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, comprising 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 while supplying oxygen, 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 amount of oxygen supplied is controlled so that the dissolved oxygen concentration in the semi-batch reaction tank is within a predetermined range, and the time of the biological treatment step is adjusted based on the amount of oxygen supplied or information regarding the amount of oxygen supplied.

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 Initiative] [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 be 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 while supplying oxygen, 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 amount of oxygen supplied is controlled so that the dissolved oxygen concentration in the semi-batch reactor is within a predetermined range, and the time of the biological treatment step is adjusted based on the amount of oxygen supplied or information regarding the amount of oxygen supplied.

[0009] Furthermore, in the method for forming the granules, it is preferable that in the biological treatment step, the amount of oxygen supplied is controlled by adjusting the opening of a valve provided in the piping that supplies the oxygen to the semi-batch reaction vessel so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, and that the time of the biological treatment step is adjusted based on the time from the start of the biological treatment step until the opening of the valve, which is information regarding the amount of oxygen supplied, falls below 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 valve opening falls below a predetermined value.

[0011] Furthermore, in the method for forming the granules, in the biological treatment step, it is preferable to control the amount of oxygen supplied by adjusting the output of an oxygen supply device provided in the piping that supplies oxygen to the semi-batch reaction vessel so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, and to adjust the time of the biological treatment step based on the time from the start of the biological treatment step until the output of the oxygen supply device, which is information regarding the amount of oxygen supplied, falls below a predetermined value.

[0012] 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 output of the oxygen supply device falls below a predetermined value.

[0013] Furthermore, in the method for forming the granules, it is preferable that in the biological treatment step, the amount of oxygen supplied is controlled so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, and the amount of oxygen supplied is monitored, and the duration of the biological treatment step is adjusted based on the time from the start of the biological treatment step until the amount of oxygen supplied falls below a predetermined value.

[0014] Furthermore, the granule forming apparatus of the present disclosure is characterized by 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 while supplying oxygen; a sedimentation step of settling the microbial sludge; and a discharge step of discharging the biologically treated water to form granules; and a control unit that controls the amount of oxygen supplied so that the dissolved oxygen concentration in the semi-batch reaction unit is within a predetermined range, and adjusts the time of the biological treatment step based on the amount of oxygen supplied and information regarding the amount of oxygen supplied. [Effects of the Invention]

[0015] According to the present disclosure, in a granule formation method using a semi-batch reactor, even if the BOD concentration of the organic matter-containing wastewater fluctuates, it is possible to provide a granule formation method capable of forming good granules and a granule formation apparatus.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic configuration diagram showing an example of a granule formation apparatus according to the present embodiment. [Figure 2] It is a schematic configuration diagram showing another example of the granule formation apparatus according to the present embodiment. [Figure 3] It is a diagram showing an example of the transition of the output of the oxygen supply apparatus during the biological treatment process. [Figure 4] It is a schematic configuration diagram showing another example of the granule formation apparatus according to the present embodiment. [Figure 5] It is a schematic configuration diagram showing another example of the granule formation apparatus according to the present embodiment. [Figure 6] It is a schematic configuration diagram showing another example of the granule formation apparatus according to the present embodiment.

Embodiments 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] <Granule Formation Method and Formation Apparatus> Figure 1 shows a schematic of an example of a granule forming apparatus according to this embodiment, 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 wastewater supply pipe 22 is connected to the wastewater inlet of the semi-batch reaction tank 10 via a wastewater inlet pump 12. A biological treatment water pipe 24 is connected to the biological treatment water outlet 16 of the semi-batch reaction tank 10 via a biological treatment water discharge valve 18. The granule forming apparatus 1 has an oxygen supply device 14. The oxygen supply device 14 is a device that supplies oxygen-containing gas such as air to the semi-batch reaction tank 10, and examples include pumps and blowers. An oxygen supply pipe 15 is connected to the oxygen supply device 14 and is connected to an aeration device 26 installed in the lower part of the inside of the semi-batch reaction tank 10.

[0019] A DO meter 40 is installed in the semi-batch reactor 10. The DO meter 40 measures the dissolved oxygen concentration in the organic matter-containing wastewater from the semi-batch reactor 10.

[0020] The granule forming apparatus 1 is equipped with a control device 20. The control device 20 consists of a microcomputer and electronic circuits, for example, a CPU that calculates programs, and ROM and RAM that store programs and calculation results. The control device 20 reads a predetermined program stored in the ROM, etc., and executes the program to control the operation of the granule forming apparatus 1. The control device 20 and the wastewater inlet pump 12, and the control device 20 and the biological treated water discharge valve 18 are electrically connected, for example. The control device 20 controls the operation and stopping of the wastewater inlet pump 12, the opening and closing of the biological treated water discharge valve 18, etc. The control device 20 is also electrically connected to the oxygen supply device 14, for example. The control device 20 controls the operation, stopping, and output of the oxygen supply device 14 when it is operating.

[0021] 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 reactor 10 as measured by the DO meter 40.

[0022] The granule forming apparatus 1 is operated in a cycle such as the following:

[0023] <(1) Inflow process> The wastewater inlet pump 12 is activated, and a predetermined amount of organic matter-containing wastewater flows into the semi-batch reaction vessel 10 through the wastewater supply pipe 22.

[0024] <(2) Biological treatment process> As the wastewater inlet pump 12 stops, oxygen-containing gases such as air introduced from the oxygen supply device 14 are supplied to the semi-batch reaction tank 10 through the oxygen supply piping 15 and the aeration device 26. Under these aerobic conditions, the substances to be treated in the organic matter-containing 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 oxygen. An anaerobic state refers to a state in which dissolved oxygen is absent, 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 oxygen supply device 14 stopped, and when performing an aerobic reaction, the oxygen supply device 14 is activated (the stirring device is also activated as needed). Note that the stirring device is not limited to the above configuration.

[0025] In the biological treatment process, the amount of oxygen supplied to the semi-batch reactor 10 is controlled by adjusting the output of the oxygen supply device 14 so that the dissolved oxygen concentration in the semi-batch reactor 10 is within a predetermined range. For example, the control device 20 monitors the dissolved oxygen concentration in the semi-batch reactor 10, measured by the DO meter 40, at predetermined intervals and adjusts the output of the oxygen supply device 14 so that the dissolved oxygen concentration falls within a predetermined range. The control device 20 also adjusts the time of the biological treatment process, as will be described later, and when the adjusted biological treatment process time is reached, the oxygen supply device 14 is stopped by the control device 20, for example (in the granule forming apparatus 1 of Figure 2, the stirring device is also stopped).

[0026] <(3) Settlement Process> After the oxygen supply device 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.

[0027] <(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.

[0028] 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, oxygen supply device 14, and agitator motor 28, 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.

[0029] 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 with 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, which is a sedimentation index of sludge. Specifically, the SVI value 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).

[0030] <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. Therefore, in this embodiment, as described below, by adjusting the timing of the biological treatment process based on the output of the oxygen supply device 14, it is possible to appropriately secure both the satiety time and the starvation time, even if the BOD concentration of the organic matter-containing wastewater fluctuates, thereby enabling the formation of good granules.

[0031] Figure 3 shows an example of the change in the output of the oxygen supply device during the biological treatment process. As shown in Figure 3, in the initial stages of the biological treatment process, the control device 20 maintains the output of the oxygen supply device 14 at a high level. This is because, when organic matter in organic matter-containing wastewater is decomposed by microbial sludge, the dissolved oxygen in the organic matter-containing water is consumed by the microbial sludge. If the output of the oxygen supply device 14 is not kept high, the dissolved oxygen concentration in the semi-batch reaction tank 10 will fall below a predetermined range. As the biological treatment process progresses and reaches a certain point, the control device 20 reduces the output of the oxygen supply device 14. This is because, as the decomposition of organic matter by 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. Therefore, if the output of the oxygen supply device 14 is not lowered, the dissolved oxygen concentration in the semi-batch reaction tank 10 will exceed a predetermined range. Furthermore, the time from the start of the biological treatment process until the output of the oxygen supply device 14 drops 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 output of the oxygen supply device 14 drops sharply until thereafter corresponds to the time when the BOD concentration is almost zero (starvation time).

[0032] Therefore, in this embodiment, for example, the control device 20 is pre-programmed to store the ratio of the time from the start of the biological treatment process until the output of the oxygen supply device 14 falls below a predetermined value / the biological treatment process time. The predetermined value for the output of the oxygen supply device 14 is not particularly limited, but it is desirable to set it to, for example, 60% or less. The control device 20 then adjusts the output of the oxygen supply device 14 to bring the dissolved oxygen concentration in the semi-batch reactor 10 within a predetermined range, measures the time until the output of the oxygen supply device 14 falls below a predetermined value, and sets the biological treatment process time from the above ratio. By operating the oxygen supply device 14 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 reactor 10 fluctuates and the satiety time increases or decreases, an appropriate starvation time can be secured, 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 until the output of the oxygen supply device 14 falls below a predetermined value.

[0033] 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, a valve 42 is installed in the oxygen supply pipe 15. The valve 42 and the control device 20 are electrically connected, for example, and the control device 20 controls the opening and closing of the valve 42. The other configurations of the granule forming apparatus 1 of Figure 4 are the same as those of the granule forming apparatus 1 of Figure 1, so their description is omitted.

[0034] In the granule forming apparatus 1 shown in Figure 4, during the biological treatment process, the opening of valve 42 is adjusted to control the amount of oxygen supplied to the semi-batch reaction vessel 10 so that the dissolved oxygen concentration in the semi-batch reaction vessel 10 is within a predetermined range. 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 adjusts the opening of valve 42 so that the dissolved oxygen concentration falls within a predetermined range. Specifically, similar to the floor output shown in Figure 3, the control device 20 increases the opening of valve 42 in the initial stages of the biological treatment process. This is because, when organic matter in organic matter-containing wastewater is decomposed by microbial sludge, the dissolved oxygen in the organic matter-containing water is consumed by the microbial sludge. If the opening of valve 42 is not increased, the dissolved oxygen concentration in the semi-batch reaction vessel 10 will fall below a predetermined range. Then, as the biological treatment process progresses and reaches a certain point, the control device 20 reduces the opening of the valve 42. This is because, as the decomposition of organic matter by 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 would normally be consumed by the microbial sludge is no longer consumed by the microbial sludge. Therefore, if the opening of the valve 42 is not reduced, the dissolved oxygen concentration in the semi-batch reaction tank 10 will exceed a predetermined range. The control device 20 then adjusts the time of the biological treatment process as follows in conjunction with this adjustment of the opening of the valve 42.

[0035] For example, the control device 20 is pre-programmed to store the ratio of the time from the start of the biological treatment process until the opening of valve 42 falls below a predetermined value / the biological treatment process time. The predetermined value for the opening of valve 42 is not particularly limited, but it is desirable to set it to, for example, 60% or less. The control device 20 then adjusts the opening of valve 42 to bring the dissolved oxygen concentration in the semi-batch reaction vessel 10 within a predetermined range, measures the time until the opening of valve 42 falls below a predetermined value, and sets the biological treatment process time from the above ratio. By operating the oxygen supply device 14 from the start of the biological treatment process until the set time, the biological treatment process can be carried out, and even if the BOD concentration of the organic matter-containing wastewater introduced into the semi-batch reaction vessel 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 until the opening of valve 42 falls below a predetermined value.

[0036] Another example of a granule forming apparatus according to this embodiment is shown in Figure 5. In the granule forming apparatus 1 of Figure 5, a flow meter 44 is installed in the oxygen supply pipe 15. The flow meter 44 measures the amount of oxygen supplied through the oxygen supply pipe 15. The flow meter 44 and the control device 20 are electrically connected, for example. The control device 20 monitors the amount of oxygen supplied measured by the flow meter 44 at predetermined intervals and adjusts the time of the biological treatment process as described later. Note that the other configurations of the granule forming apparatus 1 of Figure 5 are the same as those of the granule forming apparatus 1 of Figure 1, so their explanation is omitted.

[0037] In the granule forming apparatus 1 shown in Figure 5, similar to the granule forming apparatus 1 shown in Figure 1, the control device 20 maintains a high output of the oxygen supply device 14 in the initial stages of the biological processing process, and then reduces the output of the oxygen supply device 14 as the biological processing process progresses and reaches a certain point. Therefore, the oxygen supply is high in the initial stages of the biological processing process, and decreases as the biological processing process progresses and reaches a certain point. The control device 20 then adjusts the time of the biological processing process in accordance with these fluctuations in the oxygen supply, as follows.

[0038] For example, the control device 20 is pre-programmed with the ratio of the time from the start of the biological treatment process until the oxygen supply falls below a predetermined value / the biological treatment process time. The control device 20 then monitors the oxygen supply amount measured by the flow meter 44, measures the time from the start of the biological treatment process until the oxygen supply amount measured by the flow meter 44 falls below a predetermined value, and sets the biological treatment process time based on the above ratio. By operating the oxygen supply device 14 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 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 oxygen supply amount falls below a predetermined value.

[0039] The volumetric load of the semi-batch reactor 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.

[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 becomes possible to form better granules.

[0041] 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+ Mg 2+ It is preferable to add ions that form hydroxides, such as those mentioned above. Ordinary organic wastewater contains fine particles that act as nuclei for granules, but the addition of the above ions can further promote granule nucleation.

[0042] 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.

[0043] Another example of a granule forming apparatus according to this embodiment is shown in Figure 6. In the granule forming apparatus 1 of Figure 6, 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 treated water discharge valve 18, oxygen supply device 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.

[0044] In the granule forming apparatus 1 shown in Figure 6, 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, oxygen supply device 14, and agitator motor 28, as well as the opening and closing of the wastewater inflow valve 32 and biologically treated water discharge valve 18, may be controlled by the control device 20 or by an operator.

[0045] As described above, in the granule forming apparatus 1 shown in Figure 6, granules are formed by repeating the following steps: (1) inflow / discharge process, (2) biological treatment process, and (3) sedimentation process. The time for the (2) biological treatment process is adjusted based on the amount of oxygen supplied or information related to the amount of oxygen supplied (output of the oxygen supply device or valve opening), as previously mentioned.

[0046] In the granule forming apparatus 1 shown in Figure 6, 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]

[0047] 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.

[0048] 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.

[0049] 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.

[0050] [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 6). (2) Biological treatment process: The inflow of wastewater was stopped, and simultaneously, the biological treatment water discharge valve was closed. The oxygen supply device was activated, and the output of the oxygen supply device was adjusted to supply oxygen to the reaction tank so that the dissolved oxygen concentration in the reaction tank reached 2 mg / L. Then, the operation was carried out with the time of the biological treatment process being twice the time from the start of the biological treatment process (the start time of air supply) until the output of the oxygen supply device became 40% or less. 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 left standing for 15 minutes to allow the sludge in the reaction tank to settle. The operations in (1) to (3) above were repeated while conducting continuous operation for 30 days.

[0051] [Comparative Example] The operation cycle of the semi-batch reactor was carried out as follows. Before the operation, the activated sludge collected from the sewage treatment plant was used as the seed sludge and was put into the semi-batch reactor. (1) Inflow / discharge process: The wastewater was allowed to flow into the semi-batch reactor over 30 minutes, and simultaneously, the biological treatment water was discharged from the biological treatment water outlet (an electric valve that opens simultaneously with the start of the inflow of the wastewater) (see Figure 6). (2) Biological treatment process: The inflow of wastewater was stopped, and simultaneously, the biological treatment water discharge valve was closed. The oxygen supply device was activated to supply oxygen to 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 left standing for 15 minutes to allow the sludge in the reaction tank to settle. The operations in (1) to (3) above were repeated while conducting continuous operation for 30 days.

[0052] 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 reactor. 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

[0053] Table 1 shows the SVI of the examples and comparative examples. 30 The results were summarized.

[0054] [Table 1]

[0055] 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]

[0056] 1 Granule forming apparatus, 10 Semi-batch reaction vessel, 12 Wastewater inlet pump, 14 Oxygen supply apparatus, 15 Oxygen supply piping, 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 apparatus, 28 Motor, 30 Stirring blade, 32 Wastewater inlet valve, 34 Wastewater inlet, 36 Wastewater discharge section, 40 DO meter, 42 Valve, 44 Flow meter.

Claims

1. A method for forming granules using a semi-batch reaction tank 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 while supplying oxygen; 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, in the biological treatment step, the amount of oxygen supplied is controlled so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, and the time of the biological treatment step is adjusted based on the amount of oxygen supplied or information related to the amount of oxygen supplied.

2. The method for forming granules according to claim 1, characterized in that, in the biological treatment step, the amount of oxygen supplied is controlled by adjusting the opening of a valve provided in the piping that supplies oxygen to the semi-batch reaction vessel so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, and the time of the biological treatment step is adjusted based on the time from the start of the biological treatment step until the opening of the valve, which is information regarding the amount of oxygen supplied, falls below 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 opening of the valve falls below a predetermined value.

4. The method for forming granules according to claim 1, characterized in that, in the biological treatment step, the amount of oxygen supplied is controlled by adjusting the output of an oxygen supply device provided in the piping that supplies oxygen to the semi-batch reaction vessel so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, and the time of the biological treatment step is adjusted based on the time from the start of the biological treatment step until the output of the oxygen supply device, which is information regarding the amount of oxygen supplied, falls below a predetermined value.

5. The method for forming granules according to claim 4, 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 output of the oxygen supply device falls below a predetermined value.

6. The method for forming granules according to claim 1, characterized in that the amount of oxygen supplied is controlled in the biological treatment step so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, the amount of oxygen supplied is monitored, and the time of the biological treatment step is adjusted based on the time from the start of the biological treatment step until the amount of oxygen supplied falls below a predetermined value.

7. 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 while supplying oxygen, 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 controls the amount of oxygen supplied so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, and adjusts the time of the biological treatment process based on the amount of oxygen supplied and information regarding the amount of oxygen supplied.

Images