Horizontal sand filter and its water treatment process

Abstract

The present invention relates to a horizontal sand filter and its water treatment process. The horizontal sand filter includes a tank body, a raw water inlet assembly, a sand filter bed, a filtered water outlet assembly, an aeration assembly, and a backwash assembly. The raw water inlet assembly includes an inlet pipe and a water distribution device for delivering raw water into the sand filter bed. The inlet pipe is connected to the water distribution device, which is arranged in the sand filter bed. A plurality of outlet channels are evenly distributed on the vertical surface of the water distribution device. The filtered water outlet assembly includes a water collector and an outlet pipe. The water collector has an inlet channel on the side adjacent to the sand filter bed, and the outlet pipe is connected to the water collector. The backwash assembly includes a backwash pipe and a sewage pipe. The backwash pipe is connected to the outlet pipe, and the sewage pipe is connected to the water distribution device. The horizontal sand filter of the present invention has a large filtration area, thoroughly cleans sand particles, saves water and energy, and has a variety of expanded applications. It can not only be used as a simple filtering device, but also become an aerobic / anoxic biological filter that integrates the functions of biological contact oxidation and suspended matter filter bed interception.

Description

Technical Field

[0001] The invention relates to water treatment equipment, in particular to a horizontal sand filter and a water treatment process thereof. Background Art

[0002] Sand filters are typical filtration devices that utilize the surface area provided by the granular material in the filter layer to intercept solid particles and colloids in the water, thereby clarifying the water. Sand filters can retain impurities in water whose particle size is much smaller than the pores in the filter media, primarily through contact flocculation, followed by screening and sedimentation. Due to their numerous advantages, such as high decontamination capacity, long operating cycles, and reliable operation, sand filters are widely used in water treatment or for advanced treatment of wastewater after secondary treatment.

[0003] The operation of a sand filter primarily involves a cycle of filtration and backwashing. In existing sand filters, raw water filtration is performed only vertically, limiting the filtration area to the horizontal cross-sectional area of ​​the equipment and resulting in inadequate utilization of the sand layer. Furthermore, during the sand washing process, all sand particles are mixed together, failing to classify them based on their degree of contamination. Summary of the Invention

[0004] The object of the present invention is to provide a horizontal sand filter to solve the problems of limited sand layer filtration area, insufficient sand layer utilization and mixed flushing of filter sands with different degrees of dirtiness in existing sand filtration technology.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A horizontal sand filter comprises a tank body, a raw water inlet assembly, a sand filter bed, a filtered water outlet assembly, an aeration assembly and a backwash assembly.

[0007] The sand filter bed is located inside the tank and consists of filter sand;

[0008] The raw water inlet assembly includes a water inlet pipe and a water distribution device for delivering raw water into the sand filter bed. The water inlet pipe is connected to the water distribution device, which is arranged in the sand filter bed. A plurality of water outlet channels are distributed on the vertical surface of the water distribution device.

[0009] The filtered water outlet assembly includes a water collector and an outlet pipe. The water collector has a water inlet channel on one side adjacent to the sand filter bed, and the outlet pipe is connected to the water collector.

[0010] The backwash component comprises a backwash pipe and a sewage pipe, the backwash pipe is connected to the water outlet pipe, and the sewage pipe is connected to the water distribution device.

[0011] Preferably, the water distribution device is arranged in the axial direction of the pool body; or, is arranged on the outer wall of the sand filter bed.

[0012] As a preference, the tank body is made of concrete. According to different process requirements, the tank body can also be made of other materials, such as steel, acrylic, etc.

[0013] Preferably, the water distribution device is a water distribution riser with a water outlet channel. Further preferably, the water distribution device is formed by a sieve plate with a wedge-shaped wire filtration surface, or a perforated tube, a slotted screen, or a combination thereof; and the water collector is formed by a sieve plate with a wedge-shaped wire filtration surface, or a perforated tube, a slotted screen, a microfiltration membrane, an ultrafiltration membrane, or a combination thereof.

[0014] Preferably, the layout of the water distribution device adopts a variety of configurations such as rectangular, circular, annular or linear, or a combination of the above.

[0015] Preferably, the water collector includes a sieve plate and cover plates located at the upper and lower ends of the sieve plate, and the sieve plate and the two cover plates form a water collection space in the pool body.

[0016] Preferably, when the water distribution device is distributed along the outer wall of the sand filter bed, the water collector is arranged in the axial direction of the sand filter bed.

[0017] Preferably, the sieve plates in the water collector are curved, stepped, bent, flat, or other geometrically shaped plates arranged continuously or at intervals along the inner wall of the tank, with the protrusions of the sieve plates facing the tank body. Alternatively, the sieve plates are cylindrical with distributed water distribution holes. Depending on different process requirements, the sieve plates may also be configured in other forms, such as a continuous, rectangular, or intermittent sieve plate.

[0018] Preferably, the water collector is provided with at least one branch water collecting pipe communicating with the outside of the pool body, and the outlet of each branch water collecting pipe is connected to the outlet pipe outside the pool body.

[0019] Preferably, the aeration assembly consists of an aeration pipe and a plurality of aeration devices connected to the aeration pipe, and the aeration assembly is installed at the bottom of the tank body.

[0020] Preferably, valves are provided on the water inlet pipe, the water outlet pipe, the backwash pipe and the sewage pipe.

[0021] Preferably, a backwash water tank is added to the backwash component to store part of the filtered water. The filtered water is used as flushing water in the flushing process, which can greatly reduce the consumption of clean water.

[0022] Preferably, the aeration device is a sieve plate with a wedge-shaped wire filter surface. Depending on different process requirements, the aeration device can also be configured in other forms, such as a perforated tube, a slotted screen, or a rigid air distribution device of appropriate form / strength, or a combination thereof.

[0023] A water treatment process for a horizontal sand filter, the process comprising the following two steps:

[0024] (1) Filtration process: Raw water enters the horizontal sand filter tank through the water inlet pipe, enters the sand filter bed evenly and smoothly through the outlet channel of the water distribution device, and flows through the filter sand from inside to outside or from outside to inside along the horizontal direction of the tank body; during the filtration process, suspended particles or pollutants in the water are intercepted by the sand particles, and radial filtration maximizes the efficiency of the filter sand; finally, the filtered water is collected by the water collector and discharged to the outlet pipe;

[0025] (2) Backwashing process: The flushing water enters the water collector through the backwash pipe and then enters the sand filter bed; compressed air enters the aeration pipe and enters the sand filter bed from bottom to top in the form of bubbles through the aeration device at the bottom of the tank body. The agitation of the gas phase, the shear force of the water flow and the collision and friction between the sand particles cause the impurities and pollutants to separate from the surface of the sand particles and enter the cleaning water; the degree of gas phase agitation is adjusted to control the rolling of the sand particles. Through the reverse cleaning of the cleaning water, the dirty sand of different degrees in different areas is cleaned separately and will not be mixed; after a period of time, the cleaning water with pollutants flows into the water distribution device and is discharged from the horizontal flow sand filter through the sewage pipe.

[0026] Another water treatment process is horizontal sand filter, which includes the following two processes:

[0027] (1) Biological filtration process: Under suitable culture conditions, a layer of gel-like biofilm is formed on the surface of the filter sand. The raw water enters the horizontal sand filter through the water inlet pipe, enters the sand filter bed evenly and smoothly through the outlet channel of the water distribution device, and flows through the filter sand from inside to outside or from outside to inside along the horizontal direction of the tank body; the aeration component is turned on, and compressed air is released from the bottom to top into the sand filter in the form of small bubbles through the aeration component, fully supplying oxygen; when the raw water flows along the surface of the filter sand, the soluble, colloidal and suspended substances in the raw water are adsorbed on the biofilm and decomposed by microorganisms; finally, the filtered water is collected by the water collector and discharged to the outlet pipe;

[0028] (2) Backwashing process: The flushing water enters the water collector through the backwash pipe and then enters the sand filter bed; compressed air enters the aeration pipe and enters the sand filter bed from bottom to top in the form of bubbles through the aeration device at the bottom of the tank body. The agitation of the gas phase, the shear force of the water flow and the collision and friction between the sand particles cause the impurities and pollutants to separate from the surface of the sand particles and enter the cleaning water; the degree of gas phase agitation is adjusted to control the rolling of the sand particles. Through the reverse cleaning of the cleaning water, the dirty sand of different degrees in different areas is cleaned separately and will not be mixed; after a period of time, the cleaning water with pollutants flows into the water distribution device and is discharged from the horizontal flow sand filter through the sewage pipe.

[0029] Preferably, part of the filtered water can be temporarily stored in a backwash water tank and reused as flushing water in a subsequent backwashing process.

[0030] The horizontal quicksand filter of the present invention can achieve the following functions:

[0031] (1) Simple sand filtration to remove solid particles and colloidal suspended matter in raw water;

[0032] (2) During the filtration process, the aeration component is turned on to construct an aerobic biological filter. The sand filter layer cuts the bubbles, which prolongs the residence time of the bubbles in the filter and improves the utilization rate of oxygen.

[0033] (3) During the filtration process, the aeration component is turned off to construct an anoxic biological filter bed. Due to the excellent sewage interception capacity of the filter bed, there is no need to set up a secondary sedimentation tank.

[0034] Beneficial effects of the present invention:

[0035] 1. Increased filtration area. In existing fixed sand filters or continuous sand filtration equipment, raw water enters the sand filter bed through the bottom water distributor and is filtered upwards, resulting in a filtration area limited to the horizontal cross-sectional area of ​​the sand filter bed. However, with the water distribution device of the present invention, raw water flows horizontally through the filter bed, significantly increasing the filtration area. This improves effluent quality while reducing the amount of filter sand used.

[0036] 2. Zone-by-zone sand washing. As filtration progresses, solid contaminants gradually settle on the sand surface, and the contamination level of the sand decreases as it moves from the water distributor to the water collector. During reverse sand washing, sand with varying levels of contamination in different zones is cleaned separately, preventing mixing and resulting in a more thorough sand washing process.

[0037] 3. Water and energy conservation. By adding a backwash tank, filtered water can be partially stored and reused as flushing water during the flushing process, significantly reducing clean water consumption. This improved sand filtration efficiency extends the backwash cycle, reduces sand washing frequency, and reduces energy consumption.

[0038] 4. The horizontal sand filter of the present invention can not only be used as a simple filtration device, but under appropriate culture conditions, the sand filter material can be used to fix the biofilm, becoming a biological reaction tank that integrates the functions of biological contact oxidation and suspended matter filter bed interception. It can effectively remove suspended solids in water and reduce COD, BOD, turbidity, color, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a front view schematic diagram of the horizontal quicksand filter of the present invention.

[0040] Figure 2 It is a left side schematic diagram of the horizontal quicksand filter of the present invention.

[0041] Figure 3 It is a top view schematic diagram of the horizontal quicksand filter of the present invention.

[0042] Figure 4This is another schematic top view of the horizontal quicksand filter of the present invention.

[0043] In the figure: 1. Pool body, 2. Water inlet pipe, 3. Water distribution device, 4. Sand filter bed, 5. Water collector, 51. Screen plate, 52. Cover plate, 6. Branch water collecting pipe, 7. Water outlet pipe, 8. Backwash pipe, 9. Sewage pipe, 10. Aeration pipe, 11. Aeration device. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 1 、 Figure 2 and Figure 3 The horizontal sand filter shown is composed of a tank body 1, a raw water inlet assembly, a sand filter bed 4, a filtered water outlet assembly, an aeration assembly, and a backwash assembly. The function of the raw water inlet assembly is to send raw water into the sand filter bed and evenly distribute it.

[0047] The tank body 1 is rectangular and made of concrete;

[0048] The raw water inlet assembly consists of an inlet pipe 2 and a water distribution device 3 connected to the inlet pipe. A valve is installed on the inlet pipe 2 to direct raw water into the horizontal sand filter. The water distribution device 3 comprises four water distribution risers, each with evenly distributed outlet channels. Each water distribution riser is vertically installed and evenly distributed within the sand filter bed 4. The water distribution risers can be constructed from a sieve plate with a wedge-shaped wire filter surface. Raw water flows evenly and smoothly into the sand filter bed 4 through the sieve slits of the sieve plate. The water distribution structure of the water distribution risers of the present invention is not limited to this example; this example is merely a preferred example.

[0049] The sand filter bed 4, composed of filter sand, is located in the tank body 1 and extends upward from the bottom of the tank body 1 to filter raw water. The filter sand is the main material for raw water purification and filtration. Filter media such as quartz sand, activated carbon, anthracite, glass balls, and ceramsite can be selected. The type and particle size distribution of the filter sand should be selected according to the water quality requirements of the raw water and the filtered water.

[0050] The filtered water outlet assembly consists of a water collector 5, a branch water collection pipe 6, and an outlet pipe 7. The water collector 5 includes a sieve plate 51 with a wedge-shaped wire filter surface and cover plates 52 located at the upper and lower ends of the sieve plate. The sieve plate and the two cover plates form a water collection space on the outer wall of the tank body. The water collector 5 is provided with a branch water collection pipe 6 connected to the outside of the tank body. The outlet of each branch water collection pipe 6 is connected to the outlet pipe 7 on the outer wall of the tank body. The filtered water passing through the sand filter bed 4 enters the water collector 5 through the sieve slits of the sieve plate, as shown in FIG. Figure 3 As shown, the sieve plate of this embodiment is in the shape of an arc sheet, with the protrusion of the sieve plate facing the inside of the pool body. Four arc sheets are provided on each side inner wall of the pool body 1 and are evenly spaced along the inner wall of the pool body 1. The arc sheet-shaped sieve plate is used to better collect the filtered water filtered from the sand filter bed 4; the branch water collection pipe 6 is connected to the water collector 5; the outlet pipe 7 discharges the filtered water obtained by filtering the sand filter bed 4 out of the pool body 1.

[0051] The backwash component includes a backwash pipe 8 and a sewage pipe 9. A valve is provided on the backwash pipe 8 and connected to the outlet pipe 7. A valve is provided on the sewage pipe 9 and connected to the bottom of the four water distribution risers. The backwash water enters the water collector through the backwash pipe, and the sewage pipe discharges the sand washing wastewater out of the horizontal flow sand filter.

[0052] The aeration assembly consists of an aeration pipe 10 and multiple aeration devices 11 connected to the aeration pipe. During the backwash process of the sand filter, compressed air is released into the sand filter in the form of small bubbles through the aeration assembly; the aeration assembly is installed at the bottom of the tank.

[0053] A horizontal sand filter water treatment process includes the following two processes:

[0054] (1) Filtration process. The valve of the water inlet pipe 2 is open, the valve of the water outlet pipe 7 is open, the valve of the backwash pipe 8 is closed, and the valve of the sewage pipe 9 is closed. The raw water enters the horizontal sand filter through the water inlet pipe 2, enters the sand filter bed 4 evenly and smoothly through the water distribution riser, and flows horizontally from the inside to the outside along the tank body 1 to filter the sand. During the filtration process, large-sized suspended particles or pollutants in the water are intercepted by the inner layer of sand particles, and small-sized pollutants are deposited between the outer layer of sand particles. Filtration from the inside to the outside maximizes the efficiency of the filter sand. Finally, the filtered water is collected by the water collector 5 evenly distributed on the inner wall of the tank body 1, flows through the branch water collection pipe 6, and is discharged to the outlet pipe 7.

[0055] (2) Backwashing process. The valve of the water inlet pipe 2 is closed, the valve of the water outlet pipe 7 is closed, the valve of the backwash pipe 8 is opened, and the valve of the sewage pipe 9 is closed. Part of the temporarily stored filtered water is used as flushing water and enters the water collector 5 on the inner wall of the tank body 1 through the backwash pipe, and enters the sand filter bed 4 through the holes on the surface of the water collector 5. Compressed air is passed into the aeration pipe 10 and enters the sand filter bed 4 from bottom to top through the aeration device 11 at the bottom of the tank body 1 in the form of bubbles. The agitation of the gas phase, the shear force of the water flow, and the collision and friction between the sand particles cause the impurities and pollutants to separate from the surface of the sand particles and enter the cleaning water. During the horizontal flow filtration process, the dirtiness of the sand particles gradually decreases from the vicinity of the water distribution riser to the tank wall. By adjusting the degree of gas phase agitation, the sand particles can be controlled to roll within a certain range. Through the reverse cleaning of the cleaning water, the dirty sand with different dirtiness in different areas is cleaned separately and will not be mixed. After a period of time, the valve of the sewage pipe 9 is opened, the valve of the backwash pipe 8 is kept open, and the cleaning water with pollutants flows into the water distribution riser and is discharged from the horizontal flow sand filter through the sewage pipe 9.

[0056] The horizontal flow sand filter of the present invention can also perform the function of a biological filter. A biological filter is a method of biologically oxidizing raw water using aerobic microorganisms. Another horizontal flow biological filter water treatment process includes the following two steps:

[0057] (1) Biological filtration process. Under appropriate culture conditions, a gel-like biofilm is formed on the surface of the filter sand. The raw water enters the horizontal sand filter through the water inlet pipe 2, enters the sand filter bed 4 evenly and smoothly through the water distribution riser, and flows through the filter sand from the inside to the outside along the horizontal direction of the tank body 1. The aeration component is turned on, and compressed air is released from the bottom to the top of the sand filter in the form of small bubbles through the aeration component, fully supplying oxygen. When the raw water flows along the surface of the filter sand, the soluble, colloidal and suspended substances in the raw water are adsorbed on the biofilm and decomposed by microorganisms. Finally, the filtered water is collected by the water collector 5 on the inner wall of the tank body 1, flows through the branch water collection pipe 6, and is discharged to the outlet pipe 7.

[0058] (2) Backwash process. Same as above.

[0059] Example 2

[0060] A horizontal sand filter comprises a tank body 1, a raw water inlet assembly, a sand filter bed 4, a filtered water outlet assembly, a backwash assembly, and an aeration assembly. The specific structure of the horizontal sand filter is the same as that of Example 1, except that:

[0061] like Figure 4As shown, the tank body 1 is divided into four circular areas, each corresponding to four water distribution devices 3. The circular areas are arranged in a rectangular pattern, with a sand filter bed and a water distribution device installed in each circular area. The water inlet pipe 2 in the raw water inlet assembly is connected to each of the four water distribution devices 3. The water distribution device is a water distribution riser pipe, which can be made of a slotted screen. The bottoms of the four water distribution risers are connected to the sewage pipe.

[0062] The filtered water outlet assembly consists of a water collector 5 and an outlet pipe 7; the sieve plate 51 in the water collector 5 is a cylindrical slit sieve, which is fixed to the inner wall of the pool body 1. The cover plate 52 is determined according to the projection configuration of the sieve plate and the inner wall of the pool body on the horizontal plane. The sieve plate and the upper and lower cover plates together with the inner wall of the pool body 1 form a water collection space. The entire pool body 1 shares a water collection space, which can temporarily store filtered water; the outlet pipe 7 is connected to the above-mentioned water collection space.

[0063] The water treatment process of the horizontal quicksand filter in this embodiment is the same as that in embodiment 1, except that:

[0064] The filtered water enters the water collecting space formed by the water collector 5 and the inner wall of the pool body 1, and is uniformly discharged through the outlet pipe 7. The above-mentioned water collecting space can play the role of temporarily storing the filtered water.

[0065] The above-described embodiments are only two preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A horizontal sand filter, characterized by: The horizontal sand filter includes a tank body, a raw water inlet assembly, a sand filter bed, a filtered water outlet assembly, an aeration assembly and a backwash assembly. The sand filter bed is located inside the tank and consists of filter sand; The raw water inlet assembly includes an inlet pipe and a vertical water distribution device that delivers raw water into the sand filter bed and evenly distributes it. The inlet pipe is connected to the vertical water distribution device, and a plurality of water outlet holes are provided on the pipe wall of the vertical water distribution device. The vertical water distribution device is arranged in the sand filter bed; The filtered water obtained by filtering the sand filter bed is discharged from the pool body by a filtered water outlet assembly, comprising a water collector and a water outlet pipe. The water collector forms a water collection space on the inner wall of the pool body, and a water inlet hole is provided on the side of the water collector adjacent to the sand filter bed. The water outlet pipe is connected to the water collector; The backwash assembly includes a backwash pipe and a drain pipe. The backwash pipe is connected to the outlet pipe. The flushing water enters the water collector through the backwash pipe and then enters the sand filter bed. The drain pipe is connected to the vertical water distribution device. The vertical water distribution device is formed by surrounding a sieve plate with a wedge-shaped wire filtering surface; The water collector includes a sieve plate and cover plates located at the upper and lower ends of the sieve plate, and the sieve plate and the two cover plates form a water collection space on the inner wall of the tank body; the sieve plate is an arc plate evenly and spaced along the inner wall of the tank body, and the protrusion of the sieve plate faces the inside of the tank body; or the sieve plate is a cylinder with water distribution holes distributed thereon; the bottom of the water collector is provided with a branch water collection pipe connected to the outside of the tank body, and the outlet of each branch water collection pipe is connected to the water outlet pipe outside the tank body; the aeration assembly consists of an aeration pipe and multiple aeration devices connected to the aeration pipe, and the aeration assembly is installed at the bottom of the tank body; The vertical water distribution device is arranged in the axial direction of the pool body.

2. The horizontal quicksand filter according to claim 1, characterized in that: Valves are installed on the water inlet pipe, water outlet pipe, backwash pipe and sewage pipe.

3. A water treatment process using the horizontal quicksand filter according to claim 1, characterized in that: The process includes the following two processes; (1) Filtration process: Raw water enters the sand filter bed through the water inlet pipe, enters the sand filter bed evenly and smoothly through the vertical water distribution device, and flows from the inside to the outside along the horizontal direction of the pool body to filter the sand; During the filtration process, large suspended particles or pollutants in the water are intercepted by the inner sand particles, while small pollutants are deposited between the outer sand particles. Filtering from the inside out maximizes the efficiency of the filter sand. Finally, the filtered water is collected by the water collector on the inner wall of the tank and discharged to the outlet pipe. (2) Backwashing process: The flushing water enters the water collector through the backwash pipe and then enters the sand filter bed; the compressed air enters the aeration pipe and enters the sand filter bed from bottom to top in the form of bubbles through the aeration device at the bottom of the tank body. The agitation of the gas phase, the shear force of the water flow and the collision and friction between the sand particles cause the impurities and pollutants to separate from the surface of the sand particles and enter the cleaning water; During the horizontal flow filtration process, the dirtiness of the sand particles gradually decreases from the vicinity of the vertical water distribution device to the pool wall. The gas phase agitation degree is adjusted to control the tumbling of the sand particles. Through the reverse washing of the cleaning water, the dirty sand with different dirtiness in different areas is cleaned separately without mixing. After a period of time, the cleaning water containing pollutants flows into the vertical water distribution device and is discharged from the sand filter bed through the sewage pipe.

4. A water treatment process using the horizontal quicksand filter according to claim 1, characterized in that: The process includes the following two processes; (1) Filtration process: Under suitable culture conditions, a layer of gel-like biofilm is formed on the surface of the filter sand. Raw water enters the sand filter bed through the water inlet pipe, enters the sand filter bed evenly and smoothly through the vertical water distribution device, and flows through the filter sand from the inside to the outside along the horizontal direction of the pool body; the aeration component is turned on, and compressed air is released from the bottom to the top of the sand filter tank in the form of small bubbles through the aeration component, fully supplying oxygen; when the raw water flows along the surface of the filter sand, the soluble, colloidal and suspended substances in the raw water are adsorbed on the biofilm and decomposed by microorganisms; finally, the filtered water is collected by the water collector on the inner wall of the pool body and discharged to the outlet pipe; (2) Backwashing process: The flushing water enters the water collector through the backwash pipe and then enters the sand filter bed; the compressed air enters the aeration pipe and enters the sand filter bed from bottom to top in the form of bubbles through the aeration device at the bottom of the tank body. The agitation of the gas phase, the shear force of the water flow and the collision and friction between the sand particles cause the impurities and pollutants to separate from the surface of the sand particles and enter the cleaning water; During the horizontal flow filtration process, the dirtiness of the sand particles gradually decreases from the vicinity of the vertical water distribution device to the pool wall. The gas phase agitation degree is adjusted to control the tumbling of the sand particles. Through the reverse washing of the cleaning water, the dirty sand with different dirtiness in different areas is cleaned separately without mixing. After a period of time, the cleaning water containing pollutants flows into the vertical water distribution device and is discharged from the sand filter bed through the sewage pipe.

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