Pond zero-discharge circulating water aquaculture method

Abstract

The application belongs to the technical field of aquaculture, and particularly relates to a pond zero-waste discharge circulating water breeding method. The pond zero-waste discharge circulating water breeding method comprises the following steps: step S10, dividing a pond water surface into a high-oxygen area, a low-oxygen area and a corridor, arranging an oxygenator in the high-oxygen area, and connecting the high-oxygen area and the low-oxygen area through the corridor so that aquatic animals can freely select habitat space among the high-oxygen area, the low-oxygen area and the corridor; step S20, putting aquatic animals in the pond water surface; step S30, starting the oxygenator as needed to ensure the dissolved oxygen content of the high-oxygen area; and step S40, feeding as needed, and regularly pumping high-oxygen area bottom sewage into the low-oxygen area. The breeding method has high feed conversion rate, simple management, stable water quality all year round, realizes zero discharge of breeding wastewater and also realizes zero discharge of solid pollutants, and does not need to clean pollutants.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture technology, specifically a zero-sewage-discharge recirculating aquaculture method for ponds. Background Technology

[0002] According to statistics, as a major aquaculture country, my country's total aquaculture output in recent years has been around 52 million tons per year. According to the pollution discharge data released in the "Second National Pollution Source Census Bulletin," the pollution intensity per unit of aquaculture output in 2017 was as follows: Chemical Oxygen Demand (COD) 13.6 kg / ton, Ammonia Nitrogen 0.45 kg / ton, Total Nitrogen 2.02 kg / ton, and Total Phosphorus 0.33 kg / ton. These wastes mainly come from aquatic animal feces and uneaten feed. Traditional aquaculture typically does not treat aquaculture wastewater, easily leading to eutrophication of aquaculture water bodies, pollution of surface and groundwater, and increased carbon emissions.

[0003] To address the nitrogen and phosphorus waste generated by farmed animals during aquaculture and to achieve water recycling and zero pollutant discharge, people have conducted extensive practical explorations of recirculating aquaculture systems, which can be summarized into the following three main types.

[0004] One approach is to add aquaculture wastewater treatment unit, such as the aquaculture wastewater treatment method disclosed in Chinese patent document CN112520953A, which includes the following steps: Step S10, sedimentation treatment of aquaculture wastewater, and adsorption and denitrification treatment of the sedimented wastewater using biological barrier packing, so as to use the soluble carbon source in the wastewater for primary denitrification treatment; Step S20, purification treatment of the wastewater obtained in Step S10 using a composite microbial community, and aeration treatment and biological barrier packing treatment of the purified wastewater to improve the removal effect of organic matter and ammonia nitrogen; Step S30, adsorption treatment and secondary denitrification treatment of the wastewater obtained in Step S20 using solid carbon source packing, and deep purification treatment of the wastewater using submerged plants to obtain clean water.

[0005] The second model involves constructing a novel ecosystem where nitrogen and phosphorus produced by aquatic animals can serve as nutrients for plants. These nutrients can then be synthesized through photosynthesis and become components of newly synthesized organisms, potentially entering the food chain and being directly or indirectly utilized by farmed animals. For example, Chinese patent document CN 107950435A discloses a method combining raceway-style bass farming with rice-crayfish co-culture. In this method, uneaten feed and excrement from the bass in the raceway are collected and drained through pipes into the rice paddies where crayfish are raised. The crayfish then feed on the uneaten feed, while the rice paddies absorb the excrement and purify the water. Simultaneously, water rich in nitrogen and phosphorus discharged from the raceway is propelled into the rice paddy ditches and paddies via a waterwheel aerator, allowing aquatic plants and rice in the ditches to absorb the nitrogen and phosphorus, thus purifying the water.

[0006] Mode three is a self-purification aquaculture model for aquatic animals. Based on the feeding habits of aquatic organisms, different species are raised in separate zones. Wastewater is circulated among these zones, achieving self-purification. For example, Chinese patent document CN205865650U discloses a recirculating aquaculture system for carnivorous fish ponds, including ponds primarily for grass carp, carnivorous fish, and silver carp, connected end-to-end. This system reportedly avoids the discharge of highly polluting aquaculture water during carnivorous fish farming.

[0007] Of the three modes mentioned above, Mode 1 offers reliable treatment efficiency but suffers from high energy consumption, high treatment costs, and risks of secondary pollution and a high carbon footprint. Modes 2 and 3 represent methods for the resource recovery of wastewater, and the resource recovery process for nitrogen- and phosphorus-rich wastewater is a carbon sequestration process because nitrogen and phosphorus need to absorb carbon dioxide from the atmosphere during the synthesis of organic matter, thus representing a development trend. However, Modes 2 and 3 have complex processes, especially with slow feedback, a large management workload, and the entire system is not easily stabilized. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies represented by Modes 2 and 3, and to provide a recirculating aquaculture green aquaculture method with high feed conversion rate, simple management, and stable water quality throughout the year, achieving zero discharge of aquaculture wastewater and zero discharge of solid pollutants, without the need for cleaning.

[0009] The technical solution of the present invention is as follows:

[0010] A zero-sewage-discharge recirculating aquaculture system for ponds includes the following steps:

[0011] Step S10: Divide the pond surface into a high-oxygen zone, a low-oxygen zone, and a corridor. The high-oxygen zone is a water area where artificial oxygenation is possible and wastewater rich in fish feces and uneaten food is periodically discharged from the bottom into the low-oxygen zone. An aerator is installed in the high-oxygen zone. The low-oxygen zone is a water area where no artificial oxygenation is performed and which receives wastewater from the bottom of the high-oxygen zone. In the low-oxygen zone, organic matter entering the low-oxygen zone with the wastewater becomes nutrients for detritus organisms and returns to the food chain for use by aquatic animals. The corridor connects the high-oxygen zone and the low-oxygen zone, allowing aquatic animals to freely choose their habitat among the high-oxygen zone, the corridor, and the low-oxygen zone.

[0012] Step S20: Release aquatic animals into the pond.

[0013] Step S30: Turn on the aerator as needed to ensure the dissolved oxygen content in the high-oxygen zone, so that the dissolved oxygen in the zone is suitable for the needs of all aquatic animals.

[0014] Step S40: Feed the animals as needed and periodically pump the bottom sewage from the high-oxygen zone into the low-oxygen zone to promote the formation of a low-oxygen environment in the low-oxygen zone.

[0015] A hyperoxic zone is a clearly defined area with a relatively high dissolved oxygen content. During cloudy days and nights when photosynthesis is insufficient, aerators are used to maintain the dissolved oxygen level. Water pumps periodically discharge wastewater rich in fish feces and uneaten food from the bottom layer into the hypooxic zone. The hyperoxic zone consistently provides sufficient oxygen to meet the respiratory needs of fish and other large animals. This sustained oxygen enrichment also inhibits the excessive production of anaerobic microorganisms and suppresses the formation of nitrites, sulfides, and ammonia nitrogen, providing a stable and healthy habitat for fish and other large animals.

[0016] The corridor is a clearly defined transitional zone between high-oxygen and low-oxygen areas, playing a dual role of connecting and blocking the flow of organisms and materials on both sides. Specifically, environmental chemical indicators such as dissolved oxygen change continuously from one side to the other. Fish and other swimming animals can move freely, while other organisms (including bacteria) usually choose to stay in relatively safe and suitable areas because they move slowly and do not have time to escape predators or changes in environmental conditions.

[0017] The hypoxic zone refers to a clearly defined area that receives wastewater from the bottom layer of the hyperxic zone without artificial aeration. Dissolved oxygen in this zone comes entirely from photosynthesis and natural dissolution from the air. The accumulation of waste organic matter due to the receiving of wastewater from the hyperxic zone creates a hypoxic environment. Although photosynthesis may sometimes result in higher dissolved oxygen levels in the photoperiod layer compared to other areas, the overall dissolved oxygen content remains the lowest in the non-photoperiod layer, especially at the bottom. The hypoxic environment inhibits the oxidation of organic matter, causing a greater proportion to become nutrients for detritus organisms and return to the food chain for use by aquatic animals, indirectly improving feed conversion efficiency.

[0018] Unlike traditional aquaculture methods, the concept of this invention is as follows: (1) Dividing the pond surface into high-oxygen zone, low-oxygen zone, and corridor, the specific concepts and functions of high-oxygen zone, corridor, and low-oxygen zone are as described above. The traditional aquaculture concept of oxygenating the entire fishpond is changed to limiting the high dissolved oxygen area to a limited area, reducing the oxidation rate of waste organic matter outside the area, and giving it more time for decomposed organisms to recycle and utilize it, improving feed utilization, reducing oxygen consumption, reducing the generation of inorganic waste, forming a virtuous cycle, and achieving stable water quality; (2) The formation of dissolved oxygen difference between high-oxygen zone and low-oxygen zone includes two methods: a) periodically pumping aquatic animal feces and feed residue from the preset high-oxygen zone into the preset low-oxygen zone, b) using an aerator in the set high-oxygen zone to maintain dissolved oxygen above a certain value.

[0019] As an improvement, the high-oxygen zone and the low-oxygen zone each occupy ≥1 / 3 of the pond's surface area, and the corridor occupies ≤1 / 3 of the pond's surface area.

[0020] As a further improvement, both the high-oxygen zone and the low-oxygen zone are 30m×40m squares, and the corridor is a 7m×100m long strip.

[0021] As an improvement, the pond surface is divided by constructing dams.

[0022] As a further improvement, the pond surface is divided into a high-oxygen zone, a low-oxygen zone, and a corridor by a "T"-shaped dam.

[0023] As an improvement, the area above the horizontal line of the "T" shape is a corridor, and the two sides of the vertical line of the "T" shape are high-oxygen and low-oxygen zones.

[0024] As an improvement, the aquatic animals include one or more of fish, shrimp, crabs, or shellfish.

[0025] As an improvement, the aquatic animals include carnivorous fish, herbivorous fish, and omnivorous fish.

[0026] Carnivorous fish prey on sick farmed animals, preventing the spread of infectious diseases, and also consume some small wild omnivorous fish, forming a food chain that concentrates nutrients in the water. Herbivorous fish suppress the growth of aquatic plants, preventing drastic fluctuations in water quality. Omnivorous fish feed on uneaten food and detritus, preventing the accumulation of organic particles on the bottom and in the water column, while also consuming bacteria, algae, and zooplankton, ensuring the smooth circulation of matter in the food chain. Aquatic animals may also include shrimp, crabs, or shellfish, which also feed on uneaten food and detritus.

[0027] As a further improvement, the omnivorous fish include wild omnivorous fish. Wild omnivorous fish are highly tolerant of low oxygen levels, have a wide diet, and reproduce rapidly, serving as a necessary supplement to the ecological functions of omnivorous and herbivorous farmed animals. Wild omnivorous fish, along with other omnivorous fish, can consume excess artificial feed, as well as animal feces, biological carcasses, and detritus formed by bacteria. Wild omnivorous fish can also serve as food for carnivorous fish, becoming an important node in the food chain connecting bacteria, algae, small protozoa, small metazoa, and carnivorous fish.

[0028] As a further improvement, the carnivorous fish is at least one of the following: largemouth bass, mandarin fish, and snakehead; the herbivorous fish is at least one of the following: Wuchang bream and grass carp; the omnivorous fish is at least one of the following: crucian carp, spotted catfish, and yellow catfish; and the wild omnivorous fish is at least one of the following: minnow, wrasse, and mosquitofish.

[0029] Experiments have shown that using the aquaculture scheme described in this application results in stable water quality throughout the pond, healthy and normal growth of the fish, and no need to use disease prevention drugs or animal health products during the aquaculture cycle. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the pond water surface arrangement in Embodiment 1 of the present invention;

[0031] Figure 2 The graph shows a comparison of dissolved oxygen content monitoring values ​​between Example 1 and the Comparative Example over 15 days. It can be seen that, under the premise of synchronous oxygenation using the same aerator, the dissolved oxygen content in the high-oxygen zone 10 of Example 1 is not only greater than that in the low-oxygen zone 20, but also higher than that in the Comparative Example.

[0032] In the diagram: 10, high-oxygen zone; 20, low-oxygen zone; 30, corridor; 40, dam embankment; 50, gap; 60, sewage discharge channel; 70, aerator. Detailed Implementation

[0033] Example 1

[0034] The purpose of this invention is to establish a zero-sewage-discharge recirculating aquaculture system for ponds, comprising the following steps:

[0035] (1) Step S10 mainly focuses on the zoning of the pond water surface.

[0036] like Figure 1 As shown, the pond surface is divided into a high-oxygen zone 10, a low-oxygen zone 20, and a corridor 30 by a T-shaped dam 40. The corridor 30 is located above the horizontal line of the T-shape and is a long strip of 100m × 7m. The high-oxygen zone 10 and the low-oxygen zone 20 are located on either side of the vertical line of the T-shape, and both the high-oxygen zone 10 and the low-oxygen zone 20 are squares of 30m × 40m.

[0037] A 10m wide opening 50 is provided in the embankment 40 between the high-oxygen zone 10 and the corridor 30, and in the embankment 40 between the corridor 30 and the low-oxygen zone 20, allowing aquatic animals to move freely and inhabit the high-oxygen zone 10, corridor 30, and low-oxygen zone 20. A 3-inch sewage discharge channel 60 is provided between the high-oxygen zone 10 and the low-oxygen zone 20. The pond water in the sewage discharge channel 60 is driven by a 1.2 kW 3-inch submersible pump, and the switch is connected to the Internet of Things.

[0038] The pond water circulates between the high-oxygen zone 10, the low-oxygen zone 20, and the corridor 30, without being discharged. When the pond water evaporates significantly, water from outside the pond is added to maintain a certain water level.

[0039] (2) Step S20 concerns the aquatic animals released into the pond.

[0040] Fish are mainly released into the pond from January to early May.

[0041] This implementation method was carried out in a pond with a total area of ​​4.65 mu (approximately 0.23 hectares). From January to May 2021, 6000 largemouth bass (1500 kg), 500 Wuchang bream (20 kg), 500 silver carp (20 kg), and 200 smallmouth bass (4 kg) were stocked. In August 2021, based on the average weight of fish measured by net sampling, multiplied by the stocking quantity and minus the number of dead fish, the following was estimated: current stock of largemouth bass 3000 kg, Wuchang bream 300 kg, silver carp 250 kg, and smallmouth bass 10 kg (estimated by visual inspection), totaling 3560 kg of farmed fish, approximately 770 kg / mu (approximately 180 kg / hectare). During the farming period, no drainage or sewage treatment was carried out. Apart from adding feed to the water and using 30 kg of quicklime once, no other synthetic substances were used. The water quality remained stable, the fish grew healthily, and no diseases occurred.

[0042] The pond is mainly planted with algae, and no large plants are cultivated. Wuchang fish are used to prevent the invasion and excessive growth of aquatic plants.

[0043] It should be noted that the reason why this system is effective is that it establishes a high-oxygen zone 10 and a low-oxygen zone 20 with complementary functions, coupled with the transitional role of the corridor 30, so that the oxidation and reduction reactions of the entire ecosystem can be coordinated, and the roles of the grazing chain and the detritus chain can be coordinated.

[0044] (3) Step S30 concerns the control of dissolved oxygen content in the high-oxygen zone waters.

[0045] In hyperoxia zone 10, the aerator 70 is controlled by an IoT controller. The aerator 70 can automatically start based on the dissolved oxygen level in hyperoxia zone 10, or it can automatically start based on the intensity of sunlight. Generally, the dissolved oxygen content in hyperoxia zone 10 needs to be maintained above 2.5 mg / L.

[0046] (4) Step S40 is about daily management

[0047] Observations show a positive correlation between fish distribution and dissolved oxygen levels. High-oxygen zone 10 has the highest fish density, but hunger can also drive fish to low-oxygen zones to forage. When the dissolved oxygen content in low-oxygen zone 20 exceeds 0.8 mg / L, some small fish will feed there; when the dissolved oxygen content in low-oxygen zone 20 exceeds 1.8 mg / L, some larger fish will also prey on smaller fish. Therefore, feeding should primarily occur in high-oxygen zone 10, with low-oxygen zone 20 as a secondary feeding area, and no feeding should be provided within corridor 30.

[0048] Feeding is done as needed, depending on the weather and fish feeding behavior. Feeding frequency is generally 1-3 times daily, using high-quality feed, with a feed amount less than 20 kg / acre / day. Before each feeding, start the water pump and continue pumping for 10-30 minutes after feeding, pumping water from the bottom 10% of the high-oxygen zone through the drainage channel. The volume of water should be equivalent to the area of ​​the fish feeding zone multiplied by a depth of 0.5 meters. In this example, the pond pumping volume is 20-30 cubic meters. 3 / time, 60-100m 3 / d. To ensure timely removal of fish waste and uneaten food from high-oxygen zone 10 to low-oxygen zone 20, the water pump inlet must be placed at the deepest point on the bottom of high-oxygen zone 10. On cloudy days and at night, when aerator 70 is running in high-oxygen zone 10, the water pump should not be turned on.

[0049] The system operated for one production cycle with consistently stable water quality, maintaining normal fish growth rates and preventing disease. The main reasons are likely: a) The heterogeneity of the oxygen and temperature environments created by the system ensured diversity in prokaryotic communities such as bacteria, algae, protozoa, and small metazoans, forming a stable food chain that ultimately links small and large fish. This controlled the growth of harmful microbial populations; b) The high and stable environmental heterogeneity allowed swimming animals like fish to establish a rhythm of regularly occupying different locations, reducing stress responses and increasing resistance.

[0050] In the early stages of the experiment, the accumulation of organic matter such as fish feces and uneaten food in the low-oxygen zone 20 was not significant, and its dissolved oxygen level was within the range that the fish could adapt to. Therefore, the distribution of fish in the low-oxygen zone 20 and the high-oxygen zone 10 showed little difference. As time went on, the accumulation of organic waste in the low-oxygen zone 20 increased, and the suitable dissolved oxygen period became shorter and shorter. Larger, carnivorous fish that prefer high dissolved oxygen levels tended to reside in the high-oxygen zone 10.

[0051] In the initial stages of the experiment, herbivorous fish showed poor grazing ability. While aquatic plants grew rapidly for a period in spring, their growth was completely suppressed as the herbivorous fish increased their feeding rate. Algal changes were largely influenced by weather conditions. Prolonged periods of overcast skies, or heavy rainfall and typhoons causing turbidity, led to a rapid decrease in algae. During periods of sustained mild weather, algal density was high but remained stable, with no algal blooms. This was because the overall system exhibited high biodiversity, with stable food chains between species, thus controlling algal growth through downward influences.

[0052] Summer is the season with the worst pond water quality. The inventor commissioned a third-party testing agency to test the main indicators of the implementation pond and the control pond in the summer of 2021. The test results and our routine oxygen monitoring results are shown in the table below. Figure 2 .

[0053] Comparative Example

[0054] To compare with Example 1, a comparative experiment was conducted simultaneously in a nearby pond. The comparison pond covered 4.30 acres and was stocked primarily with yellow catfish, an omnivorous fish more tolerant of low oxygen levels than largemouth bass, supplemented with largemouth bass, grass carp, and crucian carp, with a total stock of approximately 2000 kg (465 kg / acre). The same aerators were used for aeration, and the same weight of feed was administered, but the feed had a protein content of ≥40%, slightly lower than the protein content (≥48%) in the example pond. In August, a third-party testing agency (Huzhou Shusheng Testing Technology Co., Ltd.) conducted three tests on key water quality indicators in both the implementation and comparison ponds. The results are shown in the table below (all values ​​are in mg / L):

[0055]

[0056] It is evident that the control pond had higher total nitrogen and nitrate nitrogen levels than the control pond. A comparison between the low-oxygen zone 20 and the high-oxygen zone 10 in the control pond revealed that, except for one instance where nitrate nitrogen was slightly higher in low-oxygen zone 20 than in high-oxygen zone 10, all other indicators were significantly lower in low-oxygen zone 20 than in high-oxygen zone 10. The difference in nitrate nitrogen was the largest in the last two instances, indicating that low-oxygen zone 20 had a significant purification effect on the entire control pond.

[0057] Oxygen monitoring of the high-oxygen zone 10 and low-oxygen zone 20 of the example ponds, as well as the control ponds, revealed that the dissolved oxygen concentration in the example ponds was also relatively high. Figure 2 The dissolved oxygen curves for the low-oxygen zone 20, high-oxygen zone 10, and control pond were measured daily at 3 PM from August 1st to 15th, 2021. It is evident that the dissolved oxygen in the control pond with simultaneous aeration was often lower than that in the low-oxygen zone 20 of the implemented pond. This further illustrates that by confining oxygen to a limited area, the present invention can recover more organic waste, reduce the direct oxidation of organic matter (equivalent to combustion), improve feed conversion efficiency, reduce oxygen consumption, and also reduce carbon dioxide emissions.

Claims

1. A zero-sewage-discharge recirculating aquaculture system for ponds, characterized in that: Includes the following steps, Step S10: Divide the pond surface into a high-oxygen zone, a low-oxygen zone, and a corridor using a "T"-shaped dam. The area above the horizontal line of the "T" is the corridor, and the areas on either side of the vertical line are the high-oxygen zone and the low-oxygen zone. Aerators are installed in the high-oxygen zone to ensure sufficient oxygen for fish respiration, while simultaneously reducing the oxidation rate of organic matter outside this area and extending the time available for detritus organisms to recycle and utilize it. The low-oxygen environment in the low-oxygen zone inhibits the oxidation of organic matter. The function is to ensure that a larger proportion of dissolved oxygen becomes nutrients for detritus and returns to the food chain for use by aquatic animals; the corridor connects the high-oxygen and low-oxygen zones, allowing aquatic animals to freely choose their habitat among these zones and the corridor; the dissolved oxygen content in the high-oxygen zone is above 2.5 mg / L; when the dissolved oxygen content in the low-oxygen zone is above 0.8 mg / L, some small fish will come to the low-oxygen zone to feed; when the dissolved oxygen content in the low-oxygen zone is above 1.8 mg / L, some large fish will also come to the low-oxygen zone to prey on small fish; Step S20: Introduce aquatic animals into the pond. The aquatic animals include carnivorous fish, herbivorous fish, and omnivorous fish. Carnivorous fish prey on diseased farmed animals and consume some small wild omnivorous fish. Herbivorous fish suppress the growth of aquatic plants. Omnivorous fish feed on uneaten food and detritus to prevent the accumulation of organic particles on the bottom and in the water layer. They also feed on bacteria, algae, and zooplankton to ensure the smooth circulation of food chain materials. Step S30: Use an aerator on cloudy days and at night when photosynthesis is insufficient to ensure the dissolved oxygen content in the high-oxygen zone; Step S40: Feed is added as needed, with the feeding area mainly in the high-oxygen zone and supplemented by the low-oxygen zone. Wastewater from the bottom of the high-oxygen zone is periodically pumped into the low-oxygen zone.

2. The zero-sewage-discharge recirculating aquaculture system for ponds as described in claim 1, characterized in that: The high-oxygen zone and low-oxygen zone each occupy ≥1 / 3 of the pond's surface area, while the corridor occupies ≤1 / 3 of the pond's surface area.

3. The zero-sewage-discharge recirculating aquaculture system for ponds as described in claim 2, characterized in that: Both the high-oxygen zone and the low-oxygen zone are square areas, while the corridor is a long, narrow area.

4. The zero-sewage-discharge recirculating aquaculture system for ponds as described in claim 1, characterized in that: The aquatic animals include one or more types of shrimp, crabs, or shellfish.

5. The zero-sewage-discharge recirculating aquaculture system for ponds as described in claim 1, characterized in that: The omnivorous fish mentioned include wild omnivorous fish.

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