WO2002036239A1 - Filter sand washing method and its system - Google Patents

Abstract

When backwashing a rapid filter (1) where water is washed with filter sand, a preset amount of filter sand (5) is sucked from the rapid filter (1) by a pump (2). The sucked filter sand (5) is fed to a sand washing device (3) where the contaminants on the filter sand are removed. Contaminants-removed filter sand (6) is kept in a washed-sand stock tank (4), and stored filter sand (7) is returned to the rapid filter (1) when the rapid filter is backwashed. An automatic washing of filter sand in the rapid filter is possible by repeating the steps of sucking, washing and returning filter sand, whereby a sand washing function is regenerated by a washing method other than surface washing and backwashing to thereby drastically prolong a regenerating cycle of a filter pond.

Description

 Memorandum Book Filtering stone washing, method, law and its system

 The present invention relates to a method and a system for cleaning filter sand in a filtration pond for purifying water, and more particularly, to a cleaning method and a system for removing a part of the filter sand in a rapid filtration pond for cleaning.

Background art

 In water treatment at a water treatment plant, chemicals are injected into raw water drawn from rivers and lakes to precipitate suspended solids in the raw water into chunks that are easy to sediment, and the supernatant is sent to a filtration pond, where it is further refined. This is done by removing unusual suspended matter through a layer of sand (filtered sand) and disinfecting the filtered water with chlorine. In rapid filtration basins, filtration media is generally cleaned regularly every 24 to 72 hours. For cleaning, the surface of the sand layer sprayed from the nozzle is washed by tapping, and the clean water is pressed into the filter pond from the lower pressure chamber to float the sand, and the sand is mixed with the sand to remove dirt. There is backwashing.

 Even if the filter sand used for this water purification process is used for such surface cleaning and backwashing regularly, if it is used repeatedly for many years, dirt (turbidity such as sludge) adheres to the surface. come. As the particle size of the filter sand increases due to the adhesion of turbidity, voids between the filter sands decrease, clogging due to separation of the adsorbed substance of the filter sand, and leakage due to separation of the sludge itself will occur. . This has been addressed by increasing the number of backwashing steps, but if backwashing is repeated for many years, the water pressure will also affect the gravel layer that supports the filtered sand, and it will be spread horizontally. Non-land, which is a phenomenon that the gravel layer that should have been partially thickening or thinning, occurs. When this unevenness occurs, the sand layer becomes thinner in the thicker part of the gravel layer, and the filtration becomes insufficient in that part, and the filtration function that is originally performed is reduced, and the filter pond does not work properly and the water supply is safe. Can no longer be done.

In order to restore the normal filtration function, the operation of the filter pond is stopped once, the filter medium is removed, the removed filter medium is washed and sieved, and the inside of the filter pond is inspected and repaired. It is necessary to carry out rehabilitation work to re-install the cleaned filter media in the filtration pond. However, this rehabilitation work requires enormous costs, and it is necessary to stop the operation of the filtration pond during the construction period.The period of the rehabilitation work directly lowers the water purification efficiency. There is a request from the water treatment plant to make it as long as possible.

 On the other hand, new sand may be used for the filter sand that is laid again during rehabilitation work, but only about 10 to 20% of the collected sand is actually recognized as filter sand, and strict standards are imposed on filter materials. It is enacted, and if new sand is used, the cost will increase. Therefore, filtered sand is regenerated by washing. The present inventors have already proposed a sand washing apparatus that can regenerate sand to a state close to fresh sand with a washing turbidity of 30 degrees or less by an innovative method called a kneading washing method (Japanese Patent Laid-Open No. -109051, JP-A-57526). With this device, it is possible to achieve the same purification function as a filtration pond using fresh sand without using fresh sand for the filtration sand that is laid on the filtration pond during rehabilitation work.

 However, raw water for water supply has been rapidly increasing due to the recent pollution of rivers, lakes, and oceans due to urban, industrial, and agricultural wastewater, and acid rain that has been caused by the dissolution of nitrogen oxides and sulfur oxides as air pollutants. Is getting worse. Due to such deterioration of raw water, the condition of the filter sand is becoming more polluted as shown in Table 1, and filter ponds that were able to be used for a long period of time of 7 to 0 years in normal operation, The pace has to be accelerated.

 【table 1】

On the other hand, the maintenance of the filtration sand performed in the filtration basin includes the measurement of thornlessness and particle size survey. This is done to determine the timing of rehabilitation work.Maintenance to maintain the function of the sand that has regained its original purification function by rehabilitation work includes regular filtration by surface cleaning and backwashing. It is limited to the sand cleaning process only.

 In addition, following the provisional measures against cryptosporidium enacted in 1996, the water treatment plant should meet the above guidelines to maintain the turbidity at the outlet of the filtration pond below 0.1 degrees. The frequency of washing and backwashing is increased, but during that time purification is not possible because the water cannot be purified and the amount of water that can be obtained is reduced. In addition, fine sand flows out each time washing is performed, and if the frequency of backwashing increases, the formation of unevenness will be accelerated, which may result in earlier rehabilitation work. However, it is considered that there is a limit in responding only by the washing process of backwashing.

 The present invention has been made in view of the above circumstances, and the sand purifying function is regenerated by a method other than the usual cleaning method of surface cleaning and backflow cleaning without stopping the operation of the filtration pond, so that the filtration pond can be used. It is an object of the present invention to provide a method for cleaning filtered sand and a device for the same, which enable the cycle of rehabilitation work to be drastically extended.

Disclosure of the invention

 The filter sand washing method of the present invention is characterized in that a predetermined amount of filter sand is sucked from the rapid filter pond during backflow washing of the rapid filter pond for purifying water with the filter sand, and the sucked filter sand is sent to a sand washing device. Feeding, removing dirt from the filter sand by the sand washing device, returning the filter sand from which the dirt has been removed to the rapid filtration tank at the time of backwashing of the rapid filtration tank, sucking, washing, and returning the filtered sand. The process is repeated to wash the filter sand in the rapid filtration tank.

 Further, the filter sand washing system of the present invention comprises: a rapid filter pond; a means for sucking filter sand from the quick filter pond; a sand washing device for washing the sucked filter sand; It is characterized by a means for returning the sand from which dirt has been removed to the pond. The filter sand washing system may be one that continuously performs the steps of sucking, washing, and returning the filter sand, or may be one that performs a batch process.

`` Suction of filtered sand '' is performed during backwashing of the rapid filtration pond because the filtered sand is in a state where water is filtered in a normal state. This is because there is a possibility that a portion having a small layer thickness is formed and turbidity leaks. Suction of the filtered sand can be performed even when the surface cleaning is performed simultaneously with the backwashing. Also, the `` return of filtered sand '' is performed during backwashing of the rapid filtration pond. During backwashing, the purified water is pressed into the filtration pond from the lower pressure chamber and the sand is floating. If the filter sand is returned in this state, the filter sand can form a flat layer when the backwashing is completed. The filtration sand can be returned even when backwashing and surface cleaning are performed at the same time as suction of filtration sand. "Predetermined amount" means the amount of filtration that does not affect the purification of water in the filtration pond. "Suction of filtered sand" means that the surface of the gravel layer of the rapid filtration pond has unevenness. It is preferable that the suction be performed with a suction force of a size not to be formed. The filter sand layer of the rapid filtration pond is about 60 cm, but if the filter sand is sucked with too strong suction force or if it is sucked near the boundary with the gravel layer, the gravel layer supporting the filter sand will It is preferable to absorb the filtered sand with a suction force that does not cause unevenness on the surface of the gravel layer because the sand becomes partially thin or thick. The suction of the filter sand depends on the composition of the filter layer and the suction power of the suction, but is preferably 15 to 70%, more preferably 40 to 60% of the filter sand layer from the surface of the filter sand layer. If a non-landing net is used, it can be suctioned from 100% depth, that is, just above the gravel layer. After removing the dirt from the filtered sand by the sand washing device, the filtered sand from which the dirt has been removed may be stored in a storage tank until returning to the rapid filtration pond, or the filtered sand from which the dirt has been removed may be stored in the storage tank. Without storing, the filtered sand from which the dirt has been removed may be returned before the backwashing at the time of the backwashing in which the filtered sand has been sucked is completed. When a storage tank is not provided, the steps of sucking, washing, and returning the filtered sand may be performed continuously during the backwashing.

When a storage tank is provided, it is preferable to add water or water containing an oxidizing agent so that the stored filtered sand does not come into contact with air. As the oxidizing agent, for example, chlorine is preferable. By transferring the filtered sand after washing from the sand washing device to the storage tank, it becomes possible to use the empty washing device for sand washing of other rapid filtration ponds. The manganese layer of the filter sand, which has the ability to remove manganese in raw water, is maintained by filling the storage tank with water or water containing an oxidizing agent so that the filter sand does not dry. can do. The storage tank may be large enough to store at least one predetermined amount of filtered sand sucked from the filter pond in water so as not to come into contact with air.

 The filter sand cleaning method and system of the present invention can also be applied to the filtration of filter sand from a plurality of quick filter ponds, which are connected to four to six quick filter ponds called green leaves. That is, in the method for washing filtered sand of the present invention, a predetermined amount of filtered sand is sucked from the rapid filtering pond at the time of backflow washing of the quick filtering pond for purifying water with the filtered sand, and the sucked filtered sand is sent to the sand washing device. Feeding, removing dirt from the filtered sand by the sand washing device, storing the filtered sand from which the dirt has been removed in a storage tank, and separating the stored filtered sand from the rapid filtration pond. The method is characterized in that the filter sand is returned to the rapid filtration tank during backwashing of the rapid filtration tank, and the filtration sand in the plurality of rapid filtration ponds is washed by repeating the steps of sucking, washing, storing, and returning the filtered sand.

 The reason that the stored filter sand was returned to a filter pond different from the filter pond that absorbed the filter sand was that when the filter pond was returned to the same filter pond, the filter sand that had been washed until the next backwashing of the filter pond was performed. Because it is not possible to return the filter, it takes substantially as much time to wash the filter basin one by one with filter sand. If multiple storage tanks are provided, there is no difference in the time required to wash the filter sand from a single filtration pond even if it is returned to the same filtration pond, but this requires considerable equipment costs and land. Not economic. Also, if a very large storage tank is provided, it is possible to store the filtered sand that has been sucked and washed from multiple filtration ponds, but this also requires considerable capital investment. However, in a water treatment plant where multiple rapid filtration ponds are connected, backwashing of each rapid filtration basin is not performed at the same time from the viewpoint of processing capacity, and the timing is shifted. Therefore, for example, by using this deviated timing, even if the number of the rapid filtration ponds increases, the filtration sands of all the filtration ponds can be almost the same as the time for washing all the filtration sand in one filtration basin. Cleaning can be performed, and the storage tank needs only one storage tank of the same size as that for washing the filter sand of a single filtration pond, which is preferable from the viewpoint of installation costs.

In addition, in a water treatment plant with multiple rapid filtration ponds, there may be a filtration basin with heavy filtration sand and a filtration basin with relatively little filtration sand. In such a case, Filter sand that has been sucked from a filter pond that has very bad filter sand is returned to the filter pond that has relatively little filter sand, and filter sand that has been sucked from the filter pond that has relatively little filter sand is filtered. It is more preferable to return the filter to a filter tank with heavy dirt from the viewpoint of leveling the filter sand in a plurality of filters.

 It is preferable that the repetition of each of these steps is automatically performed by sequence control. In other words, backwashing of a rapid filtration pond can be controlled with pressure loss and time as factors, and the sequence control can be used to suck, wash, and return filtered sand, or to suck, wash, store, and return filtered sand. A series of steps can be performed automatically.

 Since both suction and return of the filter sand are performed during backwashing where the filter sand is floating, it is preferable that the filter sand that has already been removed is not mixed with the filter sand that has been removed to increase the cleaning efficiency. . Therefore, it is preferable to return the filtered sand from which dirt has been removed to a position away from the position where the sand is sucked in the rapid filtration tank. That is, it is preferable that the means for sucking the filtered sand from the rapid filtration pond and the means for returning the filtered sand from which dirt has been removed are provided separately. In addition, from the viewpoint of washing efficiency of the filter sand, the position where the filter sand is sucked should be moved each time the filter sand is sucked, and the position where the filter sand after removing the dirt is returned should also be moved each time the filter sand is returned. Is preferred. That is, it is preferable that at least one of the means for sucking the filtered sand from the rapid filtration pond and the means for returning the soil-removed sand to the rapid filtration pond is movably provided.

The "sand cleaning device" includes a device as disclosed in Japanese Patent Application Laid-Open No. 10-109051, that is, a cleaning tank for storing cleaning water together with sand, and a screw rotating around a substantially vertical axis in the cleaning tank. The screw conveyor is rotated by rotating the screw conveyor at a lower portion of the screw conveyor below the surface of the washing water to raise the sand and the washing water and interpose the washing water. The dirt of the sand is removed by the contact of the sand, and the sand is flowed on the screw conveyor at the upper part of the screw conveyor on the surface of the washing water, so that the water containing the sludge is slightly contained. Means for rotating the sand at such a speed as to remove dirt from the sand by contact between the sands, and lowering the raised sand to a lower portion of the screw conveyor, and And a circulating means for ascending with the screw conveyor. It is preferred to use

 Conventionally, filter sand cleaning, which relied solely on surface cleaning and backwashing, has been replaced by a filter sand washing method according to the present invention. Is supplied to the sand washer, the dirt from the filtered sand is removed by the sand washer, and the filtered sand from which the dirt has been removed is returned to the rapid filtration pond during backwashing, and the filtered sand is repeatedly sucked, washed and returned. Since the filter sand in the filter pond is to be cleaned, the filter sand can be washed effectively without stopping the operation of the filter pond, and the cycle of filter rehabilitation work can be drastically extended. .

 More specifically, if almost all of the sand in the rapid filtration tank is automatically washed, for example, by repeatedly sucking, washing and returning the sand, the water purification function of the filtration tank can be regenerated. It becomes possible. In addition, if dirt from the filter sand is removed, it is possible to reduce the filtration resistance.Therefore, it is only necessary to carry out backwashing at the designed pressure.Therefore, it is possible to reduce the outflow of filter sand and the outflow of exfoliated sludge. Therefore, the period of rehabilitation works for filter ponds can be dramatically extended from this point.

 In addition, at the time of backwashing, a predetermined amount of filter sand is sucked from the rapid filtration pond, and the sucked filter sand is supplied to the sand washer, and the sand is removed by the sand washer, and the filtered sand is removed and stored. By storing the filtered sand in the tank and returning the stored filtered sand during backwashing of the rapid filtration pond, which is different from the rapid filtration pond that absorbed the filtered sand, and repeating the process of sucking, washing, storing, and returning the filtered sand, It is possible to efficiently wash the filter sand from a plurality of filtration ponds without stopping the operation of the filtration ponds. In addition, since the stored filtered sand is returned to the rapid filtration pond different from the rapid filtration pond that sucked the filtered sand, the time is almost the same as the time required to wash all the filtered sand in a single filtration pond. This makes it possible to wash the filtered sand from multiple filtration ponds. In addition, when returning the filter sand, the filter sand sucked from the filter pond where the filter sand is very dirty is returned to the filter pond where the filter sand is relatively less contaminated, and the filter sand is collected from the filter pond where the filter sand is less contaminated. If the filtered sand is returned to the filter pond where the filter sand is very dirty, the filter sand in the filter pond can be leveled. '

In addition, the sand cleaning method of the present invention and the sand cleaning apparatus of the system, together with the sand, A washing tank that stores washing water, a screw conveyor that rotates around a substantially vertical axis in the washing tank, and a screw conveyor that is disposed below the screw conveyor below the surface of the washing water. The rotation of the U-conveyor raises the sand and the washing water, and removes dirt from the sand by contact between the sands with the washing water interposed therebetween. Means for causing the sand to flow on the screw conveyor and rotating the sand at such a speed as to remove dirt from the sand by contact between the sands containing a small amount of water containing sludge; and If a device consisting of circulating means for lowering the screw conveyor to the lower part of the screw conveyor and raising it again by the screw conveyor is used, the sand is not crushed. Sand can be rubbed against each other to remove dirt, so that the water purification function of filtered sand can be regenerated to a state similar to fresh sand, further extending the cycle of filter tank rehabilitation work. be able to.

 In the water treatment plant, as a countermeasure against cryptosporidium, the frequency of surface washing and backwashing has been increased in the past. It is possible to maintain the temperature below this level, which helps to prevent cryptosporium and allows the water treatment plant to operate without any reduction in purification efficiency.

 BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a process diagram showing an embodiment of the filtered sand washing method of the present invention, FIG. 2 is a schematic diagram showing a first embodiment of the filtered sand washing system of the present invention, FIG. FIG. 4 is a schematic diagram showing a second embodiment of the filter sand washing system of the present invention, FIG. 4 is a process diagram showing another embodiment of the filter sand washing method of the present invention, and FIG. 6 is a process diagram showing still another embodiment of the filter sand washing method, FIG. 6 is a sectional view taken along line A--A of the rapid filtration pond shown in FIG. 2, and FIG. FIG. 8 is a diagram showing a flow of the filtration sand, and FIG. 8 is a diagram showing an example of the movement of the filtration sand between the filtration ponds.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in FIG. 2, the filter sand washing system of the present invention, as shown in FIG. 2, cleans the filter sand with dirt adhering from the rapid filtration pond 1, the rapid filtration pond 1, and the filter sand 5 with dirt adhering thereto. Stock the sand washer 3 and the filtered sand 6 washed by the sand washer 3. It is provided with a washing sand stock tank 4 to be stored, and a path 7 for returning dirt-removed sand from the washing sand stock tank 4 to the rapid filtration pond 1. (Details of the processing steps of this filter sand washing system will be described later with reference to examples.)

 Further, as shown in FIG. 3, the filter sand washing system of the present invention, as shown in FIG. 3, cleans a quick filter pond 1, a pump 2 for sucking filter sand with dirt from the quick filter pond 1, and a filter sand 5 with dirt. It may be provided with a sand washing device 3 to be cleaned and a path 7 for returning the sand from which dirt has been removed from the sand washing device 3 to the rapid filtration pond 1, that is, a device without a washing sand stock tank. In the case of a filtration sand washing system without a washing sand stock tank, it is possible to save the cost of the washing stock tank, and also to install a washing sand stock tank around the rapid filtration pond. This is a more preferable mode when there is no room.

As an example of the treatment of the filter sand cleaning system shown in Fig. 3, as shown in Fig. 4, for example, the surface cleaning and backwashing of the filtration pond 1 are performed within the time (eg, 15 to 25 minutes). the 1 m ³ of contaminated filtration sand by suction from the filtration reservoir 1 by the pump 2, sends the filtration sand sucked by the pump 2 to the sand washing device 3, washing in a short time, the sand washing device 3 (about 10 minutes) Before the surface cleaning and backwashing of the filtration pond 1 is completed, the filtered sand (clean sand) after the washing can be returned to the filtration pond 1. In this way, by performing the suction of the sand and the return of the clean sand during the time when one surface cleaning and backwashing are being performed, it becomes possible to wash the sand in a short time.

 Alternatively, as shown in Fig. 5, during the time during which surface cleaning and backwashing of filter pond 1 are performed (eg, 7 to 10 minutes), contaminated filtered sand is continuously pumped from filter pond 1 using pump 2. The filtered sand sucked by the pump 2 is continuously sent to the sand washing device 3 and continuously washed by the sand washing device 3, and the purified sand is filtered before the surface washing and backwashing of the filtration pond 1 are completed. The treatment can also be performed by a process of continuously returning to pond 1. If the treatment is performed continuously during the time during which the surface cleaning and the backwashing are performed, it is possible to wash a larger amount of soil in a short time.

As shown in FIG. 6, the rapid filtration pond 1 has a filtration sand layer 12 as a filtration layer, and 13 to 16 gravel layers supporting the filtration sand layer 12. The filter sand layer 12 is made of sand having an effective diameter of 0.6 mm and a uniformity coefficient of 1.5 or less. The gravel layer consists of four layers with different particle sizes, and the filter sand is used as a support layer. Is prevented from entering the water collection device (not shown, but the device for collecting the purified water is provided further below the rapid filtration pond 1). The gravel layers 13 to 16 are selected to be nearly spherical, hard, clean, and homogeneous in order to perform backwashing evenly. The effective diameter is 2.0 to 3.511111, the gravel layer 14 is 3.5 to 7.0 difficult, the gravel layer 15 is 7.0 to 13.Omm, and the gravel layer 16 is 13.0 to 20.Omm. Coarse grains are spread in the lower layer so that there is no irregularity. On the filtration sand layer 12, water that has been pretreated by flocculating and precipitating the turbidity of the raw water with a flocculant is introduced. Above the filter sand layer 12, a washing pipe 22 for spraying washing water for washing the filter sand layer from the surface so that the filter sand layer is hit from the surface during washing, and washing drainage for washing the surface and backwashing. An exhaust trough 21 is provided.

 Next, a general purification process of raw water will be briefly described. After the turbidity of raw water drawn from rivers and lakes into the coagulation sedimentation ponds is condensed and precipitated by a coagulant such as polyaluminum chloride, the supernatant is sent to the filtration sand layer 12 of the rapid filtration pond 1 . This filtration sand layer 12 removes fine suspended matter that could not be removed by the coagulation sedimentation basin. The filtered water is collected in a water collecting device provided at the lower part of the rapid filtration pond 1. The collected water is disinfected with chlorine and stored in a reservoir. The filtration speed is usually between 120 and 150 m / day. In general, at this filtration speed, when the head loss reaches 1.5 m at regular intervals, the filtration for water purification is stopped, and washing water is injected from the lower pressure chamber of the rapid filtration pond to lift the filter sand, and the sand is removed. Washing is performed by mixing with sand. The surface washing is performed by spraying washing water from the front washing tube 22 onto the surface of the filter sand 12 at the time of backwashing or at a certain time during the backwash cycle. Washing drainage 11 after surface washing and backwashing is discharged from trough 21. When the washing is completed, the pretreated raw water is sent again and the filtration is resumed. The process of water purification and washing is usually automated, and the timing of surface washing and backwashing is set in advance depending on the condition of the raw water at the water treatment plant where the water is treated by the rapid filtration method, or the head loss is fixed. It is set so that surface cleaning and backwashing are automatically performed when the above occurs.

As shown in Table 2, the selection standard for filtered sand (JWWA A 103-1988) is that the washing turbidity is 30 degrees or less, the hydrochloric acid solubility is 3.5% or less, the effective diameter is 0.45 to 0.70, and the uniformity coefficient is 1.7 It is stipulated below. Regularly perform general surface cleaning and backwashing as described above. Even after renovation every 10 years, the turbidity of washing was 1480 degrees, the solubility of hydrochloric acid was 9.7%, and the effective diameter was 0.533. With an equality coefficient of 1.485, turbidity adheres to the filtered sand and becomes considerably dirty.

 [Table 2]

このように、 濁質が付着した濾過砂を使用し続けると濁質による目詰まり現象が 起こり、 急激な損失水頭の上昇により逆流洗浄の回数が増加し、 その逆流洗浄の 水圧により砂利層にも影響が出て不陸の形成を早める。 不陸の形成により砂利層 が厚い部分では砂層が薄くなり、 その部分での濾過が不十分となり、 また汚泥物 質や濾過砂から剥離した吸着物質により、 ブレークスルーが起こって濾過水に悪 影響を及ぼすようになる。 このような状態になると、 更生工事が必要となってく る。

As described above, if filter sand with turbidity is continued to be used, clogging by the turbidity occurs, and the number of backwashing increases due to a sudden rise in head loss, and the gravel layer is also formed by the water pressure of the backwashing. Influence hastens the formation of unevenness. Due to the formation of unevenness, the sand layer becomes thinner in the part where the gravel layer is thicker, and the filtration in that part becomes insufficient, and the sludge substances and the adsorbed substances separated from the filter sand cause breakthrough, which adversely affects the filtered water. Will be exerted. In such a situation, rehabilitation work will be required.

 The following is an example of a filter sand washing system in which a part of the filter sand is washed with a sand washing device, and the soil-removed sand is returned to the filter tank again, in addition to the normal washing process described above. .

 (Example 1)

The sand washing device 3 includes a washing tank disclosed in Japanese Patent Application Laid-Open No. 10-109051 for storing washing water together with sand, a screw conveyor rotating around a substantially vertical axis in the washing tank, and a screw conveyor. At the lower part of the screw conveyor below the surface of the washing water, the sand and the washing water are raised by the rotation of the screw conveyor, and the sand is contacted by the sand with the washing water interposed therebetween. The dirt is removed, and the sand is flowed on the screw conveyor at the upper part of the screw conveyor on the surface of the washing water, and the sand containing the sludge-containing water is slightly contacted with the sand. Means for rotating at such a speed as to remove dirt, A device capable of realizing a kneading-washing method was used, comprising circulating means for lowering the raised sand to the lower portion of the screw conveyor and again raising the sand on the screw conveyor. As shown in Fig. 1 and Fig. 2, during the time (7 to 10 minutes) during which the surface cleaning and backwashing of filter basin 1 are performed, lm ³ of dirty filter sand is removed at the corner of filter basin 1. (La) was pumped by pump 2. The suction of the filtered sand was performed at a depth of about 10 cm from the upper part of the gravel layer 13 (the thickness of the filtered sand layer was 60 cm). The filtered sand (5) sucked by the pump 2 was sent to the sand washing device 3 and washed by the sand washing device 3 for about 1 hour. As shown in Table 3, the washing turbidity of the suctioned filter sand (5) was reduced from 1480 ° C to 11 ° C, the hydrochloric acid solubility was changed from 9.7% to 2.8%, and the coefficient of uniformity was increased by washing for about 1 hour. From 1.485, it can be seen that washing is performed to the same level as that of fresh sand.

 [Table 3]

The filtered sand (6a) after washing was stored in a washing sand stock tank filled with water. Approximately 48 hours after the filtration performed in the rapid filtration tank 1, the filtration was stopped, and surface cleaning and backwashing were started again. At this time, the corner (lb) opposite to the corner (la) ) Was returned to the filtration pond 1. By repeating this cycle, almost all the sand of 60 m ^{3 in} the filter pond 1 was washed in about 120 days.

 (Example 2)

Filtered sand cleaning was performed in the same manner as in Example 1 except that the specific sand cleaning device used in Example 1 was changed to a conventional sand cleaning device using a jet stream. As shown in Table 4, there was a slight significant difference compared to the one using the specific sand washing device of Example 1, but the sand was remarkably washed. However, in the case of Example 1, there was almost no change in the particle size of the sand, but the effective diameter was reduced and the uniformity coefficient was increased after long-time cleaning. With conventional sand washing equipment using jet water, sand is washed during washing. It can be seen that the sand crushed due to collision with the pipe wall or the like.

 [Table 4]

 Next, a method and a system for filtering sand in the case of a plurality of rapid filtration ponds will be described with reference to FIGS. FIG. 7 is a diagram showing the flow of the filter sand corresponding to a plurality of filter ponds, and FIG. 8 is a diagram showing an example of the movement of the filter sand between the filter ponds. Here, as an example, a filter sand system combining six quick filter ponds A to F as shown in Fig. 7 and one sand washing device and one storage tank is described. The principle is exactly the same whether the number is larger or smaller.

Filtration ponds AF are filtration ponds where backwashing is performed every 48 hours. As shown in Fig. 7, the interval between backwashing of each filtration pond is 8 hours. First, a predetermined amount of filter sand is sucked from filter pond A. The sucked filter sand is washed for 1 hour with a sand washing device. The filtered sand from which the dirt has been removed is stored in a storage tank filled with water or water containing an oxidizing agent. The stored filter sand after washing is returned to Filter Pond B where backwashing starts after 8 hours from backwashing of Filter Pond A. During backwashing of filtration basin B, washed filter sand is returned and dirty filter sand is absorbed. The filtered sand sucked in the filtration basin B is washed for 1 hour with a sand washing device, and the washed filtered sand is stored in a storage tank filled with water or water containing an oxidizing agent. The stored filter sand after washing is returned to Filter Pond C where backwashing starts after 8 hours from backwashing of Filter Pond B. During backwashing of filter pond C, the washed filter sand is returned and dirty filter sand is absorbed. In this way, after 48 hours, a predetermined amount of the filter sand is absorbed in all of the filter ponds A to F, and a predetermined amount of the filter sand after the washing is released. . This process can be repeated to wash all the filtered sand in the filtration ponds AF. In this way, multiple filtration ponds By matching the timing of backwashing, it is possible to wash the filter sand in multiple filtration ponds in a time that is almost the same as the time required to wash the filtration sand in a single filtration pond.

 If the filter sand from the filter pond is heavily soiled in the order of filter AF, filter sand after washing of filter A is filtered to filter E as shown in Fig. 8, and then filtered. Filter sand after washing of Pond E was returned to Filter Pond C, filtered sand after washing of Filter Pond C to Filter Pond D, and filtered sand after washing of Filter Pond D to Filter Pond A. ~ F can be leveled.

 In addition, at least three steps: a step of sucking filter sand from the rapid filtration pond, a step of washing the filter sand with a sand washing device, and a step of returning the filtered sand from which dirt has been removed to the rapid filter pond, or filtering from the rapid filter pond. Sequence control automatically performs four steps: sucking sand, washing the filtered sand with a sand washing device, storing the washed filtered sand in a storage tank, and returning the filtered sand from which dirt has been removed to the rapid filtration pond. By doing so, it is possible to maintain the filtered sand in the same state as fresh sand for a long period of time, and the cycle of rehabilitation work can be drastically extended.

Claims

The scope of the claims  (1) At the time of backwashing of a rapid filtration pond for purifying water with filter sand, a predetermined amount of filter sand is sucked from the rapid filtration pond, the sucked filter sand is supplied to a sand washing device, and the sand is washed by the sand washing device. Therefore, the filter sand is removed from the filter sand, and the filter sand from which the filter sand is removed is returned to the rapid filtration tank during backwashing of the rapid filtration tank, and the steps of sucking, washing, and returning the filter sand are repeated. A method for washing filtered sand, comprising washing filtered sand in a rapid filtration tank.  (2) As the sand washing device, a washing tank that stores washing water together with sand; a screw conveyor that rotates around a substantially vertical axis in the washing tank; and a screw conveyor that is below the surface of the washing water. The lower part of the screw conveyor, the rotation of the screw conveyor raises the sand and the washing water, and removes dirt from the sand by contact between the sands with the washing water interposed therebetween; The sand is made to flow on the screw conveyor at the upper part of the screw conveyer on the water surface at a speed such that the sand containing a small amount of water containing sludge contacts the sand to remove dirt from the sand. A rotating means, and a circulating means for lowering the raised sand to the lower part of the screw-conveyor and raising the sand again by the screw conveyor. Filtration sand washing process ranging first claim of claim, characterized in that the use of that device.  (3) After removing dirt from the filtered sand by the sand washing device, the filtered sand from which the dirt has been removed is stored in a storage tank until returned to the rapid filtration tank. Item 3. The method for washing filtered sand according to Item 2.  (4) The filtration according to claim 1 or 2, wherein the filtered sand from which the dirt has been removed is returned before the backwashing in the backwashing in which the filtered sand is sucked is completed. Sand washing method.  (5) The method according to claim 4, wherein the steps of sucking, washing, and returning the filtered sand are performed continuously during the backwashing. (6) The method according to claim 3, wherein the storage tank is filled with water or water containing an oxidizing agent so that the stored filter sand does not come into contact with air. (7) A predetermined amount of filter stones is sucked from the rapid filtration pond at the time of backwashing of the rapid filtration pond for purifying water with the filter sand, and the sucked filter sand is supplied to a sand washing device, and the sand washing device is provided. Thus, the filter sand is removed from the filter sand, and the filter sand from which the filter sand is removed is stored in a storage tank. A method for cleaning filtered sand, comprising returning to a rapid filtration tank and repeating the steps of sucking, washing, storing, and returning the filtered sand to filter sand in a plurality of rapid filtration ponds.  (8) The filtered sand cleaning method according to any one of claims 1 to 7, wherein the repetition of each step is automatically performed by sequence control.  (9) The filter sand according to any one of claims 1 to 8, wherein the filter sand from which the dirt has been removed is returned to a position in the rapid filtration tank that is away from a position where the filter sand is sucked. Filter sand washing method.  (10) The filtered sand cleaning method according to any one of claims 1 to 9, wherein a position where the filtered sand is sucked is moved every time the filtered sand is sucked. (11) The filtered sand cleaning method according to any one of claims 1 to 10, wherein a position to return the filtered sand from which the dirt has been removed is moved every time the filtered sand is returned. .  (12) The suction of the filtered sand is performed with a suction force having a magnitude that does not cause discomfort on the surface of the gravel layer of the rapid filtration tank. The method for washing filtered sand according to any one of the preceding claims.  (13) A quick filtration pond, means for sucking filtered sand from the quick filtration pond, a sand washing device for washing the sucked filtered sand, and filtration for removing dirt from the sand washing device to the quick filtration pond. And a means for returning the sand. (14) The storage device according to claim 13, further comprising a storage tank for storing the filtered sand from which dirt has been removed by the sand washing device before returning the filtered sand to the rapid filtration tank. Filter sand washing system. (15) The storage tank according to claim 14, wherein the storage tank is provided with a unit for supplying water into the storage tank so that filtered sand in the storage tank does not come into contact with air. Filter sand washing system as described. (16) The filter sand washing system according to any one of claims 13 to 14, wherein the rapid filtration pond is provided in plurality.  (17) The filter sand washing system includes a step of sucking filter sand from the rapid filtration tank, a step of washing the filter sand with the sand washing device, and a step of returning the filtered sand from which dirt has been removed to the rapid filtration tank. At least three steps, a step of sucking filter sand from the rapid filtration tank, a step of washing the filter sand with the sand washing device, a step of storing the washed filter sand in a storage tank, and a step of removing dirt to the rapid filtration tank. The method according to any one of claims 13 to 16, further comprising control means for automatically performing at least four steps of returning the removed filtered sand by sequence control. Filter sand washing system. .  (18) The means for sucking the filtered sand from the rapid filtration pond and the means for returning the sand from which dirt has been removed to the rapid filtration pond are provided at positions separated from each other in the rapid filtration pond. The filtration sand cleaning system according to any one of claims 13 to 17.  (19) At least one of a means for sucking filtered sand from the rapid filtration pond and a means for returning sand from which dirt has been removed to the rapid filtration pond is movably provided. Item 19. The filtration and washing system according to any one of Items 3 to 18. (20) The sand washing device comprises: a washing tank for storing washing water together with sand; a screw conveyor rotating around a substantially vertical axis in the washing tank; The lower part of the screw conveyer raises the sand and the washing water by rotating the screw compare, and removes dirt from the sand by contact between the sands with the washing water interposed therebetween. The sand is made to flow on the screw conveyor at the upper part of the screw conveyor on the surface of the water, at such a speed that the sand is removed by contact between the sands containing a small amount of water containing sludge. Means for rotating, and circulating means for lowering the raised sand to the lower part of the screw compare and raising the sand again with the screw compare. The filtered sand washing system according to any one of claims 13 to 19, characterized in that the filtered sand washing system is characterized in that: