JP4699198B2 - Backwashing method of sand filter for Cryptosporidium discharge - Google Patents

Description

The present invention relates to backwash method sand filtration equipment in water treatment for solid-liquid separation of Cryptosporidium and suspended solids from raw water for the purpose of beverage.

Recently, when the now infection by chlorine resistant pathogenic microorganisms Cryptosporidium like are reported, there is a possibility that chlorine resistance pathogens Cryptosporidium such as raw water is mixed In response, these the It is necessary to install a sand filter that can be removed.
The sand filtration apparatus used in the water purification process separates Cryptosporidium and other suspended solids in the raw water in the filter layer to obtain a clear treated water. If filtration is continued at this time, suspended substances accumulate in the filter bed. For this reason, if filtration is performed for a certain period of time, backwashing is required to remove substances accumulated in the filter bed.

Backwash method of sand filtration apparatus are various, but the filtered water as backwash water, there is to Way Method flow the filtered water for backwashing the lower filter layer to the filter layer top.
The backwashing speed in backwashing is generally 0.6 to 0.9 m / min, and is also described in water supply facility design guidelines. During backwashing at 0.6 to 0.9 m / min, the washing water flows from the lower part to the upper part in the expanded filter layer. At this time, turbid components accumulated in the sand layer and microorganisms such as Cryptosporidium are separated from the sand layer. Discharge. However, when the inside of the filter layer is observed microscopically, a swirl flow and a vortex flow are locally formed. For this reason, a part of Cryptosporidium or the like that is greatly influenced by the water flow stays in the filter bed without being discharged from the upper part of the filter bed due to the swirl flow / vortex flow.

This in order to filter removing stagnant material in the layer, stepwise reduces the backwash rate backwashing immediately before the end, so-called slow-down cleaning system is described as a countermeasure (Non-Patent Document 1).
“Water Supply Facility Design Guidelines 2000”, Japan Waterworks Association.

However, this slow-down cleaning method is not clear as to a specific method, for example, how many steps, what backwashing speed, and how much time is set. Furthermore, the index for judging the effect of backwashing such as slow-down washing is generally determined from its removal by measuring turbidity, and the method adopted with direct attention to the microorganisms such as Cryptosporidium treated in this case is not.

Further, in order to remove turbid components and Cryptosporidium that stay in the filter bed by swirling flow, swirling flow must be extinguished quickly, but the backwash speed is from 0.6 to 0.9 m / min. Immediately after the filter layer is lowered to such an extent that it does not expand, the swirl flow remains due to the inertial force and then gradually disappears. Until the swirling flow disappears , the backwash water is discharged wastefully. Backwash water from using filtered water, a problem that will be the water recovery rate of the entire apparatus decreases.

For this reason, the present inventors conducted a filtration experiment using a Cryptosporidium oocyst tracer and examined a method of operating a filtration apparatus for performing an optimal backwashing method.
And , the backwashing speed of the backwashing process is combined with the backwashing process of the strength that does not make the filter medium fluidized, in this order, and further, the weak backwashing process that does not make the filter medium fluidized. It is found that if the backwash time is set to a specific time, Cryptosporidium can be discharged sufficiently, and the amount of backwash water can be reduced as a whole, and the present invention is completed based on such knowledge. It came.

That is, the present invention can solve the above problems by adopting the following configuration.
(1) In a sand filtration device that filters raw water containing Cryptosporidium in a downward flow, the filtrate is passed through the filter layer at a backwash speed of 0.6 to 0.9 m / min in the direction opposite to the normal filtration direction. , performing a first backflushing step for backwashing with filtrate sand in a fluidized state, a second backwash step of performing backwashing as backwash rate 0.1 ~0.2m / min in the same direction followed by By this, Cryptosporidium staying in the filter layer is discharged.
(2) The backwashing method for the sand filtration device according to (1), wherein a backwash stop period is provided for 10 seconds to 60 seconds between the first backwashing step and the second backwashing step.
(3) When the filter bed height is L1, the height from the top of the filter bed to the backwash drainage overflow section is L2, and the backwash speed LV1 is an arbitrary set value at 0.1 to 0.2 m / min. backwashing time of the second backwash step, backwashing how the sand filtration apparatus according to claim 1, characterized in that (L1 + L2) / LV1 at determined time Tr or more.

That is, the gist of the present invention consists of the following items.
In the apparatus for performing backwashing in the present invention, in order to solve the above problem, after backwashing at a backwashing speed of 0.6 to 0.9 m / min for a predetermined time, the backwashing speed is set to 0.1 to 0.2 m / min, preferably performs backwash is lowered to 0.15~0.2m / min. Or, in order to reduce the amount of filtered water used as backwash water and improve the water recovery rate of the entire apparatus, after performing backwash for a predetermined time at a backwash speed of 0.6 to 0.9 m / min, Backwashing is stopped for 10 to 60 seconds, and backwashing is performed again at a backwashing speed of 0.1 to 0.2 m / min.
Backwashing time Tr backwash rate 0.1 ~0.2m / min, when the height of the filtration layer L1, from the filtrate layer top to backwash effluent overflow section height was L2, backwash rate LV1 (shall be the 0.1 ~0.2m / time obtained by dividing the arbitrary set value in min (L1 + L2) / LV1 or more.
By setting it as the filtration apparatus which performs backwashing as mentioned above, Cryptosporidium staying in the filter layer is fully discharged | emitted, and the safe and stable water treatment is attained.

From the above results, when backwashing a sand filtration device for treating raw water containing Cryptosporidium, after the first backwashing step of fluidizing the filter bed having a backwashing speed of 0.6 to 0.9 m / min, By performing the second back washing step with a washing speed of 0.1 to 0.2 m / min, Cryptosporidium can be sufficiently discharged from the filter bed, and safe filtered water can be obtained. . When the backwashing speed is less than 0.1 m / min, Cryptosporidium in the filter layer cannot be sufficiently discharged, and when the backwashing speed is higher than 0.2 m / min, a swirling flow is generated in a part of the filter bed. It becomes difficult to sufficiently discharge Cryptosporidium. Therefore, stable water treatment becomes possible by setting the backwashing speed within the above range. Further, annihilation backwash rate 0.6~0.9m / min of filtrate layer backwashed once from fluidized state stops 10 seconds to 60 seconds, the local flow generated in filtration layer in a first backflushing step by, then the reverse washing in the second backwashing step of backwashing speed 0.1 to 0.2 m / min, it is possible to dispense less backwash water as a whole. If the stop time is less than 10 seconds, the local flow generated in the first backwash process cannot be eliminated, and if the stop time is longer than 60 seconds, it is not appropriate because the standby time of the device becomes longer. . Further, the second backwashing step is carried out for a time Tr (= sum of backwashing water retention time in the filter bed and backwash water retention time from the top of the filter bed to the backwash water discharge port ). Emission of putospodium can be performed efficiently.

Hereinafter, the backwashing method of the sand filtration apparatus of the present invention will be described with reference to the drawings.
1 is a schematic diagram of the entire filtration tower immediately before backwashing, FIG. 2 is a schematic diagram of the entire filtration tower in a state in which the filter bed is fluidized during the first backwashing process, and FIG. 3 is fluidization during the first backwashing process. FIG. 4 is a schematic diagram enlarging a part of the filter bed during backwashing (state of the second backwashing process) in a state where the filter bed is not fluidized. .

As filtration continues, as shown in FIG. 1, trapping of turbid components and Cryptosporidium 3 becomes remarkable in the filter layer 2, resulting in clogging. For this reason, as shown in FIG. 2, backwash water 4 using filtered water is passed through the filter layer 2 from the lower part of the filter tower 1 to perform backwashing. The backwashing speed of the backwashing water 4 is normally 0.6 m / min to 0.9 m / min, and the filter layer 2 is expanded to a fluidized state. At this time, the water flow in the filter layer 2 is in a turbulent state, and the backwash water 4 flows from the lower part to the upper part in the entire filter layer part 2, but locally, as shown in FIG. Since the vortex 8 is generated, the suspended matter 6 and the part 9 of Cryptosporidium accumulated in the filter layer 2 remain without being discharged from the filter layer 2.

If the suspended matter 6 is hardly discharged even after continuing the first backwashing process in which the filter layer 2 having a backwashing speed of 0.6 to 0.9 m / min is fluidized, the valve 7 is adjusted. The backwash speed is reduced to 0.1 to 0.2 m / min. Then, the filter layer 2 stops fluidization, and the swirling flow and the vortex flow 8 in the filter layer 2 disappear . For this reason, Cryptosporidium 9 that has been retained in the swirling flow or vortex flow 8 in the filter layer 2 moves to the upper part of the filter layer 2 by the backwash water flow of 0.1 to 0.2 m / min. Drained from layer 2. Second backwashing step of backwashing rate 0.1 ~0.2m / min continues the residence time of the backwash water 4 in the backwash effluent discharge portion T r or from the filtrate layers 2 Toro layer 2 thereon.

Immediately after the backwash speed is reduced from 0.6 to 0.9 m / min to 0.1 to 0.2 m / min, the swirl flow / vortex flow 8 in the filter layer 2 remains due to inertial force. For this reason, from the state of the backwash speed of 0.6 to 0.9 m / min, the valve 7 is once closed, and after 10 to 60 seconds have elapsed, the backwash speed is again 0.15 to 0.2 m / min. When this is done, the swirl flow / vortex flow 8 in the filter layer 2 disappears , and the amount of backwash water is relatively small.

Thus, when backwashing the sand filtration device for treating raw water containing Cryptosporidium, from the first backwashing step of fluidizing the filter layer 2 having a backwash speed of 0.6 to 0.9 m / min, Tr By performing the second back washing step with a back washing speed of 0.1 to 0.2 m / min for the above time, Cryptosporidium 9 can be sufficiently discharged from the filter layer 2 to obtain safe filtered water. And stable water treatment becomes possible. The backwash rate 0.6~0.9m / min of filtrate layer 2 is temporarily stopped backwash 10 seconds to 60 seconds fluidized state, the swirling flow-vortex 8 generated in the filtration layer 2 and is extinguished during which thereafter performed backwash of the second backwashing step of backwashing rate 0.1 ~0.2m / min, it is possible to dispense less backwash water as a whole.
In addition, although there are naturally necessary operations such as valve operations of the corresponding piping lines in the operation operations of the filtration step and the backwashing step, the description thereof is omitted here.

  EXAMPLES The present invention will be specifically and specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
FIG. 5 shows a flow of Cryptosporidium tracer addition experiment. In the experiment, one set of equipment similar to that shown in FIG. 5 was installed for comparison purposes, except for the tracer injection equipment shown in FIG. Table 1 shows the specifications of the filtration tower, and Table 2 shows the water flow conditions. Experimental raw water by mixing the river water sedimentation water with an alternative tracer of Cryptosporidium (material polymethylmethacrylate, particle size 5.0μm, specific gravity 1.19, manufactured by Nippon Koken Kogyo Co., Ltd.) in the raw water tank Then, a filtration experiment was conducted using a filtration tower made of an acrylic transparent material. 5% of the filter sand was colored green in advance so that the flow state of the filter sand became clearer. In the experiment, Cryptosporidium tracer was added to carry out the first backwashing step and the second backwashing step (Experiment A). Similarly, Cryptosporidium tracer was added and 10 seconds after the first backwashing step. Another example (experiment B) of the present invention in which the backwashing is stopped for ˜60 seconds and then the second backwashing process is performed. Comparative study in which only the first backwashing process is performed without adding Cryptosporidium tracer to the precipitated water. Three experiments of (Experiment C) were performed.
In FIG. 5, 10 is the precipitated water, 11 is the Cryptosporidium tracer, 12 is the raw water tank for mixing them, 13 is the polyaluminum chloride (PAC), 14 is the treated water tank, 15 is the waste water treatment tank, It is a sand filter tower demonstrated in FIG.1 and FIG.2.

Note: According to the survey results by the former Ministry of Construction, Public Works Research Institute Data No. 3533 (January 1998), the number of Cryptosporidium oocysts in river water is 0.05 to 3.2 pieces / L (liter), which is the maximum value. 3.2 / L is the value of river water immediately after cryptosporidium infection. All of the findings except this is less than or equal to 0.1 or / L.

Doing filtration OPERATION of 47 hours 30 minutes, trapped turbid fraction 3 halo layer containing Cryptosporidium as shown in FIG. 1, the increase in filtration resistance was observed. For this reason, backwashing was performed at a backwashing speed of 0.7 m / min by adjusting the opening degree of the valve 7 as shown in FIG. 2 using filtered water as backwashing water (first backwashing step). Then, it was visually observed that the turbid component trapped in the filter layer floated above the filter layer and was discharged from the filtration tower. The filter sand particles swirled mainly in the vertical direction as a whole, and it was observed that the particles were swirling locally in other than the vertical direction. At this time, filter sand swirling the filter layer was observed while adhering turbidity to the filter sand surface. Focusing on the fine turbidity, it was observed that the water was swirling by the local water flow in the gap of the filter sand.

  Although the time of the 1st backwash process generally changes with the turbid mass trapped by the filter layer, in the experiment, the 1st backwash process was implemented for 10 minutes. Thereafter, the opening degree of the valve 7 was adjusted to reduce the backwash speed to 0.15 m / min (second backwash process). The 2nd backwashing process was implemented for 6 minutes which is the residence time of the backwashing water in a filtration layer and a filtration layer upper part. When the backwash speed was decreased from 0.7 m / min to 0.15 m / min, the sand flow gradually decreased visually in the filter layer, and was not seen after 10 to 60 seconds.

Next, the filtration operation was performed in the same manner, and after the filtration blockage, the first backwashing process with a backwashing speed of 0.7 m / min was performed, and then the backwashing was stopped for 10 to 60 seconds. Then, the flow such as the swirling of the filter sand in the filter layer was not seen in tens of seconds. Then, backwashing (second backwashing process) was performed at a backwashing speed of 0.15 m / min. In this case, the required amount of backwash water was reduced by 1 to 6 L compared with the case where backwash was not stopped. That is, the amount of backwash water could be reduced by 0.63 to 3.66%.

Table 3 shows the backwash drainage immediately before the end of the first backwash process at a backwash speed of 0.7 m / min, and Cryptosporidium when the apparatus is stopped and water is collected from the filter bed immediately after the end. The detection result of a tracer is shown. Tracers were not detected from the washing wastewater, but were detected from the water sampled from within the filter bed. From this, it is understood that Cryptosporidium staying in the filter layer cannot be sufficiently removed only by backwashing at a backwashing speed of 0.7 m / min.

  Table 4 shows the results of water quality analysis immediately after resuming filtration after completion of backwashing. When the backwashing method according to the present invention was employed, no Cryptosporidium tracer was detected. The filtered water turbidity was 0.04 degrees or less immediately after the start of filtration, and it became possible to obtain clear filtered water from the beginning of filtration. On the other hand, Cryptosporidium was detected in the comparative system, and the turbidity of the filtrate became 0.1 degrees or less after 20 minutes from the start of filtration. From this, when not using the backwashing method of this invention, it is necessary to drain (drain) filtered water for at least 20 minutes or more.

FIG. 6 shows the course of turbidity immediately after resumption of filtration. When the backwashing is stopped 10 seconds to 60 seconds between the first backwash step and 0.15 m / min of the second backwash step of backwash rate of 0.7 m / min, than without stop 10 seconds to 60 seconds However, the filtered water after the resumption of operation became relatively clear. As can be seen from the visual observation, the swirling / vortex flow in the filter layer disappears sufficiently by stopping for 10 to 60 seconds, and the particles containing Cryptosporidium are efficiently removed by the second backwashing step. Because it was able to be removed.

According to the backwashing method of the sand filtration device corresponding to Cryptosporidium discharge of the present invention, Cryptosporidium can be sufficiently discharged from the filter bed, and safe filtered water can be obtained as a whole. Since the amount of backwash water can be reduced, it can be widely used in water supply facilities.

It is a schematic diagram of the whole filtration tower just before backwashing. It is a schematic diagram of the whole filtration tower in the state where the filter layer was fluidized at the time of backwashing. It is the schematic diagram which expanded a part of filter bed in the state which the filter bed fluidized at the time of backwashing. It is the schematic diagram which expanded a part of filter layer in backwashing in the state which does not fluidize a filter layer. It is the figure which showed the apparatus flow. It is the figure which showed the measurement result of the turbidity in an Example, and is a figure which shows the effect of this invention.

1 Filtration tower 2 Filter layer (filter sand)
3 Suspended matter and Cryptosporidium accumulated in the filter layer with continued filtration 4 Flow of the entire backwash water (wash water) 5 Suspended matter and Cryptosporidium discharged from the filter layer by backwash 6 In the filter layer during backwashing Suspended in the filter bed by local flow of water and Cryptosporidium 7 valve (for backwash water adjustment)
8 Vortex generated locally in the filter layer 9 Cryptosporidium 10 Precipitation water 11 Cryptosporidium tracer 12 Raw water tank 13 PAC
14 Treated water tank 15 Wastewater treatment tank

Claims (3)

In a sand filtration device that filters raw water containing Cryptosporidium in a downward flow, filtered water is passed through the filter layer at a backwash speed of 0.6 to 0.9 m / min in the direction opposite to the normal filtration direction. by performing the performing a first backflushing step for backwashing in the fluid state, followed by a second backwash step of performing backwashing as backwash rate 0.1 ~0.2m / min in the same direction, A method for backwashing a sand filtration device, wherein Cryptosporidium staying in the filter bed is discharged.   The backwashing method for a sand filtration device according to claim 1, wherein a backwashing stop period is provided for 10 to 60 seconds between the first backwashing step and the second backwashing step. The second reverse when the height of the filter bed is L1, the height from the upper part of the filter bed to the backwash drainage overflow section is L2, and the backwash speed LV1 is an arbitrary set value at 0.1 to 0.2 m / min. the backwashing times washing step, backwashing how the sand filtration apparatus according to claim 1, characterized in that (L1 + L2) / LV1 at determined time Tr or more.

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