A method for coupling utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management

Abstract

The present invention proposes a method for coupling utilization of aquaculture wastewater based on the management of coastal low-lying saline-alkali land, which relates to the field of saline-alkali land management and wastewater treatment technology; it includes the following steps: S1: constructing a three-dimensional utilization mode of "agriculture above, fishery in the middle, and grass below": S11: building terraced fields on saline-alkali land; S12: digging pits and ponds on one side of the terraced fields to form several levels of interval pit and pond areas; S2: installing a concealed pipe flow collection and water storage system; S3: the terraced fields are provided with a drip irrigation system; S4: the first-level pit and pond are provided with aquaculture wastewater inlet pipes at the starting position; adjacent pit and pond areas are connected by connecting pipes; and aquaculture wastewater outlet pipes are provided at the end of the last-level pit and pond. The present invention forms a three-dimensional structure of "agriculture above, fishery in the middle, and grass below", and the terraced field planting, pit and pond aquaculture and pond bottom seaweed purification of aquaculture wastewater are organically combined, which not only avoids environmental pollution and water resource waste caused by the discharge of aquaculture wastewater, but also realizes the ecological management and comprehensive and efficient utilization of coastal low-lying saline-alkali land.

Description

Technical Field

[0001] The invention relates to the technical field of saline-alkali land management and wastewater treatment, and in particular to a method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management. Background Art

[0002] After long-term efforts, the development and utilization of coastal saline-alkali land in the Yellow River Delta has achieved remarkable results, but the moderately and severely saline-alkali land in low-lying areas has not yet been effectively and comprehensively utilized. The "terrace fields and ponds / agriculture above and fishing below" management model for saline-alkali land is an effective model first proposed in the practice of saline-alkali land management in the Yellow River Delta. It has a special effect on the transformation of low-lying saline-alkali land. It is an important way to manage regional saline-alkali land and has played an important role. However, due to the lack of freshwater resources in some terraced areas, planting is difficult. At the same time, the water quality and water volume of ponds vary greatly, making breeding difficult, resulting in problems such as low quality of terraced farmland, poor adaptability, low planting and breeding efficiency, weak system functions, and poor economic benefits.

[0003] Intensive aquaculture wastewater is rich in high amounts of organic matter and nitrogen and phosphorus substances, which pose an environmental pollution risk and cannot be discharged directly. In addition, the seawater required for aquaculture in production is mostly transported from the seaside to the aquaculture area over a certain distance. If the aquaculture seawater cannot be recycled, it will cause waste and increase the cost of water transportation.

[0004] Therefore, it is urgent to upgrade and innovate the existing low-lying saline-alkali terraced fields transformation and ecologically efficient utilization technology models. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention proposes a method for coupled utilization of aquaculture wastewater based on the management of coastal low-lying saline-alkali land. The present invention forms a three-dimensional structure of "agriculture above - fishing in the middle - grass below", organically combines terraced field planting, pond aquaculture and seaweed purification of aquaculture wastewater at the bottom of the pond, transforms the unstable traditional terraced field model of "agriculture above and fishing below", avoids environmental pollution and waste of water resources caused by the discharge of aquaculture wastewater, and realizes the ecological management and comprehensive and efficient utilization of coastal low-lying saline-alkali land.

[0006] The technical solution of the present invention to solve the technical problem is:

[0007] This scheme proposes a method for coupled utilization of aquaculture wastewater based on the treatment of coastal low-lying saline-alkali land, including the following steps:

[0008] S1: Construct a three-dimensional utilization model of "agriculture above, fishery in the middle, and grass below":

[0009] S11: Build several terraced fields at intervals on saline-alkali land to raise the cultivated layer of the land and form terraced fields;

[0010] S12: Ponds are excavated on one side of the terraced field to form several levels of pond areas, namely the first-level ponds, the second-level ponds, and the Nth-level ponds; the pond areas and terraced field areas are set up alternately, and there are pond areas between adjacent terraced field areas; the water bodies of the ponds are used as wastewater treatment and aquaculture areas, and the bottom areas of the ponds are used as seaweed planting areas, forming a three-dimensional utilization model of "agriculture above, fishing in the middle, and seaweed planting below";

[0011] S2: Install a concealed pipe collection and water storage system:

[0012] An impermeable geomembrane is laid below the surface of the terraced field, and a drainage concealed pipe is laid on the impermeable geomembrane. The end of the drainage concealed pipe is connected to a water storage bucket, which is used to discharge the collected infiltration precipitation into the water storage bucket for storage; the water storage bucket is provided with a drainage outlet, which is connected to a gravity pipe. When the water in the bucket is full, the water is discharged to the pond through the gravity drainage pipe;

[0013] S3: The terraced field is equipped with a drip irrigation system. A water pump is installed at the bottom of the water storage barrel. The output end of the water pump is connected to the drip irrigation system to achieve pump water drip irrigation;

[0014] S4: The first-level pond is equipped with an aquaculture wastewater inlet pipe at the starting point to connect the aquaculture wastewater; adjacent pond areas are connected by connecting pipes to achieve connectivity between ponds at all levels to achieve multi-stage purification; a clean water outlet pipe is provided at the end of the last-level pond to connect with the reuse water supply system to complete the closed loop.

[0015] Preferably, a 30 cm high cofferdam is constructed around the terraced field to collect rainwater.

[0016] Preferably, the water storage barrel adopts an underground PE water storage barrel, and the single volume is not less than 5m 3 , used to collect low-mineralized internal drainage after soil desalination for use as irrigation water.

[0017] Preferably, roads are arranged along the slopes at suitable heights on both sides of the terraced fields to form slope road areas. The area ratio of the terraced fields, slope road areas, and pond areas is 4:4:2, and the height of the terraced fields above the water surface of the ponds is not less than 2.0 m.

[0018] Preferably, the slope ratio of the slope road area is 1:1.5, the slopes above the road are protected by salt-tolerant bermudagrass and perennial vegetation, and the slopes below the road are protected by tamarisk and salsa oleifera; the road is 0.8-1.0m above the water surface and 1.5m wide, and the road surface is compacted and paved or sown with salt-tolerant bermudagrass lawn.

[0019] Preferably, the connecting pipe is in an inverted U-shaped form, and the connecting pipe is composed of an inlet vertical pipe located in the upper level pond, an outlet vertical pipe located in the lower level pond, and a horizontal pipe passing through the terraced field. The distance between the outlet of the inlet vertical pipe and the outlet vertical pipe and the bottom of the pond is L; the inlet and outlet of each level of pond are respectively arranged at the two ends of the pond, and adjacent connecting pipes are staggered.

[0020] After the planting of seaweed in the ponds is completed, seawater is put into the ponds at all levels to an initial depth set at H. When aquaculture wastewater is first put into the head of the first-level pond, the water level rises and the water depth exceeds H. At this time, the raw water of the first-level pond is discharged to the second-level pond through the siphon principle of the connecting pipe, and the first-level pond begins to treat the aquaculture wastewater for the first time; when the aquaculture wastewater is discharged for the second time, the aquaculture wastewater after the first-level purification can enter the second-level pond for further purification, and so on, until the last-level pond discharges the water after multiple stages of purification through the aquaculture wastewater outlet pipe for reuse.

[0021] Preferably, the seaweed varieties selected are at least three types of combinations of giant kelp, crinum sphaerocephala and hornwort, and are cultivated in an alternate-row intercropping manner.

[0022] Preferably, the installation position of the gravity pipe is that the top of the pipe is 5 cm below the top of the water storage barrel, the laying slope is 1%, and the water is discharged to the pond.

[0023] Preferably, whiteleg shrimp or shellfish are released into the water of the pond to carry out open-air natural farming to build a shrimp-algae or shrimp-grass, shellfish-algae symbiotic system.

[0024] Preferably, the water pump is a photovoltaic DC pump, and the terrace is provided with a photovoltaic power generation device, which is electrically connected to the photovoltaic DC pump via a controller.

[0025] The above technical solution has the following advantages or beneficial effects:

[0026] 1. In view of the current situation that coastal low-lying saline-alkali land is difficult to utilize, fresh water is extremely scarce, and rainwater resources are difficult to collect, the present invention breaks the traditional inefficient model of "agriculture above and fishery below" in terraced fields, combines it with the treatment of wastewater from facility seawater aquaculture, optimizes the construction of terraced fields-pond systems, and expands new transformation paths and comprehensive utilization methods of "agriculture above, fishery in the middle, and grass below" in coastal low-lying saline-alkali land, thereby increasing valuable arable land resources, collecting and efficiently utilizing valuable rainwater resources, and utilizing seaweed resources in the constructed terraced fields-pond systems to purify aquaculture wastewater, thus achieving efficient recycling of seawater resources for facility aquaculture, and providing a long-term and low-cost solution for the transformation and comprehensive utilization of terraced fields in low-lying coastal saline-alkali land; in addition, since the main body of pond water is seawater and the water quality is relatively stable, it can be used to carry out outdoor seawater aquaculture of suitable types, thereby forming a new model of "agriculture above, fishery in the middle, and grass below". This model not only increases arable land and collects rainwater resources, but also purifies wastewater, and has significant comprehensive breeding and farming benefits. In particular, through seaweed planting and processing and utilization, it increases blue carbon sinks and income, with significant social, ecological and economic benefits.

[0027] 2. The ponds in the present invention are multi-level and connected by connecting pipes; the connecting pipes are inverted U-shaped, and the water inlets and outlets of the ponds at each level are respectively arranged at the two ends of the ponds, and the adjacent connecting pipes are staggered; such a layout can utilize the siphon principle to realize the automatic discharge of aquaculture wastewater to the pond of the next level, and can realize the full purification of aquaculture wastewater in each level of ponds. After being fully purified by multiple levels of ponds, the organic matter, nitrogen and phosphorus content in the water body reaches the facility aquaculture reuse standard, and enters the aquaculture facility pool again for recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0029] Figure 1 It is a structural layout diagram of the terraced field area and the pond area in the present invention when viewed from above.

[0030] Figure 2 yes Figure 1 Schematic diagram of the structure of a single terraced field area and a pond area.

[0031] Figure 3 yes Figure 2 An enlarged schematic diagram of the structure of the terrace area.

[0032] Figure 4 It is a schematic diagram of the layout of photovoltaic power generation device, water storage tank and photovoltaic electric pump.

[0033] Figure 5 It is a schematic diagram of the structure of the connecting pipe.

[0034] Description of reference numerals:

[0035] 1. Aquaculture wastewater inlet pipe; 2. Connecting pipe; 201. Inlet vertical pipe; 202. Horizontal pipe; 203. Outlet vertical pipe; 3. Clean water outlet pipe; 4. Drainage concealed pipe; 5. Anti-seepage geomembrane; 6. Water storage barrel; 7. Photovoltaic DC pump; 8. Gravity pipe; 9. Underground drip irrigation pipe; 10. Photovoltaic device; 11. Power storage device; 12. Irrigation pipe; 13. Cable; a1. Terraced field area; a2. Slope road area; a3. Pond area. DETAILED DESCRIPTION

[0036] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0038] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0039] like Figure 1-Figure 5 As shown, this embodiment proposes a method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management, comprising the following steps:

[0040] S1: Construct a three-dimensional utilization model of "agriculture above, fishery in the middle, and grass below": The main process is as follows:

[0041] S11: Build several terraced fields at intervals on the saline-alkali land to raise the cultivated layer of the land to form terraced field area a1;

[0042] S12: Ponds are excavated on one side of the terraced field to form several levels of pond areas a3, namely the first-level ponds, the second-level ponds...the Nth-level ponds; the pond areas a3 and the terraced field areas a1 are arranged alternately, and pond areas a3 are arranged between adjacent terraced field areas a1; in this way, several terraced field-pond systems are formed in a combination; the water bodies of the ponds are used as wastewater treatment and aquaculture areas, and the bottom areas of the ponds are used as seaweed planting areas, forming a three-dimensional utilization model of "agriculture above, fishing in the middle, and seaweed planting below".

[0043] S2: Install a concealed pipe collection and water storage system:

[0044] An impermeable geomembrane 5 is laid below the surface of the terraced field, and a drainage concealed pipe 4 is laid on the impermeable geomembrane 5. The end of the drainage concealed pipe 4 is connected to a water storage barrel 6 for draining the collected infiltrated precipitation into the water storage barrel 6 for storage; the water storage barrel 6 is provided with a drain outlet, which is connected to a gravity pipe 8. When the water in the barrel is full, the water is discharged to the pond through the gravity drainage pipe.

[0045] S3: The terraced field is provided with a drip irrigation system, a water pump is installed at the bottom of the water storage barrel 6, and the output end of the water pump is connected to the drip irrigation system to realize pump water drip irrigation.

[0046] S4: The first-level pond is provided with an aquaculture wastewater inlet pipe 1 at the starting position for connecting the aquaculture wastewater; the adjacent pond areas a3 are connected by connecting pipes 2 to achieve connectivity between ponds at all levels to achieve multi-stage purification; a clean water outlet pipe 3 is provided at the end of the last-level pond for connection with the reuse water delivery system to complete the closed loop.

[0047] Based on the reasonable layout form, structure and interconnection mode of terraced fields and pit ponds, the above method designs salt-isolating and water-collecting measures for terraced fields in view of the current situation of high-salinity seawater in pit ponds, controls salt return, collects rainwater, and carries out efficient water-saving green planting; plants suitable seaweed species at the bottom of pit ponds, utilizes the ability of seaweed to super-accumulate nutrients, efficiently fixes carbon and nitrogen, and regulates the nutrient level in water bodies; in warm seasons, suitable shrimp and shellfish seedlings can be released into the pond water to construct a shrimp-algae (grass) and shellfish-algae symbiotic system to enhance the added value of the system. Finally, a three-dimensional structure of "agriculture above, fishery in the middle, and grass below" is formed, with the organic combination of terraced field planting, pit pond aquaculture, and seaweed at the bottom of the pond to purify aquaculture wastewater, transforming the unstable traditional terraced field model of "agriculture above and fishery below", avoiding environmental pollution and waste of water resources caused by the discharge of aquaculture tail water, and realizing the ecological management and comprehensive and efficient utilization of coastal low-lying saline-alkali land.

[0048] The following details:

[0049] In this embodiment, the number of terraced fields-pond system combinations can be determined based on the pond area and flow rate, and is generally based on the water quality reaching seawater quality standard Class II or above when it flows out of the last level of pond. The number of terraced fields-pond combinations should also be considered comprehensively based on the wastewater treatment volume, pond length, and width, and can be determined based on actual water quality testing conditions.

[0050] (1) Reasonable configuration of terraced fields and ponds system

[0051] Specifically, it is a reasonable configuration of terraced field area a1, pit pond area a3, and road slope area. In S1, mechanical excavation of pits and construction of terraced fields are adopted. A 30cm high cofferdam is built around the terraced fields to collect rainwater. Roads are arranged along the slope at an appropriate height on both sides of the terraced fields to form a slope road area a2. The area ratio of terraced field area a1, slope road area a2, and pit pond area a3 is 4:4:2, and the height of the terraced field above the water surface of the pit pond is not less than 2.0m. For example, a production road is built at a position 0.8-1.0m above the water surface on both sides of the terraced field, which also serves as a slope stabilization platform; among them, the areas of terraced field area a1, pit pond area a3, and slope road area a2 account for about 40%, 40%, and 20% respectively, and the earthwork excavation is balanced.

[0052] The terraced road surface is compacted, and salt-tolerant bermudagrass lawn is laid with a width of 1.5 meters. Salt-tolerant slope protection landscape plants can be planted on the terraced slope above the road surface. The plants can be selected from bermudagrass with strong salt tolerance or perennial flowers such as cosmos, verbena, and iris for combined planting, which is beneficial to soil and water conservation and increases the landscape effect. As a preferred embodiment, in this embodiment, the slope ratio of the slope road area a2 is 1:1.5, and the slope above the road is protected by salt-tolerant bermudagrass and perennial vegetation, and the slope below the road is planted with tamarisk and sown with alkali sedge for slope protection; the road is 0.8-1.0m above the water surface and 1.5 meters wide. After the road surface is compacted, the salt-tolerant bermudagrass lawn is laid or sown.

[0053] The width of the terraced field should be 20-25 meters, and the length should be 50-150 meters. The height of the terraced field from the designed highest water level of the pond should not be less than 2.0 meters, and it should be determined based on the balance achieved by excavation and filling. When excavating and making terraced fields, the topsoil should be stripped first, and the relatively decomposed soil of the top 30 cm should be stripped and piled in strips to one side along the length of the terraced field. After the terraced field is completed, it should be backfilled to the surface of the terraced field and leveled. A cofferdam should be built around the terraced field, with a top width of 30 cm, a bottom width of 50 cm, and a height of 30 cm.

[0054] The width of the pond should be 20-25m, the length should be 50-150m, and the water depth of the pond should be 1.2m; the slopes of the pond should be planted with saltwort and Tamarix chinensis to protect the slopes.

[0055] (2) Layout of the pond inlet-connection-outlet system

[0056] Specifically, aquaculture wastewater inlet pipe 1┉┉→first-level pond┉┉→first connecting pipe 2┉┉→second-level pond┉┉→second connecting pipe 2……┉┉→Nth-level pond┉┉→clean water outlet pipe 3.

[0057] A connecting pipe 2 is arranged on each terrace, and the connecting pipe 2 passes through the corresponding terrace.

[0058] As a feasible embodiment, the aquaculture wastewater inlet pipe 1 can be a PE threaded buried special pipe with a diameter of 500mm, located at the water inlet side of the first-level pond, and the installation height of the pipe top is flush with the water level of the pond. The clean water outlet pipe 3 can be a PE threaded pipe with a diameter of 500mm, located at the outlet end of the last-level pond, and connected to the aquaculture water reuse system outside the system.

[0059] As a feasible embodiment, the connecting pipe 2 adopts an inverted U-shaped form, and the connecting pipe 2 is composed of a water inlet vertical pipe 201 located at the upper level pond, a water outlet vertical pipe 203 located at the lower level pond, and a horizontal pipe 202 passing through the terraced field. The pipe openings of the water inlet vertical pipe 201 and the water outlet vertical pipe 203 are both at a distance of L from the bottom of the pond, in centimeters; the water inlets and water outlets of the ponds of each level are respectively arranged at the two ends of the ponds, and the adjacent connecting pipes 2 are staggered.

[0060] After the planting of seaweed in the ponds is completed, seawater is put into the ponds at all levels until the initial depth is set to H, in centimeters, for example, H is 120 cm. When aquaculture wastewater is first put into the head end of the first-level pond, the water level rises and the water depth exceeds H. At this time, the raw water of the first-level pond is discharged to the second-level pond through the siphon principle of the connecting pipe 2, and the first-level pond begins to treat the aquaculture wastewater for the first time; when the aquaculture wastewater is discharged for the second time, the aquaculture wastewater after the first-level purification can enter the second-level pond for further purification, and so on, until the last-level pond discharges the water after multiple stages of purification through the clean water outlet pipe 3 and reuses it.

[0061] In this embodiment, the connection between the horizontal pipe 202 and the water inlet vertical pipe 201 and the water outlet vertical pipe 203 is connected by a 90° equal-diameter elbow, the pipe diameter is 500mm, the length of the water inlet vertical pipe 201 and the water outlet vertical pipe 203 is 60cm, the horizontal pipe 202 is laid through the terrace, and the length is the width of the terrace plus 3m, and the ports of the water inlet vertical pipe 201 and the water outlet vertical pipe 203 are 30cm away from the bottom of the pond. The connecting pipe 2 is buried at the downstream outlet side of the first-level pond, 2-3m away from the downstream horizontal side of the pond, that is, adjacent connecting pipes 2 are staggered.

[0062] It should be noted that the clean water outlet pipe 3 installed in the last-level pond also adopts the same inverted U-shaped siphon form and material, and its structure and material are the same as those of the connecting pipe 2; it is located in the downstream outlet section of the last-level pond, passes through the pond dam, and the outlet pipe of the clean water outlet pipe 3 is connected to the aquaculture water reuse system outside the system.

[0063] The multiple ponds are connected by connecting pipes 2, and the connecting pipes 2 are inverted U-shaped. The water inlets and outlets of the ponds at each level are respectively arranged at the two ends of the ponds, and the adjacent connecting pipes 2 are staggered. Such a layout can utilize the siphon principle to realize the automatic discharge of aquaculture wastewater to the ponds of the next level, and can realize the full purification of aquaculture wastewater in each level of ponds. After being fully purified in the multiple-level ponds, the organic matter, nitrogen and phosphorus content in the water body reaches the facility aquaculture reuse standard, and enters the aquaculture facility pool again for recycling.

[0064] (3) Construction of terraced field salt isolation and water collection system

[0065] An impermeable geomembrane 5 is set at a depth of 1 meter on the surface of the terraced field as a salt barrier to prevent salt from accumulating upward, which is conducive to collecting upper soil leaching water for re-injection when the soil salt content is at a low level. The material of the impermeable geomembrane 5 can be a composite geomembrane, one cloth and one film, the thickness of the film material can be 0.4mm-0.6mm, and the protective layer geotextile can be from 200g / m 2 -300g / m 2 The membrane-laying table surface maintains a slope of 0.1% in the drainage direction along the length of the terrace, and tilts inward from both ends along the terrace horizontally, with a slope of 0.5%, so as to facilitate the collection of water in the drainage pipe 4.

[0066] A drainage concealed pipe 4 with a diameter of 110 mm is arranged along the length of the terrace field. It is made of PE material and is lowered to the water outlet at a ratio of 0.1% to keep the water supply unobstructed. The buried depth is 1m. The filter material wrapped outside the drainage concealed pipe 4 is implemented in accordance with relevant specifications. A water storage bucket 6 is set at the downstream outlet of the drainage concealed pipe 4. The position where the drainage concealed pipe 4 enters the bucket is 20cm below the top of the water storage bucket 6.

[0067] The water storage barrel 6 mainly stores rainfall leaching water or low-mineralized water discharged from the soil to provide a water source for recycling. In this embodiment, the water storage barrel 6 can be an underground PE water storage barrel 6, with a single volume of not less than 5m 3 , used to collect low-mineralized internal drainage after desalination of the soil as an irrigation water source; the number of water storage barrels 6 can also be increased according to the water collection capacity of the terrace field and the water demand requirements. The water storage barrel 6 is provided with an inlet and a outlet, and the water inlet of the water storage barrel 6 is connected to one end of the drainage concealed pipe 4. When the water in the barrel is full, it can be discharged to the pond through the gravity pipe 8. The gravity drainage pipe can be a PE pipe with a diameter of 110mm. The installation position of the gravity pipe 8 is that the top of the pipe is 5cm below the top of the barrel, and the laying slope is 1%, and it is discharged to the pond.

[0068] (4) Install photovoltaic power generation devices with appropriate power

[0069] In this embodiment, the water pump can be a photovoltaic DC pump 7, and the terrace is provided with a photovoltaic power generation device, which is electrically connected to the photovoltaic DC pump 7 through a controller.

[0070] The photovoltaic power generation device mainly includes a photovoltaic device 10, a controller and a power storage device 11, etc. A photovoltaic water pump is placed in the water storage barrel 6, and the photovoltaic water pump is driven by a DC power supply through a cable 13, so that the photovoltaic water pump can be used to discharge the remaining water in the barrel through an irrigation pipe 12 or to take water for irrigation. The drip irrigation system mainly uses an underground drip irrigation pipe 9, and the irrigation pipe 12 supplies water to the underground drip irrigation pipe 9 buried in the field to carry out efficient water-saving irrigation and save water. The underground drip irrigation pipe 9 is buried 30 cm below the surface, and the spacing is determined by the row spacing of the planted crops.

[0071] It should be noted that during the initial stage of salt washing and improving saline-alkali soil in terraced fields, high-concentration leached salt water can be temporarily pumped to the pond for discharge through the irrigation pipe 12. When the leached water quality meets the recharging requirements, water storage will begin.

[0072] (5) Terraced field planting

[0073] If there are fresh water conditions, the newly built terraced fields can be flooded to suppress salt. The amount of water used for salt washing can be calculated based on the current salt content of the 1m soil layer thickness and the target salt content for salt washing. In order to save water resources, the quality of the underground drainage water can be tested in the later stage of salt washing. When the drainage mineralization is less than 5g / L, re-irrigation and repeated salt suppression can be considered. When the soil salt content drops below 0.4%, it is considered to meet the salt washing standard. When the soil moisture is suitable, apply no less than 5 tons / mu of organic fertilizer, and mix it by rotary tillage; carry out green planting of special salt-tolerant crops. Salt-tolerant crops can include special crops such as salt-tolerant glutinous corn and salt-tolerant black wheat.

[0074] (6) Artificial planting of seaweed seedlings at the bottom of ponds

[0075] Seaweed varieties can be selected from one or a combination of eelgrass, Sichuan creeper, and hornwort. In the present embodiment, the seaweed varieties are selected from at least three suitable local seaweed varieties such as eelgrass, Sichuan creeper, and hornwort, and the cultivation method is intercropping to facilitate the synergistic purification effect and improve the biodiversity of the bottom of the pond. During planting, drain the pond water, plant seaweed seedlings at the bottom of the pond, and the seedling height is 15-20cm; the planting time is May-June, the planting depth is about 3cm, the spacing between rows and plants is 25-30cm, and the number of seedlings per mu is not less than 6,000 plants / mu. After planting, compact the soil around the roots of the seedlings. After the planting is completed, release the water to the designed water level.

[0076] Seaweed is harvested in late summer when its growth is at its maximum. It can be processed into algae (grass) powder green feed and returned to facility seawater aquaculture to achieve ecological recycling.

[0077] (7) Pond water bodies suitable for shrimp and shellfish farming

[0078] In the warm season, antibiotic-free whiteleg shrimp or shellfish are released into pond water to carry out open-air natural farming without artificial feeding, and a shrimp-algae or shrimp-grass, shellfish-algae symbiotic system is established to further increase the system benefits.

[0079] Application results:

[0080] In view of the current situation that coastal low-lying saline-alkali land is difficult to utilize, fresh water is extremely scarce, and rainwater resources are difficult to collect, the present invention breaks the traditional inefficient model of "agriculture above and fishery below" in terraced fields, combines it with the treatment of wastewater from facility seawater aquaculture, optimizes the construction of terraced fields-pond systems, and expands new transformation paths and comprehensive utilization methods of "agriculture above, fishery in the middle, and grass below" in coastal low-lying saline-alkali land, increases valuable arable land resources, collects and efficiently utilizes valuable rainwater resources, and uses seaweed resources in the constructed terraced fields-pond systems to purify aquaculture wastewater, thereby achieving efficient recycling of seawater resources for facility aquaculture, and providing a long-term and low-cost solution for the transformation and comprehensive utilization of terraced fields in low-lying coastal saline-alkali land; in addition, since the main body of pond water is seawater, the water quality is relatively stable, and suitable types of outdoor seawater aquaculture can be carried out, thereby forming a new model of "agriculture above, fishery in the middle, and grass below". This method model not only increases arable land and collects rainwater resources, but also purifies wastewater, with significant comprehensive breeding and farming benefits. In particular, it increases blue carbon sinks through seaweed planting and processing, with significant social, ecological and economic benefits.

[0081] Although the specific implementation methods of the invention have been described in conjunction with the accompanying drawings, this does not limit the scope of protection of the invention. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present invention.

Claims

1. A method for coupled utilization of aquaculture wastewater based on the treatment of coastal low-lying saline-alkali land, characterized in that: The steps include: S1: Construct a three-dimensional utilization model of "agriculture above, fishery in the middle, and grass below": S11: Build several terraced fields at intervals on saline-alkali land to raise the cultivated layer of the land and form terraced fields (a1); S12: Ponds are excavated on one side of the terraced field to form several levels of pond areas (a3), namely the first-level ponds, the second-level ponds, and the Nth-level ponds; the pond areas (a3) ​​and the terraced field areas (a1) are arranged alternately, and pond areas (a3) ​​are arranged between adjacent terraced field areas (a1); the water bodies of the ponds are used as wastewater treatment and aquaculture areas, and the bottom areas of the ponds are used as seaweed planting areas, forming a three-dimensional utilization model of "agriculture above, fishery in the middle, and seaweed planting below"; S2: Install a concealed pipe collection and water storage system: An impermeable geomembrane (5) is laid below the surface of the terraced field, and a drainage concealed pipe (4) is laid on the impermeable geomembrane (5). The end of the drainage concealed pipe (4) is connected to a water storage bucket (6) for draining the collected infiltrated precipitation into the water storage bucket (6) for storage. The water storage bucket (6) is provided with a drainage outlet, which is connected to a gravity pipe (8). When the water in the bucket is full, the water is drained into a pond through the gravity drainage pipe. S3: The terraced field is provided with a drip irrigation system, a water pump is installed at the bottom of the water storage barrel (6), and the output end of the water pump is connected to the drip irrigation system to realize pump water drip irrigation; S4: A first-stage pond is provided with an aquaculture wastewater inlet pipe (1) at the beginning for receiving aquaculture wastewater; adjacent pond areas (a3) ​​are connected via connecting pipes (2) to achieve connectivity between ponds at all levels to achieve multi-stage purification; a clean water outlet pipe (3) is provided at the end of the last-stage pond for connection with a reuse water delivery system to complete a closed loop; The connecting pipe (2) is in an inverted U-shaped form. The connecting pipe (2) is composed of a water inlet vertical pipe (201) located at the upper level pond, a water outlet vertical pipe (203) located at the lower level pond, and a horizontal pipe (202) passing through the terraced field. The pipe openings of the water inlet vertical pipe (201) and the water outlet vertical pipe (203) are both at a distance L from the bottom of the pond. The water inlet and the water outlet of each level pond are respectively located at the two ends of the pond, and adjacent connecting pipes (2) are staggered. After the planting of seaweed in the ponds is completed, seawater is added to the ponds at all levels until the initial depth is set to H. When aquaculture wastewater is first added to the head end of the first-level pond, the water level rises and the water depth exceeds H. At this time, the raw water of the first-level pond is discharged to the second-level pond through the siphon principle of the connecting pipe (2), and the first-level pond begins to treat the aquaculture wastewater for the first time; when the aquaculture wastewater is discharged for the second time, the aquaculture wastewater after the first-level purification can enter the second-level pond for further purification, and so on, until the last-level pond discharges the water after multiple stages of purification through the clean water outlet pipe (3) and reuses it.

2. The method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 1 is characterized in that: It also includes building 30cm high cofferdams around the terraced fields to collect rainwater.

3. The method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 1 is characterized in that: The water storage barrel (6) is an underground PE water storage barrel, each of which has a volume of not less than 5m3, and is used to collect low-mineralized internal drainage after soil desalination for use as an irrigation water source.

4. The method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 1 is characterized in that: Roads are arranged along the slopes at appropriate heights on both sides of the terraced fields to form a slope road area (a2). The area ratio of the terraced field area (a1), slope road area (a2) and pond area (a3) ​​is 4:4:

2. The height of the terraced field above the water surface of the pond is not less than 2.0m.

5. The method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 4 is characterized in that: The slope ratio of the slope road area (a2) is 1:1.

5. The slopes above the road are protected by salt-tolerant bermudagrass and perennial vegetation, and the slopes below the road are protected by tamarisk and salsa oleifera. The road is 0.8-1.0m above the water surface and 1.5m wide. After the road surface is compacted, salt-tolerant bermudagrass lawn is paved or sown.

6. A method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 5, characterized in that: At least three types of seaweed varieties shall be selected, namely, giant kelp, Sichuan kelp and hornwort, and the cultivation method shall be interlaced planting.

7. The method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 1 is characterized in that: The installation position of the gravity pipe (8) is such that the top of the pipe is 5 cm below the top of the water storage barrel (6), and the laying slope is 1%, and the water is discharged to the pond.

8. The method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 1 is characterized in that: Release whiteleg shrimp or shellfish into the pond water, carry out open-air natural farming, and build a shrimp-algae or shrimp-grass, shellfish-algae symbiotic system.

9. The method for coupled utilization of aquaculture wastewater based on coastal low-lying saline-alkali land management according to claim 1 is characterized in that: The water pump is a photovoltaic direct current pump (7), and the terrace is provided with a photovoltaic power generation device, which is electrically connected to the photovoltaic direct current pump via a controller.

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