JPH09168788A - Combined septic tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb the fluctuation of drain quantity by an aeration tank to perform stable treatment by measuring the quantity of inflow water of a combined septic tank and the water level in a reaction tank and controlling the taking-out quantity of permeated water by a taking-out means on the basis of the measured quantity of inflow water and the measured water level. SOLUTION: An analyser 9 operates the measured value of the flowmeter 7A provided to piping 11, that is, the quantity of waste water to the aeration tank 3 being the biological reaction tank of a combined septic tank and the measured value of a water level meter 8, that is, the drain quantity in the aeration tank 3 and a signal adjusting the number of rotations of a vacuum pump 5 is outputted on the basis of this operation result and the taking-out quantity of permeated water from an immersed membrane 4 is controlled. By this constitution, it is unnecessary to provide a raw water conditioning tank and, even when the quantity of inflow waste water is increased to a large extent, the fluctuations of the quantity of inflow waste water is absorbed by the aeration tank 3 to perform stable treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined septic tank equipped with a biological reaction tank in which a separation membrane is immersed, and in particular, it is stable even when the amount of inflowing wastewater is significantly increased without providing a raw water adjusting tank. It relates to a combined septic tank that can be treated.

[0002]

2. Description of the Related Art Conventionally, a combined purification tank has been developed and put into practical use in which a flat membrane-shaped or hollow fiber membrane-shaped MF (microfiltration) membrane or UF (ultrafiltration) membrane is immersed and arranged in an aeration tank. M in the aeration tank
By substituting the F and UF membranes for solid-liquid separation with the membranes, a sedimentation tank is not required, so it becomes a very compact device and is necessary for membrane separations, which gives high quality treated water. There are many advantages such as extremely low power consumption and easy maintenance. For this reason, merged septic tanks using dipping membranes will continue to be used in the future.

However, when a membrane is used for solid-liquid separation, there is a drawback that the life of the membrane is short.

That is, the separation membrane is treated by continuing the treatment.
The performance of the membrane deteriorates due to clogging, etc., and the performance is not fully recovered even if chemical cleaning is performed, and the membrane needs to be replaced. The period from the start of use of this membrane to the replacement is the membrane life, but when the membrane is immersed in the aeration tank for solid-liquid separation, this membrane life is short and it is necessary to replace the membrane frequently. There is a problem.

Regarding the membrane life, the membrane life is longer when the membrane is operated with a permeated water 0 which is as low as 1/2 to 1/3 of the maximum permeated water of the membrane, as compared with the case where the membrane is operated with the maximum permeated water. It is known that you can.

[0006] For example, when a certain membrane is operated at the maximum permeated water amount, it is necessary to replace the membrane within 6 months, whereas when it is operated at 1/2 to 1/3 of the maximum permeated water amount, 2 is required.
Can be operated for up to 3 years without replacing the membrane. Therefore, it is 1/100
It is industrially advantageous to operate with a permeated water amount of 2 to 1/3, although the treated water amount per hour is small, but the treatment can be continued for a long period of time, and as a result, the accumulated treated water amount increases.

From the above, in the conventional case, in the treatment by the immersion membrane, 1/2 of the maximum permeated water amount of the membrane is used.
The operation is performed with a constant permeated water amount of 1/3. For example,
In the example using the hollow fiber MF membrane, the operation is performed with the permeated water amount of the membrane being a low value of 0.4 m ³ / m ² · day or less, which is 1/3 or less of the maximum permeated water amount.

On the other hand, the amount of wastewater to be treated which flows into the combined septic tank fluctuates greatly per hour. FIG. 4 is a graph showing a time variation pattern of the amount of wastewater flowing into a general combined septic tank (change in the ratio of the amount of wastewater flowing into the combined septic tank for each time with respect to the total amount of discharged water for one day). As is clear from this figure, the time when the drainage is concentrated is in the evening from morning to around noon, and the drainage is very small from night to early morning.

As described above, in the combined septic tank in which the fluctuation of the inflowing drainage amount per hour is drastic, in order to absorb the fluctuation of the water amount and equalize it, as shown in FIG. A raw water adjusting tank 1 with a large capacity that can be installed is installed, and the drainage is transferred from the raw water adjusting tank 1 to the aeration tank 3 at a constant flow rate by the transfer pump 2, and the immersion membrane 4 of the aeration tank 3 corresponds to this transfer drainage amount. The permeated water is extracted by the decompression pump 5 for treatment (in FIG. 5, 6 is an aeration pipe, and 7 is an aeration pipe.
Is a flow meter. ). In addition, this permeated water amount is the immersion membrane 4
It is set to 1/2 to 1/3 of the maximum amount of permeated water, or less.

For example, in the fluctuation pattern shown in FIG. 4, the total amount of drainage flowing into the raw water regulating tank 1 is 10 m ³ / day.
Therefore, the maximum capacity of the raw water adjusting tank 1 is set to 10 m ³ , the capacity of the aeration tank 3 is set to 30 m ³ , and the amount of drainage transferred from the raw water adjusting tank 1 to the aeration tank 3 is 0.42 m ³ / hr for uniform transfer, The same amount of permeated water as this transfer amount is extracted from the immersion membrane 4 in the aeration tank 3.

[0011]

As described above, the conventional combined septic tank requires a raw water adjusting tank having a large capacity, and therefore has a drawback that the entire apparatus becomes large and the apparatus cannot be made compact.

Further, even when the raw water adjusting tank is provided, the fluctuation of the inflowing drainage amount cannot be absorbed and there is a risk that the drainage will overflow.

That is, in the conventional combined septic tank as shown in FIG. 5, if the fluctuation of the inflowing wastewater amount is the standard pattern shown in FIG. 4 and the total discharge amount is 10 m ³ / day, the planned discharge amount is as shown in FIG. When the amount of water transferred to the aeration tank is constant with respect to the amount of inflow water, fluctuations in the amount of discharged water (water level) in the raw water adjustment tank fall within the range of 7 to 9.3 m ³ and overflow as shown in FIG. 7. There is no such thing.

However, due to a temporary large amount of rainfall, long-term rainfall, clogging of rainwater ditch, and other unexpected special circumstances,
When water that does not originally flow into the septic tank flows into the septic tank, such as when rainwater mixes into the wastewater, the inflowing wastewater volume deviates from the standard pattern in Fig. 4. In this case, set the raw water adjustment tank capacity to 10 m ^3. However, it becomes impossible to prevent overflow of the waste water from the raw water adjusting tank. When wastewater overflows from the raw water conditioning tank, untreated domestic wastewater will flow out of the combined septic tank, which will significantly deteriorate the living environment.

The present invention solves the above-mentioned conventional problems, and in a combined septic tank having an aeration tank provided with a submerged membrane, even if the inflowing wastewater volume is significantly increased without providing the raw water adjusting tank, It is an object of the present invention to provide a combined septic tank capable of absorbing fluctuations in the aeration tank and performing stable treatment.

[0016]

The combined septic tank of the present invention comprises:
In a combined septic tank comprising a biological reaction tank in which a separation membrane is immersed and arranged, and a take-out means for taking out permeated water from the inside of the separation membrane, a means for measuring the inflow water amount of the combined septic tank, and a water level in the reaction tank And means for controlling the amount of permeated water taken out by the take-out means based on the measured inflow water amount and water level.

The advantage of immersing the separation membrane in the biological reaction tank is that the precipitation tank is not required, highly treated water is obtained, the power required for membrane separation is extremely small, and Within a limited range of permeated water from
If it is a short time, it can be changed arbitrarily. Further, even if the water level in the biological reaction tank fluctuates, operation is possible if the separation membrane is completely immersed.

As described above, when the separation membrane is immersed in the biological reaction tank, conventionally, the set permeated water amount is set as low as 1/2 to 1/3 of the maximum permeated water amount of the membrane in order to prolong the life of the membrane. ing. In such cases, several days (3-4
If the frequency is about once a day, even if the membrane is operated with the maximum amount of permeated water for about 12 hours, it will not affect the life and performance of the membrane. When operating at about ⅔ of the maximum amount of permeated water, if it is about 1 to 1.5 days, it will not affect the life of the membrane. However, when the membrane is continuously operated at the maximum permeated water amount for 3 to 4 days, the membrane life becomes short.

For example, a submerged hollow fiber membrane is operated from the inside of an aeration tank with a sludge concentration of 3000 mg / L and a permeated water amount of 0.4 m ³ / m ² · day using a decompression pump with a pressure of −0.1 Kg / cm. If the maximum amount of permeated water at that time is 1.2 m ³ / m ² · day at a pressure of −0.3 Kg / cm, the pressure of the decompression pump is lowered for about 12 hours, and the amount of water drawn from the pump is reduced. 1.2m ³ / m by increasing
Even if the permeated water is drawn out at ² · day, this does not shorten the membrane life.

In the present invention, the characteristics of such a membrane-immersed type biological reaction tank are utilized to measure the amount of waste water flowing into the biological reaction tank of the combined purification tank and the water level in the biological reaction tank. By adjusting the amount of permeated water of the membrane, that is,
By changing the amount of permeated water taken out according to the increase / decrease in the amount of inflowing wastewater and the increase / decrease in the water level in the biological reaction tank within the range that does not affect the membrane life, fluctuations in the amount of inflowing wastewater can be controlled without installing a raw water adjustment tank. Absorbs in the reaction tank and responds to abnormal fluctuations in the amount of wastewater flowing into the combined septic tank.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The combined septic tank of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the combined septic tank of the present invention.

In the combined septic tank of this embodiment, the waste water flows directly into the aeration tank 3 through the pipe 11 equipped with the flow meter 7A. An aeration pipe 6 is provided at the bottom of the aeration tank 3, and the immersion film 4 is disposed above the aeration pipe 6 by immersion. The wastewater is aerobically bioprocessed in the aeration tank 3,
By the suction of the decompression pump 5, the permeated water is permeated to be solid-liquid separated, and the permeated water is discharged as treated water through the pipe 12 and the pipe 13 including the flow meter 7B.

The aeration tank 3 is provided with a water level meter 8 for measuring the amount of drainage in the aeration tank 3, and the flow meters 7A and 7B.
The measured value of 1 and the measured value of the water level gauge 8 are input to the analyzer 9.

In the analyzer 9, the measured value of the flow meter 7A, that is, the amount of drainage water flowing into the aeration tank 3 and the measured value of the water level gauge 8, that is, the amount of drainage water in the aeration tank 3, are arithmetically processed. Based on the above, a signal for adjusting the rotation speed of the decompression pump 5 is output to control the amount of permeated water taken out from the immersion membrane 4.

That is, the amount of waste water flowing into the aeration tank 3 (flow meter 7
(Measured value of A) and the water level in the aeration tank 3 (measurement value of the water level gauge 8) are continuously taken into the analysis device 9, and at the stage when the calculation result that the water level in the aeration tank 3 rises above the set value is obtained. The rotation speed of the decompression pump 5 is increased to increase the amount of drawn permeated water to the vicinity of the maximum amount of permeated water of the immersion membrane 4.

For example, when the inflow drainage amount and the water level in the aeration tank are within the standard fluctuation range, the withdrawal permeate amount is operated at 1/2 to 1/3 of the maximum permeate amount of the immersion membrane, and the aeration is performed by increasing the inflow drainage amount. When the rise of the water level in the tank is confirmed, the withdrawal permeated water is gradually increased with respect to the maximum permeated water amount R _max as shown in (i) and (ii) below.

(I) (1/3) ・ R _max → (1/2) ・ R _max → (2 /
3) ・ R _max → R _max (ii) (1/2) ・ R _max → (2/3) ・ R _max → R _max The number of steps for increasing the amount of permeated water drawn is limited to (i) and (ii) above. Instead, the amount may be increased in more steps. If a decrease in the amount of inflowing wastewater or the water level in the aeration tank is confirmed, the amount of permeated water to be withdrawn will be reduced through the steps reverse to the above.

Even if the amount of inflowing wastewater temporarily increases,
If the water level in the aeration tank is below the set water level, it is not always necessary to increase the amount of drawn permeate, and the amount of permeated water drawn can be controlled based on both the measured inflow and outflow water levels and the water level in the aeration tank. It is possible to prevent the shortening of the membrane life by suppressing the increase period of the amount of permeated water to the necessary minimum.

That is, the basis for extending the life of the immersion film is
It is intended to operate with a small amount of permeate and to shorten the operation time with a large amount of permeate. For that purpose, some fluctuation of the inflowing wastewater is absorbed by the water level in the aeration tank, and as long as possible,
It is necessary to operate with a low amount of permeate. According to the present invention, in the analyzer, while comparing the inflow drainage amount with the preset standard fluctuation pattern, while comparing the water level in the aeration tank with the preset standard water level, a stable operation period in which the amount of permeated water from the membrane is small It can be made as long as possible and can quickly respond to an abnormal increase in the inflow of waste water.

In the present invention, the control of the amount of drawn permeated water is not limited to the adjustment of the number of rotations of the decompression pump, and [1] a plurality of decompression pumps are installed in the permeated water extraction pipe to adjust the operating number. [2] A valve is provided between the immersion membrane of the permeated water extraction pipe and the pressure reducing pump, and the opening / closing degree of this valve is adjusted. You may perform by the method of.

The combined septic tank shown in FIG. 1 is an embodiment of the present invention, and the present invention is not limited to the illustrated one as long as the gist thereof is not exceeded.

In FIG. 1, the analysis device 9 is connected to the pipe 13.
Since the amount of permeated water controlled by circulates, the flowmeter 7B is not always necessary and may not be provided. When the flow meter 7B is provided, it is possible to confirm that the permeated water amount is reliably controlled by the measured value of the permeated water amount. In addition, this measured value can be used to predict the water level in the aeration tank.

[0034]

The present invention will be described more specifically with reference to the following examples.

Example 1 As a combined septic tank for treating a drainage of 10 m ³ / day,
A hollow fiber membrane-immersed activated sludge treatment device having an aeration tank capacity of 35 m ³ as shown in FIG. 1 was designed and tested.

As the dipping film 4, Stellapore L (fractionation characteristic: 0.1 μm) manufactured by Mitsubishi Rayon Co., Ltd. was used, and the film area was 3
It was set to 0 m ² . The amount of waste water flowing into the aeration tank 3 and the amount of permeated water (treated water) from the membrane were continuously measured by the flowmeters 7A and 7B. The water level in the aeration tank 3 was continuously measured by a water level gauge 8.
When the water level in the aeration tank 3, the amount of inflowing drainage water, and the amount of permeated water are taken into the analyzer 9, and the analysis result indicates that the water level (volume) of the aeration tank reaches the set water level (volume) of 30 m ³ , the rotation speed of the decompression pump 5 Decided to increase.

When the drainage is flowing into the aeration tank 3 in a standard pattern as shown in FIG. 4, the amount of water withdrawn from the immersed hollow fiber membrane 4 is set to a constant water amount of 0.42 m ³ / hr. The internal water level (volume) was stable within 28 to ³⁰ m ³ .

Under the situation where such operation is performed,
Assuming a large change in the inflowing wastewater due to abnormalities such as heavy rain, the standard inflowing wastewater inflow pattern is 10m until the day before.
A drainage volume of ³ / day was flowing into the aeration tank 3, but 0:
Change of operating condition when rainwater of 1 m ³ / hr flows in from 00 to 10:00 and the amount of water flowing into the aeration tank 3 abnormally increases to 20 m ³ / day, which is twice the set amount of water. Was carried out by the following means.

The flowmeter 7A measures the inflowing wastewater amount, and compares the wastewater amount with the standard pattern to determine whether it is large or small. The water level in the aeration tank 3 is measured by the water level meter 8 and whether the water level (volume) is higher or lower than the set value (30 m ³ ) is measured. When the amount of inflowing wastewater is larger than the standard pattern, the rotation speed of the decompression pump 5 is adjusted to increase the amount of drawn permeate. However, even if the inflow of wastewater is larger than the standard pattern,
When the water level in the aeration tank 3 is lower than the set value, the rotation speed of the decompression pump 5 does not increase, and operation is performed at the permeated water amount at that time.

Further, even if the inflowing wastewater amount returns to the standard pattern, if the water level in the aeration tank 3 is higher than the set value, the permeated water amount is not reduced and the operation is performed at the permeated water amount at that time. Even if the inflow drainage amount is a standard pattern, the permeated water amount is increased when the water level in the aeration tank 3 is higher than the set value. The amount of permeated water drawn by the vacuum pump was 0 at standard time.
42m ³ / hr, and when it is necessary to increase the amount of drawn permeate, it is about twice the standard time, 0.8m ³ / h
r, and when further increase was required, it was set to 1.2 m ³ / hr of the maximum permeated water amount which is about 3 times the standard time.

The results of controlling the amount of permeated water by such a method are shown in FIG. 2 (graph showing changes in inflow drainage amount and withdrawal permeated water amount), and FIG. 3 (graph showing changes in aeration tank drainage amount (water level)). Shown in.

That is, as shown in FIGS. 2 and 3, the operation was normal until the previous day, but the aeration tank water level rose due to an abnormal inflow of waste water from 0:00 and reached the set capacity of 30 m ³ or more. The amount of permeated water drawn was increased to 0.8 m ³ / hr, but the abnormal inflow continued and the aeration tank water level tended to rise further. Therefore, at 6:00, the extraction permeated water amount was further increased to the maximum permeated water amount of 1.2 m ³ / hr.
The abnormal inflow of wastewater returned to the standard amount of water from 11:00, but the aeration tank water level was still higher than the set value of 30 m ³ , so operation was performed at the maximum permeated water amount. After 14:00, the water level in the aeration tank tended to return to the set value, so the amount of drawn permeated water was reduced to 0.8 m ³ / hr, and 0.42 m ³ / h
r.

As described above, it is extremely rare that rainwater of the same amount as the planned amount of water is mixed within 10 hours, but by the above method, drainage overflows from the aeration tank without installing the raw water adjusting tank. It is obvious that stable operation is possible by avoiding this.

[0044]

As described in detail above, according to the combined septic tank of the present invention, the combined septic tank which does not require a precipitation tank by immersing the separation membrane in the biological reaction tank to take out permeated water is further provided. Since the raw water adjusting tank can be eliminated,
The device can be made compact and the combined septic tank with a small device installation area can be obtained. Fully automated operation is possible even if the amount of inflowing wastewater changes. Since the permeated water from the separation membrane is set to be low at all times, the membrane has a long life and the frequency of cleaning and replacement of the membrane is low. Since the membrane-permeated water is used as the treated water, a high degree of treated water can be obtained regardless of the sludge properties of the biological reaction tank. Such an excellent effect is achieved.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a combined septic tank of the present invention.

FIG. 2 is a graph showing changes in the inflow drainage amount and the withdrawal permeate amount in Example 1.

FIG. 3 is a graph showing changes in the amount of drainage water in the aeration tank in Example 1.

FIG. 4 is a graph showing the time variation of the amount of wastewater flowing into the combined septic tank.

FIG. 5 is a system diagram showing a conventional combined septic tank.

FIG. 6 is a graph showing changes in the amount of inflow water and the amount of transfer water in the related art.

FIG. 7 is a graph showing the time variation of the amount of drainage in a conventional raw water adjustment tank.

[Explanation of symbols]

 3 Aeration tank 4 Immersion membrane 5 Decompression pump 6 Aeration pipe 7, 7A, 7B Flow meter 8 Water level meter 9 Analyzer

Claims (1)

[Claims] 1. A biological reaction tank in which a separation membrane is immersed and arranged,
In a combined septic tank equipped with a take-out means for taking out permeated water from the inside of the separation membrane, a means for measuring the inflow water amount of the combined septic tank, a means for measuring the water level in the reaction tank, and a measured inflow water amount and A combined septic tank comprising means for controlling the amount of permeated water taken out by the take-out means based on the water level.