increase in the dissolved oxygen concentration exceeds a predetermined value. The rate of increase in dissolved oxygen concentration refers to the increase in dissolved oxygen concentration per minute time. For example, the rate of increase in dissolved oxygen concentration at time t shown in Figure 3 theoretically corresponds to the slope of the tangent to the dissolved oxygen concentration curve L at time t, but it may also be a value that approximates the slope of the tangent. The specific manner in which the rate of increase in dissolved oxygen concentration is calculated is not particularly limited, but for example, the control device 20 refers to the history of dissolved oxygen concentration measured by the DO meter 40 to obtain the dissolved oxygen concentration DO1 at the time of calculation and the dissolved oxygen concentration DO2 from a predetermined time before the time of calculation. If the predetermined time is Δt, the rate of increase in dissolved oxygen concentration R is calculated by the following equation (1). R=(DO1-DO2) / Δt (1)

[0030] The control device 20 stores, for example, the ratio of the biological treatment process time to the time from the start of the biological treatment process until the rate of increase of dissolved oxygen concentration exceeds a predetermined value. The control device 20 then monitors the dissolved oxygen concentration measured by the DO meter 40 and, as described above, calculates the rate of increase of dissolved oxygen concentration as it increases, while measuring the time from the start of the biological treatment process until the rate of increase of dissolved oxygen concentration exceeds a predetermined value, and sets the biological treatment process time from the above ratio. By operating the aeration device 26 and performing the biological treatment process from the start of the biological treatment process until the set time, even if the BOD concentration of the organic matter-containing wastewater introduced into the semi-batch reaction tank 10 fluctuates and the satiety time increases or decreases, an appropriate starvation time can be ensured, making it possible to form good granules. From the viewpoint of good granule formation, it is preferable that the biological treatment process time be in the range of 1 to 5 times the time from the start of the biological treatment process until the rate of increase of dissolved oxygen concentration exceeds a predetermined value.

[0031] Furthermore, the information regarding the dissolved oxygen concentration may also be, for example, the time from the start of the biological treatment process until the inflection point of the dissolved oxygen concentration is reached. The inflection point of the dissolved oxygen concentration is the peak point where the sign of the slope changes in the differential curve obtained by differentiating the time-series change of the dissolved oxygen concentration measured by the DO meter 40.

[0032] The control device 20 stores, for example, the ratio of the time from the start of the biological treatment process to the time it takes to reach the inflection point of the dissolved oxygen concentration / the biological treatment process time. The control device 20 then monitors the dissolved oxygen concentration measured by the DO meter 40, performs the aforementioned time derivative, measures the time from the start of the biological treatment process to the time it takes to reach the inflection point of the dissolved oxygen concentration, and sets the biological treatment process time from the above ratio. By operating the aeration device 26 from the start of the biological treatment process until the set time, the biological treatment process is carried out, and even if the BOD concentration of the organic matter-containing wastewater introduced into the semi-batch reaction tank 10 fluctuates and the satiety time increases or decreases, an appropriate starvation time can be ensured, making it possible to form good granules. From the viewpoint of good granule formation, it is preferable that the time of the biological treatment process be in the range of 1 to 5 times the time from the start of the biological treatment process to the time it takes to reach the inflection point of the dissolved oxygen concentration.

[0033] 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 form better granules.

[0034] 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 becomes possible to form better granules.

[0035] In order to promote the granulation of biological sludge, Fe is added to the organic matter-containing wastewater in the semi-batch reactor 10 or to the organic matter-containing wastewater before it is introduced into the semi-batch reactor 10. 2+ Fe 3+ Ca 2+ Mg2+ It is preferable to add ions that cause hydroxide formation, such as those mentioned above. Ordinary organic wastewater contains fine particles that act as nuclei for granules, but the addition of the above ions makes it possible to further promote granule nucleation.

[0036] The organic wastewater treated by the granule formation method according to this embodiment includes organic wastewater containing biodegradable organic matter, such as wastewater from food processing plants, chemical plants, semiconductor plants, machinery plants, sewage, and human waste. Furthermore, if the wastewater contains organic matter that is difficult to decompose, it can be treated by first applying physicochemical treatment such as ozone treatment or Fenton treatment to convert it into biodegradable components. In addition, although the granule formation method according to this embodiment targets various BOD components, oil and grease may adhere to sludge and granules and have adverse effects, so it is preferable to remove them to about 150 mg / L or less before introducing them into the semi-batch reaction tank 10 using existing methods such as flotation separation, coagulation and pressurized flotation, or adsorption.

[0037] Another example of a granule forming apparatus according to this embodiment is shown in Figure 4. In the granule forming apparatus 1 of Figure 4, the wastewater supply pipe 22 is connected to the wastewater inlet 34 at the bottom of the semi-batch reaction tank 10 via the wastewater inlet pump 12 and the wastewater inlet valve 32. A wastewater discharge section 36 is connected to the wastewater inlet 34 and is installed in the lower part of the inside of the semi-batch reaction tank 10. The biological treated water outlet 16 of the semi-batch reaction tank 10 is provided above the wastewater inlet 34, and the biological treated water pipe 24 is connected to the biological treated water outlet 16 via the biological treated water discharge valve 18. The biological treated water outlet 16, which is provided above the wastewater inlet 34, is preferably provided as far away from the wastewater inlet 34 as possible in order to prevent short circuits of the incoming organic matter-containing wastewater and to form granules more efficiently, and it is more preferably provided at the water level during the settling process. The wastewater inlet pump 12, wastewater inlet valve 32, biological treatment water discharge valve 18, aeration pump 14, agitator motor 28, and DO meter 40 are each electrically connected to the control device 20, for example. The rest of the configuration is the same as that of the granule forming apparatus 1 in Figure 2.

[0038] In the granule forming apparatus 1 shown in Figure 4, it is desirable to perform both an inflow process and a discharge process. Specifically, by opening the wastewater inflow valve 32 and the biologically treated water discharge valve 18 and operating the wastewater inflow pump 12, organic matter-containing wastewater is allowed to flow from the wastewater inlet 34 through the wastewater discharge section 36 into the semi-batch reaction tank 10, and the biologically treated water in the semi-batch reaction tank 10 is discharged from the biologically treated water outlet 16 through the biologically treated water piping 24. The operation and stopping of the wastewater inflow pump 12, the aeration pump 14, and the motor 28 of the stirring device, as well as the opening and closing of the wastewater inflow valve 32 and the biologically treated water discharge valve 18, may be controlled by the control device 20 or by an operator.

[0039] As described above, in the granule forming apparatus 1 shown in Figure 4, granules are formed by repeating the following steps: (1) inflow / outflow process, (2) biological treatment process, and (3) sedimentation process. The time for the (2) biological treatment process is adjusted based on the dissolved oxygen concentration in the semi-batch reaction vessel 10, which is measured by the DO meter 40, at predetermined intervals, as described above.

[0040] In the granule forming apparatus 1 shown in Figure 4, organic matter-containing wastewater is introduced into the semi-batch reaction tank 10, and the biologically treated water is discharged from the biologically treated water outlet 16. As a result, granules with relatively small particle sizes are discharged together with the biologically treated water, and steps (1) to (3) are repeated for granules with relatively large particle sizes. Consequently, granules can be formed more efficiently. [Examples]

[0041] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0042] The following tests were conducted using a semi-batch reactor with an effective reaction volume of 33 L. The biological treatment water outlet of the semi-batch reactor is located at the water surface level during the sedimentation process.

[0043] Sewage was used for the water flow test. The BOD concentration of the sewage ranged from 70 to 180 mg / L. The BOD concentration was measured in accordance with JIS K 0102 21.

[0044] [Examples] The operating cycle of the semi-batch reactor was carried out as follows. Prior to operation, activated sludge collected from a sewage treatment plant was added to the semi-batch reactor as seed sludge. (1) Inflow / Outflow Process: Wastewater was allowed to flow into the semi-batch reaction tank over a period of 30 minutes, and the biologically treated water was discharged from the biologically treated water outlet (equipped with an electrically operated valve that opens simultaneously with the start of wastewater inflow) (see Figure 4). (2) Biological treatment process: The inflow of wastewater was stopped, and at the same time, the valve for discharging biologically treated water was closed. Air was supplied from the aeration device installed at the bottom of the reaction tank. The dissolved oxygen concentration in the reaction tank was monitored every minute, and the time when the dissolved oxygen concentration reached 2 mg / L or more was measured. The operation was carried out with the time from the start of the biological treatment process (the start time of air supply) to the above-mentioned time multiplied by 2 as the time of the biological treatment process. After the elapse of this time, the process shifted to the following sedimentation process. (3) Sedimentation process: The supply of air from the aeration device was stopped, and the mixture was allowed to stand for 15 minutes to sediment the sludge in the reaction tank. The operations in (1) to (3) above were repeated while conducting continuous operation for 30 days.

[0045] [Comparative Example] The operation cycle of the semi-batch reaction tank was carried out as follows. Before operation, the activated sludge collected from the sewage treatment plant was used as seed sludge and introduced into the semi-batch reaction tank. (1) Inflow / discharge process: The wastewater was allowed to flow into the semi-batch reaction tank over 30 minutes, and at the same time, the biologically treated water was discharged from the biologically treated water outlet (an electric valve that opens simultaneously with the start of wastewater inflow) (see Figure 4). (2) Biological treatment process: The inflow of wastewater was stopped, and at the same time, the valve for discharging biologically treated water was closed. Air was supplied from the aeration device installed at the bottom of the reaction tank. Regardless of the variation in the BOD concentration of the wastewater (70 - 180 mg / L), the operation was carried out with the time of the biological treatment process fixed at 240 minutes. After 240 minutes, the process shifted to the following sedimentation process. (3) Sedimentation process: The supply of air from the aeration device was stopped, and the mixture was allowed to stand for 15 minutes to sediment the sludge in the reaction tank. The operations in (1) to (3) above were repeated while conducting continuous operation for 30 days.

[0046] In both the example and the comparative example, the formation of granules was evaluated by measuring the SVI of the biological sludge in the semi-batch reaction tank. Note that SVI 30 was measured. 30SVI is an index of the settling properties of biological sludge and is determined by the following method. First, 1 liter of sludge is placed in a 1 liter graduated cylinder, and after gently stirring to make the sludge concentration as uniform as possible, the sludge interface is measured after standing for 30 minutes. Then, the volume percentage (%) of sludge in the graduated cylinder is calculated. Next, the MLSS (mg / L) of the sludge is measured. These values ​​are then applied to the following formula to obtain SVI. 30 Calculate the SVI. 30 A smaller value indicates that the sludge has a higher settling tendency. SVI 30 (mL / g) = Volume percentage occupied by sludge × 10,000 / MLSS

[0047] Table 1 shows the SVI of the examples and comparative examples. 30 The results were summarized.

[0048] [Table 1]

[0049] Both the examples and comparative examples are SVI. 30 A decrease was observed, but the values ​​were lower in the example. In other words, the sludge settling properties were improved in the example, and better granules were formed. [Explanation of Symbols]

[0050] 1 Granule forming apparatus, 10 Semi-batch reaction vessel, 12 Wastewater inlet pump, 14 Aeration pump, 16 Biologically treated water outlet, 18 Biologically treated water discharge valve, 20 Control device, 22 Wastewater supply piping, 24 Biologically treated water piping, 26 Aeration device, 28 Motor, 30 Stirring blade, 32 Wastewater inlet valve, 34 Wastewater inlet, 36 Wastewater discharge section, 40 DO meter.

Claims

1. A method for forming granules using a semi-batch reactor comprising: an inflow step of introducing organic matter-containing wastewater; a biological treatment step of biologically treating the target substances in the organic matter-containing wastewater with microbial sludge under aerobic conditions; a sedimentation step of settling the microbial sludge; and a discharge step of discharging the biologically treated water to form granules, wherein the granules are formed by the following steps: A method for forming granules, characterized in that the biological treatment step involves monitoring the dissolved oxygen concentration in the semi-batch reaction vessel and adjusting the time of the biological treatment step based on the information regarding the monitored dissolved oxygen concentration.

2. The method for forming granules according to claim 1, characterized in that the dissolved oxygen concentration in the semi-batch reaction vessel is monitored during the biological treatment step, and the duration of the biological treatment step is adjusted based on the time from the start of the biological treatment step until the dissolved oxygen concentration rises to or above a predetermined value.

3. The method for forming granules according to claim 2, characterized in that the time of the biological treatment step is in the range of 1 to 5 times the time from the start of the biological treatment step until the dissolved oxygen concentration rises to or above a predetermined value.

4. A semi-batch reaction tank that performs an inflow step of introducing organic matter-containing wastewater, a biological treatment step of biologically treating the target substances in the organic matter-containing wastewater with microbial sludge under aerobic conditions, a sedimentation step of settling the microbial sludge, and a discharge step of discharging the biologically treated water to form granules, A granule forming apparatus comprising: a control unit that monitors the dissolved oxygen concentration in the semi-batch reaction vessel and adjusts the time of the biological treatment process based on the information regarding the monitored dissolved oxygen concentration.

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