JPH10113650A - Back washing method for active carbon column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to prolong the period of back washing intervals, to improve back washing performance and to reduce back washing time and washing water volume by executing back washing by repeating a draining stage, stirring stage, washing stage and water level regulating stage if the required time for water level adjustment or the flow rate of waste water or the flow velocity of the waste water is below a set value. SOLUTION: When the water flow resistance is generated and the water level in a biological active carbon column 1 rises to a prescribed water level, the pressure difference between an inlet and outlet is detected by a difference pressure gage 10 and the back washing is executed by the signal from a controller 20. Namely, the solenoid valve 4A of an inflow pipe 4 is closed to lower the water level down to the set water level. The solenoid valve 5A of a treated water pipe 5 is then closed and the back washing is executed by sending the back washing water from a back washing pipe 6 and air from an air pipe 9 for back washing. The water level is lowered down to the set water level H by executing the water level adjustment after the back washing. The respective stages are repetitively executed when the time for the water level adjustment detected by a water level detecting gage 11 is above the set discharge time. As a result, the execution of the active carbon treatment at the optimum back washing intervals is made possible and the back washing time is shortened and the volume of the water to be used is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for backwashing an activated carbon tower.

[0002]

2. Description of the Related Art In an advanced water treatment system using ozone treatment and biological activated carbon treatment, in biological activated carbon treatment, microorganisms adhering to suspended water and the like or accumulating on activated carbon carriers grow as water passes. The activated carbon filled layer is closed by forming a membrane. As a result, the flow resistance increases, and the water level in the activated carbon tower rises and the amount of treated water decreases, the water quality deteriorates, and organisms leak. For this reason, it is necessary to perform a backwashing operation for washing the activated carbon packed bed to recover the processing performance. The frequency of backwashing depends on the amount of water flow and the quality of water, the change in water temperature with the season, the growth state of organisms, and the like. In summer, backwashing is performed at a frequency of 2 to 3 days / time.

[0003] Generally, an increase in the water flow resistance of biological activated carbon is detected by detecting a rise in the water level at the inlet of the activated carbon packed bed with a water level gauge, or by detecting the pressure loss at the inlet and outlet of the activated carbon packed bed. . And as a backwash method,
Backwash water flows upward from below the activated carbon packed bed,
Full-layer backwashing method to wash out sediments such as suspended matter and biological growth out of the system, method to wash the packed bed surface by mechanical stirring or jet jet, blowing air from below the activated carbon packed bed, and shearing force of bubbles There is known an air cleaning method in which sediments are separated by using water and then washed with backwash water.

[0004] In the advanced water purification treatment, a combined air cleaning method is often employed. When backwashing biological activated carbon, backwashing is performed after air is blown in and washed with backwash water, or a combination of backwashing in which backwash water and air are simultaneously flown, as well as the amount of air, backwash water, and washing time. It has been reported that simultaneous backwashing of water and air has a large cleaning effect (eg, Kojima, Sato, Tamura: Cleaning characteristics of biological activated carbon adsorption pond; 42nd National Waterworks Research Conference, H3.5, Higashino, Sakamoto , Kawasaki, Morimoto: Advanced Water Treatment Plant Demonstration Experiment in Osaka Prefecture [IV]).

[0005] Floating suspensions and fine particles having an apparent specific gravity smaller than the activated carbon deposited in the activated carbon packed bed can be washed out with backwash water. The washing time with the backwash water is set to 10 minutes or more, although the suspension concentration in the backwash water decreases in a few minutes and saturates. The following has been proposed as a conventional example of the backwashing method.
For example, Japanese Patent Application Laid-Open No. 4-87688 (Conventional Example 1) discloses that the water level raised due to pressure loss is drained and lowered, air is blown from a position slightly below the surface of the activated carbon packed bed, and backwash water is blown from the lower part. Japanese Patent Application Laid-Open No. 4-197484 (conventional example 2) discloses a backwashing method in which the inflow step is performed sequentially. The backwashing water flow rate is automatically controlled so as to keep the expansion interface of the activated carbon packed bed constant during backwashing. A method has been proposed. Also, JP-A-6-170
No. 358 (conventional example 3) and JP-A-6-170384 (conventional example 4) propose a method of controlling backwashing conditions such as backwashing time and washing water amount according to the water level change rate. .

[0006] On the other hand, the washing characteristics with backwash water are described in the above-mentioned conventional examples and the like, and the change with time of the backwash wastewater is evaluated. However, there is no description about specific detection means and washability of the activated carbon packed bed. .

[0007] When backwash water flows from the lower portion of the activated carbon packed bed for backwashing, the surface where the activated carbon flows at the flow rate of the backwash water and the apparently expanded surface of the activated carbon packed bed is defined as an expanded interface. I do.

[0008]

The problem of backwashing biologically activated carbon is to clean the activated carbon packed bed, because the quality of washing the activated carbon packed bed by backwashing affects the initial pressure loss at the time of re-watering. . If the initial pressure loss is high, the rate of pressure loss rise with the passage of water is large, and the backwash interval is short. Furthermore, in the conventional biological activated carbon backwash method, experiments verified that the suspension separated by air agitation was mixed with the activated carbon packed bed and retained in the activated carbon fluidized bed during washing with backwash water. . The conventional backwash method has the following problems.

(1) In the conventional method of backwashing an activated carbon tower, the activated carbon packed bed is washed when the concentration of suspended solids in the backwash wastewater decreases and clarity is saturated. Although the washing time is empirically set aside, the suspended matter is actually retained in the activated carbon fluidized bed, and the suspended matter retention greatly affects the initial pressure loss during re-watering. This was confirmed by experiments.

(2) An empirical formula relating to the expansion coefficient of the activated carbon packed bed is derived with reference to the theoretical equation of fluidization of the filter layer, and the relationship between the backwash water flow rate and the expansion coefficient is known. Based on this, backwash conditions have been proposed. Usually, the expansion coefficient of the activated carbon packed bed is 3
Although the backwash flow rate is set to be about 0 to 40%, the expansion rate of the activated carbon packed bed is affected not only by the backwash water flow rate but also by the water temperature. It changes under the influence of water temperature. Regarding the method of automatically controlling the backwash water flow rate as in Conventional Example 2 or controlling the backwash conditions according to the water level change rate as in Conventional Examples 3 and 4, the expansion interface of the activated carbon packed bed is kept constant, This is an effective means because activated carbon can be prevented from flowing out. However, these methods cannot remove the suspended matter retained in the activated carbon fluidized bed.

(3) The water level of the activated carbon tower rises, and the water is drained for backwashing to reduce the water level to an arbitrary set water level, and then backwashing in which air and backwash water flow in from below is a known method. However, it is considered that the method of blowing air from slightly below the activated carbon surface layer as in Conventional Example 1 focuses on the fact that the growth of organisms mainly occurs on the surface layer of the activated carbon packed bed. However, the suspended matter retained in the activated carbon fluidized bed cannot be removed as in (2).

[0012] An object of the present invention is to determine the effect of backwashing of an activated carbon packed bed and to repeat the backwashing step as necessary to effectively remove suspended matter retained in the activated carbon packed bed. . As a result, an increase in the initial pressure loss at the time of re-watering is suppressed, the water-flowing time until backwashing is lengthened, and the backwash interval is lengthened. Further, the present invention provides a method for backwashing an activated carbon tower capable of improving the backwashing performance and reducing the backwashing time and the amount of washing water.

[0013]

In order to achieve the above object, the present invention provides a method for backwashing an activated carbon tower for purifying water by passing water downward through an activated carbon packed bed. When the water level rises, the flow of water is stopped, the drainage step of lowering the raised water level to an arbitrary set water level, and thereafter, the activated carbon filling is performed by flowing backwash water from the lower part of the activated carbon tower and blowing air. A stirring step of stirring the layers to separate the suspension, etc .; a washing step of allowing only the backwash water to pass therethrough to allow the suspension, etc. to flow out together with the backwash water; and, after the washing step, the backwash water Water from the bottom of the activated charcoal tower,
A water level adjusting step of draining water to a set water level for re-watering, wherein the water level adjusting step includes a time required for draining to the set water level and / or a means for measuring the flow rate or flow velocity of drainage, and an arbitrary required time for drainage And / or setting a set value of the drainage flow rate or drainage flow rate, and if the water level adjustment is a required time longer than the set time or / and the drainage flow rate or drainage flow rate is equal to or less than the set value, the drainage step, the stirring step, the cleaning step, and the water level It is characterized in that the adjustment process is repeated and backwashing is performed.

In the washing step with backwash water, when the concentration of suspended solids in the backwash wastewater is measured by a turbidimeter, the concentration of suspended solids decreases in a washing time of several minutes, becomes clear, and becomes saturated. But,
It was confirmed by experiments that most of the suspension flowed out in the backwash water extrusion flow, but about 10% of the total recovered amount did not flow out and was retained in the activated carbon fluidized bed. This is because the suspended matter separated during the air stirring is almost uniformly mixed with all the activated carbon layers under the stirring and flowing, and during the extrusion flow of the backwash water, the suspended matter is reattached to the activated carbon fluidized bed or filtered and suppressed. Things. Furthermore, it was found that the amount of retention affected the initial pressure loss during re-flow.

The present invention focuses on the fact that the amount of retention affects the initial pressure loss. After backwashing, in the water level adjustment of draining to a predetermined water level for re-watering, the amount of detention affected the drainage time, and when the amount of detention was large, the required drainage time was large and correlated. . In addition, in the water flow treatment, the backwash interval depends on the initial pressure loss, and it was confirmed by an experiment that the backwash interval was long when the initial pressure loss was low. That is, the initial pressure loss after the backwash is almost the same as draining to the set water level for water level adjustment and re-watering. Therefore, the cleaning degree of the activated carbon packed bed can be estimated by measuring the drainage time or the flow rate and the flow velocity when adjusting the water level.

Based on this result, in the present invention, the drainage time, flow rate, and flow velocity at the time of water level adjustment after backwashing are measured, and the quality of backwashing of the activated carbon packed bed backwash is determined from an arbitrarily set value. If the washing is insufficient, the above-mentioned back washing step is controlled so as to be repeated.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a configuration of a general biological activated carbon tower introduced into a water purification plant. In the biological activated carbon tower 1, granular activated carbon is supported by a support member 2 to form an activated carbon packed bed 3. An inflow pipe 4 through which the water to be treated flows into the side surface of the biological activated carbon tower 1, and a treated water pipe 5 through which the treated water flows are provided below. The treated water flowing through the activated carbon packed bed and treated is stored in a treated water tank via a treated water pipe 5.

In the case of performing backwashing, the backwashing pump (not shown) causes the treated water to flow from the lower part of the biological activated carbon tower 1 through the backwash water pipe 6 from the treated water tank as backwash water. The backwash water overflows the inner wall of the biological activated carbon tower 1 and is discharged from the backwash drain pipe 7. Further, after the backwash, the activated carbon is refilled and the water level is adjusted from the overflow water level in the biological activated carbon tower 1 to an arbitrary set water level Hs when re-watering. Drain. A backwash air pipe 9 is provided below the support member 2 to supply air into the biological activated carbon tower 1 from a blower or a compressor (not shown). In addition, the backwash air pipe 9 may be provided at an arbitrary position of the activated carbon layer 3 instead of below the support member 2, or may be provided at both.

A differential pressure detector 10 for detecting the differential pressure between the inlet and the outlet of the activated carbon packed bed and the biological activated carbon tower 1
A water level detector 11 for detecting the level of the treated water in the biological activated carbon tower is provided at the upper part. Excess air and the like in the biological activated carbon tower 1 such as blown air at the time of back washing are introduced from an exhaust pipe 12 to an exhaust gas treatment device separately provided for treatment.

Electromagnetic valves 4A and 5A provided on the inflow pipe 4 and the treated water pipe 5, electromagnetic valves 6A and 7A provided on the backwash water pipe 6 and the backwash drain pipe 7. The drain pipe 8 includes an electromagnetic valve 8A and a flow rate measuring device 8B. Further, the solenoid valves 9A provided in the backwash air pipe 9 are connected to the control device 20, respectively.

Hereinafter, the operation of the biological activated carbon tower having this configuration will be described in detail.

FIG. 1 shows a state before backwashing in which the water flow resistance increases from the set water level Hs, which is the water flow state at the beginning of water flow, and rises to the water level Hp. In the case of highly treated purified water, the ozone oxidation treatment is performed in the first stage, and the ozonized water is supplied from the inflow pipe 4 to the biological activated carbon tower 1.
And is subjected to flow treatment in the activated carbon packed bed 2 and then stored through a treated water pipe 5. At this time, the solenoid valves 4A and 5A of the inflow pipe 4 and the treated water pipe 5 are open. Initial water level H
s causes the accumulation of suspended matter or the growth of living organisms with the passage of water, thereby blocking the activated carbon packed bed 3, causing water flow resistance and increasing the water level to Hp. The differential pressure Δp between the water levels Hs and Hp is detected by the differential pressure detector 10, and the control device 2
0 initiates the backwash operation. As a means for detecting the water flow resistance, a method of detecting with the water level detector 11 is also possible.

Next, the backwashing operation will be described with reference to the control sequence of the present invention shown in FIGS. In this embodiment, when a water flow resistance occurs and the water level in the biological activated carbon tower 1 rises to a predetermined water level, the differential pressure between the inlet and the outlet is detected by the differential pressure detector 10, and the differential pressure is detected by a signal from the control device 20. Washing is started. Then, in the draining step (1) of the control sequence of FIG. 5, the solenoid valve 4A of the inflow pipe 4 is closed, and the water level is set at the head level Hs by the head difference.
Drain and lower. When the water level reaches the set water level, the electromagnetic valve 5A of the treated water pipe is closed, and in the stirring step (2), the electromagnetic valve 6A of the backwash water pipe 6 is opened and a backwash pump (not shown).
Is operated, first, backwash water having a minimum flow rate (in this embodiment, a backwash water superficial velocity of 20 m / h) at which the activated carbon packed bed flows is caused to flow to make the activated carbon packed bed in a fluidized state, and a backwash air pipe is provided. 9
Then, backwash air is blown into the mixture and the mixture is stirred, and the suspended matter and the biological layer deposited on the activated carbon packed bed 3 are separated from the activated carbon by the shearing force of bubbles. Then, in the washing step (3), the blowing of air is stopped, and the amount of backflow water is increased so that the backwash water has an arbitrary expansion coefficient at which the activated carbon packed bed 3 flows (in the embodiment, the expansion rate is 4).
(0%, backwashing water empty speed: 36 m / h), and the suspension separated in the stirring step overflows from the inner wall of the biological activated carbon tower 1 and is washed together with the backwashing water and discharged from the backwashing drain pipe 7. . When the washing is completed, the flow of the backwash water is stopped, and the water is drained from the overflowing water level Hp to the set water level Hs and lowered (4) A water level adjusting step is performed. In this case, the suspended matter is drained from the drainage pipe 8 to flow out.

FIG. 3 shows the water level adjusting step of the present invention.
The drainage time for draining water from the water level Hp to the set water level Hs in the water level adjustment step (4) is measured by the water level level detector 11, and if it is equal to or longer than the arbitrarily set drainage time, the control sequence of stirring-washing-water level adjustment is performed. Each step is repeatedly performed.

The present invention has been found based on the following experimental results.

FIG. 6 shows a processing flow of the continuous experiment apparatus for the biological activated carbon. The biological activated carbon tower has an inner diameter of 16 cm x 250
Acrylic tower of cm height, activated carbon packed bed height is 100cm. An ozone oxidation tower and a deaeration tower by blowing air are installed in the first stage. A pressure loss occurred from the set water level Hs, and the head difference up to a predetermined water level Hp, which also served as overflow of the backwash drainage, was 100 cm.

FIG. 7 shows the pressure loss increase characteristics when the conventional backwashing and the backwashing according to the present invention are alternately repeated by continuous water flow. The conditions of water flow are shown in FIG. 6, but glucose was added at an appropriate concentration as a nutrient source for bioactive carbonization. At this time, the number of times of repeated backwashing according to the present invention was two times, and two-stage backwashing was performed. Two-stage backwashing requires about 1.5 to twice as long as the time required to reach backwashing compared to conventional backwashing. Here, when looking at the pressure loss rising speed, no remarkable difference was observed between the two types of backwashing, and it was found that the difference in the initial pressure loss due to the cleaning effect at the time of backwashing had a large effect on the water flow time. Was.

FIG. 8 shows the relationship between the initial pressure loss and the water passage time required for backwashing. In the conventional backwashing by the control sequence of FIG. 4, the initial pressure loss is 40 cmAq or more, and the water passage time to backwashing is short. From this result, if the initial pressure loss is detected, it is possible to confirm the detergency of backwashing. However, after backwashing,
If the washing is insufficient at the time of re-watering, it is not realistic in actual operation control to return to the backwashing control sequence again.

Therefore, the present invention focuses on the fact that drainage at the time of water level adjustment after backwashing and re-watering are substantially the same, and measures the drainage time at the time of water level adjustment. From the results of FIGS. 7 and 8, FIG. 9 shows the relationship between the measured drainage time and the initial pressure loss. In the case of this experimental device, if the drainage time at the time of water level adjustment is within 3 minutes, the initial pressure loss is 20 from FIG.
It has been washed to about 30 cmAq, and the water flow time is about 17
0 hours (7.0 days). On the other hand, drainage time 4
In the case of minutes, the initial pressure loss is 40 cmAq or more, and the water passage time is as short as 70 to 90 hours (about 3 to 4 days).

As another embodiment, the flow rate or drainage flow rate of the drainage water drained from the drainage pipe 8 in the water level adjustment step is measured by a flow rate measuring device 8 B installed in the drainage pipe 8. Since the water is drained with a head difference from the overflow water level Hp to the set water level Hs in the washing process using the backwash water, the drainage flow rate or flow rate changes. For this reason, the flow rate measuring device 8B can control whether to repeat the backwashing step by measuring the drainage flow rate or the flow velocity at an arbitrary measurement time point, or by judging from the drainage flow rate or the flow velocity pattern.

On the other hand, when the concentration of the suspended solids in the backwash wastewater according to the experimental example was measured with a turbidity meter, the initial concentration of the suspended solids in the backwash wastewater flowing out in the first backwash was high. At the time of the second backwash, it is about 1/10 the initial concentration. 3
In the second round, the concentration was reduced by 10% from the initial concentration in the second round of backwashing, and it was found that the amount of separation by backwashing and the amount of the activated carbon layer retained were small. Therefore, if the backwashing step is repeated twice, the activated carbon packed bed can be effectively washed. In addition, in the washing time with the second backwashing water, the concentration of the suspended matter is reduced in a short time and saturated. For this reason, as shown in the control sequence of FIG. 5, the first washing time with the backwash water is set to several minutes at which the concentration of the suspended solids in the backwash wastewater decreases and saturates, and the second washing time is even shorter. Since time is sufficient, it is also possible to shorten the cleaning time, that is, to reduce the amount of cleaning water.

Thus, an example of calculating the backwash time by the control sequence from the embodiment will be described below. As shown in FIGS. 4 and 5, the control sequence by the conventional backwashing is as follows.
Excluding the draining step of lowering the water level to the set water level based on the flow resistance in the activated carbon tower 1 or the detection of a predetermined water level, the stirring step using air and backwash water is 4 minutes, and the washing step using only backwash water is 10 minutes. The backwash was completed in a total of 14 minutes.

On the other hand, in the embodiment, the washing step in which the stirring step using air and backwash water is set to 2 minutes, and only the backwash water is circulated to overflow the suspension and the like and discharge from the backwash drain pipe 7 is performed. Set the process to 5 minutes. Then, the water is drained from the drain pipe 8 with a head difference from the overflow water level Hp shown in FIG. 3 to the set water level Hs. At this time, from the water level Hp to the set water level H
The drainage time is measured by the water level detector 11 until s, and the control unit 20 performs an arithmetic process. If the drainage time is equal to or longer than the set time of, for example, 3 minutes, an instruction for the second backwashing step is issued.
In the second backwash, the stirring process using air and backwash water was performed for 2 minutes.
The washing process using only the backwash water was set to 3 minutes. In the example,
Since the drainage time for the first water level adjustment was 3 minutes and 50 seconds, when the second backwash was performed, the drainage time was 2 minutes and 40 seconds. Therefore, the backwashing according to the embodiment takes a total of 16 minutes including the drainage time of about 4 minutes, but the cleaning time by the backwash water can be reduced to 8 minutes, so that the backwash water usage can be reduced by 20%. The initial pressure loss during re-watering at this time is 23 cmA
At q, the water flow time until the next backwash is about 180 hours.

According to the present embodiment, since the wastewater in the water level adjustment step of the backwash flows through the activated carbon packed bed, there is an advantage that it is possible to simulate the detection of the initial pressure loss at the time of re-watering. Activated carbon treatment. As a result, even if two-stage backwashing is performed, the backwashing time is 16 minutes in total, which is small in difference from the conventional backwashing time, but the amount of backwash water used can be reduced. Since the backwash water is treated water, the effect of reducing the amount of backwash water is great.

[0036]

According to the present invention, 1) By measuring the drainage time in the water level adjustment step of backwashing,
By estimating the initial pressure loss at the time of re-watering, it is possible to determine the quality of the cleaning of the activated carbon packed bed by back washing.

2) It was confirmed by experiments that the rise in water flow resistance depends on the initial pressure loss, and based on the above measurement results of the drainage time, the activated carbon packed bed was reduced so that the initial pressure loss was reduced by repeating backwashing. Can be effectively washed, and water can be passed at long-term backwash intervals.

3) According to the backwash system of the present invention, the amount of backwash water can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a biological activated carbon tower to which a backwash method of the present invention is applied.

FIG. 2 is an explanatory view of the operation principle of backwashing cleaning in FIG.

FIG. 3 is an explanatory diagram of an operation principle of drainage measurement after backwashing in FIG. 1;

FIG. 4 is an explanatory diagram showing a control sequence according to the present invention.

FIG. 5 is an explanatory diagram showing a control sequence according to a conventional backwashing method.

FIG. 6 is a system diagram of a biological activated carbon distribution experiment device.

FIG. 7 is a characteristic diagram showing experimental results of pressure loss characteristics according to the present invention.

FIG. 8 is a characteristic diagram showing a relationship between an initial pressure loss and a backwash interval.

FIG. 9 is a characteristic diagram showing a relationship between drainage time and initial pressure loss.

[Explanation of symbols]

1 ... biological activated carbon tower, 2 ... support member, 3 ... activated carbon packed bed,
4 ... Inflow pipe, 5 ... Treatment water pipe, 6 ... Backwash water pipe, 7 ... Backwash drain pipe, 8 ... Waste water pipe, 9 ... Backwash air pipe, 10 ... Differential pressure detector, 11 ... Water level detector, 12: exhaust pipe, 20: control device, 4A, 5A, 6A, 7A, 8A, 9A: solenoid valve, 8B: flow meter.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshikatsu Mori 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory, Ltd. (72) Inventor Kenji Baba 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Masamitsu Nakazawa 1-1-1, Kokubuncho, Hitachi City, Ibaraki Prefecture Inside Kokubu Plant, Hitachi Ltd. (72) Inventor Naoki Hara Omikamachi, Hitachi City, Ibaraki Prefecture 5-2-1, Hitachi, Ltd. Omika Plant

Claims (1)

[Claims] An activated carbon tower for treating water by passing water downward through an activated carbon packed bed. When the water level in the activated carbon tower rises to a predetermined water level, the water supply is stopped and the raised water level is set to an arbitrary set water level. A stirring step of stirring and flowing the activated carbon packed bed by blowing air while flowing backwash water from the lower part of the activated carbon tower to separate suspended matters,
A backwashing process consisting of a washing process in which only the backwash water flows through to discharge suspended matters, etc., and a water level adjustment process in which the backwash water is stopped, drained from the bottom of the activated carbon tower, and drained to an arbitrary water level In the method, in the water level adjustment step, a required time for draining to an arbitrary set water level is measured, and if the required drainage time is equal to or longer than the set time, the stirring step, the cleaning step, and the water level adjustment step are repeatedly performed. A method for backwashing an activated carbon tower, characterized by controlling.