A lightweight filter media ring filter device for rainwater storage tanks

Abstract

This invention discloses a lightweight filter media annular filtration device for rainwater storage tanks, comprising a primary separation device and a secondary separation device. The primary separation device can be an integrated primary separation device, a separate primary separation device, or a modified rainwater pipe network. The secondary separation device includes multiple independent filtration units, each containing a bottom perforated baffle, a floating perforated baffle, and a top perforated baffle arranged sequentially from bottom to top. Spherical filter media is filled between the floating perforated baffle and the bottom perforated baffle. The primary separation device is located above the secondary separation device. Rainwater enters the central water distribution cylinder of the secondary separation device from the primary separation device, then flows through an independent water pipe at the lower end into the filtration unit for filtration and purification, before flowing out from the top outlet. This invention enhances the rapid separation effect at the pore structure through the elastic deformation of the filter media, breaking through the highest filtration rate of existing filtration methods and improving the filtration effect. It is suitable for the preliminary purification of rainwater runoff before storage tanks.

Description

Technical Field

[0001] This invention belongs to the technical field of water treatment equipment, and relates to a filtration device, particularly a lightweight filter media annular filtration device for rainwater storage tanks. Background Technology

[0002] With rapid urbanization, traditional stormwater drainage systems, based on the principles of "end-of-pipe" and "rapid drainage," suffer from numerous water environment problems such as urban flooding, combined sewer overflows, and runoff pollution, and are no longer adequate to meet the demands of urban water environment development. To address these issues, in urban areas where surface space is limited, stormwater storage tanks have become crucial facilities for stormwater regulation and runoff pollution control. They effectively reduce peak flow, lower drainage pressure on pipe networks, and play a vital role in flood prevention, flood control, and reducing non-point source pollution.

[0003] The dense, paved surfaces of cities significantly reduce permeability, leading to a substantial increase in surface runoff. Initial stormwater runoff carries large amounts of particulate pollutants, which are discharged into stormwater storage tanks via drainage networks and accumulate at the bottom. This causes siltation and compaction, affecting the effective volume of the tanks and gradually weakening their stormwater control function. Excessive sediment accumulation at the bottom of the tanks can lead to deterioration, worsening water quality, producing odors, and negatively impacting receiving water bodies. It also weakens the tanks' ability to reduce non-point source pollution, and the accumulation of anaerobic byproducts can even endanger lives. Storage tanks typically have drainage holes at the bottom; however, the drainage process can cause large amounts of sediment to rise, and the drainage pipes are easily clogged due to the intake of large amounts of impurities, resulting in poor drainage and affecting the normal operation of the storage tanks. Therefore, it is urgent to address the problems caused by particulate pollutants, such as the reduced stormwater control function and non-point source pollution reduction effect of storage tanks, and their inability to operate normally.

[0004] Currently, the maintenance of rainwater storage tanks typically involves manual cleaning, hydraulic jet cleaning, submersible mixer cleaning, or the use of self-flushing interception equipment. Manual cleaning is relatively inexpensive but labor-intensive and poses significant safety hazards. Other methods generally suffer from high investment costs, equipment wear and tear, high operating costs, and limited flushing effectiveness. High-efficiency and rapid filtration of rainwater before it enters the storage tank to significantly reduce particulate matter content is beneficial for fully utilizing the tank's function, reducing maintenance frequency and difficulty, and optimizing the tank's ability to mitigate peak flood flows and non-point source pollution.

[0005] Limited by the structure of the filter bed, the type of filter media, and the filtration principle, the fastest filtration rate of current rapid filtration technology can only reach about 12m / h. Moreover, as the filtration rate increases, the filtration effect and operating cycle gradually decrease, making it difficult to meet the requirements of rapid and efficient filtration before the storage tank under the conditions of storm runoff. Therefore, it is urgent to break through these limitations and develop a new type of filtration device that can maintain efficient filtration at high filtration rates. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a lightweight filter media ring filtration device for rainwater storage tanks, solving the problem that existing technologies cannot meet the requirements for efficient and rapid filtration before storage tanks.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A ring-shaped filter device with lightweight filter media for rainwater storage tank includes a primary separation device and a secondary separation device.

[0009] The primary separation device can be any one of an integrated primary separation device, a separate primary separation device, or a modified rainwater pipe network; the integrated primary separation device includes an annular integrated separation chamber and an integrated inlet pipe disposed on the inner annular wall of the integrated separation chamber; the separate primary separation device includes a separate separation chamber and separate inlet pipes on its side walls; the modified rainwater pipe network includes a rainwater pipe network and an inlet baffle at its outlet.

[0010] The secondary separation device includes a coaxial central water distribution cylinder and an outer cylinder. A lower annular plate connects the lower edge of the central water distribution cylinder to the lower inner wall of the outer cylinder. A radially spaced partition plate connects the outer wall of the central water distribution cylinder and the inner wall of the outer cylinder, with the lower end of the partition plate connected to the lower annular plate. Multiple partition plates are used to divide the annular space between the central water distribution cylinder and the outer cylinder into multiple independent filtration units. Each filtration unit has a bottom perforated baffle, a floating perforated baffle, and a top perforated baffle arranged sequentially from bottom to top. Spherical filter media is filled between the floating perforated baffle and the bottom perforated baffle. The space between the bottom perforated baffle and the lower annular plate is a rectifier cavity. The lower end of the central water distribution cylinder is connected to the rectifier cavity of each filtration unit via multiple independent water pipes. A top outlet is provided on the side wall of the outer cylinder above the top perforated baffle to connect to a rainwater storage tank. Each rectifier cavity is connected to a bottom discharge pipe at its lower end, and all bottom discharge pipes converge at a bottom main discharge pipe.

[0011] The primary separation device is located above the secondary separation device. Rainwater enters the central water distribution cylinder of the secondary separation device from the integrated inlet pipe, separate inlet pipe, or inlet mesh of the primary separation device, and then enters the filtration unit through the independent water pipe at the lower end for filtration and purification. The purified rainwater flows out from the top outlet, and the filter residue is discharged from the bottom discharge pipe.

[0012] The present invention also includes the following technical features:

[0013] Specifically, the bottom perforated baffle, the floating perforated baffle, and the top perforated baffle are all hollow arc-shaped; the edge of the bottom perforated baffle is fixedly connected to the outer wall of the central water distribution cylinder, the partition plate, and the inner wall of the outer cylinder; the floating perforated baffle can move up and down along the vertical slide rails of the outer wall of the central water distribution cylinder and the inner wall of the outer cylinder; the edge of the top perforated baffle is fixedly connected to the outer wall of the central water distribution cylinder, the partition plate, and the inner wall of the outer cylinder.

[0014] Specifically, the bottom perforated baffle, the floating perforated baffle, and the top perforated baffle are all provided with multiple holes with a diameter of 3mm.

[0015] Specifically, the spherical filter media has a concentration of 0.1-0.3 g / cm³. 3 The polystyrene foam floats have a particle size of 5mm.

[0016] Specifically, the independent water pipe is equipped with an independent valve.

[0017] Specifically, a valve is installed on the bottom discharge pipe.

[0018] Specifically, the integrated separation chamber of the integrated primary separation device is formed by a cylindrical outer wall, a cylindrical inner wall, and an annular bottom wall. The annular bottom wall is inclined towards the cylindrical inner wall. An integrated water inlet pipe is located on the cylindrical inner wall, and an integrated sludge discharge pipe is located on the annular bottom wall. The integrated sludge discharge pipe is connected to the bottom main discharge pipe. Valves are provided on both the integrated water inlet pipe and the integrated sludge discharge pipe. When the integrated primary separation device is used in conjunction with the secondary separation device, the cylindrical outer wall is aligned with the upper end of the outer cylinder, and the cylindrical inner wall is aligned with the upper end of the central water distribution cylinder. Rainwater enters the integrated separation chamber from the top and then enters the central water distribution cylinder through the integrated water inlet pipe.

[0019] Specifically, the separate separation chamber of the separate primary separation device is surrounded by a cylindrical side wall and an inclined bottom wall. A separate sludge discharge pipe is provided at the lowest point of the inclined bottom wall. The separate sludge discharge pipe is connected to the bottom main discharge pipe. Valves are provided on both the separate water inlet pipe and the separate sludge discharge pipe. Rainwater enters the separate separation chamber from the top and then enters the central water distribution cylinder through the separate water inlet pipe.

[0020] Specifically, the lower annular plate is inclined towards the outer cylinder side, and one end of the bottom discharge pipe is connected to the lower annular plate and then communicates with the rectifier cavity, and is arranged close to the outer cylinder.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (1) The device of the present invention has a primary separation device at the water inlet end, which can realize the primary separation of light large-sized floating objects and heavy particles, ensuring the stable operation of the filtration unit.

[0023] (2) Compared with traditional quartz sand filter media, the elastic polystyrene foam floats selected in this invention have advantages such as large specific surface area and high zeta potential, and have better adsorption and interception effects on particulate matter in initial rainwater runoff. Traditional rapid sand filters adhere particulate matter to the filter media surface through sedimentation, inertia, diffusion, filter media interception, and water flow dynamics. In the device of this invention, in addition to the first four effects mentioned above, the polystyrene packing will undergo elastic deformation after being subjected to water flow buoyancy and baffle compression. The filter media particles are squeezed against each other to form a dense pore structure, reducing the pore size and strengthening the "narrow tube effect" (the flow velocity of liquid increases when flowing through a narrow part) at the pore structure, thereby generating a very strong "velocity separation effect" (the suspended particulate matter in the water migrates and aggregates from the high-velocity flow group to the low-velocity flow group). That is, by changing the flow field at the pore structure of the traditional filter, the effect of water flow dynamics is strengthened, optimizing its filtration effect at high filtration rates, and enabling it to adapt to the characteristics of large initial rainwater volume and high concentration of particulate pollutants.

[0024] (3) This invention relies on the rise and fall of water level to achieve the rearrangement of intercepted particles and lightweight filter media to achieve rapid backwashing without power. There is no support layer or backwashing equipment. The filter structure is simple and the operation and maintenance costs and difficulties are low.

[0025] (4) Each filter unit of the present invention can operate independently by relying on the control of the inlet valve. After a filter unit is blocked, other filter units can still maintain a good filtration effect. Combined with the fast and convenient backwashing, it can ensure uninterrupted filtration at high filtration rate and the running time can cover the rainfall duration.

[0026] (5) By reducing the concentration of particulate pollutants discharged into the rainwater storage tank, this invention ensures the long-term operation of the rainwater storage tank, transforms the traditional old model of "accumulation first, then cleaning", and realizes the sustainable operation mode of "cleaning while using", which is conducive to extending the service life and improving the hydrological and water quality protection effect. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the integrated primary and secondary separation units.

[0028] Figure 2 This is a schematic diagram of a separate primary and secondary separation unit.

[0029] Figure 3 A schematic diagram of the modified rainwater pipe network and secondary separation device;

[0030] Figure 4 The turbidity removal efficiency of the secondary separation device of the present invention at a filtration rate of 15 m / h under pilot conditions.

[0031] The meanings of the labels in the diagram are as follows:

[0032] 1. Integrated primary separation unit; 2. Separate primary separation unit; 3. Modified rainwater pipe network; 11. Integrated separation chamber; 12. Integrated inlet pipe; 21. Separate separation chamber; 22. Separate inlet pipe; 23. Separate sludge discharge pipe; 31. Rainwater pipe network; 32. Inlet baffle; 401. Central water distribution cylinder; 402. Outer cylinder; 403. Lower annular plate; 404. Bottom perforated baffle; 405. Floating perforated baffle; 406. Top perforated baffle; 407. Spherical filter media; 408. Rectifying chamber; 409. Independent water pipe; 410. Top outlet; 411. Bottom discharge pipe; 412. Bottom main discharge pipe. Detailed Implementation

[0033] This invention employs an upward-flowing annular water distribution system. By altering the flow field and particle retention pathway of traditional rapid sand filters, it improves filtration efficiency while exceeding the maximum filtration rate of existing technologies. Simultaneously, it utilizes water flow to rearrange the filter media and retained particles, achieving highly efficient backwashing without the need for backwashing facilities. Before clogging, each independent filter unit's filter layer undergoes water level fluctuations, causing friction between the filter media and retained particles, resulting in media rearrangement and particle separation. The entire process is virtually energy-efficient and requires no backwashing equipment, significantly reducing construction and operating costs. The filter unit can operate stably at a filtration rate of 15 m / h, with a maximum speed of 18 m / h. In areas with a rainstorm recurrence interval of 3-5 years, the filtration rate can be appropriately reduced to extend the operating cycle and improve filtration efficiency. By enhancing the rapid separation effect at the pore structure through elastic deformation of the filter media, it surpasses the maximum filtration rate of existing filtration methods, overcoming the problem of decreased filtration efficiency at high filtration rates. This makes it suitable for preliminary purification of rainwater runoff before rainwater storage tanks.

[0034] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0035] Example 1:

[0036] like Figures 1 to 3 As shown in the figure, this embodiment provides a lightweight filter media ring filtration device for rainwater storage tanks, including a primary separation device and a secondary separation device.

[0037] The primary separation device is any one of an integrated primary separation device 1, a separate primary separation device 2, or a modified rainwater pipe network 3; the integrated primary separation device 1 includes an annular integrated separation chamber 11 and an integrated inlet pipe 12 disposed on the inner annular wall of the integrated separation chamber 11; the separate primary separation device 2 includes a separate separation chamber 21 and separate inlet pipes 22 on its side walls; the modified rainwater pipe network 3 includes a rainwater pipe network 31 and an inlet baffle 32 at its outlet.

[0038] The secondary separation device includes a coaxial central water distribution cylinder 401 and an outer cylinder 402. A lower annular plate 403 connects the lower edge of the central water distribution cylinder 401 to the lower inner wall of the outer cylinder 402. A radially spaced partition plate connects the outer wall of the central water distribution cylinder 401 and the inner wall of the outer cylinder 402. The lower end of the partition plate is connected to the lower annular plate 403. There are multiple partition plates to divide the annular space between the central water distribution cylinder 401 and the outer cylinder 402 into multiple independent filtration units. Within each filtration unit, a bottom perforated baffle 404, a floating perforated baffle 405, and a top perforated baffle are arranged sequentially from bottom to top. Spherical filter media 407 is filled between baffle 406, floating perforated baffle 405 and lower perforated baffle 404. The space between the bottom perforated baffle 404 and the lower annular plate 403 is a rectifier cavity 408. The lower end of the central water distribution cylinder 401 is connected to the rectifier cavity 408 of each filter unit through multiple independent water pipes 409. The side wall of the outer cylinder 402 above the top perforated baffle 406 is provided with a top outlet 410 to connect to the rainwater storage tank. The lower end of each rectifier cavity 408 is connected to a bottom discharge pipe 411, and all bottom discharge pipes 411 converge at the bottom main discharge pipe 412.

[0039] The primary separation unit is located above the secondary separation unit. Rainwater enters the central water distribution cylinder 401 of the secondary separation unit from the integrated inlet pipe 12, the separate inlet pipe 22, or the inlet screen 32 of the primary separation unit, and then enters the filter unit through the independent water pipe 409 at the lower end for filtration and purification. The purified rainwater flows out from the top outlet 410, and the filter residue is discharged from the bottom discharge pipe 411.

[0040] The bottom perforated baffle 404, the floating perforated baffle 405, and the top perforated baffle 406 are all hollow arc-shaped. The edge of the bottom perforated baffle 404 is fixedly connected to the outer wall of the central water distribution cylinder 401, the partition plate, and the inner wall of the outer cylinder 402. The floating perforated baffle 405 can move up and down along the vertical slide rails of the outer wall of the central water distribution cylinder 401 and the inner wall of the outer cylinder 402. The edge of the top perforated baffle 406 is fixedly connected to the outer wall of the central water distribution cylinder 401, the partition plate, and the inner wall of the outer cylinder 402.

[0041] The bottom perforated baffle 404, the floating perforated baffle 405, and the top perforated baffle 406 are all provided with multiple holes with a diameter of 3mm.

[0042] The spherical filter media 407 has a concentration of 0.1-0.3 g / cm³. 3 The polystyrene foam floats have a particle size of 5mm.

[0043] An independent valve is installed on the independent water pipe 409.

[0044] A valve is installed on the bottom discharge pipe 411.

[0045] The integrated separation chamber 11 of the integrated primary separation device is surrounded by a cylindrical outer wall, a cylindrical inner wall, and an annular bottom wall. The annular bottom wall is inclined towards the cylindrical inner wall. An integrated water inlet pipe 12 is provided on the cylindrical inner wall, and an integrated sludge discharge pipe is provided on the annular bottom wall. The integrated sludge discharge pipe is connected to the bottom main discharge pipe 412. Valves are provided on both the integrated water inlet pipe 12 and the integrated sludge discharge pipe. When the integrated primary separation device is used in conjunction with the secondary separation device, the cylindrical outer wall is aligned with the upper end of the outer cylinder 402, and the cylindrical inner wall is aligned with the upper end of the central water distribution cylinder 401. Rainwater enters the integrated separation chamber 11 from the top and then enters the central water distribution cylinder 401 through the integrated water inlet pipe 12.

[0046] The separate separation chamber 21 of the separate primary separation device is surrounded by a cylindrical side wall and an inclined bottom wall. A separate sludge discharge pipe 23 is provided at the lowest point of the inclined bottom wall. The separate sludge discharge pipe 23 is connected to the bottom main discharge pipe 412. Valves are provided on both the separate water inlet pipe 22 and the separate sludge discharge pipe 23. Rainwater enters the separate separation chamber 21 from the top and then enters the central water distribution cylinder 401 through the separate water inlet pipe 22.

[0047] The lower annular plate 403 is inclined toward the outer cylinder 402. One end of the bottom discharge pipe 411 is connected to the lower annular plate 403 and then communicates with the rectifier cavity 408, and is arranged close to the outer cylinder 402.

[0048] In this embodiment, a primary separation device is used to separate large-sized floating impurities and some heavy impurities to ensure the stable and continuous operation of the secondary separation device. Independent valves are used to open or close independent water pipes, or to adjust the operating filtration rate of each filtration unit, so that each filtration unit can operate independently and the water level and load of the filtration unit can be flexibly adjusted; each filtration unit has an identical design and is connected in parallel with each other.

[0049] Filter media selection: 0.1-0.3 g / cm³ 3 Spherical lightweight polystyrene foam beads with a particle size of 5mm have an optimized filter layer structure and flow field due to their lightweight spherical shape, which can fully utilize the filter layer efficiency.

[0050] The bottom perforated baffle prevents the polystyrene foam beads from overflowing downwards when the filter unit is not operating or during backwashing. Its lower space serves as a flow-rectifying chamber, ensuring uniform water distribution. The floating perforated baffle rests on top of the filter media and floats with it. Made of lightweight, hydrophobic material, the floating perforated baffle features evenly distributed 3mm pores. Together with the upward flow created by the independent water pipe, it compresses the filter media, ensuring that while the media slowly rises with the water level, the polystyrene foam beads form a dense, porous filter layer that does not overflow. The top perforated baffle then prevents further upward movement, thus fixing the relative position of the filter layer within the filter media.

[0051] Specifically, the maximum design load of this device is 15m. 3 / (m 2The central water distribution cylinder has an inner diameter of 2m, an outer ring inner diameter of 30m, a filter media layer height of 1m, a filter unit height of 2m, and a maximum design flow rate of 10555m³ / h. 3 / h. Calculated according to the Xi'an City rainstorm intensity formula (as shown below), with a catchment area of ​​10 hm². 2 When the rainfall duration is 15 minutes and the design return periods are 3, 5, and 10 years, the runoff is 5659, 7190, and 9267 m³, respectively. 3 / h. This device can ensure efficient continuous filtration under heavy rainfall. Under rainfall with a return period of 3-5 years and when the concentration of particulate turbidity in rainwater runoff is not significantly different, the operating load can be appropriately reduced, thereby extending the filtration cycle, improving the filtration effect, and reducing the backwashing frequency.

[0052] Formula for calculating the intensity of rainstorms in Xi'an:

[0053]

[0054] In the formula:

[0055] q—Rainstorm intensity (L / (s·hm)) 2 ))

[0056] p—Recurrence period of heavy rainfall (in years);

[0057] t — duration of rainfall (min);

[0058] Figure 4 To demonstrate the turbidity removal efficiency of the secondary separation device of this invention under pilot conditions with a filtration rate of 15 m / h, during 16 days of continuous operation, although the content of suspended solids (SS) in the influent fluctuated between 8 and 27 mg / L, the average removal rate was still higher than 70%. This indicates that the secondary filtration device has a certain resistance to shock loads and can adapt to the relatively random pollutant occurrence characteristics in rainfall runoff, significantly reducing the solid content entering the storage tank, thereby ensuring the stable operation of the storage tank.

[0059] The working process of this invention:

[0060] First, one of the following three methods can be used to initially retain large-sized impurities and some heavy particulate matter:

[0061] (1.1) An integrated primary separation device is installed at the upper end of the central water distribution cylinder. This device adopts a submerged outflow method. First, the independent valves on the integrated inlet pipe and the integrated sludge discharge pipe embedded in the central water distribution cylinder are closed, causing the liquid level in the integrated separation chamber to rise. After the liquid level completely submerges the integrated inlet pipe to a certain height, the independent valve on the integrated inlet pipe is opened, allowing it to flow into the central water distribution cylinder in a submerged outflow manner to separate light, large-sized floating objects. During continuous operation, a certain amount of sludge will accumulate at the bottom. After the rainfall ends and the filtration device stops operating, the independent valve on the integrated inlet pipe is closed, and floating impurities on the liquid surface are removed by manual cleaning. Then, the independent valve on the integrated sludge discharge pipe is opened to discharge the bottom sludge into the backwash water discharge main / sludge discharge main. After discharge, the independent valve on the integrated sludge discharge pipe is closed, awaiting the next operation.

[0062] (1.2) Install a separate primary separation device. First, close the independent valves on the separate inlet pipe and the separate sludge discharge pipe. Rainwater flows into the separate separation chamber. When the liquid level rises to cover the separate inlet pipe and reaches a certain height, open the independent valve on the separate inlet pipe to allow it to flow into the central distribution cylinder in a submerged outflow manner to separate light, large-sized floating debris. During continuous operation, a certain amount of sludge will accumulate at the bottom. After the rainfall ends and the filtration device stops operating, close the independent valve on the separate inlet pipe and manually clean the floating impurities on the liquid surface. Then, open the independent valve on the separate sludge discharge pipe to discharge the bottom sludge into the backwash water discharge main / sludge discharge main. After completion, close the independent valve on the separate sludge discharge pipe and wait for operation.

[0063] (1.3) Install a tee and an inlet baffle at the rainwater pipe. When the water flows through the baffle, large impurities are blocked by the baffle. At the same time, the shear force of the water flow can separate the impurities from the baffle to achieve continuous and stable operation.

[0064] II. During normal operation of the secondary separation unit, the effluent from the primary separation unit first flows into the central distribution cylinder. Once the liquid level in the central distribution cylinder rises to the same height as the annular overflow weir on the top perforated baffle, the valve on the independent water pipe is opened, allowing the water to flow into the rectifying chamber. This water is then evenly distributed upwards to the filtration unit via the bottom perforated baffle, ensuring the filter media floats uniformly upwards without being dispersed by the water flow. As the filter media rises with the water flow to the top perforated baffle, it is blocked and simultaneously compressed by the water flow and the baffle, forming a dense filter layer that traps suspended particles. The filtered water is collected by the annular overflow weir into the collection channel and the top outlet, and then discharged into the rainwater storage tank.

[0065] The filtration principle of the device of this invention is as follows:

[0066] Consider a cross-section of the micro-pore structure of the filter layer, with a cross-sectional area of ​​da, a water flow density of ρ and velocity of u flowing into the cross-section, and a flow distance of dS. Then, the mass of water flowing into the cross-section during time dt is ρudadt, and the mass of water flowing out of the cross-section is:

[0067]

[0068] According to the principle of mass conservation, in a steady flow, the mass flowing into the infinitesimal element is equal to the mass flowing out, that is:

[0069]

[0070] Therefore: ρuda = C (constant)

[0071] Integrating, we get: ρuA=C, (A is the cross-sectional area of ​​the flow path), that is, at the cross-sections with areas a1 and a2: u1a1=u2a2①

[0072] According to the Carman-Kozony equation, the relationship between head loss in a filter bed and the porosity of the filter media is as follows:

[0073]

[0074] Where: h0—head loss, cm;

[0075] θ — kinematic viscosity of water, cm 2 / s;

[0076] g—acceleration due to gravity;

[0077] m0—Porosity of the filter media;

[0078] —Particle sphericity coefficient of the filter media;

[0079] d0—Diameter of a sphere with the same volume as the filter media, in cm;

[0080] l0—Filter layer thickness, cm;

[0081] v0—filtration rate, cm / s;

[0082] When the filter layer is compressed by the bottom perforated baffle and the fixed perforated baffle, the polystyrene filter media undergoes elastic deformation, and the filter layer thickness decreases. Assuming the filter layer thickness is l0-Δl and the porosity is m1, the relationship between the head loss h1 and the filtration velocity v1 is:

[0083]

[0084] Where: h1—head loss of the filter bed after compression, cm;

[0085] θ — kinematic viscosity of water, cm2 / s;

[0086] g—acceleration due to gravity;

[0087] m1—Porosity of the filter material after compression;

[0088] —Particle sphericity coefficient of the filter media;

[0089] d0—Diameter of a sphere with the same volume as the filter media, in cm;

[0090] l0—Thickness of the filter layer before compression, in cm;

[0091] Δl—The change in filter layer thickness after compression, in cm;

[0092] v1—Filtering velocity at the pores after compression, cm / s;

[0093] Since the density and mass of polystyrene foam beads are constant, their total volume remains unchanged, while the pore volume decreases. Let the pore volume after compression be v. 孔2 The volume of polystyrene foam floats is v EPS The filter layer area is A:

[0094] v EPS =Al0(1-m0)

[0095] v 孔2 =A(l0-Δl)-Al0(1-m0)=A(l0-Δl)m1

[0096] Right now:

[0097] m1=C1m0+C2

[0098] Where C1 and C2 are constants, C1 = l0 / (l0 - Δl), C2 = -Δl / (l0 - Δl)

[0099] Substituting m0 and m1 into the Carman-Kozony equation, we get:

[0100]

[0101] Where α is a constant, k = C1Δl

[0102] Due to the elastic deformation properties of polystyrene, the pore size decreases after compression. As shown in ①, the flow velocity within the pores will increase, with the increase factor as shown in ②. Controlled by an independent valve on an independent water pipe, the filtration rate within the filter tank remains constant. Therefore, the local flow field at the pore structure changes, and the velocity gradient increases significantly, enhancing the effect of velocity separation. This strengthens the mass transfer of suspended particles at the pore structure to the lower-velocity polystyrene filter media surface, utilizing the high filtration rate to enhance the velocity separation effect, thereby improving the filtration efficiency. As filtration continues, the particles trapped on the filter media surface occupy an increasingly larger pore volume, further reducing the pore volume and further enhancing the velocity separation effect, thus further improving the filtration performance.

[0103] During filtration, impurity particles, due to differences in density and particle size, experience acceleration differences under the combined influence of buoyancy, their own weight, and water flow shear force, resulting in varying rising or settling velocities. As they rise with the water flow, these velocity differences create a sieving effect, with smaller, less dense impurities having a higher rising velocity and contacting the filter bed first. Traditional filtration processes lack this sieving effect; larger impurity particles, often irregularly shaped, occupy a larger surface area after being trapped on the filter media, reducing the filter bed's dirt-holding capacity. This device utilizes the suspension characteristics of lightweight filter media to create a sieving effect below the filter unit's packing layer, overcoming the shortcomings of traditional filtration, improving filtration efficiency at high filtration rates, increasing the utilization efficiency of the filter media's surface area, and thus extending the filtration cycle to some extent.

[0104] After a period of normal operation, the filtration efficiency of the filter layer gradually decreases until it penetrates due to the trapping effect of the filter unit. Backwashing is required before penetration. To begin backwashing, first close the inlet valve on the independent water pipe, and simultaneously open the inlet valves of the remaining filter units to achieve continuous operation. Open the valves to drain the filter units through the bottom backwash water discharge / sludge discharge pipe, then close the valves and reopen the corresponding independent water pipes to raise the liquid level. The filter layer floats back to the surface with the water level. During this process, the friction between particles and the scouring effect of the water flow allow the filter media and trapped particles to rearrange, achieving the backwashing effect. Repeating this process several times will restore the filter layer to operation. Traditional air-water backwashing processes require a large amount of high-speed water flow and air to create a two-phase flow field, generating significant friction and collision on the particle surface to achieve the backwashing effect. This device, using lightweight filter media, can create friction and collision on the particle surface through a single-phase flow field generated by water level fluctuations, simplifying the backwashing process, eliminating the need for air assistance, and reducing backwashing energy consumption.

[0105] Backwash water and sludge in the rectifier chamber are collected from the bottom backwash drain pipe / sludge discharge pipe and discharged from the device via the backwash water discharge main pipe / sludge discharge main pipe. If several filter units need to be backwashed simultaneously, the independent valves on the independent water pipes corresponding to each filter unit must be closed, and the valves on the backwash water discharge pipes / sludge discharge pipes must be opened. After the liquid level drops, the valves on the backwash water discharge pipes / sludge discharge pipes must be closed again, and the valves on the independent water pipes corresponding to each filter unit must be opened again to allow the liquid level to rise again. Repeat the backwashing process several times until the filter unit resumes operation.

Claims

1. A ring-shaped filter device with lightweight filter media before a rainwater storage tank, characterized in that, It includes a primary separation unit and a secondary separation unit; The primary separation device is any one of an integrated primary separation device (1), a split primary separation device (2), or a modified rainwater pipe network (3); the integrated primary separation device (1) includes an annular integrated separation chamber (11) and an integrated inlet pipe (12) disposed on the inner annular wall of the integrated separation chamber (11); the split primary separation device (2) includes a split separation chamber (21) and a split inlet pipe (22) on its side wall; the modified rainwater pipe network (3) includes a rainwater pipe network (31) and an inlet screen (32) at its outlet; The secondary separation device includes a coaxial central water distribution cylinder (401) and an outer cylinder (402). A lower annular plate (403) connects the lower edge of the central water distribution cylinder (401) to the lower inner wall of the outer cylinder (402). A radially spaced partition plate connects the outer wall of the central water distribution cylinder (401) and the inner wall of the outer cylinder (402). The lower end of the partition plate is connected to the lower annular plate (403). There are multiple partition plates to divide the annular space between the central water distribution cylinder (401) and the outer cylinder (402) into multiple independent filtration units. The filtration unit is provided with a bottom perforated baffle (404), a floating perforated baffle (405), and a top perforated baffle (406) arranged sequentially from bottom to top. 06), spherical filter media (407) is filled between the floating perforated baffle (405) and the bottom perforated baffle (404), and the space between the bottom perforated baffle (404) and the lower annular plate (403) is a rectifier cavity (408); the lower end of the central water distribution cylinder (401) is connected to the rectifier cavity (408) of each filter unit through multiple independent water pipes (409); the side wall of the outer cylinder (402) above the top perforated baffle (406) is provided with a top outlet (410) to connect to the rainwater storage tank; the lower end of each rectifier cavity (408) is connected to a bottom discharge pipe (411), and each bottom discharge pipe (411) converges at the bottom main discharge pipe (412); The primary separation device is located above the secondary separation device. Rainwater enters the central water distribution cylinder (401) of the secondary separation device through the integrated water inlet pipe (12), the separate water inlet pipe (22), or the water inlet mesh (32) of the primary separation device, and then enters the filtration unit through the independent water pipe (409) at the lower end for filtration and purification. The purified rainwater flows out from the top outlet (410), and the filter residue is discharged from the bottom discharge pipe (411).

2. The lightweight filter media annular filtration device before the rainwater storage tank as described in claim 1, characterized in that, The bottom perforated baffle (404), floating perforated baffle (405), and top perforated baffle (406) are all hollow arc-shaped. The edge of the bottom perforated baffle (404) is fixedly connected to the outer wall of the central water distribution cylinder (401), the partition plate, and the inner wall of the outer cylinder (402). The floating perforated baffle (405) can move up and down along the vertical slide rails of the outer wall of the central water distribution cylinder (401) and the inner wall of the outer cylinder (402). The edge of the top perforated baffle (406) is fixedly connected to the outer wall of the central water distribution cylinder (401), the partition plate, and the inner wall of the outer cylinder (402).

3. The lightweight filter media annular filtration device before the rainwater storage tank as described in claim 1, characterized in that, The bottom perforated baffle (404), the floating perforated baffle (405), and the top perforated baffle (406) are each provided with multiple holes with a diameter of 3mm.

4. The lightweight filter media annular filtration device before the rainwater storage tank as described in claim 1, characterized in that, The spherical filter media (407) has a content of 0.1-0.3 g / cm³. 3 The polystyrene foam floats have a particle size of 5mm.

5. The lightweight filter media annular filtration device before the rainwater storage tank as described in claim 1, characterized in that, An independent valve is provided on the independent water pipe (409).

6. The lightweight filter media annular filtration device before the rainwater storage tank as described in claim 1, characterized in that, A valve is provided on the bottom discharge pipe (411).

7. The lightweight filter media annular filtration device before the rainwater storage tank as described in claim 1, characterized in that, The integrated separation chamber (11) of the integrated primary separation device is surrounded by a cylindrical outer wall, a cylindrical inner wall and an annular bottom wall. The annular bottom wall is inclined towards the cylindrical inner wall. An integrated water inlet pipe (12) is provided on the cylindrical inner wall. An integrated sludge discharge pipe is provided on the annular bottom wall. The integrated sludge discharge pipe is connected to the bottom main discharge pipe (412). Valves are provided on both the integrated water inlet pipe (12) and the integrated sludge discharge pipe. When the integrated primary separation device is used in conjunction with the secondary separation device, the cylindrical outer wall is aligned with the upper end of the outer cylinder (402) and the cylindrical inner wall is aligned with the upper end of the central water distribution cylinder (401). Rainwater enters the integrated separation chamber (11) from the top and then enters the central water distribution cylinder (401) through the integrated water inlet pipe (12).

8. The lightweight filter media annular filtration device before the rainwater storage tank as described in claim 1, characterized in that, The separate separation chamber (21) of the separate primary separation device is surrounded by a cylindrical side wall and an inclined bottom wall. A separate sludge discharge pipe (23) is provided at the lowest point of the inclined bottom wall. The separate sludge discharge pipe (23) is connected to the bottom main discharge pipe (412). Valves are provided on both the separate water inlet pipe (22) and the separate sludge discharge pipe (23). Rainwater enters the separate separation chamber (21) from the top and then enters the central water distribution cylinder (401) through the separate water inlet pipe (22).

9. The lightweight filter media annular filtration device for rainwater storage tanks as described in claim 1, characterized in that, The lower annular plate (403) is inclined toward the outer cylinder (402), and one end of the bottom discharge pipe (411) is connected to the lower annular plate (403) and then communicates with the rectifier cavity (408), and is arranged close to the outer cylinder (402).

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