Soil infiltration device for sewage treatment

Abstract

The present application relates to sewage treatment technical field, provide a kind of soil infiltration device for sewage treatment, including multistage infiltration unit, multistage infiltration unit includes infiltration pond body and water distribution layer, first water-permeable layer, phosphorus and nitrogen removal composite layer group and second water-permeable layer sequentially arranged in infiltration pond body from bottom to top, water distribution layer is used to input water body, second water-permeable layer is used to output water body, and phosphorus and nitrogen removal composite layer group includes the improved soil layer and functional filter material layer of alternative laying, and improved soil layer and functional filter material layer are at least provided with two layers, and improved soil layer includes mixed local loam, rice husk carbon and sponge iron.The soil infiltration device for sewage treatment provided in the present application, infiltration pond body can be built on site using common red brick and cement mortar in rural areas, the construction cost is extremely low, in improved soil layer, local loam is easy to obtain, rice husk carbon can be directly prepared using agricultural waste rice husk, and the cost of filter material is extremely low.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically to a soil infiltration device for wastewater treatment. Background Technology

[0002] Rural water environment management has become an important part of ecological civilization construction in my country. At present, the coverage rate of sewage treatment facilities in rural areas of my country is generally low. A large amount of decentralized domestic sewage is discharged directly without effective treatment, which not only pollutes rural surface water bodies and groundwater sources, but also affects the quality of life and health of rural residents.

[0003] Rural decentralized domestic sewage is characterized by small generation volume with large daily fluctuation coefficient, scattered pollution sources, complex water composition (including suspended solids, organic matter, nitrogen, phosphorus, oil, etc.), and high difficulty and cost in constructing collection pipe networks. Traditional urban sewage treatment processes (such as activated sludge process, A² / O process, etc.) rely on large structures and complex power systems, which have problems such as large construction investment, high operating energy consumption, and high operation and maintenance technical requirements. They are difficult to adapt to the actual situation of low economic development level, lack of professional and technical personnel, and scattered residence in rural areas.

[0004] Traditional wastewater treatment equipment is equipped with power technologies such as aeration and backwashing, which are complex in structure and have high operation and maintenance costs. Moreover, the filter media used are mostly special materials that are difficult to obtain locally in rural areas, resulting in high transportation and procurement costs. Therefore, traditional wastewater treatment equipment is difficult to popularize in rural areas.

[0005] Therefore, developing a wastewater treatment device that is simple to construct, low in cost, and easy to obtain filter media, and adapted to local rural resource conditions, is of great practical significance for promoting the development of rural wastewater treatment and improving the rural ecological environment. Summary of the Invention

[0006] To overcome the above-mentioned defects, embodiments of the present invention provide a soil infiltration device for sewage treatment, which solves the technical problems of high construction cost and difficulty in obtaining filter media locally in rural areas in traditional sewage treatment equipment.

[0007] According to one aspect, at least one embodiment of the present invention provides a soil infiltration device for wastewater treatment, comprising a multi-stage infiltration unit, the multi-stage infiltration unit comprising an infiltration tank body and, from bottom to top, a water distribution layer, a first permeable layer, a phosphorus and nitrogen removal composite layer group, and a second permeable layer arranged sequentially in the infiltration tank body, the water distribution layer being used for inputting water and the second permeable layer being used for outputting water. The phosphorus and nitrogen removal composite layer group includes alternating layers of improved soil and functional filter media. Both the improved soil layer and the functional filter media layer are provided in at least two layers. The improved soil layer includes a mixture of local loam, rice husk charcoal and sponge iron.

[0008] According to one embodiment of this application, the mass ratio of local loam, rice husk charcoal and sponge iron in the improved soil layer is 6.5-7.3:2.7-1.5:0.8-1.2, and a non-woven fabric isolation layer is laid between adjacent improved soil layers and functional filter media layers, wherein the functional filter media layer is zeolite.

[0009] According to one embodiment provided in this application, the thickness of the improved soil layer is 15-20cm, the thickness of the functional filter material layer is 12-18cm, and the total thickness of the phosphorus and nitrogen removal composite layer group is not less than 80cm.

[0010] According to one embodiment of this application, the water distribution layer is filled with gravel with a particle size of 3-5cm and a filling thickness of 8-12cm, the first permeable layer is filled with quartz gravel with a particle size of 2-3cm and a filling thickness of 5-8cm, and the second permeable layer is filled with gravel with a particle size of 1.5-2cm and a filling thickness of 10-15cm.

[0011] According to one embodiment of this application, a soil layer with a thickness of 25-30cm is laid above the second permeable layer for planting plants.

[0012] According to one embodiment of this application, the inner wall of the percolation tank is covered with a geomembrane, the geomembrane is made of polyvinyl chloride, and the thickness of the geomembrane is not less than 0.5 mm.

[0013] According to one embodiment of this application, a pretreatment unit is further included. The pretreatment unit includes a tank and a first partition and a second partition spaced apart inside the tank. The first partition and the second partition divide the inner part of the tank into a filter chamber, an oil-water separation chamber and an overflow chamber that are connected in sequence. The filter chamber is used to pre-filter the input sewage, the oil-water separation chamber is used to separate the grease from the sewage, and the overflow chamber is used to communicate with the water distribution layer.

[0014] According to one embodiment of this application, the tank sidewall is provided with a water inlet pipe communicating with the filter chamber, the filter chamber is provided with a grid filter screen, and the first partition is provided with a first guide pipe, which is used to connect the filter chamber and the oil-water separation chamber. The tank sidewall is provided with an oil drain port that communicates with the oil-water separation chamber. The bottom of the second partition is provided with a second guide pipe, which is used to connect the oil-water separation chamber and the overflow chamber. The overflow chamber is connected to the water distribution layer by means of a water distribution assembly.

[0015] According to one embodiment of this application, the water distribution assembly includes a main water distribution pipe and multiple branch water distribution pipes. One end of the main water distribution pipe is connected to the upper part of the overflow cavity, and the other end is connected to multiple branch water distribution pipes. The multiple branch water distribution pipes are parallel to each other and spaced apart in the water distribution layer. Multiple water distribution holes are spaced apart on each branch water distribution pipe along its own length direction.

[0016] According to one embodiment of this application, a water collection and reuse unit is also included. The water collection and reuse unit includes a reuse water storage tank, a water collection pipe, a return water pipe, a pump, and an outlet water pipe. The water collection pipe is laid in the second permeable layer. Multiple water collection holes are spaced apart along the length of the water collection pipe. The two ends of the return water pipe are respectively connected to the water collection pipe and the reuse water storage tank. The pump is installed through the top wall of the reuse water storage tank. The outlet water pipe is installed through the top wall of the reuse water storage tank and its bottom end is connected to the pump.

[0017] The soil infiltration device for wastewater treatment provided in this embodiment of the invention has the following advantages compared with the prior art: The multi-stage infiltration unit consists of a rectangular infiltration tank, which can be constructed on-site using common rural red bricks and cement mortar, resulting in extremely low construction costs compared to traditional wastewater treatment equipment. The interior of the infiltration tank, from bottom to top, comprises a water distribution layer, a first permeable layer, a phosphorus and nitrogen removal composite layer, a second permeable layer, and a soil layer.

[0018] Wastewater permeates from bottom to top through the first permeable layer and the phosphorus and nitrogen removal composite layer. After entering the phosphorus and nitrogen removal composite layer, the wastewater alternately flows through the improved soil layer and the functional filter media layer, naturally creating an alternating aerobic-anaerobic microenvironment. This is conducive to the growth and reproduction of nitrifying and denitrifying bacteria, significantly improving the nitrogen removal effect and achieving highly efficient nitrogen removal. In the improved soil layer, local loam is readily available, and rice husk charcoal can be directly prepared from agricultural waste rice husks, resulting in extremely low filter media costs. The well-developed porous structure of rice husk charcoal provides numerous attachment sites for microorganisms, which decompose the organic matter in the wastewater into carbon dioxide and water. Sponge iron reacts chemically with phosphates in the wastewater to form insoluble iron phosphate precipitates, achieving highly efficient chemical phosphorus removal. Subsequently, the wastewater enters the functional filter media layer, where ammonia nitrogen is adsorbed. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1This is a schematic diagram of the structure of a soil infiltration device for wastewater treatment provided in an embodiment of the present invention; Figure 2 This is an embodiment of the present invention. Figure 1 Schematic diagram of the structure of each layer of the intermediate infiltration tank; Figure 3 This is an embodiment of the present invention. Figure 1 A schematic diagram of the structure of the water branch pipe.

[0021] In the diagram: 200, multi-stage infiltration unit; 201, infiltration tank body; 202, water distribution layer; 203, first permeable layer; 204, phosphorus and nitrogen removal composite layer group; 205, second permeable layer; 2041, improved soil layer; 2042, functional filter media layer; 206, topsoil layer; 207, geomembrane; 100, pretreatment unit; 101, tank body; 102, first baffle; 103, second baffle; 104, filter chamber; 105 106. Oil-water separation chamber; 107. Overflow chamber; 108. Water inlet pipe; 109. Grille filter screen; 110. First guide pipe; 111. Oil outlet; 112. Second guide pipe; 113. Main water distribution pipe; 114. Branch water distribution pipe; 115. Water distribution hole; 300. Water collection and reuse unit; 301. Reuse water storage tank; 302. Water collection pipe; 303. Return water pipe; 304. Water pump; 305. Water outlet pipe; 306. Water collection hole. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0024] In the description of this application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0025] The terms "first," "second," "third," "fourth," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those illustrated or described herein.

[0026] To make the drawings concise and easy to understand, some drawings only show one of the components with the same structure or function, or only one of them is marked. In this article, "one" not only means "only one", but can also mean "more than one", and "several" includes "two" and "more than two".

[0027] Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus. It is understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. The embodiments of this application are described in detail below with reference to the accompanying drawings.

[0028] Example 1 This embodiment provides a soil infiltration device for wastewater treatment, specifically designed for the general rural decentralized domestic wastewater treatment scenario. It is designed to address the characteristics of low economic development level, lack of professional and technical personnel, scattered residences, and small and fluctuating wastewater discharge in rural areas of my country.

[0029] See Figures 1-3 As shown, the soil infiltration device for wastewater treatment in this embodiment includes a pretreatment unit 100, a multi-stage infiltration unit 200 and a water collection and reuse unit 300 connected in sequence. The whole device adopts a gravity flow design and can operate without power equipment.

[0030] In the pretreatment unit 100, the tank 101 is divided into a filtration chamber 104, an oil-water separation chamber 105, and an overflow chamber 106 by a first partition 102 and a second partition 103. A water inlet pipe 107 is installed on the upper side wall of the tank 101, which can be directly connected to the drainage pipes of the farmer's kitchen and washroom. A basket-type stainless steel grille filter 108 is detachably installed inside the filtration chamber 104. The grille filter 108 is made of stainless steel and has a basket-type structure for easy removal and cleaning. It has a pore size of 3mm and can intercept large suspended particles such as vegetable leaves, paper scraps, sand, and hair. A first guide pipe 109 is provided on the upper part of the first partition 102 to guide the filtered wastewater into the oil-water separation chamber 105. An oil drain port 110 is provided on the side wall of the oil-water separation chamber 105, located above the liquid surface, for periodically discharging the separated floating oil. The bottom of the second baffle 103 is provided with a second guide pipe 111, which guides the wastewater separated from the floating oil into the overflow chamber 106. The top of the tank 101 is provided with an openable and closable sealing cover corresponding to the positions of the filter chamber 104 and the oil-water separation chamber 105, which facilitates daily maintenance.

[0031] The multi-stage infiltration unit 200 includes a rectangular infiltration tank 201, which can be constructed on-site using common rural red bricks and cement mortar, resulting in extremely low construction costs compared to traditional wastewater treatment equipment. The inner wall of the infiltration tank 201 is fully covered with a 0.6mm thick polyvinyl chloride geomembrane 207 to prevent wastewater leakage and groundwater contamination during treatment. Inside the infiltration tank 201, from bottom to top, are arranged a water distribution layer 202, a first permeable layer 203, a phosphorus and nitrogen removal composite layer group 204, a second permeable layer 205, and a soil layer 206.

[0032] The water distribution layer 202 is uniformly filled with natural gravel with a particle size of 3cm, and the filling thickness is 10cm. The water distribution branch pipes 113 of the water distribution component are evenly laid in the water distribution layer 202. A water distribution hole 114 is opened every 10cm along the length of the water distribution branch pipe 113. The water distribution hole 114 faces downward, so that the sewage can be fully diffused in the water distribution layer 202, achieving uniform water distribution in the cross-section of the entire infiltration tank 201 and avoiding local water accumulation and channeling.

[0033] The first permeable layer 203 is filled with white quartz gravel with a particle size of 2cm and a filling thickness of 6.5cm. The white quartz gravel has a smooth surface and will not produce debris when washed by water for a long time. It is not easy for biofilm to form, thus avoiding the growth of biofilm that clogs the pores and maintaining stable permeability over a long period of time.

[0034] The phosphorus and nitrogen removal composite layer 204 consists of two alternating layers of improved soil 2041 and two layers of functional filter media 2042, with a total thickness of 82cm. The improved soil layer 2041 is 23cm thick and is made from a mixture of local rural loam, rice husk charcoal, and sponge iron in a 7:2:1 mass ratio. The local loam is readily available, and the rice husk charcoal can be directly prepared from agricultural waste rice husks, resulting in extremely low filter media costs. The functional filter media layer 2042 is 18cm thick and is filled with 2mm diameter natural zeolite. A non-woven fabric isolation layer is laid between adjacent improved soil layers 2041 and functional filter media layers 2042 to prevent mixing of different filter media and ensure the independent and stable function of each layer. Vertically inserted vent pipes are also installed within the infiltration tank 201. Multiple vent holes are evenly distributed on the pipe walls, and the top of the vent pipe protrudes above the surface of the soil layer 206, connecting with the outside atmosphere to achieve natural oxygenation, promote the growth and reproduction of aerobic microorganisms in the soil, and improve pollutant degradation efficiency.

[0035] The second permeable layer 205 is filled with a mixture of gravel with a particle size of 1.5cm and a filling thickness of 12cm. It is used to support the phosphorus and nitrogen removal composite layer 204 above and to evenly introduce the treated clean water into the water collection system.

[0036] The planting soil layer 206 is laid on top of the second permeable layer 205, with a thickness of 30cm. It is made by mixing local rural cultivated soil and decomposed organic fertilizer in a mass ratio of 9:1, and can be used to plant aquatic plants such as reeds.

[0037] The water collection and reuse unit 300 includes a reuse water storage tank 301, a water collection pipe 302, a return water pipe 303, a pump 304, and an outlet water pipe 305. The water collection pipe 302 is laid within the second permeable layer 205, with a water collection hole 306 every 10cm along its length. The water collection pipe 302 is connected to the reuse water storage tank 301 via the return water pipe 303, and the reuse water storage tank 301 can be buried underground. The pump 304 is installed through the top of the reuse water storage tank 301, and the outlet water pipe 305 is connected to the outlet of the pump 304, allowing farmers to manually access the treated clean water.

[0038] During operation, rural domestic sewage first enters the filtration chamber 104 of the pretreatment unit 100 through the inlet pipe 107. After being intercepted and removed by the bar screen 108, large suspended particles such as vegetable leaves, sand, and hair are removed. Then, it flows into the oil-water separation chamber 105 through the first guide pipe 109. In the oil-water separation chamber 105, utilizing the principle of oil-water density difference, the floating oil in the sewage rises to the surface, forming an oil layer, which is periodically discharged through the oil outlet 110. The sewage after removing the floating oil flows into the overflow chamber 106 through the second guide pipe 111 at the bottom of the second baffle 103. The two-stage pretreatment can remove most of the suspended impurities and floating oil in the sewage, reducing the amount of pollutants entering the multi-stage infiltration unit 200 from the source and reducing the risk of clogging. The sewage in the overflow chamber 106 is distributed to each water distribution branch pipe 113 through the main water distribution pipe 112, and then evenly distributed in the water distribution layer 202 through the water distribution holes 114. The gravel particles in the water distribution layer 202 are relatively large, which can form larger pores, so that the sewage is evenly distributed across the cross-section of the entire infiltration tank 201, avoiding local blockage.

[0039] Wastewater permeates sequentially from bottom to top through the first permeable layer 203 and the phosphorus and nitrogen removal composite layer group 204. After entering the phosphorus and nitrogen removal composite layer group 204, the wastewater alternately flows through the improved soil layer 2041 and the functional filter media layer 2042. In the improved soil layer 2041, rice husk charcoal has a well-developed porous structure, providing numerous attachment sites for microorganisms. The microorganisms decompose the organic matter in the wastewater into carbon dioxide and water. Sponge iron reacts chemically with phosphates in the wastewater to form insoluble iron phosphate precipitate, achieving efficient chemical phosphorus removal. Subsequently, the wastewater enters the functional filter media layer 2042, where natural zeolite adsorbs ammonia nitrogen in the wastewater through ion exchange.

[0040] The vent pipes introduce outside air into the infiltration layer, achieving natural oxygenation. Because wastewater flows from bottom to top, and the modified soil layer 2041 and functional filter media layer 2042 are alternately distributed, a microenvironment of alternating aerobic and anaerobic conditions is naturally formed inside the device. This is conducive to the growth and reproduction of nitrifying and denitrifying bacteria, significantly improving the nitrogen removal effect and achieving highly efficient nitrogen removal. The total thickness of the phosphorus and nitrogen removal composite layer group 204 is not less than 80cm, ensuring the residence time of wastewater within the filter layer and ensuring that pollutants are fully degraded.

[0041] The treated clean water permeates into the second permeable layer 205, is collected through the collection pipe 302, and flows into the reuse storage tank 301 through the return pipe 303. Farmers can use a pump 304 to extract the clean water for purposes such as farmland irrigation, courtyard greening, and toilet flushing, thus achieving water resource recycling. The plant roots in the soil layer 206 can absorb residual nitrogen, phosphorus, and other nutrients from the wastewater, further purifying the water quality; at the same time, the oxygen secretion of the plant roots can improve the microenvironment inside the filter layer and promote the growth and reproduction of microorganisms; in addition, the planted plants also beautify the environment, realizing the organic combination of wastewater treatment and ecological landscape.

[0042] The device in this embodiment operated continuously for 12 months in a rural area of ​​North China. The average removal rates of COD, NH3-N, TN, and TP in domestic sewage were 78.5%, 75.2%, 71.8%, and 89.3%, respectively, and the average effluent concentrations were 79.2 mg / L, 12.6 mg / L, 17.5 mg / L, and 0.42 mg / L, respectively, meeting the national secondary discharge standards. It can stably achieve the purification and resource utilization of rural sewage.

[0043] The device has low construction and operating costs. Routine maintenance only requires opening the sealing cover once a month to clean the grille and discharging the floating oil from the 110 drain port. Operation is simple and requires no professional technical knowledge; ordinary farmers can complete the task. The treated water has a high reuse rate, saving farmers on tap water costs each year and preventing direct sewage discharge that could pollute rural surface water bodies and groundwater sources, resulting in significant economic, social, and ecological benefits.

[0044] Example 2 This embodiment targets rural wastewater treatment scenarios with high organic matter concentrations, such as catering wastewater (e.g., from farmhouses, rural markets, school canteens, etc.). This type of wastewater has high COD concentrations and high levels of grease and suspended solids.

[0045] The device structure in this embodiment is basically the same as that in embodiment 1, except that: The phosphorus and nitrogen removal composite layer 204 consists of three alternating layers of improved soil 2041 and three layers of functional filter media 2042, with a total thickness of 108cm. The improved soil layer 2041 is 20cm thick and is made from a mixture of local rural loam, rice husk charcoal, and sponge iron in a mass ratio of 6.5:2.7:0.8. The functional filter media layer 2042 is 16cm thick and is filled with natural zeolite with a particle size of 3mm. The water distribution layer 202 is uniformly filled with natural gravel with a particle size of 5cm, and the filling thickness is 15cm. The first permeable layer 203 is filled with white quartz gravel with a particle size of 2.5cm and a filling thickness of 8cm; The second permeable layer 205 is filled with a mixture of gravel with a particle size of 1.5cm, and the filling thickness is 12cm.

[0046] Rice husk charcoal has a large specific surface area and abundant porous structure. Increasing its proportion can increase the attachment area for microorganisms and enhance the system's ability to degrade organic matter. At the same time, the porous structure of rice husk charcoal can also adsorb some recalcitrant organic matter, prolonging its residence time in the filter layer and allowing it to be fully decomposed by microorganisms.

[0047] The device in this embodiment was operated continuously for 6 months at a farmhouse restaurant. The average influent COD concentration was 680 mg / L, with a maximum of 1120 mg / L. The operational results showed that the average removal rates of COD, NH3-N, TN, and TP were 84.7%, 76.5%, 73.2%, and 90.1%, respectively, with average effluent concentrations of 62.3 mg / L, 11.8 mg / L, 16.4 mg / L, and 0.39 mg / L, respectively. These figures still met the national secondary discharge standard, demonstrating the good adaptability of the parameter adjustments in this embodiment to wastewater with high organic matter concentrations.

[0048] Example 3 This embodiment is designed for the low-temperature environment in the cold winter of northern my country, where the winter temperature can drop to below -20°C. Traditional soil infiltration devices are easily damaged by frost heave, and low temperatures will significantly inhibit the activity of microorganisms, resulting in a significant decrease in treatment effect or even failure to operate normally.

[0049] The device structure in this embodiment is basically the same as that in embodiment 1, except that: Insulation design has been added. The outer walls of the pretreatment unit 100 tank 101, the multi-stage percolation unit 200 percolation tank 201, and the reuse water storage tank 301 are all wrapped with polyurethane insulation boards with a thickness of 4cm. The outer side of the insulation boards is protected with galvanized iron sheet. Exposed pipelines such as the water distribution main pipe 112 and the return water pipe 303 are also wrapped with a polyurethane insulation layer with a thickness of 3cm. The phosphorus and nitrogen removal composite layer 204 consists of two alternating layers of improved soil 2041 and two layers of functional filter media 2042, with a total thickness of 84cm. The improved soil layer 2041 is 22cm thick and is made from a mixture of local rural loam, rice husk charcoal, and sponge iron in a mass ratio of 7:2:1. The functional filter media layer 2042 is 20cm thick and is filled with natural zeolite with a particle size of 2mm. The water distribution layer 202 is uniformly filled with natural gravel with a particle size of 4cm, and the filling thickness is 10cm. The first permeable layer 203 is filled with white quartz gravel with a particle size of 2.3cm and a filling thickness of 7cm; The second permeable layer 205 is filled with a mixture of gravel with a particle size of 2cm, and the filling thickness is 12cm.

[0050] Polyurethane insulation boards have low thermal conductivity and good insulation effect, which can reduce heat loss inside the device, prevent damage to the percolation tank 201 and pipelines due to freezing expansion, keep the average temperature inside the multi-stage percolation unit 200 above 5℃ in winter, maintain the basic activity of microorganisms, and ensure the treatment effect in low-temperature environment.

[0051] The device in this embodiment was operated continuously for 4 months during the low-temperature winter period (-18℃ to 6℃) in a rural area of ​​Northeast China. The results showed that the average removal rates of COD, NH3-N, TN, and TP were 75.1%, 71.6%, 69.2%, and 86.8%, respectively, and the average effluent concentrations were 88.7 mg / L, 14.5 mg / L, 19.6 mg / L, and 0.46 mg / L, respectively. These results still met the national secondary discharge standards, and the device did not experience any frost heave damage, proving the good adaptability of this insulation design to cold northern regions.

[0052] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A soil infiltration device for wastewater treatment, characterized in that, The system includes a multi-stage infiltration unit (200), which includes an infiltration tank body (201) and, from bottom to top, a water distribution layer (202), a first permeable layer (203), a phosphorus and nitrogen removal composite layer group (204), and a second permeable layer (205) arranged in the infiltration tank body (201). The water distribution layer (202) is used for inputting water, and the second permeable layer (205) is used for outputting water. The phosphorus and nitrogen removal composite layer group (204) includes alternating layers of improved soil (2041) and functional filter media (2042). Both the improved soil layer (2041) and the functional filter media (2042) are provided with at least two layers. The improved soil layer (2041) includes a mixture of local loam, rice husk charcoal and sponge iron.

2. The soil infiltration device for wastewater treatment according to claim 1, characterized in that, The mass ratio of local loam, rice husk charcoal and sponge iron in the improved soil layer (2041) is 6.5-7.3:2.7-1.5:0.8-1.

2. A non-woven fabric isolation layer is laid between the adjacent improved soil layer (2041) and the functional filter material layer (2042). The functional filter material layer (2042) is zeolite.

3. A soil infiltration device for wastewater treatment according to claim 2, characterized in that, The thickness of the improved soil layer (2041) is 15-25cm, the thickness of the functional filter layer (2042) is 12-20cm, and the total thickness of the phosphorus and nitrogen removal composite layer group (204) is not less than 80cm.

4. A soil infiltration device for wastewater treatment according to claim 1, characterized in that, The water distribution layer (202) is filled with gravel with a particle size of 3-5cm and a filling thickness of 8-12cm. The first permeable layer (203) is filled with quartz gravel with a particle size of 2-3cm and a filling thickness of 5-8cm. The second permeable layer (205) is filled with gravel with a particle size of 1.5-2cm and a filling thickness of 10-15cm.

5. A soil infiltration device for wastewater treatment according to claim 1, characterized in that, A soil layer (206) is laid on top of the second permeable layer (205), the soil layer (206) being 25-30cm thick and used for planting plants.

6. A soil infiltration device for wastewater treatment according to claim 1, characterized in that, The inner wall of the infiltration tank (201) is covered with a geomembrane (207), which is made of polyvinyl chloride and has a thickness of not less than 0.5 mm.

7. A soil infiltration device for wastewater treatment according to claim 1, characterized in that, It also includes a pretreatment unit (100), which includes a tank (101) and a first partition (102) and a second partition (103) spaced apart inside the tank (101). The first partition (102) and the second partition (103) divide the interior of the tank (101) into a filter chamber (104), an oil-water separation chamber (105) and an overflow chamber (106) that are connected in sequence. The filter chamber (104) is used for preliminary filtration of the input sewage, the oil-water separation chamber (105) is used to separate the grease from the sewage, and the overflow chamber (106) is used to communicate with the water distribution layer (202).

8. A soil infiltration device for wastewater treatment according to claim 7, characterized in that, The tank (101) has an inlet pipe (107) on its side wall that communicates with the filter chamber (104). The filter chamber (104) is provided with a grid filter screen (108). The first partition (102) is provided with a first guide pipe (109). The first guide pipe (109) is used to connect the filter chamber (104) and the oil-water separation chamber (105). The tank body (101) has an oil drain port (110) on its side wall that communicates with the oil-water separation chamber (105). The bottom of the second partition (103) is provided with a second guide pipe (111). The second guide pipe (111) is used to connect the oil-water separation chamber (105) and the overflow chamber (106). The overflow chamber (106) is connected to the water distribution layer (202) by means of a water distribution assembly.

9. A soil infiltration device for wastewater treatment according to claim 8, characterized in that, The water distribution assembly includes a main water distribution pipe (112) and multiple water distribution branch pipes (113). One end of the main water distribution pipe (112) is connected to the upper part of the overflow chamber (106), and the other end is connected to multiple water distribution branch pipes (113). The multiple water distribution branch pipes (113) are parallel to each other and spaced apart in the water distribution layer (202). Multiple water distribution holes (114) are spaced apart along their own length direction on the water distribution branch pipes (113).

10. A soil infiltration device for wastewater treatment according to claim 1, characterized in that, It also includes a water collection and reuse unit (300), which includes a reuse water storage tank (301), a water collection pipe (302), a return water pipe (303), a pump (304), and an outlet water pipe (305). The water collection pipe (302) is laid in the second permeable layer (205). The water collection pipe (302) has multiple water collection holes (306) spaced apart along its own length. The two ends of the return water pipe (303) are respectively connected to the water collection pipe (302) and the reuse water storage tank (301). The pump (304) is installed through the top wall of the reuse water storage tank (301). The outlet water pipe (305) is installed through the top wall of the reuse water storage tank (301) and its bottom end is connected to the pump (304).

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