Granule forming method and granule forming apparatus

Abstract

A granule forming method according to the present disclosure uses a semi-batch reaction tank (10) that forms granules by performing: an inflow step for causing organic matter-containing wastewater to flow in; a biological treatment step for biologically treating a substance to be treated in the organic matter-containing wastewater with microbial sludge under aerobic conditions; a precipitation step for precipitating the microbial sludge; and a discharge step for discharging the biologically treated water that has been biologically treated. 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 on the basis of information relating to the monitored dissolved oxygen concentration.

Description

Method for forming granules and apparatus for forming granules

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

[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, requiring additional aerobic treatment such as the activated sludge method when discharging the treated water into rivers or other bodies of water.

[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 to 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.

[0005] International Publication No. 2004 / 024638, Japanese Patent Publication No. 2008-212878, Japanese Patent No. 4975541, Japanese Patent No. 4804888

[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.

[0008] (1) 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 in the biological treatment step, the dissolved oxygen concentration in the semi-batch reactor is monitored, and the time of the biological treatment step is adjusted based on the information regarding the monitored dissolved oxygen concentration.

[0009] (2) In the method for forming granules described in (1) above, 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] (3) In the method for forming granules described in (2) above, the time 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 a predetermined value or higher.

[0011] (4) 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 under aerobic conditions; 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 monitors the dissolved oxygen concentration in the semi-batch reaction unit and adjusts the time of the biological treatment step based on the information regarding the monitored dissolved oxygen concentration.

[0012] (5) 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 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 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.

[0013] (6) In the method for forming granules described in (5) above, in the biological treatment step, it is preferable to control the amount of oxygen supplied 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 to adjust the time of the biological treatment step 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.

[0014] (7) In the method for forming granules described in (6) above, the time 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 opening of the valve falls below a predetermined value.

[0015] (8) In the method for forming granules as described in (5) above, 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.

[0016] (9) In the method for forming granules described in (8) above, the time 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.

[0017] (10) In the method for forming granules described in (5) above, in the biological treatment step, it is preferable to control the amount of oxygen supplied so that the dissolved oxygen concentration in the semi-batch reaction vessel is within a predetermined range, monitor the amount of oxygen supplied, and adjust the time of the biological treatment step based on the time from the start of the biological treatment step until the amount of oxygen supplied falls below a predetermined value.

[0018] (11) 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 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 to form granules; and a control unit that controls the amount of oxygen supplied so that the dissolved oxygen concentration in the half-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 relating to the amount of oxygen supplied.

[0019] According to this disclosure, a method for forming granules using a semi-batch reaction vessel can be provided that enables the formation of good granules even when the BOD concentration of organic matter-containing wastewater fluctuates, and a granule forming apparatus can be provided.

[0020] This is a schematic diagram showing an example of a granule forming apparatus according to this embodiment. This is a schematic diagram showing another example of a granule forming apparatus according to this embodiment. This is a diagram showing an example of the change in dissolved oxygen concentration in a semi-batch reaction vessel during the biological treatment process. This is a schematic diagram showing another example of a granule forming apparatus according to this embodiment. This is a schematic diagram showing an example of a granule forming apparatus according to this embodiment. This is a schematic diagram showing another example of a granule forming apparatus according to this embodiment. This is a diagram showing an example of the change in output of an oxygen supply device during the biological treatment process. This is a schematic diagram showing another example of a granule forming apparatus according to this embodiment. This is a schematic diagram showing another example of a granule forming apparatus according to this embodiment. This is a schematic diagram showing another example of a granule forming apparatus according to this embodiment.

[0021] Embodiments of this disclosure are described below. These embodiments are examples of implementing this disclosure, and this disclosure is not limited to these embodiments.

[0022] (First Embodiment) <Granule Forming Method and Apparatus> An outline of an example of a granule forming apparatus according to this embodiment is shown in Figure 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 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. An aeration device 26 connected to an aeration pump 14 is installed in the lower part of the inside of the semi-batch reaction tank 10. 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 wastewater in the semi-batch reaction tank 10.

[0023] The control device 20 is composed of, for example, a microcomputer consisting of a CPU that calculates programs, ROM and RAM that store programs and calculation results, and electronic circuits, etc. It reads a predetermined program stored in the ROM, etc., executes the program, and controls the operation of the granule forming apparatus 1. The control device 20 and the DO meter 40 are electrically connected, for example, and the control device 20 monitors the dissolved oxygen concentration in the semi-batch reaction vessel 10 measured by the DO meter 40. In addition, the control device 20 and the wastewater inlet pump 12, the control device 20 and the biological treated water discharge valve 18, and the control device 20 and the aeration pump 14 are electrically connected, for example, and the control device 20 controls the operation and stopping of the wastewater inlet pump 12 and the aeration pump 14, the opening and closing of the biological treated water discharge valve 18, etc.

[0024] The granule forming apparatus 1 is operated in a cycle such as the following:

[0025] <(1) Inflow Process> The wastewater inflow pump 12 is activated, and a predetermined amount of wastewater containing organic matter flows into the semi-batch reaction vessel 10 through the wastewater supply pipe 22.

[0026] <(2) Biological treatment process> When the wastewater inflow pump 12 stops, an oxygen-containing gas such as air is supplied from the aeration pump 14 to the semi-batch reactor 10, and under aerobic conditions, the target substances in the organic matter-containing wastewater in the semi-batch reactor 10 are biologically treated by microbial sludge. The biological treatment process may combine the above aerobic reaction with an anoxic reaction in which stirring is performed in an anoxic state without supplying air or the like. The anoxic state means a state in which dissolved oxygen does not exist, but oxygen derived from nitrite or nitrate exists. For example, as shown in FIG. 2, a stirring device composed of a motor 28, a stirring blade 30, a shaft connecting the motor 28 and the stirring blade 30, etc. is installed in the semi-batch reactor 10. When performing the anoxic reaction, stirring is performed by the stirring device with the aeration pump 14 stopped, and when performing the aerobic reaction, the aeration pump 14 is operated (the stirring device may also be operated as necessary). Note that the stirring device is not limited to the above configuration.

[0027] In the biological treatment process, the dissolved oxygen concentration in the semi-batch reactor 10 is measured by the DO meter 40. Further, by the control device 20, the dissolved oxygen concentration in the semi-batch reactor 10 measured by the DO meter 40 is monitored every predetermined time or continuously, and the time of the biological treatment process is adjusted as described later. When the adjusted biological treatment process time is reached, for example, the aeration pump 14 is stopped by the control device 20 (in the granule forming device 2 in FIG. 2, the stirring device is also stopped).

[0028] <(3) Sedimentation process> After the aeration pump 14 stops, the sludge in the semi-batch reactor 10 is sedimented by allowing it to stand for a predetermined time.

[0029] <(4) Discharge process> By opening the biological treatment water discharge valve 18, the supernatant water obtained in the sedimentation process is discharged as biological treatment water from the biological treatment water outlet 16 through the biological treatment water pipe 24. In this case, instead of the biological treatment water discharge valve, a pump may be used to discharge the biological treatment water.

[0030] By repeating the cycles of (1) to (4) above, granules are formed, which are aggregates in which microorganisms are densely aggregated and granulated. The operation and stop of the drainage inflow pump 12, the aeration pump 14, and the motor 28 of the stirring device, and the opening and closing of the biological treatment water discharge valve 18 may be controlled by the control device 20 or may be performed by an operator or the like.

[0031] The granules formed in the semi-batch reaction tank 10 are sludge in which self-granulation has progressed. For example, the average particle size of the sludge is 0.2 mm or more, or the biological sludge has an SVI5, which is a sedimentation index, of 80 mL / g or less. In this embodiment, whether or not granules are formed is determined by, for example, measuring the SVI, which is a sedimentation index of the sludge. Specifically, the SV is measured by a sedimentation test of the sludge in the semi-batch reaction tank 10 at regular intervals, and when the value of SVI5 calculated from the volume ratio after 5-minute sedimentation is below a predetermined value (for example, 80 mL / g or less), it is possible to determine that granules are formed. Alternatively, when the particle size distribution of the sludge in the semi-batch reaction tank 10 is measured and the average particle size becomes a predetermined value or more (for example, 0.2 mm or more), it is possible to determine that granules are formed (note that the lower the SVI value and the larger the average particle size, the better the granules can be determined).

[0032] <Adjusting the Time of the Biological Treatment Process> For granular sludge formation in a semi-batch reactor, it is important to repeat the organic matter concentration gradient within the reactor in one cycle. It is believed that a period of high BOD concentration (saturation period) and a period of near-zero BOD concentration (starvation period) are necessary. Therefore, it is desirable to set the time of the biological treatment process so that the saturation period and starvation period are appropriately secured. However, generally, the time of the biological treatment process is fixed at the time initially set. As the BOD concentration of the organic matter-containing wastewater fluctuates, for example, if the saturation period becomes long, it may not be possible to secure a sufficient starvation period. Conversely, if the saturation period becomes short, the starvation period 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 the organic matter-containing wastewater introduced into the reactor and adjust the time of the biological treatment process. However, since measuring BOD concentration generally takes time, it is not practical to use BOD concentration to adjust the time of the biological treatment process. 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.

[0033] 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).

[0034] In this embodiment, for example, the control device 20 monitors the dissolved oxygen concentration in the semi-batch reaction vessel 10, which is measured by the DO meter 40, at predetermined intervals, and the time of the biological treatment process is adjusted based on the information regarding the monitored dissolved oxygen concentration.

[0035] 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.

[0036] Furthermore, the information regarding the dissolved oxygen concentration may also include, for example, the time from the start of the biological treatment process until the rate of increase in 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 may refer to the history of dissolved oxygen concentration measured by the DO meter 40 and calculate the dissolved oxygen concentration DO at the time of calculation. １ , and the dissolved oxygen concentration DO a predetermined time before the calculation time. ２ Obtain the following. If the predetermined time is Δt, the rate of increase R in dissolved oxygen concentration can be calculated by the following formula (1). R = (DO １ -DO ２ ) / Δt (1)

[0037] 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 needed. It measures 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 based on 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.

[0038] 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 with respect to time.

[0039] The control device 20 stores, for example, in advance the ratio of the time from the start of the biological treatment process to the inflection point of the dissolved oxygen concentration to the biological treatment process time. Then, the control device 20 monitors the dissolved oxygen concentration measured by the DO meter 40, performs the above-mentioned time differentiation, measures the time from the start of the biological treatment process to 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 to the set time and performing the biological treatment process, even if the BOD concentration of the organic matter-containing wastewater introduced into the semi-batch reaction tank 10 fluctuates and the saturation time increases or decreases, an appropriate starvation time can be ensured, so that good granules can be formed. From the viewpoint of forming good granules, the time 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 to the inflection point of the dissolved oxygen concentration.

[0040] The volume load of the semi-batch reaction tank 10 is preferably in the range of 0.15 kg BOD / m ３ / day to 1.00 kg BOD / m ３ / day, and more preferably in the range of 0.30 kg BOD / m ３ / day to 0.60 kg BOD / m ３ / day. By setting the volume load of the semi-batch reaction tank 10 within the above range, it becomes possible to form better granules.

[0041] The sludge load of 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 of the semi-batch reaction tank 10 within the above range, it becomes possible to form better granules.

[0042] In terms of promoting the granulation of biological sludge, Fe ２＋ , Fe ３＋ , Ca ２＋ , Mg ２＋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.

[0043] 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 the 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.

[0044] Another example of a granule forming apparatus according to this embodiment is shown in Figure 4. In the granule forming apparatus 3 of Figure 4, the same reference numerals are used for components similar to those in the granule forming apparatus 1 of Figure 1. In the granule forming apparatus 3 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. The 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, 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 2 in Figure 2.

[0045] In the granule forming apparatus 3 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.

[0046] As described above, in the granule forming apparatus 3 of Figure 4, 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 dissolved oxygen concentration in the semi-batch reaction vessel 10, which is measured by the DO meter 40, at predetermined intervals, as described above.

[0047] In the granule forming apparatus 3 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.

[0048] (Second Embodiment) <Granule Forming Method and Forming Apparatus> An overview of an example of a granule forming apparatus according to this embodiment is shown in Figure 5, and its configuration will be described. The granule forming apparatus 4 shown in Figure 5 includes a semi-batch reaction tank 110. In the granule forming apparatus 4, a wastewater supply pipe 122 is connected to the wastewater inlet of the semi-batch reaction tank 110 via a wastewater inlet pump 112. A biological treatment water pipe 124 is connected to the biological treatment water outlet 116 of the semi-batch reaction tank 110 via a biological treatment water discharge valve 118. The granule forming apparatus 4 has an oxygen supply device 114. The oxygen supply device 114 is a device that supplies oxygen-containing gas such as air to the semi-batch reaction tank 110, and examples include pumps and blowers. An oxygen supply pipe 115 is connected to the oxygen supply device 114 and is connected to an aeration device 126 installed in the lower part of the inside of the semi-batch reaction tank 110.

[0049] A DO meter 140 is installed in the semi-batch reactor 110. The DO meter 140 measures the dissolved oxygen concentration in the organic matter-containing wastewater inside the semi-batch reactor 110.

[0050] The granule forming apparatus 4 is equipped with a control device 120. The control device 120 is composed of, for example, a microcomputer consisting of a CPU that calculates programs, ROM and RAM that store programs and calculation results, and electronic circuits, etc. It reads a predetermined program stored in the ROM, etc., executes the program, and controls the operation of the granule forming apparatus 4. The control device 120 and the wastewater inlet pump 112, and the control device 120 and the biological treated water discharge valve 118 are electrically connected, for example, and the control device 120 controls the operation and stopping of the wastewater inlet pump 112, the opening and closing of the biological treated water discharge valve 118, etc. In addition, the control device 120 and the oxygen supply device 114 are electrically connected, for example, and the control device 120 controls the operation, stopping, and output of the oxygen supply device 114 when it is operating.

[0051] The control device 120 and the DO meter 140 are, for example, electrically connected, and the control device 120 monitors the dissolved oxygen concentration in the semi-batch reaction vessel 110 as measured by the DO meter 140.

[0052] The granule forming apparatus 4 is operated in a cycle such as the following:

[0053] <(1) Inflow Process> The wastewater inflow pump 112 is activated, and a predetermined amount of wastewater containing organic matter flows into the semi-batch reaction vessel 110 through the wastewater supply pipe 122.

[0054] <(2) Biological Treatment Process> When the wastewater inlet pump 112 stops, oxygen-containing gas such as air introduced from the oxygen supply device 114 is supplied to the semi-batch reaction tank 110 through the oxygen supply pipe 115 and aeration device 126. 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 110. 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 the like. An anaerobic state means a state in which dissolved oxygen is not present, but oxygen derived from nitrite or nitrate is present. For example, as shown in Figure 6, a stirring device consisting of a motor 128, a stirring blade 130, a shaft connecting the motor 128 and the stirring blade 130, etc., is installed in the semi-batch reaction tank 110. When performing an anaerobic reaction, the oxygen supply device 114 is stopped and stirring is performed using the stirring device. When performing an aerobic reaction, the oxygen supply device 114 is activated (the stirring device is also activated as needed). Note that the stirring device is not limited to the above configuration.

[0055] In the biological treatment process, the amount of oxygen supplied to the semi-batch reactor 110 is controlled by adjusting the output of the oxygen supply device 114 so that the dissolved oxygen concentration in the semi-batch reactor 110 is within a predetermined range. For example, the control device 120 monitors the dissolved oxygen concentration in the semi-batch reactor 110, measured by the DO meter 140, at predetermined intervals and adjusts the output of the oxygen supply device 114 so that the dissolved oxygen concentration falls within a predetermined range. The control device 120 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 114 is stopped by the control device 120, for example (in the granule forming apparatus 5 of Figure 6, the stirring device is also stopped).

[0056] <(3) Settlement Process> After the oxygen supply device 114 is stopped, the sludge in the semi-batch reaction tank 110 is allowed to settle by leaving it to stand for a predetermined time.

[0057] <(4) Discharge Process> By opening the biological treated water discharge valve 118, the supernatant water obtained in the sedimentation process is discharged as biological treated water from the biological treated water outlet 116 through the biological treated water piping 124. In this case, a pump may be used to discharge the biological treated water instead of the biological treated water discharge valve.

[0058] By repeating the above cycle (1) to (4), granules are formed, which are aggregates of microorganisms that have densely gathered into granular form. The operation and stopping of the wastewater inlet pump 112, oxygen supply device 114, and agitator motor 128, as well as the opening and closing of the biologically treated water discharge valve 118, may be controlled by the control device 120 or by an operator.

[0059] The granules formed in the semi-batch reactor 110 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 the sludge. Specifically, the SVI value is measured periodically by a sedimentation test of the sludge in the semi-batch reactor 110, 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 110 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.)

[0060] <Adjusting the Time of the Biological Treatment Process> For granular sludge formation in a semi-batch reactor, it is important to repeat the organic matter concentration gradient within the reactor in one cycle. It is believed that a period of high BOD concentration (saturation period) and a period of near-zero BOD concentration (starvation period) are necessary. Therefore, it is desirable to set the time of the biological treatment process so that the saturation period and starvation period are appropriately secured. However, generally, the time of the biological treatment process is fixed at the time initially set. As the BOD concentration of the organic matter-containing wastewater fluctuates, for example, if the saturation period becomes long, it may not be possible to secure a sufficient starvation period. Conversely, if the saturation period becomes short, the starvation period 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 the organic matter-containing wastewater introduced into the reactor and adjust the time of the biological treatment process. However, since measuring BOD concentration generally takes time, it is not practical to use BOD concentration to adjust the time of the biological treatment process. 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 114, 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.

[0061] Figure 7 shows an example of the change in the output of the oxygen supply device during the biological treatment process. As shown in Figure 7, in the initial stages of the biological treatment process, the control device 120 maintains the output of the oxygen supply device 114 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 114 is not kept high, the dissolved oxygen concentration in the semi-batch reaction tank 110 will fall below a predetermined range. As the biological treatment process progresses and reaches a certain point, the control device 120 reduces the output of the oxygen supply device 114. 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. If the output of the oxygen supply device 114 is not lowered, the dissolved oxygen concentration in the semi-batch reaction tank 110 will exceed a predetermined range. Furthermore, the time from the start of the biological treatment process until the output of the oxygen supply device 114 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 114 drops sharply until thereafter corresponds to the time when the BOD concentration is almost zero (starvation time).

[0062] Therefore, in this embodiment, for example, the control device 120 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 114 falls below a predetermined value / the biological treatment process time. The predetermined value for the output of the oxygen supply device 114 is not particularly limited, but it is desirable to set it to, for example, 60% or less. The control device 120 then adjusts the output of the oxygen supply device 114 to bring the dissolved oxygen concentration in the semi-batch reactor 110 within a predetermined range, measures the time until the output of the oxygen supply device 114 falls below a predetermined value, and sets the biological treatment process time from the above ratio. By operating the oxygen supply device 114 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 110 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 duration 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 114 falls below a predetermined value.

[0063] Another example of the granule forming apparatus according to this embodiment is shown in Figure 8. In the granule forming apparatus 6 of Figure 8, the same reference numerals are used for components that are the same as those in the granule forming apparatus 4 of Figure 5. In the granule forming apparatus 6 of Figure 8, a valve 142 is installed in the oxygen supply pipe 115. The valve 142 and the control device 120 are electrically connected, for example, and the control device 120 controls the opening and closing of the valve 142. Note that the other components of the granule forming apparatus 6 of Figure 8 are the same as those of the granule forming apparatus 4 of Figure 5, so their description is omitted.

[0064] In the granule forming apparatus 6 shown in Figure 8, during the biological treatment process, the opening of valve 142 is adjusted to control the amount of oxygen supplied to the semi-batch reaction vessel 110 so that the dissolved oxygen concentration in the semi-batch reaction vessel 110 is within a predetermined range. For example, the control device 120 monitors the dissolved oxygen concentration in the semi-batch reaction vessel 110, measured by the DO meter 140, at predetermined intervals and adjusts the opening of valve 142 so that the dissolved oxygen concentration falls within a predetermined range. Specifically, similar to the floor output shown in Figure 7, the control device 120 opens valve 142 to a high degree 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 142 is not increased, the dissolved oxygen concentration in the semi-batch reaction vessel 110 will fall below a predetermined range. Then, as the biological treatment process progresses and reaches a certain point, the control device 120 reduces the opening of the valve 142. 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 142 is not reduced, the dissolved oxygen concentration in the semi-batch reaction tank 110 will exceed a predetermined range. The control device 120 then adjusts the time of the biological treatment process as follows in conjunction with this adjustment of the opening of the valve 142.

[0065] For example, the control device 120 is pre-programmed to store the ratio of the time from the start of the biological treatment process until the opening of valve 142 falls below a predetermined value / the biological treatment process time. The predetermined value for the opening of valve 142 is not particularly limited, but it is desirable to set it to, for example, 60% or less. The control device 120 then adjusts the opening of valve 142 to bring the dissolved oxygen concentration in the semi-batch reaction vessel 110 within a predetermined range, measures the time until the opening of valve 142 falls below a predetermined value, and sets the biological treatment process time from the above ratio. By operating the oxygen supply device 114 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 110 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 142 falls below a predetermined value.

[0066] Another example of a granule forming apparatus according to this embodiment is shown in Figure 9. In the granule forming apparatus 7 of Figure 9, the same reference numerals are used for components that are the same as those in the granule forming apparatus 4 of Figure 5. In the granule forming apparatus 7 of Figure 9, a flow meter 144 is installed in the oxygen supply pipe 115. The flow meter 144 measures the amount of oxygen supplied through the oxygen supply pipe 115. The flow meter 144 and the control device 120 are connected, for example, electrically. The control device 120 monitors the amount of oxygen supplied measured by the flow meter 144 at predetermined intervals and adjusts the time of the biological processing step as will be described later. Note that the other components of the granule forming apparatus 7 of Figure 9 are the same as those of the granule forming apparatus 4 of Figure 5, so their description is omitted.

[0067] In the granule forming apparatus 7 shown in Figure 9, similar to the granule forming apparatus 4 shown in Figure 5, the control device 120 maintains a high output of the oxygen supply device 114 in the initial stages of the biological processing process, and then reduces the output of the oxygen supply device 114 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 120 then adjusts the time of the biological processing process in accordance with these fluctuations in the oxygen supply, as follows.

[0068] For example, the control device 120 is pre-programmed to store 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 120 then monitors the oxygen supply amount measured by the flow meter 144, measures the time from the start of the biological treatment process until the oxygen supply amount measured by the flow meter 144 falls below a predetermined value, and sets the biological treatment process time based on the above ratio. By operating the oxygen supply device 114 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 110 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.

[0069] The volumetric load of the semi-batch reactor 110 is 0.15 kg BOD / m³. ３ / day ~1.00 kg BOD / m ３ Preferably, the range is 0.30 kg BOD / m³ / day. ３ / day ~0.60 kg BOD / m ３ A range of / day is more preferable. By setting the volumetric load of the semi-batch reaction vessel 110 within the above range, it becomes possible to form better granules.

[0070] The sludge load in the semi-batch reaction tank 110 is preferably in the range of 0.05 kg BOD / kgMLSS / day to 0.30 kg BOD / kgMLSS / day, and more preferably in the range of 0.10 kg BOD / kgMLSS / day to 0.20 kg BOD / kgMLSS / day. By setting the sludge load in the semi-batch reaction tank 110 within the above range, it becomes possible to form better granules.

[0071] In order to promote the granulation of biological sludge, Fe is added to the organic matter-containing wastewater in the semi-batch reaction tank 110 or to the organic matter-containing wastewater before it is introduced into the semi-batch reaction tank 110. ２＋ Fe ３＋ Ca ２＋ Mg ２＋ 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.

[0072] 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 110 using existing methods such as flotation separation, coagulation and pressurized flotation, or adsorption.

[0073] Another example of a granule forming apparatus according to this embodiment is shown in Figure 10. In the granule forming apparatus 8 of Figure 10, the same reference numerals are used for components similar to those in the granule forming apparatus 5 of Figure 6. In the granule forming apparatus 8 of Figure 10, the wastewater supply pipe 122 is connected to the wastewater inlet 134 at the bottom of the semi-batch reaction tank 110 via the wastewater inlet pump 112 and the wastewater inlet valve 132. The wastewater discharge section 136 is connected to the wastewater inlet 134 and is installed at the bottom of the inside of the semi-batch reaction tank 110. The biological treated water outlet 116 of the semi-batch reaction tank 110 is located above the wastewater inlet 134, and the biological treated water pipe 124 is connected to the biological treated water outlet 116 via the biological treated water discharge valve 118. The biologically treated water outlet 116, located above the wastewater inlet 134, is preferably installed as far away from the wastewater inlet 134 as possible to prevent short circuits of incoming organic matter-containing wastewater and to form granules more efficiently, and more preferably installed at the water level during the sedimentation process. The wastewater inlet pump 112, wastewater inlet valve 132, biologically treated water outlet valve 118, oxygen supply device 114, agitator motor 128, and DO meter 140 are each electrically connected to the control device 120, for example. The rest of the configuration is the same as that of the granule forming apparatus 5 in Figure 6.

[0074] In the granule forming apparatus 8 shown in Figure 10, it is desirable to perform both an inflow process and a discharge process. Specifically, by opening the wastewater inflow valve 132 and the biologically treated water discharge valve 118 and operating the wastewater inflow pump 112, organic matter-containing wastewater is allowed to flow from the wastewater inlet 134 through the wastewater discharge section 136 into the semi-batch reaction tank 110, and the biologically treated water in the semi-batch reaction tank 110 is discharged from the biologically treated water outlet 116 through the biologically treated water piping 124. Note that the operation and stopping of the wastewater inflow pump 112, oxygen supply device 114, and agitator motor 128, as well as the opening and closing of the wastewater inflow valve 132 and biologically treated water discharge valve 118, may be controlled by the control device 120 or by an operator.

[0075] As described above, in the granule forming apparatus 8 of Figure 10, 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 described above.

[0076] In the granule forming apparatus 8 shown in Figure 10, organic matter-containing wastewater is introduced into the semi-batch reaction tank 110, causing the biologically treated water to be discharged from the biologically treated water outlet 116. 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.

[0077] 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.

[0078] (Example 1, Comparative Example 1) The following tests were conducted using a half-batch reactor with an effective reactor volume of 33 L. The biological treatment water outlet of the half-batch reactor is located at the water surface level during the sedimentation process.

[0079] 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.

[0080] [Example 1] The operation cycle of the half-batch reactor was carried out as follows. Before operation, activated sludge collected from a sewage treatment plant was added to the half-batch reactor as seed sludge. (1) Inflow / Outflow Process: Wastewater was flowed into the half-batch reactor over 30 minutes, and biologically treated water was discharged from the biologically treated water outlet (an electric valve that opens simultaneously with the start of wastewater inflow was installed) (see Figure 4). (2) Biological Treatment Process: The biologically treated water discharge valve was closed simultaneously with the cessation of wastewater inflow, and air was supplied from an aeration device installed at the bottom of the reactor. The dissolved oxygen concentration in the reactor was monitored every minute, and the time when the dissolved oxygen concentration reached 2 mg / L or higher was measured. The biological treatment process was run for twice the time from the start of the biological treatment process (start of air supply) to the above time, and after the elapsed time, the process proceeded to the following sedimentation process. (3) Settlement process: The supply of air from the aeration device was stopped and the system was allowed to stand for 15 minutes to allow the sludge in the reaction tank to settle. The above operations (1) to (3) were repeated, and the system was operated continuously for 30 days.

[0081] [Comparative Example 1] The operation cycle of the half-batch reactor was carried out as follows. Before operation, activated sludge collected from a sewage treatment plant was added to the half-batch reactor as seed sludge. (1) Inflow / Outflow Process: Wastewater was flowed into the half-batch reactor over 30 minutes, and biologically treated water was discharged from the biologically treated water outlet (an electric valve that opens simultaneously with the start of wastewater inflow was installed) (see Figure 4). (2) Biological Treatment Process: The biologically treated water discharge valve was closed at the same time as the wastewater inflow was stopped, and air was supplied from an aeration device installed at the bottom of the reactor. Regardless of fluctuations in the BOD concentration of the wastewater (70-180 mg / L), the biological treatment process time was fixed at 240 minutes, and after 240 minutes, the process proceeded to the following sedimentation process. (3) Sedimentation Process: The supply of air from the aeration device was stopped and the reactor was allowed to stand for 15 minutes to allow the sludge in the reactor to settle. The above operations (1) to (3) were repeated while the system was running continuously for 30 days.

[0082] In both Example 1 and Comparative Example 1, the SVI of the biological sludge in the semi-batch reaction tank was measured. ３０ Granule formation was evaluated by measurement. 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 the sludge in the graduated cylinder is calculated. Next, the MLSS (mg / L) of the sludge is measured. These are then applied to the following formula to obtain SVI. ３０ Calculate SVI. ３０ A smaller value indicates that the sludge has high settling properties. SVI ３０ (mL / g) = Volume percentage occupied by sludge × 10,000 / MLSS

[0083] Table 1 shows the SVI for Example 1 and Comparative Example 1. ３０ The results were summarized.

[0084]

[0085] Both Example 1 and Comparative Example 1 use SVI. ３０ A decrease was observed, but the value was lower in Example 1. In other words, in Example 1, the sludge settling properties were improved, and better granules were formed.

[0086] (Example 2, Comparative Example 2) The following tests were conducted using a half-batch reactor with an effective reactor volume of 33 L. The biological treatment water outlet of the half-batch reactor is located at the water surface level during the sedimentation process.

[0087] 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.

[0088] [Example 2] The operation cycle of the half-batch reactor was carried out as follows. Before operation, activated sludge collected from a sewage treatment plant was added to the half-batch reactor as seed sludge. (1) Inflow / Outflow Process: Wastewater was flowed into the half-batch reactor over a period of 30 minutes, and biologically treated water was discharged from the biologically treated water outlet (an electric valve that opens simultaneously with the start of wastewater inflow was installed) (see Figure 10). (2) Biological Treatment Process: The biologically treated water discharge valve was closed at the same time as the wastewater inflow was stopped, and the oxygen supply device was activated. The output of the oxygen supply device was adjusted so that the dissolved oxygen concentration in the reactor was 2 mg / L, and oxygen was supplied to the reactor. The biological treatment process was run for twice the time from the start of the biological treatment process (start of air supply) until the output of the oxygen supply device fell below 40%, and after this time had elapsed, the process proceeded to the following sedimentation process. (3) Settlement process: The supply of air from the aeration device was stopped and the system was allowed to stand for 15 minutes to allow the sludge in the reaction tank to settle. The above operations (1) to (3) were repeated, and the system was operated continuously for 30 days.

[0089] [Comparative Example 2] The operation cycle of the half-batch reactor was carried out as follows. Before operation, activated sludge collected from a sewage treatment plant was added to the half-batch reactor as seed sludge. (1) Inflow / Outflow Process: Wastewater was flowed into the half-batch reactor over 30 minutes, and biologically treated water was discharged from the biologically treated water outlet (an electric valve that opens simultaneously with the start of wastewater inflow was installed) (see Figure 10). (2) Biological Treatment Process: The biologically treated water discharge valve was closed at the same time as the wastewater inflow was stopped, and the oxygen supply device was activated to supply oxygen to the reactor. Regardless of fluctuations in the BOD concentration of the wastewater (70-180 mg / L), the biological treatment process time was fixed at 240 minutes, and after 240 minutes, the process proceeded to the following sedimentation process. (3) Sedimentation Process: The supply of air from the aeration device was stopped and the reactor was allowed to stand for 15 minutes to allow the sludge in the reactor to settle. The above operations (1) to (3) were repeated while the system was running continuously for 30 days.

[0090] In both Example 2 and Comparative Example 2, the SVI of the biological sludge in the semi-batch reaction tank was measured. ３０ Granule formation was evaluated by measurement. 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 the sludge in the graduated cylinder is calculated. Next, the MLSS (mg / L) of the sludge is measured. These are then applied to the following formula to obtain SVI. ３０ Calculate SVI. ３０ A smaller value indicates that the sludge has high settling properties. SVI ３０ (mL / g) = Volume percentage occupied by sludge × 10,000 / MLSS

[0091] Table 2 shows the SVI for Example 2 and Comparative Example 2. ３０ The results were summarized.

[0092]

[0093] Both Example 2 and Comparative Example 2 use SVI. ３０ A decrease was observed, but the value was even lower in Example 2. In other words, in Example 2, the sludge settling properties improved, and better granules were formed.

[0094] 1-8 Granule forming apparatus, 10, 110 Semi-batch reaction vessel, 12, 112 Wastewater inlet pump, 14 Aeration pump, 16, 116 Biologically treated water outlet, 18, 118 Biologically treated water discharge valve, 20, 120 Control device, 22, 122 Wastewater supply piping, 24, 124 Biologically treated water piping, 26, 126 Aeration device, 28, 128 Motor, 30, 130 Stirring blade, 32, 132 Wastewater inlet valve, 34, 134 Wastewater inlet, 36, 136 Wastewater discharge section, 40, 140 DO meter, 114 Oxygen supply device, 115 Oxygen supply piping, 142 Valve, 144 Flow 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, wherein the method for forming granules is characterized in that, in the biological treatment step, the dissolved oxygen concentration in the semi-batch reactor is monitored, and the time of the biological treatment step is adjusted 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 granule forming apparatus comprising: an inflow step for introducing organic matter-containing wastewater; a biological treatment step for biologically treating the target substances in the organic matter-containing wastewater with microbial sludge under aerobic conditions; a sedimentation step for settling the microbial sludge; and a discharge step for discharging the biologically treated water to form granules; and a control unit for monitoring the dissolved oxygen concentration in the semi-batch reaction tank and adjusting the time of the biological treatment step based on the information regarding the monitored dissolved oxygen concentration.

5. 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 related to the amount of oxygen supplied.

6. The method for forming granules according to claim 5, 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.

7. The method for forming granules according to claim 6, 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.

8. The method for forming granules according to claim 5, 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.

9. The method for forming granules according to claim 8, 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.

10. The method for forming granules according to claim 5, 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, 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.

11. A granule forming apparatus 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 tank is within a predetermined range, and adjusts the time of the biological treatment step based on the amount of oxygen supplied and information related to the amount of oxygen supplied.

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