Sponge city rainwater recycling and purifying method

Abstract

This application relates to a method for rainwater harvesting and purification in sponge cities, belonging to the field of rainwater harvesting and purification treatment. It includes installing a reversing valve along the rainwater flow path, with its two outlets connected to a sewage pipe network and a collection pipe network, respectively; a linear treatment ditch is installed at the end of the collection pipe network, allowing sewage flowing out of the collection pipe network to flow in the linear treatment ditch; a gradient purification unit is installed in the linear treatment ditch to purify the sewage; and an underground water storage space is provided. Beneficial technical effects: This sponge city rainwater harvesting and purification method utilizes gravity to guide rainwater flow, and harvests and purifies the rainwater during its flow. Rainwater harvesting and purification does not consume electricity, requires no specialized equipment or chemicals, and does not require personnel, significantly reducing costs. Furthermore, it requires a small land area for rainwater harvesting and purification, perfectly integrating into the urban ecological landscape.

Description

Technical Field

[0001] This application relates to the field of rainwater harvesting and purification, and in particular to a method for rainwater harvesting and purification in sponge cities. Background Technology

[0002] Currently, in the construction of sponge cities, initial rainwater is generally discharged directly due to its high debris content, poor water quality, and lack of recycling value. Only rainwater from the middle and later stages is recycled. Therefore, the inlet valves of rainwater harvesting and purification devices are mostly opened manually based on rainfall conditions. The valve opening response speed, the quality of the recycled rainwater, and the appropriateness of the opening time are all greatly affected by the operator's skill level, making it difficult to guarantee consistently high-quality recycled rainwater and increasing treatment costs.

[0003] In addition, the recycled rainwater is mostly treated artificially with chemicals, which requires not only specialized equipment and personnel, but also a large amount of chemicals, resulting in high costs. At the same time, the specialized equipment requires a lot of land and is incompatible with the urban ecological landscape, making it difficult to promote in urban areas with limited land. Summary of the Invention

[0004] To address the issue of high operating costs associated with existing rainwater harvesting and purification devices in sponge cities, this application provides a method for rainwater harvesting and purification in sponge cities.

[0005] In one aspect of this disclosure, a method for rainwater harvesting and purification in sponge cities is proposed, comprising: A reversing valve is installed along the flow path of rainwater, with its two outlets connected to the sewage network and the collection network, respectively. A linear treatment ditch is set at the end of the collection pipeline network so that the sewage flowing out of the end of the collection pipeline network flows in the linear treatment ditch. A gradient purification unit is set in the linear treatment ditch to purify the sewage. An underground water storage space is set up, and the purified water flowing out of the linear treatment ditch enters the water storage space, which is filled with modified zeolite.

[0006] Preferably, the reversing valve is driven to reverse by the volume expansion of a temperature-sensitive phase change material, and the reversing action temperature is 2℃-35℃.

[0007] Preferably, the thermosensitive phase change material includes any one of n-dodecane + n-tetradecane, n-tetradecane + n-hexadecane, decanoic acid + lauric acid + n-hexadecane, decanoic acid + lauric acid, and lauric acid + palmitic acid.

[0008] Preferably, the mass ratio of n-dodecane to n-tetradecane is 10-20:80-90, the mass ratio of n-tetradecane to n-hexadecane is 5-90:10-95, the mass ratio of decanoic acid, lauric acid and n-hexadecane is 58-64:32-36:0-10, the mass ratio of decanoic acid and lauric acid is 64-90:10-36, and the mass ratio of lauric acid and palmitic acid is 75-78:22-25.

[0009] Preferably, the gradient purification unit includes an aerobic treatment section, an anaerobic treatment section, and an anaerobic treatment section arranged sequentially along the water flow direction, wherein the length of the aerobic treatment section is not less than the length of the anaerobic treatment section or the anaerobic treatment section.

[0010] Preferably, the aerobic treatment section is formed by placing filler material one in the linear treatment ditch and planting emergent plants on the filler material one; The filler includes particles containing iron oxide and aluminum oxide, porous particles, and carbon-based functional material. The anoxic treatment section is formed by placing a second packing material in the linear treatment ditch, and the second packing material is connected to the first packing material. The filler material 2 includes particles containing iron oxide and aluminum oxide 3, porous particles 4, carbon-based functional material 2, and slow-release carbon source; The anaerobic treatment section is formed by placing filler three in the linear treatment ditch, and filler three is connected to filler two. The filler material includes: five particles containing iron oxide and aluminum oxide, six porous particles, and three carbon-based functional materials. The particle size of particle one is greater than that of particle three, the particle size of particle three is greater than that of particle five, the particle size of particle two is greater than that of particle four, the particle size of particle four is greater than that of particle six, the particle size of carbon-based functional material one is greater than that of carbon-based functional material two, and the particle size of carbon-based functional material two is greater than that of carbon-based functional material three. The thickness of the first filler is less than the thickness of the second filler, and the thickness of the second filler is less than the thickness of the third filler.

[0011] Preferably, the filler material 2 is planted with water-tolerant plants.

[0012] Preferably, the method for preparing the modified zeolite includes: soaking the zeolite in a calcium chloride solution, stirring it for a period of time under water bath heating, and then taking it out, rinsing, drying, and calcining it to fully activate it.

[0013] Preferably, the zeolite is soaked in a calcium chloride solution with a concentration of 1-2 mol / L, heated and stirred in a water bath at 60-80℃ for 12-24 hours, then rinsed, dried, and calcined at 400-500℃ for 3-5 hours to activate it.

[0014] Preferably, the distance between the water storage space and the ground is not less than 3 meters.

[0015] Beneficial technical effects: The sponge city rainwater recycling and purification method of this application utilizes gravity to guide rainwater to flow on its own, and collects and purifies rainwater during the flow process. The rainwater recycling and purification process does not consume electricity, does not require the purchase of professional equipment and chemicals, and does not require the deployment of treatment personnel, which greatly reduces costs. Moreover, the area required for rainwater recycling and purification is small, and it is perfectly integrated into the urban ecological landscape. Attached Figure Description

[0016] Figure 1 This is a flowchart of the sponge city rainwater recycling and purification method in the embodiments of this application.

[0017] Figure 2 This is a schematic diagram of the reversing valve in this embodiment of the application performing reversing driven by the volume expansion of a temperature-sensitive phase change material.

[0018] Explanation of reference numerals in the attached diagram: 1. Valve body; 2. Valve stem; 3. Temperature measuring cylinder; 4. Temperature-sensitive phase change material; 5. Water inlet; 6. Water outlet one; 7. Water outlet two; 8. Through hole; 9. Return spring; 10. Water inlet pipe. Detailed Implementation

[0019] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore detailed descriptions of them will be omitted. Furthermore, the drawings are merely illustrative of this disclosure and are not necessarily drawn to scale.

[0020] The following is in conjunction with the appendix Figures 1-2 This application will be described in further detail.

[0021] In one aspect of this disclosure, a method for rainwater harvesting and purification in sponge cities is proposed, as shown in Figure 1, the method comprising: S1. Install a reversing valve in the flow path of rainwater, with the two outlets of the reversing valve connected to the sewage pipe network and the collection pipe network respectively.

[0022] The sewage pipe network is used to collect initial rainwater. This rainwater contains many impurities and has poor water quality, so it has no value for recycling and purification and can be discharged directly through the sewage pipe network.

[0023] As an example, the reversing valve is driven to switch by the volume expansion of the temperature-sensitive phase change material 4. The switching action temperature is 2℃-35℃. The switching action temperature refers to the temperature range of 2℃-35℃ when the temperature of rainwater is detected, at which time the volume expansion of the temperature-sensitive phase change material 4 drives the reversing valve to switch.

[0024] In the early stages of rainfall, the temperature of rainwater is usually low due to the evaporative cooling effect at high altitudes. Therefore, the initial rainwater will not trigger the volume expansion of the temperature-sensitive phase change material 4. As the rainfall continues, the air humidity tends to saturate, evaporative cooling weakens, and the temperature of the rainwater gradually rises in the middle and late stages, reaching the switching action temperature range of the reversing valve. This embodiment utilizes this natural temperature difference law, using the volume expansion of the temperature-sensitive phase change material 4 to enable the reversing valve to automatically switch between initial rainwater diversion and middle and late-stage rainwater collection without the need for electricity, relying solely on the temperature change of the rainwater itself. Compared with the method of manually opening the valve according to the rainfall situation, this rainwater collection method has a faster valve opening response, reliable and guaranteed rainwater quality, and appropriate valve opening time, which not only ensures the stable and qualified quality of the collected rainwater but also saves labor costs.

[0025] As an example, the reversing valve can be driven to switch directions by the volume expansion of the temperature-sensitive phase change material 4. Figure 2 A detailed introduction will be provided. Figure 2 The reversing valve includes a valve body 1 and a valve stem 2 that slides axially within the valve body 1. The valve stem 2 is provided with a through hole 8. The valve body 1 is provided with an inlet hole 5, an outlet hole 1 6, and an outlet hole 2 7. The inlet hole 5 is used for external rainwater to enter the reversing valve. The outlet hole 1 6 is connected to the sewage pipe network. Initially, rainwater flows into the sewage pipe network through the inlet hole 5, through hole 8, and outlet hole 1 6. The outlet hole 2 7 is connected to the collection pipe network. In the middle and later stages, rainwater flows into the collection pipe network through the inlet hole 5, through hole 8, and outlet hole 2 7.

[0026] like Figure 2 As shown, a temperature measuring cylinder 3 is installed on the left end of the valve body 1, and a return spring 9 is installed on the right end. The temperature measuring cylinder 3 is in contact with the rainwater in the inlet pipe 10 to detect the temperature of the rainwater. A temperature-sensitive phase change material 4 is installed inside the temperature measuring cylinder 3. In the early stage, the temperature of the rainwater is low, so the temperature-sensitive phase change material 4 will not expand. The inlet hole 5, through hole 8, and outlet hole 6 remain open. The initial rainwater in the inlet pipe 10 flows directly into the sewage pipe network through the reversing valve. In the middle and later stages, the temperature of the rainwater is high, and the temperature-sensitive phase change material 4 expands, pushing the valve rod 2 to the right to compress the return spring 9 and open the inlet hole 5, through hole 8, and outlet hole 7. Thus, the rainwater in the middle and later stages flows into the collection pipe network through the reversing valve. After the rain stops, the rainwater flow is interrupted, the temperature of the temperature measuring cylinder 3 drops, the volume of the temperature-sensitive phase change material 4 shrinks, and the compressed return spring 9 pushes the valve rod 2 to reset and restore the opening of the inlet hole 5, through hole 8, and outlet hole 6.

[0027] Optional, Figure 2 The reversing valve and the end of the water inlet pipe 10 shown can be installed inside a heat-insulating container to block the influence of external high / low temperature environment on the temperature-sensitive phase change material 4, ensuring that the temperature-sensitive phase change material 4 is only affected by the temperature of rainwater and is not affected by the external high / low temperature.

[0028] As an example, the thermosensitive phase change material 4 includes any one of n-dodecane + n-tetradecane, n-tetradecane + n-hexadecane, decanoic acid + lauric acid + n-hexadecane, decanoic acid + lauric acid, and lauric acid + palmitic acid. The mass ratio of n-dodecane to n-tetradecane is 10-20:80-90, the mass ratio of n-tetradecane to n-hexadecane is 5-90:10-95, the mass ratio of decanoic acid, lauric acid, and n-hexadecane is 58-64:32-36:0-10, the mass ratio of decanoic acid to lauric acid is 64-90:10-36, and the mass ratio of lauric acid to palmitic acid is 75-78:22-25.

[0029] In practical implementation, the corresponding temperature-sensitive phase change material 4 is selected according to the switching action temperature range. For example, if the switching valve needs to operate when the rainwater temperature is between 2℃ and 5.5℃ in the middle and late stages, n-dodecane + n-tetradecane can be selected. Then, the corresponding mass ratio of n-dodecane + n-tetradecane is selected according to the set specific switching action temperature value. For example, when the mass ratio of n-dodecane to n-tetradecane is 10:90, the switching action temperature value is 5.5℃, and when the mass ratio of n-dodecane to n-tetradecane is 20:80, the switching action temperature value is 2℃.

[0030] For example, if the reversing valve needs to operate when the rainwater temperature is between 5.5℃ and 18.2℃ in the middle and late stages, then n-tetradecane + n-hexadecane can be selected. Then, the corresponding mass ratio of n-tetradecane + n-hexadecane can be selected according to the specific reversing operation temperature value set. For example, when the mass ratio of n-tetradecane to n-hexadecane is 5:95, the reversing operation temperature value is 18.2℃, and when the mass ratio of n-tetradecane to n-hexadecane is 90:10, the reversing operation temperature value is 5.5℃.

[0031] For example, if the reversing valve needs to activate when the rainwater temperature is between 18.2℃ and 19.5℃ in the middle and late stages, decanoic acid + lauric acid + n-hexadecane can be selected. Then, select the corresponding mass ratio of decanoic acid + lauric acid + n-hexadecane according to the specific reversing activation temperature value. For example, when the mass ratio of decanoic acid, lauric acid and n-hexadecane is 64:36:0, the reversing activation temperature value is 19.5℃. When the mass ratio of decanoic acid, lauric acid and n-hexadecane is 58:32:10, the reversing activation temperature value is 18.2℃.

[0032] For example, if the reversing valve needs to operate when the rainwater temperature is between 19.5℃ and 32.5℃ in the middle and late stages, decanoic acid and lauric acid can be selected. Then, select the corresponding mass ratio of decanoic acid and lauric acid according to the specific reversing action temperature value set. For example, when the mass ratio of decanoic acid to lauric acid is 64:36, the reversing action temperature value is 19.5℃, and when the mass ratio of decanoic acid to lauric acid is 90:10, the reversing action temperature value is 32.5℃.

[0033] For example, if the reversing valve needs to operate when the rainwater temperature is between 32.5℃ and 35℃ in the middle and late stages, lauric acid and palmitic acid can be selected. Then, select the corresponding mass ratio of lauric acid and palmitic acid according to the specific reversing action temperature value set. For example, when the mass ratio of lauric acid to palmitic acid is 75:25, the reversing action temperature value is 35℃, and when the mass ratio of lauric acid to palmitic acid is 78:22, the reversing action temperature value is 32.5℃.

[0034] In this embodiment of the disclosure, the sponge city rainwater harvesting and purification method further includes: S2. A linear treatment ditch is set at the end of the collection pipe network so that the sewage flowing out of the end of the collection pipe network flows in the linear treatment ditch. The sewage flows from one end of the linear treatment ditch to the other end. A gradient purification unit is set in the linear treatment ditch. The sewage flows through the gradient purification unit by itself under the action of gravity, thereby purifying the sewage.

[0035] Specifically, the gradient purification unit includes an aerobic treatment section, an anaerobic treatment section, and an anaerobic treatment section arranged sequentially along the water flow direction. The length of the aerobic treatment section is not less than the length of the anaerobic or anaerobic treatment section. This design ensures that the aerobic treatment section fully degrades organic matter and completes nitrification. The aerobic treatment section is used for rapid biochemical degradation of organic matter and nitrification. The anaerobic treatment section is used to create an anaerobic environment, providing electron donors for denitrifying bacteria to reduce the nitrate nitrogen produced in the aerobic treatment section to nitrogen gas, thus achieving denitrification. The anaerobic treatment section is used to promote the deep mineralization of residual pollutants, ultimately achieving thorough water purification.

[0036] As an example, the aerobic treatment section is formed by placing a type of filler in the linear treatment ditch and planting emergent plants on the filler. The emergent plants release oxygen in their rhizosphere, creating an aerobic microenvironment in the water, which supports the metabolic activities of nitrifying bacteria and aerobic heterotrophic bacteria, ensuring the smooth progress of ammonia nitrogen nitrification and organic matter degradation. Moreover, the dense root system forms a huge specific surface area in the water, becoming a natural carrier for microbial biofilm formation, further enhancing the purification capacity. Finally, during the growth process, the emergent plants can directly absorb ammonia nitrogen, nitrate nitrogen, and phosphate in the water, fixing and removing some nitrogen and phosphorus in the form of plant biomass. In addition, planting emergent plants in the linear treatment ditch gives the ditch both water purification and ecological landscape functions, thus perfectly integrating it into the urban ecological landscape.

[0037] Specifically, the filler material one includes iron oxide and aluminum oxide particles one, porous particles two, and carbon-based functional material one. The surface hydroxyl groups of the iron oxide and aluminum oxide particles one can undergo coordination exchange and chemical precipitation reactions with phosphate ions in rainwater to achieve in-situ fixation of phosphorus. The large specific surface area and surface characteristics of the porous particles two are conducive to the rapid attachment of microorganisms and the stable growth of biofilm, providing a highly active microbial carrier for aerobic degradation of organic matter and nitrification reaction. The carbon-based functional material one can not only adsorb dissolved organic matter and a small amount of heavy metals in the water through its rich microporous structure, rapidly reducing the pollution load, but also intercept fine suspended particles and improve the transparency of the effluent. It can also provide an attachment carrier for microorganisms and regulate the matrix porosity and hydraulic properties.

[0038] As an example, the facultative anoxic treatment section is formed by placing a second packing material in a linear treatment ditch, which is connected to the first packing material. This design avoids disrupting the anoxic environment on the side of the facultative anoxic treatment section that is close to the aerobic treatment section.

[0039] Specifically, the packing material II comprises particles III containing iron oxide and aluminum oxide, particles IV with a porous structure, carbon-based functional material II, and a slow-release carbon source. The surface hydroxyl groups of particles III containing iron oxide and aluminum oxide can undergo coordination exchange and chemical precipitation reactions with phosphate ions in rainwater, achieving in-situ phosphorus fixation. The large specific surface area provided by the porous particles IV serves as a carrier for facultative anaerobic bacteria (denitrifying bacteria), while simultaneously regulating the porosity of the packing layer and maintaining suitable hydraulic conductivity. Carbon-based functional material II is used to adsorb residual dissolved organic matter in the water, providing an additional biofilm carrier for denitrifying bacteria. Furthermore, its microporous structure can locally form lower oxygen microzones, facilitating colonization by facultative anaerobic bacteria. Denitrifying bacteria require organic carbon as an electron donor to reduce nitrate nitrogen to nitrogen gas. The slow-release carbon source (such as PHBV) is insoluble in water and slowly releases small-molecule organic matter through microbial enzymatic hydrolysis, continuously and stably providing a carbon source for denitrification.

[0040] As an example, the anaerobic treatment section is formed by placing packing material three in a linear treatment ditch, which is connected to packing material two; this design avoids disrupting the anoxic environment of both the facultative and anaerobic treatment sections.

[0041] Specifically, the packing material three includes particles five containing iron oxide and aluminum oxide, porous particles six, and carbon-based functional material three. The particle size of particle one is larger than that of particle three, the particle size of particle three is larger than that of particle five, the particle size of particle two is larger than that of particle four, the particle size of particle four is larger than that of particle six, the particle size of carbon-based functional material one is larger than that of carbon-based functional material two, and the particle size of carbon-based functional material two is larger than that of carbon-based functional material three. This design synergistically constructs a triple gradient effect of increasing physical filtration precision, microbial ecological niche succession from aerobic to anaerobic, and natural decrease in dissolved oxygen, realizing the purification function of multiple tanks connected in series in a traditional sewage treatment plant within a single linear treatment ditch.

[0042] Specifically, particles five have smaller particle sizes and larger specific surface areas, further chemically adsorbing and precipitating residual phosphate ions to achieve deep phosphorus fixation. Simultaneously, the formed iron phosphate and aluminum phosphate minerals are stable under anaerobic conditions and will not be released secondary. Particles six have even smaller particle sizes and denser packing, reducing porosity and extending hydraulic retention time, providing a carrier for anaerobic bacteria and promoting the anaerobic mineralization of residual organic matter. Carbon-based functional materials three have the smallest particle sizes and the most abundant micropores, not only deeply adsorbing residual trace organic matter and heavy metals in the water but also providing an attachment carrier for anaerobic bacteria. Furthermore, some biochar can slowly release trace carbon sources to maintain the activity of anaerobic bacterial communities.

[0043] As an example, the thickness of the first packing material is less than the thickness of the second packing material, and the thickness of the second packing material is less than the thickness of the third packing material. This design compensates for the decrease in porosity caused by the reduction in particle size and ensures that the facultative and anaerobic treatment sections obtain sufficient hydraulic retention time to achieve deep degradation of organic matter and efficient removal of nitrogen and phosphorus.

[0044] As an example, the filler material 2 is planted with water-tolerant plants. The rhizosphere oxygen secretion capacity of the water-tolerant plants is significantly reduced, forming a facultative anaerobic microenvironment around the roots. This provides an attachment carrier for denitrifying bacteria without disrupting the oxygen-deficient trend of the water body. At the same time, the ditch has both water purification and ecological landscape functions, thus perfectly integrating into the urban ecological landscape.

[0045] As an example, particles one, three, and five are red brick particles, particles two, four, and six are volcanic rock, and carbon-based functional materials one, two, and three are biochar.

[0046] Furthermore, the carbon-based functional materials include biochar and activated carbon. Activated carbon is responsible for high-precision adsorption, while biochar is responsible for serving as a microbial carrier and supplementing carbon source. Their functions complement each other, ensuring better water quality in the effluent. They are particularly suitable for situations where rainwater is heavily polluted or where higher standards of effluent are required.

[0047] In this embodiment of the disclosure, the sponge city rainwater harvesting and purification method further includes: S3. An underground water storage space is set up, and the purified water flowing out of the linear treatment ditch enters the water storage space, and modified zeolite is set in the water storage space.

[0048] Setting up underground water storage spaces utilizes the constant temperature characteristics of underground soil, ensuring minimal temperature fluctuations in the stored purified water throughout the year, facilitating daily access, and reducing land occupation, thus seamlessly integrating into the urban ecological landscape. The modified zeolite installed in the water storage space efficiently adsorbs residual ammonia nitrogen and heavy metal ions in the water through ion exchange, preventing anaerobic deterioration of water quality during long-term storage, ensuring consistently fresh and odorless water. Furthermore, the completely dark underground environment of the storage space eliminates the possibility of algae growth at its source.

[0049] Preferably, the distance between the water storage space and the ground is not less than 3 meters, at which distance the temperature of the purified water stored fluctuates very little throughout the four seasons.

[0050] As an example, the preparation method of the modified zeolite includes: immersing the zeolite in a calcium chloride solution with a concentration of 1-2 mol / L, heating and stirring in a water bath at 60-80°C for 12-24 hours, removing it, rinsing and drying it, and then calcining and activating it at 400-500°C for 3-5 hours to ensure complete zeolite modification.

[0051] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," "third," and similar terms used in this application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. The terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "comprising" or "including" and similar terms mean that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including" and their equivalents, and do not exclude other elements or objects. "Above," "below," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0052] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for rainwater harvesting and purification in sponge cities, characterized in that... ,include: A reversing valve is installed along the flow path of rainwater, with its two outlets connected to the sewage network and the collection network, respectively. A linear treatment ditch is set at the end of the collection pipeline network so that the sewage flowing out of the end of the collection pipeline network flows in the linear treatment ditch. A gradient purification unit is set in the linear treatment ditch to purify the sewage. An underground water storage space is set up, and the purified water flowing out of the linear treatment ditch enters the water storage space, which is filled with modified zeolite.

2. The method for rainwater harvesting and purification in sponge cities according to claim 1, characterized in that: The reversing valve is driven to switch directions by the volume expansion of a temperature-sensitive phase change material, and the switching action temperature is 2℃-35℃.

3. The sponge city rainwater harvesting and purification method according to claim 2, characterized in that: The thermosensitive phase change material includes any one of n-dodecane + n-tetradecane, n-tetradecane + n-hexadecane, decanoic acid + lauric acid + n-hexadecane, decanoic acid + lauric acid, and lauric acid + palmitic acid.

4. The sponge city rainwater harvesting and purification method according to claim 3, characterized in that: The mass ratio of n-dodecane to n-tetradecane is 10-20:80-90, the mass ratio of n-tetradecane to n-hexadecane is 5-90:10-95, the mass ratio of decanoic acid, lauric acid and n-hexadecane is 58-64:32-36:0-10, the mass ratio of decanoic acid and lauric acid is 64-90:10-36, and the mass ratio of lauric acid and palmitic acid is 75-78:22-25.

5. The method for rainwater harvesting and purification in sponge cities according to claim 1, characterized in that: The gradient purification unit includes an aerobic treatment section, an anaerobic treatment section, and an anaerobic treatment section arranged sequentially along the water flow direction. The length of the aerobic treatment section is not less than the length of the anaerobic treatment section or the anaerobic treatment section.

6. The method for rainwater harvesting and purification in sponge cities according to claim 5, characterized in that: The aerobic treatment section is formed by placing filler material one in the linear treatment ditch and planting emergent plants on the filler material one; The filler includes particles containing iron oxide and aluminum oxide, porous particles, and carbon-based functional material. The anoxic treatment section is formed by placing a second packing material in the linear treatment ditch, and the second packing material is connected to the first packing material. The filler material 2 includes particles containing iron oxide and aluminum oxide 3, porous particles 4, carbon-based functional material 2, and slow-release carbon source; The anaerobic treatment section is formed by placing filler three in the linear treatment ditch, and filler three is connected to filler two. The filler material includes: five particles containing iron oxide and aluminum oxide, six porous particles, and three carbon-based functional materials. The particle size of particle one is greater than that of particle three, the particle size of particle three is greater than that of particle five, the particle size of particle two is greater than that of particle four, the particle size of particle four is greater than that of particle six, the particle size of carbon-based functional material one is greater than that of carbon-based functional material two, and the particle size of carbon-based functional material two is greater than that of carbon-based functional material three. The thickness of the first filler is less than the thickness of the second filler, and the thickness of the second filler is less than the thickness of the third filler.

7. The method for rainwater harvesting and purification in sponge cities according to claim 6, characterized in that: The filler material 2 is planted with water-tolerant plants.

8. The method for rainwater harvesting and purification in sponge cities according to claim 1, characterized in that: The preparation method of the modified zeolite includes: soaking the zeolite in a calcium chloride solution, stirring it for a period of time under water bath heating, and then taking it out, rinsing, drying, and calcining it to fully activate it.

9. The method for rainwater harvesting and purification in sponge cities according to claim 8, characterized in that: The zeolite is soaked in a calcium chloride solution with a concentration of 1-2 mol / L, heated and stirred in a water bath at 60-80℃ for 12-24 hours, then rinsed, dried, and calcined at 400-500℃ for 3-5 hours to activate it.

10. The method for rainwater harvesting and purification in sponge cities according to claim 1, characterized in that: The distance between the water storage space and the ground is not less than 3 meters.

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