A composite substrate for treating aquaculture effluent in a low temperature environment

Abstract

The application belongs to the technical field of aquaculture tail water treatment, and discloses a composite substrate for treating aquaculture tail water in a low-temperature environment.The technical problem to be solved by the application is that, when treating aquaculture tail water in a low-temperature environment, the existing substrate is difficult to balance the heat preservation performance and the purification performance, resulting in a significant decrease in purification efficiency.The composite substrate comprises four layers from top to bottom: an upper layer of a quartz sand layer with a particle size of 2-5 mm, accounting for 35% of the total volume; a middle layer of a coconut shell charcoal layer with a particle size of 2-5 mm, accounting for 20% of the total volume; a lower layer of a rock wool layer with a particle size of 3-8 mm, accounting for 10% of the total volume; and a bottom layer of a quartz sand layer with a particle size of 5-10 mm, accounting for 35% of the total volume.The composite substrate is formed by layering and compounding, and is used for treating aquaculture tail water in a low-temperature environment, so that heat loss in the substrate can be effectively reduced, the activity of microorganisms can be maintained, and the stable removal of pollutants such as nitrogen and phosphorus can be ensured.

Description

Technical Field

[0001] This invention relates to the field of aquaculture wastewater treatment technology, and in particular to a composite matrix for treating aquaculture wastewater under low-temperature conditions. Background Technology

[0002] Aquaculture wastewater often contains nitrogen, phosphorus, and organic pollutants, and direct discharge can cause environmental problems such as eutrophication of receiving water bodies. Ecological treatment technologies such as constructed wetlands and biofilters are widely used for purifying aquaculture wastewater due to their low operating costs and environmental friendliness. Among these technologies, the substrate, as the core functional carrier for physical interception, chemical adsorption, and microbial adhesion and degradation, directly determines the system's purification efficiency and operational stability through its material composition and structural configuration.

[0003] Currently, various substrate materials have been applied in the field of aquaculture wastewater treatment. For example, patent application CN121063715A discloses a filler-reinforced ecological floating bed for purifying aquaculture wastewater, which utilizes emergent plants such as canna lilies and straw or straw biochar as filler. Another example is patent application CN106430602B, which discloses an artificial wetland insulation structure. This structure uses an upper permeable mulch film, insulating permeable bricks, and a lower permeable mulch film to form an insulation system, wherein the insulating permeable bricks are made of non-fired, high-strength, lightweight hollow bricks.

[0004] However, the aforementioned existing technologies, as well as conventional single fillers (such as natural crushed stone, quartz sand) or simple combination fillers, still have the following shortcomings in practical applications: First, it has poor low-temperature tolerance. When the ambient temperature is below 10℃, the thermal conductivity of conventional fillers (such as quartz sand) is high (up to 4.0 W / (m·K)), and heat is rapidly dissipated through the interior of the matrix, causing the temperature inside the wetland to drop accordingly. The low-temperature environment significantly inhibits the metabolic activity of functional microorganisms such as nitrifying and denitrifying microorganisms, resulting in a significant reduction in nitrogen and phosphorus removal efficiency, making it difficult to meet the effluent discharge standards during the low-temperature season.

[0005] Secondly, it is difficult to achieve both thermal insulation and purification performance simultaneously. Some solutions employ external insulation facilities (such as covering with mulch film or constructing insulated walls) or use high-cost modified materials to mitigate the effects of low temperatures. However, these measures either increase construction and operating costs or sacrifice pollutant adsorption capacity while improving insulation. Current technologies lack a filler packing configuration scheme that can simultaneously achieve efficient thermal insulation and efficient purification, resulting in systems with either insufficient purification capacity or excessively rapid heat loss in low-temperature environments.

[0006] Finally, the economic efficiency is poor. Existing optimized solutions for low-temperature problems (such as multi-layer mulch and special permeable bricks in CN106430602B) rely on additional insulation components or special materials, which significantly increases the unit water treatment cost and limits their application in large-scale, decentralized aquaculture wastewater treatment.

[0007] Therefore, how to maintain the purification performance of aquaculture wastewater treatment systems in an economical and efficient manner under low-temperature conditions is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The present invention aims to solve the technical problems in the prior art when treating aquaculture wastewater in low-temperature environments, such as the difficulty in balancing heat preservation and purification performance, the suppression of microbial activity leading to a significant decrease in purification efficiency, and the high cost of existing optimized solutions, which are not conducive to large-scale promotion.

[0009] Specifically, the technical problems to be solved by the present invention include: first, reducing the thermal conductivity of the composite matrix to reduce the rapid loss of heat inside the system under low temperature conditions; second, ensuring efficient removal of ammonia nitrogen, phosphorus and organic pollutants while maintaining good heat preservation effect; and third, providing an economical solution that does not require additional external heat preservation facilities and is suitable for the treatment of aquaculture wastewater in low-temperature areas.

[0010] This invention provides a composite substrate for treating aquaculture wastewater in low-temperature environments. The composite substrate adopts a four-layer structure laid from top to bottom.

[0011] Specifically, the composite matrix comprises: The upper layer is a quartz sand layer with a particle size of 2 mm to 5 mm, which accounts for 35% of the total volume of the composite matrix; The middle layer is a coconut shell carbon layer with a particle size of 2 mm to 5 mm, and the middle layer accounts for 20% of the total volume of the composite matrix; The lower layer is a rock wool layer with a particle size of 3 mm to 8 mm, which accounts for 10% of the total volume of the composite matrix; The bottom layer is a quartz sand layer with a particle size of 5 mm to 10 mm, and the bottom layer accounts for 35% of the total volume of the composite matrix.

[0012] As a further description of the above technical solution, the upper layer of quartz sand serves as a water distribution layer and a preliminary filtration layer, ensuring uniform water flow and trapping large suspended particles; the middle layer of coconut shell charcoal serves as a core purification layer, utilizing its rich porous structure to adsorb ammonia nitrogen and organic pollutants, while providing attachment sites for microorganisms; the lower layer of rock wool serves as a core insulation layer, utilizing its low thermal conductivity to prevent heat loss downwards; and the bottom layer of quartz sand serves as a support layer and a water collection layer, ensuring smooth drainage and providing structural stability.

[0013] As a further description of the above technical solution, the thermal conductivity of the composite matrix is ​​from 0.6 W / (m·K) to 0.8 W / (m·K).

[0014] As a further description of the above technical solution, the porosity of the upper and lower layers of quartz sand is 40% to 47%, and the bulk density is 1.65 g / cm³. 3 Up to 1.85 g / cm 3 .

[0015] As a further description of the above technical solution, the porosity of the middle layer of coconut shell charcoal is 70% to 85%, and the bulk density is 0.45 g / cm³. 3 Up to 0.55 g / cm 3 Its iodine value is 900 mg / g to 1200 mg / g, and its specific surface area is 800 m². 2 / g to 1500 m 2 / g.

[0016] As a further description of the above technical solution, the bulk density of the lower layer of rock wool is 80 kg / m³. 3 Up to 150kg / m 3 The fiber diameter is 3 μm to 7 μm and the hydrophobicity is 98%.

[0017] As a further description of the above technical solution, the composite matrix is ​​applied to the treatment of aquaculture wastewater at an ambient temperature below 10℃. Beneficial effects

[0018] The composite matrix described above significantly improves the thermal insulation performance of aquaculture wastewater treatment in low-temperature environments. By combining rock wool (0.04-0.07 W / (m·K)) with coconut shell charcoal (0.12 W / (m·K)) in a specific ratio, the overall thermal conductivity of the composite matrix is ​​reduced to 0.6-0.8 W / (m·K), far lower than that of single quartz sand filler (approximately 4.0 W / (m·K)). In low-temperature environments of 0-10℃, this composite matrix effectively reduces heat loss within the matrix, maintaining stable internal system temperature. Experimental data shows that during 60 days of operation, the temperature difference between the internal temperature and the ambient temperature of the device using this invention can be controlled within the range of -0.38℃ to 3.24℃, exhibiting superior thermal stability compared to a single quartz sand matrix (which loses 5-8℃ of heat).

[0019] This invention describes a composite matrix for treating aquaculture wastewater in low-temperature environments, which synergistically enhances both purification and heat preservation performance. The invention employs a four-layer heterogeneous structure: a high-permeability upper layer, a high-adsorption middle layer, a high-insulation lower layer, and a high-support bottom layer, physically creating a temperature gradient field and a pollutant gradient removal field. The high specific surface area (800-1500 m² / g) and abundant pore structure (porosity 70%-85%) of the middle layer of coconut shell charcoal not only provide excellent adsorption capacity but also offer numerous attachment sites for microorganisms. Field application results show that constructed wetlands using this composite matrix achieve a total nitrogen removal rate of 59.5±4.2%, a total phosphorus removal rate of 69.5±4.3%, and a COD removal rate 25%-30% higher than traditional processes. Meanwhile, the microbial community diversity on the composite matrix (Chao1 index reached 4073.22, Shannon index reached 7.314) was significantly higher than that on the single quartz sand matrix (Chao1 index 2215.39, Shannon index 6.139), indicating that the present invention is beneficial to maintaining microbial activity, thereby ensuring biodegradability under low temperature conditions.

[0020] The composite substrate described above for treating aquaculture wastewater in low-temperature environments is economical and easy to promote. This invention eliminates the need for additional external insulation facilities (such as insulation walls or mulch films), achieving insulation solely through the composition of the substrate materials themselves. Based on market prices, the cost of the optimal formulation (FR4) is 141 yuan / m³, significantly lower than the construction cost of conventional insulated wetlands (only 60%-70% of conventional solutions), and operation and maintenance costs are reduced by more than 20% compared to existing low-temperature optimization solutions. Furthermore, the materials used (quartz sand, coconut shell charcoal, and rock wool) are widely available; coconut shell charcoal originates from the resource utilization of agricultural and forestry waste, offering environmental and low-carbon advantages. Therefore, this invention provides an economical and efficient solution for treating aquaculture wastewater in low-temperature regions, suitable for large-scale application. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the thermal insulation matrix filler ratio screening in an embodiment of the present invention; Figure 2 This is a line graph showing the internal temperature change of the matrix device configured in this embodiment of the invention over 60 days; Figure 3 This is a box-type diagram comparing the packing configuration device with the ambient temperature in an embodiment of the present invention; Figure 4 This is a schematic diagram of the optimal configuration of the thermal insulation composite matrix in an embodiment of the present invention; Figure 5 This is a schematic diagram of the operation of the composite matrix constructed wetland in an embodiment of the present invention; Figure 6This is a diagram illustrating the effect of the subsurface flow resilient wetland technology in the embodiment of the present invention for the year-round deep treatment of aquaculture wastewater. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: Composition of composite matrix This embodiment provides a composite substrate for treating aquaculture wastewater in low-temperature environments. For example... Figure 4 As shown, the composite matrix adopts a four-layer structure laid from top to bottom.

[0024] Specifically, the composite matrix includes: The upper layer is a layer of quartz sand with a particle size of 2 mm to 5 mm, accounting for 35% of the total volume of the composite matrix. The porosity of this upper layer of quartz sand is 40% to 47%, and the bulk density is 1.65 g / cm³ to 1.85 g / cm³. The upper layer of quartz sand serves as a water distribution layer and a preliminary filtration layer, ensuring uniform water flow and trapping large suspended particles.

[0025] The middle layer consists of coconut shell charcoal with a particle size of 2 mm to 5 mm, accounting for 20% of the total volume of the composite matrix. This middle layer of coconut shell charcoal has a porosity of 70% to 85%, a bulk density of 0.45 g / cm³ to 0.55 g / cm³, an iodine value of 900 mg / g to 1200 mg / g, and a specific surface area of ​​800 m² / g to 1500 m² / g. As the core purification layer, the middle layer of coconut shell charcoal utilizes its rich porous structure to adsorb ammonia nitrogen and organic pollutants, while simultaneously providing attachment sites for microorganisms, thus enhancing biodegradation.

[0026] The lower layer is a rock wool layer with a particle size of 3 mm to 8 mm, accounting for 10% of the total volume of the composite matrix. The bulk density of this lower layer of rock wool is 80 kg / m³ to 150 kg / m³, the fiber diameter is 3 μm to 7 μm, and the hydrophobicity is 98%. As the core insulation layer, the lower layer of rock wool uses its extremely low thermal conductivity (0.04-0.07 W / (m·K)) to prevent heat loss downwards, while also retaining some phosphorus.

[0027] The bottom layer consists of quartz sand with a particle size of 5 mm to 10 mm, accounting for 35% of the total volume of the composite matrix. This bottom layer of quartz sand has a porosity of 42% to 47% and a bulk density of 1.65 g / cm³ to 1.75 g / cm³. The bottom layer of quartz sand serves as a support layer and a water-collecting layer, ensuring unobstructed drainage and providing structural stability.

[0028] Calculations show that the overall thermal conductivity of the above composite matrix is ​​between 0.6 W / (m·K) and 0.8 W / (m·K).

[0029] The composite matrix in this embodiment can be laid in the following way: from bottom to top, lay the bottom layer of quartz sand, the bottom layer of rock wool, the middle layer of coconut shell carbon, and the top layer of quartz sand. After each layer is laid, it should be properly compacted and leveled. The thickness of each layer is determined according to the volume ratio mentioned above and the area of ​​the treatment tank.

[0030] Example 2: Formulation Optimization Screening Experiment To determine the optimal packing ratio, this invention designed six composite packing schemes (FR1 to FR6) with different ratios. For example... Figure 1 As shown, with quartz sand, coconut shell charcoal and rock wool as the core components, two gradients are set with the total volume ratio of quartz sand being 60% and 70%, and the volume ratio of coconut shell charcoal to rock wool being set to 3:1, 2:2, 1:3, 2:1, 1.5:1.5 and 1:2, respectively. For specific proportions, please refer to Table 1.

[0031] Table 1 Experimental Scheme for Matrix and Filler Proportioning

[0032] The thermal conductivity of each scheme was calculated using the weighted average method, with the thermal conductivity of quartz sand taken as 4.0 W / (m·K), coconut shell carbon as 0.12 W / (m·K), and rock wool as 0.07 W / (m·K). The porosity was calculated as 60%.

[0033] Thermal conductivity λ solid-mix The calculation formula is:

[0034] Where, λ s,i Let φ be the thermal conductivity of the i-th solid component. s,i Let be the volume fraction of the i-th solid phase component, and n be the number of solid phase components.

[0035] Calculation results show that the thermal conductivity of the composite filler with the six proportions ranges from 0.6 to 0.8 W / (m·K), which is much lower than that of the single quartz sand filler (4.0 W / (m·K).

[0036] The above six sets of composite fillers were respectively loaded into a simulation device, and continuous temperature monitoring was conducted for 60 days in a low-temperature environment (ambient temperature 0-10℃). Figure 2 As shown, in the early stage (days 1-25), the temperature of the six sets of devices fluctuated between 6-14℃; in the middle stage (days 25-30), the temperature dropped rapidly; and in the later stage (days 30-60), the temperature stabilized in the 0-2℃ range. Figure 3 As shown, the extreme temperatures of each device ranged from 0.1 to 13.9℃, demonstrating good thermal insulation performance. The temperature difference data between each device and the external environment are shown in Table 2. The FR4 scheme exhibited a stable thermal insulation performance with a temperature difference of -0.38±0.83℃ in the later stages.

[0037] Table 2 Temperature difference (°C) between different schemes and the external environment

[0038] Table 3 Market Prices of Different Types of Packing Material (RMB / m³)

[0039] Table 4. Calculated Costs of Different Mixing Proportions (Yuan / m³)

[0040] Table 5. Microbial Alpha Diversity under Different Schemes

[0041] Based on cost analysis (see Tables 3 and 4), the cost of the FR4 scheme (70% quartz sand, coconut shell charcoal and rock wool volume ratio 2:1) is 141 yuan / m³, which is at a relatively low level, and its thermal insulation performance meets the design requirements. Meanwhile, the microbial community on the composite matrix was analyzed, and the results are shown in Table 5. The Chao1 index of the composite matrix of this invention is 4073.22, and the Shannon index is 7.314, significantly higher than that of the single quartz sand matrix (Chao1 index 2215.39, Shannon index 6.139), indicating that the composite matrix is ​​beneficial for maintaining microbial diversity.

[0042] Therefore, this embodiment determines the FR4 mix ratio as the optimal combination, namely: the upper layer of quartz sand (2-5mm) accounts for 35% of the total matrix volume, the middle layer of coconut shell charcoal (2-5mm) accounts for 20% of the total matrix volume, the lower layer of rock wool (3-8mm) accounts for 10% of the total matrix volume, and the bottom layer of quartz sand (5-10mm) accounts for 35% of the total matrix volume.

[0043] Example 3: Application of composite substrate in constructed wetlands This embodiment applies the composite substrate described in Example 1 to an artificial wetland for treating aquaculture wastewater. For example... Figure 5As shown, a subsurface flow constructed wetland is constructed. The bottom and sides of the wetland bed are treated with impermeable materials. The interior is filled from bottom to top with bottom layer quartz sand, bottom layer rock wool, middle layer coconut shell charcoal, and top layer quartz sand. Emergent plants (such as canna lilies) are planted on the wetland surface. The water inlet method is subsurface flow, and the hydraulic retention time is adjusted according to the water quality.

[0044] In an aquaculture base in the Yangtze River Delta region, the aforementioned enhanced subsurface flow resilient wetland was used to treat aquaculture wastewater, with a cumulative application area of ​​1320 mu (approximately 88 hectares). During operation, the ambient temperature was maintained within the range of 0-10℃, and the wastewater was continuously monitored. Figure 6 As shown, the treatment results indicate that the total nitrogen removal rate is 59.5±4.2%, the total phosphorus removal rate is 69.5±4.3%, and the COD removal rate is 25%-30% higher than that of traditional constructed wetland processes. The treated effluent consistently meets discharge standards.

[0045] In addition, compared with the traditional solution that requires the addition of external insulation facilities, this embodiment does not require additional insulation measures, the construction cost is only 60%-70% of that of conventional insulated wetlands, and the operation and maintenance cost is reduced by more than 20%, which has significant economic advantages.

[0046] Example 4: Comparative Experiment To verify the thermal insulation performance of this invention, a control group was set up: a single quartz sand filler (particle size 5-10 mm) was used as a control, and its temperature was monitored under the same low-temperature environment (ambient temperature 0-10℃) as the composite matrix of Example 1. The results showed that the internal temperature of the single quartz sand filler device decreased by 5-8℃ within 24 hours of operation, while the internal temperature of the composite matrix device decreased by only 2-4℃ within 60 days, and the temperature fluctuation was significantly smaller than that of the control. Furthermore, after 30 days of operation, the ammonia nitrogen and total phosphorus concentrations in the effluent from the composite matrix device were more than 40% and 50% lower than those of the control, respectively.

[0047] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite substrate for treating aquaculture wastewater under low-temperature conditions, characterized in that, The composite matrix comprises a four-layer structure laid out from top to bottom: The upper layer is a quartz sand layer with a particle size of 2 mm to 5 mm, which accounts for 35% of the total volume of the composite matrix; The middle layer is a coconut shell carbon layer with a particle size of 2 mm to 5 mm, and the middle layer accounts for 20% of the total volume of the composite matrix; The lower layer is a rock wool layer with a particle size of 3 mm to 8 mm, which accounts for 10% of the total volume of the composite matrix; The bottom layer is a quartz sand layer with a particle size of 5 mm to 10 mm, and the bottom layer accounts for 35% of the total volume of the composite matrix.

2. The composite substrate for treating aquaculture wastewater under low-temperature conditions according to claim 1, characterized in that, The thermal conductivity of the composite matrix is ​​from 0.6 W / (m·K) to 0.8 W / (m·K).

3. The composite substrate for treating aquaculture wastewater under low-temperature conditions according to claim 1, characterized in that, The porosity of the upper and lower layers of quartz sand is 40% to 47%, and the bulk density is 1.65 g / cm³. 3 Up to 1.85 g / cm 3 .

4. The composite substrate for treating aquaculture wastewater under low-temperature conditions according to claim 1, characterized in that, The middle layer of coconut shell charcoal has a porosity of 70% to 85% and a bulk density of 0.45 g / cm³. 3 Up to 0.55 g / cm 3 Its iodine value is 900 mg / g to 1200 mg / g, and its specific surface area is 800 m². 2 / g to 1500 m 2 / g.

5. The composite substrate for treating aquaculture wastewater under low-temperature conditions according to claim 1, characterized in that, The bulk density of the lower layer of rock wool is 80 kg / m³. 3 Up to 150 kg / m 3 The fiber diameter is 3μm to 7μm and the hydrophobicity is 98%.

6. The composite substrate for treating aquaculture wastewater under low-temperature conditions according to claim 1, characterized in that, The upper layer of quartz sand has a particle size of 2 mm to 5 mm, and the lower layer of quartz sand has a particle size of 5 mm to 10 mm.

7. A composite substrate for treating aquaculture wastewater under low-temperature conditions according to any one of claims 1 to 6, characterized in that, The composite matrix is ​​used in the treatment of aquaculture wastewater when the ambient temperature is below 10℃.

8. A composite substrate for treating aquaculture wastewater under low-temperature conditions according to claim 4, characterized in that, The iodine value of the coconut shell charcoal is 900 mg / g to 1200 mg / g.

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