JPS6329570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for cleaning filter media of a gravity filtration device used in water treatment facilities.

Gravity filtration devices often used in water treatment facilities, i.e.
In the descending rapid filtration device, backwashing is performed in order to remove suspended substances captured and trapped on the surface and inside of the filter layer as filtration progresses. This backwashing is generally performed by using clear water (filtered water) that has passed through the filter medium layer in a downward flow and causing it to flow back.

During such backwashing, if the flow rate of backwash water is too high, the filter layer will be sufficiently backwashed, but on the other hand, it will consume a large amount of clear water, which is uneconomical, and in severe cases. In this case, a part of the filter medium flows out, which not only becomes uneconomical but also causes a significant drop in filtration performance. On the other hand, if the flow rate of backwash water is too low, the filter medium cleaning will naturally be incomplete. If incomplete cleaning is repeated, suspended solids that cannot be removed will gradually aggregate and grow into a mud ball shape, eventually spreading and accumulating inside the entire filter media layer. Brook-through (short circuit) occurs, resulting in a significant drop in filtration performance and deterioration in the quality of the filtered water.

However, in the conventional backwashing method, the optimum values of the flow rate of backwash water and the backwash time are set to constant values based on experience, design guidelines, etc., and the above-mentioned backwashing is performed. In such a method, as described above, it is very difficult to eliminate excess or deficiency in the flow rate of backwash water depending on the amount of suspended solids retained in the filter medium layer.

In other words, if there are many suspended solids in the raw water, the amount of suspended solids will increase proportionally, but if you ignore this amount and perform a cleaning method that keeps the backwash water flow rate constant, the backwash water flow rate will be insufficient. As a result, it becomes impossible to reliably separate and remove the suspended solids from the filter layer, and the filter layer becomes increasingly clogged, eventually resulting in the formation of mud balls as described above, which impede the filtration. Water quality will deteriorate. Moreover, when the above-mentioned retention amount is small, the flow rate of backwash water becomes excessive, resulting in the above-mentioned wasteful consumption of clear water and a decrease in filtration performance due to some of the filter medium flowing out.

If we further subdivide the backwashing process, we can see that immediately after the start of backwashing, there are many substances trapped in the filter media layer, so by increasing the flow rate of backwash water and performing powerful backwashing, as well as reducing the substances trapped, It turns out that it is better to gradually reduce the backwash water flow rate accordingly.

Therefore, in order to perform such optimal backwashing, it is sufficient to detect the remaining amount of retained substances and adjust the flow rate of backwash water, but it is extremely difficult to detect this remaining amount.

As an alternative method to detecting the remaining amount, it is known that the desired optimal backwashing method can be achieved by adjusting the backwashing water flow rate so that the surface height of the filter medium layer during backwashing is always within a certain range.

Therefore, in order to make this adjustment, several sample collection pots are installed at appropriate height positions on the filter layer, and by opening the pots at appropriate times and checking the properties of the sample liquid flowing out, Attempts have been made to check the height of the filter medium, or to check the height of the filter medium surface by sinking a weight that approximates the specific gravity of the filter medium on the surface of the filter medium layer and checking the height of the weight that floats up during backwashing. However, these methods have many problems in terms of reliability and labor saving, and therefore,
The reality is that it has not been put into practical use.

This invention was made in view of the above circumstances,
The flow rate of backwash water can be controlled so that the height position of the surface of the filter medium layer can be maintained within a certain height setting range, and the flow rate of the backwash water can be controlled to maintain the height position of the surface of the filter medium layer within a certain height setting range. It is an object of the present invention to provide a filter medium cleaning method and an apparatus therefor, which can improve backwashing efficiency by eliminating excessive or insufficient flow rates.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, reference numeral 1 denotes a filter tank of a gravity filtration device, and a first filter layer 2 made of, for example, anthracite and a second filter layer 3 made of, for example, sand are accommodated in this tank.

Here, the raw water to be filtered is supplied into the filter tank 1 by a supply means (not shown), and the first filter medium layer 2
After being filtered by sequentially passing through the second filter layer 3, the water enters the lower chamber 4 provided below the second filter layer 3, and is taken out from the lower chamber 4 as filtered clear water. .

On the other hand, a cleaning water supply pipe 5 is provided in the lower chamber 4.
One end is open. This cleaning water supply pipe 5
is for supplying wash water (for example, clear water already obtained by filtration) into the lower chamber 4 with a backwash pump 6. This washing water flows backward from the lower chamber 4 through the second filter layer 3 and the first filter layer 2, rises inside the filter tank 1, and then flows out of the tank from the upper end. This backwash water removes suspended matter trapped on each surface and inside of the first and second filter media layers 2 and 3.

Here, the height of the surface of the first filter medium layer 2 is maintained at the lowest level L _S in normal filtration conditions, but during cleaning, it rises due to the pressure of backwash water, and the height is reversed. It depends on the flow rate of washing water and the amount of suspended solids retained (degree of clogging).

Now, in the filter tank 1, there is a first filter at the time of backwashing.
Equipped with an ultrasonic reflection level meter LS for detecting the height of the filter layer 2.

This ultrasonic reflection type level meter LS has a sensor section 7 arranged at a spaced position above the first filter medium layer 2, and a detection section 9 connected to the sensor section 7 via a conductive wire 8. .

In such an ultrasonic reflection type level meter LS, the sensor section 7 includes a transmitter section that transmits ultrasonic waves of a predetermined frequency toward the surface of the first filter layer 2, and a transmitter that transmits ultrasonic waves reflected from the surface of the first filter layer 2. The detection unit 9 has a reception unit that receives the signal, and the detection unit 9 has a reception unit that receives the signal from the sensor unit 7.
The height of the surface of the first filter layer 2 is determined from the time required for the receiving section of the sensor section 7 to receive the ultrasonic waves transmitted from the transmitter to the surface of the first filter layer 2 and reflected from this surface. The detected value is extracted as a DC4 to 20mA current signal, for example.

The height of the surface of the filter medium layer during filtration is determined by the output signal of the detection unit 9 at the contact S1-1 which becomes ON after a certain stable time from the start of the filtration operation.
The data is then stored in the analog memory 10. In addition,
A contact S1-2 interlocked with the contact S1-1 is for synchronizing the analog memory 10 with the filter medium layer stabilization period, and the stored value of this analog memory 10 can be stored at the contact S2-1 provided as needed. The signal is supplied to the subtracter 11 via the subtracter 11. This subtracter 11 is
Subtraction is performed between the stored value of the analog memory 10 and the output value of the detection unit 9 of the filter medium layer surface height during backwashing, which is supplied via the contact S2-1 and the contact S2-2 linked thereto. The next comparator 12 compares this output value with the set value of the setter 11S. Contacts S2-1 and S2-2 are turned ON after the operation of the water purge device is completed to remove air bubbles attached to the surface of the sensor section 7 before each operation.
It is controlled so that

The comparator 12 is the output value of the subtractor 11 (the difference in the surface height of the first filter medium layer 2 during filtration and during backwashing).
It operates to generate an output signal until it reaches a predetermined set value (=Lm: the optimal set value for the difference in surface height of the first filter medium layer 2 during filtration and backwashing), and this output signal is It is used to drive the backwash pump 6 via the pump control section 13. A variable speed pump is used as the backwash pump 6, and a comparator 12 is used.
If the backwash pump 6 is configured to be driven at a speed corresponding to the magnitude of the deviation between the input signals, the surface height of the first filter medium layer 2 during backwashing can be maintained near the optimal setting value Lm. It is possible to automatically control the

That is, when the backwash pump 6 is started when cleaning the filter media layer, backwash water (clarified water) is supplied from the wash water supply pump 5 into the lower chamber 4, and this backwash water rises inside the filtration tank 1. By sequentially passing through the second filter medium layer 3 and the first filter medium layer 2, the retained suspended substances are separated and removed from these filter medium layers.

During such cleaning, first, the surface height of the first filter medium layer 2 is detected by the ultrasonic reflection type level meter LS, and this detected value and the stored value in the analog memory 10 are subtracted by the subtracter 11. . Next, by inputting the output value of the subtraction result from the subtracter 11 to the comparator 12, the comparator 12 compares the output value of the subtracter 11 with the setter 11S.
is compared with the optimum setting value Lm, and outputs a speed control signal to the backwash pump 6 according to their deviation values.
As a result, the backwash pump 6 is controlled to an operating speed corresponding to the deviation value, and the flow rate of the backwash water supplied from the wash water supply pump 5 is controlled by the backwash pump 6 to the surface height of the first filter medium layer 2. The flow rate is controlled to an appropriate level depending on the situation.

In this way, by controlling the flow rate of the backwash water so that the surface height of the first filter medium layer 2 is constant, if the amount of suspended solids retained is large, the amount of suspended solids can be adjusted accordingly. A large amount of backwash water is supplied, and as the amount of retention is gradually reduced, the flow rate of backwash water supplied is also gradually reduced. Therefore, the backwashing water flow rate is prevented from being excessive or insufficient, and the backwashing effect is improved.

It is preferable that the backwashing end command be issued based on the detection of a drop in suspension of the backwash water, but simply a timer may be used to set a required time based on experience.

Further, a flow rate control valve is provided at an appropriate position of the washing water supply pipe 5, and this control valve is connected to the comparator 12.
A similar effect can be obtained by controlling with the output of .

Furthermore, FIG. 2, in which the same parts as in FIG.
Alternatively, a second subtracter 11a and a comparator 12a may be provided, and the comparator 12 may control the first relay 13, and the comparator 12a may control the second relay 13a.

In this way, the first comparator 12
is the difference in surface height of the first filter medium layer 2 during filtration and backwashing, the upper limit Lh, and the second comparator 1.
In 2a, comparison is made with the set values corresponding to the lower limit Ll, and by combining both signals, ON-OFF control is performed to maintain the flow rate of backwash water between the upper limit Lh and the lower limit Ll. It is possible to do so.
Simply, by manual operation, the flow rate of the backwash water may be reduced when the upper limit bell BL is sounded, and the flow rate may be increased when the lower limit bell BZ is sounded. Note that E1 and E2 indicate power supplies.

In addition, the output signal during filtration and the output signal during backwashing are taken out in conjunction with the control contacts S1-3 and S2-3 and supplied to the one-pen recorder 14, and the first filter medium layer 2 in two states is may be recorded as mutually series recording lines. In this case, the first filter medium layer 2 in two states: during filtration and during backwashing.
In order to visually display the surface height of the two and to clearly distinguish the phase difference between the two, a two-pen type recorder 14a is used to record the output signal of the analog memory 10 and the output of the detection unit 9. A configuration may also be adopted in which the signals are recorded at the same time.

Furthermore, when controlling a large number of filtration tanks with one detection unit, by synchronizing the sensor switching device 15 and the control output signal switching device 16, one detection control unit can control a large number of filtration tanks. It is also possible to control.

As described above, according to the present invention, the height of the surface of the filter medium layer is automatically and continuously detected by the ultrasonic reflection type level meter, and the height of the surface of the filter medium layer is set within a predetermined setting range based on the detected value. The flow rate of backwash water can be controlled so that the flow rate is controlled so that the appropriate flow rate of backwash water is always sufficient to separate and remove suspended solids in accordance with the amount of suspended solids retained. Therefore, there will be no occurrence of excess or deficiency of backwash water, and any inconvenience caused by excess or deficiency of backwash water will be eliminated at once, and an optimal backwash effect can always be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a filter medium cleaning device according to one embodiment of the present invention, and FIG. 2 is a block diagram of the main parts of the device according to another embodiment. 1... Filter tank, 2... First filter medium layer, 3... Second
Filter medium layer, 7...Sensor section, 10...Analog memory, 11...Subtractor, 12...Comparator,
LS...Ultrasonic reflection level meter.

Claims (1)

[Scope of Claims] 1. A filter medium cleaning method in which a filter medium layer provided in a gravity filtration device of a water treatment facility is washed by flowing backwash water from below to above the filter medium layer,
Detecting the height position of the filter medium surface with an ultrasonic reflection type level meter having a sensor section above the filter medium layer,
A method for cleaning a filter medium in a filter device, comprising controlling the flow rate of the backwash water so that the height position falls within a set range based on the detected value. 2. Store the output value of the ultrasonic reflection level meter during filtration in an analog memory, and compare the difference between the stored value in the analog memory and the output value of the ultrasonic reflection level meter with the set value during cleaning. 2. A method for cleaning a filter medium in a filtration device according to claim 1, wherein the flow rate of said backwash water is controlled in accordance with the difference. 3. Claim 1, characterized in that the output value of the ultrasonic reflection level meter during filtration and the output value of the ultrasonic reflection level meter during cleaning are recorded with a one-pen recorder. A method for cleaning a filter medium in the filtration device described in 1. 4. The filter medium in the filtration device according to claim 2, wherein the output value of the analog memory and the output value of the ultrasonic reflection level meter during cleaning are recorded on a two-pen recorder. Cleaning method. 5. An ultrasonic reflection level meter that detects the position of the surface of the filter medium layer provided in the filtration tank, an analog memory that stores the output value of the ultrasonic reflection level meter during filtration, and an analog memory that stores the output value of the ultrasonic reflection level meter during cleaning. and a subtracter that calculates the difference between the output value of the ultrasonic reflection type level meter and the output value of the ultrasonic reflection type level meter. A filter medium cleaning device in a filtration device, comprising a comparator that generates an output for controlling the flow rate of cleaning water supplied to the filter.