JP2019205976A - Filter back washing method and device - Google Patents

Abstract

To provide a filter back washing method and device capable of effectively carrying out back washing without lowering the water level of a filter.SOLUTION: A filter back washing method and device 80 exerts excellent back washing capability by blending microbubbles and mini-bubbles in a back washing water. Further, there is no excessive hoisting of a filter medium since a fine bubble is smaller than a bubble at the time of idle washing and thus, a back washing operation can be carried out continuously from a filtration operation without needing the water level lowering of a filter 50. Thereby, the back washing having high back washing capability can be easily carried out.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a backwashing method and a backwashing device for a filter filled with a filter medium.

  In water treatment facilities and the like, filters (sand filters) are widely used as a means for separating and removing turbidity in raw water. This filter has a filter layer filled with sandy or granular filter media such as anthracite and silica sand, and agglomerates and the like are added to the raw water to agglomerate turbidity in the previous stage of the filter. The turbidity in the raw water is removed by collecting in the filter layer. However, with continuous use of the filter, collected matter accumulates between the filter media, the gap between the filter layers is blocked, and the filtration resistance gradually increases. This causes a decrease in filtration efficiency due to a decrease in the filtration flow rate, and also causes a deterioration in the water quality of the filtrate. Therefore, it is necessary to periodically wash the filter layer and restore the filtration capacity. As a washing method of the filter layer, backwash water (usually filtered water) is sent from below the filter layer, and the collected matter collected in the filter layer is discharged together with the backwash water above the filter. It is common to carry out by backwashing (water backwashing) discharged from the piping. According to the water supply facility design guidelines, for a filter layer with an effective diameter of 0.6 mm and a uniformity coefficient of 1.3, backwashing with backwashing water at a water temperature of 20 ° C. and a backwashing flow rate of about 0.6 m / min By performing the step, the expansion rate of the filter layer becomes about 20%, and it is supposed that the fluidized state is suitable for separating and removing the collected material from the filter medium.

  However, even if the water is back-washed under optimum conditions, the collected matter cannot be completely removed, and gradually accumulates to lower the filtration efficiency. Moreover, it becomes a formation factor of the turbid lump which is difficult to remove by backwashing, so-called mud balls. And this mud ball clogs the filter layer, remarkably deteriorates the filtration efficiency, and may hinder the operation of the entire water treatment facility.

  In order to solve this problem, for example, [Non-patent Document 1], [Patent Document 1], and [Patent Document 2] below combine surface cleaning or air cleaning with water backwashing in order to discharge the collected material as much as possible. Is described. In particular, [Patent Literature 1] and [Patent Literature 2] describe a back washing method using microbubbles in a combination of air washing and water back washing.

Water Supply Management Guidelines 2016 Japan Waterworks Association

Japanese Patent No. 5748338 JP, 2014-151304, A

  However, air washing (hereinafter referred to as air washing) has a large bubble size and the entire filter layer is disturbed, and the effect of peeling and subdividing the collected material from the filter medium is great, but the filter layer expands too much during washing. The filter medium may rise and flow out of the discharge pipe. For this reason, as described in [Non-Patent Document 1], it is necessary to perform air washing after lowering the water level of the filter, and there is a problem that the back washing operation becomes complicated.

  Further, as in [Patent Document 1] and [Patent Document 2], in a method of performing backwashing using a gas-liquid mixed flow (bubble flow) in which microbubbles are mixed with backwashing water, the microbubbles are retained in the filter medium. Although there is an effect of promoting separation by adhering to the collected material, the bubble diameter is hardly increased due to coalescence of the microbubbles, and the rising speed is very small. For this reason, the force which disturbs a filter medium is weak, and there is little effect which subdivides a big suspended solid (collected matter). Therefore, there is a problem that a large amount of collected matter tends to remain without being swept away at the flow rate of the backwash water, and the washing efficiency is low.

  In addition, the filter layer is often supported by a support layer in which filter gravels having different sizes are stacked from the bottom in descending order. However, the air bubbles at the time of air washing may disturb the stratification of the filter gravel of the support layer, and in this case, the filter medium may pass through the support layer and be washed away together with the filtered water. For this problem, it is conceivable to use a porous resin plate for the support layer. However, when a porous resin plate is used for the support layer, it is confirmed that bubbles at the time of air washing are biased to specific parts, and there is a problem that the entire filter layer cannot be air washed.

  This invention is made | formed in view of the said situation, and aims at provision of the backwashing method and backwashing apparatus of a filter which can perform effective backwashing without reducing the water level of a filter. .

The present invention
(1) A backwashing method for a filter 50 having a filter layer 52 configured by filling a filter medium, and a support layer 54 for supporting the filter layer 52,
The above problem is solved by providing a backwashing method for the filter 50, wherein microbubbles and minibubbles are mixed in backwash water fed from below the support layer 54.
(2) A backwash device for a filter 50 having a filter layer 52 formed by filling a filter medium and a support layer 54 for supporting the filter layer 52,
A backwash water tank 16 for storing backwash water, a backwash pipe 38 for connecting the backwash water tank 16 and the filter 50 and sending backwash water from the backwash water tank 16 below the support layer 54; A backwash pump 34 for pumping backwash water to the backwash pipe 38, and a discharge pipe 36 provided above the filtration surface of the filter 50,
Further, the present invention provides a backwash device 80 comprising fine bubble generating means 60 that is provided in the backwash pipe 38 and converts air supplied from the outside into minibubbles and microbubbles and mixes them in backwash water. Thus, the above problem is solved.

  The backwashing method and backwashing apparatus for a filter according to the present invention can have excellent backwashing ability by mixing microbubbles and minibubbles with backwash water. Moreover, the backwashing method and backwashing apparatus of the filter which concern on this invention do not need to reduce the water level of a filter at the time of backwashing, and can perform backwashing operation | movement continuously from filtration operation. Thereby, the backwashing which has a high backwashing capability can be performed easily.

It is a schematic block diagram of the filtration system provided with the backwashing apparatus which concerns on this invention. It is a figure which shows the other example of the filtration system provided with the backwashing apparatus which concerns on this invention. It is a schematic cross section which shows an example of the fine bubble production | generation means based on this invention. It is a graph which shows the backwashing effect of fine bubble mixing water. It is a graph which shows the relationship between the air supply amount and the backwashing effect.

  A filter backwashing method and a backwashing apparatus according to the present invention will be described with reference to the drawings. Here, FIG. 1 is a schematic configuration diagram of a filtration system 100 including a backwash device 80 according to the present invention. Here, those having a bubble diameter of approximately 1 μm to 100 μm are referred to as microbubbles, and those having a bubble diameter of approximately 100 μm to several mm are referred to as minibubbles.

  First, the filtration system 100 to which the present invention is applied includes, for example, a supply pipe 20 that supplies raw water, a flocculant addition unit 30 that is connected to the supply pipe 20 and adds a known flocculant to the raw water, and raw water and agglomerates. Well-known mixing means 15 such as a line mixer for mixing the agent, a filter 50 for collecting the agglomerates generated by the coagulant, and a drainage pipe for sending the filtrate that has passed through the filter 50 to the filtrate tank 16. 22 and the backwash device 80 according to the present invention.

  The filter 50 includes a filter layer 52 configured by filling a known filter medium, and a support layer 54 that supports the filter layer 52. In this example, the filter layer 52 is composed of two layers of a filter medium having a large effective diameter and a filter medium having a small effective diameter, but the number of filter layers 52 is not particularly limited, Alternatively, the number of layers may be three, four, or the like.

  Next, the configuration of the backwash device 80 according to the present invention will be described. The backwashing device 80 according to the present invention connects the backwashing water tank 16 that stores backwashing water, the backwashing water tank 16 and the filter 50, and sends backwash water in the backwashing water tank 16 below the support layer 54. The backwash pipe 38, the backwash pump 34 that pumps backwash water into the backwash pipe 38, the discharge pipe 36 provided above the filtration surface of the filter 50, and the air that supplies air from the outside It has a supply pipe 42 and fine bubble generating means 60 that is provided in the backwash pipe 38 and that is supplied from the outside into mini-bubbles and microbubbles and mixes in the backwash water. In addition, although the example which connects the air supply pipe | tube 42 to the fine bubble production | generation means 60 is shown here, the connection position of the air supply pipe | tube 42 is not specifically limited to this. In addition, as the backwash water used for backwashing, it is common to use the filtrate filtered by the filter 50. Therefore, as shown in FIG. 1, the backwash water tank 16 generally serves as the drainage water tank 16.

  Next, the operation of the filtration system 100 will be briefly described. First, raw water is pumped up from a water source such as a well or river by a pump. The pumped raw water is stored in the raw water tank 10 or the like, for example. The raw water in the raw water tank 10 flows down the supply pipe 20 and is supplied to the filtration system 100 by operating the supply pump 12 with the on-off valve 20a of the supply pipe 20 opened. Next, a known flocculant such as polyaluminum chloride (PAC) is added to the raw water supplied to the filtration system 100 by the flocculant adding unit 30. In addition, you may perform the disinfection with respect to raw | natural water by adding a well-known chlorine type disinfectant etc. before the addition of a flocculant. Next, the raw water and the flocculant are mixed by the mixing means 15, whereby the turbidity in the raw water is aggregated together with the flocculant to form an aggregate. And this aggregate is sent to the filter 50 with raw | natural water. At this time, the open / close valves 36a and 38a of the discharge pipe 36 and the backwash pipe 38 of the filter 50 are in a closed state, and the open / close valve 22a of the drainage pipe 22 is in an open state.

  Aggregates in the raw water are collected by the filter layer 52 and separated from the raw water. Then, the filtrate from which the aggregate has been removed passes through the support layer 54, flows down the filtrate pipe 22, and is stored, for example, in the filtrate tank 16. Then, after appropriate processing such as sterilization is performed as necessary, the water is supplied to a predetermined water demand through, for example, the water supply pipe 16a.

  In addition, with continuous use of the filter 50, collected matter (aggregate) accumulates in the filter layer 52, and the gap between the filter media is blocked. As a result, the filtration resistance of the filter 50 gradually increases, and the pressure in the filter on the supply pipe 20 side increases. The rise in the internal pressure of the filter is monitored by a pressure gauge (not shown), and when the internal pressure exceeds a predetermined value, the backwash device 80 performs a backwash operation.

  Here, an example of the operation of the backwash device 80 will be described. First, when the pressure inside the filter of the pressure gauge exceeds a predetermined value, the filtration system 100 stops the supply pump 12, and closes the on-off valves 20a and 22a of the supply pipe 20 and the drainage pipe 22. Thereby, supply of the raw | natural water to the filter 50 stops, and filtration operation | movement stops. Next, the controller of the backwash device 80 opens the on-off valves 36a and 38a of the discharge pipe 36 and the backwash pipe 38, and operates the backwash pump 34. Thereby, the backwash water in the backwash water tank 16 (filtered water tank 16) flows down the backwash pipe 38 and flows into the fine bubble generating means 60. Further, the backwash device 80 opens the on-off valve 42 a provided in the air supply pipe 42. Thereby, air is supplied from the air supply pipe 42 to the fine bubble generating means 60. The supplied air is refined by the fine bubble generating means 60 and becomes a mini-bubble having a bubble diameter of approximately 100 μm to several mm and a microbubble having a bubble diameter of approximately 1 μm to 100 μm and mixed in the backwash water. Then, the backwash water mixed with the fine bubbles is sent out below the support layer 54 of the filter 50.

  The mixed water mixed with the fine bubbles passes through the support layer 54 and reaches the filter layer 52. Then, the backwash water and fine bubbles increase the gap between the filter media and expand the filter layer 52, and disturb and peel off the collected matter. The separated collected substance is swept away together with the backwash water, separated from the filter layer 52, and discharged from the discharge pipe 36 above the filter 50. Thereby, the collected matter of the filter layer 52 is removed, and the filtration capability of the filter 50 is restored. At this time, since the microbubbles and minibubbles are smaller than the air bubbles at the time of conventional air washing, the filter medium is not excessively wound up. For this reason, it is not necessary to lower the water level of the filter 50 as in conventional air washing. Further, even when the support layer 54 is made of filtered gravel, the support layer 54 is not disturbed.

  Here, regarding the effect of backwashing with microbubbles and minibubbles, the zeta potential of microbubbles is negative (-), whereas the zeta potential of aggregates produced by an aggregating agent such as PAC is positive (+). Show. For this reason, microbubbles tend to adhere to the collected matter (aggregate), thereby increasing the buoyancy of the collected matter. In addition, in the process of minibubbles having a bubble diameter of several millimeters rising through the support layer 54 of the filter 50 and the inside of the filter layer 52, some of the bubbles are combined to form bubbles having a larger diameter. Is moderately disturbed from the deep part to promote separation and dispersion of the collected matter. Furthermore, the filter layer 52 has a layer (I layer) composed of solid, water, and bubbles having a high concentration of filter medium particles, and a layer (II layer) composed of water and bubbles without any filter medium particles floating above it. At the interface, a jet flow is generated at the interface between the I layer and the II layer when bubbles having a larger diameter due to the integration of some of the minibubbles in the I layer move from the I layer to the II layer. The jet stream disturbs the filter media particles and collected matter in the upper layer of the I layer and releases them from the I layer to the II layer. The filter medium particles released by the jet flow return from the II layer to the I layer again by gravity. In this way, the upper layer of the I layer is vigorously disturbed like surface cleaning, so that the collected material is peeled off or subdivided, and the filter layer 52 is easily discharged.

  In order to use the fine bubble generating means 60 and to easily control the amount of mini-bubbles and the amount of micro-bubbles, as shown in FIG. The air supply pipe 40 may be connected. Then, by opening the on-off valve 40a of the second air supply pipe 40, air is supplied from the second air supply pipe 40 to the backwash pipe 38 and mixed with the backwash water. The air in the backwash water is mixed by the backwash pump 34 to form fine bubbles (such as microbubbles). Then, the bubbles flow into the fine bubble generating means 60 together with the backwash water, and are combined with the air flowing in from the air supply pipe 42 to be micronized into micro bubbles and mini bubbles. In addition, since the air from the second air supply pipe 40 is refined by both the backwash pump 34 and the fine bubble generating means 60, the ratio of microbubbles increases. Therefore, by adjusting the air inflow amount from the air supply pipe 42 and the air inflow amount from the second air supply pipe 40, the respective amounts of microbubbles and minibubbles in the backwash water can be controlled to some extent. When backwashing is performed only with backwashing water, both the open / close valve 42a of the air supply pipe 42 and the open / close valve 40a of the second air supply pipe 40 are closed.

  Next, the verification experiment of the backwashing effect of microbubbles and minibubbles was performed as follows. The experiment was performed with a configuration including the second air supply pipe 40 shown in FIG. 2 in which the amount of each of the mini bubbles and the micro bubbles can be easily adjusted. The fine bubble generating means 60 used the fine bubble generator shown in FIG. Here, the fine bubble generating means 60 shown in FIG. 3 includes a mixing unit 66 that is connected to the air supply pipe 42 and mixes the air into the backwash water, and a first venturi pipe provided on the downstream side of the mixing unit 66. 68a, an elbow part 69 provided on the downstream side of the first venturi pipe 68a, and a second venturi pipe 68b provided on the downstream side of the elbow part 69. And when the air in backwash water passes the 1st venturi pipe 68a and the 2nd venturi pipe 68b, this is decompressed and refined | miniaturized and a mini bubble and a micro bubble are produced | generated.

(Verification experiment)
First, kaolin was added to tap water as turbidity to prepare simulated raw water having a turbidity of 2 degrees. The simulated raw water was continuously passed through the filter 50 so that the filtration speed (raw water flow rate ÷ filter cross-sectional area) was 160 m / day. In addition, the diameter of the filter 50 was 104 mm, and the filtration layer was performed by both a 600 mm quartz sand 600 mm single layer and a 1.2 mm anthracite 200 mm + 0.6 mm quartz sand 400 mm multilayer. Further, the support layer 54 was formed by laminating 12 mm to 24 mm of filtration gravel of 75 mm, 8 mm to 12 mm of filtration gravel of 75 mm, 4 mm to 8 mm of filtration gravel of 75 mm, and 2 mm to 4 mm of filtration gravel of 75 mm in order from the bottom. Moreover, the injection | pouring of the flocculant (PAC) by the flocculant addition part 30 was made into line injection, and the addition amount was 15 mg / L-20 mg / L. In addition, the turbidity of the filtrate which passed this filter 50 was 0.1 degree | times, and took the favorable value from which turbidity was fully removed. And when the pressure in the filter of the filter 50 became 20 kPa, water flow of the simulated raw water was stopped and backwashing was performed.

Backwashing is performed with backwashing speed of 0.6 m / min (backwashing) under 5 conditions of backwashing water only, mixed water containing only mini bubbles, mixed water containing only microbubbles, mixed water containing minibubbles and microbubbles, and air washing + water backwashing The washing amount was 18 L / min). The air supply amount from the air supply pipe 42 was 1 L / min, and the air supply amount from the second air supply pipe 40 was 0.5 L / min. Moreover, under the conditions of air washing + water backwashing, the water level of the filter 50 is lowered, then air washing is performed for 3 minutes at an air supply rate of 24 L / min (0.8 m / min), and the water level is returned to the original level. Back washing with back washing water was performed for 5 minutes. And the recovery rate of turbidity was calculated based on the following formula as a cleaning effect under each condition.
Recovery rate (%) = (Backwash drainage SS (mg / L) × Backwash wastewater amount (L)) / turbid mass × 100
Here, the turbid mass is the total amount of turbidity (kaolin) of simulated raw water + the amount of flocculant.

  Here, the experimental result in the filter 50 of single layer conditions is shown to Fig.4 (a). Moreover, the experimental result in the filter 50 of a multilayer condition is shown in FIG.4 (b). As shown in FIG. 4A, in the filter 50 under the single layer condition, the backwashing with the mixed water of only the mini bubbles and the mixed water of the minibubbles + microbubbles has a high recovery rate substantially equal to the backwashing conditions with the air washing + water backwashing. showed that. In addition, the mixed water containing only microbubbles showed a higher recovery rate than the backwashing condition using only backwashing water, although it was slightly inferior to the other conditions. Moreover, from FIG.4 (b), also in the filter 50 of multi-layer conditions, the backwashing with the mixed water in which the fine bubbles were mixed showed a higher recovery rate than the backwashing condition with only the backwashing water. In particular, the backwashing with the mixed water of only microbubbles and the mixed water of minibubbles + microbubbles showed a higher recovery rate than the backwashing conditions with the air washing + backwashing with water.

  Based on the above, backwashing with water mixed with minibubbles + microbubbles has a higher recovery rate than backwashing with only backwashing water (water backwashing) or backwashing with only microbubbles, and has excellent backwashing ability. It can be seen that The excellent backwashing ability is as follows. First, a mini bubble having a bubble diameter of several millimeters has a lower rising speed than bubbles during air washing, and disturbs the filter layer 52 from the depth without excessively disturbing the filter layer 52. This is thought to be due to promoting the separation and dispersion of the collected matter. Further, as described above, a part of the bubbles having a large diameter in the I layer having a high particle concentration in which the filter medium particles flow, becomes a jet flow at the heterogeneous interface when moving to the II layer without the filter medium particles. Filter media particles and collected matter are released to the II layer by the jet flow. Among them, the filter media particles are returned to the I layer again by their own weight, and by this, the collected material is separated or fragmented by vigorous disturbance of the upper layer of the flowing filter media particles. This is thought to be due to the fact that the discharge from the filter layer 52 is promoted.

  Next, the following experiment was performed by changing the air supply amount for generating mini-bubbles and micro-bubbles. First, kaolin was added to tap water as turbidity to prepare simulated raw water having a turbidity of 5 degrees. The simulated raw water was continuously passed through the filter 50 so that the filtration speed was 120 m / day. The flocculant (PAC) injection by the flocculant addition unit 30 was line injection, and the addition amount was 5 mg / L to 10 mg / L. Then, when the pressure in the filter reaches a predetermined value, the water flow is stopped, the air supply amount of the second air supply pipe 40 and the air supply pipe 42 is changed, backwashing is performed, and the recovery rate is calculated. did. The filter layer 52 was formed as a double layer of 1.2 mm anthracite 200 mm + 0.6 mm silica sand 400 mm. The support layer 54 was the same as the previous experiment.

  First, in the mini bubble + micro bubble mixed water, the air inflow amount from the air supply pipe 42 is fixed to 1 L / min, and the air inflow amount from the air supply pipe 40 is 0.2 L / min, 0.5 L / min, 1 FIG. 5 (a) shows a graph of the recovery rate when changed to 0.0 L / min and 1.5 L / min. Further, in the mixed water containing only microbubbles with the on-off valve 42a of the air supply pipe 42 closed, the air inflow from the air supply pipe 40 is 0.5 L / min, 1.0 L / min, 1.5 L / min. FIG. 5B shows a graph of the recovery rate when changed to.

  From FIG. 5A and FIG. 5B, in the backwashing with the mixed water of only the mini bubble + micro bubble mixed water and the micro bubble, the air inflow amount from the air supply pipe 40 is most at 1.0 L / min. It can be seen that the recovery rate is high. This is because if the amount of air supply is too small, the concentration of minibubbles will be insufficient and the ability to remove trapped materials will be reduced due to disturbance of the filter layer. If the amount of air supply is too large, the diameter of the microbubbles will increase and the fine microbubbles will decrease. This is thought to be due to a decrease in the amount. 5A and 5B, the air supply amount when the recovery rate is 85% or more is 0.8 L / min to 1.3 L / min. Therefore, the air for generating microbubbles and minibubbles is used. It can be seen that the supply amount is preferably 4.4% to 7.2% with respect to the amount of backwash water. Furthermore, when the recovery rate is 90% or more, the air supply amount is 0.9 L / min to 1.1 L / min. Therefore, the air supply amount is 5.0% to 6.1% with respect to the backwash water amount. Is particularly preferable.

  Next, in the mini-bubble + micro-bubble mixed water, the air inflow from the air supply pipe 40 is fixed at 1.0 L / min, and the air inflow from the air supply pipe 42 is 0.5 L / min, 1.0 L / min. FIG. 5C shows a graph of the recovery rate when changing to min, 1.5 L / min, 2.0 L / min, and 2.5 L / min. From FIG.5 (c), in the backwashing in the mini bubble and micro bubble mixed water, even if it changed the air supply amount from the air supply pipe | tube 42, the big difference was not recognized by the recovery rate. Therefore, the air supply amount from the air supply pipe 42 in the minibubble + microbubble mixed water is 0.5 L / min to 2.5 L / min, that is, 2.8% to 13.8% with respect to the backwash water amount. In addition, the air supply amount from the air supply tank 42 in the mixed water containing only the mini bubbles is 1.0 L / min to 2.5 L / min, indicating a higher recovery rate than the back washing using only the backwash water. Therefore, it is preferable that the air supply amount in the mixed water containing only minibubbles is 5.5% to 13.9% with respect to the backwash water amount.

  When the support layer 54 is made of filtered gravel, the microbubbles coalesce when passing through the filtered gravel to increase the bubble diameter and reduce the concentration of fine microbubbles. In this regard, by using a porous resin plate as the support layer 54 instead of the filter gravel, the reduction of fine microbubbles can be suppressed, and backwashing with microbubbles can be made to function more effectively. Therefore, when mixing microbubbles with backwash water, it is preferable to use a porous resin plate for the support layer 54. When the porous resin plate is used, the conventional air washing causes unevenness of bubbles, and only a part of the filter layer 52 can be air-washed. However, the microbubbles and minibubbles do not cause unevenness, and the filter layer 52 Effective backwashing with micro-bubbles and mini-bubbles can be performed as a whole.

  As described above, the filter backwashing method and backwashing apparatus 80 according to the present invention can have excellent backwashing ability by mixing microbubbles and minibubbles in the backwash water. Further, since the fine bubbles are smaller than the bubbles at the time of air washing, the filter medium is not excessively wound up. For this reason, it is not necessary to lower the water level of the filter 50, and the backwash operation can be performed continuously from the filtration operation. Thereby, the backwashing which has a high backwashing capability can be performed easily. Further, unlike air washing, the fine bubbles do not disturb the stratification of the filter gravel of the support layer 54, and the filter medium does not flow out. Further, even when a porous resin plate is used for the support layer 54, the position where fine bubbles pass is not biased, and the entire filter layer 52 can be effectively backwashed with fine bubbles.

  Furthermore, the fine bubble generating means 60 suitable for the present invention shown in FIG. 3 can be easily installed in the existing backwash pipe 38. Further, in the configuration of FIG. 2 provided with the second air supply pipe 40, each of the micro bubbles and the mini bubbles is adjusted by adjusting the open / close state of the open / close valve 42a of the air supply pipe 42 and the open / close valve 40a of the air supply pipe 40. The amount can be adjusted to change the mixing ratio of microbubbles and minibubbles to the backwash water. Further, the backwash water can be easily selected from backwash water alone, mixed water containing only minibubbles, mixed water containing only microbubbles, and mixed water containing minibubbles + microbubbles.

  The configuration of the filtration system 100, the backwash device 80, the filter 50, the fine bubble generating means 60 and the accompanying equipment, the piping path, the dimensions, the filtration operation, the conditions of the backwash operation, etc. shown in this example are examples. Besides, necessary facilities, devices, processes and the like can be inserted as appropriate, and the present invention can be modified and implemented without departing from the gist of the present invention.

16 Backwash tank
34 Backwash pump
36 Discharge piping
38 Backwash piping
42 Air supply pipe
42a On-off valve
50 Filter
52 Filter layer
54 Support layer
60 Fine bubble generating means
80 Backwash equipment
100 Filtration system

The present invention
(1) Backwashing of a filter 50 having a filter layer 52 configured to collect aggregates formed by filling a filter medium and formed by adding a flocculant, and a support layer 54 for supporting the filter layer 52 A method,
Mixing microbubbles with a bubble diameter of 1 μm to 100 μm and minibubbles with a bubble diameter of 100 μm to several mm in backwash water fed from below the support layer 54 ,
The microbubbles adhere to the aggregates and increase the buoyancy of the aggregates, and the minibubbles having a bubble diameter of several millimeters are partly merged in the process of rising in the filter layer 52 to form large diameter bubbles. The filter layer 52 is disturbed, and the large-diameter bubbles are formed at the interface between the I layer having a high filter particle concentration in the filter layer 52 and the II layer, which is located above and includes water and bubbles. By providing a method of backwashing the filter 50 , wherein a jet flow is generated when moving from the I layer to the II layer, and the filter media particles and aggregates in the upper layer of the I layer are disturbed by the jet flow. Solve the above problems.
(2) Backwashing of the filter 50 having a filter layer 52 configured to collect aggregates formed by filling a filter medium and formed by adding a flocculant, and a support layer 54 for supporting the filter layer 52. A device,
A backwash water tank 16 for storing backwash water, a backwash pipe 38 for connecting the backwash water tank 16 and the filter 50 and sending backwash water from the backwash water tank 16 below the support layer 54; A backwash pump 34 for pumping backwash water to the backwash pipe 38, and a discharge pipe 36 provided above the filtration surface of the filter 50,
Furthermore, the fine bubble generating means 60 is provided in the backwashing pipe 38 and is supplied from the outside into a minibubble having a bubble diameter of 100 μm to several mm and a microbubble having a bubble diameter of 1 μm to 100 μm and mixed in the backwash water. The above-described problem is solved by providing a backwashing device 80 comprising an air inflow amount adjusting mechanism for adjusting the amount of each of the micro bubbles and the mini bubbles .

Claims (2)

A filter backwash method comprising a filter layer configured by filling a filter medium, and a support layer for supporting the filter layer,
A backwashing method for a filter, wherein microbubbles and minibubbles are mixed in backwash water fed from below the support layer. A filter backwash device having a filter layer configured by filling a filter medium, and a support layer for supporting the filter layer,
A backwash water tank for storing backwash water;
A backwash pipe for connecting the backwash water tank and the filter, and sending backwash water of the backwash water tank below the support layer;
A backwash pump that pumps backwash water into the backwash pipe;
A discharge pipe provided above the filtration surface of the filter, and
The backwashing apparatus further comprises fine bubble generating means that is provided in the backwashing pipe and that is supplied from the outside into minibubbles and microbubbles and mixed in the backwash water.

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