CN105013244A - Multistage rainwater purification treatment device - Google Patents

Abstract

The invention discloses a multistage rainwater purification treatment device which comprises a plurality of stages of treatment pools; the plurality of stages of treatment pools comprises a pre-settling pool, a filtering pool and a water discharging pool from forth to back; a water inlet pipe is arranged in the pre-settling pool; a baffle structure is arranged between the pre-settling pool and the filtering pool; an overflowing baffle is arranged between the filtering pool and the water discharging pool; a plurality of rainwater filters are arranged in the filtering pool; the water discharging openings of the rainwater filters are communicated with the water discharging pool; a water outlet pipe is connected in the water discharging pool. According to the multistage rainwater purification treatment device, functions of gravity settling, screening, filtering and overflowing are integrated, sediments in rainwater are removed by the pre-settling pool, the baffle structure blocks floating matters in the rainwater and can perform primary purification on the rainwater, and the further filtering treatment is performed on the rainwater by the rainwater filters in the filtering pool, so that pollutants, such as particulate matters, heavy metal and organic matters, in the rainwater are removed effectively, the purification treatment efficiency and the pollutant removal efficiency are improved, the standard discharging or recycling of the rainwater is realized, the water environment is protected, and the difficult problem of water shortage is solved.

Description

Multi-stage rainwater purification treatment equipment

technical field

The invention relates to rainwater purification equipment, in particular to a multi-stage rainwater purification treatment equipment.

Background technique

The process of urbanization and industrialization has led to increasingly serious water crisis and rain and flood hazards, and fewer and fewer clean water sources. Now, almost all countries in the world have water shortages, and the problem of water shortages in my country is even more serious, especially in northern China. Therefore, people need to develop a new water resource, and it has become an important emerging topic to collect and utilize rainwater as water resource for comprehensive management. However, due to the rapid economic development, the accelerated urbanization process, and the extensive use of surface impermeable materials, the runoff pollution has become more and more serious, especially the initial rainwater with more pollutants, and the pollutant indicators of the initial rainwater in some areas are the highest. The value is much higher than that of typical urban domestic sewage.

At present, the collection and treatment of initial rainwater in my country is still in its infancy. Collecting initial rainwater is only to prevent it from being discharged into the water body to pollute the water quality, while little consideration is given to the purification and reuse of initial rainwater, even if some areas try to treat initial rainwater Purification treatment is carried out, and the existing rainwater treatment facilities in most areas are far from meeting the demand for rainwater treatment. Therefore, most of the initial rainwater is directly discharged into the municipal domestic sewage pipe network, and the concentration of pollutants in the rainwater is relatively high, especially the initial rainwater from the road. Direct discharge into the domestic sewage pipe network will bring a greater load to the sewage plant; In some areas, the initial rainwater is directly discarded, or the rainwater beyond the treatment capacity of the rainwater treatment facilities is directly discharged into the natural water body, which will cause water pollution, and the rainwater is not used rationally, resulting in waste of water resources.

Contents of the invention

The purpose of the present invention is to provide a multi-stage rainwater purification treatment equipment, which can greatly reduce the pollutant content in rainwater, and realize discharge or reuse of rainwater up to the standard.

In order to achieve the above object, the technical solution adopted by the present invention is: a multi-stage rainwater purification treatment equipment, including a multi-stage treatment pool, the multi-stage treatment pool includes a pre-sedimentation pool, a filter pool and a drainage pool in sequence from front to back. The pre-sedimentation tank is connected with a water inlet pipe, a baffle structure is provided between the pre-sedimentation tank and the filter tank, an overflow baffle is provided between the filter tank and the drainage tank; a or a plurality of rainwater filters, the outlet of the rainwater filter communicates with the drainage pool, and the drainage pool is connected with an outlet pipe.

The present invention integrates the functions of gravity sedimentation, screening, filtration and overflow to carry out multi-stage treatment of rainwater. After the rainwater passes through the pre-sedimentation tank to remove sediment, the baffle structure intercepts the floating objects in the rainwater and initially purifies the rainwater, and then The rainwater filter in the filter pool further filters the rainwater to effectively remove pollutants such as particulate matter, heavy metals and organic matter in the rainwater. The present invention uses an effective process to achieve a high purification treatment efficiency and pollutant removal rate. Meet the needs of rainwater treatment, realize the standard discharge or reuse of rainwater, which not only protects the water environment, but also alleviates the problem of water shortage; when the rainfall is heavy, the rainwater can overflow from the overflow baffle into the drainage pool , which ensures that when the rainwater entering the purification treatment equipment exceeds the processing capacity of the equipment, the purification treatment equipment can also operate normally; the purification treatment equipment has high processing efficiency, simple and convenient operation, and can operate automatically without external power. The operating cost is extremely low; the purification treatment equipment is flexible in size, can adapt to the needs of various working conditions, and can be customized according to the actual situation.

Further, the rainwater filter includes a support base plate and a cover plate, an outer filter cartridge and a central collection pipe are coaxially fixed on the support base plate, the cover plate covers the top of the outer filter cartridge, and the cover plate There is a central collection pipe through hole, and a water outlet is opened on the support base plate. The top of the central collection pipe passes through the central collection pipe through hole, and the inner side of the central collection pipe is surrounded by a drainage cavity. The bottom end of the collecting pipe is connected with the water outlet, and a filter medium is arranged between the outer filter cylinder and the central collecting pipe, and a plurality of water holes are opened on the wall of the central collecting pipe, and the water holes of each layer are always The area increases or equals from bottom to top. By ingeniously arranging the water holes on the central collection pipe, when the water level outside the filter is low, the rainwater enters the central collection pipe from the lower part of the filter. Since the total area of the water passage holes in the lower layer of the central collection pipe is small, to a certain extent The flow of rainwater entering the central collection pipe is limited, so that the external rainwater level rises, which not only prolongs the contact time between rainwater and the filter medium at the lower end, but also enables the filter medium at the upper end of the filter to be fully utilized, thereby greatly improving the filter medium. The utilization rate of the rainwater and the filter medium is prolonged, so that the rainwater and the filter medium have sufficient contact; when the total opening area of each layer of the water hole on the wall of the central collection pipe is equal, the flow rate of the outlet is also limited. It can ensure that the upper filter medium is fully utilized.

Further, the diameters of the water passage holes on the wall of the central collection pipe are the same, and the number of the water passage holes in each layer increases or is equal from bottom to top.

Further, the diameters of the water passage holes on the wall of the central collection pipe are different, and the total area of the water passage holes in each layer increases or is equal from bottom to top.

Further, an outer filter net and an inner filter net are coaxially fixed sequentially from the outside to the inside between the outer filter cartridge and the central collection pipe, and the filter medium is arranged between the outer filter net and the inner filter net.

Further, the particle size of the outer filter medium is larger than the particle size of the inner filter medium.

Further, a drainage pipe is connected to the water outlet, and a flow restriction structure is provided on the drainage pipe.

Further, the top of the central collecting pipe is sealed; or the top of the central collecting pipe is an overflow collecting port, and the height of the overflow baffle is higher than the overflow collecting port. When the top of the central collection pipe is closed, when the rainfall is heavy, the rainwater will overflow from the overflow baffle into the drainage tank, which ensures that when the rainwater entering the purification treatment equipment exceeds the treatment capacity of the equipment, the purification The treatment equipment can also operate normally; when the top of the central collection pipe is an open overflow collection port, when the rainfall is heavy, the later rainwater is relatively clean, and the later rainwater can directly enter the filter drainage main pipe through the overflow collection port and flow into the drainage In the pool; the height of the overflow baffle is higher than the overflow collection port. When the rainfall is greater, more rainwater will overflow from the top of the overflow baffle into the drainage pool, which ensures that the rainwater entering the rainwater purification treatment When the rainwater of the equipment exceeds the processing capacity of the equipment, the rainwater purification treatment equipment can also operate normally.

Further, the baffle structure includes a fixed baffle, the top end of the fixed baffle is connected with a slag blocking structure, and the bottom end of the fixed baffle is connected with a water passing structure.

Further, the slag blocking structure and the water passing structure are filter screens respectively. The filter on the top of the fixed baffle can intercept the suspended matter in the rainwater and allow the settled rainwater to enter the filter tank; when the rainwater is collected, the filter at the bottom of the fixed baffle allows the rainwater in the pre-sedimentation tank to enter the filter tank filter processing.

Further, one or more elongated grooves are arranged on the fixed baffle from top to bottom, and filter screens are arranged in the elongated grooves, or several small holes are arranged on the fixed baffle from top to bottom . After the rainwater is collected and treated, the rainwater in the pre-sedimentation tank can slowly enter the filter tank through the filter screen in the slender groove.

Further, the bottom surface of the pre-sedimentation tank is lower than the bottom surface of the filter tank. Solid particles such as sediment in the rainwater will be deposited at the bottom of the pre-sedimentation tank, and the bottom of the pre-sedimentation tank is lower than the bottom of the filter tank so that the sediment will not block the water-passing structure.

Further, the baffle structure also includes an upper baffle, the upper baffle is arranged in front of the fixed baffle parallel to the fixed baffle, and the bottom of the upper baffle is lower than the bottom of the slag retaining structure. top. An upper baffle is set next to the slag blocking structure. The bottom of the upper baffle is lower than the top of the slag blocking structure. The rainwater needs to bypass the bottom of the upper baffle and pass through the slag blocking structure before entering the filter tank, which can effectively intercept the floating in the rainwater. things.

Further, the upper baffle is fixed on the top of the multi-stage treatment pool; or the upper baffle is a floating baffle, the top of the floating baffle is above the water surface, and the bottom is below the water surface. A part of the floating baffle is below the water surface, and a part is above the water surface. It can rise with the rise of the water level and fall with the decline of the water level, completely intercepting the floating objects in the rainwater.

Further, the fixed baffle is a closed plate; or the fixed baffle is an orifice, and the diameter of the holes on the fixed baffle increases from bottom to top. When the fixed baffle is an orifice, it not only intercepts the suspended solids in the water, but also the size of the opening gradually increases from bottom to top, so the flow of water passing through the lower part of the fixed baffle is small, so that the rainwater level in the pre-sedimentation tank is kept constant. The rise prolongs the residence time of rainwater in the sedimentation tank, which is conducive to the full settlement of solid particles such as sediment in the rainwater.

Further, a plurality of rainwater filters are connected in parallel in the filter pool, and a filter drainage main pipe is provided at the bottom of the filter pool, and the outlets of each rainwater filter are respectively connected with the filter drainage main pipe, and the filter The drainage main pipe is connected with the drainage pool.

Furthermore, the multi-stage rainwater purification treatment equipment is composed of multiple multi-stage treatment pools connected in series or in parallel.

Description of drawings

Fig. 1 is a structural schematic diagram of a rainwater multi-stage purification treatment equipment.

Figure 2 is a schematic diagram of the assembly structure of the upper baffle, the slag blocking structure and the fixed baffle.

FIG. 3 is a schematic diagram of a modified structure of FIG. 2 .

Fig. 4 is a schematic structural diagram of the rainwater filter in Fig. 1 .

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings to facilitate a clearer understanding of the present invention, but they do not limit the present invention.

As shown in FIG. 1 , a multi-stage rainwater purification treatment equipment includes a multi-stage treatment pool 301 , and the multi-stage treatment pool 301 includes a pre-sedimentation pool 3011 , a filter pool 3012 and a drainage pool 3013 sequentially from front to back. The bottom surface of the pre-sedimentation tank 3011 can be lower than the bottom surface of the filter tank 3012, so that solid particles such as silt in the rainwater entering the pre-settling tank 3011 are more smoothly deposited on the bottom of the pre-settling tank 3011, and the sediment needs to be cleaned regularly. The pre-settling tank 3011 A water inlet pipe 302 is connected inside. There is a baffle structure 304 between the pre-sedimentation tank 3011 and the filter tank 3012. The baffle structure 304 includes a fixed baffle 3014 in the middle. The top of the fixed baffle 3014 is connected with a slag blocking structure 3015 for intercepting suspended matter in rainwater. The fixed baffle The bottom end of 3014 is connected with a water-passing structure 3016, and both the slag-retaining structure 3015 and the water-passing structure 3016 can use filter screens. The top of the multi-stage treatment pool 301 in front of the fixed baffle 3014 can also be provided with an upper baffle 3020 extending downwards. The baffle 3020 is arranged parallel to the fixed baffle 3014, and the bottom of the upper baffle 3020 is lower than the top of the slag blocking structure 3015, so that the rainwater needs to bypass the bottom of the upper baffle 3020 and then pass through the filter on the top of the fixed baffle 3014 for filtration Pond 3012, thereby intercepting the floating object in rainwater more effectively (as shown in Figure 2), this upper baffle 3020 also can be floating baffle 3023, and part of floating baffle 3023 is below the water surface, and a part is above the water surface (as shown 3), the floating baffle 3023 can rise with the rise of the water level, and can fall with the decline of the water level, so that the floating objects in the rainwater can be completely intercepted; the fixed baffle 3014 can be a closed plate, at this time, the fixed baffle The bottom of the plate 3014 can be provided with a valve (the valve is in a closed state at first, and when the rainwater enters the pre-settling tank 3011, the valve is still closed until the water level of the pre-settling tank 3011 reaches the highest, the valve is opened, and then until the water level of the pre-settling tank 3011 drops to the lowest, the valve is closed again), the fixed baffle 3014 can also be an orifice or a filter screen, and the opening apertures on the orifice or the filter screen increase from bottom to top, so that the flow at the bottom of the orifice or the filter screen is smaller than that at the top. The rain water level in the pre-sedimentation tank 3011 is constantly rising, which is not only beneficial to the deposition of solid particles such as sediment in the rainwater in the pre-sedimentation tank 3011, but also the orifice plate or filter screen can intercept the suspended matter in the rain water; The plate 3014 can also be provided with one or more slender grooves from top to bottom, and a filter screen is arranged in the slender grooves, or a number of small holes are arranged on the fixed baffle from top to bottom. After the rainwater collection and treatment are completed, The rainwater in the pre-sedimentation tank can slowly enter the filter tank through the filter screen in the elongated tank or the small holes on the fixed baffle. There are three rainwater filters 3018 connected in parallel in the filter pool 3012, and a filter drain main pipe 3022 is provided at the bottom of the filter pool 3012, and the outlets 3019 of each rainwater filter 3018 are respectively connected to the filter drain main pipe 3022, and the filter drain main pipe 3022 is connected to the drainage pool 3013 , the drainage pool 3013 is connected with an outlet pipe 303, the top of the rainwater filter 3018 is provided with an overflow collection port 3021, and an overflow baffle 3017 is provided between the filter pool 3012 and the drainage pool 3013, and the height of the overflow baffle 3017 is higher than the overflow Flow collection port 3021 but below the top of fixed baffle 3014. Wherein, the multi-stage rainwater purification treatment equipment can also adopt a structure form in which multiple multi-stage treatment pools 301 are connected in series or in parallel.

In the above solution, as shown in FIG. 4 , the rainwater filter 3018 includes a support base plate 101 and a cover plate 102. Both the support base plate 101 and the cover plate 102 are impervious to water, and the outer filter cartridge 103 is coaxially fixed on the support base plate 101 from outside to inside. , the outer filter screen 107, the inner filter screen 108 and the central collection pipe 104, the aforementioned structural parts are all made of corrosion-resistant materials; a filter medium 106 is arranged between the outer filter screen 107 and the inner filter screen 108, and the cover plate 102 covers the On the top of the outer filter cartridge 103, the outer filter screen 107 and the inner filter screen 108, the cover plate 102 can be disassembled. When the cover plate 102 is removed, the filter medium 106 can be replaced. The cover plate 102 has a central collection pipe through hole 102-1 , the center of the supporting bottom plate 101 has a water outlet 101-1, the top of the central collecting pipe 104 passes through the central collecting pipe through hole 102-1, the inner side of the central collecting pipe 104 forms a drainage cavity 105, and the bottom of the central collecting pipe 104 is connected to the outlet The water outlet 101-1 is connected, and the water outlet 101-1 is connected with a drain pipe 109. The drain pipe 109 is provided with a flow limiting structure 110. The flow limiting structure 110 can be a flow limiting valve. There are several holes on the wall of the central collecting pipe 104. The water hole 104-1, the total area of the water hole 104-1 of each layer increases from bottom to top, wherein, the diameter of the water hole 104-1 on the wall of the central collection pipe 104 can be different or the same. When the hole diameters of the water holes 104-1 on the wall of the central collecting pipe 104 are the same, the number of water holes 104-1 in each layer increases from bottom to top, and the top of the central collecting pipe 104 is the overflow collection port 3021, and the overflow collection port 3021 is provided with an openable filter screen 111 for the overflow collection port. Wherein, the outer filter cartridge 103, the outer filter screen 107 and the inner filter screen 108 can be in the shape of a cylinder, a square tube or a polygonal mesh tube; the central collecting pipe 104 can be in the shape of a round tube, a square tube or a polygonal tube; Remove the outer filter screen 103 and the inner filter screen 108, in this case, the central collection pipe through hole 102-1 on the outer filter cartridge 103 and the central collection pipe 104 will ensure that the filter medium 106 will not pass through the outer filter cartridge 103 and the center Collection pipe 104; In addition, the water passage hole 104-1 on the central collection pipe 104 pipe wall, each layer water passage hole 104-1 total area also can be equal, the water passage hole 104-1 aperture on the central collection pipe 104 pipe wall When the sizes are the same, the number of water holes 104-1 in each layer can also be equal. At this time, by limiting the flow of the drain outlet 3019, it can also ensure that the upper filter medium is fully utilized.

In the above scheme, as shown in Fig. 4, the filter medium 106 is granular, and can be composed of one or more of compost, vermiculite, perlite, sand, zeolite, peat, etc., and can also be made of artificially manufactured porous materials Such as active carbon and ion exchanger composition, its particle size is respectively greater than the mesh aperture of outer filter screen 107 and inner filter screen 108, to guarantee that filter medium 106 can not leak from outer filter screen 107 and inner filter screen 108; When 106 adopts multiple materials, the filter medium 106 can be divided into multiple layers in the horizontal direction according to different types and different particle sizes, and the particle size ratio of the filter medium 106 near the outer filter screen 107 side is more The particle size of the filter medium 106 is large.

The specific working principle of the rainwater filter 3018 is as follows: when the rainwater filter 3018 works normally, rainwater enters the filter medium 106 through the outer filter cartridge 103 and the outer filter screen 107 from the outside of the rainwater filter 3018, and the rainwater filtered by the filter medium is then Pass through the inner filter screen 108 and the water hole 104-1 on the central collection pipe 104 to enter the drainage cavity 105 in turn, and the filtered rainwater in the drainage cavity 105 is then discharged by the drainage pipe 109, wherein the central collection pipe 104 tube wall The total opening area of the upper water hole 104-1 increases or is equal from the lower floor to the upper floor. When the water level outside the rainwater filter 3018 is low, the rainwater enters the central collecting pipe 104 from the bottom of the rainwater filter 3018. The total area of the water hole 104-1 in the lower layer of the central collection pipe is small, which limits the rainwater flow entering the central collection pipe 104 to a certain extent, so that the external rainwater level rises, and the filter medium in the upper part of the rainwater filter 3018 can be fully absorbed like this. At the same time, a flow limiting valve is provided on the downstream of the drainpipe 109, and the rainwater can be fully contacted with the filter medium 106 by limiting the outlet flow, so as to achieve the purpose of effectively removing pollutants; as the water level continues to rise, when the rainwater When the water level outside the filter 3018 reaches the top of the central collecting pipe 104, the later stage rainwater will directly enter the drainage cavity 105 from the overflow collecting port 3021 at the top of the central collecting pipe 104 (when the rainfall is very large, the rainwater can be directly collected from the overflow. port 3021 enters the drainage cavity 105), the overflow collection port filter screen 111 at the overflow collection port 3021 can intercept the floating and suspended matter in the rainwater, and the whole filtering process not only ensures the full contact between the rainwater and the filter medium 106, It can effectively remove pollutants in the rainwater, and also ensure the treatment efficiency of the rainwater filter 3018; after the rainwater filtration process is completed, the filter medium 106 will be blocked by pollutants to a certain extent, and the openable overflow collection port filter can be removed. net 111, and close the flow limiting valve, backwash the filter medium from the top of the central collection pipe 104 with an external water source, the pollutants retained in the filter medium 106 can be washed out of the filter, and the penetration capacity of the filter medium 106 can be improved.

The working process of the multi-stage rainwater purification treatment equipment shown in Figure 1 is as follows: when the rainwater is collected, the rainwater enters the pre-sedimentation tank 3011 from the water inlet pipe 302, and because of the separation of the fixed baffle 3014, the rainwater cannot enter the filter tank 3012 very quickly at the beginning. Only a small amount of rainwater will enter the filter tank 3012 from the water passing structure 3016 below the fixed baffle 3014 (that is, the filter screen at the bottom of the fixed baffle); Solid particles such as sand can be deposited on the bottom of the pre-settling tank 3011, because the bottom surface of the pre-settling tank 3011 is lower than the bottom surface of the filter tank 3012, and the sediment will not block the water-passing structure 3016 (that is: the filter screen at the bottom of the fixed baffle plate 3014); With the rise of the water level in the pre-sedimentation tank 3011, when reaching the height of the slag blocking structure 3015 (that is: the filter screen on the top of the fixed baffle plate 3014), the settled rainwater will enter the filter pool 3012 through the slag blocking structure 3015, and the rainwater in the rainwater The suspended matter will be intercepted by the slag blocking structure 3015, and the floating matter can be intercepted by setting the upper baffle 3020 or the floating baffle 3023; after the rainwater enters the filter pool 3012, the rainwater will enter the interior of each rainwater filter 3018 from the outside of the rainwater filter 3018 , the rainwater after multiple filtration treatment by the rainwater filter 3018 will be collected in the filter drainage main pipe 3022, then flow into the drainage pool 3013, and finally be discharged from the multi-stage treatment pool 301 by the outlet pipe 303; when the rainfall is large, the later rainwater will be relatively clean , later stage rainwater can directly enter the filter drainage main pipe 3022 through the overflow collecting port 3021 of the rainwater filter and flow into the drainage pool 3013; when the rainfall is larger, more rainwater will overflow from the overflow baffle 3017 In the drainage pool 3013, this ensures that the rainwater purification treatment equipment can also operate normally when the rainwater entering the rainwater purification treatment equipment exceeds the processing capacity of the equipment.

Claims (17)

1. a multistage rainwater purification treatment facility, comprise multistep treatment pond (301), it is characterized in that: described multistep treatment pond (301) comprises pre-settling tank (3011) from front to back successively, filtering ponds (3012) and blowoff basin (3013), water inlet pipe (302) is connected with in described pre-settling tank (3011), be provided with baffle arrangement (304) between described pre-settling tank (3011) and described filtering ponds (3012), between described filtering ponds (3012) and described blowoff basin (3013), be provided with overflow baffle (3017); One or more rain water filtering device (3018) is provided with in described filtering ponds (3012), the discharge outlet (3019) of described rain water filtering device (3018) is communicated with described blowoff basin (3013), is connected with outlet pipe (303) in described blowoff basin (3013).

2. multistage rainwater purification treatment facility according to claim 1, it is characterized in that: described rain water filtering device (3018) comprises support baseboard (101) and cover plate (102), it is characterized in that: described support baseboard (101) is coaxially fixed with outer cartridge filter (103) and central collection tube (104), described cover plate (102) is covered in described outer cartridge filter (103) top, described cover plate (102) has central collection tube via hole (102-1), described support baseboard (101) had the mouth of a river (101-1), described central collection tube (104) top passes from described central collection tube via hole (102-1), described central collection tube (104) inner side surrounds draining cavity (105), described central collection tube (104) bottom is communicated with the described mouth of a river (101-1) of crossing, filter medium (106) is provided with between described outer cartridge filter (103) and central collection tube (104), described central collection tube (104) tube wall has some water holes (104-1), and the described water hole of each layer (104-1) gross area increases progressively or equal from the bottom up.

3. multistage rainwater purification treatment facility according to claim 2, it is characterized in that: the aperture of the described water hole (104-1) on described central collection tube (104) tube wall is consistent, the described water hole of each layer (104-1) quantity increases progressively or equal from the bottom up.

4. multistage rainwater purification treatment facility according to claim 2, it is characterized in that: the pore size of the described water hole (104-1) on described central collection tube (104) tube wall differs, the described water hole of each layer (104-1) gross area increases progressively or equal from the bottom up.

5. multistage rainwater purification treatment facility according to claim 2, it is characterized in that: be coaxially fixed with outer screen pack (107) and filtering net (108) from outside to inside successively between described outer cartridge filter (103) and central collection tube (104), described filter medium (106) is placed between described outer screen pack (107) and described filtering net (108).

6. multistage rainwater purification treatment facility according to claim 2, is characterized in that: the grain diameter of the described filter medium (106) in outside is greater than the grain diameter of the described filter medium (106) of inner side.

7. multistage rainwater purification treatment facility according to claim 2, it is characterized in that: described mistake on the mouth of a river (101-1) is connected with drainpipe (109), and described drainpipe (109) is provided with flow restriction (110).

8. multistage rainwater purification treatment facility according to claim 2, is characterized in that: described central collection tube (104) top seal; Or described central collection tube (104) top is overflow collection mouth (3021), the height of described overflow baffle (3017) is higher than described overflow collection mouth (3021).

9. multistage rainwater purification treatment facility according to claim 1, it is characterized in that: described baffle arrangement (304) comprises fixed dam (3014), described fixed dam (3014) top is connected with debris retaining structure (3015), and described fixed dam (3014) bottom was connected with water-bound (3016).

10. multistage rainwater purification treatment facility according to claim 9, is characterized in that: described debris retaining structure (3015) and described water-bound (3016) of crossing are respectively filter screen.

11. multistage rainwater purification treatment facilities according to claim 9, it is characterized in that: (3014) are provided with one or more elongated slot from top to bottom with described fixed dam, be provided with filter screen in described elongated slot, or described fixed dam (3014) is provided with some apertures from top to bottom.

12. multistage rainwater purification treatment facilities according to claim 1, is characterized in that: described pre-settling tank (3011) bottom surface is lower than described filtering ponds (3012) bottom surface.

13. multistage rainwater purification treatment facilities according to claim 9, it is characterized in that: described baffle arrangement (304) also comprises overhead gage (3020), the parallel described fixed dam (3014) of described overhead gage (3020) is arranged in described fixed dam (3014) front, and the bottom of described overhead gage (3020) is lower than the top of described debris retaining structure (3015).

14. multistage rainwater purification treatment facilities according to claim 13, is characterized in that: described overhead gage (3020) is fixed on described multistep treatment pond (301) top; Or described overhead gage (3020) is floating barrier (3023), described floating barrier (3023) top emerges above, and bottom is positioned at below the water surface.

15. multistage rainwater purification treatment facilities according to claim 9, is characterized in that: described fixed dam (3014) is shut; Or described fixed dam (3014) is orifice plate, and the upper open pore size of described fixed dam (3014) increases progressively from the bottom up.

16. multistage rainwater purification treatment facilities according to claim 1, it is characterized in that: in described filtering ponds (3012), be parallel with multiple rain water filtering device (3018), and described filtering ponds (3012) bottom is provided with filtration main sewer (3022), the described discharge outlet (3019) of rain water filtering device described in each (3018) is connected with described filtration main sewer (3022) respectively, and described filtration main sewer (3022) is connected with described blowoff basin (3013).

17. multistage rainwater purification treatment facilities according to claim 1, is characterized in that: described multistage rainwater purification treatment facility is formed by multiple described multistep treatment pond (301) serial or parallel connection.