A system and process for efficient nitrogen and phosphorus removal from agricultural wastewater

Abstract

This invention discloses a system and process for efficient nitrogen and phosphorus removal from agricultural wastewater, belonging to the field of wastewater treatment technology. This invention combines the IFAS process with volcanic rock and steel slag filters. The IFAS process enriches nitrifying bacteria and other aerobic microorganisms on suspended media through aeration, forming a biofilm. Nitrification is the primary process in the IFAS system, but denitrification also occurs to a certain extent. In the anoxic zone within the biofilm, denitrifying bacteria utilize readily biodegradable COD in the influent to reduce a small portion of the nitrate nitrogen produced in the IFAS tank to nitrogen gas through denitrification. The volcanic rock and steel slag filters further remove total nitrogen and total phosphorus from the wastewater, with the volcanic rock and steel slag being layered. This system has a small footprint, simple structure, and low operating costs, featuring efficient pollutant removal and a short process flow, aligning with the current development trend of efficient and convenient agricultural wastewater treatment.

Description

Technical Field

[0001] This invention relates to a system and process for achieving efficient nitrogen and phosphorus removal from agricultural wastewater, belonging to the field of wastewater treatment technology. Background Technology

[0002] Rural residents' living habits, sanitation facilities, the distribution of regional water resources, and the dispersed living environment result in agricultural wastewater being characterized by wide sources, high collection difficulty, and large fluctuations in water quality and quantity. Since there is no industrial wastewater discharge near rural areas, the quality of agricultural wastewater is relatively simple, with organic matter, nitrogen, and phosphorus as the main pollutants. In May 2020, Jiangsu Province issued the "Water Pollutant Discharge Standard for Rural Domestic Sewage Treatment Facilities" (DB32 / 3462-2020), which sets higher requirements for the discharge of rural sewage treatment facilities, including COD and NH4+. + The Class A emission standards for nitrogen, phosphorus, and total nitrogen (TN) are 60 mg / L, 8 mg / L, 20 mg / L, and 1 mg / L, respectively, significantly increasing the difficulty of wastewater treatment. Therefore, the selection of treatment processes becomes more stringent, requiring high removal efficiency for conventional pollutants such as nitrogen and phosphorus, strong resistance to shock loads, stable operation, and simple maintenance. Commonly used rural wastewater treatment processes include anaerobic-anoxic-aerobic treatment (A... 2 O) process, sequencing batch reactor (SBR), moving bed biofilm reactor (MBBR) process, constructed wetlands, etc. A 2 The O process and SBR process mainly adopt the suspended growth activated sludge method, A 2 The O process is stable, mature, and highly efficient at removing organic matter, but it is difficult to achieve efficient removal of nitrogen and phosphorus simultaneously within the same system. The SBR process has a simple structure and low equipment and operating costs, but its removal efficiency for pollutants such as nitrogen and phosphorus is not high. The MBBR process mainly uses attached biofilm growth, offering advantages such as stable effluent quality, high pollutant removal efficiency, and low sludge production. However, this process also suffers from membrane fouling, resulting in higher operation and maintenance costs, and is prone to localized packing material accumulation in practical engineering applications. Constructed wetlands can increase green space while purifying water and have low operation and maintenance costs, but they require a large area, and their pollutant removal efficiency is easily affected by the external environment. Due to the limited operation and maintenance of rural wastewater treatment facilities and increasingly stringent discharge standards, it is necessary to further improve the treatment efficiency of rural wastewater, strengthen process combinations, and enhance economic efficiency and environmental adaptability.

[0003] Activated sludge and biofilm processes each have their advantages and disadvantages, leading to widespread interest in the Activated Sludge-Biofilm Assembly (IFAS) process. In IFAS, suspended media with a specific gravity close to water are added to the biological treatment tank as a carrier for microbial growth and attachment. These media mix with the activated sludge in the reaction tank and flow freely under aeration or mechanical stirring, leveraging their respective degradation advantages to remove pollutants. Compared to single activated sludge or biofilm processes, this process offers advantages such as reduced excess sludge production, enhanced resistance to shock loads, and improved operational stability. However, the selection of suspended media requires careful consideration of various factors, including hydraulic performance, mechanical and chemical properties, adhesion, and cost. Different suspended media significantly impact the treatment efficiency of the IFAS process. Currently, MBBR suspended media is commonly used in IFAS processes. While this media is acid and alkali resistant, has a high specific surface area, and facilitates biofilm formation, it also suffers from short biofilm formation time and easy media migration. In addition, since the carbon source in agricultural wastewater is limited, when using the IFAS process to treat agricultural wastewater, additional carbon sources need to be added in order to remove nitrogen and phosphorus pollutants efficiently at the same time, which increases manpower and material resources and results in higher operation and maintenance costs. Summary of the Invention

[0004] To address one or more of the above-mentioned problems, this invention provides a system and process for achieving efficient nitrogen and phosphorus removal from agricultural wastewater, the technical solution of which is as follows:

[0005] To efficiently remove pollutants from agricultural wastewater, ensure stable effluent quality and compliance with discharge standards, and shorten the process flow, save land area, and reduce operation and maintenance costs, this invention provides a system and process for efficient nitrogen and phosphorus removal from agricultural wastewater. This invention combines the IFAS process with volcanic rock and steel slag filters. The IFAS process is a coupled activated sludge and biofilm process. Through aeration, nitrifying bacteria and other aerobic microorganisms are enriched on suspended packing material to form a biofilm. Nitrification is the primary process in the IFAS system, but denitrification also occurs to a certain extent. In the anoxic zone inside the biofilm, denitrifying bacteria utilize readily biodegradable COD in the influent to reduce a small portion of the nitrate nitrogen produced in the IFAS tank to nitrogen gas through denitrification. The main function of the IFAS tank is to remove ammonia nitrogen and COD from rural wastewater, while the main function of the volcanic rock and steel slag filters is to remove total nitrogen and total phosphorus. The volcanic rock and steel slag are layered. This system has a small footprint, simple structure, and low operating costs, and features efficient pollutant removal and a short process flow, aligning with the current development trend of efficient and convenient agricultural wastewater treatment.

[0006] The first objective of this invention is to provide a system for efficient nitrogen and phosphorus removal from agricultural wastewater, comprising an equalization tank, an IFAS tank, and volcanic rock and steel slag filters connected in sequence; the IFAS tank is connected to the equalization tank via an inlet pipe, and is filled with activated sludge and suspended packing balls, and is equipped with an aeration pipe; the packing material in the volcanic rock and steel slag filters includes a crushed stone packing layer, a volcanic rock packing layer, a ceramsite packing layer, and a steel slag packing layer.

[0007] In one embodiment, a water inlet pump is provided on the water inlet pipe.

[0008] In one embodiment, the aeration pipe is symmetrically provided with several holes of 2 mm in diameter at a 45° downward angle.

[0009] In one embodiment, the concentration of the activated sludge is 1400–1600 mg / L.

[0010] In one embodiment, the activated sludge is aerobic activated sludge.

[0011] In one embodiment, the suspended filler is made of polyurethane and is wrapped with a spherical porous plastic shell with a filling density of 35-45%. The suspended filler spheres have good flow characteristics in water, and the surface of the polyurethane filler is relatively rough, resulting in a fast biofilm formation speed and preventing microbial loss. The outer spherical porous plastic shell has high mechanical strength and is not easily corroded.

[0012] In one embodiment, the area of ​​the volcanic rock and steel slag filter pool is 2-3 m². 2 The height is 0.8 to 1.2m.

[0013] In one embodiment, the packing material in the volcanic rock and steel slag filter is layered, with a thickness of 70-90 cm. The sum of the volumes of the volcanic rock packing layer and the steel slag packing layer accounts for 60-70% of the total volume.

[0014] In one embodiment, the volume ratio of the volcanic rock packing layer to the steel slag packing layer is 3:2.

[0015] In one embodiment, the volume ratio of the crushed stone filler layer to the ceramsite filler layer is 1.5 to 2.5:1.

[0016] In one embodiment, the system further includes an electrical control cabinet for controlling the hydraulic retention time (HRT) and dissolved oxygen (DO) concentration of the IFAS tank.

[0017] In one implementation, the HRT and hydraulic load of the volcanic rock and steel slag filter are controlled by adjusting the influent flow rate through an electrical control cabinet.

[0018] The second objective of this invention is to provide a process for achieving efficient nitrogen and phosphorus removal from agricultural wastewater. The process utilizes the aforementioned system for achieving efficient nitrogen and phosphorus removal from agricultural wastewater, and includes:

[0019] The hydraulic retention time (HRT) of the IFAS tank is set at 22–26 h, the dissolved oxygen (DO) concentration is maintained at 5–6 mg / L, and the pH is controlled between 7 and 8 by adding alkalinity. The HRT of the volcanic rock and steel slag filters is 56–64 h, and the hydraulic loading, based on the filter media area, is 0.3–0.5 m². 3 / (m 2 ·d).

[0020] In one embodiment, activated sludge and suspended packing are added to the IFAS tank. Nitrifying bacteria and other aerobic microorganisms are enriched on the suspended packing to form a biofilm. Nitrifying bacteria degrade ammonia nitrogen into nitrate nitrogen through nitrification. In the anoxic zone inside the biofilm, denitrifying bacteria use the easily biodegradable COD in the influent to reduce a small portion of the nitrate nitrogen generated in the tank into nitrogen gas, thereby achieving the purpose of denitrification.

[0021] The above-mentioned systems and processes are applied to the treatment of agricultural wastewater.

[0022] The volcanic rock and steel slag filters are used for denitrification and phosphorus removal. Volcanic rock, as a primary site for microbial enrichment, mainly promotes denitrification by using COD as an electron donor and nitrate or nitrite as an electron acceptor, reducing it to nitrogen gas for final denitrification. It also forms precipitates with phosphates in the influent, achieving chemical phosphorus removal. Steel slag, as a filler material for enhanced chemical phosphorus removal, contains abundant Ca, Fe, Mg, and other metallic elements that can form precipitates with phosphates in the influent.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention innovatively combines IFAS (Integrated Failure Analysis) with volcanic rock and steel slag filters to form a complementary combined process. Experiments were conducted using rural wastewater from various locations in Wuxi City as the influent to the reactors, achieving excellent removal results for pollutants such as organic matter, nitrogen, and phosphorus. The IFAS process section achieves good COD removal and ammonia nitrification; the volcanic rock and steel slag filter section achieves good total nitrogen and total phosphorus removal. Volcanic rock, as a slow-release carbon source, solves the problem of insufficient carbon source in agricultural wastewater. Experimental results show that the effluent COD and ammonia nitrogen from the IFAS can both meet the Class A standard (COD 60 mg / L, ammonia nitrogen 8 mg / L); the effluent total nitrogen from the volcanic rock and steel slag filter can meet the Class A standard (20 mg / L), and the effluent total phosphorus can also stably meet the Class A discharge standard (1 mg / L). This combined process requires no external carbon source and has low operation and maintenance costs, making it an effective combined process for treating agricultural wastewater. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic diagram of a system for achieving efficient nitrogen and phosphorus removal from agricultural wastewater provided by the present invention;

[0027] Figure 2 This is a distribution diagram of the various packing layers in the volcanic rock and steel slag filter of the present invention;

[0028] Figure 3 This is a diagram illustrating the COD removal effect of the present invention;

[0029] Figure 4 This is a diagram illustrating the removal effect of ammonia nitrogen by the present invention;

[0030] Figure 5 This is a diagram illustrating the total nitrogen removal effect of the present invention;

[0031] Figure 6 This is a diagram illustrating the total phosphorus removal effect of the present invention;

[0032] Figure 7 This is a diagram showing the microbial community structure and diversity analysis of each process stage in this invention.

[0033] In the diagram: 1. Equalization tank; 2. Inlet pump; 3. Electrical control cabinet; 4. IFAS tank; 5. Suspended packing; 6. Aeration pipe; 7. Volcanic rock and steel slag filter; 8. Crushed stone; 9. Steel slag; 10. Volcanic rock; 11. Ceramsite. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0035] Test method:

[0036] COD determination: potassium dichromate method;

[0037] Determination of ammonia nitrogen: Nessler's reagent spectrophotometric method;

[0038] Determination of total nitrogen: Alkaline potassium persulfate digestion ultraviolet spectrophotometry;

[0039] Determination of total phosphorus: Ammonium molybdate spectrophotometric method;

[0040] Packing film formation time: observed under an electron microscope;

[0041] Microbial community structure and diversity analysis: Microbial community structure analysis employed the NR database for species taxonomic annotation. The DIAMOND software (http: / / ab.inf.uni-tuebingen.de / software / diamond / ) was used to align the non-redundant gene set with the NR database (alignment type: blastp). Species annotations were obtained using the corresponding taxonomic information from the NR database. The abundance of each species was then calculated using the sum of its corresponding gene abundances. The relative abundance of species in each sample was statistically analyzed at each taxonomic level: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.

[0042] Example 1:

[0043] like Figure 1 and 2 As shown, this embodiment provides a system for efficient nitrogen and phosphorus removal from agricultural wastewater, including an equalization tank 1, an IFAS tank 4, and a volcanic rock and steel slag filter tank 7 connected in sequence; the IFAS tank 4 is connected to the equalization tank 1 through an inlet pipe, and is filled with activated sludge and suspended packing balls 5, with an aeration pipe 6 installed inside the tank; the main packing layers of the volcanic rock and steel slag filter tank 7 include a crushed stone packing layer 8, a steel slag packing layer 9, a volcanic rock packing layer 10, and a ceramsite layer 11.

[0044] The equalization tank 1 is connected to the inlet pump 2, and the IFAS tank 4 receives water from the equalization tank 1 through the inlet pump 2.

[0045] The aeration pipes 6 in the IFAS tank 4 are symmetrically arranged at a 45° downward angle with several holes of 2 mm in diameter; the suspended packing balls 5 are filled with polyurethane packing and wrapped with a spherical porous plastic shell, with a packing density of 40%.

[0046] The area of ​​volcanic rock and steel slag filter pool 7 is 2.5m². 2 The height is 1m; the fillers in the volcanic rock and steel slag filter tank 7 are layered, with the crushed stone filler layer 8 having a height of 20cm, the steel slag filler layer 9 having a height of 20cm, the volcanic rock filler layer 10 having a height of 30cm, and the ceramsite filler layer 11 having a height of 10cm.

[0047] The system also includes an electrical control cabinet 3, which is located between the equalization tank 1 and the IFAS tank 4. The electrical control cabinet 3 controls the influent pump and aeration pipe to adjust the HRT and DO concentration in the IFAS tank.

[0048] The HRT and hydraulic load of volcanic rock and steel slag filter tanks are regulated by adjusting the influent flow rate through the electrical control cabinet.

[0049] Example 2:

[0050] This embodiment provides a process for efficient nitrogen and phosphorus removal from agricultural wastewater. Utilizing the system described in Example 1, the process includes: adjusting the total HRT (Hydraulic Retention Time) of the IFAS tank 4 to 24 hours via the electrical control cabinet 3, maintaining the DO concentration in the tank at 5-6 mg / L, and controlling the pH to be maintained between 7-8 by adding alkalinity; adjusting the HRT of the volcanic rock and steel slag filter tanks to 60 hours via the electrical control cabinet 3, with a hydraulic load of 0.4 m² based on the filter media area. 3 / (m 2 ·d).

[0051] Activated sludge and suspended packing were added to the IFAS tank before influent. The activated sludge concentration was 1500 mg / L, and the packing filling ratio was 40%. The polyurethane packing enriched nitrifying bacteria and other aerobic microorganisms to form a biofilm, which was wrapped with a spherical porous plastic shell. It could achieve good flow in the IFAS tank through aeration. Nitrifying bacteria degraded ammonia nitrogen into nitrate nitrogen through nitrification. Denitrifying bacteria in the anoxic zone inside the biofilm used bioavailable COD in the influent to reduce some of the nitrate nitrogen produced in the tank into nitrogen gas. The filter bed containing volcanic rock and steel slag is layered, with the following layer distribution from bottom to top: crushed stone layer with a height of 20cm, steel slag layer with a height of 20cm, volcanic rock layer with a height of 30cm, and ceramsite layer with a height of 10cm. The volume ratio of volcanic rock to steel slag is 3:2. The main function of this filter bed is to perform denitrification and phosphorus removal. By using COD as an electron donor and nitrate or nitrite as an electron acceptor, it is reduced to nitrogen gas to achieve the final denitrification purpose. Volcanic rock serves as the main site for microbial enrichment, acting as the primary site for denitrification. Furthermore, the metal ions on the volcanic rock can also form precipitates with phosphates in the influent to achieve chemical phosphorus removal. Steel slag serves as a filler for enhanced chemical phosphorus removal, as the rich Ca, Fe, Mg, and other metal elements in the steel slag can form precipitates with phosphates in the influent.

[0052] The influent to the experimental device consisted of rural sewage from various parts of Wuxi City. The removal efficiency of the process of this invention for COD, ammonia nitrogen, total nitrogen, and total phosphorus is as follows: Figure 3-6 As shown.

[0053] The influent COD concentration fluctuated between 74.00 and 152.00 mg / L, with an average concentration of 115.67 mg / L. The IFAS tank was the main site for COD removal; after treatment in the IFAS tank, the average COD concentration was 46.27 mg / L. The IFAS tank contributed 60%-90% to the COD removal of the entire process. The final effluent COD concentration fluctuated between 25.18 and 48.2 mg / L, with an average concentration of 37.70 mg / L. Under stable operating conditions, the effluent COD concentration met the Class A discharge standard.

[0054] Ammonia nitrogen is the main component of total nitrogen in the influent, with concentrations fluctuating between 29.03 and 94.83 mg / L, averaging 50.38 mg / L. Total nitrogen concentrations fluctuate between 37.45 and 101.83 mg / L, averaging 58.34 mg / L. Ammonia nitrogen is primarily removed by nitrifying bacteria enriched in the IFAS tank, converting it to nitrate nitrogen through nitrification. Effluent ammonia nitrogen concentrations fluctuate between 0.16 and 4.64 mg / L, averaging 2.04 mg / L, while total nitrogen concentrations fluctuate between 2.13 and 13.78 mg / L, averaging 6.37 mg / L. Under stable operating conditions, both effluent ammonia nitrogen and total nitrogen concentrations meet Class A standards and special discharge limits (8 mg / L for ammonia nitrogen and 20 mg / L for total nitrogen).

[0055] The influent total phosphorus concentration fluctuated between 1.05 mg / L and 9.80 mg / L, with an average concentration of 4.29 mg / L. The effluent total phosphorus concentration fluctuated between 0 and 0.80 mg / L, with an average concentration of 0.33 mg / L. The effluent total phosphorus concentration consistently met the Class A and special discharge limit standards (1 mg / L). This is mainly because the addition of steel slag enhanced the chemical phosphorus removal effect within the biological filter. The metal ions on the surface of the steel slag can form precipitates with phosphates, achieving the purpose of chemical phosphorus removal.

[0056] IFAS / Analysis of Microbial Community Structure and Diversity in Various Process Sections of Volcanic Rock and Steel Slag Filters

[0057] Figure 7 This is a microbial community distribution diagram for each process stage of the combined process during the stable operation phase. Functional bacteria genera related to ammonia oxidation include Nitrosomonas; those related to denitrification include Bacillus, Thermomonas, Silanimonas, Truepera, and Arenimonas; and those related to phosphorus removal include Acinetobacter.

[0058] Nitrosomonas is a typical ammonia-oxidizing functional bacterium that is distributed in IFAS ponds and volcanic rock and steel slag filters, with relative abundances of 1.67% and 1.60%, respectively. The enrichment of Nitrosomonas indicates that nitrification exists in IFAS ponds and volcanic rock and steel slag filters, which can effectively remove ammonia nitrogen.

[0059] Bacillus is an obligate aerobic or facultative anaerobic bacterium. Some Bacillus species have been reported to be highly efficient anoxic denitrifying bacteria, exhibiting the highest relative abundance (18.86%) in IFAS tanks. Thermomonas are functional microorganisms involved in promoting denitrification and organic matter degradation, with a relative abundance of 0.72% in IFAS tanks. Silanimonas are autotrophic denitrifying bacteria, exhibiting the highest relative abundance (24.14%) in volcanic rock and steel slag filters. Truepera is a thermophilic denitrifying bacterium sensitive to environmental conditions, ensuring high nitrate removal rates at 50°C; it also exhibits the highest relative abundance (2.65%) in volcanic rock and steel slag filters. Arenimonas are Pseudomonas species that ensure good PND levels, exhibiting the highest proportion (1.12%) in volcanic rock and steel slag filters. These denitrifying bacteria were distributed in the IFAS pond and the volcanic rock and steel slag filters, indicating that denitrification exists in the IFAS pond and the volcanic rock and steel slag filters, which can effectively remove nitrate nitrogen. The efficient enrichment of autotrophic denitrifying bacteria in the volcanic rock and steel slag filters also corresponds to the phenomenon of efficient nitrate nitrogen removal under low C / N ratio conditions.

[0060] Acinetobacter is a type of Acinetobacter that has the ability to absorb excess phosphorus under aerobic conditions and release phosphorus and degrade COD under anaerobic conditions. It has the highest relative abundance in the IFAS tank, at 4.29%. The enrichment of Acinetobacter indicates that this process involves both chemical and biological phosphorus removal. Wastewater first undergoes biological phosphorus removal through the IFAS process to remove a small portion of the phosphate, while the majority of the phosphate is removed through chemical phosphorus removal via volcanic rock and steel slag filters.

[0061] Comparative Example 1:

[0062] The IFAS tank operated in the same manner as in Example 2, except that different suspended packing materials were added. In Comparative Example 1, commonly used MBBR packing materials were added. These materials had a three-dimensional hollow structure and were made of polyethylene. The packing ratio was the same as in Example 2. The biofilm formation time, ammonia nitrogen, and COD removal rates of the packing materials in Example 2 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0063] Table 1

[0064]

[0065] It is evident that, compared to MBBR packing, polyurethane packing exhibits faster biofilm formation on its surface. Furthermore, due to its external spherical porous plastic shell, it flows better in water, minimizing microbial loss and exhibiting stronger resistance to shock loads. Consequently, its removal efficiency for ammonia nitrogen and COD is generally higher than that of MBBR packing. Therefore, the suspended packing balls of this invention demonstrate superior performance.

[0066] Comparative Example 2:

[0067] The volcanic rock and steel slag filter tanks operated in the same manner as in Example 2, except for the mixing method of the steel slag and volcanic rock packing. Comparative Example 2 used two methods: completely mixing and adding equal proportions of volcanic rock and steel slag packing, and placing the volcanic rock packing layer below the steel slag packing layer. The total nitrogen and total phosphorus removal rates of Example 2 and Comparative Example 2 are shown in Table 2.

[0068] Table 2

[0069]

[0070] Completely mixed biological filters offer good nitrogen and phosphorus removal efficiency. However, on one hand, aging and detached biofilms exist in volcanic rock and steel slag filters; on the other hand, phosphates react with metal ions leached from the steel slag to form precipitates. Completely mixed biological filters are prone to accelerated packing caking, leading to short-circuiting and requiring frequent packing replacement, thus increasing costs. In contrast, the biological filter in Example 2 shows little difference in nitrogen and phosphorus removal efficiency compared to the completely mixed biological filter, and its packing is easy to replace. Placing the volcanic rock packing layer below the steel slag packing layer significantly impacts nitrogen removal efficiency, potentially causing excessive total nitrogen levels in the effluent when the influent total nitrogen is high. Therefore, the optimal packing method is layered placement, with the steel slag layer placed below the volcanic rock layer.

[0071] Comparative Example 3:

[0072] The volcanic rock and steel slag filter tanks operated in the same manner as in Example 2, except for the ratio of steel slag to volcanic rock packing material. In Comparative Example 3, the volume ratios of volcanic rock to steel slag were 1:1, 2:1, and 3:1, respectively, with other conditions identical to Example 2. The total nitrogen and total phosphorus removal rates of Examples 2 and Comparative Example 3 were tested, and the results are shown in Table 3.

[0073] Table 3

[0074] example Average total nitrogen removal rate (%) Average total phosphorus removal rate (%) Example 2 (Volcanic rock: steel slag = 3:2) 89.08 92.31 Comparative Example 3 (Volcanic rock: steel slag = 1:1) 76.29 98.66 Comparative Example 3 (volcanic rock: steel slag = 2:1) 91.76 85.77 Comparative Example 3 (volcanic rock: steel slag = 3:1) 92.48 76.48

[0075] As shown in the table, under the same working volume, the system exhibits stronger denitrification performance when the volume ratio of volcanic rock is higher, and stronger phosphorus removal performance when the volume ratio of steel slag is higher. As the volume ratio of volcanic rock to steel slag gradually increases from 1:1 to 3:1, the system's denitrification performance gradually increases from 76.29% to 92.48%, but the phosphorus removal performance decreases from 98.66% to 76.48%. Because the influent contains relatively little biodegradable COD, further increasing the volcanic rock content after the volume ratio reaches 3:2 cannot significantly improve the system's denitrification performance. The optimal volume ratios of volcanic rock to steel slag for achieving stable Class A emission standards for total nitrogen are 3:2, 2:1, and 3:1.

[0076] In this process, phosphorus removal mainly relies on the chemical precipitation of metal ions and phosphates on the surface of steel slag. Therefore, when the volume ratio of steel slag is increased, the phosphorus removal performance of the system can be steadily improved. However, when the volume ratio of steel slag is large (1:1), the pH of the system is too high, which will inhibit denitrifying bacteria and thus affect the denitrification effect. The volume ratio of volcanic rock to steel slag that can stably meet the Class A emission standard for total phosphorus is 1:1 and 3:2.

[0077] Therefore, the optimal volume ratio of volcanic rock to steel slag is 3:2.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for achieving efficient nitrogen and phosphorus removal from agricultural wastewater, characterized in that, The system includes an equalization tank, an IFAS tank, and volcanic rock and steel slag filter tanks connected in sequence. The IFAS tank is connected to the equalization tank through an inlet pipe and is filled with activated sludge and suspended packing balls, and is equipped with an aeration pipe. The packing material in the volcanic rock and steel slag filter tank has a thickness of 70-90 cm and is layered. The packing material in the volcanic rock and steel slag filter tank is layered from bottom to top as follows: crushed stone packing layer, steel slag packing layer, volcanic rock packing layer, and ceramsite packing layer. The suspended filler is made of polyurethane and is wrapped with a spherical porous plastic shell, with a filling density of 35-45%. In the volcanic rock and steel slag filter tank, the sum of the volumes of the volcanic rock packing layer and the steel slag packing layer accounts for 60-70% of the total volume; The volume ratio of the volcanic rock filler layer to the steel slag filler layer is 3:2; The volume ratio of the crushed stone filler layer to the ceramsite filler layer is 1.5~2.5:

1.

2. The system according to claim 1, characterized in that, It also includes an electrical control cabinet, which is connected to the equalization tank and the IFAS tank, and is used to control the hydraulic retention time and dissolved oxygen concentration of the IFAS tank.

3. The system according to claim 1, characterized in that, The area of ​​the volcanic rock and steel slag filter pool is 2-3m². 2 The height is 0.8~1.2m.

4. A process for achieving efficient nitrogen and phosphorus removal from agricultural wastewater, characterized in that, It is implemented using the system described in any one of claims 1-3.

5. The process according to claim 4, characterized in that, The hydraulic retention time of the IFAS tank is set at 22-26 h, the dissolved oxygen concentration is maintained at 5-6 mg / L, and the pH is controlled between 7-8 by adding alkalinity. The hydraulic retention time of the volcanic rock and steel slag filters is 56-64 h, and the hydraulic loading, based on the filter media area, is 0.3-0.5 m². 3 / (m 2 ·d).

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