A biological filter device and method for synchronous nitrogen and phosphorus removal from rural sewage

Abstract

The present invention provides a biological filter device and method for synchronously removing nitrogen and phosphorus from rural sewage, belonging to the technical field of sewage treatment. The biological filter device of the present invention includes a surface layer, a nitrogen and phosphorus removal layer, a supporting layer and a bottom layer; the nitrogen and phosphorus removal layer is sequentially a biological nitrogen removal material layer, an isolation layer and an adsorption phosphorus removal material layer in the water flow direction; the biological nitrogen removal material layer is a mixture of plant fiber material and ceramsite; the isolation layer is a mixture of one or two of zeolite and red soil; the adsorption phosphorus removal material layer is a mixture of modified bentonite and red soil. The device and method of the present invention have low cost and simple management and protection, and use easily available plant fiber materials (common organic wastes, such as crop straws, rice straws, sawdust) and adsorption materials as filter materials to achieve synchronous removal of nitrogen and phosphorus and improve the sewage purification effect of the biological filter device.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and particularly relates to a biological filter device and method for synchronous nitrogen and phosphorus removal from rural sewage. Background Art

[0002] Currently, rural sewage in many areas has become an important source of nitrogen and phosphorus pollution in the basin water body, causing serious water eutrophication and even black and odorous problems. Due to the characteristics of high dispersion and complex water quality of rural sewage, it is not convenient to centrally treat it in sewage treatment plants, which poses new challenges to rural sewage treatment technologies and processes.

[0003] In recent years, ecological treatment technologies such as biological filters have been widely used in rural areas due to their low capital construction costs and simple operation, etc. However, a single ecological treatment technology may have disadvantages such as large floor area and unstable treatment effect. The filter material is the most important component of the biological filter. It not only serves as a carrier for the growth and attachment of microorganisms, promoting the transformation and degradation of water pollutants by microorganisms, but also can intercept phosphorus and suspended solids in water through processes such as adsorption and precipitation. The performance of the filter material will directly affect the water purification efficiency of the biological filter. How to screen multifunctional environmental protection materials as filter materials to strengthen the sewage treatment capacity and stability of the biological filter for rural sewage is the key problem to be solved in improving the rural sewage treatment efficiency. Therefore, by preparing sewage treatment materials that are easy to obtain and low in cost, and developing an economic and efficient biological filter sewage treatment technology suitable for the characteristics of rural sewage discharge, better sewage treatment effects can be obtained, which is an important method for effectively controlling rural sewage and has practical value and application prospects. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a biological filter device and method for synchronous nitrogen and phosphorus removal from rural sewage, which are low in cost and simple to manage and protect, and use easily obtainable plant fibers (common organic waste, such as crop straws, rice straws, sawdust) and adsorption materials, etc. as filter materials to enhance the sewage purification effect of the biological filter device.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] A biological filter device for synchronous nitrogen and phosphorus removal from rural sewage includes a surface layer, a nitrogen and phosphorus removal layer, a supporting layer and a bottom layer; the nitrogen and phosphorus removal layer is successively a biological nitrogen removal material layer, an isolation layer and an adsorption and phosphorus removal material layer in the water flow direction;

[0007] The biological nitrogen removal material layer includes a mixture of plant fiber materials and ceramsite; the isolation layer includes one or two mixtures of zeolite and red soil; the adsorption and phosphorus removal material layer includes a mixture of modified bentonite and red soil.

[0008] Preferably, the surface layer material includes volcanic rock with a particle size of 0.5 - 3 mm.

[0009] Preferably, the supporting layer material includes zeolite and volcanic rock, and the dry weight mass ratio of the zeolite to the volcanic rock is 1:2-3, and the particle size is 0.5-3 mm.

[0010] Preferably, the bottom layer includes one or two of cobblestones and gravels, the cobblestones are 0.5-2 cm, and the gravels have a particle size of 1-3 cm.

[0011] Preferably, the dry weight mass ratio of the plant fiber material to the ceramsite is 1:3-5, the plant fiber length is 2-5 cm, and the ceramsite has a particle size of 5-10 mm.

[0012] Preferably, the dry weight mass ratio of the zeolite to the red soil is 1-2:1, the zeolite has a particle size of 0.5-3 mm, and the red soil has a particle size of ≤6 mm.

[0013] Preferably, the dry weight mass ratio of the modified bentonite to the red soil is 1-1.5:1, the modified bentonite has a particle size of 0.5-3 mm, and the red soil has a particle size of ≤6 mm.

[0014] Preferably, the surface layer has a thickness of 0.1-0.2 m, the supporting layer has a thickness of 0.1-0.2 m, and the bottom layer has a thickness of 0.1-0.2 m; in the denitrification and dephosphorization layer, the biological denitrification material layer has a thickness of 0.2-0.4 m, the isolation layer has a thickness of 0.1-0.2 m, and the adsorption dephosphorization material layer has a thickness of 0.1-0.3 m.

[0015] The present invention also provides a method for synchronously denitrifying and dephosphorizing rural sewage, comprising the following steps: establishing a rural sewage collection system to collect rural sewage; subjecting the rural sewage to sedimentation treatment in a sedimentation tank; purifying the sedimentation-treated rural sewage through the above biological filter device; and discharging the rural sewage after meeting the safety discharge water quality requirements.

[0016] Preferably, the rural sewage flows through the system and the device through a PVC pipe.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The design of the process flow of the biological filter device and method of the present invention refers to the relevant theories and technologies of hydraulic engineering, ecological engineering, and sewage treatment engineering, and selects low-cost and easily available filter materials such as modified expanded soil and plant fiber materials (agricultural waste), which is beneficial to adapting to the characteristics of complex and variable components of agricultural sewage, realizing low-input and high-efficiency purification and in-depth treatment of farmland drainage and decentralized domestic and breeding sewage in villages, and providing scientific and technological support for rural ecological environment protection.

[0019] The process flow of the biological filter device and method of the present invention has high treatment efficiency and stable operation effect: suspended matter such as silt, plant residues, etc. in sewage is removed by physical sedimentation and filtration in a sedimentation tank; plant fiber carbon source and modified bentonite are used to strengthen the treatment of nitrogen and phosphorus pollutants, avoiding the problem that the biological filter is mainly used for denitrification but has poor phosphorus removal effect, and the stable removal rate of total nitrogen and total phosphorus in sewage is more than 60%, and the treated water is transparent and clear.

[0020] The process flow of the biological filter device and method of the present invention has a long normal operation time and can effectively treat sewage in winter: the biological filter composed of a variety of filter materials can avoid prominent problems such as blockage caused by a single filter material and unstable water quality of treated water, maintain a good temperature, avoid the impact of low temperatures in winter, and effectively extend the stable operation period of the biological filter.

[0021] The process flow of the biofilter device and method of the present invention has low construction and operation costs and simple management: according to the characteristics of different treatment units in the process flow, materials that are easily available in rural areas, such as plant fiber materials, pebbles, red soil, etc., are used, and the construction cost is low. The management work of the entire system mainly involves dredging of sedimentation tanks and replacement of filter media in biofilters. The replacement cycle of filter media in biofilters is based on the use cycle of plant fibers and modified bentonite, and the designed replacement cycle is 2 to 3 years / time. The replaced original filter media can be directly returned to the field nearby, and maintenance is simple. The sewage is treated in the constructed treatment process system to achieve gravity flow and meet the "zero power" operation requirements, and the power cost is 0 yuan / year. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 :Cross-section diagram of the biological filter device (taking sewage flow from bottom to top as an example);

[0023] Figure 2 : Water distribution network (left) and biofilter after filling (right). DETAILED DESCRIPTION

[0024] The present invention provides a biological filter device for simultaneous denitrification and dephosphorization of rural sewage, comprising a surface layer, a denitrification and dephosphorization layer, a support layer and a bottom layer; the denitrification and dephosphorization layer is composed of a biological denitrification material layer, an isolation layer and an adsorption and dephosphorization material layer in the direction of water flow. The present invention treats rural sewage (drainage from large tracts of farmland, rural domestic sewage, etc.) as the treatment object for simultaneous denitrification and dephosphorization, preferably collected through pipes or ditches, and constructs the above-mentioned biological filter device in a low-lying area.

[0025] The preferred surface material of the present invention includes volcanic rock with a particle size of 0.5 to 3 mm, more preferably 1 to 2 mm, and even more preferably 1.5 mm.

[0026] The biological denitrification material layer of the present invention comprises a mixture of plant fiber material and ceramsite; preferably, the dry weight mass ratio of the plant fiber material to the ceramsite is 1:3 - 5, more preferably 1:4; preferably, the plant fiber length is 2 - 5 cm, more preferably 3.5 cm, and more preferably the plant fiber material is organic waste, including one or more mixtures of rice straw, sawdust, wheat straw, and corn straw. As an implementable mode, it is a mixture of rice straw and sawdust with a dry weight mass ratio of 1:1 - 2; preferably, the ceramsite particle size is 5 - 10 mm, more preferably 7.5 mm. In the biological denitrification material layer, the plant fiber material serves as a microbial carbon source, and the ceramsite serves as a porous material, which can provide an attachment surface for the growth of microorganisms. The combination of the two is conducive to the denitrification treatment of sewage.

[0027] The isolation layer of the present invention comprises a mixture of one or two of zeolite and red soil; preferably, the dry weight mass ratio of zeolite to red soil is 1 - 2:1, more preferably 1:1; preferably, the zeolite particle size is 0.5 - 3 mm, more preferably 1.5 mm; preferably, the red soil particle size is ≤6 mm. The material properties of the biological denitrification material layer and the adsorption and phosphorus removal material layer of the present invention are quite different. For example, the pH value of the adsorption and phosphorus removal material layer can reach about 8, which is not conducive to the growth of microorganisms in the biological denitrification material layer. By setting the isolation layer, the pH of the two layers is regulated to give full play to the water purification functions of the two layers.

[0028] The adsorption and phosphorus removal material layer of the present invention comprises a mixture of modified bentonite and red soil; preferably, the dry weight mass ratio of modified bentonite to red soil is 1 - 1.5:1, more preferably 1:1; preferably, the modified bentonite particle size is 0.5 - 3 mm, more preferably 1.5 mm; preferably, the red soil particle size is ≤6 mm. The present invention preferably uses alkaline calcium-based bentonite as the modified bentonite, and more preferably the preparation method comprises: mixing natural bentonite with 3 times the mass of water to form a slurry; adding calcium hydroxide to the bentonite adjusted to a slurry state according to 5% of the bentonite mass, stirring at room temperature for 24 h to make it evenly mixed, and then drying at 105 °C to obtain alkaline calcium-based bentonite. The present invention more preferably uses thermally modified alkaline calcium-based bentonite, and the preparation method comprises roasting at 400 °C for 2 h to further obtain a thermally modified alkaline calcium-based bentonite sample. Thermal modification and base modification change the surface structure of natural bentonite to prepare a highly efficient phosphorus adsorption agent, improving the adsorption and removal ability of phosphorus in wastewater. The present invention uses modified bentonite and red soil, etc. as a combined adsorption and phosphorus removal material, which can ensure that the pH of the treated drainage is stable between 6 and 8, solve the problem of the too high pH value of single modified bentonite, and avoid causing adverse effects on the water environment.

[0029] The denitrification treatment layer of the present invention comprehensively utilizes plant fiber materials such as rice straw and modified bentonite as the main filter media to construct an efficient biological filter tank treatment technology, ensuring the simultaneous progress of biological denitrification and adsorption and phosphorus removal in the biological filter tank, achieving low-cost and efficient treatment of agricultural sewage (such as farmland drainage, rural decentralized domestic sewage, etc.), and meeting the requirements of safe discharge after treatment. In addition, the filter media for denitrification, phosphorus removal, etc. filled in the present invention can be completely taken out and returned to the field nearby as soil fertilizers and soil texture improvers after use, realizing the resource recycling of nitrogen and phosphorus nutrients, avoiding secondary pollution, and improving the popularization of this technology in rural areas.

[0030] The preferred supporting layer materials of the present invention include zeolite and volcanic rock. Further preferably, the dry weight mass ratio of zeolite and volcanic rock is 1:2 - 3, and more preferably 1:2.5 for mixing; preferably, the particle size of zeolite and volcanic rock is 0.5 - 3 mm, and more preferably 1.5 mm. The bottom layer of the present invention is a large-pore material. The denitrification and phosphorus removal layer materials or adsorption and phosphorus removal layer materials with small particle sizes are prone to leakage. By laying the supporting layer, the stability of the biological filter tank device is maintained.

[0031] The preferred bottom layer of the present invention includes one or both of cobblestones and gravel; further preferably, the particle size of cobblestones is 0.5 - 2 cm, and more preferably 1 cm; further preferably, the particle size of gravel is 1 - 3 cm, and more preferably 2 cm. When cobblestones and gravel are mixed, the present invention has no special limitation on the ratio of cobblestones and gravel.

[0032] In the biological filter tank device of the present invention, the surface layer thickness is 0.1 - 0.2 m, and more preferably 0.15 m; the supporting layer thickness is 0.1 - 0.2 m, and more preferably 0.15 m; the bottom layer thickness is 0.1 - 0.2 m, and more preferably 0.15 m; the biological denitrification material layer thickness is 0.2 - 0.4 m, and more preferably 0.3 m; the isolation layer thickness is 0.1 - 0.2 m, and more preferably 0.15 m; the adsorption and phosphorus removal material layer thickness is 0.1 - 0.3 m, and more preferably 0.2 m.

[0033] The filter media in the biological filter tank device of the present invention has good porosity and water permeability. The plant fiber material, as a carbon source, can promote denitrification, and the modified bentonite can strengthen the phosphorus removal effect, enabling the constructed biological filter tank system to effectively remove nitrogen and phosphorus pollutants in farmland drainage. At the same time, filter media such as zeolite, volcanic rock, plant fiber, ceramsite, modified bentonite, and red soil have a large surface area, can effectively adsorb pollutants such as pigments, organic carbon, nitrogen, and phosphorus in water, further purify the sewage, and reduce the turbidity of the sewage.

[0034] The present invention also provides a biological filter tank system for synchronous denitrification and phosphorus removal treatment of rural sewage, including the above-mentioned biological filter tank device, water distribution pipes, drain pipes, and covers.

[0035] The cover plate of the present invention covers the top of the biofilter device (surface layer), and the cover plate is preferably a cement plate with a thickness of 3 cm. The cover plate can prevent rainfall and debris in the air from entering the biofilter.

[0036] The water distribution pipes and drainage pipes of the present invention are arranged according to the flow direction of sewage. As an implementation method, when the sewage flows vertically from bottom to top, perforated water distribution pipes are laid on the bottom layer, with "Ш"-shaped side-by-side perforations; perforated drainage pipes are laid on the surface layer, with "∏"-shaped side-by-side perforations; and two perforated water collection pipes are arranged side by side to collect the upper layer water of the biological filter treatment system, and then the water is collected and transported to the outlet by the drainage pipe. Figure 1 As shown. The water outlet of the biological filter system is 0.3m lower than the water inlet, ensuring that the treated water in the system can be discharged by gravity. As another possible implementation method, when the sewage water flows vertically from top to bottom, perforated water pipes are laid on the top layer and perforated drainage pipes are laid on the bottom layer. The present invention preferably allows the sewage water to flow vertically from bottom to top through the biological filter system. This method is conducive to the sewage flowing fully through each layer of the system and is conducive to the sewage being fully purified.

[0037] The present invention also provides a method for simultaneously removing nitrogen and phosphorus from rural sewage, comprising the following steps: establishing a rural sewage collection system to collect rural sewage; subjecting the rural sewage to sedimentation treatment in a sedimentation tank; purifying the rural sewage after sedimentation treatment through the above-mentioned biological filter device; and discharging the rural sewage after it reaches the safe discharge water quality requirements.

[0038] The present invention preferably treats the drainage of farmland in a piece, and uses drainage ditches to directly collect the drainage of farmland according to the farmland area and runoff drainage in the treatment area; when treating the drainage of a single or two adjacent farmlands, PVC pipes of different specifications are used to connect the farmland to collect the drainage according to the farmland area and runoff drainage, and establish a farmland drainage collection system. As an implementable method, the collection of rural domestic sewage adopts a diversion system, which specifically refers to the rural domestic sewage treatment engineering technical standard (GBT51347-2019).

[0039] After the rural sewage is collected, it is first pre-treated by a sedimentation tank, which is used to filter floating objects, settle suspended matter and sediment in the sewage. The effluent of the sedimentation tank preferably enters the biofilter through a "∟"-shaped overflow drain pipe designed as a water pipe, such as Figure 2 (Left) shown.

[0040] Preferably, rural sewage flows through the system and device via PVC pipes, and the diameter of the PVC pipes is adjusted according to the scale and flow rate of the sewage to be treated. As an implementable mode, the diameter of the "∟"-shaped overflow drain pipe is 110 cm or more, and a sieve with a sieve hole diameter less than 3 mm is added to the overflow pipe orifice; the diameter of the "Ш"-shaped water distribution pipe with side-by-side openings is 32, 50 or 75 mm, the diameter of the openings of the "∏"-shaped water collecting pipe is 40, 63 or 90 mm, and the diameter of the "─"-shaped direct flow drain pipe is 110 mm or more.

[0041] Preferably, the aspect ratios of the length to the width of both the sedimentation tank and the biological filter are 1-2:1, and the area ratio of the sedimentation tank to the biological filter is designed as 1:3-5. The specific dimensions are slightly adjusted according to the total amount of sewage to be treated and the topographical features.

[0042] The technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0043] Embodiment 1

[0044] A biological filter system for synchronous denitrification and phosphorus removal of rural sewage, adopting the way of vertical subsurface flow of rural sewage from bottom to top, and the construction steps are as follows:

[0045] (1) Dig and build a biological filter;

[0046] (2) Lay a "Ш"-shaped water distribution pipe with side-by-side openings at the bottom of the biological filter, and then fill the bottom layer of cobblestones with a particle size of 0.5-2 cm and a thickness of 0.15 m;

[0047] (3) Then lay a supporting layer, filling zeolite and volcanic rock in a dry weight mass ratio of 1:2.5, with the zeolite and volcanic rock having a particle size of 0.5-3 mm and a thickness of 0.15 m;

[0048] (4) Then lay a biological denitrification material layer, filling a mixture of straw and ceramsite in a dry weight mass ratio of 1:4, with the straw having a length of 2-5 cm and the ceramsite having a particle size of 5-10 mm and a thickness of 0.3 m;

[0049] (5) Then lay an isolation layer, filling zeolite and red soil in a dry weight mass ratio of 1:1, with the zeolite having a particle size of 0.5-3 mm and the red soil having a particle size ≤ 6 mm and a thickness of 0.15 m;

[0050] (6) Then lay an adsorption and phosphorus removal material layer, filling a mixture of modified bentonite and red soil in a dry weight mass ratio of 1:1, with the modified bentonite having a particle size of 0.5-3 mm and the red soil having a particle size ≤ 6 mm and a thickness of 0.2 m;

[0051] (7) Then lay a "∏"-shaped water collecting pipe with side-by-side openings on the upper layer of the adsorption and phosphorus removal material layer, and fill the surface layer of volcanic rock with a particle size of 0.5-3 mm and a thickness of 0.5 m;

[0052] (8)Cover a cement board with a thickness of 3 cm above the surface layer to complete the biological filter tank system for synchronous denitrification and phosphorus removal of rural sewage.

[0053] Example 2

[0054] A biological filter tank system for synchronous denitrification and phosphorus removal of rural sewage, adopting the way of vertical subsurface flow of rural sewage from bottom to top, and the construction steps are as follows:

[0055] (1)Dig and build a biological filter tank;

[0056] (2)Lay a water distribution pipe with "Ш"-shaped side-by-side openings at the bottom of the biological filter tank, and then fill the bottom layer of gravel with a particle size of 1 - 3 cm and a thickness of 0.1 m;

[0057] (3)Then lay a supporting layer, fill zeolite and volcanic rock in a dry weight mass ratio of 1:2, with the particle size of zeolite and volcanic rock being 0.5 - 3 mm and a thickness of 0.1 m;

[0058] (4)Then lay a biological denitrification material layer, fill a mixture of wheat straw and ceramsite in a dry weight mass ratio of 1:3, with the straw length being 2 - 5 cm and the ceramsite particle size being 5 - 10 mm and a thickness of 0.2 m;

[0059] (5)Then lay an isolation layer, fill zeolite with a particle size of 0.5 - 3 mm and a thickness of 0.1 m;

[0060] (6)Then lay an adsorption and phosphorus removal material layer, fill a mixture of modified bentonite and red soil in a dry weight mass ratio of 1.5:1, with the particle size of modified bentonite being 0.5 - 3 mm and the red soil particle size ≤ 6 mm and a thickness of 0.1 m;

[0061] (7)Then lay a "∏"-shaped side-by-side opening collecting water pipe on the upper layer of the adsorption and phosphorus removal material layer, and fill the surface layer of volcanic rock with a particle size of 0.5 - 3 mm and a thickness of 0.1 m;

[0062] (8)Cover a cement board with a thickness of 3 cm above the surface layer to complete the biological filter tank system for synchronous denitrification and phosphorus removal of rural sewage.

[0063] Example 3

[0064] A biological filter tank system for synchronous denitrification and phosphorus removal of rural sewage, adopting the way of vertical infiltration of rural sewage from top to bottom, and the construction steps are as follows:

[0065] (1)Dig and build a biological filter tank;

[0066] (2)Lay a "∏"-shaped side-by-side opening collecting water pipe at the bottom of the biological filter tank, and then fill the bottom layer of cobblestones and gravel in a mass ratio of 1:1, with the cobblestone particle size being 0.5 - 2 cm and the gravel particle size being 1 - 3 cm and a thickness of 0.2 m;

[0067] (3) Then lay the supporting layer, filling zeolite and volcanic rock in a dry weight mass ratio of 1:3. The particle sizes of zeolite and volcanic rock are 0.5 - 3 mm, and the thickness is 0.2 m.

[0068] (4) Then lay the adsorption and phosphorus removal material layer, filling the mixture of modified bentonite and red soil in a dry weight mass ratio of 1.25:1. The particle size of modified bentonite is 0.5 - 3 mm, the particle size of red soil is ≤6 mm, and the thickness is 0.3 m.

[0069] (5) Then lay the isolation layer, filling zeolite and red soil in a dry weight mass ratio of 2:1. The particle size of zeolite is 0.5 - 3 mm, the particle size of red soil is ≤6 mm, and the thickness is 0.2 m.

[0070] (6) Then lay the biological denitrification material layer, filling the mixture of straw, sawdust and ceramsite in a dry weight mass ratio of 0.5:0.5:5. The length of straw is 2 - 5 cm, the particle size of ceramsite is 5 - 10 mm, and the thickness is 0.4 m.

[0071] (7) Then lay the water distribution pipe with "Ш"-shaped side-by-side openings on the upper layer of the biological denitrification material layer, and fill the surface volcanic rock. The particle size is 0.5 - 3 mm, and the thickness is 0.2 m.

[0072] (8) Cover a cement board with a thickness of 3 cm above the surface layer to complete the biological filter tank system for synchronous denitrification and phosphorus removal of rural sewage.

[0073] Example 4

[0074] 1. Test and demonstration project: According to the method of the present invention, supported by the national key research and development plan project, a test and demonstration project for the treatment of agricultural sewage by biological filter tank was designed and constructed in June 2019. The research site is located in Gejiashan Village, Kaihui Town, Changsha County, Hunan Province.

[0075] The specific construction situation of the test and demonstration project is as follows:

[0076] Taking the drainage of three paddy fields with an area of 2 mu each as the treatment object, a sedimentation tank with dimensions of 0.6m×0.6m×1.5m in length, width and depth is built at the drainage outlet of each paddy field. The effluent from the sedimentation tank is discharged into the biological filter through a "∟"-shaped overflow drain pipe with a diameter of 110mm. Select the original low-lying drainage area of the experimental farmland to build a biological filter with dimensions of 1.3m×1.2m×0.8m in length, width and depth. The bottom is equipped with a "Ш"-shaped water distribution pipe with a diameter of 32mm and arranged side by side with openings, covered with 10cm thick cobblestones. The method of filling the filter material of the biological filter is to mix 25kg of zeolite and 50kg of volcanic rock (support layer) in sequence from bottom to top, 75kg of ceramsite and 17.5kg of straw (biological denitrification material layer), 50kg of zeolite (isolation layer), 120kg of modified bentonite and 80kg of red soil (adsorption and phosphorus removal material layer), 100kg of volcanic rock (surface layer). A "∏"-shaped collecting pipe with an opening diameter of 40mm is installed on the surface layer. The cross-sectional structure of the construction project is as Figure 1 .

[0077] The test is divided into the initial startup stage and the formal operation stage. The hydraulic retention time in the initial startup stage is 7 days. In the formal operation stage of the test, the hydraulic retention time is 1 - 3 days. The operation cycle of the project is 1 year. The main test indicators for the collected samples are nitrate nitrogen, ammonia nitrogen, total nitrogen, phosphate, total phosphorus, COD Cr and pH value.

[0078] 2. Operation effect:

[0079] During the operation, the average concentrations of nitrate nitrogen, ammonia nitrogen, total nitrogen, phosphate, and total phosphorus in the influent are 9.96, 0.11, 10.08, 0.98, and 1.09mg·L -1 , and the pH is 6.96. During the operation, the monitored nitrate nitrogen concentration in the effluent is 0.01 - 0.66mg·L -1 , the ammonia nitrogen concentration is 0.07 - 0.38mg·L -1 , the total nitrogen concentration is 1.21 - 6.23mg·L -1 , the phosphate concentration is 0.13 - 0.41mg·L -1 , the total phosphorus concentration is 0.15 - 0.56mg·L -1 , and the pH value is between 7.27 and 8.16. The average removal rates of the main pollutants nitrate nitrogen, total nitrogen, and total phosphorus in the sewage by the demonstration project are 98.0%, 65.4%, and 87.0% respectively, and the sewage treatment effect is stable.

[0080] In practical engineering applications, considering the nitrogen and phosphorus removal effects of biological filters comprehensively, it is confirmed that the technology of the present invention is applicable to the safe treatment of farmland drainage. The entire project has good sewage treatment effects, convenient operation and management, and low investment, and is suitable for popularization in rural areas where the development of economic and social conditions is restricted, so as to control agricultural sewage, non-point source pollution and other damages to the water quality of environmental water bodies.

[0081] Example 5

[0082] 1. Test and demonstration project: According to the method of the present invention, supported by the Class A strategic pilot project of the Chinese Academy of Sciences, "Science and Technology Project for the Construction of Ecological Civilization in Beautiful China", a demonstration project for upgrading rural domestic sewage treatment facilities was designed and constructed in April 2022. The research site is located in Matang Village, Ganlin Town, Shengzhou City, Zhejiang Province.

[0083] The specific construction of the test and demonstration project is as follows:

[0084] Taking the drainage of the domestic sewage treatment project previously built in Matang Village, Ganlin Town, Shengzhou as the treatment object, the original project was designed with a drainage standard of the "Pollutant Discharge Standard for Rural Domestic Sewage Treatment Facilities" (DB33 / 973-2015) Grade I standard, and there are prominent problems such as low treatment efficiency, poor annual stability, and the need to improve the drainage water quality standard. Therefore, the method of the present invention is adopted, combined with the secondary wetland technology, to design a project for upgrading rural domestic sewage treatment facilities. The designed daily sewage treatment capacity of this project is 100m 3 / d, serving 187 households.

[0085] The main design of the biological filter in this demonstration project is as follows: A biological filter with dimensions of 5.3m×3.5m×1.3m in length, width and depth is constructed. The bottom is equipped with a water distribution pipe with a diameter of 50mm and "Ш"-type side-by-side openings, covered with 15cm thick cobblestones. The method of filling the filter material in the biological filter is as follows from bottom to top: 2 tons of zeolite and 2 tons of volcanic rock are mixed evenly (support layer), 600kg of shredded straw and 3 tons of ceramsite are mixed evenly (biological nitrogen removal material layer), 2 tons of zeolite (isolation layer), 1.5 tons of modified bentonite and 3 tons of red soil are mixed evenly (adsorption and phosphorus removal material layer). A "∏"-type water collecting pipe with an opening diameter of 110mm is installed on the surface layer and covered with 2 tons of volcanic rock (surface layer).

[0086] The demonstration project was put into operation in August 2022.

[0087] 2. Operation effect:

[0088] The monitoring data from August to November 2022 show that the removal efficiencies of COD Cr , NH4 + -N, TN and TP are basically stable, and the overall remains above 60%. Especially for NH4 +-N, TN, and TP removal efficiencies are as high as 95.53%, 89.23%, and 90.73% respectively. The effluent COD Cr , NH4 + -N, TN, and TP average concentrations are 16.16 mg·L -1 , 0.43 mg·L -1 , 1.28 mg·L -1 and 0.15 mg·L -1 , meeting the Class IV water quality standard of Environmental Quality Standards for Surface Water (GB-3838-2002). The construction of the demonstration project achieved the goal of upgrading the drainage of the original project from the first-class standard of Discharge Standard of Pollutants for Rural Domestic Sewage Treatment Facilities (DB33 / 973-2015) to the Class IV water quality standard of Environmental Quality Standards for Surface Water (GB-3838-2002).

[0089] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A biological filter device for synchronous nitrogen and phosphorus removal from rural sewage, characterized in that, It is composed of a surface layer, a denitrification and phosphorus removal layer, a supporting layer and a bottom layer; the sewage water flows vertically upward through the biological filter device from bottom to top; the denitrification and phosphorus removal layer is successively a biological denitrification material layer, an isolation layer and an adsorption phosphorus removal material layer in the water flow direction; The biological denitrification material layer is mixed with plant fiber material and ceramsite; the dry weight mass ratio of the plant fiber material to the ceramsite is 1:3 - 5, the length of the plant fiber is 2 - 5 cm, and the particle size of the ceramsite is 5 - 10 mm; The isolation layer is mixed with zeolite and red soil; the dry weight mass ratio of the zeolite to the red soil is 1 - 2:1, the particle size of the zeolite is 0.5 - 3 mm, and the particle size of the red soil is ≤6 mm; The adsorption phosphorus removal material layer is mixed with modified bentonite and red soil; the dry weight mass ratio of the modified bentonite to the red soil is 1 - 1.5:1, the particle size of the modified bentonite is 0.5 - 3 mm, and the particle size of the red soil is ≤6 mm; The modified bentonite is alkaline calcium-based bentonite, and the preparation method includes: mixing natural bentonite with 3 times the mass of water to make a slurry; adding calcium hydroxide to the bentonite adjusted to a slurry state according to 5% of the mass of the bentonite, stirring at room temperature for 24 h to make it evenly mixed, and then drying at 105 °C to obtain alkaline calcium-based bentonite; In the denitrification and phosphorus removal layer, the thickness of the biological denitrification material layer is 0.2 - 0.4 m, the thickness of the isolation layer is 0.1 - 0.2 m, and the thickness of the adsorption phosphorus removal material layer is 0.1 - 0.3 m.

2. The biological filter device for synchronous nitrogen and phosphorus removal from rural sewage according to claim 1, wherein, The surface layer material includes volcanic rock with a particle size of 0.5 - 3 mm.

3. The biological filter device for synchronous nitrogen and phosphorus removal from rural sewage according to claim 1, characterized in that, The supporting layer material includes zeolite and volcanic rock, and the dry weight mass ratio of the zeolite to the volcanic rock is 1:2 - 3, with a particle size of 0.5 - 3 mm.

4. The biological filter device for synchronous nitrogen and phosphorus removal from rural sewage according to claim 1, characterized in that, The bottom layer includes one or two of cobblestones and gravel, the particle size of the cobblestones is 0.5 - 2 cm, and the particle size of the gravel is 1 - 3 cm.

5. The biological filter device for synchronous nitrogen and phosphorus removal from rural sewage according to claim 1, characterized in that, The thickness of the surface layer is 0.1 - 0.2 m, the thickness of the supporting layer is 0.1 - 0.2 m, and the thickness of the bottom layer is 0.1 - 0.2 m.

6. A method for synchronous nitrogen and phosphorus removal from rural sewage, characterized in that, It includes the following steps: Establish a rural sewage collection system to collect rural sewage; the rural sewage is subjected to sedimentation treatment in a sedimentation tank; the sedimentation-treated rural sewage is purified by the biological filter device described in any one of claims 1 - 5; the rural sewage is discharged after meeting the requirements of safe discharge water quality.

7. The method for synchronous nitrogen and phosphorus removal from rural sewage according to claim 6, characterized in that, The rural sewage flows through the system and the device through a PVC pipe.

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