JPH10249345A - Method and device for controlling filtered water quantity constant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to be operated at a fixed amount regard lessly of the change of a membrane performance even by gravity filtering system. SOLUTION: In this method, the water level of a filtered water 9 in a treated water tank 4 is detected at a specified interval, and the variation in the water level between a nitrification tank 3 and a treated water tank 4 is enlarged or reduced by comparing a variation value ΔL' in a measured water level calculated from the detected water level with a previously set variation value ΔL in a standard water level, and actuating and stopping a water discharge pump 10 discharging the filtered water 9 in the treated water tank 4 based on the variation between both variation values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling the amount of filtrate per unit time in a membrane separation apparatus immersed and installed in a tank.

[0002]

2. Description of the Related Art As a conventional purification tank, there is, for example, a combined purification tank provided with a nitrification tank 3 provided with a denitrification tank 1, a membrane separation device 2, and a treatment water tank 4, as shown in FIG. The membrane separation device 2 is configured by arranging plate-shaped membrane elements 2b in a case 2a having an open top and bottom with the membrane surface in the up-down direction.
A diffuser 5 is provided below the membrane element 2b, and a filtered water outlet pipe 2c communicating with a filtered water flow path of the membrane element 2b.
Open in the treatment water tank 4.

In such a septic tank, the raw water 6 is supplied to the denitrification tank 1
The activated sludge mixture 8 in the nitrification tank 3 is allowed to flow into the denitrification tank 1 while a part of the activated sludge mixture 7 in the denitrification tank 1 is transferred to the nitrification tank 3. Then, denitrification treatment was performed in the denitrification tank 1 under anaerobic conditions, and nitrification treatment was performed in the nitrification tank 3 under aerobic conditions where air was diffused by the diffuser 5, and the water level in the tank was maintained at a constant level. The activated sludge mixed liquid 8 is filtered by the membrane element 2b, and the filtered water 9 is led out into the treated water tank 4 through the filtered water outlet pipe 2, and the filtered water 9 in the treated water tank 9 is appropriately discharged by the drain pump 10. .

[0004] As a filtration method of the membrane separation device 2, as shown in FIG. 2, gravity filtration utilizing a water level difference L between the activated sludge mixed liquid 8 in the nitrification tank 3 and the filtered water 9 in the treatment water tank 9. As shown in FIG. 3, there is a suction filtration method in which a suction pressure is applied to the filtered water flow path of the membrane element 2b through the filtered water outlet pipe 2 by the suction pump 11, as shown in FIG.

[0005]

By the way, in order to carry out a stable filtration operation for drawing out a constant flow rate of the filtered water 9 in the above-mentioned membrane separation device 2, in the case of the gravity filtration system shown in FIG. The water level difference L may be kept constant, but there is a problem that the membrane is clogged as the operation time elapses, and the amount of filtered water gradually decreases. On the other hand, in the case of the suction filtration method, a fixed amount of the filtered water 9 can be taken out regardless of the change in the membrane performance by interposing the flow control valve 12 in the filtered water outlet pipe 2c as shown in FIG. Regulating valve 12
However, there is a problem that it is expensive.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to make it possible to operate at a constant throughput regardless of a change in membrane performance while using a gravity filtration method.

[0007]

Means for Solving the Problems To solve the above problems, the method for controlling the amount of filtered water constant according to the present invention is characterized in that the activated sludge mixed liquid in the biological treatment tank is immersed and installed in the treatment water tank by a membrane separation device. Gravity filtration based on the water level difference of the filtered water that has passed through the membrane and flowed into the treated water tank through the filtered water outlet pipe,
Upon discharging by the pump means that starts and stops at the predetermined reference high water level and the reference low water level, when the pump means is driven or stopped, the water level of the filtered water in the treated water tank is detected after a predetermined time and detected. Calculate the water level difference between the two water levels, set the calculated water level difference as the reference water level difference value ΔL, and detect the water level of the filtered water in the treated water tank at a predetermined time when the pump means is driven or stopped thereafter. The calculated water level difference is calculated as a measured water level difference value ΔL ′, and the measured water level difference value ΔL ′ is compared with the reference water level value difference ΔL to obtain a measured water level difference value. When ΔL ′ <reference water level difference value ΔL, the pump means is stopped at least at a water level lower than the reference low water level, the water level difference between the biological treatment tank and the treatment water tank is enlarged, and the measured water level difference value ΔL ′> When the reference water level difference value ΔL is The pumping means is stopped at least at a water level higher than the reference low water level to reduce the water level difference between the biological treatment tank and the treatment water tank, whereby the amount of filtered water per unit time in the membrane separation device is controlled to be constant. Things.

[0008] The apparatus for controlling a constant amount of filtered water according to the present invention comprises a biological treatment tank in which a membrane separation device is immersed and installed, and an end portion of a filtered water discharge pipe communicating with the membrane permeation side of the membrane separation device being opened in the tank. A water tank and a purifying tank provided with a pump means for starting and stopping the filtered water in the treated water tank at a predetermined reference high water level and a reference low water level and discharging the water therefrom, and the amount of filtered water per unit time in the membrane separation device is kept constant. A constant level control device for filtered water, comprising a water level detecting means for detecting the level of filtered water in the treated water tank, and a control means for controlling the start and stop of the pump means, the control means, Based on a difference between a measured water level difference value ΔL ′ per predetermined time calculated from the water level detected by the water level detection means and a preset reference water level difference value ΔL per predetermined time, the pump means is at least It is configured to stop at a water level different from the reference low water level, expand or reduce the water level difference between the biological treatment tank and the treatment water tank, and control the amount of filtered water per unit time in the membrane separation device to be constant. .

Generally, under the condition that the cross-sectional area of the treated water tank is constant at any position in the vertical direction of the tank, the amount of filtered water is proportional to the change in the water level. By comparing the difference in water level per predetermined time as a reference, it can be determined whether the amount of filtered water per predetermined time is smaller or larger than the reference filtered water amount.

[0010] Therefore, based on the determination result, the pump means is stopped at least at a water level lower (or higher) than the reference low water level to enlarge (or reduce) the water level difference between the biological treatment tank and the treatment water tank. The amount of filtered water per predetermined time can be made closer to the reference amount of filtered water, and the amount of filtered water per unit time in the membrane separation device can be controlled to be constant.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Since the filtered water amount constant control device of the present invention can be applied to the conventional septic tank described with reference to FIG. 2, FIG. 1 shows a septic tank having the same configuration as that of the conventional septic tank. I do.

The purification tank has a nitrification tank 3 in which a denitrification tank 1 and a membrane separation device 2 are immersed and installed, and a treated water tank 4. The membrane separation device 2 is configured by arranging membrane elements 2b with a membrane surface in a vertical direction in a case 2a that is open at the top and bottom.
c is open in the treatment water tank 4 so that the activated sludge mixed liquid 8 in the tank is gravity-filtered by the membrane element 2b based on the water level difference with the filtered water 9 in the treatment water tank 4. An air diffuser 5 for supplying air into the tank is provided below the membrane element 2b.

The treated water tank 4 is a drain pump for discharging the filtered water 9 flowing into the tank from the membrane element 2b through the filtered water outlet pipe 2c while starting and stopping at a predetermined reference high water level HL and a reference low water level LL. 10 are provided. Further, a water level meter 12 for detecting the level of the filtered water 9 in the tank and a control device 13 for controlling the start and stop of the drainage pump 10 are provided. The control device 13 is electrically connected to the water level gauge 12 and the drain pump 10, and includes a timing unit, a calculation unit, and a storage unit (not shown).

In the above-mentioned septic tank, raw water is introduced into the denitrification tank 1 and a part of the activated sludge mixed solution 7 in the denitrification tank 1 is converted into a nitrification tank in the same manner as in the conventional septic tank described with reference to FIG. In the state where the activated sludge mixture liquid 8 in the nitrification tank 3 is allowed to flow to the denitrification tank 1, denitrification treatment is performed in the denitrification tank 1 under anaerobic conditions, Nitrification treatment is carried out under aerobic conditions in which air is diffused.

Further, the activated sludge mixed liquid 8 in the nitrification tank 3 maintained at a constant water level by the flow described above is gravity-filtered by the membrane element 2b, and the filtered water 9 that has passed through the membrane surface is filtered out by the filtered water outlet pipe 2c. Through the treatment water tank 4. The filtered water 9 in the treated water tank 9 is intermittently discharged by the drain pump 10 and is maintained between the reference low water level LL and the reference high water level HL.

At this time, the following operation is performed to control the amount of filtered water in the membrane separation device 2 to be constant. When the drain pump 10 is stopped, the water tank 4
Detecting the water level L ₀ of the filtered water 9 of the inner, after a predetermined time measured by the time measuring means detects the water level L ₁ of the filtered water 9 in the treatment water tank 4 by the water level gauge 12, was detected 2 water level L _0,
The level difference between L ₁ calculated by the arithmetic means, and stores the calculated level difference in the storage means as a reference level difference value [Delta] L.

When the drain pump 10 is stopped after an appropriate time,
Similarly, water gauge 12 and the time measuring means and the water level L ₀ of the filtered water 9 in the treatment water tank 4 at a predetermined time ', L _1' senses, 2 water level L ₀ is detected ', L _1' between Is calculated by the calculating means, and the calculated water level difference is stored in the storage means as the measured water level difference value ΔL '.

Next, the control unit 13 compares the measured water level difference value ΔL ′ with the reference water level difference value ΔL. When the measured water level difference value ΔL ′ <the reference water level difference value ΔL, the controller 1
3, the driving time (or driving force) of the drainage pump 10
To lower the water level in the treated water tank 4 to LL ', which is lower than the reference low water level by a fixed water level, and then drive the drainage pump 10 as usual, so that the inside of the treated water tank 9 has a low water level LL'. The water level is maintained between the water level HL ′ and the water level difference between the nitrification tank 3 and the treatment water tank 4 is further increased.

When the measured water level difference value ΔL ′> the reference water level difference value ΔL, the control unit 13 reduces the driving time (or driving force) of the drain pump 10 to reduce the water level in the treated water tank 4 to the reference low water level. By raising the water level to a higher level by a certain level (not shown), the water level difference between the nitrification tank 3 and the treated water tank 4 is further reduced.

By repeating the above-described operation, the amount of filtered water per unit time can be controlled to be constant regardless of a change in membrane performance such as membrane clogging. Conversely, it is also possible to increase or decrease the amount of filtered water in accordance with fluctuations in the inflow of raw water or fluctuations in water quality.

In the above embodiment, the measured water level difference value Δ
The water level at which the drain pump 10 is stopped is lowered (or raised) by a fixed water level depending on the magnitude of L ′ and the reference water level difference ΔL, but the difference between the measured water level difference ΔL ′ and the reference water level difference ΔL is set. The water level drop widths b0, b1, b2,... corresponding to a0, a1, a2,.
0, a1, a2..., The water level drop width b0, b1,
b2... may be selected.

In the above embodiment, the drain pump 1
Although the water level of the filtered water 9 in the treated water tank 4 is detected at the stop of 0, the water level of the filtered water 9 in the treated water tank 4 may be detected in a state where the drainage pump 10 is driven at a constant speed.

In place of the water level gauge 12, a water level detecting means such as a liquid pressure gauge or a laser water level gauge may be used. Water level meter 1
2 is connected to an alarm device (not shown), and when the water level detected by the water level gauge 12 exceeds a range suitable for gravity filtration in the membrane separation device 2, for example, up to a water level at which the membrane separation device 2 is exposed. An alarm may be displayed when the temperature decreases.

[0024]

As described above, according to the present invention, the water level of the filtered water in the treated water tank is detected after a predetermined time, and the measured water level difference value ΔL ′ calculated from the two detected water levels is set in advance. Compared with the reference water level difference value ΔL, and based on the difference between them, the water level at which the pump means for discharging the filtered water in the treated water tank is started and stopped is changed to increase the water level difference between the biological treatment tank and the treated water tank. Since the size is reduced, a constant processing operation can be performed irrespective of a change in the membrane performance even though the gravity filtration method is used. Conversely, in response to fluctuations in raw water inflow and water quality,
It is also possible to increase or decrease the amount of filtered water.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a septic tank provided with a filtered water amount constant control device according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a conventional septic tank in which a gravity filtration type membrane separation device is installed in the tank.

FIG. 3 is a longitudinal sectional view of a main part of a conventional septic tank in which a suction filtration type membrane separation device is installed in the tank.

[Explanation of symbols]

2 Membrane separation device 2c Filtration water outlet pipe 3 Nitrification tank 4 Treatment water tank 8 Activated sludge mixture 9 Filtration water 10 Drain pump 12 Water level gauge 13 Controller HL Standard high water level LL Standard low water level L ₀ , L ₁ Water level ΔL Standard water level difference Value L ₀ ', L ₁ ' Water level ΔL 'Measured water level difference value HL' High water level LL 'Low water level

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Okada 1-1-1, Hama, Amagasaki-shi, Hyogo Inside Kubota Research and Development Laboratory Co., Ltd. (72) Inventor Kazuyuki Honda 2 Takamatsu, Kosai-cho, Koga-gun, Shiga Prefecture 1 Kubota Shiga Plant

Claims (2)

[Claims] 1. The activated sludge mixed liquid in the biological treatment tank is gravity-filtered by a membrane separation device immersed and installed in the tank based on a difference in water level with the treatment water tank, passes through the membrane, and passes through the filtered water discharge pipe into the treatment water tank. When the filtered water that has flowed in is discharged by the pump means that starts and stops at the predetermined reference high water level and the reference low water level, when the pump means is driven or stopped,
Detects the level of filtered water in the treated water tank after a predetermined time,
The detected water level difference between the two water levels is calculated, the calculated water level difference is set as a reference water level difference value ΔL, and when the pump means is driven or stopped thereafter, the level of the filtered water in the treated water tank is kept for a predetermined time. Calculating a water level difference between the two detected water levels, and determining the calculated water level difference as a measured water level difference value ΔL ′,
The measured water level difference ΔL ′ is compared with the reference water level difference ΔL, and when the measured water level difference ΔL ′ <the reference water level difference ΔL, the pump means is stopped at least at a water level lower than the reference low water level. The water level difference between the biological treatment tank and the treated water tank is enlarged, and when the measured water level difference value ΔL ′> the reference water level difference value ΔL, the pump means is stopped at least at a water level higher than the reference low water level to perform biological treatment. A method for controlling a constant amount of filtered water, characterized in that the difference in water level between a tank and a treated water tank is reduced, thereby controlling the amount of filtered water per unit time in a membrane separation device to be constant. 2. A biological treatment tank in which a membrane separation device is immersed and installed, a treatment water tank in which the end of a filtered water outlet pipe communicating with the membrane permeation side of the membrane separation device is open in the tank, and a filtered water in the treatment water tank. Is provided in a purification tank provided with a pump means for discharging while starting and stopping at a predetermined reference high water level and a reference low water level, and a constant filtration water amount control device for controlling a constant amount of filtration water per unit time in the membrane separation device. There is provided a water level detecting means for detecting a water level of the filtered water in the treated water tank, and a control means for controlling start and stop of the pump means, and the control means detects a water level detected by the water level detecting means. Calculated measured water level difference value ΔL 'per predetermined time
And, based on the difference between the preset reference water level difference value ΔL per predetermined time, the pump means is stopped at least at a water level different from the reference low water level to increase the water level difference between the biological treatment tank and the treatment water tank. An apparatus for controlling the amount of filtered water constant, wherein the apparatus is reduced so as to control the amount of filtered water per unit time in the membrane separation device to be constant.