Method for forming granules and apparatus for forming granules

Abstract

This invention provides a method for forming granules using a semi-batch reaction vessel, which enables the stable formation of granules with good settling properties. [Solution] The method for forming granules according to the present disclosure is a method for forming granules using a semi-batch reactor 10 that performs an operating cycle 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 under aerobic conditions, a sedimentation step of settling the microbial sludge, and a discharge step of discharging the biologically treated water, wherein the biological treatment step is terminated based on the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reactor 10.

Description

Technical Field

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

Background Art

[0002] Conventionally, for biological wastewater treatment of organic wastewater containing organic substances and the like, the activated sludge method utilizing aggregates of microorganisms (aerobic biological sludge) called flocs has been used. However, in the activated sludge method, when separating flocs (aerobic biological sludge) and treated water in a sedimentation tank, the sedimentation rate of the flocs may be slow, so the surface area of the sedimentation tank may have to be made very large. In addition, the treatment rate of the activated sludge method depends on the sludge concentration in the biological treatment tank, and the treatment rate can be increased by increasing the sludge concentration. However, when the sludge concentration is increased to the range of 1500 to 5000 mg / L or more, solid-liquid separation becomes difficult due to bulking or the like in the sedimentation tank, and the treatment may not be able to be maintained.

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

[0004] In recent years, it has become clear that by using a semi-batch treatment system that intermittently infuses wastewater into the reaction tank, 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] The purpose of this disclosure is to provide a method for forming granules that can stably form granules with good settling properties, and a granule forming apparatus, using a semi-batch reaction vessel. [Means for solving the problem]

[0007] The method for forming granules according to the present disclosure is a method for forming granules using a semi-batch reactor that performs an operating cycle comprising: an inflow step of introducing organic matter-containing wastewater; a biological treatment step of biologically treating the target substances in the organic matter-containing wastewater with microbial sludge under aerobic conditions; a sedimentation step of settling the microbial sludge; and a discharge step of discharging the biologically treated water, wherein the biological treatment step is terminated based on the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reactor.

[0008] Furthermore, in the method for forming the granules, it is preferable that in the biological treatment step, the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel is monitored, and the biological treatment step is terminated when it is confirmed at least once that the rate of change of the soluble phosphorus concentration or phosphate phosphorus concentration is 90% or less, or less than a predetermined value.

[0009] Furthermore, in the method for forming the granules, it is preferable that the biological treatment step be terminated after a predetermined time has elapsed since the dissolved phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel became 0.5 mg P / L or less, or 0.5 mg P / L or less.

[0010] Furthermore, in the method for forming the granules, it is preferable that the biological treatment step be terminated after a predetermined time has elapsed since the dissolved phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel became 0.1 mg P / L or less, or after 0.1 mg P / L or less.

[0011] Furthermore, in the method for forming the granules, it is preferable that the operation cycle comprises a first operation cycle in which the biological treatment process is terminated based on the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel, and a second operation cycle in which the biological treatment process is performed for a longer period than the biological treatment process of the first operation cycle.

[0012] In addition, the granule forming apparatus of the present disclosure includes a semi-batch reaction tank that forms granules by performing an operation cycle having an inflow step of allowing organic matter-containing wastewater to flow in, a biological treatment step of biologically treating a target substance to be treated in the organic matter-containing wastewater with microbial sludge under aerobic conditions, a sedimentation step of sedimenting the microbial sludge, and a discharge step of discharging the biologically treated biological treatment water, and a control unit that ends the biological treatment step based on the dissolved phosphorus concentration or the phosphate phosphorus concentration in the semi-batch reaction tank.

Effects of the Invention

[0013] According to the present disclosure, it is possible to provide a granule forming method and a granule forming apparatus capable of stably forming granules with good sedimentation properties in a granule forming method using a semi-batch reaction tank.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic configuration diagram showing an example of the granule forming apparatus according to the present embodiment. [Figure 2] It is a schematic configuration diagram showing another example of the granule forming apparatus according to the present embodiment. [Figure 3] It is a diagram showing an example of the transition of the organic matter concentration and the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction tank during the biological treatment step. [Figure 4] It is a schematic configuration diagram showing another example of the granule forming apparatus according to the present embodiment. [Figure 5] It is a diagram showing the test results of Experimental Examples 1 to 6.

Modes for Carrying Out the Invention

[0015] 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.

[0016] <Granule Forming Method and Forming Apparatus> Fig. 1 shows a schematic diagram 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 reactor 10. In the granule forming apparatus 1, a drainage supply pipe 22 is connected to the drainage inlet of the semi-batch reactor 10 via a drainage inflow pump 12. A biological treatment water pipe 24 is connected to the biological treatment water outlet 16 of the semi-batch reactor 10 via a biological treatment water discharge valve 18. At the lower part inside the semi-batch reactor 10, an aeration device 26 connected to an aeration pump 14 is installed. A concentration meter 40 is installed in the semi-batch reactor 10. The concentration meter 40 measures the dissolved phosphorus concentration or the phosphate phosphorus concentration in the organic matter-containing drainage in the semi-batch reactor 10.

[0017] The granule forming apparatus 1 includes a control device 20. The control device 20 is composed of, for example, a microcomputer including a CPU that calculates a program, a ROM and a RAM that store the program and the calculation results, and an electronic circuit, etc. It 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 concentration meter 40 are, for example, electrically connected. The control device 20 receives, for example, data on the dissolved phosphorus concentration or the phosphate phosphorus concentration in the semi-batch reactor 10 measured by the concentration meter 40. Also, the control device 20 and the drainage inflow pump 12, the control device 20 and the biological treatment water discharge valve 18, and the control device 20 and the aeration pump 14 are, for example, electrically connected, and the control device 20 controls the operation / stop of the drainage inflow pump 12 and the aeration pump 14, the opening and closing of the biological treatment water discharge valve 18, etc.

[0018] The granule forming apparatus 1 is operated, for example, in the following cycle.

[0019] <(1) Inflow process> The drainage inflow pump 12 operates, and a predetermined amount of organic matter-containing drainage flows into the semi-batch reactor 10 through the drainage supply pipe 22.

[0020] <(2) Biological treatment process> As the wastewater inlet pump 12 stops, oxygen-containing gas such as air is supplied to the semi-batch reaction tank 10 from the aeration pump 14, and under aerobic conditions, the substances to be treated in the organic wastewater are biologically treated by microbial sludge in the semi-batch reaction tank 10. The biological treatment process may combine the above aerobic reaction with an anaerobic reaction in which stirring is performed in an oxygen-free state without supplying air or other gases. An anaerobic state means that dissolved oxygen is not present, but oxygen derived from nitrite or nitrate is present. For example, as shown in Figure 2, a stirring device consisting of a motor 28, a stirring blade 30, and a shaft connecting the motor 28 and the stirring blade 30 is installed in the semi-batch reaction tank 10. When performing an anaerobic reaction, stirring is performed by the stirring device with the aeration pump 14 stopped, and when performing an aerobic reaction, the aeration pump 14 is operated (the stirring device is also operated as needed). Note that the stirring device is not limited to the above configuration.

[0021] In the biological treatment process, the concentration of dissolved phosphorus or phosphated phosphorus in the semi-batch reaction vessel 10 is measured by the concentration meter 40 and transmitted to the control device 20. The control device 20 then terminates the biological treatment process based on the concentration of dissolved phosphorus or phosphated phosphorus in the semi-batch reaction vessel 10 measured by the concentration meter 40, as will be described later. When the biological treatment process is terminated, for example, the aeration pump 14 is stopped by the control device 20 (in the granule forming apparatus 1 of Figure 2, the stirring device is also stopped).

[0022] By implementing a biological treatment process, for example, organic matter in wastewater is broken down to carbon dioxide, and nitrogen-containing substances are broken down to nitrogen gas.

[0023] <(3) Settlement Process> After the aeration pump 14 is stopped, the sludge in the semi-batch reaction tank 10 is allowed to settle by leaving it undisturbed for a predetermined period of time.

[0024] <(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.

[0025] By repeating the operation cycle consisting of the above steps (1) to (4), granules, which are aggregates of microorganisms that have densely gathered into granular form, are formed. The operation and stopping of the wastewater inlet pump 12, the aeration pump 14, and the motor 28 of the stirring device, as well as the opening and closing of the biologically treated water discharge valve 18, may be controlled by the control device 20 or by an operator.

[0026] Furthermore, while it is desirable that the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reactor 10 be measured at any time using a concentration meter 40 installed in the semi-batch reactor 10, it may also be measured by known methods from organic matter-containing wastewater collected at any time by an operator in the semi-batch reactor 10.

[0027] 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).

[0028] <Completion date of the biological treatment process> Figure 3 shows an example of the changes in organic matter concentration and dissolved phosphorus concentration (or phosphate phosphorus 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 organic matter concentration and dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reactor 10 are high. Dissolved phosphorus or phosphate phosphorus is not only contained in the organic matter-containing wastewater flowing into the semi-batch reactor 10, but also includes dissolved phosphorus or phosphate phosphorus released by phosphorus-accumulating bacteria contained in the microbial sludge under anaerobic conditions such as during the inflow process. As the biological treatment process progresses, the organic matter concentration and dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reactor 10 decrease. This is because the decomposition of organic matter by microbial sludge containing phosphorus-accumulating bacteria and the uptake of dissolved phosphorus (or phosphate phosphorus) into the cells by phosphorus-accumulating bacteria progress. In this context, the formation of granular sludge in the semi-batch reaction tank 10 requires time for the biological treatment process to allow phosphorus-accumulating bacteria to take in dissolved phosphorus (or phosphate phosphorus) released under anaerobic conditions, such as during the inflow process, and dissolved phosphorus (or phosphate phosphorus) present in the wastewater.

[0029] Therefore, in this embodiment, the control device 20 stops the aeration pump 14, etc., and terminates the biological treatment process when the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction tank 10, as measured by the concentration meter 40, falls below a predetermined value. The predetermined value is preferably 0.5 mg P / L, and more preferably 0.1 mg P / L. This ensures sufficient time for the biological treatment process for phosphorus-accumulating bacteria to take in the dissolved phosphorus (or phosphate phosphorus) in the semi-batch reaction tank 10 into their cells, making it possible to form stable granular sludge with good settling properties.

[0030] Furthermore, in this embodiment, the control device 20 may stop the aeration pump 14, etc., and terminate the biological treatment process after a predetermined time has elapsed since the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction tank 10, as measured by the concentration meter 40, fell below a predetermined value. For example, as shown in Figure 3, even if the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction tank 10 falls below a predetermined value (for example, 0.5 mgP / L or less), the organic matter in the reaction tank may not have been decomposed. In such cases, by terminating the biological treatment process after a predetermined time has elapsed since the dissolved phosphorus concentration (or phosphate phosphorus concentration) fell below a predetermined value (i.e., by continuing the biological treatment process until a predetermined time has elapsed since the dissolved phosphorus concentration (or phosphate phosphorus concentration) fell below a predetermined value), it is possible to ensure both a state of high organic matter concentration (saturated state) and a state of low organic matter concentration (starvated state) in the reaction tank. This makes it possible to stably form granular sludge with good settling properties. The predetermined time is not particularly limited, but it is desirable that, for example, the time of the biological treatment process be set to be in the range of 1.2 to 5 times the time from the start of the biological treatment process until the dissolved phosphorus concentration (or phosphate phosphorus concentration) measured by the concentration meter 40 falls below a predetermined value.

[0031] If a concentration meter 40 is not installed, for example, the operator may estimate in advance the time it takes for the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction tank 10 to fall below a predetermined value, and the control device 20 may be used to control the biological treatment process during that time. The time it takes for the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction tank 10 to fall below a predetermined value can be estimated by the operator, for example, from the dissolved phosphorus absorption rate (or phosphate phosphorus absorption rate) obtained from a prior test of the amount of microbial sludge and the amount of organic matter-containing water flowing into the semi-batch reaction tank 10, or from the time-dependent change in the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction tank 10 obtained from water quality analysis.

[0032] Furthermore, in this embodiment, the control device 20 may monitor the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction vessel 10 measured by the concentration meter 40, and when it confirms at least once that the rate of change of the dissolved phosphorus concentration is 90% or less, it may stop the aeration pump 14, etc., and terminate the biological treatment process. Here, the rate of change of the dissolved phosphorus concentration in this specification is the ratio calculated from the dissolved phosphorus concentration measured last time and the dissolved phosphorus concentration measured this time, and is a value calculated by the formula ((dissolved phosphorus concentration measured this time - dissolved phosphorus concentration measured last time) / dissolved phosphorus concentration measured last time) × 100. The rate of change of phosphate phosphorus concentration is calculated similarly. Considering measurement errors in the dissolved phosphorus concentration (or phosphate phosphorus concentration), it is preferable that the control device 20 monitors the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction vessel 10, as measured by the concentration meter 40, and when it confirms that the rate of change of the dissolved phosphorus concentration (or phosphate phosphorus concentration) is 90% or less for multiple consecutive times (for example, two consecutive times), it stops the aeration pump 14, etc., and terminates the biological treatment process.

[0033] 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.

[0034] If the phosphorus concentration required for biological treatment is low relative to the organic matter concentration in the organic matter-containing wastewater, phosphorus compounds may be added to the organic matter-containing wastewater. It is desirable that the phosphorus compounds be added to the organic matter-containing wastewater such that, for example, the BOD:P ratio is 100:1 to 100:30.

[0035] 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.

[0036] The concentration of microbial sludge in the semi-batch reaction tank 10 in the biological treatment process is preferably in the range of 1500 to 30000 mg / L, for example, in terms of maintaining the integrity of the sludge (settling properties, activity, etc.).

[0037] The pH inside the semi-batch reaction vessel 10 is preferably in the range of 5 to 9, and more preferably in the range of 6 to 7.5. The pH can be adjusted by adding an acid or alkali to the semi-batch reaction vessel 10, for example.

[0038] The volumetric load of the semi-batch reaction vessel 10 is 0.15 kg BOD / m³. 3 / day ~1.00kgBOD / m 3 It is preferable that the range be within / day, and 0.30 kg BOD / m³ 3 / day ~0.60kgBOD / m 3 A range of / day is more preferable. By setting the volumetric load of the semi-batch reaction vessel 10 within the above range, it becomes possible to form better granules.

[0039] 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.

[0040] An operating cycle comprising an inflow process, a biological treatment process, a sedimentation process, and a discharge process may have a first operating cycle in which the biological treatment process is terminated based on the dissolved phosphorus concentration (or phosphate phosphorus concentration), and a second operating cycle in which the biological treatment process is performed for a longer period than the biological treatment process time of the first operating cycle.

[0041] As described above, in the biological treatment process of the first operating cycle, the aeration pump 14, etc., is stopped when the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction vessel 10, as measured by the concentration meter 40, falls below a predetermined value or after a predetermined time has elapsed since falling below the predetermined value, thereby ending the biological treatment process. The predetermined value is preferably 0.5 mg P / L, and more preferably 0.1 mg P / L. Alternatively, as described above, in the biological treatment process of the first operating cycle, the control device 20 may monitor the dissolved phosphorus concentration (or phosphate phosphorus concentration) in the semi-batch reaction vessel 10, as measured by the concentration meter 40, and when it confirms at least once that the rate of change of the dissolved phosphorus concentration (or phosphate phosphorus concentration) is below a predetermined value of 90% or less, the aeration pump 14, etc., is stopped, thereby ending the biological treatment process.

[0042] The sludge load of the semi-batch reactor 10 in the first operating cycle is preferably in the range of 0.4 kg BOD / kg MLSS / day to 2.0 kg BOD / kg MLSS / day, and more preferably in the range of 0.6 kg BOD / kg MLSS / day to 1.5 kg BOD / kg MLSS / day.

[0043] The biological treatment process in the second operating cycle may be longer than the biological treatment process time in the first operating cycle, but it is preferable to make it at least twice the biological treatment process time of the first operating cycle, and more preferably three times or more, in order to adequately ensure satiety and starvation conditions. For example, the control device 20 measures the time of the biological treatment process in the first operating cycle, and when it transitions to the second operating cycle, it calculates the time of the biological treatment process by multiplying the measured time by a predetermined coefficient, and controls the aeration pump 14, etc., so that the biological treatment process is carried out during that time.

[0044] In the second operating cycle, the sludge load in the semi-batch reactor 10 is preferably in the range of 0.02 kg BOD / kg MLSS / day to 0.3 kg BOD / kg MLSS / day, and more preferably in the range of 0.05 kg BOD / kg MLSS / day to 0.2 kg BOD / kg MLSS / day. Furthermore, the ammonia nitrogen concentration in the semi-batch reactor 10 at the end of the biological treatment process in the second operating cycle is preferably 1 mg N / L or less.

[0045] The first and second operating cycles may be repeated alternately, but for example, the first operating cycle may be repeated multiple times before the second operating cycle, or the second operating cycle may be repeated multiple times after the first operating cycle, or the second operating cycle may be repeated multiple times after the first operating cycle.

[0046] By implementing the operation cycle having the first and second operation cycles described above, it is possible to appropriately secure the time for the biological treatment process, even when treating wastewater with a low organic matter concentration, and to stably form granular sludge with good settling properties.

[0047] Another example of a granule forming apparatus according to this embodiment is shown in Figure 4. In the granule forming apparatus 1 of Figure 4, the wastewater supply pipe 22 is connected to the wastewater inlet 34 at the bottom of the semi-batch reaction tank 10 via the wastewater inlet pump 12 and the wastewater inlet valve 32. A wastewater discharge section 36 is connected to the wastewater inlet 34 and is installed in the lower part of the inside of the semi-batch reaction tank 10. The biological treated water outlet 16 of the semi-batch reaction tank 10 is provided above the wastewater inlet 34, and the biological treated water pipe 24 is connected to the biological treated water outlet 16 via the biological treated water discharge valve 18. The biological treated water outlet 16, which is provided above the wastewater inlet 34, is preferably provided as far away from the wastewater inlet 34 as possible in order to prevent short circuits of the incoming organic matter-containing wastewater and to form granules more efficiently, and it is more preferably provided at the water level during the settling process. The wastewater inlet pump 12, wastewater inlet valve 32, biological treated water discharge valve 18, aeration pump 14, agitator motor 28, and concentration 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.

[0048] In the granule forming apparatus 1 shown in Figure 4, it is desirable to perform both an inflow process and a discharge process. Specifically, by opening the wastewater inflow valve 32 and the biologically treated water discharge valve 18 and operating the wastewater inflow pump 12, organic matter-containing wastewater is allowed to flow from the wastewater inlet 34 through the wastewater discharge section 36 into the semi-batch reaction tank 10, and the biologically treated water in the semi-batch reaction tank 10 is discharged from the biologically treated water outlet 16 through the biologically treated water piping 24. The operation and stopping of the wastewater inflow pump 12, the aeration pump 14, and the motor 28 of the stirring device, as well as the opening and closing of the wastewater inflow valve 32 and the biologically treated water discharge valve 18, may be controlled by the control device 20 or by an operator.

[0049] As described above, in the granule forming apparatus 1 shown in Figure 4, granules are formed by repeating the following steps: (1) inflow / discharge process, (2) biological treatment process, and (3) sedimentation process. In (2) the biological treatment process, as mentioned above, the process is terminated based on the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel 10 measured by the concentration meter 40. The repeating of steps (1) to (3) is one form of an operating cycle having an inflow process, a biological treatment process, a sedimentation process, and a discharge process.

[0050] In the granule forming apparatus 1 shown in Figure 4, organic matter-containing wastewater is introduced into the semi-batch reaction tank 10, and the biologically treated water is discharged from the biologically treated water outlet 16. As a result, granules with relatively small particle sizes are discharged together with the biologically treated water, and steps (1) to (3) are repeated for granules with relatively large particle sizes. Consequently, granules can be formed more efficiently. [Examples]

[0051] 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.

[0052] Sewage was used for the water flow test. The BOD concentration of the sewage ranged from 50 to 200 mg / L. The BOD concentration was measured in accordance with JIS K 0102 21. The total phosphorus concentration (TP) of the sewage ranged from 0.9 to 6.0 mgP / L, and the phosphate phosphorus concentration (PO4-P) of the sewage ranged from 0.4 to 5.0 mgP / L.

[0053] 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 predetermined period of time, and the biologically treated water was discharged from the biologically treated water outlet. (2) Biological treatment process: The inflow of wastewater and the discharge of biologically treated water were stopped, and air was supplied from an aeration device installed at the bottom of the reaction tank to perform biological treatment of the wastewater for a predetermined time. After the 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 tank was left to stand for a predetermined time to allow the sludge in the reaction tank to settle. The above steps (1) to (3) were repeated.

[0054] Furthermore, when the change in phosphate phosphorus concentration (PO4-P) in the semi-batch reaction vessel during the above biological treatment process was measured in advance, it took 60 minutes for the phosphate phosphorus concentration (PO4-P) to fall below 0.1 mgP / L. At this time, the organic matter concentration was approximately 20 mg / L.

[0055] (Experiment Example 1: Day 0 to Day 45 of Operation) From day 0 to day 45 of operation, the system alternated between a first operating cycle with 50 minutes for the inflow / discharge process, 20 minutes for the biological treatment process, and 15 minutes for the sedimentation process, and a second operating cycle with 50 minutes for the inflow / discharge process, 390 minutes for the biological treatment process, and 15 minutes for the sedimentation process.

[0056] (Experiment Example 2: Days 46-67 of operation) From day 46 to day 67 of operation, the system alternated between a first operating cycle with 50 minutes for the inflow / discharge process, 60 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process, and a second operating cycle with 50 minutes for the inflow / discharge process, 390 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process.

[0057] (Experiment Example 3: Days 68-88 of operation) From day 68 to day 88 of operation, the system alternated between a first operating cycle with 50 minutes for the inflow / discharge process, 20 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process, and a second operating cycle with 50 minutes for the inflow / discharge process, 390 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process.

[0058] (Experiment Example 4: Days 89-119 of operation) From day 89 to day 119 of operation, the system alternated between a first operating cycle with 50 minutes for the inflow / discharge process, 60 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process, and a second operating cycle with 50 minutes for the inflow / discharge process, 390 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process.

[0059] (Experiment Example 5: Days 120-150 of operation) From day 120 to day 150 of operation, the system alternated between a first operating cycle with 50 minutes for the inflow / discharge process, 20 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process, and a second operating cycle with 50 minutes for the inflow / discharge process, 390 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process.

[0060] (Experiment Example 6: Days 151-200 of operation) From day 151 to day 200 of operation, the system alternated between a first operating cycle with 50 minutes for the inflow / discharge process, 60 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process, and a second operating cycle with 50 minutes for the inflow / discharge process, 390 minutes for the biological treatment process, and 1-2 minutes for the sedimentation process.

[0061] Figure 5 shows the test results for Experimental Examples 1 to 6. In Figure 5, the horizontal axis represents the number of days elapsed in operation, the left vertical axis represents the SVI value of the biological sludge, and the right vertical axis represents the time of the biological treatment process in the first cycle. SVI is an index of the settling properties of biological sludge and is determined by the following method. First, 1 L of sludge is placed in a 1 L graduated cylinder, and after gently stirring to make the sludge concentration as uniform as possible, the sludge interface is measured after standing for 5 minutes. Then, the volume percentage (%) occupied by the sludge in the graduated cylinder is calculated. Next, the MLSS (mg / L) of the sludge is measured. These are then applied to the following formula to calculate SVI5. A smaller SVI5 value indicates that the sludge has higher settling properties. SVI5 (mL / g) = Volume percentage occupied by sludge × 10,000 / MLSS (Note: When calculating SVI30, change the standing time from 5 minutes to 30 minutes.)

[0062] As shown in Experimental Examples 2, 4, and 6, performing the biological treatment process for 60 minutes until the phosphate phosphorus concentration (PO4-P) was 0.1 mgP / L or less resulted in a decrease in SVI5 and the formation of granular sludge with good settling properties. On the other hand, as shown in Experimental Examples 1, 3, and 5, when the biological treatment process was performed for 20 minutes, SVI5 increased compared to Experimental Examples 2, 4, and 6. [Explanation of Symbols]

[0063] 1 Granule forming apparatus, 10 Semi-batch reaction vessel, 12 Wastewater inlet pump, 14 Aeration pump, 16 Biologically treated water outlet, 18 Biologically treated water discharge valve, 20 Control device, 22 Wastewater supply piping, 24 Biologically treated water piping, 26 Aeration device, 28 Motor, 30 Stirring blade, 32 Wastewater inlet valve, 34 Wastewater inlet, 36 Wastewater discharge section, 40 Concentration meter.

Claims

1. A method for forming granules using a semi-batch reactor that performs an operating cycle 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 granules are formed by this operation cycle. A method for forming granules, characterized in that the biological treatment step is terminated based on the concentration of soluble phosphorus or phosphate phosphorus in the semi-batch reaction vessel.

2. The method for forming granules according to claim 1, characterized in that the biological treatment step involves monitoring the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel, and terminating the biological treatment step when it is confirmed at least once that the rate of change of the soluble phosphorus concentration or phosphate phosphorus concentration is 90% or less, or less than a predetermined value.

3. The method for forming granules according to claim 1, characterized in that the biological treatment step is terminated after a predetermined time has elapsed since the dissolved phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel became 0.5 mg P / L or less, or after 0.5 mg P / L or less.

4. The method for forming granules according to claim 1, characterized in that the biological treatment step is terminated after a predetermined time has elapsed since the dissolved phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel became 0.1 mg P / L or less, or after 0.1 mg P / L or less.

5. The method for forming granules according to any one of claims 1 to 4, wherein the operating cycle comprises a first operating cycle in which the biological treatment process is terminated based on the soluble phosphorus concentration or phosphate phosphorus concentration in the semi-batch reaction vessel, and a second operating cycle in which the biological treatment process is performed for a longer period than the biological treatment process of the first operating cycle.

6. A semi-batch reactor that forms granules by performing an operating cycle 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. A granule forming apparatus comprising a control unit that terminates the biological treatment step based on the concentration of soluble phosphorus or phosphate phosphorus in the semi-batch reaction vessel.

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