Water treatment method and water treatment device

Abstract

This water treatment method involves repeating, in a semi-batch reaction tank, an operation cycle including: an inflow step in which water to be treated containing a substance to be treated flows in; a biological treatment step for biologically treating, with a microbial sludge, the substance to be treated in the water to be treated; a sludge discharge step for discharging the microbial sludge; a sedimentation step for sedimenting the microbial sludge; and a treated water discharge step for discharging the biologically treated water obtained by the biological treatment step, the water treatment method being characterized in that whether the sludge discharge step is executed or not and / or the execution time is determined on the basis of the execution time of the biological treatment step or the accumulated time obtained by accumulating eutrophic state times from the start of the biological treatment step until the concentration of the substance to be treated in the water to be treated is reduced to a predetermined value.

Description

Water treatment method and water treatment apparatus

[0001] The present disclosure relates to a water treatment method and a water treatment apparatus.

[0002] Conventionally, for the biological wastewater treatment of organic wastewater containing organic substances and the like, the activated sludge method that utilizes an aggregate of microorganisms called flocs (aerobic biological sludge) has been used. However, in the activated sludge method, when separating the flocs (aerobic biological sludge) and the treated water in the sedimentation tank, the sedimentation rate of the flocs is 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, solid-liquid separation obstacles such as bulking in the sedimentation tank may occur, making it impossible to maintain the treatment.

[0003] On the other hand, in anaerobic biological treatment, it is common to utilize an aggregate in which microorganisms called granules are densely aggregated and granulated (anaerobic biological sludge). 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, making it possible to achieve high-speed treatment of wastewater. However, anaerobic biological treatment may have problems such as the 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 the treated water quality is poor in anaerobic biological treatment alone and it is discharged into a river or the like, it may be necessary to separately perform aerobic treatment such as the activated sludge method.

[0004] In recent years, it has become clear that by using a semi-batch treatment apparatus that intermittently flows wastewater into the reaction tank, it is possible to form granulated biological sludge with good sedimentation properties not only with anaerobic biological sludge but also with aerobic biological sludge (see, for example, Patent Documents 1 to 4). The granulated biological sludge has, for example, an average particle size of 0.2 mm or more and a sedimentation rate of 5 m / h or more. In semi-batch biological treatment, it is common to repeat four steps: (1) inflow of wastewater, (2) biological treatment of wastewater by microbial sludge, (3) sedimentation of biological sludge, and (4) discharge of treated water in one biological treatment tank.

[0005] Furthermore, Patent Document 5 discloses a semi-batch biological treatment method that repeatedly performs the following steps: (1) inflow of wastewater and discharge of treated water, (2) biological treatment of wastewater with biological sludge, and (3) sedimentation of biological sludge. This makes it possible to obtain biological sludge with high sedimentation properties, such as granulated biological sludge.

[0006] International Publication No. 2004 / 024638, Japanese Patent Publication No. 2008-212878, Japanese Patent Publication No. 4975541, Japanese Patent Publication No. 4804888, Japanese Patent Publication No. 2016-77931

[0007] Biological treatment involves converting target substances in treated water into other substances using the metabolism of microorganisms, but this process leads to the proliferation of microorganisms. Since these increased microorganisms constitute excess sludge, it is desirable to properly discharge them from the reaction tank.

[0008] Therefore, the purpose of this disclosure is to provide a water treatment method and a water treatment apparatus that can extract excess sludge at an appropriate time and / or extract an appropriate amount of excess sludge.

[0009] The present disclosure is a water treatment method that repeatedly performs an operating cycle in a semi-batch reaction tank, the cycle comprising: an inflow step of introducing water to be treated containing a substance to be treated; a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge; a sludge discharge step of discharging the microbial sludge; a sedimentation step of settling the microbial sludge; and a treated water discharge step of discharging the biologically treated water obtained from the biological treatment step, characterized in that the presence or absence of the sludge discharge step and / or the duration of the sludge discharge step are determined based on the execution time of the biological treatment step, or the accumulated time obtained by accumulating the time of satiety from the start of the biological treatment step until the concentration of the substance to be treated in the water to be treated decreases to a predetermined value.

[0010] Furthermore, in the water treatment method disclosed herein, it is preferable to perform the treated water discharge step while performing the inflow step.

[0011] Furthermore, in the water treatment method of the present disclosure, if the microbial sludge concentration in the semi-batch reaction tank during the biological treatment step is less than a predetermined value, it is preferable to either omit the sludge discharge step or set the duration of the step to zero.

[0012] Furthermore, the water treatment apparatus of the present disclosure is characterized by comprising: an inflow step of introducing water to be treated containing a substance to be treated; a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge; a sludge discharge step of discharging the microbial sludge; a sedimentation step of settling the microbial sludge; and a treated water discharge step of discharging the biologically treated water obtained from the biological treatment step; and a determination means for determining whether or not to perform the sludge discharge step and / or the duration of the performance based on the time of the biological treatment step or the time of satiety from the start of the biological treatment step until the concentration of the substance to be treated in the water to be treated decreases to a predetermined value.

[0013] According to this disclosure, it is possible to provide a water treatment method and a water treatment apparatus that can extract excess sludge at an appropriate time and / or extract an appropriate amount of excess sludge.

[0014] This is a schematic diagram showing an example of a water treatment apparatus according to the embodiment of this disclosure. This is a schematic diagram showing another example of a water treatment apparatus according to the embodiment of this disclosure. This is a flowchart showing an example of an operating cycle performed by the water treatment apparatus shown in Figure 1. This is a flowchart showing another schematic diagram showing another example of a water treatment apparatus according to the embodiment of this disclosure. This is a flowchart showing an example of an operating cycle performed by the water treatment apparatus shown in Figure 6. This is a diagram showing the change in the concentration of the target substance in the water to be treated over time in the biological treatment process.

[0015] Embodiments of this disclosure will be described below. These embodiments are examples of implementing this disclosure, and this disclosure is not limited to these embodiments.

[0016] Figure 1 shows a schematic of an example of a water treatment apparatus according to the present disclosure, and its configuration will be described. The water treatment apparatus 1 includes a semi-batch reaction tank 10. An aeration device 26 connected to an aeration pump 14 is installed in the lower part of the inside of the semi-batch reaction tank 10. The water treatment apparatus 1 also includes a wastewater supply pipe 28, a wastewater inlet pump 12, and a wastewater inlet valve 38. The wastewater supply pipe 28 is connected to a wastewater inlet 40 at the lower part of the semi-batch reaction tank 10 via the wastewater inlet pump 12 and the wastewater inlet valve 38. The water treatment apparatus 1 also includes a biological treatment water pipe 30 and a biological treatment water discharge valve 18. The biological treatment water pipe 30 is connected to a biological treatment water outlet 16 of the semi-batch reaction tank 10 via the biological treatment water discharge valve 18. The water treatment apparatus 1 also includes a sludge extraction pipe 32 and a sludge extraction pump 24. The sludge extraction pipe 32 is connected to the sludge extraction port 22 located at the bottom of the semi-batch reaction tank 10 via the sludge extraction pump 24.

[0017] The water treatment device 1 is equipped with a control device 20. The control device 20 is composed of a microcomputer consisting of a CPU for calculating programs, ROM and RAM for storing programs and calculation results, and electronic circuits, etc. It reads a predetermined program stored in the ROM, etc., executes the program, and controls the operation of the water treatment device 1. The control device 20 is electrically connected to each of the following: the wastewater inlet pump 12, the wastewater inlet valve 38, the biological treatment water discharge valve 18, the sludge extraction pump 24, and the aeration pump 14. The control device 20 controls the operation and stopping of each pump and the opening and closing of each valve during the operation of the water treatment device 1.

[0018] In the water treatment device 1, for example, the following operating cycle is performed.

[0019] (1) Inflow process: The wastewater inflow valve 38 is opened and the wastewater inflow pump 12 is activated, and the water to be treated is flowed through the wastewater supply pipe 28 into the semi-batch reaction tank 10 from the wastewater inlet 40.

[0020] The water to be treated includes, for example, wastewater from food processing plants, chemical plants, semiconductor plants, machinery plants, sewage, human waste, and river water. The water to be treated contains biodegradable substances. These substances include, for example, organic matter and nitrogen-containing substances, such as ammonia nitrogen and nitrate nitrogen. If the water contains organic matter that is difficult to decompose, it can be treated by first applying physicochemical treatments such as ozone treatment or Fenton treatment to convert it into biodegradable components. As for oil and grease, since they can adhere to microbial sludge and have adverse effects, it is preferable to remove them to a level of, for example, 150 mg / L or less using existing methods such as flotation separation, coagulation and pressurized flotation, or adsorption before introducing them into the semi-batch reaction tank 10.

[0021] (2) Biological treatment process: The wastewater inlet pump 12 is stopped, and 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. In this way, the substances to be treated in the water to be treated are biologically treated by microbial sludge in the semi-batch reaction tank 10. For example, if the water to be treated contains organic matter, the organic matter in the water to be treated is decomposed to carbon dioxide by the microbial sludge. Biological treatment is not limited to aerobic reactions; anaerobic reactions are also possible, which involve stirring without supplying air, and a combination of aerobic and anaerobic reactions is also acceptable. An anaerobic state refers to a state in which dissolved oxygen is absent, but oxygen derived from nitrite or nitrate is present. For example, as shown in Figure 2, a stirring device consisting of a motor 34, a stirring blade 36, and a shaft connecting the motor 34 and the stirring blade 36 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.

[0022] (3) Sludge discharge process: The sludge extraction pump 24 is operated to extract a predetermined amount of microbial sludge from the semi-batch reaction tank 10 through the sludge extraction pipe 32. During the extraction of microbial sludge, it is preferable to operate the aeration pump 14 and the stirring device to stir the microbial sludge.

[0023] (4) Settlement process: If the aeration pump 14 or stirring device is operating, they are stopped and left to stand for a predetermined time to allow the microbial sludge in the semi-batch reaction tank 10 to settle. As a result, biologically treated supernatant water is obtained in the semi-batch reaction tank 10.

[0024] (5) Process to discharge treated water: The biological treated water discharge valve 18 is opened and the supernatant water obtained in the sedimentation process is discharged as biological treated water from the biological treated water outlet 16 into the biological treated water piping 30.

[0025] In this embodiment, the operation cycle including steps (1) to (5) is repeated. However, the sludge discharge step (3) is controlled based on the accumulated time obtained by accumulating the execution time of the biological treatment step (2), as described below.

[0026] Figure 3 is a flowchart showing an example of an operating cycle performed by the water treatment device 1 shown in Figure 1. In step S10, the inflow process is performed, and in step S12, the biological treatment process is performed. In step S14, the control device 20 accumulates the time spent on the biological treatment process. Specifically, the control device 20 measures the time spent on the biological treatment process each time the operating cycle is repeated and accumulates the time spent on the biological treatment process. The control device 20 then compares the accumulated time spent on the biological treatment process with a predetermined time. The predetermined time is set, for example, in the range of 200 minutes to 1440 minutes. If the accumulated time is equal to or greater than the predetermined time, the control device 20 decides to perform the sludge discharge process (decision to perform), proceeds to step S16, and performs the sludge discharge process for the predetermined time. If the sludge discharge process is performed, in step S18, the control device 20 resets the accumulated time. Then, the sludge settling process in step S20 and the treated water discharge process in step S22 are performed. On the other hand, if the cumulative time is less than a predetermined time, the control device 20 decides not to perform the sludge discharge process (decision not to perform). Then, it performs the sludge settling process in step S20 and the treated water discharge process in step S22. After the treated water discharge process in step S22, it returns to step S10.

[0027] Figure 4 is a flowchart showing another example of an operating cycle performed by the water treatment device 1 shown in Figure 1. In step S30, the inflow process is performed, in step S32, the biological treatment process is performed, and in step S34, the control device 20 accumulates the execution time of the biological treatment process. Then, in step S36, the control device 20 determines the execution time of the sludge discharge process according to the accumulated time obtained by accumulating the execution time of the biological treatment process. For example, the execution time of the sludge discharge process is determined by applying the actual accumulated time to a map (which may also be a table, formula, etc.) that defines the relationship between the accumulated time and the execution time of the sludge discharge process. Alternatively, for example, the coefficient for calculating the execution time of the sludge discharge process may be obtained by applying the actual accumulated time to a map (which may also be a table, formula, etc.) that defines the coefficient for calculating the execution time of the sludge discharge process, and the value obtained by multiplying the execution time of the biological treatment process performed in step S32 by the above coefficient may be determined as the execution time of the sludge discharge process.

[0028] Then, the process proceeds to step S38, where the sludge discharge process is carried out for the duration determined in step S36. After that, in step S40, the control device 20 resets the accumulated time and carries out the sludge settling process in step S42 and the treated water discharge process in step S44. After the treated water discharge process in step S44, the process returns to step S30.

[0029] In this embodiment, both whether or not to perform the sludge discharge process and the duration of the process may be determined based on the cumulative time of the biological treatment process. For example, if the cumulative time of the biological treatment process is equal to or greater than a predetermined time, it is decided that the sludge discharge process will be performed, and the duration of the sludge discharge process is determined according to the cumulative time of the biological treatment process. If the cumulative time of the biological treatment process is less than a predetermined time, it is decided that the sludge discharge process will not be performed (the duration of the sludge discharge process may be set to zero).

[0030] Figure 5 is a flowchart showing another example of an operating cycle performed by the water treatment device 1 shown in Figure 1. In step S50, the inflow process is performed, and in step S52, the biological treatment process is performed. In step S54, the control device 20 accumulates the time spent performing the biological treatment process. The control device 20 then compares the accumulated time with a predetermined time. If the accumulated time is equal to or greater than the predetermined time, the process proceeds to step S56, where the microbial sludge concentration in the semi-batch reaction tank 10 is measured, for example, using a sludge concentration meter. The control device 20 then compares the measured microbial sludge concentration with a predetermined value. This predetermined value is set, for example, in the range of 1500 to 4000 mg / L. If the measured microbial sludge concentration is equal to or greater than the predetermined value, the control device 20 decides to perform the sludge discharge process (decision to perform), proceeds to step S58, and performs the sludge discharge process for a predetermined time. In step S60, the control device 20 resets the accumulated time and performs the sludge settling process in step S62 and the treated water discharge process in step S64. On the other hand, if the accumulated time accumulated in step S54 is less than a predetermined time, or if the accumulated time accumulated in step S54 is equal to or greater than a predetermined time but the microbial sludge concentration measured in step S56 is less than a predetermined value, the control device 20 decides not to perform the sludge discharge process (decision not to perform), and performs the sludge settling process in step S62 and the treated water discharge process in step S64. After the treated water discharge process in step S64, the process returns to step S50. Although not shown in the diagram, the decision on whether or not to perform the sludge discharge process may be replaced with a decision on the duration of the sludge discharge process, or both may be combined. For example, based on the cumulative time obtained by accumulating the execution time of the biological treatment process, it is determined whether or not to perform the sludge discharge process, and / or the execution time of the sludge discharge process. If the microbial sludge concentration in the semi-batch reaction tank 10 is equal to or greater than a predetermined value, the sludge discharge process is performed based on the above determination. On the other hand, if the microbial sludge concentration in the semi-batch reaction tank 10 is less than a predetermined value, the above determination is canceled, and it is decided not to perform the sludge discharge process (or the execution time of the sludge discharge process may be set to zero). Then, the sludge settling process of step S62 is performed without performing the sludge discharge process.

[0031] Furthermore, in the flowchart of Figure 5, the comparison of the microbial sludge concentration with a predetermined value is performed after the comparison of the accumulated time with the predetermined time, but it may also be performed before the comparison of the accumulated time with the predetermined time. For example, the microbial sludge concentration in the semi-batch reaction tank 10 is measured by a sludge concentration meter. Then, if the measured microbial sludge concentration is equal to or greater than a predetermined value, the control device 20 determines whether or not to perform the sludge discharge process, or determines the duration of the sludge discharge process, based on the accumulated time obtained by accumulating the execution time of the biological treatment process. On the other hand, if the measured microbial sludge concentration is less than a predetermined value, the control device 20 decides not to perform the sludge discharge process, without determining whether or not to perform the sludge discharge process, or determining the duration of the sludge discharge process, based on the accumulated time (it may also be decided that the duration of the sludge discharge process is zero). Then, the sludge settling process of step S62 is performed without performing the sludge discharge process.

[0032] The operation cycle of this embodiment is not limited to a configuration in which the inflow process and the treated water discharge process are performed separately, but may also be a configuration in which the treated water discharge process is performed while the inflow process is being carried out. A specific example will be given below.

[0033] Figure 6 shows a schematic of another example of a water treatment apparatus according to the embodiment of this disclosure, and its configuration will be described. In the water treatment apparatus 2 shown in Figure 6, the same reference numerals are used for components similar to those in the water treatment apparatus 1 shown in Figure 1. In the water treatment apparatus 2 shown in Figure 6, the biological treated water outlet 16 is provided at the water level of the semi-batch reaction tank 10. The wastewater inlet 40 is preferably provided at a lower position than the biological treated water outlet 16, for example, it is preferably provided at a position lower than 50% of the water level of the semi-batch reaction tank 10. The water level of the semi-batch reaction tank 10 is the water level when the liquid in the semi-batch reaction tank 10 is at rest during the sedimentation process.

[0034] In the water treatment apparatus 2 shown in Figure 6, for example, the following operating cycle is performed.

[0035] (1) Inflow process / Treated water discharge process: The wastewater inflow valve 38 is opened and the wastewater inflow pump 12 is activated, causing the treated water to flow into the semi-batch reaction tank 10 from the wastewater inlet 40 through the wastewater supply pipe 28. When the treated water flows in, the biological treated water discharge valve 18 is opened. As a result, the biological treated water (supernatant water) obtained in the sedimentation process is pushed out by the incoming treated water and discharged into the biological treated water pipe 30 from the biological treated water outlet 16.

[0036] (2) Biological treatment process: The wastewater inlet pump 12 is stopped, and 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. In this way, the substances to be treated in the water to be treated are biologically treated by microbial sludge in the semi-batch reaction tank 10.

[0037] (3) Sludge discharge process: The sludge extraction pump 24 is operated to extract a predetermined amount of microbial sludge from the semi-batch reaction tank 10 through the sludge extraction pipe 32. During the extraction of microbial sludge, it is preferable that the microbial sludge is agitated, so it is preferable to operate the aeration pump 14 to agitate with oxygen-containing gas or to operate the agitator to agitate with the agitator blades 36.

[0038] (4) Settlement process: If the aeration pump 14 or agitator is operating, they are stopped and left to stand for a predetermined time to allow the sludge in the semi-batch reaction tank 10 to settle. This yields biologically treated supernatant water.

[0039] In this embodiment, the operation cycle including steps (1) to (4) is repeated. However, the sludge discharge step (3) is controlled based on the cumulative time of the biological treatment step (2), as described above.

[0040] FIG. 7 is a flowchart showing an example of an operation cycle performed by the water treatment apparatus 2 shown in FIG. 6. In step S100, an inflow process / treated water discharge process is performed, and in step S102, a biological treatment process is performed. In step S104, the control device 20 accumulates the execution time of the biological treatment process. Then, the control device 20 compares the accumulated time obtained by accumulating the execution time of the biological treatment process with a predetermined time set in advance. If the accumulated time is equal to or longer than the predetermined time, the process proceeds to step S106, and the concentration of microbial sludge in the semi-batch reaction tank 10 is measured by a sludge concentration meter. If the measured concentration of microbial sludge is equal to or higher than a predetermined value set in advance, the control device 20 determines to perform a sludge discharge process (determination of execution), and proceeds to step S108, where the sludge discharge process is performed for a preset time. In step S110, the control device 20 resets the accumulated time and performs the sludge sedimentation process in step S112. On the other hand, if the accumulated time integrated in step S104 is less than the predetermined time, or if the accumulated time integrated in step S104 is equal to or longer than the predetermined time but the sludge concentration measured in step S106 is less than the predetermined value, the control device 20 determines not to perform the sludge discharge process (determination of non-execution) and performs the sludge sedimentation process in step S112. After the sludge sedimentation process in step S112, the process returns to step S100.

[0041] Although the description in the flowchart is omitted, in the operation cycle of performing the inflow process / treated water discharge process, as described above, based on the accumulated time of the biological treatment process, the execution time of the sludge discharge process may be determined, or both the execution and non-execution of the sludge discharge process and the execution time may be determined. Further, the comparison between the sludge concentration and the predetermined value may be made after or before the comparison between the accumulated time and the predetermined time, as described above.

[0042] By repeating the operation cycle of the present embodiment, granules in which self-granulation has progressed can be formed in the semi-batch reactor 10. Further, as described above, by determining the presence or absence and / or the execution time of the sludge discharge step based on the execution time of the biological treatment step, surplus sludge can be withdrawn at an appropriate timing and / or an appropriate amount of surplus sludge can be withdrawn. Furthermore, when the concentration of microbial sludge in the semi-batch reactor during the biological treatment step is less than a predetermined value, by combining the operation of not performing the sludge discharge step or setting the execution time to zero, even when the concentration of the target substance in the treated water decreases and the amount of surplus sludge generated in the semi-batch reactor 10 decreases, it is possible to suppress excessive withdrawal of microbial sludge from the semi-batch reactor 10.

[0043] Fig. 8 is a diagram showing the change in the concentration of the target substance in the treated water with the passage of time in the biological treatment step. As shown in Fig. 8, in the biological treatment step, since the target substance in the treated water is removed by the microbial sludge, the concentration of the target substance in the treated water decreases with the passage of time. Here, the formation of granules in the semi-batch reactor 10 is important for forming a concentration gradient of the target substance in the semi-batch reactor 10. Therefore, the execution time of the biological treatment step is preferably set so that the time in the saturated state from the start of the biological treatment step until the concentration of the target substance in the treated water decreases and reaches a predetermined value, and the time in the starving state where the concentration of the target substance is less than the predetermined value are each sufficiently ensured. The predetermined value of the target substance concentration that divides the saturated state and the starving state is preferably set within a range of, for example, 0 to 5.0 mg / L, and more preferably within a range of 0 to 1 mg / L.

[0044] In the present embodiment, the presence or absence and / or the execution time of the sludge discharge step in (3) is not limited to being determined based on the integrated time obtained by integrating the execution time of the biological treatment step in (2), and may be determined based on the time in the saturated state from the start of the above biological treatment step until the concentration of the target substance in the treated water decreases and reaches a predetermined value. And the same effect can be obtained even when the presence or absence and / or the execution time of the sludge discharge step in (3) is determined based on the time in the saturated state.

[0045] Here, whether the concentration of the target substance in the water to be treated during the biological treatment process is in a saturated state (reaching a predetermined value) or a depleted state (below a predetermined value) can be determined by using a concentration meter that can detect the concentration of the target substance in real time (for example, an organic matter concentration meter), or it can be estimated based on the behavior of the pH of the water to be treated during the biological treatment process and the ammonia concentration.

[0046] During the biological treatment process, the pH of the treated water decreases over time before rising. The decrease in pH during the biological treatment process is due to the reduction of nitrogen compounds such as organic nitrogen in the treated water to ammonia nitrogen, and the subsequent nitrification of ammonia nitrogen to nitrate and nitrite, which consumes alkalinity. In other words, while the pH of the treated water is decreasing, the concentration of the target substance is high, corresponding to a saturated state exceeding a predetermined value. On the other hand, the increase in pH of the treated water is due to decarboxylation by oxygen-containing gas supplied by the aeration device 26, indicating that there are almost no target substances present in the treated water. In other words, after the pH of the treated water rises, it corresponds to a starvation state where the concentration of the target substance is below a predetermined value.

[0047] Therefore, in this embodiment, for example, the control device 20 monitors the pH value of the water to be treated in the semi-batch reaction tank 10, which is measured by a pH meter, at predetermined intervals during the biological treatment process. The control device 20 then measures the time from the start of the biological treatment process until the pH of the water to be treated changes from decreasing to increasing (i.e., the time of satiety). This measurement of the time of satiety is performed each time the operation cycle is repeated, and the time of satiety is accumulated. Based on the accumulated time obtained by accumulating the time of satiety, the control device 20 determines whether or not to perform the sludge discharge process in (3) and / or the time to perform it. The method of determination is the same as in the case of the accumulated time obtained by accumulating the time of performance of the biological treatment process.

[0048] Furthermore, as mentioned above, in the biological treatment process, ammonia nitrogen is generated, and since this generated ammonia nitrogen is oxidized, the ammonia concentration in the treated water decreases over time. In other words, a high ammonia concentration in the treated water corresponds to a state of saturation, while a low ammonia concentration corresponds to a state of starvation.

[0049] Therefore, in this embodiment, the control device 20 monitors the ammonia concentration value in the water to be treated in the semi-batch reaction tank 10, which is measured by an ammonia concentration meter, at predetermined intervals during the biological treatment process. The control device 20 then measures the time from the start of the biological treatment process until the ammonia concentration value in the water to be treated reaches a predetermined value (i.e., the time of satiety). Then, similarly to the above, the control device 20 determines whether or not to perform the sludge discharge process in (3) and / or the time to perform it based on the accumulated time obtained by accumulating the time of satiety. The predetermined value of the ammonia concentration is preferably, for example, 1 mg / L or less, and more preferably 0.5 mg / L or less.

[0050] Furthermore, the control device 20 may monitor the concentration of the target substance in the water to be treated in the semi-batch reaction tank 10 at predetermined intervals, which is measured by a concentration meter (for example, an organic matter concentration meter) that measures the concentration of the target substance in the biological treatment process. The control device 20 then measures the time from the start of the biological treatment process until the concentration of the target substance in the water to be treated reaches a predetermined value (i.e., the time of satiety). Then, similarly to the above, the control device 20 determines whether or not to perform the sludge discharge process in (3) and / or the time to perform it based on the accumulated time obtained by accumulating the time of satiety. The predetermined value of the concentration of the target substance is preferably set within the range of 0 to 5.0 mg / L, and more preferably within the range of 0 to 1 mg / L.

[0051] In this embodiment, the duration of the biological treatment process may be fixed at the initially set time, but it is preferable to adjust the duration of the biological treatment process according to the duration of the satiety state. This ensures that even if the concentration of the target substance in the water to be treated flowing into the semi-batch reaction tank 10 fluctuates, the duration of the satiety state and the starvation state can be appropriately secured, thereby enabling good granule formation.

[0052] One way to adjust the duration of the biological treatment process according to the duration of the satiety state is, for example, as follows: The control device 20 is instructed to store a preset ratio of satiety state duration to biological treatment process duration. The control device 20 then measures the duration of the satiety state using the method described above and sets the biological treatment process duration based on the preset ratio of satiety state duration to biological treatment process duration. The preset ratio of satiety state duration to biological treatment process duration is preferably in the range of 0.4 to 0.7.

[0053] In this embodiment, even when the duration of the biological treatment process is adjusted, the presence or absence of the sludge discharge process and / or the duration of the process can be determined based on the cumulative duration obtained by accumulating the duration of the biological treatment process or the duration of the saturated state. This allows for the removal of excess sludge at an appropriate time and / or in an appropriate amount. In particular, even when the concentration of the target substance in the water to be treated flowing into the semi-batch reaction tank 10 decreases and the duration of the biological treatment process is shortened, it is possible to suppress the excessive removal of microbial sludge from the semi-batch reaction tank 10.

[0054] The granules formed in the semi-batch reactor 10 are microbial sludge that has undergone self-granulation, and are, for example, microbial 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 the microbial sludge in the semi-batch reactor 10 is granules is determined, for example, by measuring the SVI, which is a sedimentation index of microbial sludge. Specifically, if the value of SVI5 measured by a sedimentation test of the microbial sludge in the semi-batch reactor 10 is below a predetermined value (for example, 80 mL / g or less), it is possible to determine that the microbial sludge is granules. Alternatively, if the particle size distribution of the microbial 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), it is possible to determine that the microbial sludge is granules (note that the lower the SVI value and the larger the average particle size, the better the sedimentation of the granules).

[0055] The volumetric load of the semi-batch reactor 10 is 0.15 kg BOD / m³. ３ / day ~1.00 kg BOD / m ３ Preferably, the range is 0.30 kg BOD / m³ / day. ３ / day ~0.60 kg BOD / m ３ A range of one day is more preferable. By setting the volumetric load of the semi-batch reaction vessel 10 within the above range, it becomes possible to promote granule formation.

[0056] The sludge load in the semi-batch reaction tank 10 is preferably in the range of 0.05 kg BOD / kgMLSS / day to 0.30 kg BOD / kgMLSS / day, and more preferably in the range of 0.10 kg BOD / kgMLSS / day to 0.20 kg BOD / kgMLSS / day. By setting the sludge load in the semi-batch reaction tank 10 within the above range, it is possible to promote granule formation.

[0057] 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.

[0058] In order to promote granule formation, Fe is added to the water to be treated in the semi-batch reactor 10 or to the water to be treated before it is introduced into the semi-batch reactor 10. ２＋ Fe ３＋ Ca ２＋ Mg ２＋ It is preferable to add ions that cause hydroxide formation, such as those mentioned above. While ordinary treated water contains fine particles that act as nuclei for granules, the addition of the above ions can further promote granule nucleation.

[0059] The inflow rate of treated water in the inflow / treated water discharge process is preferably in the range of 10% to 100%. The inflow rate of treated water is the ratio of the amount of treated water inflow to the effective volume in the semi-batch reaction tank 10. Here, in order to promote granule formation, it is better to have as high a inflow rate of treated water as possible, but on the other hand, the higher the inflow rate of treated water, the greater the concern about deterioration of the treated water due to short circuits of treated water. Therefore, considering these factors, it is more preferable to have a inflow rate of treated water 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 reaction tank 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 inflow rate of treated water, and it is possible to set it to, for example, more than 100%. When the inflow rate of treated water exceeds 100%, it is preferable to set the upper limit of the inflow rate of treated water to 200% or less in order to suppress a decrease in the number of operating cycles.

[0060] The linear velocity of the water to be treated in the inflow process / treated water discharge process (the amount of water to be treated relative to the cross-sectional area of ​​the semi-batch reaction tank 10) is preferably 5 m / h or less. If the linear velocity of the water to be treated exceeds 5 m / h, there is a concern that the treated water may deteriorate due to short circuits of the water to be treated, granule outflow, etc. There is no particular lower limit to the linear velocity of the water to be treated in the inflow process / treated water discharge process, but it is preferable to have a value of 0.5 m / h or more in terms of shortening the time of the inflow process / treated water discharge process.

[0061] In this embodiment, a predetermined amount of granulated microbial sludge may be added to the semi-batch reaction tank 10 at the start of operation.

[0062] 1, 2 Water treatment equipment, 10 Half-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 device, 28 Wastewater supply piping, 30 Biologically treated water piping, 32 Sludge extraction piping, 34 Motor, 36 Agitator blade, 38 Wastewater inlet valve, 40 Wastewater inlet.

Claims

1. A water treatment method that repeatedly performs an operating cycle in a semi-batch reaction tank, the cycle comprising: an inflow step of introducing water to be treated containing a substance to be treated; a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge; a sludge discharge step of discharging the microbial sludge; a sedimentation step of allowing the microbial sludge to settle; and a treated water discharge step of discharging the biologically treated water obtained from the biological treatment step, characterized in that the presence or absence of the sludge discharge step and / or the duration of the sludge discharge step are determined based on the execution time of the biological treatment step, or the accumulated time obtained by accumulating the time of satiety from the start of the biological treatment step until the concentration of the substance to be treated in the water to be treated decreases to a predetermined value.

2. The water treatment method according to claim 1, characterized in that the treated water discharge step is performed while the inflow step is performed.

3. The water treatment method according to claim 1 or 2, characterized in that if the microbial sludge concentration in the semi-batch reaction tank during the biological treatment step is less than a predetermined value, the sludge discharge step is either omitted or its duration is set to zero.

4. A water treatment apparatus comprising: an inflow step of introducing water to be treated containing a substance to be treated; a biological treatment step of biologically treating the substance to be treated in the water to be treated with microbial sludge; a sludge discharge step of discharging the microbial sludge; a sedimentation step of settling the microbial sludge; and a treated water discharge step of discharging the biologically treated water obtained from the biological treatment step; and a determination means for determining whether or not to perform the sludge discharge step and / or the duration of the sludge discharge step based on the execution time of the biological treatment step, or the time of satiety from the start of the biological treatment step until the concentration of the substance to be treated in the water to be treated decreases to a predetermined value.

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