Economic and net water efficiency gain type seawater aquaculture tail water treatment system and method

Abstract

The application discloses an economic and water purification efficiency gain type seawater breeding tail water treatment system and method, which comprises a sedimentation tank, a biological purification tank and an ecological purification tank connected in sequence, and a salt-tolerant floating aquatic plant biological floating bed is arranged on the water surface of the sedimentation tank and the biological purification tank, oysters are hung under the salt-tolerant floating aquatic plant biological floating bed in the biological purification tank, and algae seedlings are hung in the ecological purification tank. The application can fully utilize physical sedimentation in the sedimentation tank, nitrogen and phosphorus absorption and light shielding and heat insulation of the floating aquatic plants, microbial mineralization and transformation of the nutritive substances and the filtering effect of the functional organisms in the physicochemical treatment tank, and the absorption effect of the large algae in the biological purification tank, so that the tail water is purified in stages and in multiple levels.

Description

Technical Field

[0001] This invention relates to aquaculture wastewater treatment systems and methods, and more particularly to an economical and water purification efficiency-enhancing mariculture wastewater treatment system and method. Background Technology

[0002] Pond aquaculture is the primary fishery production method in inland and coastal mudflats of my country. With the decline of wild fishery resources and the increasing prominence of marine pollution, pond aquaculture has become the most stable and safest way to meet people's diverse aquatic product consumption needs. However, with the development of intensive pond aquaculture, the pollution of aquaculture wastewater has increasingly attracted attention from all sectors of society. Effective treatment of aquaculture wastewater is not only related to the aquatic ecological safety of the surrounding areas of aquaculture ponds, but also to the health and sustainable development of the aquaculture industry itself.

[0003] Currently, with the improvement of relevant regulations and the tightening of policies, wastewater discharge and treatment have become one of the main factors restricting aquaculture. Although there are various technical routes for wastewater treatment in China, from an economic and operational perspective, the ecological treatment using ponds and dams is the most promising. However, this type of treatment model suffers from high land costs and insufficient treatment efficiency. To address this, some researchers, based on the concept of resource reuse, have proposed selecting functional organisms with economic value, such as fish, shellfish, and algae, to increase revenue and reduce costs while simultaneously improving the system's treatment efficiency. However, this approach also faces challenges such as high mortality rates for fish and shellfish due to excessive fluctuations in water physicochemical factors, low water transparency failing to meet the light requirements of algae, and the short growth cycle, low economic value, and narrow suitable temperature and salinity range of the selected algae. Furthermore, data shows that the settleable portions of major pollutants such as COD, nitrogen, and phosphorus in the newly discharged effluent from the high-level sedimentation tank account for 13.40%, 34.85%, and 50.46%, respectively. If large-diameter particles can be removed during the sedimentation process, the treatment load on subsequent stages can be greatly reduced, thereby improving the quality of the final effluent. Therefore, optimizing sedimentation design parameters, controlling physicochemical factors such as water temperature within the system, removing suspended particulate matter and improving transparency, as well as selecting and cultivating superior algae are key to addressing the aforementioned technical shortcomings. Summary of the Invention

[0004] One of the objectives of this invention is to provide an economical and water purification efficiency-enhancing mariculture wastewater treatment system.

[0005] Specifically, the economic and water purification efficiency-enhancing marine aquaculture wastewater treatment system provided by the present invention includes a sedimentation tank, a biological purification tank, and an ecological purification tank connected in sequence. Salt-tolerant floating plant bio-floating beds are set on the water surface of the sedimentation tank and the biological purification tank. Oysters are suspended under the salt-tolerant floating plant bio-floating beds in the biological purification tank, and algae seedlings are suspended in the ecological purification tank.

[0006] The salt-tolerant floating plant bio-floating bed in the sedimentation tank has a coverage rate of over 60%, thereby achieving the requirement of controlling the surface water temperature below 35℃. Preferably, the salt-tolerant floating plant bio-floating bed in the sedimentation tank has a coverage rate of over 90%.

[0007] The sedimentation tank is equipped with an overflow hole with a "∫" structure. Its inlet is 0.5 meters below the water surface, and its outlet is above the water surface.

[0008] The salt-tolerant floating plant bio-floating bed in the biological purification pond has a coverage rate of over 40% to achieve appropriate water temperature regulation.

[0009] Salt-tolerant floating plants include seahorse purslane.

[0010] An oxygenation device is installed at the bottom of the biological purification tank.

[0011] The density of oysters raised on the raft is 120-150 oysters / m². 2 Oysters weighing 20g or more each.

[0012] The density of algae seedlings cultured in the ecological purification pond is 30 seedlings / m². 2 The size of a single plant is 15-20g / plant, and the water depth for cultivation is 20-80cm from the surface.

[0013] Red pea leaflets were selected for the algae seedlings. Red pea leaflets are large algae that grow year-round. They have a lower limit of salinity tolerance of 13‰ and an upper limit of temperature tolerance of 37℃, which can completely cover the aquaculture cycle. At the same time, they can overcome the problems of large fluctuations in water salinity during the rainy season and the easy decay of algae during high temperature periods.

[0014] The second objective of this invention is to provide an economical and water purification efficiency-enhancing method for treating marine aquaculture wastewater.

[0015] Specifically, the present invention provides an economical and water purification efficiency-enhancing method for treating marine aquaculture wastewater, wherein the marine aquaculture wastewater sequentially enters a sedimentation tank, a biological purification tank, and an ecological purification tank for treatment. The sedimentation tank and the biological purification tank are equipped with salt-tolerant floating plant bio-floating beds on their water surfaces. Oysters are cultured under the salt-tolerant floating plant bio-floating beds in the biological purification tank, and algae seedlings are cultured in the ecological purification tank.

[0016] The salt-tolerant floating plant bio-floating bed in the sedimentation tank has a coverage rate of over 60%, thereby achieving the requirement of controlling the surface water temperature below 35℃. Preferably, the salt-tolerant floating plant bio-floating bed in the sedimentation tank has a coverage rate of over 90%.

[0017] The sedimentation tank is equipped with an overflow hole with a "∫" structure. Its inlet is 0.5 meters below the water surface, and its outlet is above the water surface.

[0018] Furthermore, the hydraulic retention time of effluent from marine aquaculture in the pond should be controlled to be more than 24 hours. After 24 hours of static sedimentation, the COD, total nitrogen, and total phosphorus in the middle and upper layers of effluent tend to stabilize. Therefore, the design of the sedimentation tank should be based on the flow rate during the drainage cycle of the aquaculture pond. That is, its volume must ensure that the hydraulic retention time of effluent in the sedimentation tank is more than 24 hours. In other words, its design standard should be based on volume rather than area.

[0019] The biological purification pond is equipped with a salt-tolerant floating plant bio-floating bed with a coverage rate of over 40% to effectively regulate water temperature. The salt-tolerant floating plant is *Portulaca grandiflora*.

[0020] An oxygenation device is installed at the bottom of the biological purification tank to control the dissolved oxygen in the water to be no less than 4.0 mg / L.

[0021] Furthermore, the hydraulic retention time of the effluent from marine aquaculture in the pool must be more than 12 hours to ensure that the transparency of the water flowing out of the pool reaches more than 1 meter.

[0022] The density of oysters raised on the raft is 120-150 oysters / m². 2 Oysters weighing 20g or more each.

[0023] The density of algae seedlings cultured in the ecological purification pond is 30 seedlings / m². 2 The size of a single plant is 15-20g / plant, and the water depth for cultivation is 20-80cm from the surface.

[0024] The algae seedlings are selected from red-feathered seaweed.

[0025] The beneficial effects of this invention are:

[0026] This invention provides a solution for treating wastewater from seawater pond aquaculture, effectively addressing issues such as vague design standards for sedimentation tanks, high water temperatures, low survival rates of shellfish in clean water, and a lack of excellent algae. Ultimately, it greatly improves the efficiency of the treatment system, reduces land occupation, and significantly increases economic output, thereby achieving a balance between economic and ecological benefits.

[0027] This invention, based on the traditional pond-dam treatment model, focuses on solving key technical issues such as the regulation of physicochemical conditions in sedimentation tanks, the removal of suspended particulate matter and improvement of water transparency in biological purification tanks, and the cultivation and management of large-scale algae in ecological purification tanks. The regulation of physicochemical factors in the sedimentation tank involves constructing a floating bed using salt-tolerant floating plants like *Odontocarpus siceraria*. Utilizing its nitrogen and phosphorus absorption and light-shielding and heat-insulating properties, the coverage rate is adjusted to maintain water temperature and microalgal biomass at a suitable level, ensuring the feeding and living water temperature requirements of functional organisms in the next treatment stage. The removal of suspended particulate matter and improvement of water transparency in the biological purification tank aim to achieve thorough purification of microalgae and suspended particulate matter by optimizing the matching relationship between the hydraulic load of the effluent, the oxygenation intensity, and the amount of functional organisms such as oysters and scallops. This significantly improves water transparency while removing microalgae and particulate matter from the effluent. The key technical points for the cultivation and management of large algae in ecological purification ponds are to design a suitable hanging culture method to ensure that *Gnaphalium affine*, a large algae with a long growth period, strong adaptability to salinity and temperature fluctuations, high economic value, and great development potential, can deeply absorb soluble nitrogen, phosphorus, and other eutrophic substances in the water, and ultimately achieve full purification of the aquaculture wastewater.

[0028] This invention effectively integrates the three technical aspects mentioned above, enabling the purification of effluent within a limited purification space. This is achieved through a multi-stage process, utilizing physical sedimentation in the sedimentation tank, nitrogen and phosphorus absorption and light-shielding insulation by floating plants, microbial mineralization and transformation of nutrient-rich substances in the physicochemical treatment tank, filtration by functional organisms such as filter-feeding shellfish, and absorption by large algae such as *Gnaphalium affine* in the biological purification tank. This model significantly improves the treatment efficiency of the dam-based water purification system. The use of filter-feeding shellfish effectively avoids the problems of filter media clogging and pollutant re-release associated with physical filtration. Furthermore, timely harvesting and harvesting of the introduced shellfish and functional organisms such as *Gnaphalium affine* can, to some extent, increase production and income, subsidize effluent treatment costs, and facilitate the resource utilization of pollutants in the effluent. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a marine aquaculture wastewater treatment system.

[0030] Figure 2 A schematic diagram of a red-feathered vegetable cultivation frame;

[0031] 51 Fixed frame, 52 Plastic mesh, 53 Algae seedlings.

[0032] Figure 3 This refers to the effect of floating bed coverage on water temperature regulation.

[0033] Figure 4 This study illustrates the growth of *Gnaphalium affine* under different salinity levels.

[0034] Figure 5 This shows the growth of red pea shoots at different temperatures.

[0035] Figure 6 This shows the trend of total nitrogen variation in the sedimentation tank.

[0036] Figure 7 The trend of total phosphorus variation in the sedimentation tank.

[0037] Figure 8 This shows the trend of COD changes in the sedimentation tank. Detailed Implementation

[0038] The present invention will be further described below through specific embodiments, but the content of the present invention is not limited thereto.

[0039] The marine aquaculture wastewater treatment system includes a sedimentation tank 1, a biological purification tank 2, and an ecological purification tank 3 connected in sequence. The volume ratio of the sedimentation tank 1, the biological purification tank 2, and the ecological purification tank 3 can be set to 55:20:35.

[0040] The volume of sedimentation tank 1 should be determined based on the flow rate during the drainage cycle of the aquaculture pond. Its volume must ensure that the hydraulic retention time of the effluent in sedimentation tank 1 is more than 24 hours; that is, its design standard should be based on volume rather than area. An overflow hole 4 with a "∫" structure is installed on the upper part of the side wall of sedimentation tank 1 on the side connecting to biological purification tank 2. Its inlet is 0.5 meters below the water surface, and its outlet is above the water surface.

[0041] After 24 hours of static sedimentation, the levels of COD, total nitrogen, and total phosphorus in the upper and middle layers of the aquaculture pond effluent tend to stabilize.

[0042] A seahorse tussock bio-floating bed 7 was installed on the surface of sedimentation tank 1. Experiments showed that the temperature regulation effect gradually increased when the floating bed coverage was 0%, 30%, 60%, and 90%, with peak water temperatures of 38.28℃, 36.24℃, 35.18℃, and 33.19℃, respectively. The temperature reduction at 30%, 60%, and 90% coverage was 5.35%, 8.11%, and 13.30%, respectively. Specifically, a 90% coverage rate ensured the water temperature remained below 35℃ throughout the day (see...). Figure 2 The water temperature data at different coverage rates at various time points are shown in the table below. Statistical analysis shows that different floating bed coverage rates and detection times both have a significant impact on water temperature.

[0043] Table 1 Water temperature at different coverage rates at various time points

[0044]

[0045] Note: Different uppercase letters indicate significant differences in water temperature at different time points with the same coverage (P<0.05); different lowercase letters indicate significant differences in water temperature at different coverage levels at the same time (P<0.05).

[0046] Therefore, the seahorse dentistry bio-floating bed 7 covers more than 90% of the sedimentation tank surface. In addition to enhancing the absorption of soluble nitrogen and phosphorus, it can stabilize the upper layer temperature of the water below 32°C during high-temperature periods. This ensures that the shellfish (Oyster simonii) in the biological purification tank meet the water temperature requirements, thus solving the main cause of shellfish mortality during the summer.

[0047] Biological purification pond 2 has a water depth of no less than 1.5 meters. A floating bed of seahorse tussock organisms 7 is set on the water surface, and a hanging cage 6 is set under the floating bed. The density of oysters weighing 20g or more is 120-150 oysters / m³. 2 An aerator is installed at the bottom of the pool to oxygenate the water, ensuring dissolved oxygen levels are not lower than 4.0 mg / L. A floating bed of seahorse oysters covers approximately 40% of the pool surface to regulate water temperature. The hydraulic retention time in the pool is controlled to be at least 12 hours to ensure the removal of suspended particulate matter and a water transparency of at least 1 meter when flowing out of the pool. Oysters are harvested and sold after reaching marketable size to generate revenue, and oyster seedlings are immediately replenished to maintain the water purification efficiency of the pool.

[0048] Red spirea 53 is cultivated in the ecological purification pond 3 using cultivation frames 5. Red spirea is a large algae that grows year-round, with a lower limit of salinity tolerance to 13‰ and an upper limit of temperature tolerance to 37℃, which can completely cover the aquaculture cycle. It also overcomes problems such as large salinity fluctuations during the rainy season and the easy rotting of algae during high-temperature periods. The algae seedlings are suspended in the water in specially designed cultivation frames throughout the pond, with a seedling density of 30 seedlings / m². 2 The individual plant size is 15-20g / plant, and the cultivation water depth is 20-80cm from the surface. Harvesting is done after the red-feathered plant has grown in large quantities. It can then be used as feed for shellfish such as abalone, or sent to factories to extract products such as carrageenan, thus generating economic benefits. Figure 2 As shown, the aquaculture frame 5 includes a rectangular frame 51, which has two plastic meshes 52 fixed on it, and the red pea seedlings are fixed between the two plastic meshes 52.

[0049] *Solieria* (formerly known as Pacific red spirea) belongs to the genus *Solieria* of the family Solieriaceae in the order Gigartinales of the phylum Rhodophyta. It grows primarily on shells or pebbles on muddy bottoms or clear pond bottoms from the mid- to low-tide zones. In China, it is mainly distributed in Guangdong and Hainan provinces. *Solieria* species have very high economic and ecological value and can be used as food, raw materials for extracting carrageenan and phycoerythrin, abalone feed, and as a tool for integrated green aquaculture and aquaculture wastewater treatment. As a tool for treating aquaculture wastewater, it has several advantages: 1) Strong water purification capacity, with excellent nitrogen and phosphorus removal effects in eutrophic waters; 2) Fast growth and long growth cycle, generally increasing fresh weight by 0.2 kg / day per square meter per month; 3) Simple farming model, low cost, easy to promote, and high propagation efficiency; 4) Good processing characteristics and great economic potential, it can be developed into special prepared dishes, functional beverage additives, or as a high-quality raw material for extracting phycobiliproteins and carrageenan. It is estimated that, under the premise of completing relevant technology research and development and industrial layout, the medium- to long-term annual output value of *Gnaphalium affine* can reach 15,000 to 20,000 yuan / mu. Furthermore, salinity and temperature adaptability tests show that the suitable salinity range for *Gnaphalium affine* is 15‰ to 35‰. Figure 4 It can grow well in water temperatures ranging from 17℃ to 33℃. Figure 5 It can withstand temperatures up to 40℃, has a wide range of suitable salinity and temperature, and is fully adapted to the characteristics of large salinity and temperature fluctuations in tailwater treatment ponds and canals.

[0050] Salinity Adaptability Test of Red-winged Vegetable

[0051] Based on the analysis of the algal body condition after 14 days of experimentation, the relative growth rate was as follows: At a salinity of 10‰, no new buds grew on the algae, the overall color of the algae became lighter, some tissues of the algae softened and rotted, and the osmotic pressure was unbalanced. Due to the hollow nature of the Red Feather algae, seawater may have seeped into the interior. The initial algal quantity was about 1.4g, which led to the experimental results being higher than expected, indicating a certain experimental error. At a salinity of 15‰, new buds sprouted on the algae. This may be due to the lower salinity, which caused osmotic pressure to occur, leading to the cells absorbing water from the outside, thus resulting in a higher relative growth rate. When the salinity was 20‰-30‰, the color of the algae was normal, and many buds sprouted. At a salinity of 20‰, the buds were dense but small. The buds at 25‰ and 30‰ were thicker and longer than those at 20‰, but the new buds were sparser at 30‰. At a salinity of 35‰, growth was slower than at 15‰-30‰, and the new buds were thinner and shorter. Based on this experiment, the salinity range that *Gnaphalium affine* can adapt to is 15‰-35‰, with a salinity of 25‰ being the most suitable. Figure 4 ).

[0052] Temperature adaptability test of red tamarind

[0053] Healthy, intact *Gnaphalium affine* thallus, approximately 1g in size, was selected without any decay. Foreign objects were carefully removed, and the initial weight of the thallus was recorded. The thallus was then placed in a 1L plastic bottle and cultured in a constant-temperature incubator. The culture conditions were: 5000 Lx light, 25 salinity, L:D = 12h:12h, with six temperature gradients (10℃, 15℃, 20℃, 25℃, 30℃, and 35℃), and three parallel experiments were conducted for each group. Disinfected seawater was changed daily. After seven days of culture, the weight of the thallus was measured, and various physiological indicators were tested to compare the changes in these indicators under different temperature stresses. The results showed that at 10℃, *Gnaphalium affine* exhibited thinner branches, and its weight decreased during the experiment. At 15℃, the thallus morphology remained largely unchanged, with a slight increase in weight. Growth was observed at 20℃, 25℃, 30℃, and 35℃, with the fastest growth at 30℃, reaching an average daily relative growth rate of approximately 5%. This experiment shows that the lowest water temperature that Red Feathers can adapt to is around 15℃, the optimal water temperature for growth is around 30℃, and the highest temperature it can tolerate is above 35℃.

[0054] Aquaculture tailwater settling characteristics test

[0055] A test was conducted on the settling efficiency of the tailwater using water samples collected from sedimentation tank 1.

[0056] The main pollutants in the upper layer of the effluent from a high-level aquaculture pond were measured after different settling times. The results showed that total nitrogen, total phosphorus, and chemical oxygen demand (COD) all decreased significantly over time (P<0.05). Among them, total nitrogen showed a final decrease of approximately 34.85% after 48 hours of settling, but the rate of decrease dropped sharply after 12 hours. Figure 6 Total phosphorus decreased by 47.74% at 6 hours, and then showed no significant decrease. Figure 7 The final decrease in COD was 13.40%, and the rate of decrease also dropped significantly after 12 hours. Figure 8 The data above shows that precipitation treatment has a significant effect on the treatment of total phosphorus, COD, and total nitrogen, with a reduction of 34.85% to 47.74% after 48 hours of settling. However, from the perspective of optimizing actual treatment efficiency, the optimal settling time should be 12 hours, at which time the reduction of the above three main pollutants can reach between 27.10% and 48.92%.

[0057] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An economical and water purification efficiency-enhancing mariculture wastewater treatment system, comprising a sedimentation tank, a biological purification tank, and an ecological purification tank connected in sequence, characterized in that, The sedimentation tank and biological purification tank are equipped with salt-tolerant floating plant bio-floating beds. Oysters are cultured beneath the salt-tolerant floating plant bio-floating beds in the biological purification tank, and algae seedlings are cultured in the ecological purification tank. The salt-tolerant floating plant bio-floating bed coverage in the sedimentation tank is over 60%, and the salt-tolerant floating plant bio-floating bed coverage in the biological purification tank is over 40%. An aeration device is installed at the bottom of the biological purification tank. The density of the cultured oysters is 120-150 oysters / m². 2 The oysters must weigh at least 20 g each; the density of algae seedlings cultured in the ecological purification pond is 30 seedlings / m². 2 The size of a single plant is 15~20 g / plant, and the water depth for cultivation is 20~80 cm from the water surface; The salt-tolerant floating plant is *Portulaca oleracea*, and the algae seedling is *Gnaphalium affine*.

2. The economic and water purification efficiency-enhancing mariculture wastewater treatment system according to claim 1, characterized in that, The salt-tolerant floating plant bio-floating bed installed in the sedimentation tank has a coverage rate of over 90%.

3. The economic and water purification efficiency-enhancing marine aquaculture wastewater treatment system according to claim 1, characterized in that, The sedimentation tank is equipped with an overflow hole, which is " "The structure has an inlet 0.5 meters below the water surface and an outlet above the water surface." 4. A method for treating mariculture wastewater that improves both economic efficiency and water purification effectiveness, wherein the mariculture wastewater sequentially enters a sedimentation tank, a biological purification tank, and an ecological purification tank for treatment, characterized in that... The sedimentation tank and the biological purification tank are equipped with salt-tolerant floating plant biological floating beds. Oysters are suspended under the salt-tolerant floating plant biological floating beds in the biological purification tank, and algae seedlings are suspended in the ecological purification tank. The sedimentation tank is equipped with a salt-tolerant floating plant bio-floating bed with a coverage rate of over 60%; the biological purification tank is equipped with a salt-tolerant floating plant bio-floating bed with a coverage rate of over 40%; the bottom of the biological purification tank is equipped with an aeration device to control the dissolved oxygen in the water to be no less than 4.0 mg / L; the hydraulic retention time of the seawater aquaculture tailwater in the biological purification tank needs to be over 12 hours; the density of the suspended oysters is 120-150 oysters / m². 2 The oysters must weigh at least 20 g each; the density of algae seedlings cultured in the ecological purification pond is 30 seedlings / m². 2 The size of a single plant is 15~20 g / plant, and the water depth for cultivation is 20~80 cm from the water surface.

5. The method for treating marine aquaculture wastewater with improved economic efficiency and water purification effectiveness according to claim 4, characterized in that, The sedimentation tank is equipped with an overflow hole, which is " The structure has an inlet 0.5 meters below the water surface and an outlet above the water surface.

6. The method for treating marine aquaculture wastewater with improved economic efficiency and water purification effectiveness according to claim 4, characterized in that, The hydraulic retention time of the marine aquaculture wastewater in the sedimentation tank should be controlled to be more than 24 hours.

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