Upward flow filter tank backwashing method and upward flow filter tank

Abstract

A water and gas distribution system (2), a filter bed (3) and a water collection tank (4) are sequentially arranged on a tank body (1) from bottom to top; the water and gas distribution system (2) comprises a water and gas distribution pipe (222) arranged at the bottom of the filter bed (3); the water and gas distribution pipe (222) is respectively communicated with a filter water inlet pipe (211), a backwashing gas inlet pipe (213), a backwashing water inlet pipe and a bottom blow-off pipe (215); the water collecting tank (4) is respectively communicated with a filtering water outlet pipe (411) and a backwashing drain pipe (413); a plurality of rotational flow holes (222a) are formed in the water and gas distribution pipe (222), and spiral water channels are formed in the inner walls of the rotational flow holes (222a). The invention further discloses a backwashing method of the upward flow filter tank. The backwashing method comprises the following steps: first-time bottom pollution discharge, rotational flow washing, second-time bottom pollution discharge, single gas washing and single water washing. According to the invention, the cleaning effect can be improved, and backwashing water consumption and backwashing time can be saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and specifically relates to an up-flow filter backwashing method and an up-flow filter. Background Art

[0002] In the prior art, water enters from the bottom and exits from the upper part of the up-flow filter, and the entire filter media layer plays a role in collecting pollutants. Since the main pollutants are concentrated in the middle and lower parts of the filter media layer, the filter backwashing method is crucial for restoring the operation effect. At present, the up-flow filter often uses the method of lowering the water level - combined air-water backwashing, that is, first lowering the filter liquid level to wash the filter media layer, and then successively performing single air washing, air-water combined washing, water washing, and rinsing processes. However, the water washing direction of the air-water combined washing is the same as the filtration direction, which is difficult to wash, requires a large amount of washing water, and it is difficult to control the filter media to be thoroughly cleaned. In the long run, it is easy to cause the filter media to cake, resulting in a long backwashing time and high backwashing water consumption. When applied to sewage treatment, there are also problems such as filter media caking. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide an up-flow filter backwashing method and an up-flow filter, which can improve the cleaning effect, save backwashing water consumption and backwashing time.

[0004] To solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0005] In the first aspect, the present invention provides an up-flow filter, the filter includes a pool body 1, and a water distribution and air distribution system 2, a filter bed 3, and a water collection tank 4 are sequentially arranged in the pool body 1 from bottom to top;

[0006] The filter bed 3 includes a filter media layer;

[0007] The water collection tank 4 is respectively communicated with a filtered water outlet pipe 411 and a backwash drain pipe 413;

[0008] The water distribution and air distribution system 2 includes a water distribution and air distribution pipe 222 arranged at the bottom of the filter bed 3, and the water distribution and air distribution pipe 222 is respectively communicated with a filtered water inlet pipe 211, a backwash air inlet pipe 213, a backwash water inlet pipe, and a bottom sewage discharge pipe 215;

[0009] A plurality of swirl holes 222a are arranged on the water distribution and air distribution pipe 222, and the inner wall of the swirl hole 222a has a spiral water channel.

[0010] Further, the spiral water channels of two adjacent swirl holes 222a have opposite rotation directions.

[0011] Further, the distance between two adjacent swirl holes 222a near the inner wall of the pool body 1 is smaller than the distance between two adjacent swirl holes 222a near the center of the pool body 1.

[0012] Further, the water outlet direction of the swirl holes 222a arranged near the inner wall of the pool body 1 faces the inner wall of the pool body 1.

[0013] Further, the backwash inlet pipe includes a first backwash inlet pipe 217 and a second backwash inlet pipe 219. The first backwash inlet pipe 217 is connected to the water distribution and air distribution pipe 222 through an air-liquid mixer 221. After the air-liquid mixer 221 quickly mixes water and air, a water-air mixture is formed. The second backwash inlet pipe 219 is connected to the water distribution and air distribution pipe 222.

[0014] On the other hand, the present invention also provides a backwashing method for an upflow filter, and the method includes the following steps:

[0015] Step S1, first bottom sewage discharge: close the filter inlet pipe 211, and the bottom sewage discharge pipe 215 starts to discharge sewage. When the liquid level drops to a first set height above the filter bed 3, stop discharging sewage;

[0016] Step S2, swirl flushing: after stopping the first bottom sewage discharge, input the water-air mixture into the water distribution and air distribution pipe 222, and the water flow after passing through the swirl holes 222a performs swirl scrubbing on the lower part of the filter media layer;

[0017] Step S3, second bottom sewage discharge: after stopping the swirl flushing, the bottom sewage discharge pipe 215 starts to discharge sewage. When the liquid level drops to a second set height above the filter bed 3, stop discharging sewage;

[0018] Step S4, single air washing: after stopping the second bottom sewage discharge, perform backwashing air intake through the backwash air inlet pipe 213 to loosen the filter media layer;

[0019] Step S5, single water washing: after stopping the single air washing, perform backwashing water intake through the backwash inlet pipe to wash the filter media layer, and the impurities washed down are discharged through the backwash drain pipe 413.

[0020] Further, it also includes:

[0021] Step S6, rinsing: water enters through the filter inlet pipe 211 to rinse the filter bed 3, and the rinsed water is discharged through the backwash drain pipe 413.

[0022] Further, if the drainage turbidity is in the first interval at the end of step S5, resume filtration;

[0023] If the drainage turbidity is in the second interval at the end of step S5, enter step S6 or extend step S5 so that the drainage turbidity is in the first interval, and then resume filtration;

[0024] If the drainage turbidity is in the third interval at the end of step S5, steps S2 to S5 are repeated until the drainage turbidity is in the first interval, and the filtration is resumed;

[0025] The first interval < the second interval < the third interval.

[0026] Furthermore, the first interval ≤ 5 NTU, the second interval > 5 NTU and < 10 NTU, and the third interval ≥ 10 NTU.

[0027] Furthermore, the first set height is 200 - 600 mm, and the second set height is 100 - 200 mm.

[0028] Beneficial effects:

[0029] For the upward flow filter provided by the present invention, the backwashing inlet water and air are quickly mixed in the gas-liquid mixer, the air is dissolved into the water body, and finally released to the bottom of the filter bed through the swirl holes opened in the water distribution and air distribution pipe. By setting swirl holes with opposite rotation directions, the gas-water mixture of adjacent holes runs in opposite directions under the action of centrifugal force, forming a local swirling scrubbing force in the filter media layer in the middle and lower parts of the filter bed, accelerating the lateral agitation of the filter media layer in the middle and lower parts, and quickly cleaning the pollutants adsorbed on the surface of the filter media. After the gas-liquid mixture is released from the swirl holes, nanobubbles are instantly formed and act on the surface of the filter media, significantly increasing the chance of contact with the surface of the filter media. Compared with traditional large bubbles, its cleaning effect is better.

[0030] For the backwashing method of the upward flow filter provided by the present invention, through the steps of the first bottom sewage discharge, swirl flushing, the second bottom sewage discharge, single air washing, and single water washing, the consumption of backwashing water and the backwashing time can be significantly saved, the problem of filter media caking caused by incomplete flushing can be solved, and the backwashing is more reasonable, with stronger operability and better flushing effect.

[0031] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings. Description of the Drawings

[0032] The accompanying drawings, as a part of the present invention, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation to the present invention. Obviously, the accompanying drawings in the following description are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. In the drawings:

[0033] Figure 1 is the schematic equipment structure diagram of the steel structure of the upward flow filter in Embodiment 1 of the present invention;

[0034] Figure 2It is a schematic diagram of the reinforced concrete structure of the upward flow filter in Embodiment 1 of the present invention;

[0035] Figure 3 is Figure 2 the top view structure schematic diagram of;

[0036] Figure 4 It is a schematic diagram of the water distribution and air distribution pipe structure in Embodiment 1 of the present invention;

[0037] Figure 5 is Figure 4 the enlarged view of the structure at position A of;

[0038] Figure 6 It is a schematic diagram of the process flow of the backwashing method of the upward flow filter in Embodiment 2 of the present invention;

[0039] Figure 7 The present invention and the turbidity effect of the effluent of the upward flow filter after traditional backwashing for 24 hours;

[0040] Figure 8 is the turbidity effect of the effluent of the upward flow filter after traditional backwashing for 72 hours of the present invention.

[0041] In the figure: 1. Pool body; 2. Water distribution and air distribution system; 3. Filter bed; 4. Collection trough;

[0042] 211. Filter inlet pipe; 212. Filter inlet valve; 213. Backwash inlet pipe; 214. Backwash inlet valve; 215. Bottom sewage pipe; 216. Bottom sewage valve; 217. First backwash inlet pipe; 218. First backwash inlet valve; 219. Second backwash inlet pipe; 220. Second backwash inlet valve; 221. Gas-liquid mixer; 222. Water distribution and air distribution pipe; 222a. Swirl hole;

[0043] 411. Filter outlet pipe; 412. Filter outlet valve; 413. Backwash drain pipe; 414. Backwash drain valve; 415. Clear water channel; 416. Gate valve; 417. Drainage channel; 418. Flap valve.

[0044] It should be noted that these drawings and text descriptions are not intended to limit the scope of the concept of the present invention in any way, but to illustrate the concept of the present invention to those skilled in the art by referring to specific embodiments. Detailed implementation manners

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0046] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0047] The terms "first", "second", etc. are only used for the purpose of distinguishing technical features, and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features or implicitly specifying the sequence relationship of the indicated technical features.

[0048] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] When the filter reaches the set backwash cycle, set head loss, or effluent turbidity, backwashing is required. The following are specific embodiments of backwashing provided by the present invention:

[0050] Embodiment 1

[0051] This embodiment provides an upward flow filter, as Figures 1 to 3 shown. The upward flow filter includes a pool body 1, and a water distribution and air distribution system 2, a filter bed 3, and a collecting trough 4 are successively arranged in the pool body 1 from bottom to top.

[0052] The water distribution and air distribution system 2 is respectively connected to a filtered water inlet pipe 211, a backwash air inlet pipe 213, a bottom drain pipe 215, and a backwash water inlet pipe. A filtered water inlet valve 212 is provided on the filtered water inlet pipe 211, a backwash air inlet valve 214 is provided on the backwash air inlet pipe 213, a bottom drain valve 216 is provided on the bottom drain pipe 215, and a backwash water inlet valve is provided on the backwash water inlet pipe.

[0053] A pebble cushion layer is arranged at the bottom of the filter bed 3, and a filter media layer is arranged at the upper part, and heavy filter media is used for the filter media.

[0054] The collecting trough 4 is connected to a clear water channel 415 through a gate valve 416, the clear water channel 415 is connected to a filtered water outlet pipe 411, and a filtered water outlet valve 412 is provided on the filtered water outlet pipe 411.

[0055] The clear water channel 415 is arranged outside the filter tank body 1. A drain channel 417 is provided outside the filter tank body 1 opposite to the clear water channel 415. The drain channel 417 is communicated with the inside of the filter tank body 1 through a flap valve 418, and the bottom of the flap valve 418 is 200 - 300 mm above the filter bed 3. The drain channel 417 is communicated with the backwash drain pipe 413, and the backwash drain pipe 413 is provided with a backwash drain valve 414.

[0056] The water collecting trough 4 is arranged on three sides of the tank body 1 and is not arranged on the inner side of the drain channel 417.

[0057] The sewage enters the tank body 1 through the filtered water inlet pipe 211, enters the filter bed 3 through the water distribution and air distribution system 2, intercepts the particulate matter in the sewage. The water purified by the filter bed 3 is collected by the water collecting trough 4, and finally flows out of the tank body 1 through the clear water channel 415 by the filtered water outlet pipe, completing the filtration step.

[0058] The backwash inlet pipe includes a first backwash inlet pipe 217 and a second backwash inlet pipe 219. The first backwash inlet pipe 217 is communicated with the water distribution and air distribution pipe 222 through an air-liquid mixer 221 and a first backwash inlet valve 218. After the air-liquid mixer 221 quickly mixes water and air, an air-water mixture is formed. The second backwash inlet pipe 219 is communicated with the water distribution and air distribution pipe 222 through a second backwash inlet valve 220.

[0059] As Figure 4 shown, a plurality of swirl holes 222a are arranged on the water distribution and air distribution pipe 222. The inner wall of the swirl hole 222a has a spiral water channel for controlling the rotation direction of the outflow water.

[0060] Preferably, the spiral water channels of two adjacent swirl holes 222a rotate in opposite directions, as shown in Figure 5 .

[0061] The backwash water and air are quickly mixed in the air-liquid mixer, and the air is dissolved in the water body. Finally, it is released to the bottom of the filter bed through the swirl holes opened on the water distribution and air distribution pipe. Since the rotation directions of adjacent swirl holes are opposite, the air-water mixtures of adjacent holes run in opposite directions under the action of centrifugal force, forming a local swirl scrubbing force in the filter media layer in the middle and lower parts of the filter bed, accelerating the lateral agitation of the filter media layer in the middle and lower parts, and quickly cleaning the pollutants adsorbed on the surface of the filter media. In addition, after the air and water are mixed, they are released from the swirl holes, instantly forming nano-bubbles that act on the surface of the filter media, significantly increasing the chance of contact with the surface of the filter media. Compared with traditional large bubbles, its cleaning effect is better.

[0062] As an alternative embodiment, in order to achieve a better cleaning effect, the spacing of the swirl holes 222a is arranged to be greater near the inner wall of the tank body 1 than at the center of the tank body 1. This is because, in the experiment, it was found that due to the rotation of the water discharged from the swirl holes, impurities would move towards the periphery of the inner wall of the tank body 1 under the action of centrifugal force. Therefore, increasing the density of the swirl holes 222a near the inner wall of the tank body 1 can effectively remove the impurities on the inner wall of the tank body 1.

[0063] Furthermore, the water discharge direction of the swirl holes 222a is arranged to face the inner wall of the tank body 1 near the inner wall of the tank body 1, so as to remove the impurities attached to the inner wall. The included angle between the water discharge direction and the inner wall of the tank body 1 is preferably less than 30 degrees.

[0064] Embodiment 2

[0065] As Figure 6 shown, the present invention also provides an up-flow filter backwashing method, including the following steps:

[0066] Step S1, bottom sewage discharge: Stop the filtered water inlet, and the bottom sewage discharge pipe 215 starts to discharge sewage. Stop discharging sewage when it is reduced to the first set height above the filter media. This step is mainly to quickly discharge the particulate matter intercepted at the bottom of the filter bed 3. The first set height range can be 200 - 600 mm.

[0067] Step S2, swirl flushing: Introduce the dissolved air water into the water distribution and air distribution system 2, and finally enter the filter media layer through the swirl holes 222a, so as to form local swirl scrubbing in the middle and lower parts of the filter bed 3;

[0068] In this step, the backwashing inlet water and air are quickly mixed in the gas-liquid mixer 221, and the air is dissolved into the water body. Finally, it is released to the bottom of the filter bed 3 through the swirl holes 222a opened on the water distribution and air distribution pipe 222. Since the rotation directions of adjacent swirl holes 222a are opposite, the gas-water mixture of adjacent holes runs in opposite directions under the action of centrifugal force, forming a local swirl scrubbing force in the middle and lower parts of the filter bed 3, accelerating the lateral agitation of the middle and lower parts of the filter media layer, and quickly cleaning the pollutants adsorbed on the surface of the filter media.

[0069] Step S3, bottom sewage discharge: Stop the swirl flushing, and the bottom sewage discharge pipe 215 starts to discharge sewage. Stop discharging sewage when it is reduced to the second set height above the filter media; the pollutants flushed down by the swirl flushing are quickly discharged from the filter bed through the bottom sewage discharge. The second set height range can be 100 - 200 mm.

[0070] Step S4, single air washing: Stop the bottom sewage discharge and perform single air washing;

[0071] Step S5, single water washing: Stop single air washing, conduct backwashing water inlet, and use the backwashing water to further quickly wash the filter media layer. Discharge the impurities washed down through the upper part of the filter tank from the backwashing drain pipe 413. This step is mainly to quickly discharge the pollutants scrubbed from the upper part of the filter bed 3 to ensure that the filter media is washed clean.

[0072] As an alternative implementation, rinsing can be carried out after step S5.

[0073] Step S6, rinsing: Open the filtration water inlet valve 212, and use the water flowing out of the filtration water inlet pipe 211 to rinse the filter bed 3. The rinsing water is discharged from the backwashing drain pipe 413 through the upper part of the filter tank.

[0074] Using the filtered water inlet to rinse the filter bed 3 is to further wash out the pollutants remaining in the upper filter media layer of the filter bed 3 and ensure the water quality of the filter tank effluent.

[0075] Furthermore, the drainage turbidity can be monitored to adjust the filtration steps as follows:

[0076] If the drainage turbidity at the end of step S5 is in the first interval, resume filtration;

[0077] If the drainage turbidity at the end of step S5 is in the second interval, enter step S6 or extend step S5 to make the drainage turbidity in the first interval and resume filtration;

[0078] If the drainage turbidity at the end of step S5 is in the third interval, repeat steps S2 to S5 until the drainage turbidity is in the first interval and resume filtration.

[0079] Optionally, the first interval ≤ 5 NTU, the second interval > 5 NTU and < 10 NTU, and the third interval ≥ 10 NTU.

[0080] In an alternative implementation, it further includes:

[0081] Step S6, rinsing: Start using the filtered water inlet to rinse the filter bed 3, and the rinsing water is discharged from the backwashing drain pipe 413 through the upper part of the filter tank.

[0082] Using the filtered water inlet to rinse the filter bed 3 further cleans the fine impurity particles remaining between the filter media to ensure the water quality effect of the effluent.

[0083] Experimental data:

[0084] 1. Conduct a comparative experiment on the backwashing method of the present invention (filter tank 1#) and the traditional upward flow filter tank backwashing method (filter tank 2#). The treatment scale is 350 m 3 / d, treating a certain aquaculture tail water, setting the backwashing cycle to 24 h, and conducting backwashing:

[0085] (1) The backwashing steps of the present invention are: bottom sewage discharge → swirl flushing → bottom sewage discharge → single air washing → single water washing. The entire backwashing time is 15 minutes, and the water consumption for backwashing is 13 m 3 .

[0086] (2) The traditional backwashing steps are: bottom sewage discharge → single air washing → air-water combined washing → single water washing → bottom sewage discharge → single air washing → air-water combined washing → single water washing. The entire backwashing time is 40 minutes, and the water consumption for backwashing is 30 m 3 .

[0087] The turbidity comparison effect of backwashing filtration for 24 hours is as Figure 7 shown.

[0088] It can be seen that under the same conditions, the filtration effect of the backwashing method of the present invention is comparable to that of the traditional backwashing method, but the backwashing time is saved by 62.5%, and the water consumption for backwashing is saved by 56.7%.

[0089] 2. A comparative experiment was conducted between the backwashing method of the present invention and the traditional upward flow filter backwashing method. The treatment scale is 350 m 3 / d, treating a certain aquaculture tail water. The backwashing cycle is set at 72 hours for backwashing:

[0090] (1) The backwashing steps of the present invention are: bottom sewage discharge → swirl flushing → bottom sewage discharge → single air washing → swirl flushing → bottom sewage discharge → single air washing → single water washing. The entire backwashing time is 25 minutes, and the water consumption for backwashing is 22 m 3 .

[0091] (2) The traditional backwashing steps are: bottom sewage discharge → single air washing → air-water combined washing → single water washing → bottom sewage discharge → single air washing → air-water combined washing → single water washing. The entire backwashing time is 54 minutes, and the water consumption for backwashing is 40 m 3 .

[0092] The turbidity comparison effect of backwashing filtration for 72 hours is as Figure 8 shown.

[0093] Therefore, under the same conditions, the filtration effect of the backwashing method of the present invention is comparable to that of the traditional backwashing method, but the backwashing time is saved by 53.7%, and the water consumption for backwashing is saved by 45%.

[0094] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of the present invention, without departing from the scope of the technical solution of the present invention, may make some changes or modifications using the technical content prompted above as equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the present invention's solution.

Claims

1. An upward flow filter, characterized in that, The filter tank includes a tank body (1), and a water distribution and air distribution system (2), a filter bed (3) and a water collection tank (4) are sequentially arranged in the tank body (1) from bottom to top; The filter bed (3) includes a filter media layer; The water collection tank (4) is respectively communicated with a filtered water outlet pipe (411) and a backwash drain pipe (413); The water distribution and air distribution system (2) includes a water distribution and air distribution pipe (222) arranged at the bottom of the filter bed (3), and the water distribution and air distribution pipe (222) is respectively communicated with a filtered water inlet pipe (211), a backwash air inlet pipe (213), a backwash water inlet pipe and a bottom sewage drain pipe (215); A plurality of swirl holes (222a) are arranged on the water distribution and air distribution pipe (222), and the inner wall of the swirl hole (222a) has a spiral water channel.

2. The upflow filter according to claim 1, characterized in that, The spiral water channels of two adjacent swirl holes (222a) have opposite rotation directions.

3. The upflow filter according to claim 2, characterized in that, The distance between two adjacent swirl holes (222a) near the inner wall of the tank body (1) is smaller than the distance between two adjacent swirl holes (222a) near the center of the tank body (1).

4. The upward flow filter according to claim 3, wherein, The water outlet direction of the swirl holes (222a) arranged near the inner wall of the tank body (1) faces the inner wall of the tank body (1).

5. The upflow filter according to any one of claims 2-4, characterized in that, The backwash water inlet pipe includes a first backwash water inlet pipe (217) and a second backwash water inlet pipe (219). The first backwash water inlet pipe (217) is communicated with the water distribution and air distribution pipe (222) through a gas-liquid mixer (221). After the gas-liquid mixer (221) quickly mixes water and air, a gas-water mixture is formed; the second backwash water inlet pipe (219) is communicated with the water distribution and air distribution pipe (222).

6. A backwashing method for the upflow filter as described in claim 5, characterized in that, The method includes the following steps: Step S1, first bottom sewage discharge: close the filtered water inlet pipe (211), the bottom sewage drain pipe (215) starts to discharge sewage, and the sewage discharge stops when the liquid level drops to a first set height above the filter bed (3); Step S2, swirl flushing: after stopping the first bottom sewage discharge, input the gas-water mixture into the water distribution and air distribution pipe (222), and the water flow after passing through the swirl holes (222a) performs swirl scrubbing on the lower part of the filter media layer; Step S3, second bottom sewage discharge: after stopping the swirl flushing, the bottom sewage drain pipe (215) starts to discharge sewage, and the sewage discharge stops when the liquid level drops to a second set height above the filter bed (3); Step S4, single air washing: after stopping the second bottom sewage discharge, perform backwash air intake through the backwash air inlet pipe (213) to loosen the filter media layer; Step S5, single water washing: after stopping the single air washing, perform backwash water intake through the backwash water inlet pipe to wash the filter media layer, and the impurities washed down are discharged through the backwash drain pipe (413).

7. The backwashing method according to claim 6, wherein It further includes: Step S6, rinsing: input water through the filtered water inlet pipe (211) to rinse the filter bed (3), and the rinsed water is discharged through the backwash drain pipe (413).

8. The backwashing method according to claim 7, wherein If the drainage turbidity is in the first interval at the end of step S5, resume filtration; If the drainage turbidity is in the second interval at the end of step S5, enter step S6 or extend step S5 to make the drainage turbidity in the first interval and resume filtration; If the drainage turbidity is in the third interval at the end of step S5, then repeat steps S2 to S5 until the drainage turbidity is in the first interval, and resume filtration; The first interval < the second interval < the third interval.

9. The backwashing method according to claim 8, wherein The first interval ≤ 5 NTU, the second interval > 5 NTU and < 10 NTU, and the third interval ≥ 10 NTU.

10. The backwashing method according to claim 6, wherein The first set height is 200 - 600 mm, and the second set height is 100 - 200 mm.

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