JPH09327601A - Method and apparatus for solid-liquid separation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for solid-liquid separation obtaining treated water constantly satisfying standard values and restraining a raise of operation cost even when quality and quantity of influents to be treated change. SOLUTION: A following step of a gravitational sedimentation tank 4 of a sedimentation process has pressure floatation equipment 6 and a bypass channel 7. When turbidity of treated water from the final sedimentation tank 4 is more than a standard value in measurement by a turbidity meter 8, the treated water is introduced into the pressure floatation equipment 6 so as to be treated thereby; when the turbidity of treated water is the standard value or less, the treated water is introduced into the bypass channel 7, and the floatation separation treatment is omitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-liquid separation method and device, and more specifically, solid-liquid separation in a water treatment facility such as a sewage treatment plant by a combination of gravity precipitation and pressure levitation. The present invention relates to a separation method and device.

[0002]

2. Description of the Related Art Conventionally, gravity sedimentation separation in which particles in a suspension are settled by gravity has been widely adopted for solid-liquid separation for obtaining secondary treated water in sewage treatment and the like. The sedimentation rate of flocs in the activated sludge, which is the target of solid-liquid separation at this time, differs greatly depending on its density, shape and size.
Widespread. Therefore, in order to achieve the discharge water standard value of SS 20 mg / l, the final settling basin should have sufficient water area so that sludge with a relatively slow sedimentation rate can be sufficiently separated in these wide range of sedimentation rates. Is designed to have. For example, in the case of sewage treatment by the high load type activated sludge method, the water area load of the final settling tank should be 2
0 to 30m ³ / m ² · day.

[0003]

However, in a small-scale treatment plant that is easily affected by fluctuations in the amount of inflow water, SS components may flow out from the final settling tank during the period when the wastewater pump operates. Further, the sedimentation property and the compaction property of the activated sludge are extremely lowered, and a phenomenon (bulking) in which the activated sludge and the treated water cannot be sufficiently separated may occur. In addition, sudden changes in the composition of inflowing sewage, inflow of harmful substances,
In some cases, activated sludge was disassembled due to excessive aeration and low pH due to nitrification, and some fine flocs flowed out. In particular, in gravity settling separation, floating solids that are difficult to settle out may flow out together with the treated water, which is a cause of deteriorating the water quality of the treated water.

Therefore, the present invention provides a solid-liquid separation method and apparatus capable of always obtaining treated water that satisfies the reference value and suppressing an increase in operating cost regardless of fluctuations in the quality of inflowing water, the amount of water, and the like. It is intended to be provided.

[0005]

In order to achieve the above object, the solid-liquid separation method of the present invention is provided with a pressure flotation separator at the latter stage of the gravity settling tank, and a bypass passing through the pressure flotation separator. When a turbidity of the treated water in the gravity settling tank exceeds a standard value by providing a flow path, the treated water is introduced into the pressure levitation separation device to perform pressure levitation separation treatment, and turbidity of the treated water When the degree is less than or equal to a reference value, the treated water is caused to flow through the bypass flow path to omit the pressure floating separation treatment,
Further, the amount of pressurized air-dissolved water supplied to the pressurized flotation device is adjusted according to the turbidity of the treated water in the gravity settling tank.

Further, the solid-liquid separation device of the present invention comprises a gravity settling tank, a pressure flotation separation device provided in the latter stage of the gravity settling tank, and a bypass flow path passing through the pressure flotation separation device.
A turbidimeter for detecting the turbidity of the treated water in the gravity settling basin, and a flow for switching the flow direction of the treated water to either a pressure levitation separator or a bypass flow channel according to the measured value of the turbidimeter. It is characterized in that it is provided with a path switching means.

Further, the solid-liquid separation device of the present invention has, as another configuration, an injection part for injecting pressurized air-dissolved water into the gravity settling tank, a discharge means for discharging the floating flotation sludge, and a gravity settling tank. A turbidimeter that detects the turbidity of the treated water that flows out;
And a control unit for controlling the injection amount of the pressurized air-dissolved water from the injection unit according to the measurement value of the turbidity meter.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. First, the sewage treatment equipment shown in FIG. 1 adopts an activated sludge method as a secondary treatment method, and the same settling basin 1, first sedimentation basin 2, aeration tank 3, and final sedimentation as in the conventional sewage treatment equipment. While having a pond 4 and a chlorine mixing basin 5, a pressure flotation separator 6 is provided between the final precipitation basin 4 which is a gravity precipitation basin and the chlorine mixing basin 5.
A bypass flow path 7 that passes through the pressure floating separation device 6 is provided.

In addition, in the treated water outflow section of the final settling tank 4,
A turbidity meter 8 for detecting the turbidity of the treated water (water treated by gravity precipitation separation) is provided, and the turbidity meter 8 from the turbidity meter 8 is provided in the inflow part of the pressure floating separation device 6 and the bypass flow path 7. Automatic valves 9 and 10 as means for automatically opening and closing according to a signal, and switching the flow path of gravity settling separation treated water from the final settling basin 4 to the pressure floating separation device 6 and the bypass flow path 7, respectively. It is provided.

The pressurized flotation / separation device 6 injects pressurized air-dissolved water into the inflowing water into the device and reduces the pressure to atmospheric pressure to generate fine bubbles from the pressurized air-dissolved water. These fine air bubbles adhere to the suspended components in the inflowing water, and the apparent specific gravity of the suspended components becomes smaller, so that the suspended components are floated and separated. It has a high removal rate of suspended components and can reliably separate and remove even fine flocs of activated sludge with a slow sedimentation rate, and completely removes easily floatable components such as hair, oil and scum that are difficult to separate by gravity sedimentation. Can be removed.

Further, the turbidimeter 8 measures the correlation between SS and turbidity of the gravity sedimentation separated treated water beforehand, and the gravity sedimentation treated water SS can be calculated by the measured value of the turbidity meter 8. Is set to.

In such a sewage treatment facility, the inflowing sewage is treated in the sand settling basin 1 and the first settling basin 2 in the same manner as before, and then mixed in the aeration tank 3 with the return sludge from the return sludge channel 11. Water treatment by the activated sludge method is performed. The activated sludge flocs generated in the aeration tank 3 have various settling speeds depending on the density, shape and size thereof, but these sludges are usually generated by gravity settling in the next final settling tank 4. Solid-liquid separation is performed. That is, the final settling basin 4 is
It is set to the ability to perform sufficient solid-liquid separation when the water quality is average.
It is set to ~ 30m ³ / m ² · day.

Therefore, when the amount of inflow water is small or the load is small, such as when the wastewater pump is not operating, the gravity sedimentation separation treated water S flowing out from the final sedimentation tank 4 is discharged.
Since S is a value that satisfies the treated water standard value, it can be discharged to a river or the like by adding chlorine in the chlorine mixing basin 5 and performing chlorine sterilization as it is.

The measured value of the turbidity meter 8 at this time is less than a preset reference value, and the automatic valves 9 and 10 which open and close by the signal of the turbidity meter 8 are pressurized floating separation. The automatic valve 9 at the inflow portion of the device 6 is closed, and the automatic valve 10 at the bypass passage 7 is open.

On the other hand, when the amount of inflow water becomes large or the wastewater pump is operated and the solid-liquid separation by gravity sedimentation in the final settling tank 4 cannot be sufficiently performed, sludge having a slow sedimentation rate is discharged from the final settling tank 4. Gravity sedimentation May be released into treated water. When sludge or the like flows out into the gravity precipitation separation treated water and the SS of the gravity precipitation separation treated water increases, the turbidity of the gravity precipitation separation treated water detected by the turbidity meter 8 increases and the detected turbidity. Exceeds the reference value or is expected to exceed the reference value, the turbidity meter 8 outputs an open / close signal to the automatic valves 9 and 10 to open the automatic valve 9 and close the automatic valve 10. . As a result, the gravity settling separation treated water having an increased turbidity is supplied to the pressure flotation separation device 6 through the automatic valve 9, is subjected to the pressure flotation separation treatment, and is then sent to the chlorine mixing tank 5.

Note that the control circuit of the pressure levitation separation device 6 is set so that the operation starts when the automatic valve 9 opens and stops when the automatic valve 9 closes. A part of the sludge generated during the operation of the pressure flotation / separation device 6 is sent to the sludge treatment facility, and together with the sludge from the final settling tank 4, the sludge is returned from the return sludge channel 11 to the aeration tank 3 as return sludge. Sent.

That is, when the SS of gravity-precipitated separated treated water calculated by the turbidity measured by the turbidimeter 8 exceeds or exceeds the discharge water standard value, the gravity-precipitated separated treated water is judged. Is introduced into the pressure floating separation device 6 to perform the pressure floating separation process.

Further, by changing the addition amount of pressurized air-dissolved water (pressurized water ratio) or the like according to the turbidity of the gravity sedimentation-treated water, for example, when the turbidity is low, the pressurized water ratio is reduced. As a result, it is possible to suppress the power cost of the pump and the compressor for generating the pressurized air-dissolved water.

When the turbidity of the gravity settled separated treated water becomes lower than the reference value, the automatic valve 9 is closed by the signal from the turbidimeter 8 and the automatic valve 10 is closed. It flows through the bypass channel 7 and is introduced into the chlorine mixing pond 5,
The pressure floating separation device 6 stops its operation.

By performing the pressure floating separation treatment according to the turbidity of the gravity settling separation treated water in this manner, the discharge water standard value of SS 20 mg / l can be reliably achieved and the pressure floating separation treatment can be achieved. Since the power cost of the separation device 6 can be suppressed and the gravity sedimentation tank such as the final sedimentation tank can be downsized, the equipment ratio and the running cost can be reduced while maintaining the water quality standard. Furthermore, even if gravity settling cannot be sufficiently performed due to scum, bulking, etc., by performing the pressure floating separation process by the pressure floating separation device 6,
A necessary and sufficient solid-liquid separation treatment can be performed.

FIG. 2 shows a sewage treatment facility showing another embodiment of the present invention. This sewage treatment facility is the same as above, including a sand basin, a first sedimentation basin, an aeration tank 3,
An injection section 21 for injecting pressurized air-dissolved water into the final settling tank 4 and a final settling tank 4 of a facility having a chlorine mixing tank, a discharging means 22 for discharging the floated floating sludge, and a process for flowing out from the gravity settling tank. A turbidimeter 23 for detecting the turbidity of water and a control means 24 for controlling the injection amount of the pressurized air-dissolved water from the injection part 21 according to the measurement value of the turbidity meter 23 are provided. is there.

The injection part 21 is provided at an appropriate water depth position in the middle part of the final settling basin 4, and is supplied with pressurized air supplied from a pressurized air-dissolved water producing apparatus 25 equipped with a pump, a compressor and the like. Dissolved water is jetted into water, and suspended components in water are floated by the same principle as the pressure floating separation device.

The discharging means 22 uses a sludge scraper 26 which is usually provided in the final settling basin 4, and the return part of the sludge scraper 26 is arranged on the water surface to remove the sludge scraper. The flying sludge is attracted by the flight 26a of the machine 26 and discharged to the outside of the pond via the pipe skimmer 27 provided on the downstream side.

The turbidity meter 23 detects the turbidity of the treated water that has flowed over the overflow weir 28 of the final settling tank 4 into the treated water tank 29. Exceeds the reference value, or is predicted to exceed the reference value, an operation signal is output to the pressurized air-dissolved water producing apparatus 25 via the control unit 24. This driving signal is
It may be one that controls only ON / OFF,
It may be a signal that changes the production amount of the pressurized air-dissolved water according to the turbidity. Further, the floating sludge discharge means 22 is
You may make it install a dedicated scratching machine etc.

As described above, by injecting the pressurized air-dissolved water into an appropriate position in the final settling tank 4, the floating solid matter can be reliably separated and removed, and the quality of the treated water can be improved. it can. At this time, the pressurized air-dissolved water may be continuously injected without providing the turbidity meter 23, or the pressurized air-dissolved water producing apparatus 25 may be operated in accordance with a change in the amount of inflow water, or in advance. Sufficient solid-liquid separation can be performed by operating according to the set time schedule, but as described above, the compressed air is compressed according to the turbidity of the treated water detected by the turbidity meter 23, that is, the SS level. The operating cost can be minimized by controlling the injection operation of the dissolved water.

Although the activated sludge method is adopted as the secondary treatment method in the above-mentioned embodiment, the present invention is not limited to this, and the sewage treatment method adopting another treatment method such as the oxidation ditch method is used. It can also be applied to equipment and various other solid-liquid separation treatments.

[0027]

As described above, according to the present invention,
Regardless of fluctuations in the quality or quantity of inflow water, the specified treated water quality can always be obtained, and the electric power cost required for pressurized flotation treatment can also be suppressed, reducing the equipment cost of sewage treatment facilities and running costs. Can be reduced. Also,
Automatic operation is also possible, and it is possible to deal with solid-liquid separation failure due to causes such as scum and bulking.

[Brief description of drawings]

FIG. 1 is a system diagram of a sewage treatment facility showing one embodiment of the present invention.

FIG. 2 is a schematic diagram of sewage treatment equipment showing another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Settling basin, 2 ... First settling basin, 3 ... Aeration tank, 4 ... Final settling basin, 5 ... Chlorine mixing pond, 6 ... Pressurization flotation / separation device, 7 ... Bypass passage, 8 ... Turbidimeter, 9, DESCRIPTION OF SYMBOLS 10 ... Automatic valve, 11 ... Return sludge flow path, 21 ... Injecting part, 22 ... Ejection means, 23 ... Turbidimeter, 24 ... Control means, 25 ... Pressurized air-dissolved water producing device, 26 ... Sludge attractor, 26a ... Flight, 27 ... Pipe skimmer, 28 ... Overflow weir, 29 ... Treated water tank

Claims (4)

[Claims] 1. A gravity flotation tank is provided with a pressure flotation separator at the latter stage of the gravity flotation tank, and a bypass flow path passing through the pressure flotation tank is provided so that the turbidity of treated water in the gravity sedimentation tank exceeds a reference value. When the turbidity of the treated water is equal to or lower than the reference value, the treated water is introduced into the bypass flow passage to pressurize the treated water. A solid-liquid separation method, characterized in that the floating separation treatment is omitted. 2. The solid-liquid according to claim 1, wherein the amount of pressurized air-dissolved water supplied to the pressurized flotation device is adjusted according to the turbidity of the treated water in the gravity settling tank. Separation method. 3. A gravity sedimentation basin, a pressure flotation separator provided at the latter stage of the gravity sedimentation pond, a bypass flow path passing through the pressure flotation separator, and a turbidity of treated water in the gravity sedimentation pond. And a flow path switching means for switching the flow direction of the treated water to either the pressurized flotation separation device or the bypass flow path according to the measurement value of the turbidity meter. A solid-liquid separation device characterized by. 4. An injection section for injecting pressurized air-dissolved water into the gravity settling tank, and an ejection means for ejecting the floating flotation sludge,
A turbidimeter for detecting the turbidity of the treated water flowing out from the gravity settling tank, and a control means for controlling the injection amount of the pressurized air-dissolved water from the injection part according to the measurement value of the turbidity meter. The solid-liquid separation device characterized in that