JP7601550B2 - Water treatment method and water treatment device - Google Patents

Description

The present invention relates to water treatment methods and water treatment device technologies.

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

On the other hand, anaerobic biological treatment generally utilizes granules, which are dense clusters of microorganisms. Granules have a very fast settling rate and the microorganisms are densely clustered, so the sludge concentration in the biological treatment tank can be increased, making it possible to treat wastewater quickly. However, anaerobic biological treatment can have problems such as the fact that the types of wastewater that can be treated are limited compared to aerobic treatment (activated sludge method) and that the temperature of the treated water needs to be maintained at around 30 to 35°C. Furthermore, when anaerobic biological treatment is used alone, the quality of the treated water is poor, and if the water is to be discharged into a river or other water source, it may be necessary to carry out aerobic treatment such as activated sludge method separately.

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 an average particle size of, for example, 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 using biological sludge, (3) settling of the biological sludge, and (4) discharge of treated water.

Patent Document 5 also 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 that has high settling properties, such as granulated biological sludge.

International Publication No. 2004/024638 JP 2008-212878 A Patent No. 4975541 Patent No. 4804888 JP 2016-77931 A

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 biological treatment to the formation of 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 kept 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, there is a risk that the biological sludge will stick to the reaction tank and become difficult to flow during the biological treatment process, or that the biological sludge will become anaerobic and lose activity due to a long period of time in the settled state, or that the biological sludge will float due to the generation of gas accompanying the anaerobic process of the biological sludge.

The object of the present invention is to provide a water treatment method and water treatment device that can carry out the sedimentation process at an appropriate time according to the sedimentation properties of the biological sludge.

This embodiment is a water treatment method which includes 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 using biological sludge, a sedimentation process of settling the biological sludge in the reaction tank, and a discharge process of discharging the biologically treated water from the reaction tank.In the sedimentation process, a detection means for detecting the concentration of the 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 sedimentation process is determined based on the rate of change of sludge concentration calculated from the detected concentration .

In the water treatment method, it is preferable to carry out the discharge step while carrying out the inflow step.

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

In addition, this embodiment is a water treatment device that is characterized by comprising a reaction tank that performs an inflow process for inflowing water to be treated, a biological treatment process for biologically treating the water to be treated using biological sludge , a sedimentation process for settling the biological sludge, and a discharge process for discharging the biologically treated water, and a control unit that determines the end time of the sedimentation process based on the rate of change of sludge concentration obtained from the detection value of the biological sludge concentration at a predetermined height in the reaction tank during the sedimentation process, detected by a detection means for detecting the biological sludge concentration.

In the water treatment device, it is preferable that the reaction tank performs the discharge process while performing the inflow process.

In the water treatment device, the detection means is preferably a sludge concentration meter that detects the concentration of the biological sludge.

The present invention provides a water treatment method and water treatment device that can carry out the sedimentation process at an appropriate time according to the sedimentation properties of the biological sludge.

1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention.

The following describes an embodiment of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

<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.

A sludge concentration meter 28 is installed in the reaction tank 10 at a predetermined height within the tank. The installation position of the sludge concentration meter 28 is, for example, in the 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.

In addition, the electromagnetic valve 18a, the electromagnetic valve 18b, and the aeration blower 24 are each electrically connected to the control device 12.

The control device 12 is composed of, for example, a microcomputer consisting of a CPU that executes a program, and ROM and RAM that store the program and calculation results, and electronic circuits, and controls the operation and stopping of the aeration blower 24, the opening and closing of valves, etc. Also, as described below, 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 the sludge concentration meter 28.

An example of the operation of the water treatment device 1 is described below.

<(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.

<(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 perform 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.

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

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

In the settling process, the biological sludge concentration in the reaction tank 10 is detected by the sludge concentration meter 28. The control device 12 also 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.

<(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 piping 22.

The treatment cycle is comprised of the following steps: (1) inflow process, (2) biological treatment process, (3) sedimentation process, and (4) discharge process. This cycle is repeated to treat the water to be treated.

In this embodiment, the inflow process and the discharge process are not limited to being performed separately, and the discharge process may be performed while the inflow process is being performed. In other words, the treatment cycle may be repeated to treat the water to be treated, with the cycle consisting of (1) inflow process/discharge process, (2) biological treatment process, and (3) sedimentation process being performed in that order.

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 with biological sludge ((2) biological treatment process). Next, the operation of the aeration blower 24 is stopped, and the reaction tank 10 is left in a stationary state for a predetermined time, allowing the biological sludge in the reaction tank 10 to settle ((3) sedimentation process). In the sedimentation 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.

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. Below are some specific examples of how to determine when to end the settling process:

<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.

In the settling process, the biological sludge in the reaction tank 10 settles over time, and the sludge interface position drops, so 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 process 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, the settling process 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 process 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 process 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 anaerobic process. Furthermore, it is believed that by carrying out the sedimentation process at an appropriate time, the granule formation period can be shortened and granule formation can be promoted.

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 above 1000 mg/L, there is a concern that the settling process time will be too short, regardless of the settling properties of the biological sludge.

The sludge concentration meter 28 is preferably installed, 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 process and the discharge process are performed simultaneously, it is more preferable to end the settling process without allowing the biological sludge to settle too much, in order to efficiently form biological sludge with high settling properties, so it is more preferable to install the sludge concentration meter 28 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 process and the discharge process are performed separately, it is more preferable to install the sludge concentration meter 28 between 1.0 m and 3.0 m from the viewpoint of ensuring a predetermined amount of clear treated water.

Below, other examples of determining the end time of the settling process will be explained, but the same effects as the above example will be obtained in these other examples. The above sludge concentration setting positions are also applied in the following examples.

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.

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.

Examples of the sludge concentration meter 28 include conventionally known types such as transmitted light, scattered light, microwave, and ultrasonic. In some cases, instruments that correlate with sludge concentration, such as a viscometer or turbidity meter, may also be used.

In addition, 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 is described below.

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 falls below a preset threshold value.

It is desirable to set the threshold value in the range of 10-70% 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 settling process time 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 settling process time will be too short, regardless of the settling properties of the biological sludge.

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 a predetermined time after 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.

Other conditions in this embodiment are explained below.

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. For example, granules can be formed in which the average particle size of the sludge is 0.1 mm or more, or the settling index SVI5 is 80 mL/g or less.

According to the water treatment device 1, it is possible to make the biological sludge (granules) with an average particle size of 0.1 mm or more 30% of the biological sludge in the reaction tank 10.

The volume load of the reaction tank 10 is preferably in the range of 0.15 kg BOD/m ³ /day to 1.00 kg BOD/m ³ /day, and more preferably in the range of 0.30 kg BOD/m ³ /day to 0.60 kg BOD/m ³ /day. By setting the volume load of the reaction tank 10 in the above range, better granules can be formed.

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, it is possible to form better granules.

Under aerobic conditions, it is preferable that the dissolved oxygen (DO) in the reaction tank 10 be 0.5 mg/L or more, and particularly 1 mg/L or more.

In order to promote the granulation of biological sludge, ions that form hydroxides, including Fe ²⁺ , Fe ³⁺ , Ca ²⁺ , Mg ²⁺ and the like, may be 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. The addition of the above ions makes it possible to promote the nucleation of granules.

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 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, which may improve the treatment efficiency of the water to be treated. In addition, 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 the biological sludge (including granules) and cause adverse effects, so existing methods such as floatation separation, coagulation pressure floatation, and adsorption may be used in advance 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).

1 Water treatment device, 10 Reaction tank, 12 Control device, 14 Treated water piping, 16 Discharge port, 18a, 18b Solenoid valve, 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 (6)

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 . The water treatment method according to claim 1, characterized in that the discharge step is carried out while the inflow step is carried out. The water treatment method according to claim 1 or 2, characterized in that the detection means is a sludge concentration meter that detects the concentration of the biological sludge. 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. 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. 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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