Filtration device

Abstract

To provide a filtration device for water purification capable of preventing deterioration of filtration performance by eliminating remarkable filtration clogging.SOLUTION: The filtration apparatus includes a filtration tank 2 to which water 14 to be treated is supplied from an upper part and from which treated water obtained by subjecting the water to be treated to filtration treatment is made to flow out from a lower part. A filter material-filled portion 4 that performs a filtration treatment of the water to be treated, a cleaning water inflow pipe 6 that allows cleaning water to pass through the filter material-filled portion in an upward flow, a cleaning water discharge pipe 7 that discharges the cleaning water from a portion above the filter material-filled portion, a chemical storage portion 8 that stores a chemical for cleaning the filter material-filled portion, and a path for supplying the chemical from the chemical storage portion to the filtration tank.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a filtration device, particularly a sand filtration device, used in water purification treatment. [Background technology]

[0002] Generally, in water purification, a rapid filtration method that combines coagulation sedimentation and rapid filtration is widely used.

[0003] In the rapid filtration method, first, aluminum sulfate (aluminum sulfate), polyaluminum chloride (PAC), or an iron-based inorganic coagulant (hereinafter referred to as "coagulant" refers to inorganic coagulants) is injected into raw tap water (hereinafter referred to as "raw water") containing suspended solids, causing it to react with the suspended solids and form coagulated flocs. Next, these coagulated flocs are separated by gravity through a coagulation and sedimentation process, and the coagulated and sedimented water is passed through a filter tank filled with filter media to remove the suspended solids, thereby removing the coagulated flocs.

[0004] On the other hand, in recent years, there has been a trend to use polymer flocculants in combination as coagulation aids in order to improve the ability to respond to fluctuations in raw water, operational control, and filtration (water quality).

[0005] For example, in the rapid filtration method shown in Figure 5, raw water undergoes rapid filtration in a filter basin, including coagulation and sedimentation, and sand filtration, before being converted into drinking water by adding a disinfectant. In domestic water purification processes, inorganic coagulants only need to be added before the water enters the filter basin. When coagulation and sedimentation are combined before filtration, as shown in Figure 5, they are often added before the coagulation and sedimentation process (before the coagulation operation). Furthermore, coagulation aids and additional coagulants before the water enters the filter basin are not necessarily required. Furthermore, if the amount of solids to be removed during water purification is small, the coagulation and sedimentation process may be bypassed or not installed at all. pH adjusters and oxidants may also be added as needed to ensure the water purification process is successful.

[0006] In the filtration equipment used in water purification, turbidity in raw water is removed mainly by adhesion to the filter media and by the sieving action of the filter layer.

[0007] Filter basins in filtration systems can be broadly classified into gravity filters, pressure filters, and natural balance filters. All of these filters have the same basic configuration. For example, as shown in the schematic diagram of Figure 6, a conventional filtration system 30 is composed of a filter tank 31, a filter inlet pipe 32, a filter outlet pipe 33 (also referred to simply as an outlet pipe or outlet channel), a wash water inlet pipe 34, a wash water outlet pipe 35 (the outlet pipe within the filter tank is also referred to as a drainage trough), a filter media filling section 36, measuring instruments such as a water level gauge 37, and, although not shown, a water collection device, a drain pipe, a support layer below the filter tank 31, support gravel, etc. If necessary, an air scrubbing device (air inlet pipe) for air scrubbing and a surface cleaning pipe for cleaning the filter media surface may also be attached. Furthermore, the filter layer is composed of filter media, and may be a single-layer filter layer made of one material or a multi-layer filter layer made of multiple materials.

[0008] The raw water or coagulation-sedimentation-treated water 38 to be treated flows into the upper water area (freeboard) 41 of the filter tank 31 via the filtration inlet pipe 32. During this time, an inorganic coagulant 39 and / or a polymer coagulant 40 may be added. The inflowing coagulation-sedimentation-treated water, i.e., the water to be treated 38, flows downward through the filter media 42 in the filter media-filled section 36 and is discharged from the filtration outlet pipe 33 as filtrate 43.

[0009] As filtration continues, the filtration layer becomes clogged with turbid matter separated from the treated water, and when the filtration function can no longer be maintained due to water quality or water volume, filtration is stopped and the filtration layer is cleaned to restore the turbidity removal capacity.

[0010] The filter media is generally cleaned by a method known as backflow cleaning (also called backwashing), in which cleaning water is passed in the opposite direction to the filtration direction to remove the suspended solids trapped in the filter layer from the media and then the removed suspended solids are discharged from the media. After the filter cleaning, raw water is again introduced through the filter inlet pipe to start filtration again.

[0011] For example, in Figure 6, cleaning water flows upward into the filter tank 31 from a cleaning water inlet pipe 34 at the bottom of the filter tank 31 to clean the filter media 42. After cleaning, the cleaning water is discharged as cleaning wastewater 44 from a cleaning water outlet pipe 35 above.

[0012] Patent Document 1, for example, is an example of a method for cleaning a filter basin. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-97370 Summary of the Invention [Problem to be solved by the invention]

[0014] In conventional water purification filtration systems, when significant filter blockage due to turbidity or coagulants progressed, a large amount of backwash water was pumped in to remove as much of the blockage as possible and discharge it out of the system. However, this approach increased the amount of wastewater, leading to a decrease in the water recovery rate ((filtered amount - backwash water amount) / filtered amount) and an increased load on the drainage equipment.

[0015] Furthermore, unlike small-scale test equipment, in actual equipment the amount of backwash water per unit time is determined by the capacity of the backwash pump. Therefore, when a filter blockage occurs, it is difficult to temporarily increase the amount of backwash water per unit time. As a result, the only option is to extend the backwash time. This means that the time taken for the backwash process in the overall filtration process becomes relatively longer, which leads to the problem of reduced filtration efficiency.

[0016] Furthermore, because increasing the amount of backwash water per unit time is more effective at removing blockages than extending the backwash time, the effect of backwashing by extending the backwash time is small, and filter blockages are not fully resolved. As a result, filter blockages cannot be fully resolved, resulting in issues such as a decline in water quality and a reduction in filtration duration after filtration resumes. In addition, extending the backwash time has almost no effect on the removal of mud balls caused by poor coagulation, etc., and this has led to issues such as the need for a large-scale overhaul to clean and replace the filter media in order to remove filter blockages and mud balls accumulated in the filter layer and restore filtration function.

[0017] For this reason, when it is expected that the amount of solids to be separated from the liquid during filtration will be large, surface cleaning equipment and air cleaning equipment are installed in addition. However, in light of the recent occurrence of sudden heavy rainfall due to global warming and the introduction of treatment methods that use coagulation aids such as polymer coagulants that have a high adhesive force to the filter media, there is a demand for filtration equipment with stronger cleaning capabilities.

[0018] The present invention has been made in consideration of the above-mentioned conventional problems, and its object is to provide a water purification filtration device that can eliminate significant filtration blockage and prevent a decrease in filtration performance. [Means for solving the problem]

[0019] That is, the above problem is solved by: The filtration device of the present invention comprises: a filtration tank into which water to be treated is supplied from an upper portion and into which treated water obtained by filtering the water to be treated flows out from a lower portion; A filter material filling section filled inside the filtration tank to perform filtration of the water to be treated; a cleaning water inlet pipe for passing cleaning water through the filter medium packed portion in an upward flow; A cleaning water discharge pipe that discharges cleaning water from above the filter medium filling portion; a chemical storage section for storing a chemical for cleaning the filter medium packed section; a path for supplying the chemical from the chemical storage unit to the filtration tank; A filtration device comprising: This can be solved by:

[0020] Another aspect of the present invention relates to the above-mentioned filtration device, wherein the path is a path for supplying the chemical into the filtration tank from above the filter medium-filled section.

[0021] Another aspect of the present invention relates to the above-mentioned filtration device, wherein the path is a path for supplying the chemical into the filtration tank from below the filter medium-filled portion.

[0022] Another aspect of the present invention relates to the above-mentioned filtering device, wherein the path is a path for supplying the chemical from a pipe installed inside the filter medium-packed section.

[0023] In another aspect of the present invention, the filter material packed section has a structure in which two or more types of filter material having different shapes are stacked in two or more layers in the direction of gravity, The present invention also relates to the above-mentioned filtering device, wherein the path is a path for supplying the chemical to at least one of filter medium interfaces between the two or more types of filter medium having different forms inside the filter medium packed section.

[0024] Another aspect of the present invention relates to the above-mentioned filtering device, further comprising an agitation washing device that physically washes the filter media by spraying washing water directly onto the filter media-packed section.

[0025] Another aspect of the present invention relates to the above-mentioned filtering device, further comprising an air supply pipe for blowing gas from below the filter medium-packed section.

[0026] Yet another aspect of the present invention relates to the above-mentioned filtration device, further comprising an accelerating drain pipe for discharging the cleaning water remaining on the top of the filtration layer after cleaning with chemicals. [Effects of the Invention]

[0027] The present invention provides a filtration device with a more powerful cleaning function that is adapted to recent environmental changes. That is, even if significant filtration blockage occurs in the filtration device, the filtration device can be cleared and the device can be restored to clean filtration processing. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram showing the concept of the filtration device of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a preferred embodiment of the filtration device of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing another preferred embodiment of the filtration device of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing another preferred embodiment of the filtration device of the present invention. [Figure 5] FIG. 5 is a flow diagram showing a conventional rapid filtration method. [Figure 6] FIG. 6 is a schematic diagram showing a conventional filtering device. DETAILED DESCRIPTION OF THE INVENTION

[0029] [Term etc.] Filtration equipment is used as a means of solid-liquid separation in a variety of fields, and there are many terms and phrases related to the elements involved.

[0030] In the present invention, terms relating to the filtration device and the elements included therein can also be rephrased as follows, for example.

[0031] The filtration device refers to the entire facility for filtration, and can also be referred to as a filtration facility or a filtration facility.

[0032] The filtration tank is an element that performs the filtering function, and can also be called a filtration pond.

[0033] The filter medium packed section is an element that is packed with filter medium, and can also be referred to as a filtration layer or a filter layer.

[0034] The water to be treated is water that flows into a filtration tank and is treated, and can also be referred to as raw water for tap water, mixing basin effluent, coagulation sedimentation treated water, or filtration basin inflow water.

[0035] The filtration inlet pipe is a pipe for passing the water to be treated into the filtration tank, and may also be referred to as an inlet pipe, a filtrate inlet pipe, or an inlet conduit.

[0036] The wash water is water for washing the filter medium, and can also be called backwash water.

[0037] The cleaning water inlet pipe is a pipe for passing cleaning water, and may also be referred to as a backwash water inlet pipe, a backwash water introduction pipe, or a cleaning pipe.

[0038] [Full view of the filtration equipment] In the filtration device of the present invention, in addition to conventional structures such as structures for cleaning with water or air, a structure for injecting chemicals to remove turbidity is also provided, so that the entire device has a structure that can effectively avoid or eliminate filtration blockages.

[0039] In FIG. 1, which shows a schematic concept of the filtration device of the present invention, the filtration device 1 comprises a filtration tank 2, a filtration inlet pipe 3, a filter medium filling section 4, a filtration outlet pipe 5, a cleaning water inlet pipe 6, a cleaning water outlet pipe 7, and further comprises a chemical storage section 8, paths 9, 10, 11, 12, and preferably an air supply pipe 13.

[0040] 1 is a schematic diagram, and therefore does not include illustrations of main valves, automatic valves, instrumentation, etc., but an actual filtration device will naturally be equipped with these commonly used devices. The same applies to Figures 2 to 4 and 6.

[0041] The filtration tank 2 is a tank into which the water to be treated 14 is supplied from the top and into which the filtered water to be treated 14 flows out from the bottom.

[0042] The filtration inlet pipe 3 is provided with an inlet above the filtration tank 2 and is a pipe for introducing the water to be treated 14 below the filtration tank 2.

[0043] The filter media filling section 4 is filled with filter media 15 and disposed inside the filter tank 2, and serves as a means for filtering the water to be treated 14 introduced via the filtration inlet pipe 3.

[0044] The filtration outflow pipe 5 is a means for causing the filtrate 16 to flow out of the filtration tank 2 after the water to be treated 14 has been filtered in the filter medium packed section 4 .

[0045] The cleaning water inlet pipe 6 is a pipe for passing cleaning water upward through the filter media packed section 4 in order to backwash the filter media 15 packed in the filter media packed section 4, and the introduced cleaning water flows upward through the filter media packed section 4. A part of this cleaning water inlet pipe 6 may also serve as the above-mentioned filtration outlet pipe 5, which is preferable because it reduces the number of pieces of equipment.

[0046] The cleaning water discharge pipe 7 corresponding to the cleaning water inlet pipe 6 is a pipe for discharging the cleaning water that has passed through the filter media filled section 4 from above the position of the filter media filled section 4 to the outside of the filter tank 2 as cleaning wastewater 17.

[0047] Furthermore, the filtration device 1 may also have means for injecting a polymeric flocculant 18 at any point in the filtration inlet pipe 3 .

[0048] As described above, the filtration device 1 of the present invention is characterized in that it includes a chemical storage section 8 that stores a chemical used to clean the filter media 15 packed in the filter media packing section 4 and remove adhering turbidity, and paths 9, 10, 11, and 12 for supplying the chemical from the chemical storage section 8 to the filtration tank 2. The chemical from the chemical storage section 8 passes through at least one of the paths 9, 10, 11, and 12 and is injected into a specific location in the filtration tank 2. In practice, these paths are also referred to as "chemical injection pipes."

[0049] 1 shows that these paths are arranged in a plurality of locations, but in reality, the locations can be determined or changed as appropriate depending on the location or degree of adhesion of suspended solids to the filter media packed section 4, and are arranged so that the suspended solids can be injected into at least one location in the filter media packed section 4. Furthermore, these paths may be arranged in any combination of two or more locations shown in FIG.

[0050] For example, the path may be arranged so that the chemical is injected from above the filter medium, or so that the chemical is injected horizontally through the side wall of the filtration tank 2. Alternatively, the path may be arranged so that the chemical is injected into the cleaning water inlet pipe 6, which is used to inject cleaning water during backwashing of the filtration tank (e.g., path 12).

[0051] That is, although details will be described later, as shown in Fig. 2, such a path can be a path that supplies the chemical into the filtration tank 2 from above the filter media-packed section 4 (path 9). Alternatively, as shown in Fig. 3, such a path can be a path that supplies the chemical into the filtration tank 2 from below the filter media-packed section (path 11). Also, as shown in Fig. 4, such a path can be a path that supplies the chemical from a pipe installed inside the filter media-packed section 4 (path 10). Furthermore, as a more practical embodiment, in a filter media-packed section structured such that two or more layers of two or more types of filter media with different shapes are stacked in the direction of gravity, such a path can be a path that supplies the chemical to the filter media boundary surface inside the filter media-packed section.

[0052] Here, the "shape" of the filter media refers to the physical and chemical properties of the filter media, such as particle size (effective diameter, uniformity coefficient, maximum and minimum diameter, etc.), density, abrasion rate, hydrochloric acid solubility, fluidity, and material (anthracite, gravel, sand, manganese sand, garnet, ceramics, activated carbon, etc.).

[0053] In the present invention, the filtration device 1 preferably further includes an agitation washing device (not shown) that sprays washing water directly onto the filter medium packed section 4 to physically wash the filter medium.

[0054] Furthermore, in addition to the chemical storage section and pathways described above, the filtration device 1 preferably includes an air supply pipe 13 for blowing in gas, such as air, from below the filter medium-filled section 4. This configuration allows the chemical injected from the pathway to be diffused quickly and uniformly within the filtration tank 2 by the blown-in air 19. Furthermore, this configuration allows the chemicals generated by air stripping after backwashing to be discharged into the atmosphere, reducing the chemical concentration in the cleaning water and reducing the post-treatment of chemical wastewater.

[0055] Preferably, the filtration device 1 further includes an accelerating drain pipe 20 for discharging cleaning water containing a large amount of turbidity that remains in the upper part of the filtration tank 2 after cleaning with chemicals.

[0056] After washing, it is usually desirable for the wash water to be completely discharged from the filter tank 2 through the wash water discharge pipe 7 as wash wastewater. However, sometimes some of the wash wastewater remains at the top of the filter tank 2 without being discharged. This remaining wash water must be removed immediately because it may become a source of turbidity and adhere to the filter media again. The accelerating drain pipe 20 is a pipe for introducing this wash wastewater as accelerating drain 21 and discharging it outside the filter tank 2. However, to prevent the filter media 15 from being discharged along with the wash wastewater, the accelerating drain pipe 20 is preferably positioned higher than the top of the filter media-packed section 4 in the filter tank 2. For example, the accelerating drain pipe 20 is preferably positioned 50 to 200 mm above the top of the filter media-packed section 4.

[0057] As described above, the filtration device of the present invention mainly has a cleaning water inlet pipe 6 and a cleaning water outlet pipe 7 as components for physical cleaning, and further mainly has a chemical storage section 8 and paths 9, 10, 11 or 12 as components for chemical cleaning.

[0058] Of these, the path can be arranged so that the chemical is supplied into the filtration tank 2 from above the filter media filling section 4, as shown in Figure 2. Here, the chemical is introduced from the chemical storage section 8 to the path 9 (upper chemical injection pipe) via the main chemical injection pipe 22.

[0059] When inorganic coagulants are used alone and coagulation is poor, some of the fine suspended solids are not incorporated into the flocs, and penetrate into the filter layer as suspended solids. In addition, even when multi-layer filtration or high-speed filtration is used, some of the suspended solids may penetrate into the filter layer. The filtration device shown in Figure 3 is useful for dealing with such situations.

[0060] Furthermore, in coagulation treatment using a polymer coagulant in combination, the coagulated flocs grow and become larger, and as filtration continues, many of the coagulated flocs tend to accumulate on the top surface of the filter medium 15, resulting in so-called cake filtration. In particular, when the raw water is river water whose raw water turbidity fluctuates greatly, the turbidity of the inflow into the filter basin also increases, and cake filtration tends to occur. This tendency is particularly pronounced when a polymer coagulant is used in combination, as the cake layer tends to become stronger.

[0061] In this way, when a large amount of filter-clogging substances accumulates on the upper part of the filter medium 15, it is possible to send a controlled concentration of chemicals directly to the area where filter-clogging substances should be removed by injecting chemicals through the path 9. This makes it possible to reduce the amount of chemicals used.

[0062] 2, the reaction characteristics of the chemicals used must be taken into consideration, but an existing surface cleaning pipe (not shown) can also be used as path 8. The surface cleaning pipe was originally intended to assist in the removal of deposits on the upper surface of filter medium 15 by the water jet force from the pipe and its rotational motion. If such a surface cleaning pipe is used, the installation of a new path 9 can be omitted.

[0063] 3, which shows another arrangement of the pathway, the pathway supplies the chemical into the filtration tank 2 from below the filter medium filling section 4. In this case, the chemical is introduced from the chemical storage section 8 to the pathway 11 (lower chemical injection pipe) via the chemical injection main pipe 22.

[0064] When inorganic coagulants are used alone and coagulation is poor, some of the fine suspended solids are not incorporated into the flocs, and penetrate into the filter layer as suspended solids. In addition, even when multi-layer filtration or high-speed filtration is used, some of the suspended solids may penetrate into the filter layer. The filtration device shown in Figure 3 is useful for dealing with such situations.

[0065] Furthermore, in coagulation treatments using polymer coagulants, the coagulated flocs become stronger and are more difficult to separate from the filter media. To address this, it is common to use a filter layer consisting of multiple filter media, with the particle size of the filter media in the upper filter layer being coarser to expand the coarse filtration area and increase the filtration rate, thereby achieving more efficient filtration.

[0066] As a result, compared to when inorganic coagulants are used alone, there is a greater concern that turbidity will flow into the bottom of the filter layer. In particular, in the water supply sector, where river water is used as raw water and turbidity fluctuates, it is difficult to constantly optimize the coagulation conditions, and there is a risk that the entire filter layer or even the lower layers will be contaminated.

[0067] In this way, when filter-clogging substances have accumulated to the bottom of the filter layer, chemicals can be injected through path 11, allowing a controlled concentration of chemicals to be sent directly to the area where filter-clogging substances must be removed. This reduces the amount of chemicals used. Furthermore, in domestic water purification plants, the lower layer of the filter basin is the final barrier for filtration, and if this layer is contaminated, it will affect the quality of tap water. Therefore, this is also effective in terms of ensuring the safety of tap water quality. Furthermore, it is possible to minimize secondary contamination of the bottom of the filter layer caused by turbidity separated from the surface of the filter media by the action of the chemicals.

[0068] 4, which shows yet another arrangement of the pathways, the pathway supplies the chemical from a pipe installed inside the filter medium-packed section 4. Here, the chemical is introduced from the chemical storage section 8 into pathway 10 (internal chemical injection pipe) via chemical injection main pipe 22.

[0069] Even when inorganic coagulants are used alone, if the raw water is expected to contain a large amount of turbidity, multi-layer filtration (for example, two-layer filtration) will be selected, resulting in deep filtration. The filtration device shown in Figure 4 is also suitable for such situations.

[0070] Furthermore, in the coagulation treatment using a polymer coagulant, the cake layer tends to become strong. In this case, so-called depth filtration is often adopted, in which the upper layer of the filter layer has a larger particle size for coarse filtration, while the lower layer of the filter layer is configured as fine sand filtration, thereby promoting the inflow of suspended solids into the filter layer and retaining them.

[0071] In cases where a large amount of filter-clogging substances have accumulated inside the filter bed, it is possible to send a controlled concentration of chemicals directly to the area where filter-clogging substances need to be removed by injecting chemicals through the path 10. This makes it possible to reduce the amount of chemicals used.

[0072] In this way, when the filter media packed section 4 is configured with two or more layers of two or more different types of filter media 23, 23' stacked in the direction of gravity to form the filter layer 24, it is preferable to provide a path for supplying a chemical between the filter media 23, 23', i.e., to the filter media boundary surface 25. In Figure 4, this path 9 is arranged so as to supply the chemical to the filter media boundary surface 25. With this configuration, it is possible to efficiently remove flocs that tend to form at the filter media boundary surface 25, partly due to the use of a polymer flocculant.

[0073] [Filter material] Examples of the filter media used in the present invention include silica sand, anthracite, manganese filter media, activated carbon, gravel, ceramics, and filter sand.

[0074] The thickness of the filter material in the filtration device is preferably in the range of 300 mm to 2000 mm, mainly in the range of 600 to 800 mm, for a single filter material.

[0075] When a plurality of filter media are stacked to form a filter layer, the layer may be formed by stacking not only filter media of the same type but also filter media of different types.

[0076] When filter layers are formed in this manner, the total layer thickness is preferably in the range of 300 mm to 3500 mm, mainly in the range of 500 mm to 3000 mm. For example, in the case of two layers of silica sand and anthracite, it is preferable that the thickness of the silica sand layer is 0 to 800 mm, and the thickness of the anthracite layer is 0 to 2400 mm. More preferably, the thickness of the silica sand layer is 200 mm to 400 mm, and the thickness of the anthracite layer is 200 mm to 600 mm.

[0077] For example, the filter layer 24 may be configured as two layers as shown in Fig. 4, or may be configured as a single layer. Table 1 below lists examples of filter layer configurations.

[0078] In Table 1, filter material 23 is anthracite, and filter material 23' is silica sand.

[0079] [Table 1]

[0080] Configuration 1 is a single layer of silica sand, which is the basic configuration used in domestic water treatment.

[0081] Configuration 2 is a two-layer configuration of anthracite and silica sand, and is a configuration when the raw water to be treated is expected to be highly turbid.

[0082] Configuration 3 is a two-layer configuration of anthracite and silica sand, and is a configuration in which a polymer flocculant is used.

[0083] Configuration 4 is a two-layer configuration of anthracite and silica sand, and is another configuration in which a polymer flocculant is used.

[0084] Configuration 5 is a single layer anthracite configuration.

[0085] [Chemicals] The chemicals used in the present invention include, for example, sodium hypochlorite, hydrochloric acid, sulfuric acid, and sodium hydroxide, but are of course not limited to these, and are selected depending on the characteristics of the filter-clogging substances to be removed.

[0086] The concentration of the chemical used, for example sodium hypochlorite, is 10 to 120,000 mg / L at the time of injection, preferably 10,000 mg / L to 100,000 mg / L, and 5 to 100 mg / L at the point of action.

[0087] In the case of hydrochloric acid, the concentration is 3 to 37 wt% at the time of injection, and the pH is 1 to 4 at the point of action.

[0088] In the case of sulfuric acid, the concentration is 10 to 98 wt% at the time of injection, and the pH is 1 to 4 at the point of action.

[0089] In the case of sodium hydroxide, the concentration is 2 to 48 wt% at the time of injection, and the pH is 10 to 12 at the point of action.

[0090] In addition to physical cleaning with water and air, the combined use of chemicals can loosen and break down suspended matter, including polymer flocculants, that is firmly attached to the filter media, facilitating its removal and discharge.

[0091] [Polymer flocculant] The polymer flocculant used in the present invention is not particularly limited, but it is preferable to use, for example, one or more selected from the group consisting of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, polymethacrylic acid, sodium polymethacrylate, potassium polymethacrylate, ammonium polymethacrylate, and acrylamide.

[0092] Particularly preferred is sodium polyacrylate. As the polyacrylamide polymer flocculant, a commercially available product which is a copolymer of polyacrylamide and poly(meth)acrylate and is an anionic polymer flocculant can be used.

[0093] These polymer flocculants are preferably added to the raw water in an amount ranging from about 0.01 to 1.0 mg / L.

[0094] [Inorganic flocculant] The inorganic flocculant used in the present invention is not particularly limited as long as it is suitable for water purification treatment, but examples include aluminum sulfate, aluminum chloride, polyaluminum chloride (PAC), ferric chloride, and polyferric sulfate (polyiron), and of these, polyaluminum chloride (PAC) is preferred because it flocculates in a short time.

[0095] The inorganic coagulant is added to the raw water in an amount generally ranging from 1.0 to 20 mg / L. [Example]

[0096] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0097] This test was conducted to confirm the effectiveness of chemical cleaning in removing turbidity in a filtration device in addition to conventional physical cleaning. The filtration device 1 shown in Figure 1 was used for the test.

[0098] (Test Example 1) Water to be filtered was introduced into the filtration device in the usual manner, and a predetermined amount of polymer flocculant was added, and filtration was started.

[0099] After a certain time had passed, the filtration volume suddenly decreased, and it was determined that, based on the operating conditions of the filtration equipment, flocculation containing polymer flocculant had occurred, causing filtration blockage to progress. For this reason, normal backwashing was repeated as physical cleaning, also using wastewater from the accelerating drain pipe 20, but it was found that brown turbidity remained in the upper part of the filter media packed section 4 and could not be removed.

[0100] (Test Example 2) After stopping the filtration, which had continued from the final stage of Test Example 1, the water was drained through the accelerated drain pipe 20, and the water level in the filter tank was positioned 50 mm above the filter layer to minimize the chemical diffusion area. Next, a sodium hypochlorite solution (used at a concentration such that the average concentration in the aquatic area (up to 50 mm above the filter layer) was 10 mg / L) was injected into the filter media-packed section 4 as a chemical cleaning chemical through path 9. Next, air 19 was sent through air pipe 13 for 1 minute to promote mixing and diffusion of the injected chemical into the filter layer, and then the system was left to stand overnight (approximately 14.5 hours).

[0101] The next morning, the sodium hypochlorite concentration in the filter tank 2 was measured and found to be 6 mg / L. Therefore, air was pumped through the air supply pipe 13 for 3 minutes to diffuse the sodium hypochlorite into the gas phase. As a result, the sodium hypochlorite concentration decreased to 2 mg / L. Subsequently, a conventional water backwash was performed. Water backwashing was first performed for 10 minutes at a washing speed (the value calculated by dividing the amount of water injected by the filtration area) of 0.6 m / min. Water was then discharged through the wash water discharge pipe 7, but some of the flocs that had detached from the filter layer were not discharged and remained in the aquifer above the filter layer. Next, the backwashing speed was reduced to 0.2 m / min, and water backwashing was performed for 5 minutes. After approximately 20 seconds of reducing the backwashing speed, the expansion of the filter layer subsided and the filter media fell into the media-packed section 4. Then, water was discharged through the accelerated drain pipe 20. As a result, the turbidity remaining in the upper part of the filter layer was discharged from the system.

[0102] Next, the water to be treated 14 was poured in, and filtration was resumed. When filtration was resumed, there was no turbidity remaining on the surface of the filter layer, and the filtration resistance at the beginning of filtration had recovered to normal, confirming that the turbidity that had accumulated in the filter layer had been removed. [Explanation of symbols]

[0103] 1 Filtration device 2 Filtration tank 3 Filtration inlet pipe 4 Filter media filled section 5 Filtration outlet pipe 6 Washing water inlet pipe 7 Washing water outlet pipe 8 Chemical storage section 9, 10, 11, 12 Path 13 Air supply pipe 14 Water to be treated 15 Filter media 16 Filtration water 17 Washing wastewater 18 Polymer coagulant 19 Air 20 Accelerated drain pipe 21 Accelerated drain 22 Chemical injection main pipe 23, 23' Filter media 24 Filter layer 25 Filter media interface 30 Conventional filtration device 31 Filtration tank 32 Filtration inlet pipe 33 Filtration outlet pipe 34 Washing water inlet pipe 35 Washing water outlet pipe 36 Filter media filled section 37 Water level gauge 38 Raw water or coagulation-sedimentation treated water 39 Inorganic coagulant 40 Polymer coagulant 41 Upper water area of ​​the filter layer (freeboard) 42 Filter media 43 Filtrate water 44 Washing wastewater

Claims

1. 1. A filtration device comprising: a filtration tank into which water to be treated is supplied from an upper portion and into which treated water obtained by filtering the water to be treated flows out from a lower portion; A filter material filling section filled inside the filtration tank to perform filtration of the water to be treated; a cleaning water inlet pipe for passing cleaning water through the filter medium packed portion in an upward flow; A cleaning water discharge pipe that discharges cleaning water from above the filter medium filling portion; a chemical storage section for storing a chemical for cleaning the filter medium packed section; a path for supplying the chemical from the chemical storage unit to the filtration tank; A filtration device comprising:

2. The filtering device according to claim 1 , wherein the path is a path for supplying the chemical into the filtering tank from above the filtering medium filling portion.

3. The filtering device according to claim 1 , wherein the path is a path for supplying the chemical into the filtering tank from below the filtering medium filling portion.

4. The filtering device according to claim 1 , wherein the path is a path for supplying the chemical from a pipe installed inside the filter medium-packed section.

5. The filter material packed section has a structure in which two or more types of filter material having different shapes are stacked in two or more layers in the direction of gravity, The filtering device according to claim 1 , wherein the path is a path for supplying the chemical to at least one filter medium interface between the two or more types of filter medium having different shapes inside the filter medium packed section.

6. The filtering device according to claim 1 , further comprising an agitation washing device that physically washes the filter media by spraying washing water directly onto the filter media-packed section.

7. The filtering device according to claim 1 , further comprising an air supply pipe for blowing gas into the filtering device from below the filter medium-filled portion.

8. 2. The filtration device according to claim 1, further comprising an accelerating drain pipe for discharging cleaning water remaining on the top of the filtration layer after cleaning with chemicals.

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