Water treatment method and water treatment device

Abstract

To provide a water treatment method and a water treatment device, capable of performing a settling step at a suitable time tailored for settleability of a biological sludge.SOLUTION: A water treatment method includes: an inflow step of making water to be treated flow into a reaction chamber; a biological treatment step of biologically treating the water to be treated in the reaction chamber with a biological sludge; a settling step of settling the biological sludge in the reaction chamber; and a discharging step of discharging biologically-treated water in the reaction chamber. In the settling step, a concentration of the biological sludge at an interface position of the biological sludge in the reaction chamber or at a predetermined level in the reaction chamber is detected by using detecting means for detecting the interface position of the biological sludge or the concentration thereof, and time to finish the settling step is determined based on the detected results.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment method and a water treatment device. [Background technology]

[0002] Conventionally, biological wastewater treatment has used the activated sludge method, which utilizes a collection of microorganisms called flocs (aerobic biological sludge). However, in the activated sludge method, when separating the flocs (aerobic biological sludge) from the treated water in the settling tank, the surface area of ​​the settling tank may need to be very large because the settling speed of the flocs is slow. In addition, the treatment speed of the activated sludge method depends on the sludge concentration in the biological treatment tank, and although the treatment speed can be increased by increasing the sludge concentration, there are cases where the treatment cannot be maintained due to solid-liquid separation problems caused by bulking in the settling tank, etc.

[0003] On the other hand, in anaerobic biological treatment, it is common to utilize a dense collection of microorganisms called granules. Granules have a very fast settling rate and the microorganisms are densely packed together, so the sludge concentration in the biological treatment tank can be increased, making it possible to realize high-speed wastewater treatment. However, anaerobic biological treatment may have problems such as the fact that the types of wastewater to be treated are limited compared to aerobic treatment (activated sludge method) and that the treated water temperature needs to be maintained at about 30 to 35°C. In addition, when anaerobic biological treatment alone is used, the quality of the treated water is poor, and when the treated water is to be discharged into a river or the like, it may be necessary to separately carry out aerobic treatment such as the activated sludge method.

[0004] In recent years, it has become clear that by treating wastewater under special conditions using a semi-batch treatment device that intermittently flows into a reaction tank, it is possible to form granulated biological sludge with good settling properties not only from anaerobic biological sludge but also from aerobic biological sludge (see, for example, Patent Documents 1 to 4). Granulated biological sludge has, for example, an average particle size of 0.1 mm or more and a settling rate of 3 m / h or more. In semi-batch biological treatment, it is common to repeatedly carry out the following steps in one reaction tank: (1) inflow of wastewater, (2) biological treatment of the wastewater with biological sludge, (3) settling of the biological sludge, and (4) discharge of treated water.

[0005] Patent Document 5 discloses a biological treatment method that repeats the steps of (1) inflow of wastewater and discharge of treated water, (2) biological treatment of the wastewater using biological sludge, and (3) settling of the biological sludge. This makes it possible to obtain biological sludge with high settling properties, such as granulated biological sludge. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2004 / 024638 [Patent Document 2] JP 2008-212878 A [Patent Document 3] Patent No. 4975541 [Patent Document 4] Patent No. 4804888 [Patent Document 5] JP 2016-77931 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the semi-batch biological treatment using granular sludge, normal floc-like sludge is often used as the seed sludge. Therefore, from the start-up of the biological treatment to the formation of the granular sludge, the settling speed of the biological sludge in the reaction tank changes dynamically, for example, from about 0.3 m / h to about 5 m / h or more. During this time, if the time of the settling process of the biological sludge is constant, the time of the settling process will be too short when the settling speed is slow, and the time of the settling process will be too long when the settling speed is fast. If the time of the settling process is too short, there is an increased risk of the biological sludge flowing out of the reaction tank. In addition, if the time of the settling process is too long, the biological sludge will stick to the reaction tank and become difficult to flow during the biological treatment process, or the biological sludge will become anaerobic and lose its activity due to the long time that has passed in the settled state, or the biological sludge will float due to the generation of gas accompanying the anaerobic state of the biological sludge.

[0008] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a water treatment method and a water treatment device capable of carrying out the settling step for an appropriate period of time in accordance with the settling properties of biological sludge. [Means for solving the problem]

[0009] The present embodiment is a water treatment method including an inflow process of inflowing water to be treated into a reaction tank, a biological treatment process of biologically treating the water to be treated in the reaction tank with biological sludge, a sedimentation process of settling the biological sludge in the reaction tank, and a discharge process of discharging the biologically treated water in the reaction tank. In the sedimentation process, Concentration Using a detection means for detecting the degree ,before Detecting the concentration of the biological sludge at a predetermined height in the reaction tank; Sludge concentration change rate calculated from detected concentration The water treatment method further comprises determining the end time of the settling step based on the above-mentioned.

[0010] In the water treatment method, it is preferable that the discharge step is carried out while the inflow step is being carried out.

[0012] In the water treatment method, the detection means is preferably a sludge concentration meter that detects the concentration of the biological sludge.

[0014] The present embodiment also includes an inflow process for inflowing water to be treated, a biological treatment process for biologically treating the water to be treated with biological sludge, and a sedimentation process for sedimenting the biological sludge. ,raw a reaction tank for discharging the treated wastewater; and a biological sludge Concentration The settling step detected by a detection means for detecting the degree of settling. In A detected concentration of the biological sludge at a predetermined height in the reaction tank. The rate of change in sludge concentration calculated from and a control unit that determines the end time of the settling process based on the result of the calculation.

[0015] In the water treatment device, it is preferable that the reaction tank performs the discharge step while performing the inflow step.

[0017] In the water treatment device, the detection means is preferably a sludge concentration meter that detects the concentration of the biological sludge. Effect of the Invention

[0019] According to the present invention, it is possible to provide a water treatment method and a water treatment device capable of carrying out the settling step for an appropriate time period in accordance with the settling properties of the biological sludge. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0022] <Water treatment method and water treatment device> An example of a water treatment device according to an embodiment of the present invention is outlined in Fig. 1, and its configuration will be described. The water treatment device 1 includes a reaction tank 10 and a control device 12. A treated water pipe 14 is disposed in the reaction tank 10, and an outlet 16 of the treated water pipe 14 is located on the bottom side of the reaction tank 10. An electromagnetic valve 18a is provided on the treated water pipe 14. A treated water pipe 22 is connected to a treated water outlet 20 of the reaction tank 10. An electromagnetic valve 18b is provided on the treated water pipe 22. An aeration device 26 connected to an aeration blower 24 is provided at the bottom of the reaction tank 10.

[0023] A sludge concentration meter 28 is installed at a predetermined height in the reaction tank 10. The installation position of the sludge concentration meter 28 is within a range of 0.5 m to 3 m below the water surface. The sludge concentration meter 28 is electrically connected to the control device 12.

[0024] Further, the electromagnetic valve 18 a, the electromagnetic valve 18 b, and the aeration blower 24 are each electrically connected to the control device 12.

[0025] The control device 12 is composed of, for example, a microcomputer consisting of a CPU that operates a program, and a ROM and RAM that store the program and operation results, etc., and an electronic circuit, and controls the operation / stop of the aeration blower 24, the opening and closing of valves, etc. As will be described later, the control device 12 determines the end time of the settling process based on the detection value of the sludge concentration in the reaction tank 10 detected by a sludge concentration meter 28.

[0026] An example of the operation of the water treatment device 1 will be described below.

[0027] <(1) Inflow process> The electromagnetic valve 18a is opened to allow a predetermined amount of the water to be treated to flow into the reaction tank 10 from the discharge port 16 of the water to be treated pipe 14. The water to be treated may be, for example, wastewater containing at least one of organic matter and nitrogen compounds, and specific examples thereof include organic wastewater containing biodegradable organic matter, such as wastewater from food processing plants, chemical plants, semiconductor plants, machine factories, sewage, and human waste.

[0028] <(2) Biological treatment process> The electromagnetic valve 18a is closed, the aeration blower 24 is operated, and oxygen-containing gas such as air supplied from the aeration blower 24 is supplied to the reaction tank 10 through the aeration device 26. As a result, in the reaction tank 10, the water to be treated is biologically treated by the biological sludge. The biological reaction is not limited to an aerobic reaction, and it is possible to carry out an anaerobic reaction by stirring without supplying air or the like, or a combination of an aerobic reaction and an anaerobic reaction. An anaerobic state refers to a state in which dissolved oxygen does not exist, but oxygen derived from nitrite or nitrate exists. For example, as shown in FIG. 2, an agitation device consisting of a motor 30, an agitation blade 32, a shaft connecting the motor 30 and the agitation blade 32, etc. is installed in the reaction tank 10, and the aeration blower 24 is stopped and stirring is performed by the agitation device. The agitation device is not limited to the above configuration.

[0029] In the biological treatment process, it is desirable to detect the biological sludge concentration in the reaction tank 10 by a sludge concentration meter 28. The control device 12 reads and stores the biological sludge concentration (detected value) detected by the sludge concentration meter 28.

[0030] <(3) Sedimentation process> The operation of the aeration blower 24 is stopped, and the reaction tank 10 is left in a stationary state for a predetermined period of time to allow the biological sludge in the reaction tank 10 to settle.

[0031] In the settling process, the biological sludge concentration in the reaction tank 10 is detected by the sludge concentration meter 28. In addition, the control device 12 reads the biological sludge concentration (detected value) detected by the sludge concentration meter 28, and determines the end time of the settling process based on the detected value.

[0032] <(4) Discharge process> Depending on the end time of the settling process determined by the control device 12, the electromagnetic valve 18b is opened and the supernatant water obtained in the settling process is discharged as treated water from the treated water discharge port 20 through the treated water pipe 22.

[0033] The treatment cycle consists of (1) the inflow process, (2) the biological treatment process, (3) the sedimentation process, and (4) the discharge process, and is repeated to treat the water to be treated.

[0034] In this embodiment, the inflow step and the discharge step are not limited to being performed separately, and the discharge step may be performed while the inflow step is being performed. That is, the treatment cycle may be repeated to treat the water to be treated, with the cycle consisting of (1) inflow step / discharge step, (2) biological treatment step, and (3) sedimentation step being one cycle.

[0035] Taking the water treatment device 1 of FIG. 1 as an example, the electromagnetic valve 18a is opened to allow the water to be treated to flow into the reaction tank 10 from the outlet 16 of the water to be treated pipe 14, while the electromagnetic valve 18b is opened to discharge the treated water in the reaction tank 10 from the treated water outlet 20 through the treated water pipe 22 ((1) inflow process / discharge process). After a predetermined time has elapsed, the electromagnetic valves 18a and 18b are closed, the aeration blower 24 is operated, and oxygen-containing gas such as air supplied from the aeration blower 24 is supplied to the reaction tank 10 through the aeration device 26, and the water to be treated is biologically treated by the biological sludge ((2) biological treatment process). Next, the operation of the aeration blower 24 is stopped, and the water is left to stand for a predetermined time, allowing the biological sludge in the reaction tank 10 to settle ((3) settling process). In the settling process, the biological sludge concentration in the reaction tank 10 is detected by the sludge concentration meter 28. In addition, the control device 12 reads the biological sludge concentration (detection value) detected by the sludge concentration meter 28, and determines the end time of the settling process based on the detection value. Depending on the end time of the settling process determined by the control device 12, the process returns to (1) the inflow process / discharge process.

[0036] Granular sludge is gradually formed in the reaction tank 10 by repeating the process in the order of (1) inflow process, (2) biological treatment process, (3) sedimentation process, and (4) discharge process, or the process in the order of (1) inflow process / discharge process, (2) biological treatment process, and (3) sedimentation process. Therefore, the settling speed of the biological sludge changes with time from the start-up of the device. In particular, the settling speed of the biological sludge changes dynamically from the start-up of the device until the formation of the granular sludge. Therefore, in the conventional technology in which the time of the settling process is constant, the time of the settling process becomes too short when the settling speed is slow, and the time of the settling process becomes too long when the settling speed is fast, which may cause the above-mentioned risk. Therefore, in this embodiment, in order to carry out the settling process at an appropriate time according to the settling property of the biological sludge, the end time of the settling process is determined based on the biological sludge concentration (detection value) detected by the sludge concentration meter 28. A specific example of a method for determining the end time of the settling step will be given below.

[0037] <Determining the end time of the sedimentation process> For example, the control device 12 reads the biological sludge concentration (detection value) detected by the sludge concentration meter 28 during the settling process at predetermined time intervals, and terminates the settling process when the read detection value becomes equal to or lower than a preset threshold value.

[0038] In the settling step, the biological sludge in the reaction tank 10 settles over time, and the sludge interface position drops, so that the detection value of the biological sludge concentration detected by the sludge concentration meter 28 installed at a predetermined height in the reaction tank 10 also drops over time. Therefore, by terminating the settling step when the detection value of the biological sludge concentration detected by the sludge concentration meter 28 installed at a predetermined height becomes equal to or lower than a preset threshold value, the settling step can be performed at an appropriate time even if the settling speed of the biological sludge changes between the start-up of the device and the formation of granular sludge. This avoids a state in which the settling step time is too short, thereby reducing, for example, the risk of biological sludge flowing out from the reaction tank 10. In addition, since the settling step time is avoided from being too long, for example, the biological sludge is prevented from adhering to the reaction tank 10, the biological sludge is anaerobic, and the biological sludge is prevented from floating up due to gas generation associated with the anaerobicity of the biological sludge. Furthermore, it is believed that by carrying out the settling step at an appropriate time, the granule formation period can be shortened and the granule formation can be promoted.

[0039] The threshold value is preferably set in the range of 0 to 1000 mg / L, and more preferably set at 250 mg / L or less. If the threshold value is set to more than 1000 mg / L, there is a concern that the time for the settling process will be too short, regardless of the settling property of the biological sludge.

[0040] The installation position of the sludge concentration meter 28 is preferably, for example, between 0.5 m and 3 m below the water surface in the reaction tank 10. However, in the case of a configuration in which the inflow step and the discharge step are performed simultaneously, biological sludge with high settling properties can be efficiently formed by ending the settling step without allowing the biological sludge to settle too much, so the installation position of the sludge concentration meter 28 is more preferably between 0.5 m and 2.5 m below the water surface in the reaction tank 10. Furthermore, in the case of a configuration in which the inflow step and the discharge step are performed separately, from the viewpoint of ensuring a predetermined amount of clear treated water, it is more preferably installed between 1.0 m and 3.0 m.

[0041] Other examples of determining the end time of the settling step will be described below, but the same effects as the above example can be obtained in the other examples. The above-mentioned setting positions for the sludge concentration are also applied to the following examples.

[0042] As another example, the control device 12 reads the biological sludge concentration (detection value) detected by the sludge concentration meter 28 in the settling process at predetermined time intervals, and terminates the settling process when the read detection value becomes equal to or less than a predetermined percentage of the detection value of the biological sludge concentration detected by the sludge concentration meter 28 in the biological treatment process.

[0043] Also, for example, the control device 12 reads the biological sludge concentration (detection value) detected by the sludge concentration meter 28 at predetermined time intervals from the start of the settling process until a predetermined time, and calculates the sludge concentration change rate (mg / L / min) from the read detection value. The control device 12 refers to reference information such as a map or table that specifies settling process times corresponding to various sludge concentration change rates, and determines the settling process time from the calculated sludge concentration change rate. The control device 12 ends the settling process when the settling process time reaches the determined settling process time.

[0044] The sludge concentration meter 28 may be of a conventional type, such as a transmitted light type, a scattered light type, a microwave type, an ultrasonic type, etc. In some cases, a meter that correlates with the sludge concentration, such as a viscometer or a turbidity meter, may be used.

[0045] Furthermore, in this embodiment, instead of a detector that detects the concentration of biological sludge, a sludge interface meter that detects the interface position of the biological sludge in the reaction tank 10 may be used. Examples of sludge interface meters include conventionally known types such as ultrasonic, turbidity detection, and transmitted light. When a sludge interface meter is used, the control device 12 determines the end time of the settling process based on the interface position (detection value) of the biological sludge in the reaction tank 10 detected by the sludge interface meter. A specific example will be described below.

[0046] For example, the control device 12 reads the interface position (detection value) of the biological sludge in the reaction tank 10 detected by the sludge interface meter during the settling process at predetermined time intervals, and terminates the settling process when the read detection value becomes equal to or lower than a preset threshold value.

[0047] The threshold value is desirably set in the range of 10 to 70% of the reaction tank depth. If the threshold value is set to more than 70% of the reaction tank depth, there is a concern that the time for the settling process will be too long regardless of the settling properties of the biological sludge, and if the threshold value is set to less than 10% of the reaction tank depth, there is a concern that the time for the settling process will be too short regardless of the settling properties of the biological sludge.

[0048] Also, for example, the control device 12 reads the interface position (detection value) of the biological sludge in the reaction tank 10 detected by the sludge interface meter after a predetermined time has elapsed since the start of the settling process, and calculates the sludge settling velocity (m / h) from the read detection value. The control device 12 refers to reference information such as a map or table that specifies settling process times corresponding to various sludge settling rates, and determines the settling process time from the calculated sludge settling velocity. The control device 12 ends the settling process when the settling process time reaches the determined settling time.

[0049] Other conditions in this embodiment will be described below.

[0050] By continuing to operate the water treatment device 1, biological sludge (so-called granules) that has undergone advanced self-granulation can be formed in the reaction tank 10, and for example, granules having an average particle size of sludge of 0.1 mm or more, or an SVI5, which is a sedimentation index, of 80 mL / g or less can be formed.

[0051] According to the water treatment device 1, the biological sludge (granules) in the reaction tank 10 can account for 30% or more of the biological sludge having an average particle size of 0.1 mm or more.

[0052] The volumetric load of the reactor 10 is 0.15 kg BOD / m 3 / day ~ 1.00kgBOD / m 3 / day, and preferably in the range of 0.30 kg BOD / m 3 / day ~ 0.60kgBOD / m 3 By setting the volume load of the reaction vessel 10 in the above range, it is possible to form better granules.

[0053] The sludge load in the reaction tank 10 is preferably in the range of 0.05 kg BOD / kg MLSS / day to 0.30 kg BOD / kg MLSS / day, and more preferably in the range of 0.10 kg BOD / kg MLSS / day to 0.20 kg BOD / kg MLSS / day. By setting the sludge load in the reaction tank 10 in the above range, better granules can be formed.

[0054] The dissolved oxygen (DO) in the reaction tank 10 is preferably set to 0.5 mg / L or more, particularly preferably 1 mg / L or more, under aerobic conditions.

[0055] In order to promote the granulation of biological sludge, Fe is added to the water to be treated in the reaction tank 10 or to the water to be treated before being introduced into the reaction tank 10. 2+ , Fe 3+ , Ca 2+ , Mg 2+ It is also possible to add ions that can form hydroxides, including the above ions. By adding the above ions, it is possible to promote the nucleation of granules.

[0056] When the water to be treated, which is the target of the present embodiment, contains a large amount of organic matter that is difficult to biodegrade, the water to be treated may be subjected to a physicochemical treatment such as ozone treatment or Fenton treatment before being supplied to the reaction tank 10. This converts the organic matter into organic matter that is easily biodegraded, and the treatment efficiency of the water to be treated may be improved. Furthermore, when the water to be treated, which is the target of the present embodiment, contains a large amount of oil and fat, the oil and fat may adhere to biological sludge (including granules) and cause adverse effects, so that the water to be treated may be subjected to existing techniques such as floatation separation, coagulation pressure floatation, and adsorption before being supplied to the reaction tank 10. This allows the concentration of oil and fat in the water to be treated to be reduced (for example, to 150 mg / L or less). [Explanation of symbols]

[0057] 1 water treatment device, 10 reaction tank, 12 control device, 14 treated water piping, 16 discharge port, 18a, 18b electromagnetic valves, 20 treated water discharge port, 22 treated water piping, 24 aeration blower, 26 aeration device, 28 sludge concentration meter, 30 motor, 32 mixing blade.

Claims

1. A water treatment method comprising the steps of: an inflow step of inflowing water to be treated into a reaction tank; a biological treatment step of biologically treating the water to be treated in the reaction tank with biological sludge; a sedimentation step of sedimenting the biological sludge in the reaction tank; and a discharge step of discharging the biologically treated water in the reaction tank, This water treatment method is characterized in that, in the settling process, a detection means for detecting the concentration of biological sludge is used to detect the concentration of the biological sludge at a predetermined height in the reaction tank, and the end time of the settling process is determined based on the rate of change of sludge concentration calculated from the detected concentration.

2. 2. The water treatment method according to claim 1, wherein the discharge step is carried out while the inflow step is being carried out.

3. 3. The water treatment method according to claim 1, wherein the detection means is a sludge concentration meter that detects the concentration of the biological sludge.

4. A reaction tank for carrying out an inflow process for inflowing water to be treated, a biological treatment process for biologically treating the water to be treated with biological sludge, a sedimentation process for sedimenting the biological sludge, and a discharge process for discharging the biologically treated water; a control unit that determines the end time of the settling process based on a sludge concentration change rate obtained from a detection value of the biological sludge concentration at a predetermined height in the reaction tank during the settling process, detected by a detection means for detecting the biological sludge concentration.

5. The water treatment device according to claim 4 , wherein the discharge step is carried out in the reaction tank while the inflow step is carried out.

6. 6. The water treatment device according to claim 4, wherein the detection means is a sludge concentration meter that detects the concentration of the biological sludge.

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