Method for forming aerobic granules, apparatus for forming aerobic granules

Abstract

To provide a method for forming aerobic granules that can stably form aerobic granules even when a large amount of slowly degradable organic matter is contained in organic-containing wastewater.SOLUTION: The present disclosure is a method for forming aerobic granules using a semi-batch reactor 10 that forms aerobic granules. The organic matter includes easily degradable organic matter and slowly degradable organic matter. The time of the biological treatment process is adjusted so that the ratio of the concentration of MLSS in the semi-batch reaction tank 10 to the BOD load of the easily degradable organic matter in the semi-batch reaction tank 10 multiplied by the time of the operation cycle / time of the biological treatment process is in the range of 0.05-0.25 kgBOD / kgMLSS / day.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for forming aerobic granules and an apparatus for forming aerobic granules.

Background Art

[0002] Conventionally, for the biological wastewater treatment of organic wastewater containing organic substances and the like, the activated sludge method utilizing an aggregate of microorganisms (aerobic biological sludge) called floc has been used. However, in the activated sludge method, when separating the floc (aerobic biological sludge) and the treated water in the sedimentation tank, the sedimentation rate of the floc is slow, so the surface area of the sedimentation tank may have to be 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 an aggregate (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 the types of wastewater to be treated being limited compared to aerobic treatment (activated sludge method), and the need to maintain the treatment water temperature at about 30 to 35°C. In addition, when discharging the treated water into a river or the like, aerobic treatment such as the activated sludge method may need to be separately carried out 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 a reaction tank, and by further shortening the settling 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 aerobic biological sludge, it is possible to achieve an average particle size of 0.2 mm or more and a settling velocity of 5 m / h or more. In a semi-batch treatment system, it is common to repeatedly perform four steps in a single biological treatment tank: (1) inflow of wastewater, (2) biological treatment of organic matter, (3) settling of biological sludge, and (4) discharge of treated water.

[0005] Furthermore, Patent Document 5 discloses a semi-batch treatment method that repeatedly performs three steps: (1) inflow of wastewater and discharge of treated water, (2) biological treatment of organic matter, and (3) sedimentation of biological sludge. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2004 / 024638 [Patent Document 2] Japanese Patent Publication No. 2008-212878 [Patent Document 3] Patent No. 4975541 [Patent Document 4] Patent No. 4804888 [Patent Document 5] Japanese Patent Publication No. 2016-77931 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, in the past, when organic matter subjected to biological treatment contained a large amount of slow-degrading organic matter, the formation of aerobic granules sometimes did not proceed smoothly.

[0008] Therefore, the purpose of this disclosure is to provide a method for forming aerobic granules and an apparatus for forming aerobic granules that can stably form aerobic granules even when organic matter-containing wastewater contains a large amount of slow-degrading organic matter. [Means for solving the problem]

[0009] This disclosure relates to a method for forming aerobic granules using a semi-batch reactor, wherein the operation cycle comprises an inflow step of introducing organic matter-containing wastewater, a biological treatment step of biologically treating the organic matter in the organic matter-containing wastewater with microbial sludge, a sedimentation step of settling the microbial sludge, and a discharge step of discharging the biologically treated water, and the organic matter includes easily decomposable organic matter and slowly decomposable organic matter, and the value obtained by multiplying the ratio of the MLSS concentration in the semi-batch reactor to the BOD load of the easily decomposable organic matter in the semi-batch reactor by [time of the operation cycle / time of the biological treatment step] is 0.05~ 0.125 The process is characterized by adjusting the time of the biological treatment step so that it falls within the range of kgBOD / kgMLSS / day, and setting the sludge retention time in the semi-batch reaction tank to a range of 5 to 25 days.

[0010] Furthermore, in the method for forming the aerobic granules, the total BOD concentration of the organic matter-containing wastewater flowing into the semi-batch reaction vessel is the same as the amount of the organic matter-containing wastewater. Slow-degrading organic matter It is preferable that the ratio of the BOD concentrations is 0.5 or higher.

[0011] Furthermore, in the method for forming the aerobic granules, it is preferable to provide the biological treatment water outlet of the semi-batch reaction tank above the wastewater inlet, and to allow the organic matter-containing wastewater to flow into the semi-batch reaction tank from the wastewater inlet, thereby discharging the biological treatment water from the biological treatment water outlet.

[0012] Furthermore, this disclosure relates to an aerobic granule forming apparatus comprising a semi-batch reactor that forms aerobic granules by performing an operating cycle comprising: an inflow step of introducing organic matter-containing wastewater; a biological treatment step of biologically treating the organic matter in the organic matter-containing wastewater with microbial sludge; a sedimentation step of settling the microbial sludge; and a discharge step of discharging the biologically treated water, wherein the organic matter includes easily decomposable organic matter and slowly decomposable organic matter, and the value obtained by multiplying the ratio of the MLSS concentration in the semi-batch reactor to the BOD load of the easily decomposable organic matter in the semi-batch reactor by [time of the operating cycle / time of the biological treatment step] is 0.05~ 0.125 The system is characterized by having means for adjusting the time of the biological treatment process so that the BOD / kgMLSS / day is within the range of kgBOD / kgMLSS / day, and the sludge retention time in the semi-batch reaction tank is in the range of 5 to 25 days.

[0013] Furthermore, this disclosure relates to a wastewater treatment method characterized by supplying aerobic granules formed by the above-described method for forming aerobic granules to a continuous biological treatment tank that biologically treats organic wastewater containing organic matter with biological sludge while continuously allowing organic wastewater to flow in.

[0014] Furthermore, the present disclosure is a wastewater treatment apparatus characterized by comprising a continuous biological treatment tank that continuously receives organic wastewater containing organic matter and biologically treats the said organic wastewater containing organic matter with biological sludge, and means for supplying aerobic granules formed by the aerobic granule forming apparatus to the continuous biological treatment tank. [Effects of the Invention]

[0015] According to this disclosure, it is possible to provide a method for forming aerobic granules and an apparatus for forming aerobic granules that can stably form aerobic granules even when a large amount of slow-degrading organic matter is contained in organic matter-containing wastewater. [Brief explanation of the drawing]

[0016] [Figure 1]It is a schematic configuration diagram showing an example of an aerobic granule formation apparatus according to an embodiment of the present disclosure. [Figure 2] It is a schematic configuration diagram showing another example of an aerobic granule formation apparatus according to an embodiment of the present disclosure. [Figure 3] It is a schematic configuration diagram showing another example of an aerobic granule formation apparatus according to an embodiment of the present disclosure. [Figure 4] It is a schematic configuration diagram showing another example of an aerobic granule formation apparatus according to an embodiment of the present disclosure. [Figure 5] It is a schematic configuration diagram showing an example of a wastewater treatment apparatus according to an embodiment of the present disclosure. [Figure 6] It is a diagram showing the daily change of SVI and average sludge particle size in a comparative example. [Figure 7] It is a diagram showing the daily change of SVI and average sludge particle size in an example.

MODE FOR CARRYING OUT THE INVENTION

[0017] Embodiments of the present disclosure will be described below. This embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to this embodiment.

[0018] <Aerobic Granule Formation Method and Formation Apparatus> An overview of an example of an aerobic granule formation apparatus according to an embodiment of the present disclosure is shown in FIG. 1, and its configuration will be described. The granule formation apparatus 1 includes a semi-batch reactor 10. In the granule formation apparatus 1, a wastewater supply pipe 28 is connected to a wastewater inlet of the semi-batch reactor 10 via a wastewater inflow pump 12. A biological treatment water pipe 30 is connected to a biological treatment water outlet 16 of the semi-batch reactor 10 via a biological treatment water discharge valve 18, and a sludge extraction pipe 32 is connected to a sludge extraction port 22 via a sludge extraction pump 24. At the lower part inside the semi-batch reactor 10, an aeration device 26 connected to an aeration pump 14 is installed.

[0019] The granule forming apparatus 1 is equipped with a control device 20. The control device 20 consists of a microcomputer comprising, for example, a CPU for calculating programs, and ROM and RAM for storing programs and calculation results, as well as 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 is electrically connected to, for example, the wastewater inlet pump 12, the biological treatment water discharge valve 18, the sludge extraction pump 24, and the aeration pump 14, and controls the operation and stopping of the pumps, the opening and closing of the valves, etc.

[0020] The granule forming apparatus 1 is operated in a cycle such as the following:

[0021] (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 28.

[0022] (2) Biological treatment process: When the wastewater inlet pump 12 is stopped, oxygen-containing gas such as air is supplied from the aeration pump 14 to the semi-batch reaction tank 10 through the aeration device 26, and the organic matter and other substances to be treated in the organic matter-containing wastewater are biologically treated by microbial sludge in the semi-batch reaction tank 10. The biological reaction is not limited to an aerobic reaction; it is also possible to perform an anaerobic reaction by stirring without supplying air, or a combination of aerobic and anaerobic reactions. An anaerobic state refers to a state in which 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 34, a stirring blade 36, a shaft connecting the motor 34 and the stirring blade 36, etc., can be installed in the semi-batch reaction tank 10, and stirring can be performed by stopping the aeration pump 14 and using the stirring device. The stirring device is not limited to the above configuration.

[0023] (3) Settlement process: The aeration pump 14 is stopped and left to stand for a predetermined time, allowing the sludge in the semi-batch reaction tank 10 to settle.

[0024] (4) Discharge process: By opening the biological treated water discharge valve 18, the supernatant water obtained in the sedimentation process is discharged as biological treated water from the biological treated water outlet 16 through the biological treated water piping 30. In this case, the biological treated water may be discharged using a pump instead of the biological treated water discharge valve 18.

[0025] By repeating the operation cycle consisting of the above steps (1) to (4), aerobic granules (hereinafter simply referred to as granules), which are aggregates of microorganisms that have densely gathered together into granular form, are formed.

[0026] The granules formed in the semi-batch reactor 10 are sludge that has undergone self-granulation, and are, for example, biological sludge with an average particle size of 0.2 mm or more, or a sedimentation index SVI5 of 80 mL / g or less. In this embodiment, whether or not granules have been formed is determined, for example, by measuring the SVI, which is a sedimentation index of sludge. Specifically, it is possible to determine that granules have been formed when the SVI5 value measured by a sedimentation test of the sludge in the semi-batch reactor 10 periodically falls below a predetermined value (for example, 80 mL / g or less). Alternatively, it is possible to determine that granules have been formed when the particle size distribution of the sludge in the semi-batch reactor 10 is measured and 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).

[0027] Incidentally, the BOD load of the semi-batch reactor 10 is determined by the product of the BOD concentration and the amount of organic matter-containing wastewater flowing into the semi-batch reactor 10. The BOD concentration is a value measured from the amount of oxygen consumed when microorganisms decompose organic matter over 5 days. However, the organic matter in the organic matter-containing wastewater includes slow-degrading organic matter, which takes approximately tens of hours to several days for biodegradation by microorganisms, and easily degradable organic matter, which takes approximately several hours to tens of hours for biodegradation by microorganisms. Therefore, the BOD concentration can be classified into the total BOD concentration, which corresponds to the amount of oxygen consumed by microorganisms when decomposing organic matter including slow-degrading and easily degradable organic matter; the BOD concentration of slow-degrading organic matter, which corresponds to the amount of oxygen consumed by microorganisms when decomposing slow-degrading organic matter; and the BOD concentration of easily degradable organic matter, which corresponds to the amount of oxygen consumed by microorganisms when decomposing easily degradable organic matter. The total BOD concentration is the sum of the BOD concentration of slow-degrading organic matter and the BOD concentration of easily degradable organic matter.

[0028] Therefore, the BOD load of the semi-batch reactor 10 can be classified into the total BOD load based on the total BOD concentration (total BOD concentration × amount of wastewater containing organic matter), the BOD load of slow-degrading organic matter based on the BOD concentration of slow-degrading organic matter (BOD concentration of slow-degrading organic matter × amount of wastewater containing organic matter), and the BOD load of easily degradable organic matter based on the BOD concentration of easily degradable organic matter (BOD concentration of easily degradable organic matter × amount of wastewater containing organic matter). The total BOD load is the sum of the BOD load of slow-degrading organic matter and the BOD load of easily degradable organic matter.

[0029] Here, for stable granule formation, it is important to control the ratio between the satiety state, when the organic matter concentration in the organic matter-containing wastewater flowing into the semi-batch reactor 10 is high, and the starvation state, when the organic matter decomposition by microbial sludge progresses and the organic matter concentration in the organic matter-containing wastewater is low. This relationship between the satiety state and the starvation state can be indirectly controlled by using the ratio of the MLSS concentration in the semi-batch reactor 10 to the BOD load. Furthermore, since processes other than the biological treatment process do not significantly contribute to the biological reaction, it is possible to control the satiety / starvation ratio more precisely by evaluating the value obtained by multiplying the ratio of MLSS concentration to BOD load by [operating cycle time / biological treatment process time]. Here, "operating cycle time" refers to the total time of the above-mentioned (1) inflow process, (2) biological treatment process, (3) sedimentation process, and (4) discharge process (in the case of the configurations shown in Figures 3 and 4 below, it refers to the total time of the (1) inflow / discharge process, (2) biological treatment process, and (3) sedimentation process).

[0030] However, if the wastewater containing organic matter contains a large amount of slow-degrading organic matter, and the ratio of MLSS concentration to total BOD load is used as the ratio of MLSS concentration to BOD load to determine the time of the biological treatment process, the balance between the satiety state and the starvation state in the operating cycle will be disrupted, making it difficult to form stable granules. Therefore, after diligent research by the inventors, it was found that when the wastewater containing organic matter contains a large amount of slow-degrading organic matter, it is important to determine the time of the biological treatment process by using the ratio of MLSS concentration to BOD load of easily degradable organic matter. Specifically, the inventors have found that stable granule formation is possible by adjusting the time of the biological treatment process so that the ratio of the MLSS concentration in the semi-batch reactor 10 to the BOD load of easily degradable organic matter in the semi-batch reactor 10 (BOD load of easily degradable organic matter / MLSS) multiplied by [operating cycle time / biological treatment process time] (hereinafter sometimes referred to as "value A") is in the range of 0.05 to 0.25 kgBOD / kgMLSS / day.

[0031] The "A value" is preferably in the range of 0.05 to 0.25 kgBOD / kgMLSS / d, and more preferably in the range of 0.075 to 0.2 kgBOD / kgMLSS / d. If this value is less than 0.05 kgBOD / kgMLSS / d, appropriate satiety and starvation states cannot be formed, making stable granule formation difficult. Conversely, if this value is greater than 0.25 kgBOD / kgMLSS / d, the starvation period will be too short, making stable granule formation difficult.

[0032] The following describes a method for calculating the BOD load of easily decomposable organic matter. The following calculation method is illustrative and not limited to it.

[0033] <Example 1 of calculating the BOD load of easily decomposable organic matter> The change in the oxygen consumption rate of microbial sludge in organic matter-containing wastewater over time is measured. The oxygen consumption rate is determined by the known OUR (Oxygen Uptake Rate) test. The OUR test is performed, for example, by mixing wastewater and microbial sludge and reacting them in batches, and measuring the oxygen consumption rate of the microbial sludge over time. It is preferable that the microbial sludge used in the OUR test is well acclimated to the wastewater under test. When well acclimated microbial sludge is used, the oxygen consumption rate is highest immediately after the start of the test and then gradually decreases. This is because the decomposition rate of easily decomposable organic matter in organic matter-containing wastewater is fast, so the amount of easily decomposable organic matter decreases over time, and the proportion of slowly decomposable organic matter increases.

[0034] Then, by dividing the oxygen consumption rate measured at any given time by the sludge concentration of the sludge under test, the change in the oxygen consumption rate per unit of microbial sludge over time is determined. The time during which the oxygen consumption rate per unit of microbial sludge is maintained at, for example, 0.4 kgO2 / kgMLVSS / d or higher is judged to indicate the presence of readily decomposable organic matter, and the cumulative oxygen consumption used up to that point is estimated to be the BOD concentration of the readily decomposable organic matter. By multiplying the estimated BOD concentration of readily decomposable organic matter by the amount of organic matter-containing wastewater introduced into the semi-batch reaction tank, the BOD load of readily decomposable organic matter is calculated.

[0035] <Example 2 of calculating the BOD load of easily decomposable organic matter> As a typical example of slow-degrading organic matter, solid organic matter is a common example. Therefore, if wastewater contains high concentrations of organic suspended solids (SS) components, the BOD concentration of the slow-degrading organic matter may be calculated using a formula (which may also be a map, table, etc.) that defines the relationship between the BOD concentration of the slow-degrading organic matter and the organic SS components, which has been determined in advance. Then, the BOD concentration of easily degradable organic matter may be determined by subtracting the BOD concentration of the slow-degrading organic matter, calculated from the total BOD concentration measured separately, and the BOD load of easily degradable organic matter may be calculated. In this case, it is also possible to determine the concentration of slow-degrading organic matter in real time by providing a means for measuring the organic SS components in the wastewater (SS meter or turbidimeter, etc.) and monitoring the concentration. This calculation method is suitable for wastewater with an SS concentration of 100 mg / L or more and is particularly effective when dealing with raw sewage (influent sewage that has not undergone pretreatment such as sedimentation) as the target wastewater.

[0036] <Example 3 of calculating the BOD load of easily decomposable organic matter> In the case of wastewater where the ratio of slow-degrading organic matter to easily degradable organic matter does not fluctuate significantly, the BOD concentration of easily degradable organic matter (or the BOD concentration of slow-degrading organic matter) can be calculated from an equation (which may also be a map, table, etc.) that defines the relationship between the BOD concentration of easily degradable organic matter (or the BOD concentration of slow-degrading organic matter) and the COD and TOC concentrations, and the BOD load of easily degradable organic matter can be calculated. In this case, the BOD concentration of easily degradable organic matter (or the BOD concentration of slow-degrading organic matter) can be determined in real time by monitoring the COD and TOC concentrations of the organic matter-containing wastewater flowing into the semi-batch reactor using a means for measuring these concentrations.

[0037] In the semi-batch reaction tank 10, the sludge retention time (SRT) is preferably in the range of 5 to 25 days, and more preferably in the range of 10 to 15 days, from the standpoint of stable granule formation. For example, the sludge extraction pump 24 shown in Figures 1 and 2 is operated so that the SRT is in the range of 5 to 25 days, and sludge is extracted from the sludge extraction port 22 through the sludge extraction pipe 32. If the "A value" is below 0.05, the proportion of microorganisms capable of growth is small, and the amount of sludge extracted cannot be increased, making it difficult to extend the SRT beyond 30 days, with 25 days being the limit.

[0038] SRT is expressed by the following formula: SRT[d] = Amount of sludge present in the tank [kg] / Amount of sludge discharged from the system per day [kg / d] Furthermore, the MLSS concentration in the semi-batch reaction vessel 10 is preferably in the range of 1500 to 10000 mg / L, and more preferably in the range of 3000 to 8000 mg / L, although this depends on the total BOD load, in terms of stable granule formation. Furthermore, the value obtained by multiplying the ratio of MLSS concentration to the total BOD load including slow-degrading and easily degrading organic matter in the semi-batch reaction tank 10 by [the time of the operation cycle / the time of the biological treatment process] is preferably in the range of 1.0 kg BOD / kg MLSS / d or less, and more preferably in the range of 0.5 kg BOD / kg MLSS / d or less. If it is 1.0 kg BOD / kg MLSS / d or more, undegraded BOD components may accumulate in the sludge in the reaction tank, worsening the settling properties, or granule formation and maintenance may become difficult due to the appearance of filamentous fungi that cause poor sludge settling.

[0039] 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 fat 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.

[0040] The pH in the semi-batch reaction vessel 10 is preferably set within a range suitable for general microorganisms, for example, preferably in the range of 6 to 9, and more preferably in the range of 6.5 to 7.5. If the pH value falls outside the above range, it is preferable to control the pH by adding an acid, alkali, etc.

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

[0042] In order to promote the granulation of microbial sludge, Fe is added to the organic matter-containing wastewater in the semi-batch reaction tank 10 or to the organic matter-containing wastewater before it is introduced into the semi-batch reaction tank 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.

[0043] Another example of a granule forming apparatus according to this embodiment is shown in Figure 3. In the granule forming apparatus 1 of Figure 3, a wastewater supply pipe 28 is connected to a wastewater inlet 40 at the bottom of a semi-batch reaction tank 10 via a wastewater inlet pump 12 and a wastewater inlet valve 38. A wastewater discharge section 42 is connected to the wastewater inlet 40 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 located above the wastewater inlet 40, and a biological treated water pipe 30 is connected to the biological treated water outlet 16 via a biological treated water discharge valve 18. Although the biological treated water outlet 16 is located above the wastewater inlet 40, it is preferable that it be located as far away from the wastewater inlet 40 as possible to prevent short circuits of incoming organic matter-containing wastewater and to form granules more efficiently, and it is even more preferable that it be located at the water level during the settling process. The control device 20 is electrically connected, for example, to the wastewater inlet pump 12, the wastewater inlet valve 38, the biological treated water discharge valve 18, the sludge extraction pump 24, the aeration pump 14, and the motor 34 of the agitator. Otherwise, the configuration is the same as that of the granule forming apparatus 1 in Figure 2.

[0044] In the granule forming apparatus 1 shown in Figure 3, in the (4) discharge process, the wastewater inlet valve 38 is opened and the wastewater inlet pump 12 is activated, allowing the wastewater containing organic matter to flow from the wastewater inlet 40 through the wastewater supply pipe 28 to the wastewater discharge section 42 and into the semi-batch reaction tank 10, thereby discharging the biologically treated water from the biologically treated water outlet 16 through the biologically treated water pipe 30.

[0045] Thus, in the granule forming apparatus 1 shown in Figure 3, granules are formed by repeating the following steps: (1) inflow / discharge process, (2) biological treatment process, and (3) sedimentation process. This 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.

[0046] In the granule forming apparatus 1 shown in Figure 3, 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.

[0047] The wastewater inflow rate in the inflow / discharge process is preferably in the range of 10% to 100%. The wastewater inflow rate is the ratio of the amount of treated water inflow in one operating cycle to the effective volume in the semi-batch reactor 10. Here, in order to increase the concentration of the substances to be treated remaining in the semi-batch reactor 10, it is better to set the inflow rate of treated water as high as possible. On the other hand, the higher the wastewater inflow rate, the greater the concern about deterioration of the treated water due to short circuits of the treated water. Therefore, considering these factors, it is more preferable to set the wastewater inflow rate in the range of 20% to 80%. However, if a treatment device such as an activated sludge tank is installed downstream of the semi-batch reactor 10, and the water quality of the final treated water after the downstream treatment device does not deteriorate, there is no particular restriction on the wastewater inflow rate, and it is possible to set it to, for example, more than 100%. When the wastewater inflow rate exceeds 100%, it is preferable to set the upper limit of the wastewater inflow rate to 200% or less in order to suppress a decrease in the number of operating cycles.

[0048] The time for the inflow / discharge process is determined, for example, according to the inflow rate of wastewater and the flow rate of water to be treated into the semi-batch reactor 10. However, if the water surface load of the semi-batch reactor 10, which is the value obtained by dividing the flow rate of wastewater into the semi-batch reactor 10 by the horizontal cross-sectional area of ​​the semi-batch reactor 10, is set high, it becomes possible to selectively discharge the lighter sludge fraction from the sludge out of the system and leave the highly sedimentable sludge fraction in the tank. This promotes the formation of highly sedimentable biological sludge, but during the start-up period when the sedimentability of the sludge is not high, there is a concern that the sludge in the tank will flow out and the biological treatment function will deteriorate. On the other hand, if the water surface load of the semi-batch reactor 10 is set low, the selective effect of the sludge will be reduced, and if the inflow rate of wastewater is further increased, there is a concern that the inflow / discharge process time will be longer and it will be difficult to form highly sedimentable sludge. Considering the above circumstances, it is preferable that the water surface load on the semi-batch reaction tank 10 be between 0.5 m / h and 20 m / h, and preferably in the range of 1 m / h to 10 m / h. Furthermore, if it becomes possible to set a higher water surface load on the semi-batch reaction tank 10 as the settling rate of the biological sludge in the tank improves, it is possible to increase the water surface load on the semi-batch reaction tank 10 according to the settling rate of the biological sludge, and shorten the inflow / outflow process time according to the water surface load and the inflow rate of the treated water.

[0049] Another example of an aerobic granule forming apparatus according to this embodiment is shown in Figure 4. In the granule forming apparatus 1 of Figure 4, a wastewater supply pipe 28 is connected to a wastewater inlet 40 at the bottom of a semi-batch reaction tank 10 via a wastewater inlet pump 12 and a wastewater inlet valve 38. A wastewater discharge section 42 is connected to the wastewater inlet 40 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 40, and a biological treated water pipe 30 is connected to the biological treated water outlet 16 via a biological treated water discharge valve 18. Although the biological treated water outlet 16 is provided above the wastewater inlet 40, it is preferable that it be provided as far away from the wastewater inlet 40 as possible in order to prevent short circuits of incoming organic matter-containing wastewater and to form granules more efficiently, and it is more preferable that it be provided at the water level during the settling process. The control device 20 is electrically connected, for example, to the wastewater inlet pump 12, the wastewater inlet valve 38, the biologically treated water discharge valve 18, the sludge extraction pump 24, and the aeration pump 14. Otherwise, the configuration is the same as that of the granule forming apparatus 1 in Figure 1.

[0050] In the granule forming apparatus 1 shown in Figure 4, in the (4) discharge process, the wastewater inlet valve 38 is opened and the wastewater inlet pump 12 is activated, allowing organic matter-containing wastewater to flow from the wastewater inlet 40 through the wastewater supply pipe 28 to the wastewater discharge section 42 and into the semi-batch reaction tank 10, thereby discharging the biologically treated water from the biologically treated water outlet 16 through the biologically treated water pipe 30. The operation and stopping of the wastewater inlet pump 12, sludge extraction pump 24, and aeration pump 14, as well as the opening and closing of the wastewater inlet valve 38 and the biologically treated water discharge valve 18, may be controlled by the control device 20.

[0051] Thus, 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.

[0052] <Wastewater treatment method and wastewater treatment apparatus> The wastewater treatment apparatus according to this embodiment includes a continuous biological treatment tank that continuously receives organic wastewater containing organic matter and biologically treats the organic wastewater containing organic matter with biological sludge. In the wastewater treatment method and wastewater treatment apparatus according to this embodiment, granules formed by the above-described aerobic granule formation method are supplied to the continuous biological treatment tank that continuously receives organic wastewater containing organic matter and biologically treats the organic wastewater containing organic matter with biological sludge.

[0053] Figure 5 shows a schematic configuration of an example of a wastewater treatment apparatus according to this embodiment. The wastewater treatment apparatus 3 comprises a wastewater storage tank 50, a semi-batch reaction tank 10, a continuous biological treatment tank 52, and a solid-liquid separation device 54.

[0054] In the wastewater treatment device 3, the outlet of the wastewater storage tank 50 and the wastewater inlet of the continuous biological treatment tank 52 are connected by a wastewater supply pipe 66 via a pump 56 and a valve 58. The outlet of the continuous biological treatment tank 52 and the inlet of the solid-liquid separator 54 are connected by a pipe 70. The treated water outlet of the solid-liquid separator 54 is connected to a treated water pipe 72. The sludge outlet of the solid-liquid separator 54 is connected to a sludge discharge pipe 74 via a valve 62, and the upstream side of the valve 62 of the sludge discharge pipe 74 and the return sludge inlet of the continuous biological treatment tank 52 are connected by a sludge return pipe 76 via a pump 64. The space between the pump 56 and the valve 58 of the wastewater supply pipe 66 and the wastewater inlet of the semi-batch reaction tank 10 are connected by a wastewater inlet valve 38 via a wastewater supply pipe 28. The biological treated water outlet of the semi-batch reaction tank 10 and the biological treated water inlet of the continuous biological treatment tank 52 are connected by a biological treated water piping 30 via a biological treated water discharge valve 18. The sludge outlet of the semi-batch reaction tank 10 and the sludge inlet of the continuous biological treatment tank 52 are connected by a sludge piping 68 via a pump 60.

[0055] The continuous biological treatment tank 52 is equipped with, for example, a stirring device, an aeration pump, and an aeration device connected to the aeration pump. The stirring device agitates the liquid inside the tank, and oxygen-containing gases such as air supplied from the aeration pump are supplied into the tank through the aeration device.

[0056] The solid-liquid separation device 54 is a separation device for separating biological sludge from treated water containing biological sludge into biological sludge and treated water, and examples of separation devices include sedimentation separation, pressurized flotation, filtration, and membrane separation.

[0057] In the wastewater treatment device 3, first, valve 58 is opened and pump 56 is activated, supplying organic matter-containing wastewater from wastewater storage tank 50 to continuous biological treatment tank 52 through wastewater supply pipe 66. In continuous biological treatment tank 52, biological treatment of wastewater with biological sludge is carried out under aerobic conditions (continuous biological treatment process). The treated water treated in continuous biological treatment tank 52 is supplied from the outlet of continuous biological treatment tank 52 through pipe 70 to solid-liquid separator 54. In solid-liquid separator 54, biological sludge is separated from the treated water (solid-liquid separation process). The treated water that has undergone solid-liquid separation is discharged out of the system from the treated water outlet of solid-liquid separator 54 through treated water pipe 72. The solid-liquid separated biological sludge is discharged out of the system through sludge discharge pipe 74 by opening valve 62. Pump 64 may be activated and at least a portion of the solid-liquid separated biological sludge may be returned to the continuous biological treatment tank 52 through sludge return pipe 76.

[0058] When operating the semi-batch reaction tank 10, the wastewater inlet valve 38 is opened, and at least a portion of the organic matter-containing wastewater in the wastewater storage tank 50 is supplied to the semi-batch reaction tank 10 through the wastewater supply pipe 28. In the semi-batch reaction tank 10, the operation cycle of (1) inlet process, (2) biological treatment process, (3) sedimentation process, and (4) discharge process (or the operation cycle of (1) inlet process / discharge process, (2) biological treatment process, and (3) sedimentation process) is repeated to form granules, and the pump 60 is operated to supply the formed granules to the continuous biological treatment tank 52 through the sludge pipe 68.

[0059] In the continuous biological treatment tank 52 shown in Figure 5, the example of biological treatment using a standard activated sludge method for treating organic matter, etc., was explained, but it is not limited to this, and the apparatus may also perform biological treatment using systems such as A2O (Anaerobic-Anoxic-Oxic Process) or AO (Anaerobic-Oxic Process) (systems that install an oxygen-free treatment tank or an anaerobic treatment tank), oxidation ditch method, or step-inflow multi-stage activated sludge method. Furthermore, the apparatus may perform biological treatment in the presence of carriers such as polyurethane, plastic, or resin.

[0060] In the wastewater treatment device 3 shown in Figure 5, a configuration equipped with a solid-liquid separator 54 was described as an example, but it is not necessarily required to include the solid-liquid separator 54. However, it is preferable for the wastewater treatment device 3 to be equipped with a solid-liquid separator 54 that separates biological sludge from treated water discharged from the continuous biological treatment tank 52, and a sludge return pipe 76 that returns the biological sludge discharged from the solid-liquid separator 54 to the continuous biological treatment tank 52, in order to improve the wastewater treatment efficiency by circulating the granules. [Examples]

[0061] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0062] A water flow test was conducted using a semi-batch reactor with an effective reaction vessel volume of 33 L (125 mm × 438 mm × effective water depth of 600 mm). Granulation was evaluated using the values ​​of SVI5 and SVI30 as indicators. 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 gently stirred to make the sludge concentration as uniform as possible, and then the sludge interface is measured after standing for 5 minutes. The volume percentage (%) of the sludge in the graduated cylinder is then calculated. Next, the MLSS (mg / L) of the sludge is measured. These values ​​are then applied to the following formula to calculate SVI5. A smaller SVI5 value indicates sludge with 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.)

[0063] The wastewater used was raw sewage that had flowed into a sewage treatment plant, and was pre-treated using a coarse screen with a mesh size of 2 mm without sedimentation. Table 1 shows the total BOD concentration, easily decomposable BOD concentration, and slowly decomposable BOD concentration of the raw sewage during the test period. The ratio of the slowly decomposable BOD concentration to the total BOD concentration of the raw sewage was 0.5 or higher.

[0064] [Table 1]

[0065] The operating cycle for the semi-batch reactor was carried out as follows. (1) Inflow / Outflow Process: Over a period of 50 minutes, wastewater was introduced into a semi-batch reaction vessel, and the supernatant water was discharged as treated water. The wastewater inflow rate was 100%. (2) Biological treatment process: The time for the biological treatment process was set so that the value obtained by multiplying the ratio of MLSS concentration to the BOD load of easily decomposable organic matter in the semi-batch reactor by [operating cycle time / biological treatment process time] (A value in the chemical formula) was the value in Table 2. During the set time, air was supplied from the aeration device installed at the bottom of the semi-batch reactor, and the biological treatment process was carried out. (3) Settlement process: The supply of air from the aeration device was stopped and the tank was left to stand for 15 to 30 minutes to allow the sludge in the semi-batch reaction tank to settle. The above operating cycles (1) to (3) were repeated as one cycle.

[0066] The value (A value) obtained by multiplying the ratio of MLSS concentration to BOD load of easily degradable organic matter in a semi-batch reactor by [operating cycle time / biological treatment process time] can be calculated, for example, as follows. A=(((BC) / 1000×(H×D / 100×G)) / (I / 1000×H)) ×(F / E) Here, B = Easily decomposable BOD concentration in wastewater [mg / L] C = Easily degradable BOD concentration after treatment [mg / L] D = Percentage of wastewater introduced per cycle relative to the effective volume of the reactor [%] E = Biological processing time per cycle [minutes] F = Total process time for one cycle [minutes] G = Number of cycles per day [cycles / day] H = Effective volume of the reaction vessel [m³ 3 ] I = MLSS [mg / L]

[0067] <Conditions for the biological treatment process> [Table 2]

[0068] Figure 6 shows the daily changes in SVI and average sludge particle size under conditions 1-2 (comparative examples) in Table 2, and Figure 7 shows the daily changes in SVI and average sludge particle size under conditions 3-4 (examples) in Table 2.

[0069] Under Condition 1, the system was operated so that the MLSS was in the range of 3000-4000 mg / L, and the biological treatment process time was set so that the A value was less than 0.04-0.05 kgBOD / kgMLSS / day. By the 20th day after the start of water flow, SVI30 decreased to approximately 80 mL / g and SVI5 to 170 mg / L. The particle size of the microbial sludge also increased, with an average particle size of 200 μm. However, after the 20th day, the decrease in SVI and the increase in microbial sludge particle size stagnated.

[0070] Under Condition 2, the system was operated so that the MLSS was in the range of 5000-6000 mg / L, and the biological treatment process time was set so that the A value was less than 0.02-0.05 kgBOD / kgMLSS / day. An increase in SVI was observed from around 40 days after the start of water flow. Under Condition 2, the particle size of the microbial sludge hardly changed.

[0071] During the third condition period, the system was operated so that the MLSS was approximately 3500 mg / L, and the biological treatment process time was set so that the A value was 0.05 to 0.1 kg BOD / kg MLSS / day. As a result, SVI5 decreased to approximately 100 mL / g. In addition, the particle size of the microbial sludge increased, with an average particle size of 300 μm.

[0072] Under condition 4, the system was operated so that the MLSS was approximately 4000-5000 mg / L, and the biological treatment process time was set so that the A value was 0.075-0.125 kgBOD / kgMLSS / day. As a result, SVI5 decreased to approximately 40 mL / g, and SVI30 decreased to approximately 30 mL / g. In addition, the particle size of the microbial sludge increased, with an average particle size of 350 μm. [Explanation of Symbols]

[0073] 1 Granule forming apparatus, 3 Wastewater treatment apparatus, 10 Semi-batch reaction tank, 12 Wastewater inlet pump, 14 Aeration pump, 16 Biologically treated water outlet, 18 Biologically treated water discharge valve, 20 Control device, 22 Sludge extraction port, 24 Sludge extraction pump, 26 Aeration apparatus, 28, 66 Wastewater supply piping, 30 Biologically treated water piping, 32 Sludge extraction piping, 34 Motor, 36 Agitator, 38 Wastewater inlet valve, 40 Wastewater inlet, 42 Wastewater discharge section, 50 Wastewater storage tank, 52 Continuous biological treatment tank, 54 Solid-liquid separation apparatus, 56, 60, 64 Pumps, 58, 62 Valves, 68 Sludge piping, 70 Piping, 72 Treated water piping, 74 Sludge discharge piping, 76 Sludge return piping.

Claims

1. A method for forming aerobic granules using a semi-batch reactor, comprising an operation cycle comprising: an inflow step of introducing organic matter-containing wastewater; a biological treatment step of biologically treating the organic matter in the organic matter-containing wastewater with microbial sludge; a sedimentation step of settling the microbial sludge; and a discharge step of discharging the biologically treated water, wherein aerobic granules are formed by performing this operation cycle. The aforementioned organic matter includes easily decomposable organic matter and slowly decomposable organic matter. The time of the biological treatment process is adjusted so that the ratio of the MLSS concentration in the semi-batch reactor to the BOD load of the easily decomposable organic matter in the semi-batch reactor, multiplied by [the time of the operation cycle / the time of the biological treatment process], is in the range of 0.05 to 0.125 kg BOD / kg MLSS / day. A method for forming aerobic granules, characterized in that the sludge retention time in the aforementioned semi-batch reaction tank is set to a range of 5 to 25 days.

2. The method for forming aerobic granules according to claim 1, characterized in that the ratio of the BOD concentration of the slow-degrading organic matter in the organic matter-containing wastewater to the total BOD concentration of the organic matter-containing wastewater flowing into the semi-batch reaction vessel is 0.5 or more.

3. The method for forming aerobic granules according to claim 1 or 2, characterized in that the biological treatment water outlet of the semi-batch reaction tank is provided above the wastewater inlet, and the organic matter-containing wastewater is allowed to flow into the semi-batch reaction tank from the wastewater inlet, thereby discharging the biological treatment water from the biological treatment water outlet.

4. An aerobic granule forming apparatus comprising a semi-batch reactor that forms aerobic granules by performing an operating cycle comprising: an inflow step of introducing wastewater containing organic matter; a biological treatment step of biologically treating the organic matter in the wastewater containing organic matter with microbial sludge; a sedimentation step of settling the microbial sludge; and a discharge step of discharging the biologically treated water. The aforementioned organic matter includes easily decomposable organic matter and slowly decomposable organic matter. The system includes means for adjusting the time of the biological treatment process such that the ratio of the MLSS concentration in the semi-batch reactor to the BOD load of the easily decomposable organic matter in the semi-batch reactor is multiplied by [the time of the operation cycle / the time of the biological treatment process] to be in the range of 0.05 to 0.125 kg BOD / kg MLSS / day. An aerobic granule forming apparatus characterized in that the sludge retention time in the aforementioned semi-batch reaction tank is in the range of 5 to 25 days.

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