JP4908542B2 - Filtration method, filtration device and filtration pond - Google Patents

Description

  In the present invention, when raw water such as water taken from rivers and lakes, groundwater pumped up, etc. is filtered through a sand layer of a predetermined thickness, organic matter is removed by a layer of microorganisms formed in the sand layer. The present invention relates to a filtration method, a filtration device, and a filtration pond that decomposes and captures suspended substances to obtain purified water.

  Tap water used for domestic water, drinking water, etc., so-called purified water is obtained by purifying raw water such as water taken from rivers, lakes, dams, or ground water pumped from the ground. The raw water contains suspended solids in which microorganisms and garbage float in a colloidal form, so it is not suitable for drinking as it is. Thus, suspended water is removed from the raw water by a predetermined filtration method, chlorine is injected so that the effective chlorine equivalent concentration is about 1 ppm, and water is distributed to households, factories, schools, and the like as tap water. As a filtration method for removing suspended substances from raw water, a sand filtration method in which filtration is performed in a filtration pond provided with a sand layer is well known, and a slow filtration method and a rapid filtration method are known as sand filtration methods. .

  The slow filtration method is a method of purifying water by the action of organisms such as bacteria and microorganisms. In the slow filtration method, raw water is first guided to a sand basin, and sand and dust floating in the water are submerged and led to a so-called slow filtration basin. The slow filtration basin is provided with a layer of sand having an average particle size of 0.8 to 1.0 mm. The slow filtration method does not inject sterilizing sodium hypochlorite, so the microorganisms do not die. Accordingly, a biological layer having a predetermined thickness is formed in the sand layer of the slow filtration pond, which is composed of sand and bacteria that have adhered to the sand and propagated. Such a biolayer is also called a biofilm because the layer is thin. When water passes through the biological layer, organic substances in the water are decomposed, so that mold odor is removed and delicious water can be obtained. Moreover, when water passes through the biological layer, fine dust floating in the water is sufficiently captured, and Cryptosporidium, which has been a problem in recent years, can be almost completely removed. Cryptosporidium is a protozoan with a size of about 5 μm and is resistant to chlorine. When Cryptosporidium is mixed with drinking water and drunk, collective diarrhea occurs. However, such Cryptosporidium is almost completely removed by the biological layer, so that safe water can be supplied. In a slow filtration pond, the biological layer is only formed to a thickness of 1 to 2 cm. Therefore, in order to sufficiently treat the water in the biological layer, the speed of water passing through the biological layer, that is, the filtration rate must be limited. Don't be. Therefore, in the slow filtration basin, the filtration rate is about 8 m / day at the maximum.

  The rapid filtration method is a purification method of water that removes suspended solids by adding chemicals to raw water. In the rapid filtration method, flocculants such as polyaluminum chloride (PAC) and a sulfuric acid band are added to raw water and led to a sedimentation basin. As a result, most of the colloidal suspended substance charged to a negative charge aggregates and precipitates in a floc form. Sodium hypochlorite is injected into the supernatant water of the sedimentation basin to sterilize it, leading to a so-called rapid filtration basin. The rapid filtration basin is provided with a layer of sand having an average particle diameter of 1 to 2 mm, and most of the suspended solids remaining while water passes through the layer of sand are filtered out. Since the rapid filtration basin filters water in which chlorine is dissolved, a biological layer is hardly formed. Therefore, the filtration rate can be 120 to 150 m / day, and a large amount of purified water can be obtained efficiently. In addition, since most of the suspended solids settle in the sedimentation basin, a so-called filtration blockage, in which the sand layer is clogged and cannot be filtered, is unlikely to occur. And even if the filter is clogged, the filter clog can be easily eliminated by carrying out so-called backwashing, in which purified water is ejected from the bottom of the sand layer of the rapid filtration pond. .

Japanese Patent Laid-Open No. 2005- 211804

  Patent Document 1 describes a two-stage filtration basin composed of a front stage and a rear stage connected in series, and a filtration method for obtaining purified water by treating raw water with these filtration ponds. Each filter basin is provided with a sand layer having a particle size of 50 μm to 300 μm, and since no chemical is injected into the raw water, a biological layer is formed in the sand layer of each filter pond. The raw water is first filtered in the preceding filtration basin so that the filtration rate is 30 to 200 m / day to remove most of the turbidity and about 50% of the organic matter. Then, it filters so that a filtration rate may be 10-75 m / day in the latter filtration pond, and the remaining turbidity and organic substance are removed. These filtration basins are backwashed at a predetermined cycle to prevent filtration blockage.

  According to the slow filtration method, water is treated by the biological layer, so that organic substances that cause mold odor are decomposed and delicious water can be obtained. Moreover, according to the rapid filtration method, the filtration rate can be increased, so that even if the area of the filtration pond is small, a large amount of purified water can be obtained efficiently, which is advantageous filtration particularly in urban areas where it is difficult to secure a site. Is the method. However, there are problems with these methods. For example, in the slow filtration method, the filtration rate cannot be increased as described above, so that the treatment efficiency is low, and a large slow filtration basin is required to obtain a large amount of purified water. There is also the problem of filtration blockage. Since the slow filtration method needs to be operated at a low filtration rate, it is necessary to reduce the water pressure difference between the surface layer and the lower layer of the sand layer, and generally the depth of the slow filtration pond is shallow. Then, if the sand layer is clogged even a little and a pressure loss of water pressure occurs, a sufficient water pressure difference cannot be secured and filtration cannot be performed. For example, when the so-called loss head, which represents the pressure loss in terms of the height of the water column, reaches about 1.5 m, filtration cannot be performed in the slow filtration basin. Furthermore, since the biological layer is thin, if raw water with a relatively high nutrient content is processed, a large amount of microorganisms propagate in the thin biological layer, and the sand layer is clogged at an early stage. The slow filtration basin, which has become unable to be filtered, requires maintenance to drain water and scrape the clogged sand surface layer, increasing labor costs. Therefore, it is difficult to secure a site for a large filtration pond, and it is difficult to adopt the slow filtration method in urban areas where the nutrients of nearby rivers are high.

  There are also problems with rapid filtration. In the rapid filtration method, since organic substances dissolved in water are not decomposed, mold odor is not decomposed and it is difficult to obtain delicious water. Moreover, since filtration is performed only with a sand layer in which no biological layer is formed, there is a risk that small particles of Cryptosporidium will flow out of the rapid filtration pond and be mixed into purified water. Furthermore, since the sediment in which the suspended solids are precipitated contains a flocculant, that is, contains a chemical, it cannot be returned to the river as it is and must be treated as industrial waste. This increases processing costs and affects the environment.

  According to the filtration method described in Patent Document 1, the filtration rate can be increased while taking advantage of the excellent point of the slow filtration method, so that the filtration method is excellent. That is, it is possible to obtain delicious water by filtering through a biological layer, and there is no danger of Cryptosporidium spillage, and a large amount of purified water can be obtained. However, there are also points that need to be improved, and specifically, there is a problem that the necessary equipment is enlarged. In other words, according to the filtration method described in Patent Document 1, two stages of filtration ponds are required. Therefore, when applying to a water purification facility equipped with a conventional filtration pond, it is necessary to newly install a filtration pond. , The whole equipment becomes large.

  The present invention has been made in view of the above-described problems. Specifically, the present invention does not require a particularly large space, and can be easily applied to conventional water purification facilities, and it is difficult to block filtration and is stable. Providing a filtration method that can treat a large amount of raw water and that can be treated with a biological layer to decompose organic matter to obtain safe and delicious water, a filtration device used for the implementation of this method, and a filtration pond It is an object.

  In order to achieve the above object, the present invention constitutes a filtration device from a fine bubble generating device and a pressure vessel provided with a sand layer. Then, air bubbles having a diameter of 80 μm or less are mixed into the water to be treated by the fine bubble generator and supplied to the pressure vessel at a pressure of 0.05 MPa or more, and a predetermined thickness formed in the sand layer Filter through the biological layer. In another aspect of the invention, a fine bubble generator that mixes fine air bubbles in the water to be treated is provided in the inflow path through which the water to be treated flows into the filtration pond. Then, air bubbles having a diameter of 80 μm or less are mixed into the water to be treated and led to the filtration basin. The water to be treated in which fine air bubbles are mixed is filtered through a biological layer having a predetermined thickness formed in the sand layer of the filtration pond.

Thus, in order to achieve the above object, the invention according to claim 1 filters the treated water taken from rivers, lakes, dams, or pumped up underground, through a predetermined layer of sand , When obtaining purified water to be used as drinking water, a biological layer having a predetermined thickness composed of sand and microorganisms that have adhered to the sand and propagated is formed in the sand layer, and the treated water is filtered by the biological layer. In the filtration method to be performed, air bubbles having a diameter of 80 μm or less are mixed into the water to be treated, and then filtered through the biological layer.
Invention of Claim 2 is comprised in the method of Claim 1, when the said bubble is mixed in the said to-be-processed water, it is comprised so that a bubble with a diameter of 10-80 micrometers may be 200 pieces / mL or more, Invention of Claim 3 is comprised in the method of Claim 1 or 2 so that the said to-be-processed water may be filtered applying the pressure of 0.05 Mpa or more, and invention of Claim 4 is set. The method according to any one of claims 1 to 3, wherein the water to be treated is agglomerated suspended substances by adding a predetermined flocculant to raw water taken from rivers, lakes, dams, etc. It is configured to be supernatant water that has been precipitated.

The invention according to claim 5, such that the rivers, lakes, purified water that is water intake from the dam, or treated water pumped up from the underground is used as domestic water and drinking water and Ru are filtered is supplied and discharged A pressure layer, a sand layer provided in the pressure vessel, and a fine bubble generator, and the water to be treated is air having a diameter of 80 μm or less by the fine bubble generator. The bubbles are mixed and supplied to the pressure vessel at a pressure of 0.05 MPa or more, and the sand layer has a predetermined thickness composed of sand and microorganisms that have adhered to the sand and propagated. configured so that is formed by the organism layer.
The invention according to claim 6 is a filtration in which treated water taken from rivers, lakes, dams, or pumped up underground is filtered to obtain purified water used as domestic water or drinking water. A pond, wherein the filtration pond is provided with a layer of sand, and in the layer of sand, a biological layer having a predetermined thickness is formed which is composed of sand and microorganisms which have adhered to and proliferated. An inflow water channel for supplying the water to be treated to the filtration basin is provided with a fine bubble generating device so that air bubbles having a diameter of 80 μm or less are mixed into the water to be treated.
The invention according to claim 7 is a filtration in which treated water taken from rivers, lakes, dams, or pumped up underground is filtered to obtain purified water used as domestic water or drinking water. A pond, wherein the filtration pond is provided with a layer of sand, and in the layer of sand, a biological layer having a predetermined thickness is formed which is composed of sand and microorganisms which have adhered to and proliferated. A fine bubble generator is provided upstream of the filtration basin, and a pond having a predetermined capacity is provided. In the pond, air bubbles having a diameter of 80 μm or less are mixed into the water to be treated and supplied to the filtration pond. Composed.
The invention according to claim 8 is a filtration in which treated water taken from rivers, lakes, dams, or pumped from underground is filtered to obtain purified water used as domestic water or drinking water. A pond, wherein the filtration pond is provided with a layer of sand, and in the layer of sand, a biological layer having a predetermined thickness is formed which is composed of sand and microorganisms which have adhered to and proliferated. A fine bubble generator is provided in the filtration basin, and is configured such that air bubbles having a diameter of 80 μm or less are mixed into the water to be treated in the filtration pond.

As described above, according to the present invention, air to be treated is taken from rivers, lakes, dams, or pumped up underground , and air bubbles having a diameter of 80 μm or less are mixed. Air is dissolved and fine bubbles are included. When such treated water is filtered through a predetermined sand layer, aerobic microorganisms suitable for water treatment are efficiently propagated and the thickness of the biological layer is increased. Therefore, since the water to be treated can be filtered with such a thick biological layer, the water to be treated can be sufficiently treated even when the filtration speed is increased, and the organic matter contained in the water to be treated is decomposed. It is possible to capture fine suspended substances contained in the water to be treated. That is, a large amount of delicious and safe purified water can be obtained. Furthermore, since it can be operated at a high filtration rate, it can be operated with a large water pressure difference between the upper and lower layers of the sand layer. Even if it becomes high, it becomes possible to continue filtering. In addition, since the biological layer is thick, microorganisms are dispersed and propagated in the thick biological layer, and it becomes difficult to block filtration. That is, the frequency of maintenance for eliminating clogging of the filtration pond is reduced. According to another invention, when air bubbles are mixed into the water to be treated, air bubbles having a diameter of 10 to 80 μm are mixed so as to be 200 / mL or more, so that a large amount of air is dissolved in the water to be treated. Fine bubbles will be included, and the effects as described above can be obtained with certainty. Furthermore, according to the invention for filtering the water to be treated by applying a pressure of 0.05 MPa or more, it is possible to increase the filtration rate, almost no filtration clogging occurs, the maintenance frequency is further reduced, and a large amount is inexpensively produced. Purified water can be obtained.
According to the invention in which the filtration device is constituted by the fine bubble generating device, the pressure vessel, and the sand layer provided in the pressure vessel, the filtration device can be installed even in a narrow space. It is possible to provide a filtration device at low cost. Further, according to the invention in which the fine bubble generating device is provided in the inflow channel for supplying the treated water to the filtration basin, or according to the invention in which the fine bubble foaming device is provided in the filtration basin, the conventional slow filtration pond Therefore, the present invention can be implemented at low cost without requiring a particularly large space. Furthermore, according to the invention in which a fine bubble generator is provided upstream of the filtration basin and a pond having a predetermined capacity is provided, it is possible to efficiently mix fine air bubbles into the water to be treated.

It is side surface sectional drawing which shows typically the filtration apparatus which concerns on embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the filtration installation which concerns on embodiment of this invention, The (a) is the filtration installation which concerns on 1st Embodiment, The (a) is the filtration which concerns on 2nd Embodiment It is side surface sectional drawing which shows an installation, respectively.

  Hereinafter, the filtration apparatus 1 which concerns on this Embodiment with FIG. 1 is demonstrated. The filtration device 1 includes raw water taken from rivers, lakes, dams, etc., that is, a fine bubble mixing tank 2 for mixing air bubbles into water to be treated, a hollow pressure vessel 3 having a predetermined shape, and a pressure vessel 3 It is comprised from the filter medium 4 etc. which are provided and filter to-be-processed water. The pressure vessel 3 is made of a steel plate having a predetermined thickness, and has a cylindrical barrel portion 6 and a head portion 7 having a dome shape that is liquid-tightly attached to the upper portion of the barrel portion 6 with bolts. The dome-shaped bottom portion 8 is liquid-tightly attached to the lower portion of the body portion 6 with bolts. An inflow pipe 9 is provided at a predetermined position on the upper portion of the body portion 6 so that the water to be treated in the fine bubble mixing tank 2 can be supplied into the pressure vessel 3. In the present embodiment, the water pump 11 is provided in a state where it is submerged in the fine bubble mixing tank 2 and is connected to the upstream side of the inflow pipe 9, so that the water to be treated is pressurized to a predetermined water pressure. It will be supplied into the pressure vessel 3. A pressure gauge 12 is interposed in the inflow pipe 9 to monitor the water pressure of the water to be treated supplied to the pressure vessel 3. The inflow pipe 9 has a predetermined length at the tip thereof drawn into the pressure vessel 2, and a jet portion 13 having a dish shape opened upward is provided at the tip. Since the jetting part 13 has a diameter expanded in the jetting direction, the treated water to be pumped is decelerated in the jetting part 13 and gently flows out upward and reaches the filter medium 4. Accordingly, the filter sand constituting the filter medium 4 does not soar in the pressure vessel 3. The bottom portion 8 of the pressure vessel 3 is provided with an outflow pipe 15 for sending filtered water to the outside. An air vent valve 16 is provided at the top of the head portion 6 of the pressure vessel 3, and when the float 17 detects a decrease in the level of the water to be treated in the pressure vessel 3, the valve automatically opens. Air accumulated in the upper portion of the pressure vessel 3 is exhausted.

  A floor for supporting the filter medium 4, that is, a filter bed 19 is provided at the bottom of the pressure vessel 3. The filter bed 19 has a flat upper surface, and a flow path is provided inside the filter bed 19. A large number of small-diameter holes communicating with the internal flow path are formed on the upper surface. Therefore, the filtered water to be treated, that is, the purified water is collected in the outflow pipe 15. Since the diameter of the hole on the upper surface of the filter bed 19 is smaller than the filter gravel constituting the filter medium 4, the filter gravel does not flow out from the outflow pipe 15. The filter medium 4 includes a plurality of filter gravel layers 21 to 24 and a filter sand layer 25 provided thereon. The 1st filtration gravel layer 21 consists of gravel with a particle size of 30-60 mm, and is provided in the thickness of about 12 cm on the filter bed. The second to fourth filtered gravel layers 22, 23, and 24 are sequentially stacked on the first filtered gravel layer 21, and gravel particles having a particle size of 20 to 30 mm, 10 to 20 mm, and 3 to 4 mm are each 10 cm. It is provided so that it may become thickness. The filtration sand layer 25 is a layer made of silica sand having an average particle diameter of 0.8 to 1.0 mm, and is provided on the fourth filtration gravel layer 24 so as to have a thickness of about 80 cm.

  In the filtration device 1 according to the present embodiment, a fine bubble generating device 26 is provided at the bottom of the fine bubble mixing tank 2. Various types of devices are known as the fine bubble generating device 26, such as a method of generating bubbles by cavitation and a method of generating bubbles by swirling water in a predetermined container to form air vortices. For example, a swirl type fine bubble generating device described in Japanese Patent No. 3397154 can be employed. When the fine bubble generating device 26 is operated, fine air bubbles of several μm to 500 μm can be generated. Among such fine bubbles, small-sized bubbles, for example, bubbles of several to 10 μm, dissolve in the water to be treated within several seconds to several tens of seconds or disappear, or the diameter becomes small and cannot be visually recognized. On the other hand, relatively large bubbles, for example, bubbles of 400 μm or more are fused together to form large bubbles and float on the water surface. Although relatively small diameter bubbles, for example, 10 to 80 μm, are partially dissolved in the water to be treated, a predetermined proportion of the bubbles remain in the water to be treated for a while. Buoyancy acts on such bubbles, but since the viscous resistance of water is large, it can only rise at a speed of several to 10 μm / second, especially bubbles of 65 μm or less are difficult to rise, and bubbles of 10 to 40 μm settle. Sometimes. Accordingly, bubbles having such a fine diameter drift in the raw water for a predetermined time while being dissolved in the water to be treated little by little and flow along with the flow of the water to be treated.

  The effect | action of the filtration apparatus 1 which concerns on this Embodiment is demonstrated. Raw water taken from rivers, lakes, dams, etc. is guided to a sand basin and stays for a predetermined time to precipitate dust and sand, and is introduced into the fine bubble mixed layer 2 as treated water 27. In FIG. 1, the sand basin is not shown. The fine bubble generator 26 is activated to mix fine air bubbles into the water 27 to be treated. Such bubbles are mixed in the water 27 to be treated so that, for example, 10 to 80 μm bubbles are 200 to several thousand pieces / ml. Dissolved in the water 27 to be treated, and bubbles of a predetermined ratio remain. The water to be treated 27 mixed with such fine bubbles is pressurized to a predetermined water pressure, for example, 0.05 MPa, 0.1 MPa, and the like by the water supply pump 11, and is pumped to the pressure vessel 3 through the supply pipe 9. .

  The water to be treated 28 supplied into the pressure vessel 3 decelerates at the ejection part 13 and reaches the filtered sand layer 25 gently. At this time, fine air bubbles also flow with the water to be treated 28 and reach the filtered sand layer 25. Thus, in the to-be-processed water 28 which reached the filtration sand layer 25, while a large amount of air is melt | dissolving, it is in the state in which the fine bubble which cannot be visually recognized, or the bubble of 10-80 micrometers was mixed. The treated water 28 is filtered with the filter sand layer 25. Then, since the air to be treated 28 contains sufficient air, aerobic bacteria are propagated efficiently. Accordingly, a layer composed of sand and bacteria that have propagated by adhering to the sand, that is, a biological layer is formed in the filtered sand layer 25, and the biological layer is sufficiently thick. Since filtration is performed by the biological layer formed thick as described above, even if the filtration speed is increased, the organic matter in the water to be treated 28 can be sufficiently decomposed, and suspended substances can be captured. That is, a large amount of purified water can be obtained efficiently. Water filtered from the filtration sand layer 25 is collected by the filter bed 19 via the first to fourth filtration gravel layers 22 to 24, and is sent to the outside via the outflow pipe 15. Sodium hypochlorite is added to the supplied water so as to have a predetermined concentration, and the water is sent to a water purification pond or a distribution pond and distributed as tap water to households and factories.

  Next, a filtration facility according to another embodiment of the present invention will be described with reference to FIG. The filtration facility 31 according to the first embodiment is provided in the upstream of the filtration basin 32 and the filtration basin 32 that are configured in the same manner as a conventionally known slow filtration basin, and fine air bubbles are used as raw water. It is comprised from the fine bubble mixing pond 33 to mix. Although not shown in FIG. 2A, the bottom of the filter basin 32 is made of unlaid bricks laid and provided with a floor for supporting the filter medium 34, that is, a filter bed. The filter bed can collect the water filtered by the filter medium 34 while preventing the filter medium 34 from flowing out. The filter medium 34 includes first to fourth filtration gravel layers 36 to 39 and a filtration sand layer 40. The 1st filtration gravel layer 36 consists of gravel with a particle size of 30-60 mm, and is provided in the thickness of about 12 cm on the filter bed. The second to fourth filtered gravel layers 37, 38, and 39 are sequentially stacked on the first filtered gravel layer 36, and gravel particles having a particle size of 20 to 30 mm, 10 to 20 mm, and 3 to 4 mm are each 10 cm. It is provided so that it may become thickness. The filtration sand layer 40 is a layer made of silica sand having an average particle diameter of 0.8 to 1.0 mm, and is provided on the fourth filtration gravel layer 39 so as to have a thickness of about 80 cm. The water filtered by the filter medium 34 and collected on the filter bed is not shown in FIG. 2A through the water purification pipe 42, but is sent to the water purification pond, distribution pond, etc. It has become so.

  The fine bubble mixing basin 33 provided on the upstream side of the filtration basin 32 will be described. The fine bubble mixing pond 33 is a pond in which fine air bubbles are mixed into raw water such as water taken from rivers, dams, lakes and the like, and groundwater pumped up. An inflow water channel 44 through which raw water flows is provided in the fine bubble mixing basin 33, and the fine bubble mixing basin 33 and the filtration basin 32 are connected by a supply water channel 45. At the bottom of the microbubble mixing pond 33, a microbubble generator 26 is provided. The fine bubble generating device 26 is the same device as the device provided in the fine bubble mixed layer 2 of the filtration device 1 according to the present embodiment.

  The effect | action of the filtration equipment 31 which concerns on this Embodiment is demonstrated. Raw water taken from rivers, lakes, dams, etc. is guided to a sedimentation basin and stays for a predetermined time to precipitate dust and sand, and is guided to a fine bubble-mixing basin 33 through an inflow water channel 44 through a landing well. FIG. 2A does not show a sand basin or landing well. The fine bubble generator 26 is activated to mix fine bubbles into the raw water 47 in the fine bubble mixing pond 33. Such bubbles are mixed into the raw water 47 so that, for example, 10 to 80 μm bubbles are 200 to several thousand pieces / ml, but a predetermined ratio of bubbles dissolves in the raw water 47 in a short time. , A predetermined proportion of bubbles remain. The raw water 47 mixed with such fine bubbles is supplied to the filtration basin 32 through the supply water channel 45.

  The raw water 48 supplied to the filtration basin 32 spreads horizontally in the filtration basin 32 and descends to reach the filtration sand layer 40. At this time, fine bubbles also flow with the raw water 48 and reach the filtered sand layer 40. In the raw water 48 that has reached the filtered sand layer 40 in this way, a large amount of air is dissolved, and fine bubbles that cannot be visually recognized or bubbles of 10 to 80 μm are mixed. The raw water 48 is filtered through the filter sand layer 40. Then, since sufficient air is contained in the raw water 48, the aerobic bacteria are efficiently propagated and formed in the filtered sand layer 40, a biological layer composed of sand and the bacteria propagated by adhering to the sand. Will be formed thick. Since filtration is performed by the biological layer formed thick in this way, even if the filtration rate is increased, the organic matter in the raw water 48 can be sufficiently decomposed, and suspended substances can be captured. That is, a large amount of purified water can be obtained efficiently. In order to increase the filtration speed, the filtration facility 31 according to the present embodiment is operated by setting the water depth h of the filtration pond 32 to 2 to 10 m, for example, and increasing the water pressure difference between the upper layer and the lower layer of the filter medium 34. be able to. If it does so, even if a loss head becomes about 1-1.5 m, since sufficient water pressure difference can be secured, it can continue filtering. The water obtained by filtering the filtered sand layer 40 is collected on the filter bed via the first to fourth filtered gravel layers 36 to 39, and is sent to the outside via the water purification pipe 42. Sodium hypochlorite is added to the supplied water so as to have a predetermined concentration, and the water is sent to a water purification pond or a distribution pond and distributed as tap water to households and factories.

  FIG. 2A shows a filtration equipment 31 ′ according to the second embodiment. The same members and devices as those of the filtration facility 31 according to the above embodiment are assigned the same reference numerals and will not be described in detail. In the filtration equipment 31 ′ according to the second embodiment, a fine bubble generating device 16 ′ is provided in the middle of inflow water channels 49 and 49 ′ that supply raw water to the filtration pond 32. Accordingly, fine air bubbles can be directly mixed into the raw water flowing through the inflow water channels 49 and 49 '. Similar to the filtration facility 31 according to the first embodiment, the raw water 48 in the filtration basin 32 is dissolved with sufficient air and mixed with fine bubbles that cannot be visually recognized and bubbles of 10 to 80 μm. Therefore, the filtration equipment 31 ′ according to the present embodiment also has the same effect as the filtration equipment 31 according to the first embodiment. Although not shown in the drawing, the fine bubble generating device 16 ′ can be provided in the outlet of the inflow water channel 49 ′, that is, in the filtration pond 32. Even if it does in this way, since the fine bubble of air can be mixed in the raw | natural water 48, there exists an effect similar to the filtration equipment 31 which concerns on 1st Embodiment.

The following experiment was conducted to examine the activity of microorganisms in raw water mixed with fine air bubbles.
(1) Experimental method:
The raw water collected from the river was put into containers A, B, and C 1 L at a time. The container A was left as it was, and the fine bubble foaming apparatus was put into the containers B and C, and the fine bubble foaming apparatus was operated for a predetermined time to mix fine air bubbles. In the container C, the fine bubble foaming apparatus was operated twice as long as the container B. The fine bubbles in the container B were 500 / mL or more of 10-80 μm bubbles, and the fine bubbles in the container C were 2000 / mL or more of 10-80 μm bubbles. Three hours later, 1 ml of raw water was collected from the containers A, B, and C, applied to a standard agar pond, and the number of general bacteria was counted from the colony count.
(2) Experimental results:
The number of general bacteria in each of containers A, B, and C was about 600, about 1000, and about 2500. It was found that when fine bubbles were mixed, microorganisms in the raw water were activated in a short time.

In order to investigate the influence of the raw water mixed with fine air bubbles on the thickness of the biological layer formed in the filtered sand layer, the following experiment was conducted.
(1) Experimental method:
Raw water collected from the river was put into containers d, e, and f. The container d was left as it was, and a fine bubble foaming device was put in the containers e and f, and the fine bubble foaming device was operated for a predetermined time to mix fine air bubbles. In the container f, the fine bubble foaming apparatus was operated twice as long as the container e. The fine bubbles in the container e were 500 / mL or more of 10-80 μm bubbles, and the fine bubbles in the container f were 2000 / mL or more of 10-80 μm bubbles.
Predetermined cylindrical containers D, E, and F were prepared, and a filter medium having a thickness of 300 mm made of silica sand having a particle diameter of 1.0 mm was provided in each container. The raw water of the containers d, e, and f was supplied to the cylindrical containers D, E, and F, respectively, and filtered at a filtration rate of 4 to 5 m / day.
Twenty-four hours after the start of filtration, each surface layer of silica sand and 50 mm deep silica sand were collected from the cylindrical containers D, E, and F, and the number of general bacteria adhering to the silica sand was examined. Similarly, 48 hours after the start of filtration, silica sand was collected from each cylindrical container D, E, F, and the number of general bacteria adhering to the silica sand was examined. The number of general bacteria was measured by putting 15 ml of collected sand into a centrifuge tube and shaking well, applying 1 ml of the obtained solution to a standard agar pond, and counting from the colony count.
(2) Experimental results:
(A) Number of general bacteria 24 hours after the start of filtration:
Cylindrical container D: surface layer 5000: 50 mm lower layer 5000
Cylindrical container E: surface layer 6000: 50 mm lower layer 6000
Cylindrical container F: Surface layer 13000: 50 mm lower layer 12000
(A) Number of general bacteria 48 hours after the start of filtration:
Cylindrical container D: surface layer 5000: 50 mm lower layer 10000
Cylindrical container E: surface layer 13000: 50 mm lower layer 12000
Cylindrical container F: Surface layer 20000: 50 mm lower layer 62000
It was found that when raw water mixed with fine air bubbles was filtered with a filtration sand layer, the formation of a biological layer was promoted compared to raw water without bubbles. In particular, when raw water mixed with fine air bubbles was filtered, it was found that the number of general bacteria increased significantly at a depth of 50 mm from the surface than at the surface. In the conventional slow filtration pond, only a biological layer, that is, a so-called biofilm is formed on the surface portion of the filtration sand layer, but in the filtration pond according to the present embodiment, even in a relatively deep layer of the filtration sand layer. A biological layer is expected to form. That is, the biological layer is expected to be thick.

  Various modifications can be made to the filtration device and the filtration equipment according to the present embodiment. For example, the raw water is described as staying in a sand basin to sink dust and sand, but may be directly led to the fine bubble mixing tank 2 or the fine bubble mixing pond 33. In particular, when the raw water is groundwater with very little suspended matter, a sand basin is not essential. Furthermore, after adding flocculants such as polyaluminum chloride and sulfuric acid band to the raw water to aggregate the suspended substances in the raw water and settling in the sedimentation basin, You may lead to the pond 33. In this way, even if the raw water contains a relatively large amount of suspended solids, most of the suspended solids can be removed, so that the filtration sand layers 25 and 40 are difficult to clog and are operated for a long time. It becomes possible to do. Alternatively, the raw water may be passed through a filter such as gravel or sand having a large particle size and then guided to the fine bubble mixing tank 2 or the fine bubble mixing pond 33. Even if it does in this way, since most of the suspended solids in raw | natural water can be removed, the filtration sand layers 25 and 40 become difficult to filter-clog.

  The fine bubble generating device can also be modified, and a device that generates bubbles by a method other than the swivel type can also be applied. Furthermore, the number of fine bubble generators to be installed may be a plurality instead of one, and in this way, fine bubbles can be efficiently mixed into the raw water. The thickness of the filtration sand layer of the filter medium, the particle size of the sand, the thickness of the filtration gravel layer, and the like can be modified, and are not limited to the present embodiment. Moreover, although the filter bed of the filtration pond is described as being formed from unglazed bricks, a conventionally well-known leopold type filter bed may be applied. In this way, when the filtration sand layer is clogged and filtration clogging occurs, so-called backwashing can be performed, in which purified water is jetted from the bottom of the filtration basin to wash the filtration sand. It is possible to further save the cost required for the operation.

DESCRIPTION OF SYMBOLS 1 Filtration apparatus 2 Microbubble mixing tank 3 Pressure vessel 4 Filter material 9 Inflow pipe 11 Water supply pump 13 Jetting part 16 Air vent valve 19 Filter bed 21-24 Filter gravel layer 25 Filtration sand layer 26 Fine bubble generator 27, 28 Water to be treated 31 Filtration equipment 32 Filtration basin 33 Fine bubble mixed basin 34 Filter media 36-39 First to fourth filtration gravel layers 40 Filtration sand layers 47, 48 Raw water

Claims (8)

When the treated water taken from rivers, lakes, dams, or pumped up underground is filtered through a predetermined layer of sand to obtain purified water used for domestic or drinking water, it adheres to the sand and the sand. predetermined thickness of the biological layer comprised of the microorganisms breeding Te is formed on the layer of sand, in the filtration method which is the so-treatment water is filtered by the organism layer,
A filtration method, wherein air bubbles having a diameter of 80 μm or less are mixed into the water to be treated, and then filtered through the biological layer. The method according to claim 1, wherein when the bubbles are mixed into the water to be treated, the bubbles are mixed so that bubbles having a diameter of 10 to 80 μm are 200 / mL or more. The method according to claim 1 or 2, wherein the water to be treated is filtered by applying a pressure of 0.05 MPa or more. The method according to any one of claims 1 to 3 , wherein the water to be treated is precipitated by adding a predetermined coagulant to raw water taken from a river, a lake, or a dam to aggregate a suspended substance. A filtration method characterized by being a supernatant water. Rivers, lakes, the water intake from the dam, or a pressure vessel purified water are discharged to treated water is used as a domestic water and drinking water and Ru are filtered are supplied pumped up from the underground, the It is composed of a layer of sand provided in the pressure vessel and a fine bubble generator ,
The water to be treated is mixed with air bubbles having a diameter of 80 μm or less by the fine bubble generator, and is supplied to the pressure vessel at a pressure of 0.05 MPa or more .
The filtration apparatus according to claim 1, wherein the sand layer is formed with a biological layer having a predetermined thickness composed of sand and microorganisms attached to the sand and propagated . A filtration pond in which treated water taken from rivers, lakes, dams, or pumped up underground is filtered to obtain purified water that can be used as domestic water or drinking water.
The filtration pond is provided with a layer of sand, and the layer of sand is formed with a biological layer of a predetermined thickness composed of sand and microorganisms attached to the sand and propagated,
The inflow channel for supplying the water to be treated to the filtration basin is provided with a fine bubble generator, and air bubbles having a diameter of 80 μm or less are mixed into the water to be treated. Filtration pond. A filtration pond in which treated water taken from rivers, lakes, dams, or pumped up underground is filtered to obtain purified water that can be used as domestic water or drinking water.
The filtration pond is provided with a layer of sand, and the layer of sand is formed with a biological layer of a predetermined thickness composed of sand and microorganisms attached to the sand and propagated,
A fine bubble generator is provided upstream of the filtration basin, and a pond having a predetermined capacity is provided. In the pond, air bubbles having a diameter of 80 μm or less are mixed into the water to be treated and supplied to the filtration pond. A filtration pond characterized by A filtration pond in which treated water taken from rivers, lakes, dams, or pumped up underground is filtered to obtain purified water that can be used as domestic water or drinking water.
The filtration pond is provided with a layer of sand, and the layer of sand is formed with a biological layer of a predetermined thickness composed of sand and microorganisms attached to the sand and propagated,
The filtration basin is provided with a fine bubble generator, and air bubbles having a diameter of 80 μm or less are mixed into the water to be treated in the filtration pond.

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