JP5317537B2 - Filtration system - Google Patents

Description

  The present invention relates to a filtration apparatus to which a slow filtration method is applied, and particularly to a filtration system for filtering and purifying water by a slow two-stage filtration method.

  The slow filtration method is a water purification method that relies on the action of trapping and oxidizing and decomposing impurities such as suspended substances and dissolved substances in water by, for example, a sand layer and a microorganism group grown on the surface of the sand layer. This method is suitable for relatively good raw water (treated water) and not only removes suspended matter and bacteria in the water, but also removes odors, iron, manganese, etc. if the function of the organism is not impaired. It is said that you can.

In the purification function, the suspended matter in the water is restrained on the surface of the sand layer as the water to be treated passes through the fine sand layer at a low speed. Algae and microorganisms propagate on this detention substance, and a biofiltration layer is formed. When this biofiltration layer is formed, the suspension rejection rate becomes extremely high.
Suspension prevention in slow filtration concentrates on the surface of the sand layer, resulting in large filtration losses in that area. Suspension suppression is performed only on the very surface layer of the sand layer, so water with high turbidity and abnormally high algae has a problem of increasing the surface head loss in a short time and shortening the filtration duration. Therefore, the water to be treated with a turbidity of 10 degrees is the limit.

That is, the slow filtration method is generally effective when the quality of the water to be treated is relatively good, but when the quality of the water to be treated is poor, the filtration efficiency and the filtration performance cannot be maintained well for a long time. .
Then, in order to implement | achieve more efficient filtration by a slow-speed filtration method, the 2 step | paragraph fine sand filter apparatus with a backwash is proposed.
Japanese Patent Laid-Open No. 2005- 211804

  Generally, a slow filtration method and a rapid filtration method are known as water purification methods. The rapid filtration method is a water filtration method widely used in Japan, in which a chemical such as a sulfuric acid band is poured into turbid water, and the precipitate is removed, followed by high-speed filtration. However, the rapid filtration method requires a place for ancillary equipment other than the filtration tank, mixes chemicals, and must add chlorine to remove organic substances and bacteria. For this reason, there is a problem that the maintenance management cost becomes expensive and a chemical fee is required.

Therefore, the inventor of the present application pays attention to the slow filtration method. In the slow filtration method, (1) scum countermeasure (proliferation algae countermeasure), (2) high turbidity countermeasure (high turbidity water can be purified) ), And (3) Measures against mixed water (water containing organic matter) were developed.
The main object of the present invention is to provide a filtration system based on a slow filtration method capable of realizing good purification even for highly turbid water.

  Another object of the present invention is to provide a filtration system based on a slow filtration method capable of suppressing the generation of proliferating algae and maintaining good filtration for a long period of time.

  Invention of Claim 1 is a filtration system which transfers the water filtered with the 1st filtration tank to the 2nd filtration tank, and further filters the water with the 2nd filtration tank, and the 1st filtration tank is The first water tank, the first filtration layer for filtering impurities contained in the water when the water passes through the first water tank, and is filtered through the first filtration layer. A first water outlet for taking out the water, and a water distribution pipe for transferring water from the first water outlet to the second filtration tank, the second filtration tank via the water distribution pipe A second water tank for storing water to be transferred; a second filtration layer that is contained in the second water tank and filters impurities contained in the water by passing water through the second water tank; The overflow port for overflowing the water accumulated in the water tank above a predetermined level and the water filtered by the second filtration layer are taken out. A second water outlet, the filtration rate of the first filtration tank is higher than the filtration rate of the second filtration tank, and the second filtration tank always has water from the overflow port. The filtration system is characterized by being provided with an overflow return device for returning water overflowing from the overflow port to the first filtration tank side.

The invention according to claim 2 is a filtration system according to claim 1, further comprising a light shielding member that covers the second water tank, wherein the light shielding member is provided with a daylighting unit having a predetermined amount of transmitted light. is there.
According to a third aspect of the present invention, there is provided a reverse cleaning tank for storing water flowing out from the second water outlet, and water stored in the reverse cleaning tank from the lower side of the first filtration layer to the first water tank. A backwashing water outlet for allowing water to flow out during backwashing is provided at an upper part of the first water tank. The filtration system described in 1.

The invention according to claim 4 is characterized in that, during backwashing, the process of causing the water stored in the backwashing tank to flow into the first water tank through the backwash water channel is performed using gravity. The filtration system according to claim 3.
The invention according to claim 5 is provided with a quantitative supply device for maintaining a constant amount of water flowing into the first water tank. System.

A sixth aspect of the present invention is the filtration system according to the fifth aspect, wherein the metering supply device includes a water transfer pump for metering water into the first water tank.
According to a seventh aspect of the present invention, the metering device is provided at an upper portion of the first water tank, and the supplied water is allowed to flow into the first water tank by a certain amount, and the remaining water is returned to the previous stage. The filtration system according to claim 5, comprising a tank.

The invention according to claim 8 is characterized in that the first filtration tank and / or the second filtration tank includes a granular filter medium heavier than the specific gravity of water. The filtration system described in 1.
The invention according to claim 9 is characterized in that the amount of water overflowing from the overflow port is changed according to the pollution degree of water flowing into the first water tank. Filtration system.

According to the first aspect of the present invention, the water to be treated is filtered by the slow filtration method in the first filtration tank and the second filtration tank, filtered in two stages, and becomes purified water from which impurities are removed.
In claim 1, the filtration rate is the amount of water filtered in a filtration tank per unit time (total amount of water to be filtered). Since the filtration speed of the first filtration tank is higher than the filtration speed of the second filtration tank, the first filtration tank performs filtration having both functions of the slow filtration method and the rapid filtration method, and biological filtration. The tank is not easily clogged, and impurities in the water to be treated are roughly removed.

And the to-be-processed water from which the impurity was roughly removed is filtered by slow filtration in a 2nd filtration tank, and turns into purified water. Since part of the water in the second filtration tank always overflows, scum can be prevented from occurring in the second filtration tank.
According to invention of Claim 2, it can be set as the filtration system which suppressed generation | occurrence | production of scum, such as cyanobacteria inappropriate for filtration, maintaining the growth of the biofiltration membrane in a 2nd filtration tank.

According to invention of Claim 3, the 1st filtration layer of a 1st filtration tank can be wash | cleaned with backwash water, and a 1st filtration layer can be maintained.
If the backwashing is configured so that backwashing water flows using gravity as described in claim 4, a large-sized drive device (such as a pump) is not required for backwashing, and the backwashing device is inexpensive. It can be set as the filtration system provided with.

According to invention of Claim 5, the to-be-processed water of the quantity corresponding to the filtration speed of a 1st filtration tank can be supplied to a 1st filtration tank. Therefore, there is no overflow of water from the first water tank or insufficient water to be filtered. Moreover, the 1st filtration tank can perform favorable filtration according to the filtration performance.
According to the sixth aspect of the present invention, river water or the like can be pumped up by the water transfer pump and quantitatively supplied to the first filtration tank.

  According to the seventh aspect of the invention, the water (treated water) flowing into the first water tank is adjusted to a constant amount in the measuring tank. Therefore, even if the water supplied to the first water tank is, for example, water flowing using gravity and the flow rate changes with time, or the water pumped up by the pump, the pumping performance of the pump Even if it is impossible to adjust, it can always be adjusted to a certain amount.

According to the invention described in claim 8, good slow filtration can be performed by using a granular filter medium heavier than the specific gravity of water, such as sand, fine sand, artificially produced ceramic particles, metal particles, and the like. it can.
According to invention of Claim 9, favorable slow filtration can be implement | achieved by the 2nd filtration tank, and generation | occurrence | production of a scum can be prevented efficiently. Furthermore, when there is much pollution of to-be-processed water, a 2nd filtration tank is obstruct | occluded in a short time by setting it as the structure which increases overflow, and the water returned by the return apparatus is refiltered in a 1st filtration tank. Can be prevented.

Hereinafter, a two-stage sand filtration system will be specifically described as an embodiment of the present invention with reference to the drawings.
FIG. 1 is a diagram showing an overall configuration of a two-stage sand filtration system according to an embodiment of the present invention. The sand filtration system according to this embodiment includes a first filtration tank 11 and a second filtration tank 12, and the first filtration tank 11 and the second filtration tank 12 are connected in series.

  The 1st filtration tank 11 has the cylindrical 1st water tank 13, and the 1st filtration for allowing the water which flows in from the upper direction into the 1st water tank 13 by natural fall, and filtering the impurity contained in water is filtered. A sand layer 14 is accommodated. In addition, a measuring tank 15 as a quantitative supply unit is provided on the upper part of the first water tank 13. The measuring tank 15 has a function of allowing a supplied amount of water to flow into the water tank 13 by a certain amount, and returning more water to the upstream side. In this embodiment, the measuring tank 15 allows water (water to be treated) to flow into the first filtration tank 11 at a flow rate of 5 to 9 L / min. In the lower part of the first water tank 13, a first water outlet 16 for taking out the water filtered by the first filter sand layer 14, and a water distribution pipe 17 for transferring the water flowing out from the first water outlet 16 by gravity, Is provided.

The dimensions of the first water tank 13 are a diameter φ = 565 mm and a height H = 2000 mm. Moreover, the 1st filtration sand layer 14 accommodated in the inside has a two-layer structure in which the lower layer is a gravel layer (filter layer thickness: 250 mm) and the upper layer is a manganese sand layer (filter layer thickness: 1000 mm).
The 2nd filtration tank 12 has the rectangular parallelepiped 2nd water tank 18 comprised with the light-shielding member. In the second water tank 18, a second filtration sand layer 19 is stored for allowing water flowing in from above to pass through by natural fall and filtering impurities contained in the water. The dimensions of the second water tank 18 are length L = 1120 mm, width W = 900 mm, and height H = 850 mm. The second filtered sand layer 19 has a two-layer structure in which the lower layer is a gravel layer (filter layer thickness: 300 mm) and the upper layer is a manganese sand layer (filter layer thickness: 200 mm). And the upper limit of the head which shows the water depth in the 2nd filtration tank 12 shall be 350 mm, and when the water (to-be-processed water) more than that flows in, the water more than the predetermined water level which flowed in overflows from the overflow port 20. It has become. An overflow return pipe 21 as an overflow return device is connected to the overflow port 20, and the overflow is returned to the sedimentation tank 22 upstream of the measuring tank 15 via the overflow return pipe 21.

Here, the water level 23 of the water stored in the first filtration tank 11 is relatively high, the water level 24 of the water stored in the second filtration tank 12 is relatively low, and there is a height difference h between the two water levels. Designed to produce ₀ . Therefore, the water filtered by the first filtration tank 11 and flowing out from the first water outlet 16 is guided to the water distribution pipe 17 and naturally flows in from the upper part of the second water tank 18 of the second filtration tank 12 by gravity.
The water filtered by the second filtration sand layer 19 in the second filtration tank 12 flows out from the second water outlet 25 provided in the lower part of the second water tank 18. Then, it is temporarily stored in the purified water buffer tank 26 and taken out as purified treated water.

Here, the filtration method of the 1st filtration tank 11 and the 2nd filtration tank 12 is demonstrated.
In principle, both the first filtration tank 11 and the second filtration tank 12 perform filtration by a slow filtration method.
Table 1 shows the filtration specifications of the first filtration tank 11 and the second filtration tank 12.

As shown in Table 1, the first filtration tank 11 has a filtration rate of 28 m / day, the second filtration tank 12 has a filtration rate of 7 m / day, and the filtration rate of the first filtration tank 11 is the second. It is faster than the filtration rate of the filtration tank 12. Specifically, in this embodiment, the filtration rate of the first filtration tank 11 is set to about 4 times the filtration rate of the second filtration tank 12.
In this embodiment, the first filtration sand layer 14 of the first filtration tank 11 has a two-layer configuration of a support layer of 250 mm and a filtration layer of 1000 mm, the support layer is composed of gravel of 1.0 to 10 mm, and the filtration layer is The ferrite manganese sand was 0.6 to 1.2 mm.

On the other hand, the second filtration sand layer 19 of the second filtration tank 12 has a two-layer configuration of a 300 mm support layer and a 200 mm filtration layer, the support layer is composed of 1.0 to 10 mm gravel, and the filtration layer is 0.3 mm. It was composed of ˜0.35 mm manganese sand. By setting the particle size of the manganese sand to 0.3 to 0.35 mm, it is possible to perform optimum filtration on organic matter.
In the slow filtration method, the suspension is concentrated on the surface of the filtration layer (sand layer), and the suspension is restrained only on the surface layer. This is because in the slow filtration, the rate of suspension is extremely increased by the growth of algae and microorganisms on the detained substance retained in the surface layer of the sand layer to form a biological filtration layer. However, when the biological filtration layer is composed only of diatoms, good filtration is performed, but since scum is generated when cyanobacteria are generated or propagated, scum generation must be prevented. Furthermore, in the slow filtration, the suspension is suppressed only in the sand layer surface layer portion, and therefore, when the loss head of the surface layer portion increases, the surface layer portion must be maintained.

  By the way, if the filtration function in the 1st filtration tank 11 is considered strictly, since the filtration speed is made faster than the 2nd filtration tank 12, the characteristic of both the characteristic of a slow filtration method and the characteristic of a rapid filtration method It is estimated that That is, it is estimated that (1) physical treatment in rapid filtration (capture of turbid components) and (2) biological treatment in slow filtration (biofiltration) are combined. Therefore, a configuration is adopted in which sand is maintained by reverse cleaning only for the first filtration tank 11.

  That is, in this embodiment, the back washing tank 30 for back washing the 1st filtration sand layer 14 of the 1st filtration tank 11 is provided. The volume of the reverse cleaning tank 30 is, for example, 500 L, and the height position of the tank inner bottom surface 30 b is installed at a position higher than the water level 23 of the first filtration tank 11. The purified water collected in the purified water buffer tank 26 is pumped out by the pump 31, passes through the pumped water channel 32, and is stored in the backwash tank 30. A float switch 33 is provided in the back washing tank 30. When the float switch 33 fills the back washing tank 30 with purified water, pumping by the pump 31 is stopped.

  Every time filtration is performed by the first filtration tank 11 for a predetermined time or every time the head loss of the first filtration tank 11 reaches a predetermined value, the purified water stored in the backwash tank 30 is backwashed water supply pipe. 34 flows from the first water outlet 16 provided in the lower part of the first water tank 13 to the lower side of the first water tank 13. The inflowing water flows in the first water tank 13 as an upward flow, and the first filtered sand layer 14 is back-washed. As a result, the detained material adhering mainly to the surface layer portion of the first filtered sand layer 14 flows out from the backwash water outlet provided in the upper part of the first water tank 13 due to overflow. After the reverse cleaning is completed, the sand having a large particle size settles first, the filter sand having a large particle size (gravel as a support material) is stratified in the lower layer, and the filter sand (fine sand layer) as a fine filter material is stratified in the upper layer To do. Therefore, after back washing, the 1st filtration sand layer 14 returns to the original state.

A valve 36 is provided in the backwash water supply pipe 34 in the vicinity of the first water outlet 16 so that water does not flow in an undesired direction between the backwash water supply pipe 34, the first water outlet 16 and the water distribution pipe 17. Similarly, a valve 37 is also provided in the water distribution pipe 17 in the vicinity of the first water outlet 16.
In order to backwash the first sand filtration layer 14 of the first filtration tank 11, when a configuration in which purified water is stored in the backwash tank 30 is adopted, water collected in the purified water buffer tank 36 is pumped by a relatively low capacity pump 31. The pump can be pumped up, and the apparatus configuration for backwashing can be simplified. In other words, if the backwash tank 30 is not provided, and water stored in the purified water buffer tank 26 is used for backwashing by the pump pressure, a pump with high capacity must be used and the equipment is expensive. End up. In this embodiment, since the reverse cleaning tank 30 is provided and the reverse cleaning water is caused to flow by gravity, the reverse cleaning can be realized with a simple configuration. Of course, it is possible to employ a configuration in which the first filtration tank is back-washed by a high-power pump or the like.

  On the other hand, the second filtration tank 12 is supplied with water that has been primarily filtered in the first filtration tank 11 through the water distribution pipe 17 at a rate higher than the filtration speed. For this reason, when the water level 24 of the second filtration tank 12 reaches the overflow port 20, excess water is returned from the overflow port 20 through the overflow return pipe 21 to the settling tank 22. In this embodiment, the water accumulated in the upper part of the second filtration tank 12 always overflows from the overflow port 20, so that scum hardly occurs on the water surface of the water collected in the second filtration tank 12.

  The second filtration tank 12 includes a second water tank 18 made of a light shielding member and a light shielding lid 27. The light shielding lid 27 is provided with a light entrance glass window having a diameter of 200 mm, for example, and only light from the glass window enters the second filtration tank 12. Other light is blocked. For this reason, together with the overflow, the cyanobacteria are prevented from growing in the second filtration tank 12. On the other hand, diatoms are grown. Therefore, good secondary filtration by slow filtration can be performed in the second filtration tank 12.

  The second water tank 18 is made of a light shielding member, and the second water tank 18 (second filtration tank 12) is covered with the light shielding member instead of the structure in which the light shielding lid 27 is covered, and the light shielding member has a predetermined size, Or it is good also as a structure by which the lighting part which has predetermined translucency is provided. That is, it is good also as a structure provided with the daylighting part (lighting window, a daylighting slit, etc.) which introduce | transduces the light which helps the growth of diatoms, although the growth of cyanobacteria is prevented.

  In the second filtration tank 12, the amount of water returned from the overflow port 20 through the overflow return pipe 21 is set in a range of 1/20 to 1/2 of the amount of water supplied to the second filtration tank 12. ing. If it is in this range, the growth of cyanobacteria can be prevented by overflowing water (a good scum measure can be realized), and the loss as a filtration system, that is, how efficiently the secondary filtration is performed without wasting the primary filtered water. The loss from the viewpoint of

  In addition, you may change the quantity of the water returned by the pollution degree of to-be-processed water. When the degree of contamination of the water to be treated is high, for example, about half of the water supplied to the second filtration tank 12 is flooded and returned to the upstream side of the first filtration tank 11. If it carries out like this, the ratio of the to-be-processed water re-filtered by the 1st filtration tank 11 will increase, and the water purified to some extent by primary filtration can be slowly filtered by the 2nd filtration tank 12. FIG. Therefore, the filtration performance of the second filtration tank 12 can be maintained for a long time, and the number of maintenance can be reduced. The amount of water returned by overflow may be a predetermined amount reduced from the above ½ as the turbidity of the water to be treated is lower.

  In this embodiment, water is transferred from the first filtration tank 11 to the second filtration tank 12 by gravity. For this reason, the overflow from the overflow port 20 of the second filtration tank 12 is returned to the sedimentation tank 22 through the overflow return pipe 21 by gravity. That is, the return destination of the overflow water was the settling tank 12 on the first filtration tank 11 side and having a lower water level than the first filtration tank 11. Instead of such a configuration, the overflow from the overflow port 20 may be configured to return to the first filtration tank 11, for example. In that case, it will return to the place where the potential energy of water is high, and it cannot return only by gravity. Therefore, a pump is inserted in the overflow return pipe 21 (the overflow return apparatus is configured by the overflow return pipe 21 and a pump (not shown)), and the overflow from the overflow port 20 is caused by the force of the pump to the first filtration tank 11 (more Specifically, it may be configured to be returned from above the first water tank 13 into the water tank 13). In this case, since the amount of overflowing water returned to the first filtration tank 11 is constant, the total amount of water flowing into the first filtration tank 11 is made constant by adjusting the amount of water supplied through the measuring tank 15. Can be maintained. Further, in this case, the overflow from the second filtration tank 12 is reliably re-filtered in the first filtration tank, and the water flowing into the second filtration tank 12 can be made relatively low in turbidity.

  Still referring to FIG. 1, in this embodiment, river water is pumped by a pump 40. On the upstream side of the pump 40 in the pumping water channel 41, there is provided a filter 42 for removing large dust composed of, for example, a wire mesh. River water (raw water) pumped up by the pump 40 is temporarily stored in the settling tank 22. The sedimentation tank 22 is provided with a float switch 43, and the on / off of the pump 40 is controlled by the float switch 43. The pumped raw water is first stored in the first tank 22a. The water accumulated in the first tank 22a flows over the partition wall 44 and into the second tank 22b. That is, the water pumped up by the pump 40 once flows into the first tank 22a, and heavy substances among the pollutants contained in the raw water are deposited on the bottom surface of the first tank 22a. And the supernatant water mainly flows into the 2nd tank 22b.

The water in the second tank 22 b of the settling tank 22 is pumped up through the pumping pipe 46 by the pump 45 and stored in the tank 47 to be treated. The tank for water to be treated 47 is provided with a float switch 48. The pump 45 is driven by the float switch 48 so that a constant amount of water to be treated is always accumulated in the water tank 47 to be treated.
The water accumulated in the tank 47 to be treated is pumped out by the pump 49 and supplied to the measuring tank 15 through the water supply pipe 50. Then, water is supplied to the first water tank 13 from above by a fixed amount by the measuring tank 15. For example, 5 L / min (a throughput of 7.2 m ³ / day) is supplied. More water is returned to the treated water tank 47 through the circulation pipe 51.

In the above configuration, the metering tank 15 and the circulation pipe 51 can be omitted by using the pump 49 as a metering pump capable of metering up, for example, 5 L / min of water.
In this embodiment, three pumps 40, 45, and 49 are used to pump up river water and supply it to the first filtration tank 11, but the water to be treated is water such as ponds and lakes in mountainous areas, for example. Of course, when the water can be guided to the first filtration tank 11 by gravity, it is possible to eliminate the need for a power source such as a pump.

FIG. 2 is an illustrative view for explaining the configuration and operation of the weighing tank 15.
The measuring tank 15 includes a small-capacity tank 61, and the upper end of the water supply pipe 50 (see FIG. 1) communicates with the bottom surface of the tank 61. The treated water pumped up by the pump 49 (see FIG. 1) is sent through the water supply pipe 50 and collected in the tank 61 from the bottom surface side of the tank 61. An outlet 62 is formed on the upper side wall of the tank 61. When the water to be treated accumulates in the tank 61 and the water level exceeds the outlet 62, the water to be treated flows out from the outlet 62 and flows into the first filtration tank 11 (first water tank 13). Since the opening area of the outflow port 62 is constant, when water flows out through the entire outflow port 62, the outflow amount is kept constant. When the amount of water to be treated supplied to the tank 61 by the water supply pipe 50 is larger than the amount of water flowing out from the outlet 62, the excess water is returned to the upper part of the tank 61 (above the outlet 62). It flows out from the port 63, passes through the circulation pipe 51, and returns to the treated water tank 47.

The configuration of the measuring tank 15 is not limited to the above-described configuration, and may be another configuration as long as it can supply the water to be treated to the first filtration tank 11 in a fixed amount.
FIG. 3 shows the turbidity performance transition in the purification of the water to be treated verified by the two-stage sand filtration system shown in FIG. Moreover, the performance transition of the chromaticity of to-be-processed water is shown in FIG.
In FIG. 3, the horizontal axis represents the number of days, and the vertical axis represents turbidity (NTU).

As shown in FIG. 3, the turbidity of the raw water varies greatly from day to day. This is because the raw water is river water, and the turbidity changes greatly due to fluctuations in pollution during rainfall.
On the other hand, the turbidity of the water after filtering in the first filtration tank 11 is considerably low, and the turbidity of the treated water filtered by the second filtration tank 12 is almost zero and stable. I can understand that.

In FIG. 3, data was missing between the 11th to 20th days and the 30th to 39th days because the device was not operated for inspection of the device.
Also in the graph of chromaticity performance transition in FIG. 4, the horizontal axis represents the number of days, and the vertical axis represents chromaticity (TCU).
Regarding the chromaticity, the river water, which is the raw water, has a large variation in pollution during rainfall, and the chromaticity varies greatly. On the other hand, it turns out that the chromaticity of the water after filtering in the 1st filtration tank 11 is reduced considerably. Furthermore, it can be understood that the water after being filtered by the second filtration tank 12 is increased to a considerably low chromaticity even when the chromaticity of the raw water is large.

Also in FIG. 4, since the apparatus was stopped and inspected between the 11th day to the 20th day and the 30th day to the 39th day, no data was taken.
FIG. 5 shows, as a reference photograph, raw water used in the sand filtration system shown in FIG. 1, water after filtration in the first filtration tank 11 and water after filtration in the second filtration tank 12.
As shown in FIG. 5, it can be understood that the raw water clouded in brown is filtered by the first filtration tank 11 and further filtered by the second filtration tank 12 so that the water is transparent.

  In the two-stage sand filtration system of this embodiment, ferritic manganese sand is used for the first filtration sand layer 14 of the first filtration tank 11, and manganese sand is used for the second filtration sand layer 19 of the second filtration tank 12. However, this is because the characteristics of the treated water (raw water) used in the water purification experiment were taken into consideration. The type and particle size of the fine sand as the filter medium may be selected appropriately according to the properties of the water to be treated, and are not limited to the contents of this embodiment.

In this embodiment, since the filtration system was configured as a sand filtration system, sand (fine sand) was used as the filter medium for both the first filtration tank 11 and the second filtration tank 12. However, in the present invention, the filter medium is not limited to sand, and a granular filter medium heavier than the specific gravity of water, for example, a filter medium other than sand such as ceramic particles and metal particles can also be used.
The present invention is not limited to the embodiment described above, and various modifications can be made within the scope of the claims.

It is a figure showing the whole 2 stage type sand filtration system composition concerning one embodiment of this invention. FIG. 3 is an illustrative view for explaining the configuration and operation of a weighing tank 15. It is a graph which shows the performance transition of the turbidity in purification of to-be-processed water verified with the two-stage type sand filtration system concerning one embodiment of this invention. It is a graph which shows the performance transition of the chromaticity in the purification | cleaning of the to-be-processed water verified by the two-stage type sand filtration system which concerns on one Embodiment of this invention. It is a reference photograph which shows the raw water used for the two-stage type sand filtration system which concerns on one Embodiment of this invention, the water after filtering with the 1st filtration tank 11, and the water after filtering with the 2nd filtration tank 12. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st filtration tank 12 2nd filtration tank 13 1st water tank 14 1st filtration sand layer 15 Measuring tank 16 1st water outlet 17 Water distribution pipe 18 2nd water tank 19 2nd filtration sand layer 20 Overflow port 21 Overflow return pipe 25 2nd water Outlet 30 Backwash tank 35 Backwash water outlet

Claims (9)

A filtration system for transferring water filtered in the first filtration tank to the second filtration tank and further filtering the water in the second filtration tank,
The first filtration tank is
A first aquarium,
A first filtration layer for filtering impurities contained in the water by being contained in the first water tank and passing through the first water tank;
A first water outlet for taking out water filtered by the first filtration layer;
A water distribution pipe for transferring water from the first water outlet to the second filtration tank;
The second filtration tank is
A second water tank for storing water transferred through the water pipe;
A second filtration layer for filtering impurities contained in the water by being contained in the second water tank and passing through the second water tank;
An overflow port for overflowing water accumulated in the second water tank above a predetermined water level;
A second water outlet for taking out the water filtered by the second filtration layer,
The filtration rate of the first filtration tank is higher than the filtration rate of the second filtration tank, and the second filtration tank is always configured to allow water to overflow from the overflow port,
A filtration system comprising an overflow return device for returning water overflowing from the overflow port to the first filtration tank side.   The filtration system according to claim 1, further comprising a light shielding member that covers the second water tank, wherein the light shielding member is provided with a daylighting unit having a predetermined amount of transmitted light. A backwash tank for collecting water flowing out of the second water outlet;
A backwash water channel for allowing water stored in the backwash tank to flow into the first water tank from below the first filtration layer,
The filtration system according to claim 1 or 2, wherein an upper part of the first water tank is provided with a backwash water outlet for discharging water during backwashing.   4. The filtration according to claim 3, wherein at the time of backwashing, the process of causing the water stored in the backwash tank to flow into the first water tank through the backwash water channel is performed using gravity. system.   The filtration system according to any one of claims 1 to 4, further comprising a fixed amount supply device for maintaining a constant amount of water flowing into the first water tank.   The filtration system according to claim 5, wherein the metering device includes a water transfer pump for metering water into the first water tank.   The quantitative supply device includes a metering tank provided in an upper part of the first water tank, and allows the supplied water to flow into the first water tank by a certain amount, and the remaining water returns to the previous stage. The filtration system according to claim 5.   The filtration system according to claim 1, wherein the first filtration tank and / or the second filtration tank includes a granular filter medium heavier than a specific gravity of water.   9. The filtration system according to claim 1, wherein the amount of water overflowing from the overflow port is changed in accordance with a pollution degree of water flowing into the first water tank.