Method and system for improving nitrogen and phosphorus removal effect of constructed wetland

Abstract

The invention discloses a method and a system for improving the nitrogen and phosphorus removal effect of a constructed wetland. The method comprises the following steps: A, constructing the constructed wetland: 1) designing and constructing the wetland; 2) plant configuration; (3) cutting and utilizing the plants; 4) wetland management and maintenance; b, putting the bellamya aeruginosa: 1) putting time; 2) putting density; 3) putting mode; 4) putting positions; and C, harvesting and utilizing the bellamya aeruginosa. The system is composed of a diversion facility, a diversion covered channel / pipe, a grit chamber, a wetland, a plastic enclosure, a wetland main water outlet, a drainage ditch and a road between the wetland and the drainage ditch. The method is easy to implement, simple and convenient to operate, low in construction and operation cost, good in treatment effect, simple in structure, convenient to use and suitable for being applied to the middle and lower reaches of the Yangtze River in China and vast subtropical hilly areas in the south, and the nitrogen and phosphorus removal efficiency of the constructed wetland is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of agricultural environment, and more specifically to a method for improving the nitrogen and phosphorus removal of agricultural non-point source pollutants in the downstream of a small watershed. It also relates to a system for aquaculture of copper-rust ring-edge snails, which is particularly suitable for ecological management of agricultural non-point source pollution and snail farming in the subtropical hilly areas south of the Yangtze River, thereby achieving an organic combination of improving water quality and aquaculture. Background Art

[0002] Rural sewage is the main source of agricultural non-point source pollution. It is widely distributed and highly random, making it difficult to treat. Nitrogen and phosphorus, as the main elements of rural sewage, have received extensive attention from scholars at home and abroad. Studies have shown that artificial wetlands can be used as the preferred ecological treatment technology for the treatment of nitrogen and phosphorus loads in decentralized rural sewage. It can remove nitrogen and phosphorus by direct absorption of nitrogen and phosphorus by plants, adsorption of nitrogen and phosphorus by substrates, and microbial transformation. However, because wetland plants grow seasonally, the water quality of wetland effluent is volatile. In order to improve the stability of wetlands, scholars have conducted many studies by exploring plant combinations, plant mowing, raising water levels, seeking substrate materials with strong adsorption properties, and optimizing C:N ratios to increase denitrification rates and improve the adsorption capacity of wetland substrates for phosphorus. Less attention has been paid to benthic animals, an important animal group in wetland systems. Benthic animals are the intermediate link in wetland ecosystems, carrying on the material cycle and energy flow in the ecosystem. At the same time, they also affect the migration and transformation of pollutants in the system, the disturbance of sediments, and the local habitat environment through their own activities. Therefore, establishing a comprehensive wetland ecosystem including benthic animals may promote the improvement of the ecological functions of artificial wetlands and the enhancement of the pollutant capacity of wetlands. Summary of the invention

[0003] The purpose of the present invention is to provide a method for improving the nitrogen and phosphorus removal effect of artificial wetlands. The method is easy to implement, simple to operate, low in construction and operation costs, and good in treatment effect. The method is suitable for application in the vast subtropical hilly areas in the middle and lower reaches of the Yangtze River in China and to the south, and can greatly improve the nitrogen and phosphorus removal efficiency of artificial wetlands.

[0004] Another object of the present invention is to provide a system for improving the efficiency of wetland treatment of agricultural non-point source pollutants in hilly areas. By releasing the copper-rust ring-edge snails, the disturbance of the copper-rust ring-edge snails can not only improve the nitrogen and phosphorus removal effect of the wetland, but its breeding can also produce certain economic benefits. The system has a simple structure, is easy to use, and completely utilizes hydraulic head for unpowered operation. It only requires a limited number of maintenance each year and has low operating costs. It is suitable for application in the vast subtropical hilly areas with abundant rainfall in the middle and lower reaches of the Yangtze River in China and to its south.

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

[0006] The technical concept is: a method for improving the nitrogen and phosphorus removal effect of artificial wetlands, which includes 1) the type of snails released; 2) the time of releasing the snails; 3) the optimal density of releasing the snails; 4) the method of releasing the snails; 5) the location of releasing the snails; 6) the harvesting and utilization of the snails.

[0007] A method for improving nitrogen and phosphorus removal efficiency in artificial wetlands, comprising the following steps:

[0008] A. Constructing artificial wetlands:

[0009] 1) Wetland design and construction: In the catchment area of ​​3-5km 2 , the proportion of farmland is not less than 30%, there are a small number of (<300 pigs) scattered breeding scales or small (breeding water surface <40 hectares) aquaculture scales in small watersheds or catchment areas downstream outlets, select a lowland with a certain drop (30-50cm): including rice fields, ponds, natural wetlands, and design filters at the inlet and outlet to prevent the escape of copper rust ring edge snails. The inlet concentration is controlled at NH 4 + -N concentration is up to 7mg / L; TN concentration is up to 10mg / L; TP concentration is up to 2mg / L; COD concentration is up to 120mg / L, and the water quality can be either surface Class V or inferior Class V or above. The hydraulic retention time is controlled at 30 days. The ditch drainage is introduced into the lowlands on the side, and the lowlands are built into surface flow artificial wetlands. The water depth is controlled at 30-40cm, and aquatic plants are planted in the wetlands to form artificial ecological wetlands. The drainage from small watersheds or catchment areas is purified in wetlands and then discharged into the ditch system. The inferior Class V water quality of the ditch water can be improved to the national standard Class III or above. In a catchment area of ​​3-5km 2 , the proportion of farmland is not less than 30%, and the drainage of small watersheds or catchments with a small amount of scattered breeding or small-scale aquaculture is discharged into the ditch system after being purified by wetlands. The lowland with a drop refers to a drop of 30-50cm from the entrance of the diversion facility to the total outlet of the wetland. The plan layout of the ecological wetland system is shown in Figure 1 The ecological wetland mainly includes: diversion facilities, sedimentation tanks, waterfalls and plastic fences.

[0010] Diversion facilities: The purpose of diversion facilities is to separate rainwater and sewage, and to direct all daily wastewater and farmland drainage generated in small watersheds or catchment areas into the wetland system for treatment. However, floods generated during rainfall do not enter the wetland system but are directly discharged from the drainage ditch to prevent floods from destroying the wetland. In order to maintain a certain natural drop in water level, diversion facilities ( Figure 1), using the natural drop (without adding artificial power) to divert ditch drainage into the wetland. The cross section of the main drainage ditch with diversion facilities (length 2-3m) should be widened by 25%-30% compared with the original one. The main purpose is to avoid reducing the flood discharge capacity of the drainage ditch due to the construction of a water retaining dam at the bottom.

[0011] Grit chamber: According to the sediment generation of the upstream water body of the small watershed, a rectangular grit chamber is set at the outlet of the diversion pipe or diversion trough (i.e. the water inlet of the wetland) to intercept part of the runoff sediment and prevent the sediment from silting in the wetland. The grit chamber is 150-200cm long, 100-150cm wide and 100-120cm deep. The side material of the grit chamber is brick-concrete structure (thickness 26-28cm) and the bottom is made of concrete (thickness 15-20cm).

[0012] Waterfall: The purpose of the waterfall is to relieve the impact of falling water from a high place and control the water flow. The waterfall is a drop structure that allows the water flow from the highland ditch to fall freely into the wetland, and the water flow from the wetland main drainage outlet to fall freely into the ditch. Waterfalls should be set at the inlet and outlet and filters should be installed to prevent water from scouring the slope and snails from escaping.

[0013] Plastic fence: The purpose is to allow the incoming water flow to circulate within the wetland.

[0014] 2) Plant configuration: According to the water flow characteristics, ecological functions and biological characteristics of aquatic plants in different parts of the ecological wetland, select perennial large-scale emergent plants with large biomass and strong regeneration ability. It is recommended that emergent plants include Pontederia cordata, Iris pseudacorus and Canna indica. The proportion of Pontederia cordata, Iris pseudacorus and Canna indica can be arbitrarily matched. The growth period of most emergent plants is from April to September of the current year, and the growth period of Iris pseudacorus is from October to April of the following year. It is recommended to plant Pontederia cordata, Iris pseudacorus and Canna indica in a ratio of 3:3:3 (combination) with a planting density of 6 plants / m 2 , evenly distributed.

[0015] 3) Plant cutting and utilization: The key to ecological wetland management is to regularly harvest the aquatic plants (yellow iris, sedge grass and canna) growing therein, remove the nitrogen and phosphorus absorbed by the aquatic plants from the sediment and water bodies out of the wetland, and avoid secondary pollution caused by the decay of biomass in the wetland. The frequency of cutting varies according to the aquatic plants. Yellow iris is harvested once a year after it dies in spring; other large emergent plants, sedge grass and canna, are harvested 2-3 times a year. The harvested emergent plant materials are mainly used for direct return of green manure to the fields or mulch in tea gardens, orchards, etc., to achieve the recycling of nitrogen and phosphorus nutrients.

[0016] 4) Wetland management and maintenance: Ecological wetlands should be inspected and maintained regularly. The main purpose is to prevent blockage of inlet and outlet filters and to promptly detect water leakage or slope collapse of waterfalls so that they can be repaired in time to ensure the normal operation of ecological wetlands.

[0017] The step A described above controls the upper limit of pollutant concentration of the ecological wetland influent and sets the optimal hydraulic retention time of the wetland.

[0018] B. Release Bellamya aeruginosa:

[0019] 1) Release time: The best time to release the copper-rust ring-shaped snail is in late autumn (October-November).

[0020] 2) Stocking density: The stocking density of the copper rust ring edge snail is 120 (ind) / m 2 The average weight of the snail is 3-5g / ind. The snails in the ecological wetland are raised in the wild and completely eat natural bait, without artificial feeding.

[0021] 3) Release method: scattering the snails, with the amount of snails scattered at one time being about 90-100g.

[0022] 4) Placement location: Evenly placing the fertilizer in the gaps between plants (such as pickerel grass, canna and yellow iris) can maximize the nitrogen and phosphorus removal effect in the wetland.

[0023] C. Harvest and Utilization of Copper Rust Ring Edge Snails:

[0024] April to November is the breeding season for the copper-rusted ring-shaped snails. In May and November of the following year, the copper-rusted ring-shaped snails in the wetland are salvaged and harvested. The harvested snails can be sold in the market, generating certain economic benefits. 600-800kg / mu of snails can be produced each year. After deducting the costs of snail seedlings and management, a net profit of 2,400-3,200 yuan / mu can be obtained each year. Artificial wetlands with snails can not only improve the governance effect, but also achieve economic benefits higher than general rice planting, killing two birds with one stone.

[0025] Through the technical measures of the above three steps: the most critical steps are the plant configuration method and the type, time, density, method and location of the snails. This main step solves the problem of unstable effluent water quality due to seasonal growth problems of plants, resulting in seasonal non-compliance. It also solves the problem that the snail density is too low, which has little effect on the removal of nitrogen and phosphorus in the wetland, and the density is too high, which leads to a decrease in dissolved oxygen in the wetland, which in turn reduces the nitrogen and phosphorus removal efficiency of the wetland. Through the above key steps, the effluent water quality of the wetland can be stably up to standard after one year, reaching the national standard Class III or above.

[0026] The advances of this invention over the prior art are mainly in 1) planting aquatic plants that grow in different seasons in combination to make up for the defects of seasonal plant growth, and 2) the types and methods of releasing snails can maximize the wetland's nitrogen and phosphorus removal effects, while harvesting the snails the following year can generate considerable economic benefits.

[0027] Compared with the prior art solutions, the invention has advantages in plant combination configuration and the types and methods of releasing benthic animals, which are not covered by the prior art.

[0028] A method for improving the nitrogen and phosphorus removal effect of artificial wetlands is constructed, the purpose of which is to further improve the water quality of wetland effluents from ordinary rice fields, ponds, natural wetlands and other lowlands, so that the annual effluent quality of wetland systems can meet the standards stably and reduce the pollution load on downstream water bodies. The removal rate of COD, total nitrogen and total phosphorus in wetland systems can reach more than 90% and less than 96% in general. According to the national surface water quality standard (GBGB3838-2002) promulgated in 2002, the wastewater treatment method of the wetland system can significantly improve the water quality of the downstream drainage of the small watershed, and the total pollutant removal rate can reach more than 90% and less than 96%. Among them, the chemical oxygen demand (COD) is improved from the inferior V class (80-120mg / L) water quality at the inlet to Class I (8-10mg / L), the total nitrogen is improved from the inferior V class (8-10mgN / L) to Class III (0.5-1mgN / L), and the total phosphorus is improved from the inferior V class (1-2mgP / L) to Class II water quality (0.05-0.08mgP / L). The effluent is generally improved to Class III water quality standards (see Table 1).

[0029] Table 1 Treatment effect of snail ecological wetland system on agricultural non-point source pollutants

[0030]

[0031] *Note: The numbers in brackets in the table refer to the national surface water quality standards (GBGB3838-2002) that the effluent meets.

[0032] A treatment system for adding copper rust ring edge snails to enhance the nitrogen and phosphorus removal effect of artificial wetlands, which is composed of diversion facilities, diversion troughs / pipes, grit chambers, drainage outlets (waterfalls), drainage ditches, and roads between wetlands and drainage ditches. The connection relationship is: the diversion facilities are connected to the grit chambers through diversion troughs / pipes, the grit chambers are connected to the wetlands, the wetland main drainage outlet is connected to the drainage ditches, the wetlands are connected to the enclosures, and the wetland end is connected to the drainage ditches by roads and steps between the troughs. Through the connection, an ecological wetland system of aquatic plants and benthic animals is formed, which can improve the inferior five-class water quality of the ditch water to the national standard III or above. A filter screen is installed at the inlet and outlet, and the appropriate aperture size of the filter screen should be between 2 and 5 mm to prevent the snails from escaping. The step A: controls the upper limit pollutant concentration of the ecological wetland water inlet, sets the optimal hydraulic retention time of the wetland, and determines the plant configuration mode; step B: determines the type, time, density, method and location of the benthic animals; step C: determines the harvesting time of the snails.

[0033] Compared with the existing pollution control methods, the present invention has the following advantages and effects:

[0034] ① It has certain innovation in the method of controlling non-point source pollution: There are many methods for the control technology of low-concentration agricultural non-point source pollutants mainly from the planting industry, mainly based on engineering and ecological measures, such as integrated purification systems, artificial wetlands, etc. The effluent water quality of these measures has not yet reached the national standard IV or above. How to further improve the effluent water quality of artificial wetlands is relatively lacking. The existing method uses small watersheds or catchment areas as units to build multi-level ecological wetlands, and by planting aquatic plants suitable for local growth to intercept and absorb nitrogen and phosphorus in the water body, thereby effectively reducing the migration of agricultural non-point source pollutants nitrogen and phosphorus to downstream water bodies, reducing the harm of agricultural non-point source pollution, the effluent water quality of this method is unstable and affected by the seasonal growth of plants. In view of the characteristics of abundant water in subtropical hilly areas, the present invention slightly transforms the existing natural drainage ditches and wetlands near the outlet to build artificial wetlands, and makes a combination of plants growing in different seasons to complement the defects of seasonal growth, and puts copper rust ring edge snails into the wetlands to further enhance the removal effect of wetlands on nitrogen and phosphorus and improve the stability of effluent water quality.

[0035] ② Low construction cost: The construction area is 5km 2 Taking the non-point source pollution control in the region as an example, the area covers 500 permanent residents and 80hm2 of farmland. 2 、Tea garden 350hm 2 , decentralized breeding scale of 200 pigs per unit, the invention builds an ecological wetland of 3500m 2The main construction costs include four parts: 100,000 yuan for earth excavation and transportation, 80,000 yuan for engineering materials and construction fees, 5,000 yuan for seedlings, 6,000 yuan for snail seedlings, and 5,000 yuan for daily maintenance in the first year. The total cost is 196,000 yuan, which is acceptable to most departments (water conservancy, agriculture, and rural collectives).

[0036] ③ Low operating cost, simple operation, and certain economic benefits: Most of the existing sewage treatment technologies require energy such as electricity, while this treatment method mainly utilizes the driving force of natural slope to achieve gravity purification of water in the ecological wetland without any external power; routine maintenance is only mowing (an average of 2-3 times a year), harvesting snails (twice a year) and daily inspections (1-2 times a month), and the operation is very simple; the harvested snails can be sold in the market, generating certain economic benefits, which also lays a good foundation for the sustainable operation of the ecological wetland.

[0037] ④Good treatment effect: This treatment method can effectively reduce the COD and nitrogen and phosphorus content of polluted water bodies through the interception and absorption of aquatic plants in ecological wetlands and the transformation of benthic animals. The water quality can be improved from the inferior Class V at the entrance to the national standard Class III (GB3838-2002) and above (COD <10mg / L, total nitrogen <1mgN / L, total phosphorus <0.08mgN / L). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the plan layout of a treatment system for enhancing the nitrogen and phosphorus removal effect of artificial wetlands by adding Copper Rust Ring Edge Snails;

[0039] Among them, 1-diversion facilities, 2-diversion troughs / pipes, 3-sand traps, 4-wetlands, 5-plastic grids, 6-wetland main drainage outlets, 7-drainage ditches, 8-roads between wetlands and drainage ditches. DETAILED DESCRIPTION

[0040] Embodiment 1:

[0041] A method for treating agricultural non-point source pollutants in hilly areas by multi-stage wetlands, comprising the following steps:

[0042] A. Constructing artificial wetlands:

[0043] 1) Wetland design and construction: In the catchment area of ​​3, 3.5, 4.5 or 5 km 2, the proportion of farmland is not less than 30%, there are a small number of (<300 pigs) scattered breeding scales or small (breeding water surface <40 hectares) aquaculture scales in the small watershed or catchment area downstream outlet, select a lowland with a certain drop (30 or 40 or 50cm): including rice fields, ponds, natural wetlands, set up water barriers on the main drainage ditch suitable for building surface flow ecological wetlands near the outlet of the small watershed or catchment area, and build diversion facilities to guide the ditch drainage into the side ecological wetland system. Filters are designed at the inlet and outlet to prevent the copper rust ring edge snail from escaping. The inlet concentration is controlled at NH 4 + -N concentration is up to 7mg / L; TN concentration is up to 10mg / L; TP concentration is up to 2mg / L; COD concentration is up to 120mg / L, and the water quality is either surface V or inferior V. The hydraulic retention time is controlled at 30 days. The water depth in the wetland is controlled at 30, 35 or 40cm, and aquatic plants are planted in the wetland to form an artificial ecological wetland. The drainage from small watersheds or catchment areas is purified in the wetland before being discharged into the ditch system. According to the national surface water quality standard (GBGB3838-2002) promulgated in 2002, the wastewater treatment method of the wetland system can significantly improve the water quality of downstream drainage of small watersheds, with the total pollutant removal rate reaching more than 90% and less than 96%. The chemical oxygen demand (COD) is improved from the inlet Class V (80-120 mg / L) water quality to Class I (8-10 mg / L), the total nitrogen is improved from Class V (8-10 mgN / L) to Class III (0.5-1 mgN / L), and the total phosphorus is improved from Class V (1-2 mgP / L) to Class II (0.05-0.08 mgP / L). The effluent is generally improved to Class III water quality standards.

[0044] 2) Plant configuration: The rational configuration of aquatic plants is one of the core elements of ecological wetland system design. According to the water flow characteristics, ecological functions and biological characteristics of aquatic plants in different parts of the ecological wetland, select perennial large-scale emergent plants with large biomass and strong regeneration ability. It is recommended that emergent plants include Pontederia cordata, Irispseudacorus and Canna indica. The proportions of Pontederia cordata, Irispseudacorus and Canna indica can be planted at any ratio. The growth period of most emergent plants is from April to September of the current year, and the growth period of Irispseudacorus is from October to April of the following year. It is recommended to plant Pontederia cordata, Irispseudacorus and Canna indica in a ratio of 3:3:3 (combination), and the planting density is 6 plants / m 2, evenly distributed. The purpose of the configuration of the emergent plants is: 1) to utilize the physical interception effect of emergent plants on water bodies (reducing flow velocity and prolonging the retention time of flowing water in the ecological wetland) and the direct absorption, transformation and fixation of nitrogen and phosphorus by aquatic plants and microorganisms, gradually absorb various forms of nitrogen and phosphorus in the water body, thereby purifying the water body; 2) Relatively tall emergent plants are configured in the ecological wetland system. The main reason is that tall emergent plants can reduce the flow velocity of water and prolong the wetland's absorption and transformation time for pollutants. At the same time, the gaps between the emergent plants can provide a favorable habitat for benthic animals (copper rust ring-shaped snails) in the wetland, promoting the transformation of nitrogen and phosphorus pollutants. Emergent plants have roots in wetland sediments and can absorb nitrogen and phosphorus from the sediments, further freeing up the sediment nitrogen and phosphorus reservoir capacity. At the same time, the disturbance caused by benthic animals can accelerate the release of sediment nitrogen and phosphorus, accelerate the absorption of sediment nitrogen and phosphorus by emergent plants, and enhance the removal of nitrogen and phosphorus by ecological wetlands. 3) Other emergent plants are planted in combination with Acorus iris. Acorus iris has a vigorous growth period from November to April of the following spring, and has a high removal efficiency for nitrogen and phosphorus in water quality, making up for the defect that most emergent plants stagnate and die from November to April of the following year, reducing the nitrogen and phosphorus removal effect of wetlands.

[0045] 3) Plant cutting and utilization: The key to ecological wetland management is to regularly harvest the aquatic plants (yellow iris, pickerel grass and canna) growing therein, and remove the nitrogen and phosphorus absorbed by the aquatic plants (yellow iris, pickerel grass and canna) from the sediment and water body out of the wetland to avoid secondary pollution caused by the decay of biomass in the wetland. The frequency of cutting varies according to the aquatic plants (yellow iris, pickerel grass and canna). Yellow iris is harvested once a year after it dies in spring; other large emergent plants are harvested 2-3 times a year. Large emergent plants such as pickerel grass, canna and yellow iris contain rich amino acids, especially a high proportion of glutamic acid. The harvested emergent plant materials are mainly used for direct return of green manure to the fields or mulch in tea gardens, orchards, etc. At the same time, it can also be tried as livestock and poultry feed to achieve the recycling of nitrogen and phosphorus nutrients.

[0046] 4) Wetland management and maintenance: In order to maintain the ecological wetland system with a good non-point source pollution control effect, the ecological wetland should be maintained regularly. The ecological wetland should be inspected and maintained regularly. The main purpose is to prevent the blockage of the inlet and outlet filter and to promptly detect the leakage of the waterfall or the collapse of the slope so as to ensure the normal operation of the ecological wetland. At the same time, the wetland sedimentation tank should be dredged. The sedimentation tank at the entrance of the ecological wetland has a good interception effect on the bedload sediment, but it should be dredged regularly (11-12 months) to maintain the effect of the sedimentation tank. In October and November every year, the snails are harvested and the accumulated water is drained, and dredging is carried out once. The silt in the sedimentation tank is generally coarse in texture and has a low nutrient content, so it can be centrally piled for treatment.

[0047] B. Release Bellamya aeruginosa:

[0048] 1) Release time: From October to November, most emergent plants are in a state of growth stagnation or death, which in turn affects the plant's promotion of wetland system microorganisms. The impact of the plant part on the wetland nitrogen and phosphorus removal ratio is sharply reduced. The release of copper rust ring-shaped snails during this period can firstly make up for the loss of plants (pike grass and canna) on the nitrogen and phosphorus removal effect. Secondly, the disturbance of the snail can also promote the microbial activity of the wetland system and improve the nitrogen and phosphorus removal efficiency of the entire wetland system.

[0049] 2) Stocking density: If the stocking density is too low, the effect on nitrogen and phosphorus removal of the entire wetland system will be too small. If the stocking density is too high (no more than 150 ind / m 2 ), the snails will consume a large amount of dissolved oxygen in the wetland, causing a large amount of nitrate nitrogen to accumulate in the wetland, thereby reducing the wetland's nitrogen removal effect. After the applicant's field test, it was found that the optimal release density of the copper rust ring edge snail is 120 (ind) / m 2 The average weight of the snail is 3-5g / ind. The snails in the ecological wetland are raised in the wild and completely eat natural bait, without artificial feeding.

[0050] 3) Release method: At the same time, the applicant has determined the release method of the copper rust ring edge snail through field experiments, which is to adopt the scattering release method, with the amount of snails scattered at one time being about 90-100g. First, excessive concentrated release will lead to more snail biomass in some places and less snail biomass in some places, which is unbalanced and affects the disturbance of the snail to the wetland system. Secondly, placing snails one by one in the wetland will make the work complicated, waste labor, and not use the snails to grow. Snails prefer to live in groups.

[0051] 4) Placement location: Place snails evenly in the gaps between plants (Acorus calamus, Pike weed and Canna indica) to provide space for snails to move around. When snails are feeding and moving, they can accelerate the conversion of nitrogen and phosphorus at the mud interface and the water interface, while affecting the redox potential of the mud-water interface, changing the activity of microorganisms, increasing the nitrification and denitrification rates of the wetland, and maximizing the nitrogen and phosphorus removal effect of the wetland.

[0052] C. Harvest and Utilization of Copper Rust Ring Edge Snails:

[0053] April to November is the breeding season for Copper Rust Ring Edge Snails. In May and November of the following year, the Copper Rust Ring Edge Snails in the wetland will be salvaged and harvested. In May of the following year, 50% of the snails can be harvested, and the remaining 50% can be allowed to further reproduce in the wetland. The harvested snails can be sold in the market, generating certain economic benefits. 600-800kg / mu of snails can be produced each year. After deducting the costs of snail seedlings and management, a net profit of 2,400-3,200 yuan / mu can be obtained each year. Artificial wetlands with added snails can not only improve the governance effect goals, but also achieve higher economic benefits than general rice planting, killing two birds with one stone.

[0054] Through the above technical measures, natural wetlands, artificial wetlands or ordinary ponds are used according to local conditions to build an artificial ecological wetland system with a water depth of 30-40cm and a shape adapted to local conditions. Aquatic plants are planted in the wetland and copper rust ring-edge snails are placed to absorb, consume and transform agricultural non-point source pollutants (nitrogen and phosphorus) generated in the upstream catchment area. The chemical oxygen demand (COD), nitrogen and phosphorus content in the terminal outlet drainage are controlled within the Class III water quality standard of the "Surface Water Environmental Quality Standard of the People's Republic of China" (GB 3838-2002). The harvested plants can be used as organic fertilizers in fruit and tea gardens, and the harvested copper rust ring-edge snails can be sold in the market. While achieving the goal of ecological governance of agricultural non-point source pollution, wetland aquatic products can generate certain economic benefits and improve the sustainability of ecological governance. This method has low construction and operation costs, is easy to operate, and generates certain economic benefits. It is suitable for application in the vast subtropical hilly areas in the middle and lower reaches of the Yangtze River in China and to the south.

[0055] Embodiment 2:

[0056] according to Figure 1 It can be seen that a treatment system for adding copper-rust ring-shaped snails to enhance the nitrogen and phosphorus removal effect of artificial wetlands is composed of a diversion facility 1, a diversion trough / pipe 2, a grit tank 3, a wetland 4, a plastic grid (to allow water to circulate internally) 5, a wetland main drainage outlet (waterfall) 6, a drainage ditch 7, and a road 8 between the wetland and the drainage ditch. The connection relationship is: the diversion facility 1 is connected to the grit tank 3 through the diversion trough / pipe 2, the grit tank 3 is connected to the wetland 4, the wetland 4 is connected to the plastic grid 5, the wetland main drainage outlet 6 is connected to the drainage ditch 7, the sewage overflows directly into the wetland 4 through the grit tank 3, the water flows to the main drainage outlet 6 through the grid 5, and flows into the drainage ditch 7 through the wetland main drainage outlet 6; the wetland 4 and the drainage ditch 7 are connected by the road 8.

[0057] The diversion facility 1 is specifically composed of a main drainage ditch 7 widened by 25-30% and a diversion trough / pipe 2. The main drainage ditch 7 is connected to the diversion trough / pipe 2 respectively. The main drainage ditch 7 and the diversion trough / pipe 2 are connected as a whole to form the diversion facility 1.

[0058] Through the above technical measures, it can be ensured that all sewage in the base flow stage of the drainage ditch flows into the wetland system, and the flood in the rainstorm stage does not enter the wetland system but flows directly downstream, so as to ensure that the ecological wetland system is not affected by the flood, and at the same time does not affect the normal flood discharge of the drainage ditch.

Claims

1. A method for improving nitrogen and phosphorus removal efficiency of artificial wetlands, characterized in that: The steps are: A. Construction of artificial wetlands: 1) Design and construction of wetlands: In the catchment area of ​​3-5km 2 , the proportion of farmland is not less than 30%, there are a small number of small-scale aquaculture or small-scale aquaculture in the downstream outlet of the small watershed or catchment area, select a lowland with a certain drop: including rice fields, ponds, natural wetlands, and design filters at the inlet and outlet, and control the inlet concentration to NH4 + The highest concentration of -N is 7mg / L; the highest concentration of TN is 10mg / L; the highest concentration of TP is 2mg / L; the highest concentration of COD is 120mg / L. The water quality is surface Class V and inferior Class V or above. The hydraulic retention time is controlled at 30 days. The drainage of the ditch is introduced into the lowland on the side. The lowland is built into a surface flow artificial wetland. The water depth is controlled at 30-40cm. Aquatic plants are planted in the wetland to form an artificial ecological wetland. The drainage of small watersheds or catchment areas is purified in the wetland and then discharged into the ditch system. The inferior Class V water quality of the ditch water is improved to the national standard Class III or above. In the catchment area of ​​3-5km 2 , the proportion of farmland area is not less than 30%, and the drainage of small watersheds or catchment areas with a small amount of scattered breeding or small-scale aquaculture is discharged into the ditch system after being purified by wetlands. The lowland with a drop refers to the drop of 30-50cm from the entrance of the diversion facility to the total outlet of the wetland. The ecological wetland mainly includes: diversion facilities, sedimentation tanks, waterfalls and plastic enclosures: Diversion facilities: The purpose of diversion facilities is to separate rainwater and sewage, and to direct all daily wastewater and farmland drainage generated in small watersheds or catchment areas into the wetland system for treatment. Floods generated during rainfall do not enter the wetland system and are directly discharged from the drainage ditch. In order to maintain a certain natural drop in water level, diversion facilities are built in the main drainage ditch near the outlet of the small watershed or catchment area where the wetland is built, and the ditch drainage is directed into the wetland using the natural drop. The cross-section of the main drainage ditch where the diversion facilities are built should be widened by 25%-30% than the original; Grit chamber: According to the sediment generation situation of the upstream water body of the small watershed, a rectangular grit chamber is set at the outlet of the diversion culvert or diversion trough to intercept part of the runoff sediment and prevent sediment accumulation in the wetland. The grit chamber is 150-200cm long, 100-150cm wide and 100-120cm deep. The side material of the grit chamber is brick-concrete structure and the bottom is made of concrete. Waterfall: Waterfalls should be set at the inlet and outlet and filters should be installed to prevent water from eroding the slope and snails from escaping; Plastic enclosure: To allow the incoming water to circulate within the wetland; 2) Plant configuration: According to the water flow characteristics, ecological functions and biological characteristics of aquatic plants in different parts of the ecological wetland, select perennial large-scale emergent plants with large biomass and strong regeneration ability. Emergent plants include pickerel grass, yellow iris, and canna. The growth period of most emergent plants is from April to September of the current year, and the growth period of yellow iris is from October to April of the following year. Combined planting with yellow iris, the planting density is 6 plants / m 2 , evenly distributed; 3) Plant cutting and utilization: The management of ecological wetlands is to regularly harvest the aquatic plants growing therein, and remove the nitrogen and phosphorus absorbed by the aquatic plants from the sediment and water bodies out of the wetlands. The frequency of cutting varies according to the aquatic plants. Acorus iris is harvested once a year after it dies in spring; other emergent plants are harvested 2-3 times a year. The harvested emergent plant materials are used as green manure and directly returned to the fields or covered in tea gardens and orchards to achieve the recycling of nitrogen and phosphorus nutrients; 4) Wetland management and maintenance: Regular inspection and maintenance of ecological wetlands is to prevent clogging of inlet and outlet filters and to promptly detect water leakage or slope collapse of waterfalls so that they can be repaired in time to ensure the normal operation of ecological wetlands; B. Release copper rust ring edge snails: 1) Release time: The best release time for the copper-rust ring-shaped snail is in late autumn: October-November; 2) Stocking density: The stocking density of the copper rust ring edge snail is 120 pieces / m 2 The average weight of the snail is 3-5g / ind. The snails in the ecological wetland are raised in the wild and completely eat natural bait, without artificial feeding. 3) Release method: Throwing snails are used, with the amount of snails thrown at one time being 90-100g; 4) Placement location: Place evenly between plants to improve the nitrogen and phosphorus removal effect of the wetland; C. Harvest and Utilization of Copper Rust Ring Edge Snails: April to November is the breeding season for the copper-rusted ring-shaped snails. The copper-rusted ring-shaped snails in the wetlands are uniformly salvaged and harvested in May and November of the following year.

2. A treatment system for enhancing nitrogen and phosphorus removal in artificial wetlands by adding copper rust ring-shaped snails as claimed in claim 1, which comprises a diversion facility (1), a diversion trough / pipe (2), a grit chamber (3), a wetland (4), a plastic enclosure (5), a wetland main drainage outlet (6), a drainage ditch (7), and a road (8) between the wetland and the drainage ditch, and is characterized in that: The diversion facility (1) is connected to the grit chamber 3 through a diversion trough / pipe (2), the grit chamber (3) is connected to the wetland (4), the wetland (4) is connected to the plastic enclosure (5), the wetland main drainage outlet (6) is connected to the drainage ditch (7), and the wetland (4) and the drainage ditch (7) are connected to a road (8).

3. The treatment system for enhancing nitrogen and phosphorus removal in artificial wetlands by adding Copper Rust Ring Edged Snails according to claim 1, characterized in that: The diversion facility 1 is composed of a main drainage ditch (7) widened by 25-30% and a diversion hidden groove / pipe (2). The main drainage ditch (7) is connected to the diversion hidden groove / pipe (2) respectively. The main drainage ditch (7) and the diversion hidden groove / pipe (2) are connected as a whole to form the diversion facility (1).

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